key: cord-0941836-8b0qnhei
authors: Douglas, Lacey D.; Rivera-Gonzalez, Natalia; Cool, Nicholas; Bajpayee, Aayushi; Udayakantha, Malsha; Liu, Guan-Wen; Anita,; Banerjee, Sarbajit
title: A Materials Science Perspective of Midstream Challenges in the Utilization of Heavy Crude Oil
date: 2022-01-06
journal: ACS Omega
DOI: 10.1021/acsomega.1c06399
sha: 0d4dbfa83022553df997523e4eab21b52a2c3730
doc_id: 941836
cord_uid: 8b0qnhei

[Image: see text] An increasing global population and a sharply upward trajectory of per capita energy consumption continue to drive the demand for fossil fuels, which remain integral to energy grids and the global transportation infrastructure. The oil and gas industry is increasingly reliant on unconventional deposits such as heavy crude oil and bitumen for reasons of accessibility, scale, and geopolitics. Unconventional deposits such as the Canadian Oil Sands in Northern Alberta contain more than one-third of the world’s viscous oil reserves and are vital linchpins to meet the energy needs of rapidly industrializing populations. Heavy oil is typically recovered from subsurface deposits using thermal recovery approaches such as steam-assisted gravity drainage (SAGD). In this perspective article, we discuss several aspects of materials science challenges in the utilization of heavy crude oil with an emphasis on the needs of the Canadian Oil Sands. In particular, we discuss surface modification and materials’ design approaches essential to operations under extreme environments of high temperatures and pressures and the presence of corrosive species. The demanding conditions for materials and surfaces are directly traceable to the high viscosity, low surface tension, and substantial sulfur content of heavy crude oil, which necessitates extensive energy-intensive thermal processes, warrants dilution/emulsification to ease the flow of rheologically challenging fluids, and engenders the need to protect corrodible components. Geopolitical reasons have further led to a considerable geographic separation between extraction sites and advanced refineries capable of processing heavy oils to a diverse slate of products, thus necessitating a massive midstream infrastructure for transportation of these rheologically challenging fluids. Innovations in fluid handling, bitumen processing, and midstream transportation are critical to the economic viability of heavy oil. Here, we discuss foundational principles, recent technological advancements, and unmet needs emphasizing candidate solutions for thermal insulation, membrane-assisted separations, corrosion protection, and midstream bitumen transportation. This perspective seeks to highlight illustrative materials’ technology developments spanning the range from nanocomposite coatings and cement sheaths for thermal insulation to the utilization of orthogonal wettability to engender separation of water–oil emulsions stabilized by endogenous surfactants extracted during SAGD, size-exclusion membranes for fractionation of bitumen, omniphobic coatings for drag reduction in pipelines and to ease oil handling in containers, solid prills obtained from partial bitumen solidification to enable solid-state transport with reduced risk of damage from spills, and nanocomposite coatings incorporating multiple modes of corrosion inhibition. Future outlooks for onsite partial upgradation are also described, which could potentially bypass the use of refineries for some fractions, enable access to a broader cross-section of refineries, and enable a new distributed chemical manufacturing paradigm.

Fossil fuels continue to play a central role in meeting global energy needs, from powering the electric grid to heating habitats and fueling the transportation infrastructure that underpins our unprecedented age of global connectivity. 1 Oil refineries process crude oil to a diverse slate of products, not just transportation and heating fuels, but also chemical feedstock and bituminous components of asphalt infrastructure, reflecting a complex entanglement of the oil and gas industry with chemicals and road infrastructure. The oil and gas industry (and by proxy, the global economy) is increasingly reliant on unconventional deposits such as heavy crude oil and bitumen for reasons of accessibility, scale, and geopolitics. 2, 3 Unconventional deposits in Canada and Venezuela contain more than one-third of the world's viscous oil reserves and have emerged as vital linchpins to meet the energy needs of growing and rapidly industrializing populations. 4 Crude oil, sweet and sour (classified based on sulfur content), light or heavy (depending on molecular weight and classified based on specific gravity; heavy oil typically has an API gravity < 22.3°, specific gravity > 920 kg/m 3 ), is transported to refineries using deepwater ports, rail links, and pipelines. In turn, an extensive network of conduits, the very arteries of global economies, carries processed fuel, chemical feedstock, plastics, and fertilizer from refineries and associated chemical plants to manufacturing and population centers across the world. The high viscosity of heavy crude oil and bitumen presents a substantial impediment to their extraction, midstream transportation, and processing. As such, challenges associated with the vexing rheological properties of these fuels have far-ranging implications for energy security, economic resilience, and manufacturing. As an illustration of the magnitude of this problem, the Canadian Oil Sands produce 4 million barrels a day, primarily sour heavy crude, amounting to 22% of total US imports. 5 The contentious debate regarding the construction of new pipelines in North America underscores the burning need for fundamental scientific innovations as well as their effective translation to viable midstream technologies. 6, 7 In this perspective article, we discuss the challenges and opportunities for materials science in midstream processing, storage, and transportation of heavy crude oils, emphasizing potential solutions for more effective utilization of hydrocarbon resources in the Athabasca region of North America.

1.1. Oil Recovery in the Canadian Oil Sands. Since the global spike in oil prices in the 1970s, significant attention has focused on the recovery of heavy crude oil from unconventional deposits. As a result of advancements in horizontal drilling, enhanced oil recovery, and associated advancements in process intensification, the production of unconventional deposits has become economically viable in large measure. The Canadian Oil Sands are a prominent example. Production is expected to increase from the current 4 million barrels a day by up to an additional 1.5 million barrels per day over the next decadealmost all of the additional production bound for consumption in the United States. Tertiary enhanced oil recovery (EOR) methods have played a central role in the emergence of viable production of bitumen and are broadly classified into two categories, thermal and nonthermal. 2, 3, 8 Nonthermal methods include cold production, chemical flooding, and miscible displacement. 2 In chemical flooding, the surface energy of the formations and deposits are modified through the addition of an amphiphile, which thereby promotes the mobilization of oil. In miscible displacement, gases are injected into the cores and the density of oil is modified to ensure mobilization. These methods are plagued by the high costs of chemical additives and the extended periods of time required to initiate the production of heavy oil. In the Canadian Oil Sands, nonthermal methods have had limited success (recovery rates limited to 12−15%) and are not as widely used as thermal alternatives. 3 The most efficient EOR methods induce flow through thermal mechanisms that fundamentally modify the viscosity of heavy oil. 2 One such method is cyclic steam stimulation (CSS), wherein a singular well is injected with high-pressure steam at 300−340°C, allowed to soak over a few days to weeks, and then the oil is pumped to the surface. As the production well flow begins to ebb, the process is repeated, typically for at least 15 cycles. 9 A modification of this approach that has been widely adopted and represents the state-of-the-art is steam-assisted gravity drainage (SAGD), which yields a recovery factor of approximately 60%. 9 In this process, as sketched in Figure 1 , two stacked horizontal wells are drilled into the formation. The topmost injection well is used to administer high-pressure steam at temperatures in the range of 90−250°C, promoting emulsification, facilitated by endogenous surfactants, which modifies the viscosity of heavy oil and enables its mobilization. 10 The secondary, production well, drilled still deeper into the reservoir, then collects the drained complex emulsions from the steam chamber; the recovered emulsions span the range from oil-in-water, water-in-oil, oil-in-water-in- oil, and water-in-oil-in-water multinary mixtures. Once pumped to the surface, complex emulsions need to be separated. The produced water is deoiled, desalinated, and recycled back to the SAGD process. The separated heavy oil is transported (sometimes with partial upgradation such as hydrogen treatment) to refineries, which requires resolution of all of the challenges incumbent from its high viscosity and sulfur content.

1.2. Materials' Chemistry Challenges in the SAGD Process. Figure 1 sketches the steps involved, highlighting the opportunities for materials science innovations in the design of membranes, surface coatings, cement sheaths, pipelines, and solutions for solid-state transport. High fluid temperatures, frigid external temperatures, high subsurface pressures, flammable liquids, and harsh corrosive environments require the design of resilient, functional materials that are tailored to resist degradation in extreme "far-from-equilibrium" environments. 11−13 Despite rapid technological advancements that have rendered SAGD methods an economically viable approach for oil production in the Canadian Oil Sands, the production of oil by such methods remains considerably more expensive as compared to extraction of sweet light crude in the Permian Basin or from plays in the Persian Gulf. As such, there is considerable interest in improved recovery rates through the incorporation of chemical additives, energy-efficient thermal cementing to prevent heat loss during SAGD (or incorporation of thermal insulation more generally across the SAGD Figure 2 . (A) Comparison of pipeline tolls and railcar transportation costs from Alberta to different refinery operations in North America depicting the daily refinery capacity (inset), reproduced with permission from Oil Sands Magazine https://www.oilsandsmagazine.com/market-insights/ crude-oil-pricing-differentials-why-alberta-crude-sells-at-deep-discount-to-wti#references. 21 (B) Yearly export volumes based on oil type from conventional, synthetic, and dilute bitumen from 1990 to 2019, information on the license can be found at https://open.canada.ca/en/opengovernment-licence-canada. 20 infrastructure), more optimal separations of the extracted emulsions, protection of base metal components exposed to harsh corrosive environments, and the design of solutions to midstream transport that mitigates myriad current challenges with pipeline and railcar transportation. 14−19 Heavy oil and bitumen are shipped using heated tankers, rail cars, trucks, and pipelines, oftentimes requiring dilution with light hydrocarbons to obtain fluids with rheological properties amenable to transportation. As such, the transportation of bitumen entails a massive energy expenditure and requires the installation and maintenance of a substantial thermal infrastructure. The need for diluents further adds substantial cost to midstream transport; ca. 30% of pipeline capacity in North America is tied up in the unproductive flow of diluents, light hydrocarbons, added simply to modify the rheology of bitumen. Figure 2A shows that whereas synthetic and conventional oil exports have remained fairly constant over the last 20 years, there has been a massive increase in Canadian exports of diluted bitumen to the United States from 170 000 barrels per day in 2000 to 2.4 million barrels per day in 2019. 20 As a result of the high viscosity and low surface tension of bitumen, the maintenance and cleaning of transportation vessels incur a considerable cost, results in substantial unrecovered residues, and engenders safety hazards for those engaged in maintaining transportation equipment.

Notwithstanding uncertainty introduced from COVID-19, the US Energy Information Administration pegs future US transportation energy needs at around 26 quadrillion BTUs in 2050 with over 80% projected to derive from hydrocarbon fuels. 1 As noted above, 22% of total US imports are derived from Canada ( Figure 2A ). 21 Pipelines are the most efficient mode to transport crude oil, yet all existing pipelines to the Unites States are at capacity. The US refineries closest to the Canadian Oil Sands in the Midwest (Petroleum Administration for Defense Districts (PADD)-2, PADD2) have a surfeit of Canadian Oil (100% of imports). A clear solution would be to transport heavy oil produced in excess of PADD2 capacities to PADD3 refineries in the Houston Gulf Coast, which have a total refining capacity of 10 million barrels a day ( Figure 2B ); these are some of the most complex refineries capable of handling heavy crude, offer the best prices for heavy and sour Canadian crude, and provide access to deepwater ports for transportation of a complex slate of products across the world. These refineries were historically constructed to handle heavy crude from Venezuela and Mexico; supplies from both countries have plummeted in recent years leading to attractive pricing for Canadian heavy and sour crude. In the absence of adequate pipeline capacity, railcar transportation has emerged as the primary means of transportation between Western Canada and the US Gulf Coast. Canada Energy Regulator and Statistics Canada estimate that 400 000 barrels of Western Canada Heavy Sour Crude from Alberta are transported daily by railcar to refineries in the United States; this number has risen sharply since railcar transport was nonexistent until 2012 and is expected to further increase with the cancellation of the Keystone XL pipeline. As shown in Figure 2 , railcar transportation is considerably more expensive as compared to other shipping methods (adding $15−22 to the cost of a barrel of oil delivered to the refinery). For both pipeline and rail transport, there is thus considerable interest in the design of surface modification approaches that will enable less fouling of the infrastructure, reduce the amount of diluents required, and enable transportation at ambient temperatures.

Alternative midstream strategies have focused on solid-state transport such as through encapsulation in polymer wastes or through reconstitution of bitumen to form solid prills wherein lighter fractions are coated by asphaltene shells. 22−24 Regardless of the mode of transportation, the vast midstream infrastructure is primarily constructed from structural steel and thus prone to corrosion. Corrosion has an impact of $2.5 trillion globally and specifically in the United States; the annual cost induced by the railways amounts to $11.16 million. 25, 26 Corrosion further risks spillage of oil in environments, which can have a devastating impact on vulnerable ecosystems. 27 A 2018 National Academies Report notes that pipeline infrastructure is more robust and has greater safeguards in place as compared to railcar transportation. Forthcoming sweeping sets of reforms will entirely alter the landscape of railcar transportation in North America by putting in place stringent specifications for rail cars as all rail cars must be built to meet DOT-117 requirements or retrofitted to comply with the transportation of Class 3 flammable liquids, ethanol, and unrefined petroleum products. 28 These new regulations address safety concerns such as top fittings and thermal insulation. Existing rail cars not meeting these standards are due to be phased out by 2029. 29 In this perspective article, we outline the formidable and distinctive materials science challenges faced by the midstream oil industry in the handling of heavy oil, delineate the underlying scientific principles to possible solutions, and discuss technological advancements based on materials' chemistry innovations that represent candidate solutions to these challenges. Such advances in materials chemistry are of pivotal importance to ensuring the economic viability of the Canadian Oil Sands and to mitigate deleterious impacts on the environment. In compiling this perspective article, we have focused on some recent contributions, which are discussed in the context of the broader literature. In the interest of presenting a succinct narrative, we have emphasized illustrative examples instead of attempting a comprehensive review. The subsequent sections discuss thermal insulation at the wellhead and in well cementing, membrane-assisted separations, corrosion protection, and solutions for midstream transportation of viscous oil. In addition to a discussion of the fundamental principles and promising outcomes in the field, we provide a prospectus for future opportunities.

INSULATION SAGD being a thermal recovery process is extremely energy intensive as it requires handling of hot fluids across different stages of operation, 30 e.g., ground transportation of steam from boilers to the wellhead, steam injection through the vertical well bore, maintaining the temperature of the steam chamber, and transportation of viscous heavy oil to refineries. 31, 32 All of these steps are critical and direct determiners of the overall productivity and cost of production. Therefore, minimizing energy losses at every step is pivotal to the efficiency and costeffectiveness of the SAGD process. 33, 34 Operational modifications aimed at reducing energy losses include the injection of a solvent intermittently with steam (solvent-assisted SAGD), 35, 36 injecting noncondensable gases with steam (NCG-SAGD), 37,38 coinjecting surfactant solutions, performing foam-assisted SAGD (FA-SAGD), 39, 40 and drilling injection and production wells perpendicular to each other (cross SAGD). 41 Alternative strategies have focused on increasing energy efficiency through improved materials selection and design without altering the basic SAGD operational process. This entails reducing energy losses by insulating all surfaces from where the heat is lost by conduction, convection, and radiation. 42, 43 Reliance on heating in SAGD oil production indeed makes thermal energy the major contributor to production costs. Hence, any loss of thermal energy input during the operation of the SAGD process has a direct impact on the economic viability of the process. The energy losses occur primarily through the surfaces of pipelines as a result of the high thermal conductivity of pipeline materials (mostly structural steels) and large thermal gradients across these conduits given frigid external temperatures in the Athabasca region. 19 Thermal conductivity is a measure of heat transfer efficiency within a material under the influence of a temperature gradient. When a material is exposed to a higher temperature at one surface, the temperature gradient that develops between the hot and the relatively cold surfaces leads to heat energy transfer across the material as per Fourier's law 44

where the heat flow, Q, is expressed as a function of the surface area, A; ΔT is the temperature difference between the hot and cold surfaces; d is the separation between the surfaces; and k is the thermal conductivity of the material. In the case of SAGD pipes that transport hot fluids, the high thermal conductivity of steel (50 W/(m·K)) and large temperature gradients (10−40°C external temperatures and ca. 180−250°C fluid temperatures) result in a large propensity for heat loss. A decrease of fluid temperature is accompanied by a sharp increase of viscosity of heavy oils, 45 which can give rise to severe transport limitations, thereby increasing the demand for steam and resulting in higher steam-to-oil ratios (SOR: barrels of steam required to produce a barrel of oil), 46 and eventually reducing the efficacy of the SAGD process. Therefore, it is imperative to reduce the thermal conductivity of these surfaces to render the process more energy efficient. As shown in Figure 3A , blanketing hot surfaces with an insulation coating reduces the overall thermal conductivity of the insulated surface as chemically dissimilar materials in contact at the heat exchange surface act as serially connected thermal resistors. The overall thermal conductivity (k total ) can be expressed as

where T s is the internal temperature of the steel pipe, T c is the external temperature of the insulating coating, and d s and d c are the thicknesses of the steel pipe and the insulating coating, respectively. Materials that impede ballistic heat transport by phonon scattering at many interfaces and are of low inherent thermal conductivity with enclosed void spaces show promise for the thermal insulation of pipelines. The means of applying insulation varies depending on the intended application of a pipeline. For example, steel pipelines used for ground transportation of crude oil need to be insulated to avoid flow constraints that would increase oil viscosity and require higher pumping pressures ( Figure 3B ). 47 Hence, insulation on such pipelines requires maintaining the inner temperature at 90−130°C, sufficiently high to maintain a flow of crude oil (<500 cP). 31, 47 In contrast, pipelines that transport steam, both above-ground (boilers to the wellhead) and underground (steam injecting wells), must maintain inner temperatures at much higher values, typically in the range of 180−290°C. In general, above-ground pipe insulation methods are more versatile than underground methods owing to their relative ease of access. Common insulation methods include insulating blankets wrapped around the outer surface of pipelines; such blankets are commonly constituted from polyurethanes, polyethylene, and porous calcium silicates optionally combined with glass fibers, mineral wool, and alumina silicate fibersall materials exhibiting low thermal conductivity and encapsulating substantial void space. 48−50 Much recent effort has focused on embedding rigid hollow structures within polymeric media to achieve a combination of low density and high porosity, which impedes heat transfer and reduces thermal conductivity down to values <1 W/(m·K). As illustrated in Figure 3C , effective heat transfer within such composite structures is governed by three fundamental pathways: (1) gaseous convection and conduction within hollow insertions, (2) solid conduction across percolative networks, and (3) thermal radiation on the surface of hollow insertions. 48 Unfortunately, the glass-transition temperature of epoxy polymers is below 150°C, which precludes their widespread application in pipelines wherein operating temperatures can be well in excess of this value. As such, considerable attention has focused on the design of high-temperature polymers, ceramic coatings, metal matrix composites, and ceramic composites. 51, 52 We have recently developed polybenzimidazole-and polyimide-based composite coatings exhibiting low thermal conductivity (as low as 0.059 W/(m· K)) at high working temperatures (250−400°C) that can be directly applied onto wellhead components and pipelines that transport steam. 53 The record low thermal conductivity values are obtained by embedding hollow glass bubbles inside the polymer matrix, which introduces void spaces and interfaces for phonon scattering. Figure 3D exemplifies a cross-sectional view of the hybrid coating.

An intriguing strategy for mitigating delamination of coatings from thermal stresses generated as a result of differentials in coefficients of thermal expansion (CTE) is based on the incorporation of negative thermal expansion (NTE) materials such as ZrV 2 O 7 and HfV 2 O 7 within hightemperature polymers. HfV 2 O 7 exhibits isotropic NTE with a CTE = −6.7 × 10 −6°C−1 in the 130−700°C range that is particularly relevant to SAGD operations. As an example of this approach, incorporation of NTE material HfV 2 O 7 in a hightemperature polybenzimidazole resin enables as much as a 67.3% reduction in thermal stress at a relatively low loading of 27 vol %, suggesting a means of accessing zero thermal expansion nanocomposite coatings that can sustain large thermal variations encountered in SAGD processes. 53 For the purpose of insulating well bores, commonly used methods include an annulus gas blanket or insulated tubing. An annulus gas blanket is formed by injecting gaseous nitrogen into the well bore. 49 Injected gas pushes the steam further into the well bore and creates a low thermal conductivity sheath that limits heat loss. Additionally, vacuum-insulated tubing (VIT) is gaining popularity as a means of reducing thermal losses at a SAGD well bore. 54, 55 Adopting a concentric or eccentric tube-in-a-tube conformation ( Figure 4A ) yields a vacuum around the steam injection pipe, thereby substantially mitigating heat losses. 55 A concentric arrangement is preferred over an eccentric arrangement as the physical contact between the tubing and the casing in eccentric arrangement leads to some conductive heat losses. Even though VIT is estimated to increase the steam quality by 4.6% as compared to bare tubing, 54 it requires vacuum conditions as high as 10 −5 −10 −6 Torr to effectively eliminate convective heat losses. 32 As an alternative approach, we have recently demonstrated that thermal energy losses in vertical injection wells can be substantially reduced by endowing thermal insulation capabilities to oil-well cement sheaths used to adhere steam pipes to the well bore. As shown in Figure 4B , we have embedded hydroxyethylcellulose-modified halloysite nanotubes (HEC-HNTs) within the cement matrix. HNTs are hollow nanotubes ( Figure 4C ) with a general formula of Al 2 Si 2 O 5 (OH) 4 and enclose a lumen surrounded by aluminate interiors and silicate exteriors ( Figure 4D ). Transient hot bridge thermal conductivity measurements ( Figure 4E ) show the highest thermal resistance for a filler loading of 2 wt %. This formulation reduces the overall thermal conductivity of oil-well cement by as much as 76% without compromising mechanical properties. 18, 19 Figure 4F demonstrates that the 28 days compressive strength of HEC-HNT-modified cement samples is well within the acceptable range for industrial operation (8−20 MPa) even after accelerated thermal cycling (heating at 250°C for 20 h and cooling at 20°C for 4 h) for 20 consecutive cycles. Indeed, the diminution in compressive strength with thermal cycling is lower for HEC-HNT-modified cement as compared to unmodified cement. As such, the introduction of HEC-HNTs introduces disparate interfaces and voids, resulting in increased phonon boundary scattering, thereby reducing thermal energy loss and ensuring steam quality while protecting the cement sheath from thermal fatigue.

Even though the primary role of these coatings is to provide thermal insulation, they are often called upon to provide additional functionality. For example, underground SAGD pipelines are prone to corrosion. 57, 58 As such, there is a need to develop insulating coatings that can withstand high temperatures on the steel surface while being resistant to corrosion. Corrosion is particularly detrimental in VIT arrangements as it increases the tendency for hydrogen permeation, which at concentrations higher than the sorption capacity of embedded getters will destroy the vacuum. 32 In addition, the geographic locations of SAGD operations in the United States and Western Canada impose stringent constraints on the performance expectations of such insulating coatings. Specifically, coatings need to withstand substantial temperature gradients and continuous cyclic thermal stresses. Additional challenges arise from the need to paint or spray coatings onto existing operational pipelines with minimal surface preparation. As such, in addition to functional performance, a key criterion is adhesion to base metal surfaces. In summary, the design of insulating coatings and sheaths that are cost effective imbue high thermal resistance and corrosion inhibition and are readily applicable to operational pipelines remains an area of active research.

Complex oil−water emulsions are pumped to the surface in the SAGD process ( Figure 1 ) and comprise water-in-oil, oil-inwater, and concentric o−w−o and w−o−w droplet dispersions. The bitumen−water interface is stabilized by endogenous surfactants comprising resins, asphaltenes, 59,60 naphthenic acids (oligomeric carboxylate surfactants), 61 and minor quantities of linear alkanoic acids, tetra-acids, sulfonic acids, asphaltenic acids, etc., as well as mineral solids such as clays, calcite, silica, and quartz. 10,62−67 In this section, we provide a succinct discussion of the chemical origins of emulsion formation as well as the possible molecular mechanisms of destabilizing emulsions, describe the concept of differential wettability underpinning membrane separations, and review recent progress in affecting the separation of complex emulsions. Finally, we delineate strategies for the creation of tailored membranes for the effective separation of complex emulsions.

The mechanism of interface stabilization is depicted in Figure 5 . Heavy fractions of bitumen contain polar functional groups and heteroatoms that interact via hydrogen bonding, intermolecular π−π interactions, covalent coordination bonds, Lewis acid−base interactions, electrostatic interactions, and van der Waals' forces. 68 It is typical for resin fractions to accumulate at the oil−water interface as a result of faster adsorption kinetics owing to a significant reduction in interfacial tension. 69 Conversely, asphaltenes display slow but irreversible adsorption kinetics and aggregate within interfacial films through intermolecular π−π interactions, which prevent droplets from coalescing. 70 Mineral solids coupled with aggregated asphaltenes can create biwettable interfaces on particle surfaces, augmenting the stability of surfactantstabilized emulsions by forming remarkably stable Pickering emulsions. 65, 71 The cation exchange capacity of solid particles, porosity of minerals, crystallite and aggregate dimensions of inorganic solids, and molecular size of asphaltenes are important parameters governing asphaltene adsorption on solid particle surfaces. 72 The exceptional stability of such emulsions derives from a combination of small droplet dimensions, highly negative ζ-potential values, 63 and an abundance of amphiphilic species. 73 Under these conditions of emulsification, the produced heavy-oil−water emulsion is exceptionally stable. As such, stable SAGD emulsions must be actively disrupted to effectively separate aqueous and hydrocarbon fractions. 63, 65, 73 In general, thermodynamically unstable emulsions are kinetically stabilized by interfacial steric or electrostatic interactions. The Gibbs−Duhem equation 74 (eq 3) describes three contributions to surface free energy: an entropy term, an interfacial energy term, and a composition term.

At constant temperature and composition

where dG σ is the differential change in Gibbs free energy, S σ is the entropy of the system, dT is the differential change in temperature, A is the interfacial area, n i is the number of moles of component i with chemical potential μ i , and γ is the interfacial tension. At constant temperature and composition, the entropy and compositional terms tend to zero (eq 4) and interfacial tension is constant (eq 5) and positive for surfaces; as such, if the interfacial area increases, the change in G σ is positive; as such, extended interfaces between phases are thermodynamically disfavored. In contrast, kinetic stabilization depends on the absorbed layer of surface-active agents on the O−W interface and the chemistry of the surface-active agent. 75 If the surface-active agent is ionic in nature, the stabilization occurs through electrostatic forces that provide the necessary repulsion between like charges on the double layers of two droplets. 76, 77 Nonionic surfactants/amphiphiles stabilize the dispersed phase through steric hinderance. The concentration of long chains increases in the area where two droplets interact. Due to this increase in the local concentration of the surface-active agent in this area (overlapped region), the dispersing phase starts diffusing to the overlapped region which eventually causes the reduction of local concentration of long chains, thereby diminishing the overlapped region and finally separating droplets from each other. It is worth noting that despite their thermodynamic instability, kinetic stabilization enables SAGD emulsions to persist for a period of months and years. The purpose of demulsification processes is to disrupt interfacial interactions, culminating ultimately in phase separation across a hierarchy of length scales. At the nanoscale, smaller droplets merge to form larger droplets, contributing to droplet growth by Ostwald ripening. 78 Laplace pressure, Δp, within the droplet is a differential pressure term defined in eq 6, where r is the radius of the spherical droplet and γ is the interfacial tension. Laplace pressure governs the diffusion of surface species from the interface of smaller droplets (higher Laplace pressure) to larger droplets (lower Laplace pressure), resulting in greater stability of the merged droplet.

On the scale of microns, when two or more droplets of the dispersed phase combine to form an aggregate, the result is flocculation. 79 The dispersed droplets can take on thermal energy from continual motion, buoyancy forces, gravitational forces, and applied mechanical forces. When the available energy surpasses a threshold value, the interface between droplets is eliminated, merging the flocculated droplets into a single larger droplet. 80 At still greater length scales, differentials in density drive the gravitational separation of droplets, which over a period of time leads to the formation of a distinct phase boundary. Sedimentation is observed when the dispersed phase is denser than the dispersing phase. In contrast, if the dispersed phase is lighter than the dispersing phase, the process is termed creaming. All of these processes need to be systematically controlled to engender macroscopic phase separation.

SAGD-extracted oil−water emulsions that are pumped to the surface are typically first sent to a water knock-out tank that uses density differentials to engender gravity-based separation of oil-and water-rich phases as well as mineral particulates. 81 Thermally driven cracking of oil-rich emulsions remains a ubiquitous means of separating the aqueous and oil fractions of SAGD emulsions, but alternatives are being actively explored because of their energy-intensive nature. The water-rich emulsion is delivered to a skim tank for primary treatment of wastewater, where the thin film of oil floating on the surface of water is removed. Secondary treatment involves the removal of suspended microscopic/nanoscopic oil droplets by induced gas flotation to facilitate coalescence and subsequently removal of the demulsified oil component using an oil removal filter. Finally, the tertiary treatment removes water hardness (calcium and magnesium) and dissolved silica by the addition of limewater at elevated temperatures known as warm lime softening. Here, limewater reacts with dissolved carbon dioxide forming carbonate and bicarbonate. This reaction shifts the equilibrium of carbonate species in the system, thereby precipitating large quantities of calcium carbonate when it exceeds its solubility product. Magnesium is removed in the same processes by a double displacement reaction. Lastly, ion-exchange absorption removes residual hardness in water by exchanging them with sodium ions. Finally, water is transported to the steam generator for reinjection. 82 Produced water generated as a byproduct of the SAGD process has been a major liability since the advent of this technology. As an unconventional oil recovery method, SAGD has a produced-water-to-oil ratio (PWOR) as much as 4-fold that of conventional recovery methods. 83 However, the separated water is usually not suitable for reinjection, disposal (discharge limit <40 ppm of oil-in-water), or recycling and requires extensive further processing. 84, 85 In particular, reuse of water from the SAGD process has stringent water quality constraints to protect boilers from scaling and corrosion.

Emerging membrane-based technologies are a promising alternative to the current flow trains used for the treatment of produced water or destabilization of water-in-oil emulsions. The interplay of the adhesive and cohesive forces on a multiphase interface can lead to preferential repulsion/ attraction of a particular phase at a surface boundary. 86, 87 Two broad regimes of wettability can be distinguished ( Figure  5B ). 88, 89 The Wenzel regime 89 describes droplets that have found their way to a global free-energy minimum wherein the liquid resides on the surface and enters grooves, thereby reducing contact angles to <90°. Equation 7 defines the contact angle in the Wenzel regime, where θ w . γ LV , γ SL , and γ SV are defined as the surface energy of liquid−vapor interface, solid−liquid interface, and solid−vapor interface, respectively. r is defined as the roughness factor (ratio of the actual contact area of solid to the projected area of contact on the solid− liquid interface).

A droplet in the Cassie−Baxter regime 88 corresponds to a metastable configuration wherein the liquid is suspended over a composite air−solid interface with minimal or no permeation within the textural elements. A modified Cassie−Baxter 90 calculation of the observed contact angle (θ CB ) is expressed in eq 8, where r f is the roughness factor (ratio of the actual contact to the projected area of contact on the solid−liquid surface) and f SL is the fraction of the solid contact surface to the apparent total contact area of unit. The modulation of interfacial interactions is achieved by the surface modification of membranes to reduce/increase the surface free energy, enabling selective permeation of liquids along surface tension gradients. 91 Surface texturation plays an important role by amplifying the inherent propensity of a surface to wet or repel a liquid droplet. 91 ,92

Interfacial interactions can initiate and propagate the process of destabilizing emulsions through a sequence of processes: disruption of molecular interactions, flocculation to form droplets, mesoscale ripening and coalescence of droplets, stabilization of a phase boundary, and selective permeation of the continuous phase through the membrane. Figure 5C depicts the aspects of the development of membrane-aided emulsion separation technologies. Membrane design must be tailored to the characteristics of the emulsion, such as the presence of suspended particulate matter and its size distribution, nature, and concentration of surfactants and the relative ratio of oil and water. Interfacial interactions can be tuned by modulating the pore size, surface texturation, and surface energy of the membrane, as well as by adding deemulsifiers or combining with thermal processes. Process design, spanning the range from the selection of flow geometries and flow profiles to backwashing sequences and multiple looping, is furthermore of the utmost importance for commercial deployment of membrane technology, which is predicated on optimization of metrics such as separation efficiency, flux rate, resistance to fouling, and operational lifetime.

Surface engineering approaches for oil−water separation typically combine selective texturation of surfaces (through embedding inorganic nanoparticles, cellulosic fibers, or structured polymers) in conjunction with chemical modification of membrane surfaces. A review by Dickhout et al. outlined the fundamental principles underpinning separation mechanisms such as surface charge, surface roughness, concentration polarization, crossflow velocity, and transmembrane pressure. 93 Although an extensive literature has focused on the relative performance metrics of membranes for oil−water separations, fundamental materials' design principles remain less explored. 94−98 Membrane function involves multiscale interactions between liquid flows and surfaces involving textural elements, surface functional groups, pore dimensions, adhesion, and adsorption-induced modification of interfaces.

In general, a membrane architecture comprises a porous support, which serves as the primary structural bulwark. The surface of the porous support is further imbued with multiscale texturation by embedding nanometer-or micron-sized morphological architectures. Surface energy is then modulated by the chemical functionalization of the textured surface. The structural support is oftentimes a periodic metal 99−101 or metal−alloy mesh, 17,102,103 ceramic membrane, 98, 104, 105 or woven microfiber textile (constructed from natural 106−108 or synthetic fibers). 109−111 Base support membranes define initial pore size and provide the primary means of size exclusion, which is further augmented through surface modification to enhance the separation of emulsions. Texturation enhances the intrinsic affinity of the surface without changing its free energy.

A variety of metal oxides that exhibit multiscale roughness are resistant to corrosion and are accessible at relatively low cost have been used as textural elements. Titanium oxides, aluminum oxide, 82,112−114 and silica 102, 115, 116 nanoparticles are the most widely used components of metal-oxide oil−water separation membranes. ZnO tetrapods have furthermore attracted recent interest because of their distinctive tetrapodal morphology, which provides a means of imbuing 3D mesoscale texturation. 15, 17, 117 Deposition of chemical/electrochemical reaction products of copper on the copper mesh has further been used to generate uniform micro/nanoscale roughness on porous surfaces. [99] [100] [101] 118 Rare-earth metal-oxide nanoparticles (CeO 2−x ) 119 have been proposed to be intrinsically hydrophobic morphological elements for inducing surface roughness. It has been suggested that octet electrons in the outer orbitals (5s 2 5p 6 ) of rare-earth atoms completely shield 4f orbitals, resulting in drastically reduced polar interactions of water with the surface. As per this hypothesis, reduced cohesion of water droplets renders lanthanide oxide surfaces hydrophobic. 120 This mechanism has been challenged in more recent work wherein X-ray photoelectron spectroscopy and dynamic water contact angle measurements indicate that rare-earth oxides are intrinsically hydrophilic but rendered hydrophobic as a result of adsorption of surface contaminants. 121 Prakash et al. found a clear correlation between the increase in water contact angle and carbon coverage resulting from hydrocarbon adsorption, further corroborating that the observed hydrophobicity is not a reflection of the electronic structure of lanthanide cations. 122 Appropriate chemical functionalization of a surface alters the surface free energy of a texturized membrane, making it selectively wettable toward permeation of either oil or water depending on the type of emulsion, thereby inducing separation at the surface. This is accomplished by preferentially diminishing adhesive interactions for water−oil with the surface while facilitating adhesive interactions (hydrogen bonding, ion−dipole interactions, and ion-induced dipole interactions) with oil−water, thereby resulting in differential wettability. Membranes functionalized with polymers have been extensively investigated over the last several decades; the majority are fabricated from poly(vinylidene difluoride) (PVDF), 123−126 polyurethane (PU), 111,127,128 polysulfone (PS), 113,129 polyacrylonitrile (PAN), 109, 130 and polybenzimidazole (PBI). 110, 131 Membrane configurations used for oil− water separations, including SAGD applications, are typically prepared by casting architected polymeric films 113,126 onto ceramic 124,125 /ceramic−polymer blend membrane supports using phase inversion. 126, 127, 132 Polymers such as polydopamine and poly(vinylidene difluoride) (PVDF) have been structured into precisely tunable porous networks, and furthermore, they can be used to modify the surface energy at solid−air and solid−liquid interfaces. 82, 113 Polymer surface modification provides a means of sensitively tuning surface energies. Polymer swelling, as well as constraints on operational temperature, 133 represents the major drawbacks of polymeric membranes. Polymer swelling is the abrupt change in the volume of a polymer network by penetration of the solvent resulting from unbalanced osmotic and viscoelastic restoring forces. 134 This swelling can be resolved to some degree by reducing voids between polymer chains; polymer grafting with a functional organic side chain can further diminish polymer solubility in specific solvents, rendering the surface more resilient to solvent interactions. 110, 135 Graphene oxide materials have also found application in membrane design and display excellent hydrophilicity, attributable to the presence of carboxyl and hydroxyl groups on the edges of their basal plane that help create hydrogen bonds with water. 136, 137 The incorporation of graphene oxide in the membrane is usually achieved by creating a dispersion with a polymer. Notable examples include reduced graphene oxide (r-GO)/graphitic carbon nitride (C 3 N 4 ) dispersed in polydopamine (PDA), 138 graphene oxide dispersed in polybenizimidazole (PBI), 110 and graphene oxide bound to amine-terminated polyacrylonitrile (PAN) fiber, 109 where amide linkages are created between carboxyl groups on the graphene oxide and amine groups on the surface of PAN fibers. Graphene oxide incorporation increases the surface density of hydroxyls, thereby enhancing surface hydrophilicity.

Perfluorinated compounds are ubiquitously used to alter the wettability of surfaces to different liquids. The low polarizability of covalently bonded fluorine atoms in organofluorine compounds results in intrinsically low intermolecular forces, yielding a low interfacial tension. 139 However, creating a surface with low free energy reduces adhesive interactions for both oil and water, 117 which is not optimal for the separation of disparate liquids. Instead, fluorosurfactants can promote differential wettability. In such compounds, the fluorinated tail inhibits polar interactions with both oil and water, whereas the anionic head promotes polar interactions with water while exhibiting limited interactions with hydrocarbons. Such precise tunability of molecular interactions is imperative to create a selectively wettable membrane surface. 17, 117, 140, 141 We have explored this facet of membrane development using potassium perfluorooctane sulfonate (PFOS) surfactant as a surfaceenergy modifier on a stainless-steel surface spray coated with tetrapodal ZnO to create mesoscale texturation and adhered with an amorphous silica network. 17 The membrane architectures exhibit excellent oil−water separation, decreasing oil content in water to <300 ppm in a single pass.

The adhesion of inorganic morphological architectures to the structural support membrane represents a substantial challenge for membrane development. Poor adhesion results in membrane degradation, fouling, and lower separation flux rates. Traditionally, organosilanes 82, 125 have been used as precursors to create amorphous three-dimensional (3D) silica networks on texturized membrane surfaces through the Stober process, 17,125 a sol−gel approach that involves hydrolysis of organosilanes, followed subsequently by condensation to form a siloxane network. Precise control of organosilane chemical activity is needed to achieve uniform surface distribution of the siloxane network on the membrane. Recent research has focused on using inorganic matrices created via condensation of aluminum phosphate 112, 142 to bind textural elements on the surface of the membrane at elevated temperatures as per 143 Thermal curing constantly depletes water that is created as a product of condensation, thereby shifting the equilibrium in the forward direction, according to Le Chatelier's principle.

One disadvantage of this approach arises from the use of corrosive acids in high concentrations at elevated temperatures. An alternative approach has focused on exploiting the crosslinking of sodium alginate, a sodium salt of copolymer alginic acid that possesses carboxyl groups as repeating sidechain units. 123 These carboxyl groups form a coordination complex in the presence of divalent metal cations. Membrane surfaces are modulated to initiate complexation by imparting a net positive charge. 124, 144 It is important to note that the techniques developed for improving adhesion are generally performed prior to chemical functionalization intended to modify surface energies and interfacial interactions at solid− liquid interfaces.

In past research, we have demonstrated the separation of SAGD viscous oil-rich emulsions exploiting the orthogonal wettability derived from the hierarchical texturation of ZnO tetrapods arrayed onto a stainless-steel mesh. 16 An amorphous silica layer was deposited to tether ZnO tetrapods onto stainless-steel through the formation of siloxane linkages ( Figure 6A−C) . The 3D textured membranes show a distinctive combination of oleophilic and superhydrophobic behavior. Membrane separation was achieved within a customdesigned thermal autoclave in the presence of endogenously generated pressure. At operational temperatures >130°C, complex emulsions were disrupted, reducing water content in the permeate to 0.69 vol % in a single pass. A related approach by Kollarigowda et al. 108 focused on the use of finely textured block copolymers applied to a cellulose fiber base, which selectively eliminates thiol contaminants along with affecting oil−water emulsion separation. A 3-(trimethoxysilyl)propyl acrylate-block-myrcene block copolymer was chemically attached to the cellulose membrane using reversible additionfragmentation chain transfer polymerization ( Figure 6D−F) . The grafting of the block copolymer reversed the wettability behavior of the cellulosic membrane from superhydrophilic to superhydrophobic and oleophilic. Myrcene moieties on the membrane surface reacted with thiol contaminants, through "thiol-ene" chemistry, 145 eliminating noxious odors from the separated water.

The cleaning of SAGD wastewater has been recently demonstrated by Mahdi et al., 113 who used a hybrid membrane incorporating hollow TiO 2 nanotubes and polyethersulfone. The overall polymer matrix possessed a mean pore radius of ca. 4 nm that varied with the TiO 2 nanotube loading. TiO 2 nanotubes (average height of 10 μm and a diameter of 250 nm), polyethersulfone (PES), and polyvinylpyrrolidone (PVP) were dispersed in dimethylacetamide solvent and cast onto a glass surface ( Figure 6G −I). Next, nonsolvent-induced phase separation in a coagulation bath of deionized water was used to prepare a superhydrophilic membrane. At 1 wt % loading of TiO 2 nanotubes, hybrid membranes removed 53.9% of dissolved organic matter from SAGD-produced water and showed a relatively low predilection for fouling.

Attallah et al. 82 have designed poly(ethylene oxide) (PEO)based membranes incorporating a γ-Al 2 O 3 /TiO 2 ceramic support tethered using organosilanes. These membranes have effective pore dimensions less than 10 nm and were successful in reducing the organic carbon content of the separated water by approximately 91%, along with a 47% reduction in sulfates. Modified membranes with a γ-Al 2 O 3 base support exhibit flux rates in the range of 50−150 L/(h m 2 ) that increase over time, significantly greater than their unmodified counterpart. In contrast, membranes modified with a TiO 2 base support exhibited higher flux rates, ranging 220−350 L/(h m 2 ) that slightly decreased over time.

The effective design of membranes for the separation of SAGD emulsions requires a deeper understanding of the nature of emulsions and their interactions with membrane surfaces. Mechanistic understanding of interfacial interactions and the development of systematic compositionmesoscalestructure−function correlationswill enable rational design of orthogonally wettable membrane architectures as well as the selection of process conditions that aid in the destabilization of emulsions. The design of membrane architectures and processes that mitigate fouling and yield high flux rates is particularly important to enable their integration within modular mobile media filtration units that are being increasingly adopted and aim to process over 10 000 barrels a day per unit.

As discussed in the preceding section, a wide variety of materials have been used to prepare membranes for the separation of oil−water emulsions based on differences in wettability. However, the selective separation of different organic molecules remains less developed. A particular problem pertains to the separation of diluents, lighter hydrocarbons added to modify the flow properties of bitumen. As noted in the introductory sections, a substantial portion of pipeline capacity is consumed in the flow of diluent back and forth between production sites and refineries in North America. 147 Globally, ca. 100 million barrels per day of oil are transported to refineries, with unconventional heavy oil that requires dilution claiming an ever-increasing share. 148 The most commonly used diluents are hydrocarbon solvents such as naphtha, kerosene, light natural gas condensates, and light crude oils. 147 The availability of energy-efficient nonthermal methods such as membrane-based technologies to separate diluents from heavier bitumen fractions would transformatively alter the economics of solvent recovery with substantial implications for the viability of the SAGD oil recovery process. 15, 117 As inspiration and rationalization for membrane design to separate dilbit, reverse osmosis membranes are widely used for water desalination and have extensively supplanted thermal desalination. Approximately 320 000 m 3 of clean water per day is produced by reverse osmosis, almost twice the volume of crude oil handled by refineries. 160, 161 Using membranes to separate mixtures of hydrocarbons is an emerging area that promises decreased operational time and reduced energy consumption; the latter derives from mitigating the liquid-tovapor phase change required in conventional separation and purification procedures. Membrane methods can potentially fractionate highly complex mixtures exploiting differences in molecular size, shape, and surface interactions and are anticipated to bring about as much as a 10× increase in energy efficiency as compared to current energy-intensive thermal methods. 148 One of the biggest challenges for membrane-based technologies is the separation of molecules with similar kinetic diameters with selective permeability for one type of organic molecule over another. Pore size exclusion and sorption− diffusion are the main mechanisms for liquid-phase separations through membranes. 162, 163 In size exclusion, the permeate is a liquid phase that travels through the pores with solute species that are below the molecular weight cutoff of the membrane. In sorption−diffusion separations, the feed as a liquid phase is partially vaporized into the membrane surface promoted by a difference in chemical potential, and that results in the diffusion of the components of the permeate into the membrane, and consequently, desorption of the permeate in the vapor phase at the downstream side of the membrane takes place. Castro-Munõz et al. note that the efficacy of separation in membrane-based technologies depends on several factors encompassing the composition of the mixture sought to be separated, operational parameters, and distinctive membrane features. 164 Specifically, it is essential to consider the type of solvent/solute, molecular weight of solute/solvent, polarity, and solute charge for enhancing efficiency. 162, 164 Furthermore, parameters such as flow rate, temperature, and pressure are also characteristics to consider for parametric optimization in the separation of different components of a solution. 164−166 In terms of the membrane design, it is important to evaluate the membrane material, the architecture and flow geometry of the module, and characteristics such as pore size, wettability, tortuosity, and porosity. 164−166 A balance between permeability and selectivity is pivotal in achieving optimal separation. Typically, an enhancement in permeability is inversely correlated with the selectivity of permeation. The pore size distribution represents a key parameter that has to be optimized to ensure optimal separation performance. 162, 167, 168 A variety of materials have been used to modulate pore dimensions to achieve the selective permeability of a membrane for liquid-phase separations. Some of these materials that can potentially engender selective separation of the mixtures of organic molecules include carbon molecular sieves (CMS), diamondlike carbon (DLC), graphene oxide (GO), crosslinked microporous polymers, linear polymers, polymers of intrinsic microporosity (PIMs), crosslinked polymers with contorted monomers, conjugated microporous polymers (CMPs), metal−organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic cages (POCs), and zeolites. 160, 162 Of these materials, COFs are covalently interconnected crystalline porous networks with tunable pore dimensions built from multifunctional structural units with substantial scope for functionalization of pore edges. Pore tuning in COFs is achieved based on engineering the length and structure of linkers, anchoring a variety of functional groups onto the pore walls of the framework, and through alterations of the stacking modes of two-dimensional (2D) frameworks. 169, 170 As an illustrative example, Dey et al. synthesized a variety of COF-based membranes through interfacial crystallization and accessed pore dimensions ranging from 1.4 to 2.6 nm. 170, 171 These modifications were achieved by the incorporation of a series of linear linkers that were combined with a framework of 1,3,5-triformylphloroglucinol (Tp) trigonal planar linkers to assemble a pore geometry that allowed for the selective permeation of small molecules such as acetonitrile, water, ethanol, and methanol.

Tuning the chemistry of pore surfaces is key to achieving liquid separations. Nagai et al. tailored the pore dimensions of COFs synthesized by condensing hexahydroxytriphenylene (HHTP) with azide-appended benzene diboronic acid (N3-BDBA) and benzene diboronic acid (BDBA). The azide units enable the use of click chemistry reactions with alkynes to generate 2-propynyl acetate on the wall of the framework, enabling reduction of pore dimensions from ca. 3.0 to 1.2 nm. In another example, Li et al. prepared nanoporous COF-based membranes by modified interfacial polymerization through the incorporation of phenolic hydroxyl groups on triformylbenzene monomers, which modified the stacking mode of the 2D COF framework from AA to AB stacking, thereby providing access to highly constrained ca. 0.6 nm channels with a uniform pore distribution. 172 This pore geometry showed an excellent ability to exclude relatively high-molecular-weight compounds such as 1-butanol and phenylcarbinol while permitting permeation of smaller molecules such as water and methanol. As such, postsynthetic modification of COFs holds considerable promise for tuning pore dimensions and enhancing membrane selectivity. 173 MOF-based membranes for liquid-phase separation have been widely used in different fields such as aromatic separations, liquid fuel purification, water treatment, gas separations, and solvent recovery. 174, 175 These crystalline porous networks exhibit high porosity, high surface area, tunable pore dimensions, scope for introducing flexibility, and thermal stability. 176 In terms of engendering separations, the key features that make these materials attractive include pore dimensions and geometries that are readily tunable based on the selection of inorganic nodes and organic linkers; furthermore, pore edges can be rendered amenable to functionalization. 175 MOF-based separations typically exploit preferential adsorption and shape selectivity. MOF-based membranes have found extensive use in gas-phase separations of hydrocarbons; liquid-phase separations are relatively underexplored. 174, 175 Nevertheless, Diestel et al. developed a polycrystalline MOF membrane utilizing a zeolitic imidazolate framework (ZIF-8) to separate liquid mixtures of n-hexane with benzene and n-hexane with 1,3,5-trimethylbenzene (mesitylene) through pervaporation. 174, 175, 177 Based on previous studies on ZIF-8 membranes, bulky alkanes and aromatics are not capable of migrating through the narrow pores of the membranes, while linear alkanes are adsorbed due to their characteristic sieve exclusion behavior. 175, 177 The experiments illustrated that the single components, n-hexane, and benzene were adsorbed onto the surface of the ZIF-8 membrane, whereas mesitylene was not adsorbed to the porous ZIF-8 framework. In the separation of n-hexanes and benzene mixtures, the more mobile component of the mixture, n-hexane, was blocked by the less mobile bulky molecule, benzene. When considering the mixture of n-hexane and mesitylene, a molecular sieving phenomenon was observed, and the flux of n-hexane was dependent on the concentration of mesitylene. Therefore, for the mesitylene to be separated from n-hexanes by the porous network, the molar mesitylene ratio in the mixture should be less than 50% since a high concentration of mesitylene can block the pore entrance for the mobile component (n-hexane).

Surface modification of MOF-based membranes has rendered a beneficial outcome in the separation and recovery of aromatic compounds, which is pivotal in the oil and gas industry. For instance, Zhao et al. developed a series of functionalized metal−organic polyhedral (MOP)/hyperbranched polymer hybrid membranes for the recovery of aromatic hydrocarbons from aromatic−aliphatic mixtures. 178 They evaluated the effects of functional groups on MOF-based membranes architectures on the separation of aromatics− aliphatic mixtures in terms of adsorption of aromatics. A hybrid MOP-SO 3 Na n H m membrane for the separation of toluene and n-heptane exhibited a permeation flux of 528 g/(m 2 h) for toluene recovery, whereas a benzene and cyclohexane mixture revealed a flux rate of 540 g/(m 2 h) for benzene recovery. The separation of benzene and cyclohexane is currently one of the most challenging separations in the chemical industry due to their indistinguishable boiling points, ca. 0.6°C of variation. 179 The presence of a sulfonate group on the modified MOP membrane enhanced the adsorption selectivity of toluene over n-heptane and of benzene over cyclohexane due to the π−π interactions between the sulfone-conjugated MOP framework and toluene. It has been demonstrated previously that polymers functionalized with a strong electron-withdrawing group, such as sulfone, can potentially interact with the πelectron clouds of aromatic hydrocarbons to increase the selectivity and permeability at the surface. 178, 180 The permeability and selectivity of these hybrid membranes were dependent on functional groups present on the surface of the framework. The MOF structures with functional groups with high polarity promoted a feasible adsorption or recovery of aromatic hydrocarbons.

Polymer-based membranes offer a combination of facile processability, flexibility, and scalability for the separation of liquid mixtures. As an illustrative example, Thompson et al. developed a highly thermally stable N-aryl-linked spirocyclic polymer membrane, which exhibited enrichment of molecules lighter than 170 Da, enabling the selective permeation of hydrocarbons with less than 12 carbon atoms and boiling points less than 200°C (Figure 7) . 148 This spirobifluorene-aryl-diamine-based membranes exhibited a mechanically robust surface with a narrow distribution of ultramicropores as a result of efficient chain packing designed through the incorporation of flexible C−N linkages that promote π−π stacking interactions at the surface. The membrane architectures enabled the separation of jet fuel and gasoline from a crude oil mixture. Thomson and co-workers suggest that the separation was engendered due to the presence of aromatic C−N linkages that provide a combination of hindered rotation and optimal pore distribution to promote the transport of molecules through the micropores at rates governed by molecular size and dimensions.

Currently, developed membrane-based methods used for the separation of organic solvent mixtures include pervaporation, nanofiltration, reverse osmosis, and forward osmosis. 160, 162 Typical membrane systems such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis exploit distinctive pore size diameters ranging from 100 to 10 000 nm, 2 to 100 nm, 0.5 to 2 nm, and 0.1 to 1 nm, respectively. 164, 181 Nanofiltration membranes designed to sieve organic molecules need to selectively permeate molecules in the range of 200− 1000 Da, contain pores below 2 nm, and exhibit chemical stability across a wide variety of solvents. 162 Indeed, organic solvent reverse osmosis membranes can sieve organic molecules with a molecular weight lower than 100 Da. 182 Some of these methods have been scaled to industrial operations. For instance, nanofiltration membranes are currently employed at ExxonMobil's Beaumont refinery to produce lube oil and as a part of dewaxing operations. 160, 183 These polymeric membranes are constituted from polyimide and are used to selectively segregate lube oil and recover a mixture of ketones or aromatics including methyl ethyl ketone, methyl isobutyl ketone, and toluene. 183 As another example, modules developed by ExxonMobil Corporation and W.R. Grace have been used to separate linear alkanes with a molecular weight less than 300 Da from lube oil molecules to successfully reduce fuel oil consumption, greenhouse gas emissions, water usage, and emissions of volatile organic materials. 183 Ideally, membranes for separating different hydrocarbons by properties such as molecular weight or boiling point should exhibit high permeability for one phase concurrent with high rejection above a threshold molecular weight or kinetic diameter. In addition, the membranes should exhibit a combination of mechanical stability, entropic selectivity, and scalability. By taking advantage of current developed concepts and technologies for liquid−liquid, liquid−solid, and gas-phase separations, membrane systems hold promise for enabling effective separation of diluent from bitumen as well as different fractions of bitumen, thereby alleviating the considerable energy and cost burden of conventional thermal distillation processes.

Corrosion is the gradual degradation of a material as a result of chemical reactions with the surrounding environment ( Figure  8 ). 14 While corrosion represents a considerable drag on resources, in the case of base metals, it is inevitability driven by strong thermodynamic driving forces. The oxidation of base metals tends to be strongly exothermic as a result of high enthalpies of metal−oxygen bonds. As such, protecting base metals essentially comes down to delaying the kinetics of corrosion reactions by establishing diffusion limitations at metal interfaces, effectuating electrochemical polarization to increase overpotentials for corrosion reactions, selectively triggering the formation of passivation layers at interfaces, or triggering sacrificial reactions that spare the components sought to be protected. 184 Throughout both upstream and midstream processes, corrosion is a challenge across the entire infrastructure spanning from the wellhead to the refinery. The SAGD infrastructure is primarily constructed from low alloy steels as a result of performance constraints and cost considerations and is subject to flow-accelerated corrosion, localized corrosion, erosion, and erosion−corrosion. 25 When looking at pipeline production failures in Alberta, Canada, from 1980 to 2005, 58% failed as a result of internal corrosion and 12% from external corrosion. 25 About 25% of transmission pipeline accidents are caused by corrosion. 25 Extensive studies have investigated fracture patterns (intergranular vs transgranular) that result from stress corrosion cracking and have identified origins as being concurrent potent environments (ranging from pH 6.5−9), use of susceptible materials, and inhomogeneous stress gradients. 185, 186 Much research has been invested in advancing mechanistic understanding so that even if corrosion cannot be entirely prevented, it can be substantially slowed down and detected before catastrophic failure. Methods to inhibit corrosion can be clubbed into five broad categories: barrier protection, cathodic protection, anodic passivation, active corrosion inhibition, and "selfhealing." 14 Barrier protection provides an impermeable layer that prevents corrosive species from reaching the substrate, thereby increasing the effective tortuosity. Cathodic protection uses a sacrificial anode that polarizes the substrate, such that the anode oxidizes rapidly before the substrate. Anodic protection uses the formation of a passivating, impermeable layer to impede the redox reaction. Active corrosion inhibition uses strongly adsorbing Lewis bases that are released upon damage to form a protective barrier at exposed interfaces. "Self-healing" mechanisms involve reconstitution of coatings from the release of monomeric precursors from micro-and nanocontainers or encapsulated particles. As an alternative strategy, corrosion is mitigated by supplanting low alloy steels in components such as piping, valves, fittings, and vessels with cement, plastics, or nanocomposites. For instance, cement pipes can then be internally coated with plastic or fiberglass to reduce friction; however, such tubing is plagued by lack of ductility and exhibits a tendency to undergo plastic deformation as a result of stresses developed during thermal cycling. 25 Plastic piping (polyester resin) is a viable alternative and affords corrosion resistance but is typically constrained in its ability to handle high pressures and temperatures. 25 Therefore, utilizing mechanisms of corrosion control is paramount to viable and efficient production within the oil sands. 199 In lease tanks, trucks, and rail cars, corrosion is likely to occur along the vessel floor as a result of the accumulation of water; the high sulfur content (sourness) of most heavy oil increases the susceptibility of midstream infrastructure to corrosion, as internal corrosion by acidic gases such as CO 2 and H 2 S are the primary origins of failure. 25 These gases can further precipitate hydrogen embrittlement, stepwise cracking, and hydrogen blistering. 25 Currently, industry-standard coatings are zinc alloys (often deposited by methods such as hot dip galvanization) that provide sacrificial cathodic protection. 187, 188 The extent of corrosion inhibition is directly proportional to the thickness of zinc alloy. Zinc alloy coatings are prone to flaking and cracking as a result of the less ductile nature of the coatings in comparison to underlying steel substrates. Chromium and other chromate coatings have been extensively explored as a means of corrosion inhibition as a result of their outstanding wear resistance, ease of plating, and corrosion resistance. The outstanding corrosion inhibition afforded by such coatings derives from the facile formation of a passivating layer triggered by changes in local pH upon initiation of corrosion and enabled by the extremely lowsolubility products of chromate salts. 189, 190 However, extensive regulations resulting from the presumed carcinogenicity of chromium have severely restricted the use of hexavalent chromium; chromium concentrations in air, water, and soil are actively monitored and subject to stringent regulations across the world. 187 Alternatives to zinc and chromate coatings include polymers, metal oxides, and self-assembled molecular monolayers. 191−193 Substantial research has focused on the development of nanocomposite thin-film coatings that incorporate nanoparticles in various base polymer matrices to activate multiple modes of corrosion inhibition. For instance, we have designed hybrid nanocomposite coatings that incorporate multiwalled carbon nanotubes or graphene with a polyetherimide (PEI) matrix to offer synergistic corrosion inhibition to low alloy steels through an "active−passive" mechanism. 187 PEI shows excellent adhesion to steel (as well as to Al alloys) and can be cast as pinhole-free films that afford considerable barrier protection. Tafel plot analysis shows the formation of an expanded passivation window upon the incorporation of graphene, translating to approximately 3 orders of magnitude diminution of corrosion rates. 187 The loading of graphene and its connectivity within the nanocomposite is crucial to corrosion inhibition. A systematic study of different graphene concentrations in PEI has identified two distinct regimes, below and above percolation thresholds for graphene. 194 At low graphene concentrations, graphene fillers induce greatly increased tortuosity of ion diffusion pathways, enabling excellent corrosion protection of underlying aluminum alloys, whereas at high concentrations, graphene flakes form a percolative network and initiate deleterious galvanic corrosion ( Figure 8C ). 194 As an alternative strategy, highly electroactive Mg nano and microparticles have been embedded within PEI and epoxy/polyamide matrices, wherein they afford sacrificial cathodic protection. 192,195−198 In a SAGD operation, tailing pipelines used for the transportation of the slurry, containing water, clay, silt, and sand that remains after the heavy oil is recovered from the oil sands are especially prone to degradation. Tailing pipelines suffer from both erosion and corrosion that is a result of synergistic mechanical abrasion and electrochemical processes. 25, 199, 200 Solutions to prevent corrosion and erosion within pipelines involve cladding with ceramic or metal composites, polymer linings, and surface modification. Success has been observed with ceramic materials (TiO 2 , SiC, and diamond with a Ni−P alloy electroless deposition) as they afford a combination of high hardness and chemical stability. 201, 202 For instance, Neville et al. have reported a tungsten carbide metal matrix composite cladding, deposited using plasma-transferred arc welding, which provides a substantial increase in corrosion resistance. The combination of hard tungsten carbide particles with the ductile metal matrix binder (Ni, Cr, Si, B, and Fe) allows for increased strength and fracture toughness of the composite. 199 Saha et al. have also explored a tungsten carbide coating incorporating cobalt deposited using high-velocity oxy-fuel process and compared the corrosion potential as a function of coating microstructure, contrasting microcrystalline and nanocrystalline coatings with pristine steel ( Figure 8C ). 201 They observed that the difference in microcrystalline and nanocrystalline coatings altered the dominant failure mechanism, in that the former failed due to erosion and the latter from corrosion. The nanocrystalline coating had a reduced erosion−corrosion rate by one-third compared to the microcrystalline coating.

The viability of heavy oil production from unconventional deposits depends not just on efficacy and cost but also on minimizing environmental impact. As such, the close monitoring of infrastructure components and ensuring their integrity is of paramount importance. Preventing failures resulting from corrosion is at the heart of this puzzle and requires integrated corrosion control systems. Incorporating coatings that exhibit multiple modes of corrosion inhibition offers the greatest defense against the synergistic mechanisms of deterioration. The development of efficient membranes that allow for the cleaning of produced water and heavy oil, as described in Section 3 will yield cleaner oil and water streams, is thus integrally linked to the preservation of midstream infrastructure. Considerable research is focused on active corrosion inhibition and self-healing coatings as a means of restoring coating integrity upon damage as well as in improved real-time diagnostics of corrosion combining electrochemical measurements and other nondestructive evaluation tools with machine learning. 203−205 6. SOLUTIONS FOR MIDSTREAM TRANSPORTATION 6.1. Coatings. Crude oils with API gravities <22.3°( specific gravities> 920 kg/m 3 ) are generally classified as being heavy oils. Extra heavy crudes have API gravities <10 and specific gravities in excess of 1000 kg/m 3 . The largest flow streams in Canada, Western Canadian Select and Access Western, have an API gravity range from 18 to 22; these streams further have sulfur content in excess of 3.5%. In comparison, Western Texas Intermediate has an API gravity of ca. 40 and a sulfur content of <0.5%. The transportation of heavy crude oils by pipeline, railcar, truck, or tanker gives rise to a substantial set of challenges stemming from the high viscosity of these fuels; for instance, bitumen has a viscosity exceeding 300 000 cP and thus requires extensive thermal jacketing or dilution with lighter hydrocarbons to induce flow. In addition, bitumen deposits in the Athabasca region of North America are landlocked, precluding the use of large tankers. As such, there is considerable reliance on pipeline transport (Figure 1) , albeit pipeline capacities are limited in every direction and unable to transport the full production of the Canadian Oil Sands to refineries.

For pipeline transport of heavy crude oil, rheological modifiers such as diluents, surfactants, polymer additives, and emulsifiers have been extensively used to reduce the viscosity, alter flow profiles, and decrease frictional forces such as to enable transportation of these fluids at reasonable pumping powers. 206−208 However, a major drawback to these approaches is that such additives must then be removed and pumped back to the point of origin; much valuable pipeline capacity is consumed in the flow of light condensates added solely for the purposes of rheology modification, which furthermore necessitate a substantial infrastructure for solvent recovery at terminals. As an entirely different approach, much recent effort has focused on the modification of the interior surfaces of pipelines to alter flow profiles. By reducing frictional forces at the solid−liquid interface, the overall drag in the system can be reduced, which in turn reduces the amount of diluent required and lowers the pumping power necessary to flow heavy crude oil within a pipeline. Such surface modification further reduces the extent of fouling of the solid surface in pipelines, bitutainers, rail cars, and shipping vessels, thereby increasing the efficiency of recovery. In this section, we will focus on surface coatings capable of facilitating drag reduction as well as alternative strategies for partial bitumen solidification to enable solid-phase transport.

To decrease drag in a system through direct modification of the solid surface, localized regions of slip must be formed to break the no-slip boundary condition in laminar flow and to reduce solid−liquid interactions under turbulent flow ( Figure  9B ). 209−216 While surface energy (measured in the form of contact angles) plays a substantial role in governing the formation of slip planes, the 3D texture of the surface is of paramount importance and determines the formation and interconnectedness of trapped air pockets known as plastrons. 15,117,209,216−218 Such plastrons provide regions of localized slip, as depicted in Figure 9B . According to Young's equation (eq 7), the surface roughness (r) acts as a scaling factor that modifies the inherent wettability of a surface, which is determined by the interplay between the solid−liquid (γ SL ), liquid−vapor (γ LV ), and solid−vapor (γ SV ) interfacial energies. 219, 220 As a result of the high surface tension of many liquids, the interfacial energy of the solid−liquid interface must be substantially reduced to prevent wetting of the surface. Plastrons resist fluid permeation and function as localized regions of slip since friction between the liquid and air pocket is very low. However, it is worth noting that the plastronic surface is metastable; beyond a specific breakthrough, the oil will permeate into the pores and establish a Wenzel wetting regime.

While the modified Young's equation suggests that the surface roughness acts solely as a scaling factor to enhance the inherent wettability of a surface, upon closer examination of the force balance between the gravitational forces acting on the test liquid and the direction of the surface tension, it becomes apparent that the details of the geometry of the plastron play a determining role. 216, 217, 221 Considering a straight pillarlike geometry ( Figure 9A ), the inherent contact angle must remain above 90°for a liquid to be repelled by the surface. However, when the plastron opening is characterized by the reentrant curvature as sketched in Figure 9A , a liquid droplet can be repelled by the surface even when the intrinsic contact angle is below 90°. This is a direct result of the force applied on the droplet by surface tension, γ, being oriented opposite in direction to the differential pressure, Δp. 217, 221 As the inherent contact angle approaches 0°, the surface tension of the liquid is directed parallel to the surface with the vertical component being oriented opposite in direction to the applied pressure. As such, a doubly reentrant surface curvature is required to repel a completely wetting liquid with an inherent contact angle of 0°. 216 Given a doubly reentrant surface opening, a completely wetting liquid spreads along the surface of the material and begins to wrap around the edges of the post; however, since a significant projection of the surface tension is oriented vertically in opposition to the direction of the applied pressure, it is able to repel the fluid from further permeating within the plastron. It is worth noting that such a scenario requires a specific ratio of topographical features with the appropriate curvature to fully repel the liquid. If there are only a sparse few topographical elements, liquid droplets are much more readily able to outweigh the breakthrough pressure; in such a scenario, the net vertical force derived from the surface tension of the liquid is readily surpassed by the positive pressure from the liquid. Analogously, if topographical units are in close proximity, the ratio of liquid in contact with the solid surface greatly exceeds the liquid in contact with air within the plastrons, once again enabling the liquid to wet the surface. As such, a stringent set of criteria must be satisfied with respect to the shape of the plastrons, their areal density, and the relative spacing between topographical features to fully repel a liquid. 216 A number of key descriptors have been discovered that can effectively bring about drag reduction and antifouling properties through the reduction of friction at the solid−liquid interface. Liu et al. made use of reactive ion etching (RIE) to form doubly reentrant structures of SiO 2 and used these precisely patterned surfaces to confirm the importance of geometry, areal density, and spacing of textural elements on omniphobicity ( Figure 10A ). 216 Not only do the authors demonstrate that the doubly reentrant SiO 2 surface is unwettable by water (with a surface tension of 72.8 mN/m) without any additional chemical functionalization, they furthermore demonstrated that it is not wetted even by perfluorohexane (C 6 F 14, 3M Fluorinert (FC-72)), which has the lowest known surface tension of all liquids at 10 mN/m. 216 These results illustrate the paramount role of texture in the design of omniphobic surfaces for drag reduction. 222−225 However, lithographic patterning of doubly reentrant architectures has limited viability for applications at the scale of midstream infrastructure, and thus efforts have focused on striking a balance between textural elements that stabilize plastrons and chemical functionalization to reduce surface energy.

An approach to define reentrant curvature at macroscopic scales inaccessible through precision patterning methods such as electron beam lithography, focused ion beam deposition, and ultraviolet lithography 226 that has attracted much recent attention is nanoimprint lithography. In this approach, a precise template with micro-and nanostructured roughness is prepared and the imprint is mechanically transferred onto the substrate. The compatibility of nanoimprint lithography with roll-to-roll and roll-to-plate processing holds promise for largescale applications ( Figure 11A ). 227 Ye et al. have demonstrated that this technique can be applied with sub-30 nm resolution. 228 Choi et al. developed an oleophobic coating by combining reverse nanoimprint lithography with reactive ion etching using a polydimethylsiloxane template; the patterned surfaces were functionalized with a fluoroalkylsilane, specifically, heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane (HDFS), self-assembled monolayer. 229 Figure 11B shows the precise control afforded by this method in the imprinting of various geometries, including arrays of cones, pillars, holes, and lines within the overhang structures. 229 Choo et al. demonstrated the use of UV-nanoimprint lithography in the precise patterning of perfluoropolyether surfaces; these authors used UV-cured polyurethane acrylate to replicate the complex texture of rose petals ( Figure 11C ). 230 Such surfaces emulate the detailed hierarchical texture of rose petals including micropapillae and nanofolds; the wettability of rose petals toward water droplets is further captured in high fidelity in these intricately patterned architectures.

A nonlithographic approach for constructing reentrant surfaces at larger scales has been developed through modification of metal meshes through techniques such as electrospinning, candle soot coating, or spray coating. 117, 231, 232 In contrast to the etched surface demonstrated by Liu et al., omniphobic meshes make use of the periodic microscale texture from the mesh along with nanoscale texture attained from surface functionalization with other textural elements such as nanoparticles and microparticles to form a hierarchically textured surface with randomly positioned reentrant elements. As an example, we have spray coated a stainless-steel mesh surface with ZnO tetrapods that have tapered arms ending in tips with nanoscale dimensions (Figure 10C ). 117 These randomly oriented reentrant structures were then functionalized with 1H,1H,2H,2H-perfluorooctanephosphonic acid to form a plastronic omniphobic surface that was manufacturable at scale and able to glide heavy crude oil. This robust, hierarchically textured surface produced contact angles of 160 ± 1°for water and 156 ± 1°for heavy crude oil. 117 To produce reentrant, hierarchically textured surfaces with excellent adhesion, we have devised an alternative strategy directed at stabilizing a porous surface embedding a high density of surface plastrons. In particular, we have used electroless nickel plating to codeposit a nickel phosphide thin film in conjunction with poly(tetrafluoroethylene) beads ( Figure 10B ). 209 The evolution of hydrogen during electroless plating gives rise to a surface pitting, thereby creating an abundance of textural elements under the appropriate process conditions. Upon functionalization with 1H,1H,2H,2H-perfluorooctanephosphonic acid, such a combination of nanoscale texture and reentrant plastronic geometries yielded an omniphobic surface that was capable of facilitating drag reduction of up to 17% for a light hydrocarbon, castor oil, in laminar flow. 209 However, plastrons were observed not to survive high flow pressures or turbulent flow conditions, underscoring the need to develop more robust crosslinked architectures. An alternative electrochemical approach involves anodization of an aluminum surface to develop surface texture followed by the self-assembly of 1H,1H,2H,2H-perfluorodecyltrichlorosilane, which yields a surface with a rapeseed oil contact angle of 150°. 233 Another strategy that we have recently demonstrated uses colloidal crystal templating to define a doubly reentrant surface using polystyrene microspheres as sacrificial templates. An inverse opal geometry is constructed from sintered TiO 2 nanospheres and upon functionalization with 1H,1H,2H,2Hperfluorooctanephosphonic acid yields a hierarchically textured, reentrant structure that glides heavy crude oil (achieving contact angles as high as 161 ± 2°) ( Figure 10D ). 218 A superoleophobic coating can be created using a variety of techniques, as long as the aforementioned key components of reduced surface energy, hierarchical texturation, and doubly reentrant curvature are maintained. Approaches for casting polymeric films such as electrospinning, templating, layer-bylayer deposition, electrochemical deposition, plasma treatment, and self-assembly provide a means of inducing surface texture and have additional advantages such as flexibility, solutionphase processability, tunability of domain geometries based on molecular constituents, and applicability at scale. 234, 226, 227 Kumar et al. engineered hierarchical textured and nonwoven porous fibers using electrospun poly(1,6-heptadiyne) fibers modified with acrylonitrile butadiene styrene (ABS) that demonstrated hydrophobic behavior, robust thermal properties, and low ice adhesion. 235 Mulazim et al. have similarly explored the deposition of a photocured fluoroacrylate resin (Fluowet AC812, CH 2 CHCOOC 2 H 4 (CF 2 CF 2 ) n , where n = 3−6) with trimethylolpropane tris(3-mercaptopropionate), triallyl 1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and silica particles treated with hexamethydisilazane, on ABS and highimpact polystyrene (HIPS). 236 These researchers observed a direct correlation between increasing hydrophobicity and oleophobicity and higher fluorine content.

Plasma nanotexturing represents an additional method to engineer oleophobic coatings. Ellinas et al. have demonstrated a superoleophobic/superhydrophobic PMMA surface prepared from the assembly of PS colloidal microparticles, subsequent plasma etching, and deposition of a fluorocarbon thin film. 237 The design of engineered surfaces that exhibit a high degree of oil repellency, excellent adhesion strength, resilience to corrosive species, and robustness to thermal cycling based on interrogation of physical mechanisms and elucidation of chemical design principles will bring disruptive innovation to the transportation and storage of heavy crude oil and bitumen. While geometric and chemical descriptors have emerged from the studies of lithographically patterned substrates and understanding of the interfacial structure, future research is focused on manufacturability of textured coatings and improving their resilience toward abrasive and corrosive species. Application at scale will further require the development of facile surface preparation procedures to enable retrofitting applications on existing infrastructure, or alternatively, the design of liners and sleeves that can be fitted onto the components.

6.2. Solid-Phase Transportation of Bitumen. To mitigate energy-intensive and wasteful processes of dilution and heating for transportation via pipelines, 152, 238, 239 as well as to mitigate the catastrophic environmental impact of oil spills on vulnerable ecosystems, much recent attention has focused on partial solidification of viscoelastic bitumen. Solid prills of bitumen can be much more safely transported using railroads, freight carriers, or container ships. A notable innovation from the Canadian National Railway Company (CN) comprises mixing and encasing bitumen within hydrocarbonaceous polymer shells. 240 The semisolid pucks are water-resistant, nonadhering, and buoyant; as such, this CanaPux technology has the potential to considerably reduce the cost and environmental risks associated with transporting liquid bitumen. However, the polymer shell wrapping the bitumen requires further processing at the point of use, and considering the massive volumes that need to be transported on a daily basis, inevitably necessitates the use of a large volume of polymeric media. An alternative method developed by BitCrude and Solideum BITTS involves the separation of the lighter fraction of bitumen and polymerization of viscous fractions under temperature or pressure to create bitumen bricks and balls. 22, 241, 242 The lighter fractions and bitumen balls are then transported separately as liquid-and solid-phase materials, respectively. This approach does not require the incorporation of extrinsic coating materials.

Recently, in collaboration with Cenovus Energy, we have developed a safe and viable method to form solid-phase bitumen microcapsules without the need for any extraneous additives. In this approach, the bitumen is reconfigured such as to encapsulate lighter fractions (saturates, aromatics, resins) of bitumen within a shell constituted from crosslinked asphaltenes. Asphaltenes, conjugated π-systems with aliphatic tails and various pendant functional groups (representative structural models of asphaltenes are shown in Figure 12A ), can be readily extracted from bitumen by precipitating with nheptane or hexanes. The asphaltenes are coated to form a shell enrobing deasphalted bitumen droplets in a core−shell configuration. Two different approaches have been developed to achieve the microencapsulation of bitumen. In the first approach, an automated jetting system equipped with a concentric nozzle facilitates the preparation of solid-phase bitumen microcapsules. The inner flow stream of concentric nozzles comprises heated bitumen, whereas the outer flow stream comprises a dispersion of asphaltenes in chlorinated organic solvents, as shown in Figure 12B . The flow stream is mechanically disrupted with an attenuator to enable the formation of uniform microcapsules. The microcapsules are collected in a water bath containing 2 wt % surfactant (poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide)) to prevent coalescence. 23 In the second approach, powdered ground asphaltenes are conformally coated onto hot bitumen droplets jetted from a singular flow nozzle onto a granular powder bath, as shown in Figure 12B . This enables thermally mediated crosslinking of asphaltenes around hot bitumen droplets. 24 In both cases, the high propensity of asphaltenes to aggregate, which represents a major source of flow impediments in reservoirs, is harnessed to facilitate crosslinking into a solid form that can be utilized for midstream transportation. The crosslinking of asphaltenes within the shells of microcapsules is a result of π−π interactions, metal−ligand interactions, thiol-ene reactions, Diels−Alder reactions, and disulfide formation.

The recovered microcapsules have been examined by confocal microscopy to differentiate between the bitumen core and asphaltene shell. The darker regions in Figure 12D correspond to solidified shells comprising solidified asphaltenes, whereas fluorescent regions ( Figure 12D (ii−iv)) in the cross-sectional image show lighter bitumen fractions that have a pronounced luminescent response. Since no extraneous chemical additives are present in solid-phase bitumen microcapsules, they can be readily fluidized into the original mixture through the application of compressive stress at a refinery, as shown in Figure 12E .

Solidification approaches that transform liquid bitumen into microcapsules, pucks, pellets, or bricks for transportation greatly expand opportunities for midstream transportation beyond pipelines and tanker cars to trucks, conventional freight cars, and container ships. As such, these represent a promising alternative to pipeline capacity constraints, energyintensive separation processes inevitable upon dilution, and mitigating environmental hazards associated with oil spills.

In this perspective article, several aspects of materials science challenges in the utilization of heavy crude oil have been highlighted with an emphasis on the Canadian Oil Sands. In particular, we have delineated the foundational principles underpinning candidate solutions for thermal insulation, membrane-assisted separations, corrosion protection, and midstream bitumen transportation. Our purpose is not to provide an exhaustive account of all of the challenges encountered in the extraction, transportation, and processing of heavy crude oil but to frame the need for surface modification and materials' design approaches with a view toward the preservation of function under extreme environments commonly observed during operations. The demanding conditions for materials and surfaces are directly traceable to the high viscosity, low surface tension, and substantial sulfur content of heavy crude oil, which necessitates extensive thermal processes, warrants dilution/emulsification to ease flow, and engenders the need to protect corrodible components. The US Energy Information Administration's predictions until 2050 demonstrate extensively and perhaps increasing worldwide reliance on heavy oil and unconventional deposits in general. 1 The materials' technologies discussed in this perspective are of paramount importance to the economic viability of heavy oil production within the Canadian Oil Sands.

Thermal insulation is pivotal to overall energy efficiency, underpins protection of the infrastructure from degradation from thermal fatigue and is essential to maintain flow streams across the SAGD, emulsion separation, and midstream transportation processes. Tailored membrane technologies provide a means of decreasing reliance on energy-intensive thermal methods and hold promise for the separation of hydrocarbons from complex emulsions, engendering the separation of bitumen−diluent mixtures, and even fractionation of the different fractions of bitumen. As such, membrane technologies could usher in a new era of distributed chemical manufacturing and reduce reliance on large-scale refineries. Since the oil and gas infrastructure is predominantly constructed from low alloy steels, corrosion inhibition remains an existential challenge that is central to maintaining the continuity of operations and preventing catastrophic failures that can discharge hydrocarbons into the environment. Incorporating multiple modes of corrosion inhibition in protective coatings along with real-time monitoring of the integrity of components using advanced sensor technologies and machine learning methods holds promise for increased safety of the midstream transportation infrastructure. Limitations on accessible pipeline capacity have led to a massive surge in interest in surface modification and encapsulation technologies, spanning the range from drag reduction of oil flow in pipelines, oleophobic surfaces that readily glide viscous oil with no detectable residues, and encapsulation technologies that enable solid-phase transport. Such technologies will greatly reduce reliance on light condensate diluents, alleviate surface fouling and associated needs for cleaning, reduce waste, and cut down on energy expenditures.

Looking to the future, three strands of research hold particular promise. As the field of petroleomics attains maturity and detailed information of speciation and molecular structure of heavy oils becomes available, the rational design of approaches to engender separations, preclude wettability, and drive selective reaction chemistry during extraction and immediate postprocessing is becoming increasingly viable. 243−245 Such an idea of "refinery at the hole" combined with a push toward distributed chemical manufacturing can enable a new richly intertwined paradigm for the interconnected oil, plastics, and chemical industries. A particular frontier involves elucidation of interfacial structure at metal, mineral, and aqueous interfaces through spectroscopic methods, X-ray/neutron scattering, and first-principles calculations. Elucidation of interfacial structure will inform the design of methods to perturb and modify interactions, thereby enhancing oil recovery, aiding in fractionation of oleic mixtures, and informing the design of flow systems. Reactive flow systems that implement partial upgradation (such as desulfurization, hydrogenation, etc.) hold great promise for improved operations in midstream transportation and for obtaining better values at the refinery.

A second major area with the potential to transform midstream transportation and processing has its origins in decreasing levelized costs of electricity, which render electrochemical processes readily accessible on site for purposes such as hydrogen generation from electrocatalysis of water, electrochemical separations, electropolymerization, and direct electrochemical transformation of heavy oil fractions into value-added products. The ability to source hydrogen and power in remote locations as a result of advances in solar photovoltaics and photocatalysis has the potential to shift a substantial amount of the processing to the sites where heavy oil are extracted, greatly mitigating the challenges with midstream transportation, potentially bypassing the use of refineries for some fractions, and overall enabling access to a broader cross-section of refineries by achieving partial upgradation and separation.

A third major strand of research that holds the promise for accelerated design of materials for function in extreme environments involves the confluence of data science, machine learning, and artificial intelligence. 246−249 These approaches are particularly useful for the simultaneous optimization of multiple objectives, e.g., superoleophobicity and adhesion strength, along a Pareto frontier. Statistical learning approaches have the ability to enable the more systematic and strategic navigation of high-dimensional design spaces. In this context, such approaches can quantify the extent to which different parameters elicit a specific response (and identify null variables), rank features in order of their importance, and establish correlations across the different variables. The oil and gas industry has large data sets such as diagnostics information from infrastructure, extensive long-term testing data, and multimodal analysis of fluids and scale products. These data sets are particularly amenable to the use of statistical learning methods, which can analyze trends, estimate the magnitude of influence, and map correlations across diverse variables. In the context of materials' design for the applications in heavy oil considered in this perspective, machine learning and sequential learning algorithms enable the construction of a response surface and its iterative improvement based on the identification of the next most valuable experiments. As such, these methods hold promise for accelerating convergence on the desired set of surface chemistries and microstructures by counterbalancing trade-offs between samples that would help to improve the extent to which the model captures the data set (exploration mode) or converge toward a predicted maximum or minimum within the response surface (exploitation mode). By mapping trends within the design space, statistical learning methods can thus help determine to identify specific metrics to optimize in subsequent experiments. Such sequential learning methods hold promise to entirely transform materials' selection, prototyping, and piloting, enabling much more rapid deployment of new materials in the oil and gas infrastructure.

Annual Energy Outlook 2021; United States Energy Information Administration

A Review of Novel Techniques for Heavy Oil and Bitumen Extraction and Upgrading

Ullmann's Encycl

GovernmentofCanada Oil Resources

GovernmentofCanada Crude Oil Facts

Explaining Attitudes Toward U.S. Energy Extraction: Offshore Drilling, the Keystone XL Pipeline, and Hydraulic Fracturing

Railroad transportation of crude oil in Canada: Developing long-term forecasts, and evaluating the impact of proposed pipeline projects

Nonthermal Methods of Recovery

Nonconventional Petroleum Resources

Effect of steam-assisted gravity drainage produced water properties on oil/water transient interfacial tension

Traversing energy landscapes away from equilibrium: strategies for accessing and utilizing metastable phase space

Drilling in Extreme Environments: Space Drilling and the Oil and Gas Industry

Materials and corrosion trends in offshore and subsea oil and gas production. npj Mater

Hybrid Nanostructured Coatings for Corrosion Protection of Base Metals: A Sustainability Perspective

Orthogonal Wettability of Hierarchically Textured Metal Meshes as a Means of Separating Water/Oil Emulsions

Separation of Viscous Oil Emulsions Using Three-Dimensional Nanotetrapodal ZnO Membranes

Functionalized Tetrapodal ZnO Membranes Exhibiting Superoleophobic and Superhydrophilic Character for Water/Oil Separation Based on Differential Wettability

Incorporation of Hydroxyethylcellulose-Functionalized Halloysite as a Means of Decreasing the Thermal Conductivity of Oilwell Cement

An Evaluation of the Reduction of Heat Loss Enabled by Halloysite Modification of Oilwell Cement

Oil Price Differentials Explained: Why Alberta Crude Sells at a Deep Discount

Canadian bitumen is engineered for transport, but the type of product produced can affect spill contingency planning

Asphaltene Microencapsulation of Bitumen as a Means of Solid-Phase Transport

Powder bed coating of bitumen with asphaltenes to obtain solid prills for midstream transportation

) Hazardous Materials: FAST Act Requirements for Flammable Liquids and Rail Tank Cars

Heat Recovery Optimization in a Steam-Assisted Gravity Drainage (SAGD) Plant. Energy

Centrifugal Pumps in Heated Bitumen Pipeline Service, Proceedings of the 21st International Pump Users Symposium

In New Advances and a Historical Review of Insulated Steam-Injection Tubing, SPE Western Regional and Pacific Section AAPG Joint Meeting

Economic Potentials and Efficiencies of Oil Sands Operations: Processes and Technologies

Energy Efficiency and Emissions Intensity of SAGD

Reducing the Energy and Steam Consumption of SAGD Through Cyclic Solvent Co-Injection

Impact of Noncondensable Gas on Performance of Steam-Assisted Gravity Drainage

Improving Steam-Assisted Gravity Drainage Using Mobility Control Foams: Foam Assisted-SAGD

Investigation of Surfactant-SAGD Process in Fractured Carbonate Reservoirs

In Thermal Efficiency and Acceleration Benefits of Cross SAGD (XSAGD), International Thermal Operations and Heavy Oil Symposium

Wellbore Heat Losses and Pressure Drop in Steam Injection

Evaluation of steam circulation strategies for SAGD startup

Measurement Techniques for Thermal Conductivity and Interfacial Thermal Conductance of Bulk and Thin Film Materials

Oil Phase Viscosity Behaviour in Expanding-Solvent Steam-Assisted Gravity Drainage

Study on the Thermal Characteristics of Crude Oil Batch Pipelining with Differential Outlet Temperature and Inconstant Flow Rate

Investigation of the Thermal Conductivity of Resin-Based Lightweight Composites Filled with Hollow Glass Microspheres

Enhanced Oil Recovery Field Case Studies

In Cost Reducing Factors in Effective Pipeline Piling Structure Design and Construction in Alberta's Thermal SAGD Gathering Pipeline Systems, International Thermal Operations and Heavy Oil Symposium

Application of High Temperature Coatings for Near-Surface Corrosion Mitigation on SAGD Wells, SPE Thermal Well Integrity and Design Symposium

The High-Temperature Resistance Properties of Polysiloxane/Al Coatings with

Negative Thermal Expansion HfV2O7 Nanostructures for Alleviation of Thermal Stress in Nanocomposite Coatings

Bare Tubing-Concentric and Eccentric Configurations: A Comparative Thermal Computational Fluid Dynamics Study, SPE Heavy Oil Conference-Canada

SAGD Circulation Phase: Thermal Efficiency Evaluation of Five Wellbore Completion Designs in Lloydminster Reservoir, SPE Thermal Well Integrity and Design Symposium

Role of silanized halloysite nanotubes on structural, mechanical properties and fracture toughness of thermoset nanocomposites

Corrosion of New-Generation Steel in Outer Oil Pipeline Environments

The Effect of Corrosion on the Structural Reliability of Steel Offshore Structures

Role of asphaltene and resin in oil field emulsions

Effects of Asphaltene Aggregation in Model Heptane-Toluene Mixtures on Stability of Water-in-Oil Emulsions

Naphthenic Acids in Crude Oils Characterized by Mass Spectrometry

Froth Treatment in Athabasca Oil Sands Bitumen Recovery Process: A Review

Phase Separation and Interfacial Viscoelasticity of Charge-Neutralized Heavy Oil Nanoemulsions in Water

Emulsification and Emulsion Flow in Thermal Recovery Operations with a Focus on SAGD Operations: A Critical Review

Interfacial sciences in unconventional petroleum production: from fundamentals to applications

Role of fine clays in bitumen extraction from oil sands

The wettability of mineral surfaces containing adsorbed asphaltene. Colloids Surf

Supramolecular Assembly Model for Aggregation of Petroleum Asphaltenes

Adsorption of Bituminous Components at Oil/Water Interfaces Investigated by Quartz Crystal Microbalance: Implications to the Stability of Water-in-Oil Emulsions

Dewatering of crude oil emulsions 2. Interfacial properties of the asphaltic constituents of crude oil

Emulsions stabilized with solid nanoparticles: Pickering emulsions

Insights into the formation of hydroxyl ions in calcium carbonate: temperature dependent FTIR and molecular modelling studies

Surface Charge at the Bitumen/Water Interface Investigated by Phase-Sensitive Sum Frequency Generation Vibrational Spectroscopy: Effects of pH, Ions, and Surfactants

Emulsion Formation, Stability, and Rheology

Degradation of kinetically-stable o/w emulsions

Theory of the stability of strongly charged lyophobic sols and the adhesion of strongly charged particles in solutions of electrolytes

Steric stabilization II

Emulsion and Emulsification Technology

Droplet-based electro-coalescence for probing threshold disjoining pressure

SAGD for Heavy Oil Recovery

Surface-Modified Multi-lumen Tubular Membranes for SAGD-Produced Water Treatment

Water issues related to transitioning from conventional to unconventional oil production in the Permian Basin

Water Issues Related to Transitioning from Conventional to Unconventional Oil Production in the Permian Basin

Produced Water Treatment Technologies

Slip between a liquid and a solid: D.M. Tolstoi's (1952) theory reconsidered. Colloids Surf

Adsorption of crude oil from crude oil−water emulsion by mesoporous hafnium oxide ceramics

Resistance of Solid Surfaces to Wetting by Water

Naz, I. Recent development of superwettable materials and their applications in oil-water separation

Impact of GDL structure and wettability on water management in polymer electrolyte fuel cells

Nanotexturation-Induced Extreme Wettability of an Elemental Tellurium Coating

Produced Water Treatment by Membranes: A Review from a Colloidal Perspective

Antifouling Membranes for Oily Wastewater Treatment: Interplay Between Wetting and Membrane Fouling

Membrane Processing of Oily Streams. Wastewater Treatment and Waste Reduction

Use of Membrane Technology for Oil Field and Refinery Produced Water Treatment A Review

Porous Metal Filters and Membranes for Oil−Water Separation

Copper Hydroxyphosphate Nanosheets-Covered Robust Membranes with Superhydrophilicity and Underwater Ultralow Adhesive Superoleophobicity for Oil/Water Separation and Visible Light Photodegradation

Nanowire-Haired Inorganic Membranes with Superhydrophilicity and Underwater Ultralow Adhesive Superoleophobicity for High-Efficiency Oil/Water Separation

Fabrication of Superhydrophobic Copper Mesh by Depositing CuCl for Oil/Water Separation

Inspired by Stenocara Beetles: From Water Collection to High-Efficiency Water-in-Oil Emulsion Separation

Fabrication of Non-Fluorinated Hydrophilic-Oleophobic Stainless Steel Mesh for Oil-Water Separation

Materials and Applications for Low-Cost Ceramic Membranes

Recent Progress in Developing Advanced Membranes for Emulsified Oil/Water Separation

In situ One-Step Fabrication of Durable Superhydrophobic-Superoleophilic Cellulose/LDH Membrane with Hierarchical Structure for Efficiency Oil/Water Separation

Modified Cellulose Membrane with Good Durability for Effective Oilin-Water Emulsion Treatment

Antifouling Cellulose hHbrid Biomembrane for Effective Oil/Water Separation

Graphene Oxide/Polyacrylonitrile Fiber Hierarchical-Structured Membrane for Ultra-Fast Microfiltration of Oil-Water Emulsion

Oil-in-Water Separation with Graphene-Based Nanocomposite Membranes for Produced Water Treatment

Ultrasonic Assisted Ultrafiltration Process for Emulsification of Oil Field Produced Water Treatment

Efficient Separation of Crude Oil-in-Water Emulsion Based on a Robust Underwater Superoleophobic Titanium Dioxide-Coated Mesh

Robust Polymer Nanocomposite Membranes Incorporating Discrete TiO2 Nanotubes for Water Treatment

Superhydrophobic sand with multifunctionalities by TiO2-incorporated mussel-inspired polydopamine

Fabrication of Superhydrophilic and Underwater Superoleophobic Quartz Sand Filter for Oil/Water Separation

Effect of Vertically Oriented Few-Layer Graphene on the Wettability and Interfacial Reactions of the AgCuTi-SiO 2f/SiO 2 System

Biomimetic Plastronic Surfaces for Handling of Viscous Oil

Cupric Phosphate Nanosheets-Wrapped Inorganic Membranes with Superhydrophilic and Outstanding Anticrude Oil-Fouling Property for Oil/Water Separation

Facile Fabrication of Superhydrophobic, Superoleophilic Photocatalytic Membrane for Efficient Oil-Water Separation and Removal of Hazardous Organic Pollutants

Hydrophobicity of rare-earth oxide ceramics

Exploring the Role of Adsorption and Surface State on the Hydrophobicity of Rare Earth Oxides

Intrinsic hydrophilic nature of epitaxial thin-film of rare-earth oxide grown by pulsed laser deposition

Smart Candle Soot Coated Membranes for On-Demand Immiscible Oil/Water Mixture and Emulsion Switchable Separation

Facile Preparation of Loess-Coated Membranes for Multifunctional Surfactant-Stabilized Oil-in-Water Emulsion Separation

Mussel-Inspired Hybrid Coatings that Transform Membrane Hydrophobicity into High Hydrophilicity and Underwater Superoleophobicity for Oilin-Water Emulsion Separation

pH-Induced Non-Fouling Membrane for Effective Separation of Oil-in-Water Emulsion

Comparative Study of Continuous and Intermittent Ultrasonic Ultrafiltration Membrane for Treatment of Synthetic Produced Water Containing Emulsion

A Prewetting Induced Underwater Superoleophobic or Underoil (Super) Hydrophobic Waste Potato Residue-Coated Mesh for Selective Efficient Oil/Water Separation

Synthesis, Characterization and Performance Studies of Polysulfone/Bentonite Nanoparticles Mixed-Matrix Ultra-Filtration Membranes Using Oil Field Produced Water

Copper Oxide (CuO) Loaded Polyacrylonitrile (PAN) Nanofiber Membranes for Antimicrobial Breath Mask Applications

Polymeric Asymmetric Membranes Made from Polyetherimide/Polybenzimidazole/Poly(ethylene glycol)(PEI/PBI/PEG) for Oil−Surfactant− Water Separation

A novel membrane showing both hydrophilic and oleophobic surface properties and its non-fouling performances for potential water treatment applications

Designing Surfaces with Wettability that Varies in Response to Solute Identity and Concentration

Solvent Swollen Polymer

Plasticization and Swelling in Polymeric Membranes in CO2 Removal from Natural Gas

Preparation and Characterization of Graphene Oxide Paper

Inside and Outside: X-ray Absorption Spectroscopy Mapping of Chemical Domains in Graphene Oxide

A Mussel-Inspired Method to Fabricate Reduced Graphene Oxide/g-C3N4 Composites Membranes for Catalytic Decomposition and Oil-in-Water Emulsion Separation

Fluorinated Coatings and Films: Motivation and Significance

Hydrophilic− Oleophobic Coatings on Cellulosic Materials by Plasma Assisted Polymerization in Liquid Phase and Fluorosurfactant Complexation

Ultrafast Oleophobic−Hydrophilic Switching Surfaces for Antifogging, Self-Cleaning, and Oil−Water Separation

Preparation of an Aluminium Phosphate Binder and its Influence on the Bonding Strength of Coating

Study of composition and structure of aluminum phosphate binder

Calcium Concentration Effects on the Mechanical and Biochemical Properties of Chondrocyte-Alginate Constructs

Mechanistic Insights into UV-Initiated Thiol−Ene Reactions on Amorphous Carbon Films

Antifouling cellulose hybrid biomembrane for effective oil/water separation

Pipeline Transportation of Heavy Oils, a Strategic, Economic and Technological Challenge

N-Aryl− Linked Spirocyclic Polymers for Membrane Separations of Complex Hydrocarbon Mixtures

Flow of Heavy Oils at Low Temperatures: Potential Challenges and Solutions

Water-Based Bitumen Recovery from Diluent-Conditioned Oil Sands

Experimental Study of Iranian Heavy Crude Oil Viscosity Reduction by Diluting with Heptane, Methanol, Toluene, Gas Condensate and Naphtha

A Review of Technologies for Transporting Heavy Crude Oil and Bitumen via Pipelines

Spills of Diluted Bitumen from Pipelines: A Comparative Study of Environmental Fate, Effects, and Response

Energy Optimization for a Multistage Crude Oil Distillation Process

Improving Energy Saving of Crude Oil Distillation Units with Optimal Operations

Design Optimization of a Crude Oil Distillation Process

Progressive Crude Oil Distillation: An Energy-Efficient Alternative to Conventional Distillation Process

From Water to Organics in Membrane Separations

Membrane Separation in Organic Liquid: Technologies, Achievements, and Opportunities

Challenges in membrane-based liquid phase separations

Membrane-based technologies as an emerging tool for separating high-added-value compounds from natural products

Advances in Membrane Distillation for Water Desalination and Purification Applications

Materials and membrane technologies for water and energy sustainability

Nanomaterials-Based Membranes Increase Flux and Selectivity to Enable Chemical Separations

Effects of membrane fouling on the nanofiltration of pharmaceutically active compounds (PhACs): Mechanisms and role of membrane pore size

Covalent organic framework-based membranes for liquid separation

Van der Bruggen, B. Covalent organic frameworks for membrane separation

Selective Molecular Separation by Interfacially Crystallized Covalent Organic Framework Thin Films

Laminated self-standing covalent organic framework membrane with uniformly distributed subnanopores for ionic and molecular sieving

Pore surface engineering in covalent organic frameworks

Metal−Organic Frameworks for Liquid Phase Applications

Metal−organic framework membranes: from synthesis to separation application

Characteristics of MOF, MWCNT and graphene containing materials for hydrogen storage: A review

Pervaporation studies of n-hexane, benzene, mesitylene and their mixtures on zeolitic imidazolate framework-8 membranes

Functionalized metal-organic polyhedra hybrid membranes for aromatic hydrocarbons recovery

A review on the separation of benzene/cyclohexane mixtures by pervaporation processes

Crosslinked polystyrene beads modified with polar groups for the separation of aromatic/aliphatic hydrocarbons

A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification

Highly improved organic solvent reverse osmosis (OSRO) membrane for organic liquid mixture separation by simple heat treatment

Membrane Separation in Solvent Lube Dewaxing

Designing green, self-healing coatings for metal protection

Review of stress corrosion cracking of pipeline steels in "low" and "high" pH solutions

A Review of Stress Corrosion Cracking of High Pressure Gas Pipelines

Graphene Nanocomposite Coatings for Protecting Low-Alloy Steels from Corrosion

The Metallurgy of Zinc-Coated Steel

Comparative Tribological Study of Hard and Crack-Free Electrodeposited Chromium Coatings

A Review on Conducting Polymer Coatings for Corrosion Protection

A Review of Modern Assessment Methods for Metal and Metal-Oxide Based Primers for Substrate Corrosion Protection

Metal/ Metal Oxide Nanoparticles as Corrosion Inhibitors

Tortuosity but not Percolation: Design of Exfoliated Graphite Nanocomposite Coatings for Extended Corrosion Protection of Aluminum Alloys

Magnesium Nanocomposite Coatings for Protection of a Lightweight Al Alloy: Modes of Corrosion Protection, Mechanisms of Failure

Nanostructured magnesium composite coatings for corrosion protection of low-alloy steels

Review of alternatives to chromate for corrosion protection of aluminum aerospace alloys

Active metal-based corrosion protective coating systems for aircraft requiring no-chromate pretreatment

Assessing Metal Matrix Composites for Corrosion and Erosion-Corrosion Applications in the Oil Sands Industry

Erosion-corrosion in oil and gas industry: a review

Erosion−Corrosion Resistance of Microcrystalline and Near-Nanocrystalline WC−17Co High Velocity Oxy-Fuel Thermal Spray Coatings

Improvement of the erosion-corrosion resistance of magnesium by electroless Ni-P/Ni (OH) 2-ceramic nanoparticle composite coatings

Nondestructive data assimilation as a tool to diagnose corrosion rate in reinforced concrete structures

Detection of specific features in the functioning of a system for the anti-corrosion protection of underground pipelines at oil and gas enterprises using neural networks. East.-Eur

Prevention/Protection, Diagnosis/Prognosis and Maintenance Strategies

On the rheological behavior of light crude oil: a review

A review of nanomaterials as viscosity reducer for heavy oil

Hydrophobically associated polymers for wettability alteration and enhanced oil recovery−Article review

Hierarchically Textured Oleophobic Internal Coatings that Facilitate Drag Reduction of Viscous Oils in Macroscopic Laminar Flow

Effective slip on textured superhydrophobic surfaces

Characterization of Superhydrophobic Surfaces for Drag Reduction in Turbulent Flow

Feature-Resolved Computational and Analytical Study of Laminar Drag Reduction by Superhydrophobic Surfaces

Drag Reduction of Newtonian Fluid in a Circular Pipe with a Highly Water-Repellent Wall

Ultrahydrophobic Surfaces. Effects of Topography Length Scales on Wettability

Apparent Slip Flows in Hydrophilic and Hydrophobic Microchannels

Turning a Surface Superrepellent Even to Completely Wetting Liquids

Design Parameters for Superhydrophobicity and Superoleophobicity

Three-Dimensional Inverse Opal TiO2 Coatings to Enable the Gliding of Viscous Oils

Superhydrophilic and Superwetting Surfaces: Definition and Mechanisms of Control

Super-Hydrophobic Surfaces: From Natural to Artificial

Candle Soot as a Template for a Transparent Robust Superamphiphobic Coating

Superoleophobic Surfaces

High-Performance Icephobic Droplet Rebound Surface with Nanoscale Doubly Reentrant Structure

Nanonails: A Simple Geometrical Approach to Electrically Tunable Superlyophobic Surfaces

Doubly Reentrant Cavities Prevent Catastrophic Wetting Transitions on Intrinsically Wetting Surfaces

A Review of Roll-to-Roll Nanoimprint Lithography

Fabrication of High Aspect Ratio Micro-Structures with Superhydrophobic and Oleophobic Properties by Using Large-Area Roll-to-Plate Nanoimprint Lithography

Making Modified Fluoropolymer Molds for Ultraviolet Nanoimprint Lithography

Fabrication of Superhydrophobic and Oleophobic Surfaces with Overhang Structure by Reverse Nanoimprint Lithography

Replication of Rose-Petal Surface Structure Using UV-Nanoimprint Lithography

Hierarchically Structured Superoleophobic Surfaces with Ultralow Contact Angle Hysteresis

A Simple Approach to Fabricate Superoleophobic Coatings

Super Oil-Repellent Surfaces

Recent Developments in Polymeric Superoleophobic Surfaces

Poly (1, 6-heptadiyne)/ABS functionalized microfibers for hydrophobic applications

Properties of Thiol−ene Photocurable Highly Hydrophobic and Oleophobic Nanocomposite Coatings on ABS and HIPS Substrates

From Superamphiphobic to Amphiphilic Polymeric Surfaces with Ordered Hierarchical Roughness Fabricated with Colloidal Lithography and Plasma Nanotexturing

Part 1: Transportation of Heavy Crude Oil and Natural Bitumen

Life cycle energy and greenhouse gas emissions from transportation of Canadian oil sands to future markets

Petroleomics: advanced molecular probe for petroleum heavy ends

The Next Grand Challenge for Chemical Analysis

Molecular Fingerprints and Speciation of Crude Oils and Heavy Fractions Revealed by Molecular and Elemental Mass Spectrometry: Keystone between Petroleomics

Navigating the design space of inorganic materials synthesis using statistical methods and machine learning

A predictive machine learning approach for microstructure optimization and materials design

Machine learning assisted design of high entropy alloys with desired property

Designing a Periodic Table for Alloy Design: Harnessing Machine Learning to Navigate a Multiscale Information Space

The authors declare no competing financial interest.