Issued February 7, 1912.
U. S. DEPARTMENT OF AGRICULTURE,
OFFICE OF PUBLIC ROADS— Circular No. 97.
LOGAN WALLER PAGE, Director.
COKE -0 YEN TARS OF THE
UNITED STATES.
BY
PRfiVOST HUBBARD,
Chemist, Office of Public Roads.
Govi rvmkvi bun pick
LETTER OF TRANSMITTAL
United States Department of Agriculture,
Office of Public Roads,
Washington, D. C, October 19, 1911.
Sir: I have the honor to transmit herewith the manuscript of a
circular by Mr. Prevost Hubbard, chemist in this office, entitled
"Coke-Oven Tars of the United States." This publication gives the
results of examinations of all the coke-oven tars at present manu-
factured in this country, together with a brief discussion of their
properties in relation to their use as road materials. I respectfully
request that this manuscript be published as Circular 97 of this office.
Respectfully,
Logan Waller Page,
Director.
Hon. James Wilson,
Secretary of Agriculture.
UR« ' '
COKE-OVEN TARS OF THE UNITED STATES.
The rapidly increasing use in this country of refined coal tar in the
treatment and construction of mads and the fact that an immense
quantity of coal tar will ultimately become available for this purpose
through the installation of by-product coke ovens make it highly
desirable to obtain accurate information as to the properties of coke-
oven tars which are being produced at present. Attention was
called by the author to the importance of this subject in a recent
publication/ as follows:
While, in the manufacture of coal gas. the production of tar is
absolutely unavoidable, this is not true of the manufacture of coke
for metallurgical purposes. There are two genera! types of coke
ovens in use at present, in one of which no attempt is made to recover
the volatile products of the coal. This is the oldesl form of oven,
known as the "beehive," and is extensively used in this country
to-day. Tt is constructed of brick and as its name implies has the
form of a beehive. Bituminous coal is placed in this oven or kiln
and a part of it burned in order to carbonize the remainder, while the
volatile products, such as gas. ammonia, and tar, are allowed to escape
through an opening in the top of the kiln, where they an' lost in II ante
and smoke.
Coke (irons in which the by-products are saved are now used to
some extent in this country, and sooner or later will undoubtedly
replace the old-style oven entirely, and thus increase our output of
tar enormously. The reason that they have not been more generally
adopted in this country is that in the United States tars are of much
less economic importance than in the European countries, where
great chemical industries are based upon the utilization of this
material. < rermany in particular is far in advance of us in this Held
and exports to this country alone coal-tar products to the value of
eral million dollars each year. With the development of the
road-tar industry, which promises to consume vast quantities of tar,
and the uecessity for refining such tars before use, t he general adopt ion
of by-product ovens is only a matter of time. What this will mean
in the increase in tar production can be imagined from the fact that in
1908, "Ut of a total of over 26,000,000 tons of coke produced in coke
ovens, only a little over 1,000,000 tons were obtained from by-product
D 'in. Mew York.
4 COKE-OVEN TARS OF THE UNTTED STATES.
ovens. About 22,000,000 tons of coke wore, therefore, produced
without recovery of the tar. As the average yield of coke per ton of
coal was 66 per cent, this would represent the consumption of over
33,000,000 tons of coal. Upon the basis of a yield of 10 gallons of
tar per ton of coal, it may be seen that over 330,000,000 gallons of
tar were lost in 1908 which might have been saved. As the actual
production of coal tar both from coke ovens and gas houses amounted
to about 101,000,000 gallons, it is evident that over three-fourths of
our possible production of tar as a by-product was lost during that
year. At a valuation of 2\ cents per gallon, this means a loss of over
$8,000,000. With such an increase in production, however, the
monetary value of coal tar would have dropped, so that this figure
may be somewhat exaggerated. In any event, at a conservative
estimate, the tar lost each year from nonrecovery coke ovens is
sufficient to build 9,000 miles of tar macadam road 15 feet wide.
This estimate was based on data taken from reports of the United
States Geological Survey. In a later report by Parker, 1 it is shown
that over 53,000,000 tons of coal were consumed in beehive ovens in
1910, so that on the same basis it would appear that over 530,000,000
gallons of tar were lost during that year. The output of tar from by-
product coke ovens, however, has also continued to increase, as
shown by the following figures taken from this report :
Tar obtained from by-product coke ovens.
Gallons.
1908 42, 720, 609
1909 60, 126, 006
1910 66, 303, 214
The tar thus produced in 1910 was valued at $1,599,453, or about
2.4 cents per gallon. It is evident, therefore, that the value of the
tar lost during that year by the use of beehive ovens amounted to
approximately $12,000,000. That the use of by-product ovens is
increasing in greater proportion than the use of the beehive oven is
shown by the fact that for the former type the increase in 1910 over
1909 in tons of coke produced was 14.13 per cent, while the production
from beehive ovens increased by only 4.57 per cent. Parker adds,
however:
While noteworthy progress has been made in the substitution of modern retort-oven
practice for the wasteful and what should be obsolete beehive or partial-combustion
method of coke making in the United States, this country is still much behind European
countries in this regard.
He says further:
The yield of coal in coke in retort ovens exceeds that obtained in beehive or other
partial-combustion ovens by about 15 per cent, and generally the quality of the coke
is improved.
i The Manufacture of Coke in 1910, United States Geological Survey. '
COKE-OVEN TABS OF THE UNITED STATES.
In order to determine the character of coke-oven tars at present
being produced in the United States, it was first necessary to obtain
samples from all of the known plants, and for this purpose reference
was made to a list of by-product and retort coke-oven plants of the
United States and Canada (Jan. 1. 1910), which was kindly loaned to
the author by Mr. Parker in advance of its publication. 1 Letters
were then written to each plant asking for the following information:
(1) a. At what maximum temperature are your retorts fired in your oven.-?
In your ovens'.'
b. What is the maximum temperature to which the charge of coal is brought in your
ovens? In your ovens?
(2) Whal is th<- specific gravity of your crude tar in your ovens? In your
ovens?
(3) What percent age of free carbon is ton ml in your crude tar from your ovens?
From your ovens?
Will you furnish us for examination a L-gallon sample of your crude tar from
your ovens? From your oveus*.' To he sent at our expense.
Very courteous replies were received from the manufacturers, and in
practically every case samples of t ar were also forwarded. The blanks
in these question- were Idled out by inserting the names of the type or
types of ovens operated by the manufacture! to whom they were sent.
It was found that, where two types of ovens were operated at the same
plant, no attempt was made to separate the tar, and the entire output
was run into a common well. In such cases the sample of tar sub-
mitted wit- a mixture obtained from both ovens. The report of these
samples is given at the bottom of Table 1.
The questions concerning temperature were asked because criticism
from an authoritative source had been received with regard to a state-
ment made by the author in a former publication- to the effect that
in the production of tar from by-product coke ovens " carbonization is
conducted at a lower temperature than in fin manufacture of coal gas.
The resulting tar, therefore, contains a smaller amount of free carbon,
averaging from 3 to 10 per cent * * *." But little reliable infor-
mation on this subject could be obtained from published literature.
although the opinion seemed to prevail that carbonization in by-
product coke ovens La conducted al a lower temperature than in mod-
ern gas-house practice. Thus, according to Lunge, 8 "Hilgenstock
(J. Gasbeleucht., 1902, 617) attributes the notorious difference be-
t ween gas-tar and coke-oven tar with reaped of t heir contents of free
carbon and other products of pyrogenetic decomposition to the fact
thai in coke ovens the escaping sapors <lo not attain temperatures
above 600°< '., and I bal t hey are, moreover, protected against decompo-
sition by the dilution of the kieavj vapors, slowrj given off from the
i Mineral Hfisour.-. of the 1 Dltod '■'• ,1909, Pari II pp 240 842,1 nit I Survey,
i Circular 93, Office of Public Road ' . 1. Department of Agriculture, p
> Coal Tar and Ammonia, 1th ed., pari L, p. 23, Van Moatrand
COKE-OVEN TABS OF THE UNITED STATES.
Table I. — Analyses of crude coke-oven tars
General information.
Answers to questions.
Serial
Nfo
Company and location.
5126 Solvay Process Co., Syracuse, N. Y. .
5123 Semet-Solvay Co., Pennsylvania
SteelCo.,Steelton,Pa.
M2-t Semet-Solvay Co., National Tube
Co., Benwood, W. Va.
5137 Semet-Solvay Co., Milwaukee Coke
& Gas Co. , 'Mil waukee , W is.
5121 Semet-Solvay Co., Pennsylvania
Steel Co., Lebanon, Pa.
5125 By-Products Coke Corporation,
South Chicago, 111.
5128 Semet-Solvay Co. , Detroit, Mich
5200 Semet-Solvey Co., Empire Coke Co.,
Geneva, N. Y.
5189 Semet-Solvay Co., Dunbar Furnace
Co., Dunbar, Pa.
51 "50 Semet-Solvay Co., Central Iron &
Coal Co., Tuscaloosa, Ala.
.„_. /Philadelphia Suburban Gas & Elec-
M " q \ trie Co., Chester, Pa.
5081 Semet-Solvay Co., Ensley , Ala
5095 The New England Gas & Coke Co.,
Everett, Mass.
, ftaQ /Lackawanna Steel Co. , Lackawanna
•'"- ,i \ Iron & Steel Co., Lebanon, Pa.
5159 Dominion Tar & Chemical Co.. Syd-
ney, Nova Scotia.
J Hamilton Otto Coke Co., Hamilton,
\ Ohio.
Carnegie Steel Co. , South Sharon, Pa
Type of
oven.
Maximum
temperature
of firing
retorts.
....do....
Otto Hoff-
man.
|....do....
..do....
5107
5086
5078
5087
5109
5188
5404
I Maryland Steel Co., Sparrows Point,
\ Md.
Citizens' Gas Co., Indianapolis, Ind.
(Pittsburg Gas & Coke Co., The
United Coke & Gas Co., Glassport,
Pa.
Zenith Furnace Co., Duluth, Minn
Semet-Sol-
vay.
....do
....do
....do
....do
do
do
do
do
do
L...do
.do....
1050-1450° C.
1050-1450° C
1050-1450° C.
10.50-1450° C
1050-1450° C.
1050-1450° C.
1050-1450° C.
1050-1450° C.
1050-1450° C.
1250° C
Maximum
tern pera-
ture to
which coal
is brought.
1050° C.
1250° C.
U100°C.
(1000° C
\(1800° F.)..
( 2 )
fim° a...
|\(2000° F.).
United 1(1666° C...
1 Otto. !\(3000°F.).
..do...
..do...
...do....
..do.
Illinois Steel Co. , Joliet, 111 | Koppers
/Illinois Steel Co., Indiana Steel Co., \\ do _
\ Gary, Ind.
Camden Coke Co., (amden, N. J.
Cambria Steel Co.. Johnstown, Va.
/1333° C.
\(2400° F.) .
/1222°C
\(2200°F.)..
( 2 )
9.50-1 150° C.
950-11.50° C.
950-1150° C,
950-1150° C.
950-1150° C
950-1150° C
950-1150° C.
950-11.50° C
950-1150 C°.
1150° C...
1000° C....
1150° a...
il200°C...
Specific
gravity
of crude
tar.
1.12-1.21
1.12-1.21
1.12-1.21
1.12-1.21
1. 12-1. 21
1.12-1.21
1.12-1.21
1.12-1.21
1.12-1.21
1.17
Per cent
of free
carbon
in tar.
3-12
3-12
3-12
3-12
3-12
3-12
3-12
3-12
3-12
5.72
(20
(15° C
1.1
1.1611
' C ) }•
1.171
:}
1000° c. . .
(1800° F.)
( 2 )
1111° c \
(2000° F.)./
1444° C...
(2600° F.).,
1222° C.... 1
(2200° F.).
1222° C.... II
(2200 o F.)./
( 2 )
[1222-1277° C. il
«200 • 2300° \\ (2)
l (F.) !|
/1444°C ! 1388° C...
\(2600°F.)...I (2500° F.)
1100° c j{ 88 £; 950 °
Otto Hoff-
man.
United
Otto.
fOttoHoff-
J man..
■ I U n i t e d
I Otto. i\(2000°F.)...
'(United /1000° C
/1000°C 833° C
\(1800°F.)...| (1500°_F.)
/1222° C
1(2200° F.)...
/1111° C
\(2000° F.)...
(1111°C
5089 Lackawanna Steel Co. , Buffalo, N. Y.
Otto. j\(1800°F.)..
Uothberg.j{l^o C V.j;;
1055° C. . . .
(1900° F.).
i 1111° C ..
(2000° F.).
i 1111°C...
(2000° F.).
1000° C. . . .
(1800° F.)
1000° C....
(1800° F.).
1.10
1.170
1.14
1.2
^ 1.19
1.14-1.15
(50° F.I
1.207
10° C
( 2 )
\l. 16-1. 20
< 1.174
1.169
1.20-1.30
5 (1.221)
8
8-10
16-24
10-1
6 1 6.
'. 09-10. 64
3 8-10
4-5
16. 59
( 2 )
12-15
4.35
7-9
5(7.3)
1 Approximately.
2 No information.
a Varies with coal. Coal with 28 per cent of volatile matter used.
* With H 2 0.
B At present.
6 Variable.
' Trace.
8 Trace of solids.
» Distillate, solid.
i« Distillate, one-fourth solid.
» Distillate, nine-tenths solid.
•2 Distillate, three-fourths solid.
" Distillate, eight-ninths solid.
u Distillate, one-half solid.
COKE-OVEN TARS OF THE UNITED STATES.
produced in the United States and Canada.
Examination, Office of Public Roads.
Spe-
cific
gravity
of tar,
25' C.
Per
cent
of free
car-
bon.
1.195
1.206
1. 176
1. 168
1. 173
1. 109
1.159
1.181
1.159
1.141
1. 17.')
1.160
1.214
1.143
1.171
I 160
I 182
1 211
I 210
7.76
8.77
7.14
6.10
4.71
1. 191 7. 49
6.56
6.07
8.85
5.05
3.96
6.90
13.94
14.05
10.81
1.U.0 8.37
1. 191 7
1.179 8.49
1.138 5.21
1.176 10.53
Per
cent
of ash.
Per
cent j
soluble j
in CS 2 , '
includ-
ing
H 3 5.
12.18
2. 78
H. 30
16 si I
0.12
.07
.04
.05
.06
.03
.11
.08
.02
.02
Distillation results.
Water.
92. 12
91.16
92.82
93.85
95. 23
92.48
'93.33
93.85
91.13
94.93
- a
m -
1.0
1.0
1. 1
1.8
.6
( 7 )
6.9
4.0
2.0
3.2
95. 99 2. 3
93.04, 3.3
86.06 2.2
85. 82 5. i
89. 1 1 3.2
91.57 :; 1
92.08 1 11
91. is 1.1
94.72 ]
1.43
.05 87. 77
.04 97.23
1 1
1.9
3. 5
06 88.64 2.2
11 10. I
83. 21 1 2. 7 2. 2
( 7 )
5.9
3.4
1.7
2.8
2.8
2.0
4.4
2.8
3.0
1.6
3.0
Light oils
up to
110° C.
8 0.3
.4
1.9
1.4
1.6
'2.8
2.6
n 1.4
2.9
» 1.4
1.9
3. 1
» 1. 6
1.3
1.1
1.1
9 1.7
» 1.3
1.8
Middle Heavy
oils, 110°- oils, 170°-
170° C. 270° C.
".5
0.3
.3
1.5
1.2
1.3
2. 3
2.1
1.0
2.3
2.5
1.2
1.2
1.0
0.8
'■> 2.0
.7
.8
.8
>'- 1. 1
9.4
.6
.2
.3
0.7
1.7
.6
.6
.6
.2 .2
. 6 ■ 5
.6
.7
9.0
.6
1.4
.5
» .2
".4
2. 3 9 . 3
.ii.it.-. two-third olid
tillate, four-fifths olid.
■ Ighth olid.
Intn »Ud.
• illate, one third olid
jo i>lst illati 1 illd,
ite, one fifth oild.
si
"13. 1
9 14.0
14.9
13 21.1
» 17. r,
is 23. 6
U 14. li
10 17.0
16 20.0
18.6
Heavy
oils, 270°-
315° C.
11.5
12.3
13.2
18.9
15.5
20.7
13.0
15.5
17.8
16.3
22.8 19.5
« 16.5 14. 1
23.5 20.4
,5 27.2
27.(1
i« 12. 1
is 17. 2
23. 9
i" 20. 9
'118.1
9 20.0
9 20.C
"20.5
1 I
10.
24.2
24.4
10.2
15.1
21.4
23.0
18.0
IS. 5
19 8.2
a>7.9
21 11.9
2° 5. 5
19 9.4
B 6. 9
I 11.4
21 6.5
107.5
ii'13.6
"9.3
i' 15. 6
n 9. 4
i>7.3
19 3.8
'9 11.0
219.6
'o ll.fi
7.3
6.9
Pitch.
Se-
rial
No.
2^70.0
» 74. 7
10.6 1 69.5
4.9*69.4
8. 4 » 70. 1
i»12.5
11 13. 4
9 7.1
5.7
10.4
"65.1
26 68. 4
2*63.8
» (VS.
8.2
14.4
8.1
0.7
3.5
9.7
8.5
10.4
6.3
12.0
6.5
7.5
2* 09. 3
55.2
- 70
**59.8
2*61.1
» 73. 7
28 69.7
2*60.8
» 63.5
Ph
79. 1 512*
77.6 5123
73. 1 5124
72.5 5137
73.7 .".121
68.9 5125
72.0 5128
67.7 5200
73.1 5189
71.5 5160
62.6 5074
73.2 5081
59.7 5095
74.6 5083
63.5 5159
64.9 5107
77.:. 5086
3.2 5078
5087
26 62.8
26 07. 1
- 66. 1
2*71.1
64. 7
07.0
67.8
00.3
70.2
75.
5109
5188
5404
5108
.-.OS'.I
» Distillate, two-fifths rolld.
" Distillate, one-seventh olid
Mate, three fifth 1 solid
■ i'ii. n, ..li and tlckj
in, 1,. \,i j ofl and tlcky.
■ ' iii, ii, hard and brittle.
»" Pitch, pi
8 COKE-OVEN TARS OF THE UNITED STATES.
interior of the coal block, with the (ire-resisting gases escaping at the
same time from the outer zone of the block. On the other hand, in
the case of gas retorts, the heavy vapors escape at once undiluted
by the fire-resisting gases which are set free afterwards, and the
heavy gases are thus exposed to the white heat of the upper part of
the retort. "
Answers given by the manufacturers with respect to this question
indicate only an approximate knowledge. In general it may be said
that carbonization below 970° C. is considered low temperature; from
970° 0. to 1,100° C, medium temperature; and from 1,100° C. to
1,540° C. high temperature; and that modern gas-house practice
involves the use of high temperatures. However this may be, it is
not the purpose of this circular to compare coke-oven tars with gas-
house tars, but to consider the former with relation to their utility
as road materials.
From a total of 31 manufacturers to whom the questions were sub-
mitted 30 replies were received, but 4 of these reported their plants
as not in operation. The remaining 26 furnished samples of their
crude tar for examination and answered the questions in so far as
they were able. Upon receipt of each sample the entire contents of
the package were thoroughly mixed and a representative sample
taken for analysis. The results of these analyses, together with the
information furnished by the manufacturers, are given in Table I.
In this table the different tars are grouped according to the type of
oven in which they were produced.
In columns 4 and 5 all temperatures are expressed in degrees
Centigrade, although where the manufacturers gave the temperatures
in degrees Fahrenheit their statements are shown in parentheses.
In column 5 it will be noticed that statements relative to the maxi-
mum temperature to which the coal is brought during distillation
indicate that two of the plants run below 970° C, that a total of
22 run not over 1,150° C, that 9 run 'from 950° C. to 1,150° C, and
that only 5 run above 1,150° C. The maximum temperature of
firing the retorts is, however, reported in most cases as being higher
than the maximum temperature to which the coal is brought.
The maximum percentage of free carbon reported is from 16 to 24
per cent, but 17 manufacturers reported the maximum percentage of
free carbon as being 12 per cent or under, and only 4 as 16 per cent
or over.
Analyses of the samples received were made in accordance with the
methods described in a former publication 1 of the office. The w r ork
consisted in determining the specific gravity, free carbon, or organic
matter insoluble in c. p. carbon disulphide upon a 15-minute digestion
at room temperature, material soluble in carbon disulphide, percent-
age of ash, and percentage of different fractions obtained by distilling
a 250 c. c. sample in a 750 c. c. tubulated glass retort with the ther-
1 Bulletin 38, Office of Public Roads, U. S. Department of Agriculture.
CUKE-OVEN TABS OF THE UNITED STATES.
9
mometer bo placed that the top of the bull) was level "\\ ith the bottom
of the juncture of the stem and body of the retort.
Jt will be noted that the gravities of the samples examined range
from 1.133 to 1.214 and that the great majority are lower than 1.200.
This in itself indicates low percentages of free carbon. The mini-
mum percentage of free carbon was 2.73, the maximum 16.80, and the
average for the 20 samples 8.38. Eighteen samples contained less
than 10 per cent of free carbon anil 8 more than 10 per cent. About
two-thirds of these products might, therefore, be considered as low-
carbon tars and the otner third as medium-carbon tars. The amount
of ash in no case exceeded 0.10 per cent, and in most cases it was
practically nil. This is, of course, also true of practically all gas-
house coal tars. The percentage oi water present varied from a
trace to 10.1 per cent by volume, but in only 3 instances did it exceed
5 per cent. Water is a variable, depending upon a number of condi-
tions, and, as it is not a. part of the true tar, has been eliminated
in Table II. Before leaving Table I. however, it is of interest to note
that 14 of the pitch residues, remaining after distillation had been
carried to 315° C, were either soft or plastic a condition which has
seldom been noticed by the author in the distillation of gas-house
coal tars. The amount of solids which crystallized or precipitated
out of the different fractions was found to vary greatly, ;ts shown
in i he foot-notes to Table I.
Table II. Analysis of coke-oven tars upon a water-free basis.
Serial
num-
ber.
Type of oven.
Percent-
age of
free car-
bon.
Fractions by weight.
Percent-
age up
toll0°C
Percent-
age from
1 10-1 70° C.
Percent-
age from
170--J7n c C,
Percent-
age from
270-315°C.
Percent-
age of
pitch.
5126
7.82
8.84
7.21
6. 19
4.73
7.49
6.97
6. 28
9.00
5.19
4.04
7.09
14.22
14.1. 9
LI. 12
g.60
5.26
10.68
12.55
2. 81
ll.fi]
17.17
0.30
.30
1. 55
1.21
1.30
.30
2.44
2.17
1.42
1.95
L.32
1.02
2. 34
1.46
1.54
l.'Jl
.91
.91
.90
1.34
1.21
1.03
i a
•_>. .-/>
30
0.70
1.71
.60
.60
.60
.31
.51
.20
.30
.81
.20
.51
. 1(1
.51
.61
.40
.40
1.31
. Ill
.M0
.20
.30
.60
1 ', 78
11.59
12.39
13.33
19.18
15.57
20. 7d
L3. 81
16. 04
IS. 10
16.76
[9.89
14.50
20. si
11.40
24. 89
25. 15
10.30
16.29
28. 83
16.39
19.07
L&fifi
Hi 12
7.35
6.95
10.70
•1. 97
s. 44
8.90
6.05
1(1. 76
5.79
1 2. 75
8, 13
14.69
v 47
9. :■>
8.61
10.61
6.86
11. II
12 19
7. 1.4
7. 52
79. 73
5123
5-24
...do
.... 88
5137
...do
73. 6!!
5121
...do
74.07
5126
do
68. 90
512*
...do
70.53
do
70. IN
:.i-'i
...do
;4. 36
6160
do
7:-t. .v.
.■5074
.do
'i ^r
GOO
..do
75.30
5095
Otto HofTm
do.
-
5159
do
65. 32
6107
do
66. 90
■
71. 11
...do
B& ii
5109
..■I-)..
68.28
5122
.do
60. 89
67.87
72. 87
5127
oho Hodman and United Otto
do.
71.45
81.57
5069
i alted Otto and Rothben
The results given in Table 11 arc calculated upon a water-free
bask i.e., the percentages arc expressed in terms of the actual tar
exclusive of water. Considering these products according to type.
10
COKE-OVEN TARS OF THE UNITED STATES.
it will be seen that the tar produced by the Koppers ovens contains
the lowest percentage of free carbon, the Semet-Solvay tars the
next lowest, the United Otto next, the Otto Hoffman next, and
the mixed tar from the United Otto and Rothberg ovens contains
the highest percentage of free carbon. For the sake of comparison
the minimum, maximum, and average percentages of free carbon
for each of these types are shown in Table III.
Table. 111. — Percentage of free carbon in coke-oven tars.
| Water-free basis.]
Type of oven.
I'ercentage of free carbon.
Minimum. Maximum. Average
Koppers
Semet-Solvay
United Otto
Otto Hoffman
Otto Hoffman and United Otto (mixed)
United Otto and Kotkberg (mixed). . ..
2.81
4.04
5.26
8.02
11.51
17.17
3.95
9.00
12.55
14. 09
13.52
17.17
3.38
(i. 74
9.00
12.10
12.51
17.17
The percentages of various fractions for the different types of
tars overlap to such an extent that no detailed comparison will
be made. The maximum, minimum, and average total distillates
to 315° C. for the different types are, however, given in Table IV.
Table IV. — Percentage by volume of total distillate to 315° C. in coke-oven tars.
[Water-free basis.]
Type of oven.
I'ercentage by volume.
Minimum. Maximum. Average
Koppers
Semet-Solvay
United Otto
Otto Hoffman ..
Otto Hoffman and United Otto (mixed)
United Otto and Rothberg (mixed). . ..
30.5
22.0
25.0
25. 3
19.9
20. 9
30.0
40.8
38.5
43. 6
32.1
20.9
33.3
29.9
32.6
30.
20.0
20. 9
From this Table it is evident that wide variations exist in the
relation of total distillate to pitch residue in the coke-oven tars
produced in this country, and this is even true of different tars
produced by the same type of oven.
Straight coal-tar road binders or refined coal tars are usually
manufactured by subjecting the crude material to a process of dis-
tillation with or without steam or air agitation. Distillation is
carried to the point at which the residuum remaining in the still has
obtained the desired consistency at normal temperatures, and this
involves the removal of certain of the more volatile oils present in
the crude material. For use in construction work a soft and almost
fluid pitch is often produced, and the consistency of this pitch is
COKE-OVEN TABS OF THE UNITED STATES. 11
controlled by means of a melting point or float test. When the
crude tar runs abnormally high in free carbon, it is sometimes mixed
with crude water-gas tar before distillation. Water-gas tar con-
tains a very low percentage of free carbon, and by properly propor-
tioning the two a product is obtained, upon distillation, which
does not carry more than the maximum limit of free carbon set by
manufacturers. What the maximum limit should be is a much
mooted question among those who have given thought to this mat-
ter. The governing considerations are: (1) What is the most econom-
ical limit from the standpoint of manufacture? and (2) What is
the proper limit with regard to the utilization of the product as a
road material? For a number of reason-, which it is unnecessary
to mention in this circular, an excessively high-carbon tar is difficult
to distill properly and. with other things equal, the lower the per-
centage of carbon the easier and shorter the distilling process. From
this standpoint, therefore, by-product coke-oven tars are well adapted
to the manufacture of road binders. Moreover, because of their
low percentage of free carbon, they may be employed in a manner
similar to water-gas tars, when it is desired to utilize a crude high-
carbon tar in the production of a medium-carbon tar road binder.
In an ordinary road tar for use in construction work where fire
carbon is present to the extent of about 20 per cent, the proportion
of total distillate, below 315° C, to pitch residue is approximately
] to 4. Where this relation exists the pitch residue is hard and
brittle. A residue which is soft or plastic is to be preferred, as
it would indicate longer life during service, and where such a residue
is present the proportion of distillate would naturally be lower
for a given consistency, as the distillates may be considered as
fluxes for the residues. If such is the case, it is evident from the
foregoing tables that coke-oven tars offer a valuable source of supply
for tar road binders. As an example, even the highest -carbon
tar, No. 5089, if distilled to the point where the proportion of dis-
tillate, below 315° C, to the pitch residue was as 1 to 4, would con-
tain less than 1 ( .) per cent of free carbon, which is at present con-
sidered as not excessive for a refined coal tar.
In conclusion it ma\ be said that indications point strongly t<>
the fact that by-product coke ovens will eventually play a mosl
important part in the road-material industry, and it is to he hoped
that their general adoption in this country will be rapid. The
future demand for economical bituminous road hinders in the United
States will undoubtedly exceed the supply, and this in spite of the
natural increase in petroleum and asphalt road hinders. If such
is the case, the present loss of enormous quantities of tar, to sa\
nothing of gas and ammonia, because of the use of beehive ovens,
is a matter Worth} <>f the utmost consideration on the part of all
who are interested in the conservat ion of our resources]
O
UC SOUTHERN REGIONAL LIBRARY FACILITY
II INI I I II I III I I
AA OOO 731 026