I
N. W. FRANKE, E. I. CROWLEYI, and H. J. ELDER Gulf Research & Development Co., P.O. Box 2038, Pittsburgh 30, Pa.
Solvent Extraction of lignite and Carbonization of Lignite Extracts Mild extraction-hydrogenation preceding carbonization points way to reducing cost of hydrogen used -one of maior obstacles to commercial exploitation of coal liquefaction
IN
MANUFACTURING synthetic liquid fuels by the hydrogenation of coal, two major obstacles to commercial exploitation are the expense of the equipment used in hydrogenation and the cost of hydrogen consumed. Much effort has been made to minimize the factors responsible for the high capital cost of the hydrogenation plant (7-3, 7). The work described in this article is designed to reduce the cost of hydrogen consumed by disproportionating the hydrogen already present in the coal to a liquid fraction which would be hydrogen-rich and a solid char which would be deficient in hydrogen. This is done in carbonization processes. In the process described, the lignite was given a mild extraction-hydrogenation before the carbonization to determine if the nature and amount of the liquid products might be improved. Although some hydrogen is added in this process, the amount used might be less than that in the more conventional coal hydrogenation process. I n lignite, relatively little of the hydrogen is recovered in liquid organic products during carbonization ; instead, a large part of the hydrogen is evolved as water and gases, and the yield of liquid hydrocarbons is very low. A 1 Presentaddress,lDavison Chemical Co., Baltimore 3, Md.
1402
light hydrogenation, such as that effected by heating with Tetralin, could alter the linkages binding coal units together and change the chemical structure, especially the oxygen bonds in the lignite, so that an appreciably greater proportion of the carbonization products would be liquid than those in the carbonization of untreated lignite. This process, if successful, would also reduce the capital outlay for a synthetic liquid fuels plant. Lignites were used entirely in this study rather than higher rank coals, because a major portion of the U. S. coal reserves are lignites, and also, from the vieivpoint of the conservation of national resources, they are of less value than the high rank coals which are in many ways superior for use as fuels and for making coke.
Experimental Work Preparation of Lignite. Three different lignites were used, and their origin and composition are given in Table I . The lignites were ground in a laboratorysize hammer mill and dried in an oven at 110" C. in a nitrogen stream to constant weight. Screen analysis of the dried lignite showed that 96 to 98% passed a standard Tyler 80-mesh screen. All work was done on material treated this way, and the calculations were made on
INDUSTRIAL AND ENGINEERING CHEMISTRY
the assumption that this was moisturefree lignite. Solvents. All solvents used in the lignite extraction were purchased from chemical suppliers, except for the partially hydrogenated derivatives of anthracene, phenanthrene, chrysene, and a recycle solvent from the extract hydrogenation. Cresol (99f cresol of which over 957; is para isomer), Gulf Oil Corp., Pittsburgh, Pa. Naphthalene, recrystallized grade, Distillation Products Industries Division of Eastman Kodak Co.: Rochester, K.Y . Tetralin, technical grade, E. I . du Pont de Nemours & Co., Wilmington 98, Del. Decalin, practical grade, Distillation Products Industries Phenanthrene, technical grade (7@y0), Distillation Products Industries Anthracene, melting point 216" to 218 C., Distillation Products Industries Pyrene, practical grade (850/0), Distilation Products Industries Chrysene, 245' C. minimum melting point, Reilly Tar & Chemical Corp., Indianapolis 4, Ind.
OCTAHYDKOANTHRACEKE. This material was prepared by heating anLhracene at 175" C. in the presence of hydrogen a t 1700 pounds per square inch gage with about 10% of a 50y0 nickel on kieselguhr catalyst until 4 moles of hydrogen had been absorbed for each
mole of anthracene present. The crude product was filtered and recrystallized from alcohol. The octahydroanthracene present estimated from the distillation curve is above 90%. T h e melting point is 55" to 61" C., and a spectroscopic examination confirmed the other physical properties which indicate the material to be 1,2,3,4,5,6,7,8-octahydroanthracene. OCTAHYDROPHENANTHRENE. This material was prepared by hydrogenating phenanthrene a t 350" C. a t a pressure of 1500 pounds per square inch gage in the presence of 10% of a 13% rnolybdena on alumina catalyst. Fractional distillation of this product showed 90% boiling between 252" and 272" C. a t 760 mm. of mercury. I t is apparently a mixture of hydrogenated phenanthrenes but was not identified further. OCTAHYDROCHRYSENE. This material was prepared by hydrogenating chrysene a t 315" C. a t a pressure of 1700 pounds per square inch gage in the presence of 40% of a 52% nickel on kieselguhr catalyst. Fractional distillation of this material showed that 90% of the material distilled a t 367" C. a t 760 mm. of mercury, and although this material was not examined carefully, it was thought to be largely octahydrochrysene. Extraction. The extraction was accomplished by heating the lignite and solvent at the desired temperature under pressure for 45 minutes. In a typical experiment, 200 grams of the dried ground lignite and 400 grams of an 80 to 20 mixture of Tetralin and cresol were placed in a 2-liter autoclave which was then sealed and placed in a rocking furnace. The autoclave was heated to 400' C. in 3 hours and held a t 400" C. for 45 minutes, after which it was cooled to a room temperature in about 1 hour. After cooling, the gas formed during the reaction was bled off and measured, the product was decanted, and the vessel was washed out with benzene. The product was filtered through a frittedglass disk, and the filter cake was washed with the benzene previously used to wash out the bomb. The filter cake was dried in an oven a t 110" C. and is the residue from the extraction. I n the experiments for studying the factors affecting the extraction, nothing was done with the extract solution, and the amount of extract was determined by subtracting the sum of the residue
Table 1.
County and State Stark, N. D. Henderson, Tex. Lewis, Wash.
8o
3
I I 0 TETRALIN-CRESOL SOLVENT
IO
A
RECYCLE SOLVENT FROM HYDROGENATION
I
360
400
380
440
420
TEMPERATURE OF EXTRACTION IN OC Figure 1,
Relationship between yield of extract and temperature
and gas from the lignite charged; however, in some experiments, the extract was sampled and analyzed by distilling off the solvent under vacuum by heating in a water bath to approximately constant weight. The yields of extract determined by this method checked the difference calculation very well. Carbonization. The carbonization of the extract solution was studied only on a small scale. The apparatus consisting of a 500-ml. Vycor or borosilicate glass flask was connected to an air condenser, a glass receiver fitted with a dry ice trap, and a wet test gas meter. The temperature was measured with a thermocouple in a well in the flask. I n a typical example, 223 grams of extract was placed in the flask and heated rapidly with a flame until the thermocouple indicated that all of the solvent had been removed. The heating was then continued slowly until no more gas was evolved. During the carbonization period, it was necessary to heat the top of the flask to reduce the foaming, and in some cases a trace Qf a silicone was added to prevent the material from foaming into the con-
denser. The final temperature in the dry residue was between 650" and 700' C. The yield of liquid product was calculated by subtracting the weight of the solvent charged from the weight of the total liquid product recovered and adjusting the yield to a no-loss basis. Atmospheric Extraction. I n the few extractions made at atmospheric pressure, the lignite and solvent were heated together in a glass flask under a reflux condenser and then worked up as described above.
Results of Extraction Studies The results on extraction are given in the tables and are classified into studies on the effect of individual variables. Gas and residue yields were determined directly, and the extract yield was determined by difference. The per cent liquefaction was determined by the formula : % liquefaction = 100 x wt. dmmf. residue - wt. dmmf. lignite where dmmf. is dry mineral matter-free.
(
Analytical Data on Lignites Used in Extraction Studies
-
Proximate Analysis, As Received
Mois-
Vol.
ture 39.04 35.20 28.30
matter
Fixed carbon
Ash
25.56 28.49 31.19
24.26 28.64 28.69
11.17 7.67 11.82
Ultimate Analysis, Moisture, Ash Free
S
B.t.u./ lb.
C
H
N
S
0 (cliff.)
2.49 0.62 1.66
6,170 7,181 7,388
75.13 78.41 75.05
5.46 4.85 6.55
1.18 1.23 1-01
5.00 1.09 2.77
13.23 14.42 14.62
VOL. 49, NO. 9
c/q
*
atomic
SEPTEMBER 1957
basis 1.15 1.36 0.92
1403
Effect of Nature of Lignite. Some experiments were made in which the effect of the nature of the lignite upon extraction yield was studied. Lignites from three different available sources were analyzed (Table I). The data from the extraction studies (Table 11) indicate relatively little relationship brtween the analyses of these lignites and rhe amount extracted or liquefied. Effect of Temperature on Yields. Three series of experiments were made to determine the effects of the extraction temperature. These data, given in Table I11 and in Figures 1 and 2, indicate that the amount of extract obtained increases rapidly with increasing temperature to about 400' C. and less rapidly above 400' C. The amount of gas formed continues to increase over the range 360' to 440' C., and the ratio of hydrocarbon gases to carbon dioxide (Figure 2) also increases over the whole range. In earlier experiments in the work and reported by others (6, a),the effectiveness of Tetralin was due to the transfer of hydrogen to the lignite. T o determine the amount of hydrogen transferred to the lignite in the reaction and the variation of this with temperature, the entire product from each experiment in the third series was charged to the pot of a fractional distillation column, and the volatile material was distilled at atmospheric pressure. The amount of Tetralin converted to naphthalene was calculated from the distillation curve, and this value was checked by the ultraviolet absorption spectra of the distillate fractions. These data indicate that the transfer of hydrogen from the Tetralin to the lignite is strongly affected by temperature. I t is somewhat surprising that the hydrogen given up by the Tetralin amounts to as much as 3y0 of the lignite at 440' C . The amount of hydrogen found in the gas from this experiment was less than 1% of the hydrogen given u p by the Tetralin. show-ing it was chemically absorbed and not simply given up by thermal decomposition of the tetralin. Effect of Temperature on Extract Composition, The products from one series of experiments which were made to study the effect of temperature were carefully analyzed. These data, Table I11 and Figure 3, show that the carbon content of the extracts increases with rising temperature, and the hydrogen content and oxygen plus sulfur content decrease with rising temperature. The trend in the carbon and hydrogen contents is illustrated more clearly by the carbon-hydrogen ratio of the extracts which rises markedly with temperature; even at the highest temperature, it is lower than the carbon-hydrogen ratio in the lignite. The carbon-hydrogen
1404
0.f
0.5
0.4
0.3
0.2
0.I I
7
T E'M PER ATU RE, "G Figure 2.
Change in gas composition with temperature
ratio increases even though more hydrogen is given up by the Tetralin as the temperature rises as in series 3. Hydrogen-rich fractions of the lignite go into solution more easily and although an increasing amount of hydrogen is added by the Tetralin as the temperature is raised and more of the lignite goes into solution, the more difficultly soluble fraction is low in hydrogen and the hydrogen added by the Tetralin does not lower the carbon-hvdrogen ratio to the level of the more easily soluble, portions. The percentages of the hydrogen and carbon going to gas and extract increase with rising temperature at the expense of the residue. The excess of hydrogen recovered in the products is due to the addition of hydrogen to the products
Table II.
INDUSTRIAL AND ENGINEERING CHEMISTRY
by the Tetralin. The amount of oxygen plus sulfur in the gas increases with increasing temperature a t the expense of the residue; whereas, the amount of oxygen plus sulfur going to the extract changes comparatively little with temperature. The oxygen plus sulfur content of all extracts is lower than that of the original lignite. This latter result is generally found in extraction and in hydrogenation and is the result o€ the elimination of the oxygen and sulfur as water and gas. Effect of Solvent to Lignite Ratio. The effect of the solvent-lignite ratio was investigated to a very limited extent. Two ratios were studied with each of two lignites. 'The results (Table 1V) indicate that a very small increase in extrac-
Effect of Lignite Nature on Product Yields from Pressure Extraction Solvent, 4 parts tetralin: 1 part cresol Solvent t o lignite, 2: 1 Temperature, 400' C.
Expt.
No. 11-18 11-46 11-56
Lignite Used Washington North Dakota Texas
%
%
%
Slp Residue
65.8
29.7 27.0 34.7
Gas 4.5 7.9
Extract
4.8
60.5
65.1
Liquefaction 86.9 93.7 75.3
LIGNITE €XTRACTION Table 111.
Effect of Extraction Temperature on Product Yields from Pressure Extraction (On Texas lignite with solvent to lignite ratio of 2 to 1 )
Series 1. Solvent, tetralin-cresol mixture Experiment No.
11-84
Temperature, C. Products, yo of dry lignite Gas Extract Residue
360
Liquefaction, % dmmfQlignite HC' Gas/COs Composition of extracts Carbon, % Hydrogen, % Nitrogen, yo Ash, % Oxygen sulfur, yo (diff.) C/H (atomic ratio)
+
Composition of residues Ash, % O n ash-free basis Carbon, yo Hydrogen, % Nitrogen, Yo Oxygen sulfur, % (diff.) C/H (atomic ratio)
+
11-83
8.3 60.3 31.4
11.9 65.5 22.6
41.5 0.041
57.6 0.139
86.8 0.184
79.1 0.302
89.3 0.542
81.59 7.64 0.69 0.15 9.93 0.894
83.39 6.98 1.12 0.53 7.98 0.994
82.27 7.13 0.84 0.48 9.28 0.962
84.57 6.76 1.60 0.20 6.87 1.03
85.26 6.25 1.46 0.55 6.48 1.14
16.82
21.82
36.77
44.78
74.9 4.76 1.60 18.86 1.31
77.0 4.74 1.66 15.61 1.36
78.0 5.45 1.88 18.77 1.19
77.5 4.15 1.63 16.60 1.55
b
...
6
... ...
... ... ...
Yo elements in lignite) 8.5 112.7 11.5 132.7
11.9 97.1 23.4 132.4
23.0 99.1 8.0 130.0
4.8 80.4 11.8
4.7 75.2 20.7
6.9 83.5 9.2
45.1 36.0 12.90
37.4 30.8 25.2
51.1 32.1 10.0
IV.
13-28 360
13-10 400
13-30 440
4.6 19.5 75.9 27.8
7.4 50.2 42.4 66.4
12.4 61.8 25.8 85.9
Solvent, Tetralin-cresol mixture
Experiment No. Temperature, C. H absorbed from Tetralin Lignite charged, % Extract, % Tetralin converted to naphthalene, % Dry mineral matter-free. Sample lost by accident. Estimated.
Table
'
Solvent, solvent fraction from hydrogenation of cxtracts
Series 3.
Q
11-76 440
9.2 66.1 24.7
Experiment No. Temperature, O C. Products, % dry lignite Gas Extract Residue Liquefaction, % dmmf" lignite
c
420
3.3 46.7 50.0
+
Series 2.
11-80
400
3.4 32.6 64.0
Distribution of elements in products (as Hydrogen H in gas 0.7 2.6 H in extract 59.4 77.6 H in residue 57.4 41.2 Total 117.5 121.4 Carbon C in gas 1.6 1.6 C in extract 39.4 57.5 C in residue 55.9 41.5 Oxygen sulfur (diff.) 0 S i n gas 19.2 16.9 0 S in extract 24.2 27.8 0 S in residue 70.1 42.5
+ + +
11-81
380
11-86 360
11-82 400
11-71 440
0.54 1.66 11.1
1.43 2.16 29.6
3.13 4.76 64.4
Effect of Solvent-Lignite Ratio on Product Yields from Pressure Extraction Temperature, 400' C. Solvent, 4 parts Tetralin, 1 part p-cresol
Expt. No.
Lignite Used
11-44 11-46 11-64 11-56
N. D. N. D. Tex. Tex.
SolventLignite Ratio 1.33 2.00 1.33 2.00
Yields (on Dry Lignite), % Gas Extract Residue 9.7 7.9 5.7 4.8
64.0 65.1 56.6 60.5
26.3 27.0 32.7 34.7
%
Liquefaction 85.0 84.2 71.9 75.3
tion results from increasing the ratio from 1.33 to 2.0. Most of the experiments in this work were made at the 2.0 ratio, because the product was more fluid and could be worked up more easily than the product from the lower ratio experiments. Effect of Gaseous Hydrogen in Presence of Solvents. TETRALIN. The noncatalytic transfer of hydrogen to lignite by Tetralin suggests the possibility of utilizing gaseous hydrogen directly in the system. A series of experiments was made to test this possibility and the results are given in Table v. In the first three experiments made at 400' C. (11-40, 11-41, and 11-45), the yield of extract increases somewhat with increasing hydrogen pressure. A second series (11-76 and 10-A) confirmed approximately the same result at 440' C. Conversion of Tetralin to naphthalene was markedly reduced by the presence of the hydrogen and molecular hydrogen was reacted in the process, more, in fact, than was represented by the drop in con. version of Tetralin. T o check the possibility that the naphthalene found in the process was hydrogenated noncatalytically, three experiments were made in which the 4 to 1 mixture of Tetralin and cresol was heated to 400' C., in one to 416' C., and held at 400' C. or over for periods up to 1 hour. In none of these experiments was any detectable hydrogen found in the gas or any change in composition found in the liquid except for a very small (less than 5%) amount of demethylation of the cresol. I n another experiment naphthalene and cresol were heated in the autoclave under hydrogen pressure for 3/4 hour above 400' C. The hydrogen pressure was 500 pounds per square inch gage cold, and the total pressure at the operating temperature was 1380 pounds per square inch gage. No detectable reaction was observed except for a very small amount of demethylation of the cresol again. These experiments demonstrate clearly that the naphthaleneTetralin-hydrogen system requires a catalyst to effect reaction a t temperatures u p to 400' C., and that the stainless steel walls of the vessel do not behave as an effective catalyst in this reaction. The hydrogenation of the lignite by the Tetralin does not appear to take place through the decomposition of Tetralin to molecular hydrogen which then reacts with the lignite. Also, the lignite can react noncatalytically with gaseous hydrogen as was shown by Orchin and Storch ( 8 )in using cresol and bituminous coal. The action of Tetralin without cresol was tested in two duplicate experiments made a t 440' C. with gaseous hydrogen. The yield of extract (Table V) is as high as that from comparable experiVOL. 49, NO. 9
SEPTEMBER 1957
1405
-~
~~
Table V.
Lignite Used
Expt. S O .
I?. D.
11-40 11-41 11-45 11-76 10-A' 10-B" 11-81 ll-Ad ll-Bd 11-131 11-134 11-133
Tex.
~
~
Effect of Solvent and Gaseous Hydrogen on Product Yields from Pressure Extraction (Ratio of solvent to lignite, 2 . 1 )
Sol-
Temp..
4 T:C 4 T:C 4 T:C 4 T:C 4 T:C T 4 T:C
400 400 400 440 440 440 400 400 400 400 400 400 400 400 400 400 400 400 400
vent,&
C C C
N N
11-C" 1 1-DC
R-1 R-1
11-Ed 21-15 21-21 21-138 21-140
4 D:C
R-1 OA
P OP
C.
Pressure, Lb./Sq. Inch _-___Ga.ge __ Yields. (on Dry Lignite), Init. ExResiHa Max. Gas tract due 0 1140 8.0 65.4 26.6 500 1700 8.0 66.4 25.6 2790 8.7 69.8 21.5 1000 1600 11.9 65.1 23.0 0 3150 11.3 68.4 20.3 1000 1000 2950 8.9 66.6 24.5 0 990 9.2 66.1 24.7 0 ioio 8.8 31.5 59.7 500 1440 6.7 49.6 44.5 1000 3000 7.5 63.0 34.4 0 780 7.7 19.6 72.7 760 6.5 44.3 49.2 0 870 7.9 45.1 46.9 500 1860 7.6 50.8 41.6 1000 2770 8.5 52.0 39.6 0 8.1 57.6 34.3 0 1030 5.3 25.4 69.0 0 9.6 13.1 77.3 0 460 6.4 46.7 46.9
..
.. ..
% Liquefaction' 92.8 95.5 100.0 88.8 91.9 87.0 86.8 46.6 62.1 75.6 31.5 58.6 61.2 67.0 69.7 75.8 35.7 26.2 61.3
%
H Absorbed
Tetralin
from
to
Tetralin, 7 6 of
Naph-. tlialene 34.7 20.7 17.2 64.4 36.6
*.
.. ..
.. ..
.. .. ..
*. *.
.. .. .. * .
Extract 2.58 1.52 1.20 4.33 2.79
.. .. ..
.. .. .. .. .. .. .. .. .. .. ..
Total Absorbed H from Gas, dbsorbed. % of % of Extract Extract 0.0 1.33 2.14 0.0 1.97 2.83 0.0 0.0 0.83 1.13 0.0 1.06 0.0 0.62 1-01
2.58 2.85 3.34 4.33 4.56
.. ..
.. .. ..
.. .,
.. .. ..
a Solvent: 4 T : C = 4partsTetralir1, 1 part cresol; 4 D : C = 4parts Decalin, 1 part cresol; O P = octahrdrophena,~threne; P = phenantilIenc. X = naphthalene; R-1 = solvent fraction from hydrogenation of extract; 0.4 = octahydroanthracene: Liquefaction = % conversion of dry ash-free lignite t o gas and liquid. c Average of three experiments. d Average of two experiments.
z
z w O(3 mo
aa Q O u>.
1.10 1.00
r 0.90
88
c-
0
t-
4
Ya
a t-X
I-
2
w
86
z
z_
2
2
I-
w
0
g
84
EJ
Q
0
W
k
y.
0
E
82
I
380
400
420
440
TEMPERATURE, OC
Figure 3.
1406
Change in extract composition with temperature
INDUSTRIAL AND ENGINEERING CHEMISTRY
ments using a Tetralin-cresol mixture. This is contrary to the finding of Orchin and Storch (8),who observed that adding cresol to Tetralin increases the yield of extraction of bituminous coal at 400' C. The explanation for the divergence undoubtedly lies in the fact that the hvdrogenation is more extensive at 440' C. with gaseous hydrogen present than under the conditions employed by Orchin and Storch. CRESOL A N D NAPHTHALENE. The role of solvent and hydrogen was explorrd further in other experiments. In one series in Table V (11-A, 11-B, and 11-131) lignite was treated with pure cresol as the solvent. and in some experiments gaseous hydrogen was added to the autoclave to the pressure indicated in the table before heating. In the experiments without hydrogen cresol is a good solvent for the lignite, but the yields of extract in the experiments where hydrogen was added are much higher. This demonstrates very clearly that gaseous hydrogen enters into the reaction and that the Tetralin is not required as an intermediate. Thc two experiments using naphthalene as a solvent (11-134 and 11-133, Table V) again show a marked increase in extraction when hydrogen is added. The yield of extract in the run without hvdrogen shows that naphthalene is a poorer solvent for lignite than cresol which agrees with work on bituminous coal ( 4 ) . A further effect of hydrogen is shown by experiments (11-C, 11-D,
LIGNITE EXTRACTION Table Vi. Temp. of Extn., O C.
Effect of Variables in Extraction-Carbonization Init. Hz Extract Yields, Press., Lb./ % of Dry LiqueGas Sq. In. Gage Lignite faction loss
Expt. NO. SolventQ NFA-122' .' 13-98 4 T:C 400 0 53.3 68:7 13-103 4 T:C 400 900 57.8 75.4 13-114 4 T:C 440 1000 67.7 92.3 21-15 0Ae 400 0 57.6 *. 21-21 4 D:C 400 0 25.4 35.4 21-140 OP 400 0 46.7 61.2 21-148 T 440 1000 65.3 86.3 22-10 T 440 1000 67.8 87.9 21-119 0 CJ 370 atm. a Solvent, 4 T . C = 4 parts Tetralin, 1 part cresol; OA = octahydroanthracene; phenanthrene; T = tetralin; OC = octahydrochrysene. b Sum of extraction residue and carbonization residue. 0 Carbonization of dry lignite, low temperature, 1000° F. d Includes 7.6% aqueous liquor. e Extraction time, 2 hours. Extraction time at atmospheric pressure, 24 hours.
...
..
..
..
and 11-E, Table V) using solvent from the hydrogenation of extract. The small increase in extract yield due to added hydrogen found with this material is comparable to the small increase found with the Tetralin-cresol mixture indicating that it is a hydrogen donor as would be expected. In all experiments with hyarogen or a hydrogen donor present, substantial amounts of hydrogen were absorbed by the lignite (last four columns, Table V). These data show that the high yields of extract in these experiments are due largely to hydrogenation of the lignite. I n the experiments on cresol and naphthalene, as little as 1% of hydrogen has a very marked effect on the lignite solution. These observations agreed with the findings on bituminous coal by Orchin and Storch ( 8 ) . OTHER HYDROGENATED AROMATIC HYDROCARBONS. A few experiments were made to extend the group of compounds known to be hydrogen transfer agents with coals, and the results are given in the last four experiments in Table V. The high yield of extract (57.6YG) obtained with the octahydroanthracene suggests very strongly that the solvent functioned as a hydrogen donor. Several attempts were made to extract the lignite with anthracene, but the high melting point and the sublimation tendencies of the anthracene made it impossible to obtain yields by the technique used in these experiments. I t can only be assumed by comparing yields from other solvents such as naphthalene and phenanthrene with that of the octahydroanthracene that it is a hydrogen donor; this is probably a justifiable assumption, as cresol-a very good solvent for both low and medium rank coals-extracted only 31.5y0 of the lignite. The hydrogenating effect of the octahydroanthracene is confirmed in carbonization experiments. With the octahydrophenanthrene, however, the effect of the hydrogenation of the solvent is very
*.
of Texas Lignite
Dry Lignite t o Extraction T~~ + L.O. Tar Ash-free Totalb Yield as % L.O. coke coke Extract 29.4d 7.6 63.0 12.0 29.4 18.2 58.6 55.0 9.2 36.8 19.4 54.1 63.6 15.8 46.0 18.2 38.2 67.9 18.6 37.5 9.6 43.9 65.0 8.3 17.2 5.2 74.5 67.6 14.5 25.2 13.4 60.3 54.0 13.1 52.2 9.5 34.7 80.0 11.8 51.9 12.4 36.3 76.6 24.3 29.0 46.7 4 D : C = 4 parts Decalin, 1 part cresol; O P = octahydro-
+
clearly shown by experiments 21-138 and 21-140. The phenanthrene extracted only 13.1% whereas the hydrogenated phenanthrene under identical conditions extracted 46.7%. Decalin was used in admixture with @-cresol as the solvent in experiment 21-21. This yield of 25.4% is much lower than in the experiment with Tetralin and the partially hydrogenated phenanthrene and anthracene, indicating that the saturated aromatic is relatively ineffective.
Results of Carbonization Studies Carbonization of Pressure Extracts. This study was undertaken to determine if the small amount of hydrogenation effected by the hydrogen transfer agents under the extraction conditions would alter the lignite sufficiently to give high yields of liquid products on carbonization. The most pertinent data from the work are given in Table VI. The liquid products contained water which was not determined because of the difficulty of separating it from the organic phase. No characterization of the product was made except for one distillation which showed that it has a wide boiling range and contains considerable heavy residue. The entire material would require further processing before finished distillate fuels could be obtained. The first experiment shows the carbonization of dry lignite in the apparatus used for the other carbonization experiments. These results are almost identical to those from carbonization at 1000° F. in two other types of apparatus. A comparison of the yields from the carbonization of Tetralin-cresol extracts with those from the carbonization of dry lignite shows a very large increase in yield of liquid products and a large decrease in the formation of gas. The data also show that the yield of liquid products increases with increasing yield of extract. This is to be expected be-
+
..
..
..
a .
cause increasing extraction under the conditions employed results from more extensive hydrogenation, and the liquid yields from carbonization should increase with increasing extent of hydrogenation. Other solvents, octahydroanthracene and octahydrophenanthrene (21-15 and 21-140, Table VI), were tested and were found to be very effective in producing liquid products, particularly the octahydroanthracene. The effect of the completely saturated compound, Decalin, was also tested. These results (21-21, Table VI) confirm the extraction results; a much lower yield is obtained showing that partially hydrogenated naphthalene is a better hydrogen transfer agent than the fully hydrogenated one. Carbonization of Atmospheric Pressure Extracts. A few experiments were made to test the possibility of carrying out the hydrogen transfer process at atmospheric pressure. If hydrogen transfer is a liquid-liquid or a liquid-solid process not requiring a gaseous hydrogen phase, it should be possible to do so; however, it would require solvents boiling a t 350' C. or higher for a substantial amount of reaction with coal as the earlier extraction studies indicated. Hydrogenated derivatives of chrysene are likely possibilities and a small quantity of chrysene was hydrogenated to an extent corresponding to octahydro- derivatives. The octahydrochrysene boiled a t 370' C., and was refluxed with lignite for 24 hours after which the mixture was carbonized in the regular manner Table V I (expt. 21-119). The substantial yield of 29.0% of liquid products shows that the hydrogen transfer process took place a t atmospheric pressure. The hydrogen transfer property also persists in aromatic structures of increasing complexity to a t least four condensed rings. Carbonization of Total Extraction The carbonization of the Product. entire extraction product inchding the VOL. 49, NO. 9
SEPTEMBER 1957
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unextracted residue was also carried out. The yield of liquid products was about the same as that from filtered products, but the gas yield was higher showing that the unextracted residue is very lean in hydrogen and decomposes to gas and coke forming little or no liquid product. The cokes from the filtered extracts were essentially ash-free and moderately hard. The cokes from the extraction of the entire unfiltered product were harder and denser than those produced from extract alone. The carbonization process was studied only on a laboratory scale, but these results indicate that a substantial yield of liquid and tarry products can be obtained by this method. The mild hydrogenation produced by the hydrogen transfer solvent treatment has the effect of directing the pyrolysis to yield greatly increased amounts of volatile liquid products instead of largely gas and coke. The process has promise of producing hard, firm cokes from lignite which may have value in metallurgical applications and for producing substantial vields of liquid products. Catalytic Hydrogenation of Extracts
In addition to the carbonization studies, several experiments were made in which a concentrated extract solution was hydrogenated over a bed of granular nickel on alumina catalyst at 1000 pounds per square inch gage. I t was found that about of the dry mineral matter-free lignite was converted to distillate, that 10.5y0 was converted to gas and coke, and that 20.870 was recovered as tar. These yields are exclusive of the solvent fraction boiling between 200’ and 400’ C. This distillate fraction was used in the experiments shown in Tables I11 and V where the solvent from hydrogenation of extracts was employed to extract the lignite. Discussion
The solvent extraction of lignite with Tetralin apparently is a mild hydrogenation of the lignite followed by solution of the hydrogenation products rather than a solvent extraction of the soluble portion of the lignite although the latter is certainly a part of the process. Tetralin at lower temperatures has been a mediocre solvent for coals ( 4 ) being less potent than cresol and many other compounds, but a t temperatures of 360’ C. and above it becomes a very powerful agent for the solution of coal. This work shows that hydrogen in amounts up to 37, of the dry lignite is transferred to the lignite by Tetralin, and that other partially hydrogenated aromatics, such as phenanthrene and chrysene, have a similar effect. Therefore, the high yields
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of extract from the hydrogen transfer agents are due to the hydrogenation of the lignite followed by solution of the hydrogenation products. The role of the hydrogenation is further demonstrated by the large increase in extract yield when gaseous hydrogen is added to the extraction with cresol and with naphthalene. It is very doubtful that cresol and naphthalene act as intermediates for the hvdrogenation as they do not absorb hydrogen at the same pressure and temperature in the absence of catalvsts and lignite. I t is much more likely that the lignite reacts with the hydrogen directly and that the solvents dissolve the reaction products along with that part of the lignite soluble in the solvent without hydrogenation. The results of this work agree with those reported by Orchin and Storch (8) who showed that Tetralin and other hydrogenated aromatics are very good solvents for bituminous coal. A clue to the mechanism of the solution of lignite may be that the hydrogen transfer process becomes most active at temperatures above 360’ C --the point at \vhich thermal decomposition of these lignites occurs. The relationship of the activity of Tetralin upon coals to their temperature of thermal decomposition has been studied ( 5 ) . This relationship suggests that the mechanism consists of the true solution of part of the coal followed by thermal breaking of bonds holding coal po1)mer units together. The activated sites, probably of a free radical nature, abstract hydrogen from the hydrogen transfer agent or the gas phase and become chemically stable units which dissolve in the solvent. Orchin and Storch (8) attribute a large part of the increased solubility of bituminous coal upon mild hydrogenation to the dirsociation and hydrogenolysis of oxvgen bonds, and this mechanism is consistent with the solution of lignite by hydrogen transfer solvents. From the limited data available it is not possible to define completely the classes of compounds which possess hydrogen transfer properties under these conditions. From the results of extraction with Tetralin and partially hvdrogenated phenanthrene, anthracene. and chrysene, it appears That the partially hydrogenated polynuclear aromatic hydrocarbons in general possess this property, The results with Decalin indicate that a completely saturated aromatic, if it possesses hydrogen transfer properties does so to a greatly reduced extent. Hydrogenated thianaphthene ( 9 ) and hydrogenated phenols of the naphthalene and diphenyl series ( 8 ) are also active hydrogen transfer agents with coal, but so far those mentioned in the literature have been hydrogenated aromatic compounds of more than one ring.
INDUSTRIAL AND ENGINEERING CHEMISTRY
’The high degree of liquefaction arid change in composition of the extracts are evidence of substantial change in the nature of the lignite during treatment with hydrogen transfer agents. The alteration of the behavior of the lignite upon carbonization, however, is even more striking. The carbonization of the raw lignite yields less than 1Oy0 of distillate; whereas, the treated lignite yields 25 to !joy0 distillate. Such a change can only be ascribed to deep seated chemical changes. Discussion of the chemical changes in the lignite and its behavior during carbonization is not warranted by the limited scope of this study, but it does appear reasonable that the principal changes are connected with the oxygen in the lignite. In the untreated lignite most of the oxygen is eliminated as carbon dioxide ; whereas, a small amount is eliminated this way in the treated lignite. The mild hydrogenation effected by the treatment with hydrogen transfer agents and with gaseous hydrogen has a strong resemblance to increasing the rank of the lignite, because the treatment. raises the yield of liquid products produced by Carbonization, and the product swells and produces a strong coke on carbonization. Acknowledgment
The authors wish to express their appreciation to Gulf Research & Development Co. for permission to publish the results of this work and especially to C. W, Montgomery for his suggestions in the work and in the preparation of the manuscript. Literature Cited
(1) Clark, E. L., Pelipetz, A?. G.? Storch, H. H., Weller, S., Schreiber, S., IND.ENG.CHEM.42, 861-5 (1950). (2) Gilbert, W. I., Montgomery, C. W. (to Gulf Research 8L Development Co.), G. S. Patent 2,654,695 (Oct. 6, 1953). ( 3 ) Hirst, L. L., Skinner, L. C., Donath, E. E., U. S. Bureau of Mines, Inform. Circ. 7486, December 1948. ( 4 ) Kiebler, M. W., IND.EXG.CHEM.32, 1389 (1940). ( 5 ) Lowry, H. H., “Chemistry of Coal Utilization,” vol. 1, pp. 677-760, Wiley, Xew York, 1945. ( 6 ) Lowry, H. H., Rose, H. J., U. S. Bureau of Mines Inform., Circ. 7420, October 1947. (7) Orchin, M., Goldbach, G. L., Wolak, M., Storch, H. H., Zbid., Rept. Invest. 4499, July 1949. (8) Orchin, M., Storch, H. H., IND.ENG. CHEM. 40, 1385-89 (1948). ( 9 ) Ruidisch, L. E., Pevere, E. F. (to Texas Co.), U. S. Patent 2,681,300 (June 15, 1954). RECEIVED for review August 6, 1956 ACCEPTED December 12, 1956 Division of Gas and Fuel Chemistry, 128th Meeting, ACS, Minneapolis, Minn., September 1955.
