Friedman, S., Kaufman, M. I,.,Wender, I., Ann. N.Y . Acud. Sci. 145, 141 (1967). Germain, J. E., Valadon, F., Bull. SOC.Chim. Fr. 1960, 11. Gomez Aranda, V., Gomez Beltran, F., Combustibles 22, 147 (1962). Kamiya, Y., Fuel 40, 149 (1961). Kamiya, Y., Fuel 42, 347 (1963). Kaufman, M. L., Friedman, S., Wender, I., Anal. Chem. 39, 1011 (1967). McKinnis, A. C. (to Union Oil Co.), U.S.Patent 2,729,674 (Jan. 3, 1956). McKinnis, A. C. (to IJnion Oil Co.), U. S. Patent 2,864,854 (Dec. 16, 1958). Montgomery, R. S., McMurtrie, R., Symposium on Technology and Use of Lignite, Bur. Mines Inform. Circ. 8234, 74-98 (1964).
Piacenti, F., Bianchi, M., Benedetti, E., Chim. Ind. (Milan) 49, 246 (1967). Slaugh, L. H., Mullineaux, R. D., J . Organometal. Chem. 13, 469 (1968). Smith, R. C . , Tomarelli, 1-2. C., Howard, I3. C., J . Amer. Chem. Soc., 61, 2398 (1939). Wender, I., Friedman, S.,Steiner, W. A., Anderson, R. B., Chem. Ind. London 1958, 1694. RECEIVED for review December 16, 1969 ACCEPTED March 21, 1970 Symposium u n Chemicals from Coal, Division of Fuel Chemistry, 168th Meeting, ACS, New York, N. Y., September 1969. Reference to a company or product name is made to facilitate understanding and does not imply endorsement by the Bureau of Mines.
Catalytic Hydrogenation of Multiring Aroma tic Coal Tar Constituents Wendell H. Wiser, Surjit Singh, Shaik A. Qader, and George R. Hill Department of Mineral Engineering, University of litah, Salt Lake City, Utah 84112
In an attempt to increase the yields of benzene derivatives from coal hydrogenation, several parameters are investigated as they affect hydrogenation of anthracene: Temperature, hydrogen pressure, catalyst, and reaction time. Below 250" C., yields of
9,10-
dihydroanthracene may approach 80 weight%. Continued hydrogenation yields 1,2,3,4tetrahydroanthracem accompanied by a loss of hydrogen from the 9 and 10 positions. Further hydrotreating yields 1,2,3,4,5,6,7,8-0ctahydroanthracenewith cracking to naphthalene derivatives concurrent with or subsequent to the formation of the octahydroanthracene. Continued hydrogenation of the naphthalene derivatives yields benzene derivatives and gases. No evidence is observed of direct hydrocracking of the 9, 10-dihydro derivative. Hydrogenation of anthracene i s first-order with respect to anthracene concentration with an activation enthalpy of 3.8 kcal per mole and an activation entropy of -58 entropy units. The rate-controlling step appears to be orientation and adsorption of the reactants on the catalyst surface. Problems associated with attempts to hydrocrack the dihydro derivatives are discussed.
B~UMINOUS
COAL is understood to consist primarily of fused ring structures joined together by various types of linkages to form an extensive network. These ring structures are highly aromatic, although considerable quantities of hydroaromatic configurations are present. The size of these structures may vary from one to several rings, an average-sized configuration containing three or four rings. As one attempts to convert coal to useful liquid materials, it seems desirable to obtain high yields of benzene and its derivatives. These compounds have wide applicability as additives in gasoline to improve the octane
350
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
rating, as raw materials for the manufacture of conventional explosives, as solvents and chemicals, etc. The higher members of the aromatic homologous series are solids a t room temperature. (The melting point of naphthalene, a two-ring structure, is 80" C.) I n coal pyrolysis, a single-ring aromatic constituent existing in the lattice structure may possibly be liberated by rupture of the bond(s) joining it to the structure, followed by stabilization of the fragment thus produced. Similarly, higher members of the aromatic homologous fused series may be produced, then liberated as volatile products as determined by their vapor pressures.
\
While aromatic-type bonds are not expected to be thermally ruptured to any significant extent in this temperature range, the single carbon-carbon bonds within the hydroaromatic structures may be ruptured. This could lead to ring opening of saturated portions of the hydroaromatic structure, followed by cracking of the side chains thus produced, yielding gases and lower aromatics. I t is probable that some of the benzene and its derivatives obtained in coal pyrolysis are produced in this manner. These processes are greatly assisted by the presence of an agent which can produce atoms or small radicals to stabilize the thermally produced fragments. Hence, dissolution in an appropriate solvent-e.g., Tetralinproduces larger quantities of lower-boiling aromatic materials. Hydrogenation in the presence of an appropriate catalyst yields yet larger quantities of lower-boiling constituents. The production of benzene and its derivatives may be increased by hydrogenation and hydrocracking of higher members of the aromatic series. For members of the series consisting of three rings or more, two possible approaches may exist. The first would consist of hydrogenation of a ring a t the end of the cluster, followed by ring opening and cracking to produce a derivative of the next lower member of the aromatic series. This procedure could be repeated, yielding ultimately one molecule of benzene or a benzene derivative for each aromatic cluster thus utilized. The second approach may be the hydrogenation of a ring within the cluster other than an end ring, followed by cracking of this ring to yield two aromatic fragments. Completion of this procedure would yield a t least two molecules of benzene or its derivatives for each cluster thus utilized. The present paper describes initial investigation of these possibilities. I n an effort to gain understanding of the basic principles involved, the study was initiated using pure compounds. The first compound was anthracene, a fused, linear, three-ringed compound. I t has long been known that anthracene can be hydrogenated in the presence of appropriate catalysts, yielding various hydro derivatives (Burger and Mosettig, 1935; Garlock and Mosettig, 1945; Johnson, 1953; Smith, 1957; Waterman et al., 1939). The catalytic hydrocracking studies were then extended to 9,lO-dihydroanthracene.
Liquids and gases were analyzed by gas chromatograph. The continued reactions of the 9,lO-dihydroanthracene at 510°C were studied using 25 grams of 9,lOdihydroanthracene of 95% purity, mixed with 2.5 grams of catalyst (kaolin pellets of %-inch diameter or fluid zeolite cracking catalyst). The techniques for hydrogenation and product analyses were similar to those described above. Results and Discussion
Typical curves from this study showing +he rate of disappearance of anthracene during catalytic hydrogenation a t various temperatures ranging from 220" to 435°C are shown in Figure 1. These data are presented as weight per cent anthracene in the product as a function of time. Figure 2 shows four chromatograms illustrating the progress of the reactions a t 390'C. Hydrogenation of anthracene to 9,10-dihydroanthracene occurs readily. As the time increases, formation of 1,2,3,4-tetrahydroanthracene becomes appreciable, followed by formation of 1,2,3,4,5,6,7&octahydroanthracene, some naphthalene ultimately being formed. Figure 3 shows four chromatograms which illustrate the progress of the hydrogenation reactions a t comparable times as a function of temperature. At the lower temperatures, hydrogenation to 9,lO-dihydroanthracene is essentially complete with only limited hydrogenation to higher stages. As the temperature is increased, progressive hydrogenation to 1,2,3,4-tetrahydroanthraceneoccurs, followed by hydrogenation to the octahydro derivative, with hydrocracking to form naphthalene derivatives ensuing. At 435" C, further hydrogenation of these derivatives, followed by cracking to form benzene derivatives, becomes appreciable. Figure 4 shows the rate of production of 9,lOdihydroanthracene during catalytic hydrogenation of anthracene. The data indicated that this is the first stable compound formed. At 220°C. yields of nearly 80 weight "c of this product were obtained. As the temperature increased, the maximum quantity of this compound in the system decreased. At 345°C and higher, the yield of 9,lO-dihydroanthracene reached a maximum, then I
4
Experimental Procedure
The equipment consisted of an autoclave of 1-liter capacity, equipped with a variable speed magnetic stirrer, a pressure gage, and a thermocouple well. Auxiliary to the autoclave were a temperature recorder to follow the rate of heating, rheostats to assist in obtaining a smooth heating curve, and a temperature controller capable of maintaining constant temperature within &3" C. The hydrogenation experiments were performed using 25 grams of anthracene of 98% purity, mixed with 2.5 grams of catalyst (nickel tungsten sulfide pellets of %inch diameter). The system was evacuated and then filled with hydrogen to a predetermined cold pressure such that the operating pressure a t the temperature of the experiment would be 1500 psi. Approximately 20 minutes were required to bring the system to operating temperature. Solid samples from the reaction products were dissolved in trichloroethylene and analyzed by a flame-ionization chromatograph, with an Apiezon-L separation column.
U
50-
@ .W
A 435'C 0 390'C
a 345'~ 300*C A
e
zso*c 220-c
3
30-
W
5
20-
U
i 4
10
O L
0
TIME, MINUTES
Figure 1. Rate of disappearance of anthracene during catalytic hydrogenation Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970 351
390'C 35mr
Anthracene Benzenes
Naphthaienes
A J - ' .
A
390' C 60 m n
1
Figure 2. Chromatograms showing product distribution on hydrogenation of anthracene at 390" C, 1500 psi, Ni-W-S catalyst
390*C I 2 0 TI"
Anthracenes
h .
6
Naphthalenes
-
2539
c
240 min
Anthracenes Benzenes
Naph thaienes
A
Anth. n
330' C 2 0 0 mli-
Anth
Figure 3. Chromatograms showing product distribution on hydrogenation of anthracene at 250" C, 1500 psi
390' C 240 min
-
Anthracenes B k.
3 9
Naphthalenes
Benzene D e r / var!ves
' 0 - v r i n i 6 % r\:
435'
c
200 m i "
.
i
Figure 4. Rate of formation of 9 , l O dihydroanthracene during catalyst hydrogenation of anthracene
,
L -
90
40
60
80
100
TIME, MINUTES
352
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
120
140
1
16C
-
I80
Figure 5 . Rate of formation of 1,2,3,4tetrahydroanthracene during hydrogenation of anthracene
01
20
40
,
I
60
80
, 100
120
1
160
I40
I80
.
200
TIME, MINUTES
A
I
/
435"~
Figure 6. Rate of formation of 1,2,3,4,5,6,7,8octahydroanthracene during hydrogenation of anthracene
20
40
60
80
100 120 TIME, MINUTES
140
160
180
decreased a t longer times because of continuing hydrogenation. Figure 5 shows the rate of formation of 1,2,3,4tetrahydroanthracene. At 250"C and lower, the yields of this product continued to approach a maximum value a t long times and did not pass through a maximum. The data indicated only traces of products representing further stages of the hydrogenation process. At higher temperatures, the yields of 1,2,3,4-tetrahydroanthracene reached a maximum value for each temperature, then diminished because of continuing hydrogenation. Figure 6 shows the rate of formation of 1,2,3,4,5,6,7,8octahydroanthracene as a continuation of the process of catalytic hydrogenation of anthracene. Since only traces of this compound were formed a t 250°C and lower, these temperatures are not represented. At 345" and 39OoC, the quantities of this compound continued to increase
200
with time, the data indicating only small quantities of further reaction products. At 435"C,a maximum quantity of 1,2,3,4,5,6,7&octahydroanthracene was observed, followed by a decrease as cracking of the molecule occurred, to yield naphthalene derivatives. Figure 7 shows the rate of formation of naphthalene and its derivatives. These compounds are apparently formed by opening a saturated ring on the end of the hydroaromatic molecule, perhaps followed by cracking of the side chain produced, to yield gas and a naphthalene derivative. Above 500" C,this reaction is appreciable, but cracking of these structures is very limited at lower temperatures. As the hydrogenation reactions continued, a second saturated ring was apparently opened, perhaps followed by cracking of the side chains thus produced, yielding gas and benzene or its derivatives. Figure 8 shows the rate Ind. Eng.
Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
353
m w ?
---
-
r----
-7---7---
A
345°C
0
0 390°C A 4359c
Figure 7. Rote of formation of naphthalene derivatives during hydrogenation and hydrocracking
I500 psi Ni W - S Cofolys! Raw T o l e r i o l Anfhrocene
7
510 0 c 300 psi Xoolin co!Olysf Row moterial 9.
-
4
"---
~
A-
-L 20
0
40
60
80
100
120
140
160
180
200
160
180
200
TIME, MINUTES
Figure 8. Rate of formation of benzene derivatives during hydrogenation and hydrocracking
0 390'C A 435'C 1500psi Nt - W S Cata/ys! Raw m a f e r i u l Antbrocene
-
Y
l
510 ' C 300 psi Kao1m Catalyst Row moler/o/ 9-10 Dihydroonthracene
80
100 120 TIME, MINUTES
I40
5IO'C 6 3 min
Figure 9. Chromatograms showing product distribution on cracking 9,lO-dihydroanthracene, 51 0" C, 300 psi
of formation of these compounds. These reactions occurred only a t the higher temperatures a t longer times. The curves a t 510°C in Figures 7 and 8 were obtained using 9,10-dihydroanthracene of 95% purity as the raw material, kaolin catalyst, and hydrogen pressure of 300 psi. The other curves a t the lower temperatures represent the continuing hydrogenation of anthracene described above. An analysis of the data a t a particular temperature-e.g., 435" C--reveals that maximum quantities of the various hydrogenation product3 appear in the order: 9,30dihydroanthracene (about 40 minutes), 1,2,3,4 tetrahydroanthracene (about 100 minutes), and 1,2,3,4,5,6,7,8octahydroanthracene (about 140 minutes). The appearance of naphthalene derivatives is subsequent to 354
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
510' C I20 m , n
or concurrent with the appearance of the octahydroanthracene, suggesting that the ring opening reactions to produce the naphthalene derivatives may occur primarily on the octahydro derivative of anthracene under the conditions of these investigations. Progress of the hydrocracking reactions a t 510" C using kaolin cracking catalyst and 9,lO-dihydroanthracene as the raw material is readily observed in Figure 9. Hydrogenation to 1,2,3,4-tetrahydroanthracene was accompanied initially by dehydrogenation to form some anthracene due to the equilibria involving these three compounds. The general pattern for hydrogenation and cracking reported above is observed with the kaolin catalyst also. However, a t 60 minutes appreciable amounts of naphthalene derivatives had appeared without
30
/
-
A 435‘C
0 390‘C 0
/ 20
-
05
-
0
O
345’C 300’C
A 250‘C
/
c 220’C
Figure 10. First-order plot for anthracene in product during hydrogenation of anthracene
-
A
20
’
30
,
-
40 TIME
50 MINUTES
1
60
70
-L-
80
significant amounts of 1,2,3,4,5,6,7,8-octahydroanthracene present in the system. I t is not known whether the kaolin catalyst permits direct hydrocracking of the 1,2,3,4derivative of anthracene or whether the hydrocracking of the octahydro derivative proceeds very rapidly in the early stages. At 240 minutes, the naphthalene derivatives amounted to approximately 44 weight % and the benzene derivatives approximately 14 weight ?C of the total product. The data for the hydrogenation of anthracene, as represented by the rate of disappearance of anthracene in Figure 1, may be analyzed by applying a first-order differential equation. If the average molecular weight of products of reaction remains essentially constant (a good approximation until cracking becomes significant), weights may be used in the equation
dx ~= k’(a - x ) dt where .y is the weight fraction of anthracene which has reacted a t time t , a is the initial weight fraction of the anthracene which reacts a t infinite time, and k‘ is the reaction velocity constant. Integrating Equation I and evaluating the constant of integration with x = 0 when t = 0 yields a
In a - - x = k’ t
2
k ‘ = ~ -keT - A H ” / R T
,AS’
R
(4)
h
where A F + , A H * , and aS’ are the free energy, heat, and entropy of activation, respectively, h is the Boltzmaiin constant, h is the Planck constant, and k is a transmission coefficient representing the fraction of activated complexes which leads to formation of products (usually considered equal to 1). Equation 4 may be written in the form:
Figure 11 represents a plot of Equations 5 from which is obtained an activation enthalpy of 3.8 kcal per mole and an entropy of activation of -58 entropy units. A reaction occurring a t a catalyst surface will, in general, include diffusion of the reactants to the surface, orientation and adsorption on the surface, reaction on the surface, desorption of the reaction products from the surface, and diffusion of the products away from the surface. The -35
L
A H * = 3 8 Kcol
(2)
A plot of Equation 2 is shown in Figure 10, where the reasonably straight lines indicate that the hydrogenation of anthracene at 1500-psi hydrogenation pressure is firstorder in the temperature range of 220” to 435°C. The rate of a chemical reaction is determined by the free energy of activation. T h e reaction velocity constant may be related to the free energy of activation by the equation (Glasstoneet al., 1941):
-3.8
-3.9
i L
L
(3)
h
or, since I F = AH -
1
90
TAS:
Figure 1 1 . Absolute reaction rate plot of hydrogenation of anthracene Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970 355
slowest of these steps will determine the rate of the overall process. Consideration of the enthalpy and entropy of activation will assist in identifying the slow step in the process. The low value of 3.8 kcal per mole obtained for the activation enthalpy is too low to be associated with a chemical reaction in the rate-controlling step. The activation enthalpy is obtained from the slope of the relationship of reaction velocity constant and absolute temperature (Figure ll), with a low value indicating only a slight change in rate of reaction with temperature. Such temperature dependence would be found in physical factors. One of the several implications associated with the concept of entropy is its relationship to probability. A large negative value for the entropy of activation, AS’, implies a small probability of the formation of the activated state. Hence; the value of -58 entropy units for AS’ obtained in the present work may be interpreted to indicate considerable difficulty in forming the activated complex for the rate-controlling step. The application of the theory of absolute reaction rates to the process of diffusion (Glasstone et al., 1941) indicates that the value for Bf for diffusion cannot be appreciably different from zero. Thus, diffusion is not considered to be the rate-controlling step in the process under consideration here. If it is assumed (as appears reasonable) that the adsorbed activated complex is an immobile molecule attached to the surface of the catalyst, then the product molecule should be very much like the activated complex and the entropy of activation for desorption would be expected to be small and positive, or nil. The entropy of activation observed in this study would thus not be associated with desorption as the rate-controlling process. The hydrogenation of linear multiring aromatic compounds of three rings or more is initiated by the addition of hydrogen to a ring position other than an end ring (Clar, 1964). The appropriate orientation of the reacting molecule (in this case, anthracene) relative to the active sites on the catalyst surface may be difficult to achieve and would be only slightly assisted by a temperature increase. The passage of an anthracene molecule from a free molecule in the liquid or gaseous state to an essentially immobile molecule on the surface of the catalyst involves a loss of several degrees of freedom (translational and rotational). This represents a considerable loss of entropy. An entropy of activation of -58 eu is of the right order of magnitude for adsorption processes. I t is believed that the rate-controlling step in the reaction sequence involves the orientation and adsorption of the reacting molecules on the catalyst surface. In the formation of a covalent bond between two atoms, the resonance energy of the electrons involved increases in magnitude as the degree of overlapping of the atomic orbitals involved increases (Pauling, 1948). (The word “overlapping” signifies the extent of coincidence of the regions in space in which the orbital wave functions have large values.) This resonance energy in large measure accounts for the energy of the covalent bond. Hence, other factors excluded, shorter bonds between two atoms would possess greater energy than longer bonds between the same two atoms. Whereas a conjugated molecule-e.g., the polyenesmanifests alternate longer and shorter bonds, aromatic compounds do not. Hence, in benzene all bonds are equal 356
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
to about 1.39 A. Variations in bond distances occur in multiring compounds, but not alternately. Hence, the observed bond distances in the anthracene molecule are as follows (Badger, 1969):
The various positions on the multiring aromatic molecule manifest different degrees of reactivity. Hence, anthracene was observed in this study (as well as by other investigators) to add hydrogen in the 9 and 10 positions to form the dihydride, producing yields of this compound as high as 80% by weight under carefully controlled conditions. As the series is ascended, the stability of the dihydro derivatives increases notably. Thus, dihydrobenzene is relatively unstable, 1,4-dihydronaphthalene is moderately stable, but 9,lO-dihydroanthracene is a stable compound. With some of the higher members of the series, the tendency to form dihydro derivatives is very marked; when heated, part of the compound is decomposed and part converted to the dihydride. The addition of hydrogen in the 9 and 10 positions of the anthracene molecule (and in comparable positions away from an end ring on the higher aromatic homologs) would alter the aromatic nature of the bonds adjacent to these positions. One might expect a reduction in the resonance energy of the electrons associated with these bonds due to this alteration in aromatic nature, with a resulting weakening and lengthening of the bonds. I t would then be theoretically possible to rupture these bonds in preference t o other bonds within the fused structure. T o date, such a rupture has not been observed. Attempts to hydrocrack the 9,lO-dihydroanthracene catalytically resulted in hydrogenation in the 1,2,3,4 positions with an accompanying shift of hydrogen from the 9 and 10 positions. This shift is probably associated with the change in electron orbitals incident to the removal of the aromaticity of the ring involving the 1,2,3,4 positions. Experiments were performed wherein the 9,lOdihydroanthracene was heated in an evacuated system in the absence of hydrogen. The result was a reduction in the amount of the dihydride, accompanied by formation of anthracene and 1,2,3,4-tetrahydroanthracene.An increase in temperature produced dehydrogenation in the 9 and 10 positions of the dihydride, the hydrogen thus produced evidently being utilized to hydrogenate the end ring of some of the molecules. Some direct hydrogen transfer from the 9 and 10 positions to the 1 and 4 positions may occur, probably associated with the hydrogenation a t the 2 and 3 positions and the resulting alteration of the aromaticity of that ring. It appears that with the use of the catalysts of this study, the temperature required for cracking the central ring of the 9,lO-dihydroanthracene is higher than that required for dehydrogenation of this material, favoring the dehydrogenation with concurrent or subsequent hydrogenation of the end ring. More appropriate catalysts must be developed for this patricular reaction if success is to be achieved. Such a catalyst would appreciably reduce the activation energy for hydrocracking the dihydroanthracene bonds adjacent to the 9 and 10 positions without aiding the hydrogenation or dehydrogenation reactions.
Literature Cited
Badger, G. M., “Aromatic Character and Aromaticity,” P. 39, Cambridge University Press, Cambridge, Great Britain, 1969. Burger, A., Mosettig, E., J . Amer. Chem. Soc. 57, 27312 (1935). Clar, E., “Polycyclic Hydrocarbons,” Academic Press, London and New York, 1964. Garlock, E . A., Mosettig, E., J . Amer. Chem. Soc. 6 7 , 22559 (1945). Glasstone, S., Laidler, K. J., Eyring, H., “Theory of Rate Processes,” Chap. 1, p. 9, McGraw-Hill, Kew York, 1941.
Johnson. W. S., J . Amer. Chem. Soc. 75, 1498-500 (1953). Pauling, L., “Nature of the Chemical Bond,” Chap. 3, Cornel1 University Press, Ithaca, N. Y., 1948. ~ E~~~~~ ~ l ~Ed,,~ vel. i 5~, Smith, H.A., ~ ~ ~ ~p. H. pp. 175-256, Reinhold, Yew York, 1955. Waterman, H. I., et al., Rec. Trav. Chim. 58, 83-92 (1939). RECEIVED for review October 20, 1969 ACCEPTED December 23, 1969 Symposium on Chemicals from Coal, Division of Fuel Chemistry. 158th Meeting, ACS, New York. N . Y., September 1969. Research supported by the U. S. Office of Coal Research and t h e bniversitv of-Utah under contract 14-01 -0001-271.
Hydrodesulfurization of Bituminous Coal Chars Charles A. Gray,’ Martin E. Sacks,’ and R. Tracy Eddinger Chemical Research and Development Center, FMC Corp., Princeton. N . J . 08540
Illinois No. 6 char was desulfurized by hydrotreatment at about 1600°F. The char initially contained about 2% organic sulfur and 1 YO inorganic sulfur (FeS) from pyrolysis of pyrite. Removal of the organic sulfur is rapid and limited primarily by an equilibrium between H2S in the gas and sulfur in the char. The reaction of the FeS with H? proceeds more slowly than would b e expected from equilibrium. The rate-limiting step appears t o be either the inherent solid-gas kinetics, or the diffusion of H:S through the reacted shell of iron surrounding the FeS. About 10% of the sulfur content of the char was not removed even by prolonged hydrotreatment; however, it i s possible to remove over 80% in 20 minutes. Because of the high equilibrium ratio of HL to HlS, an H?S acceptor material would have to be admixed with the char bed to have a commercially viable process.
A
MAJOR by-product of many of the coal-conversion processes now under development is a highly porous semicoke or char. The value of this by-product could be enhanced in many instances, if it could be desulfurized. In this manner, a low-sulfur fuel might be produced from a high-sulfur coal. Previous work a t Consolidation Coal Co. (Batchelor et al., 1960; Zielke et al., 1954) established that high temperature hydrogenation effectively removed sulfur from some chars prepared from Pittsburgh-seam coals. For a char prepared from Arkwright coal, these authors found an equilibrium between sulfur in the char and hydrogen sulfide in the gas. Contrary to our findings, Zielke et al. (1954) found the inorganic sulfur more easily removed than the organic. Partial gasification of the char increased the rate of removal of sulfur, suggesting some diffusional inhibition of the organic sulfur.
Present address, Inorganic Chemicals Division, F M C Corp.. Carteret, N. J.. 07008. -€’resent address. Stevens Institute of Technology. Hoboken, N..J., 07030.
This study was undertaken to demonstrate the technical feasibility of desulfurizing chars produced by multistage pyrolysis of coal, identify the important variables influencing the rate of desulfurization, and obtain kinetic data for process design. Experimental Apparatus
The apparatus is shown in Figure 1. The reactor was a 2-foot length of >4-inch Type 316 stainless steel pipe, mounted in a vertical tube furnace which was controlled on the basis of bed temperature. A 22-inch-long therrnowell of 14-inch 0.d. tubing ran up the center of the pipe. Reactor pressure was measured by a Rourdon gage. Gas flow was metered by rotameter and by a wet-test meter. The gas flow and reactor pressure were controlled by needle valves. Procedure
The char bed was supported in the reactor bv a ceramic wool plug resting on a coarse screen welded to the thermowell. A second ceramic wool plug blocked the reactor exit port, to retain any fines that might be elutriated. Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970 357
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