Ind. Eng. Chem. Process Des. Dev. 1986, 25, 464-471
464
Carver, M. 9. "Numerical Method of Lines Solution of Differential Equation Systems: Fundamental Principles and Recent Extensions"; Mah, R. S. H., Seider, W. D., Eds.; Engineering Foundation: Henniker, N. H., 1981, Vol. 1, p 369. Dlssinger, G. R. Ph.D. Dissertation, Lehigh University, Bethlehem, PA, 1983. Edwards, M. F.; Richardson, J. F. Chem. Eng. Sci. 1988, 2 3 , 109. Garg, D. R.; Ruthven, D. M. Adv. Chem. Ser. 1973, No. 121, 345. Jacob, P.; Tondeur, D. Chem. Eng. J . 1983, 26, 41. Kumar, R.; Sircar, S.,Chem. Eng. Commun. 1984, 26, 339. Rhee, H. K.; Heerdt, E. D.; Amundson, N. R. Chem. Eng. J . 1972, 3 2 2 .
Sakoda, A,; Suzuki, M. J . Chem. Eng. Jpn. 1984, 17 (3), 316. Sircar, S.;Kumar, R. Ind. Eng . Chem . Process Des. Dev 1985, 2 4 , 358. Yagi, S . ; Kunll, D. AIChEJ. 1057, 3 (3), 373. Yagi, S . ; Kunii, D.; Wakao, N. AIChE J . 1980, 6 (4), 543. Zwiebel, I.; Gariepy, R. L.; Schritzer, J. L. AIChE J . 1972, 18 (6), 1139
Received f o r review March 19, 1985 Revised manuscript received August 9, 1985 Accepted August 19, 1985
Generalized KOnetk Mudel for the Uncatalyzed Hydrotiquefaction of Coal A. K. Ghosh,+ 0. N. Prasad, J. 6. Agnew,z and T. Sridhar" Depafiment
ofChemical Engineering, Monash University, Clayton
Victoria, 3 168, Australia
A kinetic model, incorporating dehydrogenation of tetralin, for the liquefaction of coals has been developed and tested with data from a variety of low- and medium-rank coals. The model postulates that coal essentially consists of three lumps. Of these, one dissociates almost instantaneously, the second is characterized by slow internal hydrogen shuttling, and only the third lump requires external hydrogen. The reactivity of each lump does not vary between coals; however, different coals are found to contain different fractions of each lump. The rate of reaction of coal is about 3 orders of magnitude faster than the tetralin dehydrogenation reaction. This study clearly shows that it is not only the solvent's capacity to donate hydrogen but also the rate at which hydrogen is donated that is important in coal liquefaction.
(Kang et al., 1981),and at 450 "C with an initial hydrogen pressure of 3.45 MPa (McNeil et al., 1983). Vlieger et al. (1984) have studied the behavior of tetralin in coal liquefaction processes in a batch autoclave for long residence times. The authors studied the effect of temperature, pressure, and reaction time on tetralin dehydrogenation, isomerization, and hydrocracking. However, the authors did not propose any kinetic model that incorporates the dehydrogenationof tetralin which occurs with the progress of coal hydrogenation. Conventional kinetic modeling of the hydroliquefaction of coal in a donor solvent has visualized parallel-series schemes for coal to various products. In all such attempts, the concurrent reaction of the donor solvent to produce hydrogen has been totally ignored; i.e., the tetralin dehydrogenation reaction is assumed to be very fast. Only very recently, Skowronski et al. (1984) studied the coal hydrogenation reaction by using a deuterium tracer method to investigate which structural positions in the coal react with hydrogen gas or donor solvent during liquefaction. The study indicated that in the donor system, the abstraction of hydrogen from the solvent by coal-derived radicals is involved in the rate-determining step during the formation of the soluble products. The authors also indicated that considerable interaction of gas-phase hydrogen with the coal also occurred in the donor-solvent system. However, no attempt was made in modeling the complex interactions between gas-phase hydrogen, donor solvent, and coal. In this paper, the development of a kinetic model incorporating the dehydrogenation of tetralin in the overall scheme of coal liquefaction reaction is presented. Experimental data on the uncatalyzed liquefaction of a Victorian brown coal are used to obtain the model parameters. These parameters are used to predict the conversion behavior of two medium-rankingcoals. The effects of the solvent-to-coal ratio and the role of dissolved hy-
In most coal liquefaction processes, crushed coal is contacted with a hydrogen-donor solvent under elevated pressure and temperature. The classical H-donor, tetralin, is commonly used (Cronauer et al., 1982; Neavel, 1976) because it is considered to be one of the most convenient hydroaromatic solvents with sufficient hydrogen-donor ability. Many other hydroaromatic model solvents and coal-derived recycle solvents are also used in coal liquefaction studies (Abichandani et al., 1984). In the initial stages of liquefaction, at a temperature above 650 K, coal produces reactive fragments as free radicals which are stabilized by hydrogen from (i) more hydroaromatic portions of the coal itself, (ii) from hydrogen-donor compounds in the solvent and coal-derived liquids, and (iii) from the gas phase (Neavel, 1976; Moritomi et al., 1983). I t is well-known that the extent of coal conversion is related to the hydrogen consumed in the process. As a measure of hydrogen consumption by the coal, the degree of tetralin dehydrogenationto naphthalene has often been used (Curran et al., 1967; Vlieger et al., 1984). To obtain maximum hydrogenation of a mediumvolatile bituminous coal in excess tetralin, the presence of hydrogen gas was considered necessary (Wilson et al., 1982). However, the dehydrogenation of tetralin in the liquefaction of lignite was reported to be independent of gaseous atmosphere (Philip and Anthony, 1982). The behavior of tetralin in the presence of coal has been studied qualitatively (Kamiya et al., 1978) at 378-460 "C under hydrogen pressure of 0.98 MPa, at 400 "C and 10.2 MPa of Hz in a batch recycle system with small residence time +Research Laboratories, APM Limited, Alphington, Victoria 3078, Australia. Department of Chemical Engineering, University of Adelaide, Adelaide, S.A., Australia.
*
0196-4305/86/1125-0464$01.50/0
0
1986 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 2, 1986 465 Table I. Elemental Analysis of Coal Samples (wt 70,daf Basis) element
Morwell
Taroom
Wandoan
coal Kentucy No. 6
Illinois No. 6
Kentucky No. 9
Liddell
C
70.40 4.90 0.50 0.30 23.90
76.15 5.94 1.17 0.43 16.40
77.40 5.99 1.08 0.48 15.1
80.95 5.59 1.83 2.80 8.83
78.74 5.48 1.37 10.17 10.17
74.75 5.75 1.16 6.58 11.75
83.00 5.89 2.15 0.54 8.39
H N S 0
Table 11. ExDerimental Conditions expt no.
temp, "C
reactor type
solvent
A B C
415 395 395 395 395 375 335 315 420 400 380 420 400 415 395 375
continuous tubular continuous tubular batch batch batch continuous tubular batch batch batch batch batch batch batch batch batch batch
tetralin tetralin tetralin tetralin decalin tetralin tetralin tetralin tetralin tetralin tetralin tetralin tetralin T+D T + D T + D
D
E F G H I J K L M N 0 P
drogen in the donor solvent on the overall liquefaction process are also discussed. Experimental Section Coals. Three different coals were used in this study: (i) Victorian brown coal from the Morwell seam (Drum 289), (ii) Wandoan high-volatile subbituminous, and (iii) Taroom high-volatile subbituminous. Air-dried coal samples of particles size
