COAL LIQUEFACTION AND DESULFURIZATION
J. A. GUIN, Y. A. LIU, C. W. CURTIS, A. R. TARRER AND D. C. WILLIAMS The program is presently the Auburn University largest university-based coal research Auburn, AL 36849 program in the Southeastern region, and current support is . .. about $450,000 annually. ALABAMA IS A SIGNIFICANT producer of coal in the United States, particularly in the Gulf province. There are large reserves of coal in Ala aspects of the Auburn coal liquefaction research bama; 35 billion tons lie in the northern and program. It has made available its resources and central counties, enough for hundreds of years at facilities at the 6 tons/day solvent-refined-coal our present rate of production. Lignite deposits (SRC) pilot plant located at Wilsonville, Alabama in southern Alabama counties await the technology (90 miles from Auburn) for support of the super to properly realize their value. Thus, a strong vised internship and hands-on research training of recommendation of a statewide conference on the Auburn program. The largest utility coal user "Energy and the Future of Alabama" sponsored in the Northeast, the New England Electric by Auburn University in 1972 was for "research, System, has also actively participated in the Au development and technical liaison in the areas of burn coal desulfurization research since 1978. coal production, coal processing and coal usage." Auburn University acted upon this recommenda COAL RESEARCH FACULTY AND FACILITIES tion, and with major support from the National The Auburn coal liquefaction research program Science Foundation (NSF), established the Au is presently being directed by a number of burn Coal Conversion Research Laboratory in chemical engineering faculty, including Drs. J. A. the Department of Chemical Engineering in 1973. Guin, A. R. Tarrer, C. W. Curtis and D. C. Subsequently, with additional support from NSF Williams. These individuals have had extensive in 1975, Auburn University established a Coal coal liquefaction research experience, particularly Preparation Research Laboratory. Since their related to the aspects of transport phenomena, initiation, the Auburn Coal Research Laboratories reaction engineering, analytical chemistry, applied have been heavily involved in the graduate train ing of selected M.S. and Ph.D. students in the areas TABLE 1 of coal conversion and utilization. A major thrust of the recent and ongoing research has been Recent Sponsors of the Auburn Coal Rese arch Program placed on coal liquefaction and desulfurization. Disposable catalysts for coal liquefaction: The program is presently the largest university Air Products and Chemicals, Inc. based coal research program in the Southeastern Corrosion by coal liquids: Catalytic, Inc. region, and current support for the program is at Catalyst deactivation in coal liquefaction: a level of about $450,000 annually. Recent and Cities Service Research and Development Two-stage coal liquefaction: Electric Power Research current sponsors of the program, summarized in Institute Table 1, have included many industrial organiza Visual reactor studies of coal dissolution: tions. Of particular significance is the fact that Gulf Research and Development Company the Southern Company Services, Inc., which is Magnetofluidized beds and coal desulfurization: widely recognized in the area of coal conversion New England Power Service Company Magnetic beneficiation of coal: Union Carbide Corporation technology and applications of coal-derived fuels, Graduate training in coal conversion and utilization: has continued since 1973 to actively support many U.S. Department of Education Solvent refining of coal: U.S. Department of Energy © Copyright ChE D ivision, A SEE, 1981 Dry coal desulfurization: U.S. Department of Energy
178 CHEMICAL ENGINEERING EDlJGA'nON catalysis and separation processes. Both Drs. selected recent publications and theses from the Guin and Tarrer have served as project managers Auburn coal research program is given at the end for the Fossil Energy Program of the U. S. De of this article. partment of Energy, providing the Auburn Labo Laboratories containing approximately 4000 ratories with unique and practical insights to the ft2 in the Department of Chemical Engineering ongoing coal conversion research in the country. have been equipped for coal conversion and In addition, Dr. S. C. Worley of the Department utilization studies. Complete laboratory facilities of Chemistry and Dr. B. Tatarchuk, a new chemi for high-pressure coal conversion, coal crushing cal engineering faculty in the Fall, 1981, are di and grinding, instrumental analysis, wet chemical recting fundamental research related to catalysis analysis and coal preparation research are avail in coal liquefaction ; and Dr. R. B. Cook of the able. Complete analytical equipment for standard Department of Geology is directing the geological analyses of coal and coal-derived products is also aspects of coal conversion processes. The Auburn available in the laboratories. In addition, coal desulfurization research program is currently specialized research equipment such as a Fourier being directed by Dr. Y. A. Liu, a chemical engi Transform Infrared Spectrophotometer, an X-ray neering faculty member. Fluorescence Spectrometer, a CHONS analyzer During the past few years, the Auburn coal and a superconducting high-intensity magnetic research faculty has become nationally and inter separator are available in the laboratories. nationally recognized for its research as well as its scholastic and professional contributions re COAL LIQUEFACTION RESEARCH lated to coal liquefaction and desulfurization, and Chemistry and Technology of Coal Liquefaction magnetic separation applied to coal preparation. The research results obtained in the last few years In order to better appreciate the rese~rch have been widely publicized through publication being conducted in coal liquefaction, a brief iook of three books, two patents, and over 150 articles, at coal liquefaction chemistry and technology presentations and seminars. Further, the Auburn is desirable. Coal may be viewed as a large, Laboratories have organized and chaired two organic, amorphous, polymeric-like structure international conferences on coal desulfurization consisting of condensed polynuclear aromatic and magnetic separation (B8, B9), and one systems coupled by methylene-bridge groups, or national conference on the future of coal. A list of heteroatom linkages such as ether or sulfide
Y. A. Liv received his S.S. from National Taiwan University, M.S. coal liquefaction, solids/liquid separation, process dynamics and from Tufts University and Ph.D. from Princeton University in 1974. He control, and catalysis. (C) is presently an alumni associate professor of Chemical Engineering at Christine W. Curtis is a research associate in chemical engineering Auburn University. (L) at Auburn University. She received her B.S. from Mercer University and James A. Guin, is a professor of chemical engineering at Auburn M.S. and Ph.D. from Florida State University. Her research interests Uni~ersity. He received his B.S. and M.S. from the University of include coal liquefaction, catalytic upgrading and analysis of coal Alabama and Ph .D. from the University of Texas at Austin. His re• liquids. (RC) search interests include coal liquefaction, reactor design, and catalytic Dennis C. Williams is an assistant professor of chemical engineer upgrading of coal liquids. (LC) ing at Auburn University. He received his Ph .D. in chemical engineer Authur R. Tarrer is an associate professor of chemical engineering ing from Princeton University in 1980. His research interests include at Auburn University. He received his B.S. from Auburn University and process control, process synthesis, reactor modelling, phase behavior M.S. and Ph.D. from Purdue University. His research interests include effects in coal liquefaction, and numerical methods. (R)
FALL 1981 179 groups. Nitrogen is also a significant heteroatom available for subsequent separation and process component of the coal structure. The liquefaction ing into the desired clean fuels. A commercial coal of coal is thought to begin with the thermal rup liquefaction plant would process about 30,000 ture of scissile linkages at temperatures around tons/ day of raw coal. The only commercial opera 375°C with the resulting formation of a large tion of this magnitude today is in South Africa number of free radical species. The key to the where large quantities of liquid fuels are produced liquefaction process is to "cap off" these free via coal gasification and catalytic Fischer-Tropsch radicals by hydrogen addition before they can technology (A3). The direct production of liquid recombine with large coal fragments to form a fuels from coal by solvent extraction-hydrogena high-molecular-weight structure. This "donor" tion avoids the gasification step and offers the po hydrogen usually comes primarily from a "donor" tential of a more thermally efficient process. A solvent; however, it may also arise from gas survey of different coal liquefaction processes phase hydrogen or hydroaromatic portions of the being developed in this country can be found in coal itself. The effective "capping" of these free the excellent surveys by Klass (A4) and Perry radicals leads to the formation of products of (A5). lower molecular weight. If the reaction conditions are severe enough, a liquid product is formed. A Current Scope and Accomplishments Coal liquefaction research at Auburn centers • on the production of clean liquid and solid fuels CH2 CH3 from coal. At the present time, processes to per Stoolllzatlon ~ + ~ H2 ~ form these operations are not economically com . A~+O:,2 : CH2-CH • Tetralln CH3 - C ~ NOPhthalene petitive with the use of petroleum. The objective 01 I 3 (Spent so lvent> I 1 2
180 CHEMICAL ENGINEERING EDUCATION spectroscopies, it has been found that the hydro aromaticity of the recycle solvent is closely related to its effectiveness for coal liquefaction (B7). The objective of the ... program • Sulfur Removal. In certain coal liquefaction pro is to investigate the effects of process cesses, e.g., the SRC process, the primary objective is operating conditions, equipment configurations, to remove sulfur from the coal to produce a non and nature of raw materials upon polluting, clean burning product. By introducing the kinetics and mechanisms
certain sulfur scavenging agents, e.g., Fe20 3 , into of coal liq.uefaction. the liquefaction reactor, it has been found possible to significantly reduce the sulfur content of the SRC product (B5). • Coal Pretreatment. The oxidation of coal has been • Catalyst deactivation in upgrading of crude coal found to reduce significantly the liquid yield from liquids processing. This factor has stimulated considerable • Kinetics and mechanism of hydrogen shuttling in interest in the protocol used to store, grind, and coal liquefaction dry the fresh coal prior to liquefaction. • Tailoring of coal recycle solvent for more effective • Coal Mineral Catalysis. It has been established that liquefaction coal minerals, notably pyrite, act as weak catalysts • Catalyst poisoning by heteroatom compounds in for hydrogenation and heteroatom removal reactions coal derived liquids in the liquefaction process (B2, B4). This catalysis can be used to improve hydrogen usage selectivity and to lower the yield of non-desirable products, COAL DESULFURIZATION RESEARCH e.g., · light hydrocarbon gases (B6) . The regenera Physics and Technology of Coal Desulfurization tion of mineral residue from the reactor to produce an active catalyst is an item of current research, Physical coal desulfurization ( cleaning or as are the kinetics of the catalytic reactions. beneficiation) methods are based upon the differ • Product Characterization. The chemical nature of coal liquefaction products, e.g., asphaltenes, SRC, ences in the physical characteristics that affect etc., is vastly complex. Inroads are being made in the separation of sulfur-bearing and ash-form this area using a variety of separation techniques ing minerals from the pulverized coal. Typical such as high performance liquid chromatography physical characteristics utilized in these methods coupled with a number of spectroscopic techniques include specific gravity, electric conductivity, including Fourier transform infrared spectro magnetic susceptibility and surface properties. photometer, nuclear magnetic resonance and mass spectroscopy ( B3) . In some of the new methods being developed, chemical pretreatment is used to enhance the Work related to the above areas is now ongoing difference in physical characteristics to facilitate as part of the current coal liquefaction program the physical separation of mineral impurities from at Auburn. Some typical current research topics the pulverized coal (A6). An excellent survey of _on which graduate students are now working in the present and developing physical coal desulfuri clude: zation processes can be found in Berry (A7), and • A critical evaluation of mass transfer effects in an in-depth review of much of the new methods coal liquefaction and developments of physical coal desulfuriza . • Solvent characterization using chromatographic tion technology will soon be published (BlO) . separation with 1 H and 1ac NMR A relatively well-established technology which has been proposed for coal desulfurization applica tions is the magnetic separation technique. Pre Coal Fee d ..., lfquefoctlon ,_ Gases Solids vious investigators have indicated that most of ,--0- Reactor I00 "C, 2000 pslg Seoarotlon .- ,. Coo l Liquids the mineral impurities which contribute to coal's sulfur and ash contents are weakly magnetic, Minerals whereas coal is nonmagnetic (B8). During the Undissolved Cool Recvcte , --- So lvent past few years, the magnetic desulfurization of ! coal has been given new impetus with the introduc so t vent tion of the high gradient magnetic separation Hydrogenation '-- r- Ash
FALL 1981 181 time for reducing the fluid drag force and im Dissolution," I & EC Process Des. and Develop., 17, proving the separation efficiency. 490 (1976). A2. Berkowitz, N., An Introduction to Coal Technology, Academic Press, New York (1979). Current Scope and Accomplishments A3. Heylin, M., "South Africa Commits to Oil from Coal Process," Chem. and Eng. News, p. 13, Sept. Since 1975, the Auburn Coal Preparation 17 (1979). Laboratory has been actively involved in both A4. Klass, D. L., "Synthetic Crude Oil from Shale and basic and applied research in physical coal de Coal," Chemtech., p. 499, Aug. (1975). sulfurization, emphasizing the development and A5. Perry, H., "Coal Conversion Technology, Chem. demonstration of HGMS processes. Major results Eng., p. 88, July 22 (1980). A6. Leonard, J. W., Editor, Coal Preparation, Soc. ;from this research have included: Mining Engrs., Denver (1979). A 7. Berry, R. L., "Guide to Coal-Cleaning Methods," • The pilot-scale demonstration of the technical Chem. Eng., p. 47, Jan. 26 (1981). feasibility of magnetic separation of mineral resi due from liquefied coal (Bll) ; • The computer development and experimental verifi B. SELECTED RECENT PUBLICATIONS FROM THE cation of a practical model for predicting the AUBURN COAL RESEARCH PROGRAM technical performance of HGMS for the removal of sulfur and ash from coal/ water slurries (B12); Bl. Curtis, C. W., A. R. Tarrer and J. A. Guin, "Particle and Size Variation in the Solvent Refined Coal Process," • The experimental development of the patented I & EC Process Des. and Develop., 18, 377 (1979). Auburn fluidized-bed HGMS process for desulfuriza B2. Guin, J. A., A. R. Tarrer, J. M. Lee, H. F. Van tion of dry pulverized coal (B13). Brackle and C. W. Curtis, "Further Studies of Catalytic Activity of Coal Minerals in Coal Lique The recent and current emphasis of the Auburn faction: 1. Verification of Catalytic Activity of coal desulfurization research has been placed on Mineral Matter by Model Compound Studies, and 2. Performance of Iron and SRC Mineral Residue the continued development and demonstration of as Catalysts and Sulfur Scavengers," I & EC Pro the patented fluidized-bed HGMS process for de cess Des. and Develop., 18, 371 and 631 (1979). sulfurization of utility boiler feed coals. In par B3. C. W. Curtis, C. D. Hathaway, J. A. Guin, and ticular, a pilot-scale superconducting fluidized A. R. Tarrer, "Spectroscopic Investigation of Sol bed HGMS process development unit (PDU) has vent Refined Coal Fractions," Fuel, 59, 575 (1980). B4. Guin, J. A., J.M. Lee, C. W. Fan, C. W. Curtis, J. L. been successfully designed, constructed and tested. Lloyd and A. R. Tarrer, "The Pyrite Catalyzed The available experimental results have shown Hydrogenolysis of Benzothiophene at Coal Lique that the new fluidized-bed magnetic process can faction Conditions," I & EC Process Des. and reduce the sulfur emission level (lb S per million Develop., 19, 440 (1980). BTU) of several pulverized Eastern coals (70 to B5. Garg, D., A. R. Tarrer, J. A. Guin, C. W. Curtis and J. H. Clinton, "The Selective Action of Hema 80 % minus 200-mesh) by 55-70 % and achieve tite in Coal Desulfurization," I & EC Process Des. an average BTU recovery of 85-95 % (B14). Work and Develop., 19, 572 (1980). is continuing on the automation and optimization B6. Garg, D., A. R. Tarrer, J. A. Guin, C. W. Curtis, of the continuous PDU in order to provide the J. H. Clinton and S. M. Paranjape, "Selectivity Im necessary data for assessing the economics of the provement in the Solvent Refined Coal Process. 1. Detailed First-Stage Reaction Studies: Coal Mineral new dry magnetic process for coal desulfurization. Catalysis; and 2. Detailed Second-Stage Reaction Another emphasis of the Auburn current research Studies: Hydrotreating of Coal Liquids," Fuel Pro is the fundamental studies of magnetofluidized cess Technol., 3, 245 and 263 (1980). beds as a new gas-solid contacting technology for B7. Curtis, C. W., J. A. Guin, J. F. Jeng and A. R. reaction, separation and filtration applications. A Tarrer, "Coal Solvolysis with a Series of Coal Derived Liquids," Fuel, in press (1981). novel concept of using a packed fluidized-bed in a B8. Liu, Y. A., Editor, Proceedings of Magnetic De magnetic field for the removal of sulfur and ash sulfurization of Coal Symposium, Special Issue on from pulverized coal invented in the Auburn Magnetic Separation, IEEE Trans. on Magn., MAG- Laboratories has been described in a recent 12, 423-551 (1976). patent (B13). D B9. Liu, Y. A., Editor, Industrial Applications of Mag netic Separation, 206 pages, IEEE Publication No. 78CH1447-2 MAG, Institute of Electric and A. LITERATURE CITED Electronic Engineers, Inc., New York (1979). B10. Liu, Y. A., Editor, Physical Cleaning of Coal: Al. Guin, J. A., A. R. Tarrer, Z. L. Taylor, Jr., J. W. Prather and S. Green, "Mechanisms of Coal Particle Continued on page 213.
182 CHEMICAL ENGINEERING EDUCATION Techniques for Chemical Engineers, Sect. 1.12, Des. Develop., 19, 509 (1980). McGraw-Hill, NY, 1979. 36. Singh, G., "Crystallization from Solutions," in P. 16. Lightfoot, E. N., R. J. Sanchez-Palma and D. C. Schweitzer (ed.) Handbook of Separation Techniques Edwards, "Chromatography and Allied Fixed Bed for Chemical Engineers, McGraw Hill, NY, 1979, Sect. Separations Processes" in H. M. Schoen (ed.), Nf?/W 2.4. Chemical Engineering Separation Techniques, Inter science, NY, p. 125 (1962). 17. Lapidus, L. and N. R. Amundson, "Mathematics of Adsorption in Beds. VI. The Effect of Longitudinal COAL LIQUEFACTION Diffusion in Ion Exchange and Chromatic Columns," Continued from page 182. J. Phys. Chem., 56, 984 (1952). Present and Developing Methods, in press, Marcel 18. Thomas, H. C., "Chromatography: A Problem in Dekker, Inc., New York (1981). Kinetics," Annals New York Academy of Science, Bll. Liu, Y. A. and G. E. Crow, "Studies in Magneto 49, 161 (1948). chemical Engineering: I. A. Pilot-Scale Study of 19. Lee, M. N. Y., "Novel Separations with Molecular High-Gradient Magnetic Desulfurization of Solvent Sieves Adsorption," in N. N. Li, Recent Developments Refined Coal," Fuel, 58, 345 (1979). in Separation Science, Vol. II, (1972), p. 75. B12. Liu, Y. A. and M. J. Oak, "Studies in Magneto 20. Breck, D. W., Zeolite Molecular Sieves, Wiley, NY, chemical Engineering: II. Theoretical Development 1978. of a Practical Model for High Gradient Magnetic 21. Mantell, C. L., Carbon and Graphite Handbook, Inter Separation, and III. Experimental Applications of a science, (1968), Chapter 13. Practical Model of High Gradient Magnetic Separa 22. Wankat, P. C., and L. R. Partin, "Process for Re tion to Pilot-Scale Coal Beneficiation," AIChE J., covery of Solvent Vapors with Activated Carbon," in press (1981). Ind. Eng. Chem. Process Des. Dev., 19, 446 (1980). B13. Eissenberg, D. M. and Y. A. Liu, "High Gradient 23. May, S. W., and L. M. Landgraff, "Separation Magnetic Beneficiation of Dry Pulverized Coal via Techniques Based on Biological Specificity," in N. N. Upwardly-Directed Recirculating Fluidization," Li (ed.), Recent Developments in Separation Science, U.S. Patent number 4,212,651, issued on July 15, Vol. V., 227-255 (1979). 1980. 24. Lacey, R. E., "Membrane Separation Processes," B14. Liu, Y. A., "Novel High Gradient Magnetic Separa Chem. Eng., Sept. 4, 1972, p. 56-74. tion Processes for Desulfurization of Dry Pulverized 25. Reid, C. E., "Principles of Reverse Osmosis," in U. Coal," Chap. 9 in Recent Development in SepMation Merten (ed.), Desalination by Reverse Osmosis, 1966, Science: Volume VI, Norman N. Li, Editor, CRC p. 1-14. Press, Boca Raton, FL (1981). 26. Blatt, W. F., A. Dravid, A. S. Michaels, and L. Nelsen, in "Solute Polarization and Cake Formation in Membrane Ultrafiltration" in J. E. Flinn (ed.), Mem C. SELECTED RECENT THESES FROM THE AUBURN brane Science and Technology, p. 47-74, 1970. COAL RESEARCH PROGRAM 27. Sherwood, T. K., P. L. T. Brian, R. E. Fisher and L. Cl. McCord, T. H., "A Feasibility Study of Novel High Dresner, "Salt Concentration at Phase Boundaries in Gradient Magnetic Separation Processes for De Desalination by Reverse Osmosis," IEC Fundamentals, sulfurization of Dry Pulverized Coal" (1979). 4, 113, (1965). C2. Jeng, J. F ., "Determination of a Solvent Quality 28. Porter, M.C., "Membrane Filtration," in P. Schweitzer Index for Coal Liquefaction," (1979). (ed.), Handbook of Separation Techniques for Chemi C3. Fan, C. W., "Heteroatom Removal from Model Com cal Engineers, McGraw-Hill, NY, 1979, Sect. 2.1. pounds by Coal Mineral Catalysts," (1979). 29. Merten, U., "Transport Properties of Osmotic Mem C4. Henson, B. J., "Solubilities of H and CO in Coal branes" in U. Merten, Desalination by Reverse Os 2 2 Liquids," (1980). mosis, MIT Press (1966), Pages 15 to 54. C5 .. Majlessi, S.H.R., "Synergistic and Phase Behavior 30. Sourirajan, S. (ed.), Reverse Osmosis and Synthetic Effects Among Aliphatic and Aromatic Compounds Membrane, National Research Council, Canada, in Coal Liquefaction," (1980). (1977) . C6. Wagner, R. G., "A Feasibility Study of Novel Con 31. Hwang, S. T. and J . M. Thorman, "The Continuous tinuous Superconducting High Gradient Magnetic Membrane Column," AIChE Journal, 26, 558 (1980). Separation Process for Desulfurization of Dry Pul 32. McCabe, W. L. and J. C. Smith, Unit Operations of verized Coal," (1980). Chemical Engineering, 3rd ed. McGraw-Hill, NY, 1976, C7. Brook, D., "Effect of Pyrite on Liquefaction Chapter 28. Catalysis," (1981). 33. Larson, M. A. and A. D. Randolph, "Size Distribution CB. Crawford, J., "Kinetics of Pyrite-to-Pyrrhotite Analysis in Continuous Crystallization," CEP Symp. Transformation," (1981). Ser., Vol. 65, #95, p. 1 (1969). C9. Pehler, F. A., "Development and Demonstration of 34. Randolph, A. D. and M. A. Larson, "Theory of Par the Auburn Fluidized-Bed Superconducting High ticulate Process," Academic, NY, 1971, Chapters 4 Gradient Magnetic Separation Process for Desulfur to 9. ization of Dry Pulverized Coal," (1981). 35. Garside, J. and M. B. Shah, "Crystallization Kinetics ClO. Smith, N., "NMR Investigation of Recycle Solvent from MSMPR Crystallizers," Ind. Eng. Chem. Process Quality," (1981).
FALL 1981 213