Thermal Dissolution of Bituminous Coals (Liquefaction, Donor Solvent).

Abstract

Experimental studies of the dissolution of two high volatile bituminous coals, Kentucky #9 and Illinois #6, were conducted at or below 400(DEGREES)C in a 1-liter batch reactor under a nitrogen gas atmosphere. The solvent to coal ratio was 2.5. In general, the Kentucky #9 coal is more reactive than the Illinois #6 coal. Three solvent mixtures were used: a light aromatic solvent containing 46 wt% tetralin, 46 wt% 2-methyl naphthalene, 5 wt% 2-naphthol and 3 wt% 4-picoline; a heavy aromatic solvent containing 50 wt% of the light solvent, 25 wt% 9,10 dihydroanthracene, 20 wt% phenanthrene and 5 wt% quinoline; and a mixture containing 70 wt% of the heavy solvent and 30 wt% pyrene. The heavy solvent dissolved the coals at a lower temperature, about 20(DEGREES)C, than the light solvent. The addition of pyrene, a four ring aromatic compound, to the heavy solvent mixture did not improve the dissolution yields of Illinois #6 at 375 and 400(DEGREES)C and 25 minute holding time. The effects of temperature and holding time on coal dissolution were investigated at the temperature range of 350 to 400(DEGREES)C and holding times of 0, 25, 60 minutes in the heavy solvent mixture. For both Kentucky #9 and Illinois #6 coals, the maximum conversion to pyridine-solubles is 92 wt% DMMF coal and was achieved at 375(DEGREES)C and 25 minute holding time. The Illinois #6 coal reached an apparent equilibrium after 25 minutes of holding time. The Kentucky #9 coal is more reactive as more asphaltenes and oils produced at 400(DEGREES)C at long holding times. At above 350(DEGREES)C, hydrogen donation by the solvent was found to be significant at short contact times while hydrogen shuttling was the dominant mechanism at long contact times. The H/C ratios of coal derived liquid fractions decreased with time. The pyridine-soluble yield is independent of the temperature path to the final temperature. For the Kentucky #9 coal, the hydrogen content of asphaltenes and preasphaltenes was decreased severely while holding for more than 35 minutes at temperatures above 375(DEGREES)C. The dissolution yields and the H/C ratios of the Illinois #6 coal-derived liquid fractions were not affected by the changing temperature paths. (Abstract shortened with permission of author.)