| This dissertation work was concerned with a systematic study of the low temperature depolymerization-liquefaction reactions of representative U.S. coals, using a new stepwise procedure. Five coals of various rank were selected as feeds for the study.; The procedure involves application of three sequential reaction steps in which different types of intercluster linkages in the coal structure are subjected to preferential cleavage, i.e., (1) deep-seated impregnation of the coal sample with catalytic amounts of FeCl{dollar}sb3{dollar}, followed by mild hydrotreatment (HT); (2) base-catalyzed depolymerization (BCD) of the product from step 1, under supercritical conditions, using a methanolic KOH solution as catalyst-solvent depolymerizing agent; and (3) hydroprocessing (HPR) of the depolymerized product from the two preceding steps with a sulfided CoMo catalyst, to yield a light hydrocarbon oil.; Suitable processing conditions, e.g., temperature, pressure, reaction time and catalyst type and concentration, were determined for the depolymerizing HT and BCD steps for each of the above coals. It was found that these conditions change to some extent with coal rank but are within narrow ranges. Under the suitable conditions the above coals and lignites yield a depolymerized, THF-soluble product (yield of 72-90 wt% calculated on the MAF coal). The predominant oil fraction (57-63%) of this product consists of a mixture of simple compounds, i.e., alkylphenols, alkylarenes, alkylnaphthenoaromatics and paraffins, having low molecular weights (average molecular weights in the range of 242-286). These products were subjected to extensive structural analysis by GC/MS, GC/CIMS, TGA, {dollar}sp1{dollar}H NMR, {dollar}sp{lcub}13{rcub}{dollar}C NMR, FTIR, GC, simulated distillation, elemental analysis, etc., to obtain information on the basic building units and intercluster linkages in the original coals.; Depolymerized coals were finally subjected to hydroprocessing (HPR) to yield light hydrocarbon oils which contained 72-77% of low-boiling point fractions (gasoline, kerosene, gas oil; b.p. up to 325{dollar}spcirc{dollar}C/760 torr). These results demonstrated the high efficiency of the HT-BCD-HPR procedure for coal conversion into light liquid fuels.; The mechanism of the HT and BCD steps was elucidated by model compound studies. Results indicated that the HT step involves preferential hydrogenolytic cleavage of alkylene linkages, whereas the BCD steps leads to hydrolysis of etheric and thioetheric linkages. |
