SOLVENT-FREE LIQUEFACTION OF BROWN AND SUBBITUMINOUS COALS USING NIMOSULFIDE CATALYST SUPPORTED ON CARBON NANOPARTICLES

Single-and two-stage liquefaction processes of Yallourn (YLC), South B anko (SEC), and Tanitoharum (THC) coals were performed in an autoclave of 50-mL capacity at variable solvent (tetralin)/coal ratios from 0 t o 1.5 under the reaction hydrogen pressure of 15 MPa, using NiMo sulfi de supported on carbon nanoparticles or commercial NiMo/alumina and sy nthetic pyrite catalysts. Although the oil yield decreased very much w ith all the catalysts by reducing the amount of solvent to zero, the N iMo/carbon catalyst gave much higher oil yields of 52 and 64%, respect ively, in the single-stage (450 degrees C, 60 min) and two-stage (360 degrees C, 60 min; 450 degrees C, 60 min) liquefaction under the solve nt-free conditions compared with the yield of around 40% by the other two catalysts in both single-and two-stage liquefaction under the same conditions. The oil yield depended on the coal species under the solv ent-free conditions, being in the order of SBC > YLC > THC regardless of the reaction conditions. SBC provided the highest oil yields of 60 and 68% in the single-and two-stage liquefaction, respectively, reflec ting its higher reactivity and lower gas yield. THC gave the lowest oi l yields among the coals examined, although the oil yield reached 60% by the two-stage Liquefaction even under the solvent-free conditions. The oil produced with NiMo/carbon catalyst carried lighter fractions i n the boiling range 100-300 degrees C than those with the other cataly sts regardless of the reaction conditions and coal species. Such excel lent performance of the NiMo/carbon catalyst reflects its higher hydro genation activity as well as the high dispersion on the coal surface a t the initial stage of coal liquefaction, suppressing the retrogressiv e reactions. It is confirmed that the major portion of solid coal was solubilized during the heating and the initial stage to work as the se lf-producing solvent under the solvent-free reaction conditions. The d esign of coal liquefaction with the least use of solvent is discussed for the higher productivity.