Approach for promoting liquid yield in direct liquefaction of Shenhua coal

Single and multi-stage liquefaction of Shenhua (SH) bituminous coal and re-liquefaction of its liquefaction residue (SHLR) were carried out in an autoclave reactor to investigate the essential approach for promoting oil yield and conversion in SH coal direct liquefaction (SHDL). The multi-stage liquefaction includes pretreatment, keeping the reactor at 250 degrees C for 40 min before heating up to the reaction temperature, and two-stage liquefaction processes consisting of low temperature stage, 400 degrees C, and high temperature stage, 460 degrees C. The results show that the pretreatment has slight effect on oil yield and conversion of SHDL, especially for liquefaction at 460 degrees C. There is a positive function of two-stage liquefaction in shortening reaction time at high temperature. Increasing ratio of solvent to SHLR can promote the oil yield and abate reaction condition in SHLR re-liquefaction, that is, it can promote the conversion from preasphaltene and asphaltene to oil. The primary factor to inhibit coal liquefaction is the consumption of hydrogen free radical (H.) from solvent or H-2 and condensation of free radicals from coal pyrolysis after a period of reaction. So the essential approach for increasing oil yield and conversion of SHDL is to provide enough H. to stabilize the free radicals from coal pyiolysis. (C) 2008 Elsevier B.V. All rights reserved.