A new two-stage process for supercritical fluid extraction of coal with tetralin pretreatment

A new two-stage process for supercritical toluene extraction of coal is proposed that achieves conversion of 60 wt% and a liquid yield of 45 wt%. The first stage consists of pretreatment of the coal with tetralin liquid and vapour with a prescribed temperature-pressure-solvent programme (TPSP). In this stage, coal is pretreated with liquid tetralin up to 460 K and tetralin vapour from 460 to 653 K. In the second stage, the coal is extracted with supercritical toluene at 653 K and 20 MPa. Extractions were compared with other TPSPs including toluene-tetralin (70 : 30 w/w) mixtures and it was found that the new process could achieve similar conversions and liquid yield but with much less tetralin. The pretreatment TPSP is explained in terms of coal swelling during liquid tetralin pretreatment and inhibition of radical recombination in the pyrolysis during tetralin vapour pretreatment. Copyright (C) 1996 Elsevier Science Ltd.