Extraction of coal below 350°C in flowing non-polar solvent

Eight Argonne premium coals and an Australian brown coal (Morwell) were extracted in a flowing stream of either tetralin or 1-methylnaphthalene under 10 MPa at 200-400 degreesC to examine the dissolution/depolymerization behavior of coal in liquid phase. The flowing solvent was used to minimize the secondary interaction between the extract and the macromolecular network of coal. Four bituminous coals were extracted with negligible decomposition below 350 degreesC. The extract yield reached 65-80% for the bituminous coals at 350 degreesC, and the extract was separated into about 25-40% of soluble fraction at room temperature (soluble) and about 40% of solid precipitated at room temperature (deposit). The detailed analyses of the soluble, the deposit and the residue through ultimate analysis, C-13 solid NMR, GPC, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) enabled to examine the structure of Pittsburgh #8 (PITT) in detail. The raw PITT coal was found to contain small molecules (M-w = 130-600) and large molecules (M-w = 1300-3500) in its network. The soluble consisted of only small molecules, but both small and large molecules were involved in the deposit and the residue. The extraction method employed in this work was found to be effective to separate coal into different molecule size fractions without decomposition for bituminous coals. The soluble, being obtained in 20-40% yield and consisting of molecules smaller than 600 of M-w, and the deposit, being obtained in 40% yield at maximum and containing little ash, would be well utilized as either clean fuel or raw materials for the subsequent conversion. (C) 2001 Published by Elsevier Science Ltd.