Preparation of an ultra-low ash coal extract under mild conditions

A technique whereby substantial portions of bituminous coal are extracted, non-destructively, is demonstrated by treating raw coal with N-methylpyrrolidone (NMP). An ultra-clean, coal-derived solid material with as little as 0.1% ash and containing no pyritic sulfur was derived by following the extraction step with precipitation of the coal-based material in water and subsequent filtration. The unextracted residue and recovered extracted material were dried under vacuum to allow the determination of overall and elemental mass balances. Amounts extracted were found to be as high as 74% (m.a.f.). The operating conditions are mild at 202°C and atmospheric pressure. Solvent recovery from the NMP-water mixture using conventional distillation on a lab scale was in excess of 97%. Ultimate and proximate analyses of three different H.V. Bituminous coals, and their residues and extracts are reported.