SUPERCRITICAL-FLUID EXTRACTION OF A HIGH-ASH BRAZILIAN COAL - EXTRACTION WITH PURE ETHANOL AND ISOPROPANOL AND THEIR AQUEOUS-SOLUTIONS

The effects of extraction temperature, pressure and addition of water on the liquid yield and on the characteristics of the extracts and res idues from supercritical fluid extraction (SCFE) of a high-ash Brazili an mineral coal were experimentally investigated. The experiments were performed in a semi-batch laboratory-scale unit in the coal pyrolysis region 598-698 K at pressures up to 12.5 MPa, using supercritical eth anol and isopropanol as primary solvents. An increase in either temper ature or pressure caused an increase in the liquid yield for both the pure alcohols and alcohol-water mixtures, although at the same tempera ture and pressure, the latter led to a lower liquid yield compared wit h the pure alcohols. The extracts were characterized by a reliable, no n-destructive preparative liquid chromatography method providing eight discrete fractions with well-defined chemical functionality. The amou nt of the lightest compounds in the extract decreased with increasing pressure, while the opposite trend was observed when the temperature i ncreased. The coal after extraction maintained most of its heating val ue. Ethanol and isopropanol are compared with regard to both the liqui d yield and the gasification reactivity of residual coals. (C) 1997 El sevier Science Ltd.