Supercritical fluid extraction of a high-ash Brazilian coal: Extraction with pure ethanol and isopropanol and their aqueous solutions

Abstract

The effects of extraction temperature, pressure and addition of water on the liquid yield and on the characteristics of the extracts and residues from supercritical fluid extraction (SCFE) of a high-ash Brazilian 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 ethanol and isopropanol as primary solvents. An increase in either temperature or pressure caused an increase in the liquid yield for both the pure alcohols and alcohol-water mixtures, although at the same temperature and pressure, the latter led to a lower liquid yield compared with the pure alcohols. The extracts were characterized by a reliable, non-destructive preparative liquid chromatography method providing eight discrete fractions with well-defined chemical functionality. The amount of the lightest compounds in the extract decreased with increasing pressure, while the opposite trend was observed when the temperature increased. The coal after extraction maintained most of its heating value. Ethanol and isopropanol are compared with regard to both the liquid yield and the gasification reactivity of residual coals.