Similarities and differences of coal reactivity in liquefaction and pyrolysis

Abstract

This paper compares coal reactivity in liquefaction and pyrolysis to highlight how similarities and differences can be broadly related to the chemical and physical factors operative in particular regimes. Although no one single property of coal has found universal applicability in predicting liquid yields and total conversions, H C ratios correlate with both oil yields in hydroliquefaction and tar yields in static and fluidized bed pyrolysis. The most useful correlations with maceral contents have been obtained for primary conversions in liquefaction using relatively mild conditions. Under conditions of rapid heating in coal pyrolysis, a number of factors including solvent extractable material, additives and cation exchange have a profound influence on tar yield and composition, the control of secondary reactions being particularly important. Indeed, experiments with steam suggest that mineral matter has an even more pronounced effect on conversion than in liquefaction. More precise structural information on the nature of aromatic and aliphatic groups in coals will help to improve our understanding of the way coal structure affects both liquefaction and pyrolysis.