LIQUEFACTION BEHAVIOR OF SOLVENT-SWOLLEN COALS

Batch autoclave experiments show that pre-swelling of bituminous and lower rank coals with a suitable solvent, followed by removal of the swelling agent, significantly enhances conversion and product quality during subsequent liquefaction. The enhancement depends on coal rank and swelling agent and is a maximum for a bituminous coal. The beneficial effect of swelling may be due to the expansion of the coal macromolecular structure, making it more accessible to hydrogen donor solvent. The enhanced accessibility may enable prompt capping of the coal free radicals with concomitant reduction in retrograde reactions and facilitate solvent-induced bond cleavage reactions. These effects are reflected in high liquefaction yield and improved product quality. In addition to enhancement in liquefaction yields, swelling also obviates the need for fine grinding of coal, thus reducing grinding costs. For example, without any pre-swelling the -325 fraction of a subbituminous coal gives higher conversion and product quality than the 8 x 70 fraction. In contrast, after pre-swelling both 8 x 70 and -325 mesh samples gave the same conversion and product quality.