Chemical changes produced in coal through the action of Lewis acid catalysts

Molten Lewis acids and in pcular ZnCl//2 and SnCl//2 are known to catalyze the conversion of coal to liquid products. While the degree of liquefaction attainable with different catalysts is known, the manner in which Lewis acids promote liquefaction is not well understood. The present work was undertaken in an effort to establish more clearly the effects of Lewis acids on coal and to identify the specific chemical reactions which these catalysts affect. The results reported here concern experiments conducted with both solvent refined coal (SRC) and a variety of model compounds. The latter were selected to represent the aliphatic, ether, and sulfide linkages which connect the aromatic and hydroaromatic groups in coal. Several models of fused ring aromatic clusters were also examined. It is concluded that the products obtained from the cleavage of aliphatic, ether, and sulfide linkages can be explained by carbonium ion mechanisms.