ISOMERIZATION AND ADDUCTION OF HYDROGEN DONOR SOLVENTS UNDER CONDITIONS OF COAL LIQUEFACTION

Hydroaromatic structures are recognized as “ideal” for liquefying coal due to their ability to readily transfer hydrogen to free radical acceptors. While hydroaromatic hydrogens are preferred, substituted aromatic solvents can compete although the latter are more likely to polymerize or adduct with the acceptors. Hydroaromatic structures rearrange to isomeric forms of enhanced stability which are less likely to transfer hydrogen. Six-membered hydroaromatics such as tetralins and octahydrophenanthrenes contract to five-membered rings (methylindans, etc.). This isomerization is dependent upon temperature, reactor residence time, and, in particular, the level of acceptor radicals. At relatively low temperatures (300-425 °C), the isomerization process is preceded by the adduction of the original hydroaromatic donor with very stable acceptor molecules. This adduction appears to increase with high organic oxygen and sulfur structures. While rearrangements of the above type have been qualitatively known for several years, the present study has attempted to delineate both the kinetic and structural aspects involved. © 1979, American Chemical Society. All rights reserved.