Reaction of carboxylic acids under coal liquefaction conditions. 2. Under hydrogen atmosphere

Abstract

Pyrolytic reactions of benzoic and 2-naphthoic acids were examined in microautoclave reactors in a hydrogen atmosphere and over a temperature range typical of that used for direct liquefaction conversion of coals to synthetic liquid fuels. Reactions of selected salts and other derivatives were also examined. Reactions were also conducted in the presence of water, since the role of water in direct liquefaction is somewhat controversial. The acids converted via anhydride formation in the absence of water. Conversions at 400° were essentially identical with those N 2, indicating that H 2 is not effective in intervening in the reaction at this temperature. This is verified by comparing reactions in the presence of dihydrophenanthrene (DHP), where some hydrogenation was afforded by the DHP in either atmosphere, but no effect of H 2 was noticed. Reactions of benzoic anhydride suggest that H 2 does convert the carboxyl radical back to the acid. At 450°C, the conversion is lower in H 2 than in N 2. At 450°C, H 2 opens a new pathway, via the aldehyde, for pyrolysis. Water mainly prevents formation of anhydride species. In the presence of water, only decarboxylation and reduction reactions were dominant processes in conversion of the acids. Radical attack on the ipso-carbon atom and subsequent decarboxylation may be responsible for the acid conversion. Direct reduction of the acids occurs only at 450°C. The effect of water on reducing conversions at 450°C is not nearly so pronounced in H 2 as in N 2, supporting the idea that at this high temperature H 2 may open a new route to decomposition. The calcium and sodium salts of the acids are quite stable, but iron(III) benzoate hydrogenates readily.