Pathway for the Catalytic Conversion of Carboxylic Acids to Hydrocarbons over Activated Alumina

Abstract

Pure saturated carboxylic acids ranging from C 4 to C 12 were pyrolyzed at a WHSV of 0.46 h -1 over activated alumina at 450 °C and atmospheric pressure. The carboxylic acids produced symmetrical ketones that further degraded to methyl ketones and hydrocarbons presumably via a y-hydrogen transfer mechanism. The lower molar mass carboxylic acids yielded greater percentages of symmetrical ketones than the higher molar mass carboxylic acids. The organic liquid pyrolysate of butanoic acid (C 4 ) contained 78% 4-heptanone whereas the organic liquid pyrolysate of dodecanoic acid (C 12 ) contained negligible amounts of diundecyl ketone and greater percentages of hydrocarbons. Further pyrolysis of ketone-containing product yielded hydrocarbons. Similar compositions of the pyrolytic products from dodecanoic acid and diundecyl ketone revealed that virtually all of the carboxylic acid degraded to hydrocarbons via the symmetrical ketone. Monoenes were the major hydrocarbon products from ketones and were formed by γ-hydrogen transfer rearrangement, and/or reduction (disproportionation) to alcohol followed by dehydration. Methyl ketones had a distinct preference for reduction to monoenes (containing the same number of carbon atoms) following the latter route.