The effect of various clay minerals on the thermal decomposition of stearic acid under 'bulk flow' conditions.

The thermal decomposition of stearic acid in the presence of various clay minerals was studied in an open, inert system under isothermal (250oC) conditions and the distribution of hydrocarbons and the amount of CO₂ evolved determined. The degree of decarboxylation depended on the composition of the octahedral sheets of the clays, being greater with trioctahedral than with dioctahedral minerals. Dioctahedral minerals tended to reduce the amount of CO₂ produced below that obtained with the neat acid. Different hydrocarbon products were obtained with minerals that have accessible interlayers and channels (smectites, palygorskite-sepiolite) than with the 1:1 clays and pyrophyllite or talc. Some minerals caused cracking to light-weight hydrocarbons. Higher surface acidity of the clay interlayers enhanced this process but was not the only decisive factor. Evolution of CO₂ did not necessarily precede the formation of light- or medium-weight hydrocarbons from the parent acid.-D.J.M.