The effect of various clay minerals on the thermal decomposition of stearic acid under ‘bulk Flow’ conditions

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Abstract
The thermal decomposition of stearic acid in the presence of various clay minerals was studied in an open, inert system under isothermal (250°C) conditions. The distribution of hydrocarbons and the amount of CO2 evolved were determined. The degree of decarboxylation depended on the composition of the octahedral sheets of the clays. It was greater with trioctahedral than with dioctahedral minerals. The presence of dioctahedral minerals tended to reduce the amount of CO2 produced below that obtained with the neat acid. The nature of the hydrocarbons formed depended on the structure of the minerals. Different products were obtained with minerals that have accessible interlayers and channels (smectites, palygorskitesepiolite) 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. In the systems studied, evolution of CO2 did not necessarily precede the formation of light- or medium-weight hydrocarbons from the parent acid.