Adsorption of tetradecanoic acid on kaolinite minerals: Using flash pyrolysis to characterise the catalytic efficiency of clay mineral adsorbed fatty acids

The clay mineral kaolinite is one of the major inorganic constituents of sedimentary rocks. Kaolinite-carboxylic acid interactions are of considerable importance from the geochemical perspective. The two-fold aim of this study was to quantify the adsorption of tetradecanoic acid on kaolinite and then the flash pyrolysis of adsorbed fatty acids-kaolinite samples to understand the transformation of adsorbed fatty acids on kaolinite. Adsorption of tetradecanoic acid on kaolinite results in an s-isotherm which reflects the multilayer adsorption. Adsorption of tetradecanoic acid on kaolinite involves its both functionalities i.e. siloxane (tetrahedral face) and hydroxyl surface (octahedral face) as indicated from the pyrolysis results. Flash pyrolysis of tetradecanoic acid adsorbed kaolinite mainly yielded saturated/unsaturated hydrocarbons, aromatic hydrocarbons, and ketones while pure tetradecanoic acid generated saturated/unsaturated hydrocarbons and a series of unsaturated and saturated low molecular weight fatty acids. We have successively tested an empirical approach to identify organic compounds formed from fatty acid adsorbed kaolinite to the organic compounds obtained from fatty acid adsorbed alumina and silica. Kaolinite mainly reflects the transformation of carboxylic acids into hydrocarbons and ketones via hydroxyl surface (octahedral face). Ketonisation is mainly observed at multilayer adsorption of tetradecanoic acid on kaolinite. The major implication of the work is the understanding of fatty acids adsorption on kaolinite via both surfaces of the mineral which is helpful to understand the fate of fatty acids as they pass into the geosphere during diagenesis.