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Simulation studies of thermodynamic driving forces for the adsorption of naphthenic acid analogues on calcite surface


Naphthenic acids are important constituents of crude oil. Their adsorption on calcite, the dominant mineral surface in reservoirs, can have implications for altering the wettability of the surface and thus on the extraction/recovery of the hydrocarbon. While calcite is nominally polar, in the presence of an adsorbed layer of water, the surface shows characteristics that are expected of apolar surfaces. We find that both the acid group of naphthenic acid and the hydrocarbon tail of the acid play important roles in the adsorption. Longer-chain acids, for example, bind better to the surface than shorter-chain acids. The adsorption is also entropically driven, reminiscent of association between hydrocarbons in water.