CO2-philicity of crude oil constituents: A computational study

Abstract

The present ab initio study has investigated the affinity of CO₂ to various binding sites in molecules that consist of an aromatic ring with aliphatic substituents. The effect of unspecific solvation was included with a polarizable continuum model. In all cases, CO₂ has the largest affinity towards the aromatic ring. This preference is small (free energy differences of less than 5 kJ mol⁻¹). When evaluating the electronic interactions alone, that is using 0 K electronic energies, that complex consisting of CO₂ adhering to the organic molecule is favoured. However, when including entropy effects, that is using 298.15 K free energies, the separated species become the most favourable combination. This highlights any subtle molecular-level interaction will not play a role in the context of oil reservoirs because they are usually warmer than 100 °C. Leaving computational uncertainties aside, the repulsive interactions align with the experimental observation of minimal CO₂ solubility at room temperatures. Thus, the solubility that is relevant at reservoir conditions really is determined by bulk phenomena.