A study of solvation of o-/m-hydroxybenzoic acid in supercritical CO2–methanol co-solvent system based on intermolecular interaction by molecular dynamics simulation

Solvation behavior of o-hydroxybenzoic acid (o-HBA) and m-hydroxybenzoic acid (m-HBA) in CO2 and methanol mixtures was investigated by molecular dynamics simulation. The results indicated that the distribution of methanol around o-, m-HBA molecules was different, and it was ascribed to the different hydrogen bonding numbers formed between methanol and HBA molecules. Moreover, the interaction or hydrogen bonds between m-HBA and methanol was much stronger than that between o-HBA and methanol, and with the increasing of CO2 pressure, it did not change for the former, but decreased for the latter. In addition, the local mole fraction enhancement was also studied. It was demonstrated that the methanol molecules become less aggregate with increasing CO2 pressure.

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• The influence of co-solvent on the solubility of substrates in CO2 was investigated by molecular simulation. It is very important to understand the properties and the interactions from the molecular level.
• It was found that the distribution of methanol around o-, m-hydroxybenzoic acid molecules was different, and it ascribed to the numbers of hydrogen bonding formed between methanol and hydroxybenzoic acids.
• Based on the analysis of the total number of hydrogen bonding, the interaction between m-HBA and methanol are much stronger than that between o-HBA and methanol.
• The methanol molecules around o-HBA and m-HBA become less aggregate with increasing CO2 pressure due to the increase of the number of CO2 around o-HBA and m-HBA.