A molecular dynamics investigation of the dissociation constants of acetic and oxalic acid in supercritical water

Despite its potential for various industrial applications, supercritical water (SCW) is still far from fully understood. One challenge is to obtain a better understanding of the behaviour of acidic species at these conditions as they are known to contribute to the corrosion of SCW reactors. Previous work has highlighted the fact that pic, can vary greatly with thermodynamic conditions. In this work, classical molecular dynamics have been used to study the extent of dissociation of acetic and oxalic acid over temperatures ranging from 298 to 898 K at pressures of 507 and 1013 bar. It has been found that both dissociations are favoured by low temperatures due to destabilisation of the solute-solvent interaction at higher temperatures. Furthermore, rotation of the central carbon-carbon bond of oxalic acid can have a significant impact on the second dissociation, K. This study highlights the influence of the thermodynamic state on the pic of organic acids in SCW.