(54h) Cubic-Plus-Association (CPA) Equation of State for Water-Containing Mixtures

We report an accurate cubic-plus-association (CPA) equation of state (EOS) for water-containing mixtures where the physical contributions are represented by the Peng-Robinson (PR) equation and the chemical contributions from hydrogen bonding are described by the thermodynamic perturbation theory. For water, the higher-order correction in terms of the temperature is used to estimate the energy parameter of the physical part. For non-associating components, the equation is reduced to the original PR-EOS. The binary interaction coefficients (BICs) are assumed to be temperature-dependent. Our proposed method demonstrates excellent performance through extensive comparison for the compositions in binary water/hydrocarbon, water/CO2 and water/H2S mixtures at two-phase equilibria over a wide range of conditions. Accurate predictions of both phase compositions and densities are also observed for mixtures consisting of three and four components in both two- and three-phase envelopes. For some species with strong polar moments such as H2S and CO2, an extra cross attraction with water beyond the physical interactions is necessary. These species can be regarded as ?pseudo-associating' components and the extra cross attraction with water can be accurately described by the thermodynamic perturbation theory. Results from the work will be potentially useful for proper modeling of CO2 sequestration in saline aquifers and in steam injection in hydrocarbon reservoirs.