Measurement and thermodynamic modeling of partition coefficients in N,N-dimethylacetamide–water–carbon dioxide system

The partition coefficients of N,N-dimethylacetamide (N,N-DMA) between the water and the supercritical and near-critical carbon dioxide (CO2) phases were measured in the temperature range of 298.15–328.15 K and the pressure range of 8.3–24.1 MPa. The measurements were carried out in a 56 ml vessel by contacting the carbon dioxide and the aqueous phases. The partition coefficients of N,N-DMA increased from 0.05 to 0.150 with increasing pressure at a constant temperature and increased with temperature at a constant density. The bubble point pressures of N,N-DMA–CO2 mixtures were measured at 298.15 K, 308.15 K and 318.15 K and were found to increase with increasing mole fraction of CO2. The partition coefficients were modeled using the Peng-Robinson Equation of State (PREOS) combined with modified van der Waals mixing rule. The binary interaction parameters for the CO2–H2O pair were taken from the literature and were regressed for CO2–N,N-DMA and H2O–N,N-DMA pairs by fitting partition coefficients data. The binary interaction parameter for CO2–N,N-DMA pair was found to depend linearly on temperature. The bubble point pressures of N,N-DMA and CO2 were also measured and could be predicted fairly well using the regressed binary interaction parameters.