Prediction of phase equilibria for mixtures containing water, hydrocarbons and alcohols at high temperatures and pressures by cubic equation of state with G^E type mixing rule based on COSMO-RS

The phase equilibria for the mixtures containing water, hydrocarbons and alcohols at high temperatures and pressures were predicted by a cubic equation of state with an excess Gibbs free energy (G^E) type mixing rule using information from the conductor-like screening model for real solvents (COSMO-RS) method. The systems predicted were water + hydrocarbon, water + alcohol, hydrocarbon + alcohol binary systems and water + hydrocarbon + hydrocarbon and water + hydrocarbon + alcohol ternary systems. COSMO-RS method was used to calculate activity coefficients of the mixtures. UNIQUAC equation was adopted as an activity coefficient model in G^E type mixing rule. The interaction parameters in UNIQUAC equation were determined with the activity coefficients calculated by COSMO-RS method. The modified Huron-Vidal mixing rule (MHV1) and a modified Soave-Redlich-Kwong (MSRK) equation of state were chosen as the G^E type mixing rule and the cubic equation of state, respectively. Further, the MHV1 mixing rule was modified to apply in high temperature regions. It was found that the prediction method proposed here can represent the phase behavior of the mixtures containing water, hydrocarbons and alcohols at high temperatures and pressures. The predicted results are compared with those calculated by a predictive Soave-Redlich-Kwong (PSRK) equation of state. The predicted results in this work are more accurate than those calculated by PSRK equation of state.