A MODIFIED PENG-ROBINSON EQUATION OF STATE FOR PHASE EQUILIBRIUM CALCULATION OF LIQUEFIED, SYNTHETIC NATURAL GAS, AND GAS CONDENSATE MIXTURES

A modified Peng-Robinson equation of state, MPR2 EOS, is introduced by incorporating a new alpha function and a temperature dependent function for covolume, b. The modified cubic EOS has three input per each substance: critical temperature, critical pressure, and acentric factor. The coefficients of temperature dependence of the alpha and beta functions, relating to the parameters a and b of the new cubic EOS, are obtained by simultaneous fitting of saturated experimental vapour pressure and liquid density data for several pure components. The percent absolute average deviation (AAD%) of 1.38, 4.80 and 2.89 are obtained to correlation of the saturation vapour pressure, liquid density and vapour volume, respectively. Also the ADD% of 2.575 is computed for prediction of saturation enthalpy of vapourisation of the pure compounds. For calculation of phase equilibrium of mixture, the modified PR EOS is used for prediction of liquid density of the LNG mixtures. Also the new EOS is applied for construction of the phase envelop of synthetic natural gas, SNG, mixtures and calculation vapour-liquid equilibria of gas condensates. The results demonstrate that the new MPR2 EOS can be used for calculation of vapour-liquid equilibrium of pure components and mixtures with good accuracy.