PREDICTION OF VAPOR-LIQUID-EQUILIBRIA AT HIGH-PRESSURES USING ACTIVITY-COEFFICIENT PARAMETERS OBTAINED FROM LOW-PRESSURE DATA - A COMPARISON OF 2 EQUATION OF STATE MIXING RULES

Two recent equation of state mixing rules, one by Dahl and Michelsen (MHV2) and another by Wong and Sandler (W-S), are claimed to be useful for making vapor-liquid equilibrium predictions for nonideal mixtures at high temperatures and pressures using data obtained at low pressures. Here we compare the performance of these two mixing rules in predicting the high-pressure phase behavior of nine binary systems using published activity coefficient parameters. We also compare the predictions for two ternary systems using mixing rule parameters obtained from low-pressure binary mixture data. We find that both mixing rules can be used to make reasonable high-pressure vapor-liquid equilibrium predictions from low-pressure data. However, the errors in the predicted pressure with the W-S mixing rule when used with either the Peng-Robinson or Soave-Redlich-Kwong equation of state are, on the average, about half or less those obtained when using the MHV2 mixing rule. Also, the predictions of the MHV2 mixing rule deteriorate significantly as the temperature and pressure range increase, which is not the case with the W-S mixing rule.