VLE predictions with the Peng–Robinson equation of state and temperature dependent k ij calculated through a group contribution method

Abstract

A group contribution method allowing the estimation of the temperature dependent binary interaction parameters ( k ij ( T)) for the widely used Peng–Robinson equation of state (EOS) is proposed. A key point in our approach is that the k ij between two components i and j is a function of temperature ( T) and of the pure components critical temperatures ( T C i and T C j ), critical pressures ( P C i , P C j ) and acentric factors ( ω i , ω j ). This means that no additional properties besides those required by the EOS itself ( T C, P C, ω) are required. Because our model relies on the Peng–Robinson EOS as published by Peng and Robinson in 1978 and because the addition of a group contribution method to estimate the k ij makes it predictive, we decided to call this new model PPR78 (predictive 1978, Peng–Robinson EOS). In this paper six groups are defined: CH 3, CH 2, CH, C, CH 4 (methane), and C 2H 6 (ethane) which means that it is possible to estimate the k ij for any mixture of saturated hydrocarbons ( n-alkanes and branched alkanes), whatever the temperature. The results obtained in this study are in many cases very accurate and often better than those obtained with the best EOS/ g E models. In particular, it is shown that asymmetric systems can be accurately predicted with our model. Some comparisons are given with the LCVM model.