Evaluation of different contribution methods over the performance of Peng–Robinson and CPA equation of state in the correlation of VLE of triglycerides, fatty esters and glycerol + CO2 and alcohol

The study of biodiesel production has been intensified over the last decades. The ability of predicting the several kinds of equilibrium involved in the process of biodiesel production is highly important in order to optimize and control the processes of production and purification. This work investigated the ability of the group contribution methods to predict critical properties and acentric factor and their effect on the performance of Peng–Robinson Equation of State (PR-EOS). This was done in order to select a reliable set of methods to be used in predicting vapor–liquid equilibrium (VLE) involving triglycerides, fatty esters and glycerol. The contribution methods tested to predict critical properties were: Joback and Reid (JRM); Constantinou and Gani (CGM) and Marrero and Gani (MGM). For the acentric factor the following methods were chosen: Ptizer (PM) and Kesler and Lee (KLM). The properties evaluated by these methods were used in the PR-EOS to predict the density, vapor pressure and VLE involving triolein, methyl oleate and glycerol. The PR-EOS with the inclusion of the associative term (CPA-PR-EOS) was tested in the VLE involving alcohols. Based on the results, a set of methods for each component was selected and used to evaluate the VLE of others triglycerides and fatty esters. The results showed that the choice of the predictive method used is highly important in the performance of the cubic equation. The set of methods chosen proofed to be reliable. The addition of the association term in the cubic equation (CPA-PR-EOS) improves the performance of PR-EOS in the correlation of VLE just in a few cases, especially when the temperature of the system is around or above the critical temperature of the associative molecule.