Predicting the vapor pressure of fatty acid esters in biodiesel by group contribution method

Abstract

In this study, a group contribution method based on the Riedel equation was developed to predict the vapor pressures of fatty acid methyl, ethyl, propyl, and butyl esters. A CH2 (ester) group was introduced to distinguish the fatty acid methyl, ethyl, propyl, and butyl esters. The group parameters were regressed based on a total of 4687 vapor pressure data. The results show that, the proposed group contribution method illustrates much better performance in predicting the vapor pressures of fatty acid methyl and ethyl esters, and comparable accuracy in predicting the vapor pressures of fatty acid propyl and butyl esters in comparison with Ceriani's group contribution method (Ceriani et al., 2013). A test set of 2584 experimental data was used to further verify the reliability of the proposed method and its superiority in accurately predicting the vapor pressure within the whole temperature range over Ceriani's group contribution method. By using these two group contribution methods, vapor pressures of ten biodiesels were also predicted, and the proposed group contribution method has a better accuracy with the overall average relative deviation of 5.49%. The temperature dependency of biodiesel vapor pressure is also well reproduced by the proposed method.