New group interaction parameters of the UNIFAC model for the solubility of water in fatty acid methyl esters and biodiesel

Water content is one of the most important quality indexes of biodiesel. In this study, the group interaction parameters of UNIFAC model are optimized to improve this model in predicting the solubility of water in fatty acid methyl esters and biodiesel. To determine the binary interaction parameters between water and the main functional groups attached to the molecules of the biodiesel compounds, 55 experimental data points related to the solubility of water in nine pure fatty acid methyl esters in the temperature range of 282.2 K-323.2 K are employed. Then, the model is used to predict the water solubility in 10 different biodiesels (60 data points), to evaluate the calculated interaction parameters in predicting the solubility of water in the mixture of fatty acid methyl esters. The average absolute relative deviations of the model in predicting the water content of pure fatty acid methyl esters and biodiesel are 4.31% and 4.69%, respectively. To show the superior performance of the model, the results of the model are compared with the results of previous models.