UNIFAC correlated parameters for liquid-liquid equilibrium prediction of ternary systems related to biodiesel production process

Abstract

Two phases liquid systems composed by vegetable oil, biodiesel, fatty acids (FAs), glycerol, low molecular weight alcohols, and water are present in most of the biodiesel production process stages, including oil refining, free FAs esterification, transesterification, biodiesel and glycerol-rich phases separation and biodiesel refining by water washing. For that reason, the correct prediction of the liquid-liquid equilibrium (LLE) is a key-factor for an accurate process understanding. In this work, a new set of group interaction parameters (GIP) for the UNIFAC model that describes the LLE for all the systems involved in biodiesel production was correlated and validated. A database including 1414 LLE tie lines from 97 references was constructed and employed to correlate the GIP using a genetic algorithm. These parameters describe the LLE involved in the correlation process with an average deviation up to 2.07%. Additionally, a sensitivity analysis using the proposed GIP was performed to understand the effect of the molecular structure on the LLE behavior for the studied systems. Results showed that composition of the distributed component (alcohol, fatty acid or biodiesel) in both phases depends on the number of carbon atoms, unsaturated bonds and hydroxyl groups in the oleochemicals conforming the system. The variable with the highest incidence in the sensibility analysis was the distributed component overall mass fraction, followed by the alcohol length chain.