Liquid-liquid equilibrium data and thermodynamic modeling of systems involved in the biodiesel production in terms of acylglycerols, free fatty acids, ethyl esters, and ethanol at 303.2 and 318.2 K and local pressure

Abstract

Researches on renewable fuels as biodiesel are being done due to the global concern about the shortage of non-renewable natural energy resources. For the biodiesel production, vegetable oils are transesterified with short-chain alcohols, generating intermediate compounds as monoacylglycerols (MAG) and diacylglycerols (DAG). In order to understand the first stage of the transesterification reaction during the biodiesel production, this study reported experimental liquid-liquid equilibrium (LLE) data and the thermodynamic modeling of systems composed of refined oil (soybean, cottonseed, and rice bran) + commercial mixture of partial acylglycerols (MAG and DAG) + free fatty acids (FFA) + fatty acid ethyl esters (FAEE) + ethanol at T = (303.2 and 318.2) K. The LLE experimental data were thus used to adjust the NRTL model parameters and to evaluate three parameters sets of the UNIFAC model. Calculated results by the NRTL model were well correlated to the experimental ones, with mass deviations up to 0.32%, whereas the deviations calculated for the UNIFAC model ranged from 1.04 to 9.46%. FFA and MAG exhibited preference to the solvent-rich phase, whereas FAEE and DAG preferred the oil-rich phase. New and more complex LLE data considering partial acylglycerols, FFA, besides the FAEE, as here reported, can assist to describe the real behavior of the transesterification step involved in the biodiesel production process and, consequently, its optimization