Liquid–liquid equilibria of systems containing linseed oil biodiesel + methanol + glycerol: Experimental data and thermodynamic modeling

Abstract

Biodiesel is known as a prominent candidate for the replacement of fossil-based fuels since the sources of these fuels have been depleted in the past few years. The most convenient process to produce biodiesel is the transesterification of triglycerides with an alcohol in the presence of a suitable catalyst. At the end of the reaction, two liquid phases comprised of biodiesel (main product), glycerol (by-product) and unreacted alcohol are co-exist. Phase equilibrium study is a tool to design the equipment that involved in the biodiesel production and purification processes. In this work, biodiesel was produced through the transesterification of linseed oil with methanol. Afterwards, the liquid–liquid equilibrium (LLE) data were measured for the ternary systems containing linseed oil biodiesel, methanol and glycerol at three different temperatures and atmospheric pressure. The binodal curves were determined by the cloud-point method in isothermal conditions. The adequacy of the experimental tie-lines has been confirmed using the Othmer–Tobias correlation. The results have been correlated using NRTL and UNIQUAC models. The binary interaction parameters of system components have been adjusted via an evolutionary algorithm so-called “BSOA” without and with closure equation. To predict the equilibrium composition, UNIFAC, UNIFAC-LLE, UNIFAC-DMD and UNIFAC-LBY models were used. Average deviations between the calculated and experimental data for NRTL, UNIQUAC, UNIFAC, UNIFAC-LLE, UNIFAC-DMD and UNIFAC-LBY were 1.574%, 1.380%, 3.187%, 3.164%, 3.881% and 3.960% respectively which show that UNIQUAC model represents the best correlation of experimental tie-lines. RMSD values have been improved by implementation of the closure equation.