Liquid-liquid equilibrium for biodiesel-glycerol-methanol or ethanol systems using UNIFAC correlated parameters

Abstract

Liquid-liquid phase equilibrium (LLE) for the system of biodiesel, glycerol, methanol or ethanol is fundamental for modeling, simulation, design and economic evaluation of biodiesel production. This paper presents a correlated set of group interaction parameters (GIP) for the UNIFAC model that adequately describe the LLE of such biodiesel systems. To correlate and to verify the GIP, a database including 84 LLE experimental results reported in the literature was built. The database includes biodiesel produced using 23 different vegetable oils and 2 different alcohols (methanol and ethanol), as raw materials, at temperatures between 293.15 K and 353.15 K. The GIP were correlated using an evolutionary algorithm. The correlated set of GIP describes the LLE with an average deviation up to 0.7%, regardless of the type of biodiesel and the temperature (in the range studied). Model descriptions using the proposed set of GIP were compared with the description of others GIP reported in the literature. LLE descriptions using the new set of GIP proposed in this work exhibited the best fit between the experimental data and the calculated values for all the systems biodiesel-glycerol-methanol or ethanol evaluated.