Liquid-liquid equilibria of biodiesel plus glycerol and biodiesel plus water binary systems

The liquid-liquid equilibria (LLE) of the biodiesel + glycerol and biodiesel + water binary systems are experimentally measured at atmospheric pressure and in the temperature range from 310.35 K to 338.15 K, conditions relevant to the industrial process, solving the experimental challenges related to their direct measurement. The LLE data of these binary systems are pivotal for designing the biodiesel purification processes and determine the chemical equilibrium constant of the transesterification reaction of vegetable oil into biodiesel. However, unlike to the present study, this information is typically indirectly extrapolated from models regressed on ternary systems, undermining the reliability of the results. The experimental data were compared against the calculations provided by the UNIQUAC and UNIFAC models, with the binary interactions parameters (BIPs) of the UNIQUAC model validated on the experimental data. To ensure a thermodynamically consistent representation of the phase behaviour and smooth the experimental scattering of trace components, the BIPs are regressed by means of an algorithm that considers the experimental uncertainty. The results are compared with LLE data for biodiesel + glycerol and biodiesel + water from ternary systems measured by other laboratories.