Liquid-liquid equilibrium of FAEs – glycerol phase – ethanol in the ethanol regeneration and FAE separation stage

Abstract

Extraction and purification of biofuel components are as important as their synthesis. Synthesis of fatty acid esters in a molar excess of ethanol above 1:30 results in the formation of a homogeneous phase including the ester and glycerol phases dissolved in ethanol. It was observed that when excess ethanol was removed, the separation of the system into ester and glycerol phases did not always occur. To improve the biodiesel purification process the experimental binodal curve for the FAE-ethanol-glycerol phase system was obtained in the synthesis of biodiesel from rapeseed oil. The data was obtained from homogeneous alkaline synthesis of FAE with molar excess of ethanol 1:50. The pseudocomponent glycerol phase contains glycerol and unreacted oil (triglycerides (TGA)). The calculated liquid-liquid equilibrium (LLE) data for FAE – ethanol – glycerol and FAE – ethanol – TGA ternary mixtures were obtained by the UNIFAC (UNIQUAC Functional-group Activity Coefficients) model and compared with experimental diagram. It was found that glycerol and unreacted triglycerides affect the behavior of the system by preventing or promoting the mixing of immiscible components. The obtained results show that, depending on the conversion, the phase behavior of the FAE-ethanol-glycerol phase system will correspond to the ternary system FAE-ethanol-glycerol or FAE-ethanol-TGA. The obtained data help to predict the separation of glycerol and ester phases at the ethanol recovery stage knowing the degree of rapeseed oil conversion at the synthesis stage. Successful separation of the glycerol and FAE phases is possible at oil conversion above 53 %.