Determination and modelling of liquid-liquid phase equilibriumfor ternary systems in biodiesel production from vegetableoil and animal fat mixtures

In this study, ternary liquid-liquid equilibrium of biodiesel-methanol-glycerol systems were investigated experimentally and thermodynamically. Biodiesel samples were produced from sunflower oil and beef tallow mixtures. In the experimental studies, biodiesel samples were first produced by using potassium hydroxide catalyzed transesterification method with methanol. The solubility curves and tie-lines data for ternary liquid-liquid system of the produced biodiesel samples-methanol-glycerol were determined experimentally. The effects of biodiesel type and temperature on the solubility curves of biodiesel-methanol-glycerin ternary liquid-liquid systems were investigated. Similarly, biodiesel type and temperature effects were also determined on the equilibrium tie-lines for ternary liquid-liquid systems consisting of different amounts of biodiesel-methanol-glycerol mixtures. Biodiesel samples were produced by using catalyst of 1% (v/v) of the oil used and methanol of 1/6 (molar ratio of methanol to oil) at 60 ° C. Three types of biodiesel prepared by using beef tallow and sunflower oil mixtures of 0, 10% and 20% by volume. The solubility curves of the biodiesel-methanol-glycerol mixtures prepared in different ratios of three compounds were determined according to the cloud point titration method at 25 ° C, 35 ° C and 45 ° C. Similarly, for the ternary liquid-liquid systems consisting of mixtures of biodiesel-methanol-glycerol, the phase equilibrium tie-lines were determined by the equilibrium cell method at temperatures of 25 ° C, 35 ° C and 45 ° C. The phase compositions for equilibrium tie-lines were determined by evaporation of methanol and refractive indexes. The solubility of methanol in ternary mixtures increased with the increasing of temperature for each biodiesel sample. The solubility of three components in each other increases as the temperature increases for all biodiesel types used The accuracy of the phase equilibrium data (tie-lines) obtained from the experimentally tested by using the Othmer-Tobias correlation. Biodiesel-methanol-glycerol ternary liquid-liquid phase equilibrium data were correlated with NRTL thermodynamic activity coefficient model. Experimental and model results were found to be in good agreement with each other. Standard deviation between experimental and model results was determined as 0.663%.