Experimental determination and modelling of phase equilibrium for washing step during biodiesel production from vegetable oil and animal fat mixtures

The ternary liquid-liquid equilibrium data of biodiesel-methanol-water system involved in the biodiesel production provides important tools for the development and design of the equipment. In this investigation, the effects of temperature and amount of beef tallow in corn oil on ternary liquid-liquid equilibrium data for the system of biodiesel-methanol-water were experimentally and thermodynamically examined.. In the experimental studies, the biodiesel samples (0%, 10% and 20% v/v beef tallow) were produced using the mixtures of corn oil and beef tallow with methanol (methanol to oil: 1/6, n/n) using potassium hydroxide of %1 (w/w) at 60 °C. The solubility data were determined using the cloud point titration method, while the tie-lines data were obtained by using the equilibration cell method for biodiesel-methanol-water systems at temperatures of 25 °C, 35 °C and 45 °C. It was found that the effect of temperature on the solubility curves of ternary liquid-liquid system of biodiesel-methanol-water was negligible at low methanol compositions but had a little effect at high methanol compositions. The ternary liquid-liquid solubility curves of biodiesel-methanol-water systems did not significantly change with the increasing of the beef tallow concentration in corn oil. It was observed that water composition was low in biodiesel-rich phase and also biodiesel composition was low in water-rich phase for all tie-lines obtained. The experimental tie-line equilibrium data were correlated with the NRTL activity coefficient model and a good agreement between experimental and calculated tie-line equilibrium data were observed. Average deviation between experimental and model results was determined as 1.78%.