Liquid-Liquid Equilibrium for Cottonseed Biodiesel plus Water plus Alcohol (Methanol/Ethanol) Systems at (293.15 and 313.15) K: Experimental Data and Thermodynamic Modeling

During the biodiesel production process, generally, two purification steps are performed: The first is a settling process in order to remove the main byproduct (glycerol). Nevertheless, this simple stage is insufficient to achieve purity levels required for commercial specifications: Second, a water washing is used to remove an excess of alcohol and other contaminants. Given the importance of equilibrium data for operation and optimization for liquid liquid extraction unit operation, the study of liquid liquid equilibrium (LLE) for methylic cottonseed biodiesel + methanol + water and methylic cottonseed biodiesel + ethanol + water systems are studied at (293.15 and 313.15) K at atmospheric pressure. LLE data have been quantified by intermediate of two different techniques (titration and densimetric). From these experimental data, distribution coefficients and selectivity have been calculated: As expected, a good extraction capacity of water to remove alcohol has been observed. The reliability of the experimental data has been verified by the correlation proposed by Othmer-Tobias. In Order to describe the LLE for the experimental systems studied, three predictive thermodynamic models were used, as follows: UNIFAC, UNIFAC-LLE, and UNIFAC-Dortmund. root-mean-square deviation (RMSD) has been used as the statistical parameter, and it shows the follow deviations: 3.27 %, 3.62 %, and 4.00 % for the models UNIFAC, UNIFAC-Dortmund, and UNIFAC-LLE, respectively. Therefore, best representation of the LLE systems followed the order: UNIFAC > UNIFAC-Dortmund > UNIFAC-LLE.