Optimising biodiesel production from high acid value waste cooking oil using supercritical methanol

In this study, biodiesel production from a typical Egyptian waste cooking oil (WCO) with high acid value content (18 mg KOH/g oil) has been analysed by studying the main factors affecting biodiesel and glycerol yields. Response Surface Methodology (RSM) via Central Composite Design (CCD) has been used to analyse the effect of four independent variables, i.e. methanol to oil (M:O) molar ratio, temperature, pressure and time on the reaction responses. A quadratic model for each response has been concluded representing the interrelationships between reaction variables and reaction responses. In addition, the predicted models’ adequacy has been evaluated through Analysis of Variance (ANOVA) method. Numerical optimisation technique has been applied to conclude the optimum reaction conditions for maximum production of biodiesel resulting in 98% and 2.05% for biodiesel and glycerol yields at M:O molar ratio, temperature, pressure and time of 25:1, 265oC, 110 bar and 20 minutes, respectively. Experimental validation has been analysed for the predicted optimum conditions resulting in 98.82% biodiesel yield with 0.83% relative error.