Experimental optimization of Waste Cooking Oil ethanolysis for biodiesel production using Response Surface Methodology (RSM)

Biodiesel production from Waste Cooking Oil (WCO) is the most suitable diesel fuel substitute, due to its cleaner emissions, engine lubricity, nontoxic properties, and renewable sources. This study mainly focused on improving biodiesel experimental production using ethanol and investigating the influence of main operating parameters (ethanol-oil molar ratio, catalyst concentration and stirring speed) on biodiesel yield using Response Surface Methodology (RSM). The problem with using ethanol at the expense of the toxicity of methanol as an alcohol is mainly the separation of glycerol from biodiesel at the end of the transesterification reaction. However, the addition of 5% (v/v) glycerol and 1% (v/v) water at the end of the reaction has been found to aid this separation and improve oil conversion. The optimization of the produced biodiesel is carried out through three factors: Face-Centered-Composite Design (FCCD), building a mathematical model, and statistical analysis, shows that the experimental results agree with the predicted values; they are close to unity with the R-2 value (0.9924), indicating the correctness of the model. The optimal conditions of catalyst concentration (1.62 wt%), stirring speed (200 rpm) and molar ratio of ethanol to oil (12.9:1) were obtained, resulting in a biodiesel efficiency of 89.75%. The model was also experimentally validated, achieving about 90% biodiesel yield. The fuel properties of the ethyl ester were investigated and compared successfully with the EN and ASTM standards and with baseline local diesel (NA 8110).