Abstract:
Biofuel production in supercritical ethanol process is the one of alternative methods to produce an entirely renewable fuel. However, absolute ethanol has a high cost and consumed a very high energy. Therefore, the continuous biofuel production from palm oil in supercritical hydrated ethanol was investigated in this work in order to reduce the production cost. The effects of molar ratio of ethanol: oil (9:121:1), water content in ethanol (4.420.0 wt. %), and residence time (2.028.0 min) on the monoglyceride and ethyl ester content were investigated at fixed temperature of 400 °C and pressure of 15 MPa. The response surface methodology was applied to find out the optimal conditions. It was found that the main effect on monoglyceride content is molar ratio and water content, while the molar ratio and residence time had significant effect on ethyl ester content. The optimal conditions were determined as the ethanol: oil molar ratio of 21:1, water content of 12.77 %, and residence time of approximately 9.10 min. Under the optimal operating conditions, the predicted values of monoglyceride content and ethyl ester content were 0.80% and 53.32%, respectively. With regard to the fuel properties, it can be observed that flash point, and iodine value meet the biodiesel standard. However, the viscosity and acidity value have to exceed the standard. This is due to the remaining of free fatty acids in biofuels, which is the product of the hydrolysis reaction between triglycerides and water.