Pre-treatment of waste cooking oil with high free fatty acids content for biodiesel production: An optimization study via response surface methodology

Biodiesel is an alternative diesel fuel producing from vegetable oils or animal fats. At the present, most biodiesel is made from cooking oils with a very low amount of free fatty acid (FFA). Therefore, the cost of biodiesel is higher than petroleum diesel. However, the production cost of biodiesel can be reduced by using low-cost feedstock oils such as waste cooking oil (WCO). There are some studies about acid-catalyzed esterification process as a pretreatment of WCO with high FFA for biodiesel production. However, there have not many appropriate methods to optimize for this process. In this study, based on response surface methodology (RSM), a mathematical model was established which indicated the impact of independent experimental conditions as well as the relationship between these variables (MeOH/FFA molar ratio, H2SO4/FFA catalyst content, temperature and reaction time) to FFA conversion. This model was significant by comparison with both experimental value and predicted number of the FFA conversion, and showed strong agreement for experimental parameters. The FFA conversion of 90 % (FFA content of 0.40 wt%) was obtained in optimal conditions: MeOH/FFA molar ratio of 40.11, H2SO4/FFA catalyst content of 10.64 wt%, reaction temperature of 60 C-o and reaction time of 5 h.