The Kinetics of the Esterification of Free Fatty Acids in Waste Cooking Oil Using Fe2(SO4)3/C Catalyst

The esterification of free fatty acids (FFA) in waste cooking oil with methanol in the presence of Fe2(SO4)3/C (ferric sulfate/active carbon) catalyst was studied. The effects of different temperature, methanol/FFAmole ratio and amount of catalyst on the conversion of FFA were investigated. The results demonstrated that under optimal esterification conditions the final acid value of the resultant system can be reduced to ∼1 (mg KOH)·g−1 which met fully the requirements in post-treatment for efficient separation of glycerin and biodiesel. The kinetics ofthe esterification were also investigated under different temperatures. The results indicated that the rate-control stepcould be attributed to the surface reaction and the esterification processes can be well-depicted by the as-calculatedkinetic formula in the range of the experimental conditions.