Reduction of Free Fatty Acids of Waste Oil by Acid-Catalyzed Esterification

Clean fuels such as biodiesel are used to provide energy in the word, recently. Transesterification of waste oil in the presence of alkali catalyst is used to produce biodiesel. Since free fatty acid (FFA) and water in the waste oil will decrease process efficiency specially in washing step, so concentration of the mentioned component should be reduced to a low value (<1% FFA) using esterification before transesterification process. In this work, silica sulfuric acid is used as heterogeneous catalyst for reduction of FFA in waste cooking oils and effects of variables on the esterification reaction were also studied. To determine FFA decreasing, i.e. esterification reaction conversion, the samples were analyzed by GC and FTIR. As a result of this study, 1.5% wt catalyst, at 60, molar ratio methanol to oil 6:1 and 300 rpm are suggested as optimum conditions. Results are shown that conversion of free fatty acids to ester, in terms of waste oil is 90% and FFA concentration is less than1%.