| Waste cooking oils (WCO) which contain large amounts of free fatty acids (FFAs) produced in the restaurants are collected by the environmental protection agency in the main cities of China and should be disposed in a suitable way. In this thesis, two processes of producing biodiesel from WCO with acid value of 75.92mgKOH/g have been investigated.The first one was acid-catalyzed process; in which, sulfuric acid was used to catalyze methyl esterification of WCO. It was found that the highest conversion was achieved when the mole ratio of methanol to total fatty acids was 20:1 with addition of 5% of sulfuric acid (w/w) and reacted at 95℃ for 8h. Under these reaction conditions, 95.5% of methyl esterification product was obtained.The second one is a two-step catalyzed process. In the first step, ferric sulfate was used to catalyze the conversion of FFAs in WCO to methyl esters and it was found that 97.22% of FFAs was transferred to methyl esters when 2 % (wt) of ferric sulfate was added to the reaction mixtures containing methanol to fatty acids with 10:1 (in molar rate) and reacted at 95℃ for 4 hours. In the second step, potassium hydroxide was used to catalyze transesterification of glycerides (TGs, total glycerides, including mono-, bi- and tri- glycerides) in the WCO to methyl esters. Highest transesterification rate was obtained when 1.2 wt% of potassium hydroxide was added to the reaction mixtures containing methanol to TGs with 6:1 (in molar rate) and reacted at 65℃ for 60 minutes. After the two-step catalyzed process, 97.02% of fatty acids were transformed to methyl esters (biodiesel).A refine process by vacuum distillation has been investigated to get a high quality biodiesel. It was found that the fraction collected between 160-240℃ under the pressure of -0.1MPa was suitable to serve as engine fuel.
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