Development of Biodiesel Production Technology from Waste Cooking Oil with Calcium Oxide as Solid Base Catalyst

Waste cooking oils were investigated as the raw material for biodiesel production using calcium oxide as the solid base catalyst in refluxing methanol. Edible soybean oil and waste cooking oil from restaurants were converted into biodiesel completely within 2 h. However, catalyst recovery after the reaction markedly decreased for the waste cooking oil, due to dissolution of the solid base catalyst. Catalytic induction period was observed in the early stage of the reaction of the waste cooking oil. Most of the solid base catalyst was converted into calcium methoxide and glyceroxide, and trace of saponified calcium was collected after the reaction of the waste cooking oil. Waste cooking oil from homes increased the catalyst recovery, in comparison with waste oil from restaurants. The catalyst recovery was considerably improved by a removal of free fatty acids. Both polar fraction and moisture in the waste cooking oil were minor poisons for the solid base catalyst. Based on the above results, improvement of the biodiesel production requires protection for the solid base catalyst from the poisoning species contained in the waste cooking oil.