Two-Step Preparation of Bio-Diesel from the Used Bleaching Clay

with the shortage of the raw material oil for producing bio-diesel in China, the oil, recovered from the used bleaching clay which often be discarded by vegetable oil factory, was used to prepare bio-diesel in this trial. Two-step catalyzed process was adopted to produce biodiesel from the oil. The effect of methanol-to-oil molar ratio, alkaline catalyst quantity, reaction temperature and reaction time on the preesterification and transesterification reaction was investigated through orthogonal experiments. Thus the optimal reaction condition came out. Firstly, the optimal pre-esterification condition, under which the end acid value of the product was minimum (i.e. 1.88 mgKOH/g),was to react for 40 h at 60°C,with a methanol-to-oil molar ratio of 12:1, and by adding alkali catalyst 4% based on the oil weight. Secondly，the optimal transesterification condition, under which the maximum yield of bio-diesel can reach up to 98.2%, was to react for 2.5 h at 60°C,with the methanol-to-oil molar ratio of 7:1, and by adding catalyst 1.25% based on the oil weight.