Enzymatic conversion of waste edible oil to biodiesel fuel in a fixed-bed bioreactor

The conversion of waste edible oil to biodiesel fuel in a fixed-bed bioreactor was investigated. Three-step methanolysis of waste oil was conducted using three columns packed with 3 g of immobilized Candida antarctica lipase. A mixture of waste oil and 1/3 molar equivalent of methanol against total fatty acids in the oil was used as substrate for the first-step reaction, and mixtures of the first- and second-step eluates and 1/3 molar equivalent of methanol were used for the second- and third-step reactions, respectively. Ninety percent of waste oil was converted to the corresponding methyl esters (ME) by feeding substrate mixtures into the first, second, and third reactors at flow rates of 6, 6, and 4 mL/h, respectively. We also attempted one-step methanolysis of waste oil. When a mixture of waste oil and 90% ME-containing eluate (1:3, wt/wt) and an equimolar amount of methanol against total fatty acids in the waste oil was fed into a reactor packed with 3 g of immobilized C antarctica lipase at a flow rate of 4 mL/h, the ME content in the eluate reached 90%. The immobilized biocatalyst could be used for 100 d in the two reaction systems without significant decrease in its activity. Waste oil contained 1980 ppm water and 2.5% free fatty acids, but these contaminants had little influence on enzymatic production of biodiesel fuel.