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 bioreac tor was investigated. Three-step methanolysis of waste oil was conducted us ing 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, a nd mixtures of the first- and second-step eluates and 1/3 molar equivalent of methanol were used for the second- and third-step reactions, respectivel y. Ninety percent of waste oil was converted to the corresponding methyl es ters (ME) by feeding substrate mixtures into the first, second, and third r eactors 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 o f 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 10 0 d in the two reaction systems without significant decrease in its activit y. Waste oil contained 1980 ppm water and 2.5% free fatty acids, but these contaminants had little influence on enzymatic production of biodiesel fuel .