Additives improve the enzymatic synthesis of biodiesel from waste oil in a solvent free system

• Biodiesel was synthesized in solvent free system with waste cooking oil.
• Cyclodextrin was introduced as additive to enhance the biodiesel yield.
• Only 0.4 wt% lipase Candida sp. 99–125 was enough for 1 ton biodiesel production.
• Lipase could also be reused for 5 times.
• By the assistant function of additive, the cost of lipase was reduced to 80 CNY.

Biodiesel production from waste oil by lipase Candida sp. 99–125 assisted with cyclodextrin as additive was investigated in a solvent free system. The optimum reaction conditions was determined toward lipase dosage, agitation speed, cyclodextrin loading, water content and reuse ability of free lipase. A certain dosage of cyclodextrin showed a significant improvement of the reactions. However, the agitation speed should not be too high, to avoid breaking the weak bond between cyclodextrin and lipase. The optimal conditions were: free lipase dosage 70 U/g oil (about 0.4 wt% to the oil weight, when activity of lipase was 20,000 IU), cyclodextrin to lipase 2:1(g/g), water content 2 wt% (water/oil, g/g), and agitation speed 180 rpm. Methanol was added 30 times at 1/30 M equivalent each hour. Under the optimal conditions, the yield of FAMEs achieved 88%. After 5 cycles of reuse, no significant decrease in FAMEs yield was observed. The process has been successfully carried out at industrial scale in Shanghai, China.