Enzymatic production of biodiesel from waste oil in ionic liquid medium

In biodiesel production, catalyzed by immobilized lipase, a solvent is needed to reduce the inhibition effects caused by excessive use of short-chain alcohols and deposited glycerol. Volatile and toxic organic chemicals are commonly used to achieve this by enhancing the solubility of the alcohols and glycerol. In this work, non-volatile ionic liquids (ILs) are proposed as alternative solvents, which are safer and easier to recycle. Several ILs were tested and their effectiveness was compared to that of the conventional solvents, n-hexane and tert-butanol. Hydrophobic ILs showed much more promising results and much higher biodiesel production yields compared to hydrophilic ILs. A set of experiments was designed using full factorial (3³) experimental design to statistically evaluate the results. The effects of reaction temperature, methanol-to-oil molar ratio and enzyme loading were considered. Response surface methodology (RSM) was then used to optimize process variables. The highest yields of 72 and 48% were achieved after 14 hrs of reaction at 50°C, 6:1 molar ratio and 40% enzyme loading in [bmim][PF₆] and [bmim][NTf₂], respectively. Regression models were developed to predict the optimal production yields and found to be adequate and statistically acceptable.