The Studies On Transesterification Of Soybean Oil By Immobilized Lipase On Magnetic Microspheres

The process of immobilization of lipase was studied using two kinds of magneticmicrospheres as carrier. In addition to the factors such as enzyme load, the pH value of buffersolution, immobilization time, temperature and so on that influences the immobilization. Theproperty of immobilized lipase, for example, the thermal stability, operation stability and pHtolerance are discussed in details. The experimental results indicated that, for immobilizedlipase on magnetic chitosan microspheres by using glutaraldehyde as coupling reagent, theoptimal preparation conditions were carrier200mg, lipase concentration2.0mg·mL^-1, the pHof buffer solution7.5, temperature35℃, immobilization time3h, glutaraldehydeconcentration10%, and the optimal hydrolytic activity was temperature50℃, pH7.5. Forimmobilized lipase on magnetic poly（styrene-methacrylic acid） microspheres by activatingwith carbodiimide hydrochloride, the optimal preparation conditions were carrier200mg,lipase concentration2.0mg·mL^-1, the pH of buffer solution7.5, temperature35℃,immobilization time4h, carbodiimide hydrochloride concentration0.25%, and the optimalhydrolytic activity was temperature35℃, pH7.5. The magnetic microspheres andimmobilized lipase were confirmed by magnetic measurements, X-ray diffraction,transmission electron microscopy, enzyme assays and Fourier transform infrared spectra. Itsuggested that the lipase had been immobilized on the surface of magnetic microspheres, andthese microspheres showed superparamagnetic magnetic. The two kinds of immobilizedlipase had better resistance to temperature and pH inactivation in comparison to free lipase.Then, the catalytic activity of immobilized lipase was tested for soybean oil withmethanol transesterification reaction. Using the immobilized lipase, the major parametersaffecting the transesterification reaction, such as catalyst amount, the alcohol/oil molar ratio,water content, organic solvent and free fatty acid present in reactants were investigated toobtain the optimum reaction condition. The experimental results showed that, for immobilizedlipase on magnetic chitosan microspheres, the appreciate conditions were catalyst amount60wt.%, methanol/oil mole ratio4:1, three-step addition of methanol, reaction time30h, watercontent0.2%and the soybean oil conversion could reach84%under the above conditions.For immobilized lipase on magnetic poly（styrene-methacrylic acid） microspheres, theappreciate conditions were catalyst amount50wt.%, methanol/oil mole ratio5:1, three-step addition of methanol, reaction time30h, water content0.1%and the soybean oil conversioncould reach83%under the above conditions. In addition, the free fatty acid concentration didnot significantly decrease their catalysts. The two kinds of immobilized lipase showed gooddurability in the repeated use after recovered by magnetic separations.