Preparation Of Collagen-Magnetic Microsphere-Immobilized Lipase And Its Application For The Production Of Biodiesel From Waste Frying Oil

Waste cooking oil is a type of substance with both resource and pollution,its production is increasing with the rapid development of the economy and the food industry.Improper handling not only causes waste of resources but also pollutes the environment.Waste frying oil as a type of waste cooking oil,preparation of biodiesel from it is one of its green and environmentally friendly high-value utilization methods,and immobilized enzyme catalyzed transesterification to produce biodiesel is the most studied method at home and abroad currently.Magnetic nanoparticles(MNPs)are widely used as carriers for immobilized enzymes attribute to their large specific surface area and easy modification.Collagen,as a renewable natural polymer material,has good biocompatibility and environmental friendly.It is used as a stabilizer and carrier in the process of immobilizing enzyme on magnetic carriers,and with a good dispersion effect on magnetic nanomaterials and a better protection against immobilized enzyme activity.Therefore,a collagen-magnetic microsphere-immobilized lipase(CML)based on MNPs and collagen was prepared to catalyze the produce of biodiesel from waste frying oil.CML was used to catalyze frying waste oil to prepare biodiesel,and the catalytic conditions were optimized.The repeated catalytic performance of CML was investigated,and the fatty acid methyl ester composition of the catalytic product biodiesel was analyzed.The main contents and results are as follows:1)The effects of immobilization conditions on activity of CML and immobilization efficiency were investigated.The results indicated that the optimal immobilization conditions for lipase were: lipase concentration 3.0 mg/m L,collagen concentration 2.5%,PBS solution(p H=7.0),immobilization time 3 h,temperature at 35 °C,glutaraldehyde concentration 2.5%.The CML was characterized by TEM,XRD,VSM,and FT-IR.It suggested that the lipase was successfully immobilized on the surface of collagen-magnetic microsphere(CM),and the CML showed superparamagnetic,which could be facilitated the effective separation of products and its reuse.2)The temperature and p H tolerance of CML was stronger than that of free lipase,and CML has good operational stability and storage stability.After being stored at-20 °C,4 °C and 25 °C for 38 d,CML could still maintain about 50%,40% and 20% of initial activity,respectively,while almost all free lipase were inactivated at 28 d.3)The catalytic performance of CML was assessed for waste frying oil and methanol transesterification reaction.The results showed that the optimal preparation conditions were:the solvent was n-hexane,0.5 m L/g of n-hexane amount,15% of CML dosage,methanol/oil mole ratio 4:1,0.4% of water content,reaction time 24 h,and the biodiesel esterification could achieve 83% under the above conditions.4)Furthermore,the CML exhibited excellent reusability in the recovery use by magnetic separations.After repeated use of 5 cycles,the CML was still kept about 60% of biodiesel esterification.There are 6 kinds of fatty acid methyl esters in this biodiesel product,namely methyl palmitate,methyl linoleate,methyl oleate,methyl stearate,methyl cis-11-eicosenoate and methyl erucate.