Preparation Of Immobilized Lipase On The Magnetic Nanocomposites And Its Catalytic Performance Of Transesterificatioin Of Soybean Oil

In this study,magnetic nanocomposites Fe₃O₄@GO,Fe₃O₄@MIL-100?Fe?and Fe₃O₄@P?GMA-DVB-MAA?were successfully prepared,and then Candida rugosa lipase was immobilized on the magnetic carriers using EDC/NHS as an activating agent,affording the Fe₃O₄@GO-Lipase,Fe₃O₄@MIL-100?Fe?-Lipase and Fe₃O₄@P?GMA-DVB-MAA?-Lipase biocatalyst.The magnetic carrier materials and the immobilized lipase were fully characterized by TEM,SEM,FT-IR,XPS,XRD,N₂ adsorption-desorption and VSM techniques.The obtained results indicated that the magnetic carrier materials prepared by us have great specific surface area and uniform pore size distribution.In addition,the magnetic carrier materials possessed abundant carboxyl groups and had been successfully tethered with lipase through covalent bonds.The immobilized lipase exhibited superparamagnetic,with good magnetic separation performance,and thus which could be separated rapidly from the reaction system by using an extent magnetic field.Furthermore,the immobilized lipase could disperse well in the reaction mixture by slight shaking,as the magnetic field was removed.The catalytic performance of Fe₃O₄@GO-Lipase was assessed in the transesterification of soybean oil and methanol.The immobilization conditions of the bound lipase and the reaction conditions of transesterification were optimized.Moreover,the thermal stability and operational stability of the immobilized lipase were explored.The results displayed that the optimum immobilization conditions for immobilized lipase were:lipase concentration 2.0 mg·mL-1,immobilization temperature 30?,immobilization time 5h,and pH=7.0 of PBS buffer solution.In these conditions,the immobilization efficiency of 85.5%was attained with 64.9%of activity recovery.The immobilized lipase on the magnetic graphene oxide was prepared under the optimum preparation conditions and subsequently used to catalyze the transesterification of soybean oil and methanol for the production of biodiesel,and the optimum reaction conditions were obtained as below:25 wt.%of catalyst dosage,molar ratio of methanol to soybean oil 4:1,0.3 wt.%of water content,reaction time 60h and reaction temperature 40?.The maximal biodiesel yield of 93.2%could be achieved under the optimized reaction conditions.Furthermore,the immobilized lipase exhibited excellent thermal stability and operational stability.When the immobilized lipase was maintained at 80? for 2h,its relative activity was 51.3%.After repeated use of 5 cycles,the immobilized lipase was still kept 75.8%of the biodiesel conversion rate.By using the heterogeneous transesterification of soybean oil and methanol,the catalytic activity of Fe₃O₄@MIL-100?Fe?-Lipase was evaluated in the present study.The immobilization conditions of the immobilized lipase and the transesterification reaction conditions were optimized,and the thermal stability and operational stability for the immobilized lipase were also studied.The obtained results showed that the optimum immobilization conditions for immobilized lipase were as follow:immobilization temperature 30?,lipase concentration 2.0 mg·mL-1,immobilization time 6h and pH=7.0 of PBS buffer solution.The immobilization efficiency of 83.1%was attained with the activity recovery of 63.5%.The immobilized lipase on this magnetic metal organic framework was prepared under the optimum preparation conditions and then employed as a biocatalyst for the transesterification of soybean oil and methanol.The optimum reaction conditions were obtained as following.mole ratio of methanol to soybean oil 4:1,25 wt.%of catalyst dosage,0.2 wt.%of water content,reaction time 60h,and reaction temperature 40?.Under the optimized transesterification conditions,the biodiesel yield of 92.1%could be attained.In addition,the immobilized lipase had high thermal stability and operational stability.As the immobilized lipase was maintained at 80? for 2h,its relative activity was 60.4%,The immobilized lipase was still maintained 81.2%of the biodiesel yield after reuse of 5 times.The Fe₃O₄@P?GMA-DVB-MAA?-Lipase was used to catalyze the transesterification of soybean oil and methanol,and its catalytic performance was estimated.The preparation conditions and the reaction conditions of transesterification were optimized,then the thermal stability and operational stability of the immobilized lipase were also investigated.The acquired results showed that the optimum conditions for preparing immobilized lipase were:pH=7.0 of PBS buffer solution,lipase concentration 2.0 mg·mL-1,immobilization time 4h and immobilization temperature 30?.The immobilization efficiency of 88.5%was attained with the activity recovery of 67.3%.The immobilized lipase on the magnetic polymer microspheres prepared under the optimum immobilization conditions was used to catalyze the transesterification of soybean oil and methanol,and the optimum transesterification conditions were obtained as below,30 wt.%of catalyst dosage,0,3wt.%of water content,mole ratio of methanol to soybean oil 4:1,reaction temperature 40? and reaction time 60h.The percent conversion of transesterification was 92.8%under the optimum reaction conditions.The esterification activity of free fatty acids for the immobilized lipase was determined and the results showed that the fatty acid conversion of esterification was over 40%as the esterification was carried out at 36h,implying that the immobilized lipase not only could catalyze transesterification of soybean oil,but also could catalyze esterification of free fatty acids.Moreover,the immobilized lipase possessed good thermal stability and operational stability.The immobilized lipase was maintained maintained at 80? for 2h and its relative activity was found to keep at 56.2%.After the immobilized lipase was reused for 5 times,the transesterification conversion rate was still reached 78.7%.