Study On Biodiesel Production Using Magnetic Whole-cell Biocatalysts

With the increasing depletion of fossil fuel and a deterioration in the environment,biodiesel has attracted much attention due to its clean and renewable characteristics.To utilize the abundant resources of waste cooking oil（WCO）in China,the magnetic whole-cell biocatalysts（MWCBs）were prepared by the combination of magnetism and the immobilized cell technology for biodiesel production.Furthermore,a magnetically fluidized bed reactor（MFBR）was designed for transesterification of WCO using the MWCBs.The method developed in this work laid a basis for large-scale industrial application for its lower energy consumption and environmental pollution as compared with chemical-catalyzed method,and its simpler process and lower cost as compared with enzymatic method using extracellular lipase.The superparamagnetic nanoparticles（Fe₃O₄）of good dispersion,high stability and excellent biocompatibility were prepared according to the ultrasonic dispersion technique by adding polyethylene glycol and oleic acid in the synthesis process.Based on the synergistic theory and the interaction regularity between the composite supporters,the MWCBs with characters of strong adaptation and high enzyme activity were prepared by immobilizing the cells which secrete lipase into the organic carrier containing Fe₃O₄.Moreover,the MWCBs were proved to be of superparamagnetism by magnetic analysis and can be easily separated from the reaction system.First step,purer oil（soybean oil）was used as substrate and the catalytic transesterification was carried out in a constant temperature shaker.A biodiesel yield of 90.5%was obtained after 48 h.The MWCBs catalyzed process still gave a biodiesel yield of 85.3%after 10 cycles of operation.The results indicated that MWCBs had good catalytic effect on the transesterification of soybean oil and a further research was required on related studies of WCO with complicated components.After the pretreatment,WCO was used as substrate and the catalytic transesterification was carried out in a constant temperature shaker.A biodiesel yield of 87.0%was obtained after 48 h.The MWCBs catalyzed process still gave a biodiesel yield of 79.2%after 10 cycles of operation.The results indicated a good catalytic capability and an excellent reusability of MWCBs.To get a higher biodiesel yield and to make the operation process controllable,a new MFBR system was designed in the light of the combination of electromagnetic and fluidization technique.A high biodiesel yield of 91.0%was obtained under the operating conditions（methanol to oil molar ratio of 4:1,magnetic field intensity of140 Oe,biocatalysts concentration of 9 wt.%and reactant flow rate of 20 m L/min）.Moreover,a biodiesel yield of 86.9%could still be maintained after 10 times of usage.Control experiments were carried out using Fe₃O₄-uncontained whole cell biocatalysts in the MFBR system.A biodiesel yield of 69.5%was retained after the tenth reuse.These results indicated that an external magnetic field in the MFBR system could help control the motion of the MWCBs,reduce damages of cell leakage and keep the catalytic activity of the MWCBs.The parameters optimized with response surface methodology（RSM）in the MFBR system were methanol to oil molar ratio of 3.74:1,magnetic field intensity of136.63 Oe,biocatalysts concentration of 10.21 wt.%and reactant flow rate of 16.97m L/min.An experimental biodiesel yield of 91.8%was obtained under these parameters,which was consistent with that of the predicted result（92.0%）,indicating reliability and good precision of the RSM method.The conclusions obtained could provide reliable references for its further industrial application.