Preparation Of Magnetic Whole Cell Biocatalyst And Its Application In Biodiesel Production From Waste Cooking Oil

Biodiesel, as a renewable, biodegradable, and nontoxic fuel,which is derived from triglycerides by transesterification with methanol, has attracted considerable attention during the past decade. The main hurdle to the commercialization of biodiesel production is the cost of feedstock oil. Therefore, the use of waste cooking oil may not only significantly reduce the cost of biodiesel produced but also eliminate the environment and human health risk. Utilization of lipase as a catalyst for biodiesel-fuel production has great potential compared with chemical methods, since no complex operations are needed either to recover the glycerol or to eliminate the catalyst and salt. However, the various processes involved result in high cost and can be a barrier to widespread use of enzymatic processing. Utilizing whole cell biocatalyst for biodiesel fuel production is one way to reduce the cost of lipase since it can avoid the complicated processes of isolation and purification which account for a large part in the lipase cost. The aim of this study is to develop a kind of whole cell biocatalyst for conversion of waste cooking oil, which must be cost-effective and simply separated and a reactor system fit for this biocatalyst. The results and conclusions in this dissertation are drawn as follow:(1) A lipase producing strain CY-39 with high enzyme activity was isolated from oil contaminated soils. It can be used directly as whole cell biocatalyst for biodiesel production from waste cooking oil and its highest conversion rate was 71.2%. Based on morphological analyses and the sequence comparison of the 16 S r DNA, strain CY-39 was identified as Pseudomonas mendocina. Its enzymatic characteristics and catalytic properties were further studied in detail.(2) A mutant strain UE-7 with high catalytic performance and genetic stability was obtained through treating the P.mendocina CY-39 by UV and Ethyl methyl sulfone(EMS). Mutant strain UE-7 was used as whole cell biocatalyst for biodiesel production from waste cooking oil and obtained the highest ME content 76.8%.(3) Cells of mutant strain UE-7 were immobilized in polystyrene or chitosan(combined with nanoparticles Fe3O4) by coating method for the preparation of superparamagnetic whole cell catalysts. Comparison of these two types of whole cell catalysts indicated that superparamagnetic chitosan whole-cell catalystshowed higher catalytic ability and stability. Nanoparticles Fe3O4 and whole cell biocatalysts were characterized by X-ray diffraction, environmental scanning electron microscope and vibrating sample magnetometer instrumentl.(4) Seed culture conditions(carbon and nitrogen sources) transesterification conditions(temperature, p H, methanol-oil ratio, amount of catalyst, water content) and other affect factors of the superparamagnetic chitosan whole cell catalyst were optimized. Under the optimum conditions, the maximum methyl ester(ME) content in the reaction mixture reaches 82.6%. The superparamagnetic chitosan whole cell catalyst has a good reproducibility and 92.4% of the initial catalytic activity was maintained even after 6 batches of transesterification and the regeneration culture.(5) A magnetically stabilized fluidized bed reactor(MSFBR) system was designed using superparamagnetic chitosan whole-cell biocatalyst for repeated-batch transesterification reaction. Application of magnetic field in the MSFRB improved the ME yield and the stability of the catalyst. When stepwise addition of methanol(four molar equivalents to oils) was conducted, a high ME content of 83.4% was achieved in the first cycle of repeated-batch methanolysis under the optimum magnetic field intensity of 110 Oe and the flow rate of 17.5 ml/min and a high value of 68.3% was maintained even after 8 batch reaction cycles. The stability and recovery of the magnetic catalytic particles in MSFBR are much better than that in a conventional fluidized bed reactor without a magnetic field.These previous findings provide the basis in further development and research for industrial production of biodiesel from waste cooking oil using whole cell catalyst.