Study On Preparation Of Biodiesel By Ca/Al Composite Oxide Catalyst

Biodiesel as a green renewable energy could replace fossil fuels, and it plays a great practical role in the construction of national security, sustainable energy supply system. Based on the preliminary studies in our research group, a kind of solid base catalyst of Ca/Al composite oxide was developed which has higher activity in the transesterification of rapeseed oil with methanol by batch reactor for synthesis of biodiesel. In this thesis, Ca/Al composite oxide catalyst was further studied and characterized, and the home-made fixed-bed reactors were built for investigating continuous transesterification of rapeseed oil with methanol catalyzed by Ca/Al composite oxide to produce biodiesel.Firstly, aluminum, sodium hydroxide and calcium carbonate were used as the main raw materials to synthesize hydrated calcium aluminate through co-precipitation. Ca/Al composite oxide catalyst was obtained by drying,calcining and molded -compressing procedures in turn. In adition, the catalyst samples were characterized and analyzed with TR, XRD, BET, TG-DTA, XPS , SEM and other modern analytical techniques. The effect of the calcination temperature on the Ca/Al composite oxide catalyst ratio surface acreage, crystal structure, phase composition and micromorphology were studied. The results show that the calcination temperature has more influences on the catalytic capability. The maximum surface area of 27.36m2/g was obtained and a stable Ca/Al composite oxide catalyst was formed when the catalyst calcined at 600℃. The particles exist with no abnormal reunion, homogeneous size and smooth surface. It offers theoretic foundation and technical sustain for further discovering the relationship of catalyst structures, the catalytic capability and the preparation conditions by characterizing the catalyst samples.Three fixed-bed reactors including catalyst direct-packing type, catalyst packed-packing type and gas ascend type were established. The catalytic capability of Ca/Al composite oxide were evaluated through continuous transesterification of rapeseed oil with methanol to produce biodiesel. As poor performances of the catalyst direct-packing type and catalyst packed-packing type, the gas ascend fixed-bed reactor was mainly investigated. The influences of some factors, such as methanol feeding amount and feed flow rate of rapeseed oil, on the reaction efficiency were investigated. The experimental results indicated that the yield of methyl ester could reach to 94.4% under the optmum condition, which indicated that Ca/Al composite oxide catalyst has excellent catalytic capability. It can be concluded that continuous transesterification technology with heterogeneous catalyst for producing biodiesel has obvious advantages and wide prospects.