Study On The Heterogeneous Catalyst Used In Preparing Biodiesel

Biodiesel produced by transesterification of natural oil with alcohols is an environmental friendly alternative fuel. With a traditional homogeneous acid/base catalyst, separating transesterification product with used catalyst is difficulty. Discharge of waste catalyst induces environmental problems. Using heterogeneous base catalyst may improve the purity of products and avoid the problems of catalyst deposition. Researches of heterogeneous catalysts and relative catalytic transesterification reactions as well as the properties of products are meaningful for both the production and application of biodiesel. In this work, a series of supported CaO solid base catalysts were prepared. Effects of calcium sources, supporter oxides and preparing procedure on the catalytic activities were systematically investigated. Impregnation method was chosen to support Ca(Ac)2 onto MgO supporter. Optimal impregnating conditions are Ca(Ac)2 solution 22.6%, drying temperature 80℃and calcining temperature 700℃. No dissolution of catalyst was observed in methanol. The CaO/MgO catalysts are easy to be contaminated by absorbing H2O or CO2 from atmosphere. They were calcined in a N2 stream before using. The catalysts were characterized by X-ray diffraction(XRD), TG-DTG and CO2 temperature programmed desorption (CO2-TPD). The XRD patterns show the catalysts exposed in atmosphere contains significant amount of Ca(OH)2 and Mg(OH)2. The TG curves demostrates the catalysts loss its weight in three steps before 900 ℃. The CO2-TPD spectra exhibit three types of adsorbing sites associating with MgO over the catalyst surface. The influences of reaction conditions were studied and the optimized parameters were the methanol/oil mole ratio of 12:1 and the catalyst dosage of 2%(weight of catalyst/weight of oil). The reaction is rather slow at the beginning because methanol is insoluble in oil. It speeds up with increasing mutual oil-methanol solubility while mono-or di-glycerides forms in the reaction process. Temperature significantly influences the reaction rate. The catalyst is tolerant to free acid and water to some extent. Cosolvent tetrahydrofuran increased the reaction rate.