Fundamental Research On Biodiesel Production From Vegetable Oils Catalyzed By Solid Base

Petrochemical sources, such as coal and natural gases are supplying the majority of the energy needs of the world, but all of these sources are finite and will be consumed shortly. Therefore, research is now being directed towards the use of alternative renewable fuels. Biodiesel, a mixture of alkyl esters obtained from vegetable or animal oils, is a promising nontoxic and biodegradable fuel arising from biomass. Biodiesel is usually produced by the transesterification of triglycerides with short-chain alcohols (generally methanol and ethanol) in the presence of a catalyst. Although both acids, bases, enzymes can be used for the transesterification reaction, alkaline catalysts are more widely investigated because the rate of transesterification reaction by alkaline catalysts is much faster than that by acid catalysts and enzymes.Conventionally, homogeneous basic catalysts, such as sodium or potassium hydroxide dissolved in methanol, are used for the transesterification reaction. These traditional homogeneous catalysts have certain advantages including high activity and mild reaction conditions. The removal of these catalysts is however technically difficult, and a large amount of wastewater was produced during biodiesel separating and cleaning. In order to circumvent the difficulties with homogeneous catalysts, heterogeneous basic catalysts have been widely studied in the past decades. They have some outstanding advantages, such as simplifying of separation and no toxicity, no corrosion, or no environmental pollutionIn this thesis, several kinds of solid base have been used in transesterification of vegetable oils with methanol to biodiesel production. The catalyst was characterized by TG-DTA, XRD, FTIR, SEM, TEM and CO2-TPD, and the mechanism for the formation of basic sites was discussed. Results were as follows,1) KF loaded Rare Earth Metal Oxides (Re2O3, Re=Y, La, Sm, Eu) were prepared by incipitation impregnation method and were applied in the transesterification reaction of rapeseed oil with methanol. The mechnism for the formation of basic sites and the phase change of the KF-loaded Re2O3catalyst with different calcination temperatures is proposed.2) La2O3supported on ZrO2catalysts was prepared by impregnation method. and used in the transesterification of sunflower oil with methanol. This catalyst possess better stability than KF/Re2O3. however, leaching still occurred on this catalyst. 3) SBA-15supported CaO was prepared by one-pot synthesis method, and applied in the transesterification of different vegetable oils with methanol. This kind of catalyst showed good stability not only in transesterification reaction, but also in reactions with low contents of free fatty acids (FFA) and water.4) Rod-like CaxSiOx+2catalysts were synthesized by using one-pot hydrothermal method. Catalysts calcined at550℃were used in the transesterification reaction of soybean oil with methanol. Under methanol reflux condition, FAME yields of82%and95%were achieved on Ca4SiO6in a reaction time of1and2h, separately. Besides, a FAME yield of ca.80%can be achieved under room temperature over Ca4SiO6catalyst.