Preparation Of Mg-Al Mixed Oxide And Its Heterogeneous Catalysis For Transesterification

Bio-diesel, environmentally friendly and renewable source, was paid increasing attention to due to the short of energy sources and environmental consequence, especially in developed countries where it had been a commercial stuff. Bio-diesel produced by transesterification of natural oils with alcohols was an alternative fuel. In comparison with traditional homogeneous acid/base catalyst, the heterogeneous acid/base catalyst could obtain a purer product and avoided some problems such as purification of product, separation and pollution of used catalyst. The handles such as heterogeneous catalyst, related transesterification reaction and the properties of the reaction product were important for the improvement of bio-diesel production and application. The thesis that provided some functions for further exploitation bio-diesel was as follows:Mg-Al hydrotalcites with different Mg:Al ratios were prepared by coprecipitation at high supersaturation method and characterized by XRD, IR, TG-DTA and SEM. The XRD pattern of the 90℃dried samples showed sharp and symmetric peaks which gave clear indication that the samples were well crystallized and had hydrotalcite structure. TG-DTA peaks exhibited a two-step weight loss process. The first step below 220℃was attributed to loosely bound water in the interlayer space and the second one below 402℃was due to the simultaneous dehydroxylation and decarbonation of the lattice OH―, strongly bound water and CO32- groups. SEM results showed that the samples possed laminar, rod, needle and honeycomb structure. The catalyst sample with Mg/Al ratio of 3:1 after 12h crystallization and calcined at 500℃showed highest conversion (90.5%) of methyl ester with high selectivity at 65℃and was reusable.The transformation process of soybean oil in order to obtain biodiesel by means of transesterification was studied. It was chose for the optimization of the most important variables (temperature conditions, reactants proportion and time), with the purpose of obtaining a high quality biodiesel. The best combination of factors was that which was carried out with: molar ratio of methyl to soybean oil 6:1; 1.5 % (w/w) of catalyst quantity; 65℃temperature; 4h reaction time and rotating intensity 600 cycles /min. Finally, soybean methyl esters were characterized to test their properties as fuels in diesel engines, such as viscosity, flash point, cetane value and acid value. Results showed that the quality of obtained under the optimum conditions was up to Germany standard for bio-diesel.