Synthesis Of Environmental Friendly Biodiesel By Heterogeneous Catalyst

Because of the shortage of fossil enery and the environmental issues, looking for the substitute energy resources which are environmental friendly and renewable has become the focus of the world. Among the numerous substitute fuels, biodiesel is the very promising one, which has excellent emission and power performance and can be used in diesels directly without any modification.Presently, biodiesel is mainly produced by transesterification of vegetable oils or animal fats with alcohol using KOH as a catalyst. Although this is a mature technology, there are some shortcomings including emulsion formation during the reaction, which results in the difficulty in separation of the products, and wastewater produced from the washing of the products to remove the catalyst. Using heterogeneous catalyst may improve the purity of products and avoid the problems of catalyst deposition. Researches on heterogeneous catalysts and relative catalytic transesterification reactions are meaningful for both the production and application of biodiesel.In this work, with CaO and molecular sieves (NaY, KL and NaZSM-5) as substrate respectively, supported solid alkali catalysts such as CaO/NaY were prepared by microwave irradiation, and the transesterification of soybean oil and methanol to produce biodiesel were investigated using these catalysts. Effects of different molecular sieves, mass ratios of CaO to NaY, amount of catalyst, molar ratios of methanol to oil, reaction time, reaction temperature, acid values and water contents on the yields of biodiesel were discussed. The results showed that activity of CaO/NaY was the best, and highest biodiesel yield was obtained when mass ratio of CaO to NaY was 30%, microwave irradiation time was 20 min, molar ratio of methanol to soybean oil was 9:1, mass ratio of catalyst to soybean oil was 3%, reaction temperature was 65℃and reaction time was 3h, under which yield of biodiesel could reach about 95%. The results also indicated that the CaO/NaY catalyst was more tolerant to free fatty acid and water and its activity was still high when acid value and water content were 4mgKOH/g and 1.5%, respectively. XRD, SEM, BET analysis showed that the reactivity of CaO/NaY was improved greatly with higher surface area because CaO was dispersed in NaY well. Moreover, alkalinity (H-) of CaO/NaY was higher than 27, and total alkali content reached 3.798 mmol/g, which showed that CaO/NaY was a kind of solid super alkali catalyst.Moreover, the kinetics of the reaction was investigated, the experimental data appear to be described by pseudo first-order model for the initial stages of the reaction and followed by second-order and zero-order-model. The rate constants in the initial stages for the transesterification of soybean oil were 0.141 min^-1, 0.3178 min^-1 at 50℃, 65℃respectively. And in the second stages the rate constants were 0.905L·mol^-1·min^-1,1.173L·mol^-1·min^-1 at 50℃, 65℃respectively. The activation energy of reaction were Ea=49.32kJ·mol^-1 in the initial stages and Ea=15.69kJ·mol^-1 in the second stages.