Design Of Polyoxometalates And Invesitgation Of Their Catalytic Activity On Esterification For Production Of Biodiesel

Eco-friendly and efficient catalysts have been a focus of a much recent research.Polyoxometalates（POMs, also named heteropolyacids, HPAs） have attractedsignificant attention because of their unique properties such as high Br nsted acidity,redox property and modificability of catalytic activity, which make them available forapplications in homogeneous and heterogeneous reactions. However, POMs exhibitedlow surface area, and low thermal stability and easy solubility in polar solvents, whichlimit their utility in many catalytic reactions. The environmental friendly catalysts ofpolyoxometalates play an important roles in the heterogeneous system. In thisdissertation, a several solid POM catalysts had been designed, and had been evaluatedtheir catalytic activity in esterification and transesterification reactions. The mainresults of this work are as follows:1. H₃PW₁₂O₄₀/Agarose were prepared by sol-gel process and characterized byElemental analysis and so on. It was proved that the catalytic activity sites ofH₃PW₁₂O₄₀/Agarose did not change. It was identified that strong interaction betweenpolyhydroxyl site of agarose and H₃PW₁₂O₄₀by hydrogen bonds resulted in thehomogenous distribution of H₃PW₁₂O₄₀as well as the good mechanical properties ofthe nanocomposite films. With the help of38wt%H₃PW₁₂O₄₀/Agarose, molar ratio ofmethanol/palmitic13:1,65oC, mass of catalyst only0.25g, the highest catalyticactivity of catalyst can be obtained after7hours, and the reuse activity of catalystbeing still very good after five times; with the help of best loadings of38wt%H₃PW₁₂O₄₀/Agarose, molar ratio of methanol/Eruca sativa Gars. Oils95:1,65oC,mass of catalyst only0.50g, the highest catalytic activity of catalyst can be obtainedafter12hours, the reuse activity of catalyst being still very good after five times,active component of H₃PW₁₂O₄₀loss amount is less than5%. The thin film of38wt%H₃PW₁₂O₄₀/Agarose could be separated from mixture and H₃PW₁₂O₄₀providedcatalytic activity sites.2.(C₁₆TA)H₄PW₁₁TiO₄₀were precipitated by using long chain quaternaryammonium salt surfactants for structure-directingagent and characterized byElemental analysis and so on. It was proved that (C₁₆TA)H₄PW₁₁TiO₄₀had Br nstedacid and Lewis acid sites with Keggin structure. In a polar solvent it could formself-assembly nanoscale micelles. With the help of (C₁₆TA)H₄PW₁₁TiO₄₀, molar ratio of methanol/palmitic20:1,65oC, mass of catalyst only3.81mmol/L, the highestcatalytic activity of catalyst can be obtained after6hours, and the reuse activity ofcatalyst being still very good after six times.3. The activity of H₅BW₁₂O₄₀in esterification was investigated. H₅BW₁₂O₄₀wasproton acid which owned high charge,the proton was ionized step by step in polarsolvent and the acid strength was higher than H₃PW₁₂O₄₀. So we conducted asystematic study of the catalytic activity of H₅BW₁₂O₄₀in esterification reaction and itplayed a guiding role in designing heteropolyacid catalysts. With the help of Br nstedand high protons acid H₅BW₁₂O₄₀, molar ratio of methanol/palmitic10:1,65oC, massof catalyst only10.9mmol/L, the highest catalytic activity of catalyst can be obtainedafter3hours. The catalyst was separated from the mixture by ether extraction methodand the reuse activity of catalyst lost only2.0%after six times.4. The homogeneous catalyst H₅BW₁₂O₄₀used in esterification had problems ofseparation、reusing, so we made an effort to use long chain quaternary ammonium saltsurfactants for structure-directingagent to synthetize (C₁₆TA)H₄BW₁₂O₄₀. With thehelp of Br nsted and high protons acid (C₁₆TA)H₄BW₁₂O₄₀, molar ratio ofmethanol/palmitic18:1,65oC, mass of catalyst only4.4mmol/L, the highest catalyticactivity of catalyst can be obtained after3hours. The catalyst was separated from themixture by ether extraction method and the reuse activity of catalyst lost only1.9%after six times.5. The activity of H₅BW₁₂O₄₀in esterification was very high,so the catalyst ofH₇BW₁₁TiO₄₀owing Br nsted acid and Lewis acid sites played an important role inreaction. It was proved that H₇BW₁₁TiO₄₀still kept Keggin structure. With the help ofH₇BW₁₁TiO₄₀, molar ratio of methanol/palmitic25:1,65oC, mass of catalyst only4.68mmol/L, the highest catalytic activity of catalyst can be obtained after1hours,and the reuse activity of catalyst being still very good after six times. The double acidcatalyst H₇BW₁₁TiO₄₀performed higher activity than H₅BW₁₂O₄₀due to theintroduction of Lewis acid sites Ti4+.