Studies On The Synthesis Of DBE Catalyzed By Heteropoly Acids

It is widely used of heteropoly acids as environmental friendly catalysts. In this article, the heteropoly acids with Keggin structure are choosed as catalysts. Esterification of mixed dibasic acids and carbinol were studied.A traditional acidification method incorporated with an ether extraction technique was used to prepare silicotungstic acid and phosphotungstic acid with Keggin structure. Different methods were employed to prepare a series of activated carbon and silica gel supported HPAs respectively. The supported HPAs were characterized by IR XRD TG-DSC and Hammett. It has been found that HPAs with Keggin structure could be prepared successfully by the method employed. The supported HPAs still keep their Keggin structures sour intensities, but the thermal stabilities of HPAs improved.The HPAs are expensive. The Yields of HPAs prepared by traditional acidification method incorporated with an ether extraction technique was a little low. In this article, the ratios of material , the contents of hydrochloric acid and reaction time were studied. Then the best reaction conditions were determined by orthogonal test. It was proved that the yield of phosphotungstic was 86. 1%.The HPAs and supported HPAs were used in esterification. The catalytic activities were investigated by esterification ratios and water velocities. The results showed that the phosphotungstic had better catalytic activities than the silicotungstic acid. As for the supported HPAs, the silica gel support HPAs' catalytic activities were higher than the activated carbon support HPAs. The catalytic activities of supported phosphtungstic prepared by different methods different charge numbers and different activation temperatures were studied. The results showedthat the catalytic activities of supported HPAs prepared by circumfluence absorption were higher than prepared by isopyknic insuccation. The esterification rate was obvious high when the charge number of catalyst is 20%. 350°C is the best activation temperature. Then the catalysts of high activities were selected to be used in the preparation of mixed dibasic acid dimethyl esters(DBE).Mixed dibasic acids (DBA) are byproducts of hexanedioic acid. In this article DBE were synthesized. Factors of esterfication of mixed dibasic acid were studied: alcohol acid mol ratios, the content of the catalysts, the reaction time and the content of water carrier. The best reaction conditions were determined by orthogonal test. The results showed that phosphotungstic acid -, PW12/C and PW12/SiO2 were eminent catalysts and had no pollution. The esterification ratio was 95.4%, 92.6% and 94.3% respectively.The reclaim and reuse of catalysts were studied in this article. The results showed non-supported HPAs were difficult to separate from system; while supported HPAs were very easy to separate and could be reused in esterification. The results showed that the catalytic activities dropped slightly after 10 times recycles.