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Preparation Of The Immobilized Phosphotungstic Acid On Mesoporous Materials And Its Catalytic Performance For The Esterification Of Cyclohexene With Formic Acid

Posted on:2017-09-21Degree:MasterType:Thesis
Country:ChinaCandidate:Z W WuFull Text:PDF
GTID:2311330485452446Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
The indirect hydration of cyclohexene consists of the esterification of cyclohexene with formic acid and hydrolysis of cyclohexyl formate. The indirect hydration route overcomes the reaction kinetic limitations of the direct hydration route, thus it has a good application prospect. The cyclohexene esterification is acid catalytic reaction, so development of highly efficient solid acid catalyst is the key step to realize the indirect hydration process. This thesis studied the esterification of cyclohexene with formic acid with strong acidic cation-exchange resin Amberlyst-15. Meanwhile, a series of supported phosphotungstic acids(HPW) catalysts used mesoporous molecular sieve SBA-15 as carrier were prepared by three different methods. The structure of the supported HPW catalysts was characterized in details, and their catalytic performance were evaluated in the estrification reaction, the reusability of catalysts was also studied. This work was aimed to provide technology accumulation for the development of solid acid catalyst used in the esterification of cyclohexene with formic acid.Firstly, the catalytic performance of the strong acidic cation-exchange resin Amberlyst-15 in the reaction of the esterification of cyclohexene with formic acid was investigated, in addition, the reaction conditions were optimized. The proper reaction conditions were as followings: catalyst content 3%(w/w), mole ratio n(cyclohexene):n(formic acid)=1:3, reaction temperature 80 ?, reaction time 4 h. Under this optimal reaction conditions, the cyclohexene conversion and cyclohexyl formate selectivity were 96.9% and 98.5%, respectively. The activity of the recycled catalyst obviously decreased and the reused resin swelled into powder.Secondly, HPW were immobilized onto the surface of amine-modified mesoporous sieve SBA-15 by the method of post-grafting. The obtained catalyst HPW/NH2-SBA-15 preserved an ordered hexagonal mesostructure for SBA-15 and Keggin structure of the heteropolyanions. However, during the process of modification, HPW existed in the form of ammonium salt, which was significantly reduced the acidity of the catalysts. The catalyst HPW/NH2-SBA-15 showed low catalytic activity with 15.5% cyclohexene conversion and 96.8% selectivity for cyclohexyl formate. After being recycled, there was no significant decrease in the performance of the catalyst.Thirdly, a series of HPW catalysts were prepared by in-situ synthesis method, using mesoporous molecular sieve SBA-15 as carrier. The influences of catalysts preparation conditions, such as the additive sequence and the ratio of raw materials on the catalytic performances were investigated. The results showed that the order of adding HPW before tetraethyl orthosilicate(TEOS) was in favor of maintain the mesoporous structure. The catalysts had higher thermal stability and HPW was in a good dispersity on the carrier for twoadding sequences. Under the optimum conditions, the catalysts prepared with the order of addition HPW before TEOS showed better catalytic performance in the esterification of cyclohexene with formic acid, the conversion of cyclohexene was up to 89.0%, and the selectivity of cyclohexyl formate reached more than 98.2%. The recovering catalysts could maintain the stability of the structure, but the catalytic activity was obviously decreased. The main reason was due to the partial loss of HPW, in addition, a small amount of acid active centers covered by high boiling point polymer of the reaction was also one of the reasons.Finally, functionalized SBA-15 mesoporous molecular sieve containing sulfonic groups with HPW(denoted as HPW-SBA-15-SO3H) was synthesized by one-pot co-condensation of TEOS and mercaptopropyltrimethoxysilane(MPTES) in the presence of hydrogen peroxide under acidic conditions. The obtained material had high acid strength, high surface ares, large pore volume and pore size. The process parameters of catalyst preparation were investigated. The optimal preparation conditions were as follows: n(MPTMS) /n(MPTMS+TEOS) molar ratio 1:10, n(H2O2)/n(MPTMS) molar ratio 18:1, m(HPW):m(TEOS) mass ratio 1:10. The catalysts prepared in optimal conditions exhibited excellent catalytic activity, the esterification reaction took place with more than 86.7% conversion of cyclohexene and 98.0% selectivity of cyclohexyl formate after 6 h at 80? in the presence of mole ratio n(cyclohexene):n(formic acid)=1:3, catalyst content 5.7%(w/w). And this catalyst had high catalytic stability,the conversion of cyclohexene was up to 72.0% even reused four times. The characterization of recovering catalyst showed that the surface ares, pore volume and pore size slightly decreased. The reason was may due to amount of acid active center was covered by high boiling point polymer. There is no loss of heteropoly acid from the support, while partial loss of sulfonic acid groups was existed.
Keywords/Search Tags:Mesoporous molecular sieve, Phosphotungstic acids, Immobilization, Sulfonic functionalization, Esterification of cyclohexene with formic acid
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