MCM-41分子筛的表面修饰及其催化合成乙酸异戊酯

Surface Modification of MCM-41 Molecular Sieve and Its Catalytic Performance for Synthesis of Iso-amyl Acetate

通过后合成处理将苄基、三甲基硅烷基和磺酸基接枝到MCM-41分子筛上,制备了一种新型的有机-无机杂化S-B-MCM-41催化剂.采用X射线衍射、低温N2吸附-脱附和酸碱滴定对样品的结构和质子酸量进行了表征和测定.结果表明,S-B-MCM-41催化剂较好地保持了MCM-41分子筛的介孔结构,BET比表面积高达798m2/g,质子酸量为4.0mmol/g.将S-B-MCM-41催化剂用于乙酸与异戊醇合成乙酸异戊酯的反应,考察了各种反应条件对酯化率的影响.在乙酸用量为0.1mol,异戊醇用量为0.15mol,催化剂用量为0.2g,带水剂甲苯为15ml,反应温度为110～125℃,反应时间为2h的优化条件下S-B-MCM-41上的酯化率可达99%以上;而MCM-41分子筛上的酯化率仅为54%.经3次重复使用后,S-B-MCM-41催化剂上的酯化率依然保持在90%以上.初步探讨了S-B-MCM-41催化剂催化合成乙酸异戊酯的反应机理.

MCM-41 molecular sieve was synthesized by the sol-gel method and functionalized with benzyl sulphonic acid and trimethylchlorosilane using a post-synthetic procedure. The organic groups were covalently bonded to the surface of MCM-41 by etherification of Si-OH and thus a new S-B-MCM-41 catalyst was prepared. The structure and Br6nsted acid amount of S-B-MCM-41 catalyst were characterized by XRD, N2 adsorp- tion-desorption, and acid-base titration. The results showed that the mesoporous structure of MCM-41 was maintained in the S-B-MCM-41 catalyst with a BET surface area of 798 m^2/g and acid capacity of 4.0 mmol/g. The synthesis of iso-amyl acetate from acetic acid and iso-amyl alcohol over S-B-MCM-41 catalyst and its catalytic performance were investigated. Under the optimum conditions of acetic acid 0.1 mol, iso-amyl alcohol 0.15 mol, catalyst 0.2 g, water-entrainer toluene 15 ml, reaction temperature 110-125℃ , and reaction time 2 h, the esterification fraction was over 99 %. By comparison, the MCM-41 molecular sieve only had an esterification fraction of 54 % under the same conditions. After three times of repeated use, the esterification fraction above 90 % still maintained over S-B-MCM-41. The reaction mechanism for the esterification was discussed.