改性ZSM-5分子筛及其催化苯甲醇烷基化反应

Alkylation reaction of modified ZSM-5 molecular sieve and its catalytic benzyl alcohol

采用酸碱改性对ZSM-5分子筛进行了改性,通过XRD、SEM、N2吸-脱附和NH3-TPD等手段对处理前后的样品进行了表征,并研究改性分子筛催化剂的苯甲醇烷基化催化性能。结果表明:适宜的酸碱改性浓度分别为0.1 mol/L和0.3 mol/L,通过碱改性,可以脱除分子筛部分骨架硅,再由酸液洗涤,可去除催化剂表面的附着物,引入一定量的介孔,比表面积增大,暴露出更多的活性位。与改性前相比,介孔体积由0.10 m3/g提高至0.47 m^(3)/g,比表面积由385 m^(2)/g增至452 m^(2)/g,酸量基本保持不变;在温度460℃,总质量空速2.0 h-1,苯与甲醇摩尔比1:1,压力0.5 MPa(H2)时,最优催化剂可连续运行2 016 h,苯转化率最大为63.31%,甲苯和二甲苯选择性最大为95.71%,对二甲苯选择性为26.89%,苯甲醇烷基化催化性能和稳定性能良好。

It adopted acid-base modification to modify ZSM-5 molecular sieve, characterized the samples before and after treatment by XRD, SEM, N2absorption-desorption and NH3-TPD, and studiedthe catalytic performance of benzyl alcohol alkylation. The results showed that the appropriate concentrations of acid-base modification were 0.1 mol/L and 0.3 mol/L respectively. Part of the skeleton silicon of the molecular sieve could be removed by alkali modification, and then washed by acid solution, the adhesion on the catalyst surface could be removed, and a certain amount of mesoporous was introduced, which increased the specific surface area and exposed more active sites. Compared with that before modification, the mesoporous volume increased from 0.10 m^(3)/g to 0.47 m^(3)/g, the specific surface area increased from 385 m^(2)/g to 452 m^(2)/g, and the acid content remained unchanged. At 460 ℃, total mass air velocity 2.0 h-1, molar ratio of benzene to methanol 1:1, 0.5 MPa(H2), the optimal catalyst could run continuously for 2 016 h, the maximum benzene conversion rate was 63.31%, the maximum selectivity of toluene and xylene was 95.71%, and the maximum selectivity of p-xylene was 26.89%, showing good catalytic performance and stability of benzyl alcohol alkylation.