酸碱处理对ZSM-5分子筛物化性质和反应性能的影响

考察了碱处理、先碱后两步酸处理对HZSM-5分子筛物化性质以及苯与甲醇烷基化反应性能的影响。结果表明,碱处理在脱除分子筛中非骨架硅的同时,提高了晶孔的利用率,也中和了分子筛的强酸中心,使催化剂活化甲醇的能力减弱,苯与甲醇反应活性降低;先碱后两步酸处理既脱除了分子筛中的非骨架铝,也恢复了一部分强酸中心,提高了苯与甲醇的反应活性。进一步考察了先碱后两步酸处理中不同碱浓度的影响,结果表明,适宜浓度的碱处理后再两步酸处理,一方面,能脱除分子筛的非骨架硅铝物种,使分子筛的颗粒粒径更加均匀;另一方面,分子筛的强酸中心有所减少,降低了催化剂的积炭失活速率,苯转化率提高15%以上。

Effects of acid-alkali treatment on properties and reactivity of ZSM-5 catalyst

The effects of alkali-treatment and alkali-acid-treatment of ZSM-5 on the catalytic properties and catalytic performance of benzene alkylation with methanol were studied. The results showed that alkali treatment of ZSM-5 can remove the extra-framework Si species to enhance the diffusivity. However, it can also neutralize the strong acid sites of ZSM-5 and weaken the activation of methanol, reducing the reactivity of benzene alkylation with methanol. The twice acid treatment of alkali-treated ZSM-5 improve the catalytic performance because it can not only remove the extra-framework Al species, but also restore a part of strong acid sites neutralized in the process of alkali-treatment. Further research on the effects of alkalinity showed that the extra-framework Al species and Si species can be removed and a moderate particle size can be obtained after treatment of ZSM-5 with a moderate concentration of alkali. Moreover, the carbon deposition rate has been slowed down due to a decrease of strong acid sites. Therefore, the conversion of benzene can be improved by more than 15%.