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摘要: 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。Abstract: 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%.
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表 1 不同碱浓度处理的BAA-ZSM-5系列分子筛的粒径分布
Table 1 Particle size distribution of BAA-ZSM-5 series catalysts treated by different alkalinity
Catalyst Particle size d/μm ≤0.7 0.7-1.5 ≥1.5 HZSM-5 26.6 63.7 9.7 B1AA 13 71.4 15.6 B2AA 8 76 16 B3AA 3.3 70 26.7 表 2 酸碱处理后ZSM-5的XRF分析
Table 2 XRF results of ZSM-5 treated by alkaline and acid
Catalyst Concentration w/% SiO2/Al2O3 SiO2 Al2O3 HZSM-5 94.10 5.90 27.119 AA 94.12 5.88 27.22 B 94.08 5.92 27.027 BAA 94.09 5.91 27.112 A: 0.08mol/L HCl; B: 0.15mol/L Na2CO3 表 3 不同碱浓度处理的BAA-ZSM-5分子筛催化剂的结晶度
Table 3 Crystallinity of BAA-ZSM-5 catalysts treating by different alkalinity
Catalyst FMI peak area Crystallinity HZSM-5 30615 100 B1AA 29837 97.46 B2AA 29135 95.17 B3AA 27318 89.23 表 4 不同碱浓度处理BAA-ZSM-5催化剂的BET表征
Table 4 BET results of BAA-ZSM-5 series catalysts treated by different alkalinity
Catalyst ABET
/(m2·g-1)Amica
/(m2·g-1)vmica
/(cm3·g-1)HZSM-5 346 250 0.120 B1AA 311 239 0.115 B2AA 336 256 0.123 B3AA 314 238 0.115 a: t-plot method -
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