ZnO/HZSM-5催化甲醇制芳烃性能研究

Study on catalytic performance of ZnO/HZSM-5 for methanol to aromatics

采用浸渍法制备了负载不同质量分数ZnO的ZnO/HZSM-5(n(SiO_(2))/n(Al_(2)O_(3))=25)催化剂,利用XRD、NH;-TPD、PyIR、N_(2)吸附和TG等表征手段对所制备催化剂的晶型、酸量、酸强度、孔径分布和积炭量等进行了表征,并在小试和中试实验装置上探究了催化剂对甲醇制芳烃(MTA)的影响。结果表明,浸渍法引入ZnO相比于机械混合法制备的HZSM-5催化剂对芳烃的选择性更高,同时ZnO的引入没有改变催化剂的骨架结构,未堵塞孔道。在反应温度为450°C,ZnO质量分数为4%时,采用浸渍法制备的ZnO/HZSM-5催化剂对MTA反应的催化性能最好,反应产物中芳烃选择性达到75.00%;相同反应条件下,当ZnO质量分数为1%、6%和8%时,反应产物中芳烃选择性均约为66.00%。分析认为,HZSM-5分子筛为甲醇转化提供了活性位点,ZnO的引入主要促进了芳烃的生成。在中试实验中,采用浸渍法制备的ZnO质量分数为4%的ZnO/HZSM-5催化剂在450h内稳定性良好,油相产物苯-甲苯-二甲苯混合物选择性在60.00%以上。

ZnO/HZSM-5(n(SiO_(2))/n(Al_(2)O_(3)) = 25) catalysts loaded with different mass fractions of ZnO were prepared by primary wet impregnation method. The crystalline form, acid amount, acid strength, pore size distribution and carbon deposition of the prepared catalysts were characterized by XRD, NH;-TPD, Py-IR, N_(2)adsorption and TG respectively, and the effects of the catalysts on methanol to aromatics reaction(MTA) were explored on laboratory small-scale and pilot experimental devices. The results show that the introduction of ZnO by impregnation method has higher selectivity for aromatics than the HZSM-5 catalyst prepared by mechanical mixing method. At the same time, the introduction of ZnO does not change the skeletal structure of the catalyst and does not block the pore channels. When the reaction temperature is 450 °C and the mass fraction of ZnO is 4%, the ZnO/HZSM-5 catalyst prepared by the impregnation method has the best catalytic performance for the MTA reaction and the aromatics selectivity in reaction products reaches 75.00%. Under the same reaction conditions, the aromatics selectivity in the reaction products is all about 66.00%when the mass fraction of ZnO is 1%, 6 % and 8 %. The analysis shows that the HZSM-5 molecular sieve provides the active sites for the methanol conversion and the introduction of ZnO mainly promotes the formation of aromatics. In the pilot experiments, the ZnO/HZSM-5 catalyst with 4% ZnO mass fraction prepared by the impregnation method has good stability within 450 h, and the selectivity of benzene-toluene-xylene in oil phase products is more than 60.00%.