苯与合成气在ZnAlCrO_(x)&HZSM-5双功能催化剂上一步法制甲苯/二甲苯

One-step preparation of toluene/xylene from benzene and syngas over ZnAlCrO_(x)&HZSM-5 bifunctional catalyst

与传统的甲醇和苯烷基化反应相比,合成气和苯一步法制甲苯/二甲苯具有苯转化率高,催化剂稳定性好,经济性高等优点。本研究将系列Zn基的金属氧化物与H-ZSM-5分子筛组成双功能催化剂,实现了合成气与苯高效转化为甲苯/二甲苯,并筛选出最优的双功能催化剂为ZnAlCrO_(x)&H-ZSM-5。原位红外实验发现,单独的合成气在催化剂上的转化较弱,但加入苯之后,苯与甲氧基等中间体的烷基化反应可以有效拉动合成气的转化。这表明,双功能催化剂中金属组分和分子筛组分间的协同作用拉动了该反应的高效进行。通过Zn、Mg、Ga等元素改性H-ZSM-5分子筛,使得分子筛B酸酸量与L酸酸量的比值降低,发现比值的降低有助于苯的转化。其中Zn改性后B酸与L酸的比值降低最为显著,苯转化率增加的也最多。调变反应温度、原料空速、合成气氢碳比可以控制苯的烷基化程度,调节苯烷基化各产物的选择性。ZnAlCrO_(x)&H-ZSM-5双功能催化剂在压力3MPa、温度400℃的反应条件下,兼具高的苯转化率(90.6%)和甲苯/二甲苯选择性(74.3%),同时CO有效利用率为33.7%。

Compared with the traditional alkylation reaction of methanol and benzene,the one-stepprocess of syngas and benzene to toluene/xylene has the advantages of high benzene conversion,good catalyst stability,and high economic efficiency.In this study,a series of Zn-based metal oxides were coupled with H-ZSM-5 zeolite to form bifunctional catalysts for the efficient conversion of syngas and benzene into toluene and xylene,and the optimal bifunctional catalyst was ZnAlCrO_(x)&H-ZSM-5.In-situ FT-IR analysis showed that the conversion of syngas alone on the catalyst was weak,but after the addition of benzene,the alkylation reaction of benzene with methoxy species can effectively prompt the conversion of syngas,indicating the synergy between the metal components and zeolite components in bifunctional catalyst.The modifying of H-ZSM-5 zeolite with Zn,Mg,Ga elements to reduce the ratio of B acid to L acid in zeolite was found to contribute to the conversion of benzene.Among them,the ratio of B acid to L acid was the lowest after Zn modification,and the conversion of benzene was also the highest.The degree of benzene alkylation can be controlled by adjusting the reaction temperature,the space velocity of raw materials,and the H_(2)/CO ratio of in syngas,and the product selectivity can be adjusted.Under the reaction conditions of pressure 3MPa and temperature 400℃,ZnAlCrO_(x)&H-ZSM-5 bifunctional catalyst gives both high benzene conversion(90.6%)and toluene/xylene selectivity(74.3%),and the effective utilization rate of CO is 33.7%.