纳米HZSM-5催化剂催化烃类转化反应

制备了纳米(20~50 nm)HZSM-5催化剂, 用XRF, TEM和NH3-TPD等手段对催化剂进行了表征. 以正辛烷及苯和正辛烷混合物的转化为模型反应, 研究了单烃和混合烃在纳米HZSM-5催化剂上的转化行为, 考察了反应条件对产物分布的影响. 结果表明, 纳米HZSM-5沸石催化剂具有很强的烃类转化能力, 烃类通过芳构化、 异构化和烷基化等反应转化为高辛烷值的异构烷烃和芳烃, 产物中异构烷烃(C4~C6)和芳烃的质量分数超过90%. 直链烷烃转化为芳烃以生成苯环为主, 混合烃转化为芳烃以苯和小分子烃的烷基化为主. 控制反应条件可抑制苯和C+9芳烃的生成. 产物分析结果表明, 烃类在纳米HZSM-5催化剂上的裂解、芳构化和异构化等遵循正碳离子机理.

Conversion of Hydrocarbons over Nano-HZSM-5 Catalysts

The nanoscale HZSM-5(20—50nm) catalyst was prepared, and characterized by XRF, TEM, NH3-TPD and so on. The performance of the nanoscale HZSM-5 catalysts for conversion of n-octane, the mixture of n-octane and benzene was evaluated. The transformation behavior of both single and mixing hydrocarbons as the model reactants over the nanoscale HZSM-5 catalyst was investigated, the influences of the reaction conditions on product distribution were investigated, and reaction mechanism was also studied. The results indicate that the nanoscale HZSM-5 catalyst exhibits a higher ability to convert hydrocarbons, and the hydrocarbons were converted mainly into aromatics and iso-paraffins which have a high octane value by isomerization, aromatization, alkylation reactions and so on, as a result, the total amount of the iso-paraffins(C4—C6)and aromatics in products was above 90%(mass fraction). The aromatization from single hydrocarbons mainly produced benzene via dehydrocyclization process, whereas the aromatization from the mixing hydrocarbons formed alkyl-aromatics mostly by alkylation of benzene and small molecule hydrocarbons. The formation of benzene and C+9 could be restrained by regulating the reaction conditions. The analysis of the products shows that the cracking, aromatization and isomerization reaction of hydrocarbons such as octane and benzene-n-octane over the nanoscale HZSM-5 catalyst followed the carbonium ion mechanism.