Zn-Pt-Re/ZSM-5催化剂上烷烃芳构化反应规律的研究

STUDY ON THE REACTION RULES FOR AROMATIZATION OF ALKANE OVER Zn-Pt-Re/ZSM-5 CATALYST

以正己烷、正庚烷、正辛烷、甲基环戊烷及环己烷为模型化合物,在固定床连续微型反应器上研究不同碳数和结构的烷烃在催化剂Zn-Pt-Re/ZSM-5上的芳构化反应规律,并与传统重整催化剂的芳构化性能进行比较。结果表明:在反应温度小于450℃时不同烷烃生成芳烃从难到易的顺序为正己烷>环己烷>甲基环戊烷>正庚烷≈正辛烷;在反应温度大于450℃时芳烃收率均在90%以上。烷烃在传统重整催化剂CB-8上直接脱氢环化生成环烷烃,然后再脱氢生成芳烃。烷烃在Zn-Pt-Re/ZSM-5催化剂上的反应按两种机理进行:小部分烷烃直接脱氢环化生成环烷烃,然后再脱氢生成芳烃;大部分烷烃先裂解为低碳烯烃,再发生聚合、环化、脱氢等反应生成芳烃。

The reaction rules for aromatization of alkanes having various carbon number and structure over Zn-Pt-Re/ZSM-5 catalyst were studied on a continuous flow micro-reactor device and using n-hexane,n-heptane,n-octane,methylcyclohexane and cyclohexane as probe molecules.The aromatization performance of alkane over Zn-Pt-Re/ZSM-5 catalyst and conventional reforming catalyst CB-8 was compared.Test results show that when reaction temperature is less than 450 ℃,the sequence of generating aromatization reactions from hard to easy is n-hexane,cyclohexane,methylcyclohexane,n-heptane and n-octane;when the reaction temperature is over 450 ℃,the aromatics yields of alkanes tested are all more than 90%.It is also found that the aromatization mechanism of alkane over CB-8 catalyst and Zn-Pt-Re/ZSM-5 catalyst is different： over CB-8 catalyst,alkane is turned into cycloalkane by dehydrocyclization firstly,followed by further dehydrogenization to form aromatics;over Zn-Pt-Re/ZSM-5 catalyst,two possible reaction pathways may exist,one is the same as over CB8 catalyst,the other is alkanes crack to form light olefins firstly,followed by reactions including polymerization,cyclization and dehydrogenization to form aromatics,and it seems that the latter is the main one.