HZSM-5分子筛上C_(6～8)混合链烃和邻二甲苯的加氢裂化

Hydrocracking of C_(6～8) mixed chain hydrocarbons and o-xylene over HZSM-5 zeolite

在连续流动固定床装置上,探讨了不同酸性HZSM-5上C6-8混合链烃（以下简称混合烃）和邻二甲苯加氢裂化的变化规律,并在稳定条件下考察了反应温度、质量空速以及氢烃体积比等反应参数的影响。混合烃的加氢裂化伴随着芳构化反应,酸性较弱的HZSM-5主要发生加氢裂化反应,裂化产物以正构烷烃为主,甲烷和异构烷烃较少。酸性强的HZSM-5上,起初以芳构化反应为主,稳定之后产物分布与弱酸催化剂接近。混合烃的加氢裂化反应表现出明显的温度效应,而质量空速和氢烃体积比的影响较小。在380℃、3.0 MPa、质量空速1.02 h^-1、氢烃体积比1 000的条件下,100 h内混合烃的转化率均在99%以上,稳定的裂化反应选择性在95%以上。邻二甲苯发生加氢裂化及异构、歧化反应,酸性强的HZSM-5裂化产物收率高,裂化产物分布与混合烃的基本相同。稳定的邻二甲苯裂化反应选择性小于10%。

The hydrocracking of C6-8mixed chain hydrocarbons（mixed hydrocarbons） and o-xylene over HZSM-5 zeolites with different acidity was studied in a fixed-bed down-flow reactor,and the effects of reaction parameters such as temperature,WHSV and H2/CH volume ratio were investigated after the catalyst reached stable performance.Hydrocracking of mixed hydrocarbons was accompanied by aromatization over HZSM-5 zeolite.The hydrocracking was the main reaction with catalyst of weak acid sites,and the hydrocracking products were main normal alkanes,while both methane and isoalkane were pretty low.However,with HZSM-5 zeolite of strong acid sites,the main reaction was aromatization at the beginning.After a certain time,a stable catalytic performance was reached,presenting similar product selectivity to that of weak acidic HZSM-5.The hydrocracking of mixed hydrocarbons displayed obvious temperature effect,while both the WHSV and H2/CH volume ratio had a small effect.At 380 ℃,3.0MPa,WHSV of 1.02 h-1 and H2/CH volume ratio of 1 000,the conversion of mixed hydrocarbons kept above 99% within 100 h,and the stable hydrocracking selectivity was above 95%.o-Xylene hydroconversion was found to be a linear combination of three reactions： hydrocracking,isomerization and disproportionation.Over the strong acidic HZSM-5,the yield of hydrocracking products was higher than that of the weak acidic HZSM-5,and over both HZSM-5 the hydrocracking product distribution was similar to that of mixed hydrocarbon hydrocracking.At 380 ℃,3.0 MPa,WHSV of 1.3 h-1 and H2/CH volume ratio of 1 000,the stable hydrocracking selectivity was less than 10% for o-xylene hydroconversion.