HZSM-5分子筛上C_(6～8)混合链烃和邻二甲苯的加氢裂化

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%。

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

The hydrocracking of C_6~8 mixed 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 1.02h^-1 and H₂/CH volume ratio of 1000, the conversion of mixed hydrocarbons kept above 99% within 100h, 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℃, 3.0MPa, WHSV of 1.3h^-1 and H₂/CH volume ratio of 1000, the stable hydrocracking selectivity was less than 10% for o-xylene hydroconversion.