几种分子筛催化剂的二甲苯异构化反应性能研究

STUDY ON THE XYLENE ISOMERIZATION PERFORMANCE OF SEVERAL MOLECULAR SIEVE CATALYSTS

合成了几种具有不同孔结构的分子筛,并考察了这些分子筛的孔结构性质、酸性以及在二甲苯异构化反应中的反应性能。结果表明:对于二甲苯异构化反应,催化剂的孔结构和酸性起着重要作用;孔结构决定了反应的类型或方式,孔径过大时会因为发生烷基转移生成重芳烃而导致C8芳烃损失增加,而孔径过小时会因为脱烷基或裂解反应而导致C8芳烃损失提高;催化剂的酸性质与反应活性和选择性密切相关,酸性太强或太弱都会导致C8芳烃损失的增加。因此,反应性能良好的碳八芳烃异构化催化剂必须同时具备适宜的孔结构和酸性。

Several molecular sieves with various pore structures were synthesized. The pore struc ture and acidity of these molecular sieves were characterized by BET and NH3TPD, their catalytic per formance in xylene isomerization was investigated as well. Test results indicate that both the pore struc ture and acidity of catalyst have significant effect on xylene isomerization. The types of reactions hap pened are mostly depended on the pore structure, overlarge pores are favored for transalkylation reac tions to form heavy aromatics, which leads to increase the loss of C8 aromatics, on the other hand, ex treme small pores could also increase the loss of C8 aromatics by cracking or dealkylation reactions. The catalyst activity and selectivity are closely related with the catalyst acidity, unsuitable acidity leads to in crease the loss of C8 aromatics as well. Therefore, catalyst having good reaction performance in xylene isomerization should have appropriate pore structure and acidity simultaneously.