碳八芳烃异构化分子筛研究进展

Reasearch Progress of Molecular Sieves for C_(8) Aromatic Isomerization

综述了分子筛材料的孔结构、酸性、形貌对二甲苯异构化、乙苯脱乙基、乙苯异构化反应的影响规律。微孔孔道中反应中间体形成受限,且二甲苯异构体分子的扩散差异导致对二甲苯选择性的差别;具有三维十元环微孔孔道的分子筛,如ZSM-5,表现出良好的乙苯脱烷基反应性能;而具有十二元环微孔孔道的MOR分子筛,以及部分具备孔口催化作用的一维十元环分子筛有较高的乙苯异构化反应选择性;酸类型、酸强度和酸量的调变优化有利于提高二甲苯异构化和乙苯脱烷基反应性能;通过分子筛形貌控制,可对酸性位点在外表面或微孔孔道中的分布、各维度微孔孔道的传质进行精细调控,从而赋予不同形貌的分子筛以独特的反应性能;采用分子筛膜材料可实现二甲苯异构化反应-分离耦合,使对二甲苯选择性大幅提高,但较低的反应活性和对二甲苯通量限制了其在该领域的工业应用。

The paper reviews the influences of pore structure,acidity,and morphology of the molecular sieve materials on xylene isomerization,ethylbenzene dealkylation,and ethylbenzene isomerization reactions.The formation of reaction intermediates are limited in microporous channels,and the differences in diffusion of xylene isomer molecules lead to different selectivity towards xylene.The molecular sieves of three-dimensional 10 membered-ring(MR)micropores,e.g.,ZSM-5,exhibit good performance in ethylbenzene dealkylation reaction.MOR molecular sieves of 12 MR micropores and those of one-dimensional 10 MR micropores with pore-mouth catalysis have high selectivity for ethylbenzene isomerization reaction.The optimization and adjustment of acid type,acid strength,and acid content is beneficial to improving the performance of the xylene isomerization and ethylbenzene dealkylation reactions.The distribution of acidic sites on the outer surface or micropores and mass transfer in micropores and channels of various dimensions can be precisely regulated by morphology control of molecular sieves,thus endowing the molecular sieves of different morphologies with unique reaction performance.The application of molecular sieve membrane materials allows for the coupling of xylene isomerization reaction and separation,and greatly improves the selectivity of para xylene;however,the low reaction activity and para xylene flux limit its industrial application in this field.