改性纳米HZSM-5上对、邻二甲苯异构化反应性能的研究

STUDY ON ISOMERIZATION OF o-XYLENE AND p-XYLENE OVER MODIFIED NANOSCALE HZSM-5

采用等体积浸渍和化学反应沉积法对纳米HZSM-5外表面进行硅酯改性,并采用SEM、XRD及改进的Hammett指示剂法对硅酯改性纳米HZSM-5的形貌、结构和酸性位进行表征,也探讨了硅酯改性纳米HZSM-5催化对对二甲苯和邻二甲苯的异构化反应性能。结果表明,硅酯改性降低了HZSM-5的相对结晶度和酸性位的浓度。在温度为400℃、质量空速为2.5 h-1、常压的反应条件下,邻二甲苯仅仅在硅酯改性HZSM-5外表面的酸性位上发生异构化反应,而不是在分子筛的孔道内;对二甲苯异构化反应主要发生在硅酯改性HZSM-5催化剂的外表面。

By using the methods of equal volume-impregnations and chemical reaction deposition, the external surface of nanosclae HZSM-5 was modified. The characterization of morphology, crystallinity and acid sites on the nanoscale HZSM-5 were carried out by SEM, XRD and modified Hammett indicators. The performance of the catalytic isomerization of p-xylene and o-xylene over silicon modified nanoscale HZSM-5 was investigated. The research results showed that the relative crystallinity and the concentration of acid sites of nanoscale HZSM-5 were decreased by silicon modification. The isomerization reaction of o-xylene over modified naonscale HZSM-5 only occurred on its external acid sites and not in its internal channel under the reaction conditions of 480~C, atmospheric pressure and MHSV 2. 5 h 1. The isomerization reaction of p-xylene was mainly carried out on the external surface of modified HZSM-5.