几种分子筛催化剂的二甲苯异构化反应性能研究

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。

2,4-二氨基甲苯和2,6-二氨基甲苯在KY分子筛上的吸附分离

采用静态吸附实验方法从6种分子筛中筛选出KY分子筛作为吸附分离2,4-二氨基甲苯(2,4-TDA)和2,6-二氨基甲苯(2,6-TDA)的吸附剂,选择性系数为1.54。并对2,4-TDA和2,6-TDA的动态吸附进行了研究,结果表明2,4-TDA和2,6-TDA的平衡吸附量均随温度升高而降低。随溶液中2,4-TDA和2,6-TDA质量分数的增大,穿透时间和吸附平衡时间缩短,且平衡吸附量增大。相同条件下2,4-TDA的平衡吸附容量均小于2,6-TDA的平衡吸附容量,KY分子筛对2,6-TDA具有吸附选择性。甲醇作为脱附剂具有良好的脱附效果。研究了KY分子筛对混合TDA的动态吸附分离,可将2,4-TDA质量分数提高到99.3%,将2,6-TDA质量分数提高到99.82%。用KY分子筛进行2,4-TDA和2,6-TDA的吸附分离是可行的。

MgO/HZSM-5中MgO分散状态和催化性能的关系

以硝酸镁、醋酸镁为前身物通过浸渍法制备了不同系列MgO/HZSM5催化剂用XRD、XPS方法研究了MgO在HZSM5上的分散状态用NH3TPD方法考察了催化剂的酸性用常压连续流动微型反应装置考察MgO/HZSM5在甲苯甲醇烷基化反应中的催化性能.发现前身物不同MgO在HZSM5上的分散状态也不同催化剂的活性和选择性与MgO分散状态密切相关.MgO负载量相同时在以硝酸镁为前身物制备的催化剂中MgO在HZSM5内外表面均有分散催化剂的对位选择性较高而活性较低;在以醋酸镁为前身物制备的催化剂中MgO较多分布在HZSM5外表面催化剂的活性较高但选择性较低.使用醋酸镁为前身物通过二次浸渍和高温水汽处理适当改变MgO在分子筛表面的分布并使孔道窄化可在活性降低较少的情况下显著提高催化剂对二甲苯选择性.

Promoting Xylene Production in Benzene Methylation using Hierarchically Porous ZSM-5 Derived from a Modified Dry-gel Route

Methylation of benzene is an alternative low-cost route to produce xylenes, but selectivity to xylene remains low over conventional zeolitic catalysts. In this work, a combined dry-gel-conversion and steam-assisted- crystallization method is used to synthesize hierarchically porous zeolite ZSM-5 with varied Si/AI malar ratios. X-ray diffraction （XRD）, N2 physisorption, NH3-temperature programmed desorption （TPD）, scanning electronic microscopic （SEM） measurement and Fourier transform infrared （FT-IR） are employed to characterize the struc- ture and acidity of both hierarchically porous zeolites and their conventional counterparts. The method is found to be applicable to ZSM-5 with molar ratios of Si/A1 from 20 to 180. The ZSM-5 zeolites are used as catalysts for benzene methylation at 460 ℃ to investigate the effect of additional porosity and Si/A1 ratios. At low Si/AI ratios, the benzene conversions over conventional and hierarchical ZSM-5 are close, and selectivity to toluene is high over hierarchical ZSM-5. It is found that hierarchical porosity markedly enhances the utility of zeolite and the se- lectivity towards xylenes via improved mass transport at higher Si/Al ratios. Under an optimized hierarchical ZSM-5 catalvst, xvlene selectivity reaches 34.9% at a Si/AI ratio of 180.

Synthesis, characteristics of hierarchical EU-1 zeolite for xylene isomerization probe reaction

Introduced a method of synthesizing hierarchical EU-1 zeolite with organosilanes as additive, and studied the influences of following different kinds of organosilanes on the synthesis of hierarchical EU-1 zeolite: γ-glycidoxy propyl trimethoxy silane(GPTMS), N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxyl silane(APAEDMS),and N-(β-aminoethyl)-γ-aminopropyl dimethoxyl(ethyoxyl) silane(TMPED). The hierarchical EU-1 samples were characterized by XRD, SEM, N_2 adsorption, FT-IR and NH_3-TPD to analyze the crystallinity, morphology, surface area, pore size distribution and acidity. The results showed that hierarchical EU-1 zeolites were successfully synthesized; organosilanes have great influence on crystal morphology of EU-1 zeolites; the exterior surface area of hierarchical EU-1 zeolite, which synthesized with organosilanes(APAEDMS) adding into synthesis system, increased by 62.1% and mesopore volume increased by 129.1% compared with conventional EU-1 zeolites, thus can reduce the diffusional restriction markedly in catalytic reaction. The catalytic performance of hierarchical EU-1zeolites were evaluated in m-xylene isomerization on fixed bed reactor. The catalytic data showed that the isomerization activity PX/X of the hierarchical EU-1 zeolites reached around 24.09% in theoretical thermodynamic equilibrium from 23.83%, and the selectivity of C_8 aromatic hydrocarbon increased from 75.16% to 84.87%. The conversion of p-xylene increased from 16.30% to 18.41%.