HZSM-5分子筛择形功能优化及其对甲苯甲醇烷基化性能的研究

发布时间：2018-02-13 08:28

本文关键词： HZSM-5 甲苯甲醇烷基化 MgO 络合核壳结构　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：对二甲苯是生产对苯二甲酸的重要化工原料,其下游产品聚对苯二甲酸乙二醇酯(PET)在聚酯产品生产中占有重量级的地位。对二甲苯的合成方法有多种,其中HZSM-5分子筛催化的甲苯甲醇烷基化反应工艺是最具竞争力的生产技术。相比于其它类型分子筛催化剂体系,HZSM-5分子筛催化剂不仅具有较高的催化活性,同时还具有良好的择形选择性。研究结果表明:通过对HZSM-5分子筛进行表面修饰和功能化,可以显著提高催化剂的性能,特别是择形选择性。近期,人们仍在继续探索更加有效的后处理方法,以期研制出性能更加优异的甲苯甲醇烷基化催化剂。本论文以HZSM-5分子筛为母体,分别采用两步浸渍法和阳离子表面活性剂法等方法制备了MgO修饰的ZSM-5催化剂和具有核壳结构的MgO/ZSM-5@nSiO_2催化剂,并考察了催化剂上甲苯甲醇烷基化反应的催化性能。另外,采用XRD、SEM、TPD、N2物理吸附及TG-DTA等表征手段研究了改性后催化剂的物理化学性质,探讨了影响催化剂活性和择形选择性的主要因素。论文的主要研究内容和结果概述如下:以乙酰乙酸乙酯为络合剂,硝酸镁为镁源,采用络合浸渍(CI)和普通浸渍(GI)两步法制备了MgO修饰的ZSM-5分子筛催化剂。通过调节MgO的负载量及络合剂用量等参数,可以制备出具有较高对二甲苯选择性的催化剂体系。在反应温度为520?C,质量空速为2 h-1,甲苯甲醇摩尔比为2的条件下,3.0%Mg(GI)/15%Mg(CI)/ZSM-5催化剂上甲苯的转化率为15.5%,对二甲苯的选择性达到96.1%,性能明显优于普通浸渍法制备的MgO负载的ZSM-5催化剂。各种表征结果证实,采用两步法改性处理ZSM-5分子筛能够使大量的MgO分布在分子筛的外表面,有效地覆盖了外表面的酸性位点;同时少量进入到孔道内的镁离子对分子筛的孔径大小起到一定的调节作用,从而使催化剂在保持较高催化活性的前提下,显示出良好的对位选择性。以TEOS为硅源,采用阳离子表面活性剂法改性处理HZSM-5分子筛,制备出介孔氧化硅包覆的核壳结构ZSM-5分子筛,再通过浸渍法引入适量MgO得到了一系列MgO/ZSM-5@SiO_2催化剂。在优化的反应条件下,组成为20%MgO/ZSM-5@0.75SiO_2的催化剂上甲苯的转化率为17.7%,对二甲苯的选择性为93.7%,对二甲苯的产率达到16.1%。各种表征结果表明:核壳外部的氧化硅层中的介孔孔道与核壳内部的HZSM-5的孔道有很好的连通性,氧化硅层覆盖了HZSM-5分子筛外表面的酸性位点,而引入的镁离子则使分子筛的孔径略微缩小。这些特征使MgO修饰的核壳结构的ZSM-5分子筛催化剂对甲苯-甲醇烷基化反应表现出较高的催化活性和对位选择性。
[Abstract]:P-xylene is an important chemical raw material for the production of terephthalic acid, and its downstream product, Poly (ethylene terephthalate) (PET), occupies a heavy position in the production of polyester products. The alkylation of toluene and methanol catalyzed by HZSM-5 molecular sieve is the most competitive technology. The results show that the surface modification and functionalization of HZSM-5 molecular sieve can significantly improve the performance of the catalyst, especially the shape selectivity. People continue to explore more effective post-treatment methods for the preparation of a more excellent catalyst for toluene and methanol alkylation. In this paper, HZSM-5 molecular sieve was used as the parent. MgO modified ZSM-5 catalysts and core-shell MgO/ZSM-5@nSiO_2 catalysts were prepared by two-step impregnation and cationic surfactant methods, respectively. The catalytic properties of toluene and methanol alkylation over the catalysts were investigated. The physical and chemical properties of the modified catalyst were studied by means of physical adsorption and TG-DTA. The main factors affecting catalyst activity and shape selectivity were discussed. The main research contents and results were summarized as follows: ethyl acetoacetate was used as complexing agent and magnesium nitrate as magnesium source. The MgO modified ZSM-5 molecular sieve catalyst was prepared by two step method of complex impregnation (CI) and ordinary impregnation (GI). By adjusting the loading amount of MgO and the amount of complexing agent, etc. The catalyst system with high selectivity for p-xylene can be prepared. The conversion of toluene was 15.5and the selectivity of p-xylene was 96.1wt. The selectivity of p-xylene on the catalyst was 15.5when the mass space velocity was 2h-1, and the molar ratio of toluene to methanol was 2. The ZSM-5 catalyst prepared by ordinary impregnation method was obviously superior to the ZSM-5 catalyst supported on MgO by ordinary impregnation method. All kinds of characterization results showed that the conversion of toluene on the catalyst was 15.5and the selectivity of p-xylene was 96.1xylene, and its performance was obviously better than that of the ZSM-5 catalyst prepared by ordinary impregnation method. Using two-step modification to treat ZSM-5 molecular sieve can make a large number of MgO distribute on the outer surface of the molecular sieve and effectively cover the acidic sites on the outer surface. At the same time, a small amount of magnesium ions entering into the pore channel can regulate the pore size of molecular sieve to a certain extent, so that the catalyst exhibits good para-site selectivity on the premise of keeping high catalytic activity. TEOS is used as the silicon source. HZSM-5 molecular sieve was modified by cationic surfactant method to prepare core-shell structure ZSM-5 molecular sieve coated with mesoporous silica. A series of MgO/ZSM-5@SiO_2 catalysts were obtained by impregnation with a suitable amount of MgO. The conversion of toluene, selectivity of p-xylene and yield of p-xylene on the catalyst composed of 20 MgO / ZSM-50.75SiO _ 2 are 17.7, 93.7and 16.1.The characterization results show that the mesoporous channels in the silica layer outside the core-shell and the HZSM-5 pores in the core-shell are obtained. Tao has good connectivity, The silica layer covers the acidic sites on the outer surface of the HZSM-5 molecular sieve. The pore size of molecular sieve was slightly reduced by the introduction of magnesium ion, which made the MgO modified core-shell structure ZSM-5 molecular sieve catalyst exhibit higher catalytic activity and para-selectivity for toluene methanol alkylation.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ241.13

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