具有微孔和介孔多级孔道复合分子筛的合成及表征

发布时间：2018-02-16 15:46

本文关键词： 多级孔道复合分子筛合成包埋结构核壳结构甲醇转化　出处：《太原理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：多级孔道复合分子筛可利用微孔和介孔结构分子筛各自的优势,改善单一分子筛形貌结构、酸性分布,并协同二者孔道结构,在催化反应中表现不同的催化性能。本论文对EU-1晶种进行酸改性处理,采用两步水热晶化合成具有包埋结构特征ZSM-5/EU-1复合分子筛,根据分析可知,酸处理影响了晶种骨架结构及表面酸性,促进ZSM-5分子筛在EU-1团聚体内成核生长。该复合分子筛为同时具有微孔和介孔结构多级孔道复合分子筛,其微孔孔径为0.82nm,介孔孔径分布在1.42nm、2.20nm处,且复合以后强酸量有所增强。在甲醇转化反应中,包埋结构复合分子筛的甲醇转化率提高到98.16%,二甲苯在芳香烃产物分布中的比例达到64.65%,也进一步提升了对二甲苯在二甲苯产物中的分布。核壳结构复合分子筛因其特殊核层、壳层构造,具有较合理的酸分布和孔道结构性质,在催化反应中表现良好的催化性能。本文在添加适量柠檬酸的条件下采用双模板剂一步法,一次晶化合成高结晶度ZSM-5/EU-1核壳共生复合分子筛,通过表征可知,EU-1分子筛沿ZSM-5分子筛表面缺陷处外延生长,核壳分子筛的强酸量比单一分子筛相对提高,且核壳分子筛为融合度较高的微孔-介孔多级孔道结构,其微孔孔径达到0.94nm,明显高于包埋结构复合分子筛,在1.24nm及1.84nm处出现介孔结构。通过对合成工艺分析,获得合成核壳共生结构的最佳条件:n(citrate)/n(Al2O3)=0.8~1.2,pH为10.5~11.5,晶化时间为72~96h。推测核壳分子筛可能的生长过程为:先合成ZSM-5晶体,随着时间的延长及HMBr2的导向作用,EU-1分子筛的结构单元形成并在ZSM-5表面缺陷外延生长,从而形成ZSM-5/EU-1核壳共生复合分子筛。在甲醇转化制对二甲苯催化反应中,核壳分子筛催化产物的选择性明显高于机械复合物,而且随着柠檬酸浓度的增大,催化产物中对二甲苯的选择性也在增强。Beta分子筛由于其十二元环的特殊孔道结构及较强的酸性,具有较高的甲醇转化率,结合EU-1与Beta沸石结构相似性,合成EU-1/β多级孔道复合分子筛,可进一步提升甲醇转化率并应用于一些大分子反应。本论文采用预置晶种法,在碱性体系中,以EU-1为晶种,四乙基氢氧化铵为模板剂,水热合成EU-1/β复合分子筛。通过分析可知,Beta分子筛粘附于EU-1分子筛表面生长,复合分子筛同时具有微孔-介孔多级孔道,其微孔孔径约为0.82nm,介孔孔径分布在2.19nm左右,其酸性、酸量明显高于机械混合物,最佳合成条件为:EU-1晶种添加量10%~20%,碱硅比n(OH-)/n(SiO2)=0.24~0.48,模板剂量n(TEAOH)/n(SiO2)=0.55~0.68,晶化时间72h~96h。
[Abstract]:The advantages of micropore and mesoporous molecular sieve can be utilized to improve the morphology and acid distribution of single molecular sieve. In this paper, EU-1 seeds were modified with acid, and ZSM-5/EU-1 composite molecular sieves with entrapped structure were synthesized by two steps hydrothermal crystallization. Acid treatment affected the crystal skeleton structure and surface acidity, and promoted the nucleation and growth of ZSM-5 molecular sieve in EU-1 agglomeration. The micropore size is 0.82 nm and the mesoporous pore size is 1.42 nm and 2.20 nm. The methanol conversion of the entrapped molecular sieve increased to 98.16 and the proportion of xylene in the distribution of aromatic hydrocarbon products reached 64.65, which further enhanced the distribution of p-xylene in xylene products. The structure of the shell layer has reasonable acid distribution and pore structure, and it has good catalytic performance in the catalytic reaction. In this paper, the double template method is used under the condition of adding proper amount of citric acid. High crystallinity ZSM-5/EU-1 core-shell symbiotic composite molecular sieve was synthesized by single crystallization. The epitaxial growth of ZSM-5/EU-1 core-shell complex molecular sieve along the defects of ZSM-5 molecular sieve was obtained by characterization. The strong acid content of core-shell molecular sieve was higher than that of single molecular sieve. The core-shell molecular sieve is a microporous and mesoporous multilevel pore structure with a high degree of fusion. The micropore pore size of the core-shell molecular sieve is 0.94nm, which is obviously higher than that of the embedded composite molecular sieve. The mesoporous structure appears at 1.24nm and 1.84nm. The optimum conditions for the synthesis of core-shell symbiotic structure were obtained. The pH value and crystallization time of the core-shell core-shell molecular sieve were as follows: ZSM-5 crystal was synthesized firstly, and the pH value was 10.5 ~ 11.5H and the crystallization time was 72U / 96h. the possible growth process of the core-shell molecular sieve was as follows: first, the ZSM-5 crystal was synthesized. With the prolongation of time and the orientation of HMBr2, the structure unit of ZSM-5/EU-1 EU-1 molecular sieve was formed and epitaxially grown on the surface of ZSM-5, resulting in the formation of ZSM-5/EU-1 core-shell symbiotic composite molecular sieve. The selectivity of the catalytic products of core-shell molecular sieves was obviously higher than that of mechanical complexes, and with the increase of citric acid concentration, The selectivity of p-xylene in the catalytic product is also enhanced. Beta zeolite has higher methanol conversion due to its special pore structure and strong acidity of 12 member ring. The structure of EU-1 and Beta zeolite is similar to that of Beta zeolite. The synthesis of EU-1 / 尾 multilevel pore composite molecular sieve can further enhance methanol conversion and be used in some macromolecular reactions. In this paper, in alkaline system, EU-1 was used as seed and tetraethyl ammonium hydroxide as template. EU-1 / 尾 composite molecular sieve was synthesized by hydrothermal synthesis. It was found that the composite molecular sieve was grown on the surface of EU-1 molecular sieve. The composite molecular sieve also had micropore and mesoporous multilevel channels, its micropore pore size was about 0.82 nm, the mesoporous pore size distribution was about 2.19 nm, and its acidity. The optimum synthesis conditions are as follows: 10% EU-1 seed addition 10 ~ 20%, the ratio of alkali to silicon 0.24 ~ 0.48, the template dosage n ~ (2 +) ~ (-) ~ (-) ~ ((1)) ~ 0.55 ~ 0.68, and the crystallization time 72 h ~ 96 h ~ (-1). The optimum synthesis conditions are as follows: (1) the content of acid is significantly higher than that of the mechanical mixture, and the optimum conditions are as follows: (1) 10% EU-1 seed addition.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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