多级孔Silicalite-1分子筛的制备及气体吸附分离研究

发布时间：2018-05-01 23:02

本文选题：分子筛 + Silicalite-1　；参考：《太原理工大学》2017年硕士论文

【摘要】：分子筛是一类由四面体初级结构构成的具有规则孔道结构的笼型无机材料,因其具有有序规则的孔结构、酸碱性位、较高的水热稳定性以及廉价易生产等特性,被广泛应用于催化、吸附、分离、离子交换和主客体组装等化工领域。MFI型分子筛属于分子筛中应用最广泛的一类,近些年的研究表明,其不含铝的纯硅分子筛Silicalite-1对CH_4、N_2、O2、CO_2、C_2H_6等小分子气体具有很好的吸附效果,对于CH_4/N_2混合气的吸附选择性高于大多数普通吸附剂。随着工业生产要求的提高以及科学的发展,对于分子筛的改性手段越来越多,其中多级孔结构的分子筛是很重要的一种。多级孔分子筛的出现,解决了困扰催化多年的积碳、积大分子、催化剂效率低、扩散阻力大等问题。然而多级孔分子筛却一直没有在吸附分离领域得到应用,最主要的原因是,相比于微孔结构,多级孔结构表面积降低、微孔减少,这些直接导致多级孔分子筛对气体的吸附量和吸附选择性降低,这完全违背了一个吸附剂该有的特点,因此多级孔结构在吸附分离上的研究很少,并且也很少有研究者试图去寻找或者合成一种既不会影响吸附量和吸附选择性又可以体现多级孔结构作用的分子筛材料。基于以上两点,本文探索了以晶种法快速合成多级孔Silicalite-1分子筛和微孔Silicalite-1分子筛的方法,并利用XRD、SEM、TEM、77K氮气吸附等表征分析手段对样品的物相、形貌、孔结构进行了分析,然后对多级孔Silicalite-1分子筛和微孔Silicalite-1分子筛分别进行了CH_4/N_2/CO_2/C_2H_6的吸附分离测试,研究多级孔结构在吸附分离中的作用以及验证本文合成出的多级孔silicalite-1分子筛是否既不会影响吸附量和吸附选择性又能体现多级孔结构性能。主要研究内容和结论有以下几方面:第一,在热水条件下,以硅溶胶为硅源,探索以晶种法快速合成silicalite-1分子筛,改变其中关键反应物的添加量,最终得产生微孔silicalite-1的最佳反应物比例为1:0.1:0.1:0.15:50的二氧化硅/乙胺/四丙基溴化铵(tpabr)/氢氧化钠/蒸馏水以及质量百分数为10%sio2的晶种(二氧化硅来自于硅溶胶),合成介孔silicalite-1的最佳反应物比例只需在微孔的基础上加入0.3的氟化钾,两种孔型silicalite-1的反应温度和反应时间均为453k和20小时。与常规合成方法相比,该方法大大缩短了反应时间。基于得到的两种孔型silicalite-1,分别对其进行ch4、n2、co2、c2h6四种气体的单气吸附测试,测试结果为微孔silicalite-1具有较大的ch4、n2、co2、c2h6吸附量和较高的ch4/n2、co2/n2、co2/ch4、c2h6/ch4吸附选择性,虽然介孔silicalite-1的各气体吸附量较低一些,但是其对co2/ch4、co2/n2、c2h6/ch4的吸附选择性有所提高,对ch4/n2的吸附选择性与微孔silicalite-1的基本一致。第二,基于探索得的快速合成silicalite-1的方法,改变硅源,得以气相二氧化硅为硅源的微孔和多级孔silicalite-1分子筛,不同于以硅溶胶为硅源的微孔和介孔silicalite-1分子筛的是,气相二氧化硅得到的微孔silicalite-1和多级孔silicalite-1的表面积基本相同,并且两者对ch4、n2、co2、c2h6的吸附量以及对ch4/n2、co2/ch4、co2/n2、c2h6/ch4的吸附选择性也相同。基于以上分析,分别对两者进行ch4/n2、co2/ch4、co2/n2、c2h6/ch4四组混合气的穿透分离实验,结果表明,多级孔Silicalite-1的穿透时间均短于微孔的,并且多级孔Silicalite-1和微孔Silicalite-1对于CH_4/N_2、C_2H_6/CH_4的保留时间是一样的。进一步得出结论,当混合气中分子动力学直径较小的气体分子为弱吸附质、分子动力学直径较大的气体分子为强吸附质(穿透实验中弱吸附质先穿透出来,强吸附质后穿透出来),用多级孔Silicalite-1分离它们的时候,穿透时间变短并且保留时间不变,与微孔Silicalite-1相比,缩短了变压吸附循环时间,提高了变压吸附效率,达到了更好的分离效果。
[Abstract]:Molecular sieve is a kind of cage type inorganic material with regular pore structure consisting of the primary structure of tetrahedron. Because of its orderly and regular pore structure, acid base position, high hydrothermal stability and low cost and easy production, it is widely used in the chemical fields of.MFI type, such as catalysis, adsorption, separation, ion exchange and host and guest assembly. Sieves are one of the most widely used types of molecular sieves. In recent years, it has been shown that the pure silicon molecular sieve Silicalite-1 without aluminum has a good adsorption effect on small molecular gases such as CH_4, N_2, O2, CO_2, C_2H_6 and so on. The adsorption selectivity for CH_4/N_2 mixture is higher than that of most ordinary adsorbents. There are more and more methods for molecular sieve modification, among which multistage porous molecular sieves are very important. The emergence of multilevel porous molecular sieves has solved the problems of carbon deposition, large molecules, low catalyst efficiency and large diffusion resistance, which have plagued the catalysis for many years. However, multistage molecular sieves have not been obtained in the field of adsorption separation. The main reason is that, compared to the microporous structure, the surface area of the multistage pore structure is reduced and the micropores are reduced, which directly lead to the reduction of the adsorption and adsorption of gas, which is completely contrary to the characteristics of an adsorbent. Therefore, there are few studies on the adsorption and separation of the multistage pore structure, and there are few of them. The researchers are trying to find or synthesize a molecular sieve material that does not affect the adsorption capacity and the adsorption selectivity and can reflect the multilevel pore structure. Based on the above two points, the rapid synthesis of multistage porous Silicalite-1 molecular sieves and microporous Silicalite-1 sub sieves by crystal seed method and the use of XRD, SEM, TEM, 77K nitrogen gas are explored. The phase, morphology and pore structure of the samples were analyzed by means of adsorption and other characterization methods. Then the adsorption separation and separation of multistage Silicalite-1 molecular sieves and microporous Silicalite-1 molecular sieves were carried out respectively. The role of multistage pore structure in the adsorption separation and the verification of the multistage hole silicali in this paper were verified. The main research contents and conclusions are as follows: first, the rapid synthesis of silicalite-1 molecular sieves using silica sol as the silicon source under hot water conditions is to make a rapid synthesis of the key reactants by using the silica sol as the silicon source, and the final production of the TE-1 molecular sieve has to be produced. The optimum reactant ratio of hole silicalite-1 is 1:0.1:0.1:0.15:50, silica / ethylamine / four propyl ammonium bromide (TPABr) / sodium hydroxide / distilled water and the mass percentage of 10%sio2 (silica from silica sol). The optimum reactant ratio for mesoporous silicalite-1 is only to add 0.3 potassium fluoride on the basis of micropores. The reaction temperature and reaction time of the two pass silicalite-1 are both 453k and 20 hours. Compared with the conventional synthesis method, the method greatly shortens the reaction time. Based on the obtained two kinds of pore type silicalite-1, the single gas adsorption tests of four kinds of gas, CH4, N2, CO2, C2H6, are carried out respectively. The test result is that the microporous silicalite-1 has a larger ch. 4, N2, CO2, C2H6 adsorption capacity and higher ch4/n2, co2/n2, co2/ch4, c2h6/ch4 adsorption selectivity, although the adsorption capacity of mesoporous silicalite-1 is lower, but its adsorption selectivity to co2/ch4, co2/n2, c2h6/ch4 is improved, and the adsorption selectivity for ch4/n2 is basically consistent with that of micropores. Second, based on the exploration fast The method of synthesizing silicalite-1 is to change the silicon source, the microporous and multistage pore silicalite-1 molecular sieves of silicon dioxide as the silicon source, different from the microporous and mesoporous silicalite-1 molecular sieves with silicon sol as the silicon source, and the surface area of the microporous silicalite-1 and the multistage pore silicalite-1 obtained by the gas phase silica is basically the same, and both of them have the same surface area. The adsorption capacity of CH4, N2, CO2, C2H6 and the adsorption selectivity for ch4/n2, co2/ch4, co2/n2, c2h6/ch4 are also the same. Based on the above analysis, the penetration separation experiments of the four groups of ch4/n2, co2/ch4, co2/n2 and c2h6/ch4 are carried out respectively. The results show that the penetration time of the multistage holes is shorter than that of the micropores, and the multistage holes are used. The retention time of CH_4/N_2 and C_2H_6/CH_4 is the same as the microporous Silicalite-1. Further conclusion is that when the gas molecules with smaller molecular dynamics diameter in the mixture are weak adsorbate, the molecular dynamics of the gas molecules with larger diameter are strong adsorbate (penetrating the weak adsorbate in the penetration experiment, and penetrating after the strong adsorbate). When they are separated with multistage holes Silicalite-1, the penetration time is shorter and the retention time is constant. Compared with the microporous Silicalite-1, the pressure swing adsorption cycle time is shortened, the pressure swing adsorption efficiency is improved, and the better separation effect is achieved.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ424.25

【参考文献】