Study On Preparation And Properties Of Mesoporous Sodalite

As one of the most important components of porous materials,zeolites molecule sieves have unique advantages such as its regular structure of microporous and a large number of active sites in the framework,which make it has good application properties in the aspects such as catalys is,adsorption and separation,zeolites molecule sieves play an important role in the fields of energy and chemical engineering and environmental protection.However,the smaller pore size and longer pores hinder the diffus ion of the reactant molecules,in particular,catalyzing reactions in which some of the reactants are macromolecules will not only reduce the catalytic efficiency o f the catalyst,but also cause the occurrence of carbon deposition affects the catalytic performance of the catalyst and even deactivates it.Traditional mesoporous materials,despite their large pore size,are less hydrothermally stable than zeolite molecular s ieves and lack active sites for catalytic reactions.The introduction of mesopores into the framework of conventional zeolite molecular sieves combines the advantages of zeolite molecular s ieves with mesoporous materials,which not only solves the lack of mass transfer of zeolite molecular sieves,but also retains its structural advantages.As a high-aluminum content zeolite molecular sieve,sodalite has an abundant basic site in its structure,but it cannot be used as a base catalyst because of its extremely small pore size.In order to solve this problem,the organosiloxanes KH560-660 and KH560-540 were used as templating agents to introduce the mesopore into the framework structure of sodalite by hydrothermal synthesis,the mesoporous sodalite with a large surface area and pore volume and a concentrated pore size distribution was successfully prepared.The structure and morphology of mesoporous sodalite were analyzed and characterized by XRD,nitrogen adsorption-desorption,scanning electron microscopy and transmission electron microscopy.The ion exchange performance,hydrothermal stability and base catalytic performance were investigated and studied.The following conclusions have been drawn:（1）The best addition of the templating agent is to add it to the silicon source,while other feeding methods have a greater impact on the process of sodalite crystallization.In the process of synthesizing mesoporous sodalite using organosiloxane KH560-660 as templating agent,90℃is the optimum crystallization temperature for the synthes is of mesoporous sodalite;36 hours is the optimal crystallization time;H₂O/Na₂O=12.49 is the optimum ratio of alkali addition in the system.When the addition amount of KH560-660 is 6 mL,the pore structure parameters of the synthesized sample are the largest,and the surface area and pore volume reach 179.7 m²g^-1 and 0.21 cm³g^-1 respectively.The pore size distribution of the samples was mainly concentrated between 3-6nm,especially at 5 nm.The synthesized samples were spheres with a size range of 300-700 nm.（2）In order to improve the regularity of the mesoporous sodalite samples synthesized and reduce the effect of the nanocrystallization caused by the addition of the templating agent,an appropriate amount of inorganic salt was added to the synthesis system.It was found that the addition of fluoride（NaF,KF,NH₄F）is unfavorable for the synthes is of mesoporous sodalite.However,the addition of chloride（NaCl,KCl,NH₄Cl）to the synthesis system not only improved the relative crystallinity of the sample to 85.87%,but also improved the pore structure parameters of the sample,the maximum surface area was295.47 m²g^-1,the pore size distribution is more concentrated,and different inorganic salts will have different effects on the morphology of the sample.（3）Using the organosiloxane KH560-540 with one more methoxy group than KH560-660 as the templating agent,it was found that the best crystallization temperature is 90℃,the best crystallization time for mesoporous sodalite synthesis in this system is 24 hours,and the best ratio of the alkali addition is H₂O/Na₂O=13.73;when 6 m L of 51.5%KH560-540 methanol solution was added into the system,the pore structure parameters of the mesoporous sodalite synthes ized were significantly increased compared to samples synthesized with KH560-660 as the templating agent,the highest surface area and largest pore volume are 198.02 m²g^-1 and 0.29 cm³g^-1,respectively,and the synthesized sample has good regularity;the pore size distribution of the samples was concentrated between 3-7 nm;the particle size of the synthes ized samples was distributed in the range of 200-500 nm,and the morphology was a sphere with a rough surface.（4）After the addition of NaCl,KCl,and NH₄Cl in the synthesis system,the regularity of the synthesized samples was further improved,with the highest relative crystallinity being 79.05%.For the pore structure parameters,addition of chloride also increases the surface area and pore volume to some extent,with a maximum specific surface area of 299.50 m²g^-1,and the addition of chloride to the aluminum source is more effective.After adding the chloride,the pore size distribution is more concentrated and the surface of the particles of the sample becomes more rough.（5）The introduction of mesopores resulted in a significant increase in the maximum ion exchange capacity and exchange rate of the sample,the maximum ion exchange capacity of the mesoporous sodalite sample with a surface area of179.7 m²g^-1 reached 44.2 mg/L,which is 7 times that of the traditional sodalite sample.（6）The introduction of mesopores will make the reactants more easily contact with the active s ite of sodalite and increase the convers ion to 95%in the reaction of 1,3-dichloropropanol to prepare epichlorohydrin;The addition of chlorides enhances the hydrothermal stability of the mesoporous sodalite and further increases the conversion and selectivity of the reaction.