Preparation And Xenon Adsorption Studies Of Ion-Exchanged Molecular Sieve

Xenon gas plays a critical important role in the fields of industrial production,daily life,basic research and strategic security.Therefore,the efficient enrichment of xenon has attracted the attention by the academia and the industry.Low temperature distillation is a traditional xenon adsorption and separation method,however,high energy consumption and high cost limiting its application.Developing a more efficient and economic separation technology for xenon-krypton gases is a current research hot topic.With the advantages of low energy consumption and flexible application,solid adsorbent is the most promising rare gas capturing method in Xe and Kr separation at room temperature,and the crutial step is to obtain efficient xenon adsorption materials.Molecular sieve,which is the typical solid adsorption material,is widely used in the field of adsorption and separation because of its rich and ordered pores,high stability and good adjustability.However,in the application of trace xenon preferential adsorption,low Xe adsorption capacity or low selectivity is the common problems for most molecular sieves.Ion exchange is one of the most effective means to control the adsorption potential field on the surface of zeolite.After ion-exchange modification,the adsorption performance of zeolite is changed with the variation of its surface properties,such as pore size,pore volume and pore channel,resulting in the improvement of its adsorption capacity and selectivity.In this paper,the synthesis,ion exchange and xenon adsorption properties were studied on three kinds zeolite molecular sieves,including eight membered ring SSZ-13,ten membered ring ZSM-5,and twelve membered ring ETS-10,respectively.And the influence law of Ag ion-exchange to xenon adsorption performance of molecular sieve is explored emphatically.Following three research contents will be carried out:（1）The low-cost synthesis method of zeolite molecular sieve was discussed,and three molecular sieve materials,SSZ-13,ZSM-5,and ETS-10,were prepared successfully.Firstly,the SSZ-13 with good crystallization and perfect homogeneity was synthesized with a large proportion of cheap choline chloride as a mixed template instead of the expensive TMAda OH.The specific surface and the pore volume of SSZ-13 reached to 600 m²/g and 0.24 cc/g at the silicon to aluminum ratio of 25.Secondly,ZSM-5 with different silicon-to-aluminum ratios were synthesized using cheap aluminum sulfate as the aluminum source and N-butane as the template,with specific surface area of 353 m²/g or more,and total pore volume of 0.19 cc/g at a silicon to aluminum ratio of 38.Finally,The ETS-10 was obtained by replacing the expensive and highly corrosive Ti Cl₃ with the cheap Ti O₂ nanoparticles as the titanium source,with specific surface area of 389 m²/g and total pore volume of 0.22 cc/g.（2）The molecular sieve was modified with silver by the liquid-phase ion exchange method.The impacts of molecular sieve type,exchange temperature,reaction time and Ag ion concentration to the structure of molecular sieve were explored.The microstructures of modified materials were analysed by XRD,FTIR,SEM,XRF and BET.The results show that the eight-membered ring SSZ-13 was the most stable molecular sieve after silver ion exchange,with the increment rates of specific surface area and silver loading at 29%and 12%,respectively.The stability of the ten-membered ZSM-5 molecular sieve is slightly worse,the specific surface area is reduced by up to more than 30%after ion exchange,and the silver loading reaches 20%.Meanwhile,the 12-membered ring ETS-10 has the strongest ion exchange capacity with 30%of the silver loading,but the stability of its sturcture is poor under increased exchange numbers and harsh exchange conditions.（3）The adsorption performance of ion-exchanged zeolite molecular sieve was studied by volume adsorption method.The results show that silver ion exchange can intensify the adsorption behavior of the above three zeolite molecular sieves significantly.The equilibrium adsorption capacities of Xe and Kr reached up to 2.27 mmol/g and 1.2 mmol/g,respectively,and the ideal adsorption selectivities of Xe/N₂ and Xe/Ke were 118 and 53,respectively.In addition,the interaction ofΠcomplexation between Ag and Xe becomes more strongly as the pore size of the molecular sieve turns smaller,especially in ZSM-5 and SSZ-13 at xenon adsorption enhancement.Not only the Xe adsorption capacities exceeds 1.7 mmol/g,but also the growth rate of Xe adsorption is greatly accelerated in the low partial pressure zone.The xenon adsorption Henry coefficients of silver modified ZSM-5 and SSZ-13 reached 100mmol/g/bar and 141 mmol/g/bar,respectively,which are higher than the values of previous studies,indicating that they have strong xenon adsorption force and are the preferred materials for the adsorption and capture of trace xenon.