Study On Optimization And Simulation Of Ionic Liquid Model For Low-Concentration CO₂ Capture System

With the vigorous development of the aerospace and submarine fields,the development of emerging technologies to capture low-concentration CO₂in manned confined spaces such as space station cockpits and submarine cockpits is essential to maintain the health and safety of cabin personnel.As a new type of green material,ionic liquid（IL）has good performance in CO₂adsorption and separation.Therefore,an attempt has been made to apply IL-based adsorption technology to a low-concentration CO₂capture system,but the related research on its micro-mechanism is still not in-depth.In this paper,molecular dynamics method is used to calculate and analyze the microscopic interaction mechanism of ionic liquid and CO₂,and optimize the ionic liquid-polyimide hybrid membrane model.In this work,easily available,biodegradable amino acid ionic liquids（AAILs）with great potential for CO₂absorption in the manned closed space such as spacecraft,submarines and other manned devices are used as the basic material.Molecular dynamics simulation and ab initio calculation methods were performed for 12 AAILs([P₄₄₄₄][X]and[P₆₆₆₁₄][X],[X]=X=[Gly]^-,[Im]^-,[Pro]^-,[Suc]^-,[Lys]^-,[Asp]^2-),the dynamic characteristics and the internal mechanism of AAILs to improve CO₂absorption capacity were clarified.Based on the analysis of structural and the interaction energy including van der Waals and electrostatic interaction,revealed the fact that the anion of ionic liquids dominates the interaction between CO₂and AAILs.At the same time,the CO₂absorption capacity of AAILs increases in the order:[Asp]^2-<[Suc]^-<[Lys]^-<[Pro]^-<[Im]^-<[Gly]^-.Meanwhile,the synergistic absorption of CO₂by multiple-site of amino and carboxyl groups in anion was proved by DFT calculation.These findings show that the anion of AAILs can be an effective factor to regulate the CO₂absorption capacity.Based on the previous calculations results,this paper selected two ILs with excellent CO₂adsorption performance,mixed them with high-performance material polyimide（PI）,and established a PI-IL hybrid membrane model based on ILs to further explore the separation performance of the PI-IL mixed membrane for CO₂/N₂（CO₂/CH₄）binary gas.By changing the concentration of ILs,the effect of ILs on the gas selection performance and the pore screening performance of the mixed membrane was verified.The simulation results of density and glass transition temperature are compared with experimental results to verify the rationality of the model.Afterwards,the radial distribution function,interaction energy,number density,self-diffusion coefficient and other properties are calculated to analyze the microscopic mechanism and separation performance of the composite membrane separation mechanism,and further clarify the influence of ILs on the sieve effect of the membrane pores.