Preparation Of Ionic Liquid Microcapsules And CO₂ Adsorption Properties

The greenhouse effect caused by CO₂ has aggravated global environmental problems and has attracted more and more attention.CO₂ capture and storage（CCS）is considered to be one of the most effective technology for carbon emission reduction.The adsorbent is critical to improve CO₂ adsorption performance.In this paper,1-butyl-3-methylimidazolium hexafluorophosphate（[BMIM]PF₆）,1-butyl-3-methylimidazolium diimide salt（[BMIM]SUC）,1-butyl-3-methylimidazolium diaminoacetate（[BMIM]₂IDA）,butyl quaternary diimide salt([P₄₄₄₃]SUC)and butyl quaternary iminodiacetic acid salt([P₄₄₄₃]₂IDA)were synthesized by a two-step method.Ionic liquid microcapsule materials were prepared by sol-gel method,chemical precipitation method,solvent evaporation method and suspension polymerization method using silica,polysulfone and polystyrene as shell materials respectively.Then they were characterized by FTIR,TG and SEM.The effects of different experimental conditions on microcapsule structure,CO₂ adsorption performance,CO₂/N₂ selectivity and CO₂ adsorption cycleability were studied.The kinetic adsorption and diffusion behavior of CO₂ on ionic liquid microcapsules was studied.The main conclusions are as follows:（1）FTIR analysis showed that the ionic liquid and its microcapsule materials were successfully synthesized.The results of SEM analysis indicated that the samples prepared by the sol-gel method and the chemical precipitation method were micron-scale irregular structures with good particle dispersibility.The samples prepared by the solvent evaporation method have a nano-scale spherical structure and the surface is smooth and compact.The samples prepared by the suspension polymerization method were of micron-scale particle having a spherical structure.The results of TG analysis showed that each sample had good thermal stability for losing most of the ionic liquid after 250°C.The preparation method of ionic liquid microcapsules had a great influence on the content of ionic liquid.The sample prepared by suspension polymerization had the highest ionic liquid content（Max=85wt%）,the sol-gel method is 50-70 wt%,and the solvent evaporation method is only10-20 wt%.（2）As the sample was prepared by the sol-gel method,the ratio of 1:1 for[BMIM]PF₆ and SiO₂ and the surfactant sodium lignin sulfonate accounting for 11%of the total mass of wall material and core material.At 298 K and 0.1 MPa,CO₂adsorption capacity of the imidazolium ionic liquid microcapsules is 2.70 wt%,the CO₂/N₂ adsorption selectivity is 8.40,the cycle performance and CO₂ comprehensive performance is the best.（3）Compared with imidazolium microcapsules,the phosphonium ionic liquid microcapsules have higher CO₂ adsorption properties.When the samples were prepared by sol-gel method with[P₄₄₄₃]SUC and[P₄₄₄₃]₂IDA as core materials,SiO₂as wall material,and sodium lignosulfonate adding 11%,the CO₂ adsorption capacities were 3.4 wt%and 2.91 wt%respectively at 298 K and 0.1 MPa.The selectivity was 9.09 and 8.50,respectively,and there were good CO₂ cycleability.（4）The adsorption curves of CO₂ on ionic liquid microcapsules were fitted by quasi-secondary kinetic model,bangham adsorption rate equation and intraparticle diffusion model.The results showed that the diffusion process is surface diffusion,particle diffusion and pore diffusion work together.The adsorption process is a combination of chemical and physical adsorption.The Fick’s law was used to describe the dynamic diffusion behavior of CO₂ on ionic liquid microcapsules.The CO₂diffusion coefficient of ionic liquid microcapsules is in the range of 10^-910^-8,and it is equivalent to the blank carrier(10^-9 m²/s)and 1² orders of magnitude higher than that of ionic liquid(10^-1110^-10 m²/s).Which indicating that the ionic liquid microcapsule material can significantly increase the adsorption rate of CO₂ and reduce the equilibrium adsorption time.There are 48 figures,17 tables,and 126 references in this paper.