Synthesis And Performance Of Immobilized Imidazolium Ionic Liquid Used For CO₂ Adsorption

The immobilization of ionic liquids into silica and activated carbon supports were carried out with impregnation methods, and the immobilized ionic liquids were characterized via FTIR, TG, DSC and SEM analysis. The effects of impregnation concentration, impregnation time, the type and activitied method of supporter, the type and loading amount of ionic liquids on pore structure distribution?PSD?, CO₂ adsorption capacity, CO₂/N2 selectivity and water resistance were investigated. Furthermore, the CO₂ adsorption mechanism of immobilized ionic liquids were discussed in detail. The main findings are as follows:?1? According to the FTIR spectroscopy, the immobilization of ionic liquids into activated carbon and silica supports were synthesized successfully through impregnation method. Thermogravimetric analysis showed that all prepared samples has high thermal stability. DSC analysis indicated the [Emin]TFSI immobilized on supporters exists in free state and crystalline state and the melting points of the immobilized samples are lower than that of pure ionic liquid. The scanning electron micrographs showed that the pore structure characteristics of immobilized ionic liquids keep well.?2? The impregnation concentration, impregnation time, the type and activitied method of supporter, the type and loading amount of ionic liquids had significant effect on PSD, CO₂ adsorption capacity, CO₂/N2 selectivity and water resistance of samples. The active carbon-immobilized ionic liquid sample BMT-AC-3h under condition of 0.24 mol/L impregnation concentration and 3 h impregnation time shows a better CO₂ adsorption capacity of 8.65wt% at 298 K and 0.1 MPa. The introduction of ionic liquids on the supporters significantly enhances the CO₂/N2 selectivity and the water resistance. Sample OMT-AC-6h exhibits the best adsorption selectivity and water resistance. All tested samples exhibit good CO₂ sorption/desorption cycle capacity.?3? The adsorption isotherms of CO₂ on immobilized ionic liquids were analyzed by the Freundlich model and the results showed that Freundlich model is suitable to describe the adsorption of CO₂, which revealed that the CO₂ adsorption mechanism of immobilized ionic liquid is inclined to uneven multimolecular layer covering on the surface of adsorbent.?4? The classical homogeneous surface diffusion model?HSDM? was used to describe diffusion behavior of CO₂ in immobilized ionic liquids. The calculated values of diffusion coefficients?Ds? of CO₂ adsorption on silica-immobilized ionic liquid and activated carbon-immobilized ionic liquid are at a level of 10-7 m2/s and 10-8 m2/s respectively, which is higher than that of pure ionic liquids. The loading amount of ionic liquids obtained by double diffusion model is consistent with the result of thermogravimetric analysis. For modified activated carbon, the Ds is lower than that of bare activated carbon and the D2 of samples decreases with the impregnation time increasing, which demonstrated that with the increase of the impregnation time, more ionic liquids accessed into the pore of activated carbon and hindered the diffusion of CO₂.