Preparation Of Supported Ionic Liquids Using Supercritical Co₂ And Its Adsorption Study

CO₂ capturing becomes a research hotspot.Ionic liquids have the characteristics of non-volatilization and structure designable for CO₂ capturing.Immobilizing ionic liquids on porous materials can effectively increase the contact area of ionic liquids,decrease the ionic liquids dosage and reactor volume.In this paper,supercritical fluid deposition method and supercritical fluid adsorption method were used to immobilize ionic liquids to obtain supported ionic liquids with high ionic liquids loading and high CO₂ adsorption capacity.The main contents are as follows:Firstly,supported ionic liquids [Bmim][BF₄]@SBA-15 were prepared by supercritical fluid deposition method with supercritical CO₂ as solvent,ethanol as co-solvent,and SBA-15 as carrier.The experiments were taken under conditions that 0.5².0 mL co-solvent,0⁶0 h,50⁵00 mg ionic liquids,0.44¹.60 MPa depressurization rate.Investigating the effect of various factors on loading obtained the optimized preparation parameters were: 12 h,2.0 mL ethanol,16 MPa,0.89 MPa·h^-1,50?,the mass ratio of ionic liquid and SBA-15 was 1:1,and the loading was 92.85%.It can be seen from thermogravimetric analysis that the supported ionic liquids maintained the thermal stability of the ionic liquid and carrier.Results of physical adsorption and transmission electron microscope showed that the supported ionic liquids maintained the mesoporous structure.Secondly,[Bmim][BF₄]@SBA-15 and [Bmim][Ac]@SBA-15 were prepared by supercritical fluid adsorption method with supercritical CO₂ as solvent,ethanol as entrainer.Results showed that ionic liquids can be successfully immobilized using this method by selecting suitable experimental conditions.The experiments were taken under conditions that ionic liquids concentration 10²0 mg·mL^-1,liquid flow rate0.1⁰.4 mL·min^-1,gas flow rate 0.4¹.6 L·min^-1,0⁶ h,9¹8 MPa,40⁷0?.Investigating the effect of various factors on loading obtained the optimized preparation parameters for [Bmim][BF₄]@SBA-15 and [Bmim][Ac]@SBA-15 were: [Bmim][BF₄]/ethanol 20 mg·mL^-1,liquid flow rate 0.4 mL·min^-1,gas flow rate 0.8 L·min^-1,2 h,60?,15 MPa,loading was 83.50%;[Bmim][Ac]/ethanol 40 mg·mL^-1,liquid flow rate 0.2 mL·min^-1,gas flow rate 1.2 L·min^-1,1 h,60?,12 MPa,loading was 93.85%.It can be seen that with the similar loading,the pore characteristics of [Bmim][Ac]@SBA-15 are better.Compared with supercritical deposition method,the materials prepared by supercritical adsorption method had the lager specific surface area and pore volume.Thirdly,CO₂ adsorption performance of blank carrier and supported ionic liquids was evaluated.Results showed that compared with blank carrier,supported ionic liquids performed higher CO₂ adsorption capacity,and CO₂ adsorption amount increased with loading.With the similar loading,supported ionic liquids prepared with [Bmim][Ac] could enhance the CO₂ adsorption capacity most compared with [Bmim][BF₄].For same ionic liquid,samples prepared using supercritical adsorption method performed the higher CO₂ adsorption capacity.The better the pore characteristics of the sample prepared,the greater the amount of CO₂ adsorption can be obtained,and the highest amount could be up to 56.72 mg·g^-1.Finally,real critical parameters of CO₂ and ethanol mixture were calculated,and it could be illustrated that the supercritical fluid deposition experiments were conducted under supercritical conditions.The adsorption isotherms of supercritical fluid deposition method were proposed.Loading with the change of ionic liquid concentration in the reactor is roughly linear relationship when the co-solvent volume was less.The experimental data with larger co-solvent volume were fitted with Langmuir and Dubinin-Astakhov equations.The saturation loading of ionic liquid for carrier was max in [Bmim][BF₄]@SBA-15-ethanol,which indicated ionic liquid was completely immobilized in this system.