Preparation Of Supported Ionic Liquid Using Supercritical Fluid And CO₂ Adsorption Properties

In order to slow down the rate of global warming,CO₂ capture is a more effective way to reduce greenhouse effect and protect the environment.The ionic liquid has attracted wide attention in the field of CO₂ absorption for its nonvolatility,structure designability,non-toxic and excellent solvent properties.As the absorbent to capture CO₂,ionic liquid can effectively solve the problems of high energy consumption,solvent lossing and equipment corrosion in the traditional process.Supporting the ionic liquid in the porous material can increase the contact surface area between the ionic liquid and CO₂,and promote the absorption of CO₂ with less amount of ionic liquid.In this study,preparing supported ionic liquids with high loading and high adsorption capacity for CO₂ adsorption is the target,different kinds of ionic liquids were loaded with different loading methods.The main work is as follows:The supported ionic liquids [Bmim]BF₄@SBA-15 and [Bmim]Ac@SBA15 were prepared by the impregnation method using ordered mesoporous silica material SBA15 as the carrier and ethanol as solvent.Through characterization,it is found that the supported ionic liquid still has the pore characteristics of the carrier,but the pore structure was seriously damaged.The process optimization showed that the amount of ethanol was 3 m L,the mass ratio of ionic liquid to carrier was 2:1,25 °C,24 h,and the loading of [Bmim]Ac was 70.28%.The amount of ethanol was 3 m L,and the mass ratio of ionic liquid to carrier was 2:1,50 °C,impregnated 12 h,and the loading of [Bmim]BF₄ was 72.30%.Supported ionic liquids [Bmim]BF₄@SBA-15 and [Bmim]Ac@SBA15 were prepared using supercritical carbon dioxide assisted method with ethanol as co-solvent.The results show that supercritical carbon dioxide assisted method can be used to supporting ionic liquids on mesoporous silicon material for suitable operating conditions.And the carrier pore structure intact,with large pore volume and specific surface area.The optimized process parameters were as follows: in the [Bmim]BF₄@SBA15 system,6 m L ethanol,16 MPa,60 °C,3 h reaction,ionic liquid loading is 85.56%.In terms of the [Bmim]Ac@SBA-15 system,3 mL ethanol,16 MPa,50 °C,reacted with 6 h,with an ionic liquid loading of 93.85%.In order to explore the adaptability of supercritical carbon dioxide assisted method,supported ionic liquids were prepared using MCM41 with pore size of 1-2 nm as carrier and ethanol as cosolvent.The results show that the porous materials are porous when loaded ionic liquids.Compared with SBA15,the smaller pore size of MCM41 may cause ionic liquids to block the carrier channels and influence the loading and morphology.Therefore,the choice of suitable ionic liquids and the rational regulation of supercritical carbon dioxide,ethanol and ionic liquid three component system are expected to solve the plugging problem,thus improving the preparation stability.For the reaction system of that under the experimental conditions,the diffusion coefficient of ionic liquid in ethanol and CO₂ mixed phase was calculated by Wilke-Chang formula,the viscosity of CO₂ and ethanol was calculated by P-R model.The results show that when the pressure is greater than 12 MPa,with the increasing of pressure,the diffusion coefficient decreases;and the diffusion coefficient can be improved by increasing the amount of temperature and co-solvent ethanol.In order to test the adsorption properties of the composite,the CO₂ adsorption performance of the supported ionic liquid was evaluated.Compared with the impregnation method,the material prepared by supercritical carbon dioxide assisted method has better CO₂ adsorption performance,and the ionic liquid loading is directly proportional to the amount of CO₂ adsorption,which is linear in band shape.The results show that when loading is same,the experimental points above linear was the corresponding composite with ionic liquids supported uniformly,but the points below the line is the material with ionic liquids blocking,and attached to the outer surface of the carrier.The evaluation of the cyclic performance of the material showed that after 5 cycles,the supported ionic liquid materials still had good CO₂ adsorption capacity.