Synthesis Of Bi-functionalized Ionic Liquid-mesoporous Alumina Composite Material And Its Performance For CO₂ Capture

Large-scale emission of carbon dioxide?CO₂?as the main greenhouse gas has caused a variety of environmental issues.CO₂ is also an inexpensive and abundant chemical material,which can be applied in many fields such as chemical engineering,agricultural field and food industry.So it is necessary to achieve the separation and capture of carbon dioxide from flue gases.Ionic liquids?ILs?are favorable CO₂absorbents owing to their low melting point,benign thermal stability and widely tunable structure.However,the large-scale applications of ionic liquids are limited owing to their high viscosity and low mass transfer rate.In order to avoid these drawbacks,ionic liquids are immobilized on inorganic porous or organic polymer materials.The composite materials not only reduce the consumption of ionic liquids but also increase the contact area between ionic liquids and carbon dioxide,which are beneficial for the gas sorption.Mesoporous alumina?MA?possesses remarkable properties,such as high specific surface area and large pore volume,which give the materials extensive applications in adsorption-separation and catalysis fields.In this paper,bi-functionalized ionic liquid was synthesized and immobilized on mesoporous alumina to achieve efficient carbon dioxide capture.Firstly,bi-functionalized ionic liquid?1-ethoxymethyl-3-methylimidazolium glycinate,[EOMmim][Gly]?was synthesized by two-step method.The molecular structures of the intermediate and ionic liquid were confirmed and thermogravimetric analysis suggested[EOMmim][Gly]had good thermal stability.Then,ordered mesoporous alumina?OMA?was synthesized by solvent evaporation-induced self-assembly method.The micro-morphology and pore structure of material were investigated by using various analytical techniques.The results show that?-mesoporous alumina was synthesized with regulation and well-defined channel.The synthesized mesoporous alumina possesses large specific surface area of 350 m²/g,pore volume of 0.70 cm³/g and mean pore size of 5.38 nm.Next,bi-functionalized ionic liquid was immobilized on mesoporous alumina by ultrasonic impregnation method.The effects of dispersion solvents,ionic liquid amount and ultrasonic time were investigated,respectively.The results illustrate that micro-morphology and ordered mesoporous structures of alumina are maintained.The initial thermal degradation temperature and completed decomposition temperature are both higher than those of the ionic liquid.Loading capacity of ionic liquid on mesoporous alumina can reach 1.04 gIL/gMA under the optimal conditions when acetone as the dispersion solvent,mass ratio of ionic liquid to alumina at 4:3 and ultrasonic time of 60 min.Finally,carbon dioxide capture capacity of bi-functionalized ionic liquid,mesoporous alumina and bi-functionalized ionic liquid-mesoporous alumina?IL-MA?composite materials were studied under different temperatures or loading capacities.The capture kinetics was investigated under the optimum conditions.The results illustrate that the composite materials exhibit excellent capture performance towards carbon dioxide and 40°C is the optimal capture temperature.The IL-MA composite material possesses higher CO₂ sorption capacity?144 mg/g sorbent?than IL or MA alone.The capture capacity reduces with the increase of temperature and enhances with the increase of ionic liquid loading capacity.Capture kinetics study indicates that Pseudo-second-order model is good to describe CO₂ capture in IL-MA composite material.Furthermore,after eight times of capture-regeneration circles,the capture capacity can be maintained and the ordered structure of composite material keeps well.