Preparation Of Amino-protonic Ionic Liquids@KIT-6 Composites And Study Of CO₂ Adsorption

CO₂ is one of the main contributors to the greenhouse effect.Therefore,the reduction of CO₂ emissions from power plant flue gas and the adsorption separation of CO₂ from flue gas is the focus of research.The ionic liquid loaded solid adsorbent has the advantages of both carrier and ionic liquid,overcomes the disadvantages of ionic liquid such as high viscosity and amine leaching,and has the advantages of easy operation,low cost and environmental friendliness compared to traditional ionic liquids.In this paper,two CO₂ adsorbents,denoted as K6P-X and K6L-X,were prepared by physically impregnating the mesoporous material KIT-6 as a carrier with two ionic liquids(tetraethylenepentamine nitrate（[TEPA][NO₃]）and tetraethylenepentamine lysine salt（[TEPA][Lys]）.The CO₂ adsorption performance of the ionic liquids with different loadings（10 wt%-70 wt%）was investigated.The experimental results showed that the specific surface area and pore volume of the composite adsorbent decreased gradually with increasing loadings,and the adsorption performance of CO₂ increased first and then decreased.The optimum loadings of K6P-X or K6L-X were 60 wt%and 65 wt%,respectively,and the corresponding CO₂ adsorption capacities at 60℃were 3.20 mmol.g^-1 and 2.85 mmol.g^-1.The CO₂ adsorption capacity of both K6P-60%and K6L-65%was significantly higher than that of KIT-6（enhanced by 275.6%and 234.5%,respectively）.Additionally,the effect of adsorption temperature（30°C-90°C）on the CO₂ adsorption capacity was investigated.The adsorption capacities of the two adsorbent materials generally showed a trend of decrease with increasing temperature and the optimum adsorption temperature was 60°C.The pore-expanding carrier EX-KIT-6 was produced by adding a pore-expanding agent（1,3,5-trimethylbenzene）during the preparation of KIT-6.The composite adsorbents EX-K6P-X and EX-K6L-X were synthesized with different loadings（20 wt%-50 wt%）of ionic liquids（[TEPA][NO₃]or[TEPA][Lys]）.The experimental results showed that the specific surface area and pore volume of EX-K6P-X and EX-K6L-X gradually decreased with increasing loading,while the pore size gradually increased;the maximum CO₂ adsorption capacity was 2.67 mmol.g^-1 and 2.27 mmol.g^-1,respectively.KIT-6 was modified with the grafting agent N-[3-（trimethoxysilyl）propyl]ethylenediamine using both dry and wet grafting methods and the resulting material was further modified by impregnation with ionic liquids to produce the amine-based bifunctionalized CO₂ adsorption composites 2N-K6P-X and 2N-K6L-X.With the increase of amine loading（20 wt%-50 wt%）,the CO₂ adsorption capacity of both materials showed an increasing trend followed by a decreasing trend,with the best CO₂ adsorption capacities of1.87 mmol.g^-1（2N-K6P-30%）and 3.67 mmol.g^-1（2N-K6L-40%）at 90°C,respectively.To further investigate the CO₂ adsorption mechanism of the composite adsorbent,the CO₂ adsorption data were fitted using the pseudo-one-kinetics,pseudo-two-kinetics,Avrami and intra-particle diffusion models.The kinetic study showed that the pseudo-one-kinetics model can describe well the adsorption process of KIT-6,i.e.the CO₂ adsorption by KIT-6 is mainly physical adsorption.The CO₂ adsorption processes of the modified samples were all consistent with the Avrami model,i.e.a combination of physical and chemical adsorption.The internal diffusion model shows that CO₂ adsorption was influenced by boundary diffusion.The cycling experiments showed that the adsorption performance of the adsorbent remained stable after five adsorption and desorption cycles.