CO₂ Capture Performance Of Functionalized Ionic Liquids And Their Cross Linked Polymers

The problem of"global warming"for the increasing concentration of carbon dioxide?CO₂?in the atmosphere has caused widespread concern around the world.Ionic liquids?ILs?are used for CO₂ capture thanks for their wide liquid range,strong dissolving ability,and controllable structure.Though,designing ILs with cooperative sites is considered as attractive to enhance CO₂ capacity,in the process of CO₂capture,the acitvity of site in dual-site functionalized ILs are inhibited commonly,which affects its carbon capture performance.In addition,the anion of anion-functionalized ionic liquids are considered as counter ion and play a pivotal role in CO₂ capture.However,the influence of cations is not clear.Otherwise,the viscosity of functionalized ILs hinders it application in industrial.Therefore,in order to improve the CO₂ capture performance of ionic liquids and their operability in industrial applications,the following work are done in this paper.Firstly,cooperaction is the key to high CO₂ capacity of ILs with dual-sites,but the depression of one site is a common problem making the altive site be suppressed and low CO₂ capacity.In this work,a variety of functionalized ILs with dual sites including amino acid group?AA?and basic anion?R?were synthesized to investigate the suppression and cooperation between sites in CO₂ absorption.The basic anion was selected in this work with different basicity including sulfonate?Su?,carboxylate?Ac?,imidazolium?Im?,indolium?Ind?.These ILs([P₆₆₆₁₄]₂[AA-R])were applied to CO₂ absorption,the results present CO₂ capacity increase firstly and then decrease later with the continuous increase of the activity of anion site.Combined with CO₂absorption experiments,IR and NMR spectroscopic analysis and DFT calculation,it demonstrates the ability of one site to capture CO₂ would be suppressed when the activity of another site is much stronger.Thus,the cooperation of dual sites functionalized ILs and high CO₂ capacity might be achieved through balancing two sites to be equivalent.Based on this point,[P66614]2[Am-iPA]was further synthesized by taking the advantage of conjugated benzene ring,as expected,[P66614]2[Am-i PA]showed capacity as high as 2.38 mol CO₂ per mol IL at 30 ^oC and 1 bar and without capacity decrease within 10 times recycle performance of CO₂ absorption and desorption.The investigation of the knowledge of suppression would be better to achieve cooperation of dual-site functionalized ILs as CO₂ absorbents,and the strategy of cooperation would considered in a varity of fields.Secondly,a strategy about improving CO₂ capture performance of anion-functionalized ILs was proposed though reducing the interaction between anion and cation after the inverstigation of the effect of cation on CO₂ capture of ILs.In this work,hydroxypyridine?[2-OP]?anion was selected as probe,paired with Imidazole?[Me-C_n Mim]?,phosphine([P_nnnm]),tributylethylamine([N₄₄₄₂]),pyrrolidone?[Me-Bpr]?as cation for studing the effects of cations in CO₂ trapping.The results of CO₂ adsorption experiments show that the carbon capture capacity of the[2-OP]based cation changed,with the change of cations from 0.94 up to 1.69 mol/mol IL?30^oC,1 bar CO₂ pressure?.Spectroscopic analysis and quantitative calculation results show that hydrogen bonding interactions and the interactions between cations and anions in ILs had a great effect on the activity of[2-OP]capture CO₂.Weaken the interaction between anions and cations,the carbon capture capacity of the ionic liquid is increased.This interaction law was further analyzed by FT-IR spectroscopy.The results showed that the stronger the interaction between the cation and the anion,the localization of the charge in the anion[2-OP]to the O atom,thereby suppressing the N-site trapping CO₂ activity.Further more,[Ph-C8eim][2-OP]?Ph-C8eim=1-N-ethyl-3-N-octyl-2-phenylimidazole?was designed and synthesized based on reducing the interaction between cation and anion though the charge dispersion.It was found that the carbon capacity of the ionic liquid was as high as 1.69 and 1.83mol CO₂/mol IL at 30 and 20^oC,respectively.Compared with the reported ionic liquid[P₆₆₆₁₄][2-OP]with a capacity of 1.58 mol CO₂/mol IL,and it has a 16%increase.The research results of this work would provide theoretical support for the design of new and efficient ILs.Finally,functionalized ILs with superior carbon capture performance were used to modify the cross-linking polymers with expection of avoiding the inconvenience caused by the large IL viscosity,and achive highly capture and selective solid CO₂adsorbents.In this work,N-ethyl-2 phenylimidazole?PhEIm?was selected to synthesied cross-linked polymer?CL-PhEIm?by F-C cross-linking reaction.The traditional IL functionalized polymer?CL-PhEImBr?is obtain by reaction with bromobutane.Then,followed with ion exchange,the glycinum was introducted and got CL-PhEImGly.The structure of the synthesized polymer characterized by FT-IR and XPS spectroscopies indicted that the structure of this polymer was consistent with expectations.The morphology of the polymers have a porous structure from the SEM images.The results of CO₂ adsorption experiments demonstrated that the carbon capture capacity of the CL-PhEImBr is 56 cm³ g^-1,which is much higher than CL-PhEIm with 42 cm³g^-1.the carbon adsorption capacity further increased to 64cm³ g^-11 with CL-PhEIm Gly,along with high selectivity as 144?0.06 bar,273K?of CL-PhEIm Gly.The isothermal adsorption heat calculation and infrared spectroscopic characterization suggested the selective reaction of CO₂ with[Gly]is the key to of CL-PhEIm Gly.With in 6 times adsorption-desorption cycles,the performance of CO₂adsorption kept steady.Therefore,ILs functionalized cross-linking polymers would be potential CO₂ adsorbents.In summary,the inhibition or cooperaction of dual-sites finctionalized ILs were studied.The[P₆₆₆₁₄]₂[Am-iPA]and[Ph-C₈mim][2-OP]with cooperative dual-sites were designed as CO₂ absorbents with high capacity.Further more,ILs functionalized cross-linking polymers were synthesized by taking the advantages of ILs to absorb CO₂ with high capacity and selectivity.This work make provide new ideas and methods for designing gas trapping agents with good performance.