The Synthesis Of Anion Functionalized Ionic Liquids And Their Application In Carbon Dioxide Capture

Recently, the discharge of carbon dioxide (CO2) into the atmosphere duing to the rapid development of industry has attracted a wide attention for their intribution to climate change. Ionic liquids (ILs) have developed as potentional CO2absorbent for their unique properties such as negligible vapor pressure, wide liquid range, superior dissolved ability, and their tunable structures and properties. Followed by the first reported example of CO2chemisorption by an amino-functionalized IL, lots of works fock on optimizing the CO2capacity of amino-based ILs, but low capacity, high viscosity do exist. Thus, the development of ILs for improving CO2capture is highly desired. In this manuscript, we designed a series of azole and hydrxypydridine-based anion functionalized ILs with high CO2capacity, besides, we tried to investigate the entropy effect design on CO2capture through the ILs’structure. Taking advantage of intramolecular hydrogen bond insteads of intermolecular hydrogen bond network to avoid the sharp increase of viscosity of amino-functionalized ILs.One disadvantage of amine-functionalized ILs is its low absorption kinetics due to the relatively high viscosity of the IL during the absorption of CO2for the formation of hydrogen bond network. We developed azole-based ILs with sp2hybridization of N such as azole anion and phenolate interaction with CO2. The azole-based ILs with improved properties such as scanty active hydrogen for strong hydrogen-bond formation, fast absorption rate, ect. The stability, absorption capability, and absorption enthalpy of ILs can be facilely tuned by varying the anions with different pKa values. Thus, highly stable basic ILs [P66614][Triz] for CO2capture with desirable enthalpy of absorption and high absorption capacity can be achieved. We further put forward ILs with multiple site cooperative interactions through conjugation effect of electron to enhance capacity of CO2. Based on this assumption, we present a new method for carbon capture by several hydroxypyridine-based ILs with two kinds of different interacting sites including pyridine and phenolate. Quantum mechanical calculations and spectroscopic investigations demonstrate that such a high capacity originate from the cooperative multiple site interactions between the electronegative nitrogen and oxygen atoms in the anion. The results show that an extremely high capacity up to1.65mol CO2per mol IL can be achieved, in addition, excellent reversible process by those ILs can provide a potential alternative for CO2capture.There are lots of works investigated the effect of enthalpy on the capacity of CO2capture by ILs, however, the CO2capacity not only depends on the reaction enthalpy based on the eqution△G=△H-T△S that the entropy is another parallel factor. For CO2chemisorption, the enthalpic change would be far greater than entropic change, which makes the entropy not obvious. It is not clear how the entropy effect on CO2chemisorption. We designed some isomeric anion functionalized ILs with substituent in different position to investigate the effect of structure on entropy of CO2capture. Viscosity measurements, spectroscopic investigations, and quantum chemical calculations showed that such a unique behavior originated from the entropic effect, which was induced by the intermolecular hydrogen bonding in these ionic liquids.The sharp increase of viscosity of amino-functionalized ionic liquids through CO2capture is duing to the formation of intermolecular hydrogen bond networks. As we know, hydrogen bond includes intermolecular and intramolecular hydrogen bond, the latter would not form the strong interaction among moleculars and not infulence the viscosity of the system very much. Based on this assumption, we introduce atom N or O to the amino-functionalized ILs, we expect the N or O in the just right position and can form intramolecular hydrogen bond with H of NH or NCOOH after CO2capture. We found the viscosity of amino-functionalized ILs with acetyl group tethered at the amino have slightly decrease during the CO2capture process, while with methy group tethered at the amino, the viscosity increase violently.Summary, we developped several class of anion-functionalized ILs for CO2capture, on the basis of the relationship between CO2absorption performance and the structure of the ILs, high capacity, low absorption enthalpy, rapid absorption kinetics, and excellent reversibility can be achieved by tuning the structure of the ILs, and we did a preliminary exploration on thermodynamics, which offer new strategy for enhancing the performace of gas absorbent.