Design And Preparation Of Functional Ionic Liquids And Their Applications In Gas Trapping

Ionic liquids（Ionic liquids,ILs）have attracted a lot of attention from scientists worldwide in recent years.They are also known as room-temperature molten salts,which are salt systems composed of ani-ons and cations in a liquid state at or near room temperature.Due to the excellent chemical and thermodynamic properties of ionic liquids,such as very low vapor pressure at room tempera-ture,better thermal stability,good electrical conductivity,high ion migration rate,wide electro-chemical window and good solubility for inorganic and organic compounds,they have been rapidly developed in the field of catalysis,biomass conversion,organic synthesis,gas trapping,functional materials and other chemical and chemical fields.Ionic liquids（ILs）have been proved to be a successful platform for designing novel task-specific materials for gas separation due to their inherent properties such as negligible vapor pressure and tunable nature.In this study,a series of functional ionic liquids were designed and synthesized for gas capture.Firstly,the thermodynamic properties such as density,viscosity and conductivity of the ionic liquid solution systems were determined,and the performance of ionic liquids applied to capture CO₂ and NH₃ was investigated,including the effects of temperature,partial pressure and humidity conditions on the gas capture performance of ionic liquids.And the reversibility of ionic liquids was investigated by absorption-desorption cycle experiments,and finally the absorption mechanism was analyzed by combining quantum chemical calculations and nuclear magnetic resonance spectroscopy.In this paper,a variety of ionic liquids were prepared by the acid-base neutralization method（one-step synthesis）,including DBU-triazole ionic liquid[HDBU][Triz],DBN-imidazole ionic liquid[DBNH][Im],DBN-triazole ionic liquid[DBNH][Triz],1-butyl-3methylimidazolium dibutyl phosphate ionic liquid[C₄C₁im][DBP],1-ethyl-3methylimidazolium diethyl phosphate ionic liquid[C₂C₁im][DEP],1,3 dimethylimidazolium dimethyl phosphate ionic liquid[C₁C₁im][DMP],1-ethyl-3methylimidazolium dimethyl phosphate ionic liquid[C₂C₁im][DMP],1-butyl-3methylimidazolium dimethyl phosphate ionic liquid[C₄C₁im][DMP].The thermodynamic properties of ionic liquid in binary solution systems were studied using different organic solvents to determine their thermodynamic properties at different concentrations.Taking[HDBU][Triz]as an example,six binary solutions inculding[DBUH][Triz]/methanol,[DBUH][Triz]/ethanol,[DBUH][Triz]/isopropanol,[DBUH][Triz]/n-butanol,[DBUH][Triz]/DM F,[DBUH][Triz]/DMSO were prepared within the full range of concentrations.Then the densities,viscosities and conductivities of the systems at different temperatures were measured and experimental conductivities were fitted using the Casteel-Amis equation.The results showed that the addition of appropriate solvents to[DBUH][Triz]was effective in obtaining larger conductivities,and conductivities data can follow such order:IL+methanol>IL+ethanol>IL+isopropanol>IL+n-butanol,which was consistent with the dielectric constants of the corresponding alcohols,indicating that alcohols with higher dielectric constants were more likely to facilitate the dissociation of[DBUH][Triz].In addition the excess molar volumes of[DBNH][Im]and[DBNH][Triz]with four different alcohols was then investigated and the results were correlated and discussed using the Redich-Kister equation.The experimental results shown that the excess molar volume of DBN-type ionic liquids is influenced by a combination of hydrogen bonding,intermolecular site resistance phenomena and intermolecular geometry filling.Futhermore performance of DBN-triazole and DBN-imidazole in capturing CO₂ were uncovered.Taking[DBNH][Triz]as an example,the effect of external conditions（temperature,pressure,humidity,CO₂ flow rate）on CO₂ capture was investigated,and the reversibility of[DBNH][Triz]was verified by performing the absorption-desorption cycle experiment.And the NMR spectra and quantum chemical calculations were used to reveal the The absorption mechanism.The results have shown that[DBNH][Triz]could capture CO₂ efficiently,and the external conditions such as temperature,pressure and humidity would affect the absorption rate and maximum absorption capacity of[DBNH][Triz].Moreover,the[DBNH][Triz]absorption rate and absorption capacity were enhanced gradually with the increase of CO₂ partial pressure.In addition,the thermodynamic properties of the absorption process were investigated,,indicating that the CO₂ capture in[DBNH][Triz]is an exothermic process which is consistent with the experimental behavior.It was also found that the presence of water plays a negative role in the CO₂ absorption,which may be due to the hydrogen bonding interactions between ionic liquid and water molecules which could weaken the absorption of CO₂ by ionic liquids.The absorption mechanism of[DBNH][Triz]was revealed by DFT calculations:the two active sites N₁ and N₄ could synergistically perform chemical absorption of CO₂,forming carbamate carbonyl carbon atoms in N₁-COO^-and N₄-COO^-.The above absorption mechanism was further demonstrated using ¹³C NMR and FT-IR spectra.Finally,absorption-desorption cycling experiments were performed,and the conclusions showed that[DBNH][Triz]can be recycled repeatedly with good reversibility.Finally the article explores the solubility of ammonia in five dialkyl phosphate based ionic liquids.Pressure-temperature-composition（p-T-x）data were measured at different temperatures and NH₃ partial pressures.The results indicate that temperature and pressure as well as the structure of the ILs have important effects on the physicochemical properties and gas solubility.In addition,the experimental data showed that the solubility of NH₃ was improved by varying the cationic side chain length and anionic side chain length of the ionic liquids,and the dialkyl phosphate based ionic liquids showed satisfactory reversibility and high selectivity for NH₃.In summary,two types of ionic liquids including DBN-based ionic liquids and dialkyl phosphate ionic liquids were synthesized in this study.The thermodynamic properties of ionic liquids in solutions as well as their behavior in capturing CO₂ and NH₃ have been investigated,providing new ideas for the application of ionic liquids in gases capture.