Synthesis And Characterization Of Cholinium Amino Acid And Phosphonium Carboxylic Acid Ionic Liquids And Their Applications For CO₂Capture

Recently, ionic liquids (ILs), as one of the novel green solvents, have attractedconsiderable attention in academia and industry, and it has already successfully usedin many fields, such as organic catalysis, biomass conversion, gas separation,liquid-liquid extraction and etc. However, most of the previous works are mainlyfocused on imidazolium-and ammonium-based ILs, and these tow kinds of ILs havebeen demonstrated to be badly biodegradable, poorly biocompatible, and highly toxic.Therefore, the study of lowly toxic and environmentally benign ILs from renewablematerials has been highly conceived and proposed. In addition, for the capture of CO2by ILs, the design and preparation of novel ILs with the characteristics of lowviscosity and fast absorption rate is also a hot topic. To overcome the abovementioned issues, with the use of low-cost raw materials such as choline chloride,amino acids, and carboxylic acids, this thesis designs and synthesizescholinium-based amino acid ILs and phosphonium-based carboxylic acid ILs, andthen systematically measures their physicochemical properties and CO2absorptioncapacity. The obtained conclusions are presented as follows:1. Two kinds of ILs are synthesized successfully via two-step method: one ischolinium-based AAILs ([Ch][AA]), cholinium glycinate ([Ch][Gly]), choliniumL-alaninate ([Ch][L-Ala]), cholinium β-alaninate ([Ch][β-Ala]), cholinium prolinate([Ch][Pro]), and cholinium serinate ([Ch][Ser]); another is phosphonium-basedcarboxylic acid ILs, tetrabutylphosphonium formate ([P4444][For]),tetrabutylphosphonium acetate ([P4444][Ace]), tetrabutylphosphonium propionate([P4444][Prop]), tetrabutylphosphonium butyrate ([P4444][Buty]). The structures ofthese ILs are further characterized and confirmed bylH NMR and FTIR.2. The physicochemical properties of these ILs including density, viscosity,refractive index, and conductivity are measured in detail. The results indicate that, inthe temperature range from25oC to70oC, the density, viscosity, and refractive indexdecrease while conductivity increases with the increase of temperature, and thecoefficient of thermal expansion was considered to be nearly independent oftemperature. All the decomposition temperatures are higher than150oC, showinggood thermal stability. 3. The experimental results of CO2absorption demonstrates that CO2absorptioncapacity increases with the increase of equilibrium pressure, and the decrease oftemperature.30wt%[Ch][Pro] aqueous solution exhibits a relatively good solubilityof CO2,with0.81molar CO2/mol IL.[P4444][Buty] can achieve absorptionequilibrium within10min, and the capacity is0.68molar CO2/mol IL. Furthermore,the absorption recycle experiments show that the absorption capacity of CO2remainsunchanged for three times.