Study On Ionic Liquids Based Solvents For Carbon Dioxide Capture

CO2 emission has been considered as one of the primary contributors to climate change and global warming. Chemical absorption of CO2 is widely established and proved to be the most promising strategy in CO2 capture. Accordingly, the efficient, energy-saving and environmentally-friendly solvent is the desired theme of academic and industrial researchers. Ionic liquids (ILs) have aroused considerable interests as solvent for CO2 capture due to their unique properties, such as negligible vapor pressure, low heat capacity and tunable designability. However, the CO2 uptake of conventional ILs is low. The synthesis of functionalized ILs is tedious and the subsequent purification is challenging. Also, functionalized IL usually shows high viscosity which is detrimental to CO2 diffusivity. Therefore, it is crucial to develop novel ILs based solvent with high CO2 uptake, fast absorption rate and low heat of CO2 absorption. This dissertation serves to extend the knowledge of CO2 absorption using multiple reaction site amine, ILs-amine hybrids and novel deep eutectic solvents (DESs) from the point of industrial view, which provides insights on the industrial application of ILs in CO2 capture. The main research work and creative results of this dissertation are as follows:(1) Performance of CO2 absorption with novel multiple reaction site amine solution was studied. Absorption rate and absorption capacity of CO2 with amine solutions were determined using the home-made on-line stirred cell and vapor liquid equilibrium (VLE). The results show that the absorption rate of CO2 with HMPDA solution is faster than those of MEA and MDEA solutions. CO2 capacity in 30 wt% HMPDA solution is up to 1.5 mol CO2/mol HMPDA, which is higher than those of 30 wt%MEA (0.6 mol CO2/mol MEA) and 30 wt% MDEA (0.9 mol CO2/mol MDEA) solutions. Effects of temperature and concentration on the CO2 absorption, and the density and viscosity of amine solutions before and after CO2 absorption were investigated. Finally, heat of CO2 absorption in HMPDA solution at 313 K was investigated using BT 2.15 calorimeter. Heat of CO2 absorption in HMPDA solution is lower than that of MEA solution when CO2 loading <0.45 mol CO2/mol amine.(2) Performance of CO2 absorption with [Bmim][NO3]-MEA hybrids was studied. Physicochemical properties, such as density, viscosity, heat capacity and refractive index of hybrids were determined and found that the addition of ILs in MEA solutions increases the density, viscosity and refractive index, while decreases the heat capacity. VLE of CO2 shows that addition of ILs slightly decreases the CO2 solubility and absorption rate while increases the physical absorption of CO2 in hybrids. Also, the addition of ILs decreases the diffusivity of CO2 in hybrids, which is related to the increased viscosity due to the addition of ILs. Effects of temperature, pressure and CO2 loading on heat of CO absorption in hybrids were analyzed. It is found that heat of CO2 absorption decreases as the pressure and CO2 loading increases. Importantly, higher concentration of ILs in hybrids can lower the heat of CO2 absorption to a large extent.(3) CO2 absorption in aqueous MDEA-ILs solutions was studied. Cycle CO2 loading, heat of physical absorption were calculated and found that the cycle CO2 loading ranks as: MDEA-PZ-[Bmim][BF4]> MDEA-PZ-[Bmim][Cl]> MDEA-PZ-[Bmim][NO3]. VLE results show that CO2 solubility in MDEA-ILs solutions increases with the partial pressure of CO2 and decreases with addition of ILs. Calculated heat of CO2 absorption shows that kind of ILs has a significant role on heat of CO2 absorption. Experimental heat of CO2 absorption shows that addition of ILs lowers the heat of CO2 absorption and this phenomenon is significant when CO2 loading is and temperature is high.(4) Performance of CO2 absorption in newly synthesized deep eutectic solvents was carried out. In order to improve the CO2 uptake of existing DESs, we synthesized imidazolium based DESs and characterized the structural information of DESs using IR, Raman and NMR. Newly formed hydrogen bond in DESs is found to be responsible for the formation of eutectics and the depression of melting point up to 70 K, which broadens the application range of DESs. The thermal stability and physicochemical properties, such as density, viscosity and heat capacity of DESs were also measure over wide temperature range. Maximum CO2 uptake of DESs is up to 21.4%, which is found to be the largest CO2 uptake of DESs. Heat of CO2 absorption with DESs was experimentally determined using BT2.15 calorimeter and found that heat decreases as CO2 loading increases. Absorption mechanism between CO2 and DESs shows that CO2 is primarily bonded chemically with DESs and the hydrogen bond improved CO2 uptake of DESs.