(647b) Carbon Dioxide Absorption Into Aqueous Solution of Hydrophilic Amine-Functionalized Ionic Liquids

Carbon dioxide (CO₂), as one of the greenhouse gases (GHG), is currently responsible for over 60% of the enhanced greenhouse effect. Since global warming was aggravated, carbon capture and sequestration to reduce the release of CO₂to atmosphere is of critical importance. Chemical solvents (such as amines) have been extensive used, but still suffer some disadvantages, which restricting the promotion of the technology.

 In recent years, Ionic liquids (ILs) are frequently used as solvents for gas absorption operations due to their immeasurably low vapor pressure, which can improve the process economy and general efficiency of gas separations. However, gas dissolution in ILs is a physical phenomenon with no chemical reaction and the absorption rate is quite slow. In order to introduce chemical reaction, a variety of ILs were integrated with ions incorporating functional groups. In the open literature, functional ILs were mostly dissolved in conventional ILs and owns high viscosity, which is unbeneficial to industrial applications.

Herein, we designed ether functionalized imidazolium based ILs with glycine anions for the absorption of CO₂. And a Hydroxy group was also introduced to this ILs in order to improve the solubility of the ILs in aqueous solution. The absorption of CO₂ by hydrophilic amine-functionalized ILs ([C₂OHmim]Gly) and Sodium glycinate (SG) were investigated respectively in a double stirred-cell absorber with a planar gas–liquid interface at 15 kPa CO₂ partial pressure. The absorption rate and capacity of [C₂OHmim]Gly into aqueous solution were higher than SG solution. Moreover, the IR spectra of [C₂OHmim]Gly was also proved that the functionalized ILs containing hydroxyl and glycine anions.

It has been widely confirmed that, vaporization and decomposition during regeneration is one of most non-negligible dissipation of aqueous amine, which increases the capital cost of the process. The regenerate efficiency of solvent is important for industrial application. Therefore, the regenerate experiments were investigated in an oil bath at 375.15 ± 0.5 K, and sustained approximately 90 minutes. The multi-cycle regenerate efficiency of [C₂OHmim]Gly and SG were compared with each other. The regenerate efficiency were all decreased as the regeneration cycle was increased but [C₂OHmim]Gly were decreased quite slow. After the fourth regeneration, the efficiency of [C₂OHmim]Gly just decreased 13%, SG almost decreased 25%. The result indirectly proved that the [C₂OHmim]Gly were well recycled and has a higher stability than SG by thermal regeneration even after multi-cycle experiments

As oxygen is one of the most typical components in the flue gas and may give rise to undesired side reactions, effect of O₂ was investigated and the O₂ concentration gradually increased in a range of 0-8 % (V/V). The absorption rate and capacity of CO₂ into [C₂OHmim]Gly and SG were all decreased in the presence of oxygen, but the decline trend of [C₂OHmim]Gly was relatively small. The capacity of [C₂OHmim]Gly only reduced 5.9 %, but the capacity of SG almost reduced 17 % in 4%O₂ compared with the capacity in absence of O₂. Oxygen is susceptible to induce oxidative degradation of alkanolamines. This undesirable breakdown not only reduces their CO₂ absorption capacity but also introduces unwanted degradation products, thus forcing the solution to be eventually discarded. Therefore, the multi-cycle regenerate experiments in present of oxygen (4%O₂) were also investigated. And the differences of regenerate efficiency of these two solutions were significant.

The above experiment results indicated that the hydrophilic amine-functionalized ILs ([C₂OHmim]Gly) we synthesized not only owns a high CO₂ absorption rate and capacity but also can enhance the antioxidant capacity of the solution, and can be well recycled after multi-cycle regeneration, possesses great potential for making up the deficiencies of alkanolamine, which is beneficial to industrial applications.