Absorption Of [N₁₁₁₁][Gly] And DMEE Mixed Anhydrous Absorbent To CO₂

Excessive emissions of carbon dioxide cause the earth temperature to continue to rise, sea level to rise and other serious environmental problems. With the environmental problems becoming more and more outstanding, it is urgent to control carbon dioxide. Ionic liquids (ILs) as green solvent, has unique characteristics including non-volatility, high thermal stability and designable structure. It is composed of anions and cations, the alkaline groups of which can react with acid carbon dioxide, the absorption capacity is high and can be used to absorb carbon dioxide. At the same time, ionic liquid can be recycled as the absorbent, and it can be realized by heating or decompression.In this paper, we adopt the anhydrous absorbent of tetramethylammonium glycinate ([N1111][Gly]) and dimethyaminoethoxyetanol (DMEE) to absorb CO2 in a dual-vessel absorption system. In order to discover the influence of viscosity、 solution composition、temperature, and pressure on CO2 absorption in mixed anhydrous absorbent of dimethyaminoethoxyethanol (DMEE) and tetramethylammonium glycinate ([N1111][Gly]), this study carried out the equilibrium absorption under a wide range of pressure (0～300kPa) at three temperatures (298-318k) in a dual-vessel absorption equilibrium system. The impacts of IL concentration or DMEE and temperature on the physical properties and absorption performance of CO2 are compared in a series of anhydrous solution. The intensification of DMEE to the absorption of CO2 was studied over a wide range of IL concentration (5-60%wt), temperature (298～318 K) and CO2 pressure (0～300 kPa).It is found that with the increase of DMEE or with the decrease of IL concentration, the solution viscosity rises dramatically while the density grows slightly. Precipitate of IL-CO2 composition which could reinforce the CO2 removal was found in the CO2 absorption. The addition of DMEE can greatly accelerate the absorption and increase CO2 load in [N1111][Gly] by dropping the liquid viscosity and behavior as proton acceptor. When the equilibrium pressure is less than 10kPa, CO2 loads increase greatly as the pressure grows while temperature has little influence on the absorption capacities for all the anhydrous solution. However, when the equilibrium pressure is over 50kPa, the absorption capacity increases gradually as the pressure grows and higher temperature leads to less CO2 load in the absorbent. At low pressure, the chemical absorption of ionic liquid determines the absorption process, while under high pressure, the physical absorption is dominant.At the same time, a preliminary study on the regeneration of the mixed anhydrous absorbent was carried out. Precipitation was appeared after carbon dioxide is absorbed by solution, and the precipitation is easy to be separated. The precipitation can be regenerated by heating and be recycled. Under the condition of 353 K, the regeneration efficiency of carbon dioxide was higher than 97%, and the regeneration efficiency was not affected by repeated regeneration experiment. The anhydrous carbon dioxide absorbent has higher regeneration efficiency at lower temperature, which greatly reduces the energy consumption compared with the regeneration process of the aqueous amine solution.