CO2 capture by ionic liquid membrane absorption for reduction of emissions of greenhouse gas

Aqueous amines are the most commonly used CO2 absorbents. But they have many shortcomings such as volatile loss, thermal degradation, corrosivity and wetting on polymer membranes. Ionic liquids can avoid the shortcomings and show unique performances. Diethanolamine glycinate, a ionic liquid made of hydroxyl ammonium amino acid salt, was developed to capture CO2 for greenhouse gas emission reduction. In order to evaluate the ionic liquid performance, membrane flux, gas outlet CO2 concentration, appropriate ionic liquid concentration and operational parameters were investigated by membrane gas absorption. Membrane liquid desorption was tested for regeneration of diethanolamine glycinate. Performance of diethanolamine glycinate ionic liquid was also compared with that of glycinate and diethanolamine. Results show that diethanolamine glycinate ionic liquid had a higher membrane flux, e.g., 6.6 × 10−4 mol m−2 s−1, and a lower gas outlet CO2 concentration (yout/yin, e.g., 0.07) in membrane gas absorption. Changes in operational conditions, e.g., gas and liquid flowrates increase,  changed the membrane flux of membrane gas absorption, which increased only by 23.9%. Dominant factors affecting the membrane flux were the gas CO2 mole fraction, increasing the flux by 80.0%, and the ionic liquid concentration, increasing the flux more than 2 times. The ionic liquid was much more easily regenerated and possessed large regeneration efficiency and average regeneration velocity. Diethanolamine glycinate ionic liquid is thus an efficient and promising CO2 absorbent.