CO₂ absorption performance in advanced water-lean diamine solvents

In an effort to reduce energy penalties, a range of advanced water-lean solutions blended from one of 8 diamines, an organic solvent diluent and water, were screened. The diamines N,N-dimethyl-1,3-propanediamine and N,N-dimethyl-1,2-ethanediamine with one primary and one tertiary amino group remain homogenous during CO₂ uptake with the addition of cosolvents (1-methyl-2-pyrrolidinone or sulfolane) and are further investigated for absorption and desorption performance compared with their corresponding aqueous solutions. Water-lean solutions with different water concentrations are tested to explain the impact of water content on the solution performance. Physical properties such as density and viscosity are also measured for a versatile evaluation. The results show that diamine water-lean solutions obtain low viscosity, preferable cyclic capacities and rapid absorption and desorption rates. ENH-5% H₂O (mass ratio DMEDA: NMP: H₂O = 3:6.5:0.5) shows the most competitive advantages with comparable viscosity (1.49 mPa∙S at 313 K) to aqueous MEA-H₂O and a 140% improvement in cyclic capacity. Four-fold higher desorption rate is gained ESH-5%H₂O (mass ratio DMEDA: SFL: H₂O = 3:6.5:0.5) compared with MEA-H₂O. Considerable reduction in energy penalties is expected to be achieved in diamine water-lean solutions. In addition, the equilibrium solubility of diamine water-lean solutions also shows potential for industrial application due to their sensitivity to CO₂ partial pressure in contrast with aqueous solutions.