Experimental and modeling studies of bicarbonate forming amines for CO2 capture by NMR spectroscopy and VLE

Three tertiary diamines, N , N , N' , N' -tetramethyl-1,2-ethanediamine, N , N , N ', N '- tetramethyl-1,3-propanediamine and N , N , N ', N '-tetramethyl-1,4-butanediamine, were investigated for application in post-combustion CO 2 capture. The acid-base properties of the diamines were studied through measuring pH values of the acidified amine solutions to obtain reaction constants and corresponding enthalpies/entropies of the reactions. Competitive formation of monoprotonated and diprotonated diamines was observed. CO 2 absorption using these diamine solutions was carried out through a continuous flow method. NMR spectroscopy was used to detect speciation of the bulk solution. Then a general evaluation of the diamines was made in comparison with the monoamines in terms of equilibrium CO 2 solubility and p Ka . The results demonstrated the potential of the structurally modified diamines to be promising bicarbonate forming absorbents in CO 2 absorption. Finally, the equilibrium CO 2 solubility of aqueous N , N , N' , N' -tetramethyl-1,2-ethanediamine solution was measured at a wider range of temperatures, CO 2 partial pressures and initial amine concentrations to establish a thermodynamic model. The model provided reasonable prediction of equilibrium CO 2 solubility and species concentration profiles.