On the mechanisms of CO2 absorption and desorption with phase transitional solvents

Abstract

Two phase transitional aqueous solvent blends consisting of diethylenetriamine (DETA) and N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) were experimentally investigated to determine their CO2 absorption, phase transition, and desorption performance. Both solvents revealed higher CO2 loading capacities and desorption pressures than a 5M monoethanolamine solution under comparable conditions. The evolution of solvent species during the CO2 absorption and desorption processes was determined quantitatively by using 1H, 13C, and 2-D nuclear magnetic resonance spectroscopic techniques. Mechanisms of the CO2 absorption and desorption reactions were proposed based on the speciation analysis. Carbon dioxide absorption occurred as the carbamates and dicarbamates of DETA were formed, followed by CO2 hydration promoted by proton exchange with PMDETA. Desorption of CO2 could generally be described as a reverse absorption process, but it was also coupled with a dual phase transition.