Anhydrous tertiary alkanolamines as hybrid chemical and physical CO ₂ capture reagents with pressure-swing regeneration

Anhydrous DMEA, DEEA and DIPEA are found to absorb carbon dioxide under pressure via chemical binding and physical absorption. The chemical CO ₂-bound derivatives of these materials are zwitterionic alkylcarbonate salts which are characterized by high-pressure ¹³C NMR. DMEA, DEEA and DIPEA absorb 20 wt.%, 17 wt.% and 16 wt.% carbon dioxide, respectively, at 300 psig (20.6 ATM). An increasing chemical carbon dioxide uptake capacity trend of DMEA > DEEA > DIPEA is observed while the physical CO₂ absorption trend is DIPEA > DEEA > DMEA. DMEA captures up to 45 mole % (20 wt.%) of CO₂ at 500 psig via both chemical binding and physical absorption. The amount of chemically bound and physically absorbed CO₂ is directly linked to the CO₂ pressure over the liquid. The zwitterion DMEA-CO₂ regenerates CO ₂ and DMEA upon depressurization, allowing for an economical pressure swing regeneration rather than thermal regeneration. DMEA absorbs/releases CO₂ repeatedly with no decline in capacity.