CO2 Absorption and Sequestration as Various Polymorphs of CaCO3 Using Sterically Hindered Amine

One aspect of the attempt to restrain global warming is the reduction of the levels of atmospheric CO2 produced by fossil fuel power systems. This study attempted to develop a method that reduces CO2 emissions by investigating the absorption of CO2 into sterically hindered amine 2-amino-2-methyl-1-propanol (AMP), the acceleration of the absorption rate by using the enzyme carbonic anhydrase (CA), and the conversion of the absorption product to stable carbonates. CO2 absorbed by AMP is converted via a zwitterion mechanism to bicarbonate species; the presence of these anions was confirmed with H-1 and C-13 NMR spectral analysis. The catalytic efficiency (k(cat)/K-m), CO2 absorption capacities, and enthalpy changes (Delta H-abs) of aqueous AMP in the presence or absence of CA were found to be 2.61 x 10(6) or 1.35 X 10(2) M-1 s(-1), 0.97 or 0.96 mol/mol, and -69 or -67 kJ/mol, respectively. The carbonation of AMP-absorbed CO2 was performed by using various Ca2+ sources, viz., CaCl2 (CAC), Ca(OOCCH3)(2) (CAA), and Ca(OOCCH2CH3)(2) (CAP), to obtain various polymorphs of CaCO3. The yields of CaCO3 from the Ca2+ sources were found in the order CAP > CAA > CAC as a result of the effects of the corresponding anions. CAC produces pure rhombohedral calcite, and CAA and CAP produce the unusual phase transformation of calcite to spherical vaterite crystals. Thus, AMP in combination with CAA and CAP can be used as a CO2 absorbent and buffering agent for the sequestration of CO2 in porous CaCO3.