¹³C NMR Studies on the Dissolution Mechanisms of Carbon Dioxide in Amine-Containing Aqueous Solvents at High Pressures toward an Integrated Coal Gasification Combined Cycle−Carbon Capture and Storage Process

Carbon dioxide (CO 2 ) capture and storage (CCS) technology has emerged and become a promising tool for the control of greenhouse gas emissions. CCS is applicable to the integrated coal gasification combined cycle (IGCC) equipped with a water-gas shift reaction (IGCC−CCS). In our previous studies, we obtained novel chemical absorbents suitable for IGCC−CCS and examined vapor−liquid equilibria of the absorbents. However, the mechanisms of dissolution of pressurized CO 2 into the solvents (e.g., determination of the fractions of CO 2 absorbed chemically and physically under high CO 2 pressure conditions) were not clear, even though this information is very important for estimation of the energy requirements for the CCS process. We examined the usefulness of 13 C NMR spectroscopy to determine CO 2 solubility and the components of inorganic carbon species (bicarbonate/carbonate and molecular CO 2 ) in six different amine-containing aqueous solvents, at temperatures ranging from 40 to 70 °C and CO 2 pressures ranging from 0.5 to 4 MPa. We found that (i) the amounts of CO 2 physically absorbed into the solvents increased with increasing CO 2 pressure and comprised 15−30% of the total CO 2 in all the solvents at 40 °C and 4 MPa, and (ii) the solubility determined by 13 C NMR spectroscopic and vapor−liquid equilibrium measurements were in good agreement over the CO 2 pressure range examined. The results indicate that we could not only obtain CO 2 solubility data but also identify the inorganic carbon species in the solvents by quantitative 13 C NMR spectroscopy.