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 degrees 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 degrees 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.