An new analytical technique for carbon dioxide capture solvents

Aqueous single or mixed alkanolamines are usually used for chemical absorption of CO2 from low-pressure flue gas streams. The performance of the alkanolamines depends on their concentrations, the ratio of components in mixed alkanolamine solutions, and the CO2 loading. In order to track solution performance, it is necessary to determine the concentration of each component in both the CO2-free and CO 2 loaded solvents. The existing methods are very laborious and involve expensive chromatographic techniques (for alkanolamines) and titration for CO2 loading. The objective in this research is to develop simple, more accurate, relatively cheap and easy to use density and refractive index techniques that will replace the existing techniques for non-degraded samples. Densities and refractive indices of binaries ((water + monoethanolamine), (water + methyldiethanolamine), and (monoethanolamine + methyldiethanolamine)) and ternaries ((water + monoethanolamine + CO2), (water + methyldiethanolamine + CO2), and (water + monoethanolamine + methyldiethanolamine)) were measured over the whole range of alkanolamine compositions at temperatures from 22 to 65°C. Experimental densities were modeled empirically, while the experimental refractive indices were modeled using well established Lorenzo-Lorenz, Gladstone-Dale, Weiner, Heller, and Arago-Biot models, the relations of which have been widely used to evaluate the refractive indices of multi-component systems from the known values of pure component indices. Gladstone-Dale had the least deviation for our systems. Using the density and refractive index models, the compositions of unknown samples can be determined. The results from this technique have been compared with HPLC (high performance liquid chromatography) and standard titration results. A third independent technique (titration) was used to verify the results. The results show that the refractive index/density technique is comparable to the HPLC/titration technique, suggesting that the refractive index/density technique could indeed replace other methods for analysis of fresh samples.