CO2 Absorption into Aqueous Amine Blends containing Benzylamine (BZA), Monoethanolamine (MEA), and Sterically Hindered/Tertiary Amines

AbstractTo date, a single mono-amine solvent with ideal properties for CO2 capture processes is yet to be found. As a compromise, solvent formulations incorporating two or more individual amines into a single solvent blend have been proposed and are gaining momentum as next generation capture solvents. Recently we have identified benzylamine (BZA) for use as a CO2 capture solvent. A significant drawback with BZA is the formation of stable carbamate salts at high CO2 loadings which has severely limited the concentration of BZA which can be used. Thus, BZA is ideally placed as a candidate for use in formulations with other amines.In this study, we investigate CO2 absorption into aqueous solvent blends containing BZA, MEA, sterically hindered, and tertiary amines using a wetted-wall column contactor at 40oC, and simulations of the vapour liquid equilibrium behaviour of the blends using a software tool developed in Matlab. Overall CO2 mass transfer coefficients, KG, at 40oC are reported for blends containing 3.0M BZA together with 3.0M of the second amine component. Several of the formulations were found to possess significantly faster absorption rates than in standalone MEA solutions at similar total amine concentrations, and CO2 loadings, as in the blends. A formulation containing BZA and MEA was found to display the fastest CO2 absorption rates due to the blend containing two fast reacting components. Highly branched and sterically hindered amines in formulations with BZA limit the CO2 absorption rate due to the parallel impact of the amine structure on the physical properties of these solutions. Absorption capacities at 40oC are similar in each of the blends with 6.0M MEA, however cyclic capacities are significantly higher in the majority of the BZA blends with the largest improvement observed being 92% in a blend containing 3.0M BZA and 3.0M AMP. Overall absorption enthalpies in all of the BZA blends here were found to be larger than that observed in standalone MEA due largely to the contribution from the larger protonation enthalpy of BZA