Catalytic and non catalytic solvent regeneration during absorption-based CO2 capture with single and blended reactive amine solvents

Abstract

Molecular potential energy surface (PES) diagrams of the deprotonation of a protonated amine (AmineH+) were used in combination with ion speciation plots of the vapour liquid equilibrium (VLE) model to provide a better understanding of the reasons for the drastic reduction of energy required for CO2 stripping from some amine solutions under certain operating conditions. Experiments for CO2 stripping were performed using single and blended amines (namely, MEA, MEA–MDEA, MEA–DEAB (4-(diethylamine)-2-butanol)) with and without solid acid catalysts (Al2O3 or HZSM-5) at 90–95°C. The heat duty to regenerate 5M MEA without any catalyst was the baseline taken as 100%. The results showed that the CO2 stripping performance in terms of heat duty decreased in the order: MEA–DEAB with HZSM-5 (38%)>MEA–DEAB with γ-Al2O3 (40%)>MEA–DEAB with no catalyst (51%)>MEA with HZSM-5 (65%)>MEA with γ-Al2O3 (73%)>MEA–MDEA with γ-Al2O3/no catalyst (74%), all relative to MEA with no catalyst (100%). The results further show that the addition of MDEA or DEAB (as tertiary amines) in a blended solvent provided R3N and HCO3−, which split and thus decreased the free energy gaps. On the other hand, even though MDEA is intrinsically less basic as per the energy diagram, DEAB generated a lot more HCO3− resulting in a tremendously lower heat duty. γ-Al2O3 (Lewis acid) was more effective in the CO2 lean region by duplicating the role of HCO3−, which is negligible in the CO2 lean region, whereas HZSM-5 (Brϕnsted acid) is effective throughout the loading range by donating protons. The implication is that the use of solid acid catalysts could result in stripper size and heat duty reductions during solvent regeneration.