Catalytic and non catalytic solvent regeneration during absorption-based CO sub(2) capture with single and blended reactive amine solvents

• Published in: International journal of greenhouse gas control 2014-07, Vol.26, p.39-50
• Main Authors: Shi, Huancong, Naami, Abdulaziz, Idem, Raphael, Tontiwachwuthikul, Paitoon
• Format: Article
• Language: English
• ISSN: 1750-5836
• DOI: 10.1016/j.ijggc.2014.04.007

Molecular potential energy surface (PES) diagrams of the deprotonation of a protonated amine (AmineH super(+)) 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 CO sub(2) stripping from some amine solutions under certain operating conditions. Experiments for CO sub(2) stripping were performed using single and blended amines (namely, MEA, MEA-MDEA, MEA-DEAB (4-(diethylamine)-2-butanol)) with and without solid acid catalysts (Al sub(2)O sub(3) or HZSM-5) at 90-95 degree C. The heat duty to regenerate 5 M MEA without any catalyst was the baseline taken as 100%. The results showed that the CO sub(2) stripping performance in terms of heat duty decreased in the order: MEA-DEAB with HZSM-5 (38%) > MEA-DEAB with gamma -Al sub(2)O sub(3) (40%) > MEA-DEAB with no catalyst (51%) > MEA with HZSM-5 (65%) > MEA with gamma -Al sub(2)O sub(3) (73%) > MEA-MDEA with gamma -Al sub(2)O sub(3)/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 R sub(3)N and HCO sub(3) super(-), 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 HCO sub(3) super(-) resulting in a tremendously lower heat duty. gamma -Al sub(2)O sub(3) (Lewis acid) was more effective in the CO sub(2) lean region by duplicating the role of HCO sub(3) super(-), which is negligible in the CO sub(2) lean region, whereas HZSM-5 (Br phi nsted 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.