(474e) CO2 Capture Using Phase-Changing Bis-Iminoguanidines (BIGs) with Amino Acids

CO₂ capture using phase-changing bis-iminoguanidines (BIGs) with aqueous amino acid (sarcosine and glycine) is investigated in this study. This work seeks to understand the phase-changing bicarbonate crystallization of glyoxal-bis-iminoguanidine (GBIG). CO₂ capture processes involving BIGs are of major interest due to their comparatively lower regeneration energy requirements. Unlike in monoethanolamine (MEA), which does not change phase, only the insoluble bicarbonate precipitate undergoes thermal regeneration instead of the bulk solution, thus saving energy. A critical step in the proposed CO₂ capture mechanisms is the regeneration of the deprotonated amino acid. This regeneration was modelled and studied kinetically and thermodynamically through the crystallization of GBIGH₂²⁺(HCO₃^–)₂(H₂O)₂. A theoretical model simulating glycine regeneration was developed to determine the rate limiting step of the system. A combined analysis using experimental data and modeling results indicates that the GBIG-bicarbonate crystallization step provides most of the thermodynamic driving force for the deprotonated glycine regeneration and that the protonation of GBIG prior to crystallization is the rate-limiting step. The CO₂ loading and amino acid regeneration steps were intensified into a single-step process using a bubble column reactor. The CO₂ loading capacity of the intensified GBIG process was experimentally determined at 1.36 mol CO₂ per mol GBIG. These results provide the fundamental basis for developing an effective carbon capture technology with phase-changing amino acid/guanidine absorbents that can be used to effectively capture both point-source emissions and atmospheric CO₂.