(685c) Enhancing Monoethanolamine Regeneration at Low Temperatures Via in-Situ Precipitation of Solid Carbonates

Climate change is one of the biggest risks facing mankind and scientific evidence correlates the rise in global temperature to the concentration of CO₂ in the atmosphere. Carbon dioxide gas represents a majority of 82% of the total greenhouse gas emissions in the United States with nearly 33% of total emission coming from power generation plants that burn coal and natural gas. Currently, Carbon Capture and Sequestration (CCS) with amine solvents stands as the most effective and industrially applicable chemical separation technology demonstrated at a commercial scale. Aqueous solutions of monoethanolamine (MEA) are highly regarded as ideal chemical absorbents for CO₂ capture due to their high absorption capacity (reaching 0.5 mol CO₂/mol MEA), fast reaction kinetics, and high degree of regenerability. However, amine scrubbing processes suffer from the parasitic energy demand where half of the operational energy is devoted to thermally regenerate the rich amine solvent and the other half is to compress the captured CO₂.

Precipitating CO₂ as a solid phase represents an economical and effective way of regenerating CO₂-rich amine solutions. Particularly, reacting carbonate ions in solution with calcium ions (from various sources) takes advantage of the availability of large amounts of dissolved CO₂ in amine solutions and the spontaneous mineralization reaction to CaCO₃ – the most thermodynamically stable form of carbon. In this work, we show that CO₂ loading of 22 vol% MEA solutions can be significantly reduced from 0.28-0.42 to 0.034-0.05 mol CO₂/mol MEA by mixing the loaded solutions with stoichiometric amounts of CaO, Ca(OH)₂ and CaCl₂ at low regeneration temperatures. In our experiments, Ca(OH)₂ and CaO demonstrated an outstanding mineralization property by removing 86.9 mol% and 83.6 mol% of the absorbed CO₂, respectively, with almost no gas desorption. On the other hand, CaCl₂ was found to mineralize 72.1 mol% of the absorbed CO₂ while 13.4 mol% was desorbed as a gas. The presence of chlorine ions was found to reduce the alkalinity of the MEA solution which leads to increased gaseous CO₂ desorption during regeneration. In addition, our results demonstrate that partially mineralizing CO₂ and generating solid CaCO₃ in solution improves the kinetics of the subsequent absorption/desorption cycles. Specifically, the maximum absorption and desorption rates for the solid containing solutions showed 8.8 and 20% increase in the maximum rates of absorption and desorption, respectively, over the solid free solutions.