Energy-Efficient Amine Regeneration for Absorption-Based Carbon Capture: Kinetic Studies for CO2 Mineralization

Abstract

In point-source carbon capture, CO2 from flue gas is typically absorbed by amine solutions, and the amine is regenerated by steam stripping. The regeneration step is energy intensive. This study aims to substitute steam stripping with an energy-efficient mineralization process. The CO2-laden amine solution is treated with fly ash under near-ambient conditions (40 °C, 1 atm) to regenerate the amine and produce carbonated fly ash. This study assesses the performance of the mineralization process for primary and tertiary amines. First, dissolution of fly ash into 15 wt% monoethanolamine (MEA) or N-methyldiethanolamine (MDEA) is studied. Afterward, a 15 wt% concentration of amine solutions was saturated with a flue gas (10% CO2) and then reacted with fly ash for mineralization. Liquid samples are regularly collected and analyzed for pH and CO2 loading. After mineralization, precipitates are analyzed for carbonate content. The dissolution of Ca and Mg from fly ash occurs faster with MDEA solution compared to MEA solution of the same concentration. Adding fly ash to CO2-laden amine solutions results in the formation of CaCO3 and MgCO3 and the regeneration of the amine solution. MDEA can be fully regenerated in about 15 hours, while MEA achieves 80% regeneration in 6.5 days. The mineralization rate is kinetically limited by the dissolution of reactive compounds from fly ash in the case of tertiary amine, and by the carbamate conversion to bicarbonate in the case of primary amine. The rate of amine regeneration decelerates rapidly during the initial 5 hours with a starting rate of 0.003 M/hour. There is a 24% weight increase in the case of MEA and 30% in the case of MDEA during the mineralization. The precipitates contain ~60% carbonates in the form of CaCO3 and MgCO3. This study demonstrates that CO2 desorption from amine solutions can occur through mineralization, converting CO2 into carbonates at low pressure and temperature with fly ash. Fly ash derived from lignite and sub-bituminous coals is preferable as a reactant since it has high calcium content.