One of the permanent and environmentally benign approaches of capturing, converting and storing CO2 is via carbon mineralization to produce water insoluble calcium or magnesium carbonates. The chemical pathways involved in converting CO2 to Ca- or Mg-carbonates are thermodynamically feasible but kinetically slow. Broadly, two approaches were proposed to accelerate the kinetics of carbon mineralization. In the first approach, direct conversion of CO2 to Ca- or Mg-carbonates using a range of feedstocks including oxides, hydroxides, or silicates of Ca or Mg is achieved at elevated temperatures (&gt;100 oC) and pressures (&gt; 10 atm). In the second approach, the use of additives in multi-step processes to produce high purity Ca- or Mg-carbonates was studied. However, few studies focused on the direct capture, conversion and storage of CO2 at temperatures below 100oC and with dilute gaseous streams of CO2 given the low solubility of CO2 in water, and slow kinetics of mineral dissolution. To enhance CO2 solubility and accelerate the conversion of dissolved CO2 to Ca- or Mg-carbonate, the use of amine-bearing solvents is proposed. In this study, we investigate the influence of monoethanolamine (MEA) to capture CO2 followed by chemical regeneration via the formation of Ca- or Mg-carbonate. The approach allows us to overcome the critical limiting step of low solubility of CO2 at low CO2 partial pressures at ambient temperature. We successfully demonstrated 100% and 70% conversion of CaO and MgO to their respective carbonates at temperatures in the range of 50-75oC with 30 wt% MEA. Wide Angle X-Ray Scattering (WAXS) measurements showed the formation of a mixture of vaterite, aragonite and calcite phases and hydrated magnesium carbonate (or nesquehonite, MgCO3.3H2O) on reacting CaO and MgO, respectively. The mechanisms associated with MEA regeneration and carbonate formation were investigated using Fourier Transform-Infrared Spectroscopy (FT-IR) measurements. Sizes of the nucleated carbonates were determined using in-operando Grazing Incidence – Small Angle X-Ray Scattering (GI-SAXS) measurements.

Direct capture, conversion and storage of CO2 as calcium and magnesium carbonates using an innovative aqueous alkaline amine looping (A3L) process

2019 Fall National Meeting

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