Fabrication of a Solid Amine Microspherical Adsorbent with High CO2 Adsorption Capacity via Water-in-Water Emulsion Templating

A spherical solid amine adsorbent has been synthesized in a water-in-water (w/w) emulsion template in an environmentally friendly manner through cross-linking of polyethylenimine (PEI) and ethylene glycol diglycidyl ether. As tested in a fixed bed adsorption experiment, the adsorbent showed a CO₂ adsorption capacity of up to 9.28 mmol/g with a ratio of breakthrough capacity to equilibrium capacity of 0.81 in the presence of moisture at 25 °C, 0.1 bar. The w/w template, in addition to giving the adsorbent the ability to be shaped at low cross-linking degree, also induced the arrangement of amines toward the surface of the microspheres by forming hydrogen bonds, resulting in good swelling capacity and adsorption kinetics of the adsorbent. The adsorption process of this adsorbent was illustrated by the Avrami kinetic model to show that both physical and chemical adsorptions occur, and the diffusion behavior of CO₂ within the adsorbent was evaluated, which showed a multistep diffusion mechanism of cocontrol of intraparticles and film diffusion. After 10 adsorption–desorption cycles, the adsorbent can still maintain a relatively stable adsorption performance. The green synthesis method and the excellent and stable adsorption performance make the adsorbent have natural advantages in the application of CO₂ capture.