Toward Low-Temperature Regeneration of CO₂ Capture Adsorbents: Functionalization of Polyethylenimine

This study aimed to design materials for CO2 capture with low regeneration temperatures without compromising the adsorption capacity (AC). Branched polyethylenimine (BPEI) functionalized with acrylonitrile (AN), 2-ethylhexyl acrylate (EHA), and butyl acrylate (BA) was impregnated onto fumed silica and tested for its adsorption and desorption properties. Higher functionalization degrees led to decreased desorption temperatures (DTs) from 73 to 97 °C to as low as 25 °C, which was attributed to the higher percentages of secondary amines upon functionalization and changes in the CO2 adsorption mechanism. However, the adsorption capacities also decreased with functionalization. Bayesian optimization using machine learning models predicted optimal compositions of adsorbents for high adsorption capacities at low regeneration temperatures. The isothermal operation of CO2 capture and release was also demonstrated to lower the energy requirement for CO2 capturing systems. The functionalized BPEI materials steadily adsorb and release CO2 for 20 cycles under isothermal conditions without any deterioration of the performance. BPEI 10,000 functionalized with AN, EHA, and BA offers a promising balance between AC and DT, making it suitable for industrial applications.