Performance of PEI-modified fumed silica monoliths with honeycomb structure for direct air capture of CO2

Direct air capture (DAC) is a technology that captures low concentrations of CO 2 directly from the air. In recent years, amine-modified solid adsorbents have been widely utilized to facilitate an efficient CO 2 capture process. In industrial applications, the significant pressure drop reduced by powder accumulation results in economic losses for fans. However, previous studies on monoliths have failed to simultaneously satisfy the industrial requirements for both adsorption capacity and mechanical strength. In this work, a novel honeycomb monolith was proposed to address this issue. The seven uniformly distributed channels effectively reduced pressure drop, while the wall thickness satisfied the mechanical strength requirements under industrial application conditions. And the structure was optimized by using activated carbon. After high-temperature treatment, the new pore formed in the space previously occupied by the activated carbon. Through the secondary loading approach, the amine loading was comparable to the powder. Compared with the monoliths without activated carbon, the pore volume significantly increased (from 5.31 % to 96.26 %). The pore volume of 20AC-SiO 2 -M reached 0.84 cm 3  g −1 . At 35 °C and 400 ppm, 20AC-SiO 2 -M exhibited the best CO 2 adsorption capacity (1.94 mmol/g) and the fastest CO 2 adsorption rate (0.0395 mmol/(g.min)). Additionally, the structure strength (1.46 MPa) and pressure drop losses (0.002 psi) were tested, and both parameters met the requirements for industrial applications.