Poly(ethylenimine)‐Functionalized Monolithic Alumina Honeycomb Adsorbents for CO 2 Capture from Air

The development of practical and effective gas–solid contactors is an important area in the development of CO 2 capture technologies. Target CO 2 capture applications, such as postcombustion carbon capture and sequestration (CCS) from power plant flue gases or CO 2 extraction directly from ambient air (DAC), require high flow rates of gas to be processed at low cost. Extruded monolithic honeycomb structures, such as those employed in the catalytic converters of automobiles, have excellent potential as structured contactors for CO 2 adsorption applications because of the low pressure drop imposed on fluid moving through the straight channels of such structures. Here, we report the impregnation of poly(ethylenimine) (PEI), an effective aminopolymer reported commonly for CO 2 separation, into extruded monolithic alumina to form structured CO 2 sorbents. These structured sorbents are first prepared on a small scale, characterized thoroughly, and compared with powder sorbents with a similar composition. Despite consistent differences observed in the filling of mesopores with PEI between the monolithic and powder sorbents, their performance in CO 2 adsorption is similar across a range of PEI contents. A larger monolithic cylinder (1 inch diameter, 4 inch length) is evaluated under conditions closer to those that might be used in large‐scale applications and shows a similar performance to the smaller monoliths and powders tested initially. This larger structure is evaluated over five cycles of CO 2 adsorption and steam desorption and demonstrates a volumetric capacity of 350 molCO2  m - 3monolithand an equilibration time of 350 min under a 0.4 m s −1 linear flow velocity through the monolith channels using 400 ppm CO 2 in N 2 as the adsorption gas at 30 °C. This volumetric capacity surpasses that of a similar technology considered previously, which suggested that CO 2 could be removed from air at an operating cost as low as $100 per ton.