In-situ amine modification of porous polymer/silica spiral wound module for CO2 capture from ambient air

Traditional solid amine adsorbents in powdery morphology are not suitable for direct air capture (DAC) adsorption processes requiring high air flow rates, as the adsorber applicable for adsorbent particles unavoidably results in high pressure drop. Herein, we demonstrate a flexible membrane solid amine adsorbent based on cellulose acetate/silica composite supports that is fabricated into a spiral wound module functioning as a gas–solid contactor, presenting reduced pressure drop and comparable adsorption capacities with powdery solid amine materials. First, the phase inversion method is utilized to prepare cellulose acetate/silica membrane support, where the doping amount of silic varies from 60 wt% to 80 wt%. After assembling the support into a spiral module, poly (ethyleneimine) (PEI) is loaded in the module via an in-situ amine impregnation method, that the amine solution flows into the module which could reduce the support mass loss encountered in the conventional static impregnation method. The CO 2 adsorption capacity of the representative flexible membrane solid amine adsorbents reaches 1.6 mmol/g in 400 ppm CO 2 at 35 °C and increases to 2.37 mmol/g under humid conditions. Surprisingly, the adsorbent at a low PEI loading of 6 wt% has an adsorption capacity of 0.83 mmol/g at −10 °C, offering a high amine efficiency of 0.58 mmol CO 2 /mmol N. This is attributed to dominant CO 2 physisorption at sub-ambient temperatures, signifying its unique advantages in reduced energy penalty and adsorbent costs related to high amine efficiency. Upon exposure to the actual atmosphere (27 °C ± 2 °C, 50 %RH), the spiral module displays an impressive adsorption capacity of 1.9 mmol/g, highlighting its great potential for practical application in a DAC process.