Carbon Dioxide Removal from Humid Atmosphere by a Porous Hierarchical Silicoaluminophosphate/Carbon Composite Adsorbent

Abstract

A chabazite-type silicoaluminophosphate (SAPO-34) was grown within the meso-and macropores of activated carbon (AC) via a confined space synthesis and functionalized via the addition of strontium(II) (i.e., Sr 2+ -CSAPO-34) for the selective adsorption of CO 2 in the presence of humidity. The in situ growth of the SAPO phase was corroborated through SEM/ EDAX, XRD, and pore size distribution profiles. About 80% of the meso-and macropores of AC were occupied by the SAPO. Sr 2+ -CSAPO-34 was further characterized via XRD, TGA, ICP-OES, and water contact angle measurements. A physical mixture of Sr 2+ -SAPO-34 and AC was also prepared to contrast against the hierarchical variant. The selectivity and capacity for trace CO 2 removal were evaluated through single-component equilibrium and multicomponent fixed-bed adsorption. Bed tests (v = 200 mL min −1 and C i = 500, 1000, or 2500 ppm) showed that the CO 2 capacity remains in the presence of 90% relative humidity, with no signs of rollup. Specifically, the uptake capacity of the Sr 2+ -CSAPO-34 bed for a CO 2 feed content of 1000 ppm was 0.11 mmol per cm 3 of bed and with a breakthrough point greater than 2000 bed volumes; this is superior compared to other adsorbents for CO 2 capture under humid conditions. The Sr 2+ -CSAPO-34 composite bed was also subjected to various cycles upon vacuum-assisted thermal regeneration, and no decrease in adsorption capacity was observed. The adsorbent hierarchical design approach showed that a synergistic combination of hydrophobicity and enhanced adsorbate−adsorbent interactions at the physisorption level is a promising strategy for removing trace CO 2 under humid conditions.

Investigation of CO2-Sorption Characteristics of Readily Available Solid Materials for Indoor Direct Air Capturing

“…The major concern here is the high energy demand due to the fact that CO 2 is filtered at a very low concentration in the range of only 400-1000 ppm. However, several working groups were able to show that there is potential to lower the energy demand by either optimizing the capturing process itself or integrating it into a suitable environment [16][17][18][19][20]. To date, major limitations for using DAC on a large scale for CO 2 -separation are large mass-specific energy demands of several MWh t-1/t CO 2 [21], large investment costs for CO 2 -adsorber material, and the availability of suitable upstream and downstream technologies that create cobenefits by using DAC in sector-coupling applications.…”