Direct Air Capture of CO2 on Activated Carbon Via Temperature Swing Adsorption

Current climate models require the implementation of large-scale carbon dioxide (CO₂) removal to avoid the detrimental effects of global warming. Direct air capture (DAC) has been demonstrated as a promising method to sequester CO₂ from the atmosphere due to its scalability and low land usage compared to other methods of carbon removal. The relatively high cost of conventional CO₂ sorbents has inspired recent research investigating the performance of cheaper sorbents. Activated carbon is a highly porous carbon material typically produced from the pyrolysis of organic material in an inert environment at high temperatures; its high surface area and low cost make it an ideal sorbent for CO₂ capture. The production of activated carbon can also be a method of carbon capture by pyrolyzing biowaste or other sustainable organic materials using renewable energy sources, and thereby keeping their carbon in solid form out of the atmosphere.

In this work, the performance of an activated carbon DAC device was quantified to assess the potential for biochar as a cheap and abundant CO₂ sorbent. Ambient air was fed through a packed adsorption bed to produce a stream of air with lower concentration of CO₂ (<400 ppm). The bed was regenerated using a temperature swing adsorption (TSA) process, in which the sorbent is heated and the captured CO₂ is released, producing a stream with a high concentration of CO₂, which could be sequestered. Initial data show ambient loadings of 73.6 µg CO₂/g sorbent on unactivated commercial biochar; we hope to demonstrate capacities on activated carbon approaching those found in literature (2.28 mg CO₂/g sorbent) [Zhang et al., "Direct air capture of CO2 by KOH-activated bamboo biochar," Journal of the Energy Institute, 2022].