The Challenges of Direct Air Capture: Potential for Zeolites

Sean M.W. Wilson

TerraFixing Inc.

Global warming is being driven by increasing levels of CO2 in the atmosphere which increases global surface temperatures. The effects of global warming are particularly worrisome for polar ice-capped regions, like Greenland and Antarctica which experience more significant warming than the rest of the planet; as their ice caps melt and the sea levels rise, many costal populations will have to be displaced. To mitigate the consequences of global warming, researchers, companies, and governments are investing time and effort into finding ways to effectively reduce the amount of CO2 entering the atmosphere or to capture CO2 directly from the air. The latter, direct air capture (DAC), is a technology that captures CO2 directly from the air and concentrates it. When coupled with geological storage, DAC can be used to sequester CO2 permanently into the earth, enabling us to reach net-zero commitments as well as going beyond to clean up emissions of the past.

As promising as DAC can be, there are many challenges for a well-designed process to capture CO2 from the air. A significant challenge for DAC is that CO2 in the air is dilute and capturing 1 tonne of CO2 would require approximately 1,400,000 m3 of air. Because the concentration of CO2 in air is so low, it is uneconomical to significantly change the input air conditions (e.g., temperature, pressure, humidity) during the capture step of a DAC process. Initial studies ruled out physisorption separations for DAC because H2O would competitively adsorb over CO2. Instead, they explored chemisorption separations which favour capturing CO2 from H2O in the air, and accepted the high regeneration energy required for the process. This did not remove water as a problem however, and estimated costs for such technologies are typically greater than $300/tCO2.

Being from Canada and suffering from dry and cracking lips each winter, we can testify that not all air contains significant amounts of H2O. For physisorption separations using zeolites, cold air can be economically dried prior to capturing the CO2. Coincidentally, physisorption DAC technologies in cold climates have other advantages including the thermodynamic efficiencies and synergies of cold temperature gas separations, and that adsorption capacity loadings are substantially larger as temperature drops.

Knowing that 1) cold climates enable more thermodynamically favorable separations; 2) adsorbents (physisorbents) can adsorb significantly more CO2 in colder conditions; and 3) naturally drier air and less water to separate prior to separating the CO2, could locating an adsorbent-based DAC process in the cold dry regions of the planet be an instrument in solving global warming? In this talk, we will explore the opportunity of using affordable and industrially available zeolites in a DAC process located in cold locations such as Canada, Alaska, Greenland, and Antarctica, as a means to reach net-zero and go beyond. This talk will discuss the interplay between DAC processes and their materials, the larger carbon capture system in play, and an economical path forward for DAC.