Assessment of reasonable opportunities for direct air capture

This work explores the possibility of using CO2 captured directly from the atmosphere for several applications that require low to moderate purities. Comparisons of the minimum and real work for separating CO2 from air, natural gas combined cycle flue gas and pulverized coal combustion flue gas are proposed and discussed. Although it is widely accepted that the separation of CO2 from air to high purity is more energy-intensive than separating CO2 from more concentrated sources, this study presents select cases where the separation of CO2 from air to low and moderate purities is energetically equivalent with the work required for flue gas CO2 separation. These energetically-competitive cases are shown to be dependent on the percent capture and final CO2 purity desired. In particular, several technologies can be considered as CO2 utilization opportunities in which dilute CO2 may be an adequate feedstock. Specifically, this study is focused on enhanced oil recovery and microalgae cultivation technologies, which appear to be the most beneficial near-term applications for utilization of CO2 from direct air capture.