Direct air capture (DAC) can provide an impactful, engineered approach to combat climate change by removing carbon dioxide (CO2) from the air. However, to meet climate goals, DAC needs to be scaled at a rapid rate. Current DAC approaches use engineered contactors filled with chemicals to repeatedly capture CO2 from the air and release high purity CO2 that can be stored or otherwise used. This review article focuses on two distinctive, commercial DAC processes to bind with CO2: solid sorbents and liquid solvents. We discuss the properties of solvents and sorbents, including mass transfer, heat transfer and chemical kinetics, as well as how these properties influence the design and cost of the DAC process. Further, we provide a novel overview of the considerations for deploying these DAC technologies, including concepts for learning-by-doing that may drive down costs and material requirements for scaling up DAC technologies.

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Negative emissions technologies will play an important role in preventing 2 °C warming by 2100. The next decade is critical for technological innovation and deployment to meet mid-century carbon removal goals of 10−20 GtCO 2 /yr. Direct air capture (DAC) is positioned to play a critical role in carbon removal, yet remains under paced in deployment efforts, mainly because of high costs. This study outlines a roadmap for DAC cost reductions through the exploitation of low-temperature heat, recent U.S. policy drivers, and logical, regional end-use opportunities in the United States. Specifically, two scenarios are identified that allow for the production of compressed high-purity CO 2 for costs ≤$300/tCO 2 , net delivered with an opportunity to scale to 19 MtCO 2 /yr. These scenarios use thermal energy from geothermal and nuclear power plants to produce steam and transport the purified CO 2 via trucks to the nearest opportunity for direct use or subsurface permanent storage. Although some utilization pathways result in the re-emission of CO 2 and cannot be considered true carbon removal, they would provide economic incentive to deploying DAC plants at scale by mid-century. In addition, the federal tax credit 45Q was applied for qualifying facilities (i.e., producing ≥100 ktCO 2 /yr).

To avoid dangerous climate change, new technologies must remove billions of tonnes of CO 2 from the atmosphere every year by mid-century. Here we detail a land-based enhanced weathering cycle utilizing magnesite (MgCO 3) feedstock to repeatedly capture CO 2 from the atmosphere. In this process, MgCO 3 is calcined, producing caustic magnesia (MgO) and high-purity CO 2. This MgO is spread over land to carbonate for a year by reacting with atmospheric CO 2. The carbonate minerals are then recollected and re-calcined. The reproduced MgO is spread over land to carbonate again. We show this process could cost approximately $46-159 tCO 2 −1 net removed from the atmosphere, considering grid and solar electricity without post-processing costs. This technology may achieve lower costs than projections for more extensively engineered Direct Air Capture methods. It has the scalable potential to remove at least 2-3 GtCO 2 year −1 , and may make a meaningful contribution to mitigating climate change.

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