The struggle to cut emissions is a significant and urgent issue facing the world today, with last year seeing a new record high of over 37 billion metric tons of carbon dioxide emissions. In response, governments and researchers are turning to technology such as direct air capture to help achieve climate goals and mitigate the impacts of climate change. However, despite the existence of several direct air capture facilities globally, the technology still faces challenges, particularly in terms of high energy use. A study published in the journal ACS Energy Letters by researchers at the University of Colorado Boulder and collaborators highlighted the limitations of current approaches to reducing energy costs in direct air capture and proposed a more sustainable design for capturing CO2 and converting it to fuels.
One common approach to direct air capture involves using air contactors, which are essentially large fans that pull air into a chamber filled with a basic liquid that reacts with CO2 to form harmless carbonate or bicarbonate. Stratos, one of the world’s largest direct air capture facilities under construction in Texas, uses this method. However, to release the trapped CO2 for conversion into useful products, companies typically need to heat the carbonate and bicarbonate solution to high temperatures using fossil-based fuels such as natural gas. This process undermines the goal of capturing carbon emissions, as it requires additional emissions to release the captured CO2.
In response to these challenges, researchers are exploring new approaches such as reactive capture, which involves applying electricity to the carbonate and bicarbonate solutions to separate CO2 and the basic liquid. However, the team at the University of Colorado Boulder found that this method may not be as effective as initially thought, as the basic liquid’s ability to capture CO2 diminishes after multiple cycles. To address this issue, the researchers proposed adding electrodialysis to the reactive capture process, which involves splitting additional water into acidic and basic ions to maintain the basic liquid’s absorption capacity. Electrodialysis can run on renewable electricity, offering a potentially sustainable way to convert captured CO2 into useful products and reinforce concrete, a major emitter of carbon.
The Intergovernmental Panel on Climate Change (IPCC) emphasizes the importance of carbon dioxide removal to achieve global and national targets for net zero emissions. While over 20 direct air capture plants are currently operational worldwide and 130 more are under construction, experts like Wilson Smith stress that reducing emissions remains the most critical step in addressing climate change. Smith uses the analogy of Earth as a bathtub filling up with CO2 ‘water’ from the faucet, noting that while carbon capture technology can help scoop out some water, turning off the faucet by cutting emissions is the most effective strategy for preventing the consequences of climate change. Technologies like direct air capture offer potential solutions to mitigate emissions, but the focus should be on reducing overall emissions to avoid the most severe impacts of climate change.