Direct Air Capture

Photosynthesis, the well-known process of converting carbon dioxide into energy with the help of sunlight, is perhaps one of nature’s most important and fascinating chemical reactions. Its carbon-converting abilities have led to efforts, such as reforestation and afforestation, to reduce harmful greenhouse gas levels that trap solar energy and effectively increase global temperature. The only problem with these methods is that it can take years for forests to grow, and afforestation (the process of planting trees where there previously were none) can compete with land needed to meet the agricultural production demands of our growing global population. But what if we could replicate the photosynthetic process using technology? That is essentially what direct air capture, a new technology capable of capturing carbon dioxide from the atmosphere, aims to do.

Currently, only three notable companies are involved in direct air capture (DAC) operations, and their primary functions range from underground sequestration to conversion into fuel, plastics, and concrete. The first, Carbon Engineering, is located in Canada and operates through a closed chemical loop. The loop begins with a strong hydroxide solution that absorbs CO2 and converts it into a carbonate. The carbonate solution is then shaped and dried into small calcium carbonate pellets, which are heated until the CO2 is released in a pure and compressed form for further use, leaving behind calcium oxide. This calcium oxide is ultimately hydrated so that it can be used as the hydroxide capture solution in the first step. The second company, Climeworks, is Switzerland-based. Climeworks operates through a filter to which CO2 becomes chemically bound. Once the filter is saturated, the CO2 is heated, released, and collected in a concentrated form while the remaining “purified” air is released back into the atmosphere. The third and final company, Global Thermostat, is based in New York. Unfortunately, their exact carbon removal process has not been disclosed.

What differentiates direct air capture from traditional carbon capture methods is the fact that, rather than requiring a set up directly adjacent to CO2-emitting warehouses, direct air capture plants can be installed anywhere. This means higher flexibility with cheaper and faster transportation of end products. As mentioned previously, direct air capture also covers a wide range of services. One primary purpose of DAC is to create “negative emissions” by injecting captured carbon dioxide into geological reservoirs, mimicking how CO2 is absorbed naturally. While direct air capture hasn’t been implemented at large enough scales to significantly reduce CO2 levels (yet!), it has the unique ability to produce commonly-used materials that are low-carbon or carbon-neutral, since it’s essentially just recycling CO2 emissions already present in the atmosphere. For example, oil and gas tycoon ExxonMobil recently closed a deal with Global Thermostat to launch a “DAC-to-fuel” operation. DAC-to-fuel may be key to the transition from oil-based transportation to carbon-neutral electric, since synthetic fuels operate normally in gasoline and diesel engines, and emissions are offset by the carbon extraction processes used to make them. DAC-to-fuel is especially enticing because it offers a new energy source that could help combat the global energy crisis. Interestingly enough, the manufacture of materials such as cement, plastic, and steel serves as the third biggest contributor of greenhouse gases globally. Luckily, direct air capture has also been directed towards the manufacturing of carbon-neutral concrete and plastic. Even more fascinating is the discovery that injecting CO2 into cement (to reduce its carbon footprint) actually makes the material stronger and more durable.

A frequently-cited argument against direct air capture is that the technology is too expensive to be realistically implemented at a large scale. Up until recently, this appeared to be the case. New investments by Bill Gates, Zurich Cantonal Bank, and more, however, appear to be pushing these companies towards commercialization. A National Academy of Sciences (NAS) report last October estimated that DAC will be economically competitive with traditionally-sourced oil once CO2 extraction prices approach $100-150 per ton of carbon. Since then, Carbon Engineering has reported CO2 extraction prices as low as $94/ton at scale, and Global Thermostat has reported prices of $120/ton (predicting it can eventually reach $50/ton at scale). At this point, we can only sit back and watch how large-scale implementation of DAC pans out.

Despite DAC’s myriad benefits, there are still a number of drawbacks that need to be addressed. For example, direct air capture operation and implementation requires considerable energy input that could be counterproductive to the task at hand. For this reason, it is crucial to look at the full life cycle of carbon capture and storage solutions. Direct air capture is commonly applied towards enhanced oil recovery (EOR), a process in which CO2 is pumped into oil fields, releasing trapped oil while remaining underground. While net carbon emissions would still be low compared to traditional oil sourcing, there’s a chance this process could prolong oil usage and hinder the transition to carbon-neutral and electric transportation (although electric vehicles have a long way to go in terms of mileage and price). Carbon injection requires thorough communication with the communities it directly affects to ensure that natural landscapes won’t be destroyed. The knowledge that carbon-removing technologies like these exist could also decrease incentives to cut back on carbon footprints. And, of course, DAC is only capable of removing small percentages of atmospheric CO2 at a time. 

Ultimately, direct air capture has the ability to play a significant role in the battle against climate change (as well as the energy crisis), so long as it continues to grow in practicality and is used in conjunction with other sustainable energy practices—including traditional carbon capture technologies, reforestation, renewable energy investments, increased efficiency of solar cells and hydropower, and tighter environmental policies. In other words, cutting back on greenhouse gas usage is just as valuable as efforts to actively remove anthropomorphic emissions. It is important to remember that such a massive undertaking is going to require not one, not a few, but hundreds of different angles running simultaneously if we truly want to save the planet.