The worldview on climate change is shifting and with it, the technologies we utilize are shifting too. The levels of carbon dioxide (CO2) in our atmosphere is rising at a rate of approximately 2% per year. Many modern innovations aim to minimize our carbon footprint and research in the field of Direct Air Capture (DAC) is one such technology. The end goal of DAC is to remove CO2 from the air and subsequently, either store it or sell it. In this way, DAC works to buy time by offsetting CO2's growth trend for now and can work in tandem with renewable energy technology to reverse global warming in the future. Though this field is still young, several promising technologies are hoping to make it to the forefront of the world in the upcoming years.
Removing CO2 from Thin Air
Researchers at TU Wien have developed a technology to remove CO2 from ambient air with the help of Temperature Swing Adsorption (TSA). Adsorption is a process in which a solid binds molecules from a gas, liquid, or dissolved solid onto its surface. The adsorbent, which performs the binding, is then cleaned, removing the particles. In the case of TSA, the desorption column is hotter than the adsorption column, which gives better results. This technology can be utilized to separate CO2 from ambient air. By picking an adsorbent that selectively binds CO2, air passing through the apparatus will have its’ CO2 stripped while the other compounds are left untouched. The adsorbent can then be cleaned with the help of steam. The outcome? A stream of close to pure CO2. Researchers at TU Wien have a working prototype that can remove CO2 at an energy cost which is below the energy costs of industry competitors.
From Hazard to Helper
Professor Gregory Dipple of the University of British Columbia has developed a method of permanently removing CO2 in an energetically favorable manner… by storing it in rocks. The specific rocks are mine tailings, a waste product of mines. Currently, mine tailings serve few purposes and act as an environmental hazard. The mining industry also accounts for between 4 to 7 percent of annual global greenhouse gas emissions. Dr. Dipple’s work deals with chemically converting CO2 into bicarbonate (HCO3-) and then sequestering this product into the tailings as a hydrate (ex: MgCO3•3H2O). This reaction is a natural process that already occurs at mines around the world (although slowly) and can be sped up with a minimal energy investment. Moderate estimates have the sequestering costs at $100 per ton CO2. Dr. Dipple predicts that this method can sequester up to 10 MT of CO2 per year.
Trash to Treasure
At Aalto University in Finland, Professor Mika Järvinen and his team have developed a method of sequestering CO2 into steel slag, a waste product of the steel making process. Currently, steel is a large producer of the worlds CO2 emissions, accounting for 8% of global emissions in 2018. Aalto’s process can significantly cut into this margin. The reaction first strips the steel slag of its calcium, which is then reacted with CO2. The product of this reaction, Precipitated Calcium Carbonate (PCC), is a marketable product that has uses in the steel, paper, polymer, and healthcare industries. There are several factors which reduce energy costs for this process including that solvents in the reaction can be reused up to 10 times, the calcium extraction and carbonation steps can be combined, and the overall reaction is thermodynamically favorable. Dr. Järvinen predicts that this process can sequester up to 64 tons of CO2 annually.
Although cost-prohibitive before, DAC and carbon sequestration technologies are becoming more affordable than ever. This is great news because in the next decade, carbon removal is going to be a vital part of the fight against climate change, especially as the move to renewable energy has been so slow. DAC is just one way we can buy time for the future.
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