The increase in CO₂ emissions seems unstoppable. The fifth progress report produced by the Intergovernmental Panel on Climate Change (IPCC) confirms that more greenhouse gas than ever has been emitted. If progress on a global scale towards using alternative energy sources or slowing the pace of industrial development seem to be superhuman tasks, scientists and engineers have proposed systems to take this gas out of the atmosphere. Forever.
It is what is known as carbon capture and storage (CCUS technologies). New specially designed power plants are able to avoid the emission into the atmosphere of the CO₂ produced. The gas can then be captured and injected into geological repositories, such as exhausted oilfields, for permanent storage.
However, the idea of injecting gases into the subsurface is not without its critics. Seismic events like those that happened in September last year in the natural gas reservoir of the Castor project off the coast of Castellón have raised concerns in the neighboring towns, such as the fear that a massive leak could occur with lethal consequences. Innovative projects could solve these problems by changing the fate of the captured CO₂ from simply being stored into becoming raw material.
The first of these alternatives takes advantage of a natural process, photosynthesis, to use microscopic algae capable of converting CO₂ into hydrocarbons, used in turn as a raw material in the manufacture of plastics and fuels. Numerous petrochemical companies have been investing in the development of this technology. A recent report from Utah State University in the USA estimates that the cultivation of microalgae can produce 50 times more fuel per acre than soybeans. These facilities can be built on land that is unfit for agriculture and thus do not compete for soil, and they use non-potable or even brackish water.
Instead of using atmospheric carbon dioxide, these algae growing facilities can be coupled to power plants with CO₂ capture. If these power plants also use the biofuel generated by the algae and other sources, the resulting cycle can cause what are known as negative emissions, removing CO₂ from the atmosphere while producing energy.
Another way for nature to get rid of CO₂ is to turn it into rock, although this chemical process requires enormous periods of time. Several companies, such as Calera or Skyonic, have chosen to accelerate the reactions, in some cases using waste products from other chemical industries or producing secondary compounds that are also marketable, such as sodium bicarbonate, and that help them to achieve greater profitability.
The calcium carbonate obtained can be used as raw materials in the construction industry, for example in the production of cement. Another company, CarbonCure, has also opted for cement but with another approach: injecting the CO₂ into the production of concrete blocks so that it is captured and the carbonation occurs within this confinement.