The Emergence of Circular Carbon


Our goal for many years now has been to stop the accumulation of greenhouse gases (GHGs) in the atmosphere, especially the most abundant one, carbon dioxide (CO2), from destroying our climate’s equilibrium. Decarbonization is the word of the day. Every industry is seeking ways to achieve its ends without emitting CO2. Yet, in our efforts to eliminate it, we often forget that carbon is essential to life and essential to the planet’s energy balance. The question, therefore, is not simply to decarbonize but to manage carbon, to keep it where it ought to be.

Managing carbon entails understanding its role in both the natural and industrial worlds. Carbon cycles through many parts of these worlds by coupling and decoupling with other elements. In the natural world, plants absorb carbon dioxide from the air, and through photosynthesis, they transform it into plant matter. From there, it cycles through the soil or is eaten by animals, etc. There is an enormous potential to absorb carbon into soils and vegetation, through appropriate “carbon farming” practices and by planting forests. Peatlands are great stores of carbon, and we can leave them undisturbed. Helping ocean kelp forests survive allows them to continue to store carbon as well.

In the industrial world, people have dug up and drilled up hydrocarbons such as coal, oil, and natural gas and burned it, releasing now over 37 billion tons of CO2 every year. The first task for carbon management is to defossilize industry, and to leave the carbon in the ground. Carbon reduction includes all the ways we stop using these hydrocarbons, such as substituting renewable energy for conventional power plants, substituting electric vehicles for internal combustion engine vehicles, or substituting heat pumps for gas or fuel boilers. The accumulation of CO2 in the atmosphere and in the ocean, however, is such that it will not be sufficient to replace the burning of hydrocarbons with renewable energy. Still, we need to remove carbon dioxide as well.

Carbon dioxide removal (CDR) uses negative emissions technologies (NETs) to take CO2 out of the atmosphere and stash it away for long periods of time. It can be pumped into depleted oil wells or salt caverns indefinitely. This is what is meant by carbon capture and sequestration (CCS). Enhanced Oil Recovery (EOR) entails pumping carbon dioxide into oil wells to squeeze out much more oil. The oil and gas industry now pumps 70 to 80 million tons yearly for this purpose, part of which remains underground.

The newest frontier is carbon recycling, which takes waste carbon and transforms it into new products. By keeping carbon in endless product and energy cycling, this carbon stays out of the atmosphere and oceans. It also means we do not need to pull up more oil, coal, and gas from underground as sources of carbon, so recycled carbon can displace fossil carbon. If, in addition, we recycle carbon from non-fossil sources, the benefit doubles.

There are three broad sources of recycled carbon. First, biogenic carbon comes from organic matter. Forestry waste, after the trunks of trees are used for construction and furniture, is one source. Another is to trap the carbon-filled gases that come off the breakdown of organic matter in landfills, sewage plants, or the large anaerobic digestors of agricultural waste that many farms are now installing. Agricultural and forestry waste can also be gasified to obtain their carbon.

Secondly, the exhaust chimneys of power plants and other industrial plants, such as breweries or cement plants, rich in CO2, can be retrofitted or built to capture the CO2 for recycling. Some think this may no longer be a source of carbon in a future without fossil hydrocarbons. But we may find ourselves transforming non-fossil hydrocarbons with very carbon-rich waste streams well beyond the fossil age. Capturing CO2 when it is already very concentrated can be very efficient.

Thirdly, CO2 can be pulled from the air with technologies called Direct Air Capture (DAC). An example is the Orca plant in Iceland. Using Climeworks DAC technology, the plant pulls in air with large fans, and filters the CO2 from the rest of the air. The module then closes, and heats the CO2 so it can be released and collected.

Afterwards, using the Carbfix technology, the CO2 is dissolved in water and pumped a kilometer deep into reactive basalt rock formations. Over a period of about two years, the reactions between these rocks and the dissolved CO2 forms a solid carbonate in the pores of the rock, permanently storing it for thousands of years. The Orca plant can pull 4000 tons of C02 out of the atmosphere every year. By using renewable energy, such as Iceland’s abundant geothermal energy, the process achieves a remarkable 90% efficiency. According to their website, if we compare the Orca plant with trees, the Orca plant is 1000 times more efficient at storing carbon on the same land area.

After much learning and optimization with their first plant, they are now building a second plant, the Mammoth plant, that will pull and permanently store 36,000 tons of CO2 per year. Their plans for the future are even bigger!

The plants in Iceland are carbon removal plants, but the initial Climeworks project in Switzerland was one of the first involved in carbon recycling. They pumped CO2 into greenhouses to assist plant growth. They also put their CO2 into drinks to make them fizzy.

But carbon recycling has become a lot more sophisticated than these initial ventures. The IEA estimates that we use 230 million tons of carbon dioxide per year to produce a wide array of products.

Carbon Capture and Utilization (CCU) includes 3 new areas for recycling CO2 that are emerging as we seek to displace fossil fuels. One area is the chemical industry, where biogenic and DAC CO2 can be used to make plastics and many other chemicals. The fertilizer industry uses 130 million tons of CO2 yearly to manufacture urea. Secondly, in the building sector, CO2 can be added to concrete to make it stronger and to sequester the carbon at the same time. A third area is the creation of renewable hydrocarbons, or powerfuels, that mix green hydrogen and recycled CO2 to make a wide variety of fuels without taking any from the ground.

The US Department of Energy (DOE) plans to spend $3.5 billion to create 4 Regional Direct Air Capture Hubs, each demonstrating DAC technologies that will capture 1 million metric tons of carbon dioxide per year. The Hubs will then geologically store the CO2 or transform it into a variety of products. This is one of several efforts by the DOE, often using funds from the Bipartisan Infrastructure Law, to hasten the commercialization and maturation of the entire CO2 supply chain.

Carbon has been free-wheeling through the natural world for millennia. By managing carbon, by treating it as the valuable resource that it is, yet at the same time preventing it from overly blanketing the earth in the form of greenhouse gases, we can reach a peaceful settlement with carbon. We can stop the linear drill, burn, and emit model that abuses the earth and opt for circular renewable carbon that serves both the planet and humankind.