CCUS

Carbon capture, utilization (or “use”), and storage (or “sequestration”), abbreviated CCUS, is the process of removing carbon dioxide (CO2)—a common, planet-warming greenhouse gas—from industrial exhaust or the atmosphere directly and then either using it in a product or safely storing it. CO2 can be separated from other gases using a variety of chemical techniques.

Capture

Industrial sources of CO2 generally include coal plants, natural gas plants, chemical plants, cement factories, steel factories, and biomass energy facilities. Exhaust from these industrial point sources has a much higher concentration of CO2 (about 10–25% depending on the process) relative to the atmosphere generally (around 413 ppm, or 0.04%). This higher concentration means that point-source capture generally requires less energy than direct air capture (DAC) of CO2 from the atmosphere.

However, DAC will still likely be necessary to compensate for unabated emissions as well as eventually transition society to become carbon negative instead of merely carbon neutral. There are other carbon dioxide removal (CDR) pathways, such as soil carbon sequestration and ocean alkalinity enhancement, that can also remove CO2 from the atmosphere while potentially using less energy or taking advantage of natural energy sources. These could also help society achieve carbon negativity. If scaled massively in the coming centuries, these negative emissions technologies (NETs) could theoretically enable restoration of the concentration of CO2 in the atmosphere to pre-industrial levels.

Utilization

Once captured, there are various potential uses of carbon dioxide. The graphic below lists some of the possibilities.

Construction Materials

  • Cement and concrete
  • Asphalt
  • Timber/super hardwood

Industrial Fluids

  • Enhanced oil recovery
  • Enhanced coal bed methane recovery
  • Enhanced water recovery
  • Semiconductor fabrication
  • Power cycles

Fuels

  • Synthetic (methanol, butanol, natural gas, syngas, etc.)
  • Microalgae fuel
  • Macroalgae fuel

Plastics

  • Polyurethane foams
  • Polycarbonate (glass replacement)
  • Acrylonitrile butadiene styrene
  • Many more

Chemicals

  • Preservatives (formic acid)
  • Medicinal
  • Antifreeze (ethylene glycol)
  • Carbon black
  • Many more

New Materials

  • Carbon fiber
  • Carbon nanotubes and fullerenes

Agriculture & Food

  • Algae-based food or animal feed
  • Microbial fertilizer
  • Biochar, bio-pesticides, and bio-cosmetics

It is important to note that some of these products release the captured and utilized CO2 back into the atmosphere upon use or at their end-of-life. This is the case for many natural products such as timber and fertilizer, as these kinds of products eventually biodegrade and release the carbon back into the atmosphere. Carbon-utilizing fuels also release the initially captured CO2 upon combustion if there is no emissions capture system in place. While carbon re-enters the atmosphere from these kinds of products, it can be the same carbon that was initially captured (if using DAC or a biological source), providing a closed loop of carbon atoms. Such a system allows for the possibility of a circular economy for these products.

Potential CO2 utilization in gigatons for aggregates, fuels, concrete, methanol, and polymers
Carbon dioxide utilization potential for different pathways

Processes that utilize captured carbon can provide overall climate benefits when compared to fossil fuel manufacturing and combustion, where carbon atoms are moving in one direction from underground to the atmosphere. Even if the utilized carbon is sourced from industrial point sources, such as cement and steel plants, there can still be emissions reductions relative to existing production systems.

Some products, such as carbonated concrete and certain plastics, might not release the utilized CO2 if they convert it into a more stable chemical. Full life cycle results for carbon dioxide emissions, as well as other potential environmental impacts, become apparent upon conducting life cycle assessments as discussed throughout this website.

Additionally, carbon utilization can reduce dependence on fossil feedstocks for important fuels and chemicals, creating other environmental, economic, and even geopolitical benefits.

Storage

Captured CO2 can also be stored or sequestered in order to keep it out of the atmosphere. There are natural storage solutions that involve sequestering carbon in soil, plants, trees, oceans, or other natural sinks. While such strategies often provide co-benefits in terms of creating or restoring ecosystem services, they may also be vulnerable to the re-release of CO2 in the event of wildfires, climate change, or other occurrences that lead to degradation.

More permanent, but also generally more expensive, methods of carbon sequestration include geological sequestration where CO2 is pumped deep underground and mineral storage through enhanced weathering. Conducting full life cycle assessments is vital for understanding the holistic benefits and trade-offs from using any particular sequestration method.

Assessment

As mitigating climate change has only become a mainstream goal over the past few decades, many CCUS technologies are still in early stages of development. Technologies that have not been widely deployed yet have many uncertainties related to whether they will actually help the environment relative to the status quo and whether they will be able to survive in the marketplace.

Life cycle and techno-economic assessments of these technologies can help technology developers and other key decision-makers understand the environmental and economic benefits and drawbacks of any given technology as well as identify potential improvements. Conducting such analyses for CCUS technologies and using the results to improve their economic and environmental performance will accelerate the commercialization process as well as help them have an even more significant impact on the mitigation of climate change.

Resources

More information about CCUS technologies can be found in the resources below.