Setting the scene

What is CO2 use?

For this study, CO2 use has been defined as the process of using CO2 as a raw material for products or services with a potential market value. The range of potential applications is very large and includes direct use, where the CO2 is not chemically altered (non-conversion), and the transformation of CO2 to a useful product (conversion) (Figure 9).

Most existing commercial applications involve direct use of CO2 (non-conversion), including the production of food and beverages, metals fabrication, cooling, dry cleaning, healthcare, water treatment, fire suppression, and the injection of CO2 in oil reservoirs to enhance oil recovery (CO2-EOR). CO2 is also increasingly used to enhance yields from industrial processes, such as methanol production and crop cultivation in greenhouses. Most applications make use of several unique properties of CO2, including its large heat absorption capacity, stable and nonreactive nature, and its ability to act as a solvent. A future use of CO2 is in supercritical power cycles, where CO2 would replace water as a working fluid, increasing the efficiency of electricity generation.

The conversion route has sparked most interest in recent years, including opportunities to develop CO2-derived fuels, chemicals and building materials. There are a large number of chemical and biological pathways for CO2 conversion, many of which are still in an early stage of development but may become technically and commercially available in the future.

Figure 9. Simple classification of CO2 use pathways

CO2-derived fuels

CO2 can be used to produce many of the fuels available on the market today, such as methane, methanol, gasoline and aviation fuels.1 Most fuels have an application in the transportation sector, while some (e.g. methane) can also be used in industry, heating and power generation. CO2-derived fuels may notably be used in sectors for which few low-carbon alternatives exist, such as aviation.

The most mature conversion pathways are direct conversion of CO2 (hydrogenation), and indirect conversion whereby the CO2 is first converted into CO (reverse water-gas shift), followed by a Fischer-Tropsch (FT) process or methanol synthesis process (Figure 10). The reverse water-gas shift conversion has been successfully demonstrated on a small scale, while the hydrogenation, FT and methanol synthesis processes are technologically mature. The direct conversion of CO2 into methane and methanol is carried out in several places around the world, and it has reached the early commercialisation stage in regions with low-cost renewable electricity. The largest CO2-based fuel plant in operation today is the George Olah Renewable Methanol facility located in Svartsengi, Iceland (CRI, 2019). Other chemical and biological conversion pathways, such as artificial photosynthesis, are still in the research stage.

Figure 10. Mature conversion route for CO2-derived fuels and chemical intermediates

from natural gas and other fossil fuels. This process can be decarbonised by applying CCS. Another production route is the electrolysis of water using low-carbon energy. This technology has attracted increasing interest in recent years, mainly due to spectacular cost reductions in solar PV and wind energy technologies, and the expectation that these technologies will be widely available in the future (IEA, 2019a).

CO2-derived chemicals

CO2-derived chemicals include a wide range of organic substances, including plastics, fibres and synthetic rubber. A well-established application is in the fertiliser industry, where CO2 is used to manufacture urea. In addition to urea, CO2 can be converted into chemical intermediates, such as methanol, ethylene and propylene, which in turn can be used as a source for a myriad of more complex chemicals. As is the case for fuels, the conversion of CO2 to methanol and methane is the most technologically mature pathway, but requires considerable electricity input.

A special group of chemicals are polymers, which are used in the production of plastics and resins. CO2 can be used in the manufacturing process by replacing part of the fossil-based feedstock (Figure 11). Some polymers can contain up to 50% CO2 by weight. Unlike the conversion of CO2 to fuels and intermediate chemicals, the use of CO2 in polymer manufacturing does not require much energy input for the conversion process, because the energy is provided by the fossil feedstock in the polymer molecule that is not replaced by the CO2. A number of companies, such as Asahi Kasei Chemicals, Chi Mei Corp and Covestro, are producing polymers using CO2 (Fukuoka et al. 2007; Covestro, 2018).

Figure 11. Mature conversion pathway for CO2-derived polymers