The idea behind carbon utilization is that carbon dioxide (CO2) is a raw material that can be captured from industrial flue gas and then reused in a variety of commercially viable products and processes. It takes a different approach from merely storing CO2 underground, but the two methods are sometimes referred to together in the expression carbon capture, utilization and storage (CCUS).
Several CO2See Carbon Dioxid utilization methods have already achieved industrial maturity, including enhanced oil recovery (EOR), chemical synthesis and microalgae cultivation to produce high value-added products. However, these use only a very small amount of CO2: around 0.5% of global emissions, or less than 200 metric megatons per year (Mt CO2/year), compared with a total of more than 36,000 Mt CO2/year worldwide in 2015.
A great number of research projects in the field are currently being carried out around the world. Within the next 5 to 20 years, these could open up new prospects and eventually lead to the absorption of between 5% and 10% of emissions – provided reasonable solutions can be found to the cost issue.
0.5% The proportion of global CO2 emissions that are currently commercially used in the industry.
CO2 utilization faces three underlying challenges:
- Capturing carbon dioxide is a difficult and still costly process (see Close-Up: "Carbon Capture"). In addition, it can only viably be performed on extremely carbon-intensive industrial facilities, ruling out CO2 emissions from transportation, farming and housing. Carbon utilization is therefore just one of several drivers for bringing CO2 emissions under control, alongside other, more widely applicable solutions such as energy efficiencyIn economic terms, energy efficiency refers to the efforts made to reduce the energy consumption of a system... , energy savings, the development of renewable energies and underground storage.
- Industrial facilities that use CO2 as a raw material must be located close to the source of emissions or face prohibitive transportation costs. For this reason, carbon utilization fits neatly into an approach based on the circular economy and eco-industrial parks, where the CO2 emissions from one plant become the feedstock for another.
- CO2-based products must have existing commercial markets. These may be mass markets (such as for energy products), which are generally low value, or niche markets (such as for fine chemicals), which are high value but low volume.
- The carbon footprintThe carbon footprint (also known as greenhouse gas inventory) of a good or service measures the impact human activities have on the environment ... of a process based on CO2 utilization must be smaller than that of the conventional alternative. In other words, CO2 emissions must be lower once the entire process cycle has been taken into account. Otherwise, the CO2 has merely been shifted along the chain before finally being released into the atmosphere. Consideration must also be given to the life cycle of the products before their destruction if the aim of the processing is to store carbon.
Around 50 metric megatons of CO2 per year are reinjected into oil wells to enhance recovery.
Three main types of carbon utilization have been identified:
- Utilization without conversion, where the CO2 is used for its physical properties. This is the case for enhanced oil recovery, where the gas is injected into an oil well to force out the crude and deplete the field. Around 50 Mt CO2/year are used to this end (see Close-Up: "Carbon Capture and Storage Projects Worldwide"). Captured CO2 is also already used in existing industrial applications, such as to make the bubbles in carbonated drinks, the foam in fire extinguishers and refrigerants, as well as in the pharmaceutical industry and water treatment. And, in its "supercritical" state (between a liquid and a gas), CO2 can be used to produce solvents. Taken as a whole, these sectors consume some 20 Mt CO2/year.
- Chemical utilization, through reaction with another compound. Today, the main chemical utilization of CO2 (some 100 Mt CO2/year) is to produce ureaUrea, or carbamide, is an organic compound with the chemical formula (NH2) 2-C=O...
, a substance widely employed in farming as a nitrogen fertilizer. CO2 can be used to produce salicylic acid, a medication from which aspirin is derived. It also serves in the manufacturing processes for polycarbonate, a high-performance plastic used to make optical lenses, CDs, DVDs, contact lenses and other products, and for polymethane, which has applications including foams and rubbers. In addition, significant progress has been made in research into mineralization and carbonation of CO2, notably to harden concrete.
Above all, however, researchers are placing a lot of hope in the production of energy commodities (methanolMethanol or methyl alcohol is the simplest alcohol, with a chemical formula of CH3-OH. It is used in the production of methyl tert-butyl ether... and formic acid) and products at the end of the fuelFuel is any solid, liquid or gaseous substance or material that can be combined with an oxidant... value chain, using a broad spectrum of processes ranging from hydrogenation, reforming and electrolysis to photoelectrocatalysis and thermochemical conversion. While the volumes are potentially enormous, these processes require hydrogenThe simplest and lightest atom, the most abundant element in the universe. . And to effectively reduce CO2, this hydrogen must be produced without generating any carbon emissions, which is extremely costly. The same issue arises with anaerobic fermentation (methanation)Fermentation in the absence of air or free oxygen. , whereby CO2 is combined with hydrogen to form methane (ch4)The main component of natural gas deposits and oil deposit gas caps. Methane is produced naturally by landfills... , or natural gas. For this process to be economically viable, the price per metric ton of carbon would have to soar.
- Biological utilization, through photosynthesisProcess used by plants to fuel their growth. Light energy from the Sun is utilized to convert carbon dioxide and water into carbohydrates... within biological organisms such as microalgae, which require large amounts of CO2 to grow. Microalgae cultivation has today reached commercial maturity, yielding small, high value-added productions of pigments, omega 3 and other products. There are also good prospects for biological utilization in the animal feed and specialty chemicals industries. Looking beyond the next decade, this method also holds promise for biofuelA fuel produced from plant or animal matter. There are currently two types of biofuel... production, a field of interest for the aviation sector but hindered by the cost of development.