Carbon capture and utilization (CCU) is the process of capturing carbon dioxide (CO2) from industrial processes and transporting it via pipelines to where one intends to use it in industrial processes.
Captured CO2 can be converted to several products: one group being alcohols, such as methanol, to use as efuels and other alternative and renewable sources of energy. Other commercial products include plastics, concrete and reactants for various chemical synthesis.
Regarding a single product, CCU does not result in a net carbon positive to the atmosphere. If, in addition, this product substitutes one of fossil origin an overall CO2 emission reduction occurs.
There are several additional considerations to be taken into account. As CO2 is a thermodynamically stable form of carbon, manufacturing products from it is energy intensive. The availability of other raw materials to create a product should also be considered before investing in CCU.
Considering the different potential options for capture and utilization, research suggests that those involving chemicals, fuels and microalgae have limited potential for removal, while those that involve construction materials and agricultural use can be more effective.
The profitability of CCU depends partly on the carbon price of CO2 being released into the atmosphere. Carbon capture and utilization may offer a response to the global challenge of significantly reducing greenhouse gas emissions from major stationary (industrial) emitters.
Definition and distinction
Carbon capture and utilization (CCU) is defined as capturing from industrial processes and transporting it via pipelines to where one intends to use it in industrial processes. The pipelines are pressurized as the only option for transporting the over long distances.
CCU differs from carbon capture and storage (CCS) in that CCU does not aim nor result in permanent geological storage of carbon dioxide. Instead, CCU aims to convert the captured carbon dioxide into more valuable substances or products; such as plastics, concrete or efuel; while retaining the carbon neutrality of the production processes.
CCU and CCS are sometimes discussed collectively as carbon capture, utilization, and sequestration (CCUS).
Sources of carbon
CO2 is typically captured from fixed point sources in heavy industry such as petrochemical plants. CO2 captured from these exhaust stream itself varies in concentration. A typical coal power plant will have 10-12% CO2 concentration in its flue gas exhaust stream. A biofuel refinery produces a high purity (99%) of CO2 with small amount of impurities such as water and ethanol. The captured contains impurities and the transported through pipelines will contain impurities, such as ammonia, , , C2+. CO +, +, , + and Arsenic. Hydrogen can cause hydrogen embrittlement, and water can cause corrosion in steel pipes.
The separation process itself can be performed through separation processes such as absorption, adsorption, or membranes.
Another possible source of capture in CCU process involves the use of plantation. The idea originates from the observation in the Keeling curve that the CO2 level in the atmosphere undergoes annual variation of approximately 5 ppm (parts per million), which is attributed to the seasonal change of vegetation and difference in land mass between the northern and southern hemisphere. However, the CO2 sequestered by the plants will be returned to the atmosphere when the plants die. Thus, it is proposed to plant crops with photosynthesis, given its rapid growth and high carbon capture rate, and then to process the biomass for applications such as biochar that will be stored in the soil permanently.
Examples of technology and application
CO2 electrolysis
CO2 electroreduction to a variety of value-added products has been under development for many years. Some major targets are formate, oxalate, and methanol, as electrochemical formation of these products from CO2 would constitute a very environmentally sustainable practice. For example, CO2 can be captured and converted to carbon-neutral fuels in an aqueous catalysis process. It is possible to convert CO2 in this way directly to ethanol, which can then be upgraded to gasoline and jet fuel.
Carbon-neutral fuel
A carbon-neutral fuel can be synthesized by using the captured CO2 from the atmosphere as the main hydrocarbon source. The fuel is then combusted and CO2, as the byproduct of the combustion process, is released back into the air. In this process, there is no net carbon dioxide released or removed from the atmosphere, hence the name carbon-neutral fuel.