Carbon capture and utilization
Carbon capture and utilization is the process of capturing carbon dioxide to be recycled for further usage. Carbon capture and utilization may offer a response to the global challenge of significantly reducing greenhouse gas emissions from major stationary emitters. CCU differs from Carbon Capture and Storage in that CCU does not aim nor result in permanent geological storage of carbon dioxide. Instead, CCU aims to use the captured carbon dioxide for conversion into other substances or products with higher economic value while retaining the carbon neutrality of the production processes.
There are several technologies available in CCU, such as converting CO2 to products such as methanol, biofuel, and other forms of hydrocarbons for use as alternative and renewable sources of energy. Other forms of CCU includes the conversion of CO2 into commercial products such as plastics, concrete and reactants for various chemical synthesis.
Although CCU does not result in a net carbon positive to the atmosphere, there are several important considerations to be taken into account. The energy requirement for the additional processing of new products should not exceed the amount of energy released from burning fuel as the process will require more fuel. Manufacturing products from CO2 is energy intensive as the CO2 is a thermodynamically stable form of carbon. In addition, concerns on the scale of CCU is a major argument against investing in CCU. The availability of other raw materials to create a product should also be considered before investing in CCU.
One of the drivers for the possible implementation of CCU is a price on carbon. A price on carbon will incentivize the reduction of CO2 being released into the atmosphere. Thus, CCU can be one of the main alternatives for a company to reuse the emitted CO2 for creating useful commercial products.
Examples of technology and application
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. An example of the technology include biofuel from microalgae as discussed below.Methanol fuel
, or methyl alcohol, is the simplest member of the family of alcohol organic compound with a chemical formula of CH3OH. Methanol fuel can be manufactured using the captured carbon dioxide while performing the production with renewable energy. Consequently, methanol fuel has been considered as an alternative to fossil fuels in power generation for achieving a carbon-neutral sustainability. Carbon Recycling International, a company with production facility in Grindavik, Iceland, markets such Emission-to-Liquid renewable high octane methanol fuel with current 4,000 metric ton/year production capacity.Chemical synthesis
Also known as chemical feedstock, CO2 captured previously will be used to be converted to a diverse range of products. Some of these products include: polycarbonates or other organic products such as acetic acid, urea, and PVC. A March 2011 report suggested that this technology requires 1–5 years to commercialization. Chemical synthesis is not a permanent storage/utilization of CO2, as aliphatic compounds may degrade and release CO2 back to the atmosphere as early as 6 months.Industrial example of chemical synthesis: Novomer
is a chemicals company working in the synthesis of everyday products. They are working in two different types of plastics: polyethylene carbonate and polypropylene carbonate and claim that their products contains up to 50% CO2 by mass. A March 2011 report by Global CCS Institute foresaw annual production potential of 22.5 MtCO2/yr. They have received funding from multiple sources such as the Department of Energy and NSF to achieve commercialization as well as converting their production process from a batch process to a continuous process. Their pilot plant opened in December 2009 with a 1500L batch reactor and utilized waste stream from ethanol fermentation and flue gas as their source of CO2.The advantage of chemical synthesis by Novomer is that there is a diverse choice for characteristics of plastics being made.
This helps avoid the scarcity of resources if this technology is to be scaled up. Another advantage of this technology is that the CO2 sources won't compete with food production.
One disadvantage of this technology is that the technology is relatively new, and more research is required into synthesis components such as the zinc-based catalyst. Another is that its choice of CO2 source may give rise to the need for another separation process to increase CO2 quality. A big problem present in Novomer's case is the packaging industry, which prioritises low cost polymer, which CO2-based polymers would have to compete against.
Enhanced Oil Recovery (EOR)
In EOR, the captured CO2 is injected into depleted oil fields with the goal to increase the amount of oil to be extracted by the wells. This method is proven to increase oil output by 5-40%. The scale of CO2 utilization through this technologies ranges from 30-300 MtCO2/yr. It is a permanent and mature technology in CCU. The biggest market driver for EOR is the heavy reliance on oil. In United States, some of the additional market drivers include: tax revenue for foreign oil as well as the presence of carbon tax credits.Carbon mineralization
Carbon dioxide from sources such as flue gas are reacted with minerals such as magnesium oxide and calcium oxide to form stable solid carbonates. Sources of minerals include brine and waste industrial minerals. The carbonates can then be used for construction, consumer products, and as an alternative for carbon capture and sequestration. The scale of this technology may reach more than 300 Mt of CO2 removed per year. 0.5 tonnes of CO2 is removed from the air for every tonne of mineral carbonate produced. However, it needs 1–5 years to commercialization as the technology is not mature yet.The company Calera proposed a way to mineralize CO2 through the CMAP process. This process involves precipitating a carbonate slurry from a mixture of water, solid minerals, and flue gas. The products are concentrated pumpable carbonate suspension, fresh water, and CO2-free flue gas.
Benefits of this process includes the production of fresh water and that the CO2 used does not require separation or compression. A barrier of this technology is, however, the competition with existing cement industries.
Biofuel from microalgae
A study has suggested that microalgae can be used as an alternative source of energy. A pond of microalgae is fed with a source of carbon dioxide such as flue gas and the microalgae is then let to proliferate. The algae is then harvested and the biomass obtained is then converted to biofuel. 1.8 tonnes of CO2 is removed from the air per 1 metric tonne of dry algal biomass produced. This number actually varies depending on the species. The scale of this technology may reach more than 300Mt of CO2 removed per year. The CO2 captured will be stored non-permanently as the biofuel produced will then be combusted and the CO2 will be released back into the air. However, the CO2 released was first captured from the atmosphere and releasing it back into the air makes the fuel a carbon-neutral fuel. This technology is not mature yet.Dead algae can sink to the bottom of the lake and result in permanent storage. However, the algae needs a large area of pond and sunlight all year round to remove CO2 all year round. Furthermore, the pond environment needs to be controlled since the algae needs to live in a specific condition. There are concerns about how the algae-filled pond might affect the environment and ecosystem around it.