Carbon capture and utilization (CCU) is the process of capturing
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(
C O2) to be recycled for further usage.
Carbon capture and utilization may offer a response to the global challenge of significantly reducing
greenhouse gas emissions
Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
from major stationary (industrial) emitters. CCU differs from
carbon capture and storage
Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
(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
biofuel; while retaining the
carbon neutrality
Carbon neutrality is a state of net-zero carbon dioxide emissions. This can be achieved by balancing emissions of carbon dioxide with its removal (often through carbon offsetting) or by eliminating emissions from society (the transition to the "p ...
of the production processes.
Captured CO
2 can be converted to several products: one group being
alcohols, such as methanol, to use as biofuels and other
alternative and renewable sources of energy. Other commercial products include 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. Because CO
2 is a thermodynamically stable form of
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
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
Carbon pricing (or pricing), also known as cap and trade (CAT) or emissions trading scheme (ETS), is a method for nations to reduce global warming. The cost is applied to greenhouse gas emissions in order to encourage polluters to reduce the co ...
of CO
2 being released into the atmosphere.
Sources of carbon
CO
2 is typically captured from fixed point sources in
heavy industry
Heavy industry is an industry that involves one or more characteristics such as large and heavy products; large and heavy equipment and facilities (such as heavy equipment, large machine tools, huge buildings and large-scale infrastructure); o ...
such as
petrochemical plants. CO
2 captured from these exhaust stream itself varies in concentration. A typical coal power plant will have 10-12% CO
2 concentration in its
flue gas
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produc ...
exhaust stream.
A biofuel refinery produces a high purity (99%) of CO
2 with small amount of impurities such as water and ethanol.
The separation process itself can be performed through separation processes such as
absorption,
adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which ...
, or
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...
s.
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 CO
2 level in the atmosphere undergoes annual variation of approximately 5 ppm (
parts per million
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...
), which is attributed to the seasonal change of vegetation and difference in land mass between the northern and southern hemisphere. However, the CO
2 sequestered by the plants will be returned to the atmosphere when the plants die. Thus, it is proposed to plant crops with
C4 photosynthesis
carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960's discovery by Marshall Davidson Hatch and Charles Roger Slack that some plants, when suppl ...
, given its rapid growth and high carbon capture rate, and then to process the biomass for applications such as
biochar
Biochar is the lightweight black residue, made of carbon and
ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of ...
that will be stored in the soil permanently.
Examples of technology and application
CO2 electrolysis
CO
2 electroreduction to a variety of value-added products has been under development for many years. Some major targets are
formate,
oxalate
Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...
, and
methanol, as electrochemical formation of these products from CO
2 would constitute a very environmentally sustainable practice.
For example, CO
2 can be captured and converted to
carbon-neutral fuel
Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped ...
s in an aqueous
catalysis
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
process. It is possible to convert CO
2 in this way directly to
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
, which can then be upgraded to
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
and
jet fuel.
Carbon-neutral fuel
A carbon-neutral fuel can be synthesized by using the captured CO
2 from the atmosphere as the main hydrocarbon source. The fuel is then combusted and CO
2, 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.
Methanol fuel
A proven process to produce a hydrocarbon is to make
methanol. Traditionally, methanol is produced from natural gas. Methanol is easily synthesized from and H
2. Based on this fact the idea of a
methanol economy The methanol economy is a suggested future economy in which methanol and dimethyl ether replace fossil fuels as a means of energy storage, ground transportation fuel, and raw material for synthetic hydrocarbons and their products. It offers an alter ...
was born.
Methanol, or methyl alcohol, is the simplest member of the family of alcohol organic compound with a chemical formula of
C H3 O H.
Methanol fuel
Methanol fuel is an alternative biofuel for internal combustion and other engines, either in combination with gasoline or independently. Methanol ( C H3 O H) is less expensive to produce sustainably than ethanol fuel, although it produces more ...
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
Carbon Recycling International (CRI) is an Icelandic limited liability company which has developed a technology designed to produce renewable methanol from carbon dioxide and hydrogen, using water electrolysis or, alternatively, hydrogen captured ...
, a company with production facility in
Grindavik, Iceland, markets such Emission-to-Liquid renewable high octane methanol fuel with current 4,000
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
/year production capacity.
Chemical synthesis
As a highly desirable C
1 (one-carbon) chemical feedstock, CO
2 captured previously can be converted to a diverse range of products. Some of these products include:
polycarbonates (via Zinc based
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
) or other organic products such as
acetic acid,
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
,
and
PVC.
Currently 75% (112 million tons) of urea production, 2% (2 million tons) of methanol production, 43% (30 thousand tons) of salicylic acid production, and 50% (40 thousand tons) of cyclic carbonates production utilize CO
2 as a feedstock. Chemical synthesis is not a permanent storage/utilization of CO
2, as
aliphatic
In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...
(straight chain) compounds may degrade and release CO
2 back to the atmosphere as early as 6 months.
As the use of fossil fuels decreases, removing carbon dioxide from the air is increasingly seen as a way to stop the long-term accumulation of greenhouse gases in the atmosphere. Carbon emissions and storage coupled with reductions in fossil fuel use are known as "negative emissions"., access-date=24 October 2022,
Carbon Dioxide also could use in chemoenzymatic to synthesize starch without cells. Normally in nature, it calls photosynthesis, the plant uses the cells to synthesize starch from carbon dioxide, which is the main reason planting more plants could help capture the carbon. The methods of cells free synthesize to let Carbon dioxide is reduced to methanol with an inorganic catalyst; then methanol is converted to three carbon sugar units. The three carbon sugar units will comprise six carbon sugar units and finally polymerize into starch. Compared to photosynthesis, which has sixty biochemical reactions, cell-free synthesis needs eleven steps. It means the speed of cell-free synthesis is faster than photosynthesis. The synthesis rate is 8.5 times that of corn starch, and the absorbance rate of carbon dioxide speed is more efficient than that of plants. This method is still developing, and the first publishing was only in 2021, so there are still some problems. First, this method needs a lot of energy to synthesize, like plants need solar. It means if the electricity can not use clean energy, It still emission a lot of Carbon Dioxide. The next question is whether the costs are still really high and impossible to commercialize now.
Enhanced oil recovery (EOR)
In EOR, the captured CO
2 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%.
Enhanced gas recovery (EGR)
Carbon Sequestration with Enhanced Gas Recovery (CSEGR) is a process in which CO
2 is injected deep in the gas reservoir and as a result, at the gas wells which are some distance away, methane (CH
4) is produced. This process by active injection of CO
2 causes repressurization and methane displacement, so that the gas recovery becomes enhanced compared to water-drive or depletion-drive operations.
Carbon mineralization
Carbon dioxide from sources such as
flue gas
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produc ...
are reacted with minerals such as
magnesium oxide
Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
and
calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ...
to form stable solid
carbonates
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
. These minerals can be mined, or existing
brine and waste industrial minerals (including
slag) can be reused.
The carbonates produced can be used for construction, consumer products, and as an alternative for
carbon capture and sequestration
Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
(CCS).
Approximately 1 tonne of CO
2 is removed from the air for every 3.7 tonnes of mineral carbonate produced.
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 allowed to proliferate. The algae is then harvested and the biomass obtained is then converted to biofuel. About 1.8 tonnes of CO
2 can be removed from the air per 1 tonne of dry algal biomass produced, though this number actually varies depending on the species. The CO
2 captured will be stored non-permanently as the biofuel produced will then be combusted and the CO
2 will be released back into the air. However, the CO
2 released was first captured from the atmosphere and releasing it back into the air makes the fuel a
carbon-neutral fuel
Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped ...
. This technology is not mature yet.
Agriculture
An approach that is also proposed as a climate change mitigation effort is to perform plant-based carbon capture. The resulting biomass can then be used for
fuel, while the biochar byproduct is then utilized for applications in agriculture as soil-enhancer
Cool Planetis a private company with an R&D plant in
Camarillo, California, performed development of biochar for agricultural applications and claimed that their product can increase crops yield by 12.3% and three-fold return of investment via improvement of
soil health
Soil health is a state of a soil meeting its range of ecosystem functions as appropriate to its environment. In more colloquial terms, the health of soil arises from favorable interactions of all soil components (living and non-living) that belong ...
and nutrient retention. However, the claims on the efficacy of plant-based carbon capture for climate change mitigation has received a fair amount of skepticism.
Environmental impacts
16 life cycle environmental impact analyses have been done to assess the impacts of four main CCU technologies against conventional CCS: Chemical synthesis, carbon mineralization, biodiesel production, as well as
Enhanced Oil Recovery (EOR). These technologies were assessed based on 10
Life-cycle assessment (LCA) impacts such as: acidification potential, eutrophication potential, global warming potential, and ozone depletion potential. The conclusion from the 16 different models was that chemical synthesis has the highest global warming potential (216 times that of CCS) while enhanced oil recovery has the least global warming potential (1.8 times that of CCS).
See also
*
Carbon capture and storage
Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
*
Climate change mitigation
*
Carbon neutral fuel
Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped in ...
*
Carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in lan ...
*
Greenhouse gas removal
Carbon dioxide removal (CDR), also known as negative emissions, is a process in which carbon dioxide gas () is removed from the atmosphere and sequestered for long periods of time. Similarly, greenhouse gas removal (GGR) or negative greenho ...
*
List of energy topics
The following outline is provided as an overview of and topical guide to energy:
Energy – in physics, this is an indirectly observed quantity often understood as the ability of a physical system to do work on other physical systems. Sinc ...
*
Low-carbon economy
A low-carbon economy (LCE) or decarbonised economy is an economy based on energy sources that produce low levels of greenhouse gas (GHG) emissions. GHG emissions due to human activity are the dominant cause of observed climate change since the mi ...
*
Solar Foods Ltd.
References
Further reading
*
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New route to carbon-neutral fuels from carbon dioxide discovered by Stanford-DTU team
{{DEFAULTSORT:Carbon capture and utilization
Carbon dioxide
Climate engineering
Emerging technologies
Environmental technology
Sustainability