Carbon capture and utilization (CCU) is the process of capturing carbon dioxide (C O 2) from industrial processes and transporting it via pipelines to where one intends to use it in industrial processes. [1]
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. [2]
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. [3] 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 CO2 removal, while those that involve construction materials and agricultural use can be more effective. [4]
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. [5]
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Carbon capture and utilization (CCU) is defined as capturing CO2 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 CO2 over long distances. [6] [7]
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).
CO2 is typically captured from fixed point sources in heavy industry such as petrochemical plants. [8] 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. [9] A biofuel refinery produces a high purity (99%) of CO2 with small amount of impurities such as water and ethanol. [9] The captured CO2 contains impurities and the CO2 transported through pipelines will contain impurities, such as ammonia, N2 , H2S , C2+. CO +, O2 +, NOx, SO
x+ and Arsenic. Hydrogen can cause hydrogen embrittlement, and water can cause corrosion in steel pipes. [6] : 424
The separation process itself can be performed through separation processes such as absorption, adsorption, or membranes. [10]
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. [11] [12] 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 C4 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. [13]
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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. [14] For example, CO2 can be captured and converted to carbon-neutral fuels in an aqueous catalysis process. [15] [16] It is possible to convert CO2 in this way directly to ethanol, which can then be upgraded to gasoline and jet fuel. [17] [18]
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.
A proven process to produce a hydrocarbon is to make methanol. Traditionally, methanol is produced from natural gas. [19] Methanol is easily synthesized from CO2 and H2. Based on this fact the idea of a methanol economy was born.
Methanol, or methyl alcohol, is the simplest member of the family of alcohol organic compound with a chemical formula of C H 3 O H. 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. [20] [21] Synthesis of methanol from carbon dioxide is done through a hydrogenation reaction in the presence of a catalyst. Commonly used catalysts are copper, zinc, and palladium. These reactions are typically performed under high pressure conditions to shift the reaction equilibrium towards the methanol product via Le Chatelier's Principle. [22] 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 tonne/year production capacity. [23]
Dimethyl Ether
Dimethyl Ether has shown promise as a carbon neutral fuel as a potential alternative to diesel fuel. Dimethyl Ether has typically been synthesized from a dehydration reaction of methanol in the presence of an acid catalyst, but researchers have recently developed a one step method to convert carbon dioxide into dimethyl ether using a bifunctional catalyst and similar conditions to the synthesis of methanol from syngas. [24]
As a highly desirable C1 (one-carbon) chemical feedstock, CO2 captured previously can be converted to a diverse range of products. Some of these products include: polycarbonates (via Zinc based catalyst) or other organic products such as acetic acid, [25] urea, [25] and PVC. [26] 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 CO2 as a feedstock. [27] Chemical synthesis is not a permanent storage/utilization of CO2, as aliphatic (straight chain) compounds may degrade and release CO2 back to the atmosphere as early as 6 months. [26] 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".
Carbon dioxide also could be used in chemoenzymatic processes to synthesize starch without cells. In nature starch is usually synthesized within cells from carbon dioxide via photosynthesis. In cell-free synthesis, 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 be converted to six carbon sugar units and finally polymerize into starch. Compared to photosynthesis, which involves sixty biochemical reactions, cell-free synthesis needs eleven steps. This means cell-free synthesis can be faster than photosynthesis. The synthesis rate is 8.5 times that of corn starch, and the absorbance rate of carbon dioxide is more efficient than that of plants. [28] This method is still developing, and the first publication on the topic was only in 2021, so there are still some problems. First, this method needs significant energy inputs, just as plants need sunlight. If the electricity used is not produced cleanly, large carbon dioxide emissions will still result. Moreover, high costs present a barrier to commercialization.
In 2023, an international team of researchers at the University of Sydney and the University of Toronto developed a new acid-based electrochemical process for the conversion of CO2 captured from emission sources or directly from air. [29]
In enhanced oil recovery, 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%. [26]
Carbon Sequestration with Enhanced Gas Recovery (CSEGR) is a process in which CO2 is injected deep in the gas reservoir and as a result, at the gas wells which are some distance away, methane (CH4) is produced. This process by active injection of CO2 causes repressurization and methane displacement, so that the gas recovery becomes enhanced compared to water-drive or depletion-drive operations. [30]
Carbon dioxide from sources such as flue gas are reacted with minerals such as magnesium oxide and calcium oxide to form stable solid carbonates. These minerals can be mined, or existing brine and waste industrial minerals (including slag) can be reused. [31] The carbonates produced can be used for construction, consumer products, and as an alternative for carbon capture and sequestration (CCS).
Approximately 1 tonne of CO2 is removed from the air for every 3.7 tonnes of mineral carbonate produced. [31]
A study has suggested that microalgae can be used as an alternative source of energy. [32] 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 CO2 can be removed from the air per 1 tonne of dry algal biomass produced, though this number actually varies depending on the species. [33] 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. Microalgae biofuels are considered to be a part of the third generation of biofuels, being an alternative energy source for fossil fuels without the disadvantages accompanying first and second generation biofuels. [34] This technology is not mature yet. [35] Current microalgal culture systems have not been designed for high throughput biomass growth and carbon capture. Raceways, high-rate algal ponds, and photobioreactors are the most widely used for microalgal cultivation at a large-scale. The limitations of these systems are related to microalgal growth requirements. Ponds are operated at narrow depth to ensure sufficient light distribution and thus need a large land surface. [36]
An approach that is also proposed as a climate change mitigation effort is to perform plant-based carbon capture. [37] The resulting biomass can then be used for fuel, while the biochar byproduct is then utilized for applications in agriculture as soil-enhancer. Cool Planet is 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 and nutrient retention. [38] [ unreliable source? ] However, the claims on the efficacy of plant-based carbon capture for climate change mitigation has received a fair amount of skepticism. [39]
Pipelines can fail through either ductile fracture and/or a brittle fracture. [6] : 425
As of 2015, 16 life cycle environmental impact analyses had 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). [1] [ clarification needed ]
Life-cycle assessments (LCA) are not standardized as studies that perform them use different assessment methodologies and parameter that change the results of the LCA. Enhanced methodology guidelines and standardization of practice are necessary to better gauge and compare the impact of the various CCU technologies. [41]
In the US, Federal Energy Regulatory Commission (FERC) and the Surface Transportation Board (STB) exercise jurisdiction. [7] The Corps of Engineeers may issue nationwide permits. [42]
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The reaction is represented by this equilibrium:
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 alternative to the proposed hydrogen economy or ethanol economy, although these concepts are not exclusive. Methanol can be produced from a variety of sources including fossil fuels as well as agricultural products and municipal waste, wood and varied biomass. It can also be made from chemical recycling of carbon dioxide.
Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by reforming of natural gas.
Coal pollution mitigation, sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances, including mercury, lead, sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon dioxide (CO2), contributing to air pollution, acid rain, and greenhouse gas emissions. Methods include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction focusing on reducing the emissions of these harmful substances. These measures aim to reduce coal's impact on human health and the environment.
Biomass to liquid is a multi-step process of producing synthetic hydrocarbon fuels made from biomass via a thermochemical route.
Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies exist: (i) direct partial combustion of methane to methanol and (ii) Fischer–Tropsch-like processes that convert carbon monoxide and hydrogen into hydrocarbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon monoxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially. Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive.
Carbon capture and storage (CCS) is a process in which a relatively pure stream of carbon dioxide (CO2) from industrial sources is separated, treated and transported to a long-term storage location. For example, the carbon dioxide stream that is to be captured can result from burning fossil fuels or biomass. Usually the CO2 is captured from large point sources, such as a chemical plant or biomass plant, and then stored in an underground geological formation. The aim is to reduce greenhouse gas emissions and thus mitigate climate change. The IPCC's most recent report on mitigating climate change describes CCS retrofits for existing power plants as one of the ways to limit emissions from the electricity sector and meet Paris Agreement goals.
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon sequestration is a naturally occurring process but it can also be enhanced or achieved with technology, for example within carbon capture and storage projects. There are two main types of carbon sequestration: geologic and biologic.
An integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electricity generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. This process results in improved thermodynamic efficiency, compared to conventional pulverized coal combustion.
Oxy-fuel combustion is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated flue gas, instead of air. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame. It has also received a lot of attention in recent decades as a potential carbon capture and storage technology.
Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed (macroalgae) it can be known as seaweed fuel or seaweed oil.
Hydromethanation, [hahy-droh- meth-uh-ney-shuhn] is the process by which methane is produced through the combination of steam, carbonaceous solids and a catalyst in a fluidized bed reactor. The process, developed over the past 60 years by multiple research groups, enables the highly efficient conversion of coal, petroleum coke and biomass into clean, pipeline quality methane.
Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. BECCS can theoretically be a "negative emissions technology" (NET), although its deployment at the scale considered by many governments and industries can "also pose major economic, technological, and social feasibility challenges; threaten food security and human rights; and risk overstepping multiple planetary boundaries, with potentially irreversible consequences". The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy ("bioenergy") is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods.
Carbon Sciences is a public corporation based in Santa Barbara. The company was founded in 2006 and incorporated as Zingerang, Inc. Originally, the company was involved in mobile communication, but has since switched to developing CO2 to fuel technology. Calcium carbonate, CaCO3, was briefly looked at as another end product of CO2 recycling. On April 2, 2007, the name was changed to Carbon Sciences Inc. Their process differs from other projects in that it does not utilize high pressure or high temperature. This would be a significant advantage when trying to scale the technology up to commercial production.
Carbon dioxide reforming is a method of producing synthesis gas from the reaction of carbon dioxide with hydrocarbons such as methane with the aid of noble metal catalysts. Synthesis gas is conventionally produced via the steam reforming reaction or coal gasification. In recent years, increased concerns on the contribution of greenhouse gases to global warming have increased interest in the replacement of steam as reactant with carbon dioxide.
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 into synthetic fuels, which are made by chemically hydrogenating carbon dioxide, and biofuels, which are produced using natural CO2-consuming processes like photosynthesis.
Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide directly from the ambient air. If the extracted CO2 is then sequestered in safe long-term storage, the overall process will achieve carbon dioxide removal and be a "negative emissions technology" (NET).
Carbon tech is a group of existing and emerging technologies that are rapidly transforming oil and gas to low emissions energy. Combined, these technologies take a circular carbon economy approach for managing and reducing carbon footprints, while optimizing biological and industry processes. It builds on the principles of the circular economy for managing carbon emissions: to reduce the amount of carbon emissions entering the atmosphere, to reuse carbon emissions as a feedstock in different industries, to recycle carbon through the natural carbon cycle with bioenergy, and to remove carbon and store it. Carbon tech provides a third option for climate and environmental policy as an alternate to the binary business as usual and radical change.
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