Examples of technology and application
CO2 electrocatalysis
Electrocatalysis can be used to convert carbon dioxide (CO) into value-added products. In particular, electrochemistry allows electricity to be exchanged for chemical energy, while catalysis allows the speed of the chemical reaction to be improved.[11] CO electrocatalysis allows obtaining an enormous variety of products such as carbon monoxide (CO), formic acid (HCOOH), methanol (CHOH), methane (CH), formaldehyde (CHO), oxalic acid (HCO), ethanol (CHO) and ethylene (CH).[12] To do this, CO must be previously captured in order to can become a true carbon-neutral fuel through these electrochemical processes in an aqueous medium.[13][14][15] In this way, it is possible to convert CO directly into the aforementioned ethanol, which in turn can be transformed into gasoline or aviation fuel.[16].
Carbon neutral fuel
An emissions-neutral fuel can be synthesized using CO captured from the atmosphere as the primary source of the carbon (C) atoms that make up the hydrocarbon molecule (hydrogen atoms, H, are obtained from the electrolysis of water). After synthesizing it, the fuel is burned, for example in an internal combustion engine, and the CO that was extracted from the air to synthesize it is returned to the atmosphere. In this process there is no net extraction of CO from the atmosphere, nor net emission into it; hence the name "carbon neutral fuel." An example of this technology is microalgae biofuel, discussed below.
A common process in the synthesis of hydrocarbons is the manufacture of methanol. Methanol is easily synthesized from CO and H. Based on this fact, the idea of a methanol economy was born.
Methanol, or methyl alcohol, is the simplest member of the family of alcohols, organic compounds with a generic formula of CHOH (methanol's is CHOH). Methanol fuel "Methanol (fuel)") can be manufactured using captured carbon dioxide and providing renewable energy for the necessary chemical reactions, which are endothermic. Consequently, methanol fuel has been considered an emissions-neutral alternative to fossil fuels[17][18] (the extraction and consumption of fossil fuels increases CO in the atmosphere and thus worsens global warming, while the manufacture of synthetic fuels from atmospheric CO and renewable energy, and their subsequent consumption, does not change the amount of CO in the atmosphere. The company Carbon Recycling International, with a factory in Grindavik, Iceland, sells this renewable methanol fuel High-octane "emissions-to-liquid" with a production capacity of 4,000 tons per year.[19].
Chemical synthesis
In addition to fuels, the CO captured from the atmosphere can be used as a raw material in multiple products, such as polycarbonates (using zinc-based catalysts), acetic acid,[20] urea or PVC.[21] A report from March 2011 suggested that this technology could be commercialized in the next 5 years, which ultimately did not happen. Whether or not chemical synthesis involves the permanent removal of CO from the atmosphere depends on the compound synthesized. For example, aliphatic hydrocarbons (straight chain, that is, unbranched) can degrade, releasing CO back into the atmosphere, in a period of time as short as 6 months.
Novomer is a chemical company that works on a zinc-based catalyst for the production, as raw materials, of polyethylene carbonate (PEC) and polypropylene carbonate (PPC). A 2011 report by the Global Institute for Carbon Dioxide Capture and Storage forecast an annual production potential of 22.5 million tonnes of CO (MtCO/a). The company has received funding from multiple sources, such as the Department of Energy (DOE) ($2.6 million) or the NSF ($400,000), to achieve commercialization of its product, as well as to convert its production process from a batch process to a continuous process.[21].
In enhanced oil extraction (EOR), captured CO is injected into underground pockets of crude oil that have been so extracted that they no longer have pressure for the oil to rise to the surface. In this way, crude oil production is increased by between 5 and 40%.[21] The use of CO for these purposes amounts to between 30 and 300 MtCO/a. It is a permanent and mature technology in CCU. The biggest driver of the EOR market is the heavy dependence on oil. In the United States, some additional drivers are tariffs on foreign crude oil as well as tax breaks for emissions reductions.
Carbon dioxide mineralization
CO from flue gases is reacted with minerals such as magnesium oxide and calcium oxide to form stable solid carbonates. Mineral sources include brine and industrial waste minerals. The carbonates can then be used for construction, consumer products, and as an alternative to carbon capture and storage (CCS). This technology can extract more than 300 MtCO/a from the atmosphere. For every ton of carbonate thus produced, half a ton of CO is removed from the air. Even so, in 2016 the technology was still not mature and years of testing and prototypes were expected before achieving marketable applications.[22].
The Calera company proposed a way to mineralize CO through a process called CMAP, which involves precipitating a carbonate paste from a mixture of water, solid minerals and combustion gases. The resulting products of the process are: a pumpable suspension of carbonates, fresh water and CO-free combustion gases.
The benefits of this process include the production of fresh water and that the CO used does not require separation or compression. A barrier to this technology is, however, competition with existing cement industries.
Microalgae biofuel
One study has suggested that microalgae can be used as an alternative source of energy.[23] A microalgae pond is fed with a source of carbon dioxide, such as flue gases, and the microalgae are allowed to proliferate. When they have grown, the algae are harvested and their biomass is converted into biofuel. Each ton of dry microalgae biomass has extracted 1.8 tons of CO from the air. This technology can extract more than 300 MtCO/a from the atmosphere, although not permanently, because it will return to the air when the biofuel is consumed.
In any case, it is a carbon-neutral fuel, because the CO that is released into the atmosphere when it is consumed is the same that was removed from it when it was produced. The technology is not mature yet:[24] In 2020, a microalgae producing company, which takes advantage of part of the CO emitted by a combined cycle plant, is doubling its business volume annually, but not producing biofuels, as initially planned (that line of business has not been successful), but rather fertilizers.[25].
Dead algae can settle to the bottom of the pond and thus result in permanent storage of CO. Still, algae need extensive ponds and year-round sun to extract CO throughout the year. It is also necessary to control the pond environment, because the algae need to live in specific conditions. These ponds can affect the environment and the surrounding ecosystem.
Agriculture
To combat climate change, carbon fixation through the cultivation of plants has also been proposed.[26] When harvested, the resulting biomass can be used for fuel, while the charcoal obtained as a by-product is used in agriculture to enrich the soil (if this use is given, it is called "biochar"). Cool Planet is a private company with an R&D facility in Camarillo, California, developing the use of biochar, and claims that its product can increase yields by 12.3% and return 3 times the investment through improvements in soil fertility and nutrient retention.[27] While some question the effectiveness of carbon capture by plants for climate change mitigation,[28] it is a method generally promoted by numerous international organizations. countries.[25].