Supercritical carbon dioxide
Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when cooled and/or pressurised sufficiently.
If the temperature and pressure are both increased from STP to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid.
Supercritical CO2 is becoming an important commercial and industrial solvent due to its role in chemical extraction, in addition to its relatively low toxicity and environmental impact.
The caffeine can then be isolated for resale (e.g., to pharmaceutical or beverage manufacturers) by passing the water through activated charcoal filters or by distillation, crystallization or reverse osmosis.
Supercritical carbon dioxide is used to remove organochloride pesticides and metals from agricultural crops without adulterating the desired constituents from plant matter in the herbal supplement industry.
[10] Due to its ability to selectively dissolve organic compounds and assist enzyme functioning, sCO2 has been suggested as a potential solvent to support biological activity on Venus- or super-Earth-type planets.
The sCO2 in these processes is reacted with the alkaline components of fully hardened hydraulic cement or gypsum plaster to form various carbonates.
Upon depressurization and heating, the carbon dioxide rapidly expands, causing voids within the polymer matrix, i.e., creating a foam.
[13] sCO2 is chemically stable, reliable, low-cost, non-flammable and readily available, making it a desirable candidate working fluid for transcritical cycles.
[15] For concentrated solar power, carbon dioxide critical temperature is not high enough to obtain the maximum energy conversion efficiency.
Solar thermal plants are usually located in arid areas, so it is impossible to cool down the heat sink to sub-critical temperatures.
Therefore, supercritical carbon dioxide blends, with higher critical temperatures, are in development to improve concentrated solar power electricity production.
Candidate materials that meet these property and performance goals include incumbent alloys in power generation, such as nickel-based superalloys for turbomachinery components and austenitic stainless steels for piping.
Using gasifiers instead of conventional furnaces, coal and water is reduced to hydrogen gas, carbon dioxide and ash.
When the CO2 goes supercritical, all surface tension is removed, allowing the liquid to leave the aerogel and produce nanometer sized pores.
[34] Supercritical CO2 is an alternative for thermal sterilization of biological materials and medical devices with combination of the additive peracetic acid (PAA).
