Supercritical carbon dioxide is an attractive alternative in place of It is inert, non -toxic, has a relatively low cost and has moderate . it is a generally recognized as safe (GRAS) solvent that leaves no traces in the product. Ethyl lactate, for example, is a green solvent derived from processing corn. replaced solvents such as toluene, acetone, and xylene, resulting in a much safer workplace. . Supercritical carbon dioxide (scCO2), essentially a 'green' solvent and . Recently a number of chemicals have been used as inexpensive, “green” . Sir, I think there is no real green solvent like water but may be ethanol is next green . in the last three decades that the following are RELATIVELY SAFE " Greenish! hydrogenation carbonylation because of the stability of CO2 and its relative.
Safer, Cheaper, Greener – Solvent CO2 A
Extraction of hops during the beer brewing process is another area where CO 2 is used. Extraction of food and natural products with supercritical CO 2 consists of two steps: The separation of supercritical CO 2 from the extract can be done by either modifying the thermodynamic conditions or by using an external agent. By modifying the thermodynamic conditions via changing the pressure or temperature, the solvent power of CO 2 is changed. If an external agent is used, separation is carried out by adsorption or absorption.
If separation occurs with an external agent, no significant pressure change occurs. Therefore, the operating cost that is associated with pressure requirement is lower. But, an additional step is required, the recovery of the extract from the external agent.
In addition, higher losses of the extract can occur during the recovery step. The feed material is typically ground solid material, which is fed to the extractor. Most commercial operations for supercritical fluid extraction are batch or semi-batch operation especially when the feed material is solid.
For liquid feed material, the extraction occurs in a countercurrent column filled with random or structured packing material. However, for highly viscous liquid feed, the viscous liquid and supercritical fluid may be mixed and sprayed through a nozzle into the extractor vessel. There has been a great deal of interest in supercritical CO 2 extraction beyond caffeine extraction, particularly in the preparation of high value products, such as flavors and fragrances, food supplements and nutraceuticals.
Specialty oils, for example, are high in value and typically low in volume. They have high concentrations of bioactive lipid components that are valued because of various possible health benefits. Herbal extracts from a wide range of botanical raw materials are used as ingredients to the food-and-flavor, nutraceuticals, pharmaceuticals and the cosmetics industries.
Supercritical CO 2 extraction can also be used to purify materials that are used for the production of medical devices. These high-value-product applications typically involve small volumes.
Flexible, medium-capacity plants for supercritical CO 2 extraction offer toll processing for these smaller volume products.
The most important driving force for using supercritical CO 2 in this application area is that it is a generally recognized as safe GRAS solvent that leaves no traces in the product. GRAS is the U. Food and Drug Admin. The high capital cost of building and operating a production plant utilizing supercritical extraction promotes expanding the use of the plant to a multi-product platform. Selective extraction of multiple products can be accomplished by modifying the solvent power of the supercritical fluid.
The solvent power is modified by varying the extraction pressure or by adding a co-solvent. Another method to extract multiple products is by sequential depressurization, in which all products are extracted simultaneously.
The separation step is performed sequentially through a series of separator vessels. This process is referred to as fractional separation. In fact, extraction of food and natural products using supercritical or liquid CO 2 can be considered a relatively mature CO 2 technology.
A wide range of other applications for supercritical CO 2 has been investigated, including chemical reactions, polymer production and processing, semiconductor processing, powder production, environmental and soil remediation and dry cleaning. Commercialization for these applications has, however, proceeded at a slower pace than for extraction. Several of these applications are highlighted here. Supercritical CO 2 has been tested in a variety of industrially important reactions, such as alkylations, hydroformylations, and hydrogenation, as an alternative reaction medium.
Relatively high rates of molecular diffusion and heat transfer are possible with a homogenous, supercritical-CO 2 reaction-medium. Limitations to the use of supercritical CO 2 as a reaction medium include a poor solubility of polar and high-molecular-weight species, b no observed improvement in reaction chemistry in some cases, and c higher capital investment cost due to higher operating pressures.
For reactions not limited by reactant-gas concentrations or other mass-transfer limitations, there is no improvement in reactivity observed when using a homogeneous, supercritical CO 2 medium. Polymer production and processing. Applications of supercritical CO 2 in polymers include polymerization, polymer composite production, polymer blending, particle production, and microcellular foaming.
Several applications, particularly those involving low pressures, have been successfully commercialized. At moderate pressure, very few polymers, except for certain amorphous fluoropolymers and silicones, show any significant solubility in CO 2.
Very high pressure is typically needed to dissolve polymers in supercritical CO 2. Its solvent power is weaker than that of n -alkanes. However, high degrees of swelling of the polymer by CO 2 can occur at significantly lower pressure.
Although many polymers have very low solubility in CO 2 , the solubility of CO 2 in polymers is typically high. This has led to the use of CO 2 as a plasticizer. One example of this application area is a process to produce fluoropolymers using supercritical CO 2 as the reaction medium that was developed by scientists at the University of North Carolina Chapel Hill.
DuPont has an exclusive license for this process until The pilot plant is capable of producing 1, metric tons per year m. Several grades of melt-processable fluoropolymers produced from this process became commercially available in However, no further progress to develop the process beyond the pilot plant phase to a large-scale industrial process has occurred.
Currently, chip manufacturing involves many wet-chemical processes that use hydroxyl amines, mineral acids, elemental gases, organic solvents and large amounts of high purity water during chip fabrication. One potential application is the use of supercritical CO 2 in wafer processing. The high density allows for highly compact, microchannel-based heat exchanger technology.
It requires less compression and allows heat transfer. It reaches full power in 2 minutes, whereas steam turbines need at least 30 minutes. Further, due to its superior thermal stability and non-flammability, direct heat exchange from high temperature sources is possible, permitting higher working fluid temperatures and therefore higher cycle efficiency.
Despite the promise of substantially higher efficiency and lower capital costs, the use of s CO 2 presents material selection and design issues. Materials in power generation components must display resistance to damage caused by high-temperature , oxidation and creep.
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. Components within s CO 2 Brayton loops suffer from corrosion and erosion, specifically erosion in turbomachinery and recuperative heat exchanger components and intergranular corrosion and pitting in the piping.
Testing has been conducted on candidate Ni-based alloys, austenitic steels, ferritic steels and ceramics for corrosion resistance in s CO 2 cycles. Given the volume of carbon fuels used in producing electricity, the environmental impact of cycle efficiency increases would be significant.
Supercritical CO 2 is an emerging natural refrigerant, used in new, low carbon solutions for domestic heat pumps. Supercritical CO 2 heat pumps are commercially marketed in Asia. EcoCute systems from Japan, developed by Mayekawa, develop high temperature domestic water with small inputs of electric power by moving heat into the system from the surroundings.
Supercritical CO 2 has been used since the s to enhance recovery in mature oil fields. Using gasifiers instead of conventional furnaces, coal and water is reduced to hydrogen gas, carbon dioxide and ash. This hydrogen gas can be used to produce electrical power In combined cycle gas turbines, CO 2 is captured, compressed to the supercritical state and injected into geological storage, possibly into existing oil fields to improve yields.
The unique properties of s CO 2 ensure that it remains out of the atmosphere. Supercritical CO 2 could be used as a working fluid in enhanced geothermal systems. Possible advantages compared to water include higher energy yield resulting from its lower viscosity, better chemical interaction, CO 2 storage through fluid loss and higher temperature limit.
As of , the concept had not been tested in the field. Supercritical carbon dioxide is used in the production of silica, carbon and metal based aerogels. For example, silicon dioxide gel is formed and then exposed to s CO 2. When the CO 2 goes supercritical, all surface tension is removed, allowing the liquid to leave the aerogel and produce nanometer sized pores.
Supercritical CO 2 is an alternative for terminal sterilization of biological materials and medical devices with combination of the additive peracetic acid PAA. Supercritical CO 2 does not sterilize the media, because it does not kill the spores of microorganisms.
Moreover, this process is gentle, as the morphology, ultrastructure and protein profiles of inactivated microbes are preserved. Supercritical CO 2 is used in certain industrial cleaning processes.
Natural extracts using supercritical carbon dioxide. From Wikipedia, the free encyclopedia. DeSimone and William Tumas, eds. Journal of Food Science. Journal of Chromatography A. Archived from the original on December 27, Mayekawa Manufacturing Company Mycom. Retrieved 7 February Archived from the original on 10 February Christensen, "Effective terminal sterilization using supercritical carbon dioxide" [ permanent dead link ] , Journal of Biotechnology.
Retrieved from " https: Carbon dioxide Inorganic solvents Industrial gases Gas technologies.
Supercritical carbon dioxide
CO2 used as a solvent is recovered as a by-product from various of CO2 can be exploited and used productively in green applications. Carbon dioxide is often promoted as a green solvent, and its use in this role has . and K with a highly flammable component and hence, safe operation of a. implementation of such green solvents. Solvents, and .. Density versus pressure isotherms for liquid and supercritical carbon dioxide. cially because it is plentiful and inexpensive, . S. C. DeVito, in Designing Safer Chemicals: Green.