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Encyclopedia > Supercritical fluid

A supercritical fluid is any substance at a temperature and pressure above its thermodynamic critical point. It has the unique ability to diffuse through solids like a gas, and dissolve materials like a liquid. Additionally, it can readily change in density upon minor changes in temperature or pressure. These properties make it suitable as a substitute for organic solvents in a process called Supercritical Fluid Extraction. Carbon dioxide and water are the most commonly used supercritical fluids. Image File history File links Broom_icon. ... Fig. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ... In chemistry and condensed matter physics, a critical point specifies the conditions (temperature, pressure) at which the liquid state of the matter ceases to exist. ... This article or section does not cite any references or sources. ... A solid is a state of matter, characterized by a definite volume and a definite shape (i. ... This article does not cite any references or sources. ... Solvation is the attraction and association of molecules of a solvent with molecules or ions of a solute. ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon and hydrogen; therefore, carbides, carbonates, carbon oxides and elementary carbon are not organic (see below for more on the definition controversy... A substance is soluble in a fluid if it dissolves in the fluid. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...

Figure 1. Carbon dioxide pressure-temperature phase diagram
Figure 2. Carbon dioxide density-pressure phase diagram
Figure 2. Carbon dioxide density-pressure phase diagram

Contents

Image File history File links Carbon_dioxide_pressure-temperature_phase_diagram. ... Image File history File links Carbon_dioxide_density-pressure_phase_diagram. ...

Introduction

In 1822, Baron Charles Cagniard de la Tour discovered the critical point of a substance in his famous cannon barrel experiments. Listening to discontinuities in the sound of a rolling flint ball in a sealed cannon filled with fluids at various temperatures, he observed the critical temperature. Above this temperature, the densities of the liquid and gas phases become equal and the distinction between them disappears, resulting in a single supercritical fluid phase. In Table 1, the critical properties are shown for some components, which are commonly used as supercritical fluids. 1822 (MDCCCXXII) was a common year starting on Tuesday (see link for calendar) of the Gregorian calendar (or a common year starting on Thursday of the 12-day-slower Julian calendar). ... Charles Cagniard de la Tour (March 31, 1777 - July 5, 1859), French engineer and physicist, was born in Paris, and after attending the École Polytechnique became one of the ingenieurs geographiques. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ...


Phase diagram

The observations by de la Tour can be explained by looking at the phase diagram of a pure component, e.g. carbon dioxide. In Figures 1 and 2, two projections of the phase diagram of carbon dioxide are shown. In the pressure-temperature phase diagram (Fig. 1) the boiling line is observed, which separates the vapor and liquid region and ends in the critical point. At the critical point, the densities of the equilibrium liquid phase and the saturated vapor phases become equal, resulting in the formation of a single supercritical phase. This can be observed in the density-pressure phase diagram for carbon dioxide, as shown in Figure 2, where the critical point is located at 304.1 K and 7.38 MPa (73.8 bar). With increasing temperatures, the liquid-vapor density gap decreases, up to the critical temperature, at which the discontinuity disappears. Thus, above the critical temperature a gas cannot be liquefied by pressure. However, at extremely high pressures the fluid can solidify, as visible at the top of Figure 1. By definition, a supercritical fluid is a substance above both its critical temperature and pressure. In a practical sense, the area of interest in supercritical fluids for processing and separation purposes is limited to temperatures in the vicinity of the critical point, where large gradients in the physical properties are observed. The changes near the critical point are not limited to density. Many other physical properties also show large gradients with pressure near the critical point, e.g. viscosity, the relative permittivity and the solvent strength, which are all closely related to the density. At higher temperatures, the fluid starts to behave like a gas, as can be seen in Figure 2. For carbon dioxide at 400 K, the density increases almost linearly with pressure. In physical chemistry and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. ... The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid at a given pressure. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ... This article or section is not written in the formal tone expected of an encyclopedia article. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The bar (symbol bar) and the millibar (symbol mbar, also mb) are units of pressure. ... Viscosity is a measure of the resistance of a fluid to deform under shear stress. ... The permittivity of a medium is an intensive physical quantity that describes how an electric field affects and is affected by the medium. ...


Applications

For engineering purposes, supercritical fluids can be regarded as “hybrid solvents” with properties between those of gases and liquids, i.e. a solvent with a low viscosity, high diffusion rates and no surface tension. In the case of supercritical carbon dioxide, the viscosity is in the range of 20–100 µPa·s (0.02-0.1 cP), where liquids have viscosities of approximately 500–1000 µPa·s (0.5-1.0 cP) and gases approximately 10 µPa·s (0.01 cP), respectively. Diffusivities of solutes in supercritical carbon dioxide are up to a factor 10 higher than in liquid solvents. Additionally, these properties are strongly pressure-dependent in the vicinity of the critical point, making supercritical fluids highly tunable solvents. Of the components shown in Table 1, carbon dioxide and water are the most frequently used in a wide range of applications, including extractions, dry cleaning and chemical waste disposal. In polymer systems, ethylene and propylene are also widely used, where they act both as a solvent and as the reacting monomer. Viscosity is a measure of the resistance of a fluid to deform under shear stress. ... In physics, surface tension is an effect within the surface layer of a liquid that causes that layer to behave as an elastic sheet. ... The pascal second (symbol Pa·s) is the SI unit of dynamic viscosity. ... The poise (P) is the cgs unit of viscosity, 1 P = 1 g·cm-1·s-1 The SI analog is 1 pascal second (Pa·s) = 1 kg·m-1·s-1 = 10 P. It is named after Jean Louis Marie Poiseuille. ... Dry cleaning is any cleaning process for clothing and textiles using an organic solvent other than water — generally known as dry cleaning fluid, and typically this is tetrachloroethylene. ... A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... Ethylene (or IUPAC name ethene) is the chemical compound with the formula C2H4. ... Propylene, also known by its IUPAC name propene, is an organic compound having the chemical formula C3H6. ... A solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ...


One of the most important properties of supercritical fluids is that their solvating properties are a complex function of their pressure and temperature, independent of their density. This means that (taking a very simplistic approach) raw materials containing CO2 soluble products can be selectively extracted or selectively precipitated to obtain ultra-pure extracts. Although the details are much more complex than this, it remains the dominant chemical-free technology for the production of decaffeinated coffee, nicotine-free tobacco, and many of the world's best spice extracts.


Supercritical water reactors (SCWRs) are promising advanced nuclear systems because of their high thermal efficiency (i.e., about 45% vs. about 33% efficiency for current light water reactors (LWR) and considerable plant simplification. Supercritical water reactor scheme. ... The thermal efficiency () is a dimensionless performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example. ... A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water, also called light water, as its neutron moderator. ...

Table 1. Critical properties of various solvents (Reid et al, 1987)
Solvent Molecular weight Critical temperature Critical pressure Density
g/mol K MPa (atm) g/cm³
Carbon dioxide (CO2) 44.01 304.1 7.38 (72.8) 0.469
Water (H2O) 18.02 647.3 22.12 (218.3) 0.348
Methane (CH4) 16.04 190.4 4.60 (45.4) 0.162
Ethane (C2H6) 30.07 305.3 4.87 (48.1) 0.203
Propane (C3H8) 44.09 369.8 4.25 (41.9) 0.217
Ethylene (C2H4) 28.05 282.4 5.04 (49.7) 0.215
Propylene (C3H6) 42.08 364.9 4.60 (45.4) 0.232
Methanol (CH3OH) 32.04 512.6 8.09 (79.8) 0.272
Ethanol (C2H5OH) 46.07 513.9 6.14 (60.6) 0.276
Acetone (C3H6O) 58.08 508.1 4.70 (46.4) 0.278

The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... Standard atmosphere (symbol: atm) is a unit of pressure. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... This article describes water from a scientific and technical perspective. ... Methane is a chemical compound with the molecular formula CH4. ... Ethane is a chemical compound with chemical formula C2H6. ... Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ... Ethylene (or IUPAC name ethene) is the chemical compound with the formula C2H4. ... Propylene, also known by its IUPAC name propene, is an organic compound having the chemical formula C3H6. ... Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). ... Grain alcohol redirects here. ... The chemical compound acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and β-ketopropane) is the simplest representative of the ketones. ...

See also

Carbon dioxide pressure-temperature phase diagram Supercritical carbon dioxide refers to carbon dioxide with some unique properties. ...

References

  1. R.C. Reid, J.M. Prausnitz and B.E. Poling, The properties of gases and liquids, 4th ed., McGraw-Hill, New York, 1987.
  2. W. Wagner and A. Kruse, Properties of Water and Steam, Springer-Verlag, Berlin, 1998.

External links

  • Food Product Design

  Results from FactBites:
 
Supercritical fluid - Wikipedia, the free encyclopedia (693 words)
Carbon dioxide and water are the most commonly used supercritical fluids.
In a practical sense, the area of interest in supercritical fluids for processing and separation purposes is limited to temperatures in the vicinity of the critical point, where large gradients in the physical properties are observed.
In the case of supercritical carbon dioxide, the viscosity is in the range of 20–100 µPa·s (0.02-0.1 cP), where liquids have viscosities of approximately 500–1000 µPa·s (0.5-1.0 cP) and gases approximately 10 µPa·s (0.01 cP), respectively.
Supercritical water reactor - Wikipedia, the free encyclopedia (494 words)
The Supercritical water reactor (SCWR) is a Generation IV reactor concept that uses supercritical water as the working fluid.
Supercritical water-cooled reactors (SCWRs) are promising advanced nuclear systems because of their high thermal efficiency (i.e., about 45% vs. about 33% efficiency for current light water reactors (LWR) and considerable plant simplification.
Supercritical water-cooled reactors (SCWRs) are promising advanced nuclear systems because of their high thermal efficiency, about 45% vs. about 33% efficiency for current light water reactors (LWR), and considerable plant simplification.
  More results at FactBites »

 
 

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