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-the good reverend drone

Ipsa scientia potestas est

 
NAMF
Hive Bee   posted 02-20-2000 03:53 PM           
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keeping a aereaction going foreward., insuring seperation between the phases
minimal and slow phase as welll as controled mixxing and elluating between two layers of meteraial being processed especially usefulll in electronic processing
 
LaBTop
PimpBee   posted 02-20-2000 11:11 PM           
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What is a supercritical fluid?
A supercritical fluid is a material which can be either liquid or gas, used in a state above the critical temperature and critical pressure where gases and liquids can coexist. It shows unique properties that are different from those of either gases or liquids under standard conditions.

Phase diagram for water and carbon dioxide:
 

A supercritical fluids has both the gaseous property of being able to penetrate anything, and the liquid property of being able to dissolve materials into their components? In addition, it offers the advantage of being able to change density to a great extent in a continuous manner. On this account, use of carbon dioxide or water in the form of a supercritical fluid offers a substitute for an organic solvent in the fields of the food industry and medical supplies. Furthermore, as a new technology which is user-friendly to both human beings and the environment, it is attracting wide attention.
Currently, particular attention is being paid to uses in the field of reaction solvent where the range of applications is rapidly widening.
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New reaction solvent

Use of a supercritical fluid, with the special properties it offers such as control over solubility, excellent transportability, and the ability to dissolve substances, enables you to make use of new reaction processes for hydrolysis or partial oxidation, particularly in the case of water.
[Examples]
# Chemical recycling of PET (polyethylene terephthalate) containers, transformation of cellulose into glucose, etc.
# The new way to plastic waste recycle:
The Plant using Supercritical Water starts commercial run: http://www.kobelco.co.jp/eneka/p14/sfe09.htm 
# Characteristics and uses of supercritical water: http://www.kobelco.co.jp/eneka/p14/sfe02.htm 
# Reaction solvent effect (1): "The dielectric constant": http://www.kobelco.co.jp/eneka/p14/sfe03.htm 
# Reaction solvent effect (2): "The ion product": http://www.kobelco.co.jp/eneka/p14/sfe04.htm 
# Effect in hydrolysis reactions: http://www.kobelco.co.jp/eneka/p14/sfe05.htm 
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Applications in extraction and purification:

The dissolving power of a supercritical fluid offers a safe solvent in food processing, and enables quick extraction of spirits or rapid removal of unnecessary components at nearly room temperature. Furthermore, as a substitute for the conventional distillation method using an azeotropic mixture, it carries out separation with an energy-saving high density concentration.

[Examples]:

1. Separation and purification of oil and grease, odorants, medicinal components from flora and fauna stock, such as the removal of agrochemicals from ginseng extract.
2. Removal or concentration of impurities in chemical materials or chemical products, such as the conversion of an ethanol aqueous solution (azeotropic mixture) into an anhydrous form.
3. Fractionation and purification of polymers, such as the removal of unchanged monomers from polymers.
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Applications in materials processing:

Use of a supercritical fluid will make it possible to manufacture specially structured products and high-functional, high-quality materials, which are almost impossible to produce with conventional manufacturing methods.

[Examples]

1. Drying silica-aerogel: the manufacture of porous silica-aerogel with an extremely high hole rate.
2. Fine-graining, thin-filming, fiber-refining using the RESS (Rapid Expansion of the Supercritical Solutions) method, as in the manufacture of whisker-shaped fine particles.
3. Fine-graining or thin-filming by the poor solvent method (GAS: the gas anti-solvent method), as for the strengthening of silica-aerogel (surface coating).

Web site: http://www.kobelco.co.jp/eneka/p14/sfe01.htm 

With supercritical water it becomes possible to dissolve organic substances that do not dissolve in water under atmospheric conditions.
The dielectric constant of supercritical water is in the range from 2 to 30, which is similar to the range from a nonpolar solvent such as hexane (with a dielectric constant of about 1.8) to a polar solvent such as methanol (with a dielectric constant of 32.6).

A significant change in the dielectric constant can be obtained, depending on the pressure and/or temperature change --->
So supercritical water covers the range of solvents from polar to nonpolar --->
In the vicinity of the critical point, where the dielectric constant of a weak polar solvent appears, the dissolving power can be expected to be more like that of a conventional organic solvent ! --->
So with the proper setup, you can avoid all these nasty, environment damaging organics.
Aint that nice.

But we talk here about pressures from 220 atm up to 1000 atm, and temps around the Critical Point (C.P.) between 300 and 380 C.

So it doesn't sound directly like something a "Cook" would take in consideration.
But what more fluids can be made supercritical? At lower pressures/temps ?

Start the discussion. LT/

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WISDOMwillWIN