Degasification
Encyclopedia
Degasification is the removal of dissolved gas
es from liquid
s, especially water or aqueous solutions, in the fields of science and engineering. There are numerous possible methods for such removal of gases from solids.
Gases are removed for various reasons. Chemists remove gases from solvent
s when the compounds they are working on are possibly air- or oxygen-sensitive. The formation of gas bubbles when a liquid is frozen can also be undesirable, necessitating degassing.
of gas obeys Henry's law
, that is, the amount of a dissolved gas in a liquid is proportional to its partial pressure
. Therefore, placing a solution under reduced pressure makes the dissolved gas less soluble. Sonication
and stirring under reduced pressure can usually enhance the efficiency. This technique is often referred to as Vacuum degasification. Specialized vacuum chambers, called vacuum degassers, are used to degas materials through pressure reduction.
.
. This method has the advantage of being able to prevent redissolution of the gas, so it is used to produce very pure solvents.
The above three methods are used to remove all dissolved gasses. Below are methods for more selective removal.
and carbon dioxide
. Nitrogen
, argon
, helium
, and other inert gas
es are commonly used. To complete the substitution
, the solution should be stirred vigorously and bubbled for a long time. Because helium is not very soluble in most liquids, this technique is also used to reduce the risk of bubble formation in HPLC
systems.
, ammonium sulfite
is frequently used as a reductant because it reacts with oxygen to form sulfate
ions. Although this method can be applied only to oxygen and involves the risk of reduction
of the solute, the dissolved oxygen is almost totally eliminated.
and flash-frozen, usually with liquid nitrogen
. Next a vacuum is applied, and the flask is sealed. A warm water bath is used to thaw the fluid, and upon thawing, bubbles of gas form and escape. The process is typically repeated three times.
Wineries can often skip this step by aging their wines prior to bottling. Storing the wines in steel and wood barrels for months and sometimes years allows the gases to release from the juice and escape back into the air through air-locks.
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es from liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
s, especially water or aqueous solutions, in the fields of science and engineering. There are numerous possible methods for such removal of gases from solids.
Gases are removed for various reasons. Chemists remove gases from solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s when the compounds they are working on are possibly air- or oxygen-sensitive. The formation of gas bubbles when a liquid is frozen can also be undesirable, necessitating degassing.
Pressure reduction
The solubilitySolubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
of gas obeys Henry's law
Henry's law
In physics, Henry's law is one of the gas laws formulated by William Henry in 1803. It states that:An equivalent way of stating the law is that the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid...
, that is, the amount of a dissolved gas in a liquid is proportional to its partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
. Therefore, placing a solution under reduced pressure makes the dissolved gas less soluble. Sonication
Sonication
thumb|right|A sonicator at the [[Weizmann Institute of Science]] during sonicationSonication is the act of applying sound energy to agitate particles in a sample, for various purposes. In the laboratory, it is usually applied using an ultrasonic bath or an ultrasonic probe, colloquially known as...
and stirring under reduced pressure can usually enhance the efficiency. This technique is often referred to as Vacuum degasification. Specialized vacuum chambers, called vacuum degassers, are used to degas materials through pressure reduction.
Heating
Generally speaking, the higher the temperature of a solution becomes, the less a gas dissolves provided it doesn't react with the solvent. Consequently, heating a solution can expel the remaining gas. Ultrasonication and stirring at high heat are also effective. This method needs no special apparatus and is easy to conduct. In some cases, however, the solvent and the solute decompose, react with each other, or evaporate at high temperature, and the rate of removal is less reproducibleReproducibility
Reproducibility is the ability of an experiment or study to be accurately reproduced, or replicated, by someone else working independently...
.
Membrane degasification
Gas-liquid separation membranes allow gas but not liquid to pass through. Flowing a solution inside a gas-liquid separation membrane and vacuating outside makes the dissolved gas go out through the membraneArtificial membrane
An artificial membrane, or synthetic membrane, is a synthetically created membrane which is usually intended for separation purposes in laboratory or in industry. Synthetic membranes have been successfully used for small and large-scale industrial processes since the middle of twentieth century. A...
. This method has the advantage of being able to prevent redissolution of the gas, so it is used to produce very pure solvents.
The above three methods are used to remove all dissolved gasses. Below are methods for more selective removal.
Substitution by inert gas
Bubbling a solution with an inert gas substitutes the dissolved harmful, reactive gases such as oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. Nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, and other inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
es are commonly used. To complete the substitution
Substitution
Substitution may refer to:- Sciences :* Substitution , a syntactic transformation on strings of symbols of a formal language* Substitution of variables* Substitution cipher, a method of encryption...
, the solution should be stirred vigorously and bubbled for a long time. Because helium is not very soluble in most liquids, this technique is also used to reduce the risk of bubble formation in HPLC
High-performance liquid chromatography
High-performance liquid chromatography , HPLC, is a chromatographic technique that can separate a mixture of compounds and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.HPLC typically utilizes different types of stationary...
systems.
Addition of reductant
If oxygen should be removed, the addition of reductants is sometimes effective. For example, especially in the field of electrochemistryElectrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
, ammonium sulfite
Ammonium sulfite
Ammonium sulfite is the ammonium salt of sulfurous acid with the chemical formula 2SO3.-Preparation:Ammonium sulfite can be prepared by the reaction of ammonia with sulfur dioxide in aqueous solution:-Uses:...
is frequently used as a reductant because it reacts with oxygen to form sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
ions. Although this method can be applied only to oxygen and involves the risk of reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of the solute, the dissolved oxygen is almost totally eliminated.
Freeze-Pump-Thaw cycling
In this laboratory-scale technique, the fluid to be degassed is placed in a Schlenk flaskSchlenk flask
A Schlenk flask, or Schlenk tube is a reaction vessel typically used in air sensitive chemistry, invented by Wilhelm Schlenk. It has a side arm fitted with a PTFE or ground glass stopcock which allows the vessel to be evacuated or filled with gases...
and flash-frozen, usually with liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
. Next a vacuum is applied, and the flask is sealed. A warm water bath is used to thaw the fluid, and upon thawing, bubbles of gas form and escape. The process is typically repeated three times.
Degassing Wine
Yeast uses sugar to produce alcohol and carbon dioxide. In wine making, carbon dioxide is an undesired by-product for most wines. If the wine will be bottled quickly after fermentation, it is important to degas the wine. The most common method used is 'whipping' the wine with some form of whisk or spoon. Just after fermentation is completed and before the 'clearing' stage, the fermented juice is stirred vigorously until the majority of the gases have released from the liquid through agitation.Wineries can often skip this step by aging their wines prior to bottling. Storing the wines in steel and wood barrels for months and sometimes years allows the gases to release from the juice and escape back into the air through air-locks.