Inert gas

As inert gases are called gases , the very inert ( inert ) are so at only a few chemical reactions involved. They are noble gases or, if they are molecular compounds , they are usually characterized by a strongly negative standard enthalpy of formation. Inert gases are odorless and non-toxic, and their presence can not be perceived directly by the sense of smell , i.e. without technical aids.

The inert gases include, for example, elementary gases such as nitrogen , noble gases such as helium , neon , argon , krypton , xenon , and gaseous molecular compounds such as sulfur hexafluoride . Whether a certain gas is designated as an inert gas for a certain application also depends on the specific case. For example, nitrogen can be used as an inert gas at temperatures such as occur during soft soldering . On the other hand, when welding certain high-alloy steels, the high temperatures lead to an undesirable chemical reaction of nitrogen and in this application must be replaced by more expensive argon, which is inert as a noble gas even at higher temperatures.

Inert gases are used to keep the oxygen contained in the air (approx. 21%) away from certain chemical reactions. The use of larger quantities is, for example, the flushing of areas in which there were previously easily flammable gases and to remove the last gas residues that would otherwise constitute ignitable gas mixtures with the atmospheric oxygen. By displacing or significantly reducing oxygen, inert gases can prevent oxidative processes such as combustion , explosions or, in metalworking, the scaling of substances.

hazards

Warning symbol of the danger of suffocation from inert gases

Since most living beings and also humans depend on the availability of oxygen in the air they breathe, relevant safety rules must be observed when handling large quantities of pure inert gases, especially in closed rooms. Carbon dioxide, for example, leads to a distinct feeling of suffocation if the concentration in the air is too high. With inert gases, however, there is a risk of deliberately imperceptible asphyxia due to the displacement of oxygen . All inert gases result in unconsciousness and death from suffocation . There are several fatal accidents at work in Germany in connection with inert gases, the main causes of which are incorrectly applied work instructions and insufficient training of the employees concerned, in combination with technical defects such as leaks in gas cylinders and hoses or the leakage and sudden evaporation of large quantities of liquefied, cold gases such as nitrogen from dewar flasks in insufficiently ventilated rooms.

Explosion protection

shipping

In tankers , when the flammable liquid cargo is pumped out ( extinguished ), inert gas is filled in to fill the remaining volume in the tank in order to prevent an explosive mixture of air and gas from developing, which could be ignited by sparks. For this purpose, the inert exhaust gases of the main propulsion system are used in the oil tanker journey (diesel engine exhaust gases on motor ships or boiler exhaust gases on turbine ships).

Special inert gas systems are installed on liquid gas tankers, as the qualitative requirements for the inert gas are higher than in the oil tanker journey. Low-sulfur diesel oil is burned in a combustion chamber in such a way that the residual oxygen content in the exhaust gas does not exceed 0.2% by volume. Soot particles and water-soluble substances are then washed out using seawater. The gas is then cooled to 8 to 10 ° C with the aid of a refrigeration system (refrigeration dryer), during which the water contained in the gas condenses and is removed via a separator. The residual moisture is then removed from the pre-dried gas in an adsorption dryer in order to ensure the dew point required depending on the load. A dew point ≤ −40 ° C must be ensured during the LNG journey. In liquid gas shipping, nitrogen is used to render the barriers inert. This is either delivered on board in liquid form by tanker and evaporated there as required, or obtained from the air using membrane systems on board.

Warplanes

Similar to shipping, the fuel tanks of combat aircraft are also filled with an inert gas to prevent fire and explosion. Dry nitrogen is used here.

After a Boeing 747 crash in 1996, which was caused by the explosion of a fuel tank by sparking of the tank electrics, it was discussed whether this could also be practiced in civil aviation. In addition, one is looking for ways of influencing the kerosene in such a way that it is incombustible or at least hardly inflammable under the conditions prevailing in the tank.

Chemical industry

In the chemical industry, inert gases are used as explosion protection in storage tanks; they are also used as protective gas to safeguard production. In addition, shielding gases are often of great importance in preparative work in the chemical laboratory. So they enable z. B. Reactions with substances that would immediately decompose on contact with atmospheric oxygen or humidity. For this purpose, the air is often only replaced by a protective gas within the reaction vessel (e.g. Schlenk flask ).

Animal slaughter

Inert gases are also used for stunning before killing animals for slaughter such as pigs in the context of industrial slaughter . Carbon dioxide is primarily used in a gas pit with a paternoster system without gas locks. When killing animals, however, carbon dioxide has the disadvantage that the animals suffer a comparatively agonizing death by suffocation, as carbon dioxide triggers strong asphyxiation stimuli in the organisms. Slaughtered animals are suffocated experimentally and more gently with argon, nitrogen or helium. However, these processes are more expensive and require a technically more complex infrastructure such as gas locks in the slaughter area.

Other technical applications

• Fire protection : for fire fighting in inert gas extinguishing systems (e.g. in data centers ) or for preventive fire protection by inerting in active fire prevention systems
• Chemical synthesis if reaction components (e.g. metallic lithium) would unintentionally react with constituents of the air (protective gas or Schlenk technology )
• Packaging technology to extend the shelf life of food
• Welding , there is argon as protective gas used
• Reflow soldering , where nitrogen is used
• In gas systems , e.g. B. for leak testing
• Working in the so-called glove box
• In light bulbs to prevent the filament from burning up
• Gas chromatography , used there as a mobile phase (carrier gas)
• Anesthesia , where nitrous oxide was considered an inert gas for a long time and for this reason was not included in the toxicological assessment of anesthetic gas exposure by anesthetists
• Diving , where helium and neon are used in breathing gas mixtures to prevent nitrogen anesthesia
• As propulsion methods for space travel in space probes or space stations, mostly for control nozzles as the sole propulsion source
• Decompression models, simulate saturation through inert gases (mostly nitrogen) in different body tissues .

literature

• International Maritime Organization: Inert gas systems . 3. Edition. IMO Publishing, 1990, ISBN 92-801-1262-7 ; Digitized

Individual evidence

1. ↑ ^{a b} Hazards of inert gases and oxygen depletion. European Industrial Gases Association AISBL, 2009, accessed July 21, 2018 . 
2. ↑ Lack of oxygen - suffocation - a deadly danger. (PDF) Industriegasverband e. V., accessed on August 16, 2018 . 
3. ↑ Michael Marahrens, Inga Schwarzlose: Investigations into the stunning of slaughter pigs with a nitrogen-filled highly expansive foam under animal welfare and meat quality aspects. (PDF) Friedrich Loeffler Institute (FLI), Institute for Animal Welfare and Animal Husbandry (ITT), accessed on August 16, 2018 .