Chemical oxygen generator

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A chemical oxygen generator is a device that releases oxygen via a chemical reaction. The oxygen source is usually an inorganic superoxide, [1] chlorate, or perchlorate. Ozonides are a promising group of oxygen sources, as well. The generators are usually ignited by a firing pin, and the chemical reaction is usually exothermic, making the generator a potential fire hazard. Potassium superoxide was used as an oxygen source on early crewed missions of the Soviet space program, in submarines for use in emergency situations, for firefighters, and for mine rescue.

Contents

In commercial airliners

Diagram of a chemical oxygen generator system Aircraft oxygen generator diagram.svg
Diagram of a chemical oxygen generator system
Chemical Oxygen Generator, Cut-away View Chemical Oxygen Generator, Cut-away View.gif
Chemical Oxygen Generator, Cut-away View

Commercial aircraft provide emergency oxygen to passengers to protect them in case of loss of cabin pressure. Chemical oxygen generators are not used for the cockpit crew, who are typically supplied using compressed oxygen cylinders, also known as oxygen bottles. In narrow body airliners, for each row of seats there were overhead oxygen masks and oxygen generators. In some wide-body airliners, such as the DC-10 and IL-96, the oxygen generators and oxygen masks are mounted in the top portion of the seat backs, since the ceiling is too high above the passengers. If a decompression occurred, the panels were opened either by an automatic pressure switch or by a manual switch, and the masks are released. When the passengers pull down on the mask they removed the retaining pins and triggered the production of oxygen.

The oxidizer core is sodium chlorate (Na Cl O 3), which is mixed with less than 5 percent barium peroxide (Ba O 2) and less than 1 percent potassium perchlorate (K Cl O 4). The explosives in the percussion cap are a lead styphnate and tetrazene explosive mixture. The chemical reaction is exothermic and the exterior temperature of the generator will reach 260 °C (500 °F). It will produce oxygen for 12 to 22 minutes. [2] [3] The two-mask generator is approximately 63 mm (2.5 in) in diameter and 223 mm (8.8 in) long. The three-mask generator is approximately 70 mm (2.8 in) in diameter and 250 mm (9.8 in) long.

In May 11, 1996, accidental activation of improperly shipped expired generators, mistakenly labeled as empty "oxy canisters", [4] caused the ValuJet Airlines Flight 592 crash, killing all on board. [5] An ATA DC-10, Flight 131, was also destroyed while parked at O'Hare Airport, on August 10, 1986. The cause was the accidental activation of an oxygen generator, contained in the back of a broken DC-10 seat, being shipped in the cargo compartment to a repair station. There were no fatalities or injuries because the plane contained no passengers when the fire broke out. [6] [7]

Oxygen candle

A chlorate candle, or an oxygen candle, is a cylindrical chemical oxygen generator that contains a mix of sodium chlorate and iron powder, which when ignited smolders at about 600 °C (1,100 °F), producing sodium chloride, iron oxide, and oxygen at a fixed rate of about 6.5 man-hours per kilogram of the mixture. The mixture has an indefinite shelf life if stored properly: candles have been stored for 20 years without decreased oxygen output. Thermal decomposition releases the oxygen. The burning iron supplies the heat. The candle must be wrapped in thermal insulation to maintain the reaction temperature and to protect surrounding equipment. The key reaction is: [8]

2 NaClO3 → 2 NaCl + 3 O2

Potassium and lithium chlorate, and sodium, potassium and lithium perchlorates can also be used in oxygen candles.

In the Vika oxygen generator used on some spacecraft, lithium perchlorate is the source of oxygen. At 400 °C (750 °F), it releases 60% of its weight as oxygen: [9]

LiClO4 → LiCl + 2 O2

Pressure swing adsorption (PSA) oxygen generators

Advances in technology have provided industrial oxygen generator systems for use where air is available and a higher concentration of oxygen is desired. Pressure swing adsorption (PSA) incorporates a molecular sieve for gas separation. In the case of oxygen generation a zeolite-based sieve forces preferential adsorption for nitrogen.[ citation needed ] Clean, dry air is passed through the sieve beds on the oxygen generator, producing an oxygen-enriched gas. Nitrogen separation membrane equipment is also used.

Uses

Chemical oxygen generators are used in aircraft, breathing apparatus for firefighters and mine rescue crews, submarines, and everywhere a compact emergency oxygen generator with long shelf life is needed. They usually contain a device for absorption of carbon dioxide, sometimes a filter filled with lithium hydroxide; a kilogram of LiOH absorbs about half a kilogram of CO2.

See also

Related Research Articles

<span class="mw-page-title-main">Alkali metal</span> Group of highly reactive chemical elements

The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.

In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula O−2. The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide results from the addition of an electron which fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −1. Both dioxygen and the superoxide anion are free radicals that exhibit paramagnetism. Superoxide was historically also known as "hyperoxide".

<span class="mw-page-title-main">Oxidizing agent</span> Chemical compound used to oxidize another substance in a chemical reaction

An oxidizing agent is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent. In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens.

<span class="mw-page-title-main">Potassium chlorate</span> Chemical compound

Potassium chlorate is the inorganic compound with the molecular formula KClO3. In its pure form, it is a white solid. After sodium chlorate, it is the second most common chlorate in industrial use. It is a strong oxidizing agent and its most important application is in safety matches. In other applications it is mostly obsolete and has been replaced by safer alternatives in recent decades. It has been used

<span class="mw-page-title-main">Manganese dioxide</span> Chemical compound

Manganese dioxide is the inorganic compound with the formula MnO
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<span class="mw-page-title-main">Chlorate</span> Anion and term for chemical compounds containing it

Chlorate is the common name of the ClO−
3 anion, whose chlorine atom is in the +5 oxidation state. The term can also refer to chemical compounds containing this anion, with chlorates being the salts of chloric acid. Other oxyanions of chlorine can be named "chlorate" followed by a Roman numeral in parentheses denoting the oxidation state of chlorine: e.g., the ClO−
4 ion commonly called perchlorate can also be called chlorate(VII).

<span class="mw-page-title-main">Perchlorate</span> Ion, and compounds containing the ion

A perchlorate is a chemical compound containing the perchlorate ion, ClO−4, the conjugate base of perchloric acid. As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cation.

<span class="mw-page-title-main">Sodium chlorate</span> Chemical compound

Sodium chlorate is an inorganic compound with the chemical formula NaClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leaves sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching pulp to produce high brightness paper.

<span class="mw-page-title-main">Permanganate</span> Chemical compound

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4, the conjugate base of permanganic acid. Because the manganese atom has a +7 oxidation state, the permanganate(VII) ion is a strong oxidising agent. The ion is a transition metal ion with a tetrahedral structure. Permanganate solutions are purple in colour and are stable in neutral or slightly alkaline media. The exact chemical reaction depends on the carbon-containing reactants present and the oxidant used. For example, trichloroethane (C2H3Cl3) is oxidised by permanganate ions to form carbon dioxide (CO2), manganese dioxide (MnO2), hydrogen ions (H+), and chloride ions (Cl−).

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<span class="mw-page-title-main">Potassium superoxide</span> Chemical compound

Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a CO2 scrubber, H2O dehumidifier, and O2 generator in rebreathers, spacecraft, submarines, and spacesuits.

<span class="mw-page-title-main">Sodium peroxide</span> Chemical compound

Sodium peroxide is an inorganic compound with the formula Na2O2. This yellowish solid is the product of sodium ignited in excess oxygen. It is a strong base. This metal peroxide exists in several hydrates and peroxyhydrates including Na2O2·2H2O2·4H2O, Na2O2·2H2O, Na2O2·2H2O2, and Na2O2·8H2O. The octahydrate, which is simple to prepare, is white, in contrast to the anhydrous material.

<span class="mw-page-title-main">Sodium perchlorate</span> Chemical compound

Sodium perchlorate is an inorganic compound with the chemical formula NaClO4. It consists of sodium cations Na+ and perchlorate anions ClO−4. It is a white crystalline, hygroscopic solid that is highly soluble in water and ethanol. It is usually encountered as sodium perchlorate monohydrate NaClO4·H2O. The compound is noteworthy as the most water-soluble of the common perchlorate salts.

<span class="mw-page-title-main">Lithium perchlorate</span> Chemical compound

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A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas/smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions. Pyrotechnic substances do not rely on oxygen from external sources to sustain the reaction.

Lithium superoxide is an unstable inorganic salt with formula LiO2. A radical compound, it can be produced at low temperature in matrix isolation experiments, or in certain nonpolar, non-protic solvents. Lithium superoxide is also a transient species during the reduction of oxygen in a lithium–air galvanic cell, and serves as a main constraint on possible solvents for such a battery. For this reason, it has been investigated thoroughly using a variety of methods, both theoretical and spectroscopic.

A metal–air electrochemical cell is an electrochemical cell that uses an anode made from pure metal and an external cathode of ambient air, typically with an aqueous or aprotic electrolyte.

Methods of oxygen storage for subsequent use span many approaches, including high pressures in oxygen tanks, cryogenics, oxygen-rich compounds and reaction mixtures, and chemical compounds that reversibly release oxygen upon heating or pressure change. O2 is the second most important industrial gas.

References

  1. ↑ Hayyan M., Hashim M.A., AlNashef I.M., Superoxide Ion: Generation and Chemical Implications, Chem. Rev., 2016, 116 (5), pp 3029–3085. DOI: 10.1021/acs.chemrev.5b00407
  2. ↑ Yunchang Zhang; Girish Kshirsagar; James C. Cannon (1993). "Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen". Ind. Eng. Chem. Res. 32 (5): 966–969. doi:10.1021/ie00017a028.
  3. ↑ William H. Schechter; R. R. Miller; Robert M. Bovard; C. B. Jackson; John R. Pappenheimer (1950). "Chlorate Candles as a Source of Oxygen". Industrial & Engineering Chemistry. 42 (11): 2348–2353. doi:10.1021/ie50491a045.
  4. ↑ "McDonnell Douglas DC-9-32 | ValuJet Airlines Flight 592, N904VJ". Federal Aviation Administration . 19 December 2022. Retrieved 10 October 2024.
  5. ↑ "Fire in the Hold". Mayday . Season 12. Episode 2. 10 August 2012.
  6. ↑ "OT McDonnell Douglas DC-10-40 N184AT". Aviation Safety Network . Archived from the original on June 21, 2024.
  7. ↑ Airliners.net, Photograph, Dave Campbell
  8. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  9. ↑ M. M. Markowitz; D. A. Boryta; Harvey Stewart Jr. (1964). "Lithium Perchlorate Oxygen Candle. Pyrochemical Source of Pure Oxygen". Ind. Eng. Chem. Prod. Res. Dev. 3 (4): 321–330. doi:10.1021/i360012a016.
  10. ↑ "Exclusive: UTC-built oxygen generator fails on U.S. submarine". Reuters. 21 March 2011. Retrieved 21 February 2021.
  11. ↑ Johnson, C. W. "Degraded Modes and the 'Culture of Coping' in Military Operations: An Analysis of a Fatal Incident on-board HMS Tireless on 20/21 March 2007" (PDF).
  12. ↑ Page, Lewis (22 March 2007). "'Oxygen candle' caused explosion". The Register. Retrieved 2013-09-04.
  13. ↑ Barry, Patrick (2000). "Breathing Easy on the Space Station". National Aeronautics and Space Administration. Archived from the original on 11 March 2019. Retrieved 9 September 2012.
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