Hydrogen peroxide
(H2O2) is a very pale blue liquid which appears colorless in a dilute solution, slightly more viscous than water. It is a weak acid. It has strong oxidizing properties and is therefore a powerful bleaching agent that is mostly used for bleaching paper, but has also found use as a disinfectant, as an oxidizer, and in rocketry (particularly in high concentrations as high-test peroxide (HTP)) as a monopropellant, and in bipropellant systems. The oxidizing capacity of hydrogen peroxide is so strong that the chemical is considered a highly reactive oxygen species.
History
Hydrogen peroxide was first isolated in 1818 by Louis Jacques Thénard by reacting barium peroxide with nitric acid. An improved version of this process used hydrochloric acid, followed by sulfuric acid to precipitate the barium
sulfate byproduct. Thénard's process was used from the end of the 19th century until the middle of the 20th century. Modern production methods are discussed below.
Uses
Industrial applications
About 50% of the world's production of hydrogen peroxide in
1994 was used for pulp- and paper-bleaching. Other bleaching applications are becoming more important as hydrogen peroxide is seen as an environmentally benign alternative to chlorine-based bleaches.
Other major industrial
applications for hydrogen peroxide include the manufacture of sodium percarbonate and sodium perborate, used as mild bleaches in laundry detergents. It is used in the production of certain organic peroxides such as dibenzoyl
peroxide, used in polymerisations and other chemical processes. Hydrogen peroxide is also used in the production of epoxides such as propylene oxide. Reaction with carboxylic acids produces a corresponding peroxy acid. Peracetic
acid and meta-chloroperoxybenzoic acid (commonly abbreviated mCPBA) are prepared from acetic acid and meta-chlorobenzoic acid, respectively. The latter is commonly reacted with alkenes to give the corresponding epoxide. In PCB
manufacturing process, hydrogen peroxide mixed with sulfuric acid was used as the microetch chemical for copper surface roughening preparation.
New industrial and home applications may be developed with the discovery of a
catalytic reaction using powdered precious metal-based catalyst, hydrogen peroxide and methyl alcohol . A small plastic bottle incorporating these can produce superheated steam in one to two seconds releasing only CO2 and high
temperature steam for a variety of purposes.
Domestic uses
* Diluted H2O2 (around 15%) is used to bleach human hair, hence the phrase "peroxide blonde". It is absorbed by skin upon contact and creates a
local skin capillary embolism which appears as a temporary whitening of the skin. It is used to whiten bones that are to be put on display. The strength of a solution may be described as a percentage or volume, where 1% hydrogen
peroxide releases 3.3 volumes of oxygen during decomposition.Thus, a 3% solution is equivalent to 10 volume and a 6% solution to 20 volume, etc.
* 3% H2O2 is used medically for cleaning wounds, removing dead
tissue, and as an oral debriding agent. Most over-the-counter peroxide solutions are not suitable for ingestion.
* The Food and Drug Administration (FDA) has classified hydrogen peroxide as a Low Regulatory
Priority (LRP) drug for use in controlling fungus on fish and fish eggs. (See ectoparasite.)
* Some gardeners and users of hydroponics advocate the use of hydrogen peroxide in watering solutions. They claim
that its spontaneous decomposition releases oxygen that enhances a plant's root development and helps to treat root rot (cellular root death due to lack of oxygen).
* Laboratory tests conducted by fish
culturists in recent years have demonstrated that common household hydrogen peroxide can be used safely to provide oxygen for small fish. Hydrogen peroxide releases oxygen by decomposition when it is exposed to catalysts such as
manganese dioxide.
* Hydrogen peroxide is a strong oxidizer effective in controlling sulfide and organic related odors in wastewater collection and treatment systems. It is typically applied to a wastewater
system where there is a retention time of 30 minutes to 5 hours before hydrogen sulfide is released. Hydrogen peroxide oxidizes the hydrogen sulfide and promotes bio-oxidation of organic odors. Hydrogen peroxide decomposes to
oxygen and water, adding dissolved oxygen to the system thereby negating some Biological Oxygen Demand (BOD).
* Commercial peroxide, as bought at the drugstore in a 2.5%-3% solution, can be used to remove
bloodstains from fabrics, although it will bleach or discolor many fabrics. If a little peroxide is poured onto the stain it will bubble up in the area of the blood, due to a reaction with catalase. After a few minutes the excess
liquid can be wiped up with a cloth or paper towel and the stain will be gone.
* Hydrogen peroxide is used with phenyl oxalate ester and an appropriate dye in glow sticks as an oxidizing agent. It reacts with
the ester to form an unstable CO2 dimer which excites the dye to an excited state; the dye emits a photon (light) when it spontaneously relaxes back to the ground state.
* Hydrogen peroxide is used as a
disinfectant in CIBA Vision's Clear Care no rub contact lens cleaning solution, due to its ability to break down the proteins that build up on the lense from the eye's immune response, resulting in increased comfort for those with
sensitive eyes.
Storage
Regulations vary, but low concentrations, such as 2.5% are widely available and legal to buy for medical use. Small quantities of many different concentrations and grades can be legally
stored and used with few regulations.
Hydrogen peroxide should be stored in a container made from a material that it doesn't react with and doesn't catalyze its decomposition. Numerous materials and processes are available,
some stainless steels, many plastics, glasses and some aluminium alloys are compatible.
Peroxide is a strong oxidant and should be stored away from fuel sources and sources of catalytic contamination (see decomposition
section). Apart from obvious fire risks, peroxide vapour can react with hydrocarbons and alcohols to form contact explosives. Because oxygen is formed during the natural decomposition of the peroxide, the resulting increase in
pressure can cause a container (e.g. made of glass) to shatter. Peroxide should be kept cool, as peroxide vapour can detonate above 70 °C. Deaths have occurred from storage in inadequately labeled containers due to its apparent
similarity to water.
Use as propellant
H2O2 can be used either as a monopropellant (not mixed with fuel) or as the oxidizer component of a bipropellant rocket. Use as a monopropellant takes advantage of the decomposition of
70–98+% concentration hydrogen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber where a catalyst, usually a silver or platinum screen, triggers decomposition, producing steam at over 600 °C which is
expelled through a nozzle, generating thrust. H2O2 monopropellant produces a maximum specific impulse (Isp) of 161 s (1.6 kN·s/kg), which makes it a low-performance monopropellant. Peroxide generates much less thrust than toxic
hydrazine, but is not toxic. The Bell Rocket Belt used hydrogen peroxide monopropellant.
As a bipropellant H2O2 is decomposed to burn a fuel as an oxidizer. Specific impulses as high as 350 s (3.5 kN·s/kg) can be achieved,
depending on the fuel. Peroxide used as an oxidizer gives a somewhat lower Isp than liquid oxygen, but is dense, storable, noncryogenic and can be more easily used to drive gas turbines to give high pressures. It can also be used
for regenerative cooling of rocket engines. Peroxide was used very successfully as an oxidizer in World-War-II German rockets (e.g. T-Stoff for the Me-163), and for the low-cost British Black Knight and Black Arrow launchers.
In the 1940s and 1950s the Walter turbine used hydrogen peroxide for use in submarines while submerged; it was found to be too noisy and require too much maintenance compared to diesel-electric power systems. Some torpedoes
used hydrogen peroxide as oxidizer or propellant, but this was dangerous and has been discontinued by most navies. Hydrogen peroxide leaks were blamed for the sinkings of HMS Sidon and the Russian submarine Kursk. It was
discovered, for example, by the Japanese Navy in torpedo trials, that the concentration of H2O2 in right-angle bends in HTP pipework can often lead to explosions in submarines and torpedoes. Hydrogen peroxide is still used on Soyuz
for driving gas turbines to power turbopumps, however. SAAB Underwater Systems is manufacturing the Torpedo 2000. This torpedo, used by the Swedish navy, is powered by a piston engine propelled by HTP as an oxidizer and kerosene as
a fuel in a bipropellant system.
While rarely used now as a monopropellant for large engines, small hydrogen peroxide attitude control thrusters are still in use on some satellites. They are easy to throttle, and safer to
fuel and handle before launch than hydrazine thrusters. However, hydrazine is more often used in spacecraft because of its higher specific impulse and lower rate of decomposition.
Recently H2O2/propylene has been proposed as
an approach to inexpensive Single Stage To Orbit: a fuel tank containing propylene has a bladder floating in it containing H2O2. This combination offers 15% superior Isp to O2/RP4 (a kerosene used as rocket propellant), does not
need turbines or cryogenic storage or hardware, and greatly reduces the cost of the booster. The potential of this and other alternative systems is discussed in some detail at Dunn Engineering.
Therapeutic use
Hydrogen
peroxide is generally recognized as safe (GRAS) as an antimicrobial agent, an oxidizing agent and for other purposes by the US Food and Drug Administration.
Hydrogen peroxide has been used as an antiseptic and anti-bacterial
agent for many years due to its oxidizing effect. While its use has decreased in recent years with the popularity of better-smelling and more readily-available over the counter products, it is still used by many hospitals, doctors
and dentists in sterilizing, cleaning and treating everything from floors to root canal procedures.
* Hydrogen peroxide can be used as a toothpaste when mixed with correct quantities of baking soda and salt.
* Hydrogen peroxide and benzoyl peroxide are sometimes used to treat acne.
* Hydrogen peroxide is used as an emetic in veterinary practice.
"Alternative" uses
* Some people have tried using peroxide as a treatment for cancer. The American Cancer
Society states that "there is no scientific evidence that hydrogen peroxide is a safe, effective or useful cancer treatment", and advises cancer patients to "remain in the care of qualified doctors who use proven
methods of treatment and approved clinical trials of promising new treatments."
* Another controversial alternative medical procedure is inhalation of hydrogen peroxide at a concentration of about 1%.
Internal use of hydrogen peroxide has a history of causing fatal blood disorders, and its recent use as a therapeutic treatment has been linked to several deaths.
Manufacture
Hydrogen peroxide is manufactured today almost exclusively by the
autoxidation of 2-ethyl-9,10-dihydroxyanthracene (C16H14O2) to 2-ethylanthraquinone (C16H12O2) and hydrogen peroxide using oxygen from the air. In this reaction, the hydroxy groups on the middle ring of anthracene are deprotonated
and are turned into ketones, while two double bonds are lost from the middle ring and are replaced as C=O double bonds in the ketone groups. The anthraquinone derivative is then extracted out and reduced back to the dihydroxy
compound using hydrogen gas in the presence of a metal catalyst. The overall equation for the process is deceptively simple:
H2 + O2 ¥ H2O2
However the economics of the process depend on effective
recycling of the quinone and extraction solvents, and of the hydrogenation catalyst.
Formerly inorganic processes were used, employing the electrolysis of an aqueous solution of sulfuric acid or acidic ammonium bisulfate
(NH4HSO4), followed by hydrolysis of the peroxydisulfate ((SO4)2)2¥ which is formed.
In 1994, world production of H2O2 was around 1.9 million tonnes, most of which was at a concentration of 70% or less. In that year bulk 30%
H2O2 sold for around US $0.54 per kg, equivalent to US $1.50 per kg (US $0.68 per lb) on a "100% basis".
Concentration
Hydrogen peroxide works best as a propellant in extremely high
concentrations-- roughly over 70%. Although any concentration of peroxide will generate some hot gas (oxygen plus some steam), at concentrations above approximately 67%, the heat of decomposing hydrogen peroxide becomes large
enough to completely vaporize all the liquid at standard temperature. This represents a safety and utilization turning point, since decomposition of any concentration above this amount is capable of transforming the liquid entirely
to heated gas (the higher the concentration, the hotter the resulting gas). This very hot steam/oxygen mixture can then be used to generate maximal thrust, power, or work, but it also makes explosive decomposition of the material
far more hazardous.
Normal propellant grade concentrations therefore vary from 70 to 98%, with common grades of 70, 85, 90, and 98%. Many of these grades and variations are described in detail in the United States propellant
specification number MIL-P-16005 Revision F, which is currently available. The available suppliers of high concentration propellant grade hydrogen peroxide are generally one of the large commercial companies which make other grades
of hydrogen peroxide; including Solvay Interox, FMC, Degussa and Peroxide Propulsion. Other companies which have made propellant grade hydrogen peroxide in the recent past include Air Liquide and DuPont. DuPont recently sold its
hydrogen peroxide manufacturing business to Degussa.
Propellant grade hydrogen peroxide is available to qualified buyers. Typically this chemical is only sold to commercial companies or government institutions which have the
ability to properly handle and utilize the material. Non-professionals have purchased 70% or lower concentration hydrogen peroxide (the remaining 30% is water with traces of impurities and stabilizing materials, such as tin salts,
phosphates, nitrates, and other chemical additives), and increased its concentration themselves. Many amateurs try distillation, but this is extremely dangerous with hydrogen peroxide; peroxide vapor can ignite or detonate
depending on specific combinations of temperature and pressure. In general any boiling mass of high concentration hydrogen peroxide at ambient pressure will produce vapor phase hydrogen peroxide which can detonate. This hazard is
mitigated, but not entirely eliminated with vacuum distillation. Other approaches for concentrating hydrogen peroxide are sparging and fractional crystallization.
High concentration hydrogen peroxide is readily available in
70, 90, and 98% concentrations in sizes of 1 gallon, 30 gallon, and bulk tanker truck volumes. Propellant grade hydrogen peroxide is being used on current military systems and is in numerous defense and aerospace research and
development programs. Many privately funded rocket companies are using hydrogen peroxide, notably Blue Origin, and some amateur groups have expressed interest in manufacturing their own peroxide, for their use and for sale in small
quantities to others.
Hazards
Hydrogen peroxide, either in pure or diluted form, can pose several risks:
* Above roughly 70% concentrations, hydrogen peroxide can give off vapor that can
detonate above 70 °C (158 °F) at normal atmospheric pressure. This can then cause a boiling liquid expanding vapor explosion (BLEVE) of the remaining liquid. Distillation of hydrogen peroxide at normal pressures is thus highly
dangerous.
* Hydrogen peroxide vapors can form sensitive contact explosives with hydrocarbons such as greases. Hazardous reactions ranging from ignition to explosion have been reported with alcohols,
ketones, carboxylic acids (particularly acetic acid), amines and phosphorus. The saying is 'peroxides kill chemists'.
* Hydrogen peroxide, if spilled on clothing (or other flammable materials), will
preferentially evaporate water until the concentration reaches sufficient strength, then clothing will spontaneously ignite. ;
* Concentrated hydrogen peroxide (>50%) is corrosive, and even
domestic-strength solutions can cause irritation to the eyes, mucous membranes and skin. Swallowing hydrogen peroxide solutions is particularly dangerous, as decomposition in the stomach releases large quantities of gas (10 times
the volume of a 3% solution) leading to internal bleeding. Inhaling over 10% can cause severe pulmonary irritation.
* Low concentrations of hydrogen peroxide, on the order of 3% or less, will chemically
bleach many types of clothing it comes into contact with to a pinkish hue. Caution should be exercised when using common products that may contain hydrogen peroxide, such as facial cleaner or contact lens solution, which easily
splatter upon other surfaces.
Hydrogen peroxide is naturally produced as a byproduct of oxygen metabolism, and virtually all organisms possess enzymes known as peroxidases, which apparently harmlessly catalytically
decomposes low concentrations of hydrogen peroxide to water and oxygen (see Decomposition above).
In one incident, several people were injured after a hydrogen peroxide spill on board Northwest Airlines Flight 957 because
they mistook it for water.
During the Second World War some extermination camps experimentally killed people with hydrogen peroxide injections.
Hydrogen peroxide was also part of the ingredients in the July 21, 2005 London Underground bombs, which failed to explode.
An MSDS will contain more information on the risks of working with this chemical. |
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