Everything about Ethylene Oxide totally explained
| Section2 =
| Section3 =
| Section4 =
| Section5 =
| Section6 =
| Section7 =
| Section8 =
}}
The
chemical compound ethylene oxide is an important industrial chemical used as an intermediate in the production of
ethylene glycol and other chemicals, and as a sterilant for foods and medical supplies. It is a colorless flammable gas or refrigerated liquid with a faintly sweet odor. It is the simplest example of an
epoxide.
Its
IUPAC name is
epoxyethane. Other names for it include
oxirane and
dimethylene oxide.
History
Ethylene oxide was first prepared in
1859 by the
French chemist
Charles-Adolphe Wurtz, who prepared it by treating
2-chloroethanol with a
base. It achieved industrial importance during
World War I as a precursor to both the coolant
ethylene glycol and the
chemical weapon mustard gas. In
1931,
Theodore Lefort, another French chemist, discovered a means to prepare ethylene oxide directly from
ethylene and
oxygen, using
silver as a
catalyst. Since
1940, almost all ethylene oxide produced industrially has been made using this method.
Production
Industrially, ethylene oxide is produced when
ethylene (H
2C=CH
2) and
oxygen (O
2) react on a silver catalyst at 200–300 °C showing large Ag nanoparticles supported on
alumina. Typically, chemical modifiers such as chlorine are also included. Pressures used are in the region of 1-2MPa. The
chemical equation for this
reaction is:
» H
2C=CH
2 + ½ O
2 → C
2H
4O
The typical yield for this reaction under industrial conditions is 70-80%. In the reaction scheme above, an intermediate (oxametallacycle) is formed. Two different reaction pathways can then occur.
Ethylene oxide formation:
» H
2C=CH
2 + O → C
2H
4O
Acetaldehyde formation:
» H
2C=CH
2 + O → CH
3CHO
The latter pathway is the first step in complete
combustion, leading to
carbon dioxide and
water:
» CH
3CHO +5/2 O
2 → 2CO
2 + 2H
2O
Ethylene oxide can be conveniently produced in the laboratory by the action of an alkali hydroxide on
ethylene chlorohydrin.
» CH
2OH−CH
2Cl + OH
− → C
2H
4O + Cl
− + H
2O
with ethylene chlorohydrin being prepared easily by the action of
hypochlorous acid on
ethylene.
Several methods to produce ethylene oxide more selectively have been proposed, but none have achieved industrial importance, with notable exceptions as on May 22, 2008 Dr. Bob Benchoff President of A Check Exact labs explains "Important steps have been taken in terms of complying with such injunctions as of US Presidential Policy and Kyoto Protocol, toward overcoming pollution and global warming. Kyoto Protocol for instance lacks the higher dynamic guidance structure necessary to properly accomplish not it's proposed specifics yet rather it's reason for being, such as by the proper governmental oversight committee properly tied to free enterprise experts in the fields, as I've explained to the White House in simplified terms. In this case of ethylene oxide what once was the Kyoto position against liquid ethylene oxide such as due to it's high flammability, within modern dynamics is now faced with improved processing inventions such as RAPREX(R) in various forms of controlled heat related properties used by Sterigenics with long chain branch conditioning as for controlled rheology and many other improvements such as of better mechanical properties than historic unmodified versions, even being better than having full recyclability in the historic sense such as by rather utilizing memory effect, so that the products can be used many times prior to their being recycled in that historic sense and for instance can be used to replace oil."
Uses
Ethylene oxide gas kills
bacteria (and their
endospores),
mold, and
fungi, and can therefore be used to sterilize substances that would be damaged by sterilizing techniques such as
pasteurization that rely on heat. Ethylene oxide sterilization for the preservation of
spices was patented in
1938 by the
American chemist
Lloyd Hall, and it's still used in that role. Additionally, ethylene oxide is widely used to sterilize medical supplies such as bandages,
sutures, and surgical implements. The overwhelming majority of medical items are sterilized with ethylene oxide. Preferred methods have been the traditional chamber sterilization method, where a chamber is flooded with a mix of ethylene oxide and other gases which are later
aerated, and the more recent gas diffusion method developed in 1967 which relies on a bag that wraps the elements to be sterilized and acts a mini-chamber in order to minimize gas consumption and make the process economically feasible for small loads. Other names for this alternative method for small loads are:
Anprolene method, bag sterilization method or micro-dose sterilization method.
Most ethylene oxide, however, is used as an intermediate in the production of other chemicals. The major use of ethylene oxide is in the production of
ethylene glycol. The primary end use for ethylene glycol is in the production of
polyester polymers. Ethylene glycol is more commonly known for its use as an automotive coolant and
antifreeze.
Because of its high flammability and wide explosive concentration range in air, ethylene oxide is sometimes used as the fuel component of a
fuel-air explosive.
Reactions
Most reactions are ring openings by
nucleophiles.
In industry, epoxyethane is reacted with
water in the presence of a
sulfuric acid catalyst. A tenfold molar excess of water is used to obtain ethylene glycol:
» C
2H
4O + H
2O → HOCH
2CH
2OH
Despite the large excess of water, various types of
polyethylene glycol (PEG) or
polyethylene oxide (PEO) are still formed as secondary products. The degree of
polymerization increases as a smaller proportion of water is used:
» n(CH
2CH
2O) + H
2O → HO(CH
2CH
2O)
nH
For example, under the right conditions it can give
diethylene glycol (HOCH
2CH
2OCH
2CH
2OH),
triethylene glycol, etc.
Similarly, reaction with
ammonia can yield
ethanolamine, diethanolamine, or triethanolamine.
Ethylene oxide is also important in the manufacture of
surfactants and other
detergents, in a process called
ethoxylation.
One class of ethylene oxide derivatives that has attracted much scientific attention is the
crown ethers, which are cyclic
oligomers of ethylene oxide. These compounds have the ability to make
ionic compounds such as
salts soluble in nonpolar
solvents which they otherwise couldn't dissolve in. However, the high cost of these compounds has largely confined their use to the laboratory rather than industrial practice.
Health effects
Ethylene oxide is toxic by inhalation. Symptoms of overexposure include headache and dizziness, progressing with increasing exposure to convulsions, seizure and coma. It is also an irritant to skin and the respiratory tract, and inhaling the vapors may cause the lungs to fill with fluid several hours after exposure.
Ethylene oxide is usually stored as a pressurized or refrigerated liquid. At room temperature and pressure, it rapidly evaporates, potentially causing frostbite in cases of skin exposure.
Laboratory animals exposed to ethylene oxide for their entire lives have had a higher incidence of
liver cancer. However, studies on human beings who have worked with ethylene oxide for extended periods and may have experienced low doses during that time have found no increase in cancer risk. Chronic ethylene oxide exposure may increase the risk of
cataracts in humans.
In animals, ethylene-oxide can cause numerous reproductive effects, including
mutations and a higher rate of
miscarriages. Its reproductive effects on humans have not been well studied, but it's considered probable that ethylene oxide exposure has similar effects on human reproduction.
Ethylene oxide is classified as carcinogenic to humans by the International Agency for Research on Cancer (IARC).
Further Information
Get more info on 'Ethylene Oxide'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://ethylene_oxide.totallyexplained.com">Ethylene oxide Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
