Ethylene glycol

Not to be confused with Propylene glycol or Diethylene glycol.
Ethylene glycol
Names
IUPAC name
Ethane-1,2-diol
Other names
1,2-Ethanediol

Glycol
Ethylene Alcohol
Hypodicarbonous acid
Monoethylene glycol

1,2-Dihydroxyethane
Identifiers
3DMet B00278
Abbreviations MEG
505945
107-21-1 Yes
ChEBI CHEBI:30742 Yes
ChEMBL ChEMBL457299 Yes
ChemSpider 13835235 Yes
EC number 203-473-3
943
Jmol-3D images Image
KEGG C01380 
MeSH Ethylene+glycol
PubChem 174
RTECS number KW2975000
UNII FC72KVT52F Yes
Properties
Molecular formula
 C2H6O2
Molar mass 62.07 g·mol−1
Appearance clear, colorless liquid
Odor odorless[1]
Density 1.1132 g/cm3
Melting point −12.9 °C (8.8 °F; 260.2 K)
Boiling point 197.3 °C (387.1 °F; 470.4 K)
Miscible
Solubility soluble in most organic solvents
Vapor pressure 0.06 mmHg (20°C)[1]
Viscosity 1.61 × 10−2 N*s / m2[2]
Hazards
MSDS External MSDS
Main hazards Harmful
EU classification Harmful (Xn)
R-phrases R22 R36
S-phrases S26 S36 S37 S39 S45 S53
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
1
2
1
Flash point 111 °C (232 °F; 384 K) closed cup
410 °C (770 °F; 683 K)
Explosive limits 3.2%-15.2%[1]
US health exposure limits (NIOSH):
none[1]
none established[1]
none[1]
Related compounds
Related diols
 Propylene glycol
Diethylene glycol
Triethylene glycol
Polyethylene glycol
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
  verify (what is: Yes/?)
Infobox references

Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound primarily used as a raw material in the manufacture of polyester fibers and fabric industry, and polyethylene terephthalate resins (PET) used in bottling. A small percent is also used in industrial applications like antifreeze formulations and other industrial products. It is an odorless, colorless, syrupy, sweet-tasting liquid. Ethylene glycol is moderately toxic, with children having been particularly at risk because of its sweet taste, until it became common to add bitter flavoring to consumer antifreezes containing it.

Production

Ethylene glycol is produced from ethylene (ethene), via the intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol according to the chemical equation:

C2H4O + H2O → HO–CH2CH2–OH

This reaction can be catalyzed by either acids or bases, or can occur at neutral pH under elevated temperatures. The highest yields of ethylene glycol occur at acidic or neutral pH with a large excess of water. Under these conditions, ethylene glycol yields of 90% can be achieved. The major byproducts are the ethylene glycol oligomers diethylene glycol, triethylene glycol, and tetraethylene glycol. About 6.7 billion kilograms are produced annually.[3]

A higher selectivity is achieved by use of Shell's OMEGA process. In the OMEGA process, the ethylene oxide is first converted with carbon dioxide (CO2) to ethylene carbonate to then react with water in a second step to selectively produce mono-ethylene glycol. The carbon dioxide is released in this step again and can be fed back into the process circuit. The carbon dioxide comes in part from the ethylene oxide production, where a part of the ethylene is completely oxidized.

Historical aspects and natural occurrence

Almost all sources state that French chemist Charles-Adolphe Wurtz (1817–1884) first prepared ethylene glycol in 1856.[4] He first treated "ethylene iodide" (C2H4I2) with silver acetate and then hydrolyzed the resultant "ethylene diacetate" with potassium hydroxide. Wurtz named his new compound "glycol" because it shared qualities with both ethyl alcohol (with one hydroxyl group) and glycerin (with three hydroxyl groups).[5] In 1860, Wurtz prepared ethylene glycol from the hydration of ethylene oxide. There appears to have been no commercial manufacture or application of ethylene glycol prior to World War I, when it was synthesized from ethylene dichloride in Germany and used as a substitute for glycerol in the explosives industry.

In the United States, semicommercial production of ethylene glycol via ethylene chlorohydrin started in 1917. The first large-scale commercial glycol plant was erected in 1925 at South Charleston, West Virginia, by Carbide and Carbon Chemicals Co. (now Union Carbide Corp.). By 1929, ethylene glycol was being used by almost all dynamite manufacturers. In 1937, Carbide started up the first plant based on Lefort's process for vapor-phase oxidation of ethylene to ethylene oxide. Carbide maintained a monopoly on the direct oxidation process until 1953, when the Scientific Design process was commercialized and offered for licenses.

Uses

EG is primarily used as a raw material in the manufacture of polyester fibers and fabric industry, and polyethylene terephthalate resins (PET) used in bottling. A small percent is also used in other applications such as antifreeze formulations and other products.

Dewatering agent

EG is used in the natural gas industry to remove water vapour from natural gas before further processing, in much the same manner as TEG (triethylene glycol).

Coolant and heat transfer agent

The major use of ethylene glycol is as a medium for convective heat transfer in, for example, automobiles and liquid cooled computers. Ethylene glycol is also commonly used in chilled water air conditioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water. In geothermal heating/cooling systems, ethylene glycol is the fluid that transports heat through the use of a geothermal heat pump. The ethylene glycol either gains energy from the source (lake, ocean, water well) or dissipates heat to the source, depending if the system is being used for heating or cooling.

Pure ethylene glycol has a specific heat capacity about one half that of water. So, while providing freeze protection and an increased boiling point, ethylene glycol lowers the specific heat capacity of water mixtures relative to pure water. A 50/50 mix by mass has a specific heat capacity of about 3140 J/kg C (0.75 BTU/lb F) three quarters that of pure water, thus requiring increased flow rates in same system comparisons with water. Additionally, the increase in boiling point over pure water inhibits nucleate boiling on heat transfer surfaces thus reducing heat transfer efficiency in some cases, such as gasoline engine cylinder walls. Therefore, pure ethylene glycol should not be used as an engine coolant in most cases.

Antifreeze

Ethylene glycol disrupts hydrogen bonding when dissolved in water. Pure ethylene glycol freezes at about −12 °C (10.4 °F), but when mixed with water, the mixture does not readily crystallize, and therefore the freezing point of the mixture is depressed. Specifically, a mixture of 60% ethylene glycol and 40% water freezes at −45 °C (−49 °F).[3] Diethylene glycol behaves similarly. It is used as a de-icing fluid for windshields and aircraft. The antifreeze capabilities of ethylene glycol have made it a component of vitrification (anticrystallization) mixtures for low-temperature preservation of biological tissues and organs.

However, the boiling point for aqueous ethylene glycol increases monotonically with increasing ethylene glycol percentage. Thus, the use of ethylene glycol not only depresses the freezing point, but also elevates the boiling point such that the operating range for the heat transfer fluid is broadened on both ends of the temperature scale. The increase in boiling temperature is due to pure ethylene glycol having a much higher boiling point and lower vapor pressure than pure water; there is no chemical stabilization against boiling of the liquid phase at intermediate compositions, as there is against freezing.

Precursor to polymers

In the plastics industry, ethylene glycol is an important precursor to polyester fibers and resins. Polyethylene terephthalate, used to make plastic bottles for soft drinks, is prepared from ethylene glycol.

Hydrate inhibition

Because of its high boiling point and affinity for water, ethylene glycol is a useful desiccant. Ethylene glycol is widely used to inhibit the formation of natural gas clathrates (hydrates) in long multiphase pipelines that convey natural gas from remote gas fields to a gas processing facility. Ethylene glycol can be recovered from the natural gas and reused as an inhibitor after purification treatment that removes water and inorganic salts.

Natural gas is dehydrated by ethylene glycol. In this application, ethylene glycol flows down from the top of a tower and meets a rising mixture of water vapor and hydrocarbon gases. Dry gas exits from the top of the tower. The glycol and water are separated, and the glycol recycled. Instead of removing water, ethylene glycol can also be used to depress the temperature at which hydrates are formed. The purity of glycol used for hydrate suppression (monoethylene glycol) is typically around 80%, whereas the purity of glycol used for dehydration (triethylene glycol) is typically 95 to more than 99%. Moreover, the injection rate for hydrate suppression is much lower than the circulation rate in a glycol dehydration tower.

Niche applications

Minor uses of ethylene glycol include the manufacture of capacitors, as a chemical intermediate in the manufacture of 1,4-dioxane, and as an additive to prevent corrosion in liquid cooling systems for personal computers. Ethylene glycol is also used in the manufacture of some vaccines, but it is not itself present in these injections. It is used as a minor (1–2%) ingredient in shoe polish and also in some inks and dyes. Ethylene glycol has seen some use as a rot and fungal treatment for wood, both as a preventative and a treatment after the fact. It has been used in a few cases to treat partially rotted wooden objects to be displayed in museums. It is one of only a few treatments that are successful in dealing with rot in wooden boats, and is relatively cheap. Ethylene glycol may also be one of the minor ingredients in screen cleaning solutions, along with the main ingredient isopropyl alcohol. Ethylene glycol is commonly used as a preservative for biological specimens, especially in secondary schools during dissection as a safer alternative to formaldehyde. It can also be used in killing jars. It is also used as part of the water-based hydraulic fluid used to control subsea oil and gas production equipment.

Another interesting use is in the treatment of 'dry rot' or 'white rot' on timber joists, partially rotten or affected wood readily soaks it up and the fungus is subsequently killed. The main advantage of this type of treatment is that the glycol is hydroscopic and the wood being already water damaged readily absorbs a water based product.

Chemical reactions

Ethylene glycol is used as a protecting group for carbonyl groups in organic synthesis. Treating a ketone or aldehyde with ethylene glycol in the presence of an acid catalyst (e.g., p-toluenesulfonic acid; BF3•Et2O) gives the corresponding a 1,3-dioxolane, which is resistant to bases and other nucleophiles. The 1,3-dioxolane protecting group can thereafter be removed by further acid hydrolysis.[6] In this example, isophorone was protected using ethylene glycol with p-toluenesulfonic acid in moderate yield. Water was removed by azeotropic distillation to shift the equilibrium to the right.[7]

Toxicity

Ethylene glycol is moderately toxic with an oral LDLo = 786 mg/kg for humans.[8] The major danger is due to its sweet taste. Because of that, children and animals are more inclined to consume large quantities of it than of other poisons. Upon ingestion, ethylene glycol is oxidized to glycolic acid which is, in turn, oxidized to oxalic acid, which is toxic. It and its toxic byproducts first affect the central nervous system, then the heart, and finally the kidneys. Ingestion of sufficient amounts can be fatal if untreated.[9]

According to the annual report of the American Association of Poison Control Centers' National Poison Data System in 2007, there were about 1000 total cases resulting in 16 deaths. The 2008 American Association of Poison Control Centers' National Poison Data System annual report lists 7 deaths.[10]

Antifreeze products for automotive use containing propylene glycol in place of ethylene glycol are available. They are generally considered safer to use, as propylene glycol possesses an unpleasant taste and is converted in the body to lactic acid, a normal product of metabolism and exercise.[11]

Australia, the U.K., and seventeen U.S. states (as of 2012) require the addition of a bitter flavoring (denatonium benzoate) to antifreeze; in 2012, U.S. antifreeze manufacturers agreed voluntarily to add a bitter flavoring to all antifreeze that is sold in the consumer market of the U.S.[12]

In the environment

Ethylene glycol is a High Production Volume Chemical; it breaks down in air in about ten days, and in water or soil in a few weeks. It enters the environment through the dispersal of ethylene glycol-containing products, especially at airports where it is used in deicing agents for runways and airplanes.[13] Ethylene glycol is a teratogen. "Based on a rather extensive database, it induces [skeletal variations and malformations] in rats and mice by all routes of exposure."[14] This molecule has been observed in outer space.[15]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "NIOSH Pocket Guide to Chemical Hazards #0272". National Institute for Occupational Safety and Health (NIOSH).
  2. ↑ Elert, Glenn. "Viscosity". The Physics Hypertextbook. Retrieved 2007-10-02.
  3. ↑ 3.0 3.1 Siegfried Rebsdat; Dieter Mayer (2005), "Ethylene Glycol", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a10_101
  4. ↑ Adolphe Wurtz (1856). "Sur le glycol ou alcool diatomique (On glycol or diatomic alcohol)". Comptes rendus 43: 199–204.
  5. ↑ Wurtz (1856), page 200: "… je propose de le nommer glycol, parce qu'il se rapproche à la fois, par ses propriétés, de l'alcool proprement dit et de la glycérin, entre lesquels il se trouve placé." (… I propose to call it glycol because, by its properties, it is simultaneously close to [ethyl] alcohol properly called and glycerin, between which it is placed.)
  6. ↑ Theodora W. Greene, Peter G. M. Wuts (1999). Protective Groups in Organic Synthesis (Third ed.). John Wiley & Sons. pp. 312–322. ISBN 0-471-16019-9.
  7. ↑ J. H. Babler, N. C. Malek and M. J. Coghlan (1978). "Selective hydrolysis of α,β- and β,γ-unsaturated ketals: method for deconjugation of β,β-disubstituted α,β-unsaturated ketones". J. Org. Chem. 43 (9): 1821–1823. doi:10.1021/jo00403a047.
  8. ↑ Safety Officer in Physical Chemistry (November 23, 2009). "Safety (MSDS) data for ethylene glycol". Oxford University. Retrieved December 30, 2009.
  9. ↑ Ethylene glycol. National Institute for Occupational Safety and Health. Emergency Response Database. August 22, 2008. Retrieved December 31, 2008.
  10. ↑ http://emedicine.medscape.com/article/814701-overview Toxicity, Ethylene Glycol
  11. ↑ Pieter Klapwijk (January 27, 2010). "Ethylene Glycol Poisoning". The Rested Dog Inn. Retrieved October 11, 2012.
  12. ↑ Consumer Specialty Products Association: Antifreeze and engine coolant being bittered nationwide
  13. ↑ (CDC ToxFAQs)
  14. ↑ "Statement of the Science Report for Ethylene Glycol". 3.3.2.2 Non-neoplastic effects. Health Canada www.hc-sc.gc.ca. June 24, 2013. Retrieved 27 August 2014.
  15. ↑ J. M. Hollis, F. J. Lovas, P. R. Jewell, L. H. Coudert (2002-05-20). "Interstellar Antifreeze: Ethylene Glycol". The Astrophysical Journal 571 (1): L59–L62. Bibcode:2002ApJ...571L..59H. doi:10.1086/341148.

External links