Ethylene glycol

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^[6] 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 sink, 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. Mixture of ethylene glycol and water can also be chemically termed as Glycol Concentrate/ Compound/ Mixture/ Solution.

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, as an additive to prevent corrosion in liquid cooling systems for personal computers, and inside the lens devices of cathode-ray tube type of rear projection televisions. 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.^[7] 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.^[8]

Toxicity

Main article: ethylene glycol poisoning

Ethylene glycol is moderately toxic with an oral LD_Lo = 786 mg/kg for humans.^[9] 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.^[10]

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.^[11]

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.^[12]

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.^[13]

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.^[14] While prolonged low doses of ethylene glycol show no toxicity, at near lethal doses (>= 1000 mg/kg per day) ethylene glycol acts as a teratogen. "Based on a rather extensive database, it induces [skeletal variations and malformations] in rats and mice by all routes of exposure."^[15] This molecule has been observed in outer space.^[16]

References

1 2 3 4 5 6 "NIOSH Pocket Guide to Chemical Hazards #0272". National Institute for Occupational Safety and Health (NIOSH).
↑ Elert, Glenn. "Viscosity". The Physics Hypertextbook. Retrieved 2007-10-02.
1 2 Siegfried Rebsdat; Dieter Mayer (2005), "Ethylene Glycol", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a10_101
↑ Adolphe Wurtz (1856). "Sur le glycol ou alcool diatomique (On glycol or diatomic alcohol)". Comptes rendus 43: 199–204.
↑ 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.)
↑ http://xotxim.ru/teplonositeli/
↑ 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.
↑ 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.
↑ Safety Officer in Physical Chemistry (November 23, 2009). "Safety (MSDS) data for ethylene glycol". Oxford University. Retrieved December 30, 2009.
↑ Ethylene glycol. National Institute for Occupational Safety and Health. Emergency Response Database. August 22, 2008. Retrieved December 31, 2008.
↑ Ethylene Glycol Toxicity at eMedicine
↑ Pieter Klapwijk (January 27, 2010). "Ethylene Glycol Poisoning". The Rested Dog Inn. Retrieved October 11, 2012.
↑ Consumer Specialty Products Association: Antifreeze and engine coolant being bittered nationwide
↑ (CDC ToxFAQs)
↑ "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.
↑ 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

WebBook page for C2H6O2
ATSDR - Case Studies in Environmental Medicine: Ethylene Glycol and Propylene Glycol Toxicity
CDC - NIOSH Pocket Guide to Chemical Hazards
Medical information
Hairong Yue, Yujun Zhao, Xinbin Ma and Jinlong Gong (2012). "Ethylene glycol: properties, synthesis, and applications". Chemical Society Reviews 41 (11): 4218–4244. doi:10.1039/C2CS15359A.

Sugar alcohols

1-carbon	Methanol

2-carbon	Ethylene glycol

3-carbon	Glycerol

4-carbon	Erythritol Threitol

5-carbon	Arabitol Ribitol Xylitol

6-carbon	Mannitol Sorbitol Galactitol Iditol

7-carbon	Volemitol

Deoxy sugar alcohols	Fucitol

Cyclic sugar alcohols	Inositol

Glycylglycitols	Maltitol Lactitol Isomalt Maltotriitol Maltotetraitol Polyglycitol

Automotive engine

Part of the Automobile series

Basic terminology	Compression ratio Crank Cylinder Dead centre Diesel engine Dry sump Engine balance Engine configuration Engine displacement Engine knocking Firing order Hydrolock Petrol engine Power band Redline Spark-ignition engine Stroke Stroke ratio Wet sump

Main components	Connecting rod Crankcase Crankpin Crankshaft Crossflow cylinder head Crossplane Cylinder bank Cylinder block Cylinder head Flywheel Head gasket Hypereutectic piston Main bearing Piston Piston ring Reverse-flow cylinder head Starter ring gear Sump

Valvetrain	Cam Cam follower Camshaft Desmodromic valve Hydraulic tappet Multi-valve Overhead camshaft Overhead valve Pneumatic valve springs Poppet valve Pushrod Rocker arm Sleeve valve Tappet Timing belt Timing mark Valve float Variable valve timing

Aspiration	Air filter Blowoff valve Boost controller Butterfly valve Centrifugal-type supercharger Cold air intake Dump valve Electronic throttle control Forced induction Inlet manifold Intake Intercooler Manifold vacuum Naturally aspirated engine Ram-air intake Scroll-type supercharger Short ram air intake Supercharger Throttle Throttle body Turbocharger Twin-turbo Variable-geometry turbocharger Variable-length intake manifold Warm air intake

Fuel system	Carburetor Common rail Direct injection Fuel filter Fuel injection Fuel pump Fuel tank Gasoline direct injection Indirect injection Injection pump Lean-burn Stratified charge engine Turbo fuel stratified injection Unit injector

Ignition	Contact breaker Magneto Distributor Electrical ballast High tension leads Ignition coil Spark plug Wasted spark

Electrics and engine management	Air–fuel ratio meter Alternator Automatic Performance Control Car battery (lead–acid battery) Crankshaft position sensor Dynamo Drive by wire Electronic control unit Engine control unit Engine coolant temperature sensor Glow plug Idle air control actuator MAP sensor Mass flow sensor Oxygen sensor Starter motor Throttle position sensor

Exhaust system	Automobile emissions control Catalytic converter Diesel particulate filter Exhaust manifold Glasspack Muffler

Engine cooling	Air cooling Antifreeze (ethylene glycol) Core plug Electric fan Fan belt Radiator Thermostat Water cooling Viscous fan (fan clutch)

Other components	Balance shaft Block heater Combustion chamber Cylinder head porting Gasket Motor oil Oil filter Oil pump Oil sludge PCV valve Seal Synthetic oil Underdrive pulleys

Portal Category

Molecules detected in outer space

Molecules

Diatomic	Aluminium monochloride Aluminium monofluoride Aluminium monoxide Argon hydride Carbon monophosphide Carbon monosulfide Carbon monoxide Carborundum Cyanogen radical Diatomic carbon Fluoromethylidynium Hydrogen chloride Hydrogen fluoride Hydrogen (molecular) Hydroxyl radical Iron(II) oxide Magnesium monohydride cation Methylidyne radical Nitric oxide Nitrogen (molecular) Nitrogen monohydride Nitrogen sulfide Oxygen (molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon mononitride Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfur monohydride Sulfur monoxide Titanium oxide

Triatomic	Aluminium hydroxide Aluminium isocyanide Amino radical Carbon dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen cyanide Hydrogen isocyanide (HCN) Hydrogen isocyanide (HNC) Hydrogen sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene radical N₂H⁺ Nitrous oxide Nitroxyl Ozone Phosphaethyne Potassium cyanide Protonated molecular hydrogen Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide Silicon naphthalocyanine Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Water

Four atoms	Acetylene Ammonia Cyanic acid Cyanoethynyl Cyclopropynylidyne Formaldehyde Fulminic acid HCCN Hydrogen peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methylene amidogen Methyl radical Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thioformaldehyde Tricarbon monoxide Tricarbon sulfide Thiocyanic acid

Five atoms	Ammonium Ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy radical Methylenimine Propadienylidene Protonated formaldehyde Protonated formaldehyde Silane Silicon-carbide cluster

Six atoms	Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC₄N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene

Seven atoms	Acetaldehyde Acrylonitrile Cyanodiacetylene Ethylene oxide Hexatriynyl radical Methylacetylene Methylamine Methyl isocyanate Vinyl alcohol

Eight atoms	Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Heptatrienyl radical Hexapentaenylidene Methylcyanoacetylene Methyl formate Propenal

Nine atoms	Acetamide Cyanohexatriyne Cyanotriacetylene Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Propionitrile

Ten atoms or more	Acetone Benzene Buckminsterfullerene (C₆₀ fullerene) ("bucky-ball") C₇₀ fullerene Cyanodecapentayne Cyanopentaacetylene Cyanotetra-acetylene Ethylene glycol Ethyl formate Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propanal n-Propyl cyanide Pyrimidine

Deuterated
molecules

Unconfirmed

Book:Chemistry
Category:Astrochemistry
Category:Molecules
Portal:Astrobiology
Portal:Chemistry

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