Antifreeze

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An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allowing higher coolant temperature. [1] However all common antifreeze additives also have lower heat capacities than water and do reduce water's ability to act as a coolant when added to it. [2]

Contents

Because water has good properties as a coolant, water plus antifreeze is used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from bursting due to expansion when water freezes. Commercially, both the additive (pure concentrate) and the mixture (diluted solution) are called antifreeze, depending on the context. Careful selection of an antifreeze can enable a wide temperature range in which the mixture remains in the liquid phase, which is critical to efficient heat transfer and the proper functioning of heat exchangers. Secondarily but not less importantly, most if not all commercial antifreeze formulations intended for use in heat transfer applications include different kinds of anti-corrosion and anti-cavitation agents that protect the hydraulic circuit from progressive wear.

Principles and history

Water was the original coolant for internal combustion engines. It is cheap, nontoxic, and has a high heat capacity. It however has only a 100 °C liquid range, and it expands upon freezing. These problems are addressed by the development of alternative coolants with improved properties. Freezing and boiling points are colligative properties of a solution, which depend on the concentration of dissolved substances. Hence salts lower the melting points of aqueous solutions. Salts are frequently used for de-icing, but salt solutions are not used for cooling systems because they induce corrosion of metals. Low molecular weight organic compounds tend to have melting points lower than water, which makes them suitable for use as antifreeze agents. Solutions of organic compounds, especially alcohols, in water are effective. Alcohols - ethanol, methanol, ethylene glycol, etc. - have been the basis of all antifreezes since they were commercialized in the 1920s. [1]

Use and occurrence

Automotive and internal combustion engine use

Fluorescent green-dyed antifreeze is visible in the radiator header tank when car radiator cap is removed Antifreeze in the radiator.jpg
Fluorescent green-dyed antifreeze is visible in the radiator header tank when car radiator cap is removed

Most automotive engines are "water"-cooled to remove waste heat, although the "water" is actually antifreeze/water mixture and not plain water. The term engine coolant is widely used in the automotive industry, which covers its primary function of convective heat transfer for internal combustion engines. When used in an automotive context, corrosion inhibitors are added to help protect vehicles' radiators, which often contain a range of electrochemically incompatible metals (aluminum, cast iron, copper, brass, solder, et cetera). Water pump seal lubricant is also added.

Antifreeze was developed to overcome the shortcomings of water as a heat transfer fluid.

On the other hand, if the engine coolant gets too hot, it might boil while inside the engine, causing voids (pockets of steam), leading to localized hot spots and the catastrophic failure of the engine. If plain water were to be used as an engine coolant, it would promote galvanic corrosion. Proper engine coolant and a pressurized coolant system obviate these shortcomings of water. With proper antifreeze, a wide temperature range can be tolerated by the engine coolant, such as −34 °F (−37 °C) to +265 °F (129 °C) for 50% (by volume) propylene glycol diluted with water and a 15 psi pressurized coolant system. [3] [4]

Early engine coolant antifreeze was methanol (methyl alcohol). Ethylene glycol was developed because its higher boiling point was more compatible with heating systems.

Other industrial uses

The most common water-based antifreeze solutions used in electronics cooling are mixtures of water and either ethylene glycol (EGW) or propylene glycol (PGW). The use of ethylene glycol has a longer history, especially in the automotive industry. However, EGW solutions formulated for the automotive industry often have silicate based rust inhibitors that can coat and/or clog heat exchanger surfaces. Ethylene glycol is listed as a toxic chemical requiring care in handling and disposal.

Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and high specific heat and thermal conductivity. It also has a low viscosity and, therefore, reduced pumping requirements. Although EGW has more desirable physical properties than PGW, the latter coolant is used in applications where toxicity might be a concern. PGW is generally recognized as safe for use in food or food processing applications, and can also be used in enclosed spaces.

Similar mixtures are commonly used in HVAC and industrial heating or cooling systems as a high-capacity heat transfer medium. Many formulations have corrosion inhibitors, and it is expected that these chemicals will be replenished (manually or under automatic control) to keep expensive piping and equipment from corroding.

Biological antifreezes

Antifreeze proteins refer to chemical compounds produced by certain animals, plants, and other organisms that prevent the formation of ice. In this way, these compounds allow their host organism to operate at temperatures well below the freezing point of water. Antifreeze proteins bind to small ice crystals to inhibit growth and recrystallization of ice that would otherwise be fatal. [5] [6]

Primary agents

Ethylene glycol

Ethylene glycol Ethylene glycol chemical structure.png
Ethylene glycol

Most antifreeze is made by mixing distilled water with additives and a base product – MEG (Mono ethylene glycol) or MPG (Mono propylene glycol). Ethylene glycol solutions became available in 1926 and were marketed as "permanent antifreeze" since the higher boiling points provided advantages for summertime use as well as during cold weather. They are used today for a variety of applications, including automobiles, but there are lower-toxicity alternatives made with propylene glycol available.

When ethylene glycol is used in a system, it may become oxidized to five organic acids (formic, oxalic, glycolic, glyoxalic and acetic acid). Inhibited ethylene glycol antifreeze mixes are available, with additives that buffer the pH and reserve alkalinity of the solution to prevent oxidation of ethylene glycol and formation of these acids. Nitrites, silicates, borates and azoles may also be used to prevent corrosive attack on metal.

Ethylene glycol has a bitter, sweet taste and causes inebriation. The toxic effects of ingesting ethylene glycol occur because it is converted by the liver into 4 other chemicals that are much more toxic. The lethal dose of pure ethylene glycol is 1.4 ml/kg (3 US fluid ounces (90 ml) is lethal to a 140-pound (64 kg) person) but is much less lethal if treated within an hour. [7] (see Ethylene glycol poisoning).

Propylene glycol

Propylene glycol Propylene glycol chemical structure.png
Propylene glycol

Propylene glycol is considerably less toxic than ethylene glycol and may be labeled as "non-toxic antifreeze". It is used as antifreeze where ethylene glycol would be inappropriate, such as in food-processing systems or in water pipes in homes where incidental ingestion may be possible. For example, the U.S. FDA allows propylene glycol to be added to a large number of processed foods, including ice cream, frozen custard, salad dressings, and baked goods, and it is commonly used as the main ingredient in the "e-liquid" used in electronic cigarettes. Propylene glycol oxidizes to lactic acid. [8]

Besides cooling system corrosion, biological fouling also occurs. Once bacterial slime starts to grow, the corrosion rate of the system increases. Maintenance of systems using glycol solution includes regular monitoring of freeze protection, pH, specific gravity, inhibitor level, color, and biological contamination.

Propylene glycol should be replaced when it turns a reddish color. When an aqueous solution of propylene glycol in a cooling or heating system develops a reddish or black color, this indicates that iron in the system is corroding significantly. In the absence of inhibitors, propylene glycol can react with oxygen and metal ions, generating various compounds including organic acids (e.g., formic, oxalic, acetic). These acids accelerate the corrosion of metals in the system. [9] [10] [11] [12]

Other antifreezes

Propylene glycol methyl ether is used as an antifreeze in diesel engines. It is more volatile than glycol. [1]

Once used for automotive antifreeze, glycerol has the advantage of being non-toxic, withstands relatively high temperatures, and is noncorrosive. It is not however used widely. [1] Glycerol was historically used as an antifreeze for automotive applications before being replaced by ethylene glycol. [13] [14] Glycerol is mandated for use as an antifreeze in many sprinkler systems.

Measuring the freeze point

Once antifreeze has been mixed with water and put into use, it periodically needs to be maintained. If engine coolant leaks, boils, or if the cooling system needs to be drained and refilled, the antifreeze's freeze protection will need to be considered. In other cases a vehicle may need to be operated in a colder environment, requiring more antifreeze and less water. Three methods are commonly employed to determine the freeze point of the solution: [15]

  1. Specific gravity—(using a hydrometer test strip or some sort of floating indicator),
  2. Refractometer—which measures the refractive index of the antifreeze solution and translates it into freeze point, and
  3. Test strips—specialized, disposable indicators made for this purpose.

Although ethylene glycol hydrometers are widely available and mass-marketed for antifreeze testing, they give false readings at high temperatures because specific gravity changes with temperature. [15] Propylene glycol solutions cannot be tested using specific gravity because of ambiguous results (40% and 100% solutions have the same specific gravity). [15]

Corrosion inhibitors

Most commercial antifreeze formulations include corrosion inhibiting compounds, and a colored dye (commonly a fluorescent green, red, orange, yellow, or blue) to aid in identification. [16] A 1:1 dilution with water is usually used, resulting in a freezing point of about −34 °F (−37 °C), depending on the formulation. In warmer or colder areas, weaker or stronger dilutions are used, respectively, but a range of 40%/60% to 60%/40% is frequently specified to ensure corrosion protection, and 70%/30% for maximum freeze prevention down to −84 °F (−64 °C). [4]

Maintenance

In the absence of leaks, antifreeze chemicals such as ethylene glycol or propylene glycol may retain their basic properties indefinitely. By contrast, corrosion inhibitors are gradually used up, and must be replenished from time to time. Larger systems (such as HVAC systems) are often monitored by specialist firms which take responsibility for adding corrosion inhibitors and regulating coolant composition. For simplicity, most automotive manufacturers recommend periodic complete replacement of engine coolant, to simultaneously renew corrosion inhibitors and remove accumulated contaminants.

Traditional inhibitors

Traditionally, there were two major corrosion inhibitors used in vehicles: silicates and phosphates. American-made vehicles traditionally used both silicates and phosphates. [17] European makes contain silicates and other inhibitors, but no phosphates. [17] Japanese makes traditionally use phosphates and other inhibitors, but no silicates. [17] [18]

Organic acid technology

Certain cars are built with organic acid technology (OAT) antifreeze (e.g., DEX-COOL [19] ), or with a hybrid organic acid technology (HOAT) formulation (e.g., Zerex G-05), [20] both of which are claimed to have an extended service life of five years or 240,000 km (150,000 mi).

DEX-COOL specifically has caused controversy. Litigation has linked it with intake manifold gasket failures in General Motors' (GM's) 3.1L and 3.4L engines, and with other failures in 3.8L and 4.3L engines. One of the anti-corrosion components presented as sodium or potassium 2-ethylhexanoate and ethylhexanoic acid is incompatible with nylon 6,6 and silicone rubber, and is a known plasticizer. Class action lawsuits were registered in several states of the US, and in Canada, [21] to address some of these claims. The first of these to reach a decision was in Missouri, where a settlement was announced early in December 2007. [22] Late in March 2008, GM agreed to compensate complainants in the remaining 49 states. [23] GM (Motors Liquidation Company) filed for bankruptcy in 2009, which tied up the outstanding claims until a court determines who gets paid. [24]

According to the DEX-COOL manufacturer, "mixing a 'green' [non-OAT] coolant with DEX-COOL reduces the batch's change interval to 2 years or 30,000 miles, but will otherwise cause no damage to the engine". [25] DEX-COOL antifreeze uses two inhibitors: sebacate and 2-EHA (2-ethylhexanoic acid), the latter which works well with the hard water found in the United States, but is a plasticizer that can cause gaskets to leak. [17]

According to internal GM documents, [25] the ultimate culprit appears to be operating vehicles for long periods of time with low coolant levels. The low coolant is caused by pressure caps that fail in the open position. (The new caps and recovery bottles were introduced at the same time as DEX-COOL). This exposes hot engine components to air and vapors, causing corrosion and contamination of the coolant with iron oxide particles, which in turn can aggravate the pressure cap problem as contamination holds the caps open permanently. [25]

Honda and Toyota's new extended life coolant use OAT with sebacate, but without the 2-EHA. Some added phosphates provide protection while the OAT builds up. [17] Honda specifically excludes 2-EHA from their formulas.

Typically, OAT antifreeze contains an orange dye to differentiate it from the conventional glycol-based coolants (green or yellow), though some OAT products may contain a red or mauve dye. Some of the newer OAT coolants claim to be compatible with all types of OAT and glycol-based coolants; these are typically green or yellow in color. [16]

Hybrid organic acid technology

HOAT coolants typically mix an OAT with a traditional inhibitor, usually silicates. [26]

An example is Zerex G05, which is a low-silicate, phosphate free formula that includes the benzoate inhibitor. [17]

A HOAT coolant can have a life expectancy as high as 10 years / 180,000 miles. [26]

Phosphate hybrid organic acid technology

P-HOAT coolants mix phosphates with HOAT. [26] This technology is typically used in Asian makes and is often dyed red or blue. [26]

Silicate hybrid organic acid technology

Si-OAT coolants mix silicates with HOAT. [26] This technology is typically used in European makes and is often dyed pink. [26]

Additives

All automotive antifreeze formulations, including the newer organic acid (OAT antifreeze) formulations, are environmentally hazardous because of the blend of additives (around 5%), including lubricants, buffers and corrosion inhibitors. [27] Because the additives in antifreeze are proprietary, the safety data sheets (SDS) provided by the manufacturer list only those compounds which are considered to be significant safety hazards when used in accordance with the manufacturer's recommendations. Common additives include sodium silicate, disodium phosphate, sodium molybdate, sodium borate, denatonium benzoate and dextrin (hydroxyethyl starch).

Disodium fluorescein dye is added to conventional ethylene glycol formulas to visually distinguish leaked amounts from other vehicle fluids, and as a marker of type to distinguish it from incompatible types. [16] This dye fluoresces bright green when illuminated by blue or UV light from daylight or testing lamps.

Automotive antifreeze has a characteristic odor due to the additive tolytriazole, a corrosion inhibitor. The unpleasant odor in industrial use tolytriazole comes from impurities in the product that are formed from the toluidine isomers (ortho-, meta- and para-toluidine) and meta-diamino toluene which are side-products in the manufacture of tolytriazole. [28] These side-products are highly reactive and produce volatile aromatic amines which are responsible for the unpleasant odor. [29]

See also

Related Research Articles

A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

Ethylene glycol Chemical compound

Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound with the formula (CH2OH)2. It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odorless, colorless, sweet-tasting, viscous liquid.

Radiator

Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics.

Petrol engine Internal combustion engine designed to run on gasoline

Petrol engine or gasoline engine is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels.

Glycerol Chemical compound

Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known as glycerides. Due to having antimicrobial and antiviral properties it is widely used in FDA approved wound and burn treatments. It can be used as an effective marker to measure liver disease. It is also widely used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Owing to the presence of three hydroxyl groups, glycerol is miscible with water and is hygroscopic in nature.

Propylene glycol Chemical compound

Propylene glycol (IUPAC name: propane-1,2-diol) is a viscous, colorless liquid, which is nearly odorless but possesses a faintly sweet taste. Its chemical formula is CH3CH(OH)CH2OH. Containing two alcohol groups, it is classed as a diol. It is miscible with a broad range of solvents, including water, acetone, and chloroform. In general, glycols are non-irritating and have very low volatility.

Water cooling Method of heat removal from components and industrial equipment

Water cooling is a method of heat removal from components and industrial equipment. Evaporative cooling using water is often more efficient than air cooling. Water is inexpensive and non-toxic; however, it can contain impurities and cause corrosion.

Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator.

De-icing Process of removing ice, snow, or frost from a surface

De-icing is the process of removing snow, ice or frost from a surface. Anti-icing is understood to be the application of chemicals that not only de-ice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prevent adhesion of ice to make mechanical removal easier.

A coolant is a substance, typically liquid or gas, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.

A cryoprotectant is a substance used to protect biological tissue from freezing damage. Arctic and Antarctic insects, fish and amphibians create cryoprotectants in their bodies to minimize freezing damage during cold winter periods. Cryoprotectants are also used to preserve living materials in the study of biology and to preserve food products.

Haze machine

Haze machines, or haze generators, are effects machines similar to fog machines, designed to produce an unobtrusive, homogeneous clouds suspended in the air intended primarily to make light beams visible or create a subtle diffusion.

Ground deicing of aircraft is commonly performed in both commercial and general aviation. The fluids used in this operation are called deicing or anti-icing fluids. The initials ADF, ADAF or AAF are commonly used.

Heater core

A heater core is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes serve to increase surface area for heat transfer to air that is forced past them by a fan, thereby heating the passenger compartment.

Cooling bath

A cooling bath, in laboratory chemistry practice, is a liquid mixture which is used to maintain low temperatures, typically between 13 °C and −196 °C. These low temperatures are used to collect liquids after distillation, to remove solvents using a rotary evaporator, or to perform a chemical reaction below room temperature.

Oil cooling is the use of engine oil as a coolant, typically to remove surplus heat from an internal combustion engine. The hot engine transfers heat to the oil which then usually passes through a heat-exchanger, typically a type of radiator known as an oil cooler. The cooled oil flows back into the hot object to cool it continuously.

Glycol dehydration is a liquid desiccant system for the removal of water from natural gas and natural gas liquids (NGL). It is the most common and economical means of water removal from these streams. Glycols typically seen in industry include triethylene glycol (TEG), diethylene glycol (DEG), ethylene glycol (MEG), and tetraethylene glycol (TREG). TEG is the most commonly used glycol in industry.

Ethylene glycol poisoning is poisoning caused by drinking ethylene glycol. Early symptoms include intoxication, vomiting and abdominal pain. Later symptoms may include a decreased level of consciousness, headache, and seizures. Long term outcomes may include kidney failure and brain damage. Toxicity and death may occur after drinking even a small amount.

Radiator (engine cooling)

Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine.

Waterless coolant is a glycol-based liquid substance that does not contain water. Its boiling point of 191 °C (375 °F) is higher than that of water-based coolants and it resists the formation of corrosion. The substance was invented to circumvent the problems of vaporizing water. When water vaporizes, it retains only 4% of its thermal conductivity. Water-based coolants are safe at temperatures below the boiling point of water to maintain the pressure of the system. Waterless coolant has environmental benefits, including reducing the use of cooling fans and therefore improving fuel economy. The coolant does not generally need changing, reducing the hazardous waste following repeated coolant flushes.

References

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