Perchloroethylene or PCE, also known as tetrachloroethylene, is a very versatile, volatile, very stable and non-flammable solvent for organic materials, which is used in various industries, especially in dry cleaning. It is also used in the automotive and metallurgical industries as an excellent degreaser, as well as in the production of stain removers, degreasers and paint strippers.
It is also used as a multipurpose solvent because it is more inert and stable than many other chlorinated solvents. Perchloroethylene is safer than petroleum solvents because it has no flash point.
Physical and chemical properties
Perchloroethylene, as mentioned above, is neither flammable nor does it have a measurable flash point, which indicates that at room temperature it has a lower evaporation rate than other solvents. In addition, it does not affect the ozone layer, which is why the U.S. Environmental Protection Agency (EPA) has approved its use as a replacement for ozone-depleting solvents.
It is a colourless, volatile liquid, heavier than water and practically insoluble in water. It has an odor similar to ether or chloroform and is sensitive to light and UV radiation, so it decomposes when it remains under direct exposure for prolonged periods. It can be mixed with a wide variety of organic solvents such as ether, ethyl alcohol, benzene, chloroform and others.
Tetrachloroethylene has the ability to dissolve fats, oils and resins. The vapour it produces is not visible and is heavier than air, so it spreads at ground level. Its cold oxidation process is quite slow and it does not corrode ordinary metals, in fact, it has the ability to remove grease from metals such as aluminium and magnesium.
However, it cannot be used on metals such as zinc, lithium, barium and beryllium, which in its liquid form attacks some varieties of plastics and rubbers.
- Molecular weight: 165.85.
- Melting point:-22,4 ºC.
- Boiling point: 121 ºC.
- Relative Density (considering the density of water equal to 1): 1,62
- Vapor Density (considering air density equal to 1): 5.83.
- Vapour pressure in millibars (at 20 ºC): 18.
- Solubility in water (gr/100 ml): 0.04.
One of the most widely used methods for industrial production of perchloroethylene is the oxyhydrochlorination of chlorinated hydrocarbons at high temperature. In a catalytic fluidized bed reactor, vaporized chlorinated organics are mixed with hydrochloric acid and oxygen, so that chlorination and thermal cracking reactions occur to produce a mixture of trichloroethylene and perchloroethylene.
Both compounds are separated by distillation, the perchloroethylene obtained is purified and stabilized to avoid oxidation.
Uses of perchloroethylene
Perchloroethylene is widely used in both industrial and domestic applications. Among the most common uses are:
Perchloroethylene is the ideal solvent for this job, as it is non-flammable and offers a fast, powerful and gentle cleaning action with a minimum of effort. In addition, it does not cause damage, discoloration or wear on textiles made of natural and synthetic fibers, can be used in conjunction with any detergent and has a powerful stain-removing action.
Because it is reusable, it has a long shelf life. In addition, a perchloroethylene solution can be formed with any dry cleaning detergent to create a more effective cleaning system, so it is widely used in dry cleaning operations worldwide.
Industries such as aerospace, automotive and appliance production use perchloroethylene in vapor degreasing processes of metal parts and pieces because it can be used efficiently in situations that require a higher boiling point than water. Precisely because of its high boiling point, it is able to condense a greater amount of steam on the metal than any other solvent, allowing for more efficient washing.
One of the advantages of perchloroethylene is that it holds its action longer, removes higher melting points and waxes more easily, and is very effective in cleaning light gauge parts that are heated to temperatures above the boiling point of other solvents before completing the cleaning process. It is also used effectively for cleaning welded joints and tiny holes.
By using perchloroethylene, a vapour degreaser can be used for drying metal parts, as it can easily remove water films without losing its solvent properties.
In modern industry, perchloroethylene is used for the chemical processing of fabrics, silicones and rubber, as well as an extractant solvent in printing inks and paint strippers. It is also used to reduce the flammability of a mixture, since when added to mixtures in the right quantities it increases their flash point.
In petroleum refineries, perchloroethylene is used as a source of hydrochloric acid for catalyst regeneration processes, both in the catalytic reformer and in isomerization operations.
For several decades, perchloroethylene has been used for the production of fluorinated compounds such as refrigerants, refrigerant mixtures, among others, thanks to its stability, dielectric properties, low viscosity and low surface tension. In addition, perchloroethylene has a favorable environmental profile.
Although perchloroethylene, as mentioned, is widely used in various industries in applications such as dry cleaning and degreasing, it is rare to find information on injuries to operators from its handling. It is considered to have moderate to low toxicity, however, there are some risks to people exposed to this compound, among them:
The vapors emitted by perchloroethylene irritate the upper respiratory tract causing a narcotic effect. Exposure to these vapors may cause nervous system disorders such as neuritis or other neuropathies. The most common symptoms are dizziness, headache, nausea, lack of coordination and mental confusion. When exposure levels are high, unconsciousness may occur.
Prolonged exposure to perchloroethylene vapors may also cause kidney and liver disorders, which may manifest themselves after some time of exposure, through symptoms such as mild jaundice and dark coloration of the urine.
In order to avoid these possible effects on health in the facilities where perchloroethylene is used in industrial processes, ventilation systems are in place, which allow an adequate elimination of the vapours. When the product is used in processes where it is heated, it is always heated at temperatures below 140 ºC, which avoids the production of toxic vapours due to decomposition.
The companies also have specially designed equipment with cooling coils and suction hoods that prevent the release of perchloroethylene vapors.
When degreasing baths for metal parts are made, caustic soda is not used for the neutralization process of perchloroethylene, crumbled lime is used, which prevents the acidification of the bath, the areas where these processes are carried out are far from the areas where processes that require high temperatures are carried out.
Workers are provided with the necessary protective equipment, including face masks to ensure adequate respiratory protection. However, in case of inhalation, it is recommended that the person be removed immediately from the contaminated area and taken to fresh air or an area where artificial respiration can be applied.
In its liquid form perchloroethylene acts as a degreaser, and on contact with the skin causes irritation. Prolonged or repeated contact may cause atopic dermatitis, the symptoms being reddening of the skin and a mild burning sensation. In addition, prolonged contact with the skin is a route of penetration into the body.
In order to avoid contact with the skin of workers, safe processes have been created, which avoid the use of sponges, brushes or cotton wool, among others. In addition, workers should be provided with perchloroethylene impermeable gloves and protective clothing. In case of contact with the skin, it is recommended to wash the affected area with plenty of water and neutral soap.
Contact with ocular mucous membranes
Vapours produced by perchloroethylene irritate the mucous membranes of the eyes, causing pain, burning sensation and conjunctivitis. These symptoms are more severe when perchloroethylene (liquid) comes in contact with the ocular mucous membranes. These lesions are temporary and subside completely in two or three days.
To avoid this type of injury, workers should wear goggles or face shields designed to protect the eyes from contact with vapors and liquids. However, in the event of an accident, it is recommended that the eyes be washed with plenty of water, trying to get under the eyelids.
Perchloroethylene has a very low rate of absorption through the digestive tract, causing only temporary disturbances such as abdominal pain, headaches, dizziness, nausea and diarrhea. However, if the person who has ingested perchloroethylene has liver disease, the conditions can be much more serious.
The risks of ingestion of perchloroethylene in work areas are very low or unlikely. However, it is recommended that you do not eat, drink or smoke in areas where work involving perchloroethylene is being performed. In case of ingestion, immediately rinse mouth, drink plenty of water and induce vomiting.