What is Perchloroethylene?
Perchloroethylene, also known as tetrachloroethylene or PCE, is a highly versatile, volatile, and stable solvent widely used in various industries. It is a non-flammable solvent primarily used for cleaning, degreasing, and in chemical production due to its ability to dissolve organic materials. Its most notable application is in the dry cleaning industry, though it is also used in automotive and metallurgical sectors.
Key Properties of Perchloroethylene
Perchloroethylene’s unique chemical properties make it an invaluable solvent across several industries. Below are its main characteristics
Physical and Chemical Properties:
- Non-flammable: PCE has no measurable flash point, making it safer than petroleum-based solvents.
- Volatility: While highly volatile, its evaporation rate is lower than other solvents at room temperature.
- Environmental impact: It does not deplete the ozone layer, and its use is approved by the U.S. Environmental Protection Agency (EPA) as an alternative to ozone-depleting substances.
- Appearance: Perchloroethylene is a colorless, volatile liquid heavier than water, and is practically insoluble in water.
- Stability: It is sensitive to light and UV radiation, which can cause decomposition under prolonged exposure. It can mix with various organic solvents like ether, alcohol, and benzene.
Chemical Formula:
- Molecular weight: 165.85
- Melting point: -22.4 ºC
- Boiling point: 121 ºC
- Density: 1.62 (water = 1)
- Vapor density: 5.83 (air = 1)
- Vapor pressure (at 20 ºC): 18 millibars
- Solubility in water: 0.04 gr/100 ml
Industrial Production of Perchloroethylene
Manufacturing Process
One of the most common methods for producing perchloroethylene industrially is through the oxyhydrochlorination of chlorinated hydrocarbons at high temperatures. This process occurs in a catalytic fluidized bed reactor, where vaporized chlorinated organics are mixed with hydrochloric acid and oxygen, facilitating chlorination and thermal cracking. The result is a mixture of trichloroethylene and perchloroethylene, which are then separated by distillation.
After separation, the perchloroethylene is purified and stabilized to prevent oxidation, ensuring a stable and high-quality product.
Uses of Perchloroethylene in Industry
1. Dry Cleaning
Perchloroethylene is the preferred solvent in the dry-cleaning industry due to its non-flammable nature and its ability to effectively remove stains without damaging delicate fabrics. It is suitable for textiles made from both natural and synthetic fibers, and its reusability gives it a long shelf life.
In addition, PCE can be combined with dry-cleaning detergents to enhance the cleaning power and create a more efficient process, making it a staple in dry-cleaning operations worldwide.
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2. Steam Degreasing
Industries like aerospace, automotive, and appliance manufacturing rely on perchloroethylene for steam degreasing of metal parts. Thanks to its high boiling point, PCE is effective in vapor degreasing processes, allowing for efficient cleaning of metal surfaces by condensing more vapor on the metal compared to other solvents.
PCE’s ability to remove waxes and clean parts at high temperatures makes it ideal for cleaning light gauge parts and welded joints, as well as drying metal components by removing water films.
3. Chemical Solvent in Manufacturing
In modern industry, perchloroethylene is widely used as a chemical solvent in processes involving fabrics, silicones, rubber, and as an extractant solvent in printing inks and paint strippers. Its ability to reduce the flammability of mixtures by increasing their flash point makes it a valuable component in various formulations.
4. Catalytic Reforming in Petroleum Refineries
In petroleum refining, perchloroethylene is used as a source of hydrochloric acid for catalyst regeneration in catalytic reforming and isomerization processes. This improves the efficiency and lifespan of refining equipment, making PCE essential in the oil industry.
5. Production of Refrigerants
For several decades, perchloroethylene has been used to produce fluorinated compounds such as refrigerants. Its stability, dielectric properties, and low surface tension make it an ideal candidate for refrigerant production, providing a favorable environmental profile compared to other options.
Health and Safety Considerations
While perchloroethylene is widely used, it is important to understand the potential health risks associated with its exposure. Below are key health effects and safety guidelines for handling PCE:
Health Effects
1. Inhalation
Inhalation of perchloroethylene vapors can irritate the respiratory tract and cause symptoms such as dizziness, headache, nausea, and lack of coordination. Prolonged exposure may lead to more severe effects, such as kidney and liver disorders. It is crucial to ensure proper ventilation in areas where PCE is used.
2. Skin Contact
Direct contact with liquid perchloroethylene can cause irritation and dermatitis due to its degreasing properties. Workers should use protective clothing and gloves when handling the substance to prevent skin absorption.
3. Eye Irritation
PCE vapors can irritate the eyes, leading to symptoms like burning and conjunctivitis. In the event of eye contact, flushing with water is recommended.
4. Ingestion
While ingestion is rare, perchloroethylene can cause temporary gastrointestinal distress. Ingestion should be avoided, and safety measures should be enforced in workplaces to prevent accidental consumption.
Safety Measures in Industrial Settings
To minimize health risks, companies that use perchloroethylene implement strict safety measures, including:
- Ventilation systems to remove vapors.
- Temperature control: PCE is heated below 140ºC to prevent toxic vapor production.
- Protective equipment: Workers are provided with respirators, gloves, and goggles to prevent inhalation and contact with skin or eyes.
- Neutralization methods: Lime is used to neutralize perchloroethylene baths, avoiding the acidification of the solution.
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Conclusion
Perchloroethylene is a highly effective and versatile solvent widely used in industries such as dry cleaning, metal degreasing, and chemical manufacturing. Its unique properties and safety profile make it a preferred choice across various applications. However, proper safety measures must always be taken to minimize health risks.
