What Perchloroethylene Is
Perchloroethylene, also known as tetrachloroethylene or PCE, is a chlorinated hydrocarbon with the molecular formula C2Cl4 and the CAS number 127-18-4. It is a clear, colourless, non-flammable liquid with an ether-like odour. Its strong solvency for oils, greases, waxes and resins keeps it in steady demand as an industrial cleaning solvent, and because it does not burn it can be handled in enclosed machines where a flammable hydrocarbon would be unacceptable.
Key Physical and Chemical Properties
| Property | Typical value |
|---|---|
| CAS number | 127-18-4 |
| Molecular formula | C2Cl4 |
| Relative molecular mass | 165.83 |
| Relative density at 20 °C | 1.6220 |
| Melting point | -22.7 °C |
| Boiling point | 121.2 °C |
| Viscosity at 20 °C | 0.839 mPa·s |
| Refractive index | 1.5055 |
| Solubility in water at 25 °C | about 0.015 g/L |
| Flammability | non-flammable |
Perchloroethylene is only slightly soluble in water and is insoluble in sugar, glycerol and protein, while it is miscible with ethanol, ether, chloroform, benzene and other chlorinated hydrocarbons. It does not hydrolyse under normal conditions, which supports its chemical stability and its long service life in closed cleaning systems where the solvent is recovered and reused.
Industrial Cleaning and Metal Degreasing
In industrial cleaning the value of perchloroethylene lies in its dissolving power and in its compatibility with most metals. It lifts cutting oils, drawing lubricants, polishing compounds, mould release agents and shop soil from machined parts, stampings and castings without attacking the base metal and without leaving the residues that aqueous processes sometimes deposit in blind holes. Parts that will be plated, welded, coated or assembled are commonly cleaned in a PCE vapour or liquid-vapour cycle: the cold component enters the vapour zone, solvent condenses on the surface, dissolves the oil film and drains away together with the contamination.
The same characteristics suit electronic and precision hardware, where flux residues, oils and particulates must be removed before soldering, bonding or conformal coating. The process parameters that matter most are solvent purity, distillation rate, vapour height, freeboard and the condition of the water separator, because a build-up of acid, water or high-boiling soil will leave films and stains on a finished surface that is otherwise perfectly machined.
Vapour degreasing for parts carrying light, readily soluble oils
Liquid immersion with ultrasonics for blind holes and complex geometry
Liquid-vapour sequences where heavy soil must be rinsed before the vapour rinse
Closed-loop filtration and distillation to recover solvent and control emissions
Dry Cleaning and Textile Care
Perchloroethylene has been the benchmark solvent of the dry cleaning industry for decades. It dissolves oily stains such as grease, fat and cosmetic residues from garments without swelling or damaging most natural and synthetic fibres, and it does not shrink wool or distort structured garments the way water can. Professional plants recover the solvent by filtration and distillation, which keeps consumption and waste low and holds cleaning quality steady from one cycle to the next.
Because the solvent is non-flammable, plants avoid the fire risk that older petroleum-based cleaning fluids carried, and modern machines combine sealed transfer, vapour recovery and refrigeration to hold workplace concentrations below the applicable occupational exposure limit. Cleaning results depend on solvent clarity, detergent balance, bath temperature and moisture level, so routine titration and distillation control are part of normal plant operation rather than optional refinements.
Chemical Synthesis, Safety and Storage
Beyond cleaning, perchloroethylene serves as a reaction medium and as an intermediate in the manufacture of fluorinated compounds and other specialty organics. In certain polymerisation systems it acts as a solvent that keeps the reactants in a single phase, which promotes a uniform reaction and consistent product quality.
PCE is a volatile chlorinated solvent and must be handled as such. Work in well-ventilated areas or under local exhaust ventilation, wear solvent-resistant gloves and eye protection, and avoid breathing the vapour. Prolonged skin contact causes irritation and high vapour concentrations can affect the nervous system, and many jurisdictions treat perchloroethylene as a substance of very high concern for certain uses. Store it in tightly closed, clearly labelled containers, away from strong oxidisers and alkalis, in a cool and dry location, and always follow the safety data sheet and the local occupational exposure limits.
Frequently Asked Questions
Q: What is the CAS number of perchloroethylene?
The CAS number of perchloroethylene, also called tetrachloroethylene, is 127-18-4 and its molecular formula is C2Cl4.
Q: Is perchloroethylene flammable?
No. It is non-flammable, which is one reason it became the standard solvent for dry cleaning and for enclosed degreasing equipment.
Q: What is perchloroethylene used for in industry?
It is used for cleaning metal parts and electronic components, for the dry cleaning of garments, and as a solvent or intermediate in chemical synthesis.
Q: Is PCE soluble in water?
It is only slightly soluble in water, about 0.015 g/L at 25 °C, and it is miscible with ethanol, ether, chloroform, benzene and other chlorinated hydrocarbons.
Q: What is the boiling point of perchloroethylene?
The boiling point is about 121.2 °C at atmospheric pressure, with a melting point of about -22.7 °C.
Q: Does perchloroethylene hydrolyse?
No. It does not hydrolyse under normal conditions, which supports its stability and recyclability in closed industrial cleaning systems.