In the series of articles featured in Clean India Journal, Laundry Expert Vijay Rodda has shared his experiences gathered over four decades in the hospitality industry. Here are some facts about Percs and Hydrocarbon, commonly used in dry cleaning.
The Perchloroethylene Solvent
Known under the systematic name tetrachloroethene, or perchloroethylene, or PERC is a chloro-carbon with the
formula Cl2C=CCl2
Formula: C2Cl4
Molecular Mass: 165g/mol
Boiling Point: 121°C
Density: 1.62g/cm³
IUPAC ID (International Union of Pure and Applied Chemistry): Tetrachloroethene
Melting Point: -19°C
It is a colourless liquid widely used for dry cleaning of fabrics. It has a sweet (or some feel ‘obnoxious’) odour, detectable at a concentration of one part per million (1ppm) or around.
It is an excellent solvent for many organic materials. It is volatile, highly stable, and non-flammable. Thus, it is widely used in dry cleaning.
It is also used to de-grease metal parts in the automotive and other metal-working industries, usually as a mixture with other chloro-carbons. It appears in a few consumer products including paint-strippers and spot removers.
The International Agency for Research on Cancer: classification that tetrachloroethylene as a Group 2A carcinogen, which means that it is probably carcinogenic to humans.
Tetrachloroethylene is a central nervous system depressant and can enter the body through respiratory or dermal exposure. It dissolves fats from the skin, potentially resulting in skin irritation.
There is a lot of circumstantial evidence to show that exposure to the solvent increases the risk of developing Parkinson’s disease.
Also, it has been shown to cause liver tumors in mice and kidney tumors in male rats. At temperatures over 315°C, such as in welding, it can be oxidized into phosgene, an extremely poisonous gas. Therefore, the solvent should not be used near welding operations, flames, or hot surfaces.
It has been used as dry cleaning solvent because it bleeds not many dyes compared to other solvents, has very good oily-type soil removal properties, and is the least corrosive to metal parts.
The solvent needs to be recovered after being used for dry cleaning. And, much of the soil accumulated needs to be removed by distillation.
Hydrocarbon Solvent
As the name suggests, the solvent is combination of hydrogen & carbon, chemically combined. It is made from petroleum after refining.
It may not be cleaning as well as perc, however, it is milder on colour, decorations, sequins, embellishments or zari.
As it is hydrocarbon is flammable and can catch fire. Hence, machines using the solvent need to take all fire safety precautions, for electrical connections, static charges and welding to be done.
The solvent has flash point of 60oC plus, however, less than 93oC. It is likely to dissolve oily type soil quite readily, though not as well as perc.
Here, water separator needs to be designed differently compared to perc, as HC is lighter than water as against perc. that is heavier than water.
Design of machine is more complicated and so is maintenance of the machine. The point may be considered important while planning to add or switch to hydrocarbon machine. Detergent for hydrocarbon will be different than for perc, with some constituents being the same for both solvents.
Isoparaffins or isoalkanes are the type of hydrocarbon solvent one should choose for drycleaning. To check the information sheet on the product being considered, be sure that the aromatic content is as low as possible and that the product is completely hydrogenated.