Dry cleaning process with CO2 and its benefits

Dry cleaning is a textile cleaning process which nowadays uses PERC and CO2 in order to remove heavy chemicals like oil from the clothes and reduce water usage. This process was discovered in France in 1820, when they started using turpentine (distilled from different species of pine trees) and upgraded after a while to benzene and gas. However, these are strongly flammable and smell gas after washing. Therefore, carbon dioxide was discovered, being more environmental and the risk for being flammable decreased and so did the smell.

The process is done the same way as normal cloth washing but instead of having water, other chemicals are used and the temperature is lower than normal. There are certain materials that cannot be proceeded as normal because of its sensitive textile to the water and heat like fur, suede, leather, costumes and some dresses. Therefore, this method came to be potential for keeping the textile quality.

Supercritical CO2 is an important industrial solvent due to its role in chemical extraction, its low toxicity and environmental impact. Its ability to remove particles and organic residues from metals, polymers, ceramics, glasses and other materials has gained a lot of attention.

Usually, it behaves as a gas in air at STP (Standard Temperature and Pressure) or as a solid when frozen, when the temperature and pressure are increased above the critical point it can behave as a supercritical fluid above its critical temperature and critical pressure. These properties allows most compounds to be extracted with little damage or denaturing. In figure 1 below, there is a triple point, where the solid, liquid and gas-point all at the same time coincide with each substance. All happening at the same time during a specific pressure and temperature with CO2.

Since CO2 has a low temperature point between different forms, less energy is required to heat and no toxic chemicals are released to the environment, which makes this to a potential agent for dry cleaning.

Fig 1. High pressure and low temperature giving a solid form of CO2 while increased temperature and pressure give liquid and gas form. Triple point, where all these characters coincide.

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