CO2 makes things cleaner
3 Sep 2002
ICI and Linde have adapted a supercritical fluid used in the American aerospace industry to clean high-tech metals and developed a new dry cleaning fluid called 'Washpoint'.
The new fluid makes use of CO2 instead of existing solvents, some of which are highly regulated on a global basis and subject to widespread health and environmental concerns.
According to ICI, while being environmentally neutral, liquid carbon dioxide (CO2) has excellent cleaning properties. It dissolves dirt, fats and oils on all materials currently dry-cleaned. Thanks to its low surface tension and viscosity, it also easily penetrates garment fibres. In all other respects, it works like any traditional dry-cleaning solvent.
Better yet, CO2 is easy to handle. It is non-toxic (unless inhaled in large concentrations), non-flammable and odourless. It produces no hazardous waste or emissions that require special disposal.
Equipment used in the CO2 cleaning process is designed to handle and abolish any risks associated with the use of CO2. Solid or liquid CO2, or cold CO2 gas, for example, may cause frost burns if unprotected skin is exposed to the CO2 or the cooled equipment. For that reason, equipment based on the new cleaner works as a closed system where used liquid CO2 is filtered, distilled and recycled. Sensors linked to alarms monitor the site the equipment is installed in, and warn the user in the unlikely event any leakage should occur.
A CO2 cleaning machine itself consists of a washing chamber, storage tank, distilling unit, compressor, refrigeration unit and - depending on the machine design - a pump and a filter.
In use, laundry is first placed in the washing chamber of the machine. The chamber is then emptied of air. Next, the pressure in the washing chamber is raised by injecting gaseous CO2. Then, liquid CO2 is pumped into the washing chamber. Agitation is achieved by jet streams and/or by a rotating basket. The cleaning cycle lasts about 5 to 15 minutes and the whole process takes place at ambient temperature. The liquid CO2 goes easily into the fibres of the clothes and dissolves dirt, fats, and oils. During the washing cycle a filter cleans particles from the liquid. At the end of the cleaning process, liquid CO2 is pumped back into the storage tank. With the compressor, the remaining gaseous CO2 is pumped back into the storage tank lowering the pressure in the cleaning chamber. On its way to the storage vessel, the gas is chilled and once again condensed into its liquid form. When the pressure is low enough, the remaining CO2 is vented to the atmosphere and the door can be opened and the garments removed.
To show users how cost effective the new technology is, ICI has produced an online calculator at www.washpoint.com that works out a cost comparison between the new system and older systems that use traditional solvents like perchloroethylene.
