Perc is coming under increasingly strict regulation, says DeSimone, and many states are considering outright bans. There's lots of writing on the wall. Some companies have already redesigned dry cleaning machines to improve their ability to recapture perc and prevent its release into the environment. The rapid phasing out of CFCs, which chemically degrade Earth's protective ozone layer, prompted companies to get a head start on their search for alternatives to perc. Moreover, companies generally find that developing alternatives is economically beneficial in the long run, he notes.
Many signs point to carbon dioxide as a practical alternative to current solvents.
When vapors are compressed, they tend to condense into liquid. If a vapor is heated above a critical temperature, however, it does not condense, no matter how much it's compressed. Moreover, the fluid's properties can be tuned by adjusting temperature and pressure. When choosing a solvent for a specific application, among the most important characteristics to consider are density and viscosity, says William A. Peters, associate director for fuels and environmental research at the Massachusetts Institute of Technology's Energy Laboratory. In supercritical carbon dioxide, those properties can be varied greatly by changing temperature and pressure.