Ultrasonic cleaning in supercritical liquid CO2

Using liquid carbon dioxide as a cleaning solvent offers some great environmental advantages. Compared to conventional chlorinated solvents and detergents it is very clean, with no harmful emissions. Separating the liquid from the dissolved contaminants is easy - just reduce the pressure and allow the CO2 to boil off (after which it can be trapped and recycled). However the pressure required to maintain CO2 in liquid form (>60 bar) does present some challenges for ultrasonic tank design... Using a novel multifrequency actuator made it possible to generate ultrasonic vibrations in an autoclave with very thick walls.

This paper, written for the 2001 UIA conference by Miodrag and fellow researchers from ECO2 SA, a Swiss company specialising in supercritical fluid technology, describes the equipment they developed and results obtained.