Cleaning and Extraction
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The general process of Supercritical Fluid Cleaning and Extraction is conceptually simple. The text below details the steps involved, which is then presented graphically at the bottom of the page.
- A source of liquid carbon dioxide in a high-pressure cylinder pressurizes the carbon dioxide above its critical pressure. The temperature is then raised above its critical temperature. The carbon dioxide is now in a supercritical state where the cleaning or extraction process may begin
- The supercritical carbon dioxide flows into a chamber containing the item to be treated. After the process is completed, the fluid exits through a pressure-reducing valve and is allowed to expand into a separating vessel, where a decrease in pressure changes the carbon dioxide back into a gas.
- In the (low density) gaseous state the compounds that were soluble in the (high density) supercritical fluid state are now much less soluble and can be collected after dropping out of solution.
- The gaseous carbon dioxide is then cooled back to its liquid state and reintroduced back into the flow stream where it may be used again.
- This cleaning cycle is self-contained with all of the carbon dioxide being continuously reused; the carbon dioxide is therefore self-cleaning. Included in the figure at the bottom of the page is an animated process flow diagram of the cleaning cycle.
The results of a supercritical-based cleaning process are shown in the photo on the left. Here a waste cutting oil composition has been processed by supercritical fluid extraction (SFE) by mixing it with a dispersant to yield a recoverable oil for reuse. The metal fillings from the milling process can be recovered oil-free from the dispersant by a simple sieving process.