Stoltz Lab

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Silicone oil, the oil usually used in heating baths, is surprisingly expensive (ca. $100/liter). Dirty or cloudy oil baths can be easily reclaimed using this simple procedure.

(Taken from Davis, D. A. Aldrichimica Acta 1988, 21, #1)

Direct filtration of the oil tends to leave the oil discolored, but addition of a small amount of activated carbon dust (just enough to make the oil turn to a opaque black suspension when strirred) prior to filtration through Celite gives oil that is clear and colorless. If water is also an impurity, magnesium sulfate can be added before filtration as well, but this is typically unneccessary. A full procedure follows:

To an oil bath containing ~400 mL of contaminated silicone oil was added magnesium sulfate (~200 mg) followed by activated carbon (~200 mg) and the oil bath was stirred vigorously with a large stir bar for 10 min. The resulting black colored suspension was then gravity filtered with a plastic funnel containing a plug of cotton and a pad of Celite (about 1/2 inch thick). The filtration is quite slow and was carried out in portions. All the oil was filtered over the course of 3 days.

The filtration may also be carried out with vacuum from a water aspirator, but, for the sake of your lab mates, the gravity filtration is more quiet and unobtrusive.