16.6 What does a Soxhlet extractor do?
Description
This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
16.6 What does a Soxhlet extractor do?
The soxhlet extractor enables solids to be extracted with fresh warm solvent
that does not contain the extract. This can dramatically increase the
extraction rate, as the sample is contacting fresh warm solvent. The sample
is placed inside a cellulose or ceramic thimble and placed in the extractor.
The extractor is connected to a flask containing the extraction solvent, and
a condenser is connected above the extractor. The solvent is boiled, and the
standard extractor has a bypass arm that the vapour passes through to reach
the condenser, where it condenses and drips onto the sample in the thimble.
Once the solvent reaches the top of the siphon arm, the solvent and extract
are siphoned back into the lower flask. The solvent reboils, and the cycle
is repeated until the sample is completely extracted, and the extract is
in the lower flask.
There is an alternative design where the hot solvent vapour passes around
the thimble, thus boiling the solvent in the thimble - this can be a problem
if low-boiling azeotropes form. Procedures for using soxhlet extractors are
described ( along with illustrations which might make the above description
comprehensible :-) ), in Vogel and many other introductory organic laboratory
texts.
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