Soxhlet extractor

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A Soxhlet extractor with a Graham condenser.

A Soxhlet extractor is a piece of laboratory apparatus commonly used in continuous extractions, in the extraction of a desired compound, often an organic compound, from a solid material. Typically, a Soxhlet extraction is used when the desired compound has relative low solubility in a solvent (which may or may not change with temperature), and the impurity is completely insoluble in that solvent.

Description

A Soxhlet extractor is comprised of three sections:

  • Percolator: consists of boiler and reflux, which circulates the solvent
  • Extraction thimble, a tube made of cellulose or is a simple packed filter paper, which retains the solid to be laved
  • Siphon mechanism, which periodically empties the thimble.

How to use a Soxhlet extractor

Assembly

  • The source material containing the compound to be extracted is placed inside the thimble
  • Load the thimble into the main chamber of the Soxhlet extractor
  • Add the extraction solvent in the distillation flask
  • The flask is placed on the heating element (a heating bath is preferred over a mantle because pyrolysis may occur on the sides of the flask when the solvent level drops)
  • Connect the Soxhlet extractor atop the flask
  • Attach the reflux condenser atop the extractor
  • Connect the reflux condenser to the cooling fluid

Choose the type of condenser depending on the type of solvent you use.

Operation

  • Turn on the cooling then turn on the heating
  • As the solvent boils, it will travel up a distillation arm, condenses in the condenser and slowly fills up the chamber housing the thimble
  • The warm solvent is absorbed in the thimble and will dissolve some of the target compound
  • When the Soxhlet chamber is almost full, the chamber is emptied by the siphon, with the solvent returning to the distillation flask.
  • The thimble ensures that the rapid motion of the solvent does not transport any solid material to the still pot; this cycle may be allowed to repeat many times, over hours or days, if the target compound has extremely poor solubility in solvents.
  • The process begins again

During each cycle, a portion of the non-volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask. The advantage of this system is that instead of many portions of warm solvent being passed through the sample, just one batch of solvent is recycled.

Disassemble

  • Turn off heating and wait for the solvent to stop boiling
  • Wait until the siphon empties the Soxhlet chamber, then remove the condenser, the Soxhlet siphon chamber then the flask with solvent
  • Remove the thimble from the Soxhlet chamber and dispose of it
  • Take the flask with the solvent and attach it to a rotary evaporator to remove the solvent
  • Wash the glassware

If the extraction chamber still has some solvent and can no longer fill, add some fresh solvent until it reaches the siphoning level and wait for it to drain into the solvent flask.

Availability

Soxhlet extractors can be purchased from lab suppliers or online.

DIY Soxhlet extractor

A makeshift Soxhlet extractor can be made by connecting a pressure-equalizing dropping funnel to a boiling flask, and on top connect a reflux condenser. The target compound is added in a bag or thimble, then placed in the dropping funnel, with the stopcock closed. Fill the boiling flask with the desired solvent to begin refluxing the solvent. After the dropping funnel is full, open the stopcock just enough for the liquid collected in the funnel chamber to begin dripping back in the flask.[1]

Uses

Soxhlet extractors are commonly used when extracting oils or alkaloids from plant material.

References

  1. ↑ https://www.youtube.com/watch?v=qiRBLfezuxs

Relevant Sciencemadness threads

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