When performing an extraction, the most convenient accessory is the use of an internal basket.  The basket allows you to both load and unload your extraction vessel relatively quickly giving you two major benefits.

  1. Quick loading and unloading allows increased turnaround time speeding up the productivity of the system.
  2. Emptying and cleaning the basket can be carried out away from the system. This ensures not only that the basket is clean preventing cross contamination, but the system can be running if multiple baskets are in operation.

Why would you use a basket?

First let’s consider what happens during an extraction if a basket is not used.

The vessel will contain two filters one on the inlet and the other on the outlet of the vessel. This prevents the material from passing out of the vessel and blocking the pipework.   We will assume that the material is nicely packed and that no channeling will occur.  The CO2 passes through our material, extracts the components of interest, and is then collected in our collection vessels.

Let’s consider the same extraction now using a basket.  The process is the same but now we have one important variable to consider.  How do we ensure that all the CO2 passes through the material in the basket and doesn’t bypass it?  We now must create a seal between the basket and the vessel.

There are several ways this can be done:

  1. Radial o-ring seal. This acts to seal the basket to the side of the extraction vessel.  This is a reasonably common method of sealing usually involving a PTFE o-ring.  In-order to ensure good sealing the vessel and basket must be concentric in-order the o-ring to contact the extraction vessel wall.  Repeated loading and unloading of the basket can also cause rapid wear of the O-ring.
  2. Face Seal. This requires compression between two faces.  Much more reliable method of sealing than a radial seal and doesn’t go through the same repeated abrasion when the basket loaded and unloaded when compared to the radial seal.
  3. Radial lip seal – This ensures a better contact than o-ring due to the dynamic nature of the seal. This seals the basket against extraction vessel side wall which  relies on the vessel concentricity and surface finish.

Whichever basket design is used the seal is crucial to an efficient extraction.  Common drop in yields are usually attributed to failure in the basket seals.