Super Critical Fluid Extraction

Super Critical Fluid Extraction (SCFE) is the process of separating one component from another, using super critical fluids (SCFs).

The process of super critical fluid extraction

A supercritical fluid (SCF) can be defined as a substance above its critical temperature and pressure. The critical point represents the highest temperature and pressure at which the substance in question can exist as a vapour and liquid in equilibrium. The normal conditions for supercritical CO2 are above a ‘critical’ temperature of 31C and a ‘critical’ pressure of 74 bar. When sub critical the CO2 is in a liquid form and when it goes super critical it takes on the appearance of a dense ‘fog’.

Extraction is usually conducted on a solid matrix but it can also be taken from liquids. CO2 is the most common scf albeit occasionally it can be supplemented by co-solvents such as ethanol or methanol.

In most cases extraction is essentially a diffusion based system. i.e. the CO2 is required to diffuse and permeate the raw material enabling the targeted extract to subsequently diffuse from the matrix and into the CO2. The fluid is pumped to a heating zone, where it is heated to supercritical conditions. It then passes into the extraction vessel, where it rapidly diffuses into the solid matrix and dissolves the material to be extracted. The dissolved material is swept from the extraction cell into a separator at lower pressure, and the extracted material settles out. The CO2 can then be cooled, re-compressed and recycled.

The advantages of supercritical fluids are two fold:

  • It can permeate any raw material much faster and more easily than a liquid. As a consequence the penetration is more comprehensive allowing access to the smaller pores otherwise inaccessible to liquids;
  • These same qualities facilitate a faster and more efficient recovery of the solvent. This results in no product contamination for the customer and a faster processing speed owing to the speedier recovery of the CO2 – normally the slowest rate limiting common denominator.

CO2 SCFE is widely accepted as the optimum extraction technique available for botanicals.

Contact the CO2E team today to find out how we can help.