Supercritical fluid extraction
The
extracts obtained from plants, diterpenes (antioxidants), triterpenes
(phytosterols), or even the tetraterpenes (carotenes) which may be of interest
to the pharmaceutical sector, can be easily extracted by this method.
Supercritical fluids may also be utilised for the production of fine powders,
in particular for the formulation of active principles.
Supercritical
extraction It involves heating the CO2 to above 870 F and pumping it
above 1100 psi. Usually, this is between 6000-10000 psi. Supercritical fluid CO2
can best be described as a dense fog when CO2 is used in a dense
liquid state. Low-pressure CO2 is often the best method for
producing high quality botanical extracts. CO2 loading rate in this
state means that you have to pump many volumes of CO2 through
botanical. The loading rate is typically 10-40 volumes. For this reason, it is
important to have pumped CO2, which has a much faster loading rate
2-10 volumes and a wide range of uses.
Supercritical fluid
A supercritical fluid
is any substance at a temperature and pressure above its critical point. It can
diffuse through solids like a gas, and dissolve materials like a liquid.
Additionally, close to the critical point, small changes in pressure or
temperature result in large changes in density, allowing many properties of a
supercritical fluid to be "fine-tuned". Supercritical fluids are
suitable as a substitute for organic solvents in a range of industrial and
laboratory processes. Carbon dioxide and water are the most commonly used
supercritical fluids, being used for decaffeination and power generation,
respectively. CO2 is the kind of extraction solvents for botanicals. It leaves
no toxic residue behind. Its extraction properties can be widely and precisely
manipulated with subtle changes in pressure and temperature.
Properties of supercritical fluid
(i)
Supercritical fluids
have highly compressed gases, which combine properties of gases and liquids in
an intriguing manner.
(ii)
Supercritical fluids can lead to reactions,
which are difficult or even impossible to achieve in conventional solvents.
(iii)
Supercritical fluids have solvent power
similar to light hydrocarbons for most of the solutes. However, fluorinated
compounds are often more soluble in supercritical CO2 than in hydrocarbons;
this increased solubility is important for polymerization.
(iv)
Solubility increases with increasing density
(that is with increasing pressure). Rapid expansion of supercritical solutions
leads to precipitation of a finely divided solid. This is a key feature of flow
reactors.
(v)
The fluids are commonly miscible with
permanent gases (e.g. N2 or H2) and this leads to much higher concentrations of
dissolved gases than can be achieved in conventional solvents.
In general terms, supercritical fluids have
properties between those of a gas and a liquid
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