What is a Supercritical Fluid?

Supercritical fluids occur when sufficient temperature and pressure is applied to take it beyond its critical point.  The substances therefore no longer can be defined as being in either a liquid or gas phases. With densities similar to that of liquids but viscosities close to zero, supercritical fluids can diffuse through solids like a gas, whilst dissolving materials like a liquid.

 

Small changes in pressure or temperature result in changes in density, allowing many properties of a supercritical fluid to be adjusted. Supercritical fluids are suitable as a substitute for organic solvents in a range of industrial and laboratory processes.

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co2 phase diagram

Supercritical carbon dioxide occurs above its critical temperature of 31.10 °C and pressure 72.9 bar.

co2 phase diagram 2

 

 

 

 

 

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Why Supercritical Carbon dioxide?

Supercritical carbon dioxide is used as the extraction solvent for creation of essential oils and other herbal distillates. Its main advantages over solvents such as hexane and acetone in this process are that it is non-toxic and non-flammable. Furthermore, separation of the reaction components from the starting material is much simpler than with traditional organic solvents. The CO2 can evaporate into the air or be recycled by condensation into a cold recovery vessel. Its advantage over steam distillation is that it operates at a lower temperature, which can separate the plant waxes from the oils

co2 phase diagram 3