A supercritical fluid (SCF) is a substance above its critical temperature and pressure, where it can dissolve substances like a liquid but has a low viscosity like a gas. SCFs have properties between gases and liquids, allowing them to penetrate solids like gases but with densities close to liquids. They are useful solvents for extraction, purification, and particle formation due to their tunable dissolving power controlled by pressure and temperature changes. Common SCFs used are carbon dioxide, water, methane, and acetone.

1. SUPER CRITICAL
FLUID

2. SUPER CRITICAL FLUID (SCF)
A SCF is defined as a substance (gas) above its
critical temperature (TC) and critical pressure
(PC).
The critical point represents the highest temperature
and pressure at which the substance can exist as a
vapour and liquid in equilibrium.

3. Properties
• As pressure increases density increases
without increase in viscoscity.
• Also property of SCF to dissolve othes
substance increases.
• Gas cannot dissolve substances at NTP but SCF can
because of high pressure.

4. Properties
• Permeate solid like gas
• High densities like liquid

5. Properties
• The dissolution power of a fluid is directly related to
its overall solvation energy, which is determined by
the sum of the solute–solvent interactions.
• The density of supercritical fluids is about three
orders of magnitude greater than that of gas;
therefore, the dissolving power is increased for
supercritical fluids, because as density increases
more solute–solvent interactions will occur.
• Since supercritical fluids have great dissolving
power, they are used in a number of ways for
purification, extraction, fractionation, and
recrystallization of a wide host of material

6. Formation of
SCF

8. Here we can see the
seperate phases of carbon
dioxide. The meniscus is
easily observed.

9. With an increase in
temperature the
meniscus between liquid
and vapour phase begins
to diminish.

10. • Increasing the
temperature further
causes the gas and
liquid densities to
become more similar.
• The meniscus is less
easily observed but
still evident.

11. Once the critical
temperature and pressure
have been reached the two
distinct phases of liquid and
gas areno longer visible.
The meniscus can no longer
be seen. One homogenous
phase called the
"supercritical fluid" phase
occurs which shows
properties of bothliquids
and gases.

12. EXAMPLES OF SCF
SOLVENT
MOLECULAR
WEIGHT
CRITICAL
TEMPERATURE
CRITICAL
PRESSURE
CRITICAL
DENSITY
g/mol K (atm) g/cm3
Carbon
dioxide
(CO2)
44.01 304.1 7.38 (72.8) 0.469
Water
(H2O)
18.015 647.096 22.064
(217.755)
0.322
Methane
(CH4)
16.04 190.4 4.60 (45.4) 0.162
Acetone
(C3H6O)
58.08 508.1 4.70 (46.4) 0.278

13. Gas/SCF/Liquid
Density
(kg/m3)
Viscosity
(poice)
Diffusivity
(mm²/s)
Gases 1 10 1-10
Supercritical
Fluids 100-1000 50-100 0.01- 0.1
Liquids 1000 500-1000 0.001

14. Advantages of SCF
1.SCFs have solvating powers similar to liquid organic solvents,
but with higher diffusivities, lower viscosity, and lower surface
tension
2.Since the solvating power can be adjusted by changing the pressure
or temperature separation of analytes from solvent is fast and easy.
3.By adding modifiers to a SCF (like methanol to CO2) its polarity
can be changed for having more selective separation power.
4.In industrial processes involving food or pharmaceuticals, one does
not have to worry about solvent residuals as you would if a
"typical" organic solvent were used.
5.Candidate SCFs are generally economic, simple and safe.
6.Disposal costs are much less and in industrial processes, the fluids
can be simple to recycle.

15. Challenges
SCF technology requires sensitive
process control, which is a challenge.
In addition, the phase transitions of
the mixture of solutes and solvents
should be measured or predicted
quite accurately.
Generally the phase transitions in the
critical region is rather complex and
difficult to measure and predict.

16. APPLICATIONS
➢ Supercritical fluid extraction
➢ Dry-cleaning
➢ Supercritical drying
➢ Chemical Reactions
➢ Nano and Micro Particle Formation
over crystal growth and yielding very small and regularly
sized particles. S.C.fluids provide a number of ways of
achieving this by rapidly exceeding the saturation point
of a solute by dilution, depressurization or a combination of
these. These processes occur faster in supercritical fluids than
in liquids, promoting
➢ Supercritical fluid chromatography