Supercritical fluid extraction

SUPERCRITICAL FLUID EXTRACTION

PRAGATI SINGHAM PhD (I Year)

CONTENTS

• Introduction to SCF– Properties of SCF– Historical background

• Supercritical fluid Extraction (SFE)– Components of SFE– Critical properties of selected substances– Modes of SFE

• Methods of developments of SFE• Objectives for commercialization• Advantages• Limitations• Precautions• Applications

SUPERCRITICAL ??

Supercritical Fluid

Supercritical Fluid Extraction - SFE

CRITICAL POINT

Fig. 1 Typical Pressure-Temperature of a substance

At a certain temperature and pressure condition, liquid and vapour phases of a substance become indistinguishable. Known as CRITICAL CONDITION

Substances above critical point- “SUPERCRITICAL FLUIDS” (SCF)

Triple point

Pc

Tc

PROPERTIES OF SCF

• Physical and thermal properties of SCFs are in between pure liquid and gas, hence can also be known as ‘Compressible liquids’ or ‘dense gases’

• Changes in properties are for a SCF are as follows: – Liquid like densities (100-1000 times greater than gases)– Diffusivities higher than liquids (10-3 and 10-4 cm2/s)– Good solvating power– Reduction in surface tension – Low viscosity (10-100 times less than liquid)– Gas like compressibility properties Therefore they posses high penetrating power

HISTORICAL BACKGROUND

• Solvent properties of SCF were first reported well over 100 years ago in 1879 by Hannay and Hogarth, (measured solubility of inorganic salts in supercritical ethanol)

• Since 1980s and 1990s SCF has been used in several industrial

processes.

SUPERCRTICAL FLUID EXTRACTION

SUPERCRITICAL FLUID EXTRACTION (SFE)

Solvent extraction method

Solvent (pass through)

Solids

Dissolves solute

Supercritical fluid extraction

Supercritical Solvent (pass through)

Solids

Dissolves solute

Extract ExtractRaffinate (solvent) Raffinate (SC solvent)

Hence can say that it resembles solvent extraction process

SUPERCRITICAL FLUID EXTRACTION (SFE) CONTD..

Supercritical fluid extraction is the process of separating one component from another (the matrix) using supercritical fluids as the extracting solvent

SUPERCRITICAL FLUID EXTRACTION (SFE) CONTD..

Steps: Introduction of feed into extractor (solid feed) or extractor in modified column either co-currently or counter-

currently

Formation of mobile phase: mixing of solutes with supercritical fluid.

Exposure of mobile phase to pressures (50-500 atm) and temperatures (ambient to 300°C) near or above the critical point

for enhancing the mobile phase solvating power.

Isolation of dissolved solute by precipitation

Eg. CO2 in vapour form is compressed into a liquid before becoming supercritical and then extraction takes place.

COMPONENTS OF SFE

1. Fluid reservoir (gas cylinder in case of CO2)

2. Pump – Reciprocating pump– Syringe pump (pulse-free flow at large range of flow rates)

3. Extraction cell/column (stationary phase)– Usually stainless steel Chamber or vessel in compartment – Capable of withstanding high pressure (300-600 atm) [for

solids]– Open tubular capillary columns or packed columns [liquids]

COMPONENTS CONTD..

4. Restrictor– Maintaining pressure change inside the extraction vessel

Two types- – fixed (linear restrictor, tapered desire, integral restrictor,

ceramic frit restrictor, metal restrictor)– Variable (variable nozzle, back pressure regulator)

5. Collector (trapping system)

6. Detectors (flame ionization detector of gas chromatography)

SFE WITH RECYCLING (TRAPPING SYSTEM)

Recycling of SFE can be done-1. Reduction of pressure - SCF unable to dissolve the solute,

separation of sold under gravity and the gas at low pressure is compressed back to the supercritical conditions.

SFE WITH RECYCLING (TRAPPING SYSTEM)CONTD…

2. Reduction of temperature - solute drops and recovery of solvent without recompression

3. Pumping SCF to expansion tank - where it becomes gas resulting in very less solubility i.e. separation of solute. Spent gases are then recompressed and recycled. Heat exchangers are used to maintain temperature and prevent excessive

cooling at throttling valve called as Joule-Kelvin effect.

• Pumping SCF to expansion tank

SFE WITH RECYCLING (TRAPPING SYSTEM) CONTD…

CRITICAL PROPERTIES OF SELECTED SUBSTANCES

SUPERCRITICAL CO2

MODES OF SFE

STATIC EXTRACTION MODE (steady state)

• Sample matrix is soaked in a fixed amount of supercritical fluid

• Can be compared to a teabag in a cup of water

DYNAMIC EXTRACTION MODE (non-steady)

• Supercritical fluid continuously passes through the sample matrix

• Analogous to coffee maker

SFE CONTD..

• Sample Matrix Parameters that influence SFE:– Particle size and shape– Surface area and porosity– Moisture content– Changes in morphology– Sample size– Extractables level

• The parameters effect on solubility:– The vapour pressure of the component– Interaction with the supercritical fluid– Temperature, pressure, density and additives

METHOD DEVELOPMENT FOR SFE

OBJECTIVES FOR COMMERCIALIZATION

• Separation of multiple solutes (as solubility of solute in supercritical solvent may be a function of temperature and pressure)

• Use of entrainers/modifiers an enhance versatility and efficiency. Eg. CO2 mixed with 1-10% of methanol to solubilise more polar solutes.

MULTIPLE SOLUTES IN SFE

Separation of solutes is by using a two-stage process. Method• First extraction: similar to single stage (soluble-dissolved, less

soluble- left)• Second extraction: dissolution of the remaining solute in the

solid in the solvent will result in the isolation

Solid Solute (Extract)

Solvent First Extraction Second Extraction References

Dried Ginger

Ginger flavor CO2 79 Bars and 30◦C 246 Bars and 40◦C. Yonei, Y, et al J. Sup. Fl. 8:156–161,1995).

Coriander seeds

Flavor CO2 , (Celery powder & sage)

250 Bars and 40◦C. 70 Bars and20◦C

Catchpoole, O.J. et al. J. Sup. Fl. 9:273–279, 1996

Egg yolk Phospholipids CO2 , (CO2

ethanol 5%)414 Bars and 45◦C. 414 Bars and 45◦C Shah A. et al. J. Sup.

Fl. 30:303–313, 2004

MODIFIERS FOR SFE

ADVANTAGES

• Elimination of organic solvents i.e. reduces the risk of storage.

• Rapid (due to fast back-diffusion of analytes in the SCF reduces the extraction time since the complete extraction step is performed in about 20 min)

• Suitable for extraction and purification of compounds having low volatility present in solid or liquid

• Susceptible to thermal degradation (low operating conditions)

ADVANTAGES CONTD…

• Complete separation of solvent from extract and raffinate

• Continuous process

• Low handling cost

• Solvent recovery is easy

• Versatile and efficient (use of co-solvents and co-solutes)

LIMITATIONS

• Prolonged time (penetration of SCF into the interior of a solid is rapid, but solute diffusion from the solid into the SCF).

• Modeling is inaccurate

• Scale is not possible (due to absence of fundamental, molecular-based model of solutes in SCF)

• Expensive

• Consistency & reproducibility may vary in continuous production

PRECAUTIONS

• Adequate contact time (for penetration of solvent into solid particles and diffusion of

solute from inside the solid particles to solvent)

• Equilibrium should be achieved (i.e. proper flow of solvent such that concentration of dissolved

solutes in the solvent phase will be below the solubility of solute in solvent)

APPLICATIONS

Food science • Fat and oil samples in meat, egg, meals, chocolate, dairy

products, seeds and food snacks,

Natural products• Flavors & spices of ginger, eucalyptus, soyabean, coffee,

soybean, basil, lime peels, potato chips, popcorn

By-products recovery• Fruit and vegetable waste

REFERENCES

• Sairam, P., Ghosh, S., Jena, S., Rao, K.N.V. and Banji, D. (2012) Supercritical Fluid Extraction (SFE)-An Overview Asian J. Res. Pharm. Sci.; Vol. 2: Issue 3, Pg 112-120.

• Das, S. supercritical fluid extraction, module 10. NPTEL.

• Jonin, T.M., Adjadj, L. P and Rizvi, S.S. Food Engineering. Vol III. Encyclopedia of Life Suport System (EOLSS).

• Toledo , Supercritical fluid extraction. Chapter Extraction. Third Edition. pp 528-531

THANKYOU

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