SUPERCRITICAL FLUID SEPARATION PROCESS

&Application

What is Super Critical Fluid??Supercritical fluid is a state of matter that is intermediate between a gas and liquid in its

properties. This state formed when a gas or liquid solvent is subjected to temperature

and pressure condition exceeding a particular critical point. The temperature and

pressure at which this point occurs are known as the Critical Temperature and Critical

Pressure and are characteristic of the solvent. Beyond this point , the solvent will be

neither a gas nor a liquid , but will possess the properties of both phases. Whether this

supercritical fluid acts more like a gas or liquid will depend on the pressure as well as

temperature.

Another example of Super critical Fluid

Comparison of the properties of gas, Supercritical fluid and liquid

SCFs are used as extraction solvents (e.g. extracting caffeine from coffee beans, fats from potato chips), carrier medium for chromatography, and solvents for disposal of organic hazardous wastes

Advantages of Supercritical Fluids lower operating temperatures improved yield improved product properties favorable combination of process steps easier regeneration of the SC solvent lower production cost solvent power comparable to liquid solvents very high volatility compared to the dissolved

substances complete separation of solvent from extract and

raffinate

Disadvantages of Supercritical Fluids elevated pressures required relative high costs of investment unusual operating conditions complicated phase behavior

Supercritical Fluid ExtractionOften the analysis of complex materials requires as a preliminary step separation of the analyte or analytesform a sample matrix. Ideally, an analytical separation method should be rapid, simple and inexpensive; should give quantitative recovery of analytes without loss or degradation; should yield a solution of the analyte this is sufficiently concentrated to permit the final measurement to be made without the need for concentration; and should generate little or no laboratory wastes that have to be disposed of.

Supercritical fluid extraction Static extraction mode (steady state extraction)

Dynamic extraction mode (non-steady state extraction)

Recirculating mode

Supercritical fluid extraction

Off-line

On-lineSFE-GCSFE-LCSFE-MSSFE-SFC

Off-line SFE

Schematic diagram of on-line SFE-SFC systema) CO2 cylinder

b) pump c) extraction vessel d) cryotrapheatere) injection port f) chromatography column g) column oven h) detector i) transfer lines.

On-line SFE

Cryotrapheater

Advantages of on-line SFE Direct coupling of the analyte-containing supercritical fluid to a

chromatographic separation system with appropriate detection

Eliminating sample handling after loading in the extraction cell

Disadvantages of on-line SFE Long periods of time

Understand the nature of analytes

Supercritical Fluid Extraction apparatus

Supercritical fluid chromatography (SFC) is a hybrid of gas and liquid chromatography that combines some of the best features of each. Supercritical fluid chromatography is of importance because it permits the separation and determination of a group of compounds that are not conveniently handled by either gas liquid or liquid chromatography

Supercritical Fluid Chromatography

Theory of SFCProperties of liquid, gases and supercritical fluids are shown belowSincesupercritical fluids have properties between those of gases and liquid, their use as a mobile phase offers several advantages. Typical physical

Phase density Diffusion coefficient ViscosityGas 10-3 10-1 10-4

SL 0.3-0.9 10-3 ~10-4 10-3 ~10-

4

Liquid 1 <10-5 10-2

a. One of advantages is that supercritical fluid have lower densities and viscosities than liquids. This results in larger diffusion coefficients for solutes is SFCthan LC. This results in Better efficiencies and higher optimum linear Velocities in SFC than LC. The plate height of a SFC System is given by the van Deemter equation.

H = A + B/u + Cu

b. SFs have higher densities than gas, so that mobile phase has a greater chance of interacting with the solute than that in GC (i.e., carrier gas). This makes the mobile phase important in determining the retention of solutes on the system and give more flexibility in optimizing the separation. For example, retention of solutes in SFC can be changed by using a different column (i.e. different stationary phases) as in GC, or by changing the mobile phase strength as in LC.

c. One major advantage of SFC is its ability to use detector available for either GC or LC, such as FID, UV-Vis, and Fluorescence detectors. This gives it a wide range of both universal and selective detections for use in either analytical or preparative-scale work.

LC detectors:

Thermal conductivity detector (TCD): 10-7 M (103-fold range)

Flame Ionization detector (FID): 10-10 M (a 105-fold range)Nitrogen-phosporus detector (NPD): 10-10 M (a 106-fold range)

Electron capture detector (ECD): 10-14 ~ 10-16 M (a 103- 104 fold range)

Flame photometric detector(FPD):10-14 M (P, S)

Electrochemical detector (S, halogen,nitrogen-)

Refractive Index Detector(10-5 to 10-6 M)

Absorption Detector (UV/Vis)

(10-8 M)

Fluorescence Detector(10-10 M)

Conductivity Detector

(10-6 M)

Electrochemical Detector

(10-11 M)

GC detectors:

d. Depending on which supercritical fluid is used, it is also possible to use SFC at lower T than GC. This makes it more useful in the separation of thermally unstable compounds.

e. The stationary phases used in SFC can be similar to those in LC as well as GC. Either packed or open-tubular columns may be used.

Because of these advantages, SFC is commonly viewed as a technique which is complementary to both LC and GC.

5. Instrumentationa. Instrumentation for SFC can be obtained commercially or adapting system used for either LC and GC.

b. The main difference of a SFC

than a LC or GC system is the

need to control bother

temperature and pressure of

mobile phase. This must be done

to keep the mobile phase as a

Supercritical fluid. Control of

the pressure (density) of the

supercritical fluid can also used to vary strength of mobile

phase during the gradient elution in SFC .

Percentage extraction versus time of extraction

◆

Modifiers for SFE/SFC

The role of Modifier on SFE• Plots of modifier effects on efficiency for

nonpolar solutes on C18 column at 80 oC and 210 bar, 2.0 mL/min. Solute: (A) naphthalene; (B) anthracene;Modifier: solid line with = methanol;broken linewith = ethanol; dotted line with = 1-propanol;dashed line with = acetonitrile [Zou & Dorsey, 2000] ◆

MeOH MeCN

1-propanol

EtOH

Reduced solubility parameterΔ= δ1/δ2

δ1= 1.25 Pc1/2 [ρ/ρliq ]

δ2＝(Δε/ Δν)1/2

δ1 : solubility parameter of the fluidPc : the critical pressure

ρ : the density of the supercritical fluid ρliq: the density of the liquid gas

δ2 : solubility parameter of soluteΔε: the energy of vaporization at a given temperatureΔν: the corresponding molar volume

Calculation of the solubility parameters, δ2

Megastrol acetate

Group Δε (cal/mol) Δν (cm3/mol)

5*CH3 5(1125) 5(33.5)6*CH2 6(1180) 6(16.1)3*CH 3(820) 3(-1.0)2*HC= 2(1030) 2(13.5)3*C 3(350) 3(-19.0)2*C= 2(1030) 2(-5.5) 2*C=O 2(4150) 2(10.8)OCO 4300 18.04 ring closure 5-6 atoms 4(250) 4(16.0)2 conjugated double bonds 2(400) 2(2.2)

34735 328.1

δ2＝(Δε/ Δν)1/2= 10.29 cal1/2 cm-3/2

Chromatograms of enantiomers of -phenylethanol using different i.d. restrictors.(A) 6 m m, (B) 9 m m, (C )12 m m, (D) 15 m m.

6 m m

160 atm

9 m m

160 atm

12 m m 160 atm

15 m m

6 m m

Different i.d. restrictors

Effect of restrictor internal diameter on separation parameters

SFC: effect of Pressure

Effect of temperature in SFCFigure 1.10. Selected segments of SFC chromatograms from a complicatedsample, showing the effect of temperature on selectivity at (A) 14O C, (B) 16O C, (C) 170 °C. (D) Two families of unknown

peaks (l-3 and 4-7) overlap with some coelution at 140 C, but are resolved at 170°C.

(E) Conditions: 10-m x 50-pm i.d.open tubular column, poly(308 biphenyl)methylsiloxanestationary phase; CO,; 5 atmmin-‘, FID.

140°C

160°C

170°C

Effects of temperature and pressure on retention factors

J . Chromatogr .A 785 (1997) 57–64

Sample types Solid samples

Liquid samples

Aqueous samples

High viscosity liquids

Applications of Supercritical Fluid Separation Process Food and pharmaceutical Application

ex- Decaffeination of coffee using supercritical carbon dioxide(Kraft process)

Extraction from Aqueous Solution

Cleaning

Adsorption and Desorption

Drying and Aerogel Formation

Temperature-Controlled Residuum oil Supercritical Extraction(ROSE)

Analytical Supercritical Fluid Extraction and Chromatography

Precipitation with a Compressed Fluid Antisolvent (PCA)

Crystallization

Polymer Devolatilization and Fractionation

Thank You