super critical fluid separation process
TRANSCRIPT
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
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