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Reliable Analysis of the Light Ends of Petroleum Fractions and Crude Oil Using CapillaryFlow Backflush Technology
Roger L. FirorAgilent TechnologiesChemical Analysis GroupWilmington, DE USA Det
He
EPC1P2
IN
Oven
Purged UnionPre-Column Column 2
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Outline
• Why pre-column backflush• System configuration with CFT (Capillary Flow
Technology)• Typical method setup• Performance• Application examples
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Pre-column Backflush
• Eliminate bake out times at end of runs• Dirty samples• Late eluting compounds of no analytical interest• Need to protect column from high boilers• Interest in maximizing lab throughput and minimizing
cost of operations• Compatible with GC and GC/MSD systems
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AUX EPC
Pre-column
Purged Ultimate Union
Multimode InletTemperature programmed split
1.6 mL/min2.0 mL/min
Analytical Column
140 mL/min
FID
Basic System Configuration
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Purged Union with Columns Installed
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Pre-column
G3186B
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Advantages of Pre-column Backflush
Backflush is carried out while analysis is occurring on the analytical column
Midpoint pressure control allows analytical column to run at desired flow while pre-column is backflushed
Use of an uncoated pre-column allows transfer of components (in this application up to C12 – C13) at a relatively low temperature (i.e. 35 C) and faster backflushing of the heavier components
Sample matrix has little influence
Wide choice of pre-column and analytical column dimensions and phase ratios possible to meet specific application needs
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System Setup and Operation
• A pre-column, typically a deactivated retention gap of 2 meter length is used.
• The inlet of the pre-column is defined as the MMI (multimode inlet) and the outlet as a Aux module channel
• The analytical column (100m x 0.20mm x 0.5um HP1 for crude oil analysis) uses an Aux channel (no restrictor) as inlet and FID as outlet
• At the specified runtime the inlet pressure is dropped to reverse flow in the pre-column while the Aux maintains forward flow in the analytical column
• At backflush runtime, the MMI’s temperature is ramped to 425 C to clear out the inlet. It is held at this temp to end of run
• Single taper liner with glass wool is used
• Pressure zeros should be set on the GC for the inlet and Aux channel before use
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Backflush: Column Settings for Polywax Carbon Number Specific Backflushing
PW 500
Pre-column
Analytical column
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Backflush with Purged Tee: Polywax 500Sample: C5-C18 plus PW500
C26, 10 min
C36, 14 min
C42, 16 min
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Peak Shapes on Retention Gaps: C12 Only
min5 10 15 20
Norm.
0
50
100
150
200
250
C12
MMI
AUX
Union FID10M x 0.32mm2M x 0.32mm
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Setup for Pre-column and Analytical Column
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Pre-column
Analytical
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Pre-column Backflush of C5-C18 Mix After C14
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Retention time STD’s < 0.0019 min
1 m x 0.32 mm retention gap, 100 m x 0.25 mm x 0.50 um DB-PETRO
C14
C12
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Four Crudes From Different Regions: Backflush after C12
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Pre-column: 1.5 m x 0.32 mm deactivated RG, Analytical column: 100 m x 0.25 mm x 0.50u DB-PETRO
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12 runs of Crude Oil Overlay: Pre-column Backflush After C12
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No residual high-boiling material remains in the system run to run
2 m x 0.32 mm RG
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Backflush with Coated Pre-columns
Pre-columns with thin coating (i.e. 0.10 um films) can be used
Provides finer control of compounds that are backflushed
Backflush times will be much longer typically
Backflush of heavy compounds remaining on the pre-column will take longer
Better inertness
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Backflush of C5-C40 Mix After C11Overlay of 12 runs, 2 m x 0.32 mm x 0.10 um pre-column
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C9
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Overlay of Souide Crude OilC10 Retention time STDEV = 0.0010, % STDEV = 0.315
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C10
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Crude Oil Backflush with Coated 2 m x 0.32 mm x 0.10 um DB-1 Pre-column Conditions: Pre-column flow 1.6 ml/min, Analytical column flow 2.0 ml/min
MMI: 250 C(0.5 min) to 425 C @ 200 C/minOven Program: 35 C (4 min) to 200 C (1 min) @ 2.0 C/minAnalytical column: 100 m x 0.25 mm x 0.5 um DB-Petro
Backflush time: 4 min
Backflush time: 8 min
C10
C11
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2 m x 0.32 mm x 0.10 um Pre-column: Blue Backflush at 14 min, Red – Backflush at 16 min
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Zoom on C11 Plus Hydrocarbons
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Stable baseline shows that column is clean after each run
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Combining Pre-column Backflush with GCxGC
• Investigate possibility of analyzing heavy crudes with comprehensive gas chromatography
• Apply chemometrics to identify source or contamination
• Process 50 Hz raw data files
• Analyze four different crudes
• Column set• First Dimension: 30 m x 0.25 mm x 0.10 um DB-5HT• Second Dimension : 5 m x 0.25 mm x 0.15 um DB-17HT
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Flow Modulator Diagram: Backflush
MMI: ramped flow, negative ramp at backflush time
FIDColumn 2
PCM Micro Valve
PCM: Pressure control mode, column in constant flow
Modulator
FIDColumn 2
PCM Micro Valve
PCM: Pressure control mode, column in constant flow
Modulator
MMI
FID
Column 1
Column 2
PCM Micro Valve
PCM: Pressure control mode, column in constant flow
Modulator
AUX
Restrictor/ Pre-column
G3186B
Aux: Controls Column 1 inconstant flow
21-25 ml/min typical
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RT Stability and Effect on Modulated Area: C13
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Analysis of modulated C13
Single pulse
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Crude Oil GCxGC: Pre- column Backflush
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BF at 30 min, Oven programmed to 390 C
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Principal Component Analysis: 2D view
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Four crudes
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Principal Component Analysis: 3D view
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Summary• The CFT purged union offers a high performance alternative to traditional valved pre-column backflush systems
• Relies on precise EPC midpoint pressure control
• Backflush is concurrent while analytical column runs at constant flow
• Excellent thermal control since all parts are in the oven
• Heavy petroleum including crude oils can be routinely analyzed with complete protection of the high resolution capillary column
• The specific carbon number where backflush beginning can be easily controlled and fine tuned
• Pre-column backflush is compatible with GCxGC
• Coated pre-columns can be used for fine tuning
• Chemometrics can be applied to identify oils
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Acknowledgement
Pirouette® Chemometric Software provided by Infometrix, Inc.
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Capillary Flow Technology (CFT) Based Pre-fractionator: Pre-column Backflush System
• In oven CFT device is used in a relatively simple hardware configuration
• CFT “purged union”
• The multimode inlet is used to assist with backflushing heavy material from the inlet. Inlet is programmed to 425 C after backflush is started
• Run time backflush is easily programmed from the ChemStation
• Analytical column flow controlled from an Aux module
Key Application: Front-end detailed analysis (DHA) of crude oils
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Flow Calculator Parameters
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100M Column 2.0M RG 1.5M RG
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2 m x 0.32 mm x 0.10 um Pre-column: 12 Run Overlay of Crude Oil
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