Empirical determination of Henrys Law constants in hydrocarbon liquids

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Empirical determination of Henrys Law
constants in hydrocarbon liquids Session 1680
Fuels and Petrochemical Analysis Abstract
1680-9 Pittcon 2003 Orlando,Fl March 12,2003,
425 PM, Room 203A   LPTalarico COSA Instrument
Corporation
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Experimental design

• Literature investigation yielded no comprehensive
  source of water saturation values (ppmw) for the
  hydrocarbons of interest
• Due to the importance of ppmw(ug/g) at saturation
  ..testing began here
• Next a pilot plant was constructed to vary
  temperature, flow and moisture concentration.
  This facilitated measurements in the
  concentration ranges desired by hydrocarbon
  producers and processors
•  
• Based on the results of the first two
  investigations it became clear an ESS (Extractive
  Sample System) could link these approaches
  enabling more reliable moisture measurement. The
  system highlighted here incorporates Dew Point
  measurement with KFT(Karl Fischer Titration) and
  Gas Chromatography to ensure accuracy and
  validation with relative ease

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Henrys Law

• CakPa
• Ca(KFT ppmwug/g)
• k(Henrys constant)
• Pa (saturation vapor pressure of water at
  TmmHg)
•  
• Temperature is the key parameter..different
  T.different k
• Changes in temperature cause the saturation vapor
  pressure value and the KFT value of the
  hydrocarbon to change
• Mixtures
•  
• Average saturation values are calculated by
  weight fractions of the individual components

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Special case of Henrys Law

• Saturated hydrocarbon chains exhibit a unique
  physical property
• Their k factor does not vary significantly with
  temperature
•  
• This special case is where we did our work.
• With sample temperature falling from the
  equation our experiments investigated important
  sensor calibration and aging issues

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Physical Chemistry

• Goff-Gratch equations express the physical
  property defined as saturation vapor pressure in
  the pure phase over plane surfaces of pure water
  and pure ice
• Their integration of the Clausius-Clapeyron
  equations led to Saturation Vapor Tables adopted
  by the International Meteorological Organization
  in 1947
• References
• Keyes, F.G., Journ. Chem. Phys., vol. 15 No.8,
  pp. 602-12, 1947
• Goff, J.A and Gratch, S., Trans. Amer. Soc. Heat.
  And Vent. Eng., vol. 52, 1946
• Smithsonian Meteorological Tables, publication
  4014, 1949

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Dew Formation
The picture shown here describes equilibrium at
saturation. The excess water globules in the
organic demonstrate saturation in the liquid
phase and the dew formation demonstrates water
saturation in the gas phase
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Analytical Chemistry

• Karl Fischer Titration
•  
• H2OI2SO23BaseCH3OH---2Base.HIBase.HSO4CH3
•  
• Coulometric type
•  
• 2I- - 2e I2
•  
• Stochiometry
•  
• 10.72 coulombs---1 mole of H2O
•  
• This approach is best suited to low level
  moisture determinations Detection levels of less
  than 10 ug absolute H2O are possible
•  
• Reference
• Mitsubishi Chemical Corporation, Karl Fischer
  Reagents, 2000

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Results of the investigations

• The following hydrocarbons were chosen for
  testing
• They represent the alkane, alkene, aromatic and
  cyclic
• families
• The saturation values were calculated by KFT and
  the
• Vapor Pressures by Goff-Gratch equations yielding
  the
• following Henrys constants
• Hexanes2.5
• Benzene20.6
• Hexene8.3
• Transformer Oil2.3
• 50/50 Mixture Hexanes/Benzene11.5

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Measuring Saturation PPMW

• Method..simple form
• Prepare water saturated hydrocarbon sample
  (excess water observable) mix continuously _at_ 300
  rpm with magnetic stirrer.
• Place sample and stirrer in environmental chamber
  at set temperature.
• Prepare coulometric KF titration cell and dry to
  acceptable background. Place titrator and
  titration cell into chamber
• Connect buret to sample flask. Equilibrate by
  cycling buret to and from sample flask
• Measure the mass of 1 ml volume at set
  temperature
• Verify accuracy of KFT by check solution
  injections
• Measure moisture concentration by KFT. KFT
  samples taken after 18 hours in the
  environmental chamberenough time to reach
  equilibrium
• Comments
• Titrator temperature stabilized
• Sample temperature stabilized

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Environmental Chamber
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Environmental Chamber
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Results for various Organics tested
The raw data and graphs for hexene, transformer
oil, benzene and a mixture of benzene and hexane
are available. If you have interest please
contact me after the presentation The rest of
this presentation focuses on Hexane
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Raw dataTransformer Oil
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GraphTransformer oil
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Raw data Benzene
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Graph Benzene
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Raw dataHexene
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GraphHexene
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Raw data mixture Benzene/Hexane
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Graph mixture Benzene/Hexane
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Raw dataHexane
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GraphHexane
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Pilot Plant Measuring System

• In order to investigate Henrys constants in
  organic liquids in real world concentrations a
  number of parameters had to be controlled
• A pilot plant system was designed
• The system incorporates Dew Point measurement
  both gas and liquid with Karl Fischer Titration
  while maintaining stable temperature and flow and
  the ability to vary moisture concentration
•  

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Schematic Pilot Plant System
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Picture Pilot Plant System
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Measurements in Hexane 0.5 PPMW to 75.0 PPMW
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Graph of working range data
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Theoretical and Empirical Data Hexane
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What does this all mean

• Xentaurs Al2O3 sensor calibrated to report Dew
  Point
• seems to be good trend indicator of moisture
• concentration
• Calibration to report PVP may be more useful
• Reliable PPMW (ug/g) values are possible using
• Henrys constant (special case) if rigorous
  attention is paid to
• sensor calibration
• Simple validation will insure accuracy
• The matrix can be confirmed by GC
• The moisture can be confirmed by KFT

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A new approachESS with integral
validation
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Extractive Sample System Components

• The ESS has three components
• Xentaur AL2O3 sensor.the essence
• The Xentaur HDT.the brain
• The sample BOMB.the validation

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Xentaur Al2O3 sensor
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Comments on sensor stabilization

• Our research has confirmed with proprietary
  manufacturing procedures a stable sensor is
  produced
• Our research has confirmed sensors calibrated
  with gas can report PVP in both liquids and gases

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The HDT

• A multipoint calibration table with temperature
  compensation over the full range provides
  unsurpassed accuracy
• Loop power provides ease of use
• HART interface provides 4-20 mA and digital
  outputs and alarms

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The BOMB

• Provides possibilities for integral calibration
  and validation of both important
  parameters.matrix and moisture concentration

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Summary/Conclusions

• Al2O3 sensors measure increases and decreases in
  PVP and are good
•   moisture concentration trend indicators
• Al2O3 sensors in hydrocarbon liquid streams are
  quite stable and accurate
•  
• KFT accounts for sample matrix variations. Thus
  its the measurement
• to rely on for absolute moisture concentration
•  
• GC can verify the matrix providing concrete
  insight into Henrys Law
• constants for the sample steam of concern
•  
• By combining PVP measurement with GC and KFT via
  an Extractive
• Sample System process control is truly
  possible..NO MORE
• MYSTERY