the classification of phase behaviour according to van...
TRANSCRIPT
The classification of phase behaviour accordingto van Konynenburg and Scott
Bjørn Tore Løvfall
December 18. 2008
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Outline
• Background• Important terminology• Classification of phase behaviour• Summary
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Background
• Why is a classification system needed?• van der Waals equation of state
p = RTVm−b −
av2
m
a = (1− x)2a11 + 2(1− x)xa12 + x2a22
b = (1− x)2b11 + 2(1− x)xb12 + x2b22
• Assumes all molecules are the same size• Change of parameters• Only fluid phases• Binary systems
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Global phase diagram
ζ =
(a22 − a11
a11 + a22
)Λ =
(a11 − 2a12 + a22
a11 + a22
)
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Important terminology
• Phase behaviour• Critical points• Upper critical end point (UCEP)• Lower critical end point (LCEP)• Upper critical solution temperature (UCST)• Lower critical solution temperature (LCST)
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Important terminology (Azeotropes)Negative azeotrope
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Important terminology (Azeotropes)Positive azeotrope
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Important terminology (Azeotropes)Heteroazeotrope
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Global phase diagram
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Type I systems
• One critical line fromC1 to C2
• Simplest type ofsystems
• Typical systems:CO2-O2,Ar-Kr, N2-O2
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Type I systems
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Global phase diagram
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Type I-A systems
• One critical line fromC1 to C2
• Negative azeotrope• Typical systems: HCl
– dimethylether
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Type I-A systems
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Global phase diagram
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Type II systems
• Two critical lines fromC1 to C2 and from Cmto UCEP
• Three phase linealways between thetwo vapour pressurecurves.
• Typical systems:CO2–n-octane,CO2–n-decane andn-pentane–nitrobenzene
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Type II systems
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Global phase diagram
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Type II-A systems
• Two critical lines fromC1 to C2 and from Cmto UCEP
• Positive azeotrope• Typical systems:
CO2–C2H6, Xe–HCland H2O–phenol
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Type II-A systems
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Type II-A systems
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Global phase diagram
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Type III-HA systems
• Two critical lines fromC1 to UCEP and fromCm to C2
• Heteroazeotrope• Three phase line
always to the left ofthe two vapourpressure curves.
• Typical systems:H2O–diethylether,H2O–propane andH2O–1-butene
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Type III-HAm systems
• Two critical lines fromC1 to UCEP and fromCm to C2
• Heteroazeotrope• Three phase line
always to the left ofthe two vapourpressure curves.
• Typical systems:H2O–diethylether,H2O–propane andH2O–1-butene
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Type III-HA systems
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Global phase diagram
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Type III systems• Two critical lines from
C1 to UCEP and fromCm to C2
• Three phase linealways between thetwo vapour pressurecurves.
• UCEP at highertemperature andpressure than C1
• Typical systems:He–Xe, Ne–Kr,methane–n-heptane
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Type IIIm systems• Two critical lines from
C1 to UCEP and fromCm to C2
• Three phase linealways between thetwo vapour pressurecurves.
• UCEP at highertemperature andpressure than C1
• Typical systems:He–Xe, Ne–Kr,methane–n-heptane
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Type IIIm systems
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Global phase diagram
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Type IV systems
• Three critical linesfrom C1 to UCEP,LCEP to C2 and Cm toUCEP
• Two three phaseregions
• Typical systems:methane–1-hexene,benzene–polyisobutene andcyclohexane–polystyrene
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Type IV systems
• Three critical linesfrom C1 to UCEP,LCEP to C2 and Cm toUCEP
• Two three phaseregions
• Typical systems:methane–1-hexene,benzene–polyisobutene andcyclohexane–polystyrene
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Type IV systems
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Type IV systems
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Type IV systems
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Global phase diagram
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Type V systems
• Two critical lines fromC1 to UCEP andLCEP to C2
• Three-phase region,but not at lowtemperature
• Typical systems:ethane–ethanol,CO2–nitrobenzeneandmethane–n-hexane
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Type V systems
• Two critical lines fromC1 to UCEP andLCEP to C2
• Three-phase region,but not at lowtemperature
• Typical systems:ethane–ethanol,CO2–nitrobenzeneandmethane–n-hexane
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Global phase diagram
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Type V-A systems
• Two critical lines C1 toUCEP and LCEP toC2
• Negative azeotrope• Three phase region
but not at lowtemperature
• Typical systems:H2O–HCl
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Type V-A systems
• Two critical lines C1 toUCEP and LCEP toC2
• Negative azeotrope• Three phase region
but not at lowtemperature
• Typical systems:H2O–HCl
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Type V-A systems
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Extensions of the classification system
• Five main types, cover most real systems• Type VI• Type VII• Type VIII• Type II*-IV*
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Summary
• van der Waals equation of state• Nine different types of systems• Qualitatively correct, but quantitatively not• Cover most real systems• More advanced approaches gives limited new information
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ReferencesD. Furman and R. B. Griffiths.Global phase-diagram for a van der waals model of a binarymixture.Physical Review a, 17(3):1139–1148, 1978.
J. S. Rowlinson and F. L. Swinton.Liquids and Liquid Mixtures.Butterwoth & Co Ltd, 1982.
R. L. Scott.Van der waals-like global phase diagrams.Physical Chemistry Chemical Physics, 1(18):4225–4231, 1999.
P. H. van Konynenburg and R. L. Scott.Critical lines and phase equilibria in binary van der Waalsmixtures.Philos. Trans. R. Soc. London, Ser. A, 298(1442):495–540, 1980.
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