1 Effect of the Range of Interactions on the Properties of Fluids Equilibria of CO 2 , Acetone, Methanol and Water Ivo Nezbeda 1,2 , Ariel A. Chialvo 3,2 , and Peter T. Cummings 2,3 1 Institute of Chemical Process Fundamentals. Academic of Sciences, 16502 Prague 6 - Suchdol, Czech Republic 2 Departments of Chemical Engineering. University of Tennessee, Knoxville, TN 37996-2200, U.S.A. 3 Chemical Sciences Division. Oak Ridge National Laboratory, Oak Ridge, TN 37881-6110, U.S.A.
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Ivo Nezbeda 1,2 , Ariel A. Chialvo 3,2 , and Peter T. Cummings 2,3
Effect of the Range of Interactions on the Properties of Fluids Equilibria of CO 2 , Acetone, Methanol and Water. Ivo Nezbeda 1,2 , Ariel A. Chialvo 3,2 , and Peter T. Cummings 2,3 1 Institute of Chemical Process Fundamentals. Academic of Sciences, 16502 Prague 6 - Suchdol, Czech Republic - PowerPoint PPT Presentation
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Effect of the Range of Interactionson the Properties of Fluids
Equilibria of CO2, Acetone, Methanol and Water
Ivo Nezbeda 1,2, Ariel A. Chialvo 3,2, and Peter T. Cummings 2,3
1 Institute of Chemical Process Fundamentals. Academic of
Sciences, 16502 Prague 6 - Suchdol, Czech Republic2 Departments of Chemical Engineering. University of
Tennessee, Knoxville, TN 37996-2200, U.S.A.3 Chemical Sciences Division. Oak Ridge National Laboratory,
Oak Ridge, TN 37881-6110, U.S.A.
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Rationale Generally long-range forces have negligible effect on the microstructure of fluids
• the structure of realistic model fluids and their short-range counterpart are (for all practical purposes) identical
Thermodynamic properties of fluids are accurately estimated by those of the short-range model counterparts
• e.g., configurational energy of the short-range models account for 95% of the total property
Long-range forces affect only details of the orientational correlations
• however, the dielectric constant remains unaffected These findings support the development of fast converging perturbation expansions
about the short-range reference• i.e., long-range Coulombic interactions treated as a perturbation
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Goals
Determine the effect of the long-range Coulombic interactions on the vapor-liquid equilibria properties of polar and associating fluids
• most realistic intermolecular potential models available carbon dioxide, acetone, methanol, and water
Interpret simulation results and develop simple perturbation approaches for
rigorous modeling
• modeling of aqueous solutions without resorting to long-range interactions e.g., I. Nezbeda, Mol. Phys., 99, 1631-1639 (2001)
• truly molecular-based equation of state for engineering calculations e.g., recently proposed equation for water (Nezbeda & Weingerl, Mol. Phys., 99,
1595-1606 (2001))
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Range of Intermolecular Interactions
Basic definitions
• Separation between short- and long-range potential interaction
Gibbs-Duhem equations including force-field variables (*)
• Particular cases can be derived depending on relative sizes of the
involved properties in each phase
typical case (water and acetone)
additional cases apply to carbon dioxide and methanol
€
upert TP
l>> upert TP
υ
€
V l << V υ ≈ NkT P
€
Pfull−range ≅ Pshort −range × exp − upert TP
lkT ⎛
⎝ ⎞ ⎠
(*) Nezbeda et al. (2001)
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Summary and Final Remarks
Spatial and orientational distributions of molecules are marginally affected by long-range forces
Long-range forces affect details of the orientational ordering at short-range distances.• orientational correlations in the short- and full-range systems are
qualitatively similar
• integrals over these correlations, e.g., dielectric constant, do not differ significantly
Similar behavior is found in the dependence of thermodynamic properties, i.e., energy and pressure, on the range of the potential
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Summary and Final Remarks
Critical conditions appear to be unaffected by the long-range forces
These findings lend support to the use of perturbation expansion in the development of truly molecular-based equations of state
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Acknowledgements Research Support
• Grant Agency of the Czech Republic (Grant No 203/99/0134)
• Division of Chemical Sciences, Geosciences, and Biosciences, Office of
Basic Energy Sciences, U.S. Department of Energy under contract
number DE-AC05-00OR22725 with Oak Ridge National Laboratory,
managed and operated by UT-Battelle, LLC
For more info visit our web_sites
• http://www.icpf.cas.cz/theory/IvoNez.html
• http://www.ornl.gov/divisions/casd
• http://flory.engr.utk.edu/~aac
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