Modification of Simha-Somcynsky equation of state for small and large molecules

Ming Wang, Shigeki Takishima, Yoshiyuki Sato, Hirokatsu Masuoka

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


The Simha-Somcynsky equation of state (SS EOS) represents the PVT behavior of polymers quite satisfactorily, but cannot be applied to gases at low pressures. This work proposes a modification of the free volume contribution of the SS EOS to allow representation of gaseous state of low molecular-weight substances by introducing the perturbed hard-chain theory of Beret and Prausnitz into the EOS. In addition to this modification, two universal constants are introduced to the free volume term for better representation of properties of low molecular-weight substances. Characteristic parameters in the modified SS EOS were determined for 44 low molecular-weight substances and 64 polymers. The absolute average deviations (AADs) for critical temperature, critical pressure and vapor pressures were 0.86, 2.38 and 2.01%, respectively, while AAD for critical density and saturated liquid density at normal boiling point were somewhat larger, being 20.46 and 5.30%, respectively. The high performance of the original SS EOS for polymer PVT behavior was maintained in the modified EOS with grand AAD of 0.050% for densities.

Original languageEnglish
Pages (from-to)10-18
Number of pages9
JournalFluid Phase Equilibria
Issue number1
Publication statusPublished - 2006 Apr 5
Externally publishedYes


  • Equation of state
  • Hole theory
  • PVT behavior
  • Polymer
  • Vapor pressure

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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