Modelling the influence of pressure on the phase behavior of systems containing water oil and nonionic surfactants

K. Knudsen, E. H. Stenby, J. G. Andersen

Research output: Contribution to journalJournal articleResearchpeer-review


The MHV2 mixing rule which combines a GE-model with a two parameter cubic EOS has been used to model and predict the ternary system H2O - C8H18 - C4E1 the three respective binary subsystems and also the binary system H2O - SBA (water - 2-butanol). The UNIQUAC GE-model is combined with the SRK-EOS and a quadratic mixing rule for the covolume parameter, b, with an additional interaction parameter 11j is introduced. For the binary C4E1-H2O and SBA - H2 systems the pressure-composition behavior can not be correlated correctly with this MHV2-UNIQUAC model when using the common linear mixing rule for the covolume b-parameter in the equation of state. However by introducing a quadratic mixing rule for b, the systems can be correlated with as high an accuracy as can be expected for these very complex systems in which a decreasing closed loop immiscibility gap is observed with increasing pressure. It has been shown that the effect of the additional parameter l1j, and the quadratic mixing rule is to decrease the excess volume, VE, of the mixture. Since no experimental data is available for C8H18 - C4E1, UNIFAC-parameters were estimated to binary data for the groups entering in the ternary system. Pseudo-experimental data for C8H18 - C4E1 were created with UNIFAC and UNIQUAC-parameters were fitted to these. Having the binary parameters for the three subsystems in the ternary system H2O - C8H18-C4E1 a prediction was performed, and compared with the experimental results. Not unexpectedly it turned out to be impossible to predict this ternary system and with these parameters it was even impossible to form a liquid-liquid-liquid equilibrium (LLLE) in the system at the same condition as those used in the experiment. For the MHV2-UNIQUAC model a three phase area is found at higher temperatures and the qualitative correct behavior is found for this three phase area. At increasing temperature the composition of the surfactant rich phase moves towards more oil and at increasing pressure it moves towards more water.
Original languageEnglish
JournalFluid Phase Equilibria
Pages (from-to)55-74
Number of pages20
Publication statusPublished - 1994


  • Theory
  • Equation of state
  • Cubic
  • Liquid-liquid equilibria
  • Mixing rules
  • Water
  • Oil
  • Nonionic surfactants
  • High pressure


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