Beyond basic UNIFAC

Jens Abildskov, Rafiqul Gani, Peter Rasmussen, John P. O'Connell

Research output: Contribution to journalConference articleResearchpeer-review


A new approach is proposed to extend UNIFAC to more complex substances. While first-order solution-of-groups methods such as UNIFAC can successfully represent measured phase equilibria for structurally simple systems such as mixtures of n-alkanes and linear alkanols with good accuracy, they are not as good for branched chain and polyfunctional substances such as secondary or tertiary alcohols and diols with branched or cyclic alkanes. Our method models departure from first-order behavior by adding second-order contributions to first-order correlations. The second-order contributions are derived from perturbations with respect to structural and energetic parameters. The basis of the extension and its ability to correlate and predict effects due to structural differences in VLE, SLE, and activity coefficients at infinite dilution for binary and multicomponent systems is described. Addition of a few second-order group parameters to the UNIFAC tables has improved the results for essentially all cases where the molecular structure justifies including such effects.
Original languageEnglish
JournalFluid Phase Equilibria
Pages (from-to)349-356
Publication statusPublished - Jun 1999
EventInternational Conference on Properties and Phase Equilibria for Product and Process Design - Noordwijkerhout, Netherlands
Duration: 26 Apr 19981 May 1998
Conference number: 8


ConferenceInternational Conference on Properties and Phase Equilibria for Product and Process Design
SponsorDelft University of Technology, Shell Global Solutions International B.V., Unilever R&D


  • excess Gibbs energies
  • activity coefficients
  • group contribution
  • second-order


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