Activity coefficients and plate efficiencies in distillation of multicomponent aqueous solutions

S. Bruin

Research output: Thesisinternal PhD, WU


The thermodynamics of vapour liquid equilibria and the calculation of distillation processes of volatile flavours are studied. Various methods of reducing experimental data of equilibria of binary systems to two meaningful parameters are discussed. These parameters are building blocks in a thermodynamic model of multicomponent solutions. Recently ORYE has developed a modified Wilson equation for the excess Gibbs free energy of mixing in a multicomponent solution. In the present study three equations are deduced, using a lattice model of a liquid solution, all of which are applicable to systems showing partial miscibility. One of these equations appeared to be identical to the modified Wilson equation as proposed by Orye. The Enthalpic Λ-equation turns out to be of high accuracy for a number of binary systems investigated.

An apparatus, employing a gas chromatographic technique, was developed for measuring activity coefficients of volatile organic components in water. At infinite dilution of the volatiles the activity coefficients can be measured simultaneously in a multicomponent system. The apparatus was tested for a number of n-alcoholes and ketones and found to meet the required accuracy. Activity coefficients of some aldehydes and esters were measured with the apparatus.

A multicomponent distillation calculational procedure (MCDTG-EFF computer programme) especially suited to aroma distillations was developed. This programme takes into account the efficiencies of the individual components. In the calculational scheme the following assumptions are made:
1. The liquid on each plate is at bubble temperature;
2. The number of gas phase- and liquid phase transfer units on a plate can be obtained from an empirical correlation;
3. Complete mixing of the liquid phase occurs on each plate;
4. The efficiencies are specified for all components in the reboiler;
5. The Van Laar multicomponent equation relating activity coefficients to composition is applicable;
6. The liquid phase does not separate into two liquid layers.

Comparison of calculated results obtained with this programme with the results of a calculation based on ideal plates (MCDTG computer programme) shows large deviations.

The validity of assumption 5 was checked by experimental determination of activity coefficients in multicomponent mixtures, showing resemblance to complex food flavours.

A calculational scheme to determine multicomponent plate efficiencies from binary data, using a matrix formulation, is proposed. The theory degenerates consistently to the formulations one can deduce for as well binary systems as for dilute multicomponent solutions.

Computer programmes (FORTRAN) are given together with a detailed description and block schemes.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Leniger, H.A., Promotor
  • Thijssen, H.A.C., Promotor, External person
Award date18 Jun 1969
Place of PublicationWageningen
Publication statusPublished - 1969
Externally publishedYes


  • distillation
  • evaporation
  • food additives
  • technology
  • thermal energy
  • thermodynamics
  • cum laude


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