This paper introduces the UNIFAC group contribution approach into Butlers equation. A new method is set up to predict the surface tension of binary and multicomponent non-electrolyte systems

requiring only pure component properties and UNIFAC parameters. With the introduction of the activity coefficients γBi=αBi/xBi

γSi=αSi/xSi

Butlers equation may be transformed to give Here σm represents the surface tension of the mixture and σi the surface tension of pure component i. Ai is the molar surface area of component i and Ai its partial molar surface area in the solution

αBi

γBi and xBi stand for the activity

the activity coefficient and molar fraction of component i in the bulk liquid respectively and αSi

γSi and xSi for those 011 the surface layer of solution. N is the number of components. The value of Ai is set up equal to Ai which is calculated from the equation Ai=Vi2/3N01/3 where Vi is the liquid molar volume of pure component i and N0 Avogadros number. The bulk activity coefficients and surface activity coefficients are calculated with UNIFAC group contribution approach in a similar way. Predictions based on this approach agree well with experimental data for 100 binary

10 ternary and 2 quaternary systems. The total average relative deviations from experiment are 2.53% and 5.33% for binary and multicomponent systems respectively

within acceptable limit for engineering design.