Some Consequences of the Application of Incorrect Gas/Solid Adsorption Isotherm Equations

Adsorption Equilibrium Data Handbook (D. P. Valenzuela and A. L. Myers, Prentice-Hall, Englewood Cliffs, NJ, 1989) includes many data on single gas isotherms excellently described by the Toth and UNILAN equations. This paper proves that in spite of the good mathematical applicability, the forms of the two mentioned equations-from a thermodynamic standpoint-are incorrect. As a consequence, the correct specific surface areas of the adsorbents cannot be calculated. The Toth equation can be transformed to a correct relationship and from this modified form correct values of the specific surface areas and isosteric heats of adsorption can be calculated. This correct form does not violate the old principle of the dynamic equilibrium of physical adsorption.