NONIDEALITY CORRECTION FACTORS FOR ADSORBATES

The values of the nonideality factor, alpha, obtained by P. H. Emmett and S. Brunauer, (J. Am. Chem. Soc. 59, 1553 (1937)) with the aid of t he van der Waals equation of state for various adsorbates, and which a re routinely utilized in adsorption experiments, are valid only for no npolar gases such as nitrogen, argon, and oxygen, On the other hand, f or most gases, the alpha's from three-parameter equations of state, su ch as the virial equation involving the correlation of Fitter (PIT) an d the Peng-Robinson (P-R) equation, are in excellent conformity with t hose retrieved from experimentally measured P-V-T data. The PIT correl ation is the preferred choice for nonpolar and partially polar organic and inorganic adsorbates on account of its accuracy and amenability t o simple numerical calculations. The P-R equation, although complex, i s suited for predicting the alpha's of highly polar gases at various t emperatures of adsorption, A new set of alpha's recovered from these t wo equations for various adsorbates will potentially facilitate adsorp tion and chemisorption measurements in vacuum volumetric systems. (C) 1996 Academic Press, Inc.