CALIBRATION OF PORE VOLUME IN ADSORPTION EXPERIMENTS AND THEORETICAL-MODELS

We propose a new definition of excess adsorption for use in molecular models of adsorption. This definition implies the calibration of theor etical models in a manner mimicking the experimental calibration proce dure. The method of theoretical calibration is developed on the exampl e of helium calibration. The notions of the He calibrated pore volume and the He calibrated pore size are introduced and the He calibrated t heoretical excess isotherms are defined. The proposed method diminishe s the discrepancies between the theoretical and the experimental exces s adsorption isotherms and makes the theory and the experiment entirel y consistent. The quantitative estimates are made by means of the nonl ocal density functional theory (NLDFT) applied to the adsorption of He , N-2, and CH4 in micropores of active carbons at liquid nitrogen and ambient temperatures. It is shown that the experimental He calibration affects significantly the excess isotherms of vapors and supercritica l fluids in microporous carbons. The nonmonotonous excess isotherms in molecular size pores are predicted. The theoretical predictions of He adsorption are in qualitative agreement with the experimental isother m measured on the BPL active carbon at 77 K. The theoretical calibrati on is recommended for adjustment of any molecular model of adsorption phenomena, such as density functional theory, molecular dynamics, and grand canonical and other Monte Carlo simulations.