The onset of formation of the water liquid phase in pores of carbon adsorbents

A two-stage mechanism of adsorption, including nucleation and condensation, was proposed to describe the formation of the water liquid phase in carbon adsorbents. Adsorption is assumed to occur in cylindrical pores. Nucleatio n is described by a modified BET model, and condensation is treated by the model of a stretched liquid film on a bent surface. The onset of formation of the liquid phase (OFLP) is determined from the intersection of the adsor ption isotherms for these stages. The theoretical value of the relative pre ssure of OFLP varies over a wide range, decreasing with a decrease in the p ore radius and reaching the relative vapor pressure of 0.178 for the spinod al state of water. The comparison method using isotherms of graphitized car bon black as the reference isotherms was applied for the determination of O FLP of water in real active carbons. This resulted in good agreement betwee n theory and experiment.