ADSORPTION OF BENZENE AND PYRIDINE VAPORS BY VARIOUS CARBON ADSORBENTS

Abstract

For the first time with the help of express-method we compare adsorption of benzene and pyridine vapors by carbon adsorbents (CA) that differ in raw materials, methods of production and textural characteristics. With the BET and Aranovich (AR) equations we define the interval of relative pressure, in which the adsorption of studied components is described by suggested models of polymolecular adsorption, and calculated general characteristics of adsorption. A comparative analysis of these equations shows that adsorption isotherms of benzene vapors should be described with the Aranocich model and pyridine vapors with the BET model. It is stated that the adsorption of both benzene and pyridine is characterized by the low energy constant C that means weak adsorption localization on a carbon surface and difficulty with exact determination of monolayer capacity. We stated that with benzene adsorption by CA and pyridine adsorption by lignite sorbent the area taken by adsorbate molecule exceeds molecule’s own size. Such action is typical for realized specific sorbent-sorbate interaction which is expected by molecular structure of adsorbates and surface state of adsorbents and is proved by the amount of calculated adsorption heat. It is stated that pyridine molecules when adsorbed are oriented in parallel to the adsorbent surface and for benzene molecules such reaction exists only for granular carbon adsorbents. Random orientation of benzene molecules when adsorbed by granular CA can be connected with overall attraction-repulsion effect of π-electron system of benzene and polar groups on the adsorbent surface. We define the exponent of the Dubinin-Astakhov equation using the theory of volume filling of micropores (TVFM), calculate the limiting adsorption volume and size of pores occupied by components. We state that both benzene and pyridine adsorption proceeds similarly in available at size micro- and mesopores of adsorbents. Differences in adsorption behavior of benzene and pyridine with a filled monolayer are probably connected with peculiarities of molecule structure of pyridine which has an additional potential center of adsorption that is an unshared electron pair of nitrogen.