THEORY OF SORPTION OF GASES ON HETEROGENEOUS SOLIDS POLYMERIC SORBENTS

A simple model of mono- and multilayer sorption of gases on a flexible linear chain of a polymer is investigated. The influence of degenerat ed conformational degrees of freedom of the polymer linkages on the ad sorption isotherm GAB (Guggenheim, Anderson, de Boer) is studied. This description is an extension of the approaches presented in previous p apers1-3 and involves changes in the internal structure of the polymer chain during the sorption process. e.g., different conformational sta tes of linkages between monomers of the linear chain. To describe a co nformation of the whole chain, the one-dimensional model is used. The sorbed molecules of gas can be tightly bound to the sorption centers, or they are in an intermediate adsorption state. The molecules interac t indirectly through the conformational subsystem of the polymer. This interaction leads to a cooperative effect in the mono- and multilayer sorption isotherm. The proposed isotherm equation for a heterogeneous solid (polymeric sorbent) is a product of the isotherm equations for the adsorption of gases on a homogeneous solid surface and on the poly mer's chain. In the case of a rigid chain of the polymer the proposed equation reduces to the equation for noncooperative heterogeneous sorp tion on two kinds of centers having different adsorption energies. The thermodynamics of the model is studied by the transfer matrix method. The approach presented can give, for example, a more realistic pictur e of the mechanism of water and alcohol vapor adsorption on starch and cellulose. A comparison of experimental results with theoretical calc ulations of the model is performed for the sorption isotherm of methan ol on freeze-dried starch gel.