Thermodynamic study of sorption of n-alkanes onto 5A zeolites immobilized in photosynthetic membranes

Equil. adsorption isotherms of n-heptane and n-dodecane on composite photosynthetic membranes, prepd. by photochem. grafting an epoxy-diacrylate copolymer contg. 30 wt. % of zeolite 5A, were detd. gravimetrically in 298-373 K at partial pressures 0.01-500 Torr. Parallel adsorption runs were carried out on unsupported, free zeolite. Exptl. data were fitted to a virial equation describing the dependence of the amt. of adsorbate on pressure by means of adsorbate-adsorbate and adsorbate-adsorbate interaction coeffs. dependent on temp. By these latter, thermodn. std. values for monolayer coverage were calcd. and compared with some recent literature values measured on free sorbent, although in a higher temp. range than that of the present study. Furthermore, from monolayer surface coverage at 298 K, areas occupied by single mols. of adsorbed species were calcd., which indicate a relaxed conformation parallel to adsorption planes (coaxial configuration in the zeolite cavities). No difference was found between adsorbed amts. per unit mass of sorbent in free and immobilized conditions, within the limits of exptl. uncertainty; but when adsorption was carried out from soln., a small, but definite, decrease of surface area was noted. This fact points to an ideal behavior of the immobilized sorbent in the membrane, esp. where gas adsorption and transport are concerned.