| Popis: |
Equilibrium adsorption isotherms of n-heptane and n-dodecane onto composite photosynthetic membranes, prepared by photochemically grafting an epoxy-diacrylate copolymer containing 30 wt.% of zeolite 5A, were determined gravimetrically in the temperature range 298-373 K at partial pressures ranging from 0.01 to 500 Torr. Parallel adsorption runs were carried out onto unsupported, free zeolite. Experimental data were fitted to a virial equation describing the dependence of the amount of adsorbate on pressure by means of adsorbate-adsorbent and adsorbate-adsorbate interaction coefficients dependent on temperature. By these latter, thermodynamic standard values for monolayer coverage were calculated and compared with some recent literature values measured on free sorbent, although in a higher temperature range than that of the present study. Furthermore, from monolayer surface coverage at 298 K, areas occupied by single molecules of adsorbed species could be calculated, which indicate a relaxed conformation parallel to adsorption planes (coaxial configuration in the zeolite cavities). No difference has been found between adsorbed amounts per unit mass of sorbent in free and immobilized conditions, within the limits of experimental uncertainty; however, when adsorption was carried out from solution a small, but definite, decrease of surface area was noted. This fact points to an “ideal” behaviour of the immobilized sorbent in the membrane, particularly where gas adsorption and transport are concerned. |
