ADSORPTION OF P-XYLENE M-XYLENE GAS-MIXTURES ON BAY AND NAY ZEOLITES - COADSORPTION EQUILIBRIA AND SELECTIVITIES/

Coadsorption of the gases p-xylene and m-xylene on BaY and NaY was stu died at 150 degrees C in the range of pressure 10(-2)-3 hPa. For BaY c oadsorption isotherms and single-component adsorption isotherms are pe rfectly superimposed in the whole range of investigated pressure. The capacity of adsorption of BaY is 3 molecules alpha(-1) for each single component as well as for each mixture under 3 hPa. For NaY coadsorpti on isotherms lie between those of single p-xylene and m-xylene. The ca pacity of adsorption of NaY for mixtures is in proportion to the compo sition of the initial adsorptive mixture and varies from the capacity of adsorption for single p-xylene (3.3 molecules alpha(-1)) to that fo r single m-xylene (3.6 molecules alpha(-1)) under 3 hPa. The selectivi ty of the Y zeolite depends on the filling, the composition of the mix ture, and the exchangeable cation. Two selective adsorption processes are discerned according to the filling of a-cages. For filling lower t han 2 molecules alpha(-1), BaY and NaY exhibit the same behavior towar d the coadsorption of p-xylene and m-xylene and adsorb preferentially the more abundant isomer in initial adsorptive mixture: the selectivit y depends only on the composition of the mixture. For filling higher t han 2 molecules alpha(-1) as the last molecules of xylenes are adsorbe d in the alpha-cages, BaY is selective for p-xylene whereas NaY is sel ective for m-xylene whatever the composition of the adsorptive mixture : the selectivity depends on the exchangeable cation. The dependence o f the composition of adsorbate on the selectivity shows a nonideal beh avior of the adsorbate.