Selectivity of thiophene/toluene competitive adsorptions onto NaY and NaX zeolites

In the framework of research on desulfurization by adsorption, an experimental study of the adsorption selectivity between thiophene and toluene molecules in liquid n-heptane solutions onto NaY (Si/Al = 2.4) and NaX (Si/Al = 1.2) zeolites has been carried out. It investigates the possibility for these commercially available adsorbents to be used in a desulfurization process operated under ambient conditions without using H-2. Dynamic adsorption experiments were performed at room temperature mainly at two concentration ranges: 25 mmol, L-1 for competitive adsorptions and 1.25 mmol, L-1 for single-solute experiments. Adsorption isotherms of thiophene and toluene on NaY and NaX sorbents have been obtained. On the NaY zeolite, toluene is favorably adsorbed (alpha(thio/tol) = 0.60) while an inverse behavior is observed with NaX sorbent (alpha(thio/tol) = 1.63). This exhibits many differences in sorbate/sorbent interactions with slight changes in the adsorbent nature. Besides, the selectivity on NaY sorbents has been found to depend significantly on the concentration range. Such a phenomenon agrees with the fact that the sorbates' adsorption over NaY zeolites cannot be described by a simple Langmuir model. Thiophene adsorption onto NaY undergoes a peculiar phenomenon, since its isotherm exhibits an inflection at a coverage of 1 molecule per alpha-cage.