Influence of Si:Al-ratio of faujasites on the adsorption of alkanes, alkenes and aromatics

Abstract The influence of Si:Al-ratio on the adsorption of alkanes, alkenes and aromatics was determined in gas and liquid phase; i.e. at low and high degree of pore filling. In gas phase the pulse chromatographic method was used to determine the interaction of pure C 6 –C 8 n -alkanes and benzene at 180–420 °C on NaX (Si:Al 1.23) and NaY (Si:Al 2.55). In agreement with the cation contents, higher Henry constants and enthalpies were measured on NaX compared to NaY for all components. To study the adsorption of alkane/alkene/aromatic mixtures at room temperature in liquid phase a batch technique was used. Binary adsorption isotherms of hexene, octene and dodecene in heptane and benzene in octane were determined on NaX (Si:Al 1.23) and NaY (Si:Al 2.79). The adsorption of benzene, toluene, m -xylene and mesitylene from their mixture with octene was studied on NaLSX (Si:Al 1.02), NaX (Si:Al 1.23) and NaY (Si:Al 2.79). All binary adsorption isotherms in liquid phase could be very well fitted with a multicomponent Langmuir–Freundlich adsorption isotherm model. In liquid phase conditions alkenes are preferentially adsorbed on NaX compared to NaY, while aromatics are unexpectedly more selectively adsorbed on NaY than on NaX. At high degree of pore filling arrangement of the molecules in the supercages largely affects the selectivity. SIII/SIII′ cations affect the position of aromatics adsorbed on SII cations or benzene adsorbed in the 12 Membered Ring-window, which causes a more restricted packing inside the supercages of NaX compared to NaY lacking these SIII/SIII′ cations.