Adsorption of branched alkanes in silicalite-1: A temperature-programmed-equilibration study

The adsorption properties of several branched paraffins from C-4 to C-6 on MFI type zeolite were investigated. A temperature-programmed-equilibration method was used for this study, and the analysis of the desorption rates as a function of temperature showed two desorption peaks. The interpretation of this phenomenon is discussed, and it is revealed that the high-temperatu re desorption occurs in conditions close to equilibrium while low-temperatu re desorption is subject to diffusional limitations. Furthermore, an XRD st udy shows that the phase transition in the crystal structure can be lowered by 70 K when 3-methylpentane is adsorbed. This property shows that the low -temperature desorption peak is not due to a change of symmetry in the stru cture of the zeolite. Modeling of the high-temperature peak provided adsorp tion isosteric enthalpy and entropy variations. These values are consistent with literature data. For the first time, adsorption isosteric entropy var iations of sorption are calculated for branched alkanes in silicalite-1.