Adsorption of n-Alkanes in MFI and MEL: Quasi-Equilibrated Thermodesorption Combined with Molecular Simulations

Adsorption of n-alkanes on high silica MFI and MEL zeolites was studied by means of experimental quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA) and Monte Carlo simulations. An unusual, isobaric approach to adsorption measurements and simulations was applied. Good agreement between the experimental and calculated data observed for MFI indicates that the QE-TPDA is a reliable method for studying porosity-related adsorptive properties of molecular sieves. The calculated average occupation profiles confirmed limited mobility of hexane and heptane molecules adsorbed in the sinusoidal channels on the MFI, thus proving the concept of order-disorder phase transition postulated in explanation of the two-step desorption profiles of these alkanes observed for MFI zeolites. Partial agreement of the calculated isobars with the experimental data found for zeolite MEL indicated that adsorption of n-alkanes in this structure is more complex than assumed in the simulation model. However, two-step desorption profiles and immobilization of the molecules adsorbed in the straight channels of the MEL structure were also found for hexane. (Graph Presented).