Adsorption and diffusion of alkanes and their mixtures in silicalite studied with positron emission profiling technique

The Tracer-Exchange Positron Emission Profiling (TEX-PEP) technique has been applied for in-situ measurement of the adsorption and diffusion of hexane and 2-methylpentane mixts. in large crystallite (150mm) of silicalite-1 at 160°C under steady-state conditions. N-hexane adsorption is slightly preferred. Mobility of n-hexane strongly decreases with increasing fraction of 2-methylpentane, and it suddenly drops when the pore occupation with 2-methylpentane is much bigger then with n-hexane. A small decrease in the diffusivity of 2-methylpentane is also obsd. Pulse expts. were performed to measure isotherms of adsorption of 3-methylpentane on silicalite-1 at temps. 130-210°C. Obtained values of enthalpy and entropy of adsorption are in a good agreement with theor. calcns