Thermogravimetric studies of the equilibrated thermodesorption of n-alkanes from selected zeolites

摘要

Desorption isobars of n-hexane and n-heptane were obtained for zeolites Y,ZSM-5,HZSM-11,HFER,NaX and HMOR in thermogravimetric measurements of temperature programmed desorption under quasi-equilibrium conditions.Temperature derivatives of the isobars exhibit one main minimum for Y and X,two separate minima for ZSM-5 and ZSM-11,and two overlapping minima for HFER.Fitting these results with functions based on the Langmuir adsorption model gave the adsorption enthalpy and entropy values that are in agreement with the available literature data.The thermodesorption profiles are closely related to the micropore structure of the zeolites.Two minima observed in the thermodesorption profiles for ZSM-5 and ZSM-11 were attributed to ordering of the adsorbed molecules in the zeolite channels (the "commensurate freezing" effect).