Determination of the adsorption heat of n-hexane and n-heptane on zeolites beta, L, 5A, 13X, Y and ZSM-5 by means of quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA)

Abstract

Measurements of temperature-programmed desorption and adsorption of n-hexane and n-heptane under quasi-equilibrium conditions (QE-TPDA) were performed for several zeolites in TPD apparatus equipped with a TCD detector. One-step adsorption profiles for zeolites X and Y and two-step adsorption profiles for beta, L, 5A and ZSM-5 were observed. Approximate adsorption isobars calculated from the QE-TPDA profiles did not depend on the heating/cooling rate, proving equilibrium control of the adsorption degree. Values of the adsorption enthalpy and entropy, computed by fitting the Langmuir or dual site Langmuir model functions to the temperature derivatives of the experimental adsorption isotherms, were in agreement with the literature data. New method for determination of the initial (zero coverage) adsorption heat by fitting the linearized Henry function to the transformed high temperature experimental data was proposed. Values of the initial adsorption heat were close to those obtained using the inverse gas chromatography infinite dilution method.