Long-chain paraffins adsorption over 5A zeolites

Abstract

The nature and extent of adsorption in a zeolite depends on the size, shape as well as the interaction of the adsorbate molecules with the zeolite. Adsorption properties of 5A zeolite are known to be strongly correlated to the nature and amount of cations in the structure [1, 2]. Cations in zeolites act as adsorption sites for adsorbate molecules and influence the average electronegativity of the zeolite framework. In addition, the shape selectivity of zeolites, i.e. the free diameters of their pore and cages, strongly depend on the distribution of cations in the zeolite lattice. The aim of this work is first to point out differences in adsorption properties due to ion exchange and thermal treatment. Thermal desorption, an established method for elucidating the nature of these interactions, is used to characterise the adsorption behaviour for the different zeolites. TPD of n-paraffins on 5A zeolite samples shows strong modifications in DTg curves with the calcium exchange ratio or thermal treatment. Rietveld refinements carried out on anomalous, diffraction data allow to determine the Ca/Na cations distribution over the different potential crystallographic sites of these samples.