R. Seidel et B. Staudte, DETERIORATION OF CANAA-TYPE ZEOLITES BY HYDROTHERMAL TREATMENT AND UNDER THE CONDITIONS OF HYDROCARBON SEPARATION PROCESSES, Zeolites, 13(5), 1993, pp. 348-356
The dynamic adsorption properties of CaNaA-type zeolites are deteriora
ted after being exposed to the conditions of the hydrocarbon separatio
n process for a long period. The static adsorption properties and the
structural parameters are slightly changed, but the diffusivity of ads
orbed molecules is hindered drastically due to the origin of a surface
barrier. There are coke depositions predominantly in the surface laye
r of the zeolite crystals. The coke formation depends on the working t
ime, the composition of the mineral oil fraction, and the way the sepa
ration process is driven. We find the same microdynamical picture bein
g valid for the behavior of molecular sieves after the separation proc
ess as well as after a hydrothermal treatment: the origin of a surface
barrier. But the nature of these barriers is completely different.