SEPARATION OF OXYGEN AND NITROGEN DUE TO THE CONTROLLED PORE-OPENING SIZE OF CHEMICAL VAPOR-DEPOSITED ZEOLITE-A

Zeolite A was modified by the CVD (chemical vapor deposition) method where silicon methoxide was deposited only on the external surface of the zeolite in order to control the pore-opening size. The chemical vapor deposited zeolite A adsorbed oxygen in preference to nitrogen because of the controlled pore-opening size. This behavior for the adsorption of oxygen and nitrogen was inverse to that usually observed on zeolite A, and separation of gas due to the molecular size was obtained. Upon deposition of silica, the rate of sorption changed, the sorption capacity being kept a constant. Suppression of sorption by the deposited silica depended upon the deposition amount. For small deposition, the degree of suppression for oxygen and nitrogen was smaller than for argon and krypton due to the smaller effective sizes, while for large deposition the former was larger than the latter, probably due to the loss of kinetical motion of diatomic molecules upon adsorption.