NaX-zeolite coatings on highly porous metal fibre substrates

Abstract Syntheses of NaX-coatings on highly porous stainless steel fibre substrates were carried out via direct zeolite crystallization. Both the nucleation as well as the following crystal growth took place in situ at the metal fibre bodies. The NaX-zeolite is able to adsorb nitrogen in large quantities and thus to enrich ambient air with oxygen. The advantage of the used substrates is their large pore volume of up to 90%, which was important, in order to achieve a maximum zeolite/substrate proportion. The aim was to close the cavities of the fibre bodies almost completely, that means up to an optimal degree, with zeolite in order to get a maximum N 2 -adsorptivity. A certain amount of free accessible pore volume is necessary in order to assure a free exchange of the gases. A better oxygen yield in a pressure swing adsorption unit for the new molecular sieves than for a comparable container volume of commercial NaX-granulates was expected. Therefore the properties of the metal fibre bodies had to be adapted and an appropriate procedure for the zeolite synthesis had to be developed. In addition the N 2 -adsorption behaviour of the zeolite coated fibre bodies was measured. As a result NaX-zeolite coated stainless steel fibre bodies, whose zeolite portion is almost equal to that of commercial NaX-zeolite granulates, could be manufactured. They showed a slightly better N 2 -adsorptivity in comparison to commercial NaX-zeolite granulates. Moreover, there are still vacancies within the highly porous metal fibre substrates so that a further increase of the zeolite portion and with this of the N 2 -adsorptivity seems to be achievable. The easier handling of the compact metal fibre bodies in the adsorption units compared to the commercial granulates is another advantage.