Synthesis and characterization of FAU membranes

Abstract: Zeolites are crystalline aluminosilicates with molecular sieving properties
and are commonly used in applications such as catalysis, adsorbtion or ion
exchange. Zeolite membranes are industrially interesting due to the ability
to separate chemical compounds in continuous processes under severe
conditions. Zeolite membranes have well-defined pore size suitable for many
applications and high thermal and chemical stability. Zeolite membranes must
be thin in order to obtain a high flux and defect-free to achieve high
selectivity.

In this work, zeolite membranes of FAU type were prepared. The hydrophilic
behavior of this kind of zeolites is used
to separate polar compounds by preferential adsorption. FAU-type films with
a thickness of 0.5 µm was grown on porous alumina using a seeding method. No
organic template molecules were used during
the synthesis of the membranes, avoiding the calcination procedure that can
induce the formation of cracks. The membranes were characterized with
scanning electron microscopy, x-ray diffraction, porosimetry and separation
experiments.

The objective of this work is to obtain thin and virtually defect-free films
by using a clear synthesis solution. The synthesis conditions were modified
to study its influence on the separation performance of the membranes.
Single and dual seeding procedures were investigated in order to obtain a
dense seeded surface. It was found that a single seeding was sufficient to
obtain a dense layer of seeds. The influence of the synthesis solution
composition on the quality and growth of the FAU films was also
investigated. The thermal stability of FAU membranes was studied. It was
demonstrated that high drying temperatures do not reduce the membrane
quality. Several rinsing procedures for the prepared membranes were also
investigated. It was found that a larger amount of defects formed during
longer time of rinsing procedures. The CO2 selectivity of binary CO2/CH4
mixtures was also improved by ion exchanging the zeolite films with K+ ions.

Confidential until 2010-08-08