Lack of homogeneity of particle size in deposition techniques.
Some pores exist that are larger than the zeolite pores.
Zeolite molecular sieve membranes are thin films of a porous crystalline material with pore sizes similar to the size of small molecules. The membranes can be used to separate molecules that cannot enter the pores or move through the pores slowly from molecules that can enter and move through the pores more quickly. Only a small number of zeolites can presently be formed into films and therefore the number of potential separations with unmodified films is limited. The molecular layers apparently block imperfections in the membranes or alter the accessibility of the zeolite pores by attaching close to the pore openings or inside the pores. The change in separation properties is strongly dependent on the deposited compounds, which offers the opportunity for fine-tuning separation properties.