Influence of desorption conditions before gas separation studies in nanocomposite MFI–alumina membranes

The gas permeation and separation performance of polycrystalline MFI-type zeolite membranes is strongly dependent on the number and type of intercrystalline pores in its structure. Herein we show that the role of such domains is affected by how a membrane is pre-treated before use to remove adsorbed species (e.g. moisture and organics). This ‘pre-treatment’ step appears to be crucial not only to obtain reliable permeation data, but also to improve the membrane separation performance in practical applications. We illustrate this idea by using a collection of tubular nanocomposite MFI–alumina membranes showing different quality for the separation of n-butane/H2 mixtures and submitted to different pre-treatment protocols. The influence of each protocol on the final separation performance of the membranes depends on their quality, namely on the density of intercrystalline defects or non-zeolite pores in their structure. Moreover the quality of the support affects the final membrane performance.