Pervaporation and related properties of time-dependent growth layers of zeolite NaA on structured ceramic supports

A fundamental description is given on the H2O/EtOH pervaporation behaviour of morphologically different layers of zeolite NaA. Five unique NaA layers were prepared under similar conditions (Na2O:Al2O3:SiO2:H2O = 49:1:5:980; 85 °C), but varying crystallisation times (2.0–4.0 h). Selected layers were also synthesised on two structurally different Al2O3 supports, to investigate the role of the support microstructure and its resistance to mass flow. The separation performance of the layers on the first support (Φpore = 163 nm), was compared using a 95 wt.% EtOH feed at 45 °C. The selectivity of the semicrystalline 2.0 h layer (αW/E = 9000) compared well to that of the fully crystalline 4.0 h layer (αW/E = 8300), suggesting that the occlusion of amorphous material in the initial layers could possibly promote membrane selectivity, even though the polycrystalline component is not fully intergrown. In the type 2 layers the overall selectivity values (especially for the 2.0 h layer) were lower than for the type 1 membranes, which was attributed to the accentuated dissolution of the type 2 supports during synthesis. The fluxes through each series of membranes on a specific support remained constant, showing considerable resistances by both supports, with relative contributions of ∼60% and ∼70% to the total permeation resistance.