Direct crystallisation of a hydroxy sodalite membrane without seeding using a conventional oven

A double layered hydroxy sodalite membrane was synthesised directly onto a tubular α-alumina support without seeding using a conventional hot-air oven. The effect of different synthesis parameters including the water content, ageing period, synthesis time and temperature, on the purity and continuity of the membrane was investigated. The water content was an important factor in controlling the presence of contaminating zeolite phases in the membrane. The optimised membrane which was contaminant free was characterised by XRD, SEM and single gas permeation using He, N2 and SF6. The permeance of the three gases through the membrane ranged from 0.8 to 8 × 10−8 mol m−2 s−1 Pa−1. The selectivity (α = 2.5–2.7) compared well to the Knudsen diffusion ratio for He/N2.