Preparation of a multi-membrane module for high-temperature hydrogen separation

Hydrogen permselective multi-membrane modules were prepared by simultaneously depositing silica using a counter-diffusion chemical vapor deposition (CVD) procedure. Mesoporous gamma-alumina layer prepared over alpha-alumina substrates were arranged inside a tubular casing and attached to the casing at either ends using glass sealing. Tetramethylorthosilicate and oxygen were allowed through either sides of the gamma-alumina layer at 873 K, which produced a deposit inside this layer thereby reducing the pore diameter. This module displayed an activated transport for hydrogen molecules while effectively filtered larger molecules like N2, CH4 and CO2. Hydrogen permeation values increased from 1.57×10−10 mol m−2 s−1 Pa−1 at 373 K to 4.38×10−8 mol m−2 s−1 Pa−1 at 873 K, with activation energy (Ea) of 22.92 kJ mol−1. The permeation values for N2, CH4 and CO2 molecules remained below 10−11 mol m−2 s−1 Pa−1, yielding a selectivity ratio with H2 of >2000, which indicates the superior quality of this module. The permeance values were also comparable with that obtained for single membranes prepared using a similar method. Hydrothermal stability of this module, when analyzed under membrane reactor conditions (H2O/N2 = 3; 76 kPa), was found to be stable for more than 15 h.