Hydrogen permeation characteristics and stability of Ni-doped silica membranes in steam at high temperature

Ni-doped porous silica membranes of various Ni contents (Si/Ni =4/1-1/1) were prepared by the sol-gel techniques for separation of H-2 at high temperature around 500 degrees C. H-2-selective permeation characteristics and hydrothermal stability of the membranes were tested in steam at 500 degrees C to show that hydrothermal treatments of the membranes before exposed to H-2 were quite effective to prevent the further densification of Ni-doped amorphous silica networks due to reduction in H-2 and sintering in steam (500 degrees C, 70 kPa). Ni-doped silica membranes (Si/Ni = 2/1) fired in the steamed atmosphere (partial pressure: 90 kPa) at 650 degrees C, for examples, were found to show a asymptotic steady permeance of 1.6 x 10(-5) (m(3)(STP) m(-2) s(-1) kPa(-1)) for He and 4.6 x 10(-6) (m(3)(STP) m(-2) s(-1) kPa(-1)) for H-2 with a high selectivity of 1450 (He/N-2) and 400 (H-2/N-2) even after kept in steam (steam: 90 kPa) at 500 degrees C for about 6 days. The permeance ratio of H-2/H2O was found to be dependent not only on the permeance ratio of He/H-2 but also on the Ni content, and the maximum permeance ratio observed was 37 for a Ni-doped silica membrane (Si/Ni = 1/1). (c) 2005 Elsevier B.V. All rights reserved.