Multilayer Amorphous-Si-B-C-N/γ-Al2O3/α-Al2O3 Membranes for Hydrogen Purification

The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H-2 can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single-step under high temperature conditions. In the present work, the multilayer amorphous-Si-B-C-N/gamma-Al2O3/alpha-Al2O3 membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H-2/CO permeance. The alpha-Al2O3 support has a bimodal pore-size distribution of about 0.64 and 0.045 mu m being macro porous and the intermediate gamma-Al2O3 layer deposited from boehmite colloidal dispersion-has an average pore-size of 8 nm being mesoporous. The results obtained by the N-2-adsorption method indicate a decrease in the volume of micropores-0.35 vs. 0.75 cm(3) g(-1)-and a smaller pore size -6.8 vs. 7.4 angstrom-in membranes with the intermediate meso porous gamma-Al2O3 layer if compared to those without. The three times Si-B-C-N coated multilayer membranes show higher H-2/CO permselectivities of about 10.5 and the H2 permeance of about 1.05 x 10(-8) mol mn s(-1) Pa-1. If compared to the state of the art of microporous membranes, the multilayer Si-B-C-N/gamma-Al2O3/alpha-Al2O3 membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high-temperature and high-pressure stability.