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

Abstract

AbstractThe hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H2 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/γ‐Al2O3/α‐Al2O3 membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H2/CO permeance. The α‐Al2O3 support has a bimodal pore‐size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate γ‐Al2O3 layer—deposited from boehmite colloidal dispersion—has an average pore‐size of 8 nm being mesoporous. The results obtained by the N2‐adsorption method indicate a decrease in the volume of micropores—0.35 vs. 0.75 cm3 g−1—and a smaller pore size −6.8 vs. 7.4 Å—in membranes with the intermediate mesoporous γ‐Al2O3 layer if compared to those without. The three times Si‐B‐C‐N coated multilayer membranes show higher H2/CO permselectivities of about 10.5 and the H2 permeance of about 1.05 × 10−8 mol m−2 s−1 Pa−1. If compared to the state of the art of microporous membranes, the multilayer Si‐B‐C‐N/γ‐Al2O3/α‐Al2O3 membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high‐temperature and high‐pressure stability.