Hydrogen recovery using hollow fiber membranes in the ammonia cracking process

Abstract

This study investigates the separation performance of various hollow fiber membranes (HFMs) for hydrogen (H₂) recovery from ammonia (NH₃) cracking processes. Oxide-based (γ-Al₂O₃ and SiO₂) and metal-based (Pd and Pd–Ag–Cu) thin films were deposited on α-Al₂O₃ HFM supports and exposed to H₂, N₂ and trace of NH₃ gas at 450 °C and 0.5–2.0 bar. The separation factor was defined as the ratio of the H₂ permeate flow rate to the N₂ permeate flow rate (α H₂/N₂) and to the NH₃ permeate flow rate (α H₂/NH₃). Results show that Pd-based HFMs have better H₂ selectivity than oxide-based HFMs. The Pd–Ag–Cu/α-Al₂O₃ HFM had the highest H₂-to-NH₃ selectivity with a α H₂/NH₃ separation factor of 1.4 10⁴ over the tested pressure range. Pressure dependence varied among HFM types, metal-based HFMs showed increased H₂ selectivity at higher pressures. These results have big implications for developing advanced membrane-based gas-gas separation processes for H₂ purification in proton exchange membrane (PEM) fuel cell (FC) applications. Pd-alloy HFMs, especially Pd–Ag–Cu, are shown to be good for high-selectivity H₂ separation from NH₃ cracking products.