Application of a Pd–Ru composite membrane to hydrogen production in a high temperature membrane reactor

Abstract

In this work, a ∼5.0μm thick Pd–Ru membrane (area∼13.3cm2), supported on a porous yttria-stabilized-zirconia/stainless steel substrate (ZrOD AccuSep®, Pall Corp.) was used to carry out steam methane reforming (SMR) over a commercial Ni-based reforming catalyst at a temperature of ∼580°C and pressures up to 2.9MPa. Methane conversions in the membrane reactor ranged from 65 to over 80%, depending on the reactor’s space velocity. The conversions obtained were significantly higher than the thermodynamic equilibrium predicted for the feed composition and process variables. The effect of parameters such as space velocity and reactor pressure on methane conversion and hydrogen recovery were investigated.The long term operation on this membrane revealed the potential suitability of this Pd-alloy to be a candidate for use in SMR membrane reactors at temperature as high as 580°C. The permeate hydrogen flux was very stable at 580°C, 2.9MPa feed pressure, and a steam-to-carbon ratio (SCR) of 3 for more than 1000h of continuous testing. The hydrogen permeate purity remained >93% over the course of testing. Stable methane conversions as high as ∼80% were obtained for the duration of the long term test which may be further improved by optimizing the fluid mechanics of the reactor design or geometry. 1-Dimensional process simulations were carried out and the results suggested that the methane conversion and hydrogen flux during the membrane reactor experiments were reduced by gas phase mass transfer due to concentration polarization effects. Ongoing work will focus on further optimization and testing of scaled-up Pd–Ru membranes in SMR reactor environments.