Development of Dense Cermet Membranes for Hydrogen Separation

The Office of Fossil Energy (FE) at the U.S. Department of Energy (DOE) sponsors a wide range of research, development, and demonstration programs to maximize the use of the vast domestic fossil resources and to ensure a fuel-diverse energy sector while responding to global environmental concerns. Cost-effective, membrane-based reactor and separation technologies are of considerable interest to the DOE’s program to develop advanced coal-based power and fuel technologies.  Membrane separation units that can selectively permeate H₂ and retain CO₂ at elevated pressures are promising for pre-combustion CO₂-capture in integrated gasification combined cycle (IGCC) plants.  Supported by DOE’s FE, Argonne National Laboratory (Argonne) is developing dense cermet (i.e., ceramic-metal composite) membranes for separating hydrogen from mixed gases, particularly product streams generated during coal gasification and/or methane reforming.  Hydrogen separation with Argonne's HTMs yields high-purity hydrogen, thereby eliminating the need for post-separation purification steps.

Our project aims to identify materials with suitable hydrogen permeability and develop methods for fabricating thin, dense membranes from such materials. Extensive tests have been conducted with HTMs made by mixing ≈50 vol.% Pd with Y₂O₃-stabilized ZrO₂.  Using several feed gas mixtures, we measured the hydrogen permeation rate, or flux, for the membranes in the temperature range 400-600°C. With 90% H₂/balance He at ambient pressure as feed gas, an ≈20-μm-thick membrane on a porous substrate gave a measured flux of ≈26 cm³[STP]/min-cm² at 400°C and ≈32 cm³[STP]/min-cm² at 500°C. We also measured the hydrogen flux through a thicker (≈150 µm) membrane at 400°C using a mixture of H₂, CO, CO₂, H₂O, and He at ≈200 psig as feed gas. Because good chemical stability is critical for HTMs, due to the corrosive nature of product streams from coal gasification, we evaluated the effect of various contaminants on the chemical stability of membranes. Our membranes were found to withstand cycling of temperature and hydrogen concentration in the feed gas without exhibiting significant changes in microstructure or performance. Long-term (≈4-months) flux measurements showed that the membranes are stable at ≤500°C in wet simulated syngas mixture.  The present status of membrane development at Argonne and the challenges involved in bringing this technology to fruition will be presented in this talk.