CHEMICAL DIFFUSION AND HYDROGEN SEPARATION PROPERTIES OF LANTHENUM FERRITE AND DOPED CERIA COMPOSITE MIXED CONDUCTORS

摘要

A new method to separate hydrogen using dual phase composite mixed ionic and electronic conducting (MIEC) membranes has been proposed and is being currently investigated. In this approach methane or reformate comprising CO and H{sub}2 mixtures is fed to one side of the membrane, while steam is fed to the other side. Oxygen from the steam side of the membrane transports through coupled transport of oxygen ions and electrons across the membrane to the methane/reformate side resulting in a hydrogen rich product on the permeate side. This process requires MIEC materials that are stable, have significantly high surface exchange constant, and oxygen ion and electron conductivities at low oxygen partial pressures. Measurements made on MEECs such as strontium or calcium doped lanthanum cobalt iron oxides (LSCF and LCF) indicate that they are not stable. Transport properties, phase stability and surface exchange reaction rate measurements made on new dual phase membranes consisting of doped ceria and doped strontium titanate indicate that they are suitable for the permeation process.