Team Oxygen-Permeable Membranes
Oxygen Permeable Membranes
Oxygen transport membranes (OTM) provide an efficient way to separate oxygen from air at elevated temperatures, i.e. 500 – 900 °C. It is possible to either generate pure oxygen for any purpose, e.g. combustion processes, metallurgy, or medical applications, or to utilize the separated oxygen directly in chemical reactions such as partial oxidation of hydrocarbons to produce commodity chemicals.
OTM materials are ceramics showing mixed ionic-electronic conductivity (MIEC). The separation process does not consume any energy, making it very efficient. However, temperatures above 500 °C are necessary to realize fast ion diffusion. The selection of a suitable material depends highly on the operation conditions (particularly temperature, pressure and atmosphere), which are defined by the targeted application. IEK-1 thus established a materials tool box. Perovskite-type oxides often show MIEC behaviour (e.g. La1-xSrxCo1-yFeyO3-δ or SrTi1-xFexO3-δ ). But the transport process relies on crystal defects creating a trade-off between permeability and stability. Therefore, composite materials composed of a pure ionic (e.g. Ce0.8Gd0.2O2-δ ) and a pure electronic conductor (e.g. FeCo2O4) are also under investigation, enabling the use of inherently stable material combinations.
Optimized membranes should be as thin as possible, requiring a mechanically stable support with sufficient porosity in order to enable oxygen feed to the thin membrane layer. Ideally, fine porous surface activation layers at both sides of the membrane facilitate oxygen surface exchange. For this purpose, IEK-1 relies on ceramic manufacturing technology suitable for mass production, particularly tape casting and screen printing, complemented by modelling efforts. In addition, novel processing technologies such as freeze casting and 3D-printing are being explored. A novel thermal spray technology has been developed for the coating of OTM on robust metallic supports, which is exceedingly challenging.