Preparation of oxygen permeable gastight disk-type perovskite membranes by dry pressing

Abstract

Mixed ionic electronic conducting (MIEC) membranes have received attention as promising materials for the separation of oxygen from air. They exhibit simultaneous ionic and electronic conductivity at elevated temperatures. This feature allows of the selective oxygen separation without the use of external circuit. An advantage of this technology comes from the integration of an oxygen separation step and a reaction step, such as partial oxidation of hydrocarbons, into one unit called a membrane reactor.

The literature part of this study introduced oxygen transport mechanisms, membrane types, and the feature of membrane preparation methods. In the experimental part, self-supported disk-type membranes were created by dry pressing method. La0.6Sr0.4Co0.2Fe0.8 (LSCF) was chosen in terms of its relatively high stability and oxygen permeability among other perovskite-type compounds. The effects of various parameters, such as pressing load, binder amount, and sintering temperature, on membrane integrity were investigated.

Commercial LSCF powder was wet milled to reduce agglomeration. Subsequently, some of the milled powder was mixed with polyvinyl alcohol (PVA) organic binder (from 1.2 wt.% to 3.6 wt.%) and sieved to obtain granules with their sizes below 200 μm. Unlike fragile green disks obtained from non-treated powder, mechanically strong green disks were obtained from the binder added power. A dense disk (thickness: 0.90 mm, diameter: 17.18 mm) with a bulk density of 6.02 g/cm3 was obtained by sintering a green disk containing 1.2 wt.% of PVA at 1100 °C for 1 h in air. No visible defects were observed from the disk. By contrast, green bodies containing a larger amount of binder were easily cracked during sintering.

In the final stage, the gas-tightness of sintered disks was investigated by nitrogen pressure test and leakage test using BID-GC. The system maintained the pressure for a similar amount of time compared to a system used a commercial gastight quartz disk, and only a trace amount of nitrogen was leaked. However, better sealing is required especially to satisfy the requirement of high temperature condition (ca. 950 °C).