Liu, Wendy (Yulian) (PhD)

project title: Development of thin supported membranes for selective oxygen transportation

PhD student: Yuliang (Wendy) Liu

Brief description of the project

Oxygen is a key requirement in many industrial processes. Most of the commercial oxygen is produced by cryogenic and pressure swing adsorption, which are commonly recognised as energy intensive and expensive technologies. Obtaining high purity oxygen with low cost is always a popular topic. As an alternative technology, ceramic membranes made from mixed oxygen-ionic and electronic conducting (MIEC) perovskite oxides are attracting a lot of interest. These membranes operate at high temperatures (700–900 ) permeating 100% pure oxygen directly from air eliminating the need for expensive conventional oxygen separation techniques. In principle this membrane technology can also be integrated in some oxygen consuming reactors, thus performing the oxygen separation and catalytic process in a single step. Favourable MIEC membranes are expected to provide high oxygen permeation flux and good chemical/mechanical stability.

In order to increase the oxygen permeability, thin film membranes must be fabricated. However thin membranes usually feature insufficient mechanical strength. To optimise the oxygen permeation flux across a MIEC material, asymmetric membrane architecture composed of a porous support and a thin dense oxygen selective layer was developed. This structure can help to reduce bulk diffusion coefficient for the oxygen transport process by decreasing thickness of the selective layer without sacrificing mechanical stability of the membrane.

There have been a number of activities around the world to prepare perovskite thin films on porous substrates, but the majority of these efforts have not yielded good results. The main problem comes from incompatibility of the material for different layers of the membrane. For example, shrinkage mismatch between the connected two layers during the sintering process may result in defects and cracks in the membrane layer. Selection of suitable material and optimization of the processing condition is of great importance for the successful preparation of supported membranes.

For development of the project, a combination of some key points must be studied. An extensive review of literatures about the conduction mechanism, different membrane and support material and fabrication method for the supported MIEC membranes would provide good basis for the process. Different material will be tried for each layer of the membrane. By optimizing the processing condition, defects of the membrane layer could be minimized. Besides, by comparing the performance of the fabricated membranes, suitable material would be chosen. By surface modification, oxygen permeability and chemical stability of the membrane could be improved. A list of objectives is represented below.

Objectives

  1. Optimization of processing conditions for different MIEC oxides to minimize defects.

  2. Membrane performance tests and selection of optimal membrane materials.

  3. Modification of the surface of the fabricated membranes to improve oxygen permeability and chemical stability

  4. Oxygen transport mechanism study and modelling of the oxygen permeation through supported and coated MIEC membranes.