Dual-layer Functional Ceramic Hollow Fibre Membranes for Partial Oxidation of Methane

Due to the unique mechanism of oxygen permeation through dense ceramic membranes with the mixed ionic-electronic conducting property, these membranes have been widely studied for oxygen separation. It has been several decades since the use of a dense ceramic membrane reactor for methane conversion was proposed. One of the major reasons for persistent worldwide research efforts to develop such dense ceramic membrane reactors is the advantages that result from combining oxygen separation and catalytic reactions within a single unit. Besides the significant progress that has been made to date, more and more effort has been directed towards the development of more stable membrane materials with higher oxygen permeation, more advanced membrane micro-structures, membrane configurations with higher surface area per unit volume and better membrane reactor designs. By improving the aforementioned membrane and membrane reactor properties, lower operating temperatures, longer life time and reduced costs can be achieved. The evolution of membrane reactor designs has progressed through a number of stages, from an initial disk-type design to flat-sheet stack or tubular designs with higher surface areas. It is not until very recently that ceramic hollow fibre membrane with further increased surface area/volume ratios of up to 3000 m2/m3 has been developed. Although there has been a consistent progress in improving membrane configurations, the way that catalyst is employed in a membrane reactor is still based on packing catalyst particles on the membrane or inside the reactor. This occupies a considerable amount of space and as a consequence the actual surface area/volume ratio of a membrane reactor design is significantly lower than that of the membrane itself. In order to develop a highly compact membrane reactor design for partial oxidation of methane (POM) with the maximum possible surface area/volume ratio, this thesis focuses on the development of a functional ceramic hollow fibre membrane with a novel dual-layer structure. The outer layer is designed for oxygen separation while the inner layer can be considered as a catalytic substrate layer. Such dual-layer ceramic hollow fibre membranes can be fabricated by a novel single-step co-extrusion and co-sintering process. This new membrane fabrication process allows for the simultaneous formation of the dual-layer membrane structure with excellent adhesion between the two layers even at high operating temperatures. Moreover, as well as changes in the compositions of the membrane material, aspects of the membrane structure, such as the thickness of the outer oxygen separation layer, can be adjusted during the co-extrusion process, in order to achieve higher oxygen permeation and subsequently better reactor performance. Although the functional dual-layer ceramic hollow fibre membranes discussed in this thesis are designed for POM, there are generic advantages of such membrane structures and the membrane fabrication process. Therefore, membranes of this type can be transferred to other membrane processes of great importance, such as oxygen separation and solid oxide fuel cells (SOFC).