Dual-layer Functional Ceramic Hollow Fibre Membranes for Partial Oxidation of Methane
Author(s)
Wu, Zhentao
Type
Thesis
Abstract
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).
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).
Date Issued
2012-03
Date Awarded
2012-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
License URL
Advisor
Li, Kang
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)