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)

Effects of separation layer thickness on oxygen permeation and mechanical strength of DL-HFMR-ScSZ

It has been demonstrated in our previous studies that in order for greater methane conversion and less coke-formation, a higher oxygen permeation rate through the outer oxygen separation layer of a functional dual-layer ceramic hollow fibre membrane is needed. Besides new membrane materials with higher oxygen permeability, another way of improving oxygen permeation is to reduce the separation layer thickness, although this strategy is limited by the characteristic thickness, L c, where bulk diffusion and surface oxygen exchange are both important. As a result, a series of La 0.80Sr 0.20MnO 3-δ (LSM)-Scandia(10%)-Stabilized-Zirconia (ScSZ)/ScSZ-NiO functional dual-layer hollow fibres (DL-HF) with an outer oxygen separation layer thickness between approximately 8.0 and 72.4μm were fabricated in this study, by using the single-step co-extrusion and co-sintering process. The effects of separation layer thickness on oxygen permeation and mechanical strength were investigated. The oxygen permeation of the LSM-ScSZ separation layer is more likely to be controlled by surface exchange at higher temperatures, and changes to mixed control by both bulk diffusion and surface exchange at lower temperatures. A thicker separation layer also results in a thinner catalytic substrate layer, and subsequently decreases the mechanical strength of the dual-layer hollow fibre membrane

Use of a ceramic membrane to improve the performance of two-separate-phase biocatalytic membrane reactor

Biocatalytic membrane reactors (BMR) combining reaction and separation within the same unit have many advantages over conventional reactor designs. Ceramic membranes are an attractive alternative to polymeric membranes in membrane biotechnology due to their high chemical, thermal and mechanical resistance. Another important use is their potential application in a biphasic membrane system, where support solvent resistance is highly needed. In this work, the preparation of asymmetric ceramic hollow fibre membranes and their use in a two-separate-phase biocatalytic membrane reactor will be described. The asymmetric ceramic hollow fibre membranes were prepared using a combined phase inversion and sintering technique. The prepared fibres were then used as support for lipase covalent immobilization in order to develop a two-separate-phase biocatalytic membrane reactor. A functionalization method was proposed in order to increase the density of the reactive hydroxyl groups on the surface of ceramic membranes, which were then amino-activated and treated with a crosslinker. The performance and the stability of the immobilized lipase were investigated as a function of the amount of the immobilized biocatalytst. Results showed that it is possible to immobilize lipase on a ceramic membrane without altering its catalytic performance (initial residual specific activity 93%), which remains constant after 6 reaction cycles

A new hollow fibre catalytic converter design for sustainable automotive emissions control

State-of-the-art catalytic converters need an ever-high amount of precious-metal catalysts to meet stringent emission regulations. This research reveals an alternative design based on micro-structured ceramic hollow fibre substrates, yielding high conversion of pollutants at low catalyst costs, as well as a unique benefit of low pressure-drop, leading to high engine performances

Multi-View Vertebra Localization and Identification from CT Images

Accurately localizing and identifying vertebrae from CT images is crucial for various clinical applications. However, most existing efforts are performed on 3D with cropping patch operation, suffering from the large computation costs and limited global information. In this paper, we propose a multi-view vertebra localization and identification from CT images, converting the 3D problem into a 2D localization and identification task on different views. Without the limitation of the 3D cropped patch, our method can learn the multi-view global information naturally. Moreover, to better capture the anatomical structure information from different view perspectives, a multi-view contrastive learning strategy is developed to pre-train the backbone. Additionally, we further propose a Sequence Loss to maintain the sequential structure embedded along the vertebrae. Evaluation results demonstrate that, with only two 2D networks, our method can localize and identify vertebrae in CT images accurately, and outperforms the state-of-the-art methods consistently. Our code is available at https://github.com/ShanghaiTech-IMPACT/Multi-View-Vertebra-Localization-and-Identification-from-CT-Images.Comment: MICCAI 202

Producing carbon nanotubes from thermochemical conversion of waste plastics using Ni/ceramic based catalyst

As the amount of waste plastic increases, thermo-chemical conversion of plastics provides an economic flexible and environmental friendly method to manage recycled plastics, and generate valuable materials, such as carbon nanotubes (CNTs). The choice of catalysts and reaction parameters are critical to improving the quantity and quality of CNTs production. In this study, a ceramic membrane catalyst (Ni/Al2O3) was studied to control the CNTs growth, with reaction parameters, including catalytic temperature and Ni content investigated. A fixed two-stage reactor was used for thermal pyrolysis of plastic waste, with the resulting CNTs characterized by various techniques including scanning electronic microscopy (SEM), transmitted electronic microscopy (TEM), temperature programmed oxidation (TPO), and X-ray diffraction (XRD). It is observed that different loadings of Ni resulted in the formation of metal particles with various sizes, which in turn governs CNTs production with varying degrees of quantity and quality, with an optimal catalytic temperature at 700 °C

X-ray tomography-assisted study of a phase inversion process in ceramic hollow fiber systems – Towards practical structural design

Phase inversion-assisted extrusion processes provide a feasible approach for the development of micro-structured ceramic hollow fibers. The mass transport of the hollow fiber, which is closely correlated to the pore structure, is especially important in the application of fuel cell electrodes and membrane reactors. Whilst the relationship between the pore microstructure and the fabrication factors has been the subject of significant investigations, there remains much disagreement in the literature. Recent development in X-ray computed tomography (CT) has enabled new insight into 3D microstructures, which could help to realize practical morphology design and optimization. In this study, a series of alumina hollow fibers have been prepared with varied polymer binder (polyethersulfone, PESf) concentration and new polymer-based internal coagulant (aqueous solution of polyvinyl alcohol, PVA). For the first time, the micro-channels were characterized in 3D using X-ray CT to determine micro-channel densities and diameters in the radial direction, as well as the 2D measurement of the pore size in the sponge-like layer. Water permeation tests were then conducted to correlate the micro-structure of the hollow fiber to the permeability. Results show that the diameter of the micro-channels decreases as the concentration of polymer binder increases, but the pore size in the spongy-like layer becomes larger. When the polymer binder concentration is increased from 16 wt% to 30 wt%, the maximum micro-channel diameter is almost halved (from 29 to 15 µm), and the radial length is 60% longer, whereas the mean flow pore size in the sponge-like layer is increased from approximately 288 to 422 nm. Larger pore size in the spongy-like layer of the high PVA concentration sample contributes to a better permeability (pure water flux almost doubled), but the dimension of the micro-channels is less important. This study provides a new approach to optimize fabrication of hollow fibers for various applications

An Integrated Visual Analytics System for Studying Clinical Carotid Artery Plaques

Carotid artery plaques can cause arterial vascular diseases such as stroke and myocardial infarction, posing a severe threat to human life. However, the current clinical examination mainly relies on a direct assessment by physicians of patients' clinical indicators and medical images, lacking an integrated visualization tool for analyzing the influencing factors and composition of carotid artery plaques. We have designed an intelligent carotid artery plaque visual analysis system for vascular surgery experts to comprehensively analyze the clinical physiological and imaging indicators of carotid artery diseases. The system mainly includes two functions: First, it displays the correlation between carotid artery plaque and various factors through a series of information visualization methods and integrates the analysis of patient physiological indicator data. Second, it enhances the interface guidance analysis of the inherent correlation between the components of carotid artery plaque through machine learning and displays the spatial distribution of the plaque on medical images. Additionally, we conducted two case studies on carotid artery plaques using real data obtained from a hospital, and the results indicate that our designed carotid analysis system can effectively provide clinical diagnosis and treatment guidance for vascular surgeons