Dissertations / Theses on the topic 'Oxygen separator'

This thesis describes a novel microchanneled membrane that was fabricated using a mesh-templating phase inversion process. The microchanneled membrane showed remarkable oxygen flux, good mechanical strength and thermal compatibility. Control of the fabrication parameters and the formation mechanism are discussed. Further improvement in the oxygen flux was achieved by changing materials and coating catalysts. Finally, the different mechanisms of oxygen permeation in microchanneled membranes were studied regarding gas diffusion, and contributions from the microchannel walls.

The present Thesis is focused on the development of ceramic membranes for the production of O2, as well as their use in several industrial applications (e.g. power generation, chemical industry). Different materials such as perovskites (BSCF and LSCF), fluorites (CGO) and composites, different membrane architectures have been considered. Catalytic activation was considered for the optimization of permeation, and for improving the selectivity/yield of chemical reactions. In the chapter dedicated to BSCF, the influence of thickness and the use of porous supports in the permeation was studied. An improvement in the permeation was observed for the thinner membranes. With respect to the porous supports, it was found that they contribute with an additional resistance within the permeation process, reducing the potential improvement when reducing thickness. The conducted tests also allowed to study more in deep the different processes affecting oxygen membranes, as well as defining a permeation model for monolithic and asymmetric membranes. Aiming to improve the surface reactions involved in the oxygen permeation the use of catalytic layers was considered, by means the addition of porous BSCF backbones. The best results were obtained when coating both sides of membranes with catalytic layers. The concept of BSCF activated membranes was also considered for the production of C2H4 by means of the oxidative de-hydrogenation of C2H6, obtaining high C2H4 yields. BSCF membranes presenting tubular geometry were characterized for application such as production of O2 and production of C2H4 by means of oxidative coupling of CH4. LSCF was considered for conducting studies under CO2-containing atmospheres. For both systems it was conducted a complete permeation study with a focus on permeation performance under CO2 environments. Furthermore a study focused on the different substrates was carried out for determining the structure presenting the lower gas diffusion resistance. Despite very good results were obtained for both membrane types, even under CO2 conditions, freeze casted membranes reached higher oxygen fluxes, being optimized with the catalytic activation of membranes. Materials presenting fluorite structure stand out for their stability under reaction conditions or when exposed to CO2 environments. Nevertheless, delivered oxygen fluxes are typically low. Hence, a thin 40 micron-thick CGO-Co membrane activated with Pd nanoparticles was considered for conducting a study on O2 permeation performance, and its behaviour when exposed to CO2 and CH4-containing atmospheres. A good stability was demonstrated, as well as a significant improvement in oxygen permeation when exposed to CH4 environments. Thus, CGO membranes present promising properties for their application in oxyfuel and for the conduction of chemical reactions. Composite materials based on NFO-CTO was carried out. An evaluation of the CTO content and its relation with permeation was conducted, determining that a higher ionic phase ratio in the membrane results in a higher permeation. A composite consisting of 50NFO-50CTO was considered for performing a permeation study under harsh application conditions, with presence of SO2. Despite the significant loss in permeation, the composite material resulted to be stable after a long exposure to SO2. A broad study about the effect of CO2 and SO2 on the oxygen surface reactions was conducted by means of EIS measurements on 60NFO-40CTO electrodes. It was observed a significant effect of SO2 on the surface exchange reactions by promoting the deactivation of the O2 active sites, due to a SO2 adsorption on them. This effect was minimized by activating 60NFO-40CTO backbones with different catalysts, being characterized by EIS under CO2&SO2 conditions. This improvement was later confirmed when performing permeation tests. Permeation was improved notably by reducing membrane thickness, depositing composite membranes on LSCF porous substrates.<br>La presente tesis trata sobre el desarrollo de membranas cerámicas para la producción de O2, así como de su uso en distintas aplicaciones industriales (producción de energía, industria química). Se han considerado distintos tipos de materiales tales como perovskitas (BSCF y LSCF), fluoritas (CGO) y materiales composites, así como distintas arquitecturas de membrana. y activación catalítica para optimizar la permeación y la selectividad/rendimiento en reacciones químicas. Para el BSCF se estudió la influencia del espesor y el uso de soportes porosos en la permeación de O2, con una mejora para las membranas más finas, y también el papel de los soportes porosos, contribuyendo con una resistencia adicional en el proceso de permeación. El estudio permitió también conocer más en profundidad los procesos que afectan a los distintos tipos de membranas, y establecer un modelo de permeación para membranas. Se recurrió a la activación catalítica mediante la adición de capas porosas de BSCF, obteniendo así mejores resultados para las membranas con capas en ambos lados. El concepto de membranas de BSCF activadas superficialmente se consideró también para la producción de C2H4 a partir de la deshidrogenación oxidativa de etano (ODHE), obteniendo rendimientos de C2H4 muy elevados. Membranas de BSCF con geometría tubular fueron caracterizadas para aplicaciones de producción de O2 y C2H4 mediante acoplamiento oxidativo de metano (OCM). Se consideró al LSCF para su uso en aplicaciones con atmósferas conteniendo CO2. Se desarrollaron membranas soportadas en soportes porosos de LSCF mediante tape casting y freeze-casting, realizando completos estudios de permeación, además de estudiar el tipo de soporte poroso ofreciendo menos resistencia a la difusión de los gases. Pese que para ambos tipos de membranas se obtuvieron muy buenos flujos de oxígeno, incluso bajo condiciones de CO2, para el caso de membranas con soporte fabricado mediante freeze-casting se consiguieron mayores valores de permeación, optimizándolos incluso con la activación catalítica. Los materiales con estructura fluorita poseen alta estabilidad bajo condiciones de reacción (atmósferas reductoras) o cuando son expuestos a CO2 (aplicaciones de producción de energía). Sin embargo, los valores de permeación suelen ser muy bajos. Se consideró una membrana de CGO-Co de 40 micras de espesor activada con nanopartículas de Pd para llevar a cabo un estudio de sus propiedades para la producción de O2, su comportamiento en contacto con CO2 y con atmósferas conteniendo CH4. La buena estabilidad demostrada y la mejora sustancial de los flujos de O2 bajo ambientes reductores, hacen que este tipo de materiales posean propiedades prometedoras para aplicaciones de oxicombustión y reacciones químicas. Se realizó un estudio con materiales composites formados por NFO-CTO. Una evaluación del contenido en CTO y su relación con la permeación de O2, resultó en mayores valores para composiciones con mayor contenido en CTO. Un composite consistente en 50NFO-50CTO se consideró para la realización de tests bajo condiciones de oxicombustión, con presencia de SO2. Pese al notable descenso en los flujos de O2, el material resultó ser completamente estable tras una exposición continuada al SO2. Un amplio estudio del efecto del CO2 y del SO2 sobre las reacciones superficiales se realizó mediantes medidas de EIS en electrodos de 60NFO-40CTO, demostrando que el SO2 afecta significativamente a las reacciones superficiales mediante procesos de adsorción competitiva en los centros activos. Se minimizó el efecto del SO2 sobre las reacciones de intercambio superficial al activar las membranas con capas catalíticas porosas de 60NFO-40CTO con distintos catalizadores, confirmando posteriormente esta mejora en tests de permeación en las mismas condiciones. Así mismo, se optimizó notablemente la permeación de las membranas de 60NFO-40CTO reduciendo el espes<br>La present tesi tracta sobre el desenvolupament de membranes ceràmiques per a la producció d'O2, així com del seu ús en diverses aplicacions industrials (producció d'energia, indústria química). S'han considerat diversos materials tals com perovskites (BSCF i LSCF), fluorites (CGO) i materials composites, així com diferents arquitectures de membrana i l'activació catalítica per a millorar la permeació i la sel·lectivitat/rendiment de les reaccions químiques. Per al BSCF s'estudià la influència de l'espessor i l'ús de suports porosos en la permeació d'O2, amb una millora dels fluxos d'O2 per al cas de les membranes més fines, i també el paper dels suports porosos, els quals contribueixen afegint una resistència al procés de permeació. L'estudi també va permetre conèixer més en profunditat els processos que afecten als diferents tipus de membranes, i establir un model de permeació per a membranes. Es va recórrer a l'activació catalítica mitjançant l'adició de capes poroses de BSCF, obtenint així millors resultats per a les membranes activades a ambdós costats. El concepte de membranes de BSCF activades superficialment es va considerar també per a la producció d'etilè a mitjançant la deshidrogenació oxidativa d'età (ODHE), obtenint rendiments de C2H4 molt elevats. Membranes de BSCF amb geometria tubular van ser caracteritzades per a aplicacions de producció d'O2 i C2H4 mitjançant l'acoplament oxidatiu de metà (OCM). Es va considerar al LSCF per al seu ús en aplicacions amb atmosferes contenint CO2. Així doncs, es van desenvolupar membranes suportades sobre suports porosos de LSCF fabricats per tape càsting i freeze càsting. Es van realitzar estudis complets de permeació per a ambdós casos, a més d'estudiar el tipus de suport porós que ofereix una menor resistència a la difusió dels gasos. Malgrat que es van obtindré molts bons fluxos d'O2 per als dos tipus de membranes, inclús sota condicions amb CO2, per al cas de les membranes amb suport fabricat per freeze càsting es van aconseguir majors valors de permeació, sent inclús optimitzats amb l'activació catalítica. Els materials amb estructura fluorita destaquen per l'alta estabilitat sota condicions de reacció (atmosferes reductores) o quan són exposats a CO2 (aplicacions per a la producció d'energia). Malgrat això, els valors de permeació solen ser molt baixos. Es va considerar una membrana de CGO-Co de 40 micras d'espessor activada amb partícules de Pd per a realitzar un estudi sobre les seues propietats en quant a la producció d'O2, el seu comportament amb el contacte amb CO2 i atmosferes reductores contenint CH4. La bona estabilitat demostrada i una millora substancial dels fluxos d'O2 sota ambients reductors fan que aquest tipus de material presente propietats prometedores per a aplicacions d'oxicombustió i reaccions químiques. Es va realitzar un estudi sobre materials composites formats per NFO-CTO. Es va realitzar una avaluació del contingut en CTO i la relació amb la permeació, observant una millora de la permeació amb un major contingut de CTO. Un composite consistent en 50NFO-40CTO es va considerar per a la realització de tests de permeació en condicions d'oxicombustió amb presència de SO2. Malgrat el notable descens en els fluxos d'O2, el material resultà ser estable després d'una exposició continuada al SO2. Es mesurà l'efecte del CO2 i del SO2 sobre les reaccions superficials fent ús de la tècnica d'EIS en elèctrodes de 60NFO-40CTO. Demostrant que el SO2 afecta significativament a les reaccions superficials degut a una adsorció competitiva O2-SO2 als centres actius. Es minimitzà l'efecte del SO2 sobre les reaccions superficials al activar les membranes amb capes poroses de 60NFO-40CTO amb diferents catalitzadors. Aquestes capes van ser caracteritzades per EIS sota condicions de SO2, confirmant posteriorment la millora al realitzar tests de permeació. S'optimitzà notablement la perme<br>García Fayos, J. (2017). DEVELOPMENT OF CERAMIC MIEC MEMBRANES FOR OXYGEN SEPARATION: APPLICATION IN CATALYTIC INDUSTRIAL PROCESSES [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86189<br>TESIS<br>Premiado

This thesis is relying on modeling of MIEC membranes inside a gasifier and it seeks to find an appropriate configuration to use in gasification setup for pure oxygen production and use it inside the gasifier in a gasification process. Application of pure oxygen instead of air can play a key role in gasification processes. Since conventional methods for separation of oxygen such as cryogenic distillation are energy intensive and some of them cannot provide full purity for oxygen, an alternative method can be a good option. This substitute method which is the focus of this study, can be achieved by using specific ceramic membranes directly inside the gasifier. Although some effort have been spent on these membranes, there is still a lack of study on direct integration inside gasifier using this technology. In the present work, a modeling study of these membranes has been carried out using Engineering Equation Solver (EES). EES is a commercial software package used for solution of systems of simultaneous non-linear equations. The gasifier model was previously prepared and was studied to simulate the behavior of a downdraft gasifier. During the simulation some hypothesizes are assumed to make the available flux, model for the chosen membrane, keep working. Besides, an alternative membrane is assumed to have more precise results. Then all the suggested configurations were studied based on energy consumption and economic aspects. The economic studies was focused on the alternative which had lower flux. So, the area of the membrane required is more. Finally, the results where compared with a similar cryogenic distillation plant used to produce pure oxygen.

Ceramic membranes made from mixed ionic and electronic conductive oxide materials have received much attention over the last decade due to their ability to separate oxygen from air at 100 % selectivity. The flux through these mem- branes may be optimized by reducing their thickness. A porous support of the same composition is applied to ensure sufficient mechanical stability. The pro- cessing of these so-called asymmetric membranes is addressed in this work; for the technology to become attractive from a commercial point of view, a reliable and cost-effective processing procedure needs to be established.Phase pure La0.2Sr0.8Fe0.8Ta0.2O3&amp;#8722;&amp;#948; (LSFTa) and La0.2Sr0.8Fe0.8Al0.2O3&amp;#8722;&amp;#948; (LSFAl) powders were synthesized by solid state reaction. The powders were used to prepare porous supports by the means of aqueous based tape casting and hot-press lamination. The supports were pre-sintered at various temperatures and dip coated with an ethanol-based suspension containing sub-micrometer sized spray pyrolysis powder. Different parameters believed to affect dense layer for- mation by dip coating are discussed and related to the experimental observations. It was found that an important criteria for success is to have a similar shrinkage property in the functional and porous layer of the membrane. The most promis- ing asymmetric membrane was obtained for the LSFTa composition where dip coating two times and sintering at 1230&amp;#9702;C resulted in a 6?7 &amp;#956;m thick membrane layer and a support with 38 % open porosity.The fracture strength of LSFAl supports with &amp;#8764; 64 % porosity was also charac- terized in this work. Testing 11 specimens with the ball-on-ring method resulted in a characteristic strength of 10.7&#177;0.5 MPa and a Weibull modulus of 5.9&#177;1.8.

Dense ceramic oxygen separation membranes can pass oxygen perm-selectively at elevated temperature and have potential for improving the performance and reducing the cost of several industrial processes: such as the conversion of natural gas to syngas, or to separate oxygen from air for oxy-fuel combustion in electricity generation (to reduce NOx emissions and facilitate CO2 sequestration). These pressure-driven solid state membranes are based on fast oxygen-ion conducting ceramics, but also need a compensating flow of electrons. Dual-phase composites are attractive since they provide an extra degree of freedom, compared with single phase membranes, for optimising the overall membrane performance. In this study, composites containing gadolinia doped ceria (CGO, Ce0.9Gd0.1O2- ) and either strontium-doped lanthanum cobaltite (LSC, La0.9Sr0.1CoO3- or La0.6Sr0.4CoO3- ) or silver (Ag) were investigated for possible application as oxygen separation membranes in oxy-fuel combustion system. These should combine the high oxygen ion conductivity of CGO with the high electronic conductivity and fast oxygen surface exchange of LSC or silver. Dense mixed-conducting composite materials of LSC/CGO (prepared by powder mixing and sintering) and Ag/CGO composites (prepared by silver plus copper oxide infiltration method) showed high relative density (above 95%), low background gas leakage and also good electrical conduction. The percolation threshold of the electronic conducting component was determined to be approximately 20 vol.% for both LSC compositions and 14 vol.% for Ag. Isotopic exchange and depth profiling by secondary ion mass spectrometry was used to investigated the oxygen tracer diffusion (D*) and surface exchange coefficient (k*) of the composites. Composites just above the electronic percolation threshold exhibited high solid state oxygen diffusivity, fast surface exchange activity moderate thermal expansion and sufficient mechanical strength thus combining the benefits of their constituent materials. The preliminary work on oxygen permeation measurement showed that the reasonable magnitude of oxygen fluxes is possible to be achieved. This indicates that the composites of LSC/CGO and Ag/CGO are promising for further development as passive oxygen separation membranes.

In order to reduce the amount of pollution that is generated by burning fossil fuels alternative energy sources should be explored. Hydrogen has been identified as the most promising replacement for fossil fuels and can be produced by using the Hybrid Sulphur (HyS) cycle. Currently the SO2/O2 separation step in the HyS process has a large amount of knock out drums. The aim of this study was to investigate new technology to separate the SO2 and O2. The technology that was identified and investigated was to separate the SO2 and O2 by absorbing the SO2 into an ionic liquid. In this study the maximum absorption, absorption rate and desorption rate of SO2 from the ionic liquid [BMIm][MeSO4] with purities of 95% and 98% was investigated. These ionic liquid properties were investigated for pure O2 at pressures ranging from 1.5 to 9 bar(a) and for pure SO2 at pressures from 1.5 to 3 bar(a) at ambient temperature. Experiments were also carried out where the composition of the feed-stream to the ionic liquid was varied with compositions of 0, 25, 50, 75 and 100 mol% SO2 with O2 as the balance. For each of these compositions the temperature of the ionic liquid was changed from 30oC to 60oC, in increments of 10oC. The absorption rate of SO2 in the ionic liquid increased when the mole percentage SO2 in the feed stream was increased. When the temperature of the ionic liquid was decreased the maximum amount of SO2 that the ionic liquid absorbed increased dramatically. However, the absorption rate was not influenced by a change in the absorption temperature. The experimental results for the maximum SO2 absorption were modelled with the Langmuir absorption model. The model fitted the data well, with an average standard deviation of 17.07% over all the experiments. In order to determine if the absorption reaction was endothermic or exothermic the Clausius-Clapeyron equation was used to calculate the heat of desorption for the desorption step. The heat of desorption data indicated that the desorption of SO2 from this ionic liquid was an endothermic reaction because the heat of desorption values was positive. Therefore the absorption reaction was exothermic. From the pressure-change experiments the results showed that the mole percentage of O2 gas that was absorbed into the ionic liquid was independent of the pressure of the O2 feed.On the other hand, there was a clear correlation between the mole percentage SO2 that was absorbed into the ionic liquid and the feed pressure of the SO2. When the feed pressure of the SO2 was increased the amount of SO2 absorbed also increased, this trend was explained with Fick’s law. In the study the effect of the ionic liquid purity on the SO2 absorption capacity was investigated. The experimental results for the pressure experiments showed that the 95% and 98% pure ionic liquid absorbed about the same amount of SO2. During the temperature experiments the 95% pure ionic liquid absorbed more SO2 than the 98% pure ionic liquid for all but two of the experiments. However the 95% pure ionic liquid also absorbed small amounts of O2 at 30 and 40oC which indicated that the 95% pure ionic liquid had a lower selectivity than the 98% pure ionic liquid. Therefore, the 95% pure ionic liquid had better SO2 absorption capabilities than the 98% pure ionic liquid. These result showed that the 98% pure ionic liquid did not absorb more SO2 than the 95% pure ionic liquid, but it did, however, show that the 98% pure ionic liquid had a better selectivity towards the SO2. Hence, it can be concluded that even with the O2 that is absorbed it would be economically more advantageous to use the less expensive 95% pure ionic liquid rather than the expensive 98% pure ionic liquid, because the O2 would not influence the performance of the process negatively in such low quantities.<br>Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013

Novel unidirectional crystallization was tested in glasses of the Bi-Sr-Ca-Cu-O system to produce highly oriented microstructures. Some evidence of liquid-liquid phase separations on cooling melts of Bi₂Sr₂Ca₁Cu₂Oₓ and Pb₀ͺ₃₂Bi₁ͺ₆₈Sr₁ͺ₇₅Ca₂Cu₃Oₓ is found for the first time from Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), and Transmission Electron Microscope (TEM). This made it difficult to produce highly oriented microstructures through the present route because one of the phases in the phase separated structure is likely close to "R"-phase composition and lead to copious nucleation of "R"-phase on heating. This also resulted in sequential crystallization of the current liquids, first to "R"-phase and then to the Bi₂Sr₂Ca₁Cu₂Oₓ phase. Theoretical modelling was performed to understand general questions in the present route. The model suggests that a liquid with high interfacial energy is a good candidate for the present route to produce highly oriented microstructures. The model was tested in lithium diborate glass and showed a highly oriented microstructure. Thus, unidirectional crystallization is generally an attractive processing option for a liquid free of phase separation.

A compact air separator demonstrator based on centrifugally enhanced distillation has been studied. The full size device is meant to be used on board of a Two Stage To Orbit vehicle launcher. The air separation system must be able to extract oxygen in highly concentrated liquid form (LEA, Liquid Enriched Air) from atmospheric air. The LEA is stored before being used in a subsequent rocket propulsion phase by the second stage of the launcher. Two reference vehicles are defined, one with a subsonic first stage and one with a supersonic first stage. In both cases, oxygen collection is performed during a cruise phase (M 0.7 and M 2.5 respectively). The aim of the project is to demonstrate the feasibility of the air separation system, investigate the separation cycle design, and assess that the separator design selected is suitable for the reference vehicles.<p><p>The project is described from original base ideas to design, construction, extended testing and analysis of experimental results. Preliminary computations for a realistic layout have been performed and the motivations for the choices made during the process are explained. Test rig design, separator design and technical discussion are provided for a subscale pilot unit. Mass transport parameters and flooding limits have been estimated and experimentally measured. Performance has been assessed and shown to be sufficient for the reference Two Stage To Orbit vehicles. The technology developed is found suitable without further optimization, although some volume and mass reduction would be desirable for the supersonic first stage concept. There are many ways of optimisation that can be further investigated. The aim of this program, however, is not to fully optimize the device, but to demonstrate that a device based on a simple, robust, low-risk design is already suitable for the launch vehicles. On top of that analysis, directions for improvements are suggested and their potentials estimated. A complete assessment of those improvements requires further maturation of the technological concept through further testing and practical implementations.<p><p>Directions for future work, general conclusions and a vehicle development roadmap have also been provided.<p><br>Doctorat en Sciences de l'ingénieur<br>info:eu-repo/semantics/nonPublished

Improvement of the properties of zeolites for application in the nitrogen and<br/>oxygen separation process and in acid catalysis<br/><br/>Les zeolites són aluminosilicats cristal·lins formats per un esquelet aniònic rígid amb una microporositat en forma de cavitats i/o canals. La seva fórmula és (Mn+)x/n[(AlO2)x(SiO2)y]· mH2O, on M representa els cations situats fora de l'estructura que contraresten la càrrega de l'esquelet. Presenten una elevada àrea superficial interna, elevada cristal·linitat i estabilitat química i tèrmica, així com capacitat de bescanvi catiònic.<br/>Industrialment s'utilitzen principalment com intercanviadors iònics, adsorbents altament selectius i com a catalitzadors.<br/>L'objectiu d'aquesta tesi és modificar zeolites i utilitzar-les per millorar els processos de separació de<br/>nitrogen i oxigen de l'aire i el d'isomerització de l'òxid d'estirè al fenilacetaldehid, així com caracteritzar les mostres per correlacionar-ho amb el seu comportament.<br/>El primer capítol resumeix la bibliografia trobada per als processos de separació de nitrogen i oxigen de<br/>l'aire i d'isomerització de l'òxid d'estirè, les variables que influencien i els millors resultats trobats.<br/>El segon capítol descriu les tècniques de caracterització utilitzades i els procediments de preparació de<br/>mostres i caracterització emprats.<br/>El capítol 3 fa referència a l'aplicació de zeolites modificades en la separació de nitrogen i oxigen. S'ha<br/>utilitzar la mordenita, una zeolita natural amb una porositat en forma de canals, de manera que els cations, responsables de la interacció, es trobarien en posicions força accessibles. L'adsorció de N2 i O2 a 298 K indica que la mordenita dóna uns volums d'adsorció lleugerament superiors a la faujasita mantenint-se la selectivitat d'adsorció, degut a la major accessibilitat dels cations situats en els canals.<br/>La primera modificació ha estat introduir àtoms de fluor i mirar l'efecte en l'adsorció de N2 i O2. Els resultats indiquen que la introducció de petites quantitats de fluor millora la separació, ja que disminueix la polarització de la càrrega dels cations i augmenta la interacció amb el moment quadrupolar del N2 i O2, augmentant la selectivitat d'adsorció a baixes pressions.<br/>També s'ha provat per a la separació mordenita intercanviada amb cations Ag+, capaços d'interaccionar mitjançant &#61552;-complexació amb el N2 i O2 quan es formen espècies Agm n+. Amb la mordenita no s'ha<br/>aconseguit formar aquestes espècies probablement per la major distància entre cations, mentre que sí s'ha aconseguit amb la zeolita A, on la seva formació depèn de les condicions de preparació, de manera que els intercanivis amb cations Ag+ només tenen lloc quan s'utilitzen concentracions de Ag+ elevades.<br/>El quart capítol estudia l'aplicació d'algunes mordenites modificades amb fluor en la isomerització de l'òxid d'estirè al corresponent aldehid, reacció de gran importància en la indústria dels perfums. Els resultats obtinguts indiquen que la introducció de petites quantitats de fluor augmenta l'acidesa de Brönsted i dóna lloc a majors conversions quan s'utilitzen mètodes convencionals d'escalfament, però a la desactivació del catalitzador quan s'escalfa per microones. En canvi, amb quantitats de fluor elevades, es formen centres àcids de Lewis, que són menys actius en aquesta reacció. Així doncs, l'escalfament per microones per aquesta reacció disminueix molt els temps de reacció, però, no obstant, desactiva els<br/>catalitzadors més àcids.<br/>Per últim s'ha realitzat un seguiment per espectroscòpia Infra-Roja de l'adsorció de diferents molècules<br/>sonda en diverses mordenites i altres zeolites. Els resultats han permès conèixer millor la posició, accessibilitat, així com el tipus d'interaccions favorables que donen els cations de la mordenita. També es posa de manifest la formació d'interaccions inusuals, de tipus múltiple. L'últim capítol mostra les conclusions més rellevants, destacant la importància en la modificació de les zeolites per a la millora de les seves propietats, aconseguint-se els objectius proposats.<br/><br/>Improvement of the properties of zeolites for application in the<br/>nitrogen and oxygen separation process and in acid catalysis<br/><br/>Zeolites are crystalline aluminosilicates formed by an anionic skeleton and by a microporous system<br/> disposed in cavities and/or channels. Present the molecular formula (Mn+)x/n[(AlO2)x(SiO2)y]·<br/> mH2O, where M represents the extraframework cations that compensate the negative charge of the framework. They are characterized by high internal surface area, high cristallinity and also high chemical and thermal stabilities as well as cation exchange capacity. At industrial level they are basically used as ion exchangers,as highly selective adsorbents and also as catalysts.<br/><br/>The main objective of this thesis was to modify zeolites and use them to improve two industrial processes, which are the nitrogen and oxygen separation process and the styrene oxide isomerisation reaction to phenylacetaldehyde. It was also and other scope to characterise deep the samples andcorrelate the results with their behaviour on both processes in order to optimise them.<br/>The first chapter describes the literature found related to the nitrogen and oxygen separation process and to the isomerisation of styrene oxide, specifically, the influencing variables and themost outstanding results.<br/>In chapter two, the characterization techniques and the samples preparation and characterization<br/>procedures are described.<br/>Chapter 3 refers to the application of several modified mordenites to the nitrogen and oxygen separation. Mordenite was used because the porosity, based on channels, should favour the accessibility to cations by the adsorbate molecules. The nitrogen and oxygen adsorption results indicate that mordenite can adsorb slightly higher volumes than faujasite, fact that evidences the role of cations accessibility in this process.<br/><br/>The first modification was the introduction of fluorine ions on mordenite structure in order to see the effect on the N2 and O2 adsorption properties. The results show that the introduction of low quantities of fluorine improves the separation, since the presence of fluorine decreases the shielding on cations and therefore improve the interaction between those and the quadrupolar moment of N2 and O2 molecules, increasing also the N2/O2 selectivity at low pressures.<br/><br/>It was also studied the interaction of silver exchanged zeolites with nitrogen and oxygen molecules by &#61552;-complexation with Agm n+ species formed during the activation. We were not able to form these species inside mordenite, probably due to the bigger distances between cations, while these species were formed inside A zeolite. The adsorption results indicate that the formation of these species depends on the preparation and activation conditions and good adsorption/separation results are obtained when suitable conditions are used. In chapter four, the application of modified mordenites in the styrene oxide isomerisation reactionto phenyl acetaldehyde using microwaves as a new heating method has been studied. The obtained results show that the introduction of low amounts of fluorine increases the Brönsted acidity, which improve the conversion results when using conventional heating but deactivates the catalysts when microwaves are used. Otherwise, when higher amounts of fluorine are used, Lewis acid sites are formed, less active in this isomerisation reaction. Therefore, the use of microwaves improves reaction times on this reaction, but deactivates the more acidic catalysts.<br/><br/>In chapter five, the nature and position of several mordenites was studied by means of infrared spectroscopy by studying the adsorption desorption of several prove molecules. These studies allowed us to know better the position, accessibility and the existing interactions between the cations and the prove molecules. It was also evidenced the presence of a new interaction, unusual and probably atributed to a multiple interaction. The last chapter expose the most important conclusions, pointing out the importance of some modifications to improve their properties for application in those processes.

Mixed ionic-electronic conducting (MIEC) membranes are a promising technology for oxygen separation but they are not commercialised yet due to sealing issue and sensitivity to impurities in feedstock. In this study, La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428) was successfully sealed for long-term operation of 963 h using a gold-glass-ceramic sealant. The membrane was then tested for air separation in presence of hydrogen sulphide for 100 h and results showed that the impurity caused a drop in oxygen flux to zero within few hours. The flux could not be fully restored after hydrogen sulphide removal and only 6 to 35% was recovered. It was proposed that hydrogen sulphide was adsorbed on the membrane in the form of sulphur and it occupied oxygen vacancies. With time, strontium segregates toward sulphur to form irreversible layer of strontium sulphate. To restore the damaged surface, the membrane was treated by 1% (mol) of hydrogen for 20 h and the recovery improved from 6 to 12%. It was discovered that the poisoning mechanism is a function of oxygen partial pressure and change of partial pressure from 0.21 to 0.01 bar resulted in 90% recovery and this can be used as a strategy to reduce the damage. The next step was to test the membrane for hydrogen production using 1% (mol) of methane and results showed that methane conversion was steady at 33% for 350 h. Methane oxidation was also carried in presence of hydrogen sulphide but it resulted in drop of conversion to 8%. However, the conversion was slowly regenerating with time and it reached a constant value of 15%. This recovery was interpreted by the reaction of methane with hydrogen sulphide or methane decomposition and the membrane acted as a catalyst for these reactions. After hydrogen sulphide removal from the feed, the conversion kept on decreasing and this was linked to the change of membrane properties and therefore the membrane could not provide the sites for methane-oxygen reaction. For better stability under hydrogen sulphide, the membrane was modified by adding a powder of LSCF6428 material over the dense membrane. This dual layer membrane was stable for air separation under hydrogen for 33 h and the flux was only reduced by 5%.

Los materiales conductores mixtos de electrones e iones (oxígeno o protones) son capaces de separar oxígeno o hidrógeno de los gases de combustión o de corrientes de reformado a alta temperatura. La selectividad de este proceso es del 100%. Estos materiales, óxidos sólidos densos, pueden usarse en la producción de electricidad a partir de combustibles fósiles, así como formar parte de los procesos que forman parte del sistema de captura y almacenamiento de CO2. Las membranas de transporte de oxígeno (MTO) se pueden utilizar en las plantas energéticas con procesos de oxicombustión, así como en reactores catalíticos de membrana (RCM), mientras que las membranas de transporte de hidrógeno (MTH) se aplican en procesos de precombustión. Además, estos materiales encuentran aplicación en componentes de sistemas energéticos, como electrodos o electrolitos de pilas de combustible de óxido sólido, de ambas clases iónicas y protónicas (SOFC y PC-SOFC). Los procesos mencionados implican condiciones de operación muy severas, como altas temperaturas y grandes gradientes de presión parcial de oxígeno (pO2), probablemente combinadas con la presencia de CO2 and SO2. Los materiales más que mayor rendimiento de separación presentan y más ampliamente investigados en este campo son inestables en estas condiciones. Por tanto, existe la necesidad de encontrar nuevos materiales inorgánicos estables que proporcionen alta conductividad electrónica e iónica. La presente tesis propone una búsqueda sistemática de nuevos conductores iónicos-electrónicos mixtos (MIEC, del inglés) con diferente estructura cristalina y/o diferente composición, variando la naturaleza de los elementos y la estequiometría del cristal. La investigación ha dado lugar a materiales capaces de transportar iones oxígeno, protones o cargas electrónicas y que son estables en las condiciones de operación. La caracterización de una amplia serie de cerias (CeO2) dopadas con lantánidos proporciona una comprensión general de las propiedades estructurales y de transporte, así como la relación entre ellas. Además, se estudia el efecto de la adición de cobalto a dicho sistema. Se ha completado el análisis con la optimización de las propiedades de trasporte a partir de la microestructura. Todo esto permite hacer una clasificación inicial de los materiales basada en el comportamiento de transporte principal y permite adecuar la estructura y las condiciones de operación para obtener las propiedades deseadas para cada aplicación. Algunos de los materiales extraídos de este estudio alcanzaron las expectativas. Las familias de materiales basadas en Ce1-x Tbx O2-¿ y Ce1-x Tbx O2-¿ +2 mol% Co proporcionan flujos de oxígeno bajos pero competitivos, ya que son estables en atmósferas con CO2. Además, la inclusión de estos materiales en membranas de dos fases aumenta el flujo de oxígeno. La combinación con una espinela libre de cobalto y de metales alcalinotérreos como es el Fe2 NiO4, ha dado lugar a un material prometedor en cuanto a flujo de oxígeno y estabilidad en CO2 y en SO2, que podría ser integrado en el proceso de oxicombustión. Por otra parte, se ha añadido metales como codopantes en el sistema Ce0.9-x Mx Gd0.1O1.95. Estos materiales, en combinación con la perovskita La1- x Srx MnO3 usada comúnmente como cátodo de SOFC, han sido capaces de disminuir la resistencia de polarización del cátodo. La mejora es consecuencia de la introducción de conductividad iónica por parte de la ceria. Las perovskitas dopadas basadas en CaTiO3 forman el segundo grupo de materiales investigados. La dificultad de obtener perovskitas estables y que presenten conducción mixta iónica y electrónica se ha hecho evidente. De entre los dopantes utilizados, el hierro y la combinación hierro-magnesio han sido los mejores candidatos. Ambos materiales presentan conductividad principalmente iónica a alta temperatura, mientras que a baja predomina la conductividad electrónica tipo p. CaTi0.73Fe0.18Mg0.09O3-¿ se ha mostrado como un material competente en la fabricación de membranas de oxígeno, que proporciona flujos adecuados a la par que estabilidad en CO2. Finalmente, la perovskita La0.87Sr0.13CrO3 (LSC) ha sido dopada con el objetivo de aumentar la conductividad mixta protónica electrónica. Este estudio ha llevado al desarrollo de una nueva generación de ánodos para PC-SOFC basadas en electrolitos de LWO. Las perovskitas dopadas con Ce en el sitio del La (LSCCe) y con Ni en el sitio del Cr (LSCN) son estables en condiciones de operación reductoras, así como en contacto con el electrolito. El uso de ambos materiales como ánodo disminuye la resistencia de polarización con respecto al LSC. El LSCCe está limitado por los procesos que ocurren a baja frecuencia (BF), relacionados con los procesos superficiales, y que son atenuados en el caso del LSCN debido a la formación de nanopartículas de Ni metálico en la superficie. La infiltración posterior con nanopartículas de Ni permite disminuir la resistencia a BF lo que sugiere que la reacción superficial de oxidación del H2 está siendo catalizada. La infiltración más concentrada en Ni (5Ni) elimina completamente la resistencia a BF en ambos ánodos, de forma que los procesos que ocurren a altas frecuencias son ahora limitantes. El ánodo constituido por LSCNi20+5Ni dio una resistencia de polarización de 0.26 ¿·cm 2 at 750 ºC en H2 húmedo.<br>Mixed ionic (oxygen ions or protons) and electronic conducting materials (MIEC) separate oxygen or hydrogen from flue gas or reforming streams at high temperature in a process 100% selective to the ion. These solid oxide materials may be used in the production of electricity from fossil fuels (coal or natural gas), taking part of the CO2 separation and storage system. Dense oxygen transport membranes (OTM) can be used in oxyfuel combustion plants or in catalytic membrane reactors (CMR), while hydrogen transport membranes (HTM) would be applied in precombustion plants. Furthermore, these materials may also be used in components for energy systems, as advanced electrodes or electrolytes for solid oxide fuel cells (SOFC) and proton conducting solid oxide fuel cells (PCSOFC) working at high and moderate temperature. The harsh working conditions stablished by the targeted processes include high temperatures and low O2 partial pressures (pO2), probably combined with CO2 and SO2 containing gases. The instability disadvantages presented by the most widely studied materials for these purposes make them impractical for application to gas separation. Thus, the need to discover new stable inorganic materials providing high electronic and ionic conductivity is still present. This thesis presents a systematic search for new mixed ionic-electronic conductors. It includes different crystalline structures and/or composition of the crystal lattice, varying the nature of the elements and the stoichiometry of the crystal. The research has yielded new materials capable to transport oxygen ions or protons and electronic carriers that are stable in the working condition to which they are submitted.<br>Balaguer Ramírez, M. (2013). New solid state oxygen and hydrogen conducting materials. Towards their applications as high temperature electrochemical devices and gas separation membranes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31654<br>TESIS<br>Premiado

Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness.<br><p>QC 20131114</p><br>Steel Eco-Cycle

Le développement d'une méthode efficace de séparation/purification d'hydrogène représente une nécessité primordiale pour améliorer les rendements de production des systèmes énergétiques futurs. En effet, le procédé de reformage classique de production d'hydrogène conduit à un mélange complexe de gaz à haute température (au-delà de 523 K) qui limite l'utilisation de H2 dans diverses applications. La réalisation de membranes hautement sélectives à l'hydrogène apparaît alors comme un point essentiel pour augmenter la production d'hydrogène. Les membranes à base de silice ont largement été étudiées en vue de répondre à cette problématique. Malgré leurs excellentes performances, elles ne pourraient être compétitives à l'échelle industrielle qu'après amélioration de leur résistance à la vapeur d'eau en température (lixiviation). Des travaux antérieurs menés à l'IEM ont montré les performances de membranes « SiCN » en termes de perméance et de permsélectivité. Sur la base de ces résultats, nous avons développé des membranes non-oxydes autour du quaternaire « SiZrCN ». L'incorporation de Zr avait pour objectif d'améliorer la tenue en température des membranes et de fait leur sélectivité. Ce projet de thèse a été divisé en trois tâches principales : la première a consisté en la synthèse d'un précurseur moléculaire contenant les éléments Si, Zr, C, N ; la seconde a porté sur la préparation par PECVD de membranes denses non oxydes et la dernière partie a permis d'évaluer les performances de ces membranes en séparation de gaz. Un précurseur moléculaire « single source » a été synthétisé avec succès autour du quaternaire « SiZrCN », de tension de vapeur adéquate pour un dépôt par PECVD. Des films minces ont ainsi été déposés sur des supports variés afin d'obtenir des membranes sans défauts de surface conduisant à une perméance à He de 1,7.10-7 mol.m-2.s-1.Pa -1 et à une sélectivité idéale He/N2 (estimée) de 1300 à T = 423 K et Delta p = 1,105 Pa<br>The development of an efficient hydrogen separation/purification method represents a tremendous requirement to enhance the production yields of future energy systems. Indeed, the reforming process commonly used for hydrogen production leads to a complex gas mixture at high temperature (beyond 523 K) that limits the H2 use in various applications. The elaboration of highly hydrogen selective membranes appears to be a determining step to expand hydrogen production. Silica-based membranes have been largely studied to respond this problematics. In spite of their excellent performances, they could only be competitive from an industrial point of view after improvement of their low resistance to water vapor at high temperature (lixiviation). Previous works completed at IEM have demonstrated the good performances of “SiZrCN” membranes in terms of permeance and permselectivity. Based on these results, we developed new non-oxide membranes in the quaternary system “SiZCN”. The incorporation of Zr aimed to enhance the temperature resistance of the membranes and then their selectivity. This thesis project was divided into three major tasks : the first one has consisted in the synthesis of a molecular precursor containing the Si, Zr, C, N elements ; the second one was focused on the preparation by PECVD of dense non-oxide membranes and the last one was meant to evaluate the performances of these membranes in gas separation. A single source molecular precursor was successfully obtained in the system “SiZrCN” usable for PECVD. Thin films were thus deposited over various supports to obtain defect free membranes presenting a He permeance of 1,7.10-7 mol.m-2.s-1.Pa-1 and a (estimated) He/N2 ideal selectivity of 1300 at T = 423 K and Delta p = 1.105 Pa

Ce travail porte sur l’élaboration de matériaux nanostructurés et le contrôle de la formation de nanocristaux d’oxyde d’étain dans une matrice de silice amorphe obtenue par voie sol-gel. Préalablement à l’étude structurale et microstructurale des xérogels, une première partie de ces travaux de thèse concerne le procédé sol-gel. Le lavage des gels par des solutions hydro-alcooliques permet d’extraire une quantité importante d’acide chlorhydrique après gélification. Ainsi si les solutions de lavage sont renouvelées, 50 % de l’acide introduit peut être retiré. Ce lavage, associé avec un séchage contrôlé, a également permis de réduire significativement la durée du séchage et d’obtenir des xérogels centimétriques non fissurés.La seconde partie de ce travail a porté sur l’étude structurale et microstructurale des xérogels réalisée au travers de mesures de diffraction des rayons X ex situ ou de diffusion centrale et diffraction des rayons X couplée in situ en fonction de la température sur des lignes de lumière situées autour de sources synchrotrons. Nous avons montré que dans des xérogels contenant 10 % d’étain, la quantité de cristaux nanométriques d'oxyde d'étain peut augmenter continuellement sans que leur taille moyenne ne s’accroisse. La taille moyenne la plus faible est obtenue après un prétraitement thermique de séparation de phases préalable à celui de cristallisation et plus ce traitement est long plus la taille des cristaux est faible. Cette étude a été complétée par des traitements thermiques effectués in situ afin de suivre simultanément la séparation de phases et la cristallisation. Ces mesures ont permis d’observer le phénomène de séparation de phases dans les xérogels contenant 10 % d’étain et dont la quantité cristallisée obtenue lors d’un traitement thermique à 350 °C est la plus importante au regard des autres températures de traitement thermique et des concentrations en étain<br>This PhD work deals with the development of nanostructured oxide materials and the control of the formation of tin oxide nanocrystals in an amorphous silica matrix obtained by sol-gel process. Prior to the structural and microstructural study of xerogels, a first part of this work concerns the sol-gel process. Washing the gels with hydroalcoholic solutions allows to extract a significant quantity of hydrochloric acid after gelation. Thus, if the washing solutions are renewed, 50% of the acid introduced can be removed. This washing, combined with improvement of the drying process, allowed to reduce the drying duration and finally to obtain bulk xerogels exhibiting a centimetric size.The second part of this work focuses on the structural and microstructural evolution of xerogels through thermal treatments. The results of this second part are obtained through ex situ measurements of X-ray diffraction or coupled small angle X-ray scattering and X-ray diffraction experiments realized in situ as a function of temperature. In both cases the measurements have been performed on synchrotron beamlines. We show that in xerogels containing 10% tin, the amount of nanosized tin oxide crystals can continuously increases without increasing the average size of these crystals. The lowest average size is obtained after a phase separation thermal pretreatment before crystallization and the longer this treatment is, the smaller the size of the crystals. This study is completed by heat treatments carried out in situ in order to simultaneously evidence phase separation and crystallization. These measurements allow to observe the phenomenon of phase separation by small angle X-ray scattering in xerogels containing 10% tin and whose crystallized quantity obtained during a thermal treatment at 350 °C is the highest compared to other heat treatment temperatures and tin concentrations

Ce travail de thèse vise à concevoir de nouvelles membranes performantes pour la séparation de gaz (CO2) dans le procédé de post-combustion. La stratégie proposée repose sur la préparation de membranes hybrides organiques/inorganiques, combinant des supports poreux de dioxyde de titane (TiO2) intégrés dans une couche dense de polymère à base de poly-oxyde d'éthylène. L'un des points important de cette étude est l'ancrage de la phase organique sur le support inorganique. Deux agents de couplage : le propyl phosphonique acide 2-bromo-2-méthyl propanoate et le 3--propylamino triéthoxy silan ont été sélectionnés et greffés sur trois surface de TiO2 différentes : des nanoparticules, des surfaces denses et des surfaces poreuses. Pour chacune des deux molécules d'ancrage les meilleurs résultats ont été obtenus avec les nanoparticules. Les nanoparticules de TiO2 ainsi fonctionnalisées, ont dans une seconde étape, servi de semences pour l'élaboration de particules coeur-écorce. Deux voies de polymérisation ont été explorées avec succès : la si-ATRP et la si-ROMP. Dans le premier cas des greffons de poly-poly-éthylène glycol méthyl éther méthacrylate ont été introduits sur les nanoparticules de TiO2. Pour la si-ROMP les greffons incorporés sont à base de polynorbonène. Les résultats obtenus sur les nanoparticules de TiO2 ont été exploités afin de créer des couches polymères sur des supports poreux céramiques tubulaires commerciaux. Deux modes de conception ont été développés : la voie dite "coating onto" et celle dite "Grafting from". Les membranes composites obtenues par ces deux voies ont été testées en perméabilité des gaz afin de déterminer la qualité des couches polymères. Des essais préliminaires de séparation des gaz ont été également effectués<br>This thesis work aims towards designing hybrid membranes for CO2 separation in the post-combustion process. The different methods of existing technologies are compared ans assessed for their merit, and the decision of using inorganic titanium dioxide supports integrated with a grown polymeric/PEG layer is made. First, the structure of the interfacing group is determined and narrowed down to phosphonic-based anchoring groups. The modification of various titanium oxide surfaces (i.e. particle, flat and porous) is performed with each group, and particles were found to yield the highest surface modification. Secondly, the functionalized particles of titania were then studied for their potential with si-ATRP and si-ROMP. in the case of phosphonic acid functionalized titania, the particles yielded a bromine terminus that could be used for si-ATPR. In the case of the silane grafted titania particles, further fonctionalization was required to ultimately yield a norbornenyl group that can be used for Si-ROMP. Both teechniques were shown to work, and were thus applied to longer ceramic tubes. Finally the development of two pathways ("Coating onto" and "Grafting from") were assessed for their ability to modify the tubular ceramic support and preliminary gas separation tests were performed

Synthèse de divers 18-crowns-6 porteurs d'une partie ose condensée aptes à être fixes sur un support chromatographique ; greffage de silice pour HPLC ; synthèse de supports chromatographiques porteurs de motifs halogénure de benzyle et étude de leur fonctionnalisation par les composés crowns préparés ; complexation des éthers crowns par le potassium, le phenylglycinate d'éthyle, l'éthyl phényl ammonium ; séparation chromatographique de la phénylglycine

Ce travail de thèse constitue une contribution à la compréhension de la structure de verres à base de TeO2, notamment au sein des systèmes binaires TeO2-TiO2 et TeO2-Tl2O. La spectroscopie Raman et la diffusion totale des rayons X (extraction des fonctions de distribution de paires) ont permis de déterminer que la structure du verre évolue fortement avec l'ajout de Tl2O tandis que l'ajout de TiO2 n'entraîne pas d'évolution structurale significative. Des simulations par dynamique moléculaire sont réalisées pour la première fois dans le système TeO2-TiO2. Pour cela, nous avons affiné un jeu de potentiels interatomiques Te(IV)-O transférable aux matériaux tellurites, permettant de reproduire les structures des polymorphes de TeO2 ainsi que celles de plus d'une douzaine de composés cristallins à base de TeO2. La structure simulée du verre pur TeO2 est composé majoritairement d'unités TeO4 et TeO3, engendrant une coordinence de l'atome Te de 3,71, inférieure à celle dans les polymorphes de TeO2. L'ajout de TiO2 renforce la connectivité du réseau tellurite via la diminution de la proportion d'atomes O terminaux et la création de ponts Te-O-X (avec X = Te, Ti), ce qui justifierait une amélioration des propriétés mécaniques et thermiques de ces verres<br>This work aims to improve the structural description of the pure TeO2 glass and to give an insight of the structure of TeO2-MxOy binary glasses (M = Ti, Tl) by means of X-ray total scattering experiments and molecular dynamics (MD) simulations. We were able to determine, via Raman spectroscopy and X-ray total scattering experiments, that Tl2O causes the depolymerization of the glass structure whereas the addition of TiO2 leads to the conservation of Te(IV) environments. The MD simulations of the pure TeO2 glass and glasses within the TeO2-TiO2 system are carried out. First, we refined the Te(IV)-O interatomic potentials allowing us to reproduce TeO2 polymorphs as well as 14 crystalline structures containing TeO2. It was then demonstrated that the TeO2 glass consists largely of TeO4 and TeO3 units, giving a coordination number of 3.71, lower than that in the TeO2 polymorphs. Adding TiO2 tends to reinforce the connectivity within the tellurite framework via the reduction of the number of non-bridging oxygen atoms and the creation of Te-O-X bridges (with X = Te, Ti), which would justify the improvement of mechanical and thermal resistance of these glasses

abstract: Mixed-ionic electronic conducting (MIEC) oxides have drawn much attention from researchers because of their potential in high temperature separation processes. Among many materials available, perovskite type and fluorite type oxides are the most studied for their excellent oxygen ion transport property. These oxides not only can be oxygen adsorbent or O2-permeable membranes themselves, but also can be incorporated with molten carbonate to form dual-phase membranes for CO2 separation. Oxygen sorption/desorption properties of perovskite oxides with and without oxygen vacancy were investigated first by thermogravimetric analysis (TGA) and fixed-bed experiments. The oxide with unique disorder-order phase transition during desorption exhibited an enhanced oxygen desorption rate during the TGA measurement but not in fixed-bed demonstrations. The difference in oxygen desorption rate is due to much higher oxygen partial pressure surrounding the sorbent during the fixed-bed oxygen desorption process, as revealed by X-ray diffraction (XRD) patterns of rapidly quenched samples. Research on using perovskite oxides as CO2-permeable dual-phase membranes was subsequently conducted. Two CO2-resistant MIEC perovskite ceramics, Pr0.6Sr0.4Co0.2Fe0.8 O3-δ (PSCF) and SrFe0.9Ta0.1O3-δ (SFT) were chosen as support materials for membrane synthesis. PSCF-molten carbonate (MC) and SFT-MC membranes were prepared for CO2-O2 counter-permeation. The geometric factors for the carbonate phase and ceramic phase were used to calculate the effective carbonate and oxygen ionic conductivity in the carbonate and ceramic phase. When tested in CO2-O2 counter-permeation set-up, CO2 flux showed negligible change, but O2 flux decreased by 10-32% compared with single-component permeation. With CO2 counter-permeation, the total oxygen permeation flux is higher than that without counter-permeation. A new concept of CO2-permselective membrane reactor for hydrogen production via steam reforming of methane (SRM) was demonstrated. The results of SRM in the membrane reactor confirm that in-situ CO2 removal effectively promotes water-gas shift conversion and thus enhances hydrogen yield. A modeling study was also conducted to assess the performance of the membrane reactor in high-pressure feed/vacuum sweep conditions, which were not carried out due to limitations in current membrane testing set-up. When 5 atm feed pressure and 10-3 atm sweep pressure were applied, the membrane reactor can produce over 99% hydrogen stream in simulation.<br>Dissertation/Thesis<br>Doctoral Dissertation Chemical Engineering 2020

碩士<br>國立宜蘭大學<br>化學工程與材料工程學系碩士班<br>103<br>In this study, the oligomer, glycerol propoxylate-block-ethoxylate (GP-b-E) or the amino-modified hollow silica (NH2-HS) with different shaps as the additives were added in the ethyl cellulose (EC) polymer to prepare a series of EC composite membranes. These composite membranes were applied to the gas separation processes. The effects of the concentration of casting solution and the oligomer content on the properties and gas separation performance of membrane were investigated. The effects of the shape, surface amino-modification, and content of hollow silica on the properties and gas separation performance of membrane were also studied in this study. Scanning electron microscope (SEM) was used to observe the morphologies of the membranes and hollow silica. Fourier transform infrared (FTIR) was used to analyze the surface chemical structure of amino-modified hollow silica. Energy Dispersive X-ray spectrometer (EDX) was used to observe the distribution of hollow silica in the membrane. Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) were used to analyze the thermal properties of the membranes. Tensile tester (Instron) was used to measure the mechanical properties of the membranes. The gas sorption measurement was carried out by the microbalance to determine the adsorbed amount of gas. In the addition system of GP-b-E oligomer, from the SEM observation, the addition of the GP-b-E oligomer in the EC membrane causes the membrane morphology converts the more closed porous structure to the more connected porous structure. With an increase in the added amount of GP-b-E, connected porous structure in the membrane increased. From the results of the DSC and mechanical property measurements, the addition of the GP-b-E oligomer causes a decrease in the melting point, Young's modulus, and tensile strength and an increase in the elongation. From the results of the gas permeation experiments, the addition of the oligomer having the ether groups in the EC membrane can effectively promote the permeability coefficients of carbon dioxide and oxygen. The EC/GP-b-E composite membrane prepared by the addition content of EC:GP-b-E=1:0.5 (by weight) has the desirable gas separation performance which is the carbon dioxide and oxygen permeability coefficients of 1506.3 barrer and 228.5 barrer and the carbon dioxide/nitrogen and oxygen/nitrogen selectivities of 17.5 and 2.7, respectively. From the analysis of the solution-diffusion mechanism, the gas permeability coefficient and selectivity of the EC/GP-b-E composite membrane are dominated by it’s the gas diffusivity coefficient and diffusivity selectivity. In the addition system of HS and NH2-HS, from the results of SEM observation and FTIR analysis, the amino-modified hollow silica with different shaps was prepared successfully. From the SEM observation and EDX analysis, the spherical NH2-HS can be distributed in the EC membrane uniformly. From the result of mechanical property measurement, the addition of the spherical NH2-HS causes a decreases in Young's modulus, tensile strength and elongation. From the TGA and DSC measurements, the addition of the spherical NH2-HS in the EC membrane enhances the thermal stability of the membrane slightly but decreases the glass transition temperature (Tg) and melting point (Tm). From the results of the gas permeation experiments, the addition of the spherical HS in the EC membrane can effectively promote the permeability coefficients of carbon dioxide and oxygen. The EC/spherical NH2-HS composite membrane prepared by the addition content of EC:spherical NH2-HS=1:0.1 (by weight) has the desirable gas separation performance which is the carbon dioxide and oxygen permeability coefficients of 190.1 barrer and 33.7 barrer and the carbon dioxide/nitrogen and oxygen/nitrogen selectivities of 19.7 and 3.5, respectively.

Vortex Tube (VT) is a simple device having no moving mechanical parts, in which compressed gas at high pressure is injected through one or more tangential nozzles into a vortex chamber resulting in the separation of the inlet flow into two low pressure streams. One of the streams is the peripheral flow that is warmer than the inlet stream while the other is the central (core) flow that is colder than the inlet stream. This separation of the inlet flow into high and low temperature streams is known as temperature or energy separation. It is suggested by many investigators that compressed air of few atmospheres pressure and at room temperature can produce temperatures as high as +200ºC at the hot end (peripheral flow exit) and as low as -50ºC at the cold end (core flow exit) of the VT. Though VTs have large potential for simple heating and cooling applications, the mechanism of energy separation is not clear so far. Based on their studies, many investigators have suggested various theories, different from each other, but having specific lacunas and is an unresolved issue. Also, till date, experimental and industrial designs of the VTs are based purely on empirical correlations. Apart from heating and cooling applications, VTs can also be used for separation of binary gas mixtures and separation of oxygen from two-phase precooled air stream. The conceptual futuristic cryogenic launch vehicle designs are being attempted with in-flight liquid oxygen (LOX) collection system that significantly improves the pay load fraction. Vortex tube technology is one of the few promising technologies for futuristic in-flight LOX separation based launch vehicles. This technology has significant advantages over its counterparts as it is a simple, compact and light weight, and most importantly have no moving parts and unaffected by gravity and orientation. In order that VTs become an acceptable technology for in-flight LOX separation system, it is necessary to achieve minimum oxygen purity of 90% with more than 60% yield (separation efficiency) for the oxygen enriched stream in the VT. A survey of the available open literature has shown very little reported details, in particular, on achieving the required specifications for in-flight LOX separation systems. Till date, the highest LOX purity of 60% with 40% separation efficiency has been reported with VT technology. In view of the above mentioned facts, the work carried out has been focused on to: • Optimize the critical parameters of the VT to achieve maximum energy separation by CFD and experimental studies. • Understand the flow behaviour in the VT by estimating the velocity, temperature and pressure profiles at various locations in the VT and validation of secondary circulation flow and its effect on the performance of energy separation in VT. • Estimation of the energy transfer between the core and the peripheral layers of fluid flow in VT by analytical and CFD methods to propose the most appropriate mechanism of energy separation in VT. • Design and development of a dedicated experimental setup for both energy separation and LOX separation studies in VTs. • Design and fabrication of straight and conical VTs and experimental programme on energy separation and LOX separation. • Development of the VT air separation technology to achieve the required specifications of in-flight LOX separation system for futuristic launch vehicles. With these specific objectives and motivations, the total work was carried out with the following planned and sequential steps: • The first step was the CFD modeling of the VT with the available CFD software (Star-CD) and obtain the energy separation phenomena for a 12mm diameter VT. After gaining sufficient confidence level, optimization of the critical parameters like the air injection nozzle profile, number of nozzles, cold end orifice diameter dc, length to diameter (L/D) ratio, hot gas fraction etc of the VT was carried out through CFD and experimental studies. • The studies show that 6 convergent nozzles perform better in comparison to other configurations like circular helical, rectangular helical, 2 convergent and 6 straight nozzles. The studies also show that cold end orifice diameter (dc) plays an important role on energy separation and bring out the existence of secondary circulation flow with improper design of cold end orifice diameter. Through our studies, the effect of cold end diameter on the secondary circulation flow has been evaluated for the first time. Also, the mechanism of energy transfer in VT based on heat pump mechanism enabled by secondary circulation flow as suggested by some investigators has been evaluated in our studies. The studies show that cold end orifice diameter dc = 7mm is optimum for 12mm diameter VT, which matches fairly with the correlations given by other investigators. The studies confirms that CFD modeling carried out in this work is capable of selecting the correct dc value for a VT, without resorting to the empirical correlations as a design guide or a laborious experimental programme. • Through the CFD and experimental studies on different length to diameter (L/D) ratios and hot gas fractions, maximum hot gas temperature of 391K was obtained for L/D = 30 with hot gas fraction of 12-15 % and minimum cold gas temperature of 267K for L/D = 35 was obtained for cold gas fraction ≈ 60% (lowest cold gas fraction possible with the present experimental system). • CFD analysis has been carried out to investigate the variation of static and total temperatures, static and total pressures as well as the velocity components of the particles as it progresses in the flow field, starting from the entry through the nozzles to the exit of the VT by tracking the particles to understand the flow phenomenon and energy transfer mechanism inside the VT. The studies indicate that the mechanism of energy transfer from the core flow to the peripheral flow in VT is predominantly occurs by the tangential shear work. Thus the investigations reported in the thesis have given a clear understanding of the contributing mechanism for energy separation in VT, which has been an unresolved issue for long time. The net energy transfer between the core and the peripheral fluid has been calculated analytically and compared with the values obtained by CFD model for VTs of L/D ratios equal to 10 and 30. The net energy transfer by analytical and CFD model for VT with L/D = 10 is 159.87W and 154.2W respectively whereas the net energy transfer by analytical and CFD model for VT with L/D = 30 is 199.87W and 192.3W respectively. The results show that CFD results are in very good agreement with the analytical results and CFD can be used as a tool for optimization of the critical parameters and to analyze the flow parameters and heat transfer analysis for VTs. Also, the net energy transfer between the core and peripheral fluids calculated analytically matches very well with that of the net energy transfer by CFD analysis, without considering the effect of acoustic streaming. Thus acoustic streaming may not be the mechanism of energy separation in VT as suggested by some investigators. • By optimizing the critical parameters of the 12mm diameter straight VT through CFD and experimental studies, LOX separation studies have been carried out using both straight and conical VTs of dc = 7mm and of different L/D ratios for high LOX purity and separation efficiency. It is observed that conical (3º divergence) VTs perform better as compared to straight VTs for LOX separation whereas straight VTs perform better for energy separation. The better performance of conical VT as compared to straight VTs can be attributed to its increased surface area for condensation-evaporation phenomenon of oxygen and nitrogen molecules. Experimental studies have been conducted to evaluate the influence of the inlet pressure and the inlet temperature (liquid fraction) on LOX purity. Studies indicate that for achieving high LOX purity for the studied experimental system, the inlet pressure is to be in the range of 6-6.5bar and there exists a very narrow band of inlet temperature zone in which high LOX purity can be achieved. Experimental studies on VTs show that VT can be optimized suitably either for high LOX purity with low separation efficiency or low LOX purity with high separation efficiency by adjusting the hot end mass fraction accordingly. It is also observed that it is not possible to obtain both high purity and high separation efficiency simultaneously with the single VT. Staging approach has to be adapted to achieve higher LOX purity with higher separation efficiency. By staging the VTs, the enriched air stream (hot end outlet flow) from the first stage of VTs is introduced to the inlet of the second stage of VTs. Experimental studies have been conducted to evaluate the design parameters on staging of VTs. LOX purity of 48% with 89% separation efficiency has been achieved for conical first stage VT of L/D = 25. LOX purity of about 94% with separation efficiency of 84% has been achieved for 50% oxygen content at the inlet of the second stage VT. Similarly, LOX purity of 96% with separation efficiency of 73.5% has been achieved for 60% oxygen content at the inlet of the VT. This is the highest LOX purity and separation efficiency reported so far indicating that, conical VT of optimized diameter, L/D ratio and orifice diameter can yield the hot end flow very close to the target value of futuristic in-flight LOX separation based launch vehicles. The present investigation has focused the optimization of the critical parameters of VTs through CFD and experimental studies. It has also given an insight to the mechanism of energy transfer between the core and peripheral flow in VT by evaluating two of the existing theories on mechanism of energy transfer in VT. The studies also highlighted the fact that custom designed and precision fabricated VTs can be very useful for obtaining maximum / minimum temperatures of fluid flow as well as LOX separation with high purity and high separation efficiency needed for futuristic in-flight LOX separation based space launch vehicles.

Vortex Tube (VT) is a simple device having no moving mechanical parts, in which compressed gas at high pressure is injected through one or more tangential nozzles into a vortex chamber resulting in the separation of the inlet flow into two low pressure streams. One of the streams is the peripheral flow that is warmer than the inlet stream while the other is the central (core) flow that is colder than the inlet stream. This separation of the inlet flow into high and low temperature streams is known as temperature or energy separation. It is suggested by many investigators that compressed air of few atmospheres pressure and at room temperature can produce temperatures as high as +200ºC at the hot end (peripheral flow exit) and as low as -50ºC at the cold end (core flow exit) of the VT. Though VTs have large potential for simple heating and cooling applications, the mechanism of energy separation is not clear so far. Based on their studies, many investigators have suggested various theories, different from each other, but having specific lacunas and is an unresolved issue. Also, till date, experimental and industrial designs of the VTs are based purely on empirical correlations. Apart from heating and cooling applications, VTs can also be used for separation of binary gas mixtures and separation of oxygen from two-phase precooled air stream. The conceptual futuristic cryogenic launch vehicle designs are being attempted with in-flight liquid oxygen (LOX) collection system that significantly improves the pay load fraction. Vortex tube technology is one of the few promising technologies for futuristic in-flight LOX separation based launch vehicles. This technology has significant advantages over its counterparts as it is a simple, compact and light weight, and most importantly have no moving parts and unaffected by gravity and orientation. In order that VTs become an acceptable technology for in-flight LOX separation system, it is necessary to achieve minimum oxygen purity of 90% with more than 60% yield (separation efficiency) for the oxygen enriched stream in the VT. A survey of the available open literature has shown very little reported details, in particular, on achieving the required specifications for in-flight LOX separation systems. Till date, the highest LOX purity of 60% with 40% separation efficiency has been reported with VT technology. In view of the above mentioned facts, the work carried out has been focused on to: • Optimize the critical parameters of the VT to achieve maximum energy separation by CFD and experimental studies. • Understand the flow behaviour in the VT by estimating the velocity, temperature and pressure profiles at various locations in the VT and validation of secondary circulation flow and its effect on the performance of energy separation in VT. • Estimation of the energy transfer between the core and the peripheral layers of fluid flow in VT by analytical and CFD methods to propose the most appropriate mechanism of energy separation in VT. • Design and development of a dedicated experimental setup for both energy separation and LOX separation studies in VTs. • Design and fabrication of straight and conical VTs and experimental programme on energy separation and LOX separation. • Development of the VT air separation technology to achieve the required specifications of in-flight LOX separation system for futuristic launch vehicles. With these specific objectives and motivations, the total work was carried out with the following planned and sequential steps: • The first step was the CFD modeling of the VT with the available CFD software (Star-CD) and obtain the energy separation phenomena for a 12mm diameter VT. After gaining sufficient confidence level, optimization of the critical parameters like the air injection nozzle profile, number of nozzles, cold end orifice diameter dc, length to diameter (L/D) ratio, hot gas fraction etc of the VT was carried out through CFD and experimental studies. • The studies show that 6 convergent nozzles perform better in comparison to other configurations like circular helical, rectangular helical, 2 convergent and 6 straight nozzles. The studies also show that cold end orifice diameter (dc) plays an important role on energy separation and bring out the existence of secondary circulation flow with improper design of cold end orifice diameter. Through our studies, the effect of cold end diameter on the secondary circulation flow has been evaluated for the first time. Also, the mechanism of energy transfer in VT based on heat pump mechanism enabled by secondary circulation flow as suggested by some investigators has been evaluated in our studies. The studies show that cold end orifice diameter dc = 7mm is optimum for 12mm diameter VT, which matches fairly with the correlations given by other investigators. The studies confirms that CFD modeling carried out in this work is capable of selecting the correct dc value for a VT, without resorting to the empirical correlations as a design guide or a laborious experimental programme. • Through the CFD and experimental studies on different length to diameter (L/D) ratios and hot gas fractions, maximum hot gas temperature of 391K was obtained for L/D = 30 with hot gas fraction of 12-15 % and minimum cold gas temperature of 267K for L/D = 35 was obtained for cold gas fraction ≈ 60% (lowest cold gas fraction possible with the present experimental system). • CFD analysis has been carried out to investigate the variation of static and total temperatures, static and total pressures as well as the velocity components of the particles as it progresses in the flow field, starting from the entry through the nozzles to the exit of the VT by tracking the particles to understand the flow phenomenon and energy transfer mechanism inside the VT. The studies indicate that the mechanism of energy transfer from the core flow to the peripheral flow in VT is predominantly occurs by the tangential shear work. Thus the investigations reported in the thesis have given a clear understanding of the contributing mechanism for energy separation in VT, which has been an unresolved issue for long time. The net energy transfer between the core and the peripheral fluid has been calculated analytically and compared with the values obtained by CFD model for VTs of L/D ratios equal to 10 and 30. The net energy transfer by analytical and CFD model for VT with L/D = 10 is 159.87W and 154.2W respectively whereas the net energy transfer by analytical and CFD model for VT with L/D = 30 is 199.87W and 192.3W respectively. The results show that CFD results are in very good agreement with the analytical results and CFD can be used as a tool for optimization of the critical parameters and to analyze the flow parameters and heat transfer analysis for VTs. Also, the net energy transfer between the core and peripheral fluids calculated analytically matches very well with that of the net energy transfer by CFD analysis, without considering the effect of acoustic streaming. Thus acoustic streaming may not be the mechanism of energy separation in VT as suggested by some investigators. • By optimizing the critical parameters of the 12mm diameter straight VT through CFD and experimental studies, LOX separation studies have been carried out using both straight and conical VTs of dc = 7mm and of different L/D ratios for high LOX purity and separation efficiency. It is observed that conical (3º divergence) VTs perform better as compared to straight VTs for LOX separation whereas straight VTs perform better for energy separation. The better performance of conical VT as compared to straight VTs can be attributed to its increased surface area for condensation-evaporation phenomenon of oxygen and nitrogen molecules. Experimental studies have been conducted to evaluate the influence of the inlet pressure and the inlet temperature (liquid fraction) on LOX purity. Studies indicate that for achieving high LOX purity for the studied experimental system, the inlet pressure is to be in the range of 6-6.5bar and there exists a very narrow band of inlet temperature zone in which high LOX purity can be achieved. Experimental studies on VTs show that VT can be optimized suitably either for high LOX purity with low separation efficiency or low LOX purity with high separation efficiency by adjusting the hot end mass fraction accordingly. It is also observed that it is not possible to obtain both high purity and high separation efficiency simultaneously with the single VT. Staging approach has to be adapted to achieve higher LOX purity with higher separation efficiency. By staging the VTs, the enriched air stream (hot end outlet flow) from the first stage of VTs is introduced to the inlet of the second stage of VTs. Experimental studies have been conducted to evaluate the design parameters on staging of VTs. LOX purity of 48% with 89% separation efficiency has been achieved for conical first stage VT of L/D = 25. LOX purity of about 94% with separation efficiency of 84% has been achieved for 50% oxygen content at the inlet of the second stage VT. Similarly, LOX purity of 96% with separation efficiency of 73.5% has been achieved for 60% oxygen content at the inlet of the VT. This is the highest LOX purity and separation efficiency reported so far indicating that, conical VT of optimized diameter, L/D ratio and orifice diameter can yield the hot end flow very close to the target value of futuristic in-flight LOX separation based launch vehicles. The present investigation has focused the optimization of the critical parameters of VTs through CFD and experimental studies. It has also given an insight to the mechanism of energy transfer between the core and peripheral flow in VT by evaluating two of the existing theories on mechanism of energy transfer in VT. The studies also highlighted the fact that custom designed and precision fabricated VTs can be very useful for obtaining maximum / minimum temperatures of fluid flow as well as LOX separation with high purity and high separation efficiency needed for futuristic in-flight LOX separation based space launch vehicles.

Research Doctorate - Doctor of Philosophy (PhD)<br>Oxygen constitutes 30% share of the global industrial gas market and is the second largest-volume chemical produced in the world after sulfuric acid. Commercial applications of oxygen can be found in industry sectors as diverse as metallurgical industry, chemical synthesis, glass manufacturing, pulp and paper industry, petroleum recovery / refining, and health services. Advanced power generation systems, such as integrated gasification combined cycle (IGCC), Oxy-fuel combustion and solid oxide fuel cells, SOFC represent emerging markets for oxygen. Oxygen is commonly produced at industrial scales by air separation using cryogenic distillation and adsorption based technologies. Advanced technologies such as membrane separation (e.g. ion-transport membrane, ITM) and in-situ air separation are also being developed for small-volume point-of-use oxygen generation. While conventional cryogenic and adsorption air separation methods are matured technologies, their energy intensity and high costs can no longer be tolerated under the current economic, energy, and environmental crises. Membrane separation methods whilst less energy intensive remain expensive due to challenges associated with their fabrication, installation and integration. In view of the above, a team of researchers led by Prof Moghtaderi at the University of Newcastle devised the Chemical Looping Air Separation (CLAS) process and its variants including: (i) Integrated Chemical Looping Air Separation (ICLAS) process for oxy-fuel applications and (ii) Redox Energy Storage (RES) process for thermo-chemical energy storage. Depending on the operating temperature and frontend conditions, the energy input into the CLAS process is 50% - 80% lower than that required for the cryogenic process and, as such, the CLAS family of processes has a relatively small energy footprint. CLAS works in a cyclic fashion by continuous recirculation of metal oxide particles between a set of two interconnected reactors, where oxidation (O₂ coupling) and reduction (O₂ decoupling) of carrier particles take place, respectively. In the original version of the CLAS process the reduction half cycle is carried out in presence of steam so that the desired oxygen product can be obtained by condensing out the steam. However, the production and condensation of steam is energy consuming and if it can be replaced by an alternative method the overall energy footprint of the CLAS process can be further reduced. Motivated by this, Prof Moghtaderi and his team turned their attention on to yet another variant of CLAS named Membrane Integrated Chemical Looping Air Separation (MICLAS) where the oxygen product from the reduction reactor is separated from steam or other suitable reducing agents (e.g. N₂) using an oxygen transport membrane (OTM) system. The combination of the OTM and CLAS in the MICLAS process creates an air separation platform which is far more cost effective than the standalone OTM based processes because of the smaller volume of gases involved, thereby, smaller physical dimensions and lower capital / operating costs. The principal vision in this PhD project was to determine the fundamental science underpinning the operation of the above integrated membrane systems using a combined theoretical and experimental approach. While both steam and nitrogen compatible OTMs studied theoretically, the primary focus of the experimental investigations was on the use of OTMs compatible with nitrogen as past experience has shown that by and large steam detrimentally impacts on the operation of membranes suitable for oxygen transport. As part of the theoretical component of the project the feasibility of integrating an OTM into the CLAS process was examined using Aspen Plus simulations, in which the net amount of energy required for each process was determined. An empirical model was then developed for calculating the oxygen permeation fluxes of the membranes using both simulation results and literature-based experimental data. It was found that the energy saving of MICLAS over the conventional CLAS was approximately 30% if a 100% oxygen recovery was assumed. When the actual oxygen recovery data were employed the energy saving of MICLAS over CLAS was 12% for BSCF type perovskite membranes reported in the literature and 16% for BSCF and 22% for LSCF type perovskite membranes specifically developed as part of this PhD study. The experimental component of the project was designed to address several important research questions fundamental to the effective operation of the MICLAS process. Of these, an in-depth understanding of the mechanisms underpinning the particle deposition on a membrane and its impact on the membrane performance (i.e., the oxygen flux across the membrane and thereby the reactions taking place within the CLAS system) was the first research question examined in this study. For this purpose, a fluidised bed chamber was designed and constructed to study particle deposition on surrogate ceramic membranes. Images of the surface coverage of each membrane were taken with a Phantom V5 high speed camera and analysed using Image J software. Preliminary deposition experiments using the experimental setup with the Perspex fluidised bed created a severe electrostatic charging issue which led to the redesign and construction of the fluidised bed chamber. The modified deposition setup consisted of a combination of a fluorine-doped tin oxide (FTO) coated glass window and a complete metallic body machined from aluminium. Grounding the experimental setup, including the new fluidised bed chamber, almost completely eliminated the electrostatic charging problem. The results of this set of experiments showed that the degree of particle deposition and electrostatic forces acting upon the particle deposition in the two phase flow were minimised. The experimental results showed that the surface coverage of the surrogate membranes with particles was less than 3%. Therefore, the impact of particle deposition which was initially considered to be detrimental to the effectiveness of the membrane was found to be insignificant. The other research questions addressed in the experimental component of the project were related to the effectiveness of membrane materials and identifying the most suitable candidate for MICLAS based processes. In this context, experimental studies were directed toward the synthesis of two types of perovskite membranes and their characterisation. These were namely Ba<usb>0.5</sub>Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF5582) and La0.5Sr0.5Co0.8Fe0.2O3−δ (LSCF5582) which were prepared at different sintering temperatures and characterised. The BSCF5582 membranes were also synthesised using a modified Pechini method in collaboration with the FIMLab at the University of Queensland. The BSCF5582 and LSCF5582 membranes were sintered in the temperature ranges of 1000 °C - 1150 °C for 8 h and 1050 °C - 1350 °C for 5 h, respectively. The sintered membranes were characterised using an array of complementary techniques to determine the optimum sintering temperature in order to optimise their desired properties and oxygen permeability. The surface morphology of the membranes were examined using field emission scanning electron microscopy, which revealed that the segregation of the cobalt oxide phase occurring at the sintering temperatures of 1250 °C and 1100 °C for the LSCF5582 and BSCF5582 membranes, respectively; impacts on the oxygen permeability of the membranes. The sintering experiments also revealed that the sintering temperatures of 1350 °C and 1150 °C were impractical for the sintering of LSCF5582 and BSCF5582 membranes due to an excessive liquid phase forming at these temperatures. The phase and crystal structure of the membranes were identified using the X-ray diffraction technique. The presence of segregated phases for the membranes at high sintering temperatures was also verified using XRD and analysed using EDS techniques. The surface areas of the membranes were measured using the BET method in order to study their oxygen adsorption and desorption characteristics. A significantly lower surface area was acquired for the membranes sintered at elevated temperatures due to the formation of larger grain sizes at these temperatures. For example, the LSCF5582 fresh powder and LSCF5582 membrane sintered at 1350 °C had the highest (5.84 m².g^-1) and the lowest (0.556 m².g^-1) surface areas, respectively. Studies of the oxygen desorption/adsorption characteristics of the membranes showed a significantly higher oxygen adsorption rate over the oxygen desorption rate. The characterisation results demonstrated that the optimum sintering temperatures of the LSCF5582 and BSCF5582 membranes were 1200 °C and 1050 °C, respectively. The oxygen permeation experiments were conducted in three permeation cells with: Concentric Tube configuration, Double-Tube configuration and Multi-Tube configuration. The adjustable variables in the Concentric Tube setup were the pressure and flow rate of the sweep gas and the permeation temperature. The Double-Tube setup was used to determine the oxygen recovery of the membranes. However, sealing was the major challenge in the Double-Tube setup; therefore the Multi-Tube setup was designed and constructed. The adjustable parameters in the Multi-Tube setup were the flow rates and pressures of the feed and the sweep gas, as well as the permeation temperature. Oxygen permeation fluxes increased significantly with temperature due to the enhanced formation of oxygen vacancy concentrations in the crystal structure of the membranes with increased temperatures. As oxygen ions migrate through the vacancies, the oxygen permeation fluxes increased at elevated temperatures due to the increased oxygen vacancies. Considerably higher oxygen permeation fluxes were acquired using the Multi Tube setup than with the other permeation setups as the oxygen partial pressure gradient was adjustable in this particular setup. In order to investigate the feasibility of the integration of an OTM into the CLAS process, the reduction reactions of the oxygen carrier particles was initially examined using the TGA instrument and a fixed bed reactor. The equilibrium conversion of the metallic oxides and the concentrations of oxygen produced at different reduction temperatures were determined. Subsequently, the metallic oxides were packed in the vicinity of the LSCF and BSCF membranes using the Multi-Tube apparatus. The permeation fluxes and recoveries of oxygen obtained with the membranes were measured in the course of the reduction of the metallic oxide particles containing 17 weight percent active CuO. Finally, in a set of experiments, hypothetical oxygen carriers containing 10%, 15% and 21% oxygen concentrations were considered as future oxygen carriers for the CLAS process. The permeability and oxygen recovery of the LSCF5582 and BSCF5582 membranes were measured under simulated experimental conditions using hypothetical oxygen carriers. A mixture of oxygen and nitrogen was used to simulate the oxygen content of the hypothetical oxygen carriers. The experimental results showed that significantly higher oxygen permeation fluxes and recoveries were obtained for membranes at a 10% oxygen concentration, compared with a 21% oxygen concentration. In summary, it has been demonstrated that the OTM integrated CLAS process, even with the existing oxygen carriers which contain 0.3% oxygen, is a viable technology that can be usefully applied to a future air separation system.

碩士<br>國立成功大學<br>航空太空工程學系<br>102<br>The characteristic design of a Texaco gasifier, with a coaxial coal-slurry oxygen-jet nozzle and an outer annular oxygen-jet, has a significant influence on the gasification process. For the fuel-oxidant coaxial jet nozzle, the central oxygen-jet flow impinges on the coal-slurry stream and assists in the atomization of the coal slurry. The outer oxygen-jet, which splits the oxygen intake stream into two, makes an influence of the flame position and causes an effect of the gasification efficiency and coal conversion rate. In the study, numerical simulations of the coal slurry gasification process inside an entrained-flow gasifier with separate oxygen feeding streams are investigated using the commercial computational fluid dynamic software, ANSYS/ FLUENT. Three parameters, namely, positions of the outer annulus feeding tunnel, oxygen/carbon ratio, and oxygen feeding velocity of the outer annulus streams, have been examined to determine the effects of operating conditions on the gasification process. The numerical results show that the flame distribution is affected by the positions of the outer tunnel. As the outer tunnel is moved away from the central axis, the flame surface is extended and leads to a higher temperature in the downstream of the gasifier. In the investigations of the oxygen/carbon ratio, the lower the oxygen/carbon ratio is, the lower outlet temperature and the poorer the coal conversion rate. The distribution of the combustion region and the coal conversion rate is strongly affected by the feeding velocity of the outer annulus stream. The coal conversion rate and the cold gas efficiency are in a descending trend when the oxidant feeding is operated in high velocity. The compositions of the product gases are affected by the WGS. Moreover, the reaction rate of the WGS reaction is sensitive to the temperature of the gasification chamber.

碩士<br>中原大學<br>化學工程研究所<br>90<br>The plasma deposited nitrogen-containing polymers onto commercial poly-4-methyl-1-pentene (TPX) membrane and their application in O2/N2 separations were investigated. The first part of this study is the comparison of plasma-polymerized films from pure C2H2, C2H2/N2, C2H2/NH3, pure C2H6, and C2H6/N2 mixtures under the same operating condition. It was found that O2/N2 separation performance was drastically improved by nitrogen-containing plasma polymer. Highly cross-linked film was deposited from acetylene-based rather than ethane-based plasmas. Thus, the separation of oxygen over nitrogen in the plasma polymer is mainly determined by the diffusion rate difference of both molecules. It was also found that the addition of nitrogen into hydrocarbon plasmas enhanced the deposition rate and reduced the internal stress of plasma-polymerized film. In the second part of the study, the effects of operating parameters on C2H2/NH3 plasma polymer were investigated. It was found that the O2/N2 selectivity of the plasma polymer increases with plasma power, chamber pressure, and C2H2 flow rate. OES spectrum indicated that stronger emissions of CN (388.3 nm) radicals appeared in higher plasma power, higher chamber pressure, and lower monomer flow rate conditions. It is proposed that CN radical is the main resource of nitrogen-containing bondings in the plasma polymer.