Segui questo link per vedere altri tipi di pubblicazioni sul tema: Membrane.
Tesi sul tema "Membrane"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Membrane".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
PAGLIERO, MARCELLO. "New membranes for membrane distillation process". Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1046350.
Testo completoAbstract (sommario):
The PhD research program was focused of the development of new hydrophobic membranes suitable for membrane distillation (MD) operation. In particular, the preparation of polymeric flat sheet membranes via nonsolvent induced phase separation (NIPS) technique was investigated. This method allows to fine-tune a large number of variables in order to obtain membranes with an ample variety of different morphologies and properties. Therefore, a systematic study on the important factors affecting the membrane structure, which in turn determines the distillation performance, was carried out. The selected polymer was polyvinylidene fluoride (PVDF), the solvent was dimethylformamide (DMF).
First, the effect of the dope solution composition was evaluated. The polymer amount was found to be a key element in defining the porosity and the pore size of the final membrane. Moreover, a minimum critical concentration required to obtain a proper structure was identified on the basis of the dope solution viscosity. In fact, at lower concentrations brittle or defective films were produced.
Another important preparation parameter thoroughly investigated was the coagulation bath strength. Harsh nonsolvents induce fast precipitation creating a dense skin above a macrovoid-dominated layer, while weak coagulation media promote a delayed demixing and generate uniform and symmetric structures. Using a semi crystalline polymer such as PVDF, the precipitation rate becomes even more important because it also influences the crystallization of the polymer. The strength of the coagulation bath was regulated by adding different amounts of ethanol to the water bath, from 0% up to 96% v/v. Optimization of this parameter allowed to prepare almost superhydrophobic membranes that were able to withstand the pressure and temperature conditions during vacuum membrane distillation (VMD) tests and to deliver high distillate fluxes and total salt rejection when treating a concentrated NaCl solution.
A different approach to improve the membrane performance was exploited in further phase of activity. Different kinds of pore forming agents – such as polyethylene glycols and lithium chloride – were added to the dope solution in order to enhance the porosity and control the pore size. Since the support material can act as an added mass transfer resistance, it was decided to cast these membranes without any reinforcement. However, the absence of any rigid support caused severe shrinkage phenomena during the drying of the membranes leading to an almost complete collapse of the porous structure. It was found that the structure could be preserved by simply clamping the wet membrane on a stiff planar surface and leaving it to dry at room temperature.
The amount and type of the additive had impacts on both kinetic and thermodynamic factors governing the phase separation process. By adjusting the dope solution composition, it was possible to favour one or the other to obtain membranes with the desired structure and performance. These unsupported membranes were not able to bear the pressure difference normally applied during VMD, therefore they were tested using a direct contact membrane distillation (DCMD) setup.
Since the presence of the support material is mandatory for VMD application, the effect of different kinds of supports was investigated. In particular, several commercial nonwovens were used to prepare PVDF membranes based on the knowledge acquired during the first phase of the PhD activity. Moreover, along with the nonwovens, three polymeric nets, characterized by different structure and made with different polymers, were tested as possible supports. While the commercial nonwovens did not alter too much the performance and morphology of the PVDF membranes, using the nets some remarkable effects were registered. The alternation between holes and crests of the nets caused the formation of membranes with zones having different porosities. The VMD tests highlighted the better performance of the nonwoven casted membranes. However, the patterned surface of the net supported membranes resulted in lower flux decline when a concentrated NaCl solution was used as feed.
Polymeric membranes are the most studied type for MD application both for the easy processability and the low production costs. Moreover, the commonly used polymers can withstand the normal operation conditions for desalination or wastewater treatment applications. However, the possibility of producing membranes able to resist higher temperatures and pressures would open the way to new MD applications. One of the possible paths to reach this goal is the exploitation of ceramic membranes. Ceramic material are nevertheless naturally hydrophilic and surface modification procedures must be carried out in order to turn such membranes hydrophobic. Therefore, the reaction between the surface hydroxyl groups of alumina commercial membranes and a silanizing agent was exploited. By changing the reaction conditions, it was possible to obtain highly hydrophobic membranes without affecting the initial pore size and porosity. This functionalizing surface layer proved to be stable up to 400°C which would allow to cover any possible MD operation condition.
2
Fawzy, Mohamed Khaled Adel <1990>. "Innovative Ceramic Membranes for Sweeping Gas Membrane Distillation: Membrane Characterization and Process Development". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9284/1/PhD_Thesis_Mohamed_Fawzy.pdf.
Testo completoAbstract (sommario):
The employment of tubular hydrophobic carbon-based titania membranes in sweeping gas membrane distillation (SGMD) was studied in this PhD thesis. The characterization of some of the membrane morphological properties was implemented by experimental and modeled results of gas permeation tests. The dusty gas model was adopted in gas permeation modeling. Two different approaches were followed during modeling. The first approach considered the morphological properties of each single membrane layer. As for the second approach, average membrane morphological properties were characterized without considering the unique contribution of each layer.
The investigation of the module performance during SGMD operations was achieved by experimental and modeling studies for NaCl (aq.). The model considered the Knudsen and molecular diffusion mechanisms. The module was capable of undergoing experiments at temperatures up to 110°C. Experimental flux results went in agreement with the modeled values obtained on using the morphological properties of each membrane layer. On the contrary, the modeled values obtained on considering average membrane morphological properties deviated significantly from the experimental results. The model was also used to estimate the effect of the operating conditions and flow configuration on water flux. Other modeling studies of the modules were performed for ethanol (aq.) to predict the effect of the operating conditions on the membrane selectivity. The Maxwell-Stefan approach was followed in this case.
Eventually, a hypothetical sweater desalination process was proposed incorporating SGMD (using the modules studied in this thesis) as the desalination unit. Process development and optimization were carried out. The optimized case corresponded to SGMD liquid inlet temperature of 107°C for an SGMD vessel having a length of 5.4 m. This corresponded to a water production cost of 20.9 $/m3 such that the feed heating was the determinant cost item. This cost could be mitigated in case of using a waste heat source.
3
Rane, Mahendra. "Porous Membrane". Doctoral thesis, Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000336.
Testo completoAbstract (sommario):
Membrane processes can cover a wide range of separation problems [with a
specific membrane (membrane structure) required for every problem]. Thus,
there are membranes available that differ in their structure and consequently in
the functionality. Therefore membrane characterization is necessary to ascertain,
which membrane may be used for a certain separation. Membranes of pore size
ranging from 100nm to 1μm with a uniform pore size are very important in
membrane technology. An optimum performance is achieved when the
membrane is as thin as possible having a uniform pore size.
Here in this thesis, membranes were synthesized by particle assisted wetting
using mono-layers of silica colloids as templates for pores along with
polymerizable organic liquids on water surface. The pore size reflects the
original shape of the particles. Thus it is possible to tune the pore size by
varying the particle size. This method is effective to control pore sizes of
membranes by choosing silica particles of suitable size.
This approach gives a porous structure that is very thin, but unfortunately
limited in mechanical stability. Thus there is a need for support which is robust
and can withstand the various mechanical stresses. A small change in the
membrane or defect in the layered structure during the membrane formation can
have drastic effect on the assembly. Lateral homogeneity of the layer generated
by the particle assisted wetting can be judged by examination of its reflectivity,
but once it is transferred on any solid support this option is no more.
So a method is needed to detect the cracks or the inhomogenity of the
membrane which can be detected even after the transfer. To tackle this problem
a very simple and novel technique for characterizing the membrane by
fluorescence labeling and optical inspection was developed in this thesis. The
idea was to add a fluorescent dye which is poorly water soluble to the spreading
solution comprising of the particles and the monomer. If the dye survived the
photo-cross linking, then it would be embedded in the cross-linked polymer and
would serve as a marker. Defects and inhomogenity would show up as cracks
and spots. By the method that we have developed, we can detect our membrane
from the support and spot defects.
4
Shi, Jinjun. "Composite Membranes for Proton Exchange Membrane Fuel Cells". Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1214964058.
Testo completo
5
Roselló, Busquets Cristina. "Paper de la Sintaxina-1 i els lipid rafts en guia axonal i regeneració neural". Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668211.
Testo completoAbstract (sommario):
Durant el desenvolupament del sistema nerviós cal que les cèl·lules formades a una zona concreta migrin fins a la seva posició final o bé que projectin els seus axons per tal de contactar amb les seves cèl·lules diana. En aquest procés participen multitud de molècules de guia axonal i els seus receptors, que produiran l’atracció o la repulsió de l’axó, guiant-lo fins a la seva posició final. En aquest procés el conus de creixement té un paper clau ja que és on es localitzen la majoria d’aquests receptors i on es dona el recanvi de membrana a través de l’exocitosi i endocitosi, necessàries pel creixement de l’axó. En aquests processos de fusió de membrana participen les proteïnes SNARE, entre elles la Sintaxina-1. Una de les molècules guia més importants durant el desenvolupament del sistema nerviós és la Netrina-1. Aquesta molècula té diferents receptors i segons al receptor que s’uneixi provocarà atracció o repulsió. Estudis previs demostren que la la Sintaxina-1 interacciona amb un dels receptors de la Netrina-1, el DCC, i que aquesta interacció és necessària, durant el desenvolupament de la medul·la espinal, per a l’atracció de les neurones comissurals in vitro. Hi ha pocs estudis on s’investigui el paper de les proteïnes SNARE en guia axonal in vivo. Per aquesta raó, en aquesta tesi estudiem el paper de les proteïnes SNARE, específicament de la Sintaxina-1, en la guia axonal de les neurones comissurals, durant el desenvolupament de la línia mitja i la medul·la espinal, en tres models animals diferents (mosca, pollastre i ratolí). Per mitjà de la supressió dels gens de diferents proteïnes SNARE, demostrem que la Sintaxina-1 és necessària per la correcta guia axonal de les neurones comissurals i el correcte desenvolupament de la medul·la a les tres espècies. A més, confirmem que la pèrdua de funció de la Sintaxina-1 comporta una pèrdua de la sensibilitat de les neurones comissurals a les molècules de guia axonal Netrina-1 i Slit-2 i que la funció de la Sintaxina-1 està conservada en diferents processos de guia axonal com la repulsió depenent de Slit/ROBO a les neurones comissurals, i la repulsió depenent de Netrina-1/UNC5 a les neurones de la EGL.
La majoria dels mecanismes involucrats en la guia axonal durant el desenvolupament són molt similars als processos que es donen durant la regeneració. Gran part dels receptors que participen en guia axonal i creixement estan localitzats en microdominis de membrana rics en esfingolípids i colesterol, anomenats lipid rafts, i la seva funcionalitat depèn de la correcta localització en aquests microdominis. A més el colesterol proporciona ordre i rigidesa a les membranes. Aquí demostrem com al disminuir el colesterol de les membranes incrementem el creixement neurític, l’àrea dels conus de creixement, la densitat dels fil·lopodis i la ramificació de neurones immadures del sistema nerviós central i perifèric cultivats in vitro. A més, demostrem que la pèrdua de colesterol afavoreix la regeneració de neurones hipocampals axotomitzades in vitro, de la via perforant en cultius organotípics i del nervi ciàtic in vivo. Finalment, també demostrem que la Nistatina, una droga àmpliament utilitzada per eliminar els lipid rafts de les membranes, incrementa la regeneració in vitro de neurones d’hipocamp activant l’enzim òxid nítric sintasa i, en conseqüència, incrementant els nivells d’òxid nítric.During the nervous system development neurons have to migrate and extend their axons to connect with their targets. In this process a huge amount of axon guidance molecules and their receptors participate to produce axon attraction or repulsion, guiding them to their final position. The growth cone has a key role in this process because the majority of receptors are localized in its surface and is where membrane turnover takes place. SNARE proteins are important components for membrane fusion in both, exocytosis and endocytosis, and their participation in axon guidance has been recently described. One important molecule during the nervous system development is Netrin-1. This guidance cue has different receptors and has the ability to produce attraction or repulsion depending on the receptor it binds. Recent studies have demonstrated that one of the SNARE proteins, Syntaxin-1, interacts with the Netrin-1 receptor DCC and that this interaction is necessary for the attraction of the commissural neurons. In this thesis we study the role of Syntaxin-1 during the commissural neuron guidance in three different animal models (fly, chicken and mouse). Deleting SNARE genes, we demonstrate that Syntaxin-1 is necessary for the correct commissural axon guidance and the correct spinal cord development in the three species. The mechanisms that regulate axon growth during development are very similar to processes that take place during axon regeneration. A variety of axon guidance receptors are localized in membrane microdomains enriched in cholesterol, termed lipid rafts, whose functionality depends on the proper localization within these microdomains. Here, we demonstrate that cholesterol depletion increases neurite growth, growth cone area, filopodia density and branching in immature neurons of the central and peripheral nervous system in vitro. Moreover, cholesterol depletion enhances axon regeneration after axotomy in vitro in dissociated hippocampal neurons, in slice organotypic cultures and in sciatic nerve in vivo. Finally, we also demonstrate that hippocampal regeneration in vitro is increased when nitric oxide synthase is activated by Nystatin treatments, a well-known drug used to disrupt lipid rafts from the cell membrane.
6
Whitehead, L. "Computer simulation of biological membranes and membrane bound proteins". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297412.
Testo completo
7
Dickson, Callum. "In silico modelling of membranes and drug membrane interactions". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25070.
Testo completoAbstract (sommario):
A new all-atom force field for the simulation of phospholipid bilayers using the AMBER molecular dynamics package has been developed, which is compatible with other AMBER protein, nucleic acid, carbohydrate and small molecule force fields. The force field has been validated by simulating bilayers of six different lipid types, finding favourable comparison to experiment for properties such as area per lipid, volume per lipid, bilayer thickness, NMR order parameters, scattering data, and lipid lateral diffusion. The modular nature of this force field allows numerous combinations of head and tail groups to create different lipid types, enabling the easy insertion of new lipid species. The lipid bilayer model has then been applied to the study of the interaction between radioimaging agents and membranes in an effort to understand the phenomena of non-specific binding, which remains poorly understood yet of serious detrimental consequence to the development of new imaging tracers. The effect of different concentrations of imaging agent on a homogeneous membrane has been examined using unbiased simulations, whilst the permeability coefficient of each imaging agent through a membrane has been calculated using biased simulations. It is found that radiotracers with low non-specific binding must adopt a certain orientation to cross the head group region of a membrane - this requirement may act as a barrier to membrane entry. Furthermore, once partitioned into the membrane, simulations predict that those radiotracers displaying a high degree of non-specific binding act to order lipid tail groups to a greater extent than those with low non-specific binding, reducing the permeability of the membrane and possibly acting to 'trap' radiotracer in the membrane. These simulations also predict that non-specific binding is not related to radiotracer membrane permeability through a homogeneous bilayer.
8
Ma, Yaning. "Characterization of Membrane Permeability and Polymer-Stabilized Model Membranes". Thesis, The University of Arizona, 2007. http://hdl.handle.net/10150/193347.
Testo completoAbstract (sommario):
The permeability of lipid bilayer membranes to glucose and carboxyfluorescein has been studied in model membranes. Using an enzyme assay, the permeability of glucose was monitored spectrometrically with both large and giant unilamellar vesicles (LUVs and GUVs). The permeability of carboxyfluorescein was studied by entrapping the dye and monitoring its leakage over time from a single GUV. Permeability study using GUVs may provide new information that cannot be obtained from LUVs.The stability of lipid membranes was enhanced by incorporating polymer scaffold. LUVs were prepared with hydrophobic monomers partitioned and then polymerized inside the hydrophobic interior of the lipid bilayers. The sizes of the formed polymers were characterized using gel permeation chromatography and mass spectrometry. This study suggests that large molecular weight polymers were formed inside the lipid bilayers and that the stability of the membranes is related to the size of the polymers.
9
Lycon, David Steven. "Flux enhancement and fouling reduction in a centrifugal membrane process". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0021/NQ44796.pdf.
Testo completo
10
Keuler, Johan Nico. "Optimising catalyst and membrane performance and performing a fundamental analysis on the dehydrogenation of ethanol and 2-butanol in a catalytic membrane reactor". Thesis, Link to the online version, 2000. http://hdl.handle.net/10019.1/1277.
Testo completo
11
Barron, Olivia. "Catalyst Coated Membranes (CCMs) for polymerelectrolyte Membrane (PEM) fuel cells". Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_4757_1307336145.
Testo completoAbstract (sommario):
The main objective of this work it to produce membrane electrode assemblies (MEAs) that have improved performance over MEAs produced by the conventional manner, by producing highly efficient, electroactive, uniform catalyst layers with lower quantities of platinum electrocatalyst. The catalyst coated membrane (CCM) method was used to prepare the MEAs for the PEM fuel cell as it has been reported that this method of MEA fabrication can improve the performance of PEM fuel cells. The MEAs performances were evaluated using polarisation studies on a single cell. A comparison of polarisation curves between CCM MEAs and MEAs produced in the conventional manner illustrated that CCM MEAs have improved performance at high current densities (>
800 mA/cm2).
12
Tremblay, André Y. "The role of structural forces in membrane transport: Cellulose membranes". Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/5886.
Testo completoAbstract (sommario):
The phenomena governing Transition RO/UF (nanofiltration) membrane transport have been critically studied. The residuals and predicted pore sizes of 965 individual permeation runs performed on 70 cellulose membranes were used to discriminate between several restricted transport models and various solute-solvent-membrane material interactions. Solute-membrane interactions were found to be mediated by the presence of structured solvent at the surface of the membrane. Two new interaction parameters, $\Psi\sb{DP}$ and $\kappa\sp\prime$ describing structural solvent forces at the surface of a membrane have been quantified. For solvent mediated interactions, the potential energy of a solute molecule $\phi\sbsp{DP}{\prime}(\underline d$) at a distance $\underline d$ from the membrane surface can be obtained by combining $\Psi\sb{DP}$ and $\kappa\sp\prime$ and the Stokes-Einstein radius a$\sb{s}$ of the solute as follows:$$\phi\sbsp{DP}{\prime}(\underline d) = -\Psi\sb{DP}\ a\sb{s}\ e\sp{-\kappa\sp\prime(\underline{d}-a\sb{s})}$$ A method to evaluate $\Psi\sb{DP}$ from simple permeation experiments and $\kappa\sp\prime$ from direct force measurements is given. This approach permits the decoupling of solute size and solute-membrane material interactions in predicting separation. The inverse of $\kappa\sp\prime$ was found to be approximately equal to the diameter of a solvent molecule. A linear correlation was obtained between the square root of $\Psi\sb{DP}$ and the solubility parameter $\delta\sb{SP}$ for all solutes tested in this work. The slope of this correlation reflects the ability of the membrane material to structure water dipoles at a solid-liquid interface. The ordinate's intercept of this correlation was equal to the solubility parameter of the solvent which implies that steric solute interactions $(\Psi\sb{DP}\to 0)$ occur when $\delta\sb{SP}$ of the solute approaches that of the solvent. The results of this study indicate that a solute molecule can penetrate hydrated layers of solvent at the surface of a material to different extents depending on its size and solvent compatibility. These findings are assumed to be applicable to reverse osmosis transport and indicate that if a membrane material is to be used in RO it must be capable of structuring solvent molecules at its surface. Several parametric studies were performed using the surface force pore flow (SFPF) model to determine the exact shape of the velocity profile in the membrane pore under conditions of solute adsorption and rejection. These studies were performed at various feed concentrations and values of $\lambda$ for polyethylene glycol, of molecular weight 1000, and casein. The shape of the solute separation vs. solute radius curve was studied parametrically as a function of pressure for four restricted transport models. The shape of this curve was also determined, using a radially dependent pore model (RDPM), for adsorptive and repulsive van der Waals interactions, electrical double layer (DLVO) interactions, increased viscosity in the membrane pore and effects of chain permeability and the shape of the interacting surface. Morphological reasons are given for the general inability to reduce the pore radius of cellulose membranes below 1.5 nm. Viscometric measurements performed on cellulose casting solutions indicate that the dissolved elements of the solution exist as rigid, rod-like structures. It is proposed, that the pore size of cellulose membranes be limited by the regular occurrence of indentations on the protofibril surface and by stacking limitations, enhanced by the geometry of the protofibrils. This interpretation is conform with the folded ribbon model of a cellulose protofibril described in the literature.
13
Choi, Jonghyun. "Nanofiber Network Composite Membranes for Proton Exchange Membrane Fuel Cells". Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1260461818.
Testo completo
14
Ali, Aamer. "Evaluation of membrane characteristics and thermal polarization in membrane distillation". Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30359/document.
Testo completoAbstract (sommario):
Le présent travail de thèse met l'accent sur divers aspects de la distillation membranaire dans l'objectif de concevoir des procédés de dessalement proches du " zéro effluent liquide ". De manière générale, deux sujets sont discutés en détail: (i) la corrélation entre les caractéristiques de la membrane et les performances du procédé de distillation membranaire (ii) la compréhension et le contrôle de la polarisation thermique en DM. L'analyse de l'état de l'art en distillation membranaire porte notamment sur les progrès dans le développement des membranes, dans la compréhension des phénomènes de transport, les récents développements dans la conception des modules et le colmatage. Des phénomènes annexes et les applications innovantes sont également discutés dans la partie introductive de la thèse. L'effet des conditions de fabrication et de la composition des collodions sur les caractéristiques des membranes et la corrélation entre ces dernières et leurs performances a été discuté dans la section suivante. Il est établi que la morphologie de la membrane joue un rôle crucial dans ses performances pour des applications sur des fluides réels. En outre, on met en évidence que l'impact de la morphologie de la membrane est différente selon que la procédé fonctionne avec une phase liquide froide du côté distillat (Direct Contact Membrane Distillation - DCMD)) ou avec un courant d'air sec ou le vide (Air Gap ou Vacuum Membrane Distillation). Dans une deuxième partie, les aspects théoriques et expérimentaux de la polarisation thermique en distillation membranaire (DCMD) ont également été étudiés. Les phénomènes de polarisation thermique sur une membrane plane ont été étudiés en utilisant une cellule spécialement conçue. L'effet des conditions de fonctionnement et de la concentration de la solution sur la polarisation thermique a été étudié expérimentalement. Nous avons observé que l'augmentation de concentration de la solution favorise la polarisation thermique à cause d'une détérioration de l'hydrodynamique résultante à la surface de la membrane. Certaines techniques actives et passives pour réduire la polarisation thermique et le colmatage en distillation membranaire ont également été examinées dans l'étude cette étude. Nous avons montré que la polarisation thermique peut être considérablement réduite en générant des écoulements secondaires dans le fluide circulant à l'intérieur du canal d'alimentation, donc à l'intérieur de la fibre creuse si c'est cette configuration qui est retenue. Dans la présente étude, l'induction d'un écoulement secondaire a été réalisée en utilisant les fibres torsadées en hélice et une configuration ondulée. En raison de l'amélioration du niveau de polarisation thermique du côté de l'alimentation et du distillat, les géométries de fibres ondulées fournissent des flux et des taux de rendement supérieurs à ceux des autres configurations. La mise en œuvre d'un écoulement pulsé et intermittent pour contrôler la polarisation en distillation membranaire a également été examinée. Notre étude permet de conclure que ces types d'écoulements ont un impact positif sur les taux de rendement et le facteur d'amélioration volumique (gain en flux ramené par rapport à l'augmentation du volume de l'équipement) sans compromis sur le taux de remplissage des carters de fibres creusesThe current PhD work emphasizes on various aspects of membrane distillation for approaching zero liquid discharge in seawater desalination. In broader sense, two themes have been discussed in detail: (i) correlation between membrane features and their performance in MD (ii) understanding and control of thermal polarization in MD. Introduction and state-of-the-art studies of MD including progress in membrane development, understanding the transport phenomenon, recent developments in module fabrication, fouling and related phenomenon and innovative applications have been discussed in introductory part of the thesis. The effect of operating conditions and dope compositions on membrane characteristics and correlation between membrane features and their performance has been discussed in subsequent section. It has been established that membrane morphology plays a crucial role in performance of the membrane for real applications. Furthermore, it has been demonstrated that the effect of membrane morphology is different for direct contact and vacuum configurations. Theoretical and experimental aspects of thermal polarization in direct contact membrane distillation have also been investigated. Thermal polarization phenomenon in a flat sheet membrane has been studied by using a specifically designed cell. The effect of operating conditions and solution concentration on thermal polarization has been explored experimentally. It has been observed that increased solution concentration favors the thermal polarization due to resulting poor hydrodynamic at the membrane surface and increase in diffusion resistance to the water vapors migrating from bulk feed phase to the membrane surface. Some active and passive techniques to decrease thermal polarization and possible fouling in membrane distillation have also been discussed in the current study. Thermal polarization can be greatly reduced by inducing secondary flows in the fluid flowing inside the fiber. The induction of secondary flows in the current study has been realized by using the fibers twisted in helical and wavy configurations. Due to improvement of thermal polarization coefficient on up and downstream, the undulating fiber geometries provide high flux and superior performance ratio. Application of intermittent and pulsatile flow to control thermal polarization in MD has also been discussed. It has been inferred that these flows have positive impact on performance ratio and volume based enhancement factors without compromising on packing density of the system. The application of MD for treatment of produced water has also been studied
15
Baghbanzadeh, Mohammadali. "Nano-composite Membranes and Zero Thermal Input Membrane Distillation for Seawater Desalination". Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35742.
Testo completoAbstract (sommario):
In this PhD thesis, seawater desalination by Membrane Distillation (MD) has been explored from the perspective of process and membrane. Regarding the process, an innovative, energy efficient, and environmentally friendly Zero Thermal Input Membrane Distillation (ZTIMD) process was proposed. ZTIMD uses thermal energy stored in seawater, which makes the process sustainable by being independent of the external sources of thermal energy, which is one of the major contributors to the cost and energy consumption of conventional MD desalination processes. Economic feasibility study was carried out for the ZTIMD process, and it was demonstrated that drinking water could be produced with a cost of $0.28/m3, which is approximately half of the cost of conventional desalination processes. Regarding the membrane, novel MD membranes were developed through incorporation of nanomaterials in polyvinylidene fluoride (PVDF). Different nanomaterials including superhydrophobic SiO2, amine modified hydrophilic SiO2, CuO, and CaCO3 were used for this purpose. It was shown that membrane structure and consequently its performance could be affected by the nanoparticle properties, concentration, presence of backing material, PVDF blend ratio, and penetration time. In a best membrane developed in this work, almost 2500% increase was observed in the Vacuum Membrane Distillation (VMD) flux over that of the neat PVDF membrane at a feed temperature of 27.5 °C and vacuum pressure of 1.2 kPa, when 7.0 wt.% hydrophilic SiO2 nanoparticles were added into a PVDF membrane supported with Non-Woven Fabric (NWF) polyester. The membrane possessed near perfect selectivity.
16
Barbe, Aron Mervyn. "The fouling of hydrophobic, microporous membranes used in osmotic distillation". Thesis, Queensland University of Technology, 2001.
Cerca il testo completo
17
Malewitz, Timothy. "Modeling Equilibrium Salt Partitioning in Neosepta AMX and Selemion AMV Antion Exchange Membranes". Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1249342152.
Testo completo
18
Murugesan, Viyash. "Optimization of Nanocomposite Membrane for Membrane Distillation". Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36534.
Testo completoAbstract (sommario):
In this study, effects of nanoparticles, including 7 nm TiO2, 200 nm TiO2, and hydrophilic and hydrophobic SiO2 with mean diameter in the range of 15–20 nm and their concentration on the membrane properties and vacuum membrane distillation (VMD) performance were evaluated. The effect of membrane thickness and support materials were also investigated. The membranes were characterised extensively in terms of morphology (SEM), water contact angle, water liquid entrance pressure (LEPw), surface roughness, and pore size. While the best nanocomposite membranes with 200 nm TiO2 Nanoparticles(NPs) were obtained at 2% particle concentration, the optimal particle concentration was 5% when 7 nm TiO2 was integrated. Using nanocomposite membrane containing 2 wt% TiO2 – 200 nm nanoparticles, VMD flux of 2.1 kg/m2h and LEPw of 34 PSI was obtained with 99% salt rejection. Furthermore, it was observed that decreasing the membrane thickness would increase the portion of finger-like layer in membrane and reduce the spongy-like layer when hydrophilic nanoparticles were used. Using continuous flow VMD, a flux of 3.1 kg/m2h was obtained with neat PVDF membranes, which was 600% higher than the flux obtained by the static flow VMD with the same membrane at the same temperature and vacuum pressure. The fluxes of both static and flow-cell VMD increased with temperature. Furthermore, it was evident that the continuous flow VMD at 2 LPM yielded 300% or higher flux than static VMD at any given temperature, indicating strong effects of turbulence provided in the flow-cell VMD.
19
Chen, Cheng. "Membrane degradation studies in PEMFCs". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29712.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Fuller, Thomas; Committee Member: Beckham, Haskell; Committee Member: Hess, Dennis; Committee Member: Koros, William; Committee Member: Meredith, Carson. Part of the SMARTech Electronic Thesis and Dissertation Collection.
20
Josyula, Ratnakar. "Structural studies of yeast mitochondrial peripheral membrane protein TIM44". Thesis, Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2009p/josyula.pdf.
Testo completo
21
Guseva, Ksenia. "Formation and cooperative behaviour of protein complexes on the cell membrane". Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=203444.
Testo completoAbstract (sommario):
In this work we analyse aspects of dynamics and organization of biological membranes from a physical prospective [i.e. perspective]. We provide an analysis of the process of self-assembly and spatial organization of membrane proteins. We illustrate the analysis by considering a channel activated by membrane tension called mechanosensitive channels (MS), in E. coli and the twin arginine translocation system (Tat). We analyse the mechanism of formation of oligomeric protein complexes formed by identical subunits. By derivation of a mathematical approach based on Smoluchowski coagulation equation, we study the deficiency of the process of complex formation, taking into account both irreversible aggregation, as well as fragmentation. We find that a small fragmentation rate increases the efficiency of the formation process, however if the fragmentation rate vanishes the irreversible process is very inefficient. Our second aim is to determine how the spatial organization can affect the function of channels, which are regulated by elastic forces. We map these short-range interactions into a discretized system, from which we obtain the spatial distribution of the channels and its effect on the gating dynamics. We find that organized channels activate at lower membrane tensions, but possess a delay in the reaction time. In the last part we determine how the formation of transient pores on the membrane depends on the dynamics of its assembly process. We analyse the pores formed by the Tat complex, which is responsible for protein transport through the membrane. This system functions by polimerization in response to a signal of transport demand from a protein in the cell cytoplasm. The direct correlation of the size of the assembled pore and the size of the protein determines the speed of the translocation process. Using a differential equation approach we obtain that the flux of a given protein depends quadratically on its size.
22
Kota, Jhansi. "Membrane chaperones : protein folding in the ER membrane /". Stockholm : Karolinska institutet, 2007. http://diss.kib.ki.se/2007/978-91-7357-102-9/.
Testo completo
23
Aryanti, Nita. "Fundamentals of Membrane Emulsification and Rotating Membrane Emulsification". Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507864.
Testo completo
24
Pridmore, Catherine Jane. "Analytical methods for the study of membranes and peptide-membrane interactions". Thesis, Durham University, 2010. http://etheses.dur.ac.uk/807/.
Testo completoAbstract (sommario):
This thesis describes analytical work carried out to determine the stability and properties of lipid and peptide-lipid systems. Matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) and tandem mass spectrometry (MSMS) analyses were carried out to establish a validated protocol for the complete identification of phospholipids, including the nature of the headgroup and acyl chains and the positions of the acyl chains on the glycerol backbone. Statistical differences were observed in the relative intensities of peaks corresponding to the neutral loss of the acyl chain from the sn-1 and sn-2 positions of POPE, POPC and OPPC, with a preferential cleavage of the chain from the sn-2 position of all three in the absence of added salt and a preferential cleavage at the sn-1 position in the presence of sodium or lithium ions. This knowledge was applied to the identification of unknown lipid mixtures both on the standard MALDI target plate and directly onto thin layer chromatography plates after separation. The above techniques, together with other analytical methods including thin layer chromatography and dynamic light scattering, were applied to the study and identification of lipids modified by actions such as hydrolysis and oxidation under conditions used for binding analyses of peptides and small molecules. Long-term analyses of samples containing synthetic melittin and liposomes showed that over time melittin both promotes the hydrolysis of liposomal lipids and is itself acylated. Analyses of the binding of a prototypical peptide (human neutrophil defensin HNP-2) to membranes, using methods that included dichroism and fluorescence spectroscopy, demonstrated that HNP-2 dimers act on lipid membranes via a carpet-type mechanism and allowed the rate of the formation of bound HNP-2 states to be determined. HNP-2 was modeled as a consecutive two-step process following pseudo-first order kinetics. The first step (membrane association) was rapid, with a half-life of around 0.5 minutes, while the second step (reorientation and partial insertion into the membrane) was slower by an order of magnitude.
25
Daisley, Gavin Rhys. "Membrane Aromatic Recovery System (MARS) : improved membranes and a further application". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508324.
Testo completo
26
Xu, Lili. "Electrically tuneable membranes : revolutionising separation and fouling control for membrane reactors". Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715263.
Testo completoAbstract (sommario):
The overall aim of this research is to develop unique conducting polyaniline (PANI) membranes that can be electrically tuned to achieve different fluxes and selectivity. The target application is in a tuneable membrane reactor, where these membranes allow the fouling layer to be pushed off/through membranes by application of external potential. To achieve this, several different types of PANI membranes were examined. The permeation properties of HCl-doped PANI membranes can be modified electrically to produce in-situ tuneable separations. However, acid dopant leaching and membrane brittleness limit the further application of these membranes. Polymer acid doped PANI membranes using poly(2-acrylamido-2-methyl-1-propanesulfonic acid) or PAMPSA were investigated as a solution. These PAMPSA doped PANI membranes displayed improved mechanical strength and filtration stability. However, the membranes showed decreased electrical conductivity, leading to a limited tuneable permeance and selectivity under applied potential. To overcome this new challenge, expanded graphite and a large acid (dodecylbenzene sulfonic acid or DBSA) were incorporated into the PAMPSA doped PANI membranes to increase the conductivity. Despite increasing both conductivity and electrical tuneability, the resulting membranes were more porous with looser molecular weight cut-off (outside of the desired NF/low UF MWCO range) than without modification. Efforts to tighten PAMPSA doped membranes to the same MWCO as HCl doped membranes using volatile co-solvents (THF and acetone) were unsuccessful: porosity was due to the large acid dopants. Membranes were examined for their potential for in-situ fouling removal of model foulant bovine serum albumin under applied voltage. This was successful and defouling extent was found to be closely related to membranes with higher conductivity and greater acid stability. Overall, it has been demonstrated that the conducting polyaniline composite membranes can be made to be stable to acid leaching and be more mechanically robust, whilst also being externally electrically tuned to different molecular selectivities with the potential for in-situ fouling control.
27
LADHA, PARAG. "POLYMERIC MEMBRANE SUPPORTED BILAYER LIPID MEMBRANES RECONSTITUTED WITH BIOLOGICAL TRANSPORT PROTEINS". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1145901880.
Testo completo
28
Collins, S. E. "Membrane emulsification". Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636279.
Testo completoAbstract (sommario):
Membrane emulsification is a technique which uses the pores of a microporous membrane to disperse one of two immiscible liquids, the disperse phase, into another liquid, the continuous phase, by applying pressure. The possible advantages of using this technique are that it is a low-shear, low-energy process capable, in theory, of producing an emulsion with a narrow droplet size. The main aim of this study was to provide a systematic analysis of membrane emulsification processes for the production of O/W emulsions using commercial available equipment and membranes. An experimental approach was adopted. Two methods of membrane emulsification were investigated. The first, dead-end membrane emulsification, used an adaptation of traditional membrane filtration equipment. Several membrane types were selected and investigated, including flat-sheet polymeric micro-and ultrafiltration membranes, and a ceramic microfiltration membrane. The second method, crossflow membrane emulsification, employed a hollow fibre ultrafiltration membrane. A standard emulsion formulation and experimental protocol for emulsion formation and characterisation was employed for all experimental work. Experimental investigations showed that O/W emulsions could be reproducibly produced with each membrane type, with emulsion characteristics related to membrane characteristics and operating conditions. For all membranes the results indicated that good quality emulsions with small droplet sizes and narrow size ranges were produced at slow disperse phase flowrates, usually at the lowest operating pressure possible, and moderate stirring at 600 rpm, or low crossflow velocities. An optimum set of operating conditions was most clearly identified for the polymeric microfiltration membranes. For comparison purposes, emulsions were produced using stirring only and by vortex mixing. Characterisation of the emulsions was undertaken using optical microscopy with image analysis and particle sizing techniques. Membrane characteristics were obtained using atomic force microscopy and scanning electron microscopy.
29
Deyhim, Sina. "Deriving Gas Transport Properties of Microporous Silica Membranes from First Principles and Simulating Separation of Multi-Component Systems in Different Flow Configurations". Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31340.
Testo completoAbstract (sommario):
Amorphous silica membranes have molecular sieving properties for the separation of hydrogen from gas mixtures at high temperature. Consequently, they are considered to be applied in separation of a shifted syngas coming out of a water-gas-shift-reactor into the syngas and hydrogen. This separation is a key to an Integrated Gasification Combined Cycle (IGCC) plant, which would allow reducing the carbon footprint in power generation industry. The main objective of this thesis was to carry out a preliminary assessment of suitability of currently available amorphous silica membranes for this separation. However, the separation properties of amorphous silica membranes reported in the open literature vary by orders of magnitude. Therefore, in the first part of this thesis the separation properties of hypothetical silica membrane with different pore size distributions were predicted from first principles.
Considering different possible gas transport mechanisms, it was concluded that gas transport in amorphous silica membranes is dominated by the activated and non-activated Knudsen diffusion. The activation energy for transport of different species was predicted using the concept of suction energy. Then, with arbitrary pore size distributions gas permeance of hypothetical silica membrane was predicted for different gas species. Since the pore size distribution of amorphous silica membrane cannot be known a priori, the developed model was used to determine the pore size distribution based on experimentally measured single gas permeances of three different species (kindly provided by Natural Resources Canada, CANMET Energy Technology Center (CETC) laboratory in Ottawa) by minimizing the error of the calculated permeance ratios with respect to the experimental values. The results indicate that, depending on how the objective function is defined, more than one pore size distribution can be found to satisfy the experimental permeance ratios. It is speculated that by increasing the number of experimentally determined permeances, a more unique pore size distribution for the tested silica membrane can be obtained. However, even at this early stage, the developed model provides a rational explanation for the effect of membrane densification on the properties of silica membranes. More specifically, a simultaneous decrease in membrane permeance and selectivity due to membrane densification, reported in the literature, is explained by shrinking the size of pores beyond a certain critical value, which depends on the kinetic diameter of gas molecules that are being separated.
Comparing theoretically determined permeances, which match experimentally observed permeance ratios, revealed that the experimental permeances are considerably smaller than the theoretical values. The ratio of the two provided the basis for a scaling factor, a new concept that was introduced in this thesis.
To simulate membrane module performance, a novel approach was introduced. More specifically, co- and counter-current flow configurations as well as cross-flow configuration were modeled by assuming no change in feed composition over an infinitesimally small element of membrane area. This led to a system of linear, rather than differential equations, which was readily solved numerically.
30
Boulter, Jonathan Michael. "Structural and functional studies of the erythrocyte anion exchanger, band 3". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297079.
Testo completo
31
Araujo, Paulo Jardel Pereira. "Avaliação da permeabilidade em membrana tubular de TiO2/AL2O3 dos constituintes do sistema reacional heterogêneo para produção de biodiesel". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266802.
Testo completoAbstract (sommario):
Orientadores: Teresa Massako Kakuta Ravagnani, Leila PeresTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-18T23:18:07Z (GMT). No. of bitstreams: 1 Araujo_PauloJardelPereira_D.pdf: 15740528 bytes, checksum: bd5969744efcacfde55b69c10f951f33 (MD5) Previous issue date: 2011
Resumo: O biodiesel além de ser biodegradável e obtido de fontes renováveis, apresenta propriedades físico-químicas muito semelhantes ao diesel de petróleo, não necessitando de um novo motor para utilização do mesmo. A rota química mais comumente usada para obtenção do biodiesel é a transesterificação. Nesta, pela reação de um álcool com os triacilgliceróis (TAG) presentes principalmente em óleos vegetais e gordura animal, são produzidos o biodiesel e, como produto secundário, o glicerol em grandes quantidades. A presença deste glicerol é indesejada, pois além de diminuir a produtividade do biodiesel pelo equilíbrio termodinâmico estabelecido no processo, também aumenta seu custo pelo alto tempo de decantação e/ou uso de centrífugas para remover o glicerol do biodiesel. Devido a este inconveniente, o presente trabalho propõe rota alternativa para separação do glicerol, utilizando membrana de microfiltração (TiO2/Al2O3). Vários sistemas foram analisados, focando a separação do glicerol, o aumento do fluxo permeado e da conversão de TAG na catálise heterogênea. Inicialmente estudou-se a permeabilidade e seletividade dos reagentes e produtos obtidos na síntese do biodiesel com a membrana, através de experimentos binários. A partir destes resultados, estabeleceu-se uma nova configuração do sistema para então analisar estes fatores em misturas compostas pelos quatro constituintes do processo através de um planejamento fatorial. Os resultados apresentados geraram modelos que descrevem com 95% de confiabilidade o coeficiente de rejeição ao glicerol e o fluxo permeado frente aos fatores analisados (nível de emulsificação, razão molar óleo/etanol e conversão de TAG). Selecionou-se então, uma melhor faixa destes fatores que resultem em um máximo de rejeição ao glicerol com máximo fluxo permeado, obtendo um resultado bastante representativo do processo que apresentou um bom fluxo permeado (90,11kg/h.m2) com alta rejeição de glicerol (98,69%). Posteriormente propôs-se um estudo do processo simultâneo de reação e separação (leito fixo catalítico envolto em membrana), sendo selecionado para a reação de síntese um catalisador heterogêneo (SrO suportado em alumina), visando facilitar o processo de separação e reduzir significativamente o número de etapas de purificação dos produtos. Os resultados de conversão do TAG foram baixos, impossibilitando uma análise completa do sistema com esta configuração do ponto de vista de reação e separação concomitante
Abstract: In addition to being biodegradable and renewable, Biodiesel presents physicochemical properties very similar to those of petroleum-based diesel, so a new engine is not required for its use. The most commonly used chemical process for obtaining biodiesel is transesterification. In this process, through the reaction of an alcohol with triacylglycerols (TAG) present mainly in vegetable oils and animal fat, biodiesel is formed with large quantities of glycerol as a byproduct. The presence of glycerol is unwanted because besides reducing the productivity of biodiesel through the thermodynamic equilibrium established in the process, it also increases the cost due to the long time for settling and/or use of centrifuges for removing the glycerol from biodiesel. Taking into account this inconvenience, this paper proposes an alternative process for the separation of glycerol, using TiO2/Al2O3 membranes. Various systems were analyzed, focusing on the separation of glycerol, the increase of the permeate flux, and the increase in the TAG productivity in heterogeneous catalysis. At first we studied the permeability and selectivity of reagents and products obtained in the biodiesel synthesis with a membrane through binary experiments. From these results a new configuration of the system was established, with subsequent analysis of the new interaction in mixtures of the four components of the process (oil, Ethanol, Biodiesel, glycerol) using a factorial design as tool. Results presented in the factorial design generated models that describe with 95% reliability the glycerol rejection coefficient and the permeate flux compared to the analyzed factors (level of emulsification, molar ratio of oil/ethanol and TAG conversion). A best range of factors that result in a maximum glycerol rejection with maximum permeate flux was selected, obtaining a fairly representative result of the process showing a good permeate flux (90.11 kg/h.m2) with high glycerol rejection rate (98.69%). Subsequently, the study of the reaction and separation simultaneous process was proposed (fixed catalytic bed involved in a membrane) selecting an heterogeneous catalyst (SrO on alumina) to facilitate the separation process and significantly reduce the number of purification steps of products. Results of biodiesel conversion were low, preventing a full assessment of the system with this configuration considering simultaneous reaction and separation
Doutorado
Sistema de Processos Quimicos e Informatica
Doutor em Engenharia Química
32
Mokrani, Touhami. "Transport of gases across membranes". Thesis, Peninsula Technikon, 2000. http://hdl.handle.net/20.500.11838/878.
Testo completoAbstract (sommario):
Thesis (MTech (Chemical Engineering))--Peninsula Technikon, 2000.Oxygen transport across biofilms and membranes may be a limiting factor in the operation of a membrane bio-reactor. A Gradostat fungal membrane bio-reactor is one in which fungi are immobilized within the wall of a porous polysulphone capillary membrane. In this study the mass transfer rates of gases (oxygen and carbon dioxide) were investigated in a bare membrane (without a biofilm being present). The work provides a basis for further transport study in membranes where biomass is present. The diaphragm-cell method can be employed to study mass transfer of gases in flat-sheet membranes. The diaphragm-cell method employs two well-stirred compartments separated by the desired membrane to be tested. The membrane is maintained horizontally. -The gas (solute) concentration in the lower compartment is measured versus time, while the concentration in the upper liquid-containing compartment is maintained at a value near zero by a chemical reaction. The resistances-in-series model can be used to explain the transfer rate in the system. The two compartments are well stirred; this agitation reduces the resistances in the liquid boundary layers. Therefore it can be assumed that in this work the resistance in the membrane will be dominating. The method was evaluated using oxygen as a test. The following factors were found to influence mass transfer coefficient: i) the agitation in the two compartments; ii) the concentration of the reactive solution and iii) the thickness of the membrane.
33
Duncan, Anna Louise. "Coarse-grained molecular dynamics simulations of mitochondrial membrane proteins". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648455.
Testo completo
34
Tuan, Chik Syed Mohd Saufi. "Mixed Matrix Membrane Chromatography for Bovine Whey Protein Fractionation". Thesis, University of Canterbury. Chemical and Process Engineering, 2010. http://hdl.handle.net/10092/3647.
Testo completoAbstract (sommario):
Whey protein fractionation is an important industrial process that requires effective large-scale processes. Although packed bed chromatography has been used extensively, it suffers from low processing rates due to high back-pressures generated at high flow rates. Batch chromatography has been applied but generally has a low efficiency. More recently, adsorptive membranes have shown great promise for large-scale protein purification, particularly from large-volume dilute feedstocks. A new method for producing versatile adsorptive membranes by combining membrane and chromatographic resin matrices has been developed but not previously applied to whey protein fractionation. In this work, a series of mixed matrix membranes (MMMs) were developed for membrane chromatography using ethylene vinyl alcohol (EVAL) based membranes and various types of adsorbent resin. The feasibility of MMM was tested in bovine whey protein fractionation processes.
Flat sheet anion exchange MMMs were cast using EVAL and crushed Lewatit® MP500 (Lanxess, Leverkusen, Germany) anion resin, expected to bind the acidic whey proteins β-lactoglobulin (β-Lac), α-lactalbumin (α-Lac) and bovine serum albumin (BSA). The MMM showed a static binding capacity of 120 mg β-Lac g⁻¹ membrane (36 mg β-Lac mL⁻¹ membrane) and 90 mg α-Lac g⁻¹ membrane (27 mg α-Lac mL⁻¹ membrane). It had a selective binding towards β-Lac in whey with a binding preference order of β-Lac > BSA > α-Lac. In batch whey fractionation, average binding capacities of 75.6 mg β-Lac g⁻¹ membrane, 3.5 mg α-Lac g⁻¹ membrane and 0.5 mg BSA g⁻¹ membrane were achieved with a β-Lac elution recovery of around 80%.
Crushed SP Sepharose™ Fast Flow (GE Healthcare Technologies, Uppsala, Sweden) resin was used as an adsorbent particle in preparing cation exchange MMMs for lactoferrin (LF) recovery from whey. The static binding capacity of the cationic MMM was 384 mg LF g⁻¹membrane or 155 mg LF mL⁻¹ membrane, exceeding the capacity of several commercial adsorptive membranes. Adsorption of lysozyme onto the embedded ion exchange resin was visualized by confocal laser scanning microscopy. In LF isolation from whey, cross-flow operation was used to minimize membrane fouling and to enhance the protein binding capacity. LF recovery as high as of 91% with a high purity (as judged by the presence of a single band in gel electrophoresis) was achieved from 150 mL feed whey.
The MMM preparation concept was extended, for the first time, to produce a hydrophobic interaction membrane using crushed Phenyl Sepharose™ (GE Healthcare Technologies, Uppsala, Sweden) resin and tested for the feasibility in whey protein fractionation. Phenyl Sepharose MMM showed binding capacities of 20.54 mg mL⁻¹ of β-Lac, 45.58 mg mL⁻¹ of α-Lac, 38.65 mg mL⁻¹ of BSA and 42.05 mg mL⁻¹ of LF for a pure protein solution (binding capacity values given on a membrane volume basis). In flow through whey fractionation, the adsorption performance of the Phenyl Sepharose MMM was similar to the HiTrap™ Phenyl hydrophobic interaction chromatography column. However, in terms of processing speed and low pressure drop across the column, the benefits of using MMM over a packed bed column were clear.
A novel mixed mode interaction membrane was synthesized in a single membrane by incorporating a certain ratio of SP Sepharose cation resin and Lewatit MP500 anion resin into an EVAL base polymer solution. The mixed mode cation and anion membrane chromatography developed was able to bind basic and acidic proteins simultaneously from a solution. Furthermore, the ratio of the different types of adsorptive resin incorporated into the membrane matrix could be customised for protein recovery from a specific feedstream. The customized mixed mode MMM consisting of 42.5 wt% of MP500 anionic resin and 7.5 wt% SP Sepharose cationic resin showed a binding capacity of 7.16 mg α-Lac g⁻¹ membrane, 11.40 mg LF g⁻¹ membrane, 59.21 mg β-Lac g⁻¹ membrane and 6.79 mg IgG g⁻¹ membrane from batch fractionation of 1 mL LF-spiked whey. A tangential flow process using this membrane was predicted to be able to produce 125 g total whey protein per L membrane per h.
35
Yurdakul, Ahmet Ozgur. "Acid Doped Polybenzimidazole Membranes For High Temperature Proton Exchange Membrane Fuel Cells". Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608506/index.pdf.
Testo completoAbstract (sommario):
Acid Doped Polybenzimidazole Membranes for High Temperature
Proton Exchange Membrane Fuel Cells
Author: Ahmet Özgü
r Yurdakul One of the most popular candidates for high temperature PEMFC&rsquo
s is phosphoric acid doped polybenzimidazole (PBI) membrane due to its thermal and mechanical stability. In this study, high molecular weight PBI was synthesized by using PPA polymerization. The stirring rate of reaction solution was optimized to obtain high molecular weight. The inherent viscosity of polymer was measured at four points in 96 percent sulphuric acid solution at 30 degree centigrade by using an Ubbelohde viscometer. The highest average molecular weight was found as approximately 120,000 using the Mark-Houwink equation. The polymer was dissolved in N,N-dimethylacetamide at 70 degree centigrade with an ultrasonic stirrer. The membranes cast from this solution were doped with phosphoric acid solutions at different concentrations. The doping levels of the membranes were 6, 8, 10 and 11 moles phosphoric acid/PBI repeat unit. The mechanical strength of the acid doped membranes measured by tensile tests were found as 23, 16, 12 and 11 MPa, respectively. Conductivity measurements were made using the four probe technique. The membranes were placed in a conductivity cell and measurements were taken in humidity chamber with temperature and pressure control. The conductivity of membranes was measured at 110, 130 and 150 degree centigrade in both dry air and water vapor. The highest conductivity was 0.12 S/cm at 150 degree centigrade and 33 percent relative humidity for the membrane doped with 11 moles of H3PO4. The measurements showed that conductivity increased with increasing doping and humidity. Moreover, membranes had acceptable conductivity levels in dry air.
36
Suk, Daniel Eumine. "Development of surface modifying macromolecule blended polyethersulfone membranes for vacuum membrane distillation". Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/29319.
Testo completoAbstract (sommario):
Surface modifying macromolecule (SMM) has been developed aiming at the preparation of membranes with greater surface hydrophobicity and greater chemical resistivity at a lower cost than conventional hydrophobic membranes. Throughout the whole work in this study, the membranes, which contains SMM as an additive and PES as a base polymer, are called 'SMM blended PES membranes' or 'SMM modified PES membranes'. The objective of this study is the preparation of SMM blended membranes to be used for the removal of VOCs from their aqueous solutions by the membrane distillation process.
In the first part of this work, a SMM, "tSMM", was synthesized by a traditional method and the tSMM blended PES membranes were prepared to study the effects of tSMM on PES membranes by different methods; e.g. bubble-point method and gas permeation, pure water permeation (PWP), contact angle measurement, and X-ray photoelectron spectroscopy (XPS). In particular, based on the XPS results, the kinetics of surface migration of tSMM was studied. According to the results of experimental and theoretical studies, it was observed that the tSMM blended membranes prepared had a potential to be used in membrane distillation (MD), however to meet the requirement of MD membrane, relatively long evaporation time (over 10 minutes) and high evaporation temperature (110°C) should be needed during membrane preparations.
In the second part of this work, a novel SMM, "nSMM" was designed and synthesized. Synthesized nSMMs from two different batches (nSMM1 and nSMM2) were characterized by GPC and the weight average molecular weight (Mw) of nSMM2 was about twofold of nSMM1. Furthermore, "nSMM" blended PES membranes were prepared and characterized. According to the results, the nSMM seems to be a better alternative to tSMM for membrane distillation, since a shorter period at room temperature was required for "nSMM" to migrate to the membrane surface. The ultrafiltration (UF) tests also gave the information on the effects of nSMM on PES membranes. nSMM was fully segregated to the surface of membrane forming a distinctive surface layer and this was observed from optical microscope and scanning electron microscopy (SEM) results. In the end of the second part, the nSMM blended PES membranes were successfully applied in vacuum membrane distillation (VMD) for the removal of ethanol from water.
37
Lu, Jun-xia. "Solid-state NMR studies of phospholipid model membranes and membrane-associated macromolecules". Oxford, Ohio : Miami University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1184090235.
Testo completo
38
Bannwarth, Sebastian [Verfasser]. "Characterization of Membranes and Membrane Processes by Electrical Impedance Spectroscopy / Sebastian Bannwarth". Aachen : Shaker, 2017. http://d-nb.info/113817842X/34.
Testo completo
39
Winkler, Gudrun. "Effects of configuration on the operation of membranes in membrane biological reactors". Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7960.
Testo completoAbstract (sommario):
The aim of this work included the investigation of the impact of membrane material properties on fouling propensity and permeate flux decline in MBR biomass systems. Furthermore, the impact of membrane configuration on the respective fouling behaviour was of interest. A direct comparative study of different membrane module configurations including a multi-tubular membrane (MT), a single flat sheet module (FS) and a hollow fibre (HF) pilot scale module was undertaken. Membrane module filtration performances, especially with respect to their fouling propensity under varying hydraulic conditions, were investigated to ultimately evaluate the impact of varying parameters such as aeration and biomass make up on fouling and to determine optimised operational parameters. Subsequently, a range of different membrane materials, such as flat sheet membrane samples made of polyethylene (PE), polyethersulfone (PES), polysulfone (PS) and polyvynilidene fluoride (PVDF) and a single-tube made of PVDF and PES were characterised and their fouling propensity to MBR biomass was studied at bench-scale. Cont/d.
40
Hill, Melinda Lou. "Polymeric and Polymer/Inorganic Composite Membranes for Proton Exchange Membrane Fuel Cells". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/37597.
Testo completoAbstract (sommario):
Several types of novel proton exchange membranes which could be used for both direct methanol fuel cells (DMFCs) and hydrogen/air fuel cells were investigated in this work. One of the main challenges for DMFC membranes is high methanol crossover. Nafion, the current perfluorosulfonic acid copolymer benchmark membrane for both DMFCs and hydrogen/air fuel cells, shows very high methanol crossover. Directly copolymerized disulfonated poly(arylene ether sulfone)s copolymers doped with zirconium phosphates and phenyl phosphonates were synthesized and showed a significant reduction in methanol permeability. These copolymer/inorganic nanocomposite hybrid membranes show lower water uptake and conductivity than Nafion and neat poly(arylene ether sulfone)s copolymers, but in some cases have similar or even slightly improved DMFC performance due to the lower methanol permeability. These membranes also show advantages for high temperature applications because of the reinforcing effect of the filler, which helps to maintain the modulus of the membrane, allowing the membrane to maintain proton conductivity even above the hydrated glass transition temperature (Tg) of the copolymer. Sulfonated zirconium phenyl phosphonate additives were also synthesized, and membranes incorporating these materials and disulfonated poly(arylene ether sulfone)s showed promising proton conductivity over a wide range of relative humidities. Single-Tg polymer blend membranes were studied, which incorporated disulfonated poly(arylene ether sulfone) with varied amounts of polybenzimidazole. The polybenzimidazole served to decrease the water uptake and methanol permeability of the membranes, resulting in promising DMFC and hydrogen/air fuel cell performance.Ph. D.
41
Lu, Junxia. "Solid-state NMR studies of phospholipid model membranes and membrane-associated macromolecules". Miami University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=miami1184090235.
Testo completo
42
Hengl, Nicolas. "Conception et étude d'un évaporateur membranaire à membrane métallique". Montpellier 2, 2008. http://www.theses.fr/2008MON20167.
Testo completoAbstract (sommario):
L'Evaporation Membranaire est un nouveau type de procédé utilisant un contacteur à membrane liquide/gaz pour la concentration de produits thermosensibles à haute valeur ajoutée. Ce procédé permet de mettre en contact par l'intermédiaire d'une membrane macroporeuse métallique hydrophobe, une solution aqueuse à concentrer et une phase extractante à savoir de l'air sec. La force motrice du transfert est la différence de pression partielle de vapeur d'eau existant de part et d'autre de la membrane. Les propriétés de conduction thermique et électrique des membranes métalliques permettent un apport d'énergie au niveau des pores de la membrane pour compenser le phénomène de polarisation de température entraîné par l'évaporation du solvant. Ce travail est divisé en trois parties. La première concerne la caractérisation des membranes et la détermination de l'influence du traitement de surface, permettant de les rendre hydrophobes, sur leurs propriétés structurelles. La deuxième partie est consacrée à l'étude expérimentale du procédé d'évaporation membranaire. L'influence de nombreux paramètres opératoires sur les performances du procédé a ainsi été déterminée et des flux évaporatoires comparables à ceux obtenus en évaporation osmotique ont été obtenus démontrant ainsi la faisabilité du procédé. Un modèle théorique tenant compte des transferts de masse et de chaleur a été développé dans une troisième partie. Le modèle a été validé et a permis de prouver que dans les conditions opératoires étudiées, la résistance de la couche limite en phase gaz limite les performances du procédé. Par ailleurs, des simulations ont permis de mettre en évidence l'effet de polarisation de température se produisant à la surface de la membrane lors de la vaporisation de l'eauMembrane Evaporation is a new type of process using a liquid/gas membrane contactor for the concentration of thermo sensitive products with high added value. This process makes it possible to put in contact by means of a hydrophobic metal macroporous membrane, an aqueous solution to be concentrated with a flow of dry air which is the extracting fluid. The driving force of the transfer is the difference of water vapour partial pressure between the both sides of the membrane. Thermal and electric conduction properties of metallic membranes allow supplying, at pores level, the necessary energy to compensate the phenomenon of polarization of temperature caused by the solvent evaporation. This work is divided into three parts. The first relates to the characterization of the membranes and the determination of the influence of the surface treatment, making it possible to make them hydrophobic, on their structural properties. The second part is devoted to the experimental study of the membrane evaporation process. The influence of different operational parameters on the process performances was thus given. Evaporating fluxes reached were comparable with those of osmotic evaporation process thus proving the feasibility of the membrane evaporation process. A theoretical model taking into account mass and heat transfer was developed in a third part. The model was validated and made it possible to demonstrate that under the studied operating conditions, the resistance of the boundary layer in gas phase limits the performances of the process. In addition, simulations allowed highlighting the effect of polarization of temperature occurring at the surface of the membrane during the vaporization of water
43
Serrano, Albarrás Antonio. "Heteromeric composition of the Kv 1.3 channelosome = Composició heteromèrica del canalosoma Kv1.3". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/665245.
Testo completoAbstract (sommario):
Ion channels are transmembrane proteins containing aqueous pores which, once open, permit the pass of ions through the plasma membrane. This ion flux takes places following the electrochemical gradient for the specific ion.
Kv1.3 is a voltage-gated potassium channel which is member of the Shaker superfamily. Its basic structure consists in a protein with six transmembrane domains, while the functional channel is formed by 4 copies of this protein.
Kv1.3 participates in a great amount of physiological functions: nervous system, immune system, insulin signaling or cell proliferation. In the immune system, Kv1.3 is highly expressed both in lymphocytes as well as in mononuclear phagocytes. In both cell types, Kv1.3 regulates the immune activation and cell proliferation. Moreover, Kv1.3 is coexpressed with other ion channel proteins like Kv1.5 or KCNE4 in the immune cells.
Kv1.5 is able to heteromerize with Kv1.3, generating heterotetramers with variable stoichiometries. Those heterotetramers produce intermediate phenotypes depending on the ratio of the subunits that generate them. On the other side, KCNE4 may interact with Kv1.3, but not with Kv1.5. Kv1.3 is greatly inhibited by the association with either of the two proteins.
In the present thesis we focus in characterizing these interactions and the importance of stoichiometry in their effects. We demonstrate that the associations between Kv1.3 and Kv1.5; and between Kv1.3 and KCNE4 take place in immune cells. Moreover, by using a fusion protein we get to fix the stoichiometry of the Kv1.3-Kv1.5 complex to 1:1. With this stoichiometry, Kv1.5 acts as a dominant negative toward Kv1.3 in the complex. Further interactions are characterized by using several chimeric proteins. By using those chimaeras, it is revealed that the carboxyterminal domain is necessary for the correct function of the channel.
On the other hand, we demonstrate that KCNE4 is able to interact with Kv1.3 regardless of Kv1.5 presence. Furthermore, the presence of Kv1.5 in the Kv1.3-KCNE4 interaction results in this association potentiating the function of the channel, instead of inhibiting it. These results are replicated both in heterologous systems as well as in native cells. This discovery presents a new paradigm by which the association with several modulatory proteins may result in the modification of the effect of each one of them. Taking into account the sheer number of different ion channel subunits, the number of different potential phenotypes is increased by a huge margin.
KCNE1 is a regulatory subunit, as well as KCNE4. Unlike KCNE4, though, KCNE1 can interact with Kv1.5. In the present thesis we demonstrate for the first time that KCNE1 is not only able to associate with Kv1.5, but to potentiate its activity by a huge amount. This interaction also seems to affect the membrane microdomain targeting of Kv1.5
Finally, the 4 studied proteins are expressed in T lymphocytes, which are the main actors in the pathogenicity of autoimmune diseases. Therefore, we genotyped those genes in multiple sclerosis patients to identify different polymorphisms which could be linked to immune overactivity. After analyzing the different polymorphisms, we located some which could be of special relevance for the physiopathology of autoimmune diseases.Los canales iónicos son proteínas transmembrana que contienen poros acuosos que permiten el paso de iones a través de la membrana plasmática a favor de gradiente electroquímico. Kv1.3 es un canal de potasio dependiente de voltaje de la superfamilia Shaker. La estructura básica consiste en una proteína con seis dominios transmembrana y el canal funcional está formado por cuatro copias de esta proteína. Kv1.3 participa en multitud de funciones del organismo: sistema nervioso, sistema inmunitario, señalización de la insulina o proliferación celular. En el sistema inmunitario está altamente expresado tanto en linfocitos como en fagocitos mononucleares. En ambos tipos celulares regula la activación inmunitaria y la proliferación celular. Además, se ve coexpresado con otras proteínas de relevancia como Kv1.5 o KCNE4. Kv1.5 puede heteromerizar con Kv1.3, dando lugar a heterotrámeros de estequiometrias variables. Por otro lado, KCNE4 puede interaccionar con Kv1.3, pero no con Kv1.5. Kv1.3 se ve potentemente inhibido por ambas asociaciones. En la presente tesis nos centramos en caracterizar estas interacciones y el peso de la estequiometría en sus efectos. Demostramos que ambas asociaciones tienen lugar en células del sistema inmunitario. Además, mediante una proteína de fusión logramos fijar la estequiometría del complejo Kv1.3-Kv1-5 en 1:1. Así, Kv1.5 demuestra ejercer como dominante negativo respecto a Kv1.3 en el complejo. Estas interacciones intramoleculares son estudiadas mediante el uso de diversas proteínas quiméricas para dilucidar el peso de los extremos carboxiterminales en la formación del canal y su función. Por otro lado, demostramos que KCNE4 afecta el canal de estequiometría 1:1 aumentado su actividad, en lugar de reducirla. Este descubrimiento presenta un nuevo paradigma en que la asociación con varias proteínas reguladoras puede resultar en la modificación del efecto de cada una de ellas. KCNE1 es una proteína reguladora al igual que KCNE4, pero que interactúa con Kv1.5. En la presente tesis demostramos como KCNE1 no solo interacciona con Kv1.5, sino que aumenta en gran medida su actividad. Finalmente, también genotipamos estos genes en pacientes de una enfermedad autoinmune como es la esclerosis múltiple, llegando a localizar diversos polimorfismos de posible interés fisiopatológico.
44
Lee, Chongsoo. "Raman spectroscopy of supported lipid bilayers and membrane proteins". Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:76f4be6e-b7d3-46c5-a2a1-3dcc7a399410.
Testo completoAbstract (sommario):
Off-resonance unenhanced total internal reflection (TIR) Raman Spectroscopy was explored to investigate supported single lipid bilayers with incorporated membrane peptides/proteins at water/solid interface. A model membrane was formed on a planar supported lipid layer (pslb) by the fusion of the reconstituted small unilamellar vesicles (SUVs), and the intensity of bilayer was confirmed by a comparison of Raman spectral intensity in the C-H stretching modes with C16TAB. With prominent Raman sensitivity attained, we studied the 2-D phase transition of DMPC and DPPC pslbs and the temperature-dependent polarised spectra revealed a broad transition range of ca. 10 °C commencing at the calorimetric phase transition temperature. We applied polarised TIR-Raman Spectroscopy to pslbs formed by DMPC SUVs reconstituted with a model membrane-spanning peptide gramicidin D. A preferential channel structure formed by dissolution of trifluoroethanol could be probed by polarised Raman Spectroscopy qualitatively showing an antiparallel β-sheet conformation (different from "standard" one) and our Raman spectra by correlation with NMR and CD data confirmed single-stranded π6.3 β-helical channel structure in the single bilayer. We also studied the membrane-penetrating peptide indolicidin in the presence of DMPC pslb over the chain melting temperature and a β-turn structure was dominantly observed concomitant with membrane perturbation. Dynamic adsorption of DPPC to form pslb from a micellar solution of n-dodecyl-β- D-maltoside could be examined with high sensitivity of every 1-min acquisition. Finally we used polarised TIR-Raman scattering to porcine pancreatic phospholipase A2 hydrolytic activity on DPPC pslbs and revealed lipid-active conformation different from that of the enzyme alone.
45
Araujo, Paulo Jardel Pereira. "Modelagem e simulação da operação de um reator de leito fixo catalitico envolto em membrana permseletiva". [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266239.
Testo completoAbstract (sommario):
Orientador: Teresa Massako Kakuta RavagnaniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-08T19:44:43Z (GMT). No. of bitstreams: 1 Araujo_PauloJardelPereira_M.pdf: 1672087 bytes, checksum: 39df6a7017efe009f53dbd9aecb301b1 (MD5) Previous issue date: 2007
Resumo: Estireno é um importante monômero na fabricação de termoplásticos e borrachas sintéticas. Grande parte de sua produção é baseada na desidrogenação catalítica do etilbenzeno. O aumento da produtividade do estireno pode ser alcançado utilizando-se membranas permseletivas para remoção do hidrogênio, suprimindo as reações reversíveis e secundárias. Este trabalho apresenta a simulação do processo de desidrogenação em um reator tubular de leito fixo catalítico envolto em membrana composta permseletiva. A modelagem matemática desenvolvida considera os diferentes mecanismos de transporte de massa que prevalecem nas várias camadas da membrana e no leito fixo catalítico. A remoção do Hidrogênio do leito catalítico foi realizada estabelecendo-se um gradiente de potencial químico de hidrogênio através da membrana. Duas formas de remoção de hidrogênio foram estudadas: pela aplicação de uma diferença de pressão através da membrana e pelo arraste com gás inerte. Um programa computacional foi implementado para descrever os perfis de temperatura, pressão e concentração ao longo de todo o reator, bem como a conversão do etilbenzeno, seletividade e produtividade de estireno. Comparando os resultados obtidos no leito fixo convencional operando na condição industrial padrão com os obtidos na aplicação de diferença de pressão através da membrana, observou-se um acréscimo na conversão de etilbenzeno de 19,89 % na mesma seletividade do estireno, representando um aumento de 19,12 % na produtividade de estireno. Este mesmo aumento foi também alcançado com o uso de gás de arraste inerte. Por este motivo, este procedimento é a opção mais recomendada, por agregar custo menor ao processo. Através da simulação do sistema em diferentes condições do processo e configurações do reator e da membrana, obteve-se um acréscimo de 40,98 % na produtividade de estireno comparada a do processo com leito fixo convencional
Abstract: Styrene is an important monomer in the manufacture of thermoplastic and synthetic rubbers. Most of the production is based on the catalytic dehydrogenation of ethylbenzene. The increase of the styrene productivity can be reached using permselectives membranes for hydrogen removal, suppressing the reversible and secondary reactions. This work presents the simulation of dehydrogenation process in tubular fixed bed reactor wrapped with permselective composite membrane. The mathematical modeling was developed considering the different mechanisms of mass transport that prevail in several membrane layers and in catalytic fixed bed. The removal of the permeated hydrogen was carried out establishing a gradient of chemical hydrogen potential through the membrane. Two forms of hydrogen removal were studied: the application of transmembrane pressure drop and the employment of inert sweep gas. A computational program was implemented to describe the profiles of temperature, pressure and concentration throughout all reactor, as . well as the ethylbenzene conversion, styrene selectivity and productivity. Comparing the simulation results obtained for conventional fixed bed reactor carried on standard industrial operation condition with application transmembrane pressure drop form, it shows an increase of 19.89 % in ethylbenzene conversion in the same styrene selectivity for, meaning an increase of 19.12% in styrene productivity. The same addition was obtained when the inert sweep gas was employed. Therefore, this last proceeding has been recommended as the better option, due to its lower operation cost. Through the system simulation at various operation conditions, using different reactor and membrane configurations, an increase of 40.98 % in the styrene productivity was reached comparing to conventional fixed bed process
Mestrado
Sistemas de Processos Quimicos e Informatica
Mestre em Engenharia Química
46
Liu, Junqiang. "Development of next generation mixed matrix hollow fiber membranes for butane isomer separation". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/42807.
Testo completoAbstract (sommario):
Mixed matrix hollow fiber membranes maintain the ease of processing polymers while enhancing the separation performance of the pure polymer due to inclusion of molecular sieve filler particles. This work shows the development process of high loading mixed matrix hollow fiber membranes for butane isomer separation, from material selection and engineering of polymer-sieve interfacial adhesion to mixed matrix hollow fiber spinning.
The matching of gas transport properties in polymer and zeolite is critical for forming successful mixed matrix membranes. The nC4 permeability in glassy commercial polymers such as Ultem® and Matrimid® is too low (< 0.1 Barrer) for commercial application. A group of fluorinated (6FDA) polyimides, with high nC4 permeability and nC4/iC4 selectivity, are selected as the polymer matrix. No glassy polymers can possibly match the high permeable MFI to make mixed matrix membranes with selectivity enhancement for C4s separation. Zeolite 5A, which has a nC4 permeability (~3 Barrer) and nC4/iC4 selectivity (essentially ∞), matches well with the 6FDA polymers. A 24% nC4/iC4 selectivity enhancement was achieved in mixed matrix membranes containing 6FDA-DAM and 25 wt% treated 5A particles. A more promising mixed matrix membrane contains 6FDA-DAM-DABA matrix and 5A, because of a better match of gas transport properties in polymer and zeolite.
Dual layer hollow fibers, with cellulose acetate core layer and sheath layers of 6FDA polyimides, were successfully fabricated. Successive engineering of the 6FDA sheath layer and the dense skin is needed for the challenging C4s separation, which is extremely sensitive to the integrity of the dense skin layer. The delamination-free, macrovoid-free dual layer hollow fiber membranes provide the solution for the expensive 6FDA polyimides spinning. Mixed matrix hollow fiber membranes are spun base on the platform of 6FDA/Cellulose acetate dual layer hollow fibers. Preliminary results suggest that high loading mixed matrix hollow fiber membranes for C4s is feasible. Following research is needed on the fiber spinning with well treated zeolite 5A nanoparticles.
The key aspect of this research is elucidating the three-step (sol-gel-precipitation) mechanism of sol-gel-Grignard treatment, based on which further controlling of Mg(OH)2 whisker morphologies is possible. A Mg(OH)2 nucleation process promoted by acid species is proposed to explain the heterogeneous Mg(OH)2 growing process. Different acid species were tried: 1) HCl solution, 2) AlClx species generated by dealumination process and 3) AlCl3 supported on zeolite surfaces. Acids introduced through HCl solution and dealumination are effective on commercial 5A particles to generate Mg(OH)2 whiskers in the sol-gel-Grignard treatment. Supported AlCl3 is effective on both commercial and synthesized 5A particles (150 nm-1 µm) during the sol-gel-Grignard treatment, in terms of promoting heterogeneous Mg(OH)2 whiskers formation. But the byproduct of Al(OH)3 layer separates the Mg(OH)2 whiskers from zeolite surface, and leads to undesirable morphologies for polymer-zeolite interfacial adhesion. The elucidation of sol-gel-Grignard mechanism and importance of zeolite surface acidity on Mg(OH)2 formation, builds a solid foundation for future development towards ''universal'' method of growing Mg(OH)2 whiskers on zeolite surfaces.
47
Blazheska, Jasna. "Insight in the thin-film pollyamide membrane structure after compaction". Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/401281.
Testo completoAbstract (sommario):
La osmosi inversa (OI) és la tecnología de membrana que proporciona el nivell més fi de separació i una de les tecnologies més prometedores per a superar el problema de l'escassetat mundial d'aigua neta. El mercat de membranes de RO està dominat per les membranes de pel·lícula fina (TFC) de poliamida. Quan s'operen a alta temperatura (max 45°C) i alta pressió (màxim 82 bar), poden patir compactació, el que resulta en una reducció de la producció de permeat (> 30%), que ha de ser compensat amb un augment de la pressió d'alimentació per satisfer els paràmetres de disseny. Això acaba resultant es un augment en el cost de l'aigua produïda i una reducció substancial de la vidua útil del producte.
L'objectiu d'aquest estudi va ser obtener una comprensió fonamental dels fenòmens de compactació i la seva implicació en el mecanisme de transport. Amb aquesta finalitat es van dur a terme una sèrie d'anàlisis, amb l'objectiu de caracteritzar: (1) la modificació de la morfologia i el gruix de cada capa a la membrana, a partir d'imatges de secció transversal com a resultat de l'alta temperatura i la pressió d'operació (2) el contingut químic de poliamida després de l'operació del procés (3) la part de la pèrdua de flux de permeabilitat deguda a la compactació de la capa de poliamida i la capa de suport, per separat, i la seva contribució a la pèrdua total de flux de membrana mitjançant l'aplicació del model de resistència en sèrie, i (4) la mida de porus (el volum del forat lliure) de la capa de poliamida seca i hidratada. Un total de 11 tècniques diferents es van aplicar per intentar revelar la informació completa.
Es van identificar diverses observacions que podrien atribuir-se a la pèrdua de permeabilitat de la membrana després de l'operació. A més, els resultats indiquen que hi ha una part considerable (~50%) de la resistència extra causant la pèrdua de flux que procedeix de la capa de poliamida, el que condueix a canvis irreversibles en el rendiment de la membrana. La causa originaria d'aquestes observacions podria ser els canvis en l'estructura de poliamida que més probablement es produeix durant l'operació en les condicions combinades d'alta pressió i alta temperatura.La osmosis inversa (OI) es la tecnología de membrana que proporciona el nivel más fino de separación y una de las tecnologías más prometedoras para superar el problema de la escasez mundial de agua limpia. El mercado de membranas de RO está dominado por las membranas de material compuesto de película fina (TFC) de poliamida. Cuando se operan a altas temperaturas (max 45°C) y alta presión (máximo 82 bar), pueden sufrir compactación, lo que resulta en una reducción de la producción de permeado (> 30%), que tiene que ser compensado con un aumento de la presión de alimentación para satisfacer los parámetros de diseño. Esto acaba resultando en un aumento en el coste del agua producida y una reducción sustancial de la vida útil del producto. El objetivo de este estudio fue obtener una comprensión fundamental de los fenómenos de compactación y su implicación en el mecanismo de transporte. Con este fin se llevaron a cabo una serie de análisis, con el objetivo de caracterizar: (1) la modificación de la morfología y el espesor de cada capa en la membrana, a partir de imágenes de sección transversal, como resultado de la alta temperatura y la presión de operación (2) el contenido químico de poliamida después de la operación del proceso (3) la parte de la pérdida de flujo de permeabilidad debido a la compactación de la capa de poliamida y la capa de soporte, por separado, y su contribución a la pérdida total de flujo de membrana mediante la aplicación del modelo de resistencia en serie, y (4) el tamaño de poro (el volumen agujero libre) de la capa de poliamida seca e hidratada. En total, 11 técnicas diferentes se aplicaron en un intento de revelar la información completa. Se identificaron varias observaciones que podrían atribuirse a la pérdida de permeabilidad de la membrana después de la operación. Además, los resultados indican que hay una parte considerable (~50%) de la resistencia extra causante la perdida de flujo que procede de la capa de poliamida, lo que conduce a cambios irreversibles en el rendimiento de la membrana. La causa raíz de estas observaciones podría ser los cambios en la estructura de poliamida, que más probablemente se produce durante la operación en las condiciones combinadas de alta presión y alta temperatura.
Reverse osmosis (RO) is the finest level of membrane-technology available and one of the most promising technologies to overcome the problem of global clean water scarcity. The RO membrane market is dominated by thin-film composite (TFC) polyamide membranes. When operated at high temperature (max 45˚C) and high pressure (max 82 bar) membranes can suffer compaction, which results in reduced permeate production (>30%) so that the feed pressure has to be increased to meet the design parameters. Ultimately these translate into an increase in the cost of the water produced and substantially lower membrane product life-time. The objective of this study was to gain fundamental understanding on the compaction phenomena and its implication to the transport mechanism. With that purpose a series of analyses were conducted with the aim of characterizing: (1) the membrane morphology and thickness of each layer in the membrane from cross sectional images as a result of high temperature and pressure operation (2) the polyamide chemical content after process operation (3) the portions of permeability flow loss due to compaction of the polyamide and support layer, separately, and their contribution to the total membrane flow loss by applying the series resistance model, and (4) the pore size (free-volume hole size) of the polyamide layer in dry and swollen hydrated state. In total 11 different techniques were applied attempting to reveal complete information. Several observations were identified that might be attributed to the permeability loss of the membrane after the operation. Moreover the results indicated that there is a sizable portion (~50%) of added resistance coming from the polyamide layer to the total flow loss of the entire composite membrane, which leads to irreversible changes in the membrane performance. The root cause for these observations might be the changes in the polyamide structure that most probably occurs during the operation at combined conditions of high pressure and high temperature.
48
Poletto, Patrícia. "Caracterização de membranas de poliamida 66 preparadas pelo método de inversão de fases". reponame:Repositório Institucional da UCS, 2010. https://repositorio.ucs.br/handle/11338/573.
Testo completoAbstract (sommario):
Neste trabalho foram preparadas membranas de poliamida 66 (PA 66) pelo método de inversão de fases (IF) e caracterizadas com o objetivo de verificar sua possível aplicação em processos de separação. As membranas de PA 66 foram preparadas utilizando dois solventes diferentes, ácido fórmico (AF) e ácido clorídrico (HCl) e água como não-solvente. As membranas preparadas na forma de filmes (não suportadas) foram caracterizadas por Espectroscopia de Infravermelho com Transformada de Fourier (FT-IR) e calorimetria exploratória diferencial (DSC), onde os resultados mostraram que a estrutura química e o comportamento térmico da PA 66 não foram alterados como o uso de ácidos como solventes. Os filmes apresentaram estrutura assimétrica, com formação de camada densa na parte superior seguida de subestrutura de poros esféricos observada por microscopia eletrônica de varredura (MEV). A espessura de camada densa variou de 10 à 25 μm, para o filme preparado em AF e HCl, respectivamente. O aumento da espessura da camada densa, ou seja, a redução de espaços vazios influenciou diretamente os resultados de percentual de água absorvida e porosidade total. A porosidade foi de 15 contra 50% para os filmes preparados em AF e HCl, respectivamente. O fluxo de vapor de água foi menor para os filmes com maior espessura de camada densa, devido ao aumento da resistência ao transporte de massa. Com o objetivo de aumentar a resistência mecânica dos filmes de poliamida, foram preparadas membranas suportadas em tecido de poliéster para posterior aplicação em processos de separação que utilizam altas pressões. As membranas suportadas foram caracterizadas pelas técnicas de BET para determinação de tamanho médio de poros, ensaios de osmose inversa (OI) e ultrafiltração (UF). Ambas as membranas preparadas em AF e HCl apresentaram valores de tamanho de poro muito próximos quando analisado por BET. O ensaio de compactação com água pura realizado a 40 bar de pressão revelou que as membranas preparadas em AF sofrem maior compactação na sua estrutura apresentando fluxo de permeado em torno de 22 Lm-2h-1 enquanto a membrana preparada em HCl apresentou fluxo de 312 Lm-2h-1. No ensaio de OI, a rejeição máxima ao cloreto de sódio foi de 7% e 4% para a membrana AF-3 e HCl-3, respectivamente. Nos ensaios de ultrafiltração (UF), realizados a 15 bar, ambas as membranas apresentaram valores de rejeição próximos a 70% para albumina de ovo e 80% para albumina bovina. Com esse resultado, podemos concluir que ambas as membranas apresentaram características de tamanho de poro e rejeição para aplicações em processos de UF.Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-06-04T16:11:59Z No. of bitstreams: 1 Dissertacao Patricia Poletto.pdf: 15767648 bytes, checksum: 81ddada763fec9ceadc8f928e56747a6 (MD5)
Made available in DSpace on 2014-06-04T16:11:59Z (GMT). No. of bitstreams: 1 Dissertacao Patricia Poletto.pdf: 15767648 bytes, checksum: 81ddada763fec9ceadc8f928e56747a6 (MD5)
In the present study, polyamide 66 (PA 66) membranes were prepared by phase inversion (PI) and characterized in order to verify their potential application in separation processes. PA 66 membranes were prepared using two different solvents, formic acid (FA) and chloridric acid (HCl), and water as a non-solvent. Membranes prepared in film form (not supported) were characterized by Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) and the results showed that the chemical structure and thermal behavior of the PA 66 were not altered by the use of acids as solvents. The films revealed an asymmetric structure with a dense top layer and a porous sublayer featuring spherical pores observed by scanning electron microscopy (SEM). The thickness of the dense layer varied from 10 to 25 μm in films prepared with FA and HCl, respectively. The increase in thickness of the dense layer, i.e., the reduction of empty spaces, directly influenced the results regarding water absorption percentage and total porosity. The porosity found was 15% and 50% for films prepared with FA and HCl, respectively. Water vapor flux was lower in films with a thicker dense layer as a result of a greater resistance to mass transfer. In order to increase mechanical resistance in polyamide films, supported membranes with polyester fabric were prepared for latter application in separation processes through high pressure. Supported membranes were characterized by BET techniques for the determination of pore size, reverse osmosis and ultrafiltration assays. Both membranes prepared with FA and HCl showed very similar pore sizes when analyzed by/with BET. A compression assay with pure water performed at a pressure of 40 bar revealed that membranes prepared with FA undergo greater compaction of its structure and had a permeate flux value of approximately 22 Lm-2h-1 whereas the membrane prepared with HCl had a permeate flux value of 312 Lm-2h-1. On reverse osmosis assays, the maximum rejection to sodium chloride was 7% and 4% for FA-3 and HCl-3 membranes, respectively. On ultrafiltration assays, performed at 15 bar, both membranes had rejection values close to 70% for egg albumin and 80% for bovine albumin. Based on this result, it is possible to conclude that both membranes revealed pore size and rejection characteristics for application in ultrafiltration processes.
49
Sonnen, Andreas Franz-Peter. "Structural biology of protein-membrane interactions and membrane protein function". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514997.
Testo completo
50
Pokorná, Šárka. "Studium membránových interakcí pomocí pokročilých fluorescenčních technik: Od iontů k makromolekulám". Doctoral thesis, 2016. http://www.nusl.cz/ntk/nusl-353430.
Testo completoAbstract (sommario):
Advanced fluorescence techniques were used to explore tree distinct topics concerning biological membrane and their interactions. Following thesis is according to the topic divided into three parts: 1) Ionic effects were studied employing time dependent fluorescence shift experiments and molecular dynamic simulations. Combination of these two approaches are suitable to reveal characteristic like mobility and hydration of particular bilayer segment, lipid packing or ion binding sites. Halide anions were reported to adsorb to the cationic lipid bilayer specifically, altering membrane mobility and organization. Changes in observed parameters follows Hofmeister order. Their effect is mediated either by direct ionic interaction (soft, polarizable ions) as well as via alteration of water structure (hard, non-polarizable ions) in proximity of ion molecule. Further, divalent calcium was shown to bind strongly to neutral and negatively charged lipid bilayers. Several types of binding sites depending on calcium concentration were identified. 2) Two complementary lipopeptides, CPK and CPE, incorporated into distinct lipid bilayers serve as a minimal model inducing membrane fusion. Effectiveness of fusion event might be influenced by lipopeptide-membrane and lipopeptide-lipopeptide interaction. To reveal...