1000 resultados para Al2O3 membrane


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The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support from clear solution and the evaluation of the perfection of the as-synthesized membrane by gas permeation were investigated. When an unseeded support was used, the NaA zeolite began to transform into other types of zeolites before a continuous NaA zeolite membrane formed. When the support was coated with nucleation seeds, not only the formation of NaA zeolite on the support surface was accelerated, but also the transformation of NaA zeolite into other types of zeolites was inhibited. A continuous NaA zeolite membrane can be formed. Perfection evaluation indicated that the NaA zeolite membrane with the synthesis time of 3 h showed the best perfection after a one-stage synthesis. The perfection of NaA zeolite membrane can be improved by employing the multi-stage synthesis method. The NaA zeolite membrane with a synthesis time of 2 h after a two-stage synthesis showed the best gas permeation performance, The permselectivity of H-2/n-C4H10 and O-2/N-2 were 19.1 and 1.8, respectively, higher than those of the corresponding Knudsen diffusion selectivity of 5.39 and 0.94, which showed the molecular sieving effect of NaA zeolite. However, the permeation of n-C4H10 also indicated that the NaA zeolite membrane had certain defects, the diameter of which were larger than the NaA zeolite channels. (C) 2001 Elsevier Science B.V. All rights reserved.

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A mixed-conducting perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C-2 selectivity up to 40-70% was achieved, albeit that conversion rate were low, typically 0.5-3.5% at 800-900 degreesC with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/gamma -Al2O3 with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH4 conversion, 93.0% CO selectivity and 10.45 ml/cm(2) min oxygen permeation flux were achieved under steady state at 850 degreesC. Methane conversion and oxygen permeation flux increased with increasing temperature, No fracture of the membrane reactor was observed during syngas production. However, H-2-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875 degreesC for more than 500h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm(2) min. (C) 2001 Elsevier Science B.V. All rights reserved.

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Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/gamma-Al2O3 catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba0.5Sr0.5Co0.8Fe0.2O3 which has an oxygen permeation flux around 11.5 ml/cm(2) min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/gamma-Al2O3 in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91-93% and a H-2 selectivity of 95-97% have been achieved. (c) 2005 Elsevier B.V. All rights reserved.

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A membrane reactor allows for simultaneous separation and reaction, and thus, can play a good role to produce value-added chemicals. In this work, we demonstrated such a membrane reactor based on fluorite oxide samarium-doped ceria (SDC) using an external short-circuit concept for oxygen permeation. The fluorite phase was employed to impart its high structural stability, while its limited electronic conductivity was overcome by the application of an external short circuit to function the SDC membrane for oxygen transport. On one side of the membrane, i.e., feed side, carbon dioxide decomposition into carbon monoxide and oxygen was carried out with the aid of a Pt or Ag catalyst. The resultant oxygen was concurrently depleted on the membrane surface and transported to the other side of the membrane, favorably shifting this equilibrium-limited reaction to the product side. The transported oxygen on the permeate side with the aid of a GdNi/Al2O3 catalyst was then consumed by the reaction with methane to form syngas, i.e., carbon monoxide and hydrogen. As such, the required driving force for gas transport through the membrane can be sustained by coupling two different reactions in one membrane reactor, whose stability to withstand these different gases at high temperatures is attained in this paper. We also examined the effect of the membrane thickness, oxygen ionic transport rate, and CO2 and CH4 flow rates to the membrane reactor performance. More importantly, here, we proved the feasibility of a highly stable membrane reactor based on an external short circuit as evidenced by achieving the constant performance in CO selectivity, CH4 conversion, CO2 conversion, and O2 flux during 100 h of operation and unaltered membrane structure after this operation together with the coking resistance.

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Nanofiltration (NF) is a pressure-driven membrane process, intermediate between reverse osmosis and ultrafiltration. Commercially available polymeric membranes have been used in a wide range of applications, such as drinking, process industry and waste water treatment. For all the applications requiring high stability and harsh washing procedures inorganic membranes are preferred due to their high chemical inertia. Typically, γ – Al2O3 as well as TiO2 and ZrO2 selective layers are used; the latter show higher chemical stability in a wide range of pH and temperatures. In this work the experimental characterization of two different type of membrane has been performed in order to investigate permeation properties, separation performance and efficiency with aqueous solutions containing strong inorganic electrolytes. The influence of salt concentration and feed pH as well as the role of concentration polarization and electrolyte type on the membrane behavior are investigated. Experimentation was performed testing a multi–layer structured NF membrane in α-Al2O3, TiO2 and ZrO2, and a polymeric membrane, in polyamide supported on polysulfone, with binary aqueous solutions containing NaCl, Na2SO4 or CaCl2; the effect of salt composition and pH in the feed side was studied both on flux and salt rejection. All the NF experimental data available for the two membranes were used to evaluate the volumetric membrane charge (X) corresponding to each operative conditions investigated, through the Donnan Steric Pore Model and Dielectric Exclusion (DSPM&DE). The results obtained allow to understand which are the main phenomena at the basis of the different behaviors observed.

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In this study, a novel molecular sieve silica (MSS) membrane packed bed reactor (PBR) using a Cu/ZnO/Al2O3 catalyst was applied to the low-temperature water gas shift reaction (WGS). Best permeation results were H-2 permeances of 1.5 x 10(-6) mol(.)s(-1) m(-2) Pa-1, H-2/CO2 selectivities of 8 and H-2/N-2 selectivities of 18. It was shown that an operation with a sweep gas flow of 80 cm 3 min(-1), a feed flow rate of 50 cm(3) min(-1) and a H2O/CO molar ratio of one at 280 degreesC reached a 99% CO conversion. This is well above the thermodynamic equilibrium and achievable PBR conversion. Hydrophilic membranes underwent pore widening during the reaction while hydrophobic membranes indicated no such behaviour and also showed increased H-2 permeation with temperature, a characteristic of activated transport. (C) 2003 Elsevier Science B.V. All rights reserved.

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This work is concerned with the genetic basis of normal human pigmentation variation. Specifically, the role of polymorphisms within the solute carrier family 45 member 2 (SLC45A2 or membrane associated transporter protein; MATP) gene were investigated with respect to variation in hair, skin and eye colour ― both between and within populations. SLC45A2 is an important regulator of melanin production and mutations in the gene underly the most recently identified form of oculocutaneous albinism. There is evidence to suggest that non-synonymous polymorphisms in SLC45A2 are associated with normal pigmentation variation between populations. Therefore, the underlying hypothesis of this thesis is that polymorphisms in SLC45A2 will alter the function or regulation of the protein, thereby altering the important role it plays in melanogenesis and providing a mechanism for normal pigmentation variation. In order to investigate the role that SLC45A2 polymorphisms play in human pigmentation variation, a DNA database was established which collected pigmentation phenotypic information and blood samples of more than 700 individuals. This database was used as the foundation for two association studies outlined in this thesis, the first of which involved genotyping two previously-described non-synonymous polymorphisms, p.Glu272Lys and p.Phe374Leu, in four different population groups. For both polymorphisms, allele frequencies were significantly different between population groups and the 272Lys and 374Leu alleles were strongly associated with black hair, brown eyes and olive skin colour in Caucasians. This was the first report to show that SLC45A2 polymorphisms were associated with normal human intra-population pigmentation variation. The second association study involved genotyping several SLC45A2 promoter polymorphisms to determine if they also played a role in pigmentation variation. Firstly, the transcription start site (TSS), and hence putative proximal promoter region, was identified using 5' RNA ligase mediated rapid amplification of cDNA ends (RLM-RACE). Two alternate TSSs were identified and the putative promoter region was screened for novel polymorphisms using denaturing high performance liquid chromatography (dHPLC). A novel duplication (c.–1176_–1174dupAAT) was identified along with other previously described single nucleotide polymorphisms (c.–1721C>G and c.–1169G>A). Strong linkage disequilibrium ensured that all three polymorphisms were associated with skin colour such that the –1721G, +dup and –1169A alleles were associated with olive skin in Caucasians. No linkage disequilibrium was observed between the promoter and coding region polymorphisms, suggesting independent effects. The association analyses were complemented with functional data, showing that the –1721G, +dup and –1169A alleles significantly decreased SLC45A2 transcriptional activity. Based on in silico bioinformatic analysis that showed these alleles remove a microphthalmia-associated transcription factor (MITF) binding site, and that MITF is a known regulator of SLC45A2 (Baxter and Pavan, 2002; Du and Fisher, 2002), it was postulated that SLC45A2 promoter polymorphisms could contribute to the regulation of pigmentation by altering MITF binding affinity. Further characterisation of the SLC45A2 promoter was carried out using luciferase reporter assays to determine the transcriptional activity of different regions of the promoter. Five constructs were designed of increasing length and their promoter activity evaluated. Constitutive promoter activity was observed within the first ~200 bp and promoter activity increased as the construct size increased. The functional impact of the –1721G, +dup and –1169A alleles, which removed a MITF consensus binding site, were assessed using electrophoretic mobility shift assays (EMSA) and expression analysis of genotyped melanoblast and melanocyte cell lines. EMSA results confirmed that the promoter polymorphisms affected DNA-protein binding. Interestingly, however, the protein/s involved were not MITF, or at least MITF was not the protein directly binding to the DNA. In an effort to more thoroughly characterise the functional consequences of SLC45A2 promoter polymorphisms, the mRNA expression levels of SLC45A2 and MITF were determined in melanocyte/melanoblast cell lines. Based on SLC45A2’s role in processing and trafficking TYRP1 from the trans-Golgi network to stage 2 melanosmes, the mRNA expression of TYRP1 was also investigated. Expression results suggested a coordinated expression of pigmentation genes. This thesis has substantially contributed to the field of pigmentation by showing that SLC45A2 polymorphisms not only show allele frequency differences between population groups, but also contribute to normal pigmentation variation within a Caucasian population. In addition, promoter polymorphisms have been shown to have functional consequences for SLC45A2 transcription and the expression of other pigmentation genes. Combined, the data presented in this work supports the notion that SLC45A2 is an important contributor to normal pigmentation variation and should be the target of further research to elucidate its role in determining pigmentation phenotypes. Understanding SLC45A2’s function may lead to the development of therapeutic interventions for oculocutaneous albinism and other disorders of pigmentation. It may also help in our understanding of skin cancer susceptibility and evolutionary adaptation to different UV environments, and contribute to the forensic application of pigmentation phenotype prediction.

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Infection of plant cells by potyviruses induces the formation of cytoplasmic inclusions ranging in size from 200 to 1000 nm. To determine if the ability to form these ordered, insoluble structures is intrinsic to the potyviral cytoplasmic inclusion protein, we have expressed the cytoplasmic inclusion protein from Potato virus Y in tobacco under the control of the chrysanthemum ribulose-1,5-bisphosphate carboxylase small subunit promoter, a highly active, green tissue promoter. No cytoplasmic inclusions were observed in the leaves of transgenic tobacco using transmission electron microscopy, despite being able to clearly visualize these inclusions in Potato virus Y infected tobacco leaves under the same conditions. However, we did observe a wide range of tissue and sub-cellular abnormalities associated with the expression of the Potato virus Y cytoplasmic inclusion protein. These changes included the disruption of normal cell morphology and organization in leaves, mitochondrial and chloroplast internal reorganization, and the formation of atypical lipid accumulations. Despite these significant structural changes, however, transgenic tobacco plants were viable and the results are discussed in the context of potyviral cytoplasmic inclusion protein function.

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Conventional clinical therapies are unable to resolve osteochondral defects adequately, hence tissue engineering solutions are sought to address the challenge. A biphasic implant which was seeded with Mesenchymal Stem Cells (MSC) and coupled with an electrospun membrane was evaluated as an alternative. This dual phase construct comprised of a Polycaprolactone (PCL) cartilage scaffold and a Polycaprolactone - Tri Calcium Phosphate (PCL - TCP) osseous matrix. Autologous MSC was seeded into the entire implant via fibrin and the construct was inserted into critically sized osteochondral defects located at the medial condyle and patellar groove of pigs. The defect was resurfaced with a PCL - collagen electrospun mesh that served as a substitute for periosteal flap in preventing cell leakage. Controls either without implanted MSC or resurfacing membrane were included. After 6 months, cartilaginous repair was observed with a low occurrence of fibrocartilage at the medial condyle. Osteochondral repair was promoted and host cartilage degeneration was arrested as shown by the superior Glycosaminoglycan (GAG) maintenance. This positive morphological outcome was supported by a higher relative Young's modulus which indicated functional cartilage restoration. Bone in growth and remodeling occurred in all groups with a higher degree of mineralization in the experimental group. Tissue repair was compromised in the absence of the implanted cells or the resurfacing membrane. Moreover healing was inferior at the patellar groove as compared to the medial condyle and this was attributed to the native biomechanical features.

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A membrane filtration plant using suitable micro or ultra-filtration membranes has the potential to significantly increase pan stage capacity and improve sugar quality. Previous investigations by SRI and others have shown that membranes will remove polysaccharides, turbidity and colloidal impurities and result in lower viscosity syrups and molasses. However, the conclusion from those investigations was that membrane filtration was not economically viable. A comprehensive assessment of current generation membrane technology was undertaken by SRI. With the aid of two pilot plants provided by Applexion and Koch Membrane Systems, extensive trials were conducted at an Australian factory using clarified juice at 80–98°C as feed to each pilot plant. Conditions were varied during the trials to examine the effect of a range of operating parameters on the filtering characteristics of each of the membranes. These parameters included feed temperature and pressure, flow velocity, soluble solids and impurity concentrations. The data were then combined to develop models to predict the filtration rate (or flux) that could be expected for nominated operating conditions. The models demonstrated very good agreement with the data collected during the trials. The trials also identified those membranes that provided the highest flux levels per unit area of membrane surface for a nominated set of conditions. Cleaning procedures were developed that ensured the water flux level was recovered following a clean-in-place process. Bulk samples of clarified juice and membrane filtered juice from each pilot were evaporated to syrup to quantify the gain in pan stage productivity that results from the removal of high molecular weight impurities by membrane filtration. The results are in general agreement with those published by other research groups.

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A polycaprolactone (PCL)–collagen electrospun mesh is proposed as a novel alternative to the conventional periosteal graft in autologous chondrocyte implantation. This is the first known attempt in designing a cartilage resurfacing membrane using a mechanically resilient PCL mesh with a weight-average molecular weight of 139 300 that is enhanced with bioactive collagen. PCL–collagen 10, 20 and 40% electrospun meshes (Coll-10, Coll-20 and Coll-40) were evaluated and it was discovered that the retention of surface collagen could only be achieved in Coll-20 and Coll-40. Furthermore Coll-20 was stiffer and stronger than Coll-40 and it satisfied the mechanical demands at the cartilage implant site. When seeded with mesenchymal stem cells (MSCs), the cells adhered on the surface of the Coll-20 mesh and they remained viable over a period of 28 days; however, they were unable to infiltrate through the dense meshwork. Cell compatibility was also noted in the chondrogenic environment as the MSCs differentiated into chondrocytes with the expression of Sox9, aggrecan and collagen II. More importantly, the mesh did not induce a hypertrophic response from the cells. The current findings support the use of Coll-20 as a cartilage patch, and future implantation studies are anticipated.