• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1
  • Tagged with
  • 16
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Permeation, separation and reaction studies of palladium composite membranes

Liang, Weiqiang January 2003 (has links)
Palladium or palladium silver alloy composite membranes have been produced by electroless plating on either porous a-A!2 O 3 supports or porous stainless steel supports. It was found that the tin introduced into the membrane when using the tin-sensitisationactivation procedure decreased the durability of the membrane when being subjected to elevated temperatures. Two other activation procedures were used successfully for plating palladium on a-A!2 O3 supports. Membranes made via these new activation procedures could withstand more temperature cycles than those made via the tinsensitisation- activation procedure. The osmosis technique developed previously by other workers was used in this research to repair and produce membranes of higher quality. It was found that use of a very high osmotic pressure (3M NaCl aqueous solution) could improve the quality of a membrane by compressing the deposited palladium layer. Palladium-silver membranes were produced by plating followed by heattreatment, resulting in the formation of a palladium and silver alloy. The presence of hydrogen was helpful in this process. It was found experimentally that CO, H2 O, n-C4Hio and iso-C4Hio reduced the permeation of hydrogen through a palladium or palladium-silver composite membrane, while nitrogen had a neutral effect. Addition of CO and H2 O did not change any surface structure of the membrane, but retarded the permeation of hydrogen by competitive adsorption. Therefore, their effect disappeared after the membrane was purged by pure hydrogen for a short period of time. The adsorption tendency of H2 O was stronger than that of CO, so the former retarded the permeation of hydrogen more. The presence of n-C4Hio and iso-C4Hio caused the hydrogen permeability to decrease, and the permeability lost could not be completely recovered with a hydrogen purge. In the presence of dehydrogenation catalyst, the effect of these hydrocarbons became much more severe, and a hydrogen purge could not recover the permeability. This was due to the dehydrogenation product (olefin) causing some coke deposition on the membrane. Dilute oxygen/nitrogen mixtures could burn off the coke, leading to the recovery of the permeability. In the research, it was found that the hydrogen permeability of a composite palladium-silver membrane was affected by the permeation direction. For pure hydrogen, direction from the support to the metal film would give a higher hydrogen permeance, but for a hydrogen mixture with nitrogen, the result was just opposite. From the simulated results, it was found that the permeation direction from the metal film to the support could make the hydrogen permeation rate deviate from Sievert's law. The dehydrogenation of iso-butane was studied in a fixed bed and in a palladiumsilver membrane reactor. Pt/A^Os was used as the catalyst. While in a fixed bed reactor, total pressure reduced both the conversion of iso-butane and the selectivity of iso-butene, this was not the case in the palladium-silver membrane reactor. The removal of hydrogen from the reaction zone ensured that the experimental conversions of iso-butane in the membrane reactor were higher than the equilibrium values. The iso-butene selectivity was also increased in the membrane reactor and a flow rate of sweep gas had a favourable effect on the conversions and the selectivity. The hydrogen permeability of the membrane was much higher than the required hydrogen removal in this research, so the controlling step of the reaction was the activity of the catalyst. Counter-current sweep produced only slightly higher conversion than co-current sweep, but in the present work the co-current sweep mode was better than the counter-current sweep mode, because of a higher hydrogen partial pressure at the reactor end leading to less catalyst deactivation.
12

Organic solvent nanofiltration membrane cascades for solvent exchange and purification

Chun-Te Lin, Justin January 2008 (has links)
No description available.
13

Novel ceramic hollow fibre membranes for fluid separation and chemical reaction

Liu, Yutie January 2005 (has links)
No description available.
14

The application of enhanced fluid dynamic gauging as a fouling sensor for pressure driven membrane separations in the food industry

Jones, Sarah January 2012 (has links)
The aim of this study was to further understand the fouling and cleaning mechanisms of synthetic membranes used to filter an industrially relevant feed. The main focus of this study was to understand the fouling layer properties during pressure driven filtration. A relatively new technique known as Fluid Dynamic Gauging (FDG) was applied to examine the fouling layer thickness. This work comprised of four main themes with overlapping objectives: (i) the optimisation of Spent Sulphite Liquor fouling and cleaning conditions, (ii) the optimisation of molasses fouling and cleaning conditions, (iii) the investigation of the effect of a simple pre-treatment upon the membrane separation performance, and (iv) the application of the FDG in the study of polymeric membranes. An understanding of the mechanisms involved in fouling and cleaning of microfiltration and ultrafiltration membranes used to filter molasses and SSL has been attained. The variables affecting permeate flux and quality were optimised and mechanistic information concerning the synergistic effects between fouling and cleaning was gathered. The application of a simple NaOH pre-treatment was found to affect both the type of foulant species attaching to the membrane surface, and resulted in an altered separation and cleaning performance. Zeta potential measurements, FTIR and AFM demonstrated that both in-pore and surface fouling was present. The data collected indicated that for both membranes evaluated, different fouling species were found to have attached, depending upon the pre-treatment protocol used. These findings are significant, as they offer support to the recommendations made by some polymeric membrane manufacturers that conditioning protocols should include a NaOH step. However, in the SSL system examined, the effect of NaOH pre-treatment resulted in an improvement in the subsequent performance only over the first two or three complete filtration cycles. It is therefore necessary to study membrane systems over multiple fouling and cleaning cycles before a recommendation can be made. An improved understanding of the interaction between the surface chemistry and surface physics during membrane filtration of complex food based material will benefit both membrane manufactures and food industry based users. The technique of Fluid Dynamic Gauging was incorporated into an existing system and validated to monitor the development of cake layers over time. The FDG was also used to optimise conditions and track the thickness of the cake layer during multiple fouling cycles and its removal rate during cleaning, as an aid to understanding removal mechanisms. It has been shown that operating conditions have to be carefully chosen to minimise the effect of membrane fouling. The results show that FDG is a versatile and powerful technique for characterising the dynamics and mechanical behaviour of fouling layers on membrane surfaces. A particular advantage of the FDG technique is its ability to determine the thickness of fouling layers where other techniques would find difficulty. For example, the layers formed in this study were opaque, and consequently the determination of the development of deposit thickness with time would have been very challenging using conventional optical microscopy techniques.
15

Slotted and circular pore surface microfiltration

Bromley, Alan J. January 2002 (has links)
The work described by this thesis is a comparison of pore opening geometry for true surface microfilters. True surface microfilters can be thought of as very fine sieves, with pore sizes less than 10 microns. All other types of so-called microfiltration membranes do not rely on sieving, but obtain their pore retention rating by particle collection mechanisms similar to depth filters. Particle deposition within such microfilters results in permeate flow rate dechne, for a fixed pressure filtration, or pressure drop rise, for a fixed rate filtration. The true surface microfilter pore geometnes considered were circular and slotted, and microfilters with filtering dimension of less than 10 microns were used. The slotted pore microfilters are not commercially available and had to be made in the laboratory as part of this study. The technique used was to plate nickel onto an existing substrate, thereby reducing the pore dimension until It was within the microfiltration range. The plating was by electroless nickel solution and not by galvanic means. Significant development of the electroless platmg technique led ultimately to the successful manufacture of process scale slotted surface microfilters.
16

Effects of oxidation states of Copper (Cu), Nickel (Ni), Palladium (Pd) and Silver (Ag) on rejection by nanofiltration membranes

Brooms, Thabo John 06 1900 (has links)
Thesis (M. Tech.(Chemistry)--Vaal University of Technology)), 2010 / Mining industry produces metals which are economical and serve as high valuable commodities in South Africa. This country is regarded as the world leading producer of precious metals such as platinum group metals (PGMs). Silver (Ag), which is also a precious metal, contribute to the country’s economy wealth due to its significance during industrial applications. Base metals such as copper (Cu) and nickel (Ni), though they are low valued, play a significant role in the republics economic wealth. Mining wastewater contains some of these metals, which end up polluting the environment. A possibility to recover this was investigated using NF membranes. Mine effluent was simulated by using relevant reagents. Characterization of NF90, NF- and NF270 membranes, was done by using scanning electron microscopy (SEM), clean water permeability, single charged salts of NaCl and MgCl2 and binary mixture of NaCl/MgCl2 studies. All the rejection experiments were conducted at pH 2.0 with varying pressure and concentrations. Flux measurements indicated that water permeability through the membranes trend, NF270 > NF90 > NF-. The experiments were performed at pressures of 5 bar, 10 bar, 15 bar and 20 bar. For NF90 membrane, a rejection of Na+ monovalent ion in 20 ppm solution was less than of Mg2+ (divalent) ion. Percentage rejections of 90% (Na+) and 98% (Mg2+) were achieved. NF- had rejection of 83% and 90% for Na+ and Mg2+, respectively. In the case of NF270, the membrane had rejection of 92% (Na+) and 94% (Mg2+), respectively. At 100 ppm, all three membranes showed a decreasing trend in rejection while increasing pressure. For binary-solution mixture, Mg2+ ion still had the highest rejection compared to Na+ ion with about 94% and 85% on NF90 than on NF270 and NF-. The high rejection of divalent ion as compared to monovalent ion for charged solutes was due to solute size and electrostatic interaction between the membrane surface layer and the solute. In the case of transition metal rejection studies, Pd2+ ion had an average of 90%, with Ni2+ ion ≈ 95% and Cu2+ ion ≈ 98% as single salts on NF90 compared to NF270 and NF-. However, as for binary and trinary solution mixture, the competition amongst ions was high, where Pd2+ ion rejection was ≈ 99,0%, while Ni2+ and Cu2+ ions was > 90% on NF90 and NF-. Therefore it was excluded from the tests. For the monovalent metal ions (Ag+ and Cu+), the rejection was > 90% in almost all concentrations mixtures. During membrane fouling evaluation, AgCl salt fouled the most, compared to other metal ions, forming a concentration polarization accumulation on the membrane surface for both 20 and 100 ppm solutions. This situation leads to cake layer formation which causes a flux decline, reduces membrane life time and lowers the rejection performance of NF membranes. The aim of this study was to evaluate the performance of three commercial polymeric membranes (NF90, NF270 and NF-) during rejection of the metal

Page generated in 0.0296 seconds