Dissertations / Theses on the topic 'Membrane reactors'

Doctor of Philosophy
Chemical Engineering
Mary E. Rezac
Membrane contact reactors (MCRs) have been evaluated for the selective hydro-treating of model reactions; the partial hydrogenation of soybean oil (PHSO), and the conversion of lactic acid into commodity chemicals. Membranes were rendered catalytically active by depositing metal catalyst onto the polymer "skin" of an asymmetric membrane. Hydrogen was supplied to the support side of the membrane and permeated from the support side to the skin side, where it adsorbed directly onto the metal surface. Liquid reactant was circulated over the membrane, allowing the liquid to come into direct contact with the metal coated surface of the membrane, where the reaction occurred. Our membrane contact reactor approach replaces traditional three-phase batch slurry reactors. These traditional reactors possess inherent mass transfer limitations due to low hydrogen solubility in liquid and slow diffusion to the catalyst surface. This causes hydrogen starvation at the catalyst surface, resulting in undesirable side reactions and/or extreme operating pressures of 100 atmospheres or more. By using membrane reactors, we were able to rapidly supply hydrogen to the catalyst surface. When the PHSO is performed in a traditional slurry reactor, the aforementioned hydrogen starvation leads to a high amounts of trans-fats. Using a MCR, we were able to reduce trans-fats by over 50% for equal levels of hydrogenation. It was further demonstrated that an increase in temperature had minimal effects on trans-fat formation, while significantly increasing hydrogenation rates; allowing the system to capture higher reaction rates without adversely affecting product quality. Additionally, high temperatures favors the hydrogenation of polyenes over monoenes, leading to low amounts of saturated fats. MCRs were shown to operator at high temperatures and: (1) capture high reaction rates, (2) minimize saturated fats, and (3) minimize trans-fats. We also demonstrated lactic acid conversion into commodity chemicals using MCRs. Our results show that all MCR experiments had faster reaction rate than all of our controls, indicating that MCRs have high levels of hydrogen coverage at the catalyst. It was also demonstrated that changing reaction conditions (pressure and temperature) changed the product selectivities; giving the potential for MCRs to manipulate product selectivity.

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.

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.

The objective of this work is to study experimentally and theoretically novel multiphase microreactors and characterize them in relation to hydrodynamics and mass transfer, in order to evaluate, understand and improve their performance. In order to achieve this CO2 absorption in sodium hydroxide and amine solutions an example of a fast gas-liquid reaction has been investigated in a single microstructured metallic mesh reactor, CRL reactor, PTFE single channel membrane reactor and the silicon nitride mesh reactor. CO2 absorption in sodium hydroxide solution was initially studied experimentally and theoretically in a metal microstructured mesh reactor. The differential mass balances to describe the concentration profiles of components in the three domains (gas/membrane/liquid), were solved with Comsol Multiphysics (modeling software for finite element analysis of partial differential equations). The model indicated that the carbon dioxide is consumed within few microns from the gas – liquid interface, and the dominant resistance for mass transfer is located in the mesh because it is wetted by the liquid reactant. In order to overcome the limitation of the extra resistance to the mass transfer in the metallic mesh, PTFE membranes were used in the single channel reactor, which are considered as hydrophobic to aqueous solutions of NaOH and amines. Monoethanolamine solution (MEA) absorbed more CO2 than diethanolamine (DEA) since the reaction rate constant for MEA is higher than DEA. 8 channel (PTFE) microreactor showed much higher CO2 removal efficiency than the metallic mesh microreactor. Furthermore the model indicated partial-wetting of the PTFE membrane when NaOH solution was used as an absorbent. In order to enhance mass transfer staggered herringbones were used on the floor of the liquid side of the single channel PTFE microreactor. No enhancement of mass transfer was observed with the use of staggered herringbones. A possible reason for that is that a limit for the fast second-order reaction is reached for enhancement and that the apparent reaction rate is independent from mass transfer for our case, or that the herringbones are far away from the reaction zone and cannot create the appropriate stirring for enhancement. In order to increase throughput, carbon dioxide absorption in sodium hydroxide solution was performed in the metallic mesh ‘scale-out’ reactor (with 4 meshes). CO2 removal efficiency for the ‘scale-out’ reactor was significantly lower than the single mesh reactor, which is probably due to breakthrough of liquid in the gas phase (stagnant liquid) or uneven flow distribution in each plate of the ‘scale-out’ reactor. Finally a silicon nitride mesh reactor developed by Bayer Technology Services and FluXXion was used for CO2 absorption in aqueous solutions of NaOH and DEA. The silicon nitride mesh reactor showed better performance than the PTFE single channel reactor, the metallic 8 channel reactor and the CRL mesh reactor when NaOH was used, due to the very thin membrane of 1 μm thickness, which makes the resistance to mass transfer very small.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Andrei Fedorov; Committee Member: Srinivas Garimella; Committee Member: Timothy Lieuwen; Committee Member: William Koros; Committee Member: William Wepfer. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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.

[ES] La presente tesis doctoral se centra en el desarrollo de nuevas membranas de separación de gases, así como su empleo in-situ en reactores catalíticos de membrana para la intensificación de procesos. Para este propósito, se han sintetizado varios materiales, como polímeros para la fabricación de membranas, catalizadores tanto para la metanación del CO2 como para la reacción de síntesis de Fischer-Tropsch, y diversas partículas inorgánicas nanométricas para su uso en membranas de matriz mixta. En lo referente a la fabricación de las membranas, la tesis aborda principalmente dos tipos: orgánicas e inorgánicas. Con respecto a las membranas orgánicas, se han considerado diferentes materiales poliméricos, tanto para la capa selectiva de la membrana, así como soporte de la misma. Se ha trabajado con poliimidas, puesto que son materiales con temperaturas de transición vítrea muy alta, para su posterior uso en reacciones industriales que tienen lugar entre 250-300 ºC. Para conseguir membranas muy permeables, manteniendo una buena selectividad, es necesario obtener capas selectivas de menos de una micra. Usando como material de soporte otro tipo de polímero, no es necesario estudiar la compatibilidad entre ellos, siendo menos compleja la obtención de capas finas. En cambio, si el soporte es de tipo inorgánico, un exhaustivo estudio de la relación entre la concentración y la viscosidad de la solución polimérica es altamente necesario. Diversas partículas inorgánicas nanométricas se estudiaron para favorecer la permeación de agua a través de los materiales poliméricos. En segundo lugar, en cuanto a membranas inorgánicas, se realizó la funcionalización de una membrana de paladio para favorecer la permeación de hidrógeno y evitar así la contaminación por monóxido de carbono. El motivo por el cual se dopó con otro metal la capa selectiva de la membrana metálica fue para poder emplearla en un reactor de Fischer-Tropsch. Con relación al diseño y fabricación de los reactores, durante esta tesis, se desarrolló el prototipo de un microreactor para la metanación de CO2, donde una membrana polimérica de capa fina selectiva al agua se integró para evitar la desactivación del catalizador, y a su vez desplazar el equilibrio y aumentar la conversión de CO2. Por otro lado, se rediseñó un reactor de Fischer-Tropsch para poder introducir una membrana metálica selectiva a hidrogeno y poder inyectarlo de manera controlada. De esta manera, y siguiendo estudios previos, el objetivo fue mejorar la selectividad a los productos deseados mediante el hidrocraqueo y la hidroisomerización de olefinas y parafinas con la ayuda de la alta presión parcial de hidrógeno.
[CAT] La present tesi doctoral es centra en el desenvolupament de noves membranes de separació de gasos, així com el seu ús in-situ en reactors catalítics de membrana per a la intensificació de processos. Per a aquest propòsit, s'han sintetitzat diversos materials, com a polímers per a la fabricació de membranes, catalitzadors tant per a la metanació del CO2 com per a la reacció de síntesi de Fischer-Tropsch, i diverses partícules inorgàniques nanomètriques per al seu ús en membranes de matriu mixta. Referent a la fabricació de les membranes, la tesi aborda principalment dos tipus: orgàniques i inorgàniques. Respecte a les membranes orgàniques, diferents materials polimèrics s'ha considerat com a candidats prometedors, tant per a la capa selectiva de la membrana, així com com a suport d'aquesta. S'ha treballat amb poliimides, ja que són materials amb temperatures de transició vítria molt alta, per al seu posterior ús en reaccions industrials que tenen lloc entre 250-300 °C. Per a aconseguir membranes molt permeables, mantenint una bona selectivitat, és necessari obtindre capes selectives de menys d'una micra. Emprant com a material de suport altre tipus de polímer, no és necessari estudiar la compatibilitat entre ells, sent menys complexa l'obtenció de capes fines. En canvi, si el suport és de tipus inorgànic, un exhaustiu estudi de la relació entre la concentració i la viscositat de la solució polimèrica és altament necessari. Diverses partícules inorgàniques nanomètriques es van estudiar per a afavorir la permeació d'aigua a través dels materials polimèrics. En segon lloc, quant a membranes inorgàniques, es va realitzar la funcionalització d'una membrana de pal¿ladi per a afavorir la permeació d'hidrogen i evitar la contaminació per monòxid de carboni. El motiu pel qual es va dopar amb un altre metall la capa selectiva de la membrana metàl¿lica va ser per a poder emprar-la en un reactor de Fischer-Tropsch. En relació amb el disseny i fabricació dels reactors, durant aquesta tesi, es va desenvolupar el prototip d'un microreactor per a la metanació de CO2, on una membrana polimèrica de capa fina selectiva a l'aigua es va integrar per a així evitar la desactivació del catalitzador i al seu torn desplaçar l'equilibri i augmentar la conversió de CO2. D'altra banda, un reactor de Fischer-Tropsch va ser redissenyat per a poder introduir una membrana metàl¿lica selectiva a l'hidrogen i poder injectar-lo de manera controlada. D'aquesta manera, i seguint estudis previs, el objectiu va ser millorar la selectivitat als productes desitjats mitjançant el hidrocraqueix i la hidroisomerització d'olefines i parafines amb l'ajuda de l'alta pressió parcial d'hidrogen.
[EN] The present thesis is focused on the development of new gas-separation membranes, as well as their in-situ integration on catalytic membrane reactors for process intensification. For this purpose, several materials have been synthesized such as polymers for membrane manufacture, catalysts for CO2 methanation and Fischer-Tropsch synthesis reaction, and inorganic materials in form of nanometer-sized particles for their use in mixed matrix membranes. Regarding membranes manufacture, this thesis deals mainly with two types: organic and inorganic. With regards to the organic membranes, different polymeric materials have been considered as promising candidates, both for the selective layer of the membrane, as well as a support thereof. Polyimides have been selected since they are materials with very high glass transition temperatures, in order to be used in industrial reactions which take place at temperatures around 250-300 ºC. To obtain highly permeable membranes, while maintaining a good selectivity, it is necessary to develop selective layers of less than one micron. Using another type of polymer as support material, it is not necessary to study the compatibility between membrane and support. On the other hand, if the support is inorganic, an exhaustive study of the relation between the concentration and the viscosity of the polymer solution is highly necessary. In addition, various inorganic particles were studied to favor the permeation of water through polymeric materials. Secondly, as regards to inorganic membranes, the functionalization of a palladium membrane to favor the permeation of hydrogen and avoid carbon monoxide contamination was carried out. The membrane selective layer was doped with another metal in order to be used in a Fischer-Tropsch reactor. Regarding the design and manufacture of the reactors used during this thesis, a prototype of a microreactor for CO2 methanation was carried out, where a thin-film polymer membrane selective to water was integrated to avoid the deactivation of the catalyst and to displace the equilibrium and increase the CO2 conversion. On the other hand, a Fischer-Tropsch reactor was redesigned to introduce a hydrogen-selective metal membrane and to be able to inject it in a controlled manner. In this way, and following previous studies, the aim is to enhance the selectivity to the target products by hydrocracking and hydroisomerization the olefins and paraffins assisted by the presence of an elevated partial pressure of hydrogen.
I would like to acknowledge the Spanish Government, for funding my research with the Severo Ochoa scholarship.
Escorihuela Roca, S. (2019). Novel gas-separation membranes for intensified catalytic reactors [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/121139
TESIS

This work describes the application of porous metal supported Pd-membranes to the water-gas shift catalytic membrane reactor in the context of its potential application to the Integrated Gasification Combined Cycle (IGCC) process. The objective of this work was to develop a better understanding of Pd-membrane fabrication techniques, water-gas shift catalytic membrane reactor operation, and long-term behavior of the Pd-membranes under water-gas shift conditions. Thin (1.5 - 16 um) Pd-membranes were prepared by electroless deposition techniques on porous metal supports by previously developed methods. Pd-membranes were installed into stainless steel modules and utilized for mixed gas separation (H2/inert, H2/H2O, dry syngas, and wet syngas) at 350 - 450C and 14.5 atma to investigate boundary layer mass transfer resistance and surface inhibition. Pd-membranes were also installed into stainless steel modules with iron-chrome oxide catalyst and tested under water-gas shift conditions to investigate membrane reactor operation in the high pressure (5.0 - 14.6 atma) and high temperature (300 - 500C) regime. After the establishment of appropriate operating conditions, long-term testing was conducted to determine the membrane stability through He leak growth analysis and characterization by SEM and XRD. Pd and Pd/Au-alloy membranes were also investigated for their tolerance to 1 - 20 ppmv of H2S in syngas over extended periods at 400C and 14.0 atma. Water-gas shift catalytic membrane reactor operating parameters were investigated with a focus on high pressure conditions such that high H2 recovery was possible without a sweep gas. With regard to the feed composition, it was desirable to operate at a low H2O/CO ratio for higher H2 recovery, but restrained by the potential for coke formation on the membrane surface, which occurred at a H2O/CO ratio lower than 2.6 at 400C. The application of the Pd-membranes resulted in high CO conversion and H2 recovery for the high temperature (400 - 500C) water-gas shift reaction which then enabled high throughput. Operating at high temperature also resulted in higher membrane permeance and less Pd-surface inhibition by CO and H2O. The water-gas shift catalytic membrane reactor was capable of stable CO conversion and H2 recovery (96% and 88% respectively) at 400C over 900 hours of reaction testing, and 2,500 hours of overall testing of the Pd-membrane. When 2 ppmv H2S was introduced into the membrane reactor, a stable CO conversion of 96% and H2 recovery of 78% were observed over 230 hours. Furthermore, a Pd90Au10-membrane was effective for mixed gas separation with up to 20 ppmv H2S present, achieving a stable H2 flux of 7.8 m3/m2-h with a moderate H2 recovery of 44%. The long-term stability under high pressure reaction conditions represents a breakthrough in Pd-membrane utilization.

Pre-combustion decarbonisation is one of the three main routes widely discussed for CO2 capture from fossil fuels. This thesis focuses on the development of a catalytic hollow fibre membrane reactor for the combined steam methane reforming (SMR) and water-gas shift (WGS) reaction, using a Ni-based catalyst, and at a temperature window suitable for harvesting pure H2, a clean energy carrier, from the reaction by a Pd membrane. Apart from developing the catalyst and the Pd-based composite membrane, which are normally considered as the two essential components of a membrane reactor involving hydrogen separation, this study introduces the concept of incorporating the catalyst into a micro-structured ceramic hollow fibre substrate to promote mass transfer efficiency. Meanwhile, the impact of each fabrication step, i.e. catalyst composition and preparation, ceramic hollow fibre fabrication, catalyst incorporation and electroless plating of Pd membranes, on the assembly and final performance of the catalytic hollow fibre membrane reactor was systematically evaluated. In contrast to previous studies involving micro-structured ceramic hollow fibres for catalytic reactions, the one developed in this study possesses a plurality of unique micro-channels, with significant openings on the inner surface of the ceramic hollow fibre. In addition to reduced mass transfer resistance for both catalytic reaction and hydrogen permeation, a microstructure of this type significantly facilitates catalyst incorporation and, as a results, enable the application of this hollow fibres for a wider spectrum of catalytic reactions.

MBR process consists of a suspended growth biological reactor combined with a membrane unit. The widespread of this system for waste water treatment is contained by membrane fouling, which is strongly influenced by three factors: biomass characteristics, operating conditions and membrane characteristics. Fouling control techniques mainly include low-flux operation (sub-critical flux operation) and/or high-shear slug flow aeration in submerged. configuration. Based on the concept of the critical flux (Jo), the flux-step method has been developed to more fully characterise transmembrane pressure (TMP) behaviour during constant-fluxoperation. A zero rate of TMP increase was never attained during the trial, such that no critical flux, in its strictest definition, could be defined in this study for a submerged MBRs challenged with real and simulant sewage. Under similar operating conditions, Jc was obtained around 18 and 10 L.m-2.h-1 for a submerged MBR fed by real and synthetic sewage respectively. Three TMP-based parameters have been defined, all indicating the same flux value at which fouling starts to be more significant (the weak form of Jo). Results from factorial experimental designs revealed the relative effect of MLSS levels, aeration rate and membrane pore size on J, The MLSS effect on Jc was generally around double that of the aeration effect. The calculation of mean sub-critical values for the different TMP-based parameters suggest lower short-term fouling resistance for large pore sized membranes. A direct comparison between the two MBR configurations revealed a greater J, for the submerged compared to the SS MBR (22 and 11 L.m-2.h-1 respectively) under similar hydraulic conditions. The fluid hydrodynamics has been studied for both configurations, leading to an accurate calculation of shear at the membrane surface in SS MBR and to the determination of the minimum gas velocity required for Taylor bubble formation in submerged MBR (around 0.1 m.s-1). Finally, the effect of operating conditions such as process configuration, feed nature, and aeration type on biomass characteristics has been assessed and link to membrane fouling. Key words: Fouling, MBR, critical flux, process configuration, biomass characterisation.

Membrane waterproofing systems are a minor cost element in construction and typically constitutes only 1.5 - 2% of total expenditure. This disparity between original cost and cost of repairs is due to the fact that costs are not limited to therepair and replacement of the membrane alone. Contributing costs include access to covered membranes, consequential damage to structural, non-structural and decorative elements and loss of revenue where lettable areas are closed to allow repairs. Despite the incidence of membrane failures and the high cost of repair there appears to be little progress toward solving the root problem of why membrane systems are prone to failure. Failures can be attributed to faulty design, selection, installation and maintenance of membrane systems. Despite this there is no up to date, unbiased and unified source of reference pertaining to Australian waterproofing. Failure can also be as a result of conflicts of interest between stakeholders in the waterproofing process. These conflicts are usually profit motivated and give rise to a situation where, to some extent, failure can almost be guaranteed.

Doctor of Philosophy
Department of Chemical Engineering
Mary E. Rezac
Catalytic membrane reactors are a class of reactors that utilize a membrane to selectively deliver reactants to catalysts integrated in the membrane. The focus of this research has been on developing and characterizing polymeric catalytic membranes for three-phase hydrogenation reactions, where the membrane functions as a gas/liquid phase contactor allowing selective delivery of hydrogen through the membrane to reach catalytic sites located on the liquid side of the membrane. The benefit of conducting three-phase reactions in this manner is that delivering hydrogen through the membrane to reach catalytic sites avoids the necessity of hydrogen dissolution and diffusion in the liquid phase, which are both inherently low and often described as causing mass-transfer and reaction rate limitations for the reactive system. This work examines two types of membrane reactor systems, porous polytetrafluoroethylene and asymmetric Matrimid membranes, respectively, for the ruthenium catalyzed aqueous phase hydrogenation of levulinic acid. The highly hydrophobic PTFE material provides an almost impermeable barrier to the liquid phase while allowing hydrogen gas to freely transport through the pores to reach catalytic sites located at the liquid/membrane interface. Catalytic rates as a function of hydrogen pressure over the range 0.07 to 5.6 bar are presented and shown to be higher than those of a packed bed reactor under similar reaction conditions. An increasing catalytic benefit was obtained operating at temperatures up to 90 °C, which is attributed to increased hydrogen permeability and avoidance of the decreasing solubility of hydrogen in water with increasing temperature. The membrane reactor was shown to be stable with no decrease in catalytic activity over 200 hours of operation. The Matrimid membrane reactor work demonstrates the feasibility of applying an integrally-skinned asymmetric membrane for an aqueous phase hydrogenation reaction and focuses on the impact that membrane hydrogen permeance and catalyst loading have on catalytic activity. The non-porous nature of the separating layer in the Matrimid membrane allowed successful operation up to 150 °C. The overall catalytic rates were approximately an order of magnitude lower than those achieved in the PTFE membrane reactor system due primarily to significantly lower hydrogen permeances, nevertheless rates were still higher than control experiments. This work also focuses on characterizing Matrimid/solvent thermodynamic relationships for a variety of organic solvents, looking at sorption, diffusion, and polymer relaxation behavior in thin films ranging from 0.1 to 2.0 µm in thickness using quartz crystal microbalance techniques. Diffusion coefficients at infinite dilution for water and C1-C6 alcohols are given as a function of van der Waals molar volume and a clear dependency is shown ranging from 2E-11 to 6.5E-13 cm²/s for water and hexanol, respectively, for 0.26 µm thick films. Diffusion coefficients for all studied vapor penetrants displayed a marked dependence on thickness spanning approximately two orders of magnitude for each respective vapor penetrant over the range 0.1 to 1.0 µm. Chemically cross-linking Matrimid is a method to mitigate some of the relatively high sorption and swelling behavior exhibited in the presence of sorbing species. An in-depth analysis on the vapor phase ethylenediamine cross-linking of Matrimid films and its impact on diffusion, sorption, and relaxation is also described.

Macromolecular components, including protein and polysaccharides, are viewed as one type of major foulants in the complex feed membrane filtration systems such as membrane bioreactor (MBR). In this thesis, the mechanisms of macromolecular fouling including protein and polysaccharide in the complex feed solution are explored by using Bovine serum albumin (BSA) and alginate as model solution. During the filtration of BSA and washed yeast with 0.22 ????m PVDF membrane, it was found that the critical flux of mixture solution was controlled by washed yeast concentration while the existence of BSA significantly changed the cake reversibility of much larger particles. The fouling mechanisms of alginate, as a model polysaccharide solution, were investigated both in dead end and crossflow membrane filtration. In the dead end experiments, it was found that the cake model appears to fit the entire range of the ultrafiltration data while the consecutive standard pore blocking model and cake model are more applicable to microfiltration membranes. The alginate was featured with high specific cake resistance and low compressibility despite some variations between different membranes. The specific cake resistance ( c ) is similar to c of BSA and actual extracellular polymer substance (EPS) in MBR systems reported in the literature, and higher than that of many colloidal particles. In a system contained alginate-particles mixture, it was found that the existence of alginate dramatically increased the cake specific resistance and decreased the cake compressibility. The fouling mechanism of alginate was also studied using long term cross flow filtration under subcritical flux. A two-stage TMP profile similar to that typically observed in MBR was obtained, confirming the important role of EPS during membrane fouling in MBR. In addition to adsorption, trace deposition of alginate also contributed to the initial slow TMP increase during the subcritical filtration. TMP increase during the long-term filtration was found not only due to the increase of the amount of deposition, but also the increase of specific cake resistance. A combined standard pore blocking and cake filtration model, using a critical pore size for the transition time determination, was developed and fit the experimental results well.

Despite being the subject of peer reviewed research since the mid-1980s, the conservative nature of the wastewater treatment industry means that the commercial application of membrane aerated biofilm reactors has not realized the potential that the published research demonstrates. The early research demonstrated the ability of membrane aerated biofilm reactors to achieve good levels of pollutant removal from various types of wastewater, but also exposed several weaknesses of the technology (i.e. cost of membranes, control of biofilm thickness) which have prevented the concept of MABfRs being developed in viable wastewater treatment technologies. However, as membrane technology has developed, the cost of suitable membranes has fallen, prompting the research community to revisit the concept. This later batch of research has identified several niche applications where membrane supported biofilms can be used for effective removal of pollutants from water. Using the MABfR for the treatment of secondary effluent as a polishing step is another niche application which has been identified and is examined in this work; leading to the development of a patented treatment technology – the BioSettler.

This study investigates the efficiency of a calcia stabilised zirconia (CaSZ) solid electrolyte as an oxygen ion conductor. The study also examines the behaviour of the oxygen species conducted by the solid electrolyte compared to species provided in the gas phase for partial oxidation of hydrocarbons. In this work, an electrochemical cell of the form Air, AgHCaSZ//Ag, Carrier gas was used to investigate the electrochemical efficiency and stability of the solid electrolyte CaSZ conducting of oxygen ions under atmospheric pressure conditions at 500 degrees C by applying a range of electrical potentials from I to 16 volts across the electrochemical cell. Due to the applied potential oxygen anions are transferred across the solid electrolyte from the cathode side of the cell to the anode side. It was found that the employed electrolyte is approximately a 100% purely ionic conductor of oxygen ions in the range of electrical voltage applied from I to 10 volts. Above that range the cell started to degrade and loose its ionic efficiency. It was possible to generate gas mixtures containing trace quantities of oxygen. The viscosity of these gas mixtures as a function of oxygen concentration was determined using an established flow perturbation technique (Flux Response Technology). Partial oxidation of propene was used to investigate the difference between the oxygen species produced electrochemically via electrical potential application across the electrochemical cell Air, AgHCaSZ//Ag, Propene, Ar and oxygen provided in the gaseous state co-fed with propene over silver electrode under atmospheric pressure and 450 degrees C and 500 degrees C. It was found that the method of electrochemical provision of oxygen caused the silver catalyst to be more selective to 1,5-hexadeine, whereas the gaseous oxygen provision produced acrolein as the major product. Carbon dioxide formation was not affected by the method of oxygen provision. The Ag electrode was compared to an Au-rich Ag alloy electrode for propene partial oxidation using electrochemical provision. It was found that 1,5-hexadiene was the major product over both electrodes, but the Au-rich alloy was more selective for acrolein than the Ag electrode. This might be due to the gold serving as a separator between Ag particles which hinder the back-spill over of oxygen and allow desorption of molecular oxygen in the gas phase, which then re-adsorb molecularly on silver sites producing acrolein. The effect of the sequence of the method of oxygen provision on the partial oxidation of propene was tested using the electrochemical cell Y-BiMoHAg//CaSZ//Ag at 450 degrees C and atmospheric pressure. A sharp decrease in acrolein selectivity was found when oxygen was provided in the gas phase after treatment with electrochemical oxygen, while no significant effect was noticed when the electrochemical oxygen was used after treatment with gaseous oxygen. This large decrease in acrolein selectivity might be attributed to the severe reduction of the catalyst, which is probably caused by high electrical potential application. A temperature increase from 450 to 500 degrees C seemed to suppress the formation of acrolein for both methods of oxygen provision and enhance the 1,5-hexadiene formation.

An asymmetric ceramic hollow fibre is proposed as a substrate for the development of a catalytic hollow fibre microreactor (CHFMR) and a catalytic hollow fibre membrane microreactor (CHFMMR). The ceramic substrate that is prepared using the phase inversion and sintering technique has a finger-like structure and a sponge-like region in the inner region and the outer surface respectively. The finger-like structure consists of thousands of conical microchannels distributed perpendicularly to the lumen of ceramic hollow fibres onto which a catalyst is impregnated using the sol-gel Pechini method to improve a catalytic reaction. To further enhance the catalytic reaction, a membrane has been incorporated on the outer layer of ceramic hollow fibre. This study focuses on the use of palladium (Pd) and palladium/silver (Pd/Ag) membranes to separate hydrogen from reaction zones in the water-gas shift (WGS) reactions and the ethanol steam reforming (ESR) respectively. In the development of CHFMMR, the fabrication of Pd and Pd/Ag membranes is carried out prior to the catalyst impregnation process to avoid the dissolution of catalyst into the plating solution due to the presence of ammonia and ethylenediaminetetraacetic acid (EDTA). The catalytic activity tests show that the CHFMR, that does not have the Pd membrane on its outer surface, improves the carbon monoxide (CO) conversion compared with its fixed-bed counterpart. The presence of conical microchannels is expected to enhance the activities of the catalyst in the substrate. The incorporations of Pd and Pd/Ag membranes on the outer layer of ceramic hollow fibres enable pure hydrogen to be produced in the shell-side for both the WGS reaction and the ESR. The CHFMMR is used to remove one of the products enabling the WGS reaction to favour the formation of product. It also facilitates the small amount of catalyst to be used to produce significant amount of hydrogen in the ESR.

Dry/CO2 reforming is one the hydrocarbon processes that recently has been interesting due to it is ability of producing a lower synthesis gas ratio (H2/CO). This synthesis gas is a highly significant product since it costs more than 50% of the total capital cost of gas to liquid (GTL) process. However, since this reaction is thermodynamically limited, higher temperature or lower pressure is required to achieve higher conversion. Typically, reaction temperatures between 1073 and 1173 K are used for catalytic dry reforming reactions. Consequently, these extreme temperatures lead to a severe carbon deposition causing a catalyst deactivation which is the major difficulty related to CO2 reforming reaction. This has pushed the efforts to be focused mainly on the development of new catalysts. In fact, dry reforming of propane is an equilibrium-limited reaction which can be shifted to the product side by removing one of the products out of the system which can be achieved using a selective membrane reactor. This research is dedicated to investigate and study the catalytic performance of dry reforming of propane over cobalt-nickel catalyst under the temperature range of 773-973 K. This bimetallic catalyst supported on ??-Al2O3 has been utilized in this research since it exhibits better activity, selectivity, and deactivation resistance than monometallic catalysts. Based on this, the primary aims of this thesis are to examine this catalyst and to study the impact of using membrane reactor. In addition, the reaction mechanism and kinetic are investigated using a fixed-bed reactor. Experimental observations have exposed that the catalyst is offering good results under this reaction. The catalysts analysis has confirmed the presence of metal oxides in the catalyst. However, only at a lower carbon dioxide to propane ratio, i.e. lower than 3.5, a carbon signal has been reported. The activation energy study indicates that the process is unlimited by diffusion. The reaction order for propane and carbon dioxide has been found to be zero and 1.17 respectively. This in turn has indicated that C3H8 activation reaction is taking place rapidly and carbon dioxide is suggested to be involved in the rate determining step. In membrane reactor operation, the production rates for H2 and CO have been reported to increase as the sweep gas flow rate increases. The co-current mode offers higher production rate and more stability than counter-current mode over the range of feed ratio. On the other hand, fixed bed reactor shows stable performance and produces more CO and H2 for both modes.

Els colorants tipus azo pertanyen al grup de contaminants amb caràcter tòxic i recalcitrant per als processos convencionals que es duen a terme a les plantes de tractament d'aigües municipals. La utilització de materials carbonosos ha resultat beneficiosa per augmentar el rendiment d'aquests processos, ja que actua com a portador d'electrons entre l'oxidació d'una font de carboni secundària i la reducció del colorant azo. Per això, aquest treball planteja l'ús d'un innovador sistema combinant el material portador d'electrons i l'element separador en un mateix element. Això s'aconsegueix mitjançant la preparació de membranes de carboni suportades sobre elements ceràmics. Aquests materials presenten porus en el rang de la nanofiltració pel que ajuden a la retenció de la totalitat dels compostos biològics que porten a terme la degradació. A més, la capa de carboni facilita el trànsit d'electrons de la mateixa manera que ho feien tecnologies prèvies com els llits empacats. La síntesi de la membrana requereix condicions específiques que són discutides al llarg de la tesi, d'aquesta forma s'aconsegueix preparar una superfície uniforme i completament coberta de carboni. Aquest nou sistema permet velocitats similars de degradació del colorant azo Acid Orange 7, 80-100% (32 g • m-3 • dia-1). A més, en casos puntuals d'elevat embrutiment sobre la membrana, aquest pot ser eficientment eliminat a través de tècniques de neteges àmpliament utilitzades en aquest àmbit. Al llarg de la tesi s'estudien reactors de membrana amb diferents configuracions incloent diferents materials carbonosos.
Los colorantes tipo azo pertenecen al grupo de contaminantes con carácter tóxico y recalcitrante para los procesos convencionales que se llevan a cabo en la plantas tratamiento de aguas municipales. La utilización de materiales carbonosos ha resultado beneficiosa para aumentar el rendimiento de estos procesos ya que actúa como portador de electrones entre la oxidación de una fuente de carbono secundaria y la reducción del colorante azo. Por ello, este trabajo plantea el uso de un innovador sistema en el cual se combina el material portador de electrones y el elemento separador en un mismo componente. Esto se consigue mediante la preparación de membranas carbon soportadas sobre elementos cerámicos. Estos materiales presentan poros en el rango de la nanofiltración por lo que ayudan a la retención de la totalidad de los compuestos biológicos que llevan a cabo la degradación. Además, la capa de carbono facilita el tránsito de electrones del mismo modo que lo hacían tecnologías previas como los lechos empacados. La síntesis de la membrana requiere condiciones específicas que son discutidas a lo largo de la tesis, de esta forma se consigue preparar una superficie uniforme y completamente cubierta de carbono. Este novedoso sistema permite similares velocidades de degradación del colorante azo Acid Orange 7, 80-100% (32 g•m-3•dia-1). Además, en casos esporádicos de elevado ensuciamiento sobre la membrana, este puede ser eficientemente eliminado a través de técnicas de limpiezas ampliamente utilizadas en este campo. A lo largo de la tesis se estudian reactores de membrana con diferentes configuraciones al igual que diferentes materiales carbonosos.
The azo dyes are considered toxic and recalcitrant contaminants to conventional processes implemented in municipal wastewater treatment plants. The use of carbonaceous materials has proven beneficial to increase the performance of the degradation processes because it acts as an electron carrier between the oxidation of a secondary source of carbon and the reduction of the azo dye. Therefore, this thesis proposes the use of an innovative system combining the electron carrier and an retention system in a single element. This is possible by preparing carbon membranes supported on ceramic elements. These materials present pores in the range of the nanofiltration so ensuring the retention of all biological compounds implied in this process. Furthermore, the carbon layer facilitates the electrons transport in the same way as previous reported systems such as carbon packed beds. The membrane synthesis requires specific conditions discussed throughout the thesis in order to prepare a uniform surface and completely covered with carbon. This novel system allows similar degradation rates of Acid Orange 7, 80-100% (32 g • m-3 • day-1) as previous studies reported in the literature. Furthermore, puntual severe cases of membrane fouling can be efficiently solved by conventional cleaning techniques widely used in this field. Throughout the thesis membrane reactors with different configurations carbonaceous materials are extensively studied.

In recent years ceramic membrane technology has advanced considerably and ceramic membranes are now being applied to a number of high temperature applications, in particular in the energy industry as membrane reactors. Due to the thermal stability of ceramic materials, development in this area is extremely promising as these applications cannot be realized using polymeric membrane technology. Although a wide range of ceramic materials have been developed and processing techniques have improved considerably, the high production cost and lack of control over membrane properties when fabrication processes are scaled up are prohibitive in the commercial application of ceramic membrane technology. However, by using a dry-wet spinning process and the combined phase inversion and sintering technique, novel asymmetric hollow fibre morphologies consisting of a porous sponge-like structure and finger-like macrovoids in which catalyst may be deposited can be prepared in a cost effective way. These asymmetric hollow fibres are prepared from raw materials and are suitable for use in catalytic membrane reactors. Fibre morphology is determined by the rheological properties of the ceramic spinning suspension as well as the parameters used during fibre spinning and the effect of sintering during heat treatment. A generic mechanism has been suggested for the formation of asymmetric structures and the parameters at each of these three stages have been varied systematically in order to predict and control hollow fibre structure. Hollow fibres prepared in this way have been characterized in terms of morphology, pore size distribution, porosity and mechanical strength in terms of their applicability to membrane reactor applications. The versatility of this preparation technique is demonstrated by the inclusion of a chapter describing a catalytic membrane reactor for hydrogen production by water-gas-shift as well as a reactor for the dehydrogenation of propane. It should also be noted that this reactor design could be applied to a number of other catalytic gas phase reactions.

Es van obtenir diferents reactors catalítics de membrana (RCM) de membrana de fibra buida de Corindó i nanopartícules de Pd obtingudes per diferents metodologies: humitat incipients impregnació, polvorització catòdica, microemulsió i aliatge amb coure pel mètode de Poliol. RCMs es van provar en medi aquós, pressió ambiental i temperatura o 60 c en generació in situ de peròxid d'hidrogen, l'oxidació i hidrogenació de fenol i ibuprofè i reducció de Cr (VI). La RCM ha actuat com interfície catalítica per tal d'activar l'hidrogen i que reaccione amb oxigen o compost orgànic o inorgànic. La RCM impregnada amb Pd és l'única que van mostrar activitat i tests d'estabilitat. Aquest comportament es va deure a la presència d'àtoms i grups de Pd. La manca activitat de la resta de catalitzadors amb Pd es va deure a la formació d'hidrur de Pd en les condicions de reacció.
Se obtuvieron diferentes reactores catalíticos de membrana (RCM) desde membranas de fibra hueca de corindón y nanopartículas de paladio obtenidas por diferentes métodos: Impregnación a humedad incipiente, sputtering, microemulsion y aleación con cobre por el método del poliol. Los RCM fueron probados en medio acuoso, presión ambiental y temperatura ambiente o 60C en la generación in situ de peróxido de hidrógeno, oxidación e hidrogenación de fenol e ibuprofeno y reducción de Cr(VI). Los RCM actuaron como interfaz catalítica para que el hidrógeno se active y reaccione con el oxígeno o el compuesto orgánico o inorgánico. Los RCM con paladio por impregnación fueron los únicos que presentaron actividad y estabilidad en las pruebas. Este comportamiento se dio gracias a la presencia de átomos y clusters de paladio. La falta de actividad de los otros catalizadores de paladio se debió a la formación de hidruro de paladio en las condiciones de reacción.
Different catalytic membrane reactors (CMRs) were obtained from hollow fiber membranes corundum and palladium nanoparticles obtained by different methods: Incipient wetness impregnation , sputtering , microemulsion and copper alloy by the method of the polyol. The CMRs were tested in aqueous medium, ambient pressure and ambient temperature or 60C for the in situ generation of hydrogen peroxide, oxidation and hydrogenation of phenol and ibuprofen and reduction of Cr(VI). The catalytic CMR acted as interface for the reactions between hydrogen with oxygen or organic or inorganic compound. Only the CMRs with palladium by impregnation were actives and stabilites during the tests. This behavior occurred thanks to the presence of clusters and single atoms of palladium. The lack of activity of the other kind of palladium catalysts were due to the formation of palladium hydride in the reaction conditions.

The industrial sector is one of the largest emitters of CO2 and a great potential for retrofitting with carbon capture systems. In this work the performance of a palladium-based membrane reactor at 400°C and operating pressures between 100-400 kPa have been studied in terms of methane conversion, hydrogen recovery, hydrogen purity, and CO2 emission. It is found that the MR has the potential to produce high purity hydrogen while the methane conversion values could be as high as 40% at very moderate operating conditions and without using any sweep gases. The H2 permeation and separation properties of two Pd-based composite membranes were evaluated and compared at 400 °C and at a pressure range of 150 kPa to 600 kPa. One membrane was characterized by an approximately 8 μm-thick palladium (Pd)-gold (Au) layer deposited on an asymmetric microporous Al2O3 substrate; the other membrane consisted of an approximately 11 μm-thick pure palladium layer deposited on a yttria-stabilized zirconia (YSZ) support. At 400 °C and with a trans-membrane pressure of 50 kPa, the membranes showed a H2 permeance of 8.42 × 10−4 mol/m2·s·Pa0.5 and 2.54 × 10−5 mol/m2·s·Pa0.7 for Pd-Au and Pd membranes, respectively. Pd-Au membrane showed infinite ideal selectivity to H2 with respect to He and Ar at 400 °C and a trans-membrane pressure of 50 kPa, while the ideal selectivities for the Pd membrane under the same operating conditions were much lower. Furthermore, the permeation tests for ternary and quaternary mixtures of H2, CO, CO2, CH4, and H2O were conducted on the Pd/YSZ membrane. The H2 permeating flux decreased at the conclusion of the permeation tests for all mixtures. This decline however, was not permanent, i.e., H2 permeation was restored to its initial value after treating the membrane with H2 for a maximum of 7 h. The effects of gas hourly space velocity (GHSV) and the steam-to-carbon (S/C) ratio on H2 permeation were also investigated using simulated steam methane reforming mixtures. It was found that H2 permeation is highest at the greatest GHSV, due to a decline in the concentration polarization effect. Variations in S/C ratio however, showed no significant effect on the H2 permeation. The permeation characteristics for the Pd/YSZ membrane were also investigated at temperatures ranging from 350 to 400 °C. The pre-exponential factor and apparent activation energy were found to be 5.66 × 10−4 mol/m2·s·Pa0.7 and 12.8 kJ/mol, respectively. Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analyses were performed on both pristine and used membranes, and no strong evidence of the formation of Pd-O or any other undesirable phases was observed. The permeation tests with pure hydrogen and inert gases indicate that the MR is highly selective toward hydrogen and the produced hydrogen is an ultrahigh purity grade. The carbon capture experiments in the work consists of dehydrating the retentate stream and redirecting it to a 13X packed bed before analyzing the stream via mass spectrometry. The carbon capture studies reveal that approximately 5.96 mmole CO2 (or 262.25 mg of CO2)can be captured per g of 13X. In this study, SEM-EDS, and XRD technics have been used to characterize the crystallography and morphology of the membrane surface. These material characterization techniques reveal that the surface of the membrane has gone through significant oxidation during the steam methane reforming reaction, although this oxidation is only limited to the few nanometers of depth through the surface of the palladium membrane.

Microbial fuel cells (MFCs) are potentially advantageous as an energy-efficient approach for wastewater treatment. Integrating membrane filtration with MFCs could be a viable option for advanced wastewater treatment with a low energy input. Such an integration is termed as membrane bioelectrochemical reactors (MBERs). Comparing to the conventional membrane bioreactors or anaerobic membrane bioreactors, MBER could be a competitive technology, due to the its advantages on energy consumption and nutrients removal. By installing the membrane in the cathodic compartment or applying granular activated carbon as fluidized bed materials, membrane fouling issue could be alleviated significantly. In order to drive MBER technology to become a more versatile platform, applying anion exchange membrane (AEM) could be an option for nutrients removal in MBERs. Wastewater can be reclaimed and reused for subsequent fermentation use after a series MFC-MBR treatment process. Such a synergistic configuration not only provide a solution for sustainable wastewater treatment, but also save water and chemical usage from other non-renewable resource. Integrating membrane process with microbial fuel cells through an external configuration provides another solution on sustainable wastewater treatment through a minimal maintenance requirement.
Ph. D.

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Both porous and dense hydrogen selective membranes have recently been an active area of research. The combination of a reactor and a separator in the form of a membrane reactor is seen as a feasible application in which to perform dehydrogenation reactions. These reactions are equilibrium limited so that the removal of the product H2 by a selective membrane can improve the process effectiveness. Early Pd-based membranes were made of thin-walled tubes. In an attempt to increase permeation rates, thin supported Pd membranes have been developed. This study investigated the development and performance of a catalytic membrane reactor. The membrane reactor consists of a tubular alumina membrane support coated on the inside with a film of palladium or a palladium-copper alloy. This reactor was used for the dehydrogenation of isopropanol. The thin film was coated on the alumina support using an electroless plating process. This process occurs in a liquid medium where palladium and copper are deposited by electrolysis or electroless means. With these methods alloys can also be deposited on the support. By plating a thin film of palladium on the alumina membranes, will attract hydrogen molecules from the reaction product, which will increase the reaction rate. The electroless plating process consists of four major components: (i) (ii) (iii) (iv) reducing agent ( 0.04 M hydrazine), temperature bath, stabilised source of metal ions, and support membrane (α-alumina). Heat treatment was carried out on the coated membranes for 5 hours in a hydrogen atmosphere at 450°C. The plated membranes supplied by Atech were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle induced Xray emission (PIXE) before and after heat treatment. SEM photographs showed that the pore size of the membranes was doubtful and due to that the films were not of a dense nature. XRD results revealed that heat treatment led to the formation of smaller Pd and Cu crystallites. The concentration profiles constructed from the PIXE results indicated that Cu and Pd penetrated deep into the pores of the membrane during film preparation. Different catalysts (Al2O3, MgO and SiO2) were tested and the best one was chosen as catalyst in the membrane reactor. These catalytic runs were done in a plug flow (fixedbed) reactor. Different particle sizes of catalysts were also tested. A 9.2 Cu wt % on silica achieved the highest acetone yields for the temperatures tested. Two different types of alumina membrane reactors were used. These were supplied from SCT. One membrane only coated with palladium and the other coated with palladium and copper. Selectivity and permeability tests were also carried out on these membranes. Selectivities of up to 90.6 could be reached with the palladium coated membrane. The palladium-copper plated membrane only achieved selectivities of up to 13. With heat treatment this value decreased even more. The palladium coated membrane also achieved much better conversion to acetone in the dehydrogenation of 2-propanol. The reason for that is its better selectivity. The palladium-copper membrane reactor did not show much better results than the fixed-bed reactor.
AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die ontwikkeling en werk verrigting van ‘n katalitiese membraan reaktor. Die membraan reaktor bestaan uit ‘n dun film palladium of palladium-koper allooi wat aan die binnekant van ‘n silindriese alumina membraan geplateer word. Die alumina dien as membraanbasis. Hierdie reaktor sal gebruik word vir die dehidrogenering van isopropanol. Die dun films van metaal word neergeslaan op die alumina basis deur ‘n elektrodelose platerings proses. Hierdie proses vind plaas in ‘n vloeistof medium waar palladium en koper neerslag plaasvind op ‘n elektrodelose wyse. Met hierdie metode kan metaal allooie geplateer word op basis membrane. Deur ‘n dun palladium lagie aan die binnekant van die alumina membrane te plateer sal veroorsaak dat waterstof molekules uit die reaksie volume sal weg beweeg. Dit sal ‘n verhoging in reaksie tempo meebring. Die platerings proses bestaan uit vier komponente: (i) reduseermiddel (0.04M Hidrasien), (ii) temperatuur water bad, (iii) stabiliseerde bron van metaal ione (Pd/Cu kompleks oplossing), en (iv) basis membraan (α-alumina). Hittebehandeling vir 5 uur is uitgevoer op hierdie geplateerde membrane by 450°C in ‘n waterstofatmosfeer. Die geplateerde membrane is daarna gekarakteriseer- voor en na hittebehandeling. Dit is gekarakteriseer deur X-straal diffraksie (XRD), skanderings elektron mikroskopie (SEM) en partikel geïnduseerde X-straal emissie (PIXE). XRD eksperimente het gewys dat die koper en die palladium ‘n allooi gevorm het. Veranderinge in kristaltekstuur het voorgekom na hittebehandeling. Tydens hittebehandeling was kleiner palladium en koper kristalle gevorm. SEM resultate het getoon dat die film nie baie dig was nie en die porie grootte van die membrane was ook nie korrek nie. PIXE resultate het die konsentrasieprofiele van beide koper en palladium oor die dikte van die membraan bepaal. Dit het gewys dat die Cu en Pd diep binne die membraan penetreer het tydens voorbereiding van die membraan. Verskillende soorte kataliste (Al2O3, MgO and SiO2) is ondersoek vir die dehidrogenering van isopropanol. Hierdie katalitiese ondersoek is gedoen in ‘n propvloei reaktor. Die beste katalis is gekies om in die membraan reaktor te gebruik. Verskillende partikel groottes is ook ondersoek. ‘n 9.2 Cu massa % koper op silika katalis het die beste omsetting na asetoon verkry vir die temperature waarvoor toetse gedoen is. Twee tipes membraan reaktors is gebruik. Een met net ‘n palladium film, terwyl ‘n palladium-koper allooi op die ander membraan reaktor gedeponeer was. Selektiwiteits- en deurlaatbaarheids toetse is op altwee membrane gedoen. Selektiwiteite van 90.6% kon verkry word met die palladium membraan. Die palladium-koper membraan kon slegs ‘n selektiwiteit van 13% bereik. Met hittebehandeling daarvan het die selektiwiteit selfs meer afgeneem. Die palladium membraan het ook hoër omsettings na asetoon getoon. Die rede hiervoor is die membraan se hoë selektiwiteit. Die palladium-koper membraan het nie veel beter resultate as die propvloei reaktor gelewer nie.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2005
The white rot fungus, Phanerochaete chrysosporium, produces enzymes, which are capable of degrading chemical pollutants. It was detennined that this fungus has multiple growth phases. The study provided infonnation that can be used to classify growth kinetic parameters, substrate mass transfer and liquid medium momentum transfer effects in continuous secondary metabolite production studies. P. chrysosporium strain BKMF 1767 (ATCC 24725) was grown at 37 QC in single fibre capillary membrane bioreactors (SFCMBR) made of glass. The SFCMBR systems with working volumes of 20.4 ml and active membrane length of 160 mm were positioned vertically. Dry biofilm density was determined by using a helium pycnometer. Biofilm differentiation was detennined by taking samples for image analysis, using a Scanning Electron Microscope at various phases of the biofilm growth. Substrate consumption was detennined by using relevant test kits to quantify the amount, which was consumed at different times, using a varying amount of spore concentrations. Growth kinetic constants were detennined by using the substrate consumption and the dry biofilm density model. Oxygen mass transfer parameters were determined by using the Clark type oxygen microsensors. Pressure transducers were used to measure the pressure, which was needed to model the liquid medium momentum transfer in the lumen of the polysulphone membranes. An attempt was made to measure the glucose mass transfer across the biofilm, which was made by using a hydrogen peroxide microsensor, but without success.

The present thesis has focused on the intensive study of the methane dehydroaromatization process under non-oxidative conditions for producing benzene and H2 in a direct way. Nevertheless, MDA process is thermodynamically limited and, moreover, the catalyst quickly accumulates large amounts of carbonaceous deposits, which hinders its commercialization. Therefore, this thesis has as fundamental purposes the improvement of the catalytic activity and the stability of the catalyst on MDA reaction. The catalysts widely used on MDA reaction are Mo/zeolite, which are bifunctional, i.e., Mo sites are involved in the methane dehydrogenation and formation of CHx species, which are dimirized to C2Hy species, and Brønsted acid sites of the zeolite oligomerize these C2Hy species, forming mostly benzene and naphthalene. Thereby, different Mo/zeolite catalysts were prepared using commercial zeolites as well as zeolites synthesized on the laboratory. Thus, observing that the zeolite and the Mo content employed on the catalyst affected significantly the MDA performance. The topology and the channel dimensions of the zeolite as well as its Si/Al ratio and crystal size were also important on the MDA results obtained. Concretely, the best MDA performance was achieved by the 6%Mo/MCM-22 catalyst. Different catalyst activation procedures were tested, achieving the best MDA performance and catalyst stability using a gas mixture of CH4:H2, 1:4 (vol. ratio) during 1 h up to 700 ºC and maintaining this temperature for 2 h. This catalyst activation leads to the pre-carburization and pre-reduction of the Mo species, obtaining the most active and stable on MDA reaction. Moreover, the effect of the space velocity was studied in the present thesis. The best MDA results were reached at 1500 mL¿h-1¿gcat-1, as at higher space velocities methane barely can interact with the catalytic sites. While at lower space velocities the condensation of the heavy aromatic hydrocarbons is facilitated, causing higher coke accumulation on the catalyst. Furthermore, higher catalyst stability was obtained by co-feeding H2O, H2 and CO2 separately using the 6%Mo/HZSM-5 catalyst as well as the 6%Mo/MCM-22, due to the partial suppression of coke deposited. However, the catalytic activity was worsen by adding these co-reactants because of, on one hand, thermodynamically the addition of H2O, H2 or CO2 to the methane feed is detrimental and, on the other hand, H2O and CO2 partially re-oxidize the Mo species of the catalyst. Thermodynamically, H2 causes an equilibrium shift and, therefore, a decrease on the methane conversion; H2O favors the methane reforming reaction and coke gasification; and CO2 promotes the methane reforming reaction and the reverse Boudart reaction. The development and implementation of a catalytic membrane reactor (CMR) that integrates the 6%Mo/MCM-22 catalyst and the BZCY72 tubular membrane has been carried out on the present thesis. The MDA performance and the stability of the catalyst were exceptionally improved using this CMR by imposing a current to the electrochemical cell, changing or not the standard operating conditions. These good results were obtained due to the simultaneous H2 removal from MDA reaction side and O2 injection to this side through the BZCY72 tubular membrane. Thus, the H2 extraction results in the thermodynamic equilibrium displacement of MDA reaction, which causes the increase of the methane conversion and in turn of the aromatics yield. Moreover, the O2 injection involves the formation of H2O in low concentration, which reacts with coke accumulated (coke gasification), rising the stability of the catalyst.
La presente tesis se ha centrado en el estudio intensivo del proceso de deshidroaromatización de metano en condiciones no oxidativas para producir benceno e hidrógeno de forma directa. Sin embargo, el proceso de MDA está limitado termodinámicamente y, además, el catalizador acumula rápidamente grandes cantidades de depósitos carbonosos, lo que dificulta su comercialización. Por tanto, esta tesis tiene como objetivos fundamentales la mejora de la actividad catalítica y la estabilidad del catalizador en la reacción MDA. Los catalizadores Mo/zeolita son ampliamente utilizados en la reacción MDA, los cuales son bifuncionales, es decir, los sitios de Mo están involucrados en la deshidrogenación del metano y la formación de las especies CHx, las cuales se dimerizan a especies C2Hy, y los sitios ácidos de Brønsted de la zeolita oligomerizan éstas especies C2Hy, formando principalmente benceno y naftaleno. Por lo que, diferentes catalizadores Mo/zeolita se prepararon utilizando zeolitas tanto comerciales como sintetizadas en el laboratorio. Observando así que la zeolita y el contenido de Mo utilizados en el catalizador afectan significativamente el rendimiento de la reacción MDA. Tanto la topología y las dimensiones de los canales de la zeolita como su relación Si/Al y su tamaño de cristal son también importantes en los resultados obtenidos de la reacción MDA. Concretamente, el mejor rendimiento de MDA fue obtenido por el catalizador 6%Mo/MCM-22. Se probaron diferentes procedimientos de activación del catalizador, obteniendo el mejor rendimiento de la reacción MDA y estabilidad del catalizador usando una mezcla gaseosa de CH4:H2, 1:4 (relación en volumen) durante 1 h hasta 700 ºC y manteniendo esta temperatura durante 2 h. Esta activación del catalizador provoca la pre-carburización y pre-reducción de las especies de Mo, obteniendo las más activas y estables en la reacción de MDA. Los mejores resultados de MDA se obtuvieron con 1500 mL¿h-1¿gcat-1, ya que con mayores velocidades espaciales el metano apenas puede interaccionar con los sitios catalíticos. Mientras que con menores velocidades espaciales la condensación de los hidrocarburos aromáticos pesados se ve favorecida, provocando una mayor acumulación de coque en el catalizador. Por otra parte, co-alimentando H2O, H2 y CO2 por separado se obtuvo una mayor estabilidad tanto del catalizador 6%Mo/HZSM-5 como del 6%Mo/MCM-22, debido a la supresión parcial del coque depositado. Sin embargo, la actividad catalítica empeoró al añadir estos co-reactivos ya que, por un lado, la adición de H2O, H2 y CO2 a la alimentación de metano es perjudicial termodinámicamente y, por otro lado, el H2O y el CO2 re-oxidan parcialmente las especies Mo del catalizador. Termodinámicamente, el H2 provoca un cambio en el equilibrio y, por tanto, una disminución de la conversión de metano; el H2O favorece la reacción de reformado de metano y la gasificación de coque; y el CO2 promueve la reacción de reformado de metano y la reacción inversa de Boudart. En la presente tesis se ha llevado a cabo el desarrollo y la implementación de un reactor catalítico de membrana (CMR) que integra el catalizador 6%Mo/MCM-22 y la membrana tubular BZCY72. El rendimiento de la reacción MDA y la estabilidad del catalizador fueron excepcionalmente mejorados usando este CMR imponiendo una corriente a la celda electroquímica, cambiando o no las condiciones de operación estándar. Estos buenos resultados fueron obtenidos debido a la simultánea extracción de H2 del lado de reacción y la inyección de O2 a este lado mediante la membrana tubular BZCY72. Así, la extracción de H2 se traduce en un desplazamiento del equilibrio termodinámico de la reacción MDA, lo que causa el aumento de la conversion de metano y a su vez del rendimiento de aromáticos. Además, la inyección de O2 implica la formación de agua en baja concentración, la que reacciona con el coque acumulado (gas
La present tesi s'ha centrat en l'estudi intensiu del procés de deshidroaromatització de metà en condicions no oxidatives per produir benzé i hidrogen de forma directa. No obstant això, el procés de MDA està limitat termodinàmicament i, a més, el catalitzador acumula ràpidament grans quantitats de dipòsits carbonosos, el que dificulta la seva comercialització. Per tant, aquesta tesi té com a objectius fonamentals la millora de l'activitat catalítica i l'estabilitat del catalitzador en la reacció MDA. Els catalitzadors Mo/zeolita són àmpliament utilitzats en la reacció MDA, els quals són bifuncionals, és a dir, els llocs de Mo estan involucrats en la deshidrogenació del metà i la formació de les espècies CHx, les quals es dimeritzen a espècies C2Hy, i els llocs àcids de Brønsted de la zeolita oligomeritzan aquestes espècies C2Hy, formant principalment benzè i naftalè. Per tant, diferents catalitzadors Mo/zeolita es van preparar utilitzant zeolites tant comercials com sintetitzades al laboratori. Observant així que la zeolita i el contingut de Mo utilitzats en el catalitzador afecten significativament el rendiment de la reacció MDA. Tant la topologia i les dimensions dels canals de la zeolita com la seva relació Si/Al i el seu tamany de cristall són també importants en els resultats obtinguts de la reacció MDA. Concretament, el millor rendiment de MDA va ser obtingut pel catalitzador 6%Mo/MCM-22. Es van provar diferents procediments d'activació del catalitzador, obtenint el millor rendiment de la reacció MDA i estabilitat del catalitzador usant una mescla de gasos de CH4: H2, 1: 4 (relació en volum) durant 1 h fins a 700 ºC i mantenint aquesta temperatura durant 2 h. Aquesta activació del catalitzador provoca la pre-carburització i pre-reducció de les espècies de Mo, obtenint les més actives i estables en la reacció de MDA. A més, en la present tesi es va estudiar l'efecte de la velocitat espacial. Els millors resultats de MDA es van obtindre amb 1500 mL¿h-1¿gcat-1, ja que amb majors velocitats espacials el metà gairebé no pot interaccionar amb els llocs catalítics. Mentre que amb menors velocitats espacials la condensació dels hidrocarburs aromàtics pesants es veu afavorida, provocant una major acumulació de coc en el catalitzador. D'altra banda, co-alimentant H2O, H2 i CO2 per separat es va obtindre una major estabilitat tant del catalitzador 6%Mo/HZSM-5 com del 6%Mo/MCM-22, a causa de la supressió parcial del coc dipositat. No obstant això, l'activitat catalítica empitjorà en afegir aquests co-reactius ja que, d'una banda, l'addició d'H2O, H2 i CO2 a l'alimentació de metà és perjudicial termodinàmicament i, d'altra banda, el H2O i el CO2 re-oxiden parcialment les espècies Mo del catalitzador. Termodinàmicament, el H2 provoca un canvi en l'equilibri i, per tant, una disminució de la conversió de metà; l'H2O afavoreix la reacció de reformat de metà i la gasificació de coc; i el CO2 promou la reacció de reformat de metà i la reacció inversa de Boudart. En la present tesi s'ha dut a terme el desenvolupament i la implementació d'un reactor catalític de membrana (CMR) que integra el catalitzador 6%Mo/MCM-22 i la membrana tubular BZCY72. El rendiment de la reacció MDA i l'estabilitat del catalitzador van ser excepcionalment millorats usant aquest CMR imposant un corrent a la cel¿la electroquímica, canviant o no les condicions d'operació estàndard. Aquests bons resultats van ser obtinguts a causa de la simultània extracció d'H2 del costat de reacció i la injecció d'O2 a aquest costat per mitjà de la membrana tubular BZCY72. Així, l'extracció d'H2 es tradueix en un desplaçament de l'equilibri termodinàmic de la reacció MDA, el que causa l'augment de la conversió de metà i alhora del rendiment d'aromàtics. A més, la injecció d'O2 implica la formació d'aigua en baixa concentració, la qual reacciona amb el coc acumulat (gasificació de coc)
Zanón González, R. (2017). Intensification of methane dehydroaromatization process on catalytic reactors [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/83124
TESIS

The possibility of developing an immobilised-enzyme bioprobe, based on mushroom polyphenol oxidase, for the purely biological detection and quantification of phenolic pollutants in water was investigated. Polyphenol oxidase catalyses the bioconversion of many phenolic compounds into quinone-related coloured products. Thus, in an immobilised form, the enzyme serves as a visible indicator of the presence and concentration of phenolic pollutants in water. The objective of this research was to develop a portable, disposable bioprobe incorporating polyphenol oxidase for this purpose. The intensity of the colour changes produced by the enzyme on reaction with p-cresol, p-chlorophenol and phenol was found to increase proportionally with increasing concentrations of these substrates in solution. Immobilisation of the enzyme on various supports did not appear to significantly affect the catalytic activity of the enzyme. The enzyme was immobilised by adsorption and cross-linking on polyethersulphone, nitrocellulose and nylon membranes with the production of various colour ranges on reaction with the phenolic substrates. The most successful immobilisation of the enzyme, in terms of quantity and distribution of enzyme immobilised and colour production, was obtained with the enzyme immobilised by adsorption on nylon membranes in the presence of 3-methyl-2-benzothiazolinone hydrazone (MBTH). The enzyme, immobilised using this method, produced ranges of maroon colours in phenolic solutions and orange colours in cresylic solutions. The colour intensities produced were found to increase proportionally with increasing substrate concentration after 5 minutes exposure to the substrates. The bioprobe had a broad substrate specificity and was sensitive to substrate concentrations down to 0.05 mg/L. The enzyme activity of the bioprobe was not significantly affected in a pH range from 4 to 10 and in a temperature range from 5-25⁰C. The bioprobe activity was not affected by various concentrations of salt and metal ions and the bioprobe was able to detect and semi-quantify phenolic substrates in industrial effluent samples. These features of the bioprobe indicate that the commercialisation of such a bioprobe is feasible and this technology has been patented (Patent No. SA 97/0227).
KMBT_363
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Thesis (M.Tech-Chemical Engineering)--Cape Technikon, Cape Town, 2001
The white-rot fungus (WRF), Phanerochaete chrysosporium, is a well known microorganism which produces ligninolytic enzymes. These enzymes can play a major role in the bioremediation of a diverse range of environmental aromatic pollutants present in industrial effluents. Bioremediation of aromatic pollutants using ligninolytic enzymes has been extensively researched by academic, industrial and government institutions, and has been shown to have considerable potential for industrial applications. Previously the production of these enzymes was done using batch cultures. However, this resulted in low yields of enzyme production and therefore an alternative method had to be developed. Little success on scale-up and industrialisation of conventional bioreactor systems has been attained due to problems associated with the continuous production of the pollutant degrading enzymes. It was proposed to construct an effective capillary membrane bioreactor, which would provide an ideal growing environment to continuously culture an immobilised biofilm of P; chrysosporium (Strain BKMF-1767) for the continuous production of the ligninolytic enzymes, Lignin(LiP) and Manganese(MnP) Peroridase. A novel membrane gradostat reactor (MGR) was shown to be superior to more conventional systems of laboratory scale enzyme production (Leukes et.al., 1996 and Leukes, 1999). This concept was based on simulating the native state ofthe WRF, which has evolved on a wood-air interface and involved irnmobilisng the fungus onto an externally skinless ultrafiltration membrane. The MGR however, was not subjected to optimisation on a laboratory scale. The gradostat reactor and concept was used in this work and was operated in the deadend filtration mode. The viability of the polysulphone membrane for cultivation of the fungus was investigated. The suitability of the membrane bioreactor for enzyme production was evaluated. The effect of microbial growth on membrane pressure and permeability was monitored. A possible procedure for scaling up from a single fibre membrane bioreactor to a multi-capillary system was evaluated. Results indicated that the polysulphone membrane was ideal for the cultivation of P chrysosporium, as the micro-organism was successfully immobi1ised in the macrovoids of the membrane resulting in uniform biofilm growth along the outside of the membrane. The production of Lignin and Manganese Peroxidase was demonstrated. The enzyme was secreted and then transported into the permeate without a rapid decline in activity. Growth within the relatively confined macrovoids of the membrane contributed to the loss of membrane permeability. A modified Bruining Model was successfully applied in the prediction of pressure and permeability along the membrane The study also evaluated the effect of potential1y important parameters on the production of the enzymes within the membrane bioreactor. These parameters include air flow (Ch concentration), temperature, nutrient flow, relative redox potential and nutrient concentrations A sensitivity analyses was performed on temperature and Ch concentration. The bioreactor was exposed to normal room temperature and a controlled temperature at 37°C. The reactors were then exposed to different O2 concentration between 21% and 99"10. It was found that the optimum temperature fur enzymes production is 3TJC. When oxygen was used instead of air, there was an increase in enzyme activity. From the results obtained, it was clear that unique culture conditions are required for the production of LiP and MnP from Phanerochaete chrysosporium. These culture conditions are essential fur the optimisation and stability of the bioreactor.

Heterogeneously catalysed aerobic oxidation of alcohols has great potential in chemical synthesis, but its wide application is still limited by safety issues with the combination of gaseous oxygen and flammable organics. The aim of this thesis is to develop Teflon AF-2400 membrane reactors for the intrinsically safe use of oxygen in oxidation of alcohols. Initially, oxidation of benzyl alcohol and cinnamyl alcohol on Au-Pd/TiO2 catalyst was studied in a trickle bed microreactor. The catalyst deactivation in cinnamyl alcohol oxidation, rather than benzyl alcohol oxidation, was attributed to Pd leaching and a complex role of oxygen. Then, a Teflon AF-2400 packed tube-in-tube membrane microreactor was investigated for benzyl alcohol oxidation, which allowed continuous oxygen supply during the reaction and presented higher conversion and selectivity as compared to a reactor with oxygen pre-saturated feed. A novel approach using the tube-in-tube membrane contactor was demonstrated for measuring gas solubility in liquids. To simplify the reactor scale-up, a Teflon AF-2400 flat membrane microreactor was developed for benzyl alcohol oxidation, and the mass transfer and reaction in the reactor were experimentally and theoretically investigated with different catalysts. The oxygen transverse mass transfer in the catalyst bed, rather than oxygen permeation through membrane or oxygen internal/external transfer in the catalyst particles, was indicated to be the controlling process. An effectiveness factor analysis akin to internal/external mass transfer and reaction in a catalytic particle was provided to guide the catalyst choice and the membrane reactor design. For direct usage of small catalyst particles in continuous flow reactors, a stirred membrane reactor with a sintered metal filter and an external membrane contactor was experimentally demonstrated and mathematically simulated for benzyl alcohol oxidation. The reactant conversion and the catalyst utilization were indicated to be affected by various operation parameters, which were correlated to guide the reactor design and operation.

Biocatalytic membranes (BMs) have promising applications in a diversity of fields including food, pharmaceutical and water treatment industries. Of particular relevance, Alcalase is a commercially important protease that has been applied for the production of peptides from the hydrolysis of proteins. In this study, two different approaches were applied for the modification of electrospun polyacrylonitrile nanofibrous membranes (EPNMs) for Alcalase immobilization. The first approach is alkali modification of EPNMs followed by EDC/NHS coupling for covalent bonding with Alcalase, whereas the other is based on polydopamine coating with or without glutaraldehyde grafting as a covalent linker. Immobilized Alcalase on these prepared BMs were studied and compared with free enzymes. It was found that the stabilities of Alcalase on BMs created using both approaches were improved, which enabled their reuse of 10 cycles with significant retention of enzymatic activity. A continuous reactor housing BMs were tested for hydrolysis of both model substrate, azo-casein and soybean meal protein (SMP). It was found that decreasing flux could improve the extent of hydrolysis and that a single-layer reactor can hydrolyze about 50% of the substrate to peptides with the molecular weight of 10 kDa or less. Hydrolysis of SMPs was demonstrated in a continuous five-layer BM reactor and both BMs showed excellent hydrolysis capacity. This study provides the groundwork for the development of high-efficiency BM for continuous and cost-effective protein hydrolysis for the production of value-added peptides.

Heterogeneous functional materials, like catalytic solids, batteries and fuel cells tend to usually possess complex structures where the 3D spatial distribution of the various components of these materials is rarely uniform. Such materials are known to change with time under operating conditions. In order to gain an insight into the structure-function relationships, it is essential to study them in situ with spatially-resolved techniques. The work presented in this thesis focuses on the development and application of synchrotron X-ray tomographic imaging methods to study various catalytic materials in real time and under real process conditions. The main X-ray tomographic imaging technique used in this study is X-ray diffraction computed tomography (XRD-CT) which couples powder diffraction with “pencil” beam computed tomography. Chapters 3 and 4 of this thesis outline some of the technical achievements accomplished in this work. More specifically, Chapter 3 outlines the development of a new data processing strategy used to remove line or “streak” artefacts generated in reconstructed XRD-CT images due to the presence of large crystallites in the sample; a common problem in XRD-CT measurements. Chapter 4 introduces a new data collection strategy, termed interlaced XRD-CT, which allows, post experiment, choice between temporal and spatial resolution. This data collection strategy can in principle be applied to all pencil beam CT techniques. The results from the first multi-length scale chemical imaging experiments of an unpromoted and a La-promoted Mn-Na-W/SiO2 catalyst for the oxidative coupling of methane are presented in Chapter 5. The spatially-resolved chemical signals obtained from these operando experiments provided new chemical information that can lead to the rational design of improved OCM catalysts. In Chapter 6, the results from, the first ever reported, XRD-CT experiments of working catalytic membrane reactors are presented. It is shown that the pertinent changes in the physicochemical state of these integrated reactor systems can be spatially-resolved. The results from Rietveld analysis of a 5D diffraction imaging (>106 diffraction patterns) redox experiment of a Ni-Pd/CeO2-ZrO2/Al2O3 catalyst and the first XRD-CT study of this catalyst during partial oxidation of methane are presented in Chapter 7.

Natural gas obtained during the extraction of liquid hydrocarbons is often undesired due to the lack of infrastructure to transport the natural gas to an onshore location. As a result the natural gas is often flared causing economic waste and environmental concern. It would therefore be desirable to either convert the natural gas into some other substance which can be transported easily, or transport the natural gas in a liquid state. In that way, new field development will be more financially viable through the use of the extensive infrastructure and technology already in place in the offshore industry for transporting liquid hydrocarbons. It is considered that one feasible way of utilising offshore produced natural gas, is to convert it into synthetic gas (syngas) which can in turn be used to produce gases and fluids such as methanol, ammonia or a synthetic crude oil that can be readily pumped through the same pipelines as the produced oil. For the production of synthetic gas, membrane technology presents an attractive advantage improving conversion efficiency by operating as catalyst support, which then also increases the catalyst dispersion, resulting in optimal catalyst load and complete consumption of oxygen and methane in the partial oxidation. In the present investigation, an enhanced catalyst-dispersed ceramic membrane for low-cost synthesis gas production suitable for gas-to-liquids has been prepared, characterised and tested in a self-designed membrane reactor. The effect of temperature and feed flow rates has been studied and a kinetic model has been developed. In the novel membrane reactor, an active porous layer is located on both sides facing the oxygen and methane containing gas, adjacent is a second active porous layer and is supported by layers with increasing pore radii. Here the active porous layer on the bore side enhances the reaction between permeated oxygen and fuel species. In this study, it has also been demonstrated that the oxygen is activated prior to contacting the methane inside the membrane. This often results in 100% oxygen conversion, CO selectivity higher than 96% and syngas ratio (1-1/2 C O) of 2.2 to 1.8. Another advantage of the developed membrane system is that it can be used in high temperatures (> 1273.15K) and high pressure (80bars) processes with no variation on the flow rates, due to the mechanical strength of the ceramic support used.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 185-190).
Numerical simulations were performed to investigate the key features of oxygen permeation and hydrocarbon conversion in ion transport membrane (ITM) reactors. ITM reactors have been suggested as a novel technology to enable air separation and fuel conversion to take place simultaneously in a single unit. Possessing the mixed ionic and electronic conductivity, perovskite membranes or ion transport membranes permeate selectively oxygen ions from the air (feed) side to the sweep gas or reactive gas (permeate) side of the membrane, driven by the oxygen chemical potential gradient across the membrane at elevated temperature. When a fuel such as methane is introduced into the permeate side as a sweep gas, hydrocarbon oxidation reactions occur by reacting the fuel with the permeated oxygen. The fuel can be partially reformed, completely oxidized or converted to produce higher hydrocarbons. To utilize this technology more effectively, it is necessary to develop a better understanding of oxygen transport and hydrocarbon conversion in the immediate vicinity of the membrane or on its surface. In this thesis, a planar, finite-gap stagnation flow configuration was used to model and examine these processes. A spatially resolved physical model was formulated and used to parameterize an oxygen permeation flux expression in terms of the oxygen concentrations at the membrane surface given data on the bulk concentration. The parameterization of the permeation flux expression is necessary for cases when mass transfer limitations on the permeate side are important and for reactive flow modeling. At the conditions relevant for ITM reactor operation, the local thermodynamic state should be taken into account when the oxygen permeation rate is examined, which has been neglected. To elucidate this, the dependency of oxygen transport and fuel conversion on the geometry and flow parameters including the membrane temperature, air and sweep gas flow rates, oxygen concentration in the feed air and fuel concentration in the sweep gas was discussed. The reaction environment on the sweep side of an ITM was characterized. The spatially resolved physical model was used to predict homogeneous-phase fuel conversion processes and to capture the important features (e.g., the location, temperature, thickness and structure of a flame) of laminar oxy-fuel diffusion flames stabilized on the sweep side. The nature of oxygen permeation does not enable pre-mixing of fuel and oxidizer (i.e., sweep gas and permeated oxygen), establishing non-premixed flames. In oxy-fuel combustion applications, the sweep side is fuel-diluted with CO₂ or/and H₂O, and the entire unit is preheated to achieve a high oxygen permeation flux. This study focused on the flame structure under these conditions and specifically on the chemical effect of CO₂ dilution. The interactions between oxygen permeation and homogeneous-phase fuel oxidation reactions on the sweep side of an ITM were examined. Within ITM reactors, the oxidizer flow rate, i.e., the oxygen permeation flux, is not a pre-determined quantity, since it depends on the oxygen partial pressures on the air and sweep sides and the membrane temperature. Instead, it is influenced by the hydrocarbon oxidation reactions that are also dependent on the oxygen permeation rate, the initial conditions of the sweep gas, i.e., the fuel concentration, flow rate and temperature, and the diluent. A parametric study with respect to key operating conditions, which include the fuel concentration in the sweep gas, its flow rate and temperature and the geometry, was conducted to investigate their interactions. The catalytic kinetics of heterogeneous oxygen surface exchange and fuel oxidation for a perovskite membrane in terms of the thermodynamic state in the immediate vicinity of or on the membrane surface was investigated. Perovskite membranes have been shown to exhibit both oxygen perm-selectivity and catalytic activity for hydrocarbon conversion. However, a description of their catalytic surface reactions is still required. The kinetic parameters for heterogeneous oxygen surface exchange and catalytic fuel conversion reactions were inferred, based on permeation rate measurements and a spatially resolved physical model that incorporates detailed chemical kinetics and transport in the gas-phase. It is shown that the local thermodynamic state at the membrane surface should be accounted for when constructing and examining membrane permeation and heterogeneous chemistry. The significance of modeling both homogeneous and heterogeneous chemistry and their coupling when examining the results was discussed.
by Jongsup Hong.
Ph.D.

The enzymatic saccharification of starch with Aspergillus niger glucoamylase (GA) and the isomerisation of glucose to fructose with Actinoplanes missouriensis glucose isomerase (GI) were selected as model system to explore the possibilities of using ultrafiltration membrane (UF) devices as enzymatic membrane reactors (EMR). Cassava flour was the substrate for the production of glucose syrups in two different configurations of EMR: a dead-end cell (EMR1) and a continuous stirred tank recycled through a hollow fibre device (HFMR). The optimisation of the process in the latter was also investigated.

Thesis (M.S.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains xii, 173 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 138-142).