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Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Polyimide membranes have been used extensively in gas separation applications because of their attractive gas transport properties and the ease of processing these materials. Other applications of membranes, such as membrane reactors, which could compete with more traditional packed and slurry bed reactors across a wider range of environments, could benefit from improvements in the thermal and chemical stability of polymeric membranes. This work focuses on blending polyimide and polybenzimidazole polymers to improve the thermal and chemical stability of polyimide membranes while retaining the desirable characteristics of the polyimide. Blended dense films and asymmetric membranes were fabricated and characterized. Dense film properties are useful for studying intrinsic properties of the polymer blends. Transport properties of dense films were characterized from room temperature to 200°C. Properties including miscibility, density, chain packing and thermal stability were investigated. A process for fabricating flat sheet blended integrally skinned asymmetric membranes by phase inversion was developed. The transport properties of membranes were characterized from room temperature to 300°C. A critical characteristic of gas separation membranes is selectivity. Post-treatments including thermal annealing and vapor and liquid surface treatments were investigated to improve the selectivity of blended membranes. Vapor and liquid surface treatments with common, benign solvents including an alkane, an aldehyde and an alcohol resulted in improvements in selectivity.

Doctor of Philosophy / Department of Chemical Engineering / Peter H. Pfromm / Mary E. Rezac / Multiphase reactions are often constrained by mass transfer limitations which in many cases lead to low reaction rates and undesirable product distribution. Here we fabricate integral-asymmetric polymeric membranes decorated with metal catalysts, to supply hydrogen directly at or near the surface of the catalyst, thus minimizing mass-transfer limitations. The metal decorated polymeric membranes were used for partial hydrogenation of soybean oil with the goal to minimize trans fatty acid (TFA) formation. It was discovered that polymeric membranes with “defective” metal coatings are well suited to achieve low-TFA hydrogenation of soybean oil at quite moderate process conditions. The metal decorated polymeric membranes studied produced significantly lower trans fatty acid as compared to traditional reactors (3.5 wt% at an Iodine Value of 95 as compared to 8 wt% in slurry reactor), at pressures and temperatures which are compatible with the existing systems. The process concept is simpler than some of the alternatives being studied and no catalyst recovery from the oil is needed since the catalyst is immobilized on the membrane. Metal decorated polymeric membranes having a variety of hydrogen fluxes, skin defects, and catalyst loadings were evaluated. All the metal decorated polymeric membranes evaluated produced low TFA. Membranes with high hydrogen fluxes resulted in higher hydrogenation rates but had little influence on TFA formation. Membranes with higher catalyst loadings resulted in lower TFA but increased saturate formation. Metal decorated polymeric membranes behaved differently to changes in temperature and pressures when compared to traditional slurry reactors. They showed a minor increase in TFA with temperature (50-90 °C) as compared to traditional slurry reactors. The hydrogenation rate and cis-trans isomerization also showed a modest dependence on pressure. Due to the defective nature of the metal layer on the polymeric membrane skin and the low temperatures (50-90 °C) at which the reactor is operating, the hydrogen permeability of metals has a minor influence on hydrogenation reaction. A range of metal catalysts can be used for the given system. Repeat runs using the same membrane showed a decrease in hydrogenation activity, without any change in isomerization or hydrogenation selectivity. Initial results indicate the decreased activity may not be from leaching of catalyst from membrane surface nor from sulfur poisoning.

Direct methanol fuel cells (DMFC) are appealing as a power source for portable devices as they do not require recharging with an electrical outlet. However, the DMFC technology is confronted with the high crossover of methanol fuel from the anode to the cathode through the currently used Nafion membrane, which not only wastes the fuel but also poisons the cathode platinum catalyst. With an aim to overcome the problems encountered with the Nafion membrane, this dissertation focuses on the design and development of new polymeric membrane materials for DMFC and a fundamental understanding of their structure-property-performance relationships. Several polymeric blend membranes based on acid-base interactions between an aromatic acidic polymer such as sulfonated ploy(ether ether ketone) (SPEEK) and an aromatic basic polymer such as heterocycle tethered poly(sulfone) (PSf) have been explored. Various heterochylces like nitro-benzimidazole (NBIm), 1H-Perimidine (PImd), and 5-amino-benzotriazole (BTraz) have been tethered to PSf to understand the influence of pKa values and the size of the hetrocycles. The blend membranes show lower methanol crossover and better performance in DMFC than plain SPEEK due to an enhancement in proton conductivity through acid-base interactions and an insertion of the heterocycle side groups into the ionic clusters of SPEEK as indicated by small angle Xray scattering and TEM data. The SPEEK/PSf-PImd blend membrane shows the lowest methanol crossover due to the larger size of the side groups, while the SPEEK/PSf-BTraz blend membrane shows the highest proton conductivity and maximum power density. To further investigate the methanol-blocking effect of the heterocycles, N,N’-Bis- (1H-benzimidazol-2-yl)-isophthalamide (BBImIP) having two amino-benzimidazole groups bonded to a phenyl ring has been incorporated into sulfonated polysulfone (SPSf) and SPEEK membranes. With two 2-amino-benzimidazole groups, which could greatly increase the proton transfer sites, and three phenyl rings, which are compatible with the aromatic polymers, the BBImIP/SPSf and BBImIP/SPEEK blend membranes show suppressed methanol crossover and increased fuel cell performance in DMFC. Novel sulfonated copolymers based on poly(aryl ether sulfone) (SPS-DP) that exhibit low methanol crossover have been synthesized and explored as a methanol-barrier center layer in a multilayer membrane configuration having SPEEK as the outer layers. These multilayer membranes exhibit better performance in DMFC than plain SPEEK and Nafion 115 membranes due to suppressed methanol crossover. To address the issue of incompatibility between the new hydrocarbon-based membranes synthesized and the Nafion ionomer used in the catalyst layer in fabricating membrane-electrode assemblies (MEAs), the MEAs have been fabricated with the SPEEK membranes and 10 to 30 % SPEEK ionomer in the catalyst layer. These MEAs exhibit better performance in DMFC compared to the MEAs fabricated with the SPEEK membranes and Nafion ionomer in the catalyst layer due to lower interfacial resistance. / text

Neste trabalho de mestrado, investigou-se o desempenho de membranas poliméricas de microfiltração para retenção de microalgas (Chlorella sorokiniana) em um fotobiorreator com capacidade volumétrica de 3,5 L, alimentado por um fluxo contínuo de nutrientes com pH 7,0 em condições controladas de temperatura (21°C no meio de cultura e 24°C no meio), borbulhamento de ar e luminosidade (2500 lux, em fotoperíodo de 12/12 horas claro/escuro). Membranas comerciais de tamanho médio de poros 0,8, 1,2, 3,0 e 5,0 μm foram testadas pelo tempo suficiente para esgotamento do limite da permeação da membrana. A concentração das microalgas no fotobiorreator foi analisada através de densidade óptica (espectofotometria) ao número de células (contagem de unidades de células em lâminas do tipo Fuchs Rosenthal - Microscopia Óptica) das amostras de concentrado e permeado. O fenômeno físico de polarização sobre a superfície da membrana está diretamente relacionado ao desempenho da mesma na retenção de microalgas, portanto, fotomicrografias (MEV) da membrana antes e após a microfiltração foram analisadas e comparadas. Para analisar a composição química das microalgas, bem como sua afinidade com as membranas, foram investigadas a composição e a caracterização do fenômeno químico sobre a superfície da membrana, por análise de Energia Dispersiva de Raio-X (EDX). Análises das diferentes fases de crescimento das algas e seus componentes foram feitas em amostras secas a 40°C, através de análise elementar e análises térmicas (TG- Análise Termogravimétrica e DTA- Análise Térmica Diferencial). Os resultados experimentais obtidos neste trabalho permitiram concluir que o uso de membranas de microfiltração em fotobiorreator proporciona a retenção das microalgas, o que contribui para o aumento da concentração da biomassa algal, permitindo a manipulação da sua composição de acordo com as condições pelas quais estes microrganismos são submetidos. / This dissertation investigates the performance of polymeric microfiltration membranes for microalgae retention (Chlorella sorokiniana) in photobioreactor with a volumetric capacity of 3.5 L. The reactor is fed by a continuous flow of nutrients under controlled conditions of pH (7,0) and the temperature (21°C in culture medium and 24°C in the environment), bubbling air and light (2500 lux, with a photoperiod of 12/12 hour light/dark). Commercial membranes of the average pore sizes of 0.8, 1.2, 3.0 and 5.0 μm were tested by depletion of time sufficient to limit the permeation of the membranes. The microalgae concentration in the photobioreactor was analyzed by optical density (spectrophotometry) and number of cells (cell units count on Fuchs Rosenthal type plates-Optical Microscopy). The physical phenomenon of polarization on the surface of the membrane is directly related to its performance in the retention of microalgae therefore micrographs (SEM) of the membrane before and after the microfiltration were compared to identify the chemical affinity between the membranescomposition and the microalgae. The chemical phenomenon on the membrane surface was characterized by Energy Dispersive Analysis of X-ray (EDX). The different phases of the growth of algae and their components were measured in samples dried at 40°C, by elemental analysis and thermal analysis (TG-DTA-Thermogravimetric analysis and differential thermal analysis). The experimental results indicate that the use of microfiltration membranes provides the retention of microalgae, contributing to the increase in the concentration of algal biomass and allowing the manipulation of the composition according to the conditions under which these microrganisms are subjected.

Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Membrane reactor is a device that simultaneously carrying out reaction and membrane-based separation. The advantageous transport properties of the membranes can be employed to selectively remove undesired products or by-products from the reaction mixture, to break the thermodynamic barrier, and to selectively supply the reactant. In this work, membrane reactor technology has been exploited with robust H₂ selective polymeric membranes in the process of hydrogenation and dehydrogenation. A state-of-the-art 3-phase catalytic membrane contactor is utilized in the processes of soybean hydrogenation and bio-oil hydro-deoxygenation, where the membrane functions as phase contactor, H₂supplier, and catalytic support. Intrinsically skinned asymmetric Polyetherimide (PEI) membranes demonstrated predominant H₂permeance and selectivity. By using the PEI membrane in the membrane contactor, soybean oil is partially hydrogenated efficiently at relatively mild reaction conditions compared with a conventional slurry reactor. In the hydroprocessing of bio-oil using the same system, the membrane successfully removed water, an undesired component from bio-oil by pervaporation. The more industrially feasible membrane-assisted reactor is studied in the alkane dehydrogenation process. Viable polymeric materials and their stability in elevated temperatures and organic environment are examined. The blend polymeric material of Matrimid® 5218 and Polybenzimidazole (PBI) remained H₂permeable and stable with the presence of hydrocarbons, and displayed consistent selectivity of H2/hydrocarbon, which indicated the feasibility of using the material to fabricate thermally stable membrane for separation. The impact of membrane-assisted reactor is evaluated using finite parameter process simulation in the model reaction of the dehydrogenation of methylcyclohexane (MCH). By combining tested catalyst performance, measured transport properties of the material and hypothetical membrane configuration, by using a membrane assisted packed-bed reactor, the thermodynamic barrier of the reaction is predicted to be broken by the removal of H₂. The overall dehydrogenation conversion can be increased by up to 20% beyond equilibrium. The predicted results are justified by preliminary experimental validation using intrinsically skinned asymmetric Matrimid/PBI blend membrane. The conversions at varied temperatures partially exceeded equilibrium, indicating successful removal of H₂by the blend membrane as well as decent thermal stability of the membrane at elevated temperatures with the presence of hydrocarbons. The successful outcome of membrane contactor and membrane-assisted reactor using robust polymeric membranes shows the effectiveness and efficiency of membrane reactors in varied application. The future work should be focusing on two direction, to further develop durable and efficient membranes with desired properties; and to improve the reactor system with better catalytic performance, more precise control in order to harvest preferable product and greater yield.

Orientador: Lireny Aparecida Guaraldo Gonçalves / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-13T22:31:55Z (GMT). No. of bitstreams: 1 Campos_LucieneAra_M.pdf: 5181818 bytes, checksum: ba8a0b13f89dd6cb8e19f67be74e2cda (MD5) Previous issue date: 2009 / Resumo: Este estudo teve como objetivo a degomagem do óleo de canola por ultrafiltração com membrana polimérica em sistema semi-tangencial com intuito de determinar a melhor membrana (PES, CME, PVDF 30 kDa e PVDF 50 kDa) e condição de pressão em função dos parâmetros de fluxos de permeado (J) e retenção de fosfolipídio (Rc). Quatro abordagens diferentes de degomagem foram avaliadas: ultrafiltração do óleo bruto, ultrafiltração de miscela (óleo + hexano), microfiltração de óleo pré-tratado e degomagem convencional. Após a escolha da membrana e do tipo de degomagem foi realizado um estudo da ultrafiltração em escala piloto através de planejamento experimental, na qual foi avaliada a influência da pressão e a velocidade tangencial de escoamento nas respostas de fluxo e retenção de fosfolipídio. Os resultados mostraram que a membrana e o tipo de degomagem com melhor desempenho foi a ultrafiltração de miscela com PVDF 30 kDa, apresentando um fluxo de 36 L m-2 h-1 e Rc 86% em unidade de laboratório. Através do planejamento experimental realizado para ensaios na unidade piloto de filtração tangencial com membrana PVDF 30 kDa em miscela foram determinadas as condições ótimas de operação. Em 1,6 bar e 3,24 m s-1 foi obtido fluxo de 162 L m-2 h-1 e retenção de 88%. O estudo do comportamento de compostos minoritários frente à ultrafiltração em membranas de vários materiais demonstrou que para a membrana PVDF 30 kDa ocorreu a remoção de 79% de umidade; redução de 37% em pigmentos vermelhos e 27% de redução de clorofila. Em estudo comparativo de quatro métodos diferentes de degomagem foi observado que aquele realizado por ultrafiltração de miscela promove completa conservação de tocoferóis naturalmente presentes no óleo, enquanto que na degomagem convencional ocorre uma perda de 3,4%, induzindo a menores valores de Estabilidade oxidativa. Análise da membrana incrustada através da técnica de MEV revelou a presença de depósitos em toda superfície e a análise através da técnica de EDS evidenciou que além de compostos de carbono, elementos tais como Fe, Ca, K, Na e S estavam presentes em maior quantidade. A análise destes elementos por Espectrometria de Emissão Ótica com Acoplamento de Plasma Induzido (ICP-OES) nas amostras de óleo e na membrana evidenciou que ocorreu a concentração destes elementos no retentado e na membrana incrustada, bem como a redução de teores destes compostos no permeado, indicando que estes elementos são um dos componentes responsáveis pela incrustação / Abstract: This study focused on degumming of canola oil by ultrafiltration using polymeric membrane at semi-tangential system with intention of determining the best membrane material (PES, CME, PVDF 30 kDa e PVDF 50 kDa), condition of pressure to obtain better flux of permeate (J) and phospholipids retention (Rc). Four different degumming approaches were applied: ultrafiltration of crude oil, miscela ultrafiltration, microfiltration of pre-treated oil and conventional degumming. The results showed that the membrane and degumming approach with best results were the miscella ultrafiltration and PVDF 30 kDa membrane which presented 36 L m2 h-1 of flux and 86% of phospholipids retention at laboratory unit, semi-tangential system. After choosing the membrane and better degumming approach a study of ultrafiltration through an experimental design was performed to evaluate the influence of pressure and tangential velocity on the flux and retention of phospholipids responses. It was determined the optimized conditions and at 1.6 bar and 3.24 m s-1 it was obtained 162 m-2 h-1 of flux and 88% retention of phospholipids. The study of the behavior of minor compounds using ultrafiltration with different membranes demonstrated that the PVDF 30 kDa presented a reduction of 79% moisture, 37% on red pigments and 27% on chlorophyll. In a comparative study of four different degumming methods was observed that miscella ultrafiltration preserves total tocopherol naturally present on oil, while the conventional degumming looses 3.4% of this compound, which implies at lower value of oxidative stability.The SEM analysis performed on fouled membrane reveled presence of deposit on the whole surface membrane. EDS analysis evidenced that, besides carbon-based compounds, elements such as Fe, Ca, K, Na and S were present at higher amounts than others. The analysis of these elements by ICP-OES on the samples of oil and membranes showed that membrane processes concentrate these elements on the retentate and on the fouled membrane, leaving the permeate less concentrated than the feed. This indicates that the presence of those elements is one of the responsible for the fouling phenomenon / Mestrado / Mestre em Tecnologia de Alimentos

Neste trabalho de mestrado, investigou-se o desempenho de membranas poliméricas de microfiltração para retenção de microalgas (Chlorella sorokiniana) em um fotobiorreator com capacidade volumétrica de 3,5 L, alimentado por um fluxo contínuo de nutrientes com pH 7,0 em condições controladas de temperatura (21°C no meio de cultura e 24°C no meio), borbulhamento de ar e luminosidade (2500 lux, em fotoperíodo de 12/12 horas claro/escuro). Membranas comerciais de tamanho médio de poros 0,8, 1,2, 3,0 e 5,0 μm foram testadas pelo tempo suficiente para esgotamento do limite da permeação da membrana. A concentração das microalgas no fotobiorreator foi analisada através de densidade óptica (espectofotometria) ao número de células (contagem de unidades de células em lâminas do tipo Fuchs Rosenthal - Microscopia Óptica) das amostras de concentrado e permeado. O fenômeno físico de polarização sobre a superfície da membrana está diretamente relacionado ao desempenho da mesma na retenção de microalgas, portanto, fotomicrografias (MEV) da membrana antes e após a microfiltração foram analisadas e comparadas. Para analisar a composição química das microalgas, bem como sua afinidade com as membranas, foram investigadas a composição e a caracterização do fenômeno químico sobre a superfície da membrana, por análise de Energia Dispersiva de Raio-X (EDX). Análises das diferentes fases de crescimento das algas e seus componentes foram feitas em amostras secas a 40°C, através de análise elementar e análises térmicas (TG- Análise Termogravimétrica e DTA- Análise Térmica Diferencial). Os resultados experimentais obtidos neste trabalho permitiram concluir que o uso de membranas de microfiltração em fotobiorreator proporciona a retenção das microalgas, o que contribui para o aumento da concentração da biomassa algal, permitindo a manipulação da sua composição de acordo com as condições pelas quais estes microrganismos são submetidos. / This dissertation investigates the performance of polymeric microfiltration membranes for microalgae retention (Chlorella sorokiniana) in photobioreactor with a volumetric capacity of 3.5 L. The reactor is fed by a continuous flow of nutrients under controlled conditions of pH (7,0) and the temperature (21°C in culture medium and 24°C in the environment), bubbling air and light (2500 lux, with a photoperiod of 12/12 hour light/dark). Commercial membranes of the average pore sizes of 0.8, 1.2, 3.0 and 5.0 μm were tested by depletion of time sufficient to limit the permeation of the membranes. The microalgae concentration in the photobioreactor was analyzed by optical density (spectrophotometry) and number of cells (cell units count on Fuchs Rosenthal type plates-Optical Microscopy). The physical phenomenon of polarization on the surface of the membrane is directly related to its performance in the retention of microalgae therefore micrographs (SEM) of the membrane before and after the microfiltration were compared to identify the chemical affinity between the membranescomposition and the microalgae. The chemical phenomenon on the membrane surface was characterized by Energy Dispersive Analysis of X-ray (EDX). The different phases of the growth of algae and their components were measured in samples dried at 40°C, by elemental analysis and thermal analysis (TG-DTA-Thermogravimetric analysis and differential thermal analysis). The experimental results indicate that the use of microfiltration membranes provides the retention of microalgae, contributing to the increase in the concentration of algal biomass and allowing the manipulation of the composition according to the conditions under which these microrganisms are subjected.

The use of polymeric membranes for natural gas separation has rapidly increased during the past three decades, particularly for carbon dioxide separation from natural gas. Another valuable application is the separation of heavy hydrocarbons from methane (fuel gas conditioning), more importantly for remote area and off-shore applications. A new potential polymeric membrane that might be utilized for natural gas separations is a Tröger’s base ladder polymer (PIM-Trip-TB-2). This glassy polymeric membrane was synthesized by the polymerization reaction of 9, 10-dimethyl-2,6 (7) diaminotriptycene with dimethoxymethane. In this research, the polymer was selected due to its high surface area and highly interconnected microporous structure. Sorption isotherms of nitrogen (N2), oxygen (O¬2), methane (CH4), carbon dioxide (CO2), ethane (C2H6), propane (C3H8), and n-butane (n-C4H10) were measured at 35 °C over a range of pressures using a Hiden Intelligent Gravimetric Analyzer, IGA. The more condensable gases (C2H6, CO2, C3H8, and n-C4H10) showed high solubility due to their high affinity to the polymer matrix. The permeation coefficients were determined for various gases at 35 °C and pressure difference of 5 bar via the constant-pressure/variable-volume method. The PIM-Trip-TB-2 film exhibited high performance for several high-impact applications, such as O2/N2, H2/N2 and H2/CH4. Also, physical aging for several gases was examined by measuring the permeability coefficients at different periods of time. Moreover, a series of mixed-gas permeation tests was performed using 2 vol.% n-C4H10/98 vol.% CH4 and the results showed similar transport characteristics to other microporous polymers with pores of less than 2 nm. The work performed in this research suggested that PIM-Trip-TB-2 is suitable for the separation of: (i) higher hydrocarbons from methane and (ii) small, non-condensable gases such as O2/N2 and H2/CH4.

Membrane processes can cover a wide range of separation problems [with a specific membrane (membrane structure) required for every problem]. Thus, there are membranes available that differ in their structure and consequently in the functionality. Therefore membrane characterization is necessary to ascertain, which membrane may be used for a certain separation. Membranes of pore size ranging from 100nm to 1μm with a uniform pore size are very important in membrane technology. An optimum performance is achieved when the membrane is as thin as possible having a uniform pore size. Here in this thesis, membranes were synthesized by particle assisted wetting using mono-layers of silica colloids as templates for pores along with polymerizable organic liquids on water surface. The pore size reflects the original shape of the particles. Thus it is possible to tune the pore size by varying the particle size. This method is effective to control pore sizes of membranes by choosing silica particles of suitable size. This approach gives a porous structure that is very thin, but unfortunately limited in mechanical stability. Thus there is a need for support which is robust and can withstand the various mechanical stresses. A small change in the membrane or defect in the layered structure during the membrane formation can have drastic effect on the assembly. Lateral homogeneity of the layer generated by the particle assisted wetting can be judged by examination of its reflectivity, but once it is transferred on any solid support this option is no more. So a method is needed to detect the cracks or the inhomogenity of the membrane which can be detected even after the transfer. To tackle this problem a very simple and novel technique for characterizing the membrane by fluorescence labeling and optical inspection was developed in this thesis. The idea was to add a fluorescent dye which is poorly water soluble to the spreading solution comprising of the particles and the monomer. If the dye survived the photo-cross linking, then it would be embedded in the cross-linked polymer and would serve as a marker. Defects and inhomogenity would show up as cracks and spots. By the method that we have developed, we can detect our membrane from the support and spot defects.