Zeolite A membranes have great potential in pervaporation separation of ethanol/water mixtures with high flux and selectivity. Zeolite membranes usually synthesized from hydrogels in batch systems. In recent years, zeolite membranes are prepared in semicontinuous, continuous and recirculating flow systems to allow the synthesis of zeolite membranes with enlarged surface areas and to overcome the limitations of batch system at industrial level production. The purpose of this study is to develop a synthesis method for the preparation of good quality zeolite A membranes in a recirculated flow system from hydrogels and to test the separation performance of the synthesized membranes by pervaporation of ethanol/water mixture. In this context, three different experimental synthesis parameters were investigated with zeolite A membranes synthesized in batch system. These parameters were the composition of the starting synthesis hydrogel, silica source and the seeding technique. Syntheses were carried out using hydrogels at atmospheric pressure and at 95 &deg / C. The membranes were characterized by X-ray diffraction, scanning electron microscopy and pervaporation of 90 wt% ethanol-10 wt% water mixtures. v Pure zeolite A membranes were synthesized both in batch and flow systems. The membranes synthesized in batch system have fluxes around 0.2-0.3 kg/m2h and selectivities in the range of 10-100. Membranes with higher selectivities were obtained in batch system by using waterglass as silica source, seeding by dip-coating wiping method, and with a batch composition of 3.4Na2O:Al2O3:2SiO2:155H2O. The membranes prepared in flow system have higher pervaporation performances than the ones prepared in batch system in considering both flux and the selectivity. Fluxes were around 0.3-3.7 kg/m2h and selectivities were in the range of 102-104 for the membranes prepared in flow system which are comparable with the data reported in literature for batch and flow systems. A high quality zeolite A membrane was also synthesized from 3.4Na2O:Al2O3:2SiO2:200H2O hydrogel at 95 &deg / C for 17 hours in flow system. Pervaporation flux of this membrane was 1.2 kg/m2h with a selectivity &gt / 25,000 at 50&deg / C. Although the synthesis method is resulted with high quality membrane, reproducibility of the synthesis method is poor and it should be improved.

Separation of aromatic/aliphatic hydrocarbon mixtures by pervaporation has been of increasing interest in recent decades. Dozens of polymer materials have been reported for separations of benzene/cyclohexane and toluene/iso-ocatne mixtures. However, fundamental understanding of material structure and transport relations is not adequate to generalize guidelines for materials screening. The goals of this study are to tailor the structure of the polyimide materials, correlate the structure and transport relations, and establish guidelines for future materials. The 3, 5-Diaminobenzoic acid (DABA) containing polyimides were synthesized by both chemical and thermal solution imidization. The synthesized polyimides were formed into dense films by solution casting. The physical properties of the polyimides synthesized with monomers: 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 4, 6-trimethyl-1, 3-phenylendiamine (DAM) and DABA, were characterized by DSC, WAXD, GPC and density. The chemical structures were assessed by FTIR and NMR. The pervaporation and sorption of the synthesized polyimide membranes were tested in toluene/iso-octane mixtures at 100°C. The structure- transport property relations were established for the 6FDA-DAM/DABA membranes. The 6FDA-DAM/DABA polyimides were crosslinked by ethylene glycol. The pervaporation and sorption of the crosslinked membranes were tested in toluene/iso-octane mixtures at 100°C. Thermal imidization was found to give a higher imidization degree than chemical imidization. As a result, the polyimides made by chemical imidization contain a higher percentage of carboxylic acid groups than those made by thermal imidization. Chemical imidization gives higher film density, glass transition temperature and lower flux and higher selectivity for the toluene/iso-octane pervaporation than the thermally imidized membranes because of the higher carboxylic acid concentration. The chemically imidized membranes are slightly brittle after the crosslinking. Only the thermal imidization membranes have good flexibility and its pervaporation selectivity improves significantly after the crosslinking. Solubility selectivity and diffusivity selectivity of the 6FDA-DAM/DABA membranes were correlated with solubility parameters and fractional free volume, respectively. The structure-mass transport relations show that for the 6FDA-DAM/DABA membranes, both solubility selectivity and diffusivity selectivity contribute to the pervaporation selectivity. For the chemically imidized membranes, increased DABA concentration has a positive effect on solubility selectivity and diffusivity selectivity. For the thermally imidized membranes, increased DABA concentration has a significant effect on diffusivity selectivity only. / text

The main theme of this dissertation is the fabrication and analysis of modified mesoporous silica membranes for separation applications. Synthesis methods for mesoporous silica membranes have been developed to enhance the transport performance and quality of the membranes, such as permeability, pore volume, and surface area. Then, synthesized membranes were modified with different organic groups to tailor selectivity in separations. The collected studies of modified mesoporous silica membranes showed that appropriate functionalization on newly synthesized novel membranes leads to promising structural and permeation properties. First, a seeded growth method was developed for synthesis of MCM-48 membranes on alumina supports, thereby extending the seeded growth technique used for zeolite membranes to mesoporous silica membrane synthesis. The surface properties of the MCM-48 membranes were then modified by silylation with hexamethyldisilazane (HMDS). In comparison to MCM-48 membranes previously synthesized by the in situ growth technique, much less silica infiltration into the alumina support was observed. The pore structure of the MCM-48 membranes demonstrated that a large accessible pore volume was available for molecular permeation and pore modification to tailor selectivity. The gas permeation properties of the calcined and silylated MCM-48 membranes were consistent with a Knudsen-like mechanism, albeit with a substantial influence of gas-solid interactions in the mesopores. The silylated MCM-48 membranes were evaluated for pervaporative separation of ethanol (EtOH), methyl ethyl ketone (MEK), and ethyl acetate (EA) from their dilute aqueous solutions. The synthesized membranes exhibited high pervaporative separation factors and organic fluxes. The selective separation of organic/water mixtures with MCM-48 membranes were attributed to both the organophilic nature of the surface and the effective pore size of the silylated mesopores. Next, the synthesis and organic/water separation properties of mesoporous silica membranes supported on low-cost and scalable polymeric (polyamide-imide) hollow fibers and modified by trimethylsilylation with HMDS was studied. Thin, defect-free membranes that exhibited high gas permeances consistent with Knudsen-like diffusion through the mesopores were prepared. Silylation of these membranes did not affect the integrity of the mesoporous silica structure and the underlying polymeric hollow fiber, but led to capping of the surface silanol groups in the mesopores with trimethylsilyl groups. The silylated mesoporous membranes were evaluated for pervaporative separation of EtOH, MEK, EA, iso-butanol, and n-butanol from their dilute aqueous solutions. The membranes showed higher separation factors than those of flat membranes, along with high organic fluxes. The large increase in hydrophobicity of the membranes upon silylation allowed upgrading of the feed mixtures to permeate streams with considerably higher organic content. The selective separation of organic/water mixtures with the fiber-supported mesoporous silica membranes was attributed to both the organophilic nature of the surface (yielding good adsorption selectivity) and the effective pore size of the silylated mesopores (giving good fluxes). Comparison with other types of organic/water separation membranes revealed that the present silylated membrane platform shows good promise for use in organic/water separation applications due to its high flux, scalable and low-cost fabrication methodology, and good separation factors that can be further enhanced by tailoring the mesopore modification chemistry. Further, the gas transport properties of aziridine-functionalized mesoporous silica membranes on polymeric hollow fibers have also investigated. The mesoporous membranes were amine-functionalized with aziridine and their transport properties were studied to understand the effects of surface functionalization on gas separations. This new hybrid aminosilica membrane showed interesting and counter-intuitive N₂ selective permeation properties in dry CO₂/N₂ separations. Detailed characterization of the membrane structure and its permeation behavior showed that such behavior was due to the strong adsorption of CO₂, leading to reduced gas flux because of CO₂-induced amine crosslinking in the mesopores. This hyper-branched aminosilica membrane showed CO₂ selective properties when applied to humid gas permeation. Water molecules in the humid gas affected the adsorption of CO₂ molecules by causing a lower degree of crosslinking, allowing facilitated transport of CO₂.

Pervaporation is a selective membrane technique in which a liquid feed mixture is separated by means of partial vaporization through a non-porous perm-selective membrane. This method can be used for the recovery of heat sensitive aroma compounds to avoid them from thermal damage in beverage industries. The main objective of this study was to determine the effects of feed temperature (30, 40, 50&deg / C), composition (different model solutions, strawberry essence), concentration (50, 100, 150 ppm) and permeate pressure (4, 8 mbar) on the recovery of aroma compounds of strawberry by pervaporation in terms of mass flux and selectivity. In addition, it was aimed to optimize the extraction conditions (extraction time, temperature, agitation speed, strawberry matrix) of Solid-phase microextraction (SPME), which is used for the analysis of strawberry aroma compounds. Optimum results for SPME were obtained at 40&deg / C, 700 rpm for 30 min and no matrix effect was observed. Pervaporation experiments were performed using a hydrophobic membrane, PERVAP 1070 (PDMS). As the feed temperature increased, the mass flux and selectivity increased and the total mass flux followed an Arrhenius type relation. Decreasing downstream pressure increased both total flux and selectivity, while increase in feed concentration led to higher organic fluxes but lower selectivities. In general, PERVAP 1070 showed a higher selectivity towards Methyl butyrate (MTB) than Ethyl butyrate (ETB) and MTB flux was affected negatively by the presence of ETB in the feed solution. Pervaporation experiments were also performed with a strawberry essence and strawberry model solution. The selectivities of MTB and ETB were negatively affected by the presence of other aroma compounds.

Solvent recovery is gaining importance in the chemical production processes to reduce the costs and because of environmental concerns. Therefore separation schemes for recovery and recycle of solvents used in printing and packaging industry were developed. However, a low value by-product, mainly ethyl alcohol and isopropanol, is obtained during the solvent recovery process. If the water concentration of this mixture is decreased below 0.1% by weight, the value of it increases significantly. To dehydrate this stream, a pervaporation-adsorption separation scheme is developed in this study. The effect of pervaporation process parameters, such as temperature, feed flow rate, permeate side pressure, feed water and ethyl acetate concentration, on the performance of the PERVAP 2211 and 2201 membranes of Sulzer Chem-tech&reg / using the real industrial by-product solution obtained from a local company are investigated. Pervaporation tests were conducted using a home made experimental setup equipped with 148 cm2 rectangular shaped membrane module. Permeates obtained from these experiments were analyzed using a gas chromatograph equipped with FID and the water concentration of the feed solutions were analyzed using Karl-Fisher titration. Besides, adsorption studies were conducted using zeolite 3A in a fixed bed column. As a result of this study, PERVAP 2201 membranes showed higher fluxes with a slightly lower permeate water concentration compared to PERVAP 2211 at the at ranges studied. The increase in the pervaporation performance was observed with an increase in the temperature, permeate side vacuum and feed flow rate over the membrane. Therefore, concentrated-mode experiments were conducted at 70&deg / C, 2 torr permeate side pressure and 1.6 L/min of feed flow rate using the findings of the parametric studies and the retentate of this experiments were further dehydrated using liquid phase adsorption. Finally, the water concentration of the solution was decreased to 0.04% by weight.

Techn. Universiẗat, Diss.--Hamburg-Harburg, 2000.

Zugl.: Dortmund, Univ., Diss., 2008

Thesis (Ph.D.)--University of Waikato, 2006. / Includes bibliographical references (leaves [186]-203) Also available via the World Wide Web.

A remoção de compostos sulfurados da gasolina é um assunto de grande interesse na indústria de refino de petróleo em função das restrições ambientais cada vez mais rígidas em relação ao teor máximo de enxofre de produtos acabados. A solução mais comum para remoção de contaminantes são as unidades de hidrotratamento que operam a alta pressão e possuem alto custo de instalação e de operação além de levarem à perda de octanagem do produto acabado. O uso de membranas é uma alternativa promissora para a redução do teor de enxofre de correntes de gasolina e possui diversas vantagens em relação ao hidrotratamento convencional. O conhecimento aprofundado dos parâmetros que influenciam as etapas de sorção e difusão é crítico para o desenvolvimento da aplicação. Este trabalho avalioua seletividade e sorção do sistema formado por n-heptano e tiofeno em polímeros através de modelos termodinâmicos rigorosos, baseados em contribuição de grupos. O modelo UNIFAC-FV, variante do tradicional modelo UNIFAC para sistemas poliméricos, foi o modelo escolhido para cálculo de atividade dos sistemas estudados. Avaliou-se ainda a disponibilidade de parâmetros para desenvolvimento da modelagem e desenvolveu-se uma abordagem com alternativas para casos de indisponibilidade de parâmetros UNIFAC. Nos casos com ausência de parâmetros, o cálculo do termo residual da atividade das espécies é feito na forma proposta por Flory-Hugginsutilizando-se parâmetros de solubilidade obtidos também por contribuição de grupos. Entre os métodos de contribuição de grupos existentes para cálculo de parâmetros de solubilidade, o método de Hoy mostrou menores desvios para os sistemas estudados. A abordagem utilizada neste trabalho permite, ao final, uma análise de alterações da configuração da cadeia principal de polímeros de forma a influenciar sua seletividade e sorção para dessulfurização de naftas / The removal of sulfur compounds from gasoline is a subject of great relevance in the oil refining industry due to strict environmental restrictions related to the maximum content of sulfur in finished products. The most common solution for contaminants removal are the hydrotreating units which operate under high pressure and have high costs for installation and operation besides causing anoctane number reduction in the finished product. The utilization of membranes is a promising alternative for sulfur content reduction in gasoline and has several advantages when compared to conventional hydrotreating. A deep understanding of parameters that affect sorption and diffusion steps is critical for developing this application. This work has evaluated the selectivity and sorption of systems constituted by n-heptane and thiophene in polymers through rigorous thermodynamic models, based on group contribution. The model UNIFAC-FV, originated from UNIFAC traditional model for polymeric systems, was the chosen model for activity calculation in studied systems. It was also evaluated the availability of parameters for modeling development and an approach was developed with alternatives for those cases with unavailable UNIFAC parameters. For such cases, the calculation of the residual contribution for activity was done according to Flory-Huggins proposal using solubility parameters obtained also by group contribution. Among the existing group contribution methods for solubility parameter, the method from Hoy gave better results for systems studied in this work. The approach used in this work allows, in the end, an analysis of changes in the configuration of the polymer main chain that could influence its selectivity and sorption for naphtha desulfurization

Orientador: Prof. Dr. Reynaldo Palácios Bereche / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Energia, 2015. / No presente trabalho foi desenvolvida uma análise de desempenho da inserção da tecnologia de membranas, visando a potencialização da produção de etanol, e o impacto desta sobre a destilação convencional para a separação do etanol até o grau de etanol hidratado combustível (EHC). A pervaporação com membranas de PDMS (polidimetilsiloxano) foi adotada como alternativa tecnológica para a intensificação da fermentação alcoólica, a partir de sacarose em forma de melaço de cana. Três arranjos de operação de fermentação foram selecionados e avaliados como alternativa à intensificação da operação, a fermentação em batelada com fermentadores SBF (Simple Batch Fermenter) representa o regime transitório, para o regime estacionário foi selecionado um fermentador contínuo, CSTF (Continuous Stirred Tank Fermenter). Na operação semicontínua, o fermentador em batelada alimentada foi selecionado, FBF (Fed-Batch Fermeter). Os três tipos de operação de fermentação (em batelada, contínua e semicontínua) avaliaram-se em função do rendimento, produtividade e tempo de operação. O critério do tempo de operação discriminou-se em tempos totais de fermentação para os fermentadores SBF e FBF, em quanto ao fermentador CSTF o tempo de retenção hidráulica foi usado. Tanto os modelos da cinética da fermentação, como os parâmetros cinéticos foram tomados da literatura e adaptados ao tipo de regime avaliado. Para a explicação da pervaporação foi usada a teoria de solução-difusão, pois segundo a literatura , é a teoria mais apropriada e simples que descreve a transferência de massa através da membrana em uma pervaporação. Os modelos de transferência de massa de Fick e Maxwell-Stefan (MS), foram aplicados para determinar a taxa de transferência de massa na pervaporação, baseada nas características das membranas de PDMS. As permeabilidades do modelo de transferência de massa de Fick foram determinadas. Os parâmetros de sorção e difusão do modelo de MS foram tomados da literatura. Para a membrana de PDMS avaliada, determinou-se um fator de separação de 3,5 para o etanol e 0,14 para água sob as condições normais de fermentação, indicando um fluxo de permeato com um conteúdo de água relativamente baixo (referente à solução fermentativa) e uma concentração de 33 wt.% de etanol no permeato. Fez-se o acoplamento da modelagem dos fermentadores SBF, CSTF e FBF com o modelo de MS da membrana de pervaporação. O modelo de MS apresentou maior exatidão que o modelo de Fick na transferência de massa através da membrana. Também propôs-se os esquemas da operação híbrida para os fermentadores H-SBMF (Hybrid -Simple Batch Membrane Fermenter), H-CSTMF (Hybrid- Continuous Stirred Tank Membrane Fermenter) e H-FBMF (Hybrid-Fed Batch Membrane Fermenter). Para a fermentação híbrida com membranas, além do rendimento, produtividade e tempo de operação foi avaliada a intensificação de etanol. Para o H-SBMF, a produção de etanol aumentou 14,43% em comparação à fermentação convencional, sob as mesmas condições operacionais (Intensificação de etanol) e a produtividade teve um incremento de 2,5 vezes. O H-CSTMF apresentou um incremento máximo de etanol produzido de 30,32%, e a produtividade foi incrementada em uma faixa de 1,1 a 1,7 vezes baseado no tempo de retenção (residencia hidráulica). No H-FBMF atingiu-se até 16,13 % de etanol intensificado e um incremento de 1,6 vezes na produtividade. Os rendimentos de todas as fermentações mantiveram relativamente constantes. Os consumos energéticos (energia térmica e mecânica) foram avaliados com base nos requerimentos energéticos da pervaporação, e consumo energético na etapa de destilação para obter álcool hidratado. Conseguiu-se advertir que houve um declínio do consumo de energia térmica (calor) do processo geral (máximo de 11%), em virtude de um significante aumento da quantidade de etanol produzido na fermentação híbrida. Determinou-se que o consumo de energia na recuperação do permeato, depende explicitamente da área da membrana, o qual foi média de 0,77 kW/m2. / In this study, an analysis of performance of the membrane technology insertion to conventional ethanol production technology has been developed. Membranes separation were considered to enhance the fermentation and distillation areas of conventional process of alcohol-fuel production. Aimed an intensification of alcoholic fermentation by pervaporation with PDMS (Polydimethylsiloxane) membranes, as a back-up technology to accomplish this assignment. Three fermentation operation arrangements were picked and assessed as intensification alternative operation, SBF (Simple Batch Fermenter) for transient regime, CSTF (Continuous Stirred Tank Fermenter) for steady-state fermentation and FBF (Feed Batch Fermenter) for semicontinuous operation. These three types of operation (batch, steady-state and semicontinuous) were evaluated as function of product-yield, productivity and operation time criteria. In batch and fed-batch operation, operation time was specified by total fermentation time, for steady-state operation the operation time criteria was residence time. Fermentation kinetic models and kinetic parameters were obtained from literature and embedded to assessed operation regimes. Pervaporation phenomena was explained by the solution-diffusion theory, since according to literature it is most appropriate and simple theory to describe the mass transfer across pervaporation membranes. Fick and Maxwell-Stefan mass transport model were used to determine the pervaporation mass transfer rate, based in PDMS membranes characteristic. Permeability from Fick model was calculated and sortion and diffusivity parameters from Maxwell-Stefan were obtained from literature. For evaluated PDMS membrane, ethanol and water separation factor of 3.5 and 0.15 were achieved, respectively for a range of normal fermentation concentrations, suggesting a permeate flux with lower water containing than fermentative solution and an ethanol concentration about to 35 %. SBF, FBF and CSTF modeling, Fick and Maxwell-Stefan membrane pervaporation models were adapted and applied together. In addition, a schematic hybrid arrangement for fermenters, H-SBMF (Hybrid -Simple Batch Membrane Fermenter), H-FBMF (Hybrid-Fed Batch Membrane Fermenter) and H-CSTMF (Hybrid-Continuous Stirred Tank Membrane Fermenter) was proposed. Further product-yield, productivity and operation time criteria, performance of membrane pervaporation was evaluated in hybrid-fermentation process. For H-SBMF, product-yield referred to conventional fermentation, under the same operative conditions (ethanol profit) increased 14.43% and 2.5 times higher productivity was achieved. H-CSTMF presented 30.32% higher ethanol profit; instead, the productivity had an increased in range of 1.1-1.7 times. For H-FBMF achieved 16.13% and 1.6 times higher ethanol profit and productivity, respectively. Fermentation energy consumption was estimated based in the energetic needs in pervaporation and energy demand in distillation area, for hydrated ethanol. A decrease of global energy consumption was attended (up to 11%), consequent to a quietly higher ethanol-feed concentration, generated in a simultaneous fermentationpervaporation process. The pervaporation was integrated to high-temperature compressed permete stream, reaching a higher energy-efficient process than a non-integrated pervaporation process. Electrical consumption for permeate recovery was determined and it is only in funtion of membrane area, achieving 0.77 kW/m2.