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.

Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Reversible organic reactions, such as esterification, transesterification, and acetalisation, have enjoyed numerous laboratory uses and industrial applications since they are convenient means to synthesize esters and ketals. Reversible organic reactions are limited by thermodynamic equilibrium and often do not proceed to completion. High yields for these equilibrium driven reactions can be obtained either by adding a large excess of one of the reactants, which results a reactant(s)/product(s) mixture requiring a separation, or by the selective removal of by-products. Conventional removal techniques including distillation, adsorption, and absorption have drawbacks in terms of efficiency as well as reactor design. Pervaporation membrane reactors are promising systems for these reactions since they have simpler designs, and are more energy efficient compared to conventional downstream separation techniques. This project created a general protocol that can guide one to carry out experiments and collect necessary data for transferring membrane reactor design concepts to the construction of industrial-scale membrane reactors for organic synthesis. Demonstration of this protocol was achieved by (1) experimental evaluation of membrane reactor performance, (2) modeling, and (3) scale-up. The capability of membranes for water/organic separations and organic/organic separations during reversible reactions was investigated. Our results indicated that enhanced membrane reactors selectively removed the by-product water and methanol from reaction mixtures and achieved high conversions for all investigated reactions. Second, modeling and simulation of pervaporation membrane reactor performance for reversible reactions were carried out. The simulated performance agrees well with experimental data. Using the developed model, the effects of permeate pressure and membrane selectivity on membrane reactor yield were examined. Finally, a scale-up on transesterification membrane reactors was carried out. The membrane modules investigated included a bench-scale flat sheet membrane, a bench-scale hollow fiber membrane module, and a pilot-scale hollow fiber membrane module. A 100% conversion was obtained by the selective methanol removal. It is found that with high methanol selectivity membranes, the reaction time to achieve a given conversion continuously decreases with increasing the methanol removal capacity of the reactor system. However, this is a highly nonlinear relationship.

Zero-valent metals such as bulk iron and zinc are known to dechlorinate toxicorganic compounds. Enhancement in reaction rates has been achieved through bimetallicnanosized particles such as nickel/iron (Ni/Fe) and palladium/iron (Pd/Fe). Batchdegradation of model compounds, trichlroethylene (TCE) and 2,2'-dichlorobiphenyls(DCB), were conducted using bimetallic Ni/Fe and Pd/Fe nanoparticles. Completedegradation of TCE and DCB is achieved at room temperature. Zero-valent iron, as themajor element, undergoes corrosion to provide hydrogen and electrons for the reductivecatalytic hydrodechlorination reaction. The second dopant metals of nickel and palladium(in nanoscale) act as catalyst for hydrogenation through metal hydride formation thatproduces completely dechlorinated final product. Different compositions of bimetallicNi/Fe and Pd/Fe nanoparticles were synthesized and their reactivity was characterized interms of reaction rate constants, hydrogen generation through iron corrosion, andproducts formation. The observed TCE degradation rate constant was two orders ofmagnitude higher than the bulk iron and nanoiron, indicating that the bimetallicnanoparticles are better materials compared to the monometallic iron systems. Longevitystudy through repeated cycle experiments showed minimum loss of activity. The surfacearea-normalized rate constant was found to have a strong correlation with the hydrogengeneration by iron corrosion reaction. A mathematical model was derived thatincorporates the reaction and Langmuirian-type sorption terms to estimate the intrinsicreaction rate constant and rate-limiting step in the degradation process. Bimetallicnanoparticles were also immobilized into the chitosan matrix for the synthesis of ananocomposite membrane reactor to achieve membrane-phase destruction of chlorinatedorganics under convective flow condition. Formation of uniformly distributed nanosizedparticles is confirmed by high resolution transmission electron microscopy. Themembrane-phase degradation results demonstrated similar trends with the previoussolution phase analysis with the observed enhanced reaction rates. The advantage of themembrane system is its ability to prevent the agglomeration of the nanoparticles in themembrane matrix, to minimize the loss of precious metals into the bulk solution phase,and to prevent the formation of precipitated Fe(III) hydroxide. These are due to thechelating effect of the amine and hydroxyl functional groups in the chitosan backbones.

Biodiesel is the most successful drop-in biofuel used in transportation. It can reduce GHG emissions in transportation by 50 to 90% depending on the type of feedstock used. Waste cooking oils and fats containing free fatty acids (FFA) are less expensive feedstocks for biodiesel production than refined vegetable oils. The major issue that limits the use of these oils as feedstock is the interference of FFAs with widely used base catalyzed reaction processes. The FFAs consume base catalyst, produce water of neutralization and form soaps that create emulsions downstream in the process reducing process yields. There is an important need to develop technologies that reduce the FFA content in these oils to below 0.5 wt%; the accepted limit for a feedstock to be processed by the base catalysed reaction. Enzymes are an efficient and environmentally friendly catalyst for FFA esterification. However, they are prone to deactivation with methanol and also catalyze the hydrolysis of esters and triglycerides to FFA. Using them to pre-treat oils and fats remains a challenge: in the presence of water, enzymes can readily produce FFAs from lipids. The objective of this work was to investigate two enzymatic processes to pre-treat acidic oil below the FFA requirement of 0.5 wt%. In this study, two different continuous systems, a packed bed reactor (PBR) and membrane reactor (MR) were used in FFA enzymatic esterification to meet the 0.5 wt% requirement, improve the reusability of enzymes and reduce catalyst cost. The esterification in the PBR was carried out using CALB immobilized on a new 2D/3D nanoplatelet support (TAN). The enzyme was covalently bonded to the TAN using a hydrophobic epoxy ligand. Acidic oil containing canola oil and 2.5 wt% FFA was used as the feedstock for the esterification. It was found that the FFA concentration met the quality specification of <0.5 wt% using CALB-TAN, while it did not using the commercial Novozym 435. The surface fluid velocity was found to have an effect on the removal of water from the PBR reactor. When the velocity was too low, water was retained in the reactor and the FFA conversion was low, when it was too high the reaction time for esterification was not sufficient. It was found that feed velocity of 3 to 6 x 10-5 m/s met the 0.5 wt% requirement. In the PBR, the use of CALB-TAN successfully eliminated the hydrolysis of TG and achieved the continuous esterification of FFA for 42 days. In the MR, acidic oil containing canola oil and 10 wt% FFA was used as the feedstock for the esterification. The enzyme adsorbed on the surface of the polar phase containing glycerol and water and was successfully retained in the reactor by a 0.2-micron ceramic membrane. The addition of glycerol increased the polarity of the dispersed phase in the reactor, bounded water, and retained the liquid enzyme in the reactor. However, the added glycerol in the reactor increased the operating pressure of the reactor. The operating pressure was reduced by adding biodiesel to the feedstock prior to treatment. The lowest level of FFA from the 10 wt% FFA feedstock was 0.68 wt%. This would require a second polishing step to reach the required 0.5 wt%. The PBR and MR using CALB are technologies that limit the hydrolysis at low FFA concentrations and are promising for the pre-treatment of acidic feedstocks in base catalysed biodiesel processes.

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.

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.

L’objectif de cette étude portait sur la mise en œuvre de réacteur catalytique membranaire pour une application dans le traitement d’effluents liquides contaminés par des polluants organiques. Des phases catalytiques ont été déposées au sein des structures poreuses par différentes techniques afin de bien maîtriser la localisation des phases actives. L’optimisation des conditions opératoires a ensuite été réalisée. Ces matériaux sont actifs pour l’oxydation de polluants présents dans les effluents liquides et la configuration en mode contacteur a permis d’accroître l’efficacité et la stabilité des phases catalytiques pour ces réactions de dégradation grâce à un meilleur contact entre les réactifs et les sites actifs. / The aim of this study was to evaluate catalytic membrane reactor for wet oxidation efficiencies of pollutants in waste water. In a first part, we have prepared catalytic membrane using several techniques of deposition in order to well control the position of the active phase in the porous structure. After optimisation of the experimental parameters, the study of pollutant degradation has showed that catalytic membrane reactor, in contactor configuration present highest efficiency than conventional reactor due to optimized contacts between reactants and active sites.

Ce travail de thèse vise à développer un procédé de synthèse d'esters dans un réacteur enzymatique membranaire fonctionnant en milieu CO2 supercritique. Un tel procédé représente une alternative intéressante à la synthèse chimique classiquement utilisée en industrie car il permet, d'une part, d'utiliser le CO2 supercritique comme solvant et de substituer ainsi les solvants organiques généralement utilisés et, d'autre part, d'avoir un produit final doté d'un label naturel grâce à l'utilisation d'un catalyseur biologique. Dans cette étude, une membrane enzymatique de taille industrielle a été développée. Un pilote spécifique permettant la conduite de réactions enzymatiques en milieu supercritique a été conçu. Le procédé a été testé à l'aide d'une réaction modèle : la synthèse d'acétate d'anisyle à partir d'alcool et d'acétate de vinyle. L'influence de divers paramètres opératoires tels que la température, la pression, ou le débit sur les performances du procédé a été évaluée. Les performances du procédé ont été également comparées à celles d'un réacteur à lit fixe. / This study deals with the development of an enzymatic membrane reactor working in supercritical carbon dioxide for ester synthesis. This process is an alternative to the chemical synthesis classically used in industry because it allows, on the one hand, the use of supercritical carbon dioxide as a solvent instead of organic solvents and on the other hand it leads to natural label ester thanks to the use of a biological catalyst. In this work, an industrial size enzymatic membrane was developed. A special pilot plant was designed to achieve enzymatic reactions in supercritical carbon dioxide medium. The process was studied with a model reaction : the anisyl acetate synthesis from anisic alcohol and vinyl acetate. The impact of several operating conditions like temperature, pressure and flow rate on the process performances was studied. The enzymatic membrane developed in this study was active and showed an interesting conversion rate. The performances were compared to those obtained with a packed bed reactor.

No description available.

No description available.