A bench-scale, sweeping gas, flat-sheet Membrane Distillation (MD) unit was used to assess the importance of membrane architecture and operational variables to distillate production rate. Sweeping gas membrane distillation (SGMD) was simulated for various membrane characteristics (material, pore size, porosity and thickness), spacer dimensions and operating conditions (influent brine temperature, sweep gas flow rate and brine flow rate) based on coupled mass and energy balances. Model calibration was carried out using four membranes that differed in terms of material selection, effective pore size, thickness and porosity. Membrane tortuosity was the lone fitting parameter. Distillate fluxes and temperature profiles from experiments matched simulations over a wide range of operating conditions. Limitations to distillate production were then investigated via simulations, noting implications for MD design and operation. Under the majority of conditions investigated, membrane resistance to mass transport provided the primary limitation to water purification rate. The nominal or effective membrane pore size and the lumped parameter epsilon/delta tau (porosity divided by the product of membrane tortuosity and thickness) were primary determinants of membrane resistance to mass transport. Resistance to Knudsen diffusion dominated membrane resistance at pore diameters <0.3 mu m. At larger pore sizes, a combination of resistances to intra-pore molecular diffusion and convection across the gas-phase boundary layer determined mass transport resistance. Findings are restricted to the module design flow regimes considered in the modeling effort. Nevertheless, the value of performance simulation to membrane distillation design and operation is well illustrated.

Separation technologies with polymeric membranes are widely studied and have a wide range of applications. The membrane's heart is a dense selective layer whose permeability should strongly depend on the permeating species' properties. In turn, permeability depends on the diffusivity and solubility of the permeating species in the selective layer, which are considered intrinsic properties of the polymer forming the selective layer. When developing new membrane materials, the ultimate objective is to exceed the famous "upper bound" limit by achieving simultaneously higher selectivity and higher permeability. This objective is impossible without a reliable and accurate characterization method to determine the selective layer's intrinsic transport properties. The time-lag method is the most common membrane characterization technique, initially developed for polymeric membranes. However, as the membrane technology and material science advance, the selective layer structure becomes more complex and not limited to organic polymers. As a result, the time-lag method needs to be reviewed and adapted to these more complicated cases, which was the main objective of this thesis. Numerical simulation of dynamic gas permeation experiments is a powerful tool to examine different aspects of the time-lag method. Therefore, we have established a comprehensive variable-mesh finite-difference scheme, which was used throughout the thesis. It allowed us to investigate the effect of different random and resolution errors and an extrapolation error on the resulting time lag of an ideal membrane. We then considered more complex systems, particularly those of glassy polymers and mixed matrix membranes, to investigate the effect of different transport mechanisms on the results of dynamic and steady-state gas permeation experiments. In parallel, we also focused on developing a novel gas permeation system that would monitor dynamic gas permeation experiments based on pressure decay at the feed side. All the existing constant-volume gas permeation systems rely on monitoring pressure to rise at the membrane's permeate side. Although this work is still ongoing, we have made considerable progress. Among the numerous contributions made through this thesis, there are three of particular significance. We have developed an analytical model to predict mixed matrix membranes' relative permeability with the uniformly dispersed non-permeable fillers of different shapes. The model requires three structural parameters arising from the filler's shape and size, and it is superior to all existing analytical models, including the famous Maxwell model. We have also demonstrated that the diffusivity of mixed matrix membranes determined by the time-lag method depends on the number of layers of dispersed particles. In the limiting case of a single layer of uniformly impermeable fillers, it is possible for the diffusivity determined by the time-lag method to be greater than that of the host polymer, which might appear as counterintuitive in the absence of defects at the polymer-particle interface. In the case of glassy polymers, it is possible to observe an upward deviation from the steady-state flux, resulting from a non-instantaneous equilibrium between permeating species in Henry's and Langmuir adsorption sites.

Cette thèse présente une approche originale du procédé de distillation membranaire avec balayage gazeux pour la concentration des solutions thermosensibles (SGMD). Pour ce faire, un nouveau contacteur membranaire avec des fibres creuses métalliques a été conçu afin réaliser le procédé de distillation à basse température. La chaleur nécessaire au procédé est produite au niveau des fibres par effet Joule, plutôt qu'à partir de chaleur latente de la phase aqueuse. La génération localisée de la chaleur a comme conséquence une réduction du phénomène de polarisation de la température. Des fibres creuses en acier inoxydable ont été synthétisées avec les propriétés structurales appropriées et une bonne résistance mécanique. La surface des pores des fibres a été rendue hydrophobe par le dépôt d'une fine couche d'un élastomère. En outre, une nouvelle méthode « verte » a été développée pour fabriquer des fibres creuses en alumine et acier inoxydable. Cette méthode est basée sur la gélification ionique des bio-polymères et ne n'utilise pas des solvants nocifs. L'étude expérimentale détaillée du SGMD a permis de déterminer l'influence de différents paramètres opérationnels sur les performances du procédé. Il a été démontré que l'effet Joule permet d'améliorer le flux et l'efficacité de la séparation non seulement pour le SGMD mais aussi pour la pervaporation. / This thesis presents an original approach for the concentration of thermo-sensitive solutions: the Sweep Gas Membrane Distillation (SGMD) process. A new membrane contactor with metallic hollow fibers has been designed and allows the distillation process to be operational at low temperature. Heat is generated in the fibers by the Joule effect, rather than being supplied as latent heat in the liquid bulk. The localized generation of heat results in a reduction of temperature polarization phenomena. The stainless-steel hollow fiber membranes have been synthetized with appropriate structural properties and sufficient mechanical strength. The pore surface of the fibers has been made hydrophobic by the deposition of a thin layer of an elastomer. Moreover, a novel and green method is presented to fabricate alumina and stainless-steel hollow fibers. This method is based on ionic gelation of a biopolymer and completely avoids the use of harmful solvents. By a detailed experimental study of the SGMD the influence of different operational parameters on the process performance has been investigated. The improvements in the flux and the separation efficiency using Joule effect have been successfully demonstrated, even in the case of pervaporation.

Dans cette thèse ont été développés des modèles mathématiques pour les procédés de distillation membranaire à contact direct (DCMD) et avec balayage gazeux (SGMD) ainsi qu’un modèle sur l’hydrodynamique des bioréacteurs membranaires anaérobiques (AnMBRs) équipés d’un système de vibration membranaire induite (MMV). Les modèles pour la DCMD et la SGMD permettent de simuler le comportement des modules plats ou à fibres creuses sous différentes conditions opératoires, sans avoir recours aux données expérimentales ou à des équations empiriques pour les transferts de masse et de chaleur. Les modèles ont été validés avec des résultats expérimentaux et de la littérature et ont permis de déterminer l'influence de différents paramètres opérationnels et de la géométrie des modules sur les performances des procédés. Le modèle développé pour les AnMBRs équipés du système MMV permet d’étudier l’effet de la vibration membranaire sur l’hydrodynamique du réservoir. L’analyse paramétrique a permis d’étudier l’effet de la fréquence et de l’amplitude des vibrations sur la vitesse du fluide et la fraction volumique des solides dans le réservoir. Dans ce travail il a été démontré que les modèles proposés pourront être potentiellement appliqués à des études expérimentales préliminaires, l’optimisation des conditions opératoires, la conception des modules membranaires ainsi que pour l’estimation des coûts des procédés. / In this work have been developed general predictive models for direct contact membrane distillation (DCMD) and sweeping gas membrane distillation (SGMD) as well as a hydrodynamic model for anaerobic membrane bioreactors (AnMBRs) equipped with the induced membrane vibration (MMV) system. The DCMD and SGMD models allow simulating hollow fibre and flat sheet configurations under wide range of process conditions without empirical mass and heat transfer coefficients or laboratory experiments. The models have been validated with experimental and literature data. Indeed, the influence of operating conditions and membrane geometric characteristics on the process performance has been investigated. The model for AnMBRs with MMV studies the effect of the membrane vibration on the hydrodynamics of the AnMBR tank. The parametric study allows knowing, the effects of the vibration frequency and amplitude on the fluid velocity and volume fraction of solids. The conducted studies prove that all the proposed models would be potentially applied for the pre-experimental study, optimization of process conditions, design of membrane modules as well as for the further cost estimation of the processes.