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Pervaporation Separation of Butanol Using PDMS Mixed Matrix Membranes

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Pervaporation Separation of Butanol Using PDMS Mixed Matrix Membranes Pervaporation separation of butanol using PDMS mixed matrix membranes Hoda Azimi Thesis submitted In partial fulfilment of the requirements For the Doctorate in Philosophy in Chemical Engineering degree Department of Chemical and Biological Engineering Faculty of Engineering University of Ottawa © Hoda Azimi, Ottawa, Canada, 2017 Abstract ii Abstract The increased demand of fossil fuel along with the depletion of economical crude oil resources, environmental challenges such as the accumulation of CO2 and other greenhouse gases in the atmosphere and the reduction of the dependence on imported oil are some of the motivations for the huge interest in biofuels. Biobutanol produced from ABE fermentation has been considered to be a good partial replacement for fossil fuels. However, challenges such as the need for inexpensive feed-stocks, improved fermentation performance to achieve higher final butanol concentration and higher yield, an efficient method for solvent recovery, and water recycle are the main obstacles to make the production of this alcohol economically viable. Pervaporation, a membrane-based process, is considered to be an attractive separation method to remove butanol from ABE fermentation broth. Among the membranes used for butanol separation, PDMS membranes showed reasonable performance such as good permeability, and appropriate selectivity for butanol separation by pervaporation. However, PDMS membranes need to be improved in terms of performance to be applicable in large scale butanol production plants. In this study, activated carbon nanoparticles have been embedded into the matrix of the PDMS membrane to improve its separation performance and, in particular, the permeation flux and butanol selectivity. Result showed that the presence of nanoparticles improves the PDMS membrane performance up to a certain particle loading. Moreover, it was shown that the operating conditions have a major impact on the pervaporation membrane separation process. The best membrane for pervaporation separation of butanol from binary aqueous solutions was obtained for a 6 wt% particle concentration where the total permeation flux and butanol selectivity increased by 42.6% and 51.9%, respectively, compared to neat PDMS membranes. Moreover, the best performance for the separation of butanol from ABE model solutions was achieved for an 8 wt% nanoparticle loading. Both the selectivity for butanol and the total permeation flux more than doubled in comparison to neat PDMS membranes prepared in this study. Moreover, in order to compare the PDMS/AC mixed matrix membrane performance for pervaporation separation of butanol from binary and ABE model solutions with PDMS membranes available on the market, experiments were also performed with a commercial PDMS membrane. Result of butanol separation from ABE model solutions showed that mixed matrix Abstract iii membranes with 8 wt% nanoparticles loading had a higher permeation flux than that of the commercial membranes. It was clearly shown that the presence of activated carbon nanoparticles in the matrix of the PDMS would be beneficial for the pervaporation separation of butanol from ABE fermentation broths. To better comprehend how the presence of activated carbon nanoparticles in the polymeric membranes enhance the performance of the membranes, a series of numerical simulations were performed. A finite difference model was developed to simulate the mass transfer of permeating components through mixed matrix membranes by pervaporation for a wide range of relative permeability, nanoparticle loading, particle shape, particle size and different filler adsorption isotherms. Finally, an investigation has been performed to optimize the butanol pervaporation separation process from ABE fermentation broth at an industrial scale. Résumé iv Résumé La demande accrue en combustibles fossiles ainsi que l'épuisement des sources économiques de pétrole brut, les défis environnementaux tels que l'accumulation de CO2 et d'autres gaz à effet de serre dans l'atmosphère et la réduction de notre dépendance à l'égard du pétrole importé sont quelques-unes des raisons de l'intérêt énorme en biocarburants. Le biobutanol produit par la fermentation ABE a été considéré comme un bon remplacement pour les combustibles fossiles. Cependant, des défis tels que la nécessité de matières primaires peu coûteuses, des performances de fermentation améliorées pour atteindre une concentration finale de butanol et un rendement plus élevé, une méthode efficace pour la récupération des solvants et le recyclage de l'eau sont les principaux obstacles pour rendre cet alcool économiquement viable. La pervaporation, un procédé membranaire, a été suggérée comme un bon procédé pour extraire partiellement le butanol de la fermentation ABE. Parmi les membranes utilisées pour la séparation du butanol, les membranes en PDMS ont montré des performances raisonnables telles qu'une bonne perméabilité et une sélectivité appropriée pour la séparation du butanol par pervaporation. Cependant, les membranes en PDMS devraient être améliorées en termes de performance pour leur utilisation dans les usines de production de butanol à grande échelle. Dans cette étude, des nanoparticules de carbone activé ont été incorporées dans la matrice de les membranes en PDMS pour améliorer leur performance. Les résultats ont démontré que la présence de nanoparticules améliorait la performance des membranes jusqu'à un certain pourcentage de particules et que les conditions de fonctionnement ont un effet important sur la performance des membranes. La meilleure membrane pour la séparation par pervaporation du butanol à partir d'une solution aqueuse binaire contenait une concentration de 6% sur une base massique de particules et augmentait le flux et la sélectivité de 42,6% et 51,9%, respectivement par rapport à une membrane sans nanoparticules. De plus, une membrane en PDMS contenant 8% sur une base massique de particules a obtenu les meilleures performances pour la séparation du butanol de la solution modèle ABE. La sélectivité pour le butanol et le flux de perméation total a plus que doublé pour cette membrane par rapport aux membranes en PDMS pur préparée dans cette étude. Résumé v Pour mieux comprendre la raison de l’amélioration des performances par l’ajout des particules, la deuxième équation de Fick a été solutionnée par différences finies pour calculer le profil de concentration et le flux pour une membrane à matrice mixte. Enfin, une analyse mathématique a été effectuée pour optimiser le procédé de séparation par pervaporation butanol à partir du bouillon de fermentation ABE à l'échelle industrielle. Statement of contributions of collaborators vi Statement of contributions of collaborators Chapter 2, entitled “Effect of embedded nano-activated carbon on the performance of Polydimethylsiloxane (PDMS) membrane for pervaporation separation of butanol”, was thoroughly suggested by me. I proposed the use of carbon nanoparticles, designed the experimental setup and performed all experiments. I wrote the first draft of the paper and performed all revisions based on the editorial suggestions and comments of my supervisors and external reviewers. Chapter 3, entitled “Separation of butanol from ABE model solutions via pervaporation using AC/PDMS/PAN mixed matrix membranes”, was thoroughly suggested by me. Arian Ebneyamini helped on with some experiments related to membrane swelling measurements and pervaporation tests. I wrote the first draft of the paper and made numerous revisions based on the comments of my supervisors. Chapter 4, entitled “The impact of pH on VLE, pervaporation and adsorption of butyric acid solutions”, was coordinated and managed by me. Two COOP students assisted in performing some experiments under my supervision: (1) Hervé Guérin Kamwa helped on pervaporation and VLE experiments, and (2) Chinue Joisse De La Merced helped in adsorption experiments. I wrote the first draft of the paper and made numerous revisions based on the comments of my supervisors. Dr. Jules Thibault provided supervision and guidance throughout this series of experiments. Chapter 5, entitled “Separation of butanol using pervaporation technique: A review of mass transfer models”, is a literature review. I took the initiative to write this review with the objective to learn about the models currently used for butanol pervaporation. I wrote the first draft of the paper and made numerous revisions based on the comments of my supervisors. Chapter 6, entitled “On the Effective Permeability of Mixed Matrix Membranes”, was suggested by Dr. Jules Thibault as a way to better understand the role of nanoparticles in enhancing mixed matrix membrane performance. This work was performed conjunctly with Dr. Jules Thibault. I wrote the first draft of the paper and made numerous revisions based on the comments of my supervisors. Statement of contributions of collaborators vii Chapter 7, entitled “Optimization of the in-situ recovery of butanol from ABE fermentation broth via pervaporation”, was performed conjunctly with Dr. Jules Thibault. I provided the equations and required information on pervaporation. Simulation, optimization and coding was performed by Dr. Jules Thibault. I wrote the first draft of the paper and made numerous revisions based on the comments of my supervisors. Acknowledgments viii Acknowledgments First and for most I would like to thank my supervisors Dr. Jules Thibault and Dr. Handan Tezel for their patient guidance, encouragement and advice they have provided throughout
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