Chemical and Biomolecular Engineering - Theses

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End date: 2019 × Start date: 2010 × Subject: gas separation × Subject: membrane × Subject: polymer ×

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    Dimensional design of the polymer/MOF composite structure for gas separation membranes
    Xie, Ke ( 2017)
    Global warming and climate change concerns have triggered global efforts to reduce the emission of carbon dioxide (CO2) to atmosphere. Post-combustion CO2 capture (PCC) is considered a crucial strategy for meeting this reduction targets. Membrane based separation technics are attractive in this field, representing the potential for a more energy efficient and eco-friendly separation process. Polymers are popular materials in gas separation membranes due to their high processability, mechanical strength and good selectivity. On the other hand, the metal-organic frameworks (MOFs) are also used in such membranes owing to their high porosity, which in turn leading to high gas permeability. In most of the current membrane studies, the MOFs merely serve as additives to polymer, i.e. the MOF particle is blended into polymer membrane to yield the mixed-matrix membrane (MMM). Therefore, the potential of MOF in gas separation applications are not fully developed. In addition, the effects of MOF morphology are not fully investigated yet. This thesis reports on several novel configurations of MOF/polymer composite structure and their applications in gas separations via membrane technology. The presentation is organized by the manipulation of MOF crystal morphologies, and the efficient use of different MOF topologies are demonstrated too. This study results in several novel membrane materials with excellent CO2/N2 separation performance. The relationship between performance and membrane architecture is investigated. In the 1st part, a novel polymer@metal-organic framework nanoparticle (P@MOF) was prepared via an in-situ ATRP on the surface of MOF nanoparticles. The P@MOF shows excellent pH dependent water dispersity, and used as the pH smart catalyst carrier. The investigation on the catalytic effect on 4-nitrophenol reduction clearly shows the efficient integration of the advantage from both heterogeneous and homogeneous catalysts. The 2nd part of this study directly applied the P@MOF particles in gas separation membranes. A novel approach to improve the selectivity of mixed matrix membrane (MMM) systems was developed. MOF nanoparticles (NPs) were chemical coated by a PEG based shell and then incorporated into a polymer matrix to yield a MMM. The unique design of the core-shell MOF NPs can enhance both the membrane permeability and selectivity simultaneously. This membrane material thus exhibits excellent CO2/N2 separation performance that surpasses the latest upper bound through the most direct way. This filler was also applied in the thin-film composite membrane system, showing promising performance located in the optimized zone for post-combustion CO2 capture proposed by Merkel et al. In the 3rd part, we have developed a bottom-up approach to fabricate an ultra-thin (~30 nm), continuous and defect-free polymeric membrane on a rough micro-scale MOF layer. This polymer-on-MOF architecture exhibits promising CO2/N2 separation performance with a CO2 permeance of > 3,000 GPU and a CO2/N2 selectivity of 34. To the best of our knowledge, this membrane has the best CO2/N2 separation performance compared to any membrane reported in the open literature. A novel concept of MMM is introduced in final part. This novel MMM has a unique configuration that the MOF fibres form a continuous interconnected sheet prior to the formation of polymer. Owing to this unique configuration, the permeability of the polymer is enhanced by 19 times without significant loss of selectivity, and surpasses the CO2/N2 separation upper bound.