Molecular Organic Framework (MOF)-Polymer Architectures For Gas Separation

The control of anthropogenic carbon dioxide emission is one of the most important environmental concerns of the current era and is becoming more challenging with the rapid increase in global population, industrialization and energy demands. The major share of global energy is supported by burning of fossil fuels that is also responsible for the majority of carbon dioxide emissions. The increase of carbon dioxide is disturbing the carbon balance of our climate that influences the incoming and outgoing energy in the atmosphere, leading to global warming. Therefore, there is significant need of technologies that will reduce the level of carbon dioxide emission. The conventional carbon dioxide capture processes have high energy consumption due to the involved phase changes of constituents. A more energy efficient and cost effective process of carbon dioxide capture is through polymeric membranes but with many distinguishing advantages over conventional processes. However, performance of polymeric membranes is limited by a trade-off between membrane permeability and selectivity [1]. Over the last two decades, the research had focused on increasing the polymeric membranes performance above this trade-off curve to make it more cost competitive with conventional processes.

Mixed-matrix membranes, comprising of inorganic particles e.g. zeolites, carbon molecular sieves (CMS), metal peroxides (MOs), carbon nanotubes (CNTs), Metal organic frameworks (MOFs), dispersed in a continuous polymeric matrix provides an interesting approach for improving the gas separation properties of polymeric membranes [2]. Recent developments showed some promising features of MOFs as a gas storage media and adsorbent for gas separation. MOFs represent a class of porous materials that consist of an inorganic cluster connected by organic bridges and tuned into three dimensional arrangements (Figure 1). The high surface area, controlled porosity, adjustable chemical functionality, high affinity for certain gases and affinity with polymer chains, make them a potential candidate to make high performance mixed-matrix membranes. Virtually all designs and variations in both metal and organic linker in the MOFs are possible using appropriate chemistry [3]. MMMs frequently suffer from insufficient adhesion between the polymer matrix and the particles. However, the flexibility on MOFs design also allows us to tune the properties of the MOFs such that it integrates extensively with the polymer matrix and thus enhances the interaction between matrix polymer and particles to circumvent possible defects.

Schematic representation of the construction of MOFs.51–53

Figure 1: Schematic representation of the construction of MOFs [3]

In addition to aforementioned properties of MOFs, several of these MOFs have the striking feature of being selectively flexible during adsorption process. Different MOFs based mixed-matrix membranes have been investigated in the past but at low feed pressures with improved performance for gas separation [4-6].

This project focuses on the development of new MOFs and mixed-matrix membrane architectures for gas separation (e.g. CO2-CH4, N2-O2 etc.) with high permeability and selectivity. We study the incorporation of different MOFs in mixed-matrix membranes of different composition and effect of filler at low and elevated pressures. Next to material design and membrane fabrication in flat and hollow fiber geometries, the project focuses on the fundamental understanding of gas transport in dense gas separation membranes. It intends to identify structure-property relationships using material related characterization techniques (Thermal, SEM and spectroscopy) combined with sorption measurements.

This project is executed in the framework of the EU joint doctorate on Membrane Engineering (EUDIME). It will be performed in close collaboration with especially the University of Leuven (Belgium) and Institute Européene Montpellier (France).



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