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Crystal Engineering of Metal Organic Frameworks for application in Mixed Matrix Membranes

Final Report Summary - CRYSTENG-MOF-MMM (Crystal Engineering of Metal Organic Frameworks for application in Mixed Matrix Membranes)

Gas separation membranes offer a number of benefits over other gas separation technologies. Conventional technologies such as the cryogenic distillation, adsorption, condensation and amine absorption require a gas–liquid phase change. This phase change adds a significant energy cost. Membrane gas separation, on the other hand, does not require a phase change. In addition, gas separation membrane units are smaller than other types of plants, such as amine stripping plants, and therefore have relatively small footprints. The lack of mechanical complexity in membrane systems is another advantage. To date, only polymeric membranes have found their way towards large-scale industrial implementation in gas separation. This is to a large extent due to their easy processing and mechanical strength. However, a poor resistance to contaminants, low chemical and thermal stability and a limit in the trade-off between permeability and selectivity, the so called Robeson upper bound limit are among their main disadvantages. In parallel to the development of polymeric membrane materials, much research effort has been devoted to develop pure inorganic membranes. Although inorganic membranes offer unique properties for gas separation (i.e. excellent thermal and chemical stability, good erosion resistance and high gas flux and selectivity), certain aspects still require further attention such as mechanical resistance, reproducibility, long term stability, scaling up and, more importantly, fabrication costs. Mixed Matrix Membranes (MMMs) potentially combine the advantages in separation performances of both inorganic and polymeric membranes and overcome their drawbacks, although it introduces the issue of compatibility between the constituents.
This project has contributed to eliminate the above mentioned drawbacks of MMMs by using a new type of filler materials, the so-called metal organic frameworks (MOFs). Within the Cryst-Eng-MOF-MMM project, we have worked in three fundamental aspects of membrane development, namely: (1) understanding of crystallisation to be able to tune the MOF filler at different length scales, (2) optimisation of membrane preparation and performance, (3) gaining understanding by combining state of the art characterisation and rigorous membrane performance testing. Overall, we have been among the first to highlight the great potential that MOFs offer in this field of research, reporting some of the best performing membranes to date (specially for the separation of carbon dioxide). More importantly, we believe that research within the CrystEng-MOF-MMM project has been instrumental to boost worldwide research into these composites.