Beatriz Seoane

Beba

Van der Maasweg 9, 2629 HZ Delft 
Tel: +31 (0)15-2786955
Fax: +31 (0) 15 2789821

B.SeoanedelaCuesta@tudelft.nl




Engineering Metal Organic Framework based  Mixed Matrix Membranes

Membrane-based separation processes have received significant attention as a promising technology due to their low energy consumption, operation flexibility and simplicity, good stability, easy control and scale-up.1-3 This is demonstrated by the fact that the combined U.S. market for membranes used in liquid and gas separating applications was estimated at approximately $ 1.7 billion in 2010, and is forecast to reach $ 2.3 billion in 2015. Particularly, when gas separation is taken under consideration, membrane technology is a viable commercial alternative compared to traditional separation processes such as distillation, low temperature condensation or adsorption processes.1 The first industrial application of membrane-based gas separation processes dates back to 1980, when Permea (now a division of Air Products) launched its hydrogen-separating polysulfone (PSF) membranes. Since then, membranes have experienced an exponential growth and they have found application in the separation of other gas mixtures, mainly air enriching, air dehydration and CO2/CH4 separation.1

According to their nature, membranes can be inorganic (generally ceramic or metallic), polymeric or liquid. Whilst ceramic or inorganic membranes may have applications in special cases due to their good permselectivity and high thermal and chemical stability, the majority of membrane based gas separation industrial processes use polymeric membranes because of their easy processability and low cost.4 For example, the estimated current price for a gas separating polymeric membrane is 20 €/m2 approximately, whereas that of inorganic microporous membranes, much more selective, could be around 2000 €/m2.5

However, as Robeson reported in 19916 (updated in 2008),7 there is a trade-off between permeability and selectivity in the separation of gas mixtures by polymers (see Figure). Therefore, despite the common use of membranes at an industrial scale in different processes, such as filtration, reverse osmosis or electrodialysis, gas separation is still in development and it is still necessary to propose and develop new materials and membrane structures to improve polymer permselectivity.

Figura Description Beba

 

Figure. Robeson’s plot for CO2/CH4 together with common permselectivity values for different fillers, such as zeolites or MOFs.

In recent years, several approaches have been developed to overcome this limitation. One approach, that started being explored during the 70’s by Paul and Kemp,8 is fabricating the so-called mixed matrix membranes (MMMs), which consist of a composite comprising two phases: a polymer matrix and a dispersed phase (also named fillers), normally porous. These hybrid membranes have the advantage of combining the benefits of both phases: the superior gas transport properties of the filler and the desirable mechanical properties, low prices and good processability of polymers.9

The first MMMs were prepared using conventional fillers such as zeolites, carbon molecular sieves and silicas. However, over the last few years new materials have been incorporated, e. g. carbon nanotubes, clay layered silicates, metal organic frameworks (MOFs) or graphene. One of the main problems of zeolite based MMMs is the formation of voids at the interface because of the poor affinity between the inorganic and the organic phase, thus lowering the selectivity of the membrane and therefore causing it to underperform.10 However, in the case of MOFs the organic ligand may improve the filler-polymer interaction, avoiding the presence of non-selective micro gaps.11 Moreover, MOFs have several advantages when compared with other traditional inorganic porous materials. Among them, it is worth mentioning their easier synthesis, the possibility of rational design of the structures in some cases, the affinity to some adsorbates of several members of this family of materials, their higher specific surface area and their flexibility.

In order to obtain MMMs with good permselectivity, several factors must be taken into account. Among them, pore size, dispersion, particle size and particle size distribution of the filler and its compatibility with the polymer matrix require special attention. For this reason, this project involves not only the preparation and characterization of MMM, but also the study of new strategies for MOFs synthesis (in order to achieve MOF particles with proper size and morphology, whose dispersion in the polymer would lead to a good contact between the matrix and the filler).

The aim of this project is the preparation of MOF based MMM in order to outperfomr the state of the art polymeric membranes for the separation of CO2 from CH4 and CO2 from N2 and opening up the non-existing membrane separation of light olefin/paraffin mixtures.

Acknowledgements

This research receives funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 335746, CrystEng-MOF- MMM


References

[1] Baker, R. W., Future directions of membrane gas separation technology, Industrial & Engineering Chemistry Research 2002, 41, 1393-1411.

[2] Schell, W. J., Commercial applications for gas permeation membrane systems, Journal of Membrane Science 1985, 22, 217-224.

[3] Koros, W. J.; Fleming, G. K., Membrane-based gas separation, Journal of Membrane Science 1993, 83, 1-80.

[4] Gascon, J.; Kapteijn, F.; Zornoza, B.; Sebastian, V.; Casado, C.; Coronas, J., Practical approach to zeolitic membranes and coatings: state of the art, opportunities, barriers, and future perspectives, Chemistry of Materials 2012, 24, 2829-2844.

[5] Gorgojo, P., Desarrollo de materiales laminares porosos para la preparación de membranas híbridas, PhD dissertation, Universidad de Zaragoza, Zaragoza 2010.

[6] Robeson, L. M., Correlation of separation factor versus permeability for polymeric membranes, Journal of Membrane Science 1991, 62, 165-185.

[7] Robeson, L. M., The upper bound revisited, Journal of Membrane Science 2008, 320, 390-400.

[8] Paul, D. R.; Kemp, D. R., Diffusion time lag in polymer membranes containing adsorptive fillers, Journal of Polymer Science Part C-Polymer Symposium 1973, 79-93.

[9] Goh, P. S.; Ismail, A. F.; Sanip, S. M.; Ng, B. C.; Aziz, M., Recent advances of inorganic fillers in mixed matrix membrane for gas separation, Separation and Purification Technology 2011, 81, 243-264.

[10] Moore, T. T.; Koros, W. J., Non-ideal effects in organic-inorganic materials for gas separation membranes, Journal of Molecular Structure 2005, 739, 87-98.

[11] Zornoza, B.; Tellez, C.; Coronas, J.; Gascon, J.; Kapteijn, F., Metal organic framework based mixed matrix membranes: an increasingly important field of research with a large application potential, Microporous and Mesoporous Materials, 2013, 166, 67-68.