Hollow Filler Based Mixed Matrix Membranes for Separation of Ethanol-Water Mixture By Pervaporation

The concept of mixed matrix membranes (MMMs)^[1] was developed in the field of membrane technology to overcome the limitations of polymeric and inorganic membranes.^[1-3] Polymeric membranes possesses limitations due to a general trade-off between flux and selectivity, often referred to as Robeson upper boundary.^[2] Although, inorganic membranes overcome this boundary, they are less used in applications due to the high costs for materials, defect-free preparation and up scaling.^[1] Mixed matrix membranes have the potential to combine high selectivities with high membrane fluxes.^{[1-3 ]} Zeolites are one of the most attractive inorganic fillers used in MMMs, as their defined pore structure increases the selectivity. The porous zeolite fillers reduced swelling of PDMS in the solvents like hexane, toluene without lowering the intrinsic fluxes. Zeolite-filled PDMS membranes have been developed for pervaporation which showed superior membrane performance.^[4]

In this work, membrane flux and selectivity is enhanced by the further development of a recent concept, applying hollow fillers.^[5] The incorporation of hollow spheres in micrometre size range with a hydrophobic shell consisting of nanosized zeolite-crystals in PDMS was investigated. A high increase in permeability was expected, since the hollow fillers allow a fast flow of the permeating compound. At the same time, selectivity  should be maintained by the hydrophobicity and crosslinking effect of the zeolite shell. Moreover, good dispersions should be realised easily. Examples of such hollow spheres are abundantly present in the literature. Many different synthesis techniques are employed, most commonly self-assembly and layer-by-layer deposition, to obtain hollow zeolite spheres of a variety of sizes and with different characteristics.^[6–7] In this work, self-synthesized hollow spheres are used, tuned and modified for the purpose.

References

[1]     T. S. Chung, L. Y. Jiang, Y. Li and S. Kulprathipanja, Prog. Polym. Sci., 32, 2007, 483.

[2]     L. M. Robeson, J. Membr. Sci, 62, 1991, 165.

[3]     C. M. Zimmerman, A. Singh, W. J. Koros, J. Membr. Sci., 137, 1997, 145.

[4]     R.D. Offeman, C.N. Ludvik J. Membr. Sci,  380, 2011, 163.

[5]     Vanherck. K, Aerts. A, Martens. J, Vankelecom. I,  Chem. Comm, 46, 2010, 2492.

[6]     S. P. Naik, A. S. T. Chiang, R. W. Thompson, F. C. Huang, Chem. Mater, 15, 2003, 787.[

[ 7]   A. Kulak, Y. J. Lee, Y. S. Park, H. S. Kim, G. S. Lee, K. B. Yoon, Adv. Mater, 14, 2002, 526.