Mixed matrix membrane

Zeolite/polymer mixed-matrix membranes can be fabricated into dense film, asymmetric flat sheet, or asymmetric hollow fiber. Similar to commercial polymer membranes, mixed-matrix membranes need to have an asymmetric membrane geometry with a thin selective skin layer on a porous support layer to be commercially viable. The skin layer should be made from a zeohte/polymer mixed-matrix material to provide the membrane high selectivity, but the non-selective porous support layer can be made from the zeohte/polymer mixed-matrix material, a pure polymer membrane material, or an inorganic membrane material. 

Current polymeric materials are inadequate to fully meet all requirements for the various different types of membranes (cf. Section 2.2) or to exploit the new opportunities for application of membranes. Mixed-matrix membranes, comprising inorganic materials (e.g., metal oxide, zeolite, metal or carbon particles) embedded in an organic polymer matrix, have been developed to improve the performance by synergistic combinations of the properties of both components. Such improvement is either with respect to separation performance (higher selectivity or permeability) or with respect to membrane stability (mechanical, thermal or chemical). 

In contrast to ordinary membranes, mixed matrix membranes are composed of an organic polymer and therein embedded inorganic particles such as zeolites, carbon molecular sieves, or nanoparticles. Mixed matrix membranes are believed to achieve higher performance than conventional polymeric membranes. In addition, the poor mechanical properties of inorganic membranes can be improved by embedding them in a flexible polymeric matrix. ... 

J. Campbell, G. Szekely, R.P. Davies, D.C. Braddock, A.G. Livingston, Fabrication of hybrid polymer/metal organic framework membranes mixed matrix membranes versus in situ growth, Journal of Materials Chemistry A 2 (2014) 9260-9271. 

Potential of adsorbents/fillers in membranes (mixed-matrix membranes)... 

Based on the need of a more efficient membrane than polymer and inorganie membranes, a new type of membranes, mixed-matrix membranes, has been developed recently. Mixed-matrix membranes are hybrid membranes containing solid, liquid, or both solid and liquid fillers embedded in a polymer matrix." The various material combinations possible with mixed-matrix technology are represented in Figure 30.2. All of these combinations, with the exception of supported liquids, will be covered in this chapter. 

J. (1986) Mixed matrix membrane for separation of gases. US Patent 6,726,744. 

This chapter provides a brief introduction to polymer and inorganic zeolite membranes and a comprehensive introduction to zeolite/polymer mixed-matrix membranes. It covers the materials, separation mechanism, methods, structures, properties and anticipated potential applications of the zeolite/polymer mixed-matrix membranes. 

Both zeolitic and non-zeolihc inorganic materials have been used as the dispersed phase for making mixed-matrix membranes. 

Up to now, a variety of non-zeolite/polymer mixed-matrix membranes have been developed comprising either nonporous or porous non-zeolitic materials as the dispersed phase in the continuous polymer phase. For example, non-porous and porous silica nanoparticles, alumina, activated carbon, poly(ethylene glycol) impregnated activated carbon, carbon molecular sieves, Ti02 nanoparticles, layered materials, metal-organic frameworks and mesoporous molecular sieves have been studied as the dispersed non-zeolitic materials in the mixed-matrix membranes in the literature [23-35]. This chapter does not focus on these non-zeoUte/polymer mixed-matrix membranes. Instead we describe recent progress in molecular sieve/ polymer mixed-matrix membranes, as much of the research conducted to date on mixed-matrix membranes has focused on the combination of a dispersed zeolite phase with an easily processed continuous polymer matrix. The molecular sieve/ polymer mixed-matrix membranes covered in this chapter include zeolite/polymer and non-zeolitic molecular sieve/polymer mixed-matrix membranes, such as alu-minophosphate molecular sieve (AlPO)/polymer and silicoaluminophosphate molecular sieve (SAPO)/polymer mixed-matrix membranes. 

Zeolite/polymer mixed-matrix membranes are excellent candidates to address the issues of both polymer membranes and zeolite membranes. Kulprathipanja... 

Concept of Zeolite/Polymer Mixed-Matrix Membranes... 

It has been reported in the literature that the properties of mixed-matrix membranes can be predicted by using a Maxwell model [40]. The Maxwell model equa-hon is as follows ... 

Concept of Zeolite/Polymer Mixed-Matrix Membranes 335 Pz+2Pp-2[Pg.335]

In Eq. (11.1), P is permeability, < z is the volume fraction of the dispersed zeolite, the MMM subscript refers to the mixed-matrix membrane, the P subscript refers to the continuous polymer matrix and the Z subscript refers to the dispersed zeolite. The permeabiUty of the mixed-matrix membrane (Pmmm) can be estimated by this Maxwell model when the permeabilities of the pure polymer (Pp) and the pure zeoUte (Pz), as well as the volume fraction of the zeoUte (< ) are known. The selectivity of the mixed-matrix membrane for two molecules to be separated can be calculated from the Maxwell model predicted permeabiUties of the mixed-matrix membrane for both molecules. 

Figure 11.2 Selection of proper zeolite material for a mixed-matrix membrane (MMM) using the Maxwell model.

The Maxwell model can also guide the selection of a proper polymer material for a selected zeolite at a given volume fraction for a target separation. For most cases, however, the Maxwell model cannot be applied to guide the selection of polymer or zeolite materials for making new mixed-matrix membranes due to the lack of permeabihty and selectivity information for most of the pure zeolite materials. In addition, although this Maxwell model is well-understood and accepted as a simple and effective tool for estimating mixed-matrix membrane properties, sometimes it needs to be modified to estimate the properties of some non-ideal mixed-matrix membranes. 

The development of a successful zeolite/polymer mixed-matrix membrane with properties superior to the corresponding polymer membrane depends upon good performance match and good compatibility between zeolite and polymer materials, as well as small enough zeolite particle size for membrane manufacturing on a large scale. 

Glassy polymers with much higher glass transition temperatures and more rigid polymer chains than rubbery polymers have been extensively used as the continuous polymer matrices in the zeolite/polymer mixed-matrix membranes. Typical glassy polymers in the mixed-matrix membranes include cellulose acetate, polysul-fone, polyethersulfone, polyimides, polyetherimides, polyvinyl alcohol, Nafion , poly(4-methyl-2-pentyne), etc. 

It has been demonstrated by many studies that mixed-matrix membranes with a good match between the permeabihty of proper zeolite materials and these glassy polymers exhibit separahon properties superior to the corresponding pure glassy... 

---