Zeolites mixed-matrix membranes

Most reported zeolite/polymer mixed-matrix membranes, however, have issues of aggregation of the zeolite particles in the polymer matrix and poor adhesion at the interface of zeolite particles and the polymer matrix. These issues resulted in mixed-matrix membranes with poor mechanical and processing properties and poor separation performance. Poor compatibility and poor adhesion between the polymer matrix and the zeolite particles in the mixed-matrix membranes resulted in voids and defects around the zeolite particles that are larger than the micropores of the zeolites. Mixed-matrix membranes with these voids and defects exhibited selectivity similar to or even lower than that of the continuous polymer matrix and could not match that predicted by Maxwell model [59, 60]. 

Pechar, T.W., Tspatsis, M., Marand, E., and Davis, R. (2002) Preparation and characterization of a glassy fluorinated polyimide zeolite mixed matrix membrane. Desalination, 146, 3-9. 

C., Tatlier, M., Erdem-Senatalar, A., Schoeman, B., and Sterte, J. (2000) Effect of zeolite particle size on the performance of polymer-zeolite mixed matrix membranes./. Membr. Sci., 175 (2), 285-288. 

Estimation of the interphase thickness and permeability in polymer-zeolite mixed matrix membranes... 

Suer MG, Ba N, Yilmaz L. Gas permeation characteristics of polymer-zeolite mixed-matrix membranes. J MembrSci 1994 91(l-2) 77-86. 

Khan, AL, Cano-Odena, A, Gutierrez, Minguilldn, C and Vankelecom, IFJ (2010), Hydrogen separation and purification using polysulfone acrylate-zeolite mixed matrix membranes, J Membr Sci, 350,340-346. 

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... 

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... 

Various zeolites have been studied as the dispersed phase in the mixed-matrix membranes. Zeolite performance in the zeolite/polymer mixed-matrix membrane is determined by several key characteristics including pore size, pore dimension, framework structure, chemical composition (e.g., Si/Al ratio and cations), crystal morphology and crystal (or particle) size. These characteristics of zeolites are summarized in Chapter 6. 

Mixed-matrix membranes comprising small-pore zeolite or small-pore non-zeolitic molecular sieve materials will combine the solution-diffusion separation mechanism of the polymer material with the molecular sieving mechanism of the zeolites. The small-pore zeolite or non-zeolitic molecular sieve materials in the mixed-matrix membranes are capable of separating mixtures of molecular species... 

Small-pore zeolite Nu-6(2) has a NSI-type structure and two different types of eight-membered-ring channels with limiting dimensions of 2.4 and 3.2 A [54]. Gorgojo and coworkers developed mixed-matrix membranes using Nu-6(2) as the dispersed zeolite phase and polysulfone Udel as the continuous organic polymer phase [55]. These mixed-matrix membranes showed remarkably enhanced H2/ CH4 selectivity compared to the bare polysulfone membrane. The H2/CH4 selectivity increased from 13 for the bare polysulfone membrane to 398 for the Nu-6(2)/ polysulfone mixed-matrix membranes. This superior performance of the Nu-6(2)/ polysulfone mixed-matrix membranes is attributed to the molecular sieving role played by the selected Nu-6(2) zeoHte phase in the membranes. 

The chemical composihons of the zeolites such as Si/Al ratio and the type of cation can significantly affect the performance of the zeolite/polymer mixed-matrix membranes. MiUer and coworkers discovered that low silica-to-alumina molar ratio non-zeolitic smaU-pore molecular sieves could be properly dispersed within a continuous polymer phase to form a mixed-matrix membrane without defects. The resulting mixed-matrix membranes exhibited more than 10% increase in selectivity relative to the corresponding pure polymer membranes for CO2/CH4, O2/N2 and CO2/N2 separations [48]. Recently, Li and coworkers proposed a new ion exchange treatment approach to change the physical and chemical adsorption properties of the penetrants in the zeolites that are used as the dispersed phase in the mixed-matrix membranes [56]. It was demonstrated that mixed-matrix membranes prepared from the AgA or CuA zeolite and polyethersulfone showed increased CO2/CH4 selectivity compared to the neat polyethersulfone membrane. They proposed that the selectivity enhancement is due to the reversible reaction between CO2 and the noble metal ions in zeolite A and the formation of a 7i-bonded complex. 

Zeolites used for the preparation of mixed-matrix membranes not only should have suitable pore size to allow selective permeation of a particular molecular component, but also should have appropriate particle size in the nanometer range... 

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