Mixed-matrix membranes liquid-polymer

The strategy for the development of mixed-matrix membranes is to combine the advanced features of polymer membrane and inorganic membrane into one composite membrane. As discussed in the previous section, this is done by incorporating dispersed fillers into continuous polymer matrices. As noted in the introduction, there are three main types of mixed-matrix membranes reported in the literature solid-polymer, liquid-polymer, and solid-liquid-polymer mixed-matrix membranes. The polymer matrices providing low cost and easy processability are selected from either glassy polymers (e.g., polyimide, polysulfone, polyethersulfone, or cellulose acetate) or rubbery polymers (e.g., silicone rubber). The dispersed fillers include solid, liquid, or both solid and liquid. 

For the liquid-polymer mixed-matrix membranes, the physical state of the fillers incorporated into the continuous polymer matrix is liquid such as poly(ethylene glycol) (PEG). Because of the long-term stability concern of liquid polymer encapsulated in the continuous polymer matrix, a new type of mixed-matrix membranes, solid-hquid-polymer mixed-matrix membrane, has been developed recently. The solid such as activated carbon impregnated with liquid polymer such as PEG is functioned as stabilizer of the liquid polymer in the continuous polymer phase. Besides, activated carbon enhances the mixed-matrix membrane performance. 

For liquid-polymer mixed-matrix membranes, the physical state of the IUIcts incorparated into the continuous polymer matrix is hquid such as PEG and amines. The following section provides an introduction to this less common mixed-matrix technology. Since the existing hterature on this new type of membrane is less developed, more detail is provided here. 

Preparation of Liquid-Polymer Mixed-Matrix Membranes In one... 

In another approach, a liquid-polymer mixed-matrix membrane was prepared by first soaking a wet porous support membrane (e.g., polysulfone) in a solution containing liquid fillers (e.g., glycerol) for a period of 2 h, followed by drying for a period of 10 h at room temperature. The treated porous support membrane was then coated with the emulsified solution described above to form a liquid-polymer mixed-matrix membrane. 

Zeolite/polymer mixed-matrix membranes have been investigated for liquid separations such as purification ofp-xylene [76], separation of ethanol-water mixtures [93-96] and water desalination [83]. 

Another potential application for zeolite/polymer mixed-matrix membranes is the separation of various liquid chemical mixtures via pervaporation. Pervapora-tion is a promising membrane-based technique for the separation of liquid chemical mixtures, especially in azeotropic or close-boihng solutions. Polydime thy 1-siloxane (PDMS), which is a hydrophobic polymer, has been widely used as the continuous polymer matrix for preparing hydrophobic mixed-matrix membranes. To achieve good compatibility and adhesion between the zeolite particles and the PDMS polymer, ZSM-5 was incorporated into the PDMS polymer matrix, the resulting ZS M -5/ P DM S mixed-matrix membranes showed simultaneous enhancement in selectivity and flux for the separation of isopropyl alcohol from water. It was demonstrated that the separation performance of these membranes was affected by the concentration of the isopropyl alcohol in the feed [96]. 

Liu C, Kulprathipanja S, Schott ME, Wilson ST. Ionic liquid-solid-polymer mixed matrix membranes for gas separations. U.S. Patent 7943543 Bl 2011. 

Casado-Coterillo C, L6pez-Guerrero MM, Irabien A. Synthesis and characterisation of ETS-lO/acetate-based ionic liquid/chitosan mixed matrix membranes for CO /N permeation. Membranes 2014 4 287-301. Lianga L, Ganb Q, Nancarrowa P. Composite ionic liquid and polymer membranes for gas separation at elevated temperatures. J Membr Sci 2014 450 407-17. 

Hanid NA, Wahit MU, Guo Q, Mahmoodian S, Soheilmoghaddam M (2014) Development of regenerated cellulose/halloysites nanocomposites via ionic liquids. Carbohydr Polym 99 91-97 Hashemifard SA, Ismail AF, Matsuura T (2011) Mixed matrix membrane incorporated with large pore size halloysite nanotubes (HNT) as filler for gas separation experimental. J Colloid Interf... 

Mixed matrix membranes (MMM) consist of a nanopaiticle filler like zeolite, metal-organic framework ionic liquid or carbon, in a continuous polymer phase thereby combining the molecular sieving or another property of the filler with the established processability of the polymers in one membrane. The concept of zeolite-based mixed matrix membranes is followed for more than 30 years. However, in most cases these zeolite-based MMMs did not show an improvement of the selectivity because of an imperfect embedding of the zeolite crystals into the polymer matrix as shown schematically in Fig. 19. 

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. 

The use of polymeric catalytic membranes in distributor/contactor-type reactors for hydrogenation or oxidation reactions has been widely described in several former and recent reviews. Mixed-matrix membranes of PDMS hlled with Pd particles, composite membranes of ionic liquid-polymer gels filled with Pd/C, ° ionic liquids containing rhodium complexes and supported in polystyrene sheets in a corrugated configuration, have been used for the selective gas-phase hydrogenation of hydrocarbons in contactor-type membrane reactors. 

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