Zeolite matrix composite membrane

Fig. 1 Schematic of the three types of zeolite membranes (A) a polycrystalline zeolite membrane (B) a zeolite matrix composite membrane and, (C) a zeolite crystal layer.

Different ways have been proposed to prepare zeolite membranes. A layer of a zeolite structure can be synthesized on a porous alumina or Vycor glass support [27, 28]. Another way is to allow zeolite crystals to grow on a support and then to plug the intercrystalline pores with a dense matrix [29], However, these two ways often lead to defects which strongly decrease the performance of the resulting membrane. A different approach consists in the direct synthesis of a thin (but fragile) unsupported monolithic zeolite membrane [30]. Recent papers have reported on the preparation of zeolite composite membranes by hydrothermal synthesis of a zeolite structure in (or on) a porous substrate [31-34]. These membranes can act as molecular sieve separators (Fig. 2), suggesting that dcfcct-frcc materials can be prepared in this way. The control of the thickness of the separative layer seems to be the key for the future of zeolite membranes. 

Since the pioneering work of Tehennepe et al. [108] in 1987 many efforts have been made filling the polymeric matrix with zeolites to improve their stability. There are several companies, such as Sulzer Chemtech, that offer pervaporation organic membranes and composite membranes [109]. 

One of the first zeolite based membranes were composite membranes, obtained by dispersion of zeolite crystals in dense polymeric films in order to make zeolite filled polymeric membranes [59,60,61], These membranes have been developed at the end of the 80 s for both gas separation and pervaporation. The clogging of zeolite pores by the matrix and the quality of the interface between the zeolite crystals and the polymer matrix (non-selective diffusion pathways) were key points. 

Since the pioneering work of Tehennepe et al. [152] in 1987, many efforts have been made filling the polymeric matrix with zeolites in order to improve their stability. There are several companies that offer pervaporation organic membranes and composite membranes such as Sulzer Chemtech [153]. Commercial pervaporation and vapor permeation installations utilize polymeric membranes, like PVA (Sulzer Chemtech), polyimide (Vaperma), per-fiuoropolymers (MTR and Compact Membrane Systems), and polyelectrolytes (GKSS) or ceramic membranes, like zeolite A (Mitsui, Mitsubishi, Inocermic) and silica... 

In particular, for the synthesis of optically pure chemicals, several immobilization techniques have been shown to give stable and active chiral heterogeneous catalysts. A step further has been carried out by Choi et al. [342] who immobilized chiral Co(III) complexes on ZSM-5/Anodisc membranes for the hydrolytic kinetic resolution of terminal epoxides. The salen catalyst, loaded into the macroporous matrix of Anodise by impregnation under vacuum, must exit near the interface of ZSM-5 film to contact with both biphasic reactants such as epoxides and water. Furthermore, the loading of chiral catalyst remains constant during reaction because it cannot diffuse into the pore channel of ZSM-5 crystals and is insoluble in water. The catalytic zeolite composite membrane obtained acts as liquid-liquid contactor, which combines the chemical reaction with the continuous extraction of products simultaneously (see Figure 11.28) the... 

Yawalkar et al. (2001) has developed a model for a three-phase reactor based on the use of a dense polymeric composite membrane containing discrete cubic zeolite particles (Fig. 4.5) for the epoxidation reaction of alkene. Catalytic particles of the same size are assumed vdth a cubic shape and uniformly dispersed across the polymer membrane cross-section. Effects of various parameters, such as peroxide and alkene concentration in liquid phase, sorption coefficient of the membrane for peroxide and alkene, membrane-catalyst distribution coefficient for peroxide and alkene and catalyst loading, have been studied. The results have been discussed in terms of a peroxide effidency defined as the ratio of flux of peroxide through the membrane utilized for alkene oxidation to the total flux of organic peroxide through the membrane. The paper aimed to show that, by using an organophilic dense membrane and the catalysts confined in the polymeric matrix, the oxidant concentration (in that reaction peroxides) can be controlled on the active site with an improvement of the peroxide efficiency and selectivity to desired products. 

Various treatment methods based on conventional, modem and hybrid technologies have been applied for remediation of F , U and As in many parts of the world. These techniques have been critically reviewed in this chapter. Metal organic framework based mixed-matrix membranes have been reported to outperform state-of-art polymers. These composite membranes containing various adsorbents/fillers such as zeolites have high application potential and should be studied further for removal of heavy metals from wastewater. 

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. 

The geometries for asymmetric mixed-matrix membranes include flat sheets, hollow fibers and thin-fihn composites. The flat sheet asymmetric mixed-matrix membranes are formed into spirally wound modules and the hollow fiber asymmetric mixed-matrix membranes are formed into hollow fiber modules. The thin-film composite mixed-matrix membranes can be fabricated into either spirally wound or hollow fiber modules. The thin-film composite geometry of mixed-matrix membranes enables selection of different membrane materials for the support layer and low-cost production of asymmetric mixed-matrix membranes utilizing a relatively high-cost zeolite/polymer separating layer on the support layer. 

Jia and coworkers prepared thin-film composite zeolite-filled silicone rubber membranes by a dip-coating method [82]. The membranes have a thin silicalite-1/ silicone rubber mixed-matrix selective layer on top of a porous polyetherimide support. 

Buttal, T., Bac, N., and Yilmaz, L. (1995) Effect of feed composition on the performance of polymer-zeolite mixed matrix gas separation membranes. Sep. Sci. Technol, 30 (11), 2365-2384. 

Figure 33 Composite catalytic membrane as heterogeneous cytochrome P-450 mimic, matrix polydimethylsiloxane (PDMS), filler FePc-loaded zeolite Y (30 wt%) [91]...

Figure 11.19b. The most studied structure is the MFI, followed by LTA, and a similar number of publications could be found about FAU and MOR. The section others corresponds to FER, BETA, MEL, ZSM-11, and related materials like ETS-10 or ETS-4. The distribution of the zeotypes studied in the period 2(X)5-2011 does not change that much, although the proportion of mixed matrix membranes or composites decreases to approximately 10%. The number of publications referred to MFI, FAU, LTA, or MOR is multiplied by three compared to the period 1995-2(X)5 and CHA structure has also been introduced. After the excellent review published by Falconer and Noble in 2004 [158], the work on pervaporation and zeolites has been reviewed in specific or general reviews of zeolite membranes and pervaporation [1,3,159].

The CS-based mixed matrix membranes are also suitable for pervaporation application. Patil and Aminbhavi [96] prepared mixed matrix membranes of CS by incorporating sili-calite zeolite particles in 5 and 10 wt.% for the pervaporation separation of toluene/methanol and toluene/ethanol feeds in compositions of 10-40 wt.% of toluene at 30°C. The membranes were toluene selective than alcohol selective. Flux of toluene/methanol and toluene/ethanol mixtures decreased, but selectivity increased with increasing alcohol content of the feed. Toluene permeated preferentially with a selectivity of 264 and fluxes of 0.019-0.027 kg/m h for toluene/ methanol mixture. Selectivity of 301 with fluxes ranging from 0.019 to 0.026 kg/m h was observed for tolnene/etha-nol mixtures. Flux increased, while selectivity decreased with increasing toluene content of the feeds. An increase in silicalite content of the MMMs gave increased pervaporation performances. 

The available range of membrane materials includes polymeric, carbon, silica, zeolite and other ceramics, as well as composites. Each type of membrane can have a different porous structure, as illustrated in Figure 5.2. Membranes can be thought of as having a fixed (immovable) network of pores in which the gas molecule travels, with the exception of most polymeric membranes [28,44]. Polymeric membranes are composed of an amorphous mix of polymer chains whose interactions involve mostly van der Waals forces. However, some polymers reveal a behaviour that is consistent with the idea of existence of opened pores within their matrix. This is especially true for high free volume, high... 

A promising route to membranes of improved transport characteristics consists in incorporation of inorganic additives with suitable structure (e.g., zeolites, carbon molecular sieves, microporous silica) into polymer matrix [17]. Some of polymer-inorganic composite materials showed much higher permeabilities but similar or even improved selectivity... 

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