Composite membranes silica

Monoglyceride (MG) is one of the most important emulsifiers in food and pharmaceutical industries [280], MG is industrially produced by trans-esterification of fats and oils at high temperature with alkaline catalyst. The synthesis of MG by hydrolysis or glycerolysis of triglyceride (TG) with immobilized lipase attracted attention recently, because it has mild reaction conditions and avoids formation of side products. Silica and celite are often used as immobilization carriers [281], But the immobilized lipase particles are difficult to reuse due to adsorption of glycerol on this carriers [282], PVA/chitosan composite membrane reactor can be used for enzymatic processing of fats and oils. The immobilized activity of lipase was 2.64 IU/cm2 with a recovery of 24%. The membrane reactor was used in a two-phase system reaction to synthesize monoglyceride (MG) by hydrolysis of palm oil, which was reused for at least nine batches with yield of 32-50%. 

Finally the synthesis of inorganic-polymer composite membranes should be mentioned. Several attempts have been made to combine the high permeability of inorganic membranes with the good selectivity of polymer membranes. Furneaux and Davidson (1987) coated a anodized alumina with polymer films. The permeability increased by a factor of 100, as compared to that in the polymer fiber, but the selectivities were low (H2/O2 = 4). Ansorge (1985) made a supported polymer film and coated this film with a thin silica layer. Surprisingly, the silica layer was found to be selective for the separation mixture He-CH4 with a separation factor of 5 towards CH4. The function of the polymer film is only to increase the permeability. No further data are given. 

Fig. 3. (a) permeate flux and separation factor in H2/CO2 mixture/MTES silica composite membrane system at 293K, (b) permeate rate of N2 in MTES silica composite membrane at 293K (c) predicted pressure profile of CO2 on TPABr silica membrane at 4atm... 

Similarly, Sano et al. [1994] added colloidal silica to a stirred solution of tetrapropylammonium bromide and sodium hydroxide to synthesize a hydrogel on a stainless steel or alumina support with a mean pore diameter of 0.5 to 2 pm. The composite membrane is then dried and heat treated at 500 C for 20 hours to remove the organic amine occluded in the zeolite framework. The silicalite membranes thus obtained are claimed to be free of cracks and pores between grains, thus making the membranes suitable for more demanding applications such as separation of ethanol/water mixtures where the compound molecules are both small. The step of calcination is critical for synthesizing membranes with a high permselectivity. 

FIGURE 25.8 SEM images of the ferromagnetic composite membranes prepared by impregnation of porous substrates (a) silica-coated y-FejOj (b) Fe2Co04. 

Polytetrafiuoroethylene (PTEE) microporous composite membranes were prepared in a similar way [62] using silica derivatives and ion exchange or iminodiacetate-cellulose resins embedded in the PTEE matrix and is used mainly for protein separation and water purification. 

Fig. 4.9 Photograph of composite membrane between 2-acrylamido-2-methyl propane sulfonic acid and three-dimensionally ordered macroporous silica...

Table 4.1 Proton conductivity and methanol permeability of the composite membrane with three-dimensionally ordered macroporous silica matrix. Measurement temperature 30°C, Methanol concentration 10 mol dm ...

The thin film composite membrane exhibited superior overall rejection performance in these tests, with ammonia and nitrate rejection showing an outstanding improvement. It has also been reported that silica rejection by the thin film composite membranes is superior to that of cellulose acetate. While the above data indicates a marginal improvement in the rejection of chemical oxygen demand (COD), which is an indication of organic content, other tests conducted by membrane manufacturers show that the polyurea and polyamide membrane barrier layers exhibit an organic rejection that is clearly superior to that of cellulose acetate. Reverse osmosis element manufacturers should be contacted for rejection data on specific organic compounds. ... 

Polymer-silica composite membranes for Direct Methanol Fuel Cells... 

A classic example of a composite membrane is that patented in 1916 by Snelling who used porous ceramics to support dense layers of palladium, 25 p,m thick [1]. Variations of his theme remain at the forefront of research [2, 3]. Examples include use of porous alumina, silica, perovskites, and stainless steel to support thin layers of Pd and its alloys [2, 3]. Snelling addressed issues of perforations and pinholes... 

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... 

Moparthi A, Uppaluri R, GUI BS. Economic feasibility of silica and palladium composite membranes for industrial dehydrogenation reactions. Chem Eng Res Des 2010 88 1088-1101. 

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