Catalytic membranes

In the case of a catalytic membrane reactor (CMR), the membrane is (made) intrinsically catalytically active. This can be done by using the intrinsic catalytic properties of the zeolite or by making the membrane catalytically active. When an active phase is deposited on top of a membrane layer, this is also called a CMR because this becomes part of the composite membrane. In addition to the catalytic activity of the membrane, a catalyst bed can be present (PBCMR). The advantages of a CMR are as follows ... 

In the recent years, many researchers have devoted attention to the development of membrane science and technology. Different important types of membranes, such as these for nanofiltration, ultrafiltration, microfiltration, separation of gases and inorganic membranes, facilitated or liquid membranes, catalytic and conducting membranes, and their applications and processes, such as wastewater purification and bio-processing have been developed [303], In fact, almost 40 % of the sales from membrane production market are for purifying wastewaters. 

The membrane is inherently catalytic (Figure 7.2b) or modified with catalytically active species distributed in or at the entrance of the membrane pores as individual particles or as a layer (Figure 7.2c). The catalytic activity is adjusted to the membrane (catalytically active membrane). In this way the strongest interaction between membrane transport properties and catalytic activity can be achieved. 

In nature many enzymes are embedded in membranes, which not only serve as a scaffold but also regulate the transport of substrates and products, and control the concentrations of protons and other ions. Instead of embedding molecular catalysts into artificial membranes, as was done for the cytochrome P450 mimic, it is also possible to make amphiphiles that constitute the membranes catalytic themselves. 

Briley, M. S. and Eisenthal, R. 1974. Association of xanthine oxidase with the bovine milk-fat-globule membrane. Catalytic properties of the free and membrane-bound enzyme. Biochem. J. 143, 149-157. 

S. Elnashaie, T. Moustafa, T. Alsoudani, S.S. Elshishini, Modeling and basic characteristics of novel integrated dehydrogenation-hydrogenation membrane catalytic reactors, Computers Chemical Engineering, 24(2-7) 2000, 1293-1300... 

Lin Y.-M., Rei M.-H. An integrated purification and production of hydrogen with a palladium membrane-catalytic reactor. Catalysis Today 1998 44 343-349. 

Dissimilatory nitrate reductase (membrane) catalytic a subunit Cytochrome c and d containing nitrite reductase (cdl-NiR)... 

Fig. 11.5. Formaldehyde yields in various reactors under similar experimental conditions. V, conventional plug-flow reactor , a PBMR using a Pd/AljCb dense composite membrane A, a PBMR using a mesoporous AI2O3 membrane , a CMR using a mesoporous AI2O3 membrane catalytically impregnated by a sol-gel technique. Reproduced from Deng and Wu [61] with permission.

A novel catalyst consisting of colloidal palladium adsorbed onto the surface of a water-insoluble polymer, polyvinylpyrrolidone, has been shown to hydrogenate only the outer leaflet of rat platelets [59]. The effect of hydrogenation was to influence the asymmetric distribution of the phospholipids of the membrane. Catalytic hydrogenation of a phytopathogenic fungus [60] has also been reported. 

Bipolar plates connecting adjacent cells can be considered as combination the functions, current collector, gas distribution (flow field), gas separation and coolant layer into one subunit. Integration of electrolyte membrane, catalytic layers and gas diffusion layers into a Membrane Electrode Assembly (MEA) results into a second major subunit for fuel cell stack integration. Combination of a catalytic layer and a gas diffusion layer to a gas diffusion electrode is yet another possibility of integrating functional layers to subunits. 

The electrolyte membrane is in contact with catalyst layers consisting of platinum nanoparticles typically supported on a porous carbon black. The thickness of the catalyst layer is in the range from 5 to 20 pm which is contacted by a gas diffusion layer (GDL) of thickness 100-250 pm. The functional layers electrolyte membrane, catalytic layer and gas diffusion layer are making up the active part of the MEA. A detailed discussion of electro catalysts and catalyst layers is given in [9]. 

In recent years there has been tremendous interest in porous ceramics because of their applications as filters, membranes, catalytic substrates, thermal insulation, gas-burner media and refractory materials. These are due to their superior properties, such as low bulk density, high permeability, high temperature stability, erosion/corrosion resistance and excellent catalytic activity. One branch of this field is porous SiC ceramics, owing to their low thermal expansion coefficient, high thermal conductivity and excellent mechanical properties. However, it is difficult to sinter SiC ceramics at moderate temperatures due to their covalent nature. In order to realize the low temperature fabrication of porous SiC ceramics, secondary phases may be added to bond SiC. Oxidation bonded porous SiC ceramics have been found to exhibit good thermal shock resistance owing to the microstructure with connected open pores. 

Membrane catalytic reactors. Catalytic elements, in the form of membranes thin two-sided layers of a permeable liquid catalyst, or a porous solid catalyst, has the main advantage in its two-sided configurations, so it is possible to design more complex and efficient catalytic reactors, as some, already investigated, or only considered systems ... 

Membrane catalytic reactors with separated reactants ... 

Design and engineering of metallic membranes 683 Metallic membrane Catalytic reactor... 

Considering the characteristic of strength and productivity, it was stated that the Ni-Al support was the most suitable for the formation of the membrane catalytic systems (Tsodikov et al., 2011). In particular, the catalytic components of Table 4.18 were tested after their deposition on the internal surface of membrane channels. 

These proposed classifications can be further extended in two ways considering the reactor design (how it is clearly shown in the matrix of Figure 19.10) and considering the possibility of using inert membranes (inert pervaporafion membrane reactors (I-PVMRs)) or catalytic membranes (catalytic pervaporation membrane reactors (C-PVMRs)), as shown in Figure 19.11. 

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