Membrane reactor catalytic ceramic

There are three main types of dense ceramic membranes disk/flat sheet, tubular, and hollow fibers. The disk/flat sheet membranes are applied mostly in research work because they can be fabricated easily in laboratories with a small amount of membrane material. Comparatively, the hollow fiber membranes can provide the largest membrane area per volume but low mechanical strength, while the tubular membranes possess a satisfactory specific membrane area, high mechanical strength, and are easy to assemble in membrane reactors. Dense ceramic MRs can be constructed and operated in either packed bed MR or catalytic MR configurations. 

Juste E, Julian A, Geffroy P-M, Vivet A, Condert V, Richet N, Prrovano C, Chartier T and Del Gallo P (2010), Influence of microstructure and architectnre on oxygen permeation of La(i., )SrxFe(i.y)(Ga, Ni)Y03 5 perovskite catalytic membrane reactor , / Eur Ceramic Soc, 30,1409-1417. 

As an example the use of ceramic membranes for ethane dehydrogenation has been discussed (91). The constmction of a commercial reactor, however, is difficult, and a sweep gas is requited to shift the product composition away from equiUbrium values. The achievable conversion also depends on the permeabihty of the membrane. Figure 7 shows the equiUbrium conversion and the conversion that can be obtained from a membrane reactor by selectively removing 80% of the hydrogen produced. Another way to use membranes is only for separation and not for reaction. In this method, a conventional, multiple, fixed-bed catalytic reactor is used for the dehydrogenation. After each bed, the hydrogen is partially separated using membranes to shift the equihbrium. Since separation is independent of reaction, reaction temperature can be optimized for superior performance. Both concepts have been proven in bench-scale units, but are yet to be demonstrated in commercial reactors. 

Catalytic A catalytic-membrane reactor is a combination heterogeneous catalyst and permselective membrane that promotes a reaction, allowing one component to permeate. Many of the reactions studied involve H2. Membranes are metal (Pd, Ag), nonporous metal oxides, and porous structures of ceramic and glass. Falconer, Noble, and Sperry [in Noble and Stern (eds.), op. cit., pp. 669-709] review status and potential developments. 

Schematics of an oxygen membrane reactor for catalytic POx of methane. A blown up section on the left-hand side shows the details of the ceramic membrane wall explaining the mechanism of oxygen permeation across the membrane. /- is the chemical potential of oxygen and ai and

Porous ceramic membrane layers are formed on top of macroporous supports, for enhanced mechanical resistance. The flow through the support may consist of contributions due to both Knudsen-diffusion and convective nonseparative flow. Supports with large pores are preferred due to their low resistance to the flow. Supports with high resistance to the flow decrease the effective pressure drop over the membrane separation layer, thus diminishing the separation efficiency of the membrane (van Vuren et al. 1987). For this reason in a membrane reactor it is more effective to place the reaction (catalytic) zone at the top layer side of the membrane while purging at the support side of the membrane. 

Porous ceramic membranes for catalytic reactors - overview and new ideas. Journal of Membrane Science, 181, 3-20. 

ANDERSON ETAL. Catalytic Ceramic Membranes Membrane Reactors 199... 

Many catalytic processes of industrial importance, however, involve the combination of high temperature and chemically harsh environments, a factor that strongly favors inorganic membranes. So with the introduction of commercially available glass, ceramic and metal membranes, there has been a dramatic surge of interest in the field of membrane reactor or membrane catalysis. 

Forccd flow mode. Invertase, an enzyme, can be chemically immobilized to the surfaces of ceramic membrane pores by the technique of covalent bonding of silane-glutaraldehyde [Nakajima et al., 1989b]. The substrate (reactant), during the sucrose conversion process, enters the membrane reactor in a crossflow mode. Under suction from the other side of the membrane, the substrate flows into the enzyme-immobilized membrane pores where the bioconversion takes place. Both the product and the unreacted substrate indiscriminately pass through the membrane pores. Thus, no permselective properties are utilized in this case. The primary purpose of the membrane is to provide a well-engineered catalytic path for the reactant, sucrose. 

Coupling two operations like membrane separation and a catalytic reaction or adsorption in a given process of synthesis, purification, or decontamination of effluents is intrinsically interesting from a general technical-economical point of view. Ceramic membranes are ideal solid-fluid contactors, which can be efficiently used to couple separation and heterogeneous catalysis for membrane reactor applications. ... 

Lafaiga D., Santamaria J. and Menendez M., Methane oxidative coupling using porous ceramic membrane reactors. Part I. Reactor development, Chem. Eng. ScL 49 2005 (1994). Sloot H.J., Smolders C.A., van Swaaij W.P.M. and Versteeg G.F., High-temperature membrane reactor for catalytic gas-solid reactions, AIChE J. J5 887 (1992). 

Julbe A, Farrussseng D, and Guizard C. Porous ceramic membranes for catalytic reactors—overview and new ideas. J. Membr. Sci. 2001 181 3-20. 

Binkerd CR, Ma YH, Moser WR, and Dixon AG. An experimental study of the oxidative coupling of methane in porous ceramic radial-flow catalytic membrane reactors. Proceedings of ICIM4 (Inorganic Membranes), Gatlinburg, TN D.E. Fain (ed.), 1996 441-450. Yeung AKL, Sebastian JM, and Varma A. Mesoporous alumina membranes synthesis, characterization, thermal stability and nonuniform distribution of catalyst. J. Membr. Sci. 1997 131 9-28. 

Research on separation of hydrogen isotopes is focused on the aspects related to safe operation of nuclear reactors and separation of tritium. Apart from separators based on palladium alloys [142-145], one can find catalytic units with different metallic membranes and various types of integrated systems with catalytic ceramic reactors [146-154]. 

Existing ceramic, mesoporous membranes (with a 4 nm pore diameter) perform most gas separations according to Knudsen diffusion. The obtainable separation factors (Section 9.3.2.) are usually not economical for most gas separations and provide incremental but limited conversion enhancement in catalytic membrane reactor applications. Capillary condensation and preceding surface flow yield economically interesting separation factors but this mechanism is limited to easily condensable gases and is limited to rather low pressure drops due to stability problems (Sections 9.2.3. and 9.3.3.). 

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