Flow-through catalytic membrane reactors

In the catalytically active membrane wall, the differential material and energy balances are expressed as 

Transport of components within the porous membrane can be expressed using the dusty gas model, which is based on the Maxwell-Stefan equations for multi-component molecular diffusion [8]  

is the Poiseuille constant (m ), Dj. and D. are the Knudsen diffusion coefficient and molecular diffusion coefficient (m s ), respectively. Both the Knudsen and molecular diffusion coefficients are then multiplied by the square of the porosity to allow for the combined effect of porosity and tortuosity [9]. 

The mass transfer flux from the bulk gas to the membrane interface on the tube side and shell side of the membrane can be given by 

In order to solve the axial mass and energy balances, the differential equations (9.21) and (9.22) are first arranged by replacing first- and 

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Westermann T and Melin T. Flow-through catalytic membrane reactors—Principles and appheations. Chem. Eng. Process. 2009 48 17-28. 

Westermann, T., Melin, T. (2009). Review — flow-through catalytic membrane reactors — principles and applications. Chemical Engineering and Processing, 48, 17—28. 

Motamedhashemi, M., Egolfopoulos, F. and Tsotsis, T. (2011). Application of a Flow-Through Catalytic Membrane Reactor (FTCMR) for the Destruction of a Chemical Warfare Simulant, J. Membrane Sci., 376, pp. 119-131. 

Flow-through catalytic membrane reactor Catalytic reactions take place while the reactants flow through the membrane FTCMR... 

In some applications the membrane is not required to be perm-selective but only to provide reactive sites. Such devices are called catalytic non-perm-selective membrane reactors (CNMRs). The reactants can flow into the membrane from opposite sides, and the membrane s role is to provide a controlled reactive interface. If the reactants flow through the membrane from one side to the other while the reaction takes place instantly, such a reactor is also called a flow-through catalytic membrane reactor (FTCMR). 

FLOW-THROUGH CATALYTIC MEMBRANE REACTORS The boundary conditions for Eqs (9.26)-(9.28) are... 

Takeuchi et al. 7 reported a membrane reactor as a reaction system that provides higher productivity and lower separation cost in chemical reaction processes. In this paper, packed bed catalytic membrane reactor with palladium membrane for SMR reaction has been discussed. The numerical model consists of a full set of partial differential equations derived from conservation of mass, momentum, heat, and chemical species, respectively, with chemical kinetics and appropriate boundary conditions for the problem. The solution of this system was obtained by computational fluid dynamics (CFD). To perform CFD calculations, a commercial solver FLUENT has been used, and the selective permeation through the membrane has been modeled by user-defined functions. The CFD simulation results exhibited the flow distribution in the reactor by inserting a membrane protection tube, in addition to the temperature and concentration distribution in the axial and radial directions in the reactor, as reported in the membrane reactor numerical simulation. On the basis of the simulation results, effects of the flow distribution, concentration polarization, and mass transfer in the packed bed have been evaluated to design a membrane reactor system. 

Schmidt, A., Haidar, R., and Schomacker, R. (2005) Selectivity of partial hydrogenation reactions performed in a pore-through-flow catalytic membrane reactor. Catal. Today, 104, 305-312. 

Contact modalities and concentration profiles in catalytic membrane reactors for three-phase systems.The concentration of reactants is represented on the y-axis and the spatial coordinate along the membrane cross-section is represented on the x-axis. Below the scheme of each case the sequence of the mass transfer (MT) resistances and of the reaction event (R) are reported. (a)Traditional slurry reactor (b) supported thin porous catalytic layer with the liquid impregnating the porosity and the gas phase in contact with the catalytic layer (c) supported thin porous catalytic layer with the liquid impregnating the porosity and the liquid phase in contact with the catalytic layer (d) supported dense membrane which is perm-selective to the gas-phase reactant (e) dense catalytic membrane perm-selective to both reactants in the gas and liquid phases (f) forced flow of the liquid phase enriched with the gas-phase reactant through the thin catalytic membrane layer. 

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. 

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. 

The flow directions (e.g., co-currcni, counter-current and flow-through) and flow patterns (e.g., plug flow, perfect mixing and fluidized bed) of feed, permeate and retentate streams in a membrane reactor can significantly affect the reaction conversion, yield and selectivity of the reaction involved in different ways. These variables have been widely investigated for both dense and porous membranes used to carry out various isothermal and non-isothermal catalytic reactions, particularly dehydrogenation and hydrogenation reactions. 

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