Palladium membrane reactors model

Membrane reactor models of various configurations, complexity, and ranges of applicability have been previously reported [Sun and Khang, 1988 Itoh and Govind, 1989 Liu et al., 1990], Several previous investigators have presented water-gas shift membrane reactor models. A model of the iron-chromium oxide catalyzed water-gas shift reaction at 673 K in a cylindrical, palladium membrane reactor was developed to demonstrate... 

Then Uemiya et al. [2] reported another Pd membrane reactor for WGS reaction using Fe-Cr oxide catalysts. The model of flow in the palladium membrane reactor is illustrated in Figure 6.3. They proposed that hydrogen is permeated through palladium membrane via a solution diffusion transport mechanism, and the rate of hydrogen permeation, /, per unit area of membrane, is written in terms of Fick s first law as follows ... 

FIGURE 6.3 Flow model of reaction and permeation in palladium membrane reactor. (Taken from Figure 1 of S. Uemiya, N. Sato, H. Ando, E. Kikuchi, Ind. Eng. Chem. Res. 30 (1991) 581.)... 

Fernandez F, Soares A Jr (2006) Methane steam reforming modeling in a palladium membrane reactor. Fuel 85 569-573... 

Itoh, N. (1992). Development of a one-side uniform model for palladium membrane reactors. 

Itoh, N., Shindo, Y., Haraya, K. (1990). Ideal flow models for palladium membrane reactor. Journal of Chemical Engineering of Japan, 23, 420. 

Similarly to the single-tube type, a CFD model for analysing and designing a multi-tube type of palladium membrane reactor will be developed, where the three-dimensional mass and heat transfer for the dehydrogenation of cyclohexane occurring in the catalyst-packed bed is taken into account (Mimura et al, 2010b). 

Three-dimensional CFD model for the multi-tube palladium membrane reactor... 

A CFD model for analysing and designing a multi-tube type of palladium membrane reactor was presented, where the three-dimensional mass and... 

While most of the membrane reactor studies on ethylbenzene dehydrogenation employ fixed-bed membrane reactors, Abdalla and Elnashaie [1995] evaluated the concept of a fluidized-bed membrane reactor through modeling. Since hydrogen is released from the reaction, a palladium-based membrane can be used for this application. 

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. 

In the past, there was no need for small-scale (< 1 MW) distributed hydrogen production from hydrocarbons where such reactors would likely be first employed. In any case, unsupported palladium membranes have required too much expensive metal to be economically feasible for all but special purposes. The potential availability of cost effective, high hydrogen permeance, palladium membranes supported on porous, stainless steel, tubular substrates combined with the advent of stable, high volumetric activity WGS catalysts is the driving force behind the system modeling... 

A large number of hydrogenation and dehydrogenation reactions were tested in the early studies of dense-metal membrane reactors (see listing in Shu et al. [34], Hsieh [35], and Gryaznov and Orekhova [36]). Many works tested the dehydrogenation of cyclohexane to benzene as a model reaction since it can be carried out at low temperature with no side reactions and no deactivation a conversion of 99.5% was achieved with a palladium membrane, compared with 18.7% at equilibrium, at 200°C [31]. 

Key words CFD model, membrane reactor, palladium membrane, single tube, multi-tube, dehydrogenation, hydrogen. 

First, the basic CFD model for a single palladium membrane tube reactor with the simplest configuration is developed. The model established, which takes account of a lot of information on the physical properties, the chemical kinetics, the membrane properties and so on, will be proved by comparing with the practical reactor performances. 

Numerical model for the single palladium membrane tube reactor... 

Dense palladium-based membranes. Shown in Table 10.1 are modeling studies of packed-bed dense membrane shell-and-tube reactors. All utilized Pd or Pd-alloy membranes except one [Itoh et al., 19931 which used yttria-stabilized zirconia membranes. As mentioned earlier, the permeation term used in Ihe governing equations for the tube and shell sides of the membrane is expressed by Equation (10-51b) with n equal to 0.5 [c.g., Itoh, 1987] or 0.76 [e.g., Uemiya et al., 1991]. 

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