Modeling of Fluidized Bed Membrane . Reactors

In this appendix the constitutive equations used in the modeling of fluidized bed membrane reactors are listed. Components properties have be evaluated by making use of book The Properties of Gases and Liquids. 

Ye, G., Xie, D., Qiao, W., Grace, J. R., Lim, C. J. (2009). Modeling of fluidized bed membrane reactors for hydrogen production from steam methane reforming with Aspen Plus. International Journal of Hydrogen Energy, 34, 4755—4762. 

J. F. De Jong, H. J. van Gerner, M. van Sint Annaland and J. A. M. Kuipers, Development of a Novel Hybrid Discrete Particle - Immersed Boundary Model for Fluidized Bed Membrane Reactors, Seventh International Conference on CFD in the Minerals and Process Industries. CSIRO, Melbourne, 2009. 

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. 

Adhs. A.M., 1994, A Fluidized Bed Membrane Reactor for Steam Methane Reforming Experimental Verification and Model Validation, Ph.D. dissertation, Univ. of British Columbia, Vancouver, Canada. 

Rakib, M.A. and Alhumaizi, K.I. Modeling of a fluidized bed membrane reactor for the steam reforming of methane Advantages of oxygen addition for favorable hydrogen production. Energy Fuels, 2005, 19, 2129. 

A new development in this field is the use of fluidized-bed systems instead of a packed bed. For this purpose, steam reforming of methane has been used as a model reaction [88]. From experimental and theoretical work it can be concluded that fluidized-bed membrane reactors potentially represent a promising system as problems of heat transfer and equilibrium limitations can be addressed simultaneously. As one of the major problems encountered is to provide sufficient membrane area per volume, possible solutions are the use of hollow-fiber systems [13] or membranes based on microsystem technology. In Fig. 5.7 an indication can be obtained for the potential of this approach to enlarge the effective membrane area versus the superficial area of the wafers used [89]. 

A typical ID two-phase model for a membrane assisted fluidized bed reactor can be used for the simulation of the fluidized bed membrane reactor for hydrogen production via methane reforming. A schematic representation of the gas flows between the compartments of the bubble and emulsion phases is depicted in Figure 10.6. The model main assumptions are ... 

Recently, Mahecha-Botero and co-workers presented a generalized comprehensive model which characterizes multiple phases and regions (low-density phase, high-density phase, staged membranes, freeboard region) with the possibility to include new features or simplifications in order to simulate different fluidized bed (membrane) reactors. For a more detailed description of the model and assumptions an interested reader is referred to. ... 

All the models proposed for fluidized bed membrane reactors have the same limitations. These models are phenomenological models that make use of closure equations originally derived for fluidized bed without internals. Although it is known that the presence of internals (membranes and permeation of gas through them) may vary the behavior of bubbles, mass transfer and solid circulation inside the bed, reliable closure equations for membrane assisted fluidized bed are not yet available. A way to solve this problem is to use a so-called multi-scale modeling of dense gas-solid systems, where low level... 

I. A. Abba, J. R. Grace and H. T. Bi, Application of the generic fluidized-bed reactor model to the fluidized-bed membrane reactor process for steam methane reforming with oxygen input, Ind. Eng. Chem. Res., 2003, 42, 2736-2745. 

A. Mahecha-Botero, J. R. Grace, C. Jim Lim, S. S. E. H. Elnashaie, T. Boyd and A. Gulamhusein, Pure hydrogen generation in a fluidized bed membrane reactor Application of the generalized comprehensive reactor model, Chem. Eng. Sci., 2009, 64, 3826-3846. 

A mathematical model was used in literature (Abashar, 2004) based on the combination of SRM and dry reforming in a fluidized bed membrane reactor showing complete conversion of methane at low temperature. The produced carbon dioxide in the SR was used in dry reforming to produce syngas. A comparison between the traditional reactor and MR was discussed the higher performance was obtained for the fluidized bed MR. 

Marin, P., Hamel, C., Orddnez, S., V. Dlez, F., Tsotsas, E., Seidel-Morgenstem, A. (2010). Analysis of a fluidized bed membrane reactor for butane partial oxidation to maleic anhydride 2D modeling. Chemical Engineering Science, 65, 3538—3548. 

Rakih MA, Grace JR, Lim CJ, Elnashaie SSEH Modeling of a fluidized bed membrane reactor for hydrogen production by steam reforming of hydrocarbons, Ind Eng Chem Res 50(6) 3110-3129, 2011. 

Ostrowski, T., Giroir-Fendler, A., Mirodatos, C. and Mleczko, L. (1998) Comparative study of the catalytic partial oxidation of methane to synthesis gas in fixed-bed and fluidized-bed membrane reactors. Part I-A modeling approach. Catalysis Today, 40, 181-190. 

In Chapter 2 we discussed a number of studies with three-phase catalytic membrane reactors. In these reactors the catalyst is impregnated within the membrane, which serves as a contactor between the gas phase (B) and liquid phase reactants (A), and the catalyst that resides within the membrane pores. When gas/liquid reactions occur in conventional (packed, -trickle or fluidized-bed) multiphase catalytic reactors the solid catalyst is wetted by a liquid film as a result, the gas, before reaching the catalyst particle surface or pore, has to diffuse through the liquid layer, which acts as an additional mass transfer resistance between the gas and the solid. In the case of a catalytic membrane reactor, as shown schematically in Fig. 5.16, the active membrane pores are filled simultaneously with the liquid and gas reactants, ensuring an effective contact between the three phases (gas/ liquid, and catalyst). One of the earliest studies of this type of reactor was reported by Akyurtlu et al [5.58], who developed a semi-analytical model coupling analytical results with a numerical solution for this type of reactor. Harold and coworkers (Harold and Ng... 

Andres, M. B., Chen, Z., Grace, J. R., Elnashaie, S. S. E. H., Jim Lim, C., Rakib, M., et al. (2009). Comparison of fluidized bed flow regimes for steam methane reforming in membrane reactors a simulation study. Chemical Engineering Science, 64, 3598—3613. Ayturk, M. E., Kazantzis, N. K., Ma, Y. H. (2009). Modeling and performance assessment of Pd- and Pd/Au-based catalytic membrane reactors for hydrogen production. Energy Environmental Science, 2, 430—438. 

It is the opinion of the author that future research on reactor modeling should focus on developing models for reactors and processes which are as yet poorly understood. Examples of such systems include fluidized-bed reactors, membrane reactors, reactors used for the synthesis of ceramics, and low-pressure reactors used for the deposition and etching of thin films. 

Marin et al. (250) attempted to model a reactor similar to that used by Alonso and co workers. Their simulations were compared with simulations representing a fixed-bed reactor operated under similar conditions. They concluded that the membrane reactor (with the external fluidized bed) was a viable technology for n-butane oxidation, but that it offered only a modest increase in MA yields relative to those realized in a fixed-bed reactor. Nonetheless, the safer operating conditions which keep the O2 and hydrocarbon flows separate, particularly with the oxidation of butane to MA, are desirable. Presently, MA yields are chiefly governed by the explosive limits of butane in air (i.e., 1.8%). Increasing the butane concentration with an optimized membrane reactor may increase overall MA yields. 

The direct benefit of having a permselective membrane in a fluidized-bed steam reformer can be evaluated by modeling the reactor with and without the membrane for otherwise identical reactor features and feed conditions. An example of the comparison... 

As a building block for simulating more complex and practical membrane reactors, various membrane reactor models with simple geometries available from the literature have been reviewed. Four types of shell-and-tube membrane reactor models are presented packed-bed catalytic membrane reactors (a special case of which is catalytic membrane reactors), fluidized-bed catalytic membrane reactors, catalytic non-permselecdve membrane reactors with an opposing reactants geometry and catalytic non-permselective membrane multiphase reactors. Both dense and porous inorganic membranes have been considered. 

---