Model plug flow membrane reactor

Using a developed plug-flow membrane reactor model with the catalyst packed on the tube side, Mohan and Govind [1986] studied cyclohexane dehydrogenation. They concluded that, for a fixed length of the membrane reactor, the maximum conversion occurs at an optimum ratio of the permeation rate to the reaction rate. This effect will be discussed in more detail in Chapter 11. They also found that, as expected, a membrane with a highly permselective membrane for the product(s) over the reactant(s) results in a high conversion. 

In addition to these experiments, a simplified isothermal 1-D dispersed plug-flow reactor model of the membrane reactor was used to carry out theoretical studies [47]. The model used consisted of the following mass balance equations for the feed and sweep sides ... 

Sousa J M and Mendes A M (2005), Modelling a catalytic membrane reactor with plug-flow pattern and a hypothetical equilibrium gas-phase reaction with An O , Catal Today, 104,336-343. 

The viability of one particular use of a membrane reactor for partial oxidation reactions has been studied through mathematical modeling. The partial oxidation of methane has been used as a model selective oxidation reaction, where the intermediate product is much more reactive than the reactant. Kinetic data for V205/Si02 catalysts for methane partial oxidation are available in the literature and have been used in the modeling. Values have been selected for the other key parameters which appear in the dimensionless form of the reactor design equations based upon the physical properties of commercially available membrane materials. This parametric study has identified which parameters are most important, and what the values of these parameters must be to realize a performance enhancement over a plug-flow reactor. 

Again, the simple isothermal 1-D plug-flow reactor model provides a good basis for quantitative descriptions. This model allows to explore the potential of using series connections of several membrane reactor segments. The corresponding mass balance for a component i and a segment k can be formulated as follows ... 

Fig. 12.18. Comparison of the optimized reduced amounts that should be dosed and the corresponding internal compositions for a fixed-bed reactor (discrete dosing, top) and a membrane reactor (continuous dosing, bottom). A triangular network of parallel and series reactions was analyzed using an adapted plug-flow reactor model, Eq. 48. One stage (left) and 10 stages connected in series (right) were considered. All reaction orders were assumed to be 1, except for those with respect to the dosed component in the consecutive and parallel reactions (which were assumed to be 2) [66].

Figure 10.2 Schematic diagram of a plug-flow macroscopic model for a packed-bed membrane shell-and-tube reactor...

None of the above studies, however, deals with the detailed hydrodynamics in a membrane reactor. It can be appreciated that detailed information on the hydrodynamics in a membrane enhances the understanding and prediction of the separation as well as reaction performances in a membrane reactor. All the reactor models presented in Chapter 10 assume very simple flow patterns in both the tube and annular regions. In almost all cases either plug flow or perfect mixing is used to represent the hydrodynamics in each reactor zone. No studies have yet been published linking detailed hydrodynamics inside a membrane reactor to reactor models. With the advent of CFD, this more complete rigorous description of a membrane reactor should become feasible in the near future. 

Mohan and Govind [1988a] modeled co-current and counter-current plug-flow microporous membrane reactors for the following reaction... 

The following assumptions were made in developing the equations for the model for the plug-flow pervaporation membrane reactor (PFPVMR) The reactor behaves as an... 

Many smdies have successfiiUy simulated the observed behavior, in various membrane reactors and using independent kinetics and transport information the applied models were too specific and complex to allow a general analysis. The models commonly assume plug flow and isothermal conditions on the tube and shell sides. Simulations included the dehydrogenation of 1-butene in a dense-... 

The ID pseudo-homogeneous model is the most used model to describe packed bed membrane reactors, especially for laboratory-scale applications. In its simplest form, namely the plug flow steady state model, the model describes only axial profiles of radially averaged temperatures and concentrations. 

Chapter 5 is devoted to the basic reactor models used in chemical engineering the batch reactor, the CSTR, the plug-flow reactor, and the TAP reactor with its modification, the thin-zone TAP reactor. Special attention is paid to the reaction-diffusion reactor, the detailed analysis of which opens up wide perspectives for the understanding of different types of reactors, such as catalytic, membrane and biological reactors. 

Keuler, J.N. and Lorenzen, L. (2002) Comparing and modeling the dehydrogenation of ethanol in a plug-flow reactor and a Pd-Ag membrane reactor. Industrial and Engineering Chemistry Research, 41, 1960-1966. 

For example, different fermentation schemes have been developed for the production of ethanol. Conventional batch, continuous, cell recycle and immobilized cell processes, as well as membrane, extraction and vacuum processes, which selectively remove ethanol from the fermentation medium as it is formed, were compared on identical bases using a consistent model for yeast metabolism (Maiorella et al., 1984). The continuous flow stirred tank reactor (CSTR) with cell recycle, tower and plug flow reactors all showed similar cost savings of about 10% compared to batch fermentation. Cell recycle increases cell density inside the fermentor, which is important in reducing fermentation cost. 

---