Configuration of Membrane Reactors

Unlike conventional reactors, MRs have two compartments separated by the membrane and thus are characteristic of at least three inlets/out-lets for the feed and product streams. They are designed and fabricated based on the membrane configuration and the application conditions. 

Disk/flat sheet MRs are applied mostly in research work because they can be fabricated easily in the laboratory with a small amount of 

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Several profound theoretical and experimental studies performed on the laboratory scale have been reported which focus on the use of various configurations of membrane reactors as a reactant distributor in order to improve selectivity-conversion performances. In particular, several industrially relevant partial oxidations have been investigated, including the oxidative coupling of methane [56], the oxidative dehydrogenations of propane [57], butane [58], methanol [59, 60], the epoxidation of ethylene [61], and the oxidation of butane to maleic anhydride [62]. 

The increasing interest in inorganic membranes for gas applications is undoubtedly due to their excellent high temperature resistance. Inorganic membrane reactors (including carbon membranes) may thus have a very nice potential for industrial applications. The various configurations of membrane reactors will however not be discussed in the current chapter. Their separation properties may be understood on the basis of the materials used, kinetics, and process conditions. 

Mirvakili, A., Samimi, F., and Jahanmiri, A. (2014) Simultaneous ammonium nitrate decomposition and NO emission reduction in a novel configuration of membrane reactor a simulation study. 

Under certain conditions, scale-up of membrane reactors is straightforward. Provided that (i) the reactor contents are well mixed so that the reactor is operated as a CSTR, and that (ii) the membrane is configured for filtration in the tangential mode, the pertinent design criterion, besides constant residence time T in the reactor, is constant fluidity F of the substrate/product solution through the membrane at all reactor scales. Fluidity is defined by Eq. (19.36) (V = ultrafiltered volume, AP = transmembrane pressure, t = filtration time, and A = membrane area). 

Membrane reactors have, for a long time, been the focus of intensive research, and a variety of membrane reactor configurations have either been developed or suggested. The state of the art with regard to this broad field has been the subject of several excellent reviews [1-10], while comprehensive summaries have recently been provided by Sanchez Marcano and Tsotsis [11] and Dixon [12]. Modern developments were reported on a regular basis during the International Congresses on Catalysis in Membrane Reactors - ICCMR [13]. 

Zaspalis and Burggraaf [47] have summarized typical membrane reactor configurations, different membrane/ catalyst combinations, and a large number of membrane reactor studies. Their article clearly shows that inorganic membranes prepared by the sol-gel method, with their dual ability in catalysis and separation, have many unique advantages over other product forms. At the same time, it is important to realize that the parameters which affect a membrane s characteristics and the advantages which the sol-gel process offers are similar to what has been presented thus far. 

The geometry of the membrane reactor and the relative locations and flow directions of the feed, permeate and reientate streams all play important roles in the reactor performance. The simplest, but not efficient, membrane reactors consist of disk or foil membranes with a flow-through configuration [Mischenko et al., 1979 Fumeaux et al., 1987]. The same type of membrane reactor can also be consu cted and operated in the more common crossflow mode. 

In the second configuration (Figure 11.45), a membrane is fabricated into a bank of seamless thin-walled tubes to form flat double spiral partitions. One spiral is placed on top of the other such that each succeeding spiral is in a mirror symmetry with the adjacent one. This type of membrane reactor has been utilized for hydrogenation of liquid compounds [Gryaznov et al., 1981]. 

Finally, possible causes for deactivation of catalytic membranes are described and severad aspects of regenerating catalytic membrane reactors are discussed. A variety of membrane reactor configurations are mentioned and some unique membrane reactor designs such as double spiral-plate or spiral-tube reactor, fuel cell unit, crossflow dualcompartment reactor, hollow-fiber reactor and fluidized-bed membrane reactor are reviewed. 

The different types of membrane reactor configurations can also be classified according to the relative placement of the two most important elements of this technology the membrane and the catalyst. Three main configurations can be considered (Figure 25.13) the catalyst is physically separated from the membrane the catalyst is dispersed in the membrane or the membrane is inherently catalytic. The first configuration is often called the inert membrane reactor (IMR), in contrast to the two other ones, which are catalytic membrane reactors (CMRs).5o... 

The temperature profiles for both feed and sweep sides are shown in Figure 9.13 with a maximum for each profile. Since the overall module was adiabatic, the feed gas was heated by the exothermic WGS reaction. The highest feed-side temperature was 158 °C at about z = 15 cm. Beyond that, the feed-side temperature reduced, and it became very close to the sweep-side temperature at the end of membrane reactor. This was due to the efficient heat transfer provided by the hollow-fiber configuration. 

In this study the feasibility of implementing ceramic membranes on an industrial scale in the styrene production process is treated. Therefore, a model has been set up in the flowsheeting package ASPEN PLUS , which describes a styrene process production plant. Some modelling has been done with different types of membrane reactors in different reactor section configurations to investigate the influence on the performance of the production of styrene. 

With Pe = 0.5, it has been calculated that under the chosen conditions in all configurations of the reactor section a membrane surface area of approximately 43,000 m is required for microporous and palladium membranes and 3,300 m for Knudsen diffusion membranes. 

There is a multitude of different configurations that have been proposed in the literature in order to combine the membrane separation module and the reactor into a single unit (Figure 1.4b). Sanchez and Tsotsis [1.24] have classified these configurations for catalytic membrane reactors into six basic types, as indicated in Table 1.1 and Figure 1.5. This classification and acronyms are also applicable to other types of membrane reactors, and will be used throughout this book. 

There are a number of membrane reactor systems, which have been studied experimentally, that fall outside the scope of this model, however, including reactors utilizing macroporous non-permselective membranes, multi-layer asymmetric membranes, etc. Models that have been developed to describe such reactors will be discussed throughout this chapter. In the membrane bioreactor literature, in particular, but also for some of the proposed large-scale catalytic membrane reactor systems (e.g., synthesis gas production) the experimental systems utilized are often very complex, in terms of their configuration, geometry, and, of course, reaction and transport characteristics. Completely effective models to describe these reactors have yet to be published, and the development of such models still remains an important technical challenge. 

Types of Membrane and Reactor Configurations - Membrane reactors may be classified by the geometry and materials of the membrane, and by the configuration of the reactor. 

Some new work on assessing the limits of membrane reactors, and on comparing them to other reactor configurations, appeared at the ISCRE-15 conference. McGregor et a/.have extended attainable region theory to include separation processes. This work aims to synthesize the structures of optimal reactor-separator networks, which has implications for the design of membrane reactors. The question of what conversion is achievable in a membrane reactor has been revisited,with identification of operating conditions at which maximum conversion occurs. 

This reactor obviously has two catalystic zones, the packed bed and the membrane itself. As already stated, although theoretically daunting, it offers the best configuration for a complete analysis of membrane reactors. Experimental studies on the dehydrogenation of ethane showed considerable enhancement over both tube and shell side equilibrium conversions (Tsotsis et al., 1992). Further improvement was possible with an increase in the sweep ratio. 

Tosti et al. tested Pd-Ag membrane reactor for 12 months for H2 permeation [14]. Excellent stability was observed for 12 months of operation. In fact, the complete hydrogen selectivity and none failure (formation of cracks, holes) were observed. They proposed that the reliability is a result of both the tube manufacturing procedure and the reactor design configuration (finger-like). Figure 6.11 shows the picture of membrane reactor before and after the 12 months of operation. 

Many efforts devoted to the development of membrane competitive applications by the most prestigious research centers worldwide attest the strategic importance and the potentiality of membrane reactors for the industry. The scientific production dealing with selective membrane reactors is growing exponentially as reported in Chap. 2, 750 papers on membrane reactors have been published in 2009, of which 220 on Pd-based membranes. The main processes in which R D departments are focusing the attention are those devoted to hydrogen production, for which two configurations are imder study ... 

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