FBMR configuration

Figure 1.5. Different MR configurations. 1 tubeside, 2 catalytic membrane, 3 inert membrane, 4 catalyst bed, 5 shellside. a) CMR, CNMR, b) PBMR, FBMR, c) PBCMR, FBCMR.

Similar terminology is used if the membrane is a flat plate, and by extension, if the membrane is used with a fluidized bed then FBMR and FBCMR are used for the two possible configurations. 

Different types of membrane reactors for hydrogen production have been proposed in the literature. Most of the previous work has been performed in packed bed membrane reactors (PBMRs) however, there is an increasing interest in novel configurations such as fluidized bed membrane reactors (FBMRs) and membrane micro-reactors (MMRs), especially because better heat management and decreased mass transfer limitations can be obtained in these novel reactor configurations. 

Therefore, the topic of this chapter is to give an overview of the most relevant progress realized in the MSR field by using the aforementioned two different MR configurations. Moreover, a summary on the mathematical models developed for simulating the MSR process in PBMRs and FBMRs is also given. 

Regarding the FBMR, a typical configuration consists of a bundle of membranes immersed in a catalytic bed operated in the bubbling or mrbulent regime. A representative FBMR was proposed and was well illustrated by Adris et al. (1994). 

However, each configuration, PBMR and FBMR, presents benefits and drawbacks. In particular, PBMR is characterized by a very simple configumtion in which catalyst particles can be packed. The particles dimension plays an important role for the performance of this kind of reactor. Indeed, very small particles can increase pressure drop and, on the contrary, big particles can limit the internal mass transfer. Moreover, other drawbacks can occur by using PBMR, such as the mass transfer limitafion from bed to wall, which negatively influences the hydrogen permeation and remarkable temperature profile along the reactor, with a consequent detrimental effect on catalyst and membrane (Roses et al., 2013). 

Regarding the FBMRs, Adris, Elnashaie, and Hughes (1991) were the first to propose this kind of reactor configuration by mathematical models. In their work, they showed that complete methane conversion could be realized by using typical operating industrial temperatures. 

Successively, many other scientific papers have dealt with FBMRs for performing the MSR, demonstrating the benefits of this configuration. In most of them, a modeling investigation was performed. Indeed, from our best knowledge, few authors have experimentally performed the MSR reaction in FBMRs (Adris et al., 1997 Patil et al., 2006, 2007 Roses et al., 2013), probably because of the difficulties in reactor construction, membrane sealing, and its erosion. For instance, Adris et al. (1997)... 

The studies have proven that both MRs can realize better performance in terms of methane conversion and hydrogen production than the CRs, working also at milder operating conditions. By making a comparison between the two reactor configurations, it has been shown that a PBMR has a very simple configuration whereas an FBMR is typically characterized by enhanced mass and heat transfer rates, which favor more uniform temperature profiles. Nevertheless, possible bubble-to-emulsion mass transfer... 

By far the most commonly referred to reactor is the packed bed membrane reactor (PBMR), in which the reaction function is provided by a packed bed of catalysts in contact with the membrane. The membrane itself is not catalytic or at least not intentionally so, but is used to add or remove certain species from the reactor. If the membrane is highly perm-selective, this configuration appears ideal for situations where two complementary reactions take place on either side of the membrane - the product of the reaction on one side acting as a reactant on the other side, while the endothermicity of one reaction is compensated by the exothermicity of the other. When the catalysts at work are present in a fluidized mode, the reactor is then called a fluidized bed membrane reactor (FBMR). 

Figure 7.5 shows schematically a two-zone FBMR for alkane catalytic dehydrogenation [11], This configuration aims to combine in-situ catalyst regeneration with hydrogen separation using the Pd membrane. The hydrocarbon reactant is fed at an intermediate point, while a second... 

In this case two different reactor configurations are usually distinguished the packed-bed membrane reactor (PBMR), and the fluidized-bed membrane reactor FBMR). 

Firstly, the catalyst may be deposited within the membrane structure this includes the case where the membrane itself may be intrinsically catalyti-cally active, as in the CMR. Secondly, the catalyst particles may be packed adjacent to the membrane, as in the PBMR, either on a single side as for flat sheet geometries or, for tubular geometries, the catalyst may be placed inside or outside the membrane tube. Thirdly, combining these two options yields catalyst both in the membrane pores and packed as particles in or around the membrane, as in the PBCMR. Similar configurations are available for the cases where the membranes are used with fluidized beds, such as the FBMR and the FBCMR. Researchers employing silica membranes... 

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