Extractor-type membrane reactors

Highly selective and still sufficiently permeable membranes are required for the efficient use of extractor-type membrane reactors. 

As described above, the principle of an extractor-type membrane reactor has been extensively demonstrated, most often with mbular membranes of 5-10 mm diameter and catalysts having a particle size of around 1 mm in small laboratory reactors where the catalyst is placed as a packed bed inside or around the membrane tube. For Pd-alloy membranes... 

Extractor-type membrane reactors Applied to PCMRs and PIMRs. This type of reactor is based on the selective removal of one or more reaction products, which could result in an increase of the conversion for equUibrium-limited reactions or in the improvement of the catalytic activity if the removed products are reaction-rate inhibitors. Dehydrogenation membrane reactors or pervaporation membrane reactors are examples of extractor-type membrane reactors. 

Pervaporation-assisted catalysis is a typical example of an operation eflide-ntly carried out in extractor-type catalytic membrane reactors. Esterification is by far the most studied reaction combined with pervaporation. " Esters are a class of compounds with wide industrial appUcation, from polymers to fragrance and flavour industries. Esterification, a reaction between a carboxylic acid and an alcohol with water as a by-product, is an equilibrium-limited reaction. So, this is a typical reaction that can be carried out advantageously in a extractor-type membrane reactor. By selectively removing the reaction product water, it is possible to achieve a conversion enhancement over the thermodynamic equilibrium value based on the feed conditions. 

Extractor-type membrane reactors and particularly pervaporation membrane reactors illustrate quite well the versatility of PIMRs. Van der Bruggen distinguishes between pervaporation type reactors R1 and R2, wherein the extracted component is the main product or is a by-product, respectively. However, a variety of reactor configurations is possible for those two reactor types, as exemplified in Fig. 1.8. 

Catalyst placement in extractor, distributor and two contactor-type membrane reactors (A, B reactants P product) (Miachon and Dalmon, 2004). 

Improved selectivity in the liquid-phase oligomerization of i-butene by extraction of a primary product (i-octene C8) in a zeolite membrane reactor (acid resin catalyst bed located on the membrane tube side) with respect to a conventional fixed-bed reactor has been reported [35]. The MFI (silicalite) membrane selectively removes the C8 product from the reaction environment, thus reducing the formation of other unwanted byproducts. Another interesting example is the isobutane (iC4) dehydrogenation carried out in an extractor-type zeolite CMR (including a Pt-based fixed-bed catalyst) in which the removal of the hydrogen allows the equilibrium limitations to be overcome [36],... 

Daramola M. O., Burger A. J., Giroir-Fendler A., Miachon S., Lorenzen L. 2010. Extractor-type catalytic membrane reactor with nanocomposite MFI-alumina membrane tube as separation unit Prospect for ultra-pure para-Xylene production from m-Xylene isomerization over Pt-HZSM-5 catalyst. Applied Catalysis A General 386(1-2) 109-115. 

Packed bed membrane reactors have two main limitations (i) the difficult heat management that can be very detrimental for highly exothermic reactions like in perovskite membrane reactors and (ii) the extent of bed-to-wall mass transfer limitations that are more important for extractor-type reactors like Pd-based membrane reactors (due to the high permeation fluxes of membranes). In fact, the bed-to-wall mass transfer limitations would decrease the partial pressure of hydrogen close to the membrane surface and thus decrease the membrane flux. 

Dyk, L.V., Lorenzen, L., Miachon, S. and Dalmon, J.-A. (2005) Xylene isomerization in an extractor type catalytic membrane reactor. Catalysis Today, 104, 274-280. 

Abstract The objective of this chapter is to give an overview of the use of polymeric membranes in membrane reactors. Since the stndy of polymeric membrane reactors is a multidisciplinary activity, the chapter begins with some basic concepts of polymer science and polymer membranes. In the following, the different types of polymeric membrane reactors, classified into two main groups - polymeric inert membrane reactors (PIMRs) and polymeric catalytic membrane reactors (PCMRs), are presented and discussed. For each of these group , examples of the main reactor types are given extractors, forced-flow or contactors. Finally, there is a discussion of the modelhng aspects of membrane reactors with dense polymeric catalytic membranes reported in the literature. 

Key words catalytic/inert polymeric membranes, polymeric membranes preparation, membrane reactors, extractor-type, distributor/contactor-type, forced-flow-type, polymeric inert membrane reactors (PIMRs), polymeric catalytic membrane reactors (PCMRs), modelling. 

The use of a non-pervaporative extractor-type catalytic polymeric membrane reactor has been reported for light alcohol/acetic acid esterifications. A cross-linked poly(styrene sulfonic acid) (PSA)/PVA blend flat membrane was assembled in the reactor in a vertical configuration, separating two chambers. One of the chambers was loaded with an aqueous solution of ethanol and acetic acid, while the other chamber was filled with chlorobenzene. The esterification equilibrium is displaced to the product s side by the continuous extraction of the formed ester. In the esterifications of methanol, ethanol and n-propanol with acetic acid, the reactivity through the PSA/PVA membrane was higher than that with HCl as catalyst. In that of n-butanol with acetic acid, however, it was viceversa. 

The use of an extractor-type polymeric catalytic membrane reactor has also been described by Wu et for phenol allylation. Ion-exchange membranes, consisting of poly (styrene quaternary ammonium halide) cross-linked with divinylbenzene paste on polypropylene non-woven fabric, were assembled in a two-chamber flat membrane reactor, either in a horizontal configuration or in a vertical configuration. One of the chambers was filled with an aqueous solution of phenol and sodium hydroxide, while the other chamber was filled with a solution of allylbromide in dichloroethane, the membranes acting as phase transfer catalysts according to the mechanism depicted in Fig. 1.5. 

An example of the use of extractor-type PlMRs in reactions other than esterification is the gas-phase decomposition of MTBE catalysed by tung-stophosphoric acid. Lee et reported the use of closed-loop recycle membrane reactors by using polycarbonate, polyarylate or cellulose acetate membranes to selectively permeate the formed methanol in a flat membrane reactor configuration, with the catalyst packed in the retentate side and by using helium as sweep gas in the permeate side. The authors also used a tube-and-shell reactor configuration with the catalyst packed in the shell side being the sweep gas fed to the tube side. 

Daramola M O, Burger A J and Giroir-Fendler A (2011), Modelling and sensitivity analysis of a nanocomposite MFI-alumina based extractor-type zeolite catalytic membrane reactor for m-Xylene isomerization over Pt-HZSM-5 catalyst , Chem Eng J, 171,618-627. 

Membranes are used nowadays typically for the purification and separation of gases in several industrial processes. The role of catalysts in the development of membrane reactors (MRs) has in many cases been ignored in some levels, as the research has been concentrated on the membrane and development of new membranes. There is, however, a need for a catalyst in the MR to perform the desired reaction. The MRs containing a catalyst have been classified in three categories, namely extractor, distributor and contactor reactors (Miachon and Dalmon, 2004 van Dyk et ai, 2003). These reactor types are presented in Fig. 11.1. 

In the extractor-type reactor one of the reaction products is removed through the membrane from the reactor. The distributor type is used for reactant delivery along the catalyst bed. In the contactor type the flow either goes through the membrane and catalyst bed, or is introduced from both sides of the membrane to the catalyst bed. It is also worth noting that the amount of catalyst needs to be sufficient for the reactor type, and that both the membrane and the catalyst have an influence on the efficiency of... 

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