Catalytic pervaporation membrane reactor

Figure 19.11 Catalytic pervaporation membrane reactor configurations (a) suspended catalyst membrane reactor (SC-MR), (b) catalytic-packed bed membrane reactor (CB-MR), and (c) a membrane reactor using a membrane with catalytic properties (CMR).

These proposed classifications can be further extended in two ways considering the reactor design (how it is clearly shown in the matrix of Figure 19.10) and considering the possibility of using inert membranes (inert pervaporafion membrane reactors (I-PVMRs)) or catalytic membranes (catalytic pervaporation membrane reactors (C-PVMRs)), as shown in Figure 19.11. 

Marconi, J.G.S. Tsotsis, T.T. Pervaporation membrane reactors. In Catalytic Membranes and Membrane Reactors, Wiley-VCH Weinheim, 2002 Chapter 3, 15-96. 

The way membranes (in various forms, i.e., cylindrical, coaxial, flat-sheet, spiral-wound, and hollow fiber, etc.) couple with the bioreactor depends on the role the membrane performs. As with catalytic and pervaporation membrane reactors, the simplest configuration consists of two separate but coupled units, one being the bioreactor the other the membrane module. The biocatalyst (e.g., enzymes, bacteria, yeasts, mammalian cells) could, in this case, be suspended in a solution and continuously circulated through the... 

Key words pervaporation, membrane reactors, integrated process, process intensification, catalytic 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. 

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 efforts and advances during the last 15 years in zeolite membrane and coating research have made it possible to synthesize many zeolitic and related-type materials on a wide variety of supports of different composition, geometry, and structure and also to predict their transport properties. Additionally, the widely exploited adsorption and catalytic properties of zeolites have undoubtedly opened up their scope of application beyond traditional separation and pervaporation processes. As a matter-of-fact, zeolite membranes have already been used in the field of membrane reactors (chemical specialties and commodities) and microchemical systems (microreactors, microseparators, and microsensors). 

Similar TS-1 films have been applied for phenol hydroxyl-ation reaction to dihydroxybenzenes (hydroquinone and catechol) [354] and catalytic oxidation of styrene to benzaldehyde and phenylacetaldehyde [355] with hydrogen peroxide as oxidant in batch-type membrane reactors. The dihydroxybenzenes and phenylacetaldehyde selectivity values increased with in-framework Ti content. In order to reduce the TS-1 membrane costs, Chen et al. [356] have successMly synthesized TS-1 on mullite tubes by replacing TPAOH with TPABr/EtjNH system (4% of the initial cost). The catalytic activity was tested in the probe reaction of isopropyl alcohol oxidation with hydrogen peroxide under pervaporation condition at 60°C. In general, future work on TS-1 film catalysts is required to improve mass transfer resistances and reaction conversion without compromising selectivity. 

Zeolite membranes show high thermal stability and chemical resistance compared with those of polymeric membranes. They are able to separate mixtures continuously on the basis of differences in the molecular size and shape [18], and/or on the basis of different adsorption properties [19], since their separation ability depends on the interplay of the mixture adsorption equilibrium and the mixture. Different types of zeolites have been studied (e.g. MFI, LTA, MOR, FAU) for the membrane separation. They are used still at laboratory level, also as catalytic membranes in membrane reactors (e.g. CO clean-up, water gas shift, methane reforming, etc.) [20,21]. The first commercial application is that of LTA zeolite membranes for solvent dehydration by pervaporation [22], Some other pervaporation plants have been installed since 2001, but no industrial applications use zeolite membranes in the GS field [23]. The reason for this limited application in industry might be due to economical feasibility (development of higher flux membranes should reduce both costs of membranes and modules) and poor reproducibility. 

A particular case of the contact mode sketched in Fig. 4.3f is represented by the use of catalytic dense polymeric membranes working in cross-flow mode on the liquid feed side and in pervaporation mode through the membrane (Bengston et al, 2002). This particular class will be not discussed further, since Chapter 1 of Handbook of membrane reactors Volume 1 Fundamental materials science, design and optimisation is dedicated to polymeric membrane reactors.. 

Cuperus F.P., van Gemert R.W. Dehydration using ceramic silica pervaporation membranes the influence of hydrodynamic conditions. Separ. Purif. Technol. 2002 27 225-229 Dalmon J.A. Catalytic membrane reactors. In Handbook of Heterogeneous Catalysis, Ertl G., Knbzinger H., Weitkamp J., eds. VCH Publication, 1997, Chapter 9.3 DeFriend K.A., Barron A.R. A simple approach to hierarchical ceramic ultrafiltration membranes. J. Membr. Sci. 2003 212 29-38... 

One of them employs membrane-based separation processes connected to the esterification reaction. In this respect, vapor permeation and pervaporation process have been tested and dn-ee different layouts have been reported for ethyl lactate production. In one of them, membrane module is located outside the reactor unit and the retenate is recirculated to the reactor." " In another scheme, the membrane module is placed inside the reactor, but the membrane does not participate in the reaction directly and simply acts as a filter," " and in the third configuration, membrane itself participates in die reaction catalysis (catalytic membrane reactor)." Different hydrophilic membranes, such as polymeric, ceramic, zeolites and organic-inorganic hybrid membranes were tested. ... 

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. 

In spite of the growing research effort, with the exception of fuel cells, there are only a few examples of industrial applications of non-biocatalytic polymeric membrane reactors, such as the Remedia Catalytic Filter System for the destruction of dioxins and furans from industrial combustion sources or pervaporation-assisted esterification processes. More research is required in order to find long-lasting high-performance and cheap polymeric materials and catalysts that can effectively compete with the traditional processes. On pursuing this quest, mathematical modelling and simulation are fundamental tools for the better understanding of membranes behaviour and optimization. 

Bengtson G, Panek D and Fritsch D (2007), Hydrogenation of acetophenone in a pervaporative catalytic membrane reactor with online mass spectrometric monitoring ,/Memh Sci, 293,29-35. 

In open fibers the fiber wall may be a permselective membrane, and uses include dialysis, ultrafiltration, reverse osmosis, Dorman exchange (dialysis), osmotic pumping, pervaporation, gaseous separation, and stream filtration. Alternatively, the fiber wall may act as a catalytic reactor and immobilization of catalyst and enzyme in the wall entity may occur. Loaded fibers are used as sorbents, and in ion exchange and controlled release. Special uses of hoUow fibers include tissue-culture growth, heat exchangers, and others. 

MFI zeolite membranes (silicalite-1, ZSM-5), on either flat or tubular porous supports, have been the most investigated for gas separation, catalytic reactors, and pervaporation applications. The structural porosity of MFI zeolite consists of channels of about 5.5 A, in diameter, the sihca-rich compositions induce... 

Figueiredo K C S, Salim V M M and Borges C P (2008), Synthesis and characterization of a catalytic membrane for pervaporation-assisted esterification reactors , Catal Today, 133-135,809-814. 

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