Polymeric catalytic membrane reactors

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. 

Polymeric catalytic membrane reactors (PCMRs), if the membrane is itself catalyticafly active. 

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. 

The dimerization of isobutene carried out in a forced-flow polymeric catalytic membrane reactor was reported by D. Fritsch and co-workers. The authors prepared composite porous membranes consisting of a catalytic layer made of solid add catalysts, such as siUca supported Naflon , Nafion NR50, Amberlyst 15 and silica supported tungstophosphoric add dispersed in polymeric binders such as Teflon AF, Hyflon AD, polytrim-ethylsilylpropyne, or polydimethylsiloxane (PDMS), cast on microporous support membranes made of polyacrylonitrile (PAN) or Torlon . The membranes were assembled in the membrane reactor into which isobutene was fed in the retentate side with a build-up pressure of 4 bar. The liquid product was collected on the permeate side. 

Buonomenna et aV reported the liquid-phase oxidation of dibenzylamine to the correspondent nitrone using a polymeric catalytic membrane reactor. 

Brandao L, Fritsch D, Mendes A M and Madeira L M (20(17), Propylene hydrogenation in a continuons polymeric catalytic membrane reactor , Ind Eng Chem Res, 46,5278-5285. 

Brandao L, Madeira L M and Mendes A M (2007), Propyne hydrogenation in a continuous polymeric catalytic membrane reactor , Chem Eng Sci, 62, 6768-6776. 

Sousa J M, Cruz P and Mendes A M (2001), A study on the performance of a dense polymeric catalytic membrane reactor , Catal Today, 67,281-291. 

Sousa J M and Mendes A M (2003), Simulation study of a dense polymeric catalytic membrane reactor with plug-flow pattern , Chem EngJ, 95,67-81. 

Sousa J M and Mendes A M (2006), Consecutive-parallel reactions in noniso-thermal polymeric catalytic membrane reactors , Ind Eng Chem Res, 45, 2094-2107. 

In a dense polymeric catalytic membrane the catalyst can be a thin layer on the membrane surface or distributed in the thickness of the polymeric matrix. An exhaustive review of methods for the preparation of catalytic polymeric membranes has been reported by Ozdemir et al. (2006). Vankelecom (2002) thoroughly reviewed the application of polymeric membranes in catalytic reactors. 

Bottino, A., Capannelli, G, Comite, A., Di Felice, R., 2002. Polymeric and ceramic membranes in three-phase catalytic membrane reactors for the hydrogenation of methylenecyclohexane. Desalination 144,411 16. 

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. ... 

An innovative potential application of membrane technology in catalysis and in catalytic membrane reactors is the possibility to produce catalytic crystals with a weU-defined size, size distribution, and shape by membrane crystallization (Fig. 27.9) (Di Profio et al., 2003, 2005). This innovative technology makes use of the evaporative mass transfer of volatile solvents through microporous hydrophobic membranes in order to concentrate feed solutions above their samration limit, thus attaining a supersaturated environment where crystals may nucleate and grow. In addition, the presence of a polymeric membrane increases the probability of nucleation with respect to other locations in the system (heterogeneous nucleation). 

The use of polymeric catalytic membranes in distributor/contactor-type reactors for hydrogenation or oxidation reactions has been widely described in several former and recent reviews. Mixed-matrix membranes of PDMS hlled with Pd particles, composite membranes of ionic liquid-polymer gels filled with Pd/C, ° ionic liquids containing rhodium complexes and supported in polystyrene sheets in a corrugated configuration, have been used for the selective gas-phase hydrogenation of hydrocarbons in contactor-type membrane reactors. 

Because of their intrinsic characteristics, mostly dense rubbery polymers have been considered for the preparation of polymeric catalytic membranes. The mass-transport mechanism considered has been the well-known sorption-diffusion model.ii Modelling the kinetics of the reaction(s) occurring at the occluded catalyst level is a much more complex task. The reaction may be carried out under special operating conditions, for example in a batch reactor where the catalyst is dispersed in a support - or directly inside the catalytic membrane, -" a reaction-rate model is assumed and the related parameters are determined by fitting the global model to the experimental data. In other cases, the kinetic models determined by other authors are used. - In some theoretical studies, a hypothetical reaction-rate model and the respective model parameters are assumed. 

Volkov V. V, Petrova I. V, Lebedeva V. I., Roldughin V. I. and Tereshchenko G.F. (2011), Palladium-loaded polymeric membranes for hydrogenation in catalytic membrane reactors, in A. Basile and F. Gallucd (Eds), Membranes for Membrane Reactors Preparation, Optimization and Selection, John Wiley Sons Ltd, Chichester, UK, 531-548. 

Zeolite membranes have attracted a lot of interest for their uniform pore size at molecular scale, which allows the separation of liquid and gaseous mixtures in a continuous way. Because of their thermal and chemical stability, they can also be used in processes at high temperatures and in the presence of organic solvents where polymeric membranes fail. In addition, zeolite materials exhibit intrinsic catalytic properties which clearly suggests the use of zeolite membranes as catalytic membrane reactors (CMRs). In the last two decades, enormous progress on zeolite membrane synthesis has been made, but only 20 structures are used for membrane preparation even if 170 zeolitic structures are available today (Baerlocher et al, 2007). The high cost and poor reproducibility in the synthesis step hinder the application of the zeolite membranes at industrial level (Caro et al, 2005 Mcleary et al., 2006). Until now, only NaA and T-type zeolite membranes... 

Chapter 4 (Santucci, Tosti, Basile) is mainly focused on the development of membranes based on metals other than Pd, such as Ni, Nb, V and Ti, which are considered today promising substitutes for the Pd-alloys. Particular attention is given to the synthesis of these membranes as well as to the effect of alloying on their chemical-physical properties. The chapter also provides a description of two porous (ceramic and glass) membranes used as a support for the new metal alloys, in gas separation and in membrane reactors, respectively. The objective of Chapter 5 (Gugliuzza) is to document what is known about nanocomposite polymeric membranes and the procedures of fabrication. Their potentialities in catalytic membrane reactors, bioreactors and membrane operations for alternative power production are highlighted. 

Another type of reactor that may have considerable future potential for use in homogeneous catalytic reactions is called the membrane reactor. These reactors have been successfully used for the commercialization of manufacturing processes based on enzyme catalysis. In fact, 75% of the global production of l-methionine is performed in an enzyme reactor. A membrane is basically an insoluble organic polymeric film that can have variable thickness. The catalyst... 

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