Catalysts membrane reactors

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

Figure 3.5 Membrane reactor catalyst-in-tube- (a) and catalyst-in-shell (b) configurations...

Fluidized-bed membrane reactor Catalysts in the reactor are present in a fluidized mode FBMR... 

Figure 4.9 Scheme of a Pd-membrane reactor Catalyst packed in lumen. 

Figure 4.10 Scheme of a finger-like membrane reactor Catalyst on the shell side. 

Key words catalytic membrane, packed-bed membrane reactor, catalyst distribution, deactivation, hydrogen spill-over, sustainability. 

Cross-sectional view of the palladium membrane reactor (catalyst 0.5 wt% Pt/AljOs pellets, membrane 3 mm OD, 5 pm-thick Pd/Al203 tube). 

Membrane Reactor. Another area of current activity uses membranes in ethane dehydrogenation to shift the ethane to ethylene equiUbrium. The use of membranes is not new, and has been used in many separation processes. However, these membranes, which are mostly biomembranes, are not suitable for dehydrogenation reactions that require high temperatures. Technology has improved to produce ceramic and other inorganic (90) membranes that can be used at high temperatures (600°C and above). In addition, the suitable catalysts can be coated without blocking the pores of the membrane. Therefore, catalyst-coated membranes can be used for reaction and separation. 

Catalytic A catalytic-membrane reactor is a combination heterogeneous catalyst and permselective membrane that promotes a reaction, allowing one component to permeate. Many of the reactions studied involve H9. Membranes are metal (Pd, Ag), nonporous metal oxides, and porous structures of ceran iic and glass. Falconer, Noble, and Speriy [in Noble and Stern (eds.), op. cit., pp. 669-709] review status and potential developments. 

Membrane reactors are defined here based on their membrane function and catalytic activity in a structured way, predominantly following Sanchez and Tsotsis [2]. The acronym used to define the type of membrane reactor applied at the reactor level can be set up as shown in Figure 10.4. The membrane reactor is abbreviated as MR and is placed at the end of the acronym. Because the word membrane suggests that it is permselective, an N is included in the acronym in case it is nonpermselective. When the membrane is inherently catalytically active, or a thin catalytic film is deposited on top of the membrane, a C (catalytic) is included. When catalytic activity is present besides the membrane, additional letters can be included to indicate the appearance of the catalyst, for example, packed bed (PB) or fluidized bed (FB). In the case of an inert and nonpermselective... 

Most research reports involve an inert, selective membrane that encloses a PB of catalyst particles, a packed-bed membrane reactor (PBMR). It must be noted that the catalyst bed can also be fluidized or fixed, but types other than PBs are rarely found in literature. The following are the advantages of this type of reactor ... 

In the case of a catalytic membrane reactor (CMR), the membrane is (made) intrinsically catalytically active. This can be done by using the intrinsic catalytic properties of the zeolite or by making the membrane catalytically active. When an active phase is deposited on top of a membrane layer, this is also called a CMR because this becomes part of the composite membrane. In addition to the catalytic activity of the membrane, a catalyst bed can be present (PBCMR). The advantages of a CMR are as follows ... 

Whilst the basic process for generation and conversion of syngas is well established, production from biomass poses several challenges. These centre on the co-production of tars and hydrocarbons during the biomass gasification process, which is typically carried out at 800 °C. Recent advances in the production of more robust catalysts and catalytic membrane reactors should overcome many of these challenges. 

The auto-thermal reaction of ethanol occurred in the shell side of a palladium membrane reactor in which a Zn-Cu/AlaOs industrial catalyst (MDC-3) was packed with silica powder. Ethanol-water mixture (nH2o/nEioH=l or 3) and oxygen (noa/nEioH=0.2,0.776 or 1.035) are fed concurrently to the shell side. The reaction temperatures were set at 593-723 K and the pijrasures were 3 10 atm. 

Figure 4. Comparison of Propane Aromatization Performances of a Palladium Membrane Reactor (PMR) and a Conventional Reactor (CR) using a Ga-H-ZSM-5 Catalyst...

One of the most studied applications of Catalytic Membrane Reactors (CMRs) is the dehydrogenation of alkanes. For this reaction, in conventional reactors and under classical conditions, the conversion is controlled by thermodynamics and high temperatures are required leading to a rapid catalyst deactivation and expensive operative costs In a CMR, the selective removal of hydrogen from the reaction zone through a permselective membrane will favour the conversion and then allow higher olefin yields when compared to conventional (nonmembrane) reactors [1-3]... 

Catalytic testings have been performed using the same rig and a conventional fixed-bed placed in the inner volume of the tubular membrane. The catalyst for isobutane dehydrogenation [9] was a Pt-based solid and sweep gas was used as indicated in Fig. 2. For propane oxidative dehydrogenation a V-Mg-0 mixed oxide [10] was used and the membrane separates oxygen and propane (the hydrocarbon being introduced in the inner part of the reactor). 

In the isobutane dehydrogenation the catalytic membrane reactor allows a conversion which is twice the one observed in a conventional reactor operating under similar feed, catalyst and temperature conditions (and for which the performance corresponds to the one calculated from thermodynamics) [9]. 

Figure 3.26 Schematic of a membrane reactor packed with filamentous catalyst [8. ...

Kragl and Dreisbach (1996) have carried out the enantioselective addition of diethyl zinc to benzaldehyde in a continuous asymmetric membrane reactor using a homogeneous soluble catalyst, described in their paper. Here a,a-diphenyl-L-proline was used as a chiral ligand, coupled to a copolymer made from 2-hydroxy ethyl methacrylate and octadecyl methacrylate, which had a sufficiently high molecular weight to allow separation by ultra-filtration (U/F). The solvent-stable polyaramide U/F Hoechst Nadir UF PA20 retained more than 99.8% of the catalyst. The ee was 80 %, compared to 98 % for a noncoupled catalyst. 

Catalytic Membranes Falconer, Noble, and Sperry (Chap. 14— Catalytic Membrane Reactors in Noble and Stem, op. cit., p. 669-712) give a detailed review and an extensive bibhography. Additional information can be found in a work by Tsotsis et al. [ Catalytic Membrane Reactors, pp. 471-551, in Becker and Pereira (eds.), Computer-Aided Design of Catalysts, Dekker, 1993]. 

One of the main applications of dendrimers is in catalysis allowing easy recycling of the homogeneous catalyst by means of nanofiltration. Carbosilane dendrimers functionalized with diphenylphosphine groups at the periphery have been synthesized and characterized. Palladium complexes of these dendrimers have been used as catalysts in the allylic alkylation reaction. These dendrimeric catalysts can be used in a continuous process using a membrane reactor.509... 

Ishihara, T. et al., Decomposition of methane over Ni/Si02 catalysts with membrane reactor for the production of hydrogen, Chem. Lett., 93, 1995. 

Homogeneous Catalysts Applied in Membrane Reactors N.J. RONDE AND D. VOGT... 

The separation of homogeneous catalysts by means of membrane filtration has been pioneered by Wandrey and Kragl. Based on the enzyme-membrane-reactor (EMR),[3,4] that Wandrey developed and Degussa nowadays applies for the production of amino acids, they started to use polymer-bound ligands for homogeneous catalysis in a chemical membrane reactor (CMR).[5] For large enzymes, concentration polarization is less of an issue, as the dimension of an enzyme is well above the pore-size of a nanofiltration membrane. 

Using unmodified Ru-BINAP and Rh-Et-DUPHOS catalysts Jacobs et al. performed hydrogenation reactions of dimethylitaconate (DMI) and methyl-2-acetamidoacrylate (MAA), respectively. [11,47] The continuous hydrogenation reaction was performed in a 100 mL stirred autoclave containing an MPF-60 membrane at the bottom, which also acts as a dead-end membrane reactor. The hydrogenation reactions will be discussed in paragraph 4.6.1. 

After reaching its maximum productivity (after ca. 8 hours.) the [Gl]-Nii2 showed a fast deactivation when applied in continuous catalysis performed in a membrane reactor (Figure 4.12). The fast loss of activity cannot be due to a lack of retention of the catalyst. Due to the high retention measured, this process should be much slower. A model study revealed that this deactivation process probably takes place by the formation of insoluble Ni(III) species (see Section 4.5 for further details). 

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