Product catalytic membrane reactor

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. 

Ozone decomposition in airplanes Selective catalytic reduction of NOx Arrays of corrugated plates Arrays of fibers Gauzes Ag Methanol -> formaldehyde Pt/Rh NO production from ammonia HCN production from methane Foams Catalytic membranes reactors... 

Catalytic membrane reactors are not yet commercial. In fact, this is not surprising. When catalysis is coupled with separation in one vessel, compared to separate pieces of equipment, degrees of freedom are lost. The MECR is in that respect more promising for the short term. Examples are the dehydrogenation of alkanes in order to shift the equilibrium and the methane steam reforming for hydrogen production (29,30). An enzyme-based example is the hydrolysis of fats described in the following. 

The availability of new membrane processes such as membrane contactors and catalytic membrane reactors, the progresses in membrane-fouling control and the development of new membranes with well-controlled structures and properties, are recognized as key factors for the design of alternative production systems. 

Alexeeva OK, Alexeev S.Yu., Shapir B.L., Tulskii M.N. Modified tubular catalytic membrane reactor for hydrogen production from hydrocarbons. Eds. M.D. Hampton et al. Hydrogen Materials Science and Chemistry of Metal Hydrides, 2002 Kluwer Academic Publishers, NATO Science Series 11/71, 339-347. 

The conditions are substantially more favorable for the microporous catalytic membrane reactor concept. In this case the membrane wall consists of catalyti-cally active, microporous material. If a simple reaction A -> B takes place and no permeate is withdrawn, the concentration profiles are identical to those in a catalyst slab (Fig. 29a). By purging the permeate side with an inert gas or by applying a small total pressure difference, a permeate with a composition similar to that in the center of the catalyst pellet can be obtained (Fig. 29b). In this case almost 100% conversion over a reaction length of only a few millimeters is possible. The advantages are even more pronounced, if a selectivity-limited reaction is considered. This is shown with the simple consecutive reaction A- B- C where B is the desired product. Pore diffusion reduces the yield of B since in a catalyst slab B has to diffuse backwards from the place where it was formed, thereby being partly converted to C (Fig. 29c). This is the reason why in practice rapid consecutive reactions like partial oxidations are often run in pellets composed of a thin shell of active catalyst on an inert support [30],... 

One major disadvantage of catalytic membrane reactors is the fact that so far no convincing large scale concepts have been proposed. This concerns both the implementation of large membrane areas necessary for the production of bulk chemicals within a chemical reactor and its combination with devices for the addition or removal of the required heat of reaction. Membrane reactor concepts are therefore presently limited to lab scale investigations while the above mentioned sorptive methods seem closer to a large scale realization. 

Catalytic Membrane Reactors Membrane reactors combine reaction and separation in a single vessel. By removing one of the products of reaction, the membrane reactor can make conversion beyond thermodynamic equilibrium in the absence of separation. 

Besides total conversion, other reaction performance index may benefit from optimizing the catalyst distribution and location. Examples are product purity on the feed or p>ermeate side and product molar Row rate on the feed or permeate side. Yeung et al. [1994] have also investigated these aspects and provided comparisons among IMRCF, FBR and catalytic membrane reactor (CMR) in Figure 9.8. It is apparent that the various reaction performance indices call for different optimal catalyst distributions. 

Two of the main types of catalytic membrane reactors are shown in Fti, me 4-12, The reactor in the middle is called an inert membrane reactor ivi/ i catalyst pellets on the feed side (IMRCF). Here the membrane is inert 8i..1 serves as a batrier to the reactants and some of the products. The reactor on ih bottom is a catalytic membrane reactor (CMR). The catalyst is deposiid directly on the membrane and only specific reaction products are able to e it the permeate side. For example, in the reversible reaction... 

Takeuchi et al. 7 reported a membrane reactor as a reaction system that provides higher productivity and lower separation cost in chemical reaction processes. In this paper, packed bed catalytic membrane reactor with palladium membrane for SMR reaction has been discussed. The numerical model consists of a full set of partial differential equations derived from conservation of mass, momentum, heat, and chemical species, respectively, with chemical kinetics and appropriate boundary conditions for the problem. The solution of this system was obtained by computational fluid dynamics (CFD). To perform CFD calculations, a commercial solver FLUENT has been used, and the selective permeation through the membrane has been modeled by user-defined functions. The CFD simulation results exhibited the flow distribution in the reactor by inserting a membrane protection tube, in addition to the temperature and concentration distribution in the axial and radial directions in the reactor, as reported in the membrane reactor numerical simulation. On the basis of the simulation results, effects of the flow distribution, concentration polarization, and mass transfer in the packed bed have been evaluated to design a membrane reactor system. 

An interesting application of catalytic membrane reactors [14,136] relates to the production of tritium which together with deuterium will be the fuel for the fusion reactors of the future. Tritium is produced by mearts of a nuclear reaction between neutrons and lithium atoms in a breeder reactor. The tritium thus produced must be further purified to reach the purity levels that are required in the fusion reactor. For the extraction and purification process Basile and... 

Reactive distillation and catalytic membrane reactors separate products of reactions before secondary reactions can occur. Think of some places where they can be applied to favor mono-, rather than diadditions or substitutions. 

The catalytic dehydrogenation of light alkanes is, potentially, an important process for the production of alkenes, which are valuable starting chemical materials for a variety of applications. This reaction is endothermic and is, therefore, performed at relatively high temperatures, to improve the yield to alkenes, which is limited, at lower temperatures, by the thermodynamic equilibrium. Operation at high temperatures, however, results in catalyst deactivation (thus, requiring frequent reactivation), and in the production of undesired by-products. For these reasons, this reaction has been from the beginning of the membrane reactor field the most obvious choice for the application of the catalytic membrane reactor concept, and one of the most commonly studied reaction systems. 

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