Membrane reactors operating temperature

Universal gas constant A-component reaction rate Hydrogen reaction rate /-Component reaction rate Selective membrane radius Hydrogen solubility Reactor operating temperature Permeation zone temperature Temperature of heating/cooling fluid Reaction zone temperature Temperature on catalyst surface Temperature inside catalyst particle Reactor tube wall temperature... 

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]... 

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]. 

Because Pd-alloy membranes operate at high temperatures in the range of WGS reaction and on the lower end of methane reforming reaction, they can be used in a membrane reactor configuration for the simultaneous separation of hydrogen. As discussed earlier,... 

For the application of membrane reactors it can be concluded that these are accepted as proven technology for many biotechnological apphcations. The membranes used in this area can operate under relatively mild conditions (low temperature and aqueous systems). However, there is a tremendous potential for membrane reactors in the chemical industry, which often requires apphcation in nonaqueous systems. Long term stability of the membrane materials in these systems will require an ongoing development from the side of materials scientists. As reaction selectivity is of major importance in the production of fine chemicals and pharmaceutical products, it seems plausible to expect that membrane reactors will find their way in the production of chemicals through applications in these areas. 

The possibility of having membrane systems also as tools for a better design of chemical transformation is today becoming attractive and realistic. Catalytic membranes and membrane reactors are the subject of significant research efforts at both academic and industrial levels. For biological applications, synthetic membranes provide an ideal support to catalyst immobilization due to their biomimic capacity enzymes are retained in the reaction side, do not pollute the products and can be continuously reused. The catalytic action of enzymes is extremely efficient, selective and highly stereospecific if compared with chemical catalysts moreover, immobilization procedures have been proven to enhance the enzyme stability. In addition, membrane bioreactors are particularly attractive in terms of eco-compatibility, because they do not require additives, are able to operate at moderate temperature and pressure, and reduce the formation of by-products. 

At first sight, adsorption and reaction are well-matched functionalities for integrated chemical processes. Their compatibility extends over a wide temperature range, and their respective kinetics are usually rapid enough so as not to constrain either process, whereas the permeation rate in membrane reactors commonly lags behind that of the catalytic reaction [9]. The phase slippage observed in extractive processes [10], for example, is absent and the choice of the adsorbent offers a powerful degree of freedom in the selective manipulation of concentration profiles that lies at the heart of all multifunctional reactor operation [11]. Furthermore, in contrast to reactive distillation, the effective independence of concentration and temperature profiles... 

The use of a membrane reactor in steam reforming has several advantages. Because of the lower temperature operation, the energy consumption of the process is reduced which results in lower emission of C02. The lower temperature also requires less expensive catalyst, tubing and other reactor materials. Since hydrogen of sufficient purity is produced directly from the reformer, the downstream shift conversion can be omitted. Moreover, the dimensions of the C02 removal and final purification units can be reduced. Hence, significant savings in equipment costs can be expected. 

The choice of the catalyst is of large influence on the behaviour of the reforming process. Ni-based catalyst are most common, but recently more advanced catalysts have been developed as well. As indicated before, one of the advantages of a membrane reactor is that it can be operated at much lower temperatures but with the consequence that state-of-the-art catalysts might not be sufficiently active anymore. In this paragraph, an overview is provided on commonly used catalysts and some of the problems that may be encountered [7],... 

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