Catalytic Membrane

One of the earliest catalytic membrane configurations employed was that of the reactive tube. In this configuration, the material used to construct the tube fulfils both the roles of separation medium and catalyst. Few materials have this special capability. Palladium is one. Palladium has the ability to transport hydrogen through the matrix by a process of adsorption, dissociation, diffusion, and then reassociation on the low pressure side. Palladium is also a reasonable catalyst for many of the reactions detailed in Table 1, especially hydrogenation and dehydrogenation reactions. Thus, using this material to achieve both functions was an obvious consideration.

Transport can only be achieved through a chemical potential driving force of the hydrogen from the reaction zone to the separation zone. Such a driving force has been established with the use of a sweep gas on the permeate side to keep the hydrogen concentrations low. The sweep gas may either be inert or reactive with the hydrogen. Inert sweep gases offer the advantage of being simple to employ. Unfortunately, to achieve a partial pressure difference across the membrane, the sweep gas rate must be high and the permeated hydrogen is recovered as a dilute component in the sweep gas.

Reactive sweep gases offer other engineering possibilities and challenges. The use of air as a sweep gas in catalytic dehydrogenation membrane systems has been reported. At dehydrogenation temperatures (300-600°C), oxygen can react with hydrogen to form water. This reaction is highly exothermic. In contrast, the dehydrogenation reaction is endother-mic. Thus, thermal matching of the heat released by the hydrogenation of oxygen and the heat consumed by the dehydrogenation reaction would allow for an isothermal system. Because the hydrogenation reaction is rapid, the effective partial pressure on the permeate side of the membrane can be maintained near zero.

Catalytic membrane systems require that the membrane material be stable for both reaction and separation and that it operates well in both modes simultaneously.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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