Introduction

The concept of completing both a reaction and separation in a single process unit has motivated research into the development of catalytic membrane reactors. For example, it has long been recognized that palladium metal has the capacity both to permeate hydrogen and to promote a variety of reactions. Thus, harnessing both of these features in a single device seemed a logical combination. In the mid 1960s, Wood and co-workers demonstrated that the dehyd-rogenation of cyclohexane to cyclohexene could be increased if the hydrogen produced was removed from the reaction vessel through semipermeable palladium walls. In this case, the palladium walls also acted to catalyse the dehydrogenation reaction. A membrane reactor of this type is illustrated in Figure 1.

In Russia, Gryaznov conducted much of the research that followed. Starting in the late 1970s, Gry-aznov began publishing his results on the use of palladium membrane reactors both to produce and to recover hydrogen from a myriad of dehydrogenation reactions. In the dehydrogenation reactions, hydrogen leaves the reactor by permeating through the semipermeable membrane. However, reactors can also be used in reactions where hydrogen or other reaction products enter the reaction chamber by penetration through the membrane. The commonest classes of reactions that have been successfully influenced by the use of membrane reactor technology are listed in Table 1. Details relating to the large volume of research reported are provided in the Further Reading section. None of these membrane reactors are in commercial use. But some - the selective oxidation of methane, for example - are the subject of a very large industrial research effort. If successfully developed, this process would change the feedstock basis of a number of petrochemical processes.

Most research on the development of membrane reactors involves the use of these devices to shift equilibrium-limited reactions (often dehydrogena-tions). The thermodynamic equilibrium of the react-ants and products at the temperature and pressure of the reaction determine the conversion achievable in any given reaction. For dehydrogenation reactions, increasing temperature and decreasing pressure promote an enhanced reaction. Unfortunately, each of these solutions has an associated cost. Increasing the reaction temperature typically results in a reduced

Figure 1 Schematic of a membrane reactor using hydrogen-permeable palladium membranes to shift the equilibrium of the dehydrogenation reaction cyclohexane to cyclohexene.
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.

Get My Free Ebook


Post a comment