Reactors as Tools for Improved Catalytic Oxidation Processes

Membrane Reactors as Tools for Improved Catalytic Oxidation Processes 

This chapter reviews the possibilities that the application of a membrane in a catalytic reactor can improve the selectivity of a catalytic oxidation process to achieve a more compact system or to otherwise increase competitiveness. Classification differentiates between those reactors using dense membranes and those using porous membranes. Dense membranes provide high selectivity towards oxygen or hydrogen and the selective separation of one of these compounds under the reaction conditions is the key element in membrane reactors using such membranes. Porous membranes may have many different operation strategies and the contribution to the reaction can be based on a variety of approaches reactant distribution, controlled contact of reactants or improved flow. Difficulties for the application of membrane reactors in industrial operation are also discussed. 

Porous Microporous Zeolites, silica, Vycor May act as molecular sieve, selective in several mixtures 

The shape of the membranes employed in laboratory studies is usually tubular (i.e. tubes with an external diameter of around 1 cm), and this is clearly the preferred option when a catalyst bed is located inside a membrane. However, flat membranes are also used when the material is made in the laboratory and in some pilot plant applications. In some of the most recent works, hollow fiber membranes have been developed. This shape has the advantage of providing a large surface-to-volume ratio and requires a smaller amount of material per unit of surface area, both factors contributing to a lower cost. 

Dense membranes are those in which the pores of the membrane material do not cross from one side of the membrane to the other. As shown in Table 27.1, two categories of dense membranes are employed for catalytic oxidations ceramic membranes and metallic membranes. 

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