Potential for metal foams to act as structured catalyst supports in fixed-bed reactors

• High rates of heat transfer can be achieved between tube wall and the reactants.
• In reactors use as: foam pellets, or solid foams (with/without radiation gaps).
• Geometric surface area of metal foams ≫ conventional pellets.
• Metal foams provide easier access to catalytic sites than conventional pellets.
• Metal foams offer another step-change to improve steam methane reforming catalysts.

Experiments were performed in which the benefits of flow through the large interconnecting cavities in structured metal foams (acting as catalyst supports) could be better understood. For example, using tablet shaped (8 mm × 8 mm × 3 mm) metal foam pellets (1200 μm cavity size), at a pressure drop of 0.5 bar across a 2 m long packed bed (i.d. = 71.7 mm, flow = 0.039 kg/s), the forced convective bulk flow through the foam pellets was found to represent 38% of the total flow, thereby demonstrating the ease with which reactants could access the internal cavities of the metal foam pellet and hence the catalyst layer.In another example it is shown how a metal foam structure could be exploited in a high temperature fixed bed application (e.g. for endothermic reactions). Experiments were performed in a 74 mm i.d. column, which contained different forms of catalyst supports, such that the depth of the fixed bed was 600 mm. To represent a gaseous mixture in a process application, compressed air (e.g. 0.008 kg/s) was electrically pre-heated (e.g. up to 500 °C), and then fed into the fixed-bed which was surrounded by an electrical furnace (e.g. tube surface 650–950 °C). From these experiments it was shown that, depending on the application, the metal foam structure could: (a) completely fill the channel as a continuous structure; (b) be used in the form of catalyst foam pellets; and (c) be installed with gaps between segments to exploit heat transfer by radiation (from the walls of the channel).

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