Rotating Foam Stirrer Reactor: Effect of Catalyst Coating Characteristics on Reactor Performance

Rotating foam stirrer reactors have a promising application in multiphase reactions. In this reactor, highly porous open-celled materials, solid foams, are used both as a catalyst support and as stirrer blades. One of the advantages of such a foam stirrer is easy catalyst handling. This paper presents a preparation method for catalysts on solid foam supports. The performance of the alumina foam catalysts is tested in the hydrogenation of a functionalized alkyne. A stable and homogeneous catalytic coating was deposited on aluminum foams by a combination of anodization and wash coating using the slurry method. Anodization produced a rough and porous material that improved the adhesion of the catalytic coating. The use of a slurry with a bimodal particle size distribution increased the catalytic coating stability. The mass loss of the catalytic coating after applying ultrasonic vibrations was less than 10 wt %, which indicates a good adhesion. A high specific surface area was achieved by increasing the foam cell density, that is, the number of pores per linear inch (ppi), and the catalytic coating thickness. With the wash-coating method, catalytic coatings were produced having a thickness between 10 and 40 mu m, a porosity of around 50%, and a specific surface area up to 28.5 m(2)/g(foam). The hydrogenation of 3-methyl-1-pentyn-3-ol was chosen as the test reaction. Internal and external mass transfers limit the reaction rate of this fast reaction. High activity and selectivity were reached by combining a high specific surface area with a thin catalytic coating on the foam. Increasing the foam cell density up to 20 ppi led to enhanced liquid-solid mass transfer because of the high specific surface area combined with the fast refreshment of the catalyst surface. Coating thicknesses of less than 20 mu m led to improved internal mass transfer due to shorter diffusion paths.