(769f) Selective Hydrogenation of a Functionalized Alkyne In Horizontal Rotating Foam Stirrer Reactors

Three-phase catalytic selective hydrogenations are key processes in fine chemicals production. This work presents the development of a new multi-phase reactor configuration for this type of application based on solid foams. These porous structures are used to mix the phases and, at the same time, as catalyst support. The foam surface area is further increased by deposition of a catalyst washcoat. By immobilizing the catalyst to the stirrer, the drawbacks of the slurry reactors, which is often used in the fine chemical industry, can be overcome, i.e., the catalyst separation step is not longer needed and the re-usage of the catalyst is possible.

The foam stirrer design presented in this work consists of a donut-shaped foam block mounted on a horizontal shaft. The reactor is partially filled with liquid and thus, the foam is alternately being in contact with gas and liquid. Due to the centrifugal forces at high rotational speeds, the gas is separated from the catalyst only by a very thin liquid film. This enhances the liquid-solid mass transfer of the gas reactant which is often the rate limiting step. Moreover, the formation of a “spray regime” leads to excellent gas-liquid mass transfer rates. Using the hydrogenation of 3-methyl-1-pentyn-3-ol as a model reaction, the observed reaction rate is higher in the foam stirrer than in the Rusthon stirrer. The foam stirrer performance can be optimized by using different foam geometrical surface areas. RTD measurements show that nearly plug-flow behavior can be achieved when dividing the horizontal vessel in several compartments using vertical donut baffles. This results in higher selectivity towards the desired product.