Experimental Evaluation of a Micromesh Gas/Liquid Reactor for Catalytic Asymmetric Transfer Hydrogenation

Asymmetric transfer hydrogenation of acetophenone with isopropanol as a hydrogen donor in the presence of a homogeneous catalyst and simultaneous acetone removal by stripping has been performed in a microstructured mesh contactor that consists of parallel metal plates, gaskets and a microstructured mesh so that passages for gas and liquid phases are formed. The function of the micromesh is to stabilize the gas/liquid interface in its pores. The gas and liquid layers are 200 μm thick, while the stainless steel mesh is 50 μm thick, has 76 μm holes and 23 % open area. The removal of the acetone by-product from the reaction system shortens the required reaction time to achieve high conversion and reduces the enantiomeric excess erosion, as compared to a batch reactor with nitrogen bubbling as well as a continuous reactor without acetone stripping at 30 °C. Lower acetophenone concentration leads to higher enantiomeric excess for both the batch and the mesh reactor, with the latter providing superior performance in all cases. The final enantioselectivity is in the range 80–86 % for the mesh reactor and 70–85 % for the batch reactor. In the mesh reactor, the reaction reaches completion within 15 min. In the batch reactor, it takes more than 3 h to complete the reaction. At 15 °C, the mesh reactor reduces the required time to achieve a certain conversion, but does not affect reaction enantioselectivity, as compared to the batch reactor.