Robust and flexible continuous operation of homogeneous catalysis in thermomorphic multiphase systems − On-stream switching of substrates and reactions in amine production

This work presents the first continuous, multipurpose operation of a miniplant with integrated catalyst recycling using a thermomorphic multiphase system (TMS). Five different tertiary product amines were produced via the homogeneously catalyzed hydroaminomethylation and reductive amination in three consecutive miniplant experiments with a cumulative operating time of 275 h. These investigations involved on-stream switching of the substrates (alkene, secondary amine, aldehyde) as well as type of reaction. Analysis of more than 700 GC and ICP samples provided valuable insights into the robustness of the applied methanol/n-dodecane TMS regarding system variations. Next to consistently high reaction performance with yields of up to 71 % to the tertiary amines, efficient phase separation was maintained over the entire operating time. In addition, highly efficient removal of the potentially destabilizing coproduct water by organic solvent nanofiltration (OSN) was demonstrated: water was removed at a rate equal to its rate of formation, thus ensuring stable long-time operation. Extremely low losses of the valuable rhodium catalyst via the product phase with consistently less than 1.7 mg Rh per kg of product highlight the efficiency of thermomorphic multiphase systems. Together with the demonstrated high operational robustness, our results allow an optimistic view on the application of TMS in future industrial processes.