Next-generation multiphase systems for homogeneous catalyst recycling: overcoming the reactivity vs. separation dilemma

Abstract

A new generation of thermomorphic multiphase systems combines the crucial advantages of classic homogeneous catalyst recycling methods: the reaction occurs under monophasic conditions in green solvents without mass transport limitations. Meanwhile, as in aqueous biphasic systems, the products form a separate and ideally solvent-free phase after reaction, enabling efficient separation from both the homogeneous catalyst and the solvents. This principle is demonstrated in three next-generation multiphase systems using the green solvents water, methanol, ethylene glycol, and γ-valerolactone, applying the rhodium-catalyzed hydroaminomethylation of 1-decene as a model reaction. Using a structured approach, phase-behavior experiments supported by LLE predictions via PC-SAFT enabled efficient identification of suitable solvent compositions. Validating their reaction performance in single- and recycling-batch experiments, all systems were then upscaled to continuous miniplant operation, where 268 hours of cumulative runtime revealed stability and high separation efficiency. An ethylene glycol/methanol solvent system stood out by combining high yields (79%) and selectivities (83%), very low catalyst loss into the product phase at just 0.8 mg rhodium per kg of product, and a directly attainable product – an amine purity of 72%, reducing subsequent purification efforts. These findings highlight the strong potential of thermomorphic systems to advance sustainable catalytic processes and streamline product purification in industrial applications.