Conceptual study of co-product separation from catalyst-rich recycle streams in thermomorphic multiphase systems by OSN

Homogeneous transition metal catalysts allow for high selectivity at mild reaction conditions. However, very high recoveries of the precious catalyst are decisive for the development of economic processes, especially in case of reactions with an atom economy below 100% since co-products and their potential accumulation have to be considered. To address this issue, an innovative process concept is investigated, which exploits thermomorphic multiphase systems combined with organic solvent nanofiltration for homogeneous catalyst recovery and co-product removal. In this concept, the reaction takes place at elevated temperature in a homogeneous liquid phase, while the reactor effluent is cooled down, inducing a phase split. This allows for the separation of a product-rich non-polar and a catalyst-rich polar phase that is recycled into the reactor. The current article investigates this concept considering a reductive amination reaction as case study based on an experimental membrane screening and a model-based evaluation. DuraMem 150 (T1) proved to be the best membrane for all tested solvents as catalyst ligand rejections higher than 99% and a removal of the co-product water were achieved. The model-based evaluation indicated a final OSN-process of three stages for the solvent methanol and the requirement of a subsequent solvent recovery that is realized by distillation. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.