Towards continuous Rh-hydroformylation of long chain alkenes: handling methodology for the long-term stability of Biphephos in a continuous reactor with an attached membrane separation unit

Abstract

Diphosphites like Biphephos are known for their combination of high activity and high linear selectivity in the Rh-catalyzed hydroformylation of terminal alkenes. However, like most phosphite-type ligands, Biphephos is prone to hydrolysis under acidic conditions and oxidation in the presence of oxygen, resulting in detrimental catalyst performance loss. In this work, we identified practical aspects that safeguard the long-term stability of Biphephos during the Rh-catalyzed hydroformylation of alkenes. Furthermore, different additives (amines and one epoxide) were explored as stabilizers for Biphephos. The Biphephos/Rh/stabilizer system was first extensively investigated via³¹P-NMR, followed by batch autoclave experiments (100 ml reactors), and finally applied in an upscaled reactor (300 ml) with an attached nanofiltration membrane unit for catalyst retention. With cyclohexene oxide (CHO) as a stabilizer for the ligand, stable operation with high catalyst retention (95%) was achieved for over 100 h at high product selectivity (l/b = 78).