Direct Electrochemical Recovery of Rhodium from Spent Hydroformylation Catalyst Streams

Abstract Homogeneous Rhodium-based catalysts are essential for hydroformylation because of their high activity, but recovering these valuable critical metals from spent reaction streams remains difficult using conventional energy- and chemical-intensive methods. Here, the direct recovery of the spent Rh from a post-reaction hydroformylation stream is achieved via electrowinning at both cathode and anode, followed by electro-stripping in diluted acid. Under optimized conditions, a single electrowinning stage recovered 37.6% of the spent Rh catalyst (19.3% from the cathode and 18.3% from the anode). A multi-stage cascade was able to bring recovery close to 77%. Mass spectrometry confirmed that the stripped Rh in the acidic solution existed as chloride- or nitrate- ligated complexes. X-ray photoelectron spectroscopy (XPS) revealed reduction of the spent Rh catalyst to Rh(0) at the working electrode and oxidation to Rh(III) at the counter electrode. A techno-economic analysis indicates that the process achieves cost savings of more than 100,000 USD per kilogram of Rh recovered. This work provides the first demonstration of direct electrochemical recovery of spent homogeneous hydroformylation catalysts from industrial con