The separation of the decomposition products in two phase systems which accumulate hi life time of the catalyst from the rhodium complex and the excess free ligands is very difficult. Ruhrchemie (now a subsidiary of Hoechst) has developed a process to remove the decomposition products chemically by a two stage combination of extraction and reextraction with a pre-separation by membranes. Hoechst Ruhrchemie also developed the first successful industrial application of membrane technology for uni-phase systems allowing the continuous and simple separation of the catalyst system from the reaction product and its direct recycling into the catalysis.
Müller, T., & Bahrmann, H. (1997). Separation of catalyst compounds in two-phase and uni-phase systems by membranes. Journal of Molecular Catalysis A: Chemical, 116(1–2), 39–42. https://doi.org/10.1016/S1381-1169(96)00365-2