Integrated recovery and recycling of homogeneous catalysts by reverse flow adsorption: Selection of suitable adsorbents

A promising concept for the recovery of homogeneous catalysts is Reverse Flow Adsorption. In actual homogeneous catalyzed processes, a homogeneous transition-metal catalyst is at equilibrium with its free transition-metal center and ligands. Therefore, to apply Reverse Flow Adsorption, a combination of two adsorbents has to be used to reversibly adsorb: the transition-metal center and its ligands. The transition-metal center can be adsorbed by a suitable ligand immobilized onto a solid carrier, while the ligand is adsorbed by an immobilized transition-metal. Two groups of potential adsorbents were selected by the Hard and Soft Acid and Base (HSAB) theory for the adsorption of Co(II) and PPh3: (1) phosphor (polymer bound PPh3), sulfur (polymer bound methylsufanylmethyl) and chloride (polymer bound benzylchloride) functionalized adsorbents and (2) metal (Ag+, Co2+ and Na+) functionalized Amberlyst 15. The CoCl2 adsorption decreased, as predicted by the HSAB theory, according to: P > S > Cl. Metal functionalized adsorbents adsorbed the PPh3 With capacities decreasing, as predicted by the HSAB theory: Ag+ > Co2+ > Na+. All adsorption interactions proved to be reversible.