Reverse Flow Adsorption Technology for Homogeneous Catalyst Recycling

Catalysis is a very important process from an industrial point of view as the production of most industrially important chemicals involves catalysis. Two types of catalysis are generally distinguished: heterogeneous – or heterogenized – catalysts and homogeneous catalysts. From these two, the heterogeneous type of catalyst is the major one in today’s chemistry. With the increasing demands for more complex chemicals in the fine chemical industry, the selectivity becomes more and more important. In these new evolving fields of catalysis, homogeneous catalysts become of a more and more increasing popularity. In spite of the advantages, homogeneous catalysis is still not as common utilized as heterogeneous catalysis due to important draw-backs of the standard recovery methods, among which: decomposition during distillation, need for additional solvents during extraction or leaching of catalyst compounds in membrane filtration.

To avoid the drawbacks of the various methods for catalyst recovery, we have suggested an alternative recovery of the homogenous catalyst: Reverse Flow Adsorption. By using a selective adsorbent, the homogeneous catalyst can be retained in an adsorption bed while the product flow continues to the product purification. Just before breakthrough of the homogenous catalyst from the adsorption bed, the saturated adsorption bed is regenerated by the reversal of the flow provided that the adsorption is reversible. During this regeneration process, the homogeneous catalyst is recycled to the reactor and a semi-continuous recovery and recycling process is gained. 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.