Synthesis and Evaluation of Metal-Ligand Complexes for Selective Olefin Solubilization in Reactive Solvents

The separation of 1-hexene from Fischer-Tropsch streams is an expensive and difficult separation because of the low relative volatilities encountered. Applying metal-ligand complexes, which -complex olefins, can increase the selectivity and capacity of these separations. In this paper, potential metal-ligand combinations are screened for this purpose using ethylene as the olefin. Ethylene solubility measurements with the metalligand complexes show a qualitative relationship between the stability and ability of the metal-ligand complex. The ligands LIX 26 (a hydroxyquinoline) and LIX 54 (a diketone) do not easily extract silver, and the resulting metal-ligand complex is unstable as silver precipitates. In contrast, Cyanex 301 and 302, thiophosphoric acids, easily extract silver and are very stable, but here the silver ion no longer forms complexes. The ligands, bis(2-ethylhexyl)phosphoric acid and dinonylnaphthalenesulfonic acid, result in a stable metal-ligand complex that can also selectively complex ethylene relative to ethane.