Highly CO2-Soluble Chelating Agents for Supercritical Extraction and Recovery of Heavy Metals

Carbon dioxide is an attractive organic solvent in today's chemical process environment in that it is non-flammable, inexpensive, and exhibits low toxicity. Further, materials solubilized in carbon dioxide are easily and completely recovered/concentrated from solution via a simple pressure quench. Despite these favorable properties, CO2 is non-polar, and as such is a very poor solvent for materials such as conventional metal chelating agents, thus blocking application of carbon dioxide in metal extraction/recovery. Consequently, we are exploring the molecular design of materials which are highly CO2-philic, that is, they exhibit solubilities in carbon dioxide which are significantly greater than alkanes with the same number of main-chain atoms. By functionalizing chelating moieties with CO2-philic oligomers, we have generated materials which both effectively extract metals from solid matrices and which dissolve in carbon dioxide in significant quantities.