The environmentally benign nature of CO2 and the ever-increasing regulations on the use of conventional solvents present CO2 as a solvent of choice for extraction processes for remediation of contaminated media, as a substitute for CFCs in precision cleaning processes, etc. However, because of the low solubility of metal ions and conventional metal chelating agents, there has been only limited progress in use of CO2 as a solvent in the extraction of metals. Consequently, we have embarked on the molecular design and synthesis of several novel, highly CO2-soluble chelating agents. This paper describes the synthesis and evaluation of these chelating agents that exhibit solubilities in excess of 100 mmol/L of CO2 at room temperature and pressures of 1100−2000 psi and extract as much as 98% of metals such as mercury, lead, arsenic, chromium, and iron from various matrices in laboratory-scale extractions that use pure CO2 as the solvent.

No abstract

No abstract

No abstract

Carbon dioxide is an attractive organic solvent in today's chemical process environment, in that it is nonflammable, 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 nonpolar and therefore 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 phillic, 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-phillic oligomers, we have generated materials that both effectively extract metals from solid matrices and that dissolve in carbon dioxide in significant quantities. The application of such chelating agents is not limited to soil cleaning operations. In fact, these chelates make the use of CO2 possible in many applications where precision cleanup/recovery of metal ions are required. For example, CO2 has been promoted as a replacement for CFC's in cleaning processes in the electronics industry. Use of these chelates would allow the removal of metals, along with other impurities in a CO2 cleanup procedure.