Determination of metal-chelate complex solubilities in supercritical carbon dioxide

With new interest in the processing of heavy metals by chelation incorporated with supercritical fluid extraction, an accurate metal-chelate complex solubility database has become increasingly important. To measure these solubilities, a dynamic measurement technique was developed to determine organometallic complex solubility as well as chelate agent or ligand solubility in supercritical carbon dioxide. This technique utilizes a mixed-solvent stream to eliminate potential clogging and pressure increases during expansion, problems inherent with most dynamic techniques used to measure solubilities in supercritical fluids. In addition, the technique may be readily used in conjunction with basically any analytical chemical method. After proving the accuracy of the new method by measuring phenanthrene solubility in supercritical carbon dioxide, solubility measurements of two commercially available chelate complexes, cupric acetylacetonate and diethyldithiocarbomate copper salt, were made at near ambient temperatures. A thermodynamic model was then incorporated to predict solubility in supercritical carbon dioxide at varying operational conditions. The model uses Peng-Robinson equation of state and van der Waals-1 mixing rules.