Solvent effect on distribution ratio of Pd(II) in supercritical carbon dioxide extraction and solvent extraction using 2-methyl-8-quinolinol

摘要

The distribution ratio (D_M) of Pd(II) by the extraction with 2-methyl-8-quinolinol (HMQ) was determine dusing the supercritical carbon dioxide medium (SF-CO_2) and organic solvent media such as perfluoro-methylcyclohexane, heptane, cyclohexane, carbon tetrachloride and benzene. From experimental results of the slopes of log D_M versus pH plot and log D_M versus HMQ concentration plot, the extracted species both in the SF-CO_2 extraction (SFE) and the sovlent extraction (SE) were determined to be Pd(MQ)_2. The distribution constant of HMQ (K_(D, HMQ)) in teh SFE and SE systems were determined from the dependence of the distribution ratio of HMQ (D_HMQ) on the pH. A linear relationship was observed between long K_(D,HMQ) and the solubility parameter (delta) of the extraction medium based on the regular solution theory in both the SFE using SF-CO_2 at the pressure of 8.5-40 MPa and the SE systems. The difference in the slope of the log K_(D, HMQ) versus delta plot between the SFE and the SE systems is attributable to the extent of the specific interaction of the solute HMQ with the solvent molecules, i.e. CO_2 molecules and the organic solvent molecules. The D_M values delta plot obtained under a given extraction condition using SF-CO_2 (11-40 MPa) and organic solvents showed clear linearity. The D_M obtained using SF_CO_2 at relatively low pressure range from 8.5 to 11 MPa was independent of the pressure and the delta of SF_CO_2, which coincides with the experimental fact that the solubility of Pd(MQ)_2 in the SF-CO_2 at 8.5-11 MPa was practically constant.