Abstract
Three new CO2-philic open-chain organophosphorous chelating ligands, i.e. ethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphate (EG2IPE), triethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphate (EG3IPE), and tetraethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphate (EG4IPE), were synthesized and characterized. Solubilities of these ligands in scCO2 were determined at different combinations of temperature (313.15333.15K) and pressure (920MPa), which generally showed considerable solubility in each case. These experimental data are in agreement with computed data via a semi-empirical model, in which the average absolute relative deviations lie in the range of 4.094.95%. The effect of these ligands on supercritical fluid extraction of selected rare earth metals (La3+, Ce3+, Pr3+, Nd3+, Sm3+, Gd3+, Er3+, and Yb3+) was investigated at 313.15K and 20MPa. The extraction efficiency of this system was found to increase in the order EG4IPE<EG3IPE<EG2IPE with a range from 55% to 79%. The rationale behind different selectivities toward these metals was also discussed in comparison to other traditional organophosphorous agents. A detailed experimental analysis of the complexation patterns by means of a combination of IR, 1H NMR and ESI-MS has revealed that the interaction of ether oxygen group in EG4IPE with metals and the corresponding extraction mechanism.
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