Studies On Reactive Extraction Of Hydroxypyridine Using DI-(2-ethylhexyl) Phosphoric Acid

Reactive extraction is a new separation technique that is a chemical reaction of functional group of thesolutes separated and extractants, then obtained the regained rolutes and the recycled extractants bychanging pH and temperature. It possesses of high efficiency and high selectivity for polar organicseparation of dilute solution.Amphoteric compounds, which contain two typical functional groups of Lewis acidic and Lewis basicgroups, possess of particular physical, chemical and biological properties. Reactive extractions of a kind ofamphoteric compounds named hydroxypyridine including o-hydroxypyridine, m-hydroxypyridine,p-hydroxypyridine, using Di(2-ethylhexyl)phosphoric acid(D2EHPA)in1-octanol and kerosene andD2EHPA+tributylphosphate (TBP) in1-octanol as extractants, were systematically studied. The influencesof the concentration of extractants, the type of diluents, the pH value of aqueous solutionand and the initialconcentration of hydroxypyridine on distribution coefficient (D) were discussed. The result displays thatthe D increased with the increase of the concentration of D2EHPA, decreased with the increase of theconcentration of hydroxypyridine and the D increased with the increase of the pH value first then decreasedand the peak value of the D appears the neutral molecules of hydroxypyridine of the corresponding pHvalue area. Polar dilutes(1-octanol) provide with higher D for extracting hydroxypyridine with D2EHPA.The interaction mechanisms between D2EHPA in1-octanol and kerosene and hydroxypyridine werevalidated with Infrared spectroscopic analysis by comparing the characteristic peaks change of thefunctional groups with the solute, the extractant and the loading organic phase. The effect of the variouspH on the interaction mechanisms was analysised. The results showed: it could be concluded D2EHPAmainly reacted with hydroxypyridine to form ion-pair complexes through its–OH interacting with–N–ofhydroxypyridine to form the complexes of the same structure whether in1-octanol or kerosene. The pHvalue of the aqueous solution has no influence on the interaction mechanisms.The electronic parameters of solutes (i.e. pKa,pKband lgP) were of great influences on extractionequilibrium. Based on the experiment of reactive extraction on hydroxypyridine, the effect of the electronicparameters and the type of dilutes on the D was preliminarily studied. The results showed: the electronicparameters(pKa,pKb),the lipophilicity parameters (lgP) and the type of the dilutes has great influence on the D.The synergistic extraction is a new separation method separaed the dilute solution of the organicmatter put forward recently. It possesses of the both merits of synergistic and reactive extraction,possessing of higher efficiency and higher selectivity, and has been successfully used in the metalextraction separation. The extraction of hydroxypyridine using the composite extractants(D2EHPA andTBP) in1-octanol was preliminarily studied. The result showed: It was obvious synergistic effect onhydroxypyridine between D2EHPA and TBP in1-octanol. It exists the best tatio of D2EHPA to TBP incomposite extractants. It was the same trendency comparing to the single extraction, the D increased withthe increase of the concentration of mixtured extractants(the constant Rs) and the increase first and thendecrease with the increase of the pH value. The mixtured extractants and hydroxypyridne form the ion-complexes. The separaed extraction and the synergistic extraction exist simultaneously in the synergisticprocess using D2EHPA and TBP in1-octanol.