Intensified reactive extraction of 4-hydroxypyridine with di(2-ethylhexyl) phosphoric acid in 1-octanol by using tributyl phosphate

Abstract

Tributyl phosphate (TBP) exhibit significant intensification effect toward the extraction of 4-hydroxypyridine by di(2-ethylhexyl) phosphoric acid in 1-octanol via a more tendency to form (1:1) type complexes. The efficient separation of amphoteric organic compounds from dilute solutions is of great importance in the industrial field. In the present work, the reactive extractions of 4-hydroxypyridine (4-HP) with tributyl phosphate (TBP), di(2-ethylhexyl) phosphoric acid (D2EHPA) and TBP + D2EHPA dissolved in 1-octanol were investigated, respectively. The influences of the initial concentrations of TBP, D2EHPA and TBP + D2EHPA on distribution ratio ( D ) were discussed, as well as the reactive extraction mechanism were proposed. The obvious intensification effect was observed when the mixture of TBP and D2EHPA was used as extractant. The best extraction conditions were found to be of the molar ratio of D2EHPA and TBP at 2:1 and the equilibrium aqueous pH at 3.50–4.50. D values increased with the increase of the total concentration of TBP and D2EHPA in 1-octanol. Especially, the analysis on the extraction mechanisms clearly indicate (i) TBP in 1-octanol shows negligible reactive extraction toward 4-HP, (ii) D2EHPA in 1-octanol exhibits moderate extraction effect by forming 4-HP:D2EHPA (1:1) and 4-HP:2D2EHPA (1:2) type complexes, while (iii) D2EHPA in TBP/1-octanol demonstrates the maximum distribution ratio with the 4-HP:D2EHPA (1:1) type complex domination. The discussion provides new insights on the mechanism and opens a new way for the intensified extraction of amphoteric organic compounds by using the mixture of multiple extractants in the diluent.