Separation of p-Nitrophenol and o-Nitrophenol with three-liquid-phase extraction system

Three-liquid-phase systems containing polyethylene glycol with different molecular weight were explored to investigate the partitioning behavior of simulated wastewater-containing isomers of p-Nitrophenol (p-NP) and o-Nitrophenol (o-NP). The distribution behaviors of p-NP and o-NP with different parameters in three-liquid-phase system were investigated. The results showed a great effect of the solution pH, extractant type on the partition coefficient of the two isomers. In the three-liquid-phase systems, the satisfying separation results were obtained with hexane as extractant. At pH = 4.00, about 85% o-NP and 90% p-NP partitioned into the top organic phase and middle polymer-rich phase, respectively. The separation factor decreased sharply with the increase of the solution pH from 6.5 to 8.5. After once back extraction with 10 wt.% sodium hydroxide, high recovery percentage of o-NP was obtained from the top phase. The removal efficiency of phenolic compounds in the polymer-rich phase could reach 95% when the middle phase was extracted with butyl acetate (BA) twice. p-NP could be recovered when the BA phase was back extracted with 10 wt.% sodium hydroxide aqueous solution.