Studies On Reactive Extraction Of Hydroxybenzoic Acid From Dilute Solution

Reactive extraction is an extraction method based on the reversible reaction between Lewis acidic (basic) groups of solutes and Lewis basic (acidic) groups of extractants. Recently, it has received increasing attention because of its high selectivity and high efficiency for the separation of polar organics. This method has become one of the approaches to the preparations of high purity materials and the treatments of wastewaters containing organics at high concentration. Especially, it has been successfully used in the treatments of phenol-containing and amine-containing waterwaters.According to the principle of Lewis acid-base, the molecules, ions, or atomic groups which could accept (donate) electron-pair are Lewis acids (bases), while those compounds could not only accept but also donate electron-pair are called as amphoteric compounds. Based on the large amount of literature collections on the reactive extraction equilibrium behavior of acidic organic compounds, we used tributyl phosphate (TBP) and trialkylamine(7301) as extractants, and n-octanol and solvent-extracted oil as diluents to investigate the extraction equilibrium behaviors of o-hydroxybenzoic acid (o-HBA), m-hydroxybenzoic acid (m-HBA), and p-hydroxybenzoic acid (p-HBA) between aqueous and organic phases. The factors that affect extraction equilibrium, such as extractants, diluents, the concentrations of solutes and extractants, equilibrium pH, were discussed. Based on the mass action law, as well as the physical extraction and chemical extraction, the models of extraction equilibrium were established, by which the complexation ratio and the apparent reactive extraction equilibrium constants were calculated. Results indicated both TBP and7301have better efficiencies for extraction of HBA in the pH range investigated. The extraction efficiencies of polar diluent n-octanol are better than those of nonpolar diluent solvent-extracted oil. Aqueous equilibrium pH is the key role that affects extraction equilibrium. The distribution ratio decreased as the increase of equilibrium pH.Based on the experimental studies on reactive extractions of HBA, the effects of the electrical parameters of the solutes (namely pKai and pKa2) on extraction equilibrium were discussed with selected four systems including TBP/solvent-extracted oil, TBP/n-octanol,7301/solvent-extracted oil and7301/n-octanol. It showed that the electrical parameters of the solutes play critical roles on extraction efficiency, and the better efficiency always was received under aqueous pH between pKai and pKa2.