Studies On Reactive Extraction Of Hydroxyquinoline In Dilute Solution

Reactive extraction, which based on interactions between Lewis acid （alkali） of the solute andLewis base （or acid） functional groups of the extracting agent, has been attracting increasing attention andthoroughly researched for its high efficiency and high selectivity in separation of dilute polar organicsolution. This method has become one of the directions of high purity material preparation and highconcentration organic wastewater treatment. Especially in China, this method has been successfully used inthe clean production of wastewater containing phenol and amine process.According to the electronic theory of acid and alkali, acid can accept foreign electronic groups onthe molecules, while alkali can provide electronic groups on the molecules. Thus those who were able toaccept and provide electron called amphoteric compounds. Therefore, amphoteric compounds have uniquechemical, physical and biological properties. A large number of literature research and system analysishas been investigated on the reactive extraction equilibrium behavior of polar amphoteric compounds. Inthis paper, tributyl phosphate （TBP） and di-（2-ethyl hexyl） phosphoric acid （D2EHPA） were used asextractants and kerosene and n-octanol as diluents. The balancing features of extracting hydroxyquinoline（HQ, including2-HQ,4-HQ and8-HQ） were studied and investigated the related factors affecting theextraction equilibrium, such as kinds of extractants and diluents, concentraction of extractant and soluent,the balanced pH value of aqueous phase. Four extravtion systems—TBP-kerosene, TBP-n-octanol,D2EHPA-kerosene and D2EHPA-n-octanol—were inspected detailed. The results show that for8-HQ,the best extraction system was TBP-n-octanol system; for4-HQ, D2EHPA-n-octanol system shows up thebest extraction effect; for2-HQ, there is little difference between TBP and D2EHPA in n-octanol.Extraction effect of the polar diluent n-octanol was superior to the nonpolar diluent kerosene. Theequilibrium pH value of aqueous phase was one of the important factors that affect the extraction effect.Adopting the law of mass action and taking the physical extraction and chemical extraction into account atthe same time, mathematical models was set up for the extraction systems, and the composition ofcomplexes and the apparent equilibrium association constrants of the extraction systems were derived,respectively.Under appropriate assumptions and combined with the law of mass action, chemical extraction and physical extraction models were established, the expression of deviation degree Δ betweenexperimental value of distribution coefficient K_Dand the ideal value were obtained by fitting to K_DandK_D,ideal. Then the double logarithmic coordinate method was used to calculate the apparent equilibriumconstant K and the composition of extraction complexes n of each extraction system. Results show that inaddition to the ratio of4-HQ and TBP-n-octanol extraction system was found to be1:2, the other extractioncomplexes were generated by1:1type, at the same time, the change rule between the apparent equilibriumconstant K value and the extraction effect of the corresponding reaction system kept consistene.Based on the experimental study of hydxyquinoline extraction, effect of the electrical parametersof the solutes (pK_a1、pK_a2) and hydrophobic parameter （LogP） on the extraction equilibrium were discussed.It turned out that the parameters is one of the important factors affecting the extraction effects, effectiveexteaction results appears when the solute pH value is between pK_a1、pK_a2in general; extraction effect isalso associated with the hydrophobic parameters of solute, LogP of2-HQ,4-HQ and8-HQ is in line withthe changing rule of the distribution ratio in physical extraction and TBP as extractant which reacting withHQ by hydrogen bond.