二(2-乙基己基)磷酸/磷酸三丁酯复合萃取剂协萃对氨基苯甲酸

Synergistic extraction behavior of p-aminobenzoic acid by di-2-ethylhexylphosphoric acid and tri-n-butylphosphate

为强化两性官能团化合物的萃取分离性能,以对氨基苯甲酸(PABA)为被分离溶质,二(2乙基己基)磷酸(D2EHPA)/磷酸三丁酯(TBP)/正庚烷的混合物为萃取剂进行了萃取平衡特性的研究,考察了溶液的pH值、D2EHPA浓度、TBP浓度对于萃取平衡的影响,建立了复合萃取剂协同萃取PABA的萃取平衡分配系数的表达式.结果表明,D2EHPA/TBP/正庚烷复合萃取剂萃取PABA具有明显的协萃效应,协萃机理为D2EHPA及TBP分别与PABA的Lewis碱性官能团(—NH2)和Lewis酸性官能团(—COOH)缔合形成亲油性更强的萃合物,且D2EHPA与TBP的浓度差异越小,协萃效应越明显.根据萃取平衡分配系数表达式拟合求取了表观萃取平衡常数,复合萃取剂的值远大于D2EHPA、TBP单独作为萃取剂的值,进一步证明了本文提出的协萃机理.

Synergistic extraction equilibrium of p-aminobenzoic acid by the mixture extractant of di-2-ethylhexyl phosphoric acid （D2EHPA） and tri-n-butylphosphate （TBP） in heptane was investigated at various initial pH values and D2EHPA, TBP concentrations, and a mathematical model was proposed to describe the extraction equilibrium. The results showed that the extraction of p-aminobenzoic acid with the mixed solvent presented synergistic effect by TBP bonded to -NH2 on p-aminobenzoic acid and D2EHPA associated with -COOH on p-aminobenzoic acid, and the synergistic effect was more obvious when D2EHPA concentration was close to TBP concentration. The apparent extraction equilibrium constants were obtained by fitting the experimental data to the models proposed in this paper, and the apparent extraction equilibrium constants for the mixture solvent of D2EHPA and TBP were much higher than those for D2EHPA and TBP solvent alone.