三辛胺萃取分离苹果酸的特性

Extraction Behaviors of Malic Acid by Tri-octylamine

为探讨有机羧酸的成键机理,以二元有机酸——苹果酸为分离溶质,实验测定了三辛胺(TOA)在正辛醇、甲基异丁基酮(MIBK)和氯仿三种稀释剂中萃取苹果酸的平衡及负载溶剂红外光谱特性。结果表明,TOA浓度、稀释剂种类对萃取平衡的影响与苹果酸的浓度有关;平衡水相酸的浓度较低时,萃取剂可提供较大的萃取能力,TOA的化学计量饱和后,存在“过载”现象,且过载量为MIBK > 正辛醇 > 氯仿。TOA萃取苹果酸的萃合物主要为酸胺比为(2:1)、(1:1)和(1:2)等三种形式,其中(1:2)萃合物中苹果酸与TOA之间的结合一个是离子对成盐,一个是氢键缔合。同时,以质量作用定律为基础,建立了描述萃取平衡的数学模型,求得了相应的反应萃取平衡常数K11、K12、K21。

Reactive extraction is high in capacity and selectivity for separating polar organic chemicals from dilute solution. Phase equilibria governing the reactive extraction of malic acid from aqueous solution into solution of tri-octylamine(TOA) in the single solvent, such as n-octanol, 4-methyl-2-pentanone (MIBK) or chloroform, were investigated, and FT-IR spectrum of organic phase samples loaded with malic acid were analyzed to obtain stoichiometrics of the complex. The effect of diluent and TOA concentration in the organic phase on extraction behavior depends on the concentration of malic acid. The high extraction capability in protonated diluent appeared at low equilibrium malic acid concentration in the aqueous phase. After TOA was stoichiometric saturated, the overload phenomena was observed, the order of the extraction overload was MIBK>n-octanol>chloroform, and the overload capacity for various diluents appeared in the same order as the degree of extraction. According to the analyses of FT-IR spectrum and the extraction behavior, the stoichiometric ratio of malic acid bonded to TOA in the complex was found to be 1:2, 1:1 and 2:1. For (1:2) type complex, one carboxyl of malic acid is bonded to TOA with ion-pair association and another with hydrogen bond. Based on the mass action law and some assumptions, an expression of extraction equilibrium was derived, and the apparent extraction equilibrium constants were correlated. The predict equilibrium curves agreed well with the experimental data.