草酸与乙醛酸的萃取分离

SEPARATION OF OXALIC ACID AND GLYOXYLIC ACID BY EXTRACTION

以草酸和乙醛酸的稀溶液为分离对象 ,采用三辛胺 (TOA)为萃取反应剂、正辛醇为稀释剂 ,研究了单溶质、双溶质有机酸的萃取分离特性 ,测定了溶液pH值、萃取反应剂的浓度等因素对双溶质有机酸萃取的影响 ,提出了萃取的化学反应发生在有机相中的假定 ,建立了TOA萃取草酸的数学模型 .实验结果表明 ,草酸与TOA的萃合物有 1∶1和 1∶2两种形式 .在本实验的条件范围内 ,草酸的分配系数较乙醛酸大 ,且随溶液pH值的增大而下降 ,草酸对乙醛酸的分离系数随pH值的增大而减小 .随萃取反应剂浓度的增大 ,两酸的分配系数皆随之增大 ,分离系数也随之增大 ,而且对于高浓度的萃取反应剂在较高的溶液pH值下草酸仍具有较大的分离系数 .采用单溶质萃取反应平衡常数及纯稀释剂中双溶质的分配系数预测双溶质萃取的结果 。

The diluent solution of glyoxylic acid and oxalic acid was used as the separation object. TOA (in n-octanol) was used as the solvent. The extraction characteristics of single acid and two-acid solution were studied, and the influence of pH and the concentration of complexing agent on the distribution coefficients were measured. The suitable mathematical models were proposed to describe the relationship between TOA and carboxylic acid based on assumed extraction reaction in organic phase. The experimental results show that the ratio of oxalic acid to TOA is 1:1 and 1:2 in the organic phase. The distribution coefficient of oxalic acid is larger than that of glyoxylic acid, and both of them decreases with the increase of pH. The selectivity of oxalic acid to glyoxylic acid also decreases with the increase of pH. In the extent of this experiment, the distribution coefficients for each acid and the selectivity increase with the concentration of complexing agent, and a higher selectivity and the distribution coefficients can be obtained at higher pH for a larger concentration of complexing agent. The calculated results are close to the experimental data based on the models using the parameters K11 and K12 from the single acid experiment and mA and mB from the two-acid experiment in the presence of 100% n-octanol.