Complexation Extraction Of Glycolic Acid From Edta Synthetic Solution

As a widely used chemical product and fine chemical intermediate, glycolic acid has a wide range of uses in the areas like cleaning, cosmetics, biodegradation and so on. A certain amount of glycolic acid exists in the EDTA synthetic solution because of the side reaction, so the recovery of glycolic acid can be both environmental and economical. The complexation extraction of glycolic acid from EDTA synthetic solution using solvents was proposed in this paper. Various factors which affecting the extraction efficiency were studied, and the complexion extraction and back-extraction process were determined. Finally, the extraction mechanism of glycolic acid was discussed.Using trioctylamine as extractant,1-octanol as diluent, through the complexation extraction of glycolic acid from the EDTA synthetic solution and back-extraction under high temperature with deionized water added in, the much purer glycolic acid solution was obtained. The influence factors of complexation extraction such as trioctylamine proportion compared with octanol, water to oil ratio, extraction temperature, mixing time, extraction series were tested, and the factors on back-extraction efficiency of glycolic acid like extraction time, temperature, oil to water ratio, back-extraction series were also investigated. Experimental results showed that using60%tri-octylamine and40%n-octanol as extraction solvents, water to oil ratio as1:1, extracting with stirring at room temperature for30min, after three series of extraction, more than90%glycolic acid could be extracted from the EDTA synthetic solution. Then, using deionized water as back-extracion solvent, oil to water ratio as1:0.7, extracting with stirring at85℃for2hours, by three series of extraction, the recovery rate of glycolic acid could be90%or more.Based on the theoretical methods like corresponding solution method,equilibrium equation, saturated solution method and IR spectra,the complexation extraction mechanism of glycolic acid was discussed.Combined the glycolic acid concentration in extraction equilibrium with the corresponding solution method,the ratio of physical extraction to complexation extraction was inspected;through physical extraction equilibrium, complexation extraction equilibrium and ionization equilibrium,the balanced extraction equation was described,and the model equation of the distribution coefficient of glycolic acid had been deduced;according to the model formula and the extracted equilibrium concentration of glycolic acid,the combined ratio between trioctylamine and glycolic acid was calculated,and the result was verified by saturated solution method; finally,the bonding mechanism of glycolic acid was studied with the help of the infrared spectra of the extraction phase.The results showed that during the extraction of glycolic acid, the equilibrium constant of distribution averaged about0.033,which indicated that the ratio of complexation extraction was much larger than that of physical extraction; the model formula of distribution coefficient could be expressed as;the complexation compounds formed by glycolic acid and trioctylamine existed in two forms of2:1and1:1,and mostly in the form of2:l;the bonding mechanism between extraction phase and glycolic acid were both ion bonding and hydrogen bonding.