| Good quality glycolic acid is one of most important fine chemicals, which is short supply in our country. Its production bottleneck is the separation technique. The previous technique such as extraction-esterification, is contaminative, high-cost, and need more chemical materials and the product quality is unstable. In the paper anew technique------electrodialysis membrane separation technique has beenintroduced for purifying glycolic acid, which takes good result.The best technological conditions have been got by means of the experiments: The material is purified by condensation and filtration to remove the salts and solid impurity, and precise filtration is conducted to fulfill the necessity of membrane separation; it takes a good yield but need less time using homogeneous membranes, and can solve the key problem in commercial process. When the pH value keeps 1.2-1.5 the lost is lowest. It reduces the polarization and shortens the time by Sectionalized constant voltage. The voltage is 80V before 75% NaCl removed and the subsequent is 40V. The strong salt solution has to be replaced with water to reduce the effect of differential concentration when the voltage change, but it isn't reused simply before condensation and filtrate. The overall yield of glycolic acid is greater than 98%.The end-point is determined precisely by content of sodium chloride which is measured by spectropHtometer when it has been found approximatively by conductivity apparatus in the separation process. The percentage purity of product is greater than 99% except water and the ignition residue percentage is smaller than 0.1%. The white and clarity product meets the necessity of cosmetic and medical material.The technique described in this paper, which doesn't need any other chemical material, hardly releases waste water, and takes a good yield, is one of the appropriate methods in commercial process and may solve the problem of producing good quality glycolic acid in our country.
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