Diffusion dialysis for separating acidic HCl/glyphosate liquor

Abstract

Acidic HCl/glyphosate liquor is produced largely during the production of glyphosate herbicide, which contains 2.5–3.0molL−1HCl, 1.1–1.5molL−1 glyphosate and 34–35wt% other organic components. The acidic liquor is traditionally neutralized to pH 1.5 by alkali (NaOH) for the maximum crystallinity of glyphosate. Here the acidic liquor is separated by commercial anion exchange membrane 9010 through batch diffusion dialysis (DD). The DD process shows the advantages including recovery of HCl, crystallization of glyphosate, and low dosage or avoidance of alkali. The DD performances are evaluated by acid concentration, dialysis coefficients of HCl (UH) and separation factor (S) with respect to the time.DD running 12h shows that the acid concentration decreases from 3.57 to 2.60molL−1 for the acidic liquor, and the UH values are in the range of 0.0048–0.0062mh−1. The relatively low UH values are attributed to the existence of other organic components in the acidic liquor. DD running 24h shows that most of HCl can be recovered, the concentration of recovered acid is in the range of 0.29–0.78molL−1, and the separation factors are in the range of 53–66. Moreover, 53.2% glyphosate can be recovered and thus 62% NaOH can be saved. DD running 36h shows reduced performance due to the decreasing acid concentration and the water osmosis. Hence, DD performances can be optimized to separate the acidic liquor for producing glyphosate.