Water osmosis in separating acidic HCl/glyphosate liquor by continuous diffusion dialysis

- Acidic HCl/glyphosate liquor is separated by continuous diffusion dialysis.
- Water osmosis is more serious for commercial membrane than self-prepared membrane.
- Optimized HCl recovery (RH) is 68-81% and glyphosate rejection (ηGly) is 83-94%.
- Water osmosis reduces Cres-Gly and RH but has insignificant effect on Cd-H and ηGly.

Acidic HCl/glyphosate liquor is the intermediate product during the production of glyphosate herbicide. The liquor contains about 2.4 mol/L (M) HCl, 1.1 M glyphosate and 35 wt% other organic components, which can be separated by continuous diffusion dialysis (DD) to recover HCl. The residual solution is further precipitated to obtain glyphosate product at pH around 1.5. The continuous DD dialyzer equipped with commercial membrane TWDD-III shows high water osmosis coefficients of 2.23-5.98 × 10−4 m/h, while the self-prepared QPPO/PVA membrane shows the lower values of 1.95-2.93 × 10−4 m/h.The water osmosis is mainly attributed to the high content of organic solvent in the acidic liquor. The water osmosis reduces the Gly concentration and productivity together with the HCl recovery (RH), but the recovered HCl concentration (Cd-H) and Gly rejection (ηGly) are less affected. The flow rate and flow ratio between water and acidic liquor are optimized (0.63 L/(m2 h), 3:1) to obtain Cd-H of 1.01 M, RH of 80.9% and ηGly of 83.2% for the commercial membrane. The residual solution contains only 0.43 M Gly and thus needs to be highly concentrated to obtain 60.7% Gly productivity with the purity of 71.3%. The QPPO/PVA membrane under optimized running conditions (0.83 L/(m2 h), 2:1) can obtain Cd-H of 0.95 M, RH of 68.1% and ηGly of 94.2%. The residual solution contains 0.65 M Gly and thus needs less to be concentrated to precipitate Gly product due to the lower water osmosis.