Removal of glyphosate in neutralization liquor from the glycine-dimethylphosphit process by nanofiltration

摘要

Nanofiltration (NF) was investigated for the removal of glyphosate in the neutralization liquor produced by the glycine-dimethylphosphit process. The Desal-5 DK membrane was chosen as the most suitable membrane for the NF process when compared to the DL and NTR7450 membranes according to retention of glyphosate and the permeate flux. The effects of applied pressure, temperature, and feed pH on the performances of the DK membrane were investigated. An applied pressure of 2 MPa was found to be optimum since a high glyphosate rejection of 95.5% was obtained with a high flux of 7.32 L/(h m~2); temperature had a slight impact on the retention of glyphosate with an increase in flux; both the minimum glyphosate retention and maximum permeate flux were achieved when the feed pH was around the isoelectric point of the DK membrane. In batch NF, the permeate flux decreased gradually but glyphosate rejection remained higher than 90%. After 8h of NF, glyphosate recovery from the neutralization liquor reached 89.6% with an average permeate flux of around 4 L/(h m~2). Moreover, membrane surface crystallization induced by concentration polarization probably caused the flux to decline during the process of batch NF.