Study On The Purification Of The Byproduct Salt From The Glyphosate Production Process

Large amount of solid salt will be produced as the byproduct during the production of glycine glyphosate. The solid salt contains lots of organic compounds and is usually discharged as solid waste, resulting in a waste of Na Cl resources. Therefore, it is great of importance and economic benefit to explore and develop new technologies to remove the organics so as to reclaim the salt.This study focused on the purification of the byproduct salt from a pesticide manufacturing company which using the glycine glyphosate production process in Jiangsu Province. The removal of organics was performed through membrane separation process, precipitation, oxidation, washing the solid salt by solvent, as well as combined processes. The quality of the treated and purified saline was estimated for the feasibility in chlor-alkali industry. The kinetics of the oxidation of the permeate strem from NF membrane were also investigated to set up mathematical models for the design of pilot-scale test. Finally, the stability and performance of the combined process developed were also studied through a pilot-scale test. The conclusions obtained from the experimental results were as follows:1. Nanofiltration membrane could efficiently remove the organics contained in the saline aqueous prepared by byproduct salt. Under the conditions of p H ≥10.45, operating pressure between 2.5-3.0MPa, temperature of 25℃ and concentrating ratio of 5.0, the removals of TOC、TN、TP were up to 86、75、94%, respectively.2. The results of phosphorus removal of the permeate stream from NF membrane by precipitation showed that the complexing ability of the metal ions with phosphorus followed the order of Fe³⁺>Fe²⁺>Ca²⁺. The phosphorus removal of oxidation followed precipitation was higher than direction complexing of precipitation; The demand TP content was less than 0.5 mg/L which could be attained through Na Cl O oxidation followed by precipitation using Fe²⁺ or Fe³⁺.3. The results of the oxidation of the permeate stream from NF membrane showed that TOC removal by Fenton oxidation was low due to the complexation of organophosphorus with Fe²⁺ in saline and the quenching of ·OH through the reaction with Cl-. To the oxidation agent Na Cl O, TOC removal of higher than 82% and TN removal up to 77% could be reached under the optimal oxidation conditions of Na Cl O/TOC mole ratio=3.86, p H≥9, oxidation temperature≤25℃.4. The organics contained in the byproduct salt could also be effectively removed through the washing process using solvent. However, the removal efficiency declined constantly with the decreasing dosage of washing agent. The concentrated stream from the nanofiltration membrane could be used to prepare the washing agent and solid salt could be obtained by evaporating the washing agent after washing process.5. The hybrid process of nanofiltration + Na Cl O oxidation was demostrated to be effective in removal of the organics in the saline. After oxidation with Na Cl O, the organics remianed in the saline could not be further oxidated by Fenton oxidation. When treated with the hybrid process of solvent washing + NF + oxidation + precipitation, the TOC of the treated saline was less than 20 mg/L, TN and TP contents could meet the index requirements of primary chlor-alkali refining brine. The removals of TOC、TN and TP were mainly afftected by the concentration of oxidation agent in the process of oxidation using Na Cl O.6. The oxidation kinetics equation for the lab-scale oxidation process using Na Cl O was under the condtions of TOC 192.55mg/L, Na Cl O 2500mg/L, and temperature 25℃, while the oxidation kinetics equation for the pilot-scale oxidation process using Na Cl O was 7. The results of pilot-scale experiment showed that the organics in byproduct salt from glyphosate production could be effectively removed through the hybrid process of solvent washing + NF + oxidation + precipitation with good stability. The TOC content of final treated effluent was less than 20 mg/L, which was close to index requirment of chlor-alkali industry. The TN and TP contents were less than 4 and 0.1mg/L, respectively, and also met index requirments of chlor-alkali industry. Additionally, the hybrid process could also be used to remove the orgincs contained in the byproduct solid salt from trimethyl phosphate production, showing good applicability. The estimated cost of the hybrid process developed to refine the byproduct salt from glyphosate production was about 26 yuan per tone of saline, showing good economic benefit.