Process Optimization for Preparation of Glyphosate by Hydrogen Peroxide Method
|Keywords||N-phosponomethylglycine N-phosphonomethylliminodiacetic acid hydrogen peroxide orthogonal experiment solubility|
N-phosphonomethylglycine(PMG),known also by its common name glyphosate,is a high effective、good bioactivity、low toxicity and broad-sprectrum herbicide.It is widely used for weeding in forests、orchards、shelterbelts and so on.Because its superior performance,now it is the largest amount of herbicides in the world. According to literatures, there are mainly two methods being used to synthesize glyphosate.One way is using glycine as the starting material;the other way is using iminodiacetic acid as the starting material.In recent years, the method of iminodiacetic acid is rapidly developing and now it is the mainstream in domestic. The most important step of this way is to prepare glyphosate by oxidation reaction with N-phosphonomethylliminodiacetic acid(PMIDA). The technology of oxidation of PMIDA using hydrogen peroxide is a simple process and its investment in equipment is less,but the crystal yield of PMG and the total yield of PMIDA are low.So we optimize the process to synthsize glyphosate by hydrogen peroxide method to impove the crystal yield and contents of PMG, which has vital signification.This thesis is mainly to optimize and to improve the manufacturing technics of glyphosate by the conversion of N-phosphonomethylliminodiacetic acid(PMIDA)to glyphosate using hydrogen peroxide. Having looked up of a great amount of technical literature both domestic and foreign,at the base of analysising the effection of some factors ,such as the concentration of PMIDA、the molar ratio of H2O2 to PMIDA、the reaction temperature、the dropping time of H2O2、heat preservation time and so on,on the oxidation reaction, we further optimize the process condition by Orthogonal experiment.We found the optimal reaction condition: the concentration of PMIDA is 44%, the molar ratio of H2O2 to PMIDA is 1.15:1, the reaction temperature is 65℃, the dropping time of H2O2 is 1.5h, heat preservation time is 0.5h.At this condition,oxidation reaction is steady, the conversion ratio of PMIDA is above 97%,the total yield of the PMG is above 95% and higher than the industrial production about 3%.We studied the solubility of PMG and PMIDA in the liquid solution at different temperature,and we fit the experiment datas of the solubility of PMG and PMIDA. We obtained the phase diagram of ternary system of PMG—PMIDA—H2O. Then we analysised the affction of impurity on the solubility of PMG in the reaction system.All these can provide some theoretical guide for impoving the crystal yield and the content of PMG.Finally through analysising the effection of some factors,such as the temperature of reducing reaction、the molar ratio of reducing agent to PMIDA、the dropping manner、the dropping time of reducing agent、the crystallization end-point temperature and so on,on the crystal content of the PMG and the crystal yield of PMG.We obtained the optimal reaction conditions: the dropping manner of reducing agent is independently dropping FeSO4 and Na2SO3, ,the amount of reducing agent to PMIDA is about 2/100, the temperature of reducing reaction is 30-40℃the dropping time of reducing agent is 10min,the crystallization end-point temperature is 20℃.At this reaction condition,the crystal content of PMG is above 97%,the crystal yield of the PMG is above 84%.