| Glyphosate (N-(phosphono-methyl-glycine)) is non-selective and broad-spectrum herbicide for annual and perennial deep-rooted weeds in many crops. It was commercialized by Monsanto Corporation in 1974, and be widely used in forestry, orchards, non-farmland and No-Till. The demand for glyphosate grows rapidly and it has become one kind of agrochemical with the world's largest sales and fastest growth rate.Glyphosate was prepared by oxidation of PMIDA (N-(phosphono-methyl-iminodiacetic acid) with hydrogen peroxide and air/oxygen in IDA (iminodiacetic acid) process. Now most of the enterprises in China still use hydrogen peroxide method in PMIDA oxide process. The yield of technical product is low (only 75～80%) in hydrogen peroxide oxidation along with other disadvantages, such as more waste, not large scale and difficult to complete continuous device. Many problems of air/oxygen oxidation method which was developed by western countries were not solved such as high energy consuming and production cost of catalyst. There were so many problems in air/oxygen oxidation method which was developed by China such as high investment and long reaction time. That slurry process of glyphosate which was prepared by oxiding high concentration PMIDA was developed and many problems were solved in above oxidation method such as high pollution, energy consuming, investment and production cost.. In this paper, novel catalyst with industrial economic benefit, operational condition, kinetic and cooling crystallizer with circulation were emphasized. It paved the way for the domestic production of industrial glyphosate manufacture technology.The development of catalyst is the key point of PMIDA oxidation process. In this paper, active carbons were prepared by water vapor activation and modified by specific thermal treatments. The structure of the catalysts were confirmed by means of TEM, TPD and XPS technique. Through comparison, catalyst was selected due to its high catalytic activity for PMIDA oxidation. It was concluded that active carbon from coal has a higher catalytic activity than active carbon from coconut shell, and the catalytic activity of active carbon was improved afer modified by specific thermal treatments.The foundation of confirming industrial operational conditions is optimization of process conditions for catalytic oxidation of PMIDA. The effect of operational condition on oxidation reaction was discussed in detail. The optimal process conditions were obtained that m(catalyst)/m(PMIDA)=1/5.3(wt.) with water as solvent, initial concentration of PMIDA was 40%, flow rate of oxygen was 80～120 mL/min, reaction temperature was 45℃, reaction pressure was 0.5 MPa and reaction time was 5 h. Under the above operational conditions, the conversion of PMIDA was 99.4%, the selectivity of glyphosate reached 97.6% and the yield of glyphosate was 97.1%.Research on reaction kinetics of PMIDA oxidation with active carbon was a blank till now. However, the reaction kinetics could serve an important basis for scale-up of industrial apparatus and optimization of operational conditions. The experiments were carried out in a stainless steel reactor with a heater under the temperature 45～75℃, with the flow rate of oxygen 80～120 mL/min. The raw material was PMIDA, and the catalyst was active carbon. The initial mass fraction is 40%. That the process obeyed the mechanism of reactions in series, the macroscopic kinetic equations were found, and the apparent activation energy of reactions were calculated. The macroscopic mechanism was verified by the experiments data, and the average relative error is 0.8‰. The model has a good value for the industrial application.The model of cooling crystallizer with circulation was set up, and the simulation was carried out by using CFD software FLUENT. According to the simulation of cooling crystallizer with circulation, the crystal size distribution is in good agreement with actual operation. It indicates that the Population Balance Model can be used to forecast the particle size distribution of crystal.
|
PDF Full Text Request