| Acephate,CAS name O,S-dimethyl acetylphosphoramidothioate,is a new kind of organophosphate insecticide,which has an advantages of high efficiency,low toxicity,low residue,long duration,no drug resistance and so on.It will certainly replace of mathamidophos in the future's pesticide market,to become a large tonnage varieties and make a spectacular flash.However,the current production of acephate is still exist ensufficient,such as lower reaction yield,incomplete separation,produce a large number of organic phosphorus wastewater hard to deal with,as well as the complex operating process,high production costs and other shortcomings.Therefore,optimize the synthesis process of acephate and reutilization of by-product separated from acylated crude oil is of great meaning,not only in economic value,but also in social aspect which can save natural resources,reduce environmental pollution and conducive to promotion.In this paper,a detail optimization and improvement has been implemented to overcome the defect of the acephate production process.First of all,during the isomerization process of methamidophos,in order to improve the purity of methamidophos and the selectivity of next acetylation step,using crystallization and extraction to separate about 10% remaining raw materials in the solution.Secondly,in the separation step of acephate,to remove the corrosive acetic acid,we adopt the method of vacuum distillation at a pressure of 0.08 MPa and a temperature of 55 ° C for 1 hour to recover 58% of acetic acid.The remaining acephate supersaturated solution was crystallized under suitable conditions to obtain a total yield of 65.83% and a mass fraction of 98.53% of acephate crystals.Thirdly,an organic solvent extraction experiment were carried out to separate the O,O-dimethyl-N-acetyl-phoshoramidothioate and acetic acid from acephate crude oil.The experiment using toluene as extracting agent.Under the optimized conditions of the mass ratio of extractant to crude oil of 1.25:1,extraction temperature 45 ?,extraction time 60 min and resting time 90 min.The separation coefficient of O,O-dimethyl-N-acetyl-phoshoramidothioate and acetic acid with acephate is greater than 1,thus O,O-dimethyl-N-acetyl-phoshoramidothioate and acetic acid can be effectively separated by extraction.At the same time in order to enhance extraction and mass transfer separation effectly,multi-stage countercurrent extraction experiment was carried out.The results showed that when the extraction stage was 5,the O,O-dimethyl-N-acetyl-phoshoramidothioate and acetic acid's extraction rate can reach 97.63% and 98.77% respectively.After separation of the extraction phase and the raffinate phase,we can continue to crystallizate to get O,O-dimethyl-N-acetylphoshoramidothioate crystal and acephate crystal of high purity.Finally,we studied the isomerization of O,O-dimethyl-N-acetyl-phoshoramidothioate from different sources,with dimethyl sulfate as catalyst,adding 10% to 12% or 18% of the catalyst to the liquid mass,reacting 3 to 4 hours.The maximum yield of the obtained acephate crude oil was 55%,the selectivity can be greater than 100%,this can provide the basic foundation for the rational utilization of the separated O,O-dimethyl-N-acetyl-phoshoramidothioate. |
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