Study On Production And Purification Process Of β-trifluoromethylpyridine Compounds

2-chloro-5-(trifluoromethyl)pyridine(2,5-CTF)is an important chemical raw material for preparing pharmaceuticals,agricultural chemicals and biological agents,especially for the production of fluorine-containing pesticides like highly active herbicide fluazifop-p-butyl,pesticide Chlorfluazuron,bactericide SHIRLAN etc.These pesticides have been widely used at home and abroad for advantages of long duration,high effect,low toxicity,broad-spectrum and inner attracts etc.There are many methods for production of 2,5-CTF,among which one-step chlorofluorination of 3-methyl pyridine has the highest utilization value in industry.This method had been monopolized Ishihara Sangyo Kaisha Ltd until its patent protection period expired in recent year.China has a large market demand for 2,5-CTF and its derivatives.However,domestic researchers haven’t got great progress on its production process.In this research,a fluid bed process for chlorofluorating 3-methyl pyridine,probable reaction mechanism and deactivation mechanism of catalysts were studied;besides,an industrial separation process for products was designed.The corresponding results were concluded as follow:(1)Catalysts formed by pestle and spray dryer had many similar properties,such as specific surface,pore structure,acid property,activity and so on.However,catalyst formed by spray dryer had a higher strength for resisting attrition thus it’s more preferable for industrial use.(2)The yield of main products was improved through filling more catalysts and mounting baffles,which also reduced coke formation.With the improvement of reaction temperature,the yield of 2,5-CTF enhanced,but the yield of 3-trifluoromethyl pyridine(3-TF)decreased.At 250℃,the yield of 3-TF was about 80%while 2,5-CTF was only 1%;at 350℃,the yield of 3-TF was 8%while 2,5-CTF was about 20%.(3)The chlorofluorination reaction was divided into three steps;the last one was the chlorination of pyridine ring,which was mainly caused by radical substitution.It was found that coke formation on acid sites was main reason for decrease in catalytic activity.(4)A vacuum distillation/melting crystallization coupling process was designed for purifying 2,5-CTF.The effects of some distillation and melting crystallization operation parameters on the purity and yield of 2,5-CTF were studied.Compared with solid layer crystallization,operation with N2 bubble had a better purification result.Under optimum conditions,greater than 99%2,5-CTF could be obtained by one time bubble crystallization and the yield was 72.5%.At last,the recycling yield of coupling process was simply calculated through some hypothesis.