Continuous Synthesis Of Tributyl Phosphate

Tributyl phosphate is an important phosphorus-containing organic compound,as an extractant for nonferrous metal hydrometallurgy,and also for extraction of phenol-containing wastewater.It is also used as industrial defoamer and plasticizer for polyvinyl chloride.In recent years,with the development and improvement of extraction technologies,its market demand is keeping growing constantly.Tributyl phosphate is generally prepared from n-butanol and phosphorus oxychloride by direct esterification.The hydrogen chloride generated during the reaction has to be removed under pretty low pressure and temperature in order to minimize the side reactions with tributyl phosphate and n-butanol,this results in a lower product yield and high consumption of n-butanol.Therefore,it is of great significance to explore new process synthetic methods.In this paper,the feasibility of batchwise synthesis of tributyl phosphate from sodium butoxide was studied.The experimental results showed that this route worked well.The experimental results were obtained by optimizing the reaction conditions.Reaction of n-butanol with metal sodium gave 22% sodium n-butoxide solution and esterification of sodium n-butoxide and phosphorus oxychloride gave tributyl phosphate in a yield of 93.0%,the excess butanol recovery rate reached 89.1%.On the basis of the batchwise experiments tributyl phosphate was synthesized by single-pot and two-pot continuous process.For single-pot process,the reaction temperature,residence time and molar ratio of reactants were determined as the main object of the study via three factors four levels of general factorial experiments and three factors three levels of orthogonal experiments.The optimum reaction conditions were as follows: reaction temperature was 40?,average residence time was 60 min,the molar ratio of phosphorus oxychloride to sodium butoxide was 1:3.1,the yield of tributyl phosphate was 91.2% and the purity was 99.3%.The orthogonal experiment results indicated that the order of key factor was reaction temperature > residence time > malar ratio.The optimum conditions for the synthesis of tributyl phosphate from sodium butoxide and phosphorus oxychloride were obtained by orthogonal experiments.The reaction temperature was 45?,the average residence time was 65 min,molar ratio of phosphorus oxychloride to sodium butoxide was 1:3.3,the yield of tributyl phosphate was 90.7%.Further verifying experimental results was as follows: reaction temperature was 40~45?,the average reaction time is 60~65min;the molar ratio phosphorus oxychloride to sodium butoxide was 1:3.1~3.15,and the yield tributyl phosphate reached 91.4%.Based on single-pot process,two-pot continuous process was studied.The optimum conditions were as follows: the molar ratio phosphorus oxychloride to sodium butoxide was 1:3.1,total residual time was 80 min,the temperature in the first reactor was 30?,the temperature in the second reactor was 50?.Under these conditions,the yield of tributyl phosphate was 93.3% and the purity was 99.6%.