Study On The Synthesis Of Ethylenediamine With A Tubular Reactor

Amines are important intermediates for organic chemical industry. A large number of drugs, pesticides and dyes are made from them.Ethylenediamine was prepared by aminolysis of dichlorethane with a tubular reactor in this paper.The effects of several factors were investigated and the optimized conditions in the isothermal tubular reactor with inner diameter of 4mm and length of 13m were: the molar ratio of ammonia and dichlorethane 30:1, the concentration of the ammonia 60%, the volume velocity 2L/h, the reaction temperature 160℃, the system pressure 6MPa. Thus the conversion of dichlorethane was 98.7% per pass and the yield was 51.6%.The apparent kinetics of the reaction was studied on some assumed conditions as follows: the only by-product of the reaction is diethylenetriamine; the concentration of ammonia is regarded as constant; the fluid state in the reactor is ideal plug flow. The apparent kinetics equations were established as follows:in which C_A was the concentration of dichlorethane, C_B was the concentration of ethylenediamine, C_C was the concentration of diethylenetriamine. The rate constant of main reaction k₁=1.3211×10⁶×e^-53144/RT, the rate constant of side reactionk₂=1.5594×10⁸×e^-73997/RT.The activity energy of the main and side reaction were53144J/mol and 73997J/mol respectively.The activity energy of the main reaction was lower than that of the side reaction according to the kinetics equations. It was known that higher temperature was favorable to the reaction which had higher activity energy. Therefore the non-isothermal reaction was considered to be suitable to improve the selectivity of ethylenediamine. High temperature was adopted in early period to improve the main reaction rate and low temperature was adopted in later period to restrain the side reaction. Compared to the isothermal reaction with the same length of the reactor pipe, the yield of the target product was increased by caculations based on the kinetics equations obtained above.By investigating the effects of several factors in the non-isothermal tubular reactor with inner diameter of 4mm and the overall length of 27m, the optimized conditions were: the temperature of the first reaction pipe 160℃, the reaction time 1.5min. The temperature of second reaction pipe 130℃, the reaction time 8.5min. The other conditions were the same as in isothermal reaction. Thus the conversion of dichlorethane was 98.6% per pass and the yield was 60.1%. To achieve the same yield in isothermal reaction, the suitable conditions were: the temperature 130℃, the reaction time 15min (the length of the pipe was 40m correspondingly). The length of the reactor pipe was shortened by 33% compared to the isothermal reaction.The ethylenediamine solution with the concentration of 96% was obtained from the crude product through flash evaporation, neutralization, dehydration, azeotropic distillation and extraction.