Study On The Synthesis Process Of Dioctyl Terephthalate

The esterification of dioctyl terephthalate (DOTP) is a reversible endothermic process which includes both reaction and distillation. The reaction rate can be influenced by many process factors, such as kind and dosage of catalyst, reaction temperature, the mole ratio of 2-EH to TPA and the separation efficiency of 2-EH and H2O. As the reaction is heterogeneous, the solid-liquid distribution in stirred tank also has important effect on the reaction rate.In this paper, a series of experiments were carried out systematically to investigate the influence factors on the synthesis process of DOTP. The results showed that titanium catalyst TBT and TPT had efficient catalytic effect on the esterification with optimized reaction conditions as follows: heating temperature 260-280°C, the mass ratio of catalyst 0.6% -0.8%, the mole ratio of 2-EH to TPA from 2.6:1 to 2.8:1. Besides, the reaction rate could also be accelerated by improving the separation efficiency by increasing the diameter and height of the rectifying columns.Based on the single factor experiments, Box-Behnken central composite design was adopted in the experiments of esterification process to obtain the regression equation and the response surface graph with the influence factors on the conversion of TPA including the heating temperature, amount of catalyst TPT and the mole ratio of 2-EH to TPA. According to the results, the most significant individual effect on the response was attributed to the heating temperature, while the mole ratio of TPA to 2-EH had the lowest effect. The optimum synthesis condition was as follow: heating temperature 272 "C, the mass ratio of catalyst 0.8%, the mole ratio of TPA to 2-EH 2:88:1. With the above conditions, the conversion of TPA could achieve 97.92% after the reaction time 120min.Furthermore, the semi-empirical equations were used to calculate the critical suspension speed NjS of the industrial agitation reactor of DOTP. Result showed that NjS was 0.83s"1 which meant that most part of the reactor met the requirements of off-bottom particle suspension. Meanwhile, computational fluid dynamics CFD method was used to simulate the mixing and suspending characteristics of solid-liquid phases flow under different conditions.