Study On Reaction Kinetics Of Polyester And Simulation And Optimization Of Flow Field In Reactor

Polyester was one of important synthetic in food packaging materials and medical materials. With the rapid development of the food industry, the demand of polyester packaging materials were expanded, especially in edible oil, seasoning commodities, wine, dairy products and other food packaging. And it also appeared to the beer, wine and dairy products penetrate the development trend. Therefore, the research hot of polyester synthesis were improving the polyester production efficiency, reducing energy consumption and improving the performance of the polyester characteristics.In this paper, aimed at the problem of low efficiency, long production cycle and the water content was higher of the esterification in the process of polyester production. Collection and analysis of the actual production data, establish polyester reaction kinetics model, optimal solution kinetic parameters, on this basis, simulation flow field variation of reactor and optimizing the structure parameters of stirring paddle by using computational fluid dynamics(CFD).The main research contents were as follows:(1) According to field data of the polyester reaction process were collected. Condensation reaction scheme of terephthalic acid and neopentyl glycol were analyzed. According to the characteristics of the reaction, the polyester synthesis process was divided into three stages: the direct esterification stage, the pre poly-condensation stage and the final poly-condensation stage. Reaction kinetics model of three stages were established with Structure guide lumped method(Structure- Oriented Lump, SOL) and Flory theory.(2)Reaction kinetics parameters of the three stages were determined integrated with genetic algorithm and nonlinear optimization algorithm.I. The direct esterification stage: Reaction order is 2 grade. Positive and reverse reaction activation energy Ea were 29.6 k J/mol-1and 93.7 k J/mol-1. Pre exponential factor of positive and reverse reaction were 1.03 ? 106 kg/(mol-1?min-1) and 6.4 ? 104 kg/(mol-1?min-1).II. The pre poly-condensation stage: Reaction order is 2.2 grade. Positive and reverse reaction activation energy Ea were 71.7 k J/mol-1and 167.9 k J/mol-1. Pre exponential factor of positive and reverse reaction were 1.21 ? 106 kg/(mol-1?min-1) and 1.02 ? 104 kg/(mol-1?min-1).III. The final poly-condensation stage: Reaction order is 2.5 grade. Positive and reverse reaction activation energy Ea were 134.8 k J/mol-1and 236.1 k J/mol-1. Pre exponential factor of positive and reverse reaction were 2.5 ? 105 kg/(mol-1?min-1)and 1.62 ?104 kg/(mol-1?min-1).Kinetic models were verified. The correlation coefficient of the model calculation and production data were 0.9970~0.9980, results showed that better match degree and models were credible.(3)Reaction time was preliminary optimization according to the dynamic model. The reaction time of direct esterification, pre poly-condensation and final poly-condensation stage can shortened 1h, 2h and 4h. The synthesis reaction time of the whole polyester can be reduced by 4h.(4) In this paper, the software FLUENT of numerical simulation was used to simulate fluid mixing paddle reactor which plant operation were simulated by using multiple reference frame(MRF) and the standard k- epsilon model. The reactor distribution and velocity vector of the current operating conditions velocity flow field in different stages were analyzed. And calculated the stirring power. Through the analysis of the flow field of mixing in the reaction kettle, result showed that the phenomenon of non-uniform fluid mixing and "dead zones" of the fluid in the stirred tank reactor(5) Simulation and optimization of the reactor by changing the reactor stirring paddle(increase small stirring paddle) and impeller structural parameters(radius r=0.7m, 0.8m, 0.9m and tilt angle= 30 °, 45 °and 60 °) and other methods. Optimization was obtained when the propeller speed 60r/min, the radius of the mixing paddle 0.8m and the inclination angle of 60°, the flow field is more uniform, the fluid mixture is better, and the fluid "dead zone" disappeared. And the stirring power was slightly increased(about 2.57%).