| The application of polycondensation products such as polyester and polyamide has surpassed the traditional textile and garment industries.High-tech fibers and new synthetic materials have been utilized for aerospace,agriculture,architecture,transportation,water conservancy,environmental protection,etc.The gas-liquid phase pre-polycondensation process(i.e.,the polyester esterification stage or the preliminary polymerization stage of the polyamide salt)is a very important stage that affects the energy consumption of the entire process and the quality of the polymer product.Therefore,the intensification of the gas-liquid phase pre-reaction processes has important research value and broad industrial application prospects.The dissolution of reaction monomers,the gas-liquid phase equilibirum of the small molecule,the gas-liquid contact mode,the boiling heat transfer and other factors make the gas-liquid phase pre-polycondensation processes very complicated.How to analyze the processes through accurate and efficient modeling methods and effectively control the process is the basis for intensification of gas-liquid phase pre-polycondensation processes.In this thesis,the gas-liquid phase pre-polycondensation processes are studied from process scale to reaction unit scale.A process scale simulation method that is universal for the general polycondensation process and a reaction unit scale simulation method involving non-ideal multiphase flow characteristics and interphase transfer are established.And a coupling simulation method is developed to correlate the two scale models.Achieved results as follows:A comprehensive mathematical model including co-polycondensation kinetics,volatile small molecule gas-liquid equilibrium and monomer solid-liquid equilibrium is established using ideal flow models to quantitatively describe a new co-esterification-co-condensation polymerization process of biodegradable PBST polyester.The model is used to simulate the influence of the operating conditions of 20,000 ton/a PBST copolymerization process on the reaction performance,and the industrial trial production is successfully realized.The simulation results show that proper negative pressure operation helps to increase the molecular weight of the product and reduces the yield of by-products,and higher temperatures help to increase the esterification rate.The mechanism of the influence of different gas-liquid contact modes of the PET esterification reactor is explored by the combination of ideal reactor models.Two reactor strategies with new gas-liquid contact mode are established and compared with the other four existing industrial reactors.The effects of feed composition and operating parameters are investigated and it is found that the multi-stage column reactor exhibited better reaction efficiency than a single CSTR reactor.The gas-liquid countercurrent operation of the column reactors have better reaction performance,and its production efficiency can be further improved by means of relocating the gas outlet.The reactor strategy of gas-liquid cocurrent operation balances reaction performance and energy consumption.Polycondensation reactors with complex non-ideal flow inside are studied from the reaction unit scale.Based on the conceptual design and the mechanism of gas-liquid contact mode on the gas-liquid pre-polycondensation process,integrated multi-stage gas-liquid concurrent flow tower reactors with various configurations are constructed for the pre-reaction stage with low viscosity reaction system.The cold model experiment and computational fluid dynamics(CFD)simulation prove that the liquid inside the tray is well mixed with the vigorous bubbling of gas.Through the RTD experiment,the overall virtual series N of the reactor consisting of three trays is between 3 and 3.4.Thus,the feasibility of gas-liquid cocurrent flow in this reactors is verified.In order to study the reaction characteristics inside the multiphase pre-polycondensation unit,a CFD approach coupled with complex gas-liquid phase transfer models and polycondensation kinetics is developed to analyze the gas-liquid mass and heat transfer,the species content and the degree of polymerization in liquid phase during the heating and boiling process.The industrial PA66 tubular reactor is simulated,and the simulation results show that the liquid phase appears a kind of periodic eddy current due to the disturbance of water boiling and evaporation in the front and middle sections of the tubular reactor,where the liquid components change gently.In the latter part of the reactor,the periodicity of the vortex is destroyed by the violent boiling of the water,and the liquid flow pattern trums to the complete mixing flow.The degree of polymer polymerization rises rapidly in the transition zone between the middle part and latter part.Finally,with the aid of ActiveX/COM technology and the GUI/TUI command codes supported by CFD software,the modular data interaction between process scale and reaction unit scale is realized in Matlab platform,and an accurate and controllable polycondensation process simulation method is established.This method successfully implemented a cross-scale full-process simulation replacing an ideal flow reaction unit with a non-ideal flow reaction unit in a conventional process simulation.Taking the industrial 10,000 ton/a PA66 continuous polycondensation process as an example,an optimization method for the structure and operating conditions of a new internal circulation reactor without any mechanical stirring parts is established.The reactor has strong heat transfer capability,and the heat exchange capacity per unit volume is about 1.5 times that of the tubular reactor.Thus,the reactor outlet component content and product properties can easily reach similar levels of product at the outlet of the industrial tubular reactor.In addition,the simulation results show that the operating temperature and the structure of the reactor have a significant influence on the internal circulation flow,which in turn affect the reaction efficiency. |
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