A Simulation and Analysis Method for Polyester Falling Film Thickening Reaction Process

Abstract

This invention relates to the chemical industry and discloses a simulation and analysis method for the polyester falling film viscosity-enhancing reaction process. This invention employs an interactive method combining numerical calculation and process simulation software to establish a model of the polyester falling film viscosity-enhancing reaction process. By utilizing physical equations such as reaction kinetics, mass transfer kinetics, and fluid kinetics, the material balance equations for the polyester falling film viscosity-enhancing process are decoupled and calculated. This effectively and conveniently obtains the distribution of basic physical quantities (such as intrinsic viscosity, molecular weight, and terminal carboxyl group content) of the polyester falling film reaction process, thus providing excellent guidance for experimental research and industrial design. Furthermore, the simulation and analysis method for the falling film viscosity-enhancing reaction process proposed in this invention has a certain degree of versatility and can be applied to the simulation of various polyester falling film melt polycondensation reaction processes.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and in particular to a method for simulating and analyzing the polyester falling film thickening reaction process. Background Technology

[0002] Polyester is one of the most important polymers today, including aliphatic polyesters such as polybutylene succinate (PBS), semi-aromatic polyesters such as polyethylene terephthalate (PET), fully aromatic polyesters such as para-hydroxybenzoate (PHB), modified copolyesters such as poly(butylene terephthalate-butylene adipate) (PBAT), and carbonate-based polyesters such as bisphenol A polycarbonate (PC). Everyday items such as clothing, curtains, films, drinking bottles, appliance housings, automotive headlight covers, switches and sockets, as well as industrial products such as car seat belts, tire cords, advertising fabrics, and mooring ropes are all polyester products. In the industrial production of polyester, melt polycondensation is usually required after esterification. When higher mechanical properties are required, a further re-polymerization step to increase the molecular weight is generally necessary.

[0003] Melt polycondensation is a core component of polyester production. Under specific reactor and process conditions, it involves the chain-growth reaction that transforms short-chain polyester molecules into high-molecular-weight polyesters, directly impacting production efficiency and product quality. When improving melt polycondensation efficiency is required, existing conventional processes are limited by melt flow structures, hindering efficiency gains. Alternatively, when a rapid increase in polyester molecular weight is needed, long and energy-intensive solid-phase polycondensation routes may be necessary.

[0004] Falling film flow possesses excellent characteristics such as large film area and high gas-liquid heat and mass transfer efficiency. However, its flow structure is large-scale, and conducting gas-liquid flow processes under actual working conditions is time-consuming and labor-intensive. Furthermore, when the fluid is a high-viscosity polymer melt undergoing a harsh melt polycondensation reaction, the construction and operation costs of the experimental setup are too high, hindering process analysis and the efficient acquisition of large amounts of experimental data. Process simulation can effectively conduct process and result analysis of falling film melt polycondensation reactions, exploring the effects of falling film viscosity reactions.

[0005] A review of existing technologies revealed no reports on the use of process simulation to analyze the polyester falling film melt polycondensation reaction process and results to explore the effects of falling film viscosity enhancement. Therefore, there is an urgent need for effective and convenient methods and techniques to analyze the material flow process and the distribution of basic physical quantities (such as viscosity, end carboxyl group and end vinyl group content) at various axial positions during the actual polyester falling film viscosity enhancement process. This would allow for an understanding of the reaction patterns in the continuous polymerization-viscosification production process, providing effective guidance for experimental research and industrial design. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a simulation and analysis method for the polyester falling film viscosity-enhancing reaction process. This invention employs an interactive approach combining numerical calculations and process simulation software to establish a model of the polyester falling film viscosity-enhancing reaction process. By utilizing physical equations such as reaction kinetics, mass transfer kinetics, and fluid kinetics, the material balance equations for the polyester falling film viscosity-enhancing process are decoupled and calculated. This effectively and conveniently obtains the distribution of basic physical quantities (such as intrinsic viscosity, molecular weight, and terminal carboxyl group content) during the polyester falling film reaction process, thus providing excellent guidance for experimental research and industrial design. Furthermore, the simulation and analysis method for the falling film viscosity-enhancing reaction process proposed in this invention has a certain degree of versatility and can be applied to the simulation of various polyester falling film melt polycondensation reaction processes.

[0007] The specific technical solution of this invention is: a method for simulating and analyzing the polyester falling film thickening reaction process, comprising:

[0008] Polymerization reaction kinetics model analysis, gas-liquid two-phase mass transfer analysis, and falling film fluid dynamics behavior analysis were performed on polyester.

[0009] The reaction kinetics model, gas-liquid two-phase mass transfer model and fluid dynamics model were used to perform material balance calculations on the entire polyester falling film thickening reaction process. Boundary conditions and initial conditions were set, and the material balance equations were solved by numerical calculation to establish a polyester falling film thickening reactor model.

[0010] Based on the polyester reaction production process, a complete process of polyester melt falling film thickening reaction was constructed. Using the index parameters of polyester melt with a certain degree of polymerization obtained through polycondensation as input values, the partial differential equation system of reaction rate was calculated, and the performance parameters of polymerization products and the content information of each characteristic component were output. The simulation results of polyester falling film thickening reaction process were analyzed.

[0011] The falling film thickening reactor typically has a melt chamber, a membrane structure, and a falling film support to support the flow of the melt fluid. The polyester melt, after polycondensation, flows axially along the falling film support while the volatilization of small molecule by-products of polycondensation is removed and the thickening reaction is completed, thereby increasing the molecular weight.

[0012] This invention is applicable to prepolymerization reactions following esterification, polycondensation reactions following prepolymerization, and secondary and subsequent polycondensation reactions. The principle of this invention is based on the high viscosity of polyester melts. During wall-mounted falling film flow, it maintains plug flow characteristics, consistently preserving a large film-forming area and effectively improving the gas-liquid interface renewal rate. Based on a thorough understanding of the mass transfer characteristics of polycondensation reactions and the fluid dynamics of high-viscosity materials, this invention utilizes falling film flow to enhance polymer devolatilization. The application results of this technology are obtained through process simulation.

[0013] Preferably, the polymerization reaction kinetic model includes a chain growth reaction process that generates byproducts water and hydroxyl compounds; more preferably, it also includes, but is not limited to, the production of byproducts such as terminal alkenyl compounds, aldehydes, hydroxyl condensates, etc.

[0014] The polymerization reaction kinetic model analysis includes the following steps:

[0015] (1) Determine the main and side reactions in the polymerization process: Use the "chain segment analysis" method to simplify the reaction into a combination of a limited number of basic chain segment units, with the polycondensation chain growth reaction as the main factor, and determine the reaction equations for generating aldehydes, hydroxy compounds, hydroxy condensates, water and terminal alkenyl groups;

[0016] (2) Determination of reaction rate constant and equilibrium constant: The effect of temperature on reaction rate constant is described by the Arrhenius equation, the pre-exponential factor and activation energy in the equation are specified, the equilibrium constant of reversible reaction is determined, and the forward and reverse reaction rate values ​​are solved.

[0017] (3) Establishment of reaction kinetic equations: The reaction kinetic equations of each component are analyzed using the reaction kinetic model, and the established equation set is compiled and imported into the executable function script file in the numerical calculation software.

[0018] Preferably, the gas-liquid two-phase mass transfer analysis includes the following steps:

[0019] (1) Based on the target components to be analyzed in the gas-liquid two-phase system, select an appropriate physical property model and set relevant attribute values, including but not limited to one or more of the following: relative molecular mass, critical temperature, pressure, compressibility, gas-liquid phase pressure, molar volume, polymer molecular weight and viscosity characteristics. Store the attributes in a global data array.

[0020] (2) For the simulation analysis method of small molecule devolatilization process of high viscosity polymer melt, the volatile components in the system are determined according to the gas-liquid phase equilibrium process, the gas-liquid equilibrium equation at the interface is constructed by calling the attribute group of each component, and the corresponding settings are made in the numerical calculation software.

[0021] The volatile components are specifically: based on the degree of significant influence of each volatile component on the reaction process, the volatile components in the gas phase are mainly considered to include, but are not limited to, hydroxyl compounds and water, and the volatile components in the liquid phase include, but are not limited to, hydroxyl compounds, water, condensates of hydroxyl compounds and aldehydes. Phase equilibrium process parameters are set for the volatile components in the gas and liquid phases.

[0022] (3) Determine the reactor equipment structure and process condition parameters of the falling film thickening reaction process that affect the gas-liquid mass transfer rate, introduce the mass transfer coefficient to calculate the mass transfer flux of the gas phase component, and iteratively calculate the mass transfer coefficient based on the gas phase mass transfer flux during reactor operation in industry.

[0023] (4) Initialize the output property group of each component to complete the iterative solution calculation and obtain the mass transfer flux of gas phase volatile components in the polyester falling film thickening reaction process.

[0024] Preferably, the falling film fluid dynamics behavior analysis includes the following steps: determining the molecular diffusion coefficient during the flow process based on the low-speed laminar polymer motion at extremely low Reynolds numbers, establishing the convection-diffusion equation, and setting relevant model parameters in numerical calculation software, including material flow rate, dynamic viscosity, and flow velocity of micro-elements in the free falling film region.

[0025] Preferably, the construction of the polyester falling film thickening reactor model includes the following steps:

[0026] (1) Based on polymerization reaction kinetics, gas-liquid mass transfer kinetics and falling film fluid dynamics, establish the volumetric infinitesimal mass balance equation in the falling film thickening reactor along the axial flow direction of the fluid.

[0027] (2) Set boundary conditions based on the operating parameters of falling film thickening reactors in industry, select the discrete scheme, and use numerical integration method to solve the material balance equation;

[0028] (3) Define and initialize variables, constants and parameters, use the software solver to solve the material balance equation, and output the performance indicators of key gas-liquid phase processes.

[0029] Preferably, in step (3) of constructing the polyester falling film thickening reactor model, the variables, constants and parameters include one or more of the following: number of components, number of spatially discrete points, number of ordinary differential equations to be solved, and flow rate of melt polymer; the key process performance indicators of the gas-liquid phase include one or more of the following: number average molecular weight, intrinsic viscosity and end carboxyl group content.

[0030] Preferably, the construction of the entire process of the polyester melt falling film thickening reaction includes the following steps:

[0031] (1) Call the automatic control interface of the process simulation software to import the output data of the preceding reaction process of the falling film thickening reactor as the model input value, run the numerical calculation software to calculate the material balance equation, and obtain the changes of variables with the reaction process.

[0032] (2) Create a component object model for process simulation, open the running model file, set the visibility of the user interface, and run it in the numerical calculation software to obtain the output information of each component.

[0033] Preferably, in step (1) of constructing the entire process of the polyester melt falling film thickening reaction, the automatic control interface (ActiveX) of Aspen Plus is called to import the output data of its process as the model input value, and MATLAB is run to calculate the material balance equation to obtain the changes of variables with the reaction process.

[0034] More preferably, the ActiveX interface specifically involves: creating a component object model object of Aspen Plus, opening and running the model file according to the .bkp file path, setting the visibility of the user interface, and running it in MATLAB to obtain the output information of each component.

[0035] More preferably, the variables include, but are not limited to, one or more of the following: molecular weight of the polymer product, concentration of terminal carboxyl groups, concentration of terminal hydroxyl groups, content of hydroxyl condensates, and intrinsic viscosity.

[0036] Preferably, the analysis of the simulation results of the polyester falling film thickening reaction also includes conducting process simulation calculations under different operating conditions of the falling film thickening reactor, and analyzing the impact of operating conditions on the falling film thickening reaction effect. Wherein:

[0037] The specific steps for analyzing the simulation results of the polyester falling film thickening reaction include: importing the process simulation file into numerical calculation software for processing, outputting and displaying the acquired data as one or more of the following: data tables, graphs or curves, observing and analyzing the simulation results, and understanding the distribution of the performance indicators of each component along the axial direction in the falling film thickening process.

[0038] More preferably, the specific steps for analyzing the simulation results of the polyester falling film thickening reaction include: importing the Aspenplus simulation file into MATLAB software for processing, outputting and displaying the acquired data as graphs or curves, observing and analyzing the simulation calculation results, and understanding the distribution of the performance indicators of each component along the axial direction during the falling film thickening process;

[0039] The specific steps for analyzing the operating conditions of the polyester falling film thickening reaction simulation include: performing iterative calculations on the falling film thickening reactor unit module in numerical calculation software, systematically adjusting and analyzing the impact of different operating parameters on the reaction effect. Through multiple simulation runs, key operational data are collected and compared.

[0040] More preferably, the specific steps for analyzing the operating conditions of the simulated polyester falling film thickening reaction include:

[0041] In MATLAB software, iterative calculations were performed on the falling film viscosity-enhancing reactor unit module to systematically adjust and analyze the effects of different operating parameters (such as temperature and pressure) on the reaction effect. Through multiple simulation runs, key data (such as reaction product concentration, polymer molecular weight, viscosity changes, etc.) were collected and compared and analyzed.

[0042] More preferably, the different operating parameters include one or more of temperature and pressure; the key data include one or more of reaction product concentration, polymer molecular weight, and viscosity change.

[0043] Preferably, the polyester includes aliphatic polyesters, semi-aromatic polyesters, aromatic polyesters, copolyesters, and modified products with a polyester content of not less than 80% containing ester groups or carbonate groups on the main chain; more preferably, the polyester refers to semi-aromatic polyesters, copolyesters, and modified products thereof with a molecular main chain content of more than 85% obtained by reacting binary or more carboxyl and hydroxyl monomers, or esterifications thereof with the monomers.

[0044] More preferably, the polyester refers to bisphenol A type polycarbonate containing carbonate groups;

[0045] More preferably, the polyester refers to a polyester obtained by reacting a semi-aromatic dicarboxylic acid with an aliphatic diol.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] (1) This invention can intuitively show the axial distribution of key component performance indicators in polyester during the falling film thickening process in the falling film thickening reactor, as well as the axial distribution of key component performance indicators under different temperature and pressure effects; it can directly reflect the distribution law of each indicator of polyester melt during the falling film thickening reaction, thereby judging the quality of the exported product under the current working conditions.

[0048] (2) This invention can simulate and calculate the flow and reaction process in the falling film thickening reactor during the polyester falling film thickening reaction. It can effectively and conveniently obtain the axial distribution of key component performance indicators (such as molecular weight, viscosity, end carboxyl content, etc.) at various locations in the falling film thickening reactor, thus providing a good guide for experimental research and industrial design. At the same time, the polyester falling film thickening reaction simulation method proposed in this invention has a certain degree of universality.

[0049] (3) This invention is applicable to the simulation of the distribution of performance indicators of components outside the melt tube and the analysis of process operating conditions during the polyester falling film thickening process in the falling film thickening reactor. It provides a theoretical basis for industrial operation, promotes the molecular weight increase of various polyester melt polycondensation processes, and realizes the design and development of high molecular weight polyester melt direct spinning process. It provides a comprehensive and reliable modeling method for the development of melt polycondensation reactors, saves development costs, and has good application prospects and economic value.

[0050] (4) The present invention establishes a falling film thickening reaction process model by using the interactive method of MATLAB and Aspen Plus. It fully considers the physical and chemical changes inside the reaction, overcomes the disadvantages of large investment and long cycle of experimental testing, and can predict the distribution of key component performance indicators in the reaction process, thereby realizing the analysis of falling film melt polycondensation process. Attached Figure Description

[0051] Figure 1 A schematic diagram of the free-falling liquid film flow on the wall of the internal components of the falling film viscosity-enhancing reactor;

[0052] Figure 2 This is a flowchart of the MATLAB workflow of the present invention;

[0053] Figure 3 This is a process flow model diagram of the Aspen Plus software of the present invention;

[0054] Figure 4 This is a flowchart illustrating the interaction between MATALB and Aspen Plus in this invention.

[0055] Figure 5 This is a molecular weight axial distribution diagram during the falling film thickening reaction of the present invention;

[0056] Figure 6 This is a diagram showing the axial distribution of terminal carboxyl and terminal hydroxyl groups during the falling film thickening reaction of this invention.

[0057] Figure 7 This is a diagram showing the axial distribution of diethylene glycol and terminal diethylene glycol groups during the falling film thickening reaction of this invention.

[0058] Figure 8 This is a molecular weight axial distribution diagram during the film thickening reaction at different temperatures according to the present invention;

[0059] Figure 9 This is a diagram showing the axial distribution of terminal carboxyl groups during the film thickening reaction at different temperatures according to the present invention.

[0060] Figure 10 This is a diagram showing the axial distribution of terminal vinyl groups during the film thickening reaction at different temperatures according to the present invention.

[0061] Figure 11This is a diagram showing the axial distribution of molecular weight during the film thickening reaction under different pressures according to the present invention.

[0062] Figure 12 This is a diagram showing the axial distribution of terminal carboxyl groups during the film thickening reaction under different pressures according to the present invention. Detailed Implementation

[0063] To further understand the embodiments of the present invention, the present invention will be described in more detail below with reference to specific embodiments, the content of which does not affect the scope of protection of the present invention.

[0064] Example 1

[0065] This invention utilizes the interactive methods of MATLAB and Aspen Plus software to simulate the falling film thickening reaction process of polyester (PET). This includes constructing a falling film thickening reactor module in MATLAB that couples reaction kinetics, gas-liquid two-phase mass transfer kinetics, and falling film fluid kinetics; linking the Aspen Plus output results to MATLAB to construct the entire falling film thickening process; and analyzing the simulation results and process operating conditions after running the MATLAB simulation. Specifically:

[0066] (I) Analysis of Polymerization Reaction Kinetics Model for Polyester

[0067] First, the main and side reactions of the polymerization process are determined: using the "chain segment analysis" method, the reaction is simplified into a finite combination of basic chain segment units, with the condensation chain growth reaction as the dominant reaction, and the side reaction equations for the formation of acetaldehyde, diethylene glycol, water, and terminal vinyl groups are determined. The effect of temperature on the reaction rate constant is described using the Arrhenius equation, specifying the pre-exponential factor and activation energy in the equation, determining the reversible reaction equilibrium constant, and solving for the forward and reverse reaction rates. A second-order reaction kinetic model is used to analyze the reaction kinetic equations of each component, and the established equation set is compiled and imported into an executable function script file in MATLAB. Taking the main reaction of polyester condensation chain growth as an example, the rate equation of the reaction is determined using second-order reaction kinetics, and its reaction equilibrium constant is calculated using the Arrhenius equation and empirical data. A custom program is used to compile the rate equations and import them into the executable script for calculation.

[0068] (II) Gas-liquid two-phase mass transfer analysis of polyester

[0069] Based on the target components to be analyzed in the gas-liquid two-phase system, a suitable physical property model is selected and relevant attribute values ​​are set, including relative molecular mass, critical temperature, pressure, compressibility, gas-liquid phase pressure and molar volume, polymer molecular weight and viscosity characteristics, and the attributes are stored in a global data array. For the simulation analysis method of small molecule devolatilization process in high-viscosity polymer melt, based on the gas-liquid phase equilibrium process, the volatile components in the simplified system are simplified, and the gas-liquid equilibrium equation at the interface is constructed by calling the attribute groups of each component, and the corresponding settings are made in MATLAB.

[0070] The volatile components are specifically defined as follows: based on the degree of significant influence of each volatile component on the reaction process, the volatile components in the gas phase mainly include ethylene glycol and water, and the liquid phase includes ethylene glycol, water, diethylene glycol and acetaldehyde. Phase equilibrium process parameters are set for the volatile components in both the gas and liquid phases.

[0071] The vapor-liquid equilibrium equation at the interface is determined as follows, where the components involved are ethylene glycol, water, and diethylene glycol; the saturated vapor pressure and molar volume of the components involved are calculated.

[0072] (III) Analysis of falling film hydrodynamic behavior of polyester

[0073] The effects of reactor equipment structure and process conditions (temperature, pressure) on the gas-liquid mass transfer rate in the falling film thickening reaction process were determined. The mass transfer coefficient was introduced to calculate the mass transfer flux of the gas phase components. Based on the gas phase mass transfer flux during reactor operation in industry, the mass transfer coefficient was iteratively calculated. The output attribute set of each component was initialized to complete the iterative solution calculation, and the mass transfer flux of the volatile gas phase components in the falling film thickening reaction process was obtained. The mass transfer coefficients of water and ethylene glycol were then substituted.

[0074] It is necessary to process the polymer flow behavior on the internal components of the falling film viscosity-enhancing reactor. The polymer flow is assumed to be a low-speed laminar flow at an extremely low Reynolds number, with the liquid film thickness much smaller than the axial dimension of the falling film tube. Based on the full development of the liquid film flow, the development process of the liquid film flow with the variable viscosity fluid needs to be effectively observed and analyzed.

[0075] See Figure 1 The polyester viscosity-enhancing falling film viscosity-enhancing reactor of this invention uses vertical, smooth, and vertically aligned tubing. The melt forms a liquid film under the action of gravity and flows circumferentially along the smooth outer wall. The liquid film forms a three-dimensional symmetrical flow pattern in the central axis of the falling film tube. As the reaction proceeds, the devolatilization efficiency increases, and the polymer viscosity gradually increases. As the liquid film flow of the viscous fluid develops, the axial velocity distribution of the polymer is uneven when flowing outside the tube. This invention uses MATLAB software to establish the free falling liquid film flow process outside the tube of the falling film viscosity-enhancing reactor.

[0076] (IV) Construction of Falling Film Viscosity Enhancement Reactor Model

[0077] The main approach involves substituting reaction kinetics, gas-liquid two-phase mass transfer, and fluid dynamics models into the material balance equations to construct a set of partial differential equations. The input values ​​within the falling film thickening reactor serve as the initial conditions, and the final boundary conditions are defined by the zero first-order partial derivatives of each component's changes. The number of partial differential equations, time steps, and spatial discretization points are set. The material balance equations are discretized using the finite difference method, and the discretized ordinary differential equations are solved using the ODE15 function in MATLAB.

[0078] Reference Figure 2 The MATLAB workflow diagram shows that importing the above modules into the material balance equation allows for the solution stage of the falling film reaction unit module. Each setting needs to be configured in MATLAB, as detailed below:

[0079] (1) Initially set the reactor length, flow rate, diffusion coefficient, number of spatial discrete points, spatial step, time span, and units in the computational domain to be consistent with Aspen Plus units; set the basic function solution method, which is ODE15s to solve the equation in this invention.

[0080] (2) Set the operating conditions. In this invention, the operating pressure is 100 Pa and the temperature is 560 K. The initial flow rate is set considering the melt viscosity.

[0081] (3) Model setup: In order to more realistically predict the falling film thickening process, this invention uses a combination of reaction kinetics analysis, gas-liquid two-phase mass transfer analysis, and high-viscosity fluid dynamics behavior analysis to describe the changes of polymers in the falling film thickening reactor.

[0082] (4) This invention solves the material balance equation by calling the function files in the .m script files of each module. (V) Construction of the entire process of falling film thickening reaction

[0083] The process output data is imported into the Aspen Plus automatic control interface (ActiveX) as the model input value. MATLAB is then used to calculate the material balance equation and obtain the changes of variables such as polyester molecular weight, terminal carboxyl groups, terminal hydroxyl groups, diethylene glycol content, and intrinsic viscosity as the reaction progresses.

[0084] See Figure 3 This invention uses a typical five-reactor polyester process flow as a reference. The first esterification reactor, the second esterification reactor, and the first prepolymerization reactor adopt a fully mixed flow model, while the second prepolymerization reactor and the final polymerization reactor adopt a plug flow model. This invention uses Aspen Plus to construct a five-reactor polyester process model.

[0085] (VI) Analysis of Simulation Results of Falling Film Thickening Process / Analysis of Operating Conditions of Falling Film Thickening Process

[0086] Reference Figure 4 This diagram illustrates the workflow between MATLAB and Aspen Plus, importing the results from Aspen Plus into MATLAB for processing and calculation. This method effectively improves the flexibility of process flow design. The interaction involves importing the Aspen Plus automatic control interface (Active X) into MATLAB, where the node path for the ethylene glycol component in the output stream is Aspen.Application.Tree.FindNode('\Data\Streams\HP-L\Output\MOLEFLOW\MIXED\EG').

[0087] Figure 5 The diagram shows the axial distribution of molecular weight (MWN) in the polyester falling film reaction. The molecular weight at the reactor inlet is 21290 g / mol. According to the simulation results of this invention, the molecular weight of the material at the reactor outlet is 39681 g / mol, and its molecular weight gradually increases along the axial direction.

[0088] Figure 6 The diagram shows the axial distribution of terminal carboxyl groups ([T-COOH]) and terminal hydroxyl groups ([T-OH]) in the polyester falling film thickening reactor. According to the simulation results of this invention, the content of terminal carboxyl groups and terminal hydroxyl groups gradually decreases along the axial direction as the reaction proceeds. The content of terminal carboxyl groups in the reactor outlet material is 18 mmol / kg, and the content of terminal hydroxyl groups is 32 mmol / kg.

[0089] Figure 7 The diagram shows the mass fraction of diethylene glycol (DEG) and the axial distribution of terminal diethylene glycol groups ([T-DEG]) in the polyester falling film thickening reactor. According to the simulation results of this invention, the generation of byproducts diethylene glycol and terminal diethylene glycol groups is suppressed as the reaction proceeds.

[0090] Figure 8 The diagram shows the axial distribution of molecular weight (MWN) in the falling film thickening reactor at different temperatures. According to the simulation results of this invention, as the temperature gradually increases, the molecular weight of the polymer increases linearly in the axial direction. When the temperature reaches 563K, due to the intensification of the thermal decomposition reaction, the molecular weight growth rate is negatively correlated with the temperature. It is better to maintain the overall temperature of the falling film thickening reactor between 553-563K.

[0091] Figure 9 and Figure 10The diagram shows the axial distribution of terminal carboxyl groups ([T-COOH]) and terminal vinyl groups ([T-VIN]) in the membrane thickening reactor at different temperatures. According to the simulation results of this invention, it can be concluded that after the temperature reaches 563K, the number of terminal carboxyl groups and terminal vinyl groups gradually increases in the axial direction, which will cause the downstream polymer products to turn yellow and be easily hydrolyzed.

[0092] Figure 11 The diagram shows the axial distribution of molecular weight (MWN) in a falling film thickening reactor under different pressures. According to the simulation results of this invention, the molecular weight gradually increases with the increase of vacuum. After the pressure reaches 0.1 kPa, the rate of increase of molecular weight slows down. It is better to maintain the overall pressure of the falling film thickening reactor at around 0.1 kPa.

[0093] Figure 12 The diagram shows the axial distribution of terminal carboxyl groups ([T-COOH]) inside the falling film thickening reactor under different pressures. According to the simulation results of this invention, the higher the vacuum level, the lower the content of terminal carboxyl groups inside the falling film thickening reactor.

[0094] In summary, this invention aims to analyze the regularity of continuous polymerization-falling film thickening reaction process through process simulation, and clearly demonstrates the influence of temperature and pressure within the reactor on component distribution. This provides excellent guidance for the industrial operation of falling film thickening processes. This invention proposes a simulation method and process operation condition analysis method applicable to the distribution of component performance indicators outside the melt tube in the falling film thickening reactor during the falling film thickening process. It provides a feasible approach for costly experimental testing and industrial improvement, promotes the design and development of direct spinning processes for liquid-phase thickening melts, and provides a comprehensive and reliable modeling method for the development of high-viscosity melt polycondensation reactors in liquid-phase thickening processes. To this end, this invention employs a polyester falling film thickening reaction process simulation method. Based on the interactive method of MATLAB and Aspen Plus, a falling film thickening reaction process model is established, fully considering the physical and chemical changes within the reaction. This simulation method consists of six parts: polymerization reaction kinetic model analysis, gas-liquid two-phase mass transfer analysis, falling film fluid dynamics behavior analysis, falling film thickening reactor model construction, falling film thickening reaction full process construction, and falling film thickening process simulation result analysis / falling film thickening process operation condition analysis. This invention is mainly used for the design and manufacture of falling film thickening reactors in liquid phase thickening and for the improvement of industrial production processes in liquid phase thickening.

Claims

1. A method for simulating and analyzing the polyester falling film thickening reaction process, characterized in that... include: Polymerization reaction kinetics model analysis, gas-liquid two-phase mass transfer analysis, and falling film fluid dynamics behavior analysis were performed on polyester. Material balance calculations were performed on the entire polyester falling film thickening reaction process using reaction kinetics, gas-liquid two-phase mass transfer, and fluid dynamics models. Boundary and initial conditions were set, and the material balance equations were solved numerically to establish a polyester falling film thickening reactor model, including: A) Establish the volumetric infinitesimal mass balance equation along the axial flow direction of the fluid in the falling film thickening reactor based on polymerization reaction kinetics, gas-liquid mass transfer kinetics, and falling film fluid kinetics. B) Set boundary conditions based on the operating parameters of falling film thickening reactors in industry, select the discrete scheme, and use numerical integration method to solve the material balance equation; C) Define and initialize variables, constants, and parameters, solve the material balance equation using a software solver, and output key performance indicators of the gas-liquid phase process; the variables, constants, and parameters include one or more of the following: number of components, number of spatially discrete points, number of ordinary differential equations solved, and flow rate of melt polymer; the key performance indicators of the gas-liquid phase process include one or more of the following: number-average molecular weight, intrinsic viscosity, and terminal carboxyl group content. Based on the polyester reaction production process, a complete process for polyester melt falling film thickening reaction is constructed, including: 1) Import the output data of the preceding reaction process of the falling film thickening reactor into the automatic control interface of the process simulation software as the model input value, and run the numerical calculation software to calculate the material balance equation to obtain the changes of variables with the reaction process; the variables include one or more of the following: molecular weight of polymerization product, concentration of terminal carboxyl group, concentration of terminal hydroxyl group, content of hydroxyl condensate, and intrinsic viscosity. 2) Create component object model objects for process simulation, open and run the model file, set the visibility of the user interface, and run it in the numerical calculation software to obtain the output information of each component; Using the parameters of polyester melt with a certain degree of polymerization obtained through polycondensation as input values, the partial differential equations for the reaction rate are calculated, and the performance parameters of the polymerization product and the content information of each characteristic component are output. The simulation results of the polyester falling film thickening reaction process are then analyzed.

2. The method according to claim 1, characterized in that: The polymerization reaction kinetic model includes a chain growth reaction process that generates byproducts water and hydroxyl compounds; The polymerization reaction kinetic model analysis includes the following steps: S1: Determine the main and side reactions in the polymerization process: Use the "chain segment analysis" method to simplify the reaction into a combination of a limited number of basic chain segment units, with the condensation chain growth reaction as the main factor, and determine the reaction equations for the formation of aldehydes, hydroxy compounds, hydroxy condensates, water and terminal alkenyl groups; S2: Determination of reaction rate constant and equilibrium constant: The effect of temperature on the reaction rate constant is described by the Arrhenius equation, the pre-exponential factor and activation energy in the equation are specified, the equilibrium constant of the reversible reaction is determined, and the forward and reverse reaction rate values ​​are solved. S3: Establishment of reaction kinetic equations: Analyze the reaction kinetic equations of each component using the reaction kinetic model, and compile and import the established equation set into an executable function script file in the numerical calculation software.

3. The method according to claim 1, characterized in that: The gas-liquid two-phase mass transfer analysis includes the following steps: (a) Based on the target components to be analyzed in the gas-liquid two-phase system, select an appropriate physical property model and set relevant attribute values, including one or more of the following: relative molecular mass, critical temperature, pressure, compressibility, gas-liquid phase pressure, molar volume, polymer molecular weight and viscosity characteristics, and store the attributes in a global data array. (b) A simulation analysis method for the small molecule devolatilization process of high viscosity polymer melts: Based on the gas-liquid phase equilibrium process, the volatile components in the system are determined, the gas-liquid equilibrium equation at the interface is constructed by calling the property groups of each component, and the corresponding settings are made in the numerical calculation software. The volatile components are specifically defined as follows: based on the degree of significant influence of each volatile component on the reaction process, the volatile components in the gas phase include two parts: hydroxyl compounds and water, and the volatile components in the liquid phase include hydroxyl compounds, water, condensates of hydroxyl compounds and aldehydes. Phase equilibrium process parameters are set for the volatile components in both the gas and liquid phases. (c) Determine the reactor equipment structure and process condition parameters of the falling film thickening reaction process that affect the gas-liquid mass transfer rate, introduce the mass transfer coefficient to calculate the mass transfer flux of the gas phase component, and iteratively calculate the mass transfer coefficient based on the gas phase mass transfer flux during reactor operation in industry. (d) Initialize the output property groups of each component to complete the iterative solution calculation and obtain the mass transfer flux of the gas phase volatile components in the polyester falling film thickening reaction process.

4. The method according to claim 1, characterized in that: The falling film fluid dynamics analysis includes the following steps: determining the molecular diffusion coefficient during the flow process based on the low-speed laminar polymer motion, establishing the convection-diffusion equation, and setting relevant model parameters in numerical calculation software, including material flow rate, dynamic viscosity, and flow velocity of micro-elements in the free falling film region.

5. The method according to claim 1, characterized in that: The analysis of the simulation results of the polyester falling film thickening reaction also includes conducting process simulation calculations under different operating conditions of the falling film thickening reactor, and analyzing the impact of operating conditions on the effect of the falling film thickening reaction, including: Import the process simulation file into numerical calculation software for processing, output the acquired data and display it as one or more of the following: data table, graph or curve. Observe and analyze the simulation results to understand the distribution of the performance indicators of each component along the axial direction in the falling film thickening process. In numerical calculation software, iterative calculations are performed on the falling film viscosity-enhancing reactor unit module to systematically adjust and analyze the effects of different operating parameters on the reaction effect; key operational data are collected and compared and analyzed through multiple simulation runs.

6. The method according to claim 5, characterized in that: The different operating parameters include one or more of temperature and pressure.

7. The method according to claim 5, characterized in that: The key data includes one or more of the following: reaction product concentration, polymer molecular weight, and viscosity change.

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