A method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization

Abstract

The present invention discloses a method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization reactions, comprising measuring the temperature and pressure inside a reactor during a blank experiment and during the ethylene homopolymerization or copolymerization reaction to be tested; obtaining a correlation equation for the change in compression work pressure to the change in system temperature based on the blank experiment data; processing the data of the homopolymerization or copolymerization reaction to be tested using the correlation equation to eliminate the effect of pressure on the reaction temperature; and fitting the kinetic parameters of the ethylene homopolymerization or copolymerization reaction based on the processed data. The present invention provides that the effect of pressure on the reaction temperature can be effectively eliminated through precise temperature and pressure monitoring and the application of the thermodynamic equation of state, and that the reaction kinetic parameters can still be accurately fitted under operating conditions with large pressure fluctuations. The method is simple to operate and has accurate measurement, providing important technical support for the optimization and control of high-pressure polymerization processes.

Description

Technical Field

[0001] The present invention relates to the field of high-pressure ethylene polymerization, and in particular to a method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization. Background Art

[0002] The polymer products obtained by homopolymerization or copolymerization of ethylene under high temperature and high pressure conditions are widely used in the fields of film materials, packaging materials, cable materials, etc. due to their good performance.

[0003] Kinetic parameters are important parameters for reactor modeling. Appropriate kinetic parameters can be used to predict the temperature and pressure trends during the reaction, determine the initiator feed rate, and determine reaction conditions, thereby improving conversion while avoiding ethylene decomposition. The kinetic parameters of ethylene polymerization reactions can be measured experimentally, most commonly through laser pulse polymerization (PLP) experiments (e.g., Hungenberg K, et al. Modeling and Simulation in Polymer Reaction Engineering: A Modular Approach [J]. 2018). Kinetic parameters can also be obtained through DFT calculations (e.g., Cauter KV, et al. Ab Initio Study of Free-Radical Polymerization: Polyethylene Propagation Kinetics [J]. 2010). However, the intrinsic kinetics obtained through experiments or theoretical calculations are affected by factors such as flow field, temperature distribution, and viscosity in actual reactions, and cannot effectively explain the phenomena of actual reactions. By treating kinetic parameters as uncertain variables and calibrating them within a certain range, experimental phenomena can be better simulated (e.g., Mitrasupa, et al. Handling Uncertainty in Kinetic Parameters in Optimal Operation of a Polymerization Reactor[J]. 2011). The resulting apparent kinetics have better industrial applications. However, when modeling a reactor, the system temperature and pressure are usually constant. When the pressure fluctuates significantly, the temperature fluctuations caused by the pressure fluctuations cannot be ignored. In this case, the kinetic parameters obtained from the reactor model will deviate to a certain extent from those under steady-state operation.

[0004] Therefore, establishing a method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization reactions under conditions of large pressure fluctuations remains a major challenge in this field. The present invention employs a thermodynamic equation of state to preprocess the temperature-pressure curve of the reaction system, eliminating the effects of pressure fluctuations. The kinetic data are then fitted, thereby establishing a method that can produce kinetics suitable for industrial operations under conditions of pressure fluctuations. Summary of the Invention

[0005] The purpose of the present invention is to establish a method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization reactions. By preprocessing the temperature-pressure curve of the reaction system using the thermodynamic equation of state, the influence of pressure fluctuations on the estimation of kinetic parameters is eliminated, thereby obtaining kinetic parameters suitable for industrial operation under conditions of large pressure fluctuations.

[0006] The present invention provides a method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization, which comprises the following steps:

[0007] 1) providing at least one temperature sensor and one pressure sensor in the reactor to respectively collect the temperature and pressure inside the reactor during a blank experiment and a polymerization reaction to be measured; wherein the polymerization reaction to be measured is an ethylene homopolymerization reaction or a copolymerization reaction;

[0008] 2) Fitting the thermodynamic physical properties of ethylene using the temperature-pressure correlation in the thermodynamic equation of state and the temperature and pressure signals collected from the blank experiment;

[0009] The temperature-pressure correlation formula is:

[0010]

[0011] Where c v is the molar constant volume heat capacity, p is the pressure, V is the molar volume, and T is the temperature;

[0012] 3) obtaining pressure fluctuation data of the reaction to obtain dp based on the collected temperature and pressure signals of the polymerization reaction to be measured, obtaining the temperature fluctuation dT affected by the pressure through the temperature-pressure correlation equation, and correcting the collected temperature signal of the polymerization reaction to be measured to T-dT to eliminate the influence of the pressure fluctuation on the temperature;

[0013] 4) Based on the corrected temperature data obtained in step 3) and the collected pressure signal of the polymerization reaction to be measured, and simultaneously through the heat balance of the reactor and the molecular weight distribution information of the product, the kinetic parameters of the ethylene homopolymerization or copolymerization reaction are fitted.

[0014] As a preferred embodiment of the present invention, the reaction temperature for the blank experiment and the polymerization reaction to be tested (ethylene homopolymerization or copolymerization) in step 1) is 100-350°C, the reaction pressure is 300-3500 bar, and the ethylene flow rate is 0-20 kg / h. Preferably, the reaction temperature for the blank experiment and the polymerization reaction to be tested is 140-280°C, the reaction pressure is 1000-3200 bar, and the ethylene discharge flow rate is 0.5-6 kg / h. The reactor wall is insulated with a jacket having a constant temperature, and the temperature of at least one of the outer wall, middle portion, and inner wall of the jacket is monitored in real time.

[0015] As a preferred embodiment of the present invention, the feeding mode of the reactor is intermittent feeding or continuous feeding, and the discharging mode of the reactor is intermittent discharging or continuous discharging.

[0016] As a preferred embodiment of the present invention, the wall of the reactor is insulated with a jacket having a constant temperature, and the temperature at at least one position of the outer wall, the middle and the inner wall of the jacket is monitored;

[0017] As a preferred embodiment of the present invention, the blank experiment uses only ethylene feed without adding initiator, the ethylene oxygen content of the blank experiment feed is less than 5ppm, and the conversion rate is less than 0.5%;

[0018] As a preferred embodiment of the present invention, the initiation mode of the ethylene homopolymerization or copolymerization reaction includes oxygen-initiated polymerization and peroxide-initiated free radical polymerization, and the reaction conversion rate is less than 5%; the reaction temperature corresponding to the half-life of the peroxide at normal pressure of 1 hour is 60°C to 200°C, and the optimal initiation range of the ethylene homopolymerization reaction or the copolymerization reaction of ethylene and other media is within the range of 100-350°C, preferably within the initiation temperature range of 140-280°C;

[0019] As a preferred embodiment of the present invention, the comonomers of the ethylene copolymerization include acrylate system, methacrylate system, vinyl acetate, acrylic acid, etc.; the acrylate system includes methyl acrylate, ethyl acrylate, butyl acrylate, etc.; the methacrylate system includes methyl methacrylate, ethylene methacrylate, butyl methacrylate, etc.

[0020] As a preferred embodiment of the present invention, the thermodynamic equation of state in step (3) is one of PC-SAFT, Lee-Kesler, Benedict-Webb-Rubin and cubic equation of state. The cubic equation of state includes but is not limited to Peng-Robinson, Redlich-Kwong and Redlich-Kwong-Soave.

[0021] As a preferred embodiment of the present invention, the kinetic parameter fitting method in step (4) is one of an unconstrained optimization algorithm, a constrained optimization algorithm, and a random optimization algorithm. The unconstrained optimization algorithm is an unconstrained optimal algorithm using a direct search method and an unconstrained optimal algorithm using a gradient algorithm; the constrained optimization algorithm is such as a constrained nonlinear least squares method; and the intelligent algorithm is such as a genetic algorithm, a particle swarm algorithm, etc.

[0022] As a preferred embodiment of the present invention, the molecular weight distribution information of the product is the molecular weight distribution of the product, as well as the comonomer content (during copolymerization) and the degree of branching.

[0023] The present invention has the following advantages: The method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization reactions, through precise temperature and pressure monitoring and the application of the thermodynamic equation of state, effectively eliminates the effect of pressure on reaction temperature. This allows accurate fitting of reaction kinetic parameters even under operating conditions with large pressure fluctuations. The method is simple to operate and offers accurate measurements, providing important technical support for the optimization and control of high-pressure polymerization processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic diagram of an embodiment of measuring the kinetics of high-pressure ethylene homopolymerization or copolymerization reaction.

[0025] Figure 2 This is the temperature fluctuation curve of ethylene homopolymerization experiment.

[0026] Figure 3 These are the separation and pressure fluctuation curves of ethylene homopolymerization experiment. DETAILED DESCRIPTION

[0027] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0028] The principle of the method of the present invention is to first measure the temperature and pressure inside the reactor during a blank experiment and a test ethylene polymerization reaction (which can be an ethylene homopolymerization reaction or a copolymerization reaction); then, based on the blank experiment data, obtain a correlation equation for the change in compression work pressure to the change in system temperature; then, use the correlation equation to process the temperature data of the test homopolymerization reaction or copolymerization reaction to eliminate the effect of pressure on the reaction temperature; and finally, fit the kinetic parameters of the ethylene homopolymerization or copolymerization reaction based on the processed data. Through precise temperature and pressure monitoring and the application of the thermodynamic equation of state, the present invention can effectively eliminate the effect of pressure on the reaction temperature, and can still accurately fit the reaction kinetic parameters under operating conditions with large pressure fluctuations.

[0029] In a preferred embodiment of the present invention, the device used to measure the kinetics of high pressure ethylene homopolymerization or copolymerization is as follows: Figure 1 As shown, the device includes:

[0030] An ethylene injection module includes ethylene compression pumps 1 to 4, which increase the pressure of ethylene from 20 bar to 3000 bar through four-stage compression;

[0031] an initiator injection module, comprising an initiator pump 6 and an initiator injection stop valve 12;

[0032] a comonomer injection module comprising a comonomer pump 5 and a comonomer injection stop valve 11;

[0033] A reactor module comprising a reactor 7 and a reactor injection valve 13;

[0034] The separator module comprises a separator 10, a gas phase outlet valve 14 and a liquid phase outlet valve 15; wherein a temperature monitoring point 8 and a pressure monitoring point 9 are provided in the reactor module.

[0035] Figure 2 and Figure 3 They are the temperature fluctuation curve and pressure fluctuation curve of the ethylene homopolymerization experiment. Due to the small volume of the measuring device, the pressure fluctuation is generally ±100 bar. At this time, the temperature change caused by the pressure fluctuation cannot be ignored.

[0036] Example 1: Testing the kinetics of high-pressure ethylene homopolymerization

[0037] (1) Blank test method (reaction temperature 200°C, pressure 2000 bar, ethylene flow rate 2 kg / h, no initiator added), the specific experimental steps are as follows:

[0038] Detect the ethylene oxygen content to ensure that the oxygen content in ethylene is less than 5ppm;

[0039] The reactor was preheated to 220°C;

[0040] The reactor was pressurized to 2000 bar by continuous feeding and discharging.

[0041] Adjust the ethylene flow rate to 2 kg / h;

[0042] The reactor wall temperature was adjusted to control the reaction temperature at 200°C, and the temperature and pressure inside the reactor were recorded in real time.

[0043] (2) Ethylene homopolymerization experimental method, the specific experimental steps are as follows:

[0044] Detect the ethylene oxygen content to ensure that the oxygen content in ethylene is less than 5ppm;

[0045] The reactor was preheated to 200°C;

[0046] The reactor was pressurized to 2000 bar by continuous feeding and discharging.

[0047] Adjust the ethylene flow rate to 2 kg / h;

[0048] injecting an initiator;

[0049] After the reaction temperature stabilized, the reactor wall temperature was adjusted to control the reaction temperature to 200°C. The temperature and pressure inside the reactor were recorded in real time during the reaction.

[0050] (3) Data processing and kinetic parameter fitting methods

[0051] The data were preprocessed and the data with stable reaction temperature and reaction pressure were selected for kinetic parameter fitting.

[0052] The effect of pressure fluctuation on temperature (correlation) satisfies the following relationship:

[0053]

[0054] Where c v is the molar constant volume heat capacity, p is the pressure, V is the molar volume, and T is the temperature;

[0055] According to the collected temperature and pressure signals of the ethylene homopolymerization reaction, dp is obtained according to the pressure fluctuation data of the reaction with a step size of 0.01 second, and the temperature fluctuation dT affected by the pressure is obtained by the correlation formula, and the temperature is corrected to T-dT to eliminate the influence of the pressure fluctuation on the temperature;

[0056] The present invention further fits the kinetic parameters of the ethylene homopolymerization or copolymerization reaction based on the corrected temperature data and the collected pressure signal of the ethylene polymerization reaction, combined with the heat balance of the reactor and the molecular weight distribution information of the product. The kinetic parameters include chain initiation, chain growth, chain transfer, chain termination, etc. The present invention does not limit the fitting method of the kinetic parameters. In this embodiment, the moment method is used to fit the kinetic parameters of the ethylene homopolymerization. The kinetic model used is as follows:

[0057]

[0058]

[0059] Among them, k i is the initiator decomposition rate constant, k p is the chain growth rate constant, k tc , k td is the disproportionation termination, coupled termination rate constant, k fm , k fp , k fsis the rate constant of chain transfer to monomer, polymer and solvent. Since the double bond structure of polymer is not considered in this paper, k s ,k db ,k b is the rate constant for backbiting, β-cleavage, and terminal double bond reactions.

[0060] According to the corrected temperature and molecular weight data of polyethylene products, the gradient descent algorithm is used to fit the pre-exponential factors and activation energies of the reaction rate constants of elementary reactions such as chain initiation, chain growth, and chain termination.

[0061] The kinetic fitting calculation results of this example are as follows:

[0062] Table 1 - Ethylene homopolymerization kinetic data

[0063]

[0064] Example 2: Testing the kinetics of high-pressure ethylene copolymerization

[0065] This example carried out an ethylene-vinyl acetate copolymerization experiment, and the specific experimental steps are as follows:

[0066] Detect the ethylene oxygen content to ensure that the oxygen content in ethylene is less than 5ppm;

[0067] The reactor was preheated to 200°C;

[0068] The reactor was pressurized to 2000 bar by continuous feeding and discharging.

[0069] Adjust the ethylene flow rate to 2 kg / h;

[0070] injecting an initiator;

[0071] Inject comonomer at a comonomer flow rate of 10 mL / min;

[0072] After the reaction temperature stabilized, the reactor wall temperature was adjusted to control the reaction temperature to 200°C. The temperature and pressure inside the reactor were recorded in real time during the reaction.

[0073] The blank test was the same as in Example 1, and the same method as in Example 1 was used for fitting. The obtained kinetic data were as follows:

[0074] Table 2 - Kinetic parameters of ethylene-vinyl acetate copolymerization

[0075]

[0076] The results of this example show that under conditions of large pressure fluctuations, through precise temperature and pressure monitoring and the application of the thermodynamic equation of state, the effect of pressure on the reaction temperature can be effectively eliminated, and the reaction kinetic parameters can still be accurately fitted under operating conditions with large pressure fluctuations.

[0077] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization, characterized in that: The following steps are involved: 1) at least one temperature sensor and one pressure sensor are provided in the reactor to respectively collect the temperature and pressure inside the reactor during a blank experiment and a polymerization reaction to be tested; the polymerization reaction to be tested is an ethylene homopolymerization reaction or a copolymerization reaction; 2) Fitting the thermodynamic physical properties of ethylene using the temperature-pressure correlation in the thermodynamic equation of state and the temperature and pressure signals collected from the blank experiment; The temperature-pressure correlation formula is: ； Where, is the molar heat capacity at constant pressure, For pressure, is the molar volume, is temperature; 3) obtaining pressure fluctuation data of the reaction dp based on the collected temperature and pressure signals of the polymerization reaction to be measured, obtaining the temperature fluctuation dT affected by the pressure through the temperature-pressure correlation equation, and correcting the collected temperature signal of the polymerization reaction to be measured to T-dT to eliminate the influence of the pressure fluctuation on the temperature; 4) Based on the corrected temperature data obtained in step 3) and the collected pressure signal of the polymerization reaction to be measured, and through the heat balance of the reactor and the molecular weight distribution information of the product, the kinetic parameters of the ethylene homopolymerization or copolymerization reaction are fitted.

2. The method according to claim 1, characterized in that In step 1), the reaction temperature of the blank experiment and the polymerization reaction to be tested is 100-350° C., the reaction pressure is 300-3500 bar, and the ethylene flow rate is 0-20 kg / h.

3. The method according to claim 1, characterized in that The feeding mode of the reactor is intermittent feeding or continuous feeding, and the discharging mode of the reactor is intermittent discharging or continuous discharging.

4. The method according to claim 1, wherein The wall surface of the reactor is insulated by a jacket with a constant temperature.

5. The method according to claim 1, wherein The blank experiment used only ethylene feed without adding initiator, and the oxygen content in the feed ethylene was less than 5 ppm.

6. The method according to claim 1, characterized in that In the polymerization reaction to be tested, the reaction initiation methods include oxygen-induced polymerization and peroxide-induced polymerization, and the reaction conversion rate is controlled to be less than 5%.

7. The method according to claim 6, characterized in that The reaction temperature corresponding to the half-life of the peroxide at normal pressure of 1 hour is 60° C. to 200° C.

8. The method according to claim 1, characterized in that The comonomer used in the ethylene copolymerization reaction includes at least one of an acrylate compound, a methacrylate compound, vinyl acetate, and acrylic acid.

9. The method according to claim 1, characterized in that The thermodynamic state equation is one of PC-SAFT, Lee-Kesler, Benedict-Webb-Rubin and cubic state equation.

10. The method according to claim 1, characterized in that The method for fitting the kinetic parameters of ethylene homopolymerization or copolymerization is one of a constrained optimization algorithm, an unconstrained optimization algorithm, and an intelligent algorithm.

Images