Method for testing kinetics of homopolymerization reaction or copolymerization reaction of high-pressure ethylene

Abstract

The invention discloses a method for testing kinetics of high-pressure ethylene homopolymerization or copolymerization. The method comprises the following steps: measuring temperature and pressure in a reaction kettle during a blank experiment and to-be-tested ethylene homopolymerization or copolymerization; based on blank experiment data, a correlation formula of compression acting pressure change to system temperature change is obtained; processing the data of the homopolymerization reaction or copolymerization reaction to be detected by using the correlation formula, and eliminating the influence of pressure on the reaction temperature; and fitting kinetic parameters of ethylene homopolymerization reaction or copolymerization reaction based on the processed data. According to the method, through accurate temperature and pressure monitoring and application of the thermodynamic state equation, the influence of pressure on the reaction temperature can be effectively eliminated, and reaction kinetic parameters can still be accurately fitted under the working condition that the operation condition pressure fluctuation is large. The method is simple and convenient to operate and accurate in measurement, and provides important technical support for optimization and control of a high-pressure polymerization process.

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 changing trend of temperature and pressure during the reaction, determine the amount of initiator feed, determine the reaction conditions, and avoid the occurrence of ethylene decomposition reactions while improving the conversion rate. The kinetic parameters of ethylene polymerization reactions can be measured experimentally. The common measurement method is through laser pulse polymerization (PLP) experiments (such as Hungenberg K, et al. Modeling and Simulation in Polymer Reaction Engineering: A Modular Approach [J]. 2018), and the kinetic parameters can also be obtained through DFT calculations (such as Cauter KV, et al. Ab Initio Study of Free-Radical Polymerization: Polyethylene Propagation Kinetics [J]. 2010). However, the intrinsic kinetics obtained by experiments or theoretical calculations are affected by factors such as flow field, temperature distribution, and viscosity in actual reactions, and cannot explain the phenomena of actual reactions well. By treating the kinetic parameters as uncertain variables and correcting them within a certain range, the experimental phenomena can be better simulated (such as Mitrasupa, et al. Handling Uncertainty in Kinetic Parameters in Optimal Operation of a Polymerization Reactor [J]. 2011). The apparent kinetics obtained at this time have better industrial applications. However, when modeling the reactor, the system temperature and pressure are usually constant. When the pressure fluctuates greatly, the temperature fluctuation caused by the pressure fluctuation cannot be ignored. At this time, the kinetic parameters obtained by the reactor model will have a certain degree of deviation from the stable operating state.

[0004] Therefore, it is still a big problem in this field to establish a method for testing the kinetics of high-pressure ethylene homopolymerization or copolymerization under the condition of large pressure fluctuation. The present invention hopes to use the thermodynamic state equation to pre-process the temperature-pressure curve of the reaction system, eliminate the influence of pressure fluctuation, and then fit the kinetic data to establish a method that can still obtain kinetics suitable for industrial operation under pressure fluctuation conditions. 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 reaction, by preprocessing the temperature-pressure curve of the reaction system by a thermodynamic state equation, thereby eliminating the influence of pressure fluctuations on the estimation of kinetic parameters, thereby still being able to obtain 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) at least one temperature sensor and one pressure sensor are arranged 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;

[0008] 2) Fitting the thermodynamic physical property parameters of ethylene through the temperature-pressure correlation in the thermodynamic state equation combined with the temperature and pressure signals collected from the blank experiment;

[0009] The temperature-pressure correlation is:

[0010]

[0011] In the formula, 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 the pressure fluctuation data of the reaction according to the collected temperature and pressure signals of the polymerization reaction to be measured to obtain dp, obtaining the temperature fluctuation dT affected by the pressure through the temperature-pressure correlation formula, 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 temperature data corrected 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.

[0014] As a preferred embodiment of the present invention, the reaction temperature of 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 of 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 wall of the reactor is insulated by a jacket with a constant temperature, and at least one temperature of the outer wall, middle part and inner wall of the jacket is monitored in real time.

[0015] As a preferred embodiment of the present invention, the feeding method of the reactor is intermittent feeding or continuous feeding, and the discharging method 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 by 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 1h is 60°C to 200°C, and the optimal initiation interval of the ethylene homopolymerization reaction or the copolymerization reaction of ethylene and other media is in the range of 100-350°C, and the preferred initiation temperature interval is 140-280°C;

[0019] As a preferred embodiment of the present invention, the comonomers of the ethylene copolymerization include an acrylate system, a 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 state equation of step (3) is one of PC-SAFT, Lee-Kesler, Benedict-Webb-Rubin and cubic state equation. The cubic state equation 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; a constrained optimization algorithm is such as a constrained nonlinear least squares method; an 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 high-pressure ethylene homopolymerization or copolymerization kinetics test method provided by the present invention can effectively eliminate the influence of pressure on reaction temperature through accurate temperature and pressure monitoring and application of the thermodynamic state equation, and can still accurately fit the reaction kinetics parameters under the condition of large pressure fluctuation in operating conditions. The method is simple to operate and has accurate measurement, and provides 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 implementation method for 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 on the premise of the technical solution of the present invention, and a detailed implementation method and specific operation process are given, but 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 an ethylene polymerization reaction to be tested (which may be an ethylene homopolymerization reaction or a copolymerization reaction); then, based on the blank experiment data, obtain a correlation equation of the change in compression work pressure to the change in system temperature; then, use the correlation equation to process the temperature data of the homopolymerization reaction or the copolymerization reaction to be tested, and eliminate the influence of pressure on the reaction temperature; finally, fit the kinetic parameters of the ethylene homopolymerization reaction or the copolymerization reaction based on the processed data. The present invention can effectively eliminate the influence of pressure on the reaction temperature through accurate temperature and pressure monitoring and the application of the thermodynamic state equation, and can still accurately fit the reaction kinetic parameters under the condition of large pressure fluctuations in the operating conditions.

[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 comprises:

[0030] An ethylene injection module, comprising ethylene compression pumps 1 to 4, pressurizing 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, which includes a comonomer pump 5 and a comonomer injection stop valve 11;

[0033] A reactor module, which includes 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 arranged 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 to 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. During the reaction, the temperature and pressure inside the reactor were recorded in real time.

[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 length of 0.01 second, and the temperature fluctuation dT affected by the pressure is obtained through 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 ethylene homopolymerization or copolymerization 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. This embodiment uses the moment method to fit the kinetic parameters of ethylene homopolymerization, and 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. During the reaction, the temperature and pressure inside the reactor were recorded in real time.

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

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

[0075]

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

[0077] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached 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 arranged 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 property parameters of ethylene through the temperature-pressure correlation in the thermodynamic state equation combined with the temperature and pressure signals collected from the blank experiment; The temperature-pressure correlation is: In the formula, c v is the molar heat capacity at constant pressure, p is the pressure, V is the molar volume, and T is the temperature; 3) obtaining the pressure fluctuation data of the reaction according to the collected temperature and pressure signals of the polymerization reaction to be measured to obtain dp, obtaining the temperature fluctuation dT affected by the pressure through the temperature-pressure correlation formula, 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 temperature data corrected 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 adopts one of intermittent feeding and continuous feeding, and the discharging mode of the reactor adopts one of intermittent discharging and continuous discharging.

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

5. The method according to claim 1, characterized in that The blank experiment uses only ethylene feed without adding initiator, and the oxygen content in the feed ethylene is 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-initiated polymerization and peroxide-initiated 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 1h 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 acrylate compounds, methacrylate compounds, 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 high-pressure polymerization kinetics is one of a constrained optimization algorithm, an unconstrained optimization algorithm, and an intelligent algorithm.

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