A device and method for testing the decomposition characteristics of organic peroxides above 50 MPa

Abstract

The application discloses a device and method for testing decomposition characteristics of organic peroxide above 50MPa, wherein the organic peroxide to be tested and at least one inert solvent are mixed to obtain a first material, and the first material is continuously added into an autoclave through a high-pressure feeding unit to simulate the decomposition process of the organic peroxide under a real flow mixing environment. The application can change the mixing conditions and reaction conditions in the testing process, and provides a measuring method for various product concentrations based on the high-pressure testing conditions, so that the decomposition characteristics of the organic peroxide under different mixing and reaction conditions can be tested, and the measuring range covers high-pressure and super-high-pressure conditions, and the sensitivity and accuracy are high.

Description

TECHNICAL FIELD

[0001] The present application relates to the study of organic peroxide reaction mechanism under high pressure and super-high pressure conditions, more particularly to a test device and method for the decomposition characteristics of organic peroxide above 50 MPa. BACKGROUND

[0002] The free radical polymerization process for preparing polymers is a typical polymerization process. Free radical initiators usually have weak covalent bonds, which produce free radicals through homolysis or heterolysis of covalent bonds, and initiate monomers to undergo polymerization reaction. Commonly used free radical initiators include peroxide initiators, azo initiators and redox initiators, etc.

[0003] At present, it is known in the art that in the preparation of low-density polyethylene, ethylene-vinyl acetate copolymer and other products by high-pressure free radical polymerization process, the reaction temperature is as high as 100-350℃, the reaction pressure is above 50 MPa, and especially in the production of low-density polyethylene, the reaction pressure is as high as above 120 MPa, and the commonly used initiators are organic peroxides, oxygen and their mixtures. The current test methods for testing the decomposition reaction of organic peroxides include differential scanning calorimetry (DSC), adiabatic accelerating rate calorimetry (ARC), gas chromatography (GC) and other methods.

[0004] When the reaction pressure is above 50 MPa, the decomposition reaction rate of the initiator is significantly affected by the pressure. Foreign scholars use high-pressure DSC to study the decomposition reaction kinetics of initiators (J. Solution Chem. 2024, 53:43-59). This method uses a specially designed high-pressure resistant calorimetric cell to measure the heat release of organic peroxide decomposition accurately by continuously scanning the heat change during the temperature rise, and calculates the decomposition reaction rate of peroxide. However, it is known in the art that the decomposition process of free radical initiators is a complex network of reactions and mass transfer coupling, i.e. there is a so-called "cage effect". Therefore, neither DSC, ARC nor GC can measure the decomposition efficiency of the initiator under real mixed mass transfer conditions.

[0005] Therefore, a test device for the decomposition characteristics of organic peroxide above 50 MPa is proposed, which can measure the decomposition reaction rate constant of organic peroxide while measuring the efficiency of organic peroxide by simulating the real flow mixing environment. SUMMARY

[0006] The purpose of the present application is to solve the problem that the decomposition characteristics of organic peroxide under real mixing conditions under high pressure and super-high pressure conditions are difficult to measure, and a device and method are proposed to simulate the real flow mixing environment and measure the decomposition characteristics of organic peroxide above 50 MPa.

[0007] The present application solves the technical problem by adopting the following technical scheme.

[0008] The present application provides a test method for the decomposition characteristics of organic peroxide above 50MPa, which simulates the mixing mass transfer and decomposition process of organic peroxide in the high-pressure radical polymerization process above 50MPa, and the method comprises:

[0009] (1) mixing the organic peroxide to be tested and at least one inert solvent to obtain a first material, and then continuously feeding the first material into an autoclave through a high-pressure feeding unit;

[0010] (2) increasing the pressure of the autoclave to a set pressure, maintaining the heat exchange jacket temperature of the autoclave at a preset simulated reaction temperature, and starting the stirring paddle so that the stirring Reynolds number of the stirring paddle is 4000-50000; wherein the calculation formula of the stirring Reynolds number Re is Re=d 2 ×N×ρ / μ, d is the blade diameter of the stirring paddle, N is the stirring speed, ρ is the density of the material in the autoclave, and μ is the viscosity of the material in the autoclave; by changing the stirring Reynolds number of the stirring paddle, the initiator decomposition characteristics of the real flow, heat transfer, mass transfer and reaction environment can be simulated;

[0011] (3) controlling the opening of the first pressure reducing valve to control the pressure in the autoclave to the required test pressure, and introducing the decomposed material in the autoclave into a discharge tank through the first pressure reducing valve;

[0012] (4) adjusting the heat exchange jacket temperature to change the test temperature, adjusting the opening of the first pressure reducing valve to change the test pressure, recording the temperature, pressure and conversion rate of the organic peroxide in the autoclave with time, and calculating the decomposition kinetics of the organic peroxide at different temperatures and pressures;

[0013] Wherein, the conversion rate of the organic peroxide is calculated according to the concentration of the organic peroxide in the discharge tank and the concentration of the organic peroxide at the inlet of the high-pressure feeding unit, and the specific formula is as follows:

[0014] X=1-C1 / C0

[0015] In the formula, X is the conversion rate of the organic peroxide, C1 is the concentration of the organic peroxide in the discharge tank, and C0 is the concentration of the organic peroxide at the inlet of the feeding unit.

[0016] In one embodiment of the present application, the test pressure of the autoclave is adjusted in the range of 50 MPa to 400 MPa, and the test temperature of the autoclave is adjusted in the range of 20°C to 350°C; the pressure in the discharge tank is 0.1 MPa to 50 MPa, and the temperature of the discharge tank is controlled by a heat exchange medium to be 20°C to 150°C. Preferably, the pressure in the discharge tank is 0.1 MPa to 30.0 MPa, and the temperature of the discharge tank is 30°C to 100°C.

[0017] In one embodiment of the present application, the inert solvent is an alkane, and preferably, the number of carbon atoms of the alkane is the same as that of the olefin monomer in the simulated free radical polymerization process. Preferably, the mass ratio of the organic peroxide to the inert solvent in the first material is the same as that of the organic peroxide to the polymerization monomer in the simulated free radical polymerization process. Preferably, when there are multiple monomers in the simulated free radical polymerization process, multiple inert solvents are also correspondingly selected, and the number of carbon atoms of the multiple inert solvents and the mass ratio among the multiple inert solvents are the same as those of the polymerization monomers in the simulated free radical polymerization process, so as to achieve the purpose of truly simulating the decomposition efficiency of the initiator under the mixed mass transfer conditions.

[0018] In one embodiment of the present application, the discharge tank has a window, and the concentration of the organic peroxide in the discharge tank can be measured by Raman spectroscopy or infrared spectroscopy. The corresponding relationship between the peroxide concentration and the spectroscopic signal is calibrated under offline conditions, and the corresponding relationship is an empirical correlation, a data table, etc., and the concentration of the organic peroxide in the discharge tank is calculated based on the corresponding relationship.

[0019] In one embodiment of the present application, the autoclave has a window, and the concentration of the organic peroxide in the autoclave can be measured by Raman spectroscopy or infrared spectroscopy. The corresponding relationship between the peroxide concentration and the spectroscopic signal is calibrated under offline conditions, and the corresponding relationship is an empirical correlation, a data table, etc., and the concentration of the organic peroxide in the discharge tank is calculated based on the corresponding relationship.

[0020] In one embodiment of the present application, the discharge tank has at least one sampling port, and the concentration of the organic peroxide in the discharge tank can be measured by sampling. In some embodiments, the concentration of the organic peroxide in the discharge tank can be measured offline by gas chromatography, and in other embodiments, the concentration of the organic peroxide in the discharge tank can be measured offline by titration.

[0021] In one embodiment of the present application, the temperature in the reaction kettle is controlled by the control unit according to a set temperature change curve to test the influence of the temperature on the decomposition characteristics of the organic peroxide, and the temperature change curve is, for example, a temperature rise curve, a temperature drop curve, or a periodic change curve composed of multiple temperature rise curves and temperature drop curves.

[0022] The application also provides a device for testing decomposition characteristics of organic peroxide above 50MPa, which comprises a high-pressure feeding unit, a high-pressure reactor, a first pressure-reducing valve, a discharge tank and a control unit,

[0023] The high-pressure feeding unit is used for continuously feeding a first material containing the organic peroxide to be tested and inert solvent into the high-pressure reactor, and comprises a feeding pump and a first stop valve, wherein the outlet of the feeding pump is connected to at least one inlet of the high-pressure reactor through the first stop valve.

[0024] The high-pressure reactor has at least one inlet, one outlet and one overpressure discharge port.

[0025] The inlet of the first pressure-reducing valve is connected to one outlet of the high-pressure reactor, and the outlet of the first pressure-reducing valve is connected to the inlet of the discharge tank.

[0026] The control unit comprises at least one thermocouple and at least one pressure sensor installed on the high-pressure reactor, at least one thermocouple installed on the outlet of the first pressure-reducing valve, and a computer, which collects temperature and pressure signals from the thermocouples and pressure sensors, and processes the signals and sends control signals to control the temperature and pressure of the high-pressure reactor and the outlet pressure of the first pressure-reducing valve.

[0027] In an embodiment of the application, the discharge tank is provided with at least one sampling port and a second pressure-reducing valve, wherein the second pressure-reducing valve is used to control the pressure in the discharge tank to collect the product in a desired phase. For example, when liquid and gas products need to be collected and analyzed, the discharge tank is kept at a certain set pressure by the second pressure-reducing valve to achieve gas-liquid separation of the material in the discharge tank, and the corresponding products are obtained. Preferably, the discharge tank, the pipeline between the discharge tank and the first pressure-reducing valve are provided with a quenching unit (such as a quenching device or other units or methods capable of quenching), so as to reduce the long residence time of the organic peroxide at high temperature after the pressure-reducing valve, thereby improving the accuracy of the measuring device.

[0028] In an embodiment of the application, the outlet of the first pressure-reducing valve is provided with at least one thermocouple for detecting the outlet temperature of the first pressure-reducing valve, and the high-pressure reactor and the discharge tank are respectively provided with at least one pressure transmitter. The high-pressure reactor or the discharge tank is provided with at least one set of windows through which light can pass through the high-pressure reactor or the discharge tank, so as to observe the state of the organic peroxide inside the high-pressure reactor or the discharge tank.

[0029] In one embodiment of the present application, the device is further provided with a rupture disc and / or a safety valve, which can quickly reduce the pressure of the reaction system, thereby avoiding damage to the device caused by excessive pressure in the autoclave.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] 1. The present application proposes a test device comprising a high-pressure feeding unit, a high-pressure autoclave with stirring, a first pressure-reducing valve, a discharge tank, and a control unit, which fully considers the safety of testing under high pressure and the operability of the test process. The test method effectively simulates the decomposition efficiency of organic peroxide (initiator) under real mixed mass transfer conditions by mixing the organic peroxide to be tested and inert solvent, feeding them into the high-pressure autoclave with stirring, and setting the stirring Reynolds number, test temperature, and test pressure. The test method is equipped with multiple ways to obtain the concentration of the decomposition products, which can be selected or combined to correct the concentration of the decomposition products according to the specific test scenario, thereby improving the accuracy. The test process can be carried out intermittently or continuously, among which the intermittent test can better simulate the initiator decomposition characteristics of the free radical initiation process in a tubular reactor, while the continuous test can better simulate the initiator decomposition characteristics of the free radical initiation process in a tank reactor. The test pressure of the decomposition test is 50 MPa to 400 MPa, and the temperature is 20℃ to 350℃, which can completely cover the condition range of high-pressure bulk method free radical polymerization process.

[0032] 2. The present application can effectively control the temperature and pressure in the discharge tank, reduce measurement errors, and also has the ability to measure the concentration of organic peroxide online by spectroscopy and offline by sampling, with perfect device functions and high measurement accuracy.

[0033] 3. The present application can measure the initiator decomposition behavior under the condition of multiple physical and chemical fields coupling of flow, heat transfer, mass transfer, and reaction, while the existing technology cannot measure the decomposition efficiency of the initiator under real mixed mass transfer conditions through DSC, ARC, or GC. Therefore, the present application can more effectively guide the analysis and application of initiators in industrial reactors. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a schematic diagram of an organic peroxide decomposition characteristic test device in one embodiment of the present application.

[0035] Figure 2 is a schematic diagram of an organic peroxide decomposition characteristic test device in another embodiment of the present application. DETAILED DESCRIPTION

[0036] The following will be described in detail the embodiments of the present application, the embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0037] As shown in Figure 1 Fig. 1 is a schematic diagram of an organic peroxide decomposition characteristic test device in an embodiment, which comprises a feed pump 1, an autoclave 2, a discharge tank 3, a first stop valve 4, a first pressure reducing valve 5, a second pressure reducing valve 6 and a third pressure reducing valve 7, a safety valve 8, pressure sensors 9 / 10, thermocouples 11 / 12. The feed pump 1 is connected to the inlet of the autoclave 2 through the first stop valve 4, and the autoclave 2 is provided with the safety valve 8, the pressure sensor 9 and the thermocouple 11; the outlet of the autoclave 2 is connected to the inlet of the discharge tank 3 through the first pressure reducing valve 5, and the downstream of the first pressure reducing valve 5 is provided with the thermocouple 12, and the discharge tank 3 is provided with the pressure sensor 10 and has two outlets, and the two outlets are respectively provided with the second pressure reducing valve 6 and the third pressure reducing valve 7.

[0038] The autoclave 2 has a stirring paddle and a heat exchange jacket. The stirring paddle is driven by magnetic coupling or mechanically. By applying different stirring speeds, different flow and mixing conditions in the autoclave can be simulated. In some embodiments, various types of stirring paddles can be used, such as turbine paddles, screw paddles, and propeller stirring paddles. The autoclave has a heat exchange jacket, which has a heating subsystem and a cooling subsystem, and a heat conducting layer is provided between the heat exchange jacket and the autoclave, wherein the heating subsystem can be one of electric heating, heat conducting oil heating or steam heating, and the cooling subsystem can be one of heat conducting oil cooling or water cooling.

[0039] As shown in Figure 2 Fig. 2 is a schematic diagram of an organic peroxide decomposition characteristic test device in another embodiment, which comprises a feed pump 1, an autoclave 2, a discharge tank 3, a first stop valve 4, a first pressure reducing valve 5, a second pressure reducing valve 6 and a third pressure reducing valve 7, a safety valve 8, pressure sensors 9 / 10, thermocouples 11 / 12, a viewing window 13. The main difference between this device and the device shown in Figure 1 Fig. 1 is that the autoclave 2 is provided with a transparent viewing window 13. Based on the viewing window 13, the concentration of organic peroxide in the autoclave can be measured by Raman spectroscopy or infrared spectroscopy. The correspondence between the peroxide concentration and the spectral signal is calibrated under offline conditions, and the correspondence is an empirical correlation, a data table, etc., and the concentration of organic peroxide in the discharge tank is calculated based on the correspondence.

[0040] The technical parameters of the test device proposed in this invention are as follows: test pressure of the autoclave: 50MPa~400MPa; test temperature of the autoclave: 20℃~350℃; pressure of the discharge tank: 0.1MPa~50MPa; temperature of the discharge tank: 20℃~150℃; heat exchange medium of the discharge tank: chilled water; sampling frequency of the thermocouple: 10Hz; sampling frequency of the pressure sensor: 10Hz~100Hz.

[0041] The experimental method for the decomposition characteristics of organic peroxides in this embodiment is as follows:

[0042] use Figure 1 The aforementioned organic peroxide decomposition characteristic testing apparatus mixes the organic peroxide DTBP and ethane at a mass ratio of 1:1000 to obtain a first material, wherein the molar concentration of DTBP is C0. This first material is then pressurized by a feed pump 1 and enters a high-pressure reactor 2 through a first shut-off valve 4. The pressure is monitored by a pressure sensor 9, which controls the continuous feeding of the liquid feed pump 1 into the high-pressure reactor 2. When the pressure reaches a set value, the liquid feed pump 1 is stopped, and the first shut-off valve 4 is closed. The stirring inside the high-pressure reactor 2 is activated, and the temperature of the heat exchange jacket of the high-pressure reactor is kept constant.

[0043] After the pressure inside the autoclave stabilizes for a period of time, based on the half-life data of DTBP measured at atmospheric pressure and combined with the temperature inside the reactor, the predicted half-life of DTBP under the autoclave temperature conditions is calculated, and the intermittent reaction time of the first material in the autoclave is set. During the reaction, at time t1, the first pressure reducing valve is opened to send a portion of the first material into the discharge tank, where the material is cooled for a period of time. Samples are taken through the third pressure reducing valve, and the concentration of DTBP is analyzed offline by gas chromatography to obtain the molar concentration of DTBP after the reaction, C(t1). The conversion rate of DTBP at time t1 is then calculated.

[0044] X(t1)=1-C1(t1) / C0

[0045] By repeating the above process, the conversion rates X(t1) to X(tn) of DTBP at times t1 to tn can be obtained. Based on the relationship between conversion rate and time, and combined with the Arrhenius equation considering the pressure effect, the reaction kinetic parameters and efficiency of DTBP can be calculated.

[0046] use Figure 1 or Figure 2The method can also perform continuous test of organic peroxide decomposition characteristics, in which the first material is continuously fed into the autoclave 2, the discharge tank 2 continuously collects the material after the decomposition of the autoclave, and the discharge tank 2 continuously or intermittently discharges the collected material. The opening degree of the first pressure reducing valve 5 is controlled to change the test pressure; the heat exchange jacket temperature is adjusted to change the test temperature. The test temperature can be controlled according to a set temperature change curve to test the influence of the temperature on the decomposition characteristics of the organic peroxide, and the temperature change curve can be a temperature rise curve, a temperature drop curve, or a periodic change curve composed of multiple temperature rise curves and temperature drop curves, etc. The data of the temperature, pressure and conversion rate of the organic peroxide in the autoclave with time are recorded, and the reaction kinetic parameters and efficiency of the DTBP of the organic peroxide under different temperatures and pressures are calculated offline or online.

[0047] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A test method for the decomposition characteristics of organic peroxides at pressures above 50 MPa, characterized in that, The experimental method simulates the mixing, mass transfer, and decomposition processes of organic peroxides during high-pressure free radical polymerization above 50 MPa. The method includes: (1) The organic peroxide to be tested is mixed with at least one inert solvent to obtain a first material, and then the first material is continuously added to the autoclave through a high-pressure feeding unit; (2) Increase the pressure of the autoclave to the set pressure, maintain the temperature of the autoclave heat exchange jacket at the preset simulated reaction temperature, and start the agitator so that the stirring Reynolds number of the agitator is 4000~50000. (3) By controlling the opening of the first pressure reducing valve, the pressure inside the high pressure vessel is controlled to the required test pressure, and the decomposed material inside the high pressure vessel is introduced into the discharge tank through the first pressure reducing valve; (4) The test temperature is changed by adjusting the temperature of the heat exchange jacket, and the test pressure is changed by controlling the opening of the first pressure reducing valve. The temperature, pressure and conversion rate of organic peroxide in the autoclave are recorded over time, and the decomposition kinetics of organic peroxide at different temperatures and pressures are calculated. The conversion rate of the organic peroxide is calculated based on the concentration of organic peroxide in the discharge tank and the concentration of organic peroxide at the inlet of the high-pressure feeding unit, as shown in the following formula: X = 1 - C1 / C0 In the formula, X is the conversion rate of organic peroxide, C1 is the concentration of organic peroxide in the discharge tank, and C0 is the concentration of organic peroxide at the inlet of the feeding unit.

2. The method according to claim 1, characterized in that, The pressure adjustment range of the high-pressure reactor is 50 MPa to 400 MPa, and the temperature adjustment range of the high-pressure reactor is 20 ℃ to 350 ℃; the pressure in the discharge tank is 0.1 MPa to 50 MPa, and the temperature of the discharge tank is controlled by the heat exchange medium to be 20 ℃ to 150 ℃.

3. The method according to claim 1 or 2, characterized in that, The discharge tank and / or the autoclave have a viewing window for measuring the concentration of organic peroxides in the discharge tank or autoclave by Raman spectroscopy or infrared spectroscopy.

4. The method according to claim 3, characterized in that, The concentration of organic peroxide in either the discharge tank or the autoclave is sampled and measured, and the Raman or infrared spectroscopy measurement results are corrected based on the concentration of organic peroxide obtained from the sampling measurement.

5. The method according to claim 1, characterized in that, The temperature inside the reactor is controlled by the control unit to change according to a set temperature change curve, which is a periodic change curve of heating curve, cooling curve, or a combination of multiple heating curves and cooling curves.

6. The method according to claim 1, characterized in that, The inert solvent is an alkane, and the number of carbon atoms in the alkane is the same as the number of carbon atoms in the monomer in the simulated free radical polymerization process.

7. An apparatus for testing the decomposition characteristics of organic peroxides according to claim 1, characterized in that, It includes a high-pressure feeding unit, an autoclave, a first pressure reducing valve, a discharge tank, and a control unit. The high-pressure feeding unit is used to continuously feed a first material containing the organic peroxide to be tested and an inert solvent into the autoclave. It includes a feed pump and a first shut-off valve, wherein the outlet of the feed pump is connected to at least one inlet of the autoclave via the first shut-off valve. The autoclave has at least one inlet, one outlet, and one overpressure discharge port; The inlet of the first pressure reducing valve is connected to one outlet of the autoclave, and the outlet of the first pressure reducing valve is connected to the inlet of the discharge tank. The control unit includes at least one thermocouple and at least one pressure sensor installed in the autoclave, at least one thermocouple installed at the outlet of the first pressure reducing valve, and a computer. Temperature and pressure signals are collected by the thermocouples and pressure sensors, and the computer processes the signals and issues control signals to control the temperature and pressure of the autoclave and the outlet pressure of the first pressure reducing valve.

8. The test apparatus according to claim 7, characterized in that, The discharge tank is equipped with at least one sampling port and a second pressure reducing valve, and the autoclave and the discharge tank each have at least one pressure sensor.

9. The experimental apparatus according to claim 7, characterized in that, The high-pressure reactor has a stirring paddle, which is driven by a magnetic coupling driver or a mechanical driver.

10. The test apparatus according to claim 7, characterized in that, The pressure vessel has a heat exchange jacket, which has a heating subsystem and a cooling subsystem. A heat-conducting layer is provided between the heat exchange jacket and the pressure vessel. The heating subsystem uses one of electric heating, thermal oil heating or steam heating. The cooling subsystem uses one of thermal oil cooling or water cooling.

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