Device and method for testing decomposition characteristics of organic peroxides of 50 MPa or above

Abstract

The invention discloses a device and a method for testing decomposition characteristics of organic peroxides of more than 50MPa. The method comprises the following steps: mixing the organic peroxides to be tested and at least one inert solvent to obtain a first material, and continuously adding the first material into a high-pressure kettle through a high-pressure feeding unit, and the decomposition process of the organic peroxide in a real flowing mixed environment is simulated. According to the invention, the mixing condition and the reaction condition in the test process can be changed, and a method for measuring the concentration of various products is provided based on the high-pressure test condition, so that the organic peroxide decomposition characteristic test under different mixing and reaction conditions is realized, the measurement range covers the high-pressure and ultrahigh-pressure conditions, and the sensitivity and the accuracy are high.

Description

Technical Field

[0001] The present invention relates to the research on the reaction mechanism of organic peroxide under high pressure and ultra-high pressure conditions, more specifically to a test device and method for the decomposition characteristics of organic peroxide above 50MPa. Background Art

[0002] The preparation of polymers by free radical polymerization is a typical polymerization process. Free radical initiators usually have weak covalent bonds, and generate free radicals through homolysis or heterolysis of covalent bonds, and initiate polymerization of monomers. Common free radical initiators include peroxide initiators, azo initiators, and redox initiators.

[0003] At present, it is well known in the art that when preparing low-density polyethylene, ethylene-vinyl acetate copolymer and other products by high-pressure free radical polymerization, the reaction temperature is as high as 100°C-350°C, the reaction pressure is above 50MPa, and especially when producing low-density polyethylene, the reaction pressure is as high as 120MPa or more, and the commonly used initiators are organic peroxides, oxygen and mixtures thereof. The test methods currently used to test the decomposition reaction of organic peroxides include differential scanning calorimetry (DSC), adiabatic accelerating calorimetry (ARC), gas chromatography (GC) and other methods.

[0004] When the reaction pressure exceeds 50MPa, the decomposition reaction rate of the initiator is significantly affected by the pressure. Foreign scholars use high-pressure DSC to study the kinetics of initiator decomposition reaction (J. Solution Chem. 2024, 53: 43–59). This method uses a specially designed high-pressure resistant calorimetric cell to continuously scan the heat changes during the heating process to achieve accurate measurement of the heat release of organic peroxide decomposition and calculate the peroxide decomposition reaction rate. However, it is well known in the art that the decomposition process of free radical initiators is a complex network of coupled reactions and mass transfer, that is, there is a so-called "cage effect". Therefore, whether DSC, ARC or GC is used, it is impossible to measure the decomposition efficiency of the initiator under real mixed mass transfer conditions.

[0005] Therefore, a test device for the decomposition characteristics of organic peroxides above 50 MPa is proposed. By simulating a real flow mixing environment, the efficiency of the organic peroxide can be measured while measuring the decomposition reaction rate constant of the organic peroxide. Summary of the invention

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

[0007] The present invention solves the technical problem by adopting the following technical solution.

[0008] The present invention proposes a test method for the decomposition characteristics of organic peroxides above 50 MPa, which simulates the mixed mass transfer and decomposition process of organic peroxides in a high-pressure free radical polymerization process above 50 MPa. The method comprises:

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

[0010] (2) Raise the pressure of the autoclave to the set pressure, maintain the temperature of the heat exchange jacket of the autoclave at the preset simulated reaction temperature, start the stirring paddle, and make the stirring Reynolds number of the stirring paddle be 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 speed of the stirrer, 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 desired test pressure, and introducing the decomposed material in the autoclave into the discharge tank through the first pressure reducing valve;

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

[0013] The conversion rate of the organic peroxide is calculated based on the organic peroxide concentration in the discharge tank and the organic peroxide concentration at the inlet of the high-pressure feed unit. The specific formula is as follows:

[0014] X=1-C1 / C0

[0015] Wherein, 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 feed unit.

[0016] In one embodiment of the present invention, the test pressure adjustment range of the autoclave is 50MPa to 400MPa, and the test temperature adjustment range of the autoclave is 20°C to 350°C; the pressure in the discharge tank is 0.1MPa to 50MPa, 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 0.1MPa to 30.0MPa, and the temperature of the discharge tank is 30°C to 100°C.

[0017] In one embodiment of the present invention, the inert solvent is an alkane, and preferably, the carbon atom number of the alkane is the same as the carbon atom number 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 the mass ratio of the organic peroxide to the polymerized monomer in the simulated free radical polymerization process. Preferably, when there are multiple monomers in the simulated free radical polymerization process, the inert solvent is also selected in multiple ways, and the carbon atom numbers and mass ratios of the multiple inert solvents are the same as the carbon atom numbers and mass ratios of the polymerized monomers in the simulated free radical polymerization process, so as to achieve the purpose of truly simulating the decomposition efficiency of the initiator under mixed mass transfer conditions.

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

[0019] In one embodiment of the present invention, the autoclave has a window, and the concentration of organic peroxides 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, such as an empirical correlation formula, a data table, etc., and the concentration of the organic peroxide in the material tank is calculated based on the correspondence.

[0020] In one embodiment of the present invention, the discharge tank has at least one sampling port, which can be used to sample and measure the concentration of organic peroxides in the discharge tank. In some embodiments, the concentration of organic peroxides in the discharge tank can be measured offline by gas chromatography, and in other embodiments, the concentration of organic peroxides in the discharge tank can be measured offline by titration.

[0021] In one embodiment of the present invention, the temperature in the reactor is controlled by the control unit according to a set temperature change curve to test the effect of temperature on the decomposition characteristics of the organic peroxide. The temperature change curve is a periodic change curve such as a heating curve, a cooling curve or a combination of multiple heating curves and cooling curves.

[0022] The present invention also provides a device for testing the decomposition characteristics of organic peroxides above 50 MPa, which comprises a high-pressure feeding unit, an autoclave, a first pressure reducing valve, a discharge tank and a control unit.

[0023] The high-pressure feeding unit is used to continuously deliver a first material containing an organic peroxide to be tested and an inert solvent into the autoclave, 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 autoclave via the first stop valve;

[0024] The autoclave has at least one inlet, one outlet and one overpressure vent;

[0025] The inlet of the first pressure reducing valve is connected to an outlet of the autoclave, and the outlet of the first pressure reducing valve is connected to the inlet of the discharge tank;

[0026] 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. The thermocouple and the pressure sensor collect temperature and pressure signals, and the computer processes the signals and sends control signals to control the temperature and pressure of the autoclave and the outlet pressure of the first pressure reducing valve.

[0027] In one embodiment of the present invention, the discharge tank is equipped 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 the desired phase. For example, when it is necessary to collect and analyze liquid products and gas products, the discharge tank is maintained at a certain set pressure by the second pressure reducing valve so that the material in the discharge tank is separated into gas and liquid, and the corresponding product can be obtained. Preferably, the discharge tank, the pipeline between the discharge tank and the first pressure reducing valve are all provided with quenching (such as a quencher or other unit or method capable of quenching), reducing the organic peroxide after the pressure reducing valve. The organic peroxide continues to decompose rapidly due to the long residence time of the organic peroxide under high temperature conditions, thereby improving the accuracy of the measuring device.

[0028] In one embodiment of the present invention, at least one thermocouple is installed at the outlet of the first pressure reducing valve to detect the outlet temperature of the first pressure reducing valve, and the autoclave and the discharge tank each have at least one pressure transmitter. The autoclave or the discharge tank is installed with at least one set of windows, wherein light can pass through the windows through the autoclave or the discharge tank, so as to observe the state of the organic peroxide inside the autoclave or the discharge tank.

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

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

[0031] 1. The present invention proposes a test device comprising a high-pressure feeding unit, an 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 is to mix the organic peroxide to be tested with an inert solvent and send it into an autoclave with stirring, and set the stirring Reynolds number, test temperature and test pressure to effectively simulate the decomposition efficiency of the organic peroxide (initiator) under real mixed mass transfer conditions. The test method is equipped with a variety of concentration acquisition methods for decomposition products, which can be selected according to the specific test scenario or selected in combination to correct the concentration of the decomposition product and improve the accuracy. The test process can be carried out intermittently or continuously, wherein the intermittent test can better simulate the initiator decomposition characteristics of the free radical initiation process in the tubular reactor, and the continuous test can better simulate the initiator decomposition characteristics of the free radical initiation process in the kettle reactor. The test pressure of the decomposition test is 50MPa~400MPa, and the temperature is 20℃~350℃, which can completely cover the range of high-pressure bulk free radical polymerization process conditions.

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

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

[0034] Figure 1 Schematic diagram of an organic peroxide decomposition characteristic test device in one embodiment of the present invention.

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

[0036] 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 a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0037] like Figure 1 As shown, it is a schematic diagram of an organic peroxide decomposition characteristic test device in an embodiment, which includes 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, a pressure sensor 9 / 10, and a thermocouple 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 a safety valve 8, a pressure sensor 9 and a 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 a thermocouple 12 is provided downstream of the first pressure reducing valve 5, and the discharge tank 3 is provided with a pressure sensor 10 and has two outlets, and the second pressure reducing valve 6 and the third pressure reducing valve 7 are provided on the two outlets respectively.

[0038] The autoclave 2 has a stirring paddle and a heat exchange jacket. The stirring paddle is driven by magnetic coupling or mechanical drive. By applying different stirring speeds, simulation of different flow and mixing conditions in the autoclave is achieved. In some embodiments, various types of stirring paddles can be used, such as turbine propellers, ribbon propellers, propeller stirring paddles, etc. The autoclave has a heat exchange jacket, and the heat exchange jacket has a heating subsystem and a cooling subsystem. A heat conductive layer is provided between the heat exchange jacket and the autoclave, wherein the heating subsystem can be one of electric heating, thermal oil heating or steam heating, and the cooling subsystem can be one of thermal oil cooling and water cooling.

[0039] like Figure 2 , which is a schematic diagram of an organic peroxide decomposition characteristic test device in another embodiment, comprising 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, a pressure sensor 9 / 10, a thermocouple 11 / 12, and a window 13. The device is Figure 1 The main difference of the device shown is that a transparent window 13 is provided on the autoclave 2. The concentration of organic peroxides in the autoclave can be measured by Raman spectroscopy or infrared spectroscopy based on the window 13. The correspondence between the peroxide concentration and the spectral signal is calibrated under offline conditions, such as an empirical correlation formula, a data table, etc., and the concentration of organic peroxides in the material tank is calculated based on the correspondence.

[0040] The technical parameters of the test device proposed in the present 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; acquisition frequency of the thermocouple: 10Hz; acquisition frequency of the pressure sensor: 10Hz~100Hz.

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

[0042] use Figure 1 The organic peroxide decomposition characteristic test device is characterized in that the organic peroxide DTBP and ethane are mixed at a mass ratio of 1:1000 to obtain a first material, wherein the molar concentration of DTBP is C0, and then the first material is pressurized by a feed pump 1 and enters an autoclave 2 through a first stop valve 4. The pressure is monitored by a pressure sensor 9, and the liquid feed pump 1 is controlled to continuously feed the autoclave 2. When the pressure reaches a set value, the liquid feed pump 1 is stopped, and the first stop valve 4 is closed. The stirring in the autoclave 2 is started and the temperature of the heat exchange jacket of the autoclave is kept constant.

[0043] After the pressure in the autoclave remains stable for a period of time, the half-life data of DTBP measured under normal pressure is combined with the temperature in the reactor to calculate the predicted half-life value of DTBP under the temperature conditions of the autoclave, and set the intermittent reaction time of the first material in the autoclave. During the reaction, the first pressure reducing valve is opened at time t1 to send part of the first material into the discharge tank, and the material is cooled in the discharge tank 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. The molar concentration of DTBP after the reaction is obtained as C(t1), and the conversion rate of DTBP at time t1 is

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

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

[0046] use Figure 1 or Figure 2The method can also be used to conduct a continuous test of the decomposition characteristics of organic peroxides. In the continuous test, the first material is continuously conveyed into the autoclave 2, and the material after the decomposition of the autoclave is continuously collected by the discharge tank 2, and the collected material is continuously or intermittently discharged by the discharge tank 2. The test pressure is changed by controlling the opening of the first pressure reducing valve 5; the test temperature is changed by adjusting the temperature of the heat exchange jacket. Among them, the test temperature can be controlled according to a set temperature change curve to test the influence of temperature on the decomposition characteristics of organic peroxides. The temperature change curve can be a heating curve, a cooling curve, or a periodic change curve of a combination of multiple heating curves and cooling curves, etc. By recording the temperature, pressure and conversion rate of organic peroxides in the autoclave over time, the reaction kinetic parameters and efficiency of DTBP of organic peroxides at different temperatures and pressures are calculated offline or online.

[0047] 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 test method for the decomposition characteristics of organic peroxides above 50 MPa, characterized in that: The test method simulates the mixed mass transfer and decomposition process of organic peroxides in a high-pressure free radical polymerization process above 50 MPa, and the method comprises: (1) mixing an organic peroxide to be tested and at least one inert solvent to obtain a first material, and then continuously adding the first material into an autoclave through a high-pressure feeding unit; (2) increasing the pressure of the autoclave to a set pressure, maintaining the temperature of the heat exchange jacket of the autoclave at a preset simulated reaction temperature, and starting a stirring paddle so that the stirring Reynolds number of the stirring paddle is 4000 to 50000; (3) controlling the opening of the first pressure reducing valve to control the pressure in the autoclave to the desired test pressure, and introducing the decomposed material in the autoclave into the discharge tank through the first pressure reducing valve; (4) changing the test temperature by adjusting the temperature of the heat exchange jacket, changing the test pressure by controlling the opening of the first pressure reducing valve, recording the change data of the temperature, pressure and conversion rate of the organic peroxide in the autoclave over time, and calculating the decomposition kinetics of the organic peroxide at different temperatures and pressures; The conversion rate of the organic peroxide is calculated based on the organic peroxide concentration in the discharge tank and the organic peroxide concentration at the inlet of the high-pressure feed unit. The specific formula is as follows: X=1-C1 / C0 Wherein, 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 feed unit.

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

3. The method according to claim 1 or 2, characterized in that: The discharge tank and / or the autoclave has a window, and the concentration of organic peroxide in the discharge tank or the autoclave is measured by Raman spectroscopy or infrared spectroscopy.

4. The method according to claim 3, characterized in that The concentration of the organic peroxide in one of the discharge tank or the autoclave is measured by sampling, and the measurement result of the Raman spectrum or the infrared spectrum is corrected according to the concentration of the organic peroxide obtained by the sampling measurement.

5. The method according to claim 1, characterized in that The temperature in the reactor is controlled by the control unit to change according to a set temperature change curve, wherein the temperature change curve is a heating curve, a cooling curve or a periodic change curve of 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. Preferably, the carbon number of the alkane is the same as the carbon number of the polymerization monomer in the simulated free radical polymerization process.

7. An organic peroxide decomposition characteristic testing device for implementing the method of 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 deliver a first material containing an organic peroxide to be tested and an inert solvent into the autoclave, 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 autoclave via the first stop valve; The autoclave has at least one inlet, one outlet and one overpressure vent; The inlet of the first pressure reducing valve is connected to an 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. The thermocouple and the pressure sensor collect temperature and pressure signals, and the computer processes the signals and sends control signals to control the temperature and pressure of the autoclave and the outlet pressure of the first pressure reducing valve.

8. The test device 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 are respectively equipped with at least one pressure sensor.

9. The test device according to claim 7, characterized in that: The autoclave is provided with a stirring paddle, and the stirring paddle adopts a magnetic coupling drive or a mechanical drive.

10. The test device according to claim 7, characterized in that: The autoclave has a heat exchange jacket, which has a heating subsystem and a cooling subsystem. A heat conductive layer is provided between the heat exchange jacket and the autoclave. The heating method adopted by the heating subsystem is one of electric heating, thermal oil heating or steam heating. The cooling method adopted by the cooling subsystem is one of thermal oil cooling and water cooling.

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