Device and method for testing the thermal decomposition half-life of nuclear-grade polyacrylic dispersants

Abstract

The application discloses a testing device and a testing method for a thermal decomposition half-life period of a nuclear-grade polyacrylic acid dispersant, and the testing device comprises a kettle body and an expansion pipeline; the kettle body and the expansion pipeline are connected through a sampling pipeline and a sample inlet pipeline, the inlet of the sampling pipeline is inserted into the bottom of the kettle body, a sampling valve is arranged on the sampling pipeline, the outlet of the sampling pipeline is connected to the sample inlet pipeline, and the expansion pipeline is arranged on the sample inlet pipeline; a heating unit for heating the polyacrylic acid dispersant is arranged in the kettle body, and a sample solution of the polyacrylic acid dispersant is located in the kettle body; saturated steam is generated after the sample solution is heated, and the sample solution is sequentially conveyed into the expansion pipeline through the sampling pipeline and the sample inlet pipeline under the pressure of the saturated steam; the testing method comprises the following steps: preparing a standard solution, preparing a sample solution, carrying out a constant-temperature decomposition reaction, sampling, detection and calculation. The application can realize online sampling, rapidly cool the sample solution through the expansion pipeline, and improve the accuracy of PAA concentration measurement and thermal decomposition half-life period calculation.

Description

Technical Field

[0001] This invention relates to the field of polymer thermal decomposition half-life testing technology, and in particular to a testing device and method for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant. Background Technology

[0002] The long-term online application of polyacrylic acid (PAA) dispersant in nuclear power plants can continuously increase the discharge of corrosion products from the steam generator (SG) via the steam generator blowdown system (APG) during operation, reducing the accumulation of deposits in the SG and thus reducing the frequency of SG chemical cleaning, or even eliminating the need for SG chemical cleaning. When PAA is used long-term online, it needs to be injected into the secondary loop through the unit's chemical dosing system during the unit's power operation. At this time, the maximum temperature in the secondary loop reaches 280°C, at which temperature PAA will undergo thermal decomposition. Therefore, it is necessary to determine the half-life of PAA concentration under secondary loop operating conditions for accurate PAA dosage control.

[0003] Thermogravimetric analysis (TGA) is generally used to test the thermal decomposition half-life of polymers. The measurement process involves loading a quantitative sample into a sample dish of a thermogravimetric analyzer, placing the dish on a thermal balance, recording the initial mass, setting the temperature and heating rate, and calculating the decomposition rate of the polymer using a weight loss curve. However, this experimental process is completely different from the application conditions of PAA (polyacrylamide). The thermal decomposition mechanism and kinetics of PAA in high-temperature, high-pressure water media differ from the thermogravimetric analysis process and environment.

[0004] Existing research, through simulating PAA under nuclear power plant operating conditions, has focused on studying the loss rate of carboxyl functional groups, changes in molecular weight, and decomposition products after PAA decomposition. However, it has not proposed a quantitative testing method for the concentration change half-life of PAA after thermal decomposition under nuclear power plant dosing conditions. Furthermore, existing experimental setups cannot achieve real-time sampling; samples can only be obtained after the reactor has completely cooled down and been opened, a cooling time typically taking 2–4 hours. During this period, PAA will also undergo thermal decomposition, leading to inaccurate measurement results. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a testing device and a testing method for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a test device for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant, including a vessel and an expansion pipeline;

[0007] The vessel body and expansion pipeline are connected by a sampling pipeline and an injection pipeline. The inlet of the sampling pipeline extends into the bottom of the vessel body, and a sampling valve is installed on the sampling pipeline. The outlet of the sampling pipeline is connected to the injection pipeline, and the expansion pipeline is installed on the injection pipeline.

[0008] The reactor is equipped with a heating unit for heating the polyacrylic acid dispersant. The sample solution of the polyacrylic acid dispersant is located inside the reactor. After the sample solution is heated, saturated steam is generated. Under the pressure of the saturated steam, the sample solution is sequentially transported to the expansion pipeline through the sampling pipeline and the injection pipeline.

[0009] Preferably, the outlet of the injection pipeline is connected to the sample container, and an injection valve is provided between the expansion pipeline and the sample container.

[0010] Preferably, the outlet of the sampling pipeline is also connected to a discharge pipeline, the discharge pipeline is equipped with a discharge valve, and the outlet of the discharge pipeline is connected to a waste treatment unit.

[0011] Preferably, the heating units are distributed inside the bottom wall and side wall of the vessel; and / or the vessel is provided with a temperature control unit for adjusting the temperature of the heating units.

[0012] Preferably, the vessel body is equipped with a pressure gauge and a safety valve.

[0013] A method for testing the thermal decomposition half-life of a nuclear-grade polyacrylic acid dispersant, using the aforementioned testing apparatus for the thermal decomposition half-life of a nuclear-grade polyacrylic acid dispersant, includes the following steps:

[0014] S1. Preparation of standard solutions: Weigh different masses of polyacrylic acid dispersant standard substances and dissolve them in water to prepare several standard solutions with gradient mass concentrations. The mass concentration of each standard solution is 0-2 g / L. Then, the absorbance of the standard solutions is measured, and the measured absorbance is linearly fitted to the corresponding mass concentration.

[0015] S2. Preparation of sample solution: Dry the nuclear-grade polyacrylic acid dispersant sample, then dissolve it in water to prepare a stock solution with a mass concentration of 0.5-1.5 g / L; add hydrazine solution to the stock solution to obtain a solution with a hydrazine concentration of 150-250 μg / L, adjust the pH to 9.5-10.0, and obtain the sample solution.

[0016] S3. Isothermal decomposition reaction: Place the sample solution in the vessel of the test device and fill it with protective gas to remove oxygen; close the sampling valve, adjust the temperature inside the vessel to 250-300℃, and increase the pressure inside the vessel to the saturated vapor pressure corresponding to the temperature. The sample solution undergoes an isothermal decomposition reaction inside the vessel.

[0017] S4. Sampling: Sampling is carried out at different constant temperature times. When sampling, the sampling valve is opened first, and the sample solution is transported to the expansion pipe for cooling under the pressure inside the vessel. Then the sampling valve is closed, and the cooled sample solution is discharged from the expansion pipe.

[0018] S5. Detection and Calculation: The absorbance of the sample solution at different isothermal times is detected. Based on the linear fitting results of step S1, the concentration of polyacrylic acid in the sample solution is obtained. Based on the rate of change of polyacrylic acid concentration at different isothermal times, the thermal decomposition concentration half-life of polyacrylic acid is calculated.

[0019] Preferably, in step S2, the nuclear-grade polyacrylic acid dispersant sample is dried at 80-120°C to constant weight, and then 0.25-0.75g of the dried sample is dissolved in 500mL of water to prepare a mother liquor.

[0020] Preferably, in step S2, the concentration of the hydrazine solution is 150-250 mg / L, and / or the pH is adjusted using an ammonia solution with a mass fraction of 8-12%.

[0021] Preferably, in step S3, the protective gas is nitrogen or argon, and the protective gas is introduced for 20-40 minutes.

[0022] Preferably, in step S5, the concentration of polyacrylic acid in the sample solution at different isothermal times is linearly fitted to obtain the rate of change of polyacrylic acid concentration at different isothermal times, and the thermal decomposition concentration half-life of polyacrylic acid is calculated using equation (1), which is expressed as follows:

[0023]

[0024] Where k is 1 / C t The slope of the linear fitting equation, C t The values ​​represent the polyacrylic acid concentrations corresponding to different isothermal times, where t represents different isothermal times; C0 represents the polyacrylic acid concentration corresponding to an isothermal time of 0 h.

[0025] The beneficial effects of this invention are:

[0026] The device for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant of the present invention can realize real-time online sampling. During the sampling period, the heating unit continues to operate and the vessel is not shut off. The sample solution is rapidly cooled through the expansion pipe to avoid changes in the concentration of polyacrylic acid dispersant during long-term cooling, which would affect the accuracy of the test results.

[0027] The present invention provides a method for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid (PAA) dispersant. This method involves preparing a PAA sample solution with a specific hydrazine concentration, placing the solution in the reactor of a testing device for thermal decomposition, and taking real-time samples for detection to calculate the PAA thermal decomposition concentration half-life. This method provides highly accurate PAA concentration measurements and highly accurate PAA thermal decomposition half-life calculations. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0029] Figure 1 This is a schematic diagram of the structure of the testing device for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant of the present invention; the reference numerals in the figure are as follows: 1. Reactor body; 11. Heating unit; 12. Temperature control unit; 13. Pressure gauge; 14. Safety valve; 15. Sampling pipeline; 151. Sampling valve; 16. Inlet pipeline; 161. Inlet valve; 17. Discharge pipeline; 171. Discharge valve; 2. Expansion pipeline; 3. Sample container; 4. Waste treatment unit;

[0030] Figure 2 This is an embodiment of the invention showing the relationship between polyacrylic acid concentration and time (1 / C). t Linear fitting plot of ~t). Detailed Implementation

[0031] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the orientations or positional relationships indicated by terms such as "front," "rear," "upper," "lower," "left," "right," "longitudinal," "horizontal," "vertical," "horizontal," "top," "bottom," "inner," "outer," "head," and "tail" are based on the orientations or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific orientation. They are only for the convenience of describing this technical solution and do not indicate that the device or element referred to must have a specific orientation; therefore, they should not be construed as limitations on this invention.

[0032] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "linking," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. When an component is referred to as being "on" or "below" another component, the component can be located "directly" or "indirectly" on the other component, or there may be one or more intermediary components. The terms "first," "second," "third," etc., are only for the convenience of describing this technical solution and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0033] Figure 1 This invention illustrates a testing apparatus for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant in some embodiments, used to test the thermal decomposition concentration half-life of polyacrylic acid (PAA) dispersant in the secondary loop of a nuclear power plant. The testing apparatus includes a vessel body 1 and an expansion pipe 2. The vessel body 1 and the expansion pipe 2 are connected by a sampling pipe 15 and an inlet pipe 16. The inlet of the sampling pipe 15 extends into the bottom of the vessel body 1, and a sampling valve 151 is provided on the sampling pipe 15. The outlet of the sampling pipe 15 is connected to the inlet pipe 16, and the expansion pipe 2 is provided on the inlet pipe 16.

[0034] The vessel body 1 is equipped with a heating unit 11 for heating the polyacrylic acid dispersant. The sample solution of the polyacrylic acid dispersant is located inside the vessel body 1, and the sample solution generates saturated vapor after heating. The heating unit 11 can be distributed inside the bottom wall and side wall of the vessel body 1, thereby improving the heating efficiency of the sample solution. In some embodiments, the vessel body 1 is equipped with a temperature control unit 12 to adjust the temperature of the heating unit 11, which can achieve temperature control within the vessel body 1 with an accuracy of ±0.5℃. The volume of the vessel body 1 can be 1.5-2.5L.

[0035] Under the action of heating unit 11, PAA in the sample solution undergoes a thermal decomposition reaction within the sealed vessel 1. When the vessel 1 heats up to the test temperature, the vapor pressure generated by the sample solution within the vessel 1 increases, sufficient to push the sample solution to the sampling pipeline 15. When sampling is required, the vessel 1 does not need to stop operating; the sampling valve 151 on the sampling pipeline 15 is opened. Under the pressure of saturated vapor, the sample solution is sequentially transported through the sampling pipeline 15 and the injection pipeline 16 to the expansion pipeline 2. As the sample solution increases in volume upon entering the expansion pipeline 2, it cools rapidly.

[0036] In some embodiments, the vessel body 1 is equipped with a pressure gauge 13 and a safety valve 14. The pressure gauge 13 is used to monitor the pressure inside the vessel body 1 in real time, and the safety valve 14 is used to prevent overpressure in the vessel body 1. The safety valve 14 may be a burst valve. It is understood that the heating unit 11, the pressure gauge 13, and the safety valve 14 may all adopt existing technologies, and will not be described in detail here.

[0037] The outlet of the injection line 16 is connected to the sample container 3. An injection valve 161 is provided between the expansion line 2 and the sample container 3. After the sample solution is cooled in the expansion line 2, the injection valve 161 is opened to allow the sample solution to enter the sample container 3 through the outlet of the injection line 16. Then the injection valve 161 is closed.

[0038] The outlet of the sampling pipeline 15 is also connected to the discharge pipeline 17, which is equipped with a discharge valve 171. The outlet of the discharge pipeline 17 is connected to the waste treatment unit 4. After PAA sampling is completed, the discharge valve 171 is opened, and the high-temperature and high-pressure liquid in the vessel 1 enters the waste treatment unit 4 for collection and treatment through the sampling pipeline 15 and the discharge pipeline 17.

[0039] The device for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant of the present invention can realize real-time online sampling. During the sampling period, the heating unit 11 runs continuously and the vessel 1 is not turned off. The sample solution is rapidly cooled through the expansion pipe 2. There is no need to wait for the vessel 1 to be completely cooled before the vessel can be opened for sampling, thus avoiding changes in PAA concentration during long-term cooling, which would affect the accuracy of the test results.

[0040] This invention also proposes a method for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersants. The method utilizes the aforementioned testing apparatus for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersants and includes the following steps:

[0041] S1. Preparation of Standard Solutions: Weigh different masses of polyacrylic acid dispersant standard material (e.g., certified standard material) and dissolve them in water (e.g., high-purity water) to prepare several standard solutions with gradient mass concentrations. The mass concentration of each standard solution is 0-2 g / L. The mass concentrations of the standard solutions can be 0 g / L, 0.5 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.5 g / L, 2 g / L, etc., and the standard solutions should have at least five mass concentrations, including a mass concentration of 0 g / L (blank). Then, measure the absorbance of the standard solutions and perform linear fitting between the measured absorbance and the corresponding mass concentration to obtain the absorbance-mass concentration standard curve.

[0042] S2. Preparation of Sample Solution: Dry the nuclear-grade polyacrylic acid dispersant sample, then dissolve it in water (e.g., high-purity water) to prepare a stock solution with a mass concentration of 0.5-1.5 g / L. Add hydrazine solution to the stock solution to obtain a solution with a hydrazine concentration of 150-250 μg / L. Adjust the pH to 9.5-10.0 to obtain the sample solution. The mass concentration range of the standard solution must include the mass concentration of the stock solution.

[0043] Specifically, the nuclear-grade polyacrylic acid dispersant sample is dried at 80-120℃ to constant weight. The temperature can be selected from 80℃, 90℃, 105℃, 110℃, 120℃, etc. In some embodiments, the sample drying can be carried out in a forced-air drying oven. Then, 0.25-0.75g (accurate to 0.1mg) of the dried sample is accurately weighed and dissolved in 500mL of water to prepare a stock solution. The sample amount can be 0.25g, 0.4g, 0.5g, 0.6g, 0.75g, etc. In some embodiments, the sample amount and the amount of water used are not specifically limited, as long as the mass concentration of the stock solution is 0.5-1.5g / L. The amounts of the stock solution and the hydrazine solution are not specifically limited, as long as the hydrazine concentration of the solution is 150-250μg / L. The concentration of hydrazine in the solution can be 150 μg / L, 180 μg / L, 200 μg / L, 220 μg / L, 250 μg / L, etc.; the pH value of the sample solution can be 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, etc.

[0044] Furthermore, hydrazine solution is added to the mother liquor to simulate the actual application conditions of polyacrylic acid dispersant. The concentration of the hydrazine solution can be 150-250 mg / L, such as 150 mg / L, 175 mg / L, 200 mg / L, 225 mg / L, 250 mg / L, etc. The pH is adjusted using an 8-12% ammonia solution, where the mass fraction of the ammonia solution can be 8%, 9%, 10%, 11%, 12%, etc. In some embodiments, alkaline solutions of other components can also be used to adjust the pH, as long as the pH of the sample solution is 9.5-10.0.

[0045] S3. Isothermal Decomposition Reaction: The sample solution is placed in the vessel 1 of the above-mentioned testing device. The sampling valve 151 and the discharge valve 171 are opened, and the injection valve 161 is closed. Protective gas is introduced for deoxygenation. The sampling valve 151 and the discharge valve 171 are closed, and the temperature inside the vessel 1 is adjusted to 250-300℃. The pressure inside the vessel 1 is increased to the saturated vapor pressure corresponding to the temperature. The sample solution undergoes an isothermal decomposition reaction inside the vessel 1. The temperature inside the vessel 1 can be 250℃, 270℃, 280℃, 290℃, 300℃, etc.; the saturated vapor pressure corresponding to this temperature is 4-8 MPa, which is not specifically limited in this invention.

[0046] Specifically, the protective gas is nitrogen or argon, preferably high-purity nitrogen or high-purity argon, which can improve the deoxygenation effect; the protective gas is introduced for 20-40 minutes, and the introduction time can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, etc.

[0047] S4. Sampling: Sampling is performed at different isothermal times. During sampling, sampling valve 151 is opened first, and the sample solution is transported to expansion pipe 2 for cooling under pressure inside vessel 1. After 3-5 minutes, sampling valve 151 is closed, and injection valve 161 is opened. The cooled sample solution is discharged from expansion pipe 2 into sample container 3. After sampling, injection valve 161 is closed, and sampling valve 151 and discharge valve 171 are opened to allow the high-temperature and high-pressure liquid in vessel 1 to enter waste treatment unit 4.

[0048] Specifically, the sampling time is different isothermal times, such as 0h, 0.5h, 1h, 2h, and 4h. Sampling is performed at least five times, with the first sampling being conducted at 0h. The sampling volume can be 15-25mL, preferably 20mL.

[0049] S5. Detection and Calculation: The absorbance of the sample solution at different isothermal times is detected. Based on the linear fitting results of step S1, the concentration of polyacrylic acid in the sample solution is obtained. Based on the rate of change of polyacrylic acid concentration at different isothermal times, the thermal decomposition concentration half-life of polyacrylic acid is calculated.

[0050] In this invention, size exclusion chromatography (SEC) is used to detect the absorbance of standard solutions and sample solutions, and the polyacrylic acid concentration of the sample solution is obtained by external standard method. The detection instruments and detection parameters of SEC chromatography are shown in Table 1.

[0051] Table 1. Testing Instruments and Parameters

[0052] detector 2996 Diode Array Ultraviolet Spectrometer chromatographic column TSKgelG4000WXL, Φ7.8×30, 10μm solvent water Standard materials Sodium polyacrylate (weight average molecular weight 1K) Column temperature 35℃ Flow rate 0.6 mL / min Injection volume 100μL Sample processing methods 0.2μM membrane needle filter filtration

[0053] Furthermore, linear fitting was performed on the polyacrylic acid concentration of the sample solution at different isothermal times to obtain the polyacrylic acid concentration change rate at different isothermal times. Specifically, based on the thermal decomposition chemical reaction kinetics of PAA, the PAA thermal decomposition reaction was set as a second-order reaction kinetic process. According to the principle of chemical reaction kinetics calculation, the PAA concentration (1 / C) at different isothermal times was obtained. t Linear fitting was performed on ~t), and the thermal decomposition concentration half-life of polyacrylic acid was calculated using equation (1), which is expressed as follows:

[0054]

[0055] Where k is 1 / Ct The slope of the linear fitting equation, C t The values ​​represent the polyacrylic acid concentrations corresponding to different isothermal times, where t represents different isothermal times; C0 represents the polyacrylic acid concentration corresponding to an isothermal time of 0 h.

[0056] The present invention provides a method for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid (PAA) dispersant. This method involves preparing a PAA sample solution with a specific hydrazine concentration, placing the sample solution in the reactor of a testing device for thermal decomposition, and performing real-time sampling and detection to calculate the PAA thermal decomposition concentration half-life. This method provides highly accurate PAA concentration measurements and highly accurate PAA thermal decomposition half-life calculations.

[0057] The following examples illustrate this:

[0058] This invention proposes a method for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant, using the testing apparatus described above. The testing method includes the following steps:

[0059] S1. Preparation of standard solutions: Weigh different masses of certified standard substances of polyacrylic acid dispersant and dissolve them in high-purity water to prepare standard solutions with mass concentrations of 0 g / L, 0.5 g / L, 1.0 g / L, 1.5 g / L, and 2 g / L, respectively. Then, measure the absorbance of the above standard solutions and perform linear fitting between the measured absorbance and the corresponding mass concentration to obtain an absorbance-mass concentration standard curve.

[0060] S2. Preparation of Sample Solution: Place the nuclear-grade polyacrylic acid dispersant sample (weight-average molecular weight 103158) in a forced-air drying oven and dry it to constant weight at 105℃. Then, accurately weigh 0.5g (accurate to 0.1mg) of the dried sample and dissolve it in 500mL of high-purity water to prepare a stock solution with a mass concentration of 1g / L. Add a hydrazine solution with a concentration of 200mg / L to the stock solution to obtain a hydrazine solution with a concentration of 200μg / L. Adjust the pH to 9.7 using a 10% ammonia solution to obtain the sample solution.

[0061] S3. Isothermal decomposition reaction: Place the sample solution in the vessel 1 of the above-mentioned test device, open the sampling valve 151 and the discharge valve 171, close the injection valve 161, and continuously purge with high-purity nitrogen gas for 30 minutes to remove oxygen; close the sampling valve 151 and the discharge valve 171, adjust the temperature inside the vessel 1 to 280℃, and increase the pressure inside the vessel 1 to the saturated vapor pressure corresponding to the temperature. The sample solution undergoes an isothermal decomposition reaction inside the vessel 1.

[0062] S4. Sampling: Sampling is performed at different isothermal times: 0h, 0.5h, 1h, 2h, and 4h, for a total of five time periods. The sampling volume is 20mL, resulting in five samples. During sampling, sampling valve 151 is first opened, and the sample solution is transported to the expansion pipe 2 under pressure within the vessel 1 for cooling. After 3-5 minutes, sampling valve 151 is closed, and injection valve 161 is opened. The cooled sample solution is discharged from expansion pipe 2 into sample container 3. After sampling, injection valve 161 is closed, and sampling valve 151 and discharge valve 171 are opened, allowing the high-temperature, high-pressure liquid in vessel 1 to enter waste treatment unit 4.

[0063] S5. Detection and Calculation: The absorbance of the sample solution at different isothermal times was measured. Based on the linear fitting results of step S1, the concentration of polyacrylic acid in the sample solution was obtained. The thermal decomposition concentration half-life of polyacrylic acid was calculated based on the rate of change of polyacrylic acid concentration at different isothermal times. SEC chromatography was used to detect the absorbance of the standard solution and the sample solution. The external standard method was used to obtain the polyacrylic acid concentration of the sample solution. The detection instruments and parameters for SEC chromatography are shown in Table 1 above, and the detection results are shown in Table 2.

[0064] Table 2 PAA Concentration Detection Results

[0065] 0 246.7 0.0041 0.5 173.4 0.0058 1 156.5 0.0064 2 125.4 0.0080 4 72.2 0.014

[0066] Furthermore, the concentration of polyacrylic acid (1 / C) of the sample solution under different isothermal times was investigated. t Perform linear fitting on ~t), such as Figure 2 As shown, the rate of change of polyacrylic acid concentration (i.e., slope k) for different isothermal times was obtained. The thermal decomposition concentration half-life of polyacrylic acid was calculated using equation (1), which is expressed as follows:

[0067]

[0068] Where k is 1 / C t The slope of the linear fitting equation, C t The values ​​represent the polyacrylic acid concentrations corresponding to different isothermal times, where t represents different isothermal times; C0 represents the polyacrylic acid concentration corresponding to an isothermal time of 0 h.

[0069] Depend on Figure 2 Given the slope k = 0.0024 and C0 = 246.7 mg / L, the thermal decomposition concentration half-life t of polyacrylic acid can be calculated using equation (1). 1 / 2 =1.69h.

[0070] All parts not described in detail in this invention are existing technologies.

[0071] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A testing device for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant, characterized in that, Includes the vessel body (1) and the expansion pipe (2); The vessel body (1) and the expansion pipe (2) are connected by a sampling pipe (15) and an inlet pipe (16). The inlet of the sampling pipe (15) extends into the bottom of the vessel body (1). A sampling valve (151) is provided on the sampling pipe (15). The outlet of the sampling pipe (15) is connected to the inlet pipe (16). The expansion pipe (2) is installed on the inlet pipe (16). The vessel body (1) is equipped with a heating unit (11) for heating polyacrylic acid dispersant. The sample solution of polyacrylic acid dispersant is located in the vessel body (1). After the sample solution is heated, saturated steam is generated. Under the pressure of the saturated steam, the sample solution is transported to the expansion pipe (2) through the sampling pipe (15) and the injection pipe (16) in sequence. The sample solution will cool down rapidly after entering the expansion pipe (2) due to the increase in volume.

2. The testing apparatus for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant according to claim 1, characterized in that, The outlet of the injection pipeline (16) is connected to the sample container (3), and an injection valve (161) is provided between the expansion pipeline (2) and the sample container (3).

3. The apparatus for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant according to claim 1, characterized in that, The outlet of the sampling pipeline (15) is also connected to the discharge pipeline (17), the discharge pipeline (17) is equipped with a discharge valve (171), and the outlet of the discharge pipeline (17) is connected to the waste treatment unit (4).

4. The apparatus for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant according to claim 1, characterized in that, The heating unit (11) is distributed inside the bottom wall and side wall of the vessel body (1); and / or the vessel body (1) is provided with a temperature control unit (12) for adjusting the temperature of the heating unit (11).

5. The apparatus for testing the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant according to claim 1, characterized in that, The vessel body (1) is equipped with a pressure gauge (13) and a safety valve (14).

6. A method for testing the thermal decomposition half-life of a nuclear-grade polyacrylic acid dispersant, characterized in that, The test apparatus for the thermal decomposition half-life of nuclear-grade polyacrylic acid dispersant according to any one of claims 1 to 5, the test method comprising the following steps: S1. Preparation of standard solutions: Weigh different masses of polyacrylic acid dispersant standard substances and dissolve them in water to prepare several standard solutions with gradient mass concentrations. The mass concentration of each of the standard solutions is 0-2 g / L. Then, the absorbance of the standard solutions is measured, and the measured absorbance is linearly fitted to the corresponding mass concentration. S2. Preparation of sample solution: Dry the nuclear-grade polyacrylic acid dispersant sample, then dissolve it in water to prepare a mother liquor with a mass concentration of 0.5-1.5 g / L; add hydrazine solution to the mother liquor to obtain a solution with a hydrazine concentration of 150-250 μg / L, adjust the pH to 9.5-10.0, and obtain the sample solution. S3. Isothermal decomposition reaction: The sample solution is placed in the vessel (1) of the test device and a protective gas is introduced to remove oxygen; the sampling valve (151) is closed, the temperature inside the vessel (1) is adjusted to 250-300℃, the pressure inside the vessel (1) is increased to the saturated vapor pressure corresponding to the temperature, and the sample solution undergoes an isothermal decomposition reaction inside the vessel (1). S4. Sampling: Sampling is carried out at different constant temperature times. When sampling, the sampling valve (151) is opened first. The sample solution is transported to the expansion pipe (2) under the pressure in the vessel body (1) for cooling. Then the sampling valve (151) is closed and the cooled sample solution is discharged from the expansion pipe (2). S5. Detection and Calculation: The absorbance of the sample solution at different isothermal times is detected. Based on the linear fitting results of step S1, the concentration of polyacrylic acid in the sample solution is obtained. Based on the rate of change of polyacrylic acid concentration at different isothermal times, the thermal decomposition concentration half-life of polyacrylic acid is calculated.

7. The method for testing the thermal decomposition half-life of the nuclear-grade polyacrylic acid dispersant according to claim 6, characterized in that, In step S2, the nuclear-grade polyacrylic acid dispersant sample is dried at 80-120°C to constant weight, and then 0.25-0.75g of the dried sample is dissolved in 500mL of water to prepare a mother liquor.

8. The method for testing the thermal decomposition half-life of the nuclear-grade polyacrylic acid dispersant according to claim 6, characterized in that, In step S2, the concentration of the hydrazine solution is 150-250 mg / L, and / or the pH is adjusted using an ammonia solution with a mass fraction of 8-12%.

9. The method for testing the thermal decomposition half-life of the nuclear-grade polyacrylic acid dispersant according to claim 6, characterized in that, In step S3, the protective gas is nitrogen or argon, and the protective gas is introduced for 20-40 minutes.

10. The method for testing the thermal decomposition half-life of the nuclear-grade polyacrylic acid dispersant according to claim 6, characterized in that, In step S5, the concentration of polyacrylic acid in the sample solution at different isothermal times is linearly fitted to obtain the rate of change of polyacrylic acid concentration at different isothermal times, and the thermal decomposition concentration half-life of polyacrylic acid is calculated using equation (1). Equation (1) is expressed as follows: （1） Where k is 1 / C t The slope of the linear fitting equation, C t The values ​​represent the polyacrylic acid concentrations corresponding to different isothermal times, where t represents different isothermal times; C0 represents the polyacrylic acid concentration corresponding to an isothermal time of 0 h.

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