A process for producing urea for vehicles with effective delay and reduction of crystallization

Abstract

The present application relates to the technical field of urea production, in particular to a production process for vehicle urea capable of effectively delaying and reducing crystallization, comprising the following steps: S1, dissolving urea and deionized water with an electric conductivity of 10 muS / cm or less at 35-45 DEG C, adjusting the mass fraction of urea to 31.8%-33.2%, cooling to 20-30 DEG C, and then entering a waiting tank for homogenization after being filtered through a filter with a pore size of 0.2-0.5 mu m; sampling the main batch liquid in the production process, setting a detection sample and a reference sample, treating the reference sample according to the corresponding heat preservation, cooling and filtration treatment conditions, comparing the changes in crystallization induction time before and after the treatment, obtaining the crystallization response differences of different batches of vehicle urea solution to the treatment process, and determining whether the main batch liquid is suitable for heat preservation, cooling and filtration treatment.

Description

Technical Field

[0001] This invention relates to the field of urea production technology, and in particular to a production process for automotive urea that effectively delays and reduces crystallization. Background Technology

[0002] As a reducing agent in the selective catalytic reduction (SCR) system of diesel engines, the stability of automotive urea solution directly affects the normal operation of the exhaust gas treatment system. During actual storage, transportation, and vehicle use, automotive urea solution may crystallize due to low-temperature environments, reducing solution homogeneity and potentially affecting the normal operation of delivery pipelines and injection devices.

[0003] Currently, in the production process of automotive urea, crystallization is typically delayed or reduced by controlling the purity of raw materials, adjusting the concentration of the urea solution, employing filtration, and conducting low-temperature stability testing. Filtration is primarily used to remove insoluble particles from the solution, while low-temperature stability testing is used to evaluate the product's crystallization stability under low-temperature conditions.

[0004] However, in actual production, different batches of automotive urea solution exhibit varying crystallization behaviors under low-temperature conditions. Existing testing methods can typically determine whether a product meets low-temperature stability requirements, but they are insufficient to further determine whether batches exhibiting crystallization tendencies can have their crystallization induction time extended or premature crystallization reduced through subsequent heat preservation, cooling, and filtration treatments.

[0005] For production batches exhibiting a tendency for low-temperature crystallization, existing production processes typically require rework or isolation to control the issue. However, there is a lack of criteria for selecting appropriate treatments based on the specific crystallization behavior of different batches. This may result in some products that can be improved through process treatment being directly isolated, or products that are difficult to improve being subjected to ineffective treatment, thereby increasing production costs and reducing the efficiency of production process control.

[0006] Therefore, how to effectively identify the low-temperature crystallization behavior of different batches of products during the production of automotive urea, and determine whether they are suitable for subsequent heat preservation, cooling and filtration treatments, so as to achieve targeted production control and improve the accuracy of product release judgment, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and propose an effective process for producing automotive urea that delays and reduces crystallization.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: an effective process for producing automotive urea that delays and reduces crystallization, comprising the following steps: S1, dissolving urea in deionized water with a conductivity ≤10μS / cm at 35-45℃, adjusting the urea mass fraction to 31.8%-33.2%, cooling to 20-30℃ and filtering through 0.2-0.5μm before entering the release tank for homogenization;

[0009] S2. Take a sample from the main circulation pipeline, mix it thoroughly, and divide it into test sample and reference sample. Keep the reference sample at 40-45℃ for 20-40 min, cool it to 20±0.2℃ at a rate not exceeding 1℃ / min, and filter it. Adjust the test sample to 20±0.2℃. After degassing, both samples are simultaneously cooled to −10.5±0.3℃ at a rate of 0.3-0.8℃ / min. Crystallization is determined when the intensity of the 90° scattered light increases by 15% compared to the average value 30s before cooling and remains so for 15s.

[0010] S3. If crystallization occurs before reaching the target temperature, it is judged as premature crystallization. When the target temperature is reached, the timing starts. The crystallization induction time of the test sample and the reference sample are recorded as t1 and t2, respectively. If no crystallization occurs after 30 minutes of constant temperature, it is recorded as 30 minutes.

[0011] S4. If the reference sample crystallizes prematurely or t2 < 10 min, the main batch of liquid enters the isolation tank; if the test sample crystallizes prematurely but the reference sample does not crystallize prematurely, or if t2 ≥ 10 min and t1 < 0.8t2, the main batch of liquid is treated according to the reference sample conditions and then retested. If the retest is qualified, it enters the finished product tank; if the retest is unqualified, it enters the isolation tank; the remaining main batch of liquid enters the finished product tank.

[0012] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0013] This invention samples the master batch of urea solution during the production process and sets up test samples and reference samples. The reference sample is treated according to corresponding heat preservation, cooling, and filtration conditions. By comparing the changes in crystallization induction time before and after treatment, the differences in crystallization response of different batches of automotive urea solution to the treatment process can be obtained, thereby determining whether the master batch solution is suitable for heat preservation, cooling, and filtration treatment. Compared with the prior art, which only judges whether the product meets the requirements based on the low-temperature stability test results, this application can further distinguish the crystallization response of different batches of products after treatment, providing a basis for subsequent treatment path selection. For master batch solutions that meet the treatment judgment conditions, the corresponding treatment process of the reference sample can be improved, and the consistency between the actual treatment results and the reference sample treatment results can be verified by detecting the crystallization induction time after treatment, thereby improving the reliability of batch treatment judgment. At the same time, by selecting the treatment, isolation, or release path based on the test results, the same treatment method can be avoided for batches with different crystallization behaviors, realizing production process control for different batch characteristics. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the steps of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] Example 1: This invention provides an effective process for delaying and reducing crystallization in the production of automotive urea, which uses a method to determine whether a batch of products is suitable for heat preservation, cooling, and filtration based on a reference sample simulation treatment response.

[0017] This embodiment establishes a comparison relationship between the test sample and the reference sample, allowing the reference sample to be simulated under the actual heat preservation, cooling, and filtration conditions to be used in the master batch solution. By comparing the changes in crystallization induction time and insoluble particle concentration before and after treatment, it is determined whether the corresponding batch of automotive urea solution has the potential to improve low-temperature crystallization behavior through heat preservation, cooling, and filtration treatment.

[0018] In this embodiment, the heat preservation, cooling and filtration treatment refers to sequentially heating and maintaining the temperature of the automotive urea solution, slowly cooling it and filtering it to reduce unstable factors that may affect the low-temperature crystallization behavior.

[0019] First, the urea raw material is added to deionized water with a conductivity of no more than 10 μS / cm and dissolved at 35–45°C to ensure complete dissolution of the urea in the aqueous system. The mass fraction of the resulting urea solution is then adjusted to 31.8%–33.2%.

[0020] After dissolution, the resulting urea solution is cooled to 20–30°C and filtered through a filter element with a pore size of 0.2–0.5 μm to remove insoluble particles. The filtered urea solution is then homogenized in a release tank to obtain the master batch solution for testing.

[0021] Samples are taken from the main circulation pipeline of the main batch of liquid to be tested, and after the samples are thoroughly mixed, they are divided into test samples and reference samples.

[0022] Among them, the test sample is used to characterize the low-temperature crystallization behavior of the master batch solution without heat preservation, cooling and filtration treatment; the reference sample is used to simulate the crystallization response change of the master batch solution after the treatment process.

[0023] The reference sample was subjected to simulated treatment under the conditions to be used in the actual production process of the master batch liquid. Specifically, the reference sample was kept at 40–45°C for 20–40 minutes to allow it to undergo a temperature holding process corresponding to the actual treatment process. Subsequently, the reference sample was cooled to 20 ± 0.2°C at a cooling rate of no more than 1°C / min. After cooling, the reference sample was filtered to obtain the simulated treatment reference sample.

[0024] Through the above simulation process, the reference sample undergoes state changes corresponding to the actual improvement process of the master batch solution under experimental conditions, thereby obtaining the response of the treatment process to the crystallization behavior.

[0025] Subsequently, low-temperature crystallization induction detection was performed on the test sample and the reference sample after simulation treatment.

[0026] Before testing, the test sample and the reference sample were adjusted to 20±0.2℃ and degassed. Then, the sample temperature was simultaneously reduced at a cooling rate of 0.3~0.8℃ / min until it reached -10.5±0.3℃.

[0027] During the cooling process, the changes in the crystallization state inside the sample were monitored in real time using 90° scattered light detection. When the intensity of the 90° scattered light on the sample increased by 15% relative to the average intensity of the scattered light in the 30 seconds before cooling, and this increase was sustained for 15 seconds, the sample was determined to have crystallized.

[0028] If the sample crystallizes before reaching the target temperature, it is recorded as premature crystallization. If the timing starts after the sample reaches the target temperature, the corresponding crystallization induction time is obtained. If no crystallization occurs within 30 minutes of constant temperature, the crystallization induction time of the sample is recorded as 30 minutes.

[0029] The crystallization induction time Tdetection for the test sample and the crystallization induction time Treference for the reference sample after treatment were obtained. Tdetection was used to characterize the crystallization stability of the master batch solution in its untreated state, while Treference was used to characterize the crystallization response of the master batch solution after simulated treatment.

[0030] Furthermore, to analyze the effects of heat preservation, cooling, and filtration on changes in insoluble particles in the sample, the concentration of insoluble particles was measured before and after the reference sample was treated.

[0031] In this embodiment, the insoluble particle concentration represents the mass content of insoluble particles per unit volume of sample, expressed in mg / L.

[0032] During the testing process, the reference samples before and after treatment were tested using the same testing equipment, under the same testing conditions, and using the same testing methods to ensure that the test data before and after treatment were comparable.

[0033] Detection yielded: Pre-treatment concentration of insoluble particles (C);

[0034] The concentration C of insoluble particles after treatment.

[0035] Where: when Cafter < Cbefore, it means that the content of insoluble particles in the reference sample decreased after heat preservation, cooling and filtration treatment;

[0036] When C after ≥ C before, it indicates that the treatment process did not reduce the concentration of insoluble particles.

[0037] Furthermore, a correlation analysis was conducted between the changes in the concentration of insoluble particles before and after the reference sample treatment and the changes in crystallization induction time.

[0038] When the reference sample undergoes heat preservation, cooling, and filtration treatment, it simultaneously meets the following conditions:

[0039] The concentration of insoluble particles C after treatment is lower than the concentration of insoluble particles C before treatment.

[0040] The crystallization induction time of the treated reference sample was prolonged compared to that before treatment;

[0041] The test sample did not show the same change in crystallization induction time in the same direction as the reference sample;

[0042] It is believed that the low-temperature crystallization behavior of this batch of automotive urea solution can be improved through heat preservation, cooling and filtration treatment.

[0043] At this point, the output of the main batch of liquid is the result of the suitability judgment for heat preservation, cooling and filtration treatment, and this result is used as the basis for selecting the subsequent main batch of liquid treatment path.

[0044] If, after simulation treatment, the crystallization induction time of the reference sample does not increase, or the concentration of insoluble particles does not decrease, or there is no significant difference in crystallization response between the test sample and the reference sample, the output will be that the suitability judgment results for heat preservation, cooling and filtration treatments are not met, indicating that the batch of master solution will not be treated for improvement at this time.

[0045] The following test data were obtained by testing a batch of automotive urea master batch solution actually prepared using the method of this embodiment.

[0046] During the testing process, both the test sample and the reference sample were tested according to the aforementioned low-temperature crystallization testing conditions.

[0047] The test results showed that the concentration of insoluble particles in the reference sample before treatment was 15 mg / L. After heat preservation, cooling and filtration, the concentration of insoluble particles decreased to 6 mg / L. At the same time, the crystallization induction time of the reference sample before treatment was 8 min, and after simulation treatment, the crystallization induction time was extended to 22 min, while the crystallization induction time of the untreated test sample remained at 8 min.

[0048] Based on the above test results, it can be seen that after the simulation treatment, the concentration of insoluble particles in the reference sample decreased and the crystallization induction time was significantly prolonged, while the test sample did not show corresponding changes. Therefore, it is determined that this batch of automotive urea solution meets the applicability conditions for heat preservation, cooling and filtration treatment.

[0049] The method described in this embodiment can not only detect whether low-temperature crystallization occurs in the production process of automotive urea, but also simulate the actual processing process using a reference sample to obtain the changes in crystallization response after processing in advance, and determine whether different batches of automotive urea solutions are suitable for heat preservation, cooling and filtration treatment by combining the changes in the concentration of insoluble particles.

[0050] Compared to existing technologies that rely solely on low-temperature stability test results to determine whether a product meets requirements, this embodiment can further identify batches with potential for improvement, providing a basis for subsequent processing, isolation, or release.

[0051] Example 2

[0052] This embodiment provides a method for processing automotive urea master batch liquid based on the applicability judgment results of Embodiment 1, and for determining whether the master batch liquid meets the release conditions through process control and processing result verification.

[0053] Based on the suitability judgment results of the heat preservation, cooling and filtration treatment of the master batch liquid obtained in Example 1, this embodiment implements corresponding treatment on the master batch liquid that meets the treatment suitability conditions, and verifies the actual treatment effect by dynamic filtration monitoring during the treatment process and crystallization induction time detection after treatment.

[0054] In this embodiment, effective treatment means that the master batch liquid did not crystallize prematurely after heat preservation, cooling and filtration, the crystallization induction time met the preset release requirements, and the crystallization response change trend after treatment was consistent with the crystallization response change trend after the reference sample simulation treatment in Example 1.

[0055] In the specific implementation process, the applicability judgment result of the master batch liquid treatment output in Example 1 is obtained first.

[0056] When a batch of master liquid meets the suitability conditions for heat preservation, cooling and filtration, the batch of master liquid is transported to the processing step and the master liquid is actually processed according to the processing conditions corresponding to the reference sample in Example 1.

[0057] During the process, the master batch solution is first kept at a constant temperature to reach the temperature conditions corresponding to those in the simulation process of the reference sample, and this temperature is maintained for a corresponding period of time to change the unstable factors inside the master batch solution that affect the low-temperature crystallization behavior.

[0058] After the heat preservation treatment is completed, the master batch solution is cooled. During the cooling process, a cooling rate corresponding to the simulated treatment process of the reference sample in Example 1 is adopted to reduce the temperature of the master batch solution to the preset treatment temperature range.

[0059] After cooling, the master batch solution is circulated and filtered to reduce the content of insoluble particles in the master batch solution.

[0060] During the cyclic filtration process, filtered samples were continuously acquired from the filtration outlet and the concentration of insoluble particles in the filtration outlet samples was detected using the same insoluble particle concentration detection method as in Example 1, under the same detection equipment and detection conditions.

[0061] In this embodiment, the insoluble particle concentration represents the mass content of insoluble particles per unit volume of sample, expressed in mg / L.

[0062] The data on the change in the concentration of insoluble particles during the cyclic filtration process are obtained by continuous monitoring, and the filtration status is judged based on the trend of the concentration of insoluble particles with filtration time.

[0063] When the concentration of insoluble particles at the filter outlet is less than the set range in multiple consecutive detection cycles, it is determined that the concentration of insoluble particles at the filter outlet has stabilized, and the cyclic filtration is considered to have reached a stable processing state.

[0064] The continuous detection cycle is determined based on the detection frequency in the actual production process, and the set variation range is set according to the requirements of the production process for the filtration effect.

[0065] Once the circulating filtration reaches a stable processing state, stop the circulating filtration and resample the processed master batch solution.

[0066] The test sample was obtained from the processed master batch solution and tested according to the low-temperature crystallization detection method in Example 1.

[0067] During the testing process, the sample temperature was adjusted to 20±0.2℃, and after degassing, the sample temperature was lowered to -10.5±0.3℃ at a cooling rate of 0.3~0.8℃ / min.

[0068] Whether crystallization has occurred in the sample is determined by the change in the intensity of 90° scattered light. When the intensity of 90° scattered light increases by 15% relative to the average value within 30 seconds before cooling and remains so for 15 seconds, it is determined that the sample has crystallized, and the crystallization induction time corresponding to the master batch solution after treatment is obtained.

[0069] The crystallization induction time refers to the time from when the sample reaches the target detection temperature until crystallization occurs, in minutes. If no crystallization occurs within 30 minutes of constant temperature, the crystallization induction time is recorded as 30 minutes.

[0070] Furthermore, the crystallization induction time of the treated master batch solution was compared with the crystallization induction time of the reference sample after simulated treatment in Example 1.

[0071] When the treated master batch liquid does not crystallize prematurely, and the crystallization induction time meets the preset release requirements, and the crystallization induction time of the treated master batch liquid is consistent with the trend of the crystallization induction time of the reference sample after simulated treatment, the batch of master batch liquid is deemed to be effectively treated, and the treated master batch liquid is transported to the finished product tank.

[0072] If the processed master batch of liquid crystallizes prematurely, or the crystallization induction time does not meet the preset release requirements, or the processed master batch of liquid shows a significant difference from the crystallization response of the reference sample after simulated treatment, it is determined that the processing result of the master batch of liquid has not met expectations, and the master batch of liquid is transferred to the isolation tank.

[0073] If a batch of master batch liquid does not meet the applicability conditions for heat preservation, cooling and filtration treatment in Example 1, it will not enter the above treatment process, but will enter the isolation treatment process according to the test results.

[0074] The method described in this embodiment was used to process and verify a batch of automotive urea master batch obtained in the actual production process.

[0075] After testing in Example 1, this batch of master solution was determined to meet the suitability conditions for heat preservation, cooling, and filtration treatment. Specifically, the crystallization induction time for the untreated test sample was 8 minutes, while the crystallization induction time for the reference sample treated under simulated conditions was 22 minutes.

[0076] Subsequently, the master batch of liquid was processed according to the insulation temperature, insulation time, cooling rate and filtration process corresponding to the reference sample.

[0077] During the processing, the concentration of insoluble particles in the filtered outlet sample is continuously monitored. When the change in the concentration of insoluble particles is less than the set range within several consecutive monitoring cycles, the cyclic filtration is stopped.

[0078] After processing, the master batch solution was resampled and tested.

[0079] The test results showed that the treated master batch did not crystallize prematurely, the crystallization induction time reached more than 20 minutes, and the crystallization response change trend after treatment was consistent with the change trend of the reference sample after simulation treatment.

[0080] Therefore, the treatment of this batch of master batch liquid was deemed effective, and the treated master batch liquid was transported to the finished product tank.

[0081] Using the method of this embodiment, the treatment response can be simulated based on the reference sample obtained in Example 1, and different batches of automotive urea master batch solution can be treated differently. The filtration endpoint can be dynamically determined based on the trend of insoluble particle concentration change during the cyclic filtration process. At the same time, the actual treatment effect can be verified by detecting the crystallization induction time after treatment.

[0082] Compared to existing technologies that use fixed processing times or uniform rework methods to handle all abnormal batches, this embodiment can select the corresponding processing path based on the crystallization response characteristics of different batches of master batch liquid, thereby improving the accuracy and reliability of low-temperature crystallization risk control in the production process of automotive urea.

[0083] This embodiment is based on the simulated treatment response of the reference sample obtained in Example 1 and the actual treatment results of the master batch liquid obtained in Example 2. By recording the test results of the test sample, reference sample and the master batch liquid after actual treatment in multiple consecutive production batches, and analyzing the correspondence between the simulated treatment results of the reference sample and the actual treatment results of the master batch liquid, the adjustment direction of the heat preservation time, cooling rate and circulation filtration time in subsequent production batches is determined according to the influence of different treatment parameter changes on crystallization induction time and insoluble particle concentration.

[0084] In this embodiment, the multiple production batches are master batches of automotive urea solution continuously prepared using the same production process.

[0085] During the production process, the test data corresponding to each batch of master batch liquid are recorded.

[0086] The recorded data includes: the crystallization induction time of the untreated sample in Example 1;

[0087] The crystallization induction time of the reference sample in Example 1 after heat preservation, cooling and filtration treatment;

[0088] Concentration of insoluble particles before and after treatment of the reference sample in Example 1;

[0089] In Example 2, the crystallization induction time of the master batch solution after actual treatment under the reference sample conditions;

[0090] The actual holding time, cooling rate, and circulation filtration time during the main batch liquid treatment process in Example 2.

[0091] The crystallization induction time was obtained according to the detection methods in Examples 1 and 2.

[0092] During testing, the sample temperature was adjusted to 20±0.2℃, and after degassing, the sample temperature was lowered to -10.5±0.3℃ at a cooling rate of 0.3~0.8℃ / min.

[0093] During the cooling process, the crystallization state of the sample is determined by the change in the intensity of the scattered light at 90°.

[0094] When the intensity of the 90° scattered light of the sample increases by 15% relative to the average intensity of the scattered light within 30 seconds before cooling, and this increase continues for 15 seconds, it is determined that the sample has crystallized. The time between reaching the target temperature and the occurrence of crystallization is recorded as the crystallization induction time of the sample.

[0095] The unit for crystallization induction time is min.

[0096] If no crystallization occurs within 30 minutes of constant temperature of the sample, the crystallization induction time is recorded as 30 minutes.

[0097] The concentration of insoluble particles was obtained using the same detection method as in Examples 1 and 2.

[0098] During the testing process, samples from different production batches were tested using the same testing equipment and under the same testing conditions.

[0099] The concentration of insoluble particles indicates the mass content of insoluble particles per unit volume of sample, expressed in mg / L.

[0100] After obtaining test data from multiple production batches, the consistency between the simulated treatment results of the reference sample and the actual treatment results of the master batch solution is first assessed.

[0101] Specifically, the changes in crystallization induction time of the reference sample in each production batch after heat preservation, cooling and filtration are compared with the changes in crystallization induction time of the corresponding master batch after actual treatment.

[0102] When the crystallization induction time change trend after reference sample treatment is consistent with the change trend after actual treatment of master batch liquid in multiple consecutive production batches, it is determined that the simulated treatment result of reference sample can reflect the actual treatment effect of master batch liquid.

[0103] After confirming that the simulation results of the reference sample can reflect the actual treatment effect, the correspondence between the changes in different process parameters and the changes in treatment results during the actual treatment process is analyzed.

[0104] The analysis included the correlation between changes in heat preservation time and changes in crystallization induction time after treatment.

[0105] The correspondence between changes in cooling rate and changes in crystallization induction time after treatment;

[0106] The correlation between changes in circulating filtration time and changes in the concentration of insoluble particles after treatment.

[0107] The direction for adjusting processing parameters is determined based on the test results of multiple production batches.

[0108] If multiple production batches show that, with consistent urea mass fraction, raw material conditions, and other processing conditions, the crystallization induction time after prolonged heat preservation continuously increases, then the heat preservation time should be increased in subsequent production batches.

[0109] If multiple production batches show that, under the same processing conditions, the crystallization induction time continues to increase after reducing the cooling rate, then the cooling rate should be reduced in subsequent production batches.

[0110] If multiple production batches show that, under the same processing conditions, the concentration of insoluble particles continues to decrease after extending the circulation filtration time, then the circulation filtration time should be increased for subsequent production batches.

[0111] After adjusting the processing parameters, the adjusted production batch was retested and verified.

[0112] During the verification process, the test sample and reference sample were re-acquired according to the detection method in Example 1, and the relationship between the crystallization induction time of the test sample and the reference sample in the adjusted production batch was detected.

[0113] Meanwhile, the adjusted master batch solution was actually processed according to the processing method in Example 2, and the changes in crystallization induction time and insoluble particle concentration of the processed master batch solution were detected.

[0114] When the adjusted production batch meets the following conditions:

[0115] No premature crystallization occurred in the treated master batch solution;

[0116] The crystallization induction time increased after the treatment compared to the production batch before the adjustment;

[0117] The concentration of insoluble particles after treatment was lower than that of the production batch before adjustment.

[0118] Furthermore, the actual treatment results of the master batch solution are consistent with the simulated treatment results of the reference sample;

[0119] The adjusted processing parameters are then determined to meet the processing requirements of the current production batch, and will be used as reference parameters in subsequent production processes.

[0120] If the adjusted production batch does not meet the above conditions, the test data of subsequent production batches will continue to be collected, and the effects of different processing parameters on crystallization induction time and insoluble particle concentration will be re-analyzed.

[0121] Taking multiple batches of automotive urea master solution obtained from continuous production as an example, the test results of each batch were recorded.

[0122] The analysis results show that in some production batches, the crystallization induction time of the reference sample was prolonged after simulated treatment, and the crystallization induction time of the corresponding master batch solution also showed the same trend after actual treatment.

[0123] Further analysis revealed that, with other production conditions remaining constant, increasing the circulation filtration time could reduce the concentration of insoluble particles at the filtration outlet and simultaneously increase the crystallization induction time of the treated master batch.

[0124] Based on the above analysis results, the cyclic filtration time was increased for subsequent production batches, and the detection methods in Examples 1 and 2 were used for verification.

[0125] The verification results showed that in the production batch after adjusting the circulation filtration time, the treated master batch liquid did not crystallize prematurely, the crystallization induction time was increased compared with that before the adjustment, the concentration of insoluble particles was reduced, and the actual treatment results were consistent with the simulated treatment results of the reference sample.

[0126] Therefore, it is determined that the direction of parameter adjustment is valid.

[0127] The method in this embodiment can utilize test results from multiple production batches to adjust the heat preservation time, cooling rate, and circulating filtration time during the production process of automotive urea, thereby creating a processing parameter adjustment mechanism driven by feedback from actual test results.

[0128] Compared to production methods with fixed processing parameters, this embodiment can adjust processing conditions according to the actual crystallization response changes of different batches of master batch liquid, thereby improving the stability of low-temperature crystallization risk control for automotive urea.

[0129] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A production process for automotive urea that effectively delays and reduces crystallization, characterized in that, Includes the following steps: S1. Dissolve urea in deionized water with a conductivity ≤10μS / cm at 35-45℃, adjust the urea mass fraction to 31.8%-33.2%, cool to 20-30℃ and filter through 0.2-0.5μm before entering the release tank for homogenization; S2. Take a sample from the main circulation pipeline, mix it thoroughly, and divide it into test sample and reference sample. Keep the reference sample at 40-45℃ for 20-40 min, cool it to 20±0.2℃ at a rate not exceeding 1℃ / min, and filter it. Adjust the test sample to 20±0.2℃. After degassing, both samples are simultaneously cooled to −10.5±0.3℃ at a rate of 0.3-0.8℃ / min. Crystallization is determined when the intensity of the 90° scattered light increases by 15% compared to the average value 30s before cooling and remains so for 15s. S3. If crystallization occurs before reaching the target temperature, it is judged as premature crystallization. When the target temperature is reached, the timing starts. The crystallization induction time of the test sample and the reference sample are recorded as t1 and t2, respectively. If no crystallization occurs after 30 minutes of constant temperature, it is recorded as 30 minutes. S4. When the reference sample crystallizes prematurely or t2 < 10 min, the main batch of liquid enters the isolation tank. If the test sample crystallizes prematurely while the reference sample does not, or if t2 ≥ 10 min and t1 < 0.8t2, the main batch of liquid is treated according to the reference sample conditions and then retested. If the retest is qualified, it enters the finished product tank; if the retest is unqualified, it enters the isolation tank. The remaining main batch of liquid enters the finished product tank.

2. The automotive urea production process according to claim 1, characterized in that, Before and after the reference sample was subjected to heat preservation, cooling and filtration treatment, the concentration of insoluble particles in the reference sample was measured to obtain the particle concentration before treatment and the particle concentration after treatment. Crystallization induction tests were performed on the test sample and the reference sample respectively to obtain the corresponding crystallization induction time for the test sample and the reference sample; When the reference sample undergoes heat preservation, cooling, and filtration, and the crystallization induction time is prolonged compared to the time before treatment, while the test sample does not show a corresponding prolonged crystallization induction time, the master batch solution is determined to meet the criteria for improvement treatment.

3. A production process for automotive urea that effectively delays and reduces crystallization according to claim 2, characterized in that, When the master batch of liquid meets the criteria for improvement treatment, the master batch of liquid will be treated according to the treatment conditions corresponding to the reference sample. The processing conditions include the holding temperature, holding time, cooling rate, and filtration process; After processing, the master batch solution was resampled to form a test sample, and the crystallization induction time of the test sample was measured. When the processed test sample does not crystallize prematurely during the target cooling process and the crystallization induction time reaches the preset release judgment value, the processed master batch liquid is transported to the finished product tank.

4. A production process for automotive urea that effectively delays and reduces crystallization according to claim 3, characterized in that, During the main batch liquid circulation filtration process, the concentration of insoluble particles at the filtration outlet is continuously monitored; The filtration process is judged based on the change in the concentration of insoluble particles obtained from continuous monitoring. When the change in the concentration of insoluble particles within a continuous detection cycle is less than the preset change threshold, the cyclic filtration is stopped, and the processed master batch solution is subjected to crystallization induction detection.

5. A production process for automotive urea that effectively delays and reduces crystallization according to claim 2, characterized in that, The reference sample was treated according to the treatment conditions corresponding to the actual improvement process of the master batch solution; The processing conditions include the holding temperature, holding time, cooling rate, and filtration process; By detecting the change in crystallization induction time before and after the reference sample treatment, the crystallization response change of the master batch solution after the corresponding treatment can be obtained.

6. A production process for automotive urea that effectively delays and reduces crystallization according to claim 2, characterized in that, Based on the relationship between the crystallization induction time of the test sample and the reference sample, it is determined whether the master batch solution has been subjected to heat preservation, cooling and filtration treatment; Among them: when the crystallization induction time of the reference sample is prolonged after heat preservation, cooling and filtration, and the test sample does not show a corresponding prolonged trend, the main batch solution is determined to adopt the treatment process; If the crystallization induction time of the reference sample is not prolonged after heat preservation, cooling and filtration, the master batch solution is determined not to use the treatment process.

7. A production process for automotive urea that effectively delays and reduces crystallization according to claim 6, characterized in that, The changes in the concentration of insoluble particles before and after the treatment of the reference sample were compared with the changes in crystallization induction time. When the concentration of insoluble particles decreases and the crystallization induction time is prolonged, the relationship between the changes will be used as the basis for determining whether to use heat preservation, cooling and filtration treatment.

8. A production process for automotive urea that effectively delays and reduces crystallization according to claim 6, characterized in that, When the master batch of liquid meets the criteria for heat preservation, cooling and filtration, the master batch of liquid will be treated according to the corresponding treatment conditions of the reference sample. When the main batch of liquid does not meet the judgment conditions, the main batch of liquid is transferred to the isolation tank; When the crystallization induction time obtained from the main batch liquid detection reaches the preset release judgment value, the main batch liquid is transported to the finished product tank.

9. A production process for automotive urea that effectively delays and reduces crystallization according to claim 8, characterized in that, The treated master batch solution was resampled, and its crystallization induction time was tested. The crystallization induction time of the treated master batch solution was compared with the crystallization induction time of the reference sample after treatment. When the crystallization induction time of the treated master batch liquid and the crystallization induction time of the treated reference sample both reach the preset release judgment value, it is determined that the treatment result of the master batch liquid is consistent with the treatment result of the reference sample.

10. A production process for automotive urea that effectively delays and reduces crystallization according to claim 9, characterized in that, Record the crystallization induction time, insoluble particle concentration, and crystallization test results of the test samples and reference samples corresponding to multiple batches of master batch solution; Based on the consistency between the crystallization induction time variation trend of the reference sample after treatment in multiple batches and the crystallization induction time variation trend of the corresponding master batch solution after treatment, the adjustment direction of the holding time, cooling rate or circulation filtration time in the subsequent batch improvement treatment process is determined.

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