A low-residue ADC foaming agent and a preparation method thereof

Abstract

This invention relates to a low-residue ADC foaming agent and its preparation method, belonging to the field of foaming agent preparation technology, and includes the following steps: S1: Screening the biuret intermediate through a sieve and placing it in a constant temperature environment for later use to avoid moisture absorption, to obtain a pretreated biuret intermediate; drying chlorine gas for later use; pulverizing and sieving the activator for later use; S2: Adding deionized water and the pretreated biuret intermediate to a container, continuously stirring to form a suspension, adding the activator to the system, and stirring until completely dissolved; S3: Raising the system temperature to 42-45℃, introducing chlorine gas, then switching from continuous to intermittent gas flow, and dynamically adjusting the chlorine gas flow rate, intermittently gasifying until the endpoint; S4: After the reaction reaches the target, purging with nitrogen gas, adding a neutralizing agent to adjust the pH of the system to 6.5-7.5, stirring, pressing and filtering, collecting the filter cake, washing and drying, to obtain the low-residue ADC foaming agent.

Description

Technical Field

[0001] This invention belongs to the field of foaming agent preparation technology, specifically, it relates to a low-residue ADC foaming agent and its preparation method. Background Technology

[0002] Existing azodicarbonamide (ADC) foaming agents face numerous key technical bottlenecks in their application in building profiles, severely restricting their market application and product quality upgrades. In traditional ADC foaming agent preparation processes, the oxidation reaction often employs a continuous aeration mode throughout, making it impossible to dynamically adjust the chlorine gas flow rate according to the reaction progress. This easily leads to over-chlorination or incomplete reactions, resulting in high impurity content in the product, with thermal decomposition residues generally exceeding 5%. These residues directly affect the pore quality of building profiles, causing problems such as uneven pore size and insufficient structural strength. Simultaneously, existing technologies use a single activator with insufficient precise control over its addition amount; some processes even omit the activator addition step, resulting in higher decomposition temperatures and larger fluctuations in gas evolution of the ADC foaming agent, making it difficult to meet the stringent requirements for decomposition temperature and gas evolution stability during building profile processing. Furthermore, the raw material pretreatment process is relatively rudimentary. The biuret intermediate is prone to moisture absorption and clumping, and poor control of chlorine moisture content leads to poor uniformity of the reaction system, further exacerbating the problem of uneven particle size distribution. Some products have a particle size (Dn50) exceeding 18 μm, resulting in poor uniformity. In the post-treatment process, issues such as incomplete dechlorination, insufficient precision in neutralization pH control, and vague washing standards not only introduce additional impurities but also cause the product to absorb moisture and deteriorate, affecting its stability in subsequent use. Simultaneously, some neutralizing agents or activators used in certain processes pose a risk of residue and have poor compatibility, further limiting the application of ADC foaming agents in high-end building profiles. Therefore, there is an urgent need to develop a preparation method that can solve the above problems and achieve large-scale production of ADC foaming agents with low residue, high stability, and uniform particle size.

[0003] Based on this, the present invention provides a low-residue ADC foaming agent and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a low-residue ADC foaming agent and its preparation method to solve the problems mentioned in the background art.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing a low-residue ADC foaming agent includes the following steps:

[0007] S1: The biuret intermediate is sieved through a sieve and placed in a constant temperature environment for later use to obtain a pretreated biuret intermediate; the chlorine gas is dried for later use; the activator is crushed and sieved for later use.

[0008] S2: Add deionized water and pretreated biuret intermediate to a container, stir continuously to form a suspension, add activator to the system, and stir until completely dissolved;

[0009] S3: Raise the system temperature to 42-45℃, introduce chlorine gas, then switch from continuous to intermittent gas flow, and dynamically adjust the chlorine gas flow rate, intermittently gas flow until the endpoint;

[0010] S4: After the reaction reaches the target, purge with nitrogen, add a neutralizing agent to adjust the pH of the system to 6.5-7.5, stir and filter, collect the filter cake and wash and dry it to obtain low-residue ADC foaming agent.

[0011] Furthermore, a method for preparing a low-residue ADC foaming agent includes the following steps:

[0012] S1: The biuret intermediate is screened and placed in a constant temperature environment of 25℃ for later use to avoid moisture absorption, thus obtaining a pretreated biuret intermediate; chlorine gas is dried twice through a silica gel drying tower to ensure that the moisture content is ≤0.03%, and then set aside; the activator is pulverized and then sieved, and then set aside.

[0013] S2: Add deionized water to the container, turn on the stirrer, set the speed to 300-400 r / min, add the pretreated biuret intermediate, and stir continuously for 30 min to form a suspension with a concentration of 200 g / L. During the process, monitor the temperature of the suspension and maintain it at 25-30℃. Then add the activator to the system, keep the stirring speed at 350 r / min, and stir continuously for 15 min until the activator is completely dissolved.

[0014] S3: Raise the system temperature to 42-45℃, introduce chlorine gas, and record the temperature, chlorine content and particle size data every 15 minutes to ensure that the particle size drops below 25μm. Then switch from continuous gas supply to intermittent gas supply and dynamically adjust the chlorine gas flow rate. Continue intermittent gas supply until the endpoint is reached.

[0015] S4: After the reaction reaches the standard, purge with nitrogen, add a neutralizing agent to adjust the pH of the system to 6.5-7.5, stir and filter under pressure, set the pressure to 0.4-0.6 MPa, collect the filter cake and wash it until the washing liquid is titrated with silver nitrate and no chloride ion residue remains; dry the washed filter cake to a moisture content ≤0.3% to obtain low residue ADC foaming agent.

[0016] In step S1 above, each raw material is pretreated to remove impurities, clumps, and moisture through physical processing, ensuring the homogeneity and stability of the reaction system and preventing subsequent reaction imbalances caused by raw material defects. A 100-200 mesh sieve is used for pretreatment of the biuret intermediate. Clumps will lead to uneven dispersion of the suspension, insufficient chlorine content in certain areas during the oxidation reaction, and uneven product particle size. A 100-200 mesh sieve effectively removes clumps, retaining uniform particles. Biuret absorbs moisture and forms hydrogen bonds, and the moisture reacts with chlorine in the oxidation reaction to form HClO, exacerbating side reactions. Maintaining a constant temperature of 25℃, below the critical moisture absorption temperature of biuret (30℃), avoids moisture absorption. Chlorine is dried; if the chlorine moisture content is >0.03%, it will react with the hydroxyl groups on the surface of biuret, reducing reactivity. The generated moisture will also dilute the chlorine content, leading to incomplete reaction. Silica gel desiccant has high adsorption efficiency and can reduce the moisture content to ≤0.03%, ensuring chlorine purity. If activators such as urea and citric acid have excessively large particles, their dissolution rate in the suspension is slow, leading to excessively high local concentrations of the activator and uneven decomposition temperature of the ADC foaming agent. A 180-250 mesh sieve can refine the particles to ≤80μm, accelerating dissolution and ensuring uniform dispersion.

[0017] The purpose of step S2 above is to construct a uniform solid-liquid suspension system, ensuring thorough dispersion of the biuret particles. After the activator dissolves uniformly, it forms a weak interaction with the biuret surface, laying the foundation for subsequent oxidation reactions and decomposition performance regulation. During the process, the suspension concentration is set at approximately 200 g / L. Too low a concentration leads to low reaction efficiency, while too high a concentration causes particle agglomeration. The shear force of mechanical stirring at 300-400 r / min can break up slight agglomeration, maintaining uniform dispersion at a concentration of 200 g / L. Urea and citric acid are selected as activators. These substances contain active groups such as amino and carboxyl groups, which can form weak coordination interactions with the ADC foaming agent molecules, reducing the lattice energy of the ADC and thus lowering the decomposition temperature.

[0018] In step S3 above, the biuret intermediate undergoes an oxidation reaction with chlorine to generate ADC foaming agent, and the reaction formula is as follows: By segmented aeration and dynamic flux adjustment, the reaction rate is controlled to suppress the side reactions of perchlorination producing byproducts (such as cyanuric acid) and the decomposition of ADC into nitrogen and carbon dioxide. The reaction temperature is set between 42-45℃. Below 42℃, the oxidation reaction rate is too slow, the reaction is incomplete, and excessive residual biuret is produced. Above 45℃, the solubility of chlorine decreases, and ADC is easily decomposed, increasing thermal decomposition residues. 42-45℃ represents the equilibrium point between reaction rate and product stability.

[0019] In step S4 above, dechlorination, neutralization, filtration, washing, and drying are performed to remove reaction byproducts such as HCl and excess chlorine, impurities, and moisture, ensuring product purity and storage stability.

[0020] Further, in step S1, the activator is at least one of ammonium bicarbonate, urea, caprolactam, and citric acid.

[0021] Further, in step S1, the amount of activator added is 0.1-2.0 wt% of the mass of the biuret intermediate.

[0022] Further, in step S1, the activator is urea, and the amount added is 0.5-1.5 wt% of the mass of the biuret intermediate.

[0023] Furthermore, in step S3, the initial flow rate of chlorine gas is 0.8-1.0 m³ / h, and the chlorine content of the reaction liquid is monitored in real time to maintain the chlorine content at 0.8-1.2 g / L.

[0024] Further, in step S3, the criteria for determining the transition from continuous ventilation to intermittent ventilation are: when the particle size Dn50 ≤ 25 μm and the chlorine content is consistently measured at 1.0-1.2 g / L for three consecutive tests, the mode conversion program is initiated.

[0025] Further, in step S3, the intermittent ventilation parameters are as follows: 0.2-0.3 m³ of chlorine gas is introduced each time, the ventilation time is 5-10 min, the ventilation interval is 10-20 min, and the cycle is repeated.

[0026] Furthermore, in step S3, the criteria for determining the endpoint are: particle size (Dn50) ≤ 15 μm, gas generation 224-226 mL / g, thermal decomposition residue ≤ 4%, and passing the standard in two consecutive tests.

[0027] Further, in step S4, the pressure filtration is performed at a pressure of 0.4-0.6 MPa for a time of 20-40 minutes.

[0028] Further, in step S4, the neutralizing agent is at least one of sodium bicarbonate, ammonia, potassium carbonate, sodium hydroxide, magnesium hydroxide, and disodium hydrogen phosphate.

[0029] A low-residue ADC foaming agent prepared by the method described above.

[0030] The beneficial effects of this invention are:

[0031] (1) In the technical solution of the present invention, through refined raw material pretreatment, the biuret intermediate is screened for moisture protection and chlorine is dried twice to ensure the consistency and stability of the raw materials, laying a solid foundation for the uniformity of the subsequent reaction and effectively avoiding reaction fluctuations caused by raw material impurities or moisture absorption.

[0032] (2) In the technical solution of the present invention, a continuous ventilation and intermittent ventilation segmented oxidation mode is adopted, combined with dynamic chlorine flow regulation and quantitative conversion standard, which greatly reduces the over-chlorination reaction and decomposition side reaction, reduces the thermal decomposition residue of the product, and significantly improves the opening quality and structural stability of building profiles.

[0033] (3) In the technical solution of this invention, the optimization of the activator system and the precise control of its addition amount not only lowers the decomposition temperature of the ADC foaming agent to match the processing temperature requirements of building profiles, but also stabilizes the gas generation and significantly narrows the fluctuation range, solving the problem of insufficient gas generation stability of existing products. At the same time, the standardized post-treatment process thoroughly removes impurities and moisture from the product through nitrogen dechlorination, precise neutralization, washing without chloride ion residue, and constant temperature and humidity cooling, ensuring the stability of product storage and use.

[0034] (4) In the technical solution of this invention, the equipment used in the preparation method of ADC foaming agent is all conventional configuration in the chemical industry. The raw materials are easy to obtain, the process parameters are clear and controllable, and it is suitable for large-scale industrial production. The production cost is comparable to that of existing processes, but it can produce high-performance products, meet the stringent requirements of high-end building profiles, and has broad market application prospects and significant economic value. The tail gas, wastewater and solid waste in the preparation process are all treated in a standardized manner, which meets the environmental protection requirements. It takes into account both technological advancement and environmental friendliness, and provides reliable technical support for the upgraded application of ADC foaming agent in the field of building profiles. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] The specific parameters of the raw materials used in this invention are as follows:

[0037] Biurea intermediate: Industrial grade, model HL-LDE-01, particle size Dn50≤20μm, purity≥92%, moisture≤0.5%;

[0038] Chlorine: Industrial grade liquid chlorine, purity ≥99.6%, water content ≤0.05%, free impurities;

[0039] Urea: Industrial grade, purity ≥99.5%, particle size ≤500μm, no caking;

[0040] Deionized water: conductivity ≤10μS / cm, pH 6.5-7.5;

[0041] Neutralizing agent: 5wt% sodium carbonate solution, industrial grade, purity ≥98%.

[0042] In the following examples and comparative examples, the tail gas from the oxidation reaction was treated by an absorption tower with a 10wt% sodium hydroxide solution, and the chlorine absorption rate was ≥99.9%; the filtration and washing wastewater was treated by adjusting the pH value to neutral in a neutralization tank and then by a sedimentation tank before entering the sewage treatment system. It was discharged after COD ≤100mg / L. The unqualified products and filter residues generated were collected centrally and entrusted to a professional organization for harmless treatment.

[0043] Example 1

[0044] A method for preparing a low-residue ADC foaming agent includes the following steps:

[0045] S1: The biuret intermediate is screened through a 100-mesh sieve to remove agglomerated particles and placed in a constant temperature environment of 25℃ for later use to avoid moisture absorption, thus obtaining a pretreated biuret intermediate; chlorine gas is dried a second time through a silica gel drying tower to ensure that the moisture content is ≤0.03%, and then set aside; the activator (urea is selected) is pulverized and passed through a 200-mesh sieve, and then set aside.

[0046] S2: Add 500L of deionized water to a 1000L stainless steel oxidation reactor, turn on the stirrer, set the speed to 350r / min, add 100kg of pretreated biuret intermediate, and stir continuously for 30min to form a suspension with a concentration of 200g / L. Monitor the temperature of the suspension during the process and maintain it at 25℃. Then add the pulverized and sieved activator to the system, maintain the stirring speed at 350r / min, and stir continuously for 15min until the activator is completely dissolved. Sampling and observation confirm that there are no solid particles remaining. The amount of activator added is 0.5wt% of the mass of the biuret intermediate.

[0047] S3: Raise the system temperature to 42℃, with temperature fluctuations not exceeding ±1℃, introduce chlorine gas, set the initial chlorine gas introduction rate to 0.8 m³ / h, monitor the chlorine content of the reaction liquid in real time using an online chlorine content monitor, maintain the chlorine content at 0.8 g / L ± 0.01 g / L, continuously introduce gas for the reaction, and record the temperature, chlorine content, and particle size data every 15 minutes to ensure that the particle size (Dn50) drops below 25 μm. When the online particle size analyzer shows Dn50 ≤ 25 μm, and the chlorine content is stable at 1.0 g / L ± 0.01 g / L for 3 consecutive tests, start the mode conversion program to switch from continuous gas introduction to intermittent gas introduction, and dynamically adjust the chlorine gas flow rate, intermittently introducing gas until the endpoint;

[0048] The intermittent ventilation parameters are as follows: 0.2 m³ of chlorine gas is introduced each time, the ventilation time is 5 min, the ventilation interval is 10 min, and the cycle is repeated; the endpoint determination criteria are: particle size (Dn50) ≤ 15 μm, gas generation 225 mL / g, thermal decomposition residue ≤ 4%, and the standard is met in two consecutive tests.

[0049] S4: After the reaction reaches the target, turn off the chlorine supply and purge the reactor with nitrogen (flow rate 1 m³ / h) for 30 minutes to remove residual chlorine. Confirm the chlorine content in the tail gas is ≤0.5 ppm using a chlorine detector. Then, add a neutralizing agent (5 wt% sodium carbonate solution) to the system to adjust the pH to 7.0, stir for 15 minutes to ensure no acidic residue remains in the reaction solution. Start the plate and frame filter press, set the pressure to 0.5 MPa, filter the reaction solution, collect the filter cake, and filter for 30 minutes at 30℃. Wash with deionized water, using 80L each time, until the washing liquid is titrated with silver nitrate and no chloride ion residue remains (test standard: chloride ion content in washing liquid ≤0.001%). Transfer the washed filter cake to a vacuum drying oven, set the drying temperature to 75℃ and the vacuum degree to -0.09MPa, and dry until the moisture content is ≤0.3%. After drying, transfer the product to a constant temperature and humidity storage room (temperature 25℃, humidity ≤40%) to cool to room temperature to avoid moisture absorption and fluctuations in gas evolution, thus obtaining a low-residue ADC foaming agent.

[0050] Example 2

[0051] A method for preparing a low-residue ADC foaming agent includes the following steps:

[0052] S1: The biuret intermediate is screened through a 100-mesh sieve to remove agglomerated particles and placed in a constant temperature environment of 25℃ for later use to avoid moisture absorption, thus obtaining a pretreated biuret intermediate; chlorine gas is dried a second time through a silica gel drying tower to ensure that the moisture content is ≤0.03%, and then set aside; the activator (urea is selected) is pulverized and then passed through a 200-mesh sieve, and then set aside.

[0053] S2: Add 500L of deionized water to a 1000L stainless steel oxidation reactor, turn on the stirrer, set the speed to 350r / min, add 100kg of pretreated biuret intermediate, and stir continuously for 30min to form a suspension with a concentration of 200g / L. Monitor the temperature of the suspension during the process and maintain it at 30℃. Then add the pulverized and sieved activator to the system, maintain the stirring speed at 350r / min, and stir continuously for 15min until the activator is completely dissolved. Sampling and observation confirm that no solid particles remain. The amount of activator added is 1.0wt% of the mass of the biuret intermediate.

[0054] S3: Raise the system temperature to 45℃, with temperature fluctuations not exceeding ±1℃, introduce chlorine gas, set the initial chlorine gas introduction rate to 0.8 m³ / h, monitor the chlorine content of the reaction liquid in real time using an online chlorine content monitor, maintain the chlorine content at 1.0 g / L ± 0.01 g / L, continuously introduce gas for the reaction, and record the temperature, chlorine content, and particle size data every 15 minutes to ensure that the particle size (Dn50) drops below 25 μm. When the online particle size analyzer shows Dn50 ≤ 25 μm, and the chlorine content is stable at 1.0 g / L ± 0.01 g / L for 3 consecutive tests, start the mode conversion program to switch from continuous gas introduction to intermittent gas introduction, and dynamically adjust the chlorine gas flow rate, intermittently introducing gas until the endpoint;

[0055] The intermittent ventilation parameters are as follows: 0.2 m³ of chlorine gas is introduced each time, the ventilation time is 10 min, the ventilation interval is 20 min, and the cycle is repeated; the endpoint determination criteria are: particle size (Dn50) ≤ 15 μm, gas generation 225 mL / g, thermal decomposition residue ≤ 4%, and the standard is met in two consecutive tests.

[0056] S4: After the reaction reaches the target, turn off the chlorine supply and purge the reactor with nitrogen (flow rate 1 m³ / h) for 30 minutes to remove residual chlorine. Confirm the chlorine content in the tail gas is ≤0.5 ppm using a chlorine detector. Then, add a neutralizing agent (5 wt% sodium carbonate solution) to the system to adjust the pH to 7.0, stir for 15 minutes to ensure no acidic residue remains in the reaction solution. Start the plate and frame filter press, set the pressure to 0.5 MPa, filter the reaction solution, collect the filter cake, and filter for 30 minutes at 30℃. Wash with deionized water, using 80L each time, until the washing liquid is titrated with silver nitrate and no chloride ion residue remains (test standard: chloride ion content in washing liquid ≤0.001%). Transfer the washed filter cake to a vacuum drying oven, set the drying temperature to 75℃ and the vacuum degree to -0.09MPa, and dry until the moisture content is ≤0.3%. After drying, transfer the product to a constant temperature and humidity storage room (temperature 25℃, humidity ≤40%) to cool to room temperature to avoid moisture absorption and fluctuations in gas evolution, thus obtaining a low-residue ADC foaming agent.

[0057] Example 3

[0058] A method for preparing a low-residue ADC foaming agent includes the following steps:

[0059] S1: The biuret intermediate is screened through a 100-mesh sieve to remove agglomerated particles and placed in a constant temperature environment of 25℃ for later use to avoid moisture absorption, thus obtaining a pretreated biuret intermediate; chlorine gas is dried a second time through a silica gel drying tower to ensure that the moisture content is ≤0.03%, and then set aside; the activator (urea is selected) is pulverized and then passed through a 200-mesh sieve, and then set aside.

[0060] S2: Add 500L of deionized water to a 1000L stainless steel oxidation reactor, turn on the stirrer, set the speed to 350r / min, add 100kg of pretreated biuret intermediate, and stir continuously for 30min to form a suspension with a concentration of 200g / L. Monitor the temperature of the suspension during the process and maintain it at 30℃. Then add the pulverized and sieved activator to the system, maintain the stirring speed at 350r / min, and stir continuously for 15min until the activator is completely dissolved. Sampling and observation confirm that no solid particles remain. The amount of activator added is 1.5wt% of the mass of the biuret intermediate.

[0061] S3: Raise the system temperature to 45℃, with temperature fluctuations not exceeding ±1℃, introduce chlorine gas, set the initial chlorine gas introduction rate to 0.8 m³ / h, monitor the chlorine content of the reaction liquid in real time using an online chlorine content monitor, maintain the chlorine content at 1.2 g / L ± 0.01 g / L, continuously introduce gas for the reaction, and record the temperature, chlorine content, and particle size data every 15 minutes to ensure that the particle size (Dn50) drops below 25 μm. When the online particle size analyzer shows Dn50 ≤ 25 μm, and the chlorine content is stable at 1.0 g / L ± 0.01 g / L for 3 consecutive tests, start the mode conversion program to switch from continuous gas introduction to intermittent gas introduction, and dynamically adjust the chlorine gas flow rate, intermittently introducing gas until the endpoint;

[0062] The intermittent ventilation parameters are as follows: 0.3 m³ of chlorine gas is introduced each time, the ventilation time is 10 min, the ventilation interval is 20 min, and the cycle is repeated; the endpoint determination criteria are: particle size (Dn50) ≤ 15 μm, gas generation 225 mL / g, thermal decomposition residue ≤ 4%, and the standard is met in two consecutive tests.

[0063] S4: After the reaction reaches the target, turn off the chlorine supply and purge the reactor with nitrogen (flow rate 1 m³ / h) for 30 minutes to remove residual chlorine. Confirm the chlorine content in the tail gas is ≤0.5 ppm using a chlorine detector. Then, add a neutralizing agent (5 wt% sodium carbonate solution) to the system to adjust the pH to 7.0, stir for 15 minutes to ensure no acidic residue remains in the reaction solution. Start the plate and frame filter press, set the pressure to 0.5 MPa, filter the reaction solution, collect the filter cake, and filter for 30 minutes at 30℃. Wash with deionized water, using 80L each time, until the washing liquid is titrated with silver nitrate and no chloride ion residue remains (test standard: chloride ion content in washing liquid ≤0.001%). Transfer the washed filter cake to a vacuum drying oven, set the drying temperature to 75℃ and the vacuum degree to -0.09MPa, and dry until the moisture content is ≤0.3%. After drying, transfer the product to a constant temperature and humidity storage room (temperature 25℃, humidity ≤40%) to cool to room temperature to avoid moisture absorption and fluctuations in gas evolution, thus obtaining a low-residue ADC foaming agent.

[0064] Example 4

[0065] The difference between this embodiment and embodiment 3 is that the activator used in this embodiment is citric acid, and the amount added is 0.3 wt% of the mass of the biuret intermediate.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 3 is that the switching between continuous and intermittent ventilation is eliminated, and continuous ventilation oxidation is used throughout the process. The remaining steps and raw materials are the same as in Example 3. Specifically, the operation of step S3 in this comparative example is as follows:

[0068] S3: Raise the system temperature to 45℃, with temperature fluctuation not exceeding ±1℃, introduce chlorine gas, set the initial chlorine gas introduction rate to 0.8m³ / h, monitor the chlorine content of the reaction liquid in real time using an online chlorine content detector, maintain the chlorine content at 1.2g / L±0.01g / L, maintain continuous aeration throughout the process, do not start the intermittent aeration mode, record the temperature, chlorine content and particle size data every 15min until the endpoint judgment criteria are met (particle size Dn50≤15μm, gas generation 225mL / g, thermal decomposition residue ≤4%, two consecutive tests meet the criteria).

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 3 is that step S2 skips the activation step and directly proceeds to the oxidation reaction in step S3. Specifically, the operation of step S2 in this comparative example is as follows:

[0071] S2: Add 500L of deionized water to a 1000L stainless steel oxidation reactor, turn on the stirrer, set the speed to 350r / min, add 100kg of pretreated biuret intermediate, and stir continuously for 30min to form a suspension with a concentration of 200g / L. Monitor the temperature of the suspension during the process and maintain it at 30℃. Then proceed directly to the S3 oxidation reaction stage.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 3 is that the chlorine flow rate is fixed in this comparative example and is not dynamically adjusted. Specifically, the operation of step S3 in this comparative example is as follows:

[0074] S3: Raise the system temperature to 45℃, with temperature fluctuations not exceeding ±1℃, introduce chlorine gas, and set the chlorine gas introduction rate to a fixed 0.8m³ / h. Do not adjust the flow rate according to the chlorine content of the reaction liquid throughout the process. Record the temperature, chlorine content, and particle size data every 15 minutes. When the online particle size analyzer shows Dn50≤25μm and the chlorine content is stable at 1.0g / L±0.01g / L for 3 consecutive tests, start the intermittent ventilation mode until the endpoint.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Example 3 is that the neutralization pH value is set to 8.0 in this comparative example. Specifically, the specific operation of step S4 in this comparative example is as follows:

[0077] S4: After the reaction reaches the target, turn off the chlorine supply and introduce nitrogen gas (flow rate 1 m³ / h) into the reactor to purge for 30 min to remove residual chlorine. Confirm the chlorine content in the tail gas is ≤0.5 ppm using a chlorine detector. Then add a neutralizing agent (5 wt% sodium carbonate solution) to the system, adjust the pH value of the system to 8.0, stir for 15 min, and the remaining operations such as pressure filtration, washing, and drying are the same as in Example 3.

[0078] The performance of the low-residue ADC foaming agents prepared in Examples 1-4 and Comparative Examples 1-4 was tested; the specific test items and methods are as follows:

[0079] (1) Gas generation: Refer to the standard GB / T16773-2014, use the water displacement method for testing, use 5g of sample, test temperature 200℃, conduct 3 parallel tests, and record the average value.

[0080] (2) Decomposition temperature: The differential scanning calorimeter was used to test the temperature in a nitrogen atmosphere. The heating rate was 10℃ / min and the test range was 180-220℃. The peak decomposition temperature was recorded.

[0081] (3) Thermal decomposition residue: The muffle furnace ignition method was used for testing. The sample amount was 2g, the ignition temperature was 550℃, the holding time was 2h, and after cooling to room temperature, the residual mass was weighed and the residual mass percentage was calculated.

[0082] (4) Foaming performance test:

[0083] (4.1) Foaming stability test: 10g of the low residual ADC foaming agent prepared in Examples 1-4 and Comparative Examples 1-4 were taken as samples, and the gas generation was tested in 5 tests. The relative standard deviation of the 5 test results was calculated.

[0084] (4.2) Foaming pore size uniformity test: The low residual ADC foaming agent samples prepared in Examples 1-4 and Comparative Examples 1-4 were mixed with PVC resin at a mass ratio of 1:100. The PVC resin used was commercially available SG-5 type polyvinyl chloride resin. The samples were injection molded into standard samples with a size of 100mm×10mm×2mm. After slicing, the cross-section was observed using a scanning electron microscope, and the coefficient of variation of 50 pore sizes was statistically analyzed.

[0085] The test results for gas generation, decomposition temperature and thermal decomposition residue are shown in Table 1, and the test results for foaming performance are shown in Table 2.

[0086] Table 1. Test results of gas production, decomposition temperature, and thermal decomposition residue.

[0087]

[0088] Table 2 Foaming performance test results

[0089]

[0090] As can be seen from the results in Tables 1 and 2, Examples 1, 2, 3 and 4 all exhibit excellent comprehensive performance, demonstrating the scientific nature and effectiveness of the technical solution of the present invention.

[0091] A comparison of the results from Example 3 and Comparative Example 1 shows that the Example 3, employing a segmented mode of continuous and intermittent ventilation, precisely controls the reaction process through quantitative conversion standards, effectively suppressing the overchlorination reaction and decomposition side reactions, significantly outperforming Comparative Example 1, which uses a continuous ventilation scheme throughout the process. This indicates that the segmented reaction mode can achieve dynamic matching between reaction intensity and material conversion efficiency, avoiding local reaction imbalances caused by a single reaction mode.

[0092] A comparison of the results from Examples 1-4 and Comparative Example 2 shows that Examples 1-3 used urea as an activator, and Example 4 used citric acid as an activator. Both examples achieved a precise match between decomposition temperature and gas generation by adjusting decomposition kinetics, with a gas generation stability RSD ≤ 0.5%. However, Comparative Example 2 had a decomposition temperature as high as 210℃, resulting in decreased gas generation stability. This highlights the synergistic effect between the activator system and the reaction system, providing key technical support for adapting foaming agents to the processing temperature of building profiles.

[0093] The results of Example 3 and Comparative Example 3 show that Example 3, by adjusting the chlorine flow rate in real time based on chlorine content feedback, ensured that the chlorine concentration in the reaction system remained stable at 0.8-1.2 g / L, providing a stable reaction environment for reducing residue. In contrast, Comparative Example 3, which used a fixed flow rate, experienced uneven reaction due to fluctuations in chlorine content, resulting in a residue increase to 4.5%. This demonstrates that dynamic control strategy is the core guarantee for improving product uniformity.

[0094] The results of Example 3 and Comparative Example 4 show that the Example strictly controlled the neutralization pH in the range of 6.5-7.5, avoiding product hydrolysis and impurity residue. Comparative Example 4 (pH=8.0) caused slight hydrolysis due to excessive neutralization, and the gas generation dropped to 220mL / g. This proves that the standardized post-processing process is an important link to ensure product stability.

[0095] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0096] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined by the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A process for the preparation of a low residue ADC blowing agent characterized in that, Includes the following steps: S1: The biuret intermediate is sieved through a sieve and placed in a constant temperature environment for later use to obtain a pretreated biuret intermediate; the chlorine gas is dried for later use; the activator is crushed and sieved for later use. S2: Add deionized water and pretreated biuret intermediate to a container, stir continuously to form a suspension, add activator to the system, and stir until completely dissolved; S3: Raise the system temperature to 42-45℃, introduce chlorine gas, then switch from continuous to intermittent gas flow, and dynamically adjust the chlorine gas flow rate, intermittently gas flow until the endpoint; S4: After the reaction reaches the target, purge with nitrogen, add a neutralizing agent to adjust the pH of the system to 6.5-7.5, stir and filter, collect the filter cake and wash and dry it to obtain low-residue ADC foaming agent.

2. A process for the preparation of a low residue ADC blowing agent according to claim 1, characterized in that, In step S1, the activator is at least one of ammonium bicarbonate, urea, caprolactam, and citric acid, and the amount of activator added is 0.1-2.0 wt% of the mass of the biuret intermediate.

3. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S1, the activator is urea, and the amount added is 0.5-1.5 wt% of the mass of the biuret intermediate.

4. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S3, chlorine gas is introduced at an initial rate of 0.8-1.0 m³ / h, and the chlorine content in the reaction liquid is monitored in real time to maintain it at 0.8-1.2 g / L.

5. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S3, the criteria for determining the transition from continuous ventilation to intermittent ventilation are: when the particle size Dn50 ≤ 25 μm and the chlorine content is consistently between 1.0-1.2 g / L for three consecutive tests, the mode switching procedure is initiated.

6. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S3, the intermittent ventilation parameters are as follows: 0.2-0.3 m³ of chlorine gas is introduced each time, the ventilation time is 5-10 min, the ventilation interval is 10-20 min, and the cycle is repeated.

7. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S3, the criteria for determining the endpoint are: particle size (Dn50) ≤ 15 μm, gas generation 224-226 mL / g, thermal decomposition residue ≤ 4%, and two consecutive tests meeting the criteria.

8. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S4, the pressure filtration is performed at a pressure of 0.4-0.6 MPa for a time of 20-40 minutes.

9. The method for preparing a low-residue ADC foaming agent according to claim 1, characterized in that, In step S4, the neutralizing agent is at least one of sodium bicarbonate, ammonia, potassium carbonate, sodium hydroxide, magnesium hydroxide, and disodium hydrogen phosphate.

10. A low-residue ADC foaming agent prepared by the preparation method according to any one of claims 1-9.

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