Molecular regulation-based modification method and process for ADC foaming agent

Abstract

This invention discloses a molecularly controlled method and process for modifying ADC foaming agents, belonging to the field of ADC foaming agent modification technology. The method involves adding biuret mortar, sodium bromide, and glyoxal modifier to an oxidation reactor to form a dispersed suspension. Under controlled temperature, stirring, and circulating dispersion conditions, chlorine gas is continuously introduced, with the chlorine gas flow rate sequentially adjusted, causing biuret to oxidize into azodicarbonamide in the chlorine-bromine oxidation system. Glyoxal is used to regulate the hypochlorous acid concentration and oxidation reaction rate, reduce the instantaneous supersaturation of the liquid phase, inhibit explosive nucleation and secondary crystal nucleation, and promote the orderly growth of ADC crystals. After the reaction, the mixture is rinsed, centrifuged, washed, dried, and cyclone-screened to obtain a large-particle-size ADC foaming agent with a D50 of 19.5 ± 3 μm. This method can reduce overchlorination and side reactions, narrow the particle size distribution, and is suitable for foaming materials such as XPE.

Description

Technical Field

[0001] This invention relates to the field of chemical foaming agent preparation and modification technology, and more specifically, to a method and process for modifying ADC foaming agents based on molecular regulation. Background Technology

[0002] Azodicarbonamide, or ADC blowing agent for short, is a widely used chemical blowing agent. It can be used in the foaming process of materials such as polyethylene, polyvinyl chloride, polypropylene, ABS resin, and rubber to impart properties such as lightweight, cushioning, resilience, and thermal and sound insulation to foamed products. With the continuous expansion of the application fields of plastic products, rubber products, and composite foam materials, downstream users have put forward higher requirements for the decomposition characteristics, particle size distribution, dispersibility, foaming ratio, cell uniformity, and processing adaptability of ADC blowing agents.

[0003] Existing ADC foaming agent products typically require modification for different downstream systems. For example, in EVA, PE, and PP secondary foaming and cross-linking foaming systems, the particle size and particle size distribution of the foaming agent directly affect its dispersion state, decomposition synchronization, and cell structure in the resin matrix. In XPE foam materials, if the ADC powder particle size is too small or the particle size distribution is too wide, it can easily lead to uneven local foaming, insufficient cell stability, or a narrowed processing window. Therefore, ADC manufacturers are gradually shifting from supplying single products to providing foaming solutions for different application scenarios, and have conducted extensive research in areas such as surface modification, compound synergy, low-dust granulation, and particle size control.

[0004] Currently, most commercially available methods for modifying ADC foaming agents involve secondary processing after the ADC powder is obtained. These processes include surface treatment, additive compounding, coating, granulation, or post-mixing to improve the dispersibility, decomposition temperature, or dust characteristics of the foaming agent. While these methods can improve product performance to some extent, their main effect occurs after the powder is produced. They have limited control over the nucleation and growth behavior of ADC crystals during the oxidation reaction, making it difficult to stably obtain ADC powder with a specific particle size and narrow distribution from the reaction-crystallization source.

[0005] Existing technologies also include methods for directly controlling particle size during ADC preparation. For example, Jiangsu Suopu Chemical Co., Ltd.'s CN109734629B discloses a method for preparing a uniformly dispersed ultrafine ADC foaming agent, which controls the ADC particle size and prepares an ultrafine ADC foaming agent with uniform particle size by adding a surfactant to reduce the Gibbs free energy of the ADC crystals; Hangzhou Haihong Fine Chemical Co., Ltd.'s patent 201210358003.3 discloses a method for preparing an ADC foaming agent with uniform particle size by adding inorganic acid and ultrafine ADC foaming agent powder seed crystals in the biuret oxidation process; other technologies control the particle size of the ADC foaming agent by adding melamine-formaldehyde prepolymer microspheres, surfactants containing phosphate ester groups, β-cyclodextrin, and other components in the oxidation process.

[0006] However, most of the aforementioned technologies focus on the miniaturization, homogenization, or dispersion improvement of ADC particles, with the goal of obtaining ADC products with small or ultrafine particle sizes. For ADC blowing agents with uniform distribution and large particle size required for foaming systems such as XPE, existing technologies are scarce. Especially in acidic or weakly alkaline ADC production processes, the D50 of the dried ADC powder obtained by chlorine oxidation of biurea is typically concentrated around 12-17 μm. If relying solely on conventional oxidation conditions, the system is prone to generating a large number of fine crystal nuclei due to excessively rapid local oxidation rates and high instantaneous supersaturation, resulting in insufficient crystal growth time and making it difficult to stably obtain ADC products with large particle sizes and narrow distributions.

[0007] Therefore, there is an urgent need to provide molecularly regulated methods and processes for modifying ADC foaming agents to solve these problems. Summary of the Invention

[0008] The purpose of this invention is to solve the technical problems mentioned in the background section and to provide a method and process for modifying ADC foaming agents based on molecular regulation.

[0009] The above-mentioned objective of this invention is achieved as follows: a method for modifying an ADC foaming agent based on molecular regulation, comprising mixing biuret with an aqueous system containing sodium bromide to form a suspension, adding glyoxal modifier to the suspension, and introducing chlorine gas to carry out an oxidation reaction, thereby oxidizing biuret to generate azodicarbonamide; wherein, the glyoxal modifier is used to regulate the concentration of hypochlorous acid and the oxidation reaction rate in the chlorine-bromine oxidation system, reduce the instantaneous supersaturation of the liquid phase, inhibit explosive nucleation, and promote the growth of azodicarbonamide crystals on the surface of existing crystal nuclei, thereby obtaining a large-particle-size ADC foaming agent.

[0010] As a preferred technical solution of the present invention, the molecular formula of the biuret is NH2CONHNHCONH2, and the structural formula of the azodicarbonamide is NH2CON=NCONH2.

[0011] As a preferred technical solution of the present invention, the glyoxal modifier is prepared by diluting a 40% glyoxal solution with water to a 20% glyoxal solution.

[0012] As a preferred technical solution of the present invention, the glyoxal meets the following quality indicators: acid content (calculated as acetic acid) is less than 0.8%, pH is greater than 1.5, ash content is less than 0.1%, and specific gravity at 20 / 20℃ is 1.26-1.31.

[0013] As a preferred embodiment of the present invention, the D50 of the large particle size ADC foaming agent is 19.5±3μm.

[0014] This invention also provides a molecularly controlled ADC foaming agent production process, comprising the following steps:

[0015] S1. After centrifuging and washing the biuret intermediate, add water containing sodium bromide to make a slurry, and then send it into an oxidation reactor to adjust the concentration with water.

[0016] S2. Dilute the glyoxal solution with water to prepare a glyoxal modifier solution;

[0017] S3. Add the mortar obtained in step S1 and the glyoxal modifier solution obtained in step S2 into the oxidation reactor, turn on the stirring and start the circulation pump to make the materials form a dispersed suspension, and control the temperature of the oxidation reactor at the same time.

[0018] S4. Chlorine gas is continuously introduced into the dispersed suspension, and the amount of chlorine gas introduced is changed sequentially according to different reaction stages, so that biuret is oxidized in the chlorine-bromine oxidation system to generate azodicarbonamide;

[0019] S5. After the reaction is complete, the reaction solution is rinsed, centrifuged, washed, dried and cyclone screened to obtain ADC foaming agent.

[0020] As a preferred technical solution of the present invention, in step S1, the mass concentration of biuret in the mortar is 26.4%.

[0021] As a preferred technical solution of the present invention, in step S3, the temperature of the oxidation kettle is controlled at 20°C before chlorine gas is introduced, and the reaction temperature is controlled at 40°C after chlorine gas is introduced; after adding mortar and glyoxal modifier solution, the mixture is first stirred at 30 r / min and dispersed by circulating pump, and the stirring speed is increased to 100 r / min before chlorine gas is introduced.

[0022] As a preferred technical solution of the present invention, in step S4, the sequential conversion of chlorine gas flow rate includes: introducing chlorine gas at 50 kg / h for 20 min, introducing chlorine gas at 250 kg / h for 60 min, introducing chlorine gas at 400 kg / h for 200 min, introducing chlorine gas at 300 kg / h for 30 min, and then introducing chlorine gas at 150 kg / h until the reaction endpoint.

[0023] As a preferred technical solution of the present invention, in step S4, the reaction endpoint is determined comprehensively based on the redox potential, the color change of the tail gas caused by the escape of bromine, the pressure of the oxidation reactor, and the residual biuret content in the slurry, and the redox potential at the end of the reaction is not lower than 800mV.

[0024] Compared with the prior art, the present invention adds glyoxal modifier to the process of preparing ADC by biuret chlorine oxidation. By utilizing the consumption effect of glyoxal on hypochlorous acid in the system, the local strong oxidation process of chlorine-bromine oxidation system is buffered, the oxidation reaction rate and the instantaneous supersaturation of the liquid phase are reduced, thereby reducing the occurrence of explosive nucleation and excessive oxidation side reactions from the source.

[0025] This invention reduces the generation of secondary crystal nuclei by selectively adsorbing glyoxal and its oxidation products onto high-energy sites of ADC crystals. Combined with the regulation of the bromide ion-bromine molecule catalytic cycle, ADC molecules preferentially grow slowly and orderly on the surface of existing crystal nuclei, thereby obtaining an ADC foaming agent with larger particle size and narrower particle size distribution.

[0026] This invention combines sequential conversion of chlorine gas flow rate, temperature control, stirring dispersion, and ORP endpoint control to achieve synergistic regulation of the oxidation reaction process and the crystal growth process. The resulting ADC foaming agent D50 can reach 19.5±3μm, which can better adapt to secondary foaming and cross-linking foaming of EVA, PE, and PP, and is especially suitable for XPE foaming materials. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the molecular regulation-based ADC foaming agent modification method and production process of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Any equivalent substitutions or conventional adjustments made based on the technical concept of the present invention—namely, the use of glyoxal to regulate the chlorine-bromine oxidation system, reduce the oxidation reaction rate, and regulate the growth of ADC crystals—should be included within the scope of protection of the present invention.

[0029] like Figure 1As shown, the production process of this invention uses biuret slurry preparation and glyoxal modifier preparation as preliminary steps. After stirring and dispersing, circulating mass transfer and temperature control, a reaction suspension system is formed. Then, the oxidation reaction is completed by sequential conversion of chlorination. The endpoint is determined by combining ORP, tail gas color, oxidation kettle pressure and residual biuret content. Finally, the large particle size ADC foaming agent is obtained by rinsing, centrifugation, washing, drying and cyclone screening.

[0030] The ADC foaming agent described in this invention is azodicarbonamide. Biuret is oxidized to azodicarbonamide in a chlorine-bromine oxidation system, and its main reaction can be represented as follows:

[0031] NH2CONHNHCONH2+Cl2→NH2CON=NCONH2+2HCl

[0032] Wherein, NH₂CONHNHCONH₂ is biuret, and NH₂CON=NCONH₂ is azodicarbonamide. When chlorine gas is introduced into the aqueous system, the following equilibrium reaction occurs:

[0033] Cl₂ + H₂O ⇌ HCl + HClO

[0034] In an acidic oxidizing environment, glyoxal can react with hypochlorous acid in the system, and the reaction can be represented as follows:

[0035] 2OHC-CHO+3HClO+2H⁺→2CO2+3HCl+3H2O

[0036] Therefore, glyoxal can preferentially consume some of the hypochlorous acid in the system, buffer the chlorine oxidation process, reduce the instantaneous supersaturation of the liquid system, and inhibit the explosive nucleation of ADC crystals. At the same time, glyoxal and its oxidation products can selectively adsorb onto the high-energy sites of ADC crystals, reduce the generation of secondary crystal nuclei, and by regulating the catalytic cycle of bromide ions and bromine molecules, make ADC molecules more inclined to grow slowly and orderly on the surface of existing crystal nuclei, thereby obtaining ADC foaming agents with larger particle size and narrower distribution.

[0037] Combination Figure 1 In one specific embodiment, a method for modifying an ADC foaming agent based on molecular regulation includes: mixing biuret with an aqueous system containing sodium bromide to form a suspension; adding glyoxal modifier to the suspension; and introducing chlorine gas into the system to carry out an oxidation reaction, thereby oxidizing biuret to azodicarbonamide. The glyoxal modifier, by regulating the concentration of hypochlorous acid and the oxidation reaction rate in the chlorine-bromine oxidation system, prevents the generated ADC molecules from instantaneously precipitating as a large number of fine crystal nuclei, but instead preferentially continues to grow on the surface of existing crystal nuclei, thus obtaining a large-particle-size ADC foaming agent with a D50 of 19.5 ± 3 μm.

[0038] according to Figure 1 The process flow shown, in one specific production process, involves first centrifuging and washing the biuret intermediate, then adding dissolved water containing sodium bromide to prepare biuret slurry. This slurry is then fed into an oxidation reactor where water is added to adjust the concentration, resulting in a biuret mass concentration of 26.4%. Next, a 40% glyoxal solution is diluted with water to prepare a 20% glyoxal modifier solution. The glyoxal preferably meets the following specifications: acid content (based on acetic acid) below 0.8%, pH above 1.5, ash content below 0.1%, and specific gravity at 20 / 20℃ of 1.26-1.31.

[0039] In one specific embodiment, a method for modifying an ADC foaming agent based on molecular regulation includes: mixing biuret with an aqueous system containing sodium bromide to form a suspension; adding glyoxal modifier to the suspension; and introducing chlorine gas into the system to carry out an oxidation reaction, thereby oxidizing biuret to azodicarbonamide. The glyoxal modifier, by regulating the concentration of hypochlorous acid and the oxidation reaction rate in the chlorine-bromine oxidation system, prevents the generated ADC molecules from instantaneously precipitating as numerous fine crystal nuclei, but instead preferentially continues to grow on the surface of existing crystal nuclei, thus obtaining a large-particle-size ADC foaming agent with a D50 of 19.5 ± 3 μm.

[0040] In one specific production process, the biuret intermediate is first centrifuged and washed, then dissolved in water containing sodium bromide to prepare biuret slurry. This slurry is then fed into an oxidation reactor where water is added to adjust the concentration, resulting in a biuret mass concentration of 26.4%. Next, a 40% glyoxal solution is diluted with water to prepare a 20% glyoxal modifier solution. The glyoxal preferably meets the following specifications: acid content (based on acetic acid) below 0.8%, pH above 1.5, ash content below 0.1%, and specific gravity at 20 / 20℃ of 1.26-1.31.

[0041] Subsequently, biuret slurry and glyoxal modifier solution are added to the oxidation reactor. The stirring device is turned on, and the oxidation reactor circulation pump is started to ensure that biuret, sodium bromide, and glyoxal are fully dispersed in the aqueous system to form a dispersion suspension. Before introducing chlorine gas, the oxidation reactor temperature is controlled at 20°C, and a cooling medium is introduced through the oxidation reactor jacket to maintain the oxidation reactor temperature within the range of 10-40°C during the reaction. After introducing chlorine gas, the reaction temperature is preferably controlled at 40°C. After adding the materials, the stirring and dispersion can be carried out at 30 r / min, and mass transfer can be enhanced by the circulation pump. Before introducing chlorine gas, the stirring speed of the oxidation reactor is increased to 100 r / min to ensure that the oxidation reaction and crystallization process proceed uniformly.

[0042] When introducing chlorine gas, a sequential switching method is used to control the amount of chlorine added. Specifically, chlorine gas is first introduced at a rate of 50 kg / h for 20 min to allow the system to smoothly enter the oxidation stage; then, chlorine gas is introduced at a rate of 250 kg / h for 60 min to increase the oxidation rate of biurea; subsequently, chlorine gas is introduced at a rate of 400 kg / h for 200 min to allow the oxidation reaction to continue; then, chlorine gas is introduced at a rate of 300 kg / h for 30 min; finally, chlorine gas is introduced at a rate of 150 kg / h to reach the endpoint. This staged chlorination method avoids over-chlorination and localized severe oxidation caused by instantaneous excess of oxidant. Combined with the regulatory effect of glyoxal on hypochlorous acid and crystal growth, this results in an increase in the particle size of ADC crystals and a narrowing of the particle size distribution.

[0043] The reaction endpoint can be determined comprehensively based on the redox potential, the color change of the tail gas caused by the escape of elemental bromine, the pressure of the oxidation reactor, and the residual biuret content in the slurry. Preferably, the reaction ends when the redox potential reaches or exceeds 800mV, combined with the tail gas color, reactor pressure, and residual biuret detection results. After the reaction, the reaction solution is sent to a slurry washing tank and centrifugation process for solid-liquid separation. The collected solid phase is then washed, dried, and cyclone-screened to obtain large-particle-size ADC foaming agent. The obtained ADC foaming agent can be used for secondary foaming or cross-linking foaming of EVA, PE, and PP, and is especially suitable for XPE foaming materials.

[0044] Example 1: 8 tons of water, 3 tons of biuret, and 150 kg of sodium bromide were added to a 32 m³ stainless steel slurry mixing tank and mechanically stirred until uniformly mixed to obtain biuret slurry. Separately, 170 kg of hot water and 170 kg of a 40% glyoxal solution were added to a 2 m³ stainless steel liquid mixing tank and stirred for 30 min to prepare a 20% glyoxal modifier solution. 8 tons of deionized water were added to a 20 m³ oxidation reactor, the stirring device was turned on, and the speed was set to 30 r / min. The biuret slurry and glyoxal modifier solution were added, and stirring was continued. The circulation pump was started, and the circulation flow rate was adjusted to Q = 40 m³ / h. The jacket coolant temperature was controlled at 20°C.

[0045] Subsequently, the stirring speed of the oxidation reactor was increased to 100 r / min, the chlorine valve was opened, and chlorine gas was continuously introduced. The chlorine gas introduction procedure was as follows: chlorine gas was introduced at 50 kg / h for 20 min, chlorine gas at 250 kg / h for 60 min, chlorine gas at 400 kg / h for 200 min, chlorine gas at 300 kg / h for 30 min, and then chlorine gas was introduced at 150 kg / h for 100 min. When the oxidation-reduction potential reached 810 mV, the chlorine gas introduction was stopped. After the reaction was completed, the liquid was sent to a slurry washing tank and centrifugation process for solid-liquid separation. The solid phase was washed, dried, and cyclone screened to obtain the ADC foaming agent. The DV(50) of the obtained ADC foaming agent was tested to be 19.1 μm, and the particle size was within the target range of 19.5 ± 3 μm for large particle size ADC foaming agents.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for modifying ADC foaming agents based on molecular regulation, characterized in that, A suspension is formed by mixing biuret with an aqueous system containing sodium bromide. Glyoxal modifier is added to the suspension, and chlorine gas is introduced to carry out an oxidation reaction, causing biuret to be oxidized to azodicarbonamide. The glyoxal modifier is used to regulate the concentration of hypochlorous acid and the oxidation reaction rate in the chlorine-bromine oxidation system, reduce the instantaneous supersaturation of the liquid phase, inhibit explosive nucleation, and promote the growth of azodicarbonamide crystals on the surface of existing crystal nuclei, thereby obtaining a large-particle-size ADC foaming agent.

2. The method for modifying the ADC foaming agent according to claim 1, characterized in that, The molecular formula of the biuret is NH2CONHNHCONH2, and the structural formula of the azodicarbonamide is NH2CON=NCONH2.

3. The method for modifying the ADC foaming agent according to claim 1, characterized in that, The glyoxal modifier is prepared by diluting a 40% glyoxal solution with water to a 20% glyoxal solution.

4. The method for modifying the ADC foaming agent according to claim 1, characterized in that, The glyoxal meets the following quality indicators: acid content (calculated as acetic acid) is less than 0.8%, pH is greater than 1.5, ash content is less than 0.1%, and specific gravity at 20 / 20℃ is 1.26-1.

31.

5. The method for modifying the ADC foaming agent according to claim 1, characterized in that, The D50 of the large particle size ADC foaming agent is 19.5±3μm.

6. A molecularly controlled ADC foaming agent production process, characterized in that, Includes the following steps: S1. After centrifuging and washing the biuret intermediate, add water containing sodium bromide to make a slurry, and then send it into an oxidation reactor to adjust the concentration with water. S2. Dilute the glyoxal solution with water to prepare a glyoxal modifier solution; S3. Add the mortar obtained in step S1 and the glyoxal modifier solution obtained in step S2 into the oxidation reactor, turn on the stirring and start the circulation pump to make the materials form a dispersed suspension, and control the temperature of the oxidation reactor at the same time. S4. Chlorine gas is continuously introduced into the dispersed suspension, and the amount of chlorine gas introduced is changed sequentially according to different reaction stages, so that biuret is oxidized in the chlorine-bromine oxidation system to generate azodicarbonamide; S5. After the reaction is complete, the reaction solution is rinsed, centrifuged, washed, dried and cyclone screened to obtain ADC foaming agent.

7. The ADC foaming agent production process according to claim 6, characterized in that, In step S1, the mass concentration of biuret in the mortar is 26.4%.

8. The ADC foaming agent production process according to claim 6, characterized in that, In step S3, the temperature of the oxidation reactor is controlled at 20°C before chlorine is introduced, and the reaction temperature is controlled at 40°C after chlorine is introduced. After adding mortar and glyoxal modifier solution, the mixture is first stirred at 30 r / min and dispersed by circulating pump. Before chlorine is introduced, the stirring speed is increased to 100 r / min.

9. The ADC foaming agent production process according to claim 6, characterized in that, In step S4, the sequential conversion of chlorine gas flow rate includes: introducing chlorine gas at 50 kg / h for 20 min, introducing chlorine gas at 250 kg / h for 60 min, introducing chlorine gas at 400 kg / h for 200 min, introducing chlorine gas at 300 kg / h for 30 min, and then introducing chlorine gas at 150 kg / h until the reaction endpoint.

10. The ADC foaming agent production process according to claim 6, characterized in that, In step S4, the reaction endpoint is determined by a combination of the redox potential, the color change of the tail gas caused by the escape of bromine, the pressure of the oxidation vessel, and the residual biuret content in the slurry, and the redox potential at the end of the reaction is not lower than 800mV.

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