Method for controlling oxidation reaction of ADC (azodicarbonamide) foaming agent by intermittently introducing chlorine

Abstract

The invention provides a method for controlling an oxidation reaction of an ADC (azodicarbonamide) foaming agent by intermittently introducing chlorine, which comprises the following steps: dissolving biurea and water in a reaction kettle according to a solid-to-liquid ratio of 1: (2-3) to obtain biurea slurry; adding halide into the biurea slurry as an oxidation aid, and introducing chlorine into the reaction kettle for reaction under the condition that the temperature in the reaction kettle is adjusted to 10-40 DEG C; when the reaction is carried out to 85%-90%, chlorine introduction is stopped, polyoxyethylene stearate is added into the reaction kettle to serve as a surfactant, and the mass ratio of reactants in the reaction kettle to polyoxyethylene stearate is 100: (0.01-0.1); continuously introducing chlorine into the reaction kettle, and controlling the chlorine to be intermittently introduced into the reaction kettle until the reaction is finished; the chlorine introduction time is 1-30 min / time, and the intermittent time is 1-40 min / time; filtering and cleaning reactants in the reaction kettle step by step, and drying, crushing, grading and the like after the pH value of the reactants reaches 6.5 to obtain a finished product ADC foaming agent. The end point of the ADC oxidation reaction can be effectively controlled, and excessive chlorine is prevented from decomposing the product.

Description

Technical Field

[0001] This application belongs to the field of foaming agent production technology, and specifically relates to a method for intermittently controlling the oxidation reaction of ADC foaming agent by chlorination. Background Technology

[0002] Azodicarbonamide (ADC) is a safe and efficient foaming agent used in plastic and rubber products. It has the advantages of high decomposition temperature, non-toxicity, non-polluting and non-combustible properties, and can provide high gas production and good dispersibility.

[0003] In the oxidation process of preparing the ADC foaming agent, the washed biuret is prepared into a suspension of a certain concentration, and an oxidizing agent is added in proportion and sent to the reaction vessel to react with chlorine gas to produce azodicarbonamide. The reaction equation is as follows: NH2CONHNHCONH2+Cl2→NH2CONNCONH2+2HCl In this reaction, excessive chlorine gas under certain conditions can come into contact with the generated ADC product and cause its decomposition, while insufficient chlorine gas can lead to low gas production in the ADC product, thus reducing product quality. To better control the reaction endpoint, Chinese Patent CN103214401A discloses a method to reduce the oxidation cost of ADC foaming agent and improve quality. Specifically, it discloses using dry or wet chlorine gas to oxidize biuret in the presence of an oxidizing agent, and using intermittent chlorine gas flow in the middle and later stages of the reaction to control the endpoint of the ADC oxidation reaction. However, this technical solution, relying solely on intermittent chlorine flow for control, is prone to imprecise reaction control, making it difficult to precisely match the chlorine gas flow rate and reaction rate. This can lead to unstable product quality and even side reactions, affecting product purity and yield. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a method for intermittently chlorinating to control the oxidation reaction of ADC foaming agent. By adding a surface catalyst during the oxidation reaction to change the phase state of the reactants, the contact between chlorine and the finished ADC foaming agent is reduced, thereby reducing the decomposition of ADC foaming agent by chlorine and improving the purity and yield of the product.

[0005] To address the aforementioned problems of this application, this application provides a method for intermittently controlling the oxidation reaction of an ADC foaming agent, comprising the following steps: (1) Dissolve biuret and water in a reaction vessel at a solid-liquid ratio of 1:2~3 to obtain biuret slurry; (2) Add a halide as an oxidizing agent to the biuret slurry, and when the temperature inside the reactor is adjusted to between 10 and 40°C, introduce chlorine gas into the reactor to carry out the reaction; (3) When the reaction reaches 85%~90%, stop the chlorination and add polyoxyethylene stearate as a surfactant to the reactor. The mass ratio of the reactants in the reactor to the polyoxyethylene stearate is 100:0.01~0.1. (4) Continue to introduce chlorine into the reactor and control the chlorine gas to be introduced into the reactor intermittently until the reaction is completed; the chlorine introduction time is 1~30min / time, and the intermittent time is 1~40min / time; (5) The reactants in the reactor are filtered and cleaned step by step. After the pH value of the reactants reaches 6.5, they are dried, crushed, and graded to obtain the finished ADC foaming agent.

[0006] Furthermore, in step (4), the rate of chlorine gas introduced intermittently decreases uniformly each time.

[0007] Furthermore, in step (4), the chlorine gas introduction rate for the (n+1)th time is 80% of the chlorine gas introduction rate for the nth time.

[0008] Furthermore, in step (2), the rate at which chlorine gas is introduced into the reactor is 200 m / s. 3 / h.

[0009] Further, in step (2), the mass ratio of biuret to the halide is 100:0.1~1.

[0010] Furthermore, the halide includes any one of sodium bromide, ammonium bromide, and sodium chloride.

[0011] Furthermore, following step (2), the following steps are also included: During the reaction, the reactants are sampled and analyzed periodically; Calculate the reaction conversion rate based on the analysis results to determine the extent of the reaction.

[0012] The beneficial effects of this application are as follows: This application proposes a method to slow down the decomposition of the ADC foaming agent by chlorine by adding polyoxyethylene stearate as a surfactant in the later stage of the oxidation reaction between biuret and chlorine. Polyoxyethylene stearate has both hydrophilic (polyoxyethylene) and hydrophobic (stearate) groups. In the reaction system, it forms micelles that encapsulate the foaming agent particles, altering the phase state of the reaction system and making it difficult for chlorine to directly contact the particles. Furthermore, this change in phase state affects the solubility and diffusion rate of chlorine, indirectly influencing the contact between chlorine and the foaming agent particles and reducing the decomposition rate of the ADC foaming agent. By controlling the intermittent introduction of chlorine, the reaction rate and the amount of chlorine introduced can be precisely adjusted, avoiding product decomposition due to excessive chlorine and low gas production due to insufficient chlorine. This method not only improves the production efficiency of the ADC foaming agent but also significantly enhances product quality, ensuring product purity and yield, and has broad industrial application value. Attached Figure Description

[0013] Figure 1 This is a schematic flowchart of a method for intermittently controlling the oxidation reaction of an ADC foaming agent according to this application. Detailed Implementation

[0014] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to more clearly illustrate the technical solution of this application, and are therefore merely examples and should not be used to limit the scope of protection of this application. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0015] Figure 1 A schematic flowchart of a method for intermittently controlling the oxidation reaction of an ADC foaming agent according to this application is shown, as follows: Figure 1 As shown, this application provides a method for intermittently controlling the oxidation reaction of an ADC foaming agent, comprising the following steps: (1) Dissolve biuret and water in a reaction vessel at a solid-liquid ratio of 1:2~3 to obtain biuret slurry; (2) Add a halide as an oxidizing agent to the biuret slurry, and when the temperature inside the reactor is adjusted to between 10 and 40°C, introduce chlorine gas into the reactor to carry out the reaction; (3) When the reaction reaches 85%~90%, stop the chlorination and add polyoxyethylene stearate as a surfactant to the reactor. The mass ratio of the reactants in the reactor to the polyoxyethylene stearate is 100:0.01~0.1. (4) Continue to introduce chlorine into the reactor and control the chlorine gas to be introduced into the reactor intermittently until the reaction is completed; the chlorine introduction time is 1~30min / time, and the intermittent time is 1~40min / time; (5) The reactants in the reactor are filtered and cleaned step by step. After the pH value of the reactants reaches 6.5, they are dried, crushed, and graded to obtain the finished ADC foaming agent.

[0016] Specifically, since biuret has low solubility in water, step (1) can be performed by stirring thoroughly with a stirrer to promote the dispersion and dissolution of biuret. In step (2), halide salts can be selected as oxidizing agents, preferably including any one of sodium bromide, ammonium bromide, and sodium chloride. Before introducing chlorine gas into the reactor in step (2) for reaction, ensure that other inert gases in the reactor have been purged to prevent explosion after chlorination. At the same time, during the chlorination process, it is necessary to monitor the pressure and temperature inside the reactor to maintain a slightly negative pressure state and avoid excessive pressure. Preferably, a rupture membrane should be installed on the reactor to prevent excessive pressure from causing boiling over and overflowing, which would lead to the decomposition of the ADC foaming agent and the generation of a large amount of flammable gas.

[0017] Under certain conditions, chlorine gas can cause the product to decompose when it comes into contact with the generated ADC foaming agent. As the reactant biuret gradually decreases, the reaction rate of chlorine oxidizing biuret slows down; as the product ADC foaming agent is continuously generated, the possibility of chlorine gas decomposing the ADC foaming agent increases, especially near the end stage. If the chlorine flow rate is too fast or the chlorine flow is excessive, it often leads to severe product decomposition. Therefore, the loss of yield in the oxidation process mainly occurs at the end of the reaction. In step (3), chlorine flow is stopped in the middle and late stages of the reaction, and a small amount of polyoxyethylene stearate is added as a surfactant. Polyoxyethylene stearate is a nonionic surfactant that can reduce the surface tension of the liquid, making it easier for the liquid to disperse into small droplets or form an emulsion. Therefore, it can effectively reduce the contact between chlorine gas and ADC foaming agent.

[0018] Even with the addition of a surfactant in step (3), the chlorination rate remains crucial for controlling the endpoint of the oxidation process. Therefore, step (4) involves intermittent chlorination to continue the oxidation process.

[0019] While intermittent chlorine gas introduction helps control the reaction process, an excessively fast chlorine introduction rate can still lead to the decomposition of the ADC foaming agent. Therefore, the chlorine introduction rate needs to be adjusted according to the actual reaction conditions. In one implementation, the rate of intermittent chlorine gas introduction in step (4) decreases uniformly each time.

[0020] Specifically, the initial chlorine flow rate is preset based on factors such as the volume of the reactor, reactant concentration, and temperature. Since this embodiment uses polyoxyethylene stearate as a surfactant, which affects the contact between chlorine and the raw materials, the initial rate of chlorine flow in step (4) can be the same as the chlorine flow rate in step (2). In one implementation, the rate at which chlorine is introduced into the reactor in step (2) is 200 m³ / s. 3 / h.

[0021] Preferably, in step (4) above, the chlorine gas introduction rate for the (n+1)th time is 80% of the chlorine gas introduction rate for the nth time.

[0022] In one implementation, the mass ratio of biuret to the halide in step (2) above is 100:0.1~1.

[0023] Preferably, in order to determine the extent of the reaction, a surfactant is added in a timely manner. In one implementation, after step (2) above, the process further includes: During the reaction, the reactants are sampled and analyzed periodically; Calculate the reaction conversion rate based on the analysis results to determine the extent of the reaction.

[0024] Specifically, this step can employ conventional sampling and analysis methods in the art to determine the extent of the reaction. For example, samples are taken from the reaction vessel, and the concentration of the biuret conversion product ADC foaming agent or hydrochloric acid is quantitatively analyzed using liquid chromatography-mass spectrometry (LC-MS). The conversion rate is calculated based on the ratio of the peak area of ​​the conversion product to the initial biuret peak area. Based on the calculated reaction conversion rate, the extent of the reaction is determined. This application utilizes polyoxyethylene stearate as a surfactant in the later stages of the oxidation reaction between biuret and chlorine to slow down the decomposition of the ADC blowing agent product by chlorine. Polyoxyethylene stearate possesses both hydrophilic (polyoxyethylene) and hydrophobic (stearate) groups. In the reaction system, it forms micelles that encapsulate the blowing agent particles, altering the phase state of the reaction system. This makes it difficult for chlorine to directly contact the blowing agent particles. Furthermore, the change in the phase state of the reaction system can affect the solubility and diffusion rate of chlorine, thereby indirectly affecting the contact between chlorine and the blowing agent particles and reducing the decomposition rate of the ADC blowing agent. By controlling the intermittent introduction of chlorine, the reaction rate and the amount of chlorine introduced can be precisely adjusted, avoiding the problems of product decomposition due to excessive chlorine and low gas generation due to insufficient chlorine.

[0025] Based on the embodiments provided in this application, some specific experiments have been conducted on this application. From these embodiments and comparative examples, it can be seen that the solution provided in this application has achieved good results. It should be noted that the following embodiments are only used to illustrate the present invention in detail and do not limit the scope of protection of the invention in any way.

[0026] Example 1 A method for intermittently controlling the oxidation reaction of an ADC foaming agent includes the following steps: S1: Add 100g of biuret to 200g of water and dissolve it completely under stirring until a uniform biuret slurry is formed. Then, put the biuret slurry into a 2L reactor.

[0027] S2: Add 1g of sodium bromide as an oxidizing agent to the biuret slurry and stir until homogeneous. Control the reactor temperature at 25℃±5℃. (The last part, "200m," appears to be an unrelated instruction and is omitted from the translation.) 3 Chlorine gas is introduced at a ventilation rate of / h to carry out the reaction.

[0028] S3: When the reaction reaches 85%, stop the chlorination. Quickly add 0.1g of polyoxyethylene stearate and continue stirring to ensure the surfactant is evenly dispersed in the reactants.

[0029] S4: Continue to introduce chlorine gas, using an intermittent chlorine introduction method for the reaction. Each chlorine introduction time is 15 minutes, with an interval of 20 minutes. The chlorine introduction rate for the (n+1)th time is 80% of the chlorine introduction rate for the nth time.

[0030] S5: After the reaction is complete, stop the chlorine flow and allow the temperature inside the reactor to drop to room temperature. Filter and wash the reactants step-by-step until the pH of the filtrate reaches 6.5. Dry the filtered reactants in a drying oven until constant weight is achieved. Then, pulverize the dried material using a pulverizer and classify it using a classifying sieve to obtain the finished ADC foaming agent.

[0031] Examples 2-4 The differences between Examples 2-4 and Example 1 are in the amount of substances added in each step and the process control. Otherwise, they are the same as Example 1. The control parameters for each step in Examples 2-4 are detailed in Table 1.

[0032] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, polyoxyethylene stearate is not added as a surfactant in step S3, and step S4 is performed directly.

[0033] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, chlorine gas is introduced at the same rate as in step S2 in step S4 until the reaction is completed, without intermittent chlorine introduction.

[0034] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step S4, Comparative Example 3 does not control the rate of intermittent chlorine gas introduction to decrease, but only introduces chlorine gas at a fixed gas flow rate.

[0035] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, chlorination was stopped and polyoxyethylene stearate was added when the reaction reached 75%.

[0036] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in Comparative Example 5, chlorine was stopped when the reaction reached 95% and polyoxyethylene stearate was added.

[0037] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the mass of polyoxyethylene stearate added in Comparative Example 6 is 0.5g.

[0038] Table 1. Parameter configuration for each step in each embodiment. Experimental results and data: The finished ADC foaming agents obtained in step S5 for each of Examples 1-4 and Comparative Examples 1-6 were weighed, and the yield of the ADC foaming agent for each example and comparative example was calculated. The purity of the finished ADC foaming agent obtained in step S5 was analyzed by high performance liquid chromatography. The gas volume generated by the decomposition of the finished ADC foaming agent obtained in step S5 at 200°C was measured using an RVT foaming apparatus to determine the gas evolution of the ADC foaming agent. The test results are detailed in Table 2.

[0039] Table 2. Results of yield, purity, and gas generation of the finished ADC foaming agent obtained in step S5 for each example and comparative example. According to the data in Table 2, adding polyoxyethylene stearate when the reaction was 85%-90% complete in Examples 1-4 significantly improved the yield and purity. This is consistent with the theory, because in the later stages of the reaction, the ADC blowing agent is gradually generated, increasing the contact opportunity between chlorine and ADC, leading to decomposition. The addition of surfactant reduces the contact between chlorine and ADC by changing the phase state of the reaction system, thereby reducing the decomposition of ADC. The different amounts and timing of surfactant addition in different examples and comparative examples resulted in differences in yield and purity. For example, Comparative Example 1 did not add surfactant, while Comparative Example 6 added excessive surfactant, resulting in significantly reduced yield and purity. The timing of surfactant addition in Comparative Examples 4 and 5, being too early or too late, also affected the results. Therefore, it can be concluded that the timing and amount of surfactant addition can affect the contact between chlorine and blowing agent particles, reducing the decomposition rate of the ADC blowing agent, and that adding polyoxyethylene stearate at a mass ratio of 100:0.01-0.1 to the reactants when the reaction is 85%-90% complete is the optimal control condition.

[0040] Examples 1-4, employing a decreasing chlorine infeed rate, showed slightly improved yield and purity compared to Comparative Example 2. This indicates that a decreasing chlorine infeed rate better controls the reaction rate, preventing excessively rapid reaction leading to ADC decomposition. Comparative Example 3, using a fixed chlorine infeed rate, achieved slightly lower yield and purity than Examples 1-4 with decreasing rates, further validating the necessity of the decreasing rate. Therefore, it can be concluded that a decreasing rate of intermittent chlorine infeed is more conducive to controlling the endpoint of the oxidation reaction.

[0041] The amounts and types of oxidizing agents (sodium bromide, ammonium bromide, sodium chloride) used in Examples 1-4 are different, but overall they have little impact on the yield and purity. This may be because the oxidizing agents mainly act as catalysts for the reaction, rather than directly participating in product formation.

[0042] As can be seen from the above embodiments, comparative examples, and experimental conclusions, the method for intermittently controlling the oxidation reaction of ADC foaming agent provided in this application changes the phase state of the reactants by adding a surface catalyst during the oxidation reaction, reducing the contact between chlorine and the finished ADC foaming agent, thereby reducing the decomposition of the ADC foaming agent by chlorine and improving the purity and yield of the product. Furthermore, the beneficial effects of this application are significant.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for intermittently controlling the oxidation reaction of an ADC foaming agent, characterized in that, Includes the following steps: (1) Dissolve biuret and water in a reaction vessel at a solid-liquid ratio of 1:2~3 to obtain biuret slurry; (2) Add a halide as an oxidizing agent to the biuret slurry, and when the temperature inside the reactor is adjusted to between 10 and 40°C, introduce chlorine gas into the reactor to carry out the reaction; (3) When the reaction reaches 85% to 90%, stop the chlorination and add polyoxyethylene stearate as a surfactant to the reactor. The mass ratio of the reactants in the reactor to the polyoxyethylene stearate is 100:0.01 to 0.

1. (4) Continue to introduce chlorine into the reactor and control the chlorine gas to be introduced into the reactor intermittently until the reaction is completed; the chlorine introduction time is 1~30min / time, and the intermittent time is 1~40min / time; (5) The reactants in the reactor are filtered and cleaned step by step. After the pH value of the reactants reaches 6.5, they are dried, crushed, and graded to obtain the finished ADC foaming agent.

2. The method as described in claim 1, characterized in that, In step (4), the rate of chlorine gas introduced intermittently decreases uniformly each time.

3. The method as described in claim 2, characterized in that, In step (4), the chlorine gas introduction rate for the (n+1)th time is 80% of the chlorine gas introduction rate for the nth time.

4. The method as described in claim 1, characterized in that, In step (2), the rate at which chlorine gas is introduced into the reactor is 200 m / s. 3 / h.

5. The method as described in claim 1, characterized in that, In step (2), the mass ratio of biuret to the halide is 100:0.1~1.

6. The method as described in claim 5, characterized in that, The halide includes any one of sodium bromide, ammonium bromide, and sodium chloride.

7. The method as described in claim 1, characterized in that, Following step (2), the following is also included: During the reaction, the reactants are sampled and analyzed periodically; Calculate the reaction conversion rate based on the analysis results to determine the extent of the reaction.

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