Production method for improving ADC foaming agent yield

Abstract

The invention provides a production method for improving the yield of an ADC foaming agent, which comprises the following steps: fully mixing urea and hydrazine hydrate in a premixing tank according to the mass ratio of (2.4-3.5): 1 to obtain a premixed solution; continuously adding the premixed solution into the condensation reaction kettle, dropwise adding concentrated hydrochloric acid with the concentration of more than 31% until the pH value of the materials in the condensation reaction kettle is 2.0-3.0, heating the materials in the condensation reaction kettle to 90-110 DEG C, and carrying out condensation reaction; adjusting the gas phase ammonia partial pressure in the condensation reaction kettle according to the progress of the condensation reaction; when the concentration of hydrazine hydrate in the condensation reaction kettle is lower than 1g / L, stopping the condensation reaction, carrying out solid-liquid separation and washing on materials in the condensation reaction kettle to obtain a biurea solid, and carrying out an oxidation process on the biurea solid to obtain the ADC foaming agent. According to the production method for improving the yield of the ADC foaming agent, the self-condensation reaction of urea can be effectively inhibited, and the yield of the ADC foaming agent is improved.

Description

Technical Field

[0001] This application belongs to the technical field of foaming agent production. Specifically, it relates to a production method for improving the yield of ADC foaming agent. Background Art

[0002] As a highly efficient foaming agent, azodicarbonamide (ADC) is widely used in the foaming processes of polymer materials such as plastics and rubbers. At present, the condensation process of the vast majority of urea-based ADC manufacturers is carried out under acidic conditions. After hydrazine hydrate and urea are mixed and prepared in a certain proportion, acid is added to the condensation reaction kettle for the condensation reaction.

[0003] However, there are some technical problems in the traditional urea-based production of ADC foaming agent. One of them is the side reaction problem in the condensation reaction stage. Urea is prone to self-condensation reaction under high temperature conditions. The intermolecular amino group (NH2) and carbonyl group (C=O) undergo condensation, and one molecule of ammonia (NH3) is removed to form biuret. The self-condensation of urea results in a reduction of ADC foaming agent raw materials and a decrease in yield.

[0004] In order to reduce the generation of biuret, most of the existing technologies adopt a stepped heating strategy, raising the temperature of the condensation reaction kettle to 100 - 120 °C at a certain heating rate for the reaction, rather than directly carrying out the high-temperature reaction. However, there are many influencing factors for the self-condensation of urea, and the effect of reducing biuret formation by only adjusting the reaction temperature is limited.

[0005] Therefore, developing a production method that can effectively inhibit the self-condensation reaction of urea, improve the yield of ADC foaming agent, and is simple to operate and low in cost is still an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by this application is: to provide a production method for improving the yield of ADC foaming agent, which can effectively inhibit the self-condensation reaction of urea and improve the yield of ADC foaming agent.

[0007] To solve the above problems of this application, this application provides a production method for ADC foaming agent with low by-products, including: Urea and hydrazine hydrate are fully mixed in a premixing tank according to a mass ratio of 2.4 - 3.5:1 to obtain a premixed liquid; the premixed liquid is continuously fed into the condensation reactor, and concentrated hydrochloric acid with a concentration greater than 31% is added dropwise until the pH of the material in the condensation reactor reaches 2.0 - 3.0. Then, the material in the condensation reactor is heated to 90 - 110 °C for condensation reaction; according to the progress of the condensation reaction, the partial pressure of gaseous ammonia in the condensation reactor is adjusted; when the concentration of hydrazine hydrate in the condensation reactor is lower than 1 g / L, the condensation reaction is stopped, and the material in the condensation reactor is subjected to solid-liquid separation and washing to obtain semicarbazide solid, and the semicarbazide solid is subjected to an oxidation process to obtain ADC foaming agent.

[0008] In this solution, by optimizing the mass ratio of urea to hydrazine hydrate and the feeding method of urea, the self-condensation caused by excessive urea is reduced. And by adjusting the temperature and partial pressure of gaseous ammonia in the reaction system to balance the concentration of ammonia in the reaction system, because urea self-condensation produces ammonia, and the self-condensation reaction is a reversible reaction. According to the principle of chemical equilibrium, an appropriate ammonia partial pressure can inhibit the self-condensation reaction between urea molecules, thereby shifting the reaction equilibrium towards the direction of the target product semicarbazide, reducing the formation of by-product biuret, and improving the yield of ADC foaming agent.

[0009] Further, heating the material in the condensation reactor to 90 - 110 °C for condensation reaction includes: in the first stage of the condensation reaction, heating the material in the condensation reactor to 90 - 105 °C at a heating rate of 3 - 5 °C / min; in the second stage of the condensation reaction, heating the material in the condensation reactor to 105 - 110 °C at a heating rate of 1 - 3 °C / min; in the third stage of the condensation reaction, maintaining the temperature of the material in the condensation reactor at 105 - 110 °C.

[0010] Further, adjusting the partial pressure of gaseous ammonia in the condensation reactor according to the progress of the condensation reaction includes: maintaining the partial pressure of gaseous ammonia in the condensation reactor not less than 15 kPa in the first stage; reducing the partial pressure of gaseous ammonia in the condensation reactor to 10 - 12 kPa in the second stage; adjusting the partial pressure of gaseous ammonia in the condensation reactor not greater than 5 kPa in the third stage.

[0011] Further, the adjustment of the partial pressure of gaseous ammonia is achieved by the following method: extracting ammonia gas in the gas phase in the condensation reactor through a vacuum pump; compressing the ammonia gas to 0.2 - 0.5 MPa and then injecting it back into the condensation reactor.

[0012] As a better choice, adding dropwise concentrated hydrochloric acid with a concentration greater than 31% includes: adding dropwise concentrated hydrochloric acid with a concentration greater than 31% evenly through a plurality of injection ports distributed on the side wall of the condensation reactor.

[0013] Further, the multiple injection ports are annularly distributed along the side wall of the condensation reactor.

[0014] In this solution, through the design of multiple injection ports, concentrated hydrochloric acid can be evenly distributed in the reactor, reducing the enrichment of concentrated hydrochloric acid in local areas, avoiding the rapid decomposition of urea or other side reactions caused by excessive local acid, and ensuring the smooth progress of the condensation reaction.

[0015] Further, after heating the materials in the condensation reactor to 90 - 110 °C for condensation reaction, it further includes: adding dilute hydrochloric acid with a concentration of 15% - 20% to the condensation reactor through the multiple injection ports, and maintaining the pH value in the condensation reactor at 2.0 - 3.0.

[0016] In one implementation, the temperature of the premixing tank is 60 - 80 °C.

[0017] The beneficial effects of this application are as follows: 1. The solution of this application reduces the self - condensation caused by excessive urea by optimizing the mass ratio of urea to hydrazine hydrate and the feeding method of urea. And by adjusting the temperature of the reaction system and the partial pressure of gaseous ammonia to balance the concentration of ammonia in the reaction system, because urea self - condensation generates ammonia and the self - condensation reaction is a reversible reaction, according to the principle of chemical equilibrium, an appropriate ammonia partial pressure can inhibit the self - condensation reaction between urea molecules, thereby shifting the reaction equilibrium towards the direction of the target product biurea and reducing the generation of by - product biuret, improving the yield of ADC foaming agent.

[0018] 2. The solution of this application enables concentrated hydrochloric acid to be evenly distributed in the reactor through the design of multiple injection ports, reducing the enrichment of concentrated hydrochloric acid in local areas, avoiding the occurrence of side reactions such as the rapid decomposition of urea caused by excessive local acid, and ensuring the smooth progress of the condensation reaction. Specific Embodiments

[0019] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, so they are only examples and cannot be used to limit the protection scope of this application. In addition, 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.

[0020] This application provides a production method for improving the yield of ADC foaming agent, including the following steps: Fully mix urea and hydrazine hydrate in a premixing tank according to a mass ratio of 2.4 - 3.5:1 to obtain a premixed solution; Continuously feed the premixed liquid into the condensation reactor, and drop concentrated hydrochloric acid with a concentration greater than 31% until the pH of the materials in the condensation reactor reaches 2.0 - 3.0. Heat the materials in the condensation reactor to 90 - 110 °C for condensation reaction; Adjust the partial pressure of gaseous ammonia in the condensation reactor according to the progress of the condensation reaction; When the concentration of hydrazine hydrate in the condensation reactor is lower than 1 g / L, stop the condensation reaction, and perform solid-liquid separation and washing on the materials in the condensation reactor to obtain semicarbazide solid, and the semicarbazide solid is obtained as ADC blowing agent through the oxidation process.

[0021] Specifically, the purpose of premixing is to promote the complete dissolution of urea, make urea and hydrazine hydrate fully mixed, and form a uniform reaction system. The temperature of the premixing tank is preferably 60 - 80 °C. Optionally, the premixing tank can be a jacketed premixing tank, and the temperature is maintained by circulating hot water or steam externally, and the temperature of the premixed liquid is monitored in real time.

[0022] In one implementation, heating the materials in the condensation reactor to 90 - 110 °C for condensation reaction includes: In the first stage of the condensation reaction, heat the materials in the condensation reactor to 90 - 105 °C at a heating rate of 3 - 5 °C / min; In the second stage of the condensation reaction, heat the materials in the condensation reactor to 105 - 110 °C at a heating rate of 1 - 3 °C / min; In the third stage of the condensation reaction, maintain the temperature of the materials in the condensation reactor at 105 - 110 °C.

[0023] In one implementation, adjusting the partial pressure of gaseous ammonia in the condensation reactor according to the progress of the condensation reaction includes: In the first stage, maintain the partial pressure of gaseous ammonia in the condensation reactor not less than 15 kPa; In the second stage, reduce the partial pressure of gaseous ammonia in the condensation reactor to 10 - 12 kPa; In the third stage, adjust the partial pressure of gaseous ammonia in the condensation reactor not greater than 5 kPa.

[0024] Specifically, during the rapid temperature increase in the first stage, the urea concentration in the reaction system is relatively high. Therefore, maintaining the partial pressure of gaseous ammonia in the condensation reactor at not less than 15 kPa can inhibit the self-condensation of urea and improve the utilization rate of urea. In the second stage, the reactant concentration and reaction state change, and too high a partial pressure of ammonia may inhibit the progress of the main reaction. Therefore, the partial pressure of gaseous ammonia in the condensation reactor is reduced to promote the forward progress of the condensation reaction and increase the yield of biurea. The reduction of the partial pressure of gaseous ammonia can be controlled by adjusting the pumping speed of the vacuum pump or the flow rate of the inert gas introduced. In the third stage, the reaction is approaching the end, and a lower partial pressure of ammonia can reduce the influence of ammonia on the product and ensure the complete progress of the reaction. At the same time, it can also reduce the impurity content in the reaction system and improve the quality of the final product.

[0025] Preferably, the adjustment of the partial pressure of gaseous ammonia is achieved by the following method: Extracting ammonia gas in the gaseous phase in the condensation reactor through a vacuum pump; Compressing the ammonia gas to 0.2 - 0.5 MPa and then injecting it back into the condensation reactor.

[0026] In one implementation, the dropping of concentrated hydrochloric acid with a concentration greater than 31% includes: Dropping concentrated hydrochloric acid with a concentration greater than 31% uniformly through a plurality of injection ports distributed on the side wall of the condensation reactor.

[0027] Specifically, the concentrated hydrochloric acid enters the reaction kettle from multiple directions and comes into full contact with the material. Compared with the problem of local accumulation of concentrated acid that may be caused by traditional single-point dropping, this embodiment avoids the situation of too high local acid concentration and overheating, thereby inhibiting the decomposition side reaction of urea in the strong acid microenvironment.

[0028] Preferably, the plurality of injection ports are annularly distributed along the side wall of the condensation reactor.

[0029] It should be understood that during the condensation reaction, the continuous consumption of H + and the generation of reaction products cause the pH value of the reaction system to increase. To maintain the pH dynamic balance, in one implementation, after heating the material in the condensation reactor to 90 - 110 °C for condensation reaction, it further includes: Adding dilute hydrochloric acid with a concentration of 15% - 20% into the condensation reactor through the plurality of injection ports to keep the pH value in the condensation reactor at 2.0 - 3.0.

[0030] According to the embodiments provided in the present application, some specific tests have been conducted on the present application. From these examples and comparative examples, it can be seen that the solution provided in the present application has achieved good results. It should be noted that the following examples are only used to illustrate the present invention in detail and do not limit the protection scope of the invention in any way.

[0031] Example 1 Step 1: Add urea and hydrazine hydrate with a concentration of 4.5% into the premixing tank according to a mass ratio of 3:1. Control the temperature of the premixing tank at 70°C and stir well to obtain a premixed solution. Step 2: Continuously input the premixed solution into the condensation reactor, and drop concentrated hydrochloric acid with a concentration of 35% through multiple injection ports until the pH of the materials in the condensation reactor reaches 2.5 ± 0.1. In the first stage, heat up to 100°C at a rate of 4°C / min and maintain the gas-phase ammonia partial pressure at 15 kPa; in the second stage, heat up to 108°C at a rate of 2°C / min and simultaneously reduce the ammonia partial pressure to 12 kPa; in the third stage, maintain 108°C ± 1°C and adjust the ammonia partial pressure not to exceed 5 kPa by injecting ammonia back through a vacuum pump. Step 3: When the concentration of hydrazine hydrate in the condensation reactor is lower than 1 g / L, stop the condensation reaction, and perform solid-liquid separation and washing on the materials in the condensation reactor to obtain biurea solid. The biurea solid is washed 3 times with deionized water and then sent to the oxidation process to obtain ADC blowing agent.

[0032] Examples 2 to 4 Examples 2 to 4 are different from Example 1 in the amount of substances added and process control in each step, and the others are the same as Example 1. The control parameters of each step in Examples 1 to 4 are shown in Table 1.

[0033] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Step 1 of Comparative Example 1, the mass ratio of urea to hydrazine hydrate is higher than that in Example 1.

[0034] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in Step 2 of Comparative Example 2, concentrated hydrochloric acid is dropped through a single injection port.

[0035] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in Step 2 of Comparative Example 3, the ammonia partial pressure is maintained at not less than 15 kPa throughout the process.

[0036] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in Step 2 of Comparative Example 3, the ammonia partial pressure is maintained at not more than 5 kPa throughout the process.

[0037] Table 1 Parameter configuration of each step in each example Experimental results and data: Detect the products and condensation reaction duration obtained in Step 3 of each example and comparative example in Examples 1 to 4 and Comparative Examples 1 to 4. The detection results are shown in Table 2.

[0038] Table 2 Detection Results of Each Example and Comparative Example From the experimental results of Examples 1-4 and Comparative Example 1, it can be analyzed that the biuret content and yield of Example 1 are better than those of Example 2 and Example 3. It is speculated that the reason is that too low ratio of urea to hydrazine hydrate may limit the material ratio of the main reaction, while too high ratio may slightly exacerbate the self-condensation of urea. The biuret content and yield of Comparative Example 1 are significantly inferior to those of all examples, verifying that excessive urea is the main cause of side reactions. It is speculated that the reason is that excessive urea is more likely to undergo self-condensation in a high-temperature acidic environment, and at the same time, free urea may consume H⁺ through competitive reactions, resulting in the hindrance of the main reaction.

[0039] From the experimental results of Examples 1-4 and Comparative Example 2, it can be analyzed the influence of the dropping method of concentrated hydrochloric acid on the yield of ADC foaming agent and the biuret content. In Examples 1-4, concentrated hydrochloric acid was uniformly dropped through multiple injection ports distributed on the side wall of the condensation reaction kettle, with a lower biuret content and a higher yield of ADC foaming agent; in Comparative Example 2, concentrated hydrochloric acid was dropped through a single injection port, resulting in an increase in biuret content and a decrease in the yield of ADC foaming agent. It is speculated that the reason is that dropping concentrated hydrochloric acid through a single injection port is likely to cause local high acid concentration and overheating, which will promote the decomposition side reaction of urea in a strong acid microenvironment, while uniform dropping through multiple injection ports can disperse concentrated hydrochloric acid more evenly in the reaction system, avoiding this adverse situation and inhibiting the occurrence of side reactions.

[0040] From the experimental results of Examples 1-4 and Comparative Example 3, it can be analyzed the influence of the regulation method of gas-phase ammonia partial pressure on the yield of ADC foaming agent, the biuret content and the total duration of the condensation reaction. In Examples 1-4, the gas-phase ammonia partial pressure was regulated in different stages, with a lower biuret content, a higher yield of ADC foaming agent, and a relatively shorter total duration of the condensation reaction; in Comparative Example 3, the ammonia partial pressure was maintained at not less than 15 kPa throughout step 2, resulting in an increase in biuret content, a decrease in the yield of ADC foaming agent, and a significant prolongation of the total duration of the condensation reaction. It is speculated that the reason is that the environment of high ammonia partial pressure throughout the process may change the chemical equilibrium and reaction rate of the reaction, making side reactions such as the self-condensation reaction of urea more likely to occur, while inhibiting the progress of the main reaction, resulting in an extended reaction time and a reduced yield.

[0041] From the experimental results of Examples 1-4 and Comparative Example 4, it can be analyzed the influence of the regulation method of gas-phase ammonia partial pressure on the yield of ADC foaming agent and the biuret content. In Examples 1-4, the ammonia partial pressure was regulated in stages, with a low biuret content and a high yield; in Comparative Example 4, the ammonia partial pressure was maintained at not more than 5 kPa throughout step 2, resulting in a significant increase in biuret content and a significant decrease in the yield of ADC foaming agent. It is speculated that the reason is that a low ammonia partial pressure cannot effectively inhibit the self-condensation reaction of urea, making it easier for urea to undergo self-condensation to form biuret, thereby reducing the reactants for generating ADC foaming agent and lowering the yield of the main product.

[0042] It can be seen from the above embodiments, comparative examples and experimental conclusions that a production method for improving the yield of ADC blowing agent provided by the present application can effectively inhibit the self-condensation reaction of urea and improve the yield of ADC blowing agent. Further, it can be seen that the beneficial effects of the present 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 of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements 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 production method for improving the yield of ADC blowing agent, characterized in that, include: Thoroughly mix urea and hydrazine hydrate in a premixing tank at a mass ratio of 2.4-3.5:1 to obtain a premixed solution; The premixed liquid is continuously added to the condensation reaction kettle, concentrated hydrochloric acid with a concentration greater than 31% is added dropwise until the pH of the material in the condensation reaction kettle reaches 2.0-3.0, and the material in the condensation reaction kettle is heated to 90-110° C. to carry out a condensation reaction; According to the progress of the condensation reaction, adjusting the gas phase ammonia partial pressure in the condensation reaction kettle; When the hydrazine hydrate concentration in the condensation reaction kettle is lower than 1 g / L, the condensation reaction is stopped, and the materials in the condensation reaction kettle are subjected to solid-liquid separation and washing to obtain a biurea solid, and the biurea solid is subjected to an oxidation process to obtain an ADC foaming agent.

2. The production method according to claim 1, characterized in that, The step of heating the materials in the condensation reaction kettle to 90-110° C. to carry out the condensation reaction comprises: In the first stage of the condensation reaction, the materials in the condensation reaction kettle are heated to 90-105°C at a heating rate of 3-5°C / min; In the second stage of the condensation reaction, the materials in the condensation reaction kettle are heated to 105-110° C. at a heating rate of 1-3° C. / min; In the third stage of the condensation reaction, the temperature of the materials in the condensation reactor is maintained at 105-110°C.

3. The production method according to claim 2, characterized in that, The step of adjusting the gas phase ammonia partial pressure in the condensation reaction kettle according to the progress of the condensation reaction comprises: In the first stage, the gas phase ammonia partial pressure in the condensation reactor is maintained at not less than 15 kPa; In the second stage, the gas phase ammonia partial pressure in the condensation reactor is reduced to 10-12 kPa; In the third stage, the gas phase ammonia partial pressure in the condensation reactor is adjusted to be no greater than 5 kPa.

4. The production method according to any one of claims 1 to 3, characterized in that, The gas phase ammonia partial pressure is regulated by: extracting ammonia in the gas phase in the condensation reaction kettle by a vacuum pump; The ammonia gas is compressed to 0.2-0.5 MPa and then injected back into the condensation reactor.

5. The production method according to claim 1, characterized in that, The concentrated hydrochloric acid having a concentration greater than 31% is added dropwise and comprises: Concentrated hydrochloric acid with a concentration greater than 31% is added dropwise at a uniform rate through multiple injection ports distributed on the side wall of the condensation reactor.

6. The production method according to claim 4, characterized in that, The multiple injection ports are distributed in a ring shape along the side wall of the condensation reactor.

7. The production method according to claim 4, characterized in that, After heating the materials in the condensation reaction kettle to 90-110° C. for condensation reaction, the method further comprises: Dilute hydrochloric acid with a concentration of 15%-20% is added into the condensation reaction kettle through the multiple injection ports to maintain the pH value in the condensation reaction kettle at 2.0-3.

0.

8. The production method according to claim 1, wherein, The temperature of the premixing tank is 60-80°C.

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