Method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide

Abstract

The invention provides a method for producing an ADC foaming agent by oxidizing HDCA with nitrogen dioxide. The method comprises the following steps: preparing a biurea solid and a sulfuric acid solution into slurry, continuously introducing nitrogen dioxide gas, and oxidizing to prepare azodicarbonamide. The method has the advantages that the water phase can be recycled, other catalysts are not added, and enrichment of inorganic salt in the wastewater can be effectively avoided; meanwhile, the nitrogen oxide gas can be recycled, and high-purity nitrogen dioxide is regenerated through oxygen supplementation in a water-free and acid-free environment. Based on the characteristics, the method does not generate waste water, does not enrich salts, and reduces the process flow.

Description

Technical Field

[0001] The present invention relates to the technical field of blowing agents, and mainly relates to a method for producing ADC blowing agent by oxidizing HDCA with nitrogen dioxide. Background Art

[0002] Azodicarbonamide (ADC blowing agent) is a general-purpose blowing agent with a large gas generation amount. Currently, in China, the production process using hydrazine hydrate synthesized by the urea method as the raw material is commonly adopted. Urea reacts with sodium hypochlorite to generate a dilute hydrazine hydrate solution. After desalting and refining, the hydrazine hydrate solution reacts with urea under the condition of pH = 4 - 5 by acid condensation to produce biurea, and then it is oxidized with chlorine to obtain azodicarbonamide.

[0003] This production process has the following problems: 1. The yield of the hydrazine hydrate synthesis process is low, the concentration of the obtained hydrazine hydrate solution is low, and a large amount of wastewater is generated during the production process; 2. By-products ammonia and sodium carbonate generated during the acid condensation production of biurea need to be neutralized with sulfuric acid, generating a large amount of wastewater containing ammonium sulfate and sodium sulfate; 3. The energy consumption in the whole production process is very high, which is not conducive to energy conservation and environmental protection. In view of the above problems, for the purpose of green production and cost reduction, various methods for oxidizing biurea to prepare azodicarbonyl have emerged.

[0004] Taking the patent CN202410044792.6 as an example, it discloses a method for producing azodicarbonamide by oxidizing biurea with pure oxygen. In this method, biurea is configured into a solid slurry in an acidic medium, with a halogen element simple substance or salt as the main catalyst, a nitrate or nitrite as the co-catalyst, and pure oxygen as the oxidant to react to generate azodicarbonamide. Although compared with the traditional method, part of the acidic mother liquor is recycled, reducing the cost of wastewater treatment, there are still a large number of inorganic salts in the recycled mother liquor, and the mother liquor treatment process needs to be increased, thus increasing the cost. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies existing in the prior art, and provide a method for producing ADC blowing agent by oxidizing HDCA with nitrogen dioxide.

[0006] The purpose of the present invention is achieved by the following technical solutions. A method for producing ADC blowing agent by oxidizing HDCA with nitrogen dioxide, including the following steps:

[0007] S1. In a slurry tank, raw material biurea HDCA and a sulfuric acid solution with a concentration of 0.1% - 1% are formulated into a slurry with a solid content of 30% - 60%;

[0008] S2. Feed the slurry into the reaction kettle, and continuously introduce nitrogen dioxide gas from the bottom of the slurry under mechanical stirring conditions through a mechanical stirring device. Maintain the reaction temperature at 40°C to 70°C and the pressure in the kettle at 0.01 MPa to 0.5 MPa, and react for 4 to 8 hours.

[0009] S3. The slurry in the reaction kettle flows out from the discharge port, and the solid phase is obtained by centrifugation through a centrifugal separation device, and the azodicarbonamide ADC solid is obtained after washing and drying.

[0010] Furthermore, in step S2, the gas that has not completely reacted flows out through the upper pipeline, and after oxygen supplementation in the gas recovery tank, it is pumped into the slurry again through a gas pump.

[0011] Furthermore, the mechanical stirring device uses a self-priming stirrer.

[0012] Furthermore, in step S2, the introduced nitrogen dioxide gas has a NO content of less than 10%, and the gas flow rate is 0.1 L / min to 2.0 L / min.

[0013] Furthermore, in step S3, when the pH of the aqueous phase after centrifugal separation is detected to be less than 3, it can be directly recycled; when the pH > 3, 20% to 50% sulfuric acid solution is added to the aqueous phase and then recycled.

[0014] Furthermore, in step S3, the gas phase after centrifugal separation is returned to the gas recovery tank.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] 1. No discharged wastewater is generated, effectively avoiding the enrichment of inorganic salts in the wastewater. It only needs to adjust the pH of the subsequent centrifuged aqueous phase with sulfuric acid and then it can be recycled.

[0017] 2. The reaction uses NO2 gas for oxidation. After the oxidation is completed, the produced NO gas is discharged and then re-oxygenated in the gas recovery tank in an anhydrous and acid-free environment to generate NO2, reducing the potential corrosion of the gas to the equipment and increasing the gas utilization rate.

[0018] 3. By adopting an optimized process design and device layout, fully considering the material utilization rate and heat utilization rate, further cost savings are achieved, and it has high industrial feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the following described drawings are only some embodiments of the present invention. For those skilled in the art or ordinary technicians, other drawings can be obtained based on these drawings without creative efforts. Figure 1Schematic diagram of the reaction process of the present invention.

[0020] Explanation of reference numerals in the drawings: slurry tank 1, raw material inlet 2, reaction kettle 3, centrifugal separation device 4, nitrogen dioxide gas cylinder 5, gas recovery tank 6, oxygen gas cylinder 7, gas content detector 8. Specific embodiments

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] As Figure 1 shown, a method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide includes the following steps:

[0023] S1. In the slurry tank 1, feed through the raw material inlet 2 to prepare a slurry with a solids content of 30% - 60% by mixing the raw material biurea HDCA with a sulfuric acid solution having a concentration of 0.1% - 1%.

[0024] S2. Feed the slurry into the reaction kettle 3. The mechanical stirring device uses a self-priming stirrer. Under mechanical stirring conditions, continuously introduce nitrogen dioxide gas (provided by the nitrogen dioxide gas cylinder 5) from the bottom of the slurry. The introduced nitrogen dioxide gas has a NO content of less than 10%, and the gas flow rate is 0.1 L / min - 2.0 L / min. Maintain the reaction temperature at 40°C - 70°C and the pressure in the kettle at 0.01 MPa - 0.5 MPa, and react for 4 - 8 hours. The gas that has not been completely reacted flows out through the upper pipeline. After replenishing oxygen in the gas recovery tank 6 (provided by the oxygen gas cylinder 7), it is pumped into the slurry again through a gas pump. A gas content detector 8 can be provided on the pipeline.

[0025] Preferably, the device for continuously introducing nitrogen dioxide gas and adjusting the reaction pressure includes a gas flow meter, a pressure reducing valve, a back pressure valve, a solenoid valve, and a needle valve.

[0026] S3. The slurry in the reaction kettle 3 flows out from the discharge port, and the solid phase is obtained by centrifugation through the centrifugal separation device 4, and the azodicarbonamide ADC solid is obtained after washing and drying. When the pH of the aqueous phase after centrifugal separation is < 3, it can be directly recycled; when the pH > 3, 20% - 50% sulfuric acid solution is added to the aqueous phase and then recycled. The gas phase after centrifugal separation is returned to the gas recovery tank.

[0027] Mechanism of the present invention: Firstly, chlorine gas in the traditional method is replaced by nitrogen dioxide gas, and sulfuric acid is used to adjust the pH of the mother liquor to increase the reaction rate. In the method disclosed in the present invention, there is no need to discharge wastewater, avoiding the enrichment of a large amount of inorganic salts, and the prepared slurry can be directly recycled after simple centrifugation. At the same time, a recycling scheme is designed for the discharged nitrogen oxide gas: in the gas recovery tank outside the reaction kettle, after adding a certain concentration of oxygen under anhydrous and acid-free conditions, it is re-converted from NO to NO2 and then re-injected into the slurry to participate in the reaction. The present invention has the advantages that the aqueous phase can be recycled, no other catalysts are added, and the enrichment of inorganic salts in the wastewater can be effectively avoided; at the same time, the nitrogen oxide gas can be recycled, and high-purity nitrogen dioxide is regenerated by adding oxygen in an anhydrous and acid-free environment. Based on the above characteristics, this method produces no wastewater, no enrichment of salts, and reduces the process flow.

[0028] Example 1:

[0029] Mix biurea with 0.5% sulfuric acid solution to prepare a slurry with a solid content of 50%, stir at a speed of 300 rpm, introduce nitrogen oxide gas from the bottom of the liquid surface at a flow rate of 0.2 L / min, detect that the NO2 content > 95%, ensure the pressure in the slurry kettle is 0.05 MPa, the temperature in the kettle is 50 °C, after cyclic reaction for 6 hours, take a small amount of the bottom slurry, add excessive NaOH, heat and dissolve with stirring, if it is completely dissolved, the reaction ends, discharge the slurry in the kettle from the discharge port, centrifuge to obtain solids, measure the pH of the centrifuged liquid aqueous phase = 2.74, inject it into the liquid preparation tank for standby, wash and dry the solids to obtain azodicarbonamide solids, and the titration analysis purity is 98.32%.

[0030] Example 2:

[0031] Mix biurea with 1.0% sulfuric acid solution to prepare a solid content of 30%, stir at a speed of 500 rpm, introduce nitrogen oxide gas from the bottom of the liquid surface at a flow rate of 0.1 L / min, detect that the NO2 content > 99%, ensure the pressure in the slurry kettle is 0.1 MPa, the temperature in the kettle is 65 °C, after cyclic reaction for 8 hours, take a small amount of the bottom slurry, add excessive NaOH, heat and dissolve with stirring, if it is completely dissolved, the reaction ends, discharge the slurry in the kettle from the discharge port, centrifuge to obtain solids, measure the pH of the centrifuged liquid aqueous phase = 1.98, inject it into the liquid preparation tank for standby, wash and dry the solids to obtain azodicarbonamide solids, and the titration analysis purity is 99.48%.

[0032] Example 3:

[0033] Mix biurea with 1.0% sulfuric acid solution to prepare a slurry with a solid content of 60%. Stir at a speed of 300 rpm. Introduce nitrogen oxide gas from the bottom of the liquid surface at a flow rate of 0.1 L / min. Detect that the NO2 content is >99%. Ensure that the pressure in the slurry kettle is 0.15 MPa and the temperature in the kettle is 65°C. After reacting cyclically for 6 hours, take a small amount of the bottom slurry, add excessive NaOH, heat and dissolve it with stirring. If it is completely dissolved, the reaction ends. Pump out the slurry in the kettle from the discharge port, and centrifuge to obtain a solid. Measure that the pH of the centrifugate aqueous phase is 2.01, and pump it into the liquid preparation tank for standby. Wash and dry the solid to obtain azodicarbonamide solid, and the purity is 99.01% by titration analysis.

[0034] Example 4:

[0035] Mix biurea with 0.2% sulfuric acid solution to prepare a slurry with a solid content of 40%. Stir at a speed of 600 rpm. Introduce nitrogen oxide gas from the bottom of the liquid surface at a flow rate of 0.5 L / min. Detect that the NO2 content is >99%. Ensure that the pressure in the slurry kettle is 0.36 MPa and the temperature in the kettle is 65°C. After reacting cyclically for 8 hours, take a small amount of the bottom slurry, add excessive NaOH, heat and dissolve it with stirring. If it is completely dissolved, the reaction ends. Pump out the slurry in the kettle from the discharge port, and centrifuge to obtain a solid. Measure that the pH of the centrifugate aqueous phase is 3.24, adjust the pH to 2.05 with concentrated sulfuric acid, and then pump it into the liquid preparation tank for standby. Wash and dry the solid to obtain azodicarbonamide solid, and the purity is 98.33% by titration analysis.

[0036] As described above, it is only the specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide, characterized in that: The steps include: S1. In a slurry tank, the raw material HDCA and a sulfuric acid solution with a concentration of 0.1% to 1% are mixed to form a slurry with a solid content of 30% to 60%; S2, the slurry is sent into the reactor, and nitrogen dioxide gas is continuously introduced from the bottom of the slurry through a mechanical stirring device under mechanical stirring conditions, the reaction temperature is maintained at 40°C to 70°C, the pressure in the reactor is maintained at 0.01MPa to 0.5MPa, and the reaction is carried out for 4 to 8 hours; S3, the slurry in the reactor flows out from the discharge port, is centrifuged through a centrifugal separation device to obtain a solid phase, and is washed and dried to obtain azodicarbonamide ADC solid.

2. The method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide according to claim 1, characterized in that: In step S2, the gas that has not been completely reacted flows out from the upper pipeline, is supplemented with oxygen in the gas recovery tank, and is pumped into the slurry again through the gas pump.

3. The method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide according to claim 2, characterized in that: The mechanical stirring device adopts a self-priming stirrer.

4. The method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide according to claim 3, characterized in that: In step S2, the nitrogen dioxide gas introduced has a NO content of less than 10% and a gas flow rate of 0.1 L / min to 2.0 L / min.

5. The method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide according to claim 4, characterized in that: In step S3, the aqueous phase after centrifugal separation can be directly recycled when the pH is detected to be less than 3; when the pH is greater than 3, 20% to 50% sulfuric acid solution is added to the aqueous phase and then recycled.

6. The method for producing ADC foaming agent by oxidizing HDCA with nitrogen dioxide according to claim 5, characterized in that: In the step S3, the gas phase after centrifugal separation is returned to the gas recovery tank.

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