Process for the preparation of an azodicarbonamide

Abstract

The application provides a preparation method of azodicarbonamide, which comprises the following steps: step (1), mixing biurea, a ferrous compound catalyst and water according to a certain proportion to prepare a biurea suspension; step (2), adjusting the pH value of the biurea suspension prepared in step (1) to 2-6, and heating the biurea suspension with the pH value of 2-6 to 50-100 DEG C to obtain a second suspension; step (3), slowly dropping hydrogen peroxide solution into the second suspension obtained in step (2) to react for a certain time to obtain solid azodicarbonamide; and step (4), separating and washing the solid azodicarbonamide prepared in step (3), so that azodicarbonamide is obtained. In the application, hydrogen peroxide is used as an oxidant, a ferrous compound is used as a catalyst, and the ferrous compound and hydrogen peroxide are reacted, so that biurea can be efficiently oxidized to obtain azodicarbonamide, there is no risk of harmful gas leakage, no waste salt is generated, the preparation process is clean and green.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of azodicarbonamide preparation, and particularly relates to a preparation method of azodicarbonamide. BACKGROUND

[0002] Azodicarbonamide (English name azodicarbonamide) is a light yellow powder, non-toxic, odorless, non-polluting, non-discoloring, non-flammable, and self-extinguishing. It is soluble in alkali, insoluble in gasoline, alcohol, benzene, pyridine and water. Azodicarbonamide is a foaming agent commonly used in industry, which can be used as a foaming agent for polyvinyl chloride, polyethylene, polypropylene, polyamide 11, neoprene, acetonitrile rubber, butyl rubber, butadiene-styrene rubber and silicone rubber, and can be applied to both normal pressure foaming and pressurized foaming.

[0003] At present, the preparation process of azodicarbonamide in industry mainly uses chlorine or hydrogen peroxide to oxidize biurea to obtain azodicarbonamide, and the catalyst is bromine, bromide salt, iodine or iodide salt. The application with the publication number CN109734629B and the title of "a preparation method of uniformly dispersed ultra-fine ADC foaming agent" uses chlorine as an oxidizing agent, sodium bromide as a catalyst, and biurea as a raw material to prepare azodicarbonamide. The application with the publication number CN108276309B and the title of "a foaming agent, a preparation method and application thereof" uses hydrogen peroxide as an oxidizing agent and sodium bromide as a catalyst to oxidize biurea to obtain azodicarbonamide. However, in the process of preparing azodicarbonamide, bromine, bromide salt, iodine or iodide salt will generate gaseous bromine or iodine, which not only corrodes the equipment but also spreads into the air to cause harm to the human body. SUMMARY

[0004] Therefore, the application provides a preparation method of azodicarbonamide, which solves the technical problem that, in the prior art, bromide or iodide is used as a catalyst, bromine, bromide salt, iodine or iodide salt will generate gaseous bromine or iodine, which not only corrodes the equipment but also spreads into the air to cause harm to the human body.

[0005] The application provides a preparation method of azodicarbonamide, which comprises the following preparation steps: step (1), mixing biurea, a ferrous compound catalyst and water in a certain proportion to prepare a biurea suspension; step (2), adjusting the pH value of the biurea suspension prepared in step (1) to 2-6, and heating the biurea suspension with the pH value of 2-6 to 50-100 DEG C to obtain a second suspension; step (3), slowly dropping hydrogen peroxide solution into the second suspension obtained in step (2) and reacting for a certain time to obtain solid azodicarbonamide; and step (4), separating and washing the solid azodicarbonamide prepared in step (3) to obtain azodicarbonamide.

[0006] In an embodiment, the biuret suspension prepared in step (1) is added with dilute sulfuric acid to adjust the pH value of the biuret suspension to 2-6.

[0007] In the present application, hydrochloric acid, nitric acid and the like can also be used to adjust the pH value of the biuret suspension. It should be understood that the reagent for adjusting the pH value is not limited in the present application, as long as the purpose of adjusting the pH value can be achieved.

[0008] In an embodiment, the ferrous compound catalyst includes any one or more of ferrous oxide, ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous acetate, iron hydroxide and ferrous oxalate dihydrate.

[0009] In an embodiment, in step (1), the mass ratio of the biuret to water is (0.5-2):1, and the amount of the catalyst added is 2-20 wt% of the biuret.

[0010] In an embodiment, in step (1), the mass ratio of the biuret to water is (0.8-1.5):1, and the amount of the catalyst added is 10-20 wt% of the biuret.

[0011] In an embodiment, in step (2), the pH value of the biuret suspension is 3-5.

[0012] In an embodiment, in step (2), the heating temperature of the biuret suspension is 60-80°C.

[0013] In an embodiment, in step (3), the molar ratio of hydrogen peroxide in the hydrogen peroxide solution to the biuret is (0.8-2.0):1, and the concentration of the hydrogen peroxide solution is 10-60 wt%.

[0014] In an embodiment, the molar ratio of hydrogen peroxide in the hydrogen peroxide solution to the biuret is (1-1.5):1, and the concentration of the hydrogen peroxide solution is 30-50 wt%.

[0015] In an embodiment, the mass space velocity of the hydrogen peroxide solution is 0.14-0.43 h -1 , wherein the calculation formula of the mass space velocity is: mass space velocity=(mass of hydrogen peroxide (g) / mass of biuret (g)) / adding time of hydrogen peroxide solution (h).

[0016] The application provides a preparation method of azodicarbonamide, which comprises the following steps: step (1), mixing biurea, a catalyst and water according to a certain proportion to prepare a biurea suspension; step (2), adjusting the pH value of the biurea suspension prepared in step (1) to 2-6, and heating the biurea suspension with the pH value of 2-6 to 50-100 DEG C to obtain a second suspension; step (3), slowly adding hydrogen peroxide solution into the second suspension obtained in step (2) to react for a certain time to obtain solid azodicarbonamide; and step (4), separating and washing the solid azodicarbonamide prepared in step (3) to obtain azodicarbonamide, and the liquid after washing can be recycled. The application can efficiently oxidize biurea to prepare azodicarbonamide by using hydrogen peroxide as an oxidant and a ferrous compound as a catalyst, the ferrous compound can react with hydrogen peroxide, no bromide or iodide is needed as a catalyst, no auxiliary agent is needed, therefore, no bromine vapor and iodine vapor are generated, the preparation process has no risk of harmful gas leakage and no waste salt is generated, and the preparation process is clean and green. DETAILED DESCRIPTION

[0017] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with other embodiments. All combinations of embodiments described herein are within the scope of the application.

[0018] Unless otherwise defined, all reagents used in the application are commercially available.

[0019] Example 1

[0020] The preparation method of azodicarbonamide in Example 1 is as follows:

[0021] Step (1), 50.00 g of biurea, 50 g of deionized water and 5 g of ferrous oxide are added into a container to prepare a biurea suspension;

[0022] Step (2), dilute sulfuric acid is added dropwise into the biurea suspension prepared in step (1) to adjust the pH value of the biurea suspension to 3, and the biurea suspension is heated while adjusting the pH value, and the biurea suspension is heated to 80 DEG C;

[0023] Step (3), 43.22 g of hydrogen peroxide solution with a concentration of 50 wt% was added to the hydrazine carbonate suspension using a peristaltic pump to react, the addition time of the hydrogen peroxide solution was 4 h, and solid hydrazinecarboxamide was prepared;

[0024] Step (4), the solid hydrazinecarboxamide prepared in step (3) was separated by suction filtration and the solid was washed, and the solid hydrazinecarboxamide was washed twice with deionized water, and hydrazinecarboxamide 47.01 g was obtained, with a purity of 99.21%.

[0025] In step (3), hydrogen peroxide reacts with ferrous ions to generate hydroxyl radicals with strong oxidizing properties (as shown in formula 1), which further oxidize hydrazine carbonate to produce hydrazinecarboxamide, in addition, the generated ferric ions can also react with hydrogen peroxide to generate oxidizing radicals to participate in the oxidation process of hydrazine carbonate (as shown in formula 2), achieving the purpose of recycling iron ions.

[0026] Fe 2+ +H2O2→Fe 3+ +·OH+OH- Formula 1

[0027] Fe 3+ +H2O2→Fe 2+ +·OOH+H+ Formula 2

[0028] Example 2

[0029] The preparation method of hydrazinecarboxamide in Example 2 is as follows:

[0030] Step (1), 50.00 g of hydrazine carbonate, 50 g of deionized water and 5 g of ferrous hydroxide were added to the reaction kettle to mix and prepare a hydrazine carbonate suspension;

[0031] Step (2), dilute sulfuric acid was added dropwise to the hydrazine carbonate suspension prepared in step (1) to adjust the pH value of the hydrazine carbonate suspension to 3, and the hydrazine carbonate suspension was heated while adjusting the pH value, and the hydrazine carbonate suspension was heated to 80°C;

[0032] Step (3), 43.22 g of hydrogen peroxide solution with a concentration of 30 wt% was added to the hydrazine carbonate suspension using a peristaltic pump to react, the addition time of the hydrogen peroxide solution was 4 h, and solid hydrazinecarboxamide was prepared;

[0033] Step (4), the solid hydrazinecarboxamide prepared in step (3) was separated by suction filtration and the solid was washed, and the solid hydrazinecarboxamide was washed twice with deionized water, and hydrazinecarboxamide 46.55 g was obtained, with a purity of 99.31%.

[0034] Example 3

[0035] The preparation method of the azodicarbonamide of Example 3 is as follows:

[0036] Step (1), 50.00 g of biuret, 50 g of deionized water, 5 g of ferrous sulfate were added to the reaction kettle to prepare a biuret suspension;

[0037] Step (2), add dilute sulfuric acid dropwise to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 4, heat the biuret suspension while adjusting the pH, and heat the biuret suspension to 85°C;

[0038] Step (3), use a peristaltic pump to add 43.22 g of 30 wt% hydrogen peroxide solution to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 4 h, and solid azodicarbonamide is prepared;

[0039] Step (4), the solid azodicarbonamide prepared in step (3) is separated by suction filtration and the solid is washed, the solid azodicarbonamide is washed twice with deionized water, and 47.25 g of azodicarbonamide with a purity of 99.03% is obtained.

[0040] Example 4

[0041] The preparation method of the azodicarbonamide of Example 4 is as follows:

[0042] Step (1), 50.00 g of biuret, 50 g of deionized water, 2.5 g of ferrous oxide and 2.5 g of ferrous hydroxide were added to the reaction kettle to prepare a biuret suspension;

[0043] Step (2), add dilute sulfuric acid dropwise to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 4, heat the biuret suspension while adjusting the pH, and heat the biuret suspension to 85°C;

[0044] Step (3), use a peristaltic pump to add 43.22 g of 30 wt% hydrogen peroxide solution to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 4 h, and solid azodicarbonamide is prepared;

[0045] Step (4), the solid azodicarbonamide prepared in step (3) is separated by suction filtration and the solid is washed, the solid azodicarbonamide is washed twice with deionized water, and 47.25 g of azodicarbonamide with a purity of 99.03% is obtained.

[0046] Example 5

[0047] The preparation method of the azodicarbonamide of Example 5 is as follows:

[0048] Step (1), 50.00 g of biuret, 50 g of deionized water, 2.5 g of ferrous hydroxide and 2.5 g of ferrous sulfate were mixed in a reaction kettle to prepare a biuret suspension;

[0049] Step (2), dilute sulfuric acid was added dropwise to the biuret suspension prepared in step (1) to adjust the pH value of the biuret suspension to 4, and the biuret suspension was heated while adjusting the pH value, and the biuret suspension was heated to 85°C;

[0050] Step (3), 43.22 g of 50wt% hydrogen peroxide solution was added to the biuret suspension for reaction using a peristaltic pump, and the hydrogen peroxide solution was added for 4 h to prepare solid azodicarbonamide;

[0051] Step (4), the solid azodicarbonamide prepared in step (3) was separated by suction filtration and the solid was washed, and the solid azodicarbonamide was washed twice with deionized water to obtain azodicarbonamide 48.67 g with a purity of 99.13%.

[0052] Example 6

[0053] The preparation method of azodicarbonamide in Example 6 is as follows:

[0054] Step (1), 50.00 g of biuret, 50 g of deionized water, 2.5 g of ferrous hydroxide and 2.5 g of ferrous sulfate were mixed in a reaction kettle to prepare a biuret suspension;

[0055] Step (2), dilute sulfuric acid was added dropwise to the biuret suspension prepared in step (1) to adjust the pH value of the biuret suspension to 4, and the biuret suspension was heated while adjusting the pH value, and the biuret suspension was heated to 80°C;

[0056] Step (3), 43.22 g of 50wt% hydrogen peroxide solution was added to the biuret suspension for reaction using a peristaltic pump, and the hydrogen peroxide solution was added for 4 h to prepare solid azodicarbonamide;

[0057] Step (4), the solid azodicarbonamide prepared in step (3) was separated by suction filtration and the solid was washed, and the solid azodicarbonamide was washed twice with deionized water to obtain azodicarbonamide 46.66 g with a purity of 99.77%.

[0058] Example 7

[0059] The preparation method of azodicarbonamide in Example 7 is as follows:

[0060] Step (1), 50.00 g of biuret, 75 g of deionized water, 5 g of ferrous oxide and 5 g of ferrous sulfate were mixed in a reaction kettle to prepare a biuret suspension;

[0061] Step (2), dilute sulfuric acid was added dropwise to the biuret suspension prepared in step (1) to adjust the pH of the biuret suspension to 2, and the biuret suspension was heated while adjusting the pH, and the biuret suspension was heated to 60°C;

[0062] Step (3), 43.22 g of 50 wt% hydrogen peroxide solution was added to the biuret suspension using a peristaltic pump for reaction, and the hydrogen peroxide solution was added for 4 h to prepare solid azodicarbonamide;

[0063] Step (4), the solid azodicarbonamide prepared in step (3) was separated by suction filtration and the solid was washed, and the solid azodicarbonamide was washed twice with deionized water to obtain 48.95 g of azodicarbonamide with a purity of 98.60%.

[0064] Example 8

[0065] The preparation method of azodicarbonamide in Example 8 is as follows:

[0066] Step (1), 40.00 g of biuret, 50 g of deionized water, 6.0 g of ferrous sulfate were mixed in a reaction kettle to prepare a biuret suspension;

[0067] Step (2), dilute sulfuric acid was added dropwise to the biuret suspension prepared in step (1) to adjust the pH of the biuret suspension to 5, and the biuret suspension was heated while adjusting the pH, and the biuret suspension was heated to 100°C;

[0068] Step (3), 43.22 g of 50 wt% hydrogen peroxide solution was added to the biuret suspension using a peristaltic pump for reaction, and the hydrogen peroxide solution was added for 4 h to prepare solid azodicarbonamide;

[0069] Step (4), the solid azodicarbonamide prepared in step (3) was separated by suction filtration and the solid was washed, and the solid azodicarbonamide was washed twice with deionized water to obtain 36.20 g of azodicarbonamide with a purity of 99.05%.

[0070] Example 9

[0071] The preparation method of azodicarbonamide in Example 9 is as follows:

[0072] Step (1), 50.00 g of biuret, 50 g of deionized water, and 5.0 g of ferrous sulfate were added to a reaction kettle to prepare a biuret suspension;

[0073] Step (2), dilute sulfuric acid was added dropwise to the biuret suspension prepared in step (1) to adjust the pH of the biuret suspension to 4, and the biuret suspension was heated while adjusting the pH, and the biuret suspension was heated to 80℃;

[0074] Step (3), 30.0 g of 50wt% hydrogen peroxide solution was added to the biuret suspension using a peristaltic pump for reaction, and the hydrogen peroxide solution was added for 3 h to prepare solid azodicarbonamide;

[0075] Step (4), the solid azodicarbonamide prepared in step (3) was separated and washed by suction filtration, and the solid azodicarbonamide was washed twice with deionized water to obtain azodicarbonamide 48.52 g with a purity of 97.38%.

[0076] Example 10

[0077] The preparation method of azodicarbonamide in Example 10 is as follows:

[0078] Step (1), 50.00 g of biuret, 50 g of deionized water, and 5.0 g of ferrous sulfate were added to a reaction kettle to prepare a biuret suspension;

[0079] Step (2), dilute sulfuric acid was added dropwise to the biuret suspension prepared in step (1) to adjust the pH of the biuret suspension to 4, and the biuret suspension was heated while adjusting the pH, and the biuret suspension was heated to 50℃;

[0080] Step (3), 43.22 g of 50wt% hydrogen peroxide solution was added to the biuret suspension using a peristaltic pump for reaction, and the hydrogen peroxide solution was added for 3 h to prepare solid azodicarbonamide;

[0081] Step (4), the solid azodicarbonamide prepared in step (3) was separated and washed by suction filtration, and the solid azodicarbonamide was washed twice with deionized water to obtain azodicarbonamide 48.93 g with a purity of 93.27%.

[0082] Example 11

[0083] The preparation method of azodicarbonamide in Example 11 is as follows:

[0084] Step (1), 50.00 g of biuret, 50 g of deionized water, and 5.0 g of ferrous sulfate were added to a reaction kettle to prepare a biuret suspension;

[0085] Step (2), add dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 6, and heat the biuret suspension while adjusting the pH value, and heat the biuret suspension to 80°C;

[0086] Step (3), use a peristaltic pump to add 23.52 g of hydrogen peroxide solution with a concentration of 50 wt% to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 3 h, and solid azodicarbonamide is prepared;

[0087] Step (4), separate the solid azodicarbonamide prepared in step (3) by suction filtration and wash the solid, and wash the solid azodicarbonamide with deionized water twice to obtain azodicarbonamide 48.17 g with a purity of 78.33%.

[0088] Example 12

[0089] The preparation method of the azodicarbonamide of Example 12 is as follows:

[0090] Step (1), mix 50.00 g of biuret, 50 g of deionized water and 2.5 g of ferrous chloride in a reaction kettle to prepare a biuret suspension;

[0091] Step (2), add dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 4, and heat the biuret suspension while adjusting the pH value, and heat the biuret suspension to 80°C;

[0092] Step (3), use a peristaltic pump to add 23.52 g of hydrogen peroxide solution with a concentration of 50 wt% to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 3 h, and solid azodicarbonamide is prepared;

[0093] Step (4), separate the solid azodicarbonamide prepared in step (3) by suction filtration and wash the solid, and wash the solid azodicarbonamide with water to prepare azodicarbonamide 48.50 g with a purity of 92.99%.

[0094] Example 13

[0095] The preparation method of the azodicarbonamide of Example 13 is as follows:

[0096] Step (1), mix 50.00 g of biuret, 25 g of deionized water and 5.0 g of ferrous chloride in a reaction kettle to prepare a biuret suspension;

[0097] Step (2), add dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 1, heat the biuret suspension while adjusting the pH, and heat the biuret suspension to 80°C;

[0098] Step (3), use a peristaltic pump to add 43.22 g of hydrogen peroxide solution with a concentration of 20 wt% to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 3 h, and solid azodicarbonamide is prepared;

[0099] Step (4), separate the solid azodicarbonamide prepared in step (3) by suction filtration and wash the solid, wash the solid azodicarbonamide with deionized water twice, and azodicarbonamide 47.56 g with a purity of 91.43% is prepared.

[0100] Example 14

[0101] The preparation method of azodicarbonamide in Example 14 is as follows:

[0102] Step (1), mix 50.00 g of biuret, 100 g of deionized water and 5.0 g of ferrous chloride in a reaction kettle to prepare a biuret suspension;

[0103] Step (2), add dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 4, heat the biuret suspension while adjusting the pH, and heat the biuret suspension to 80°C;

[0104] Step (3), use a peristaltic pump to add 43.22 g of hydrogen peroxide solution with a concentration of 50 wt% to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 3 h, and solid azodicarbonamide is prepared;

[0105] Step (4), separate the solid azodicarbonamide prepared in step (3) by suction filtration and wash the solid, wash the solid azodicarbonamide with deionized water twice, and azodicarbonamide 48.32 g with a purity of 95.64% is prepared.

[0106] Comparative Example 1

[0107] In the preparation of azodicarbonamide in Comparative Example 1, sodium bromide is used as the catalyst, and the preparation method is as follows:

[0108] Step (1), mix 50.00 g of biuret, 50 g of deionized water and 1.0 g of sodium bromide in a reaction kettle to prepare a biuret suspension;

[0109] Step (2), add dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 3, heat the biuret suspension while adjusting the pH, and heat the biuret suspension to 85°C;

[0110] Step (3), use a peristaltic pump to add 43.22 g of hydrogen peroxide solution with a concentration of 50 wt% to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 3 h, and solid azodicarbonamide is prepared;

[0111] Step (4), separate and wash the solid azodicarbonamide prepared in step (3) by suction filtration, wash the solid azodicarbonamide with deionized water twice, and azodicarbonamide 48.00 g with a purity of 99.09% is prepared.

[0112] Comparative Example 2

[0113] In the preparation of azodicarbonamide in Comparative Example 2, sodium bromide is used as the catalyst, and the preparation method is as follows:

[0114] Step (1), mix 50.00 g of biuret, 50 g of deionized water, and 2.0 g of sodium bromide in a reaction kettle to prepare a biuret suspension;

[0115] Step (2), add dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjust the pH value of the biuret suspension to 4, heat the biuret suspension while adjusting the pH, and heat the biuret suspension to 85°C;

[0116] Step (3), use a peristaltic pump to add 43.22 g of hydrogen peroxide solution with a concentration of 50 wt% to the biuret suspension for reaction, the addition time of the hydrogen peroxide solution is 3 h, and solid azodicarbonamide is prepared;

[0117] Step (4), separate and wash the solid azodicarbonamide prepared in step (3) by suction filtration, wash the solid azodicarbonamide with deionized water twice, and azodicarbonamide 47.35 g with a purity of 99.71% is prepared.

[0118] Comparative Example 3

[0119] In the preparation of azodicarbonamide in Comparative Example 3, iodine standard solution is used as the catalyst, and the preparation method is as follows:

[0120] Step (1), mix 50.00 g of biuret, 50 g of deionized water, and 2 g of iodine standard solution (0.1 mol / L) in a reaction kettle to prepare a biuret suspension;

[0121] Step (2), adding dilute sulfuric acid drop by drop to the biuret suspension prepared in step (1), adjusting the pH value of the biuret suspension to 3, and heating the biuret suspension while adjusting the pH value, and heating the biuret suspension to 80°C;

[0122] Step (3), using a peristaltic pump to add 43.22 g of hydrogen peroxide solution with a concentration of 50 wt% to the biuret suspension for reaction, and the hydrogen peroxide solution is added for 3 h, and a solid azodicarbonamide is prepared;

[0123] Step (4), separating the solid azodicarbonamide prepared in step (3) by suction filtration and washing the solid, and washing the solid azodicarbonamide with deionized water twice, and azodicarbonamide 48.80 g with a purity of 85.23% is prepared.

[0124] Table 1 comparison table of examples 1-14 and comparative examples 1-3

[0125]

[0126] As can be seen from Table 1, in the process of preparing azodicarbonamide by oxidizing biuret, when using ferrous compounds as catalyst, the purity of azodicarbonamide reaches more than 99%, which is consistent with the result of using sodium bromide and potassium iodide in industry. The amount of hydrogen peroxide and catalyst added is the main factor affecting the purity of azodicarbonamide. Generally, the molar ratio of hydrogen peroxide to biuret is greater than 1, and the catalyst is more than 10% of the mass of biuret, and azodicarbonamide with a purity of 99% can be obtained.

[0127] In example 6, 43.22 g of hydrogen peroxide solution with a concentration of 50 wt% is added, which is 100% of the theoretical amount of hydrogen peroxide solution, so the purity of the azodicarbonamide prepared therefrom is 99.77%, close to the theoretical value of 100%.

[0128] In example 11, 23.52 g of hydrogen peroxide solution with a concentration of 50 wt% is added, which is 80% of the theoretical amount of hydrogen peroxide solution, so the purity of the azodicarbonamide prepared therefrom is 78.35%, close to the theoretical value of 80%.

[0129] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing azodicarbonamide, characterized in that, The preparation steps include the following: Step (1): Prepare a biuret suspension by mixing biuret, ferrous compound catalyst and water in a certain proportion; Step (2): Adjust the pH of the biuret suspension obtained in step (1) to 2-5, and heat the biuret suspension with pH 2-5 to 50-100℃ to obtain a second suspension; Step (3): Hydrogen peroxide solution is slowly added dropwise to the second suspension obtained in step (2) and reacted for a certain period of time to obtain solid azodicarbonamide; Step (4): Separate and wash the solid azodicarbonamide prepared in step (3) to obtain azodicarbonamide; The ferrous compound catalyst is selected from any one or more of ferrous oxide, ferrous sulfate, ferrous nitrate, ferrous chloride, and ferrous hydroxide; In step (1), the mass ratio of biuret to water is (0.5~2):1, and the amount of catalyst added is 2~20 wt% of biuret. In step (3), the molar ratio of the hydrogen peroxide solution to the biuret is (1~1.5):1; the concentration of the hydrogen peroxide solution is 30~50 wt%. The mass hourly space velocity (MSV) of the hydrogen peroxide solution is 0.14–0.43 h⁻¹. -1 .

2. The method for preparing azodicarbonamide according to claim 1, characterized in that, In step (1), the mass ratio of biuret to water is (0.8~1.5):1; the amount of catalyst added is 10~20wt% of biuret.

3. The method for preparing azodicarbonamide according to claim 1, characterized in that, In step (2), the pH value of the biuret suspension is 3 to 5.

4. The method for preparing azodicarbonamide according to claim 1, characterized in that, In step (2), the heating temperature of the biuret suspension is 60~80℃.

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