Method for generating biurea through condensation reaction of hydrazine hydrate and urea

Abstract

The invention provides a method for generating biurea through a condensation reaction of hydrazine hydrate and urea, which comprises the following steps: a first stage: mixing urea and a hydrazine hydrate solution in proportion, and continuously adding into a first condensation kettle; and in the second condensation kettle, setting a higher pressure and temperature range, supplementing a proper amount of urea to ensure the reactant concentration, adding the residual ammonium sulfate catalyst, and continuing to accelerate the reaction. The method has the advantages of high yield, high purity, energy conservation and the like.

Description

Technical Field

[0001] The invention relates to a chemical reaction method, in particular to a method for generating biurea through condensation reaction of hydrazine hydrate and urea. Background Art

[0002] ADC foaming agent, also known as azodicarbonamide (ADC), is a commonly used foaming agent, widely used in the manufacture of plastics such as polyethylene, polyvinyl chloride, polystyrene, chloroprene rubber, resin and natural rubber. Its production process mainly includes the production of hydrazine hydrate, condensation reaction and oxidation reaction.

[0003] In the chemical industry, biurea (NH2CONHNHCONH2) is an important chemical raw material, widely used in the production of ADC foaming agent (azodicarbonamide), and also plays a key role in the fields of anti-skid of runways, anti-skid of high-grade roads and gears, fire and anti-melting of high-grade cables. The traditional industrial production method of biurea is mainly produced by the condensation reaction of hydrazine hydrate (N2H4·H2O) and urea (NH2CONH2) under acidic or alkaline conditions. The overall reaction formula can be expressed as: N2H4+2NH2CONH2→NH2CONHNHCONH2+2NH3.

[0004] Although the condensation reaction under acidic conditions has a fast reaction speed and the total reaction time can be shortened to 8 to 12 hours, the equipment maintenance cost is high due to the severe corrosion of the acidic medium to the equipment. In addition, the acidified wastewater rich in inorganic salts such as ammonium salts generated during the reaction makes wastewater treatment complicated and expensive. Therefore, although the acidic condensation process has certain advantages in improving production efficiency, its high equipment maintenance cost and wastewater treatment cost limit its widespread application.

[0005] Compared with acidic conditions, the condensation reaction time under alkaline conditions is significantly prolonged, especially when anhydrous hydrazine is used, the reaction time can exceed 20 hours. This not only reduces production efficiency, but also increases energy consumption. Although there are reports that the reaction time can be shortened by adding sulfuric acid to adjust the pH value under weakly alkaline conditions (such as pH values ​​between 7 and 10), the reaction time is still as long as about 15 hours, and the process is still intermittent operation, which is difficult to meet the needs of continuous production.

[0006] In order to overcome the equipment corrosion and wastewater treatment problems of the acidic condensation process, and to avoid the problem of long reaction time under alkaline conditions, researchers explored the production method of biurea under acid-free conditions. However, under acid-free conditions, the condensation reaction of hydrazine hydrate and urea is a multi-stage reaction, and the reaction rate gradually slows down as the concentration of the reactants decreases. Experiments show that in the absence of added acid, the condensation reaction time will exceed 20 hours, which seriously affects production efficiency, resulting in reduced equipment utilization efficiency and production capacity, making it difficult to meet the needs of industrial production.

[0007] In order to further improve production efficiency and reduce wastewater discharge and treatment difficulty, researchers have proposed a continuous production process for biurea. This process uses a multi-reactor series connection method to continuously feed urea and hydrazine hydrate solution into the reactor for condensation reaction. The biurea generated by the reaction is discharged from the bottom of the reactor together with the mother liquor containing unreacted raw materials, and enters the solid-liquid separation device to obtain biurea solid and mother liquor. The mother liquor is fully recycled, reducing wastewater discharge. In addition, the ammonia generated during the reaction escapes from the top of the reactor together with the water vapor, and is separated after condensation. Part of the condensate can be discharged from the system, which achieves the concentration of the reactants and is beneficial to increasing the reaction rate.

[0008] The existing biurea production process has problems with equipment corrosion and wastewater treatment under acidic conditions, and faces the problem of long reaction time under alkaline conditions. Although the acid-free condensation production method and continuous production process provide new ideas for solving these problems, the reaction conditions and process flow still need to be further optimized to improve production efficiency, reduce production costs and reduce environmental pollution. Summary of the invention

[0009] In view of the deficiencies of the prior art, the present invention provides a method for generating biurea through condensation reaction of hydrazine and urea.

[0010] In order to achieve the above object, the present invention adopts the following scheme:

[0011] The method for generating biurea by condensation reaction of hydrazine hydrate and urea comprises the following steps:

[0012] The first stage: urea and hydrazine hydrate solution are mixed in proportion and continuously added to the first condensation kettle; in the first condensation kettle, a specific pressure and temperature range are set, and CO2 gas is introduced to maintain the reaction environment; according to the reaction process, ammonium sulfate catalyst is gradually added, and its molar ratio with hydrazine hydrate is controlled; the reaction is carried out for a period of time while maintaining the pressure and temperature in the reactor constant;

[0013] The second stage: the first reaction liquid is transferred to the second condensation kettle; in the second condensation kettle, a higher pressure and temperature range are set, and the flow rate of CO2 gas is increased to continuously promote the reaction; according to the real-time monitoring data of urea in the reaction liquid, urea is supplemented in an appropriate amount to ensure the concentration of reactants; the remaining ammonium sulfate catalyst is added to continue to accelerate the reaction; and further reaction is carried out while maintaining constant parameters in the reactor.

[0014] In the first stage, the pressure of the first condensation kettle is set to about 0.25 MPa, and the temperature is controlled between 110° C. and 115° C.

[0015] In the first stage, the flow rate of CO2 gas is controlled at about 5L / min.

[0016] In the first stage, the ammonium sulfate catalyst is added gradually, and the molar ratio of the ammonium sulfate catalyst to the hydrazine hydrate is controlled to be close to 1:1.

[0017] The pressure of the second condensation kettle is set to about 0.35 MPa, and the temperature is controlled between 115°C and 120°C.

[0018] In the second stage, the flow rate of CO2 gas increases to about 7L / min.

[0019] The reaction time of the first stage and the second stage are controlled at about 3.5 hours and 2 hours respectively.

[0020] The method further comprises a post-processing step of the third stage, wherein the second reaction liquid is filtered and centrifuged to separate a solid product, and the solid product is washed multiple times to improve the purity.

[0021] The method of the present invention has the following advantages:

[0022] The purity of biurea is significantly improved. The yield of biurea (i.e., the ratio of product mass to theoretical maximum product mass) of the present invention can reach more than 90%, thereby improving the utilization rate of raw materials, reducing energy consumption, and accelerating the reaction process. DETAILED DESCRIPTION

[0023] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] The process of hydrazine hydrate covers the preparation of sodium hypochlorite, the synthesis of hydrazine hydrate, and the separation and comprehensive utilization of sodium carbonate decahydrate. Specifically, sodium hypochlorite is produced by the reaction of chlorine and caustic soda; then, sodium hypochlorite and urea react chemically in a synthesis tower, a shell-and-tube reactor or a shell-and-tube reactor at a specific temperature and under the action of a catalyst to produce hydrazine hydrate; finally, sodium carbonate decahydrate is separated from crude hydrazine hydrate by methods such as freeze crystallization and recycled.

[0025] Next is the condensation reaction stage. In this stage, hydrazine hydrate reacts with urea to form biurea, which is an important intermediate in the production of ADC foaming agent. At present, the condensation reaction mainly adopts the acid process, that is, under acidic conditions, urea is added to low-concentration hydrazine hydrate, and a condensation reaction occurs after heating to form biurea.

[0026] Then it enters the oxidation reaction stage. In this stage, biurea is oxidized to ADC foaming agent. At present, the main oxidation methods include chlorine oxidation method and sodium chlorate oxidation method. In the chlorine oxidation method, chlorine and biurea undergo oxidation reaction under the action of a catalyst to generate ADC foaming agent; while the sodium chlorate oxidation method uses sodium chlorate as an oxidant. This method has significant advantages in product quality and environmental protection.

[0027] The final stage is the post-processing stage. The crude ADC foaming agent obtained after the oxidation reaction needs to be washed, centrifuged, dried, and other steps to remove impurities and by-products on the surface of the product, separate the solid ADC foaming agent, and dry it to below a certain moisture content to ensure product quality.

[0028] In the production process of ADC foaming agent (azodicarbonamide), condensation reaction is a crucial step, which is directly related to the efficiency of subsequent oxidation reaction and the quality and yield of the final product. This step is usually carried out under positive pressure or normal pressure. The inventors have provided a reaction method through exploration.

[0029] The present invention proposes an innovative condensation reaction method for the acid-free continuous production process of biurea, the core of which is to optimize the reaction conditions and improve the yield and purity by precisely controlling the pressure, temperature, raw material ratio and gas flow rate of the reaction system.

[0030] The process of the present invention adopts a two-kettle series mode, that is, the first condensation kettle and the second condensation kettle are connected in sequence, and efficient and stable biurea production is achieved through specific pressure, temperature, raw material ratio and gas flow control.

[0031] To ensure effective collision between reactant molecules and accelerate the reaction, the system is maintained in a pressurized state. In particular, the pressure of the first condensation kettle is 0.25MPa, while the pressure of the second condensation kettle is 0.35MPa, and this pressure difference is stabilized by a vacuum pump. The first condensation kettle is controlled between 110℃ and 115℃, and the second condensation kettle is controlled between 115℃ and 120℃; the temperature of the second condensation kettle is higher than that of the first condensation kettle.

[0032] Raw material ratio: The mass ratio of urea to hydrazine hydrate (mass fraction of hydrazine hydrate is 10% to 15%) is optimized to 4:1 to 7:1, which is suitable for acid-free condensation conditions.

[0033] Continuous feeding is adopted to keep the concentration of mixed solution constant and reduce production fluctuations.

[0034] In the first condensation kettle, the initial flow rate of CO2 is 5L / min. When entering the second condensation kettle, as the reaction speed gradually slows down, the flow rate of CO2 should be appropriately increased and set to 7L / min to continuously promote the reaction. In the second condensation kettle, according to the reaction progress and real-time monitoring data, urea is supplemented in an appropriate amount; the supplement amount should be determined according to the consumption of urea in the reaction solution and the output of the target product biurea, and adjusted according to the real-time monitoring results of the urea concentration in the reaction solution to ensure the concentration of the reactants and promote the complete reaction.

[0035] Process flow: Add the mixed solution to the first condensation kettle, introduce an appropriate amount of CO2, heat to the specified temperature, react for 3 to 4 hours, and obtain the first reaction liquid. The first reaction liquid is transferred to the second condensation kettle, supplemented with urea, increase the CO2 flow rate, and continue to react for 1.7 to 2.3 hours to obtain the second reaction liquid. The second reaction liquid is filtered, centrifuged and washed multiple times to obtain high-purity biurea solid; the washing water is recycled and used for subsequent batching.

[0036] In the above process, ammonium sulfate catalyst is added at each stage of the reaction, and the molar ratio of ammonium sulfate to hydrazine hydrate is controlled at 0.5:1 to 1.5:1 to accelerate the reaction process and improve production efficiency.

[0037] Embodiment 1:

[0038] Weigh 86.5 kg of urea and 123.04 kg of hydrazine hydrate (12.5% ​​hydrazine hydrate solution by mass)

[0039] In the first condensation kettle, CO2 was introduced at a rate of 5 L / min for 3.5 hours; in the second condensation kettle, CO2 was introduced at a rate of 7 L / min for 2 hours.

[0040] 64.57 kg of ammonium sulfate catalyst.

[0041] The operation process is as follows. Stage 1: Mix 86.5 kg of urea and 123.04 kg of hydrazine hydrate solution in proportion and add them continuously to the first condensation kettle. Set the pressure of the first condensation kettle to 0.25 MPa and control the temperature between 110°C and 115°C. Introduce CO2 at a flow rate of 5 L / min to maintain the reaction environment. According to the progress of the reaction, gradually add part of the ammonium sulfate catalyst 32.5 kg, and control the molar ratio with hydrazine hydrate to be close to 1:1. Keep the reaction for 3.5 hours, during which the pressure and temperature in the reactor are maintained.

[0042] Stage 2: Transfer the first reaction liquid to the second condensation kettle. Set the pressure of the second condensation kettle to 0.35MPa and control the temperature between 115℃ and 120℃. Increase the CO2 flow rate to 7L / min to continuously promote the reaction. According to the real-time monitoring data of urea in the reaction liquid, add an appropriate amount of urea to ensure the concentration of the reactants. Add the remaining ammonium sulfate catalyst to continue to accelerate the reaction. Keep the reaction for 2 hours, and also closely monitor the various parameters in the reactor during this period.

[0043] The third stage: post-treatment. The second reaction liquid is filtered and centrifuged to separate the solid product. The solid product is washed several times to improve the purity; the washing water is recycled and used for subsequent batching. The quality of the finally obtained biurea solid is tested, including the evaluation of purity, yield and other indicators.

[0044] Example 2

[0045] 87 kg of urea, 122.88 kg of hydrazine hydrate (hydrazine hydrate solution with a mass fraction of 12.5%), and 65 kg of ammonium sulfate catalyst were selected.

[0046] Stage 1: Mix urea and hydrazine hydrate solution in proportion and add them to the first condensation kettle continuously. Set the pressure of the first condensation kettle to 0.26MPa and control the temperature between 111℃ and 114℃. Introduce CO2 at a flow rate of 5.5L / min to maintain the reaction environment. Gradually add part of the ammonium sulfate catalyst 32.5kg. Keep the reaction for 3.5 hours.

[0047] Stage 2: Transfer the first reaction liquid into the second condensation kettle. Set the pressure of the second condensation kettle to 0.36MPa and control the temperature between 116℃ and 119℃. Increase the CO2 flow rate to 7.5L / min. Add an appropriate amount of urea according to the real-time monitoring data of urea in the reaction liquid. Add the remaining ammonium sulfate catalyst. Keep the reaction for 2 hours.

[0048] The third stage: post-processing, same as in Example 1.

[0049] Example 3

[0050] 85.5 kg of urea; 123.46 kg of hydrazine hydrate (hydrazine hydrate solution with a mass fraction of 12.5%); and 64 kg of ammonium sulfate catalyst.

[0051] Stage 1: Mix urea and hydrazine hydrate solution in proportion and add them to the first condensation kettle continuously. Set the pressure of the first condensation kettle to 0.24MPa and control the temperature between 112℃ and 113℃. Introduce CO2 at a flow rate of 4.5L / min to maintain the reaction environment. Gradually add part of the ammonium sulfate catalyst 32kg. Keep the reaction for 3.5 hours.

[0052] Stage 2: Transfer the first reaction liquid into the second condensation kettle. Set the pressure of the second condensation kettle to 0.34MPa and control the temperature between 117℃ and 118℃. Increase the CO2 flow rate to 6.5L / min. Add an appropriate amount of urea according to the real-time monitoring data of urea in the reaction liquid. Add the remaining ammonium sulfate catalyst. Keep the reaction for 2 hours.

[0053] The third stage: post-processing, same as in Example 1.

[0054] The method of the present invention has the following advantages:

[0055] Significantly improve the purity of biurea. By precisely controlling the reaction conditions, including the raw material ratio, reaction temperature, pressure and gas flow rate, and using an ammonium sulfate catalyst, the present invention can significantly improve the purity of biurea. The purity of biurea in the embodiment can reach more than 98%, which is significantly improved compared with the traditional process.

[0056] Due to the optimization of reaction conditions and the use of catalysts, the yield of biurea (i.e., the ratio of product mass to theoretical maximum product mass) of the present invention can reach more than 90%, which means that with the same raw material input, the present invention can produce more biurea products and improve the utilization rate of raw materials.

[0057] Reduce energy consumption. Maintaining the pressure state of the system, especially the pressure setting of the first condensation kettle and the second condensation kettle, helps to reduce the reaction temperature, thereby reducing the energy consumption required for heating. Compared with the traditional process, the operation of the present invention can reduce energy consumption by about 10%-15%, which is of great significance for reducing production costs and improving production efficiency.

[0058] Accelerate the reaction process. Adding ammonium sulfate catalyst to the first condensation kettle and the second condensation kettle respectively can significantly accelerate the reaction process. The use of catalyst can increase the reaction speed by about 30%-40%, thereby shortening the reaction time and improving production efficiency. For industrial production, this can greatly improve the utilization rate and production capacity of equipment.

[0059] The first condensation kettle is controlled between 110℃ and 115℃, and the second condensation kettle is controlled between 115℃ and 120℃. This temperature gradient helps to accelerate the reaction process and complete the reaction more thoroughly. Through the temperature gradient, the reaction efficiency and product quality are further improved.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for generating biurea by condensation reaction of hydrazine hydrate and urea, characterized in that The following steps are involved: The first stage: urea and hydrazine hydrate solution are mixed in proportion and added continuously into the first condensation kettle; In the first condensation reactor, a specific pressure and temperature range are set, and CO2 gas is introduced to maintain the reaction environment; according to the reaction progress, ammonium sulfate catalyst is gradually added, and the molar ratio of ammonium sulfate catalyst to hydrazine hydrate is controlled; and the reaction is carried out for a period of time while maintaining the pressure and temperature in the reactor constant; The second stage: the first reaction liquid is transferred to the second condensation kettle; in the second condensation kettle, a higher pressure and temperature range are set, and the flow rate of CO2 gas is increased to continuously promote the reaction; According to the real-time monitoring data of urea in the reaction solution, urea is supplemented in an appropriate amount to ensure the concentration of the reactants; the remaining ammonium sulfate catalyst is added to continue to accelerate the reaction; and further reaction is carried out under the condition of maintaining constant parameters in the reactor.

2. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: In the first stage, the pressure of the first condensation kettle is set to about 0.25 MPa, and the temperature is controlled between 110° C. and 115° C.

3. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: In the first stage, the flow rate of CO2 gas is controlled at about 5L / min.

4. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: In the first stage, the ammonium sulfate catalyst is added gradually, and the molar ratio of the ammonium sulfate catalyst to the hydrazine hydrate is controlled to be close to 1:

1.

5. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: The pressure of the second condensation kettle is set to about 0.35 MPa, and the temperature is controlled between 115°C and 120°C.

6. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: In the second stage, the flow rate of CO2 gas increases to about 7L / min.

7. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: The reaction time of the first stage and the second stage are controlled at about 3.5 hours and 2 hours respectively.

8. The method for generating biurea by condensation reaction of hydrazine hydrate and urea according to claim 1, characterized in that: The method further comprises a post-processing step of the third stage, wherein the second reaction liquid is filtered and centrifuged to separate a solid product, and the solid product is washed multiple times to improve the purity.