Hydrazine hydrate and preparation method thereof

Abstract

The invention provides hydrazine hydrate and a preparation method thereof, and relates to the technical field of synthesis processes of nitrogen-containing compounds. According to the invention, sodium hypochlorite is atomized and dispersed into fine liquid drops to form a tiny reaction unit, so that the sodium hypochlorite is instantaneously and completely reacted with excessive ammonia gas without backmixing; the two-stage condensation design is adopted, so that uniform contact and thorough separation of materials are ensured, the side reaction that the product hydrazine hydrate is oxidized by sodium hypochlorite is effectively avoided, and meanwhile, the yield of the hydrazine hydrate can reach 90% or above and is far higher than that of a traditional Raschig method by 60%-70%; the mass concentration of the generated hydrazine hydrate can reach 5%-15%, and is obviously higher than 1%-2% of a Raschig method and 2%-4% of a urea method; due to the high-concentration product, the energy consumption in the subsequent evaporation and concentration process is greatly reduced; the whole technological process of the method is high in continuity degree, operation parameters are easy to control, and the method is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of synthetic process technology for nitrogen-containing compounds, and in particular to a hydrated hydrazine and its preparation method. Background Technology

[0002] Hydrazine hydrate, as an important fine chemical raw material, is widely used in pharmaceuticals, pesticides, dyes, water treatment and aerospace fuels. Optimizing its preparation process is of great significance for improving product quality, reducing production costs and achieving environmentally friendly production.

[0003] Currently, the main methods for preparing hydrazine hydrate include the Raschig process, urea process, ketazine process, hydrogen peroxide process, and air oxidation process. Industrial production primarily uses the urea process and the ketazine process. The hydrogen peroxide process is costly and not used by any domestic manufacturers, while the air oxidation process is still immature and remains only at the laboratory stage.

[0004] The Raschig process, also known as the Raschig process, was the first method to achieve industrial-scale production of hydrazine hydrate. This method synthesizes hydrazine hydrate from ammonia and sodium hypochlorite, producing some chloramines in the process, hence it is also called the chloramine process.

[0005] The chemical equations involved in the Raschig process for producing hydrazine hydrate are as follows:

[0006]

[0007]

[0008] The overall reaction equation is:

[0009]

[0010] The main side effects are:

[0011]

[0012]

[0013]

[0014] The Raschig process first involves reacting 8% excess NaOH with Cl2 to produce NaClO, which then reacts with ammonia absorbed by pure water under pressure at 120-170 °C. The high temperature and pressure are used to increase the reaction rate. To further accelerate the reaction, catalysts such as gelatin can be added. The resulting system contains hydrazine hydrate, NaCl, residual NaOH, unreacted NH3, and some byproducts. Excess NH3 is first removed using a stripping column. The bottom liquid from the stripping column is then fed into a distillation column to remove the byproducts NaCl and excess NaOH. The distillate is then concentrated to obtain hydrazine hydrate that meets production requirements.

[0015] The hydrazine hydrate obtained by this method is a 1%-2% dilute aqueous solution (not exceeding 4%), and the overall reaction yield can only reach 67%. A considerable amount of heat is required to concentrate the hydrazine hydrate from the dilute solution, thus consuming a large amount of steam during the subsequent concentration process. For every 1 kg of hydrazine hydrate recovered, 40-110 kg of water needs to be distilled off. Due to the use of excessive ammonia, a recovery device is required, and large amounts of salts such as NaCl and NH4Cl are produced as byproducts, requiring a series of subsequent processes for recovery and reuse.

[0016] The main advantage of the Raschig process is its mature production technology and readily available raw materials (all simple chemical products), making it suitable for large-scale production. However, due to the large number of byproducts generated and the relatively dilute hydrazine hydrate solution, subsequent concentration processes require significant energy consumption, resulting in relatively high overall energy consumption. With the rise of environmental protection and green chemistry concepts, this method has been largely phased out both domestically and internationally.

[0017] The urea process, also known as the Schestakoff process, is actually a further improvement on the Raschig process, using urea instead of ammonia as the nitrogen source. The chemical equations involved in the urea process for producing hydrazine hydrate are as follows:

[0018] NH2CONH2+NaClO+2NaOH→N2H4•H2O+NaCl+Na2CO3

[0019] N2H4•H2O + 2NaClO → N2 + 3H2O + 2NaCl (side reaction)

[0020] The main process of urea production is as follows: First, Cl2 and NaOH react in a reactor to generate NaClO. Then, NaClO reacts with urea in a hydrazine reactor. The resulting crude hydrazine solution undergoes a series of processes, including freezing to remove alkali, evaporation to remove salt, and distillation to concentrate, to obtain a hydrated hydrazine solution of the concentration required for industrial applications.

[0021] Because NaClO is a strong oxidizing agent and the reaction product hydrazine has strong reducing properties, strong side reactions occur during the reaction. N₂H₄ in the product is oxidized, resulting in a low overall yield, typically in the range of 70%-80%. Improper operation or raw material ratios can also easily lead to blowout accidents. To suppress side reactions, the concentration of hydrazine in the reactor needs to be controlled at a low level (usually 2%-3%), which leads to a large energy consumption during subsequent distillation and concentration. Furthermore, the reaction produces a large amount of byproduct alkali (the amount of which is 12 times that of hydrazine), requiring freeze crystallization to remove the byproducts, which consumes a significant amount of thermal and mechanical energy in subsequent processing.

[0022] Because the urea process uses urea as the nitrogen source, it reduces equipment complexity and investment to some extent, making the synthesis process simpler and easier to master. However, the raw material costs of this method are higher than other methods, resulting in a lack of market competitiveness during large-scale industrial production. Therefore, this process has been largely phased out abroad.

[0023] The ketazine process is a relatively advanced method, using ketones to protect hydrazine from oxidation by sodium hypochlorite, thus improving the yield. However, it introduces organic matter, generating large amounts of highly concentrated organic waste brine that is difficult to manage and cannot be recycled. Currently, the most effective method is evaporation, dehydration, and crystallization to form salt, which significantly increases energy consumption and is not conducive to energy conservation and environmental protection.

[0024] Patent CN201810617679.7 mentions an improved Raschig process, which uses a two-stage reaction of sodium hypochlorite aqueous solution and ammonia or liquid ammonia, achieving a yield of up to 90%. However, hydrazine hydrate is a strong reducing agent, while sodium hypochlorite and chloramine are both strong oxidizing agents, and hydrazine is easily oxidized by sodium hypochlorite or chloramine. The traditional Raschig process uses a large excess of ammonia to dilute the product hydrazine hydrate, reducing the side reaction of hydrazine oxidation by sodium hypochlorite and chloramine. However, the method described in this patent uses a small amount of excess ammonia and no water for dilution. The intermediate product chloramine and the product hydrazine hydrate cannot be effectively diluted, and no other measures are taken to reduce side reactions. In the presence of a large amount of sodium hypochlorite, the more reducing hydrazine will be preferentially oxidized and decomposed by sodium hypochlorite or chloramine before ammonia. The chloramine generated in the first-stage reaction will react with sodium hypochlorite and be consumed, and the hydrazine generated in the second-stage reaction will also be oxidized by sodium hypochlorite and chloramine. This results in a very low actual yield, much lower than that of the traditional Raschig process. Experimental verification shows that the concentration of hydrazine hydrate in the reaction solution is similar to that of the traditional Raschig process, only about 1-2%, and the yield calculated based on sodium hypochlorite is only about 10-20%.

[0025] The above methods have problems such as low yield, high energy consumption, and generation of organic waste brine. Therefore, there is an urgent need to develop a high-yield, high-concentration, energy-saving, environmentally friendly method for preparing hydrazine hydrate that can achieve material recycling in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0026] The purpose of this invention is to provide a hydrazine hydrate and its preparation method, aiming to solve the problems of low yield, low product concentration, and high energy consumption of the existing Raschig process, the large amount of by-products, high cost, high energy consumption and poor environmental performance of the urea process, and the large amount of organic waste brine generated by the ketone azo process, so as to achieve efficient, low-consumption and environmentally friendly production of hydrazine hydrate and achieve material recycling.

[0027] In a first aspect, this application provides a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0028] S1 reaction stage: Sodium hypochlorite solution and ammonia are used as raw materials. The sodium hypochlorite solution is atomized and dispersed into fine sodium hypochlorite droplets, forming tiny reaction units that react with ammonia.

[0029] S2 Secondary condensation separation stage: The mist after the reaction in step S1 is condensed into liquid by primary condensation to obtain crude hydrazine hydrate solution I containing sodium chloride and ammonia. The uncondensed portion is further condensed by secondary condensation to obtain crude hydrazine hydrate aqueous solution II. The remaining non-condensable ammonia gas reacts repeatedly with sodium hypochlorite droplets. The temperature of primary condensation and secondary condensation is between 0-50℃, with the temperature of primary condensation being higher than that of secondary condensation.

[0030] S3 Distillation and Concentration Stage: Combine crude hydrazine hydrate solution I and crude hydrazine hydrate solution II, remove ammonia, and then distill to remove salt, concentrate and purify to obtain hydrazine hydrate product.

[0031] Preferably, a stripping tower is used to remove ammonia.

[0032] Furthermore, the temperature of the first-stage condensation is 15~45℃, and the temperature of the second-stage condensation is 0~7℃.

[0033] Furthermore, in step S1, the sodium hypochlorite solution is cooled to 5-10°C before atomization. Cooling to 5-10°C increases the stability of sodium hypochlorite and reduces side reactions.

[0034] Furthermore, in step S1, the atomized droplet size of the sodium hypochlorite solution is 2~20μm.

[0035] Preferably, in step S1, the atomized droplet size of the sodium hypochlorite solution is 3~10 μm.

[0036] Atomizing the sodium hypochlorite solution promotes a rapid and complete reaction of the sodium hypochlorite, which reduces the oxidation of the generated hydrazine hydrate by unreacted sodium hypochlorite.

[0037] Furthermore, the available chlorine in the sodium hypochlorite solution is 5-30 wt%.

[0038] Preferably, the sodium hypochlorite solution contains 10-20 wt% available chlorine.

[0039] Furthermore, the molar ratio of ammonia to sodium hypochlorite must be greater than 3:1.

[0040] Preferably, the molar ratio of ammonia to sodium hypochlorite is 3-6:1.

[0041] Furthermore, in step S1, the reaction does not require heating; the reaction itself releases heat, which will raise the temperature of the reactants. The reaction temperature is controlled at 50-80°C.

[0042] Furthermore, in step S1, the reactor is either a batch reactor or a tubular reactor. A tubular reactor is preferred.

[0043] In step S3, a stripping tower is used for ammonia removal. The removed ammonia gas is collected and returned to the reactor in the S1 reaction stage to react with sodium hypochlorite droplets for reuse.

[0044] Optionally, in step S3, after distillation and desalination, hydrazine hydrate with a mass concentration of 60% to 80% can be obtained by evaporation and concentration.

[0045] Furthermore, a method for preparing hydrazine hydrate also includes a salt recycling stage S4; specifically, S4 involves adding a small amount of sodium hypochlorite to the salt containing ammonia nitrogen obtained in step S3 (containing only a small amount of ammonia nitrogen and no organic matter or other impurities) to remove the ammonia nitrogen, after which the salt can be directly recycled to electrolytic production of caustic soda, and then made into sodium hypochlorite, which is the raw material of this invention, thereby realizing material recycling.

[0046] Furthermore, in step S4, the amount of sodium hypochlorite added for removing ammonia nitrogen is 0.5% to 2% of the salt mass.

[0047] This invention uses sodium hypochlorite and ammonia as raw materials. By atomizing sodium hypochlorite into fine droplets, countless tiny reaction units are formed, greatly increasing the reaction area and preventing backmixing. This allows for rapid and complete reaction with excess ammonia, effectively avoiding the reaction between sodium hypochlorite and the product hydrazine hydrate. Combined with two-stage condensation separation, distillation desalination, and material recycling processes, low-consumption and environmentally friendly production is achieved.

[0048] S1 Reaction Stage: First, ammonia gas is introduced into the reactor at a stable flow rate (either a batch reactor or a pipeline reactor can be used, with a pipeline reactor being preferred as it can achieve continuous and uniform contact of materials and improve reaction efficiency).

[0049] Sodium hypochlorite solution is fed into an atomizer for atomization, and the droplet size is controlled within 2~30μm (this droplet size range maximizes the contact area between sodium hypochlorite and ammonia, ensuring complete instantaneous reaction; the larger the droplet size, the greater the probability of hydrazine being oxidized by sodium hypochlorite, leading to a decrease in yield).

[0050] The preferred atomized droplet size is 2~20μm.

[0051] A more preferred atomized droplet size is 5~10μm.

[0052] The atomized sodium hypochlorite is introduced into the reactor to react with ammonia. The reaction does not require additional heating. The temperature is maintained by the exothermic reaction itself, and the reaction temperature must be controlled below 80°C (preferably 50-80°C, as this temperature range can suppress side reactions while ensuring the reaction rate).

[0053] The molar ratio of ammonia to sodium hypochlorite should be controlled to be greater than 3:1, preferably 3 to 6:1. (Excess ammonia can ensure that sodium hypochlorite reacts completely and avoids its oxidation product hydrazine hydrate, but too much ammonia will be wasteful).

[0054] S2 Secondary Condensation Separation Stage: The ultrafine mist after atomization is relatively difficult to condense, so secondary condensation is adopted. The mist generated by the reaction first enters the primary condenser and is cooled by ordinary circulating water at 15~45℃, so that most of the mist condenses into liquid, resulting in crude hydrazine hydrate solution I containing hydrazine hydrate, ammonia and salt (sodium chloride).

[0055] The portion that is not condensed by the primary condenser (mainly ammonia and a small amount of hydrazine hydrate vapor) enters the secondary condenser and is deeply cooled by chilled water at 0~7℃. After condensation, a salt-free hydrazine hydrate aqueous solution II is obtained.

[0056] The non-condensable residual ammonia gas (high purity, free of impurities) in the secondary condenser is returned to the reactor for reuse, reducing the waste of ammonia raw materials.

[0057] S3 Distillation and Concentration Stage: The crude hydrazine hydrate solutions I and II obtained in step S2 are mixed and sent to a stripping tower to remove ammonia (the removed ammonia can also be returned to the reactor for recycling), and then sent to a distillation tower to remove the salt (sodium chloride) to obtain a salt-free hydrazine hydrate solution.

[0058] Based on market demand, the desalted hydrazine hydrate solution can be evaporated and concentrated to obtain hydrazine hydrate products of various specifications (such as 60%, 80%, etc.).

[0059] S4 Salt Recycling Stage: The salt removed by distillation in step S3 is relatively pure sodium chloride containing only a small amount of ammonia nitrogen, and does not contain organic matter or other impurities, so no complicated purification is required.

[0060] The sodium chloride is oxidized by adding an appropriate amount of sodium hypochlorite to remove ammonia nitrogen, and then it can be directly reused in the electrolytic production of caustic soda (sodium hydroxide).

[0061] The caustic soda produced can be further reacted with chlorine to prepare sodium hypochlorite, which is used as a raw material for the preparation of hydrazine hydrate in this invention, forming a material cycle of "sodium chloride-caustic soda-sodium hypochlorite-sodium chloride", realizing efficient utilization of resources, reducing raw material costs, and achieving green and environmentally friendly production.

[0062] Secondly, this application provides a hydrazine hydrate prepared using the method described in this application.

[0063] Beneficial effects: 1. This application atomizes sodium hypochlorite, dispersing it into fine droplets to form tiny reaction units, allowing it to react instantly and completely with excess ammonia without backmixing; and adopts a two-stage condensation design to ensure uniform material contact and thorough separation, effectively avoiding the side reaction of hydrazine hydrate being oxidized by sodium hypochlorite. At the same time, the yield of hydrazine hydrate can reach more than 90%, which is much higher than the traditional Raschig process (60%-70%); the mass concentration of the generated hydrazine hydrate can reach 5%~15%, which is significantly higher than the Raschig process (1%-2%) and the urea process (2%-4%); the high concentration of the product greatly reduces the energy consumption of the subsequent evaporation and concentration process; the method of this application has a high degree of continuity in the entire process flow, and the operating parameters are easy to control, making it suitable for large-scale industrial production.

[0064] 2. The preparation method of this application only produces sodium chloride salt and does not contain organic matter. After ammonia nitrogen removal, the brine can be directly reused for electrolytic alkali production, and then used to prepare sodium hypochlorite raw material, forming a closed-loop material cycle. At the same time, unreacted ammonia gas can be recycled, with no wastewater or waste residue discharge, which is in line with the industrial policies of energy conservation, environmental protection and circular economy. Furthermore, the reaction of this application does not require additional heating, and the temperature is maintained by its own exothermic reaction (50-80℃). The pipeline reactor (preferred) and the two-stage condensation design ensure uniform material contact and thorough separation. The entire process has a high degree of continuity, and the operating parameters are easy to control, making it suitable for large-scale industrial production. Detailed Implementation

[0065] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0066] Example 1: A method for preparing hydrazine hydrate, comprising the following preparation steps:

[0067] Ammonia gas was introduced into a tubular reactor at a flow rate of 1000 ml / min (0.04 mol / min). 100 g of sodium hypochlorite solution (10% available chlorine) was cooled to 8°C and then atomized in an atomizer with a particle size controlled at 3-8 μm. The atomized solution was then introduced into the tubular reactor at a flow rate of 6.8 g / min (0.01 mol / min) to react with the ammonia gas. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2°C. The resulting mist first entered the primary condenser and was cooled with ordinary circulating water at 25°C. The gas that did not condense in the primary condenser (mainly ammonia gas and some hydrazine hydrate mist) entered the secondary condenser and was cooled with chilled water at 5°C. The remaining ammonia gas that did not condense in the secondary condenser was returned to the reactor as raw material again. The condensates from the primary and secondary condensers were collected and mixed to obtain 111.5 g of crude hydrazine hydrate solution (ammonia was also dissolved in it). The mass concentration of hydrazine hydrate was measured to be 5.89%, and the yield was 93.1% based on sodium hypochlorite.

[0068] Example 2, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0069] Ammonia gas was introduced into a tubular reactor at a flow rate of 1000 ml / min (0.04 mol / min).

[0070] 100g of sodium hypochlorite solution (15% available chlorine) was cooled to 8℃ and then atomized in an atomizer with a particle size controlled at 3-8μm. The atomized solution was then fed into a tubular reactor at a flow rate of 5.0 g / min (0.01mol / min) to react with ammonia. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2℃. The resulting mist first entered a primary condenser and was cooled with ordinary circulating water at 25℃. The uncondensed gas in the primary condenser (mainly ammonia and some hydrazine hydrate mist) entered a secondary condenser and was cooled with chilled water at 5℃. The remaining uncondensed ammonia in the secondary condenser was returned to the reactor as feedstock. The condensates from the primary and secondary condensers were collected and mixed to obtain 117.2g of crude hydrazine hydrate solution. The hydrazine hydrate concentration was determined to be 8.40%, and the yield based on sodium hypochlorite was 93.0%.

[0071] Example 3, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0072] Ammonia gas was introduced into a tubular reactor at a flow rate of 1000 ml / min (0.04 mol / min).

[0073] 100g of sodium hypochlorite solution (20% available chlorine) was cooled to 8℃ and then atomized in an atomizer with a particle size controlled at 3-8μm. The atomized solution was then fed into a tubular reactor at a flow rate of 3.75 g / min (0.01mol / min) to react with ammonia. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2℃. The resulting mist first entered a primary condenser and was cooled with ordinary circulating water at 25℃. The uncondensed gas from the primary condenser (mainly ammonia and some hydrazine hydrate mist) entered a secondary condenser and was cooled with chilled water at 5℃. The remaining uncondensed ammonia in the secondary condenser was returned to the reactor as a fresh feedstock. The condensates from the primary and secondary condensers were collected and mixed to obtain 122.3g of crude hydrazine hydrate solution. The hydrazine hydrate concentration was determined to be 10.68%, and the yield based on sodium hypochlorite was 92.6%.

[0074] Example 4, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0075] Ammonia gas was introduced into a tubular reactor at a flow rate of 1000 ml / min (0.04 mol / min).

[0076] 100g of sodium hypochlorite solution (15% available chlorine) was cooled to 8℃ and then atomized in an atomizer with a particle size controlled at 15~30μm. The atomized solution was then fed into a tubular reactor at a flow rate of 5.0 g / min (0.01mol / min) to react with ammonia. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2℃. The resulting mist first entered a primary condenser and was cooled with ordinary circulating water at 25℃. The uncondensed gas in the primary condenser (mainly ammonia and some hydrazine hydrate mist) entered a secondary condenser and was cooled with chilled water at 5℃. The remaining uncondensed ammonia in the secondary condenser was returned to the reactor as a fresh feedstock. The condensates from the primary and secondary condensers were collected and mixed to obtain 117.8g of crude hydrazine hydrate solution. The hydrazine hydrate concentration was determined to be 8.21%, and the yield based on sodium hypochlorite was 91.4%.

[0077] Comparative Example 1, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0078] Ammonia gas was introduced into a tubular reactor at a flow rate of 1000 ml / min (0.04 mol / min).

[0079] 100g of sodium hypochlorite solution (15% available chlorine) was cooled to 8℃ and then atomized in an atomizer with a particle size controlled at 50~100μm. The atomized solution was then fed into a tubular reactor at a flow rate of 5.0 g / min (0.01mol / min) to react with ammonia. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2℃. The resulting atomized gas first entered a primary condenser and was cooled with ordinary circulating water at 25℃. The uncondensed gas in the primary condenser (mainly ammonia and some hydrazine hydrate vapor) entered a secondary condenser and was cooled with chilled water at 5℃. The remaining uncondensed ammonia in the secondary condenser was returned to the reactor as feedstock. The condensates from the primary and secondary condensers were collected and mixed to obtain 118.1g of crude hydrazine hydrate solution. The hydrazine hydrate concentration was measured to be 7.25%, and the yield based on sodium hypochlorite was 80.95%. The yield decreased significantly with increasing atomized particle size.

[0080] Comparative Example 2, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0081] Ammonia gas was introduced into a tubular reactor at a flow rate of 500 ml / min (0.02 mol / min).

[0082] 100g of sodium hypochlorite solution (15% available chlorine) was cooled to 8℃ and then atomized in an atomizer with a particle size controlled at approximately 3-8μm. The atomized solution was then fed into a tubular reactor at a flow rate of 5.0 g / min (0.01mol / min) to react with ammonia. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2℃. The resulting atomized gas first entered a primary condenser and was cooled with ordinary circulating water at 25℃. The uncondensed gas from the primary condenser (mainly ammonia and some hydrazine hydrate vapor) entered a secondary condenser and was cooled with chilled water at 5℃. The remaining uncondensed ammonia in the secondary condenser was returned to the reactor as feedstock. The condensates from the primary and secondary condensers were collected and mixed to obtain 113.1g of crude hydrazine hydrate solution. The hydrazine hydrate concentration was determined to be 5.25%, and the yield, calculated based on sodium hypochlorite, was 56.1%. This indicates that without excess ammonia, numerous side reactions significantly reduced the yield.

[0083] Comparative Example 3, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0084] A long, vertical column reactor was prepared, with a spring-loaded dispersing device placed inside. Ammonia gas was introduced into the bottom of the reactor at a flow rate of 1000 ml / min (0.04 mol / min). 100 g of sodium hypochlorite solution (15% available chlorine) was cooled to 8°C and then added dropwise from the top of the reactor at a flow rate of 5.0 g / min (0.01 mol / min). The solution was dispersed into a thin liquid film by the dispersing device and reacted with the ammonia gas coming from the bottom. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 65-80°C. The reaction liquid was collected at the bottom of the reactor, yielding 117.5 g of crude hydrazine hydrate solution. The hydrazine hydrate concentration was determined to be 4.52%, and the yield based on sodium hypochlorite was 50.2%. The yield is significantly lower than that of the atomization reaction.

[0085] Comparative Example 4, a method for preparing hydrazine hydrate, comprising the following preparation steps:

[0086] A sodium hypochlorite solution with an effective chlorine content of 18% is continuously pumped into the first-stage tubular reactor after being metered by a metering pump. Simultaneously, liquid ammonia is also continuously added into the first-stage tubular reactor after being metered by a flow meter. The molar flow ratio of sodium hypochlorite to ammonia is 1:1. The reaction temperature is controlled at 0℃~5℃, and the residence time is 60s. Then, it enters the second-stage tubular reactor. Liquid ammonia is then continuously added into the second-stage tubular reactor after being metered by a flow meter. The molar flow ratio of liquid ammonia to sodium hypochlorite pumped into the first-stage tubular reactor is 1.5:1. The reaction temperature is controlled at 30℃~40℃, and the residence time is 75s. The reaction is vigorous, with a large amount of heat release, and water-insoluble gases are generated. The hydrazine hydrate content at the reactor outlet was only 1.56%, which is similar to the crude hydrazine concentration obtained by the traditional Raschig process. However, the reaction yield was lower, at only 13.73% (based on sodium hypochlorite). This indicates that 85% of the sodium hypochlorite was consumed by side reactions. This may be because the yield is very low when sodium hypochlorite and ammonia are directly mixed and reacted in the pipeline. When the concentration of hydrazine hydrate is high, it is easily oxidized and decomposed by sodium hypochlorite, and the side reaction of hydrazine hydrate oxidation is unavoidable. The patent in this application uses atomization into micro-reaction units to suppress oxidation side reactions, thereby increasing the yield.

[0087] Comparative Example 5, a method for preparing hydrazine hydrate, differs from Example 1 in that: instead of primary condensation, secondary condensation is used, and the specific operation is as follows:

[0088] Ammonia gas was introduced into a tubular reactor at a flow rate of 1000 ml / min (0.04 mol / min). 100 g of sodium hypochlorite solution (10% available chlorine) was cooled to 8°C and then atomized in an atomizer with a particle size controlled at 3-8 μm. The atomized solution was then introduced into the tubular reactor at a flow rate of 6.8 g / min (0.01 mol / min) to react with the ammonia gas. After the reaction, the temperature rose, and the cooling water was adjusted to stabilize the reaction temperature at 68±2°C. The resulting atomized gas entered the first and second stage condensers, both of which were cooled with ordinary circulating water at 25°C. The remaining ammonia gas that did not condense in the second stage condenser was returned to the reactor as raw material again. The condensate was collected to obtain 109.7 g of crude hydrazine hydrate solution, with a hydrazine hydrate mass concentration of 5.91%. The yield, calculated based on sodium hypochlorite, was 91.9%, which was about 1% lower than that in Example 1. This indicates that the condensation temperature has a certain impact on the yield. At higher temperatures, a small amount of hydrazine hydrate will be carried away by the uncondensed gas. The two-stage method, using ambient temperature circulating water and chilled water respectively, saves refrigeration energy. The fine sodium hypochlorite droplets form tiny reaction units, which react fully with ammonia, ensuring a higher yield.

[0089] Performance testing

[0090] Yield calculation method: Calculate the amount of hydrazine hydrate obtained under theoretical lossless conditions according to the main reaction equation. Divide the actual amount of hydrazine hydrate obtained by the theoretical amount and then multiply by 100% to get the yield of hydrazine hydrate.

[0091] One mole of available chlorine is equivalent to one mole of sodium hypochlorite.

[0092] Sodium hypochlorite content = available chlorine × sodium hypochlorite molecular weight / chlorine molecular weight.

[0093] Theoretically, the mass of hydrazine hydrate obtained = mass of sodium hypochlorite solution × sodium hypochlorite content × molecular weight of hydrazine hydrate / molecular weight of sodium hypochlorite = mass of sodium hypochlorite solution × available chlorine content × molecular weight of hydrazine hydrate / molecular weight of chlorine gas = mass of sodium hypochlorite × available chlorine content × 50 / 70.9.

[0094] The actual mass of hydrazine hydrate obtained = mass of crude hydrazine hydrate solution × concentration of crude hydrazine hydrate.

[0095] Yield calculation formula: Hydrazine hydrate yield = actual mass of hydrazine hydrate obtained / theoretical mass of hydrazine hydrate obtained × 100% = (mass of crude hydrazine hydrate solution × concentration of crude hydrazine hydrate) / (mass of sodium hypochlorite × available chlorine content × 50 / 70.9) × 100%.

[0096] Table 1. Main technical parameters and yields in the preparation methods of the examples and comparative examples.

[0097] distinguish Sodium hypochlorite available chlorine concentration / % Atomized particle size range / μm Molar ratio of ammonia to sodium hypochlorite hydrazine hydrate concentration / % Yield / % (based on sodium hypochlorite) Example 1 10 3-8 4:1 5.89 93.1 Example 2 15 3-9 4:1 8.4 93 Example 3 20 3-10 4:1 10.68 92.6 Example 4 15 15-30 4:1 8.21 91.4 Comparative Example 1 15 50-100 4:1 7.25 80.95 Comparative Example 2 15 3-8μm 2:1 5.25 56.1 Comparative Example 3 15 Sodium hypochlorite was added in liquid film form at a flow rate of 5.0 g / min. 4:1 4.52 50.2 Comparative Example 4 18 The molar flow ratio of sodium hypochlorite solution to liquid ammonia is 1:1. 2.5:1 1.56 13.73 Comparative Example 5 10 3-8 4:1 5.91 91.9

[0098] The embodiments described herein merely illustrate several implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing hydrazine hydrate, characterized in that, The preparation steps include the following: S1 reaction stage: Sodium hypochlorite solution and ammonia are used as raw materials. The sodium hypochlorite solution is atomized and dispersed into fine sodium hypochlorite droplets, forming tiny reaction units that react with ammonia. S2 Secondary condensation separation stage: The mist after the reaction in step S1 is condensed into liquid by primary condensation to obtain crude hydrazine hydrate solution I containing sodium chloride and ammonia. The uncondensed portion is further condensed by secondary condensation to obtain crude hydrazine hydrate aqueous solution II. The remaining non-condensable ammonia gas reacts repeatedly with sodium hypochlorite droplets. The temperature of primary condensation and secondary condensation is between 0-50℃, with the temperature of primary condensation being higher than that of secondary condensation. S3 Distillation and Concentration Stage: Combine crude hydrazine hydrate solution I and crude hydrazine hydrate solution II, remove ammonia, and then distill to remove salt, concentrate and purify to obtain hydrazine hydrate product.

2. The method for preparing hydrazine hydrate according to claim 1, characterized in that, The temperature of the first-stage condenser is 15~45℃, and the temperature of the second-stage condenser is 0~7℃.

3. A method for preparing hydrazine hydrate according to claim 1 or 2, characterized in that, In step S1, the sodium hypochlorite solution is cooled to 5-10°C before atomization.

4. The method for preparing hydrazine hydrate according to claim 1, characterized in that, In step S1, the atomized droplet size of the sodium hypochlorite solution is 2~30μm.

5. A method for preparing hydrazine hydrate according to any one of claims 1, 2, and 4, characterized in that, The sodium hypochlorite solution contains 5-30 wt% available chlorine.

6. The method for preparing hydrazine hydrate according to claim 5, characterized in that, The molar ratio of ammonia to sodium hypochlorite is greater than 3:

1.

7. The method for preparing hydrazine hydrate according to claim 1, characterized in that, In step S1, the reaction does not require heating. The reaction itself releases heat, which will raise the temperature of the reactants. The reaction temperature is controlled at 50-80℃.

8. The method for preparing hydrazine hydrate according to claim 1, characterized in that, In step S1, the reactor is either a batch reactor or a pipeline reactor. In step S3, a stripping tower is used for ammonia removal. The removed ammonia gas is collected and returned to the reactor in the S1 reaction stage to react with sodium hypochlorite droplets for reuse.

9. The method for preparing hydrazine hydrate according to claim 1, characterized in that, It also includes the S4 salt recycling stage; specifically, S4 involves adding a small amount of sodium hypochlorite to the salt containing ammonia nitrogen obtained in step S3 to remove the ammonia nitrogen, after which the salt can be directly reused in the electrolysis to produce caustic soda, and then produced into sodium hypochlorite, thus realizing material recycling.

10. A hydrazine hydrate prepared by the method according to any one of claims 1-9.