Method for efficiently and greenly synthesizing hydrazine hydrate

Abstract

The present application relates to the field of hydrazine hydrate, and particularly relates to a method for efficiently and greenly synthesizing hydrazine hydrate. The method for efficiently and greenly synthesizing hydrazine hydrate comprises the following steps: mixing chlorine, sodium hydroxide and water, and performing a reaction to obtain a sodium hypochlorite solution; mixing the sodium hypochlorite solution, urea and a catalyst, and performing a reaction to obtain hydrazine hydrate, tail gas and by-products; and recycling the tail gas and the by-products. Through mechanism-driven process design, the method realizes the efficiency, greenness and economy of hydrazine hydrate synthesis, and provides a sustainable solution for industrial application.

Description

Technical Field

[0001] This invention relates to the field of hydrazine hydrate, and more specifically, to a method for the efficient and green synthesis of hydrazine hydrate. Background Technology

[0002] Hydrazine hydrate (N₂H₄·H₂O) is an important chemical raw material and fine chemical intermediate, widely used in foaming agents, pesticides, pharmaceuticals, water treatment agents, rocket propellants, and other fields. Its unique strong reducing properties and high reactivity make it irreplaceable in industrial production. Currently, the mature industrial methods for synthesizing hydrazine hydrate mainly include the Raschig process, the hydrogen peroxide process (ketone azide process), and the urea process.

[0003] Raschig process: This method uses ammonia and sodium hypochlorite as raw materials to react and produce hydrazine hydrate under high pressure and in the presence of a catalyst. Although this method was applied earlier, it has significant drawbacks: (1) poor reaction selectivity, excessive ammonia, resulting in severe side reactions, producing large amounts of ammonium chloride and nitrogen as byproducts, and low hydrazine hydrate yield (usually less than 30%); (2) high energy consumption, requiring distillation to recover excess ammonia and treatment of high-salt wastewater; (3) serious environmental pollution, with large amounts of ammonia-containing wastewater and waste salt difficult to treat, which does not conform to the development trend of green chemistry.

[0004] Hydrogen peroxide method: This method uses ammonia, hydrogen peroxide and ketones (such as acetone and methyl ethyl ketone) as raw materials to produce hydrazine hydrate through a ketone azo intermediate. This method has high selectivity, but its main drawbacks are: (1) high raw material costs, hydrogen peroxide is expensive, and ketone solvents are volatile and flammable, posing safety hazards; (2) long process flow, involving the recovery and recycling of ketones, resulting in high equipment investment and operating costs.

[0005] Urea process: The urea process uses sodium hypochlorite and urea as raw materials. The process route is relatively simple and the raw materials are cheap and readily available. However, the traditional urea process also has many problems: (1) The reaction efficiency and selectivity are not ideal. The reaction between urea and sodium hypochlorite is exothermic. If not properly controlled, hydrazine hydrate is easily over-oxidized and decomposed into nitrogen gas, resulting in unstable yield and purity; (2) There is a lack of efficient catalysts. The catalysts used in the traditional process (such as potassium permanganate, manganese sulfate, etc.) have low activity and poor selectivity, and cannot effectively suppress side reactions; (3) The reactor design is unreasonable. The traditional batch reactor has problems such as low mass and heat transfer efficiency and uneven temperature distribution, which further aggravates the decomposition of hydrazine hydrate; (4) The three wastes are prominent. If the tail gas (containing ammonia, chloramine, etc.) and wastewater containing high concentrations of sodium chloride produced by the reaction are not effectively treated, they will cause environmental pollution.

[0006] Furthermore, in the aforementioned methods, sodium hypochlorite, a key raw material, typically needs to be purchased externally, and its production and transportation processes also pose certain safety and environmental risks. If sodium hypochlorite could be efficiently and accurately prepared on-site and directly used in subsequent synthesis, the integration and economic efficiency of the entire process could be further improved.

[0007] Therefore, developing a green synthesis method with mild reaction conditions, high raw material utilization, good selectivity, environmental friendliness, and low cost has become an urgent need in the field of hydrazine hydrate production. Summary of the Invention

[0008] In view of this, the present invention aims to provide an efficient and green method for synthesizing hydrazine hydrate, which is efficient, green and economical.

[0009] To solve the above-mentioned technical problems, this application is implemented as follows:

[0010] This invention provides a highly efficient and green method for synthesizing hydrazine hydrate, comprising the following steps:

[0011] (1) Chlorine gas, sodium hydroxide and water are mixed and reacted to obtain sodium hypochlorite solution;

[0012] (2) Sodium hypochlorite solution, urea and catalyst are mixed and reacted to obtain hydrazine hydrate, tail gas and by-products. The catalyst includes magnesium chloride-rare earth composite catalyst.

[0013] (3) Recover exhaust gas and by-products.

[0014] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, in step (1), the ratio of chlorine gas to sodium hydroxide is 1:1.15~1.25;

[0015] In step (1), the mass ratio of chlorine gas to water is 1:4.5~5.5.

[0016] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, the reaction temperature in step (1) is 25~35℃.

[0017] In this invention, a reaction temperature of 25-35°C can significantly reduce the disproportionation reaction rate of sodium hypochlorite and increase the yield.

[0018] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, the mass ratio of urea in step (2) to sodium hydroxide in step (1) is 1:1.4~1.6;

[0019] In step (2), the mass ratio of urea to catalyst is 50~80:1.

[0020] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, step (2) involves the preparation of the magnesium chloride-rare earth composite catalyst, which includes:

[0021] Magnesium chloride, rare earth chloride, and water were mixed and activated to obtain a magnesium chloride-rare earth composite catalyst.

[0022] The molar ratio of rare earth elements in the magnesium chloride and the rare earth chloride is 10:0.5~1;

[0023] The activation conditions are: pH 5.5-6.5, temperature 40-50℃, and time 1-1.5h.

[0024] In this invention, in the magnesium chloride-rare earth composite catalyst, Mg 2+ It can activate the N-Cl bond of the intermediate through coordination, thereby lowering the decomposition energy barrier; it can also regulate the electronic environment of the reaction system and inhibit the oxidation of hydrazine hydrate by sodium hypochlorite.

[0025] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, in step (2), the reaction process is as follows:

[0026] In step (2), the mixed materials are placed in a segmented temperature-controlled static mixing tubular reactor for reaction;

[0027] The reaction temperature is controlled in stages: 80-90℃ at the inlet, 110-115℃ in the middle, and 95-100℃ at the outlet. The reaction time is 60-90 minutes.

[0028] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, step (3) includes the following process for recovering the tail gas:

[0029] The exhaust gas is treated by a two-stage series absorption tower;

[0030] The temperature of the first tower in the series absorption tower is 35~40℃, and the temperature of the second tower in the series absorption tower is 5~15℃.

[0031] Preferably, in the above-mentioned efficient and green method for synthesizing hydrazine hydrate, the by-product recovery process in step (3) includes:

[0032] The byproducts were then subjected to evaporation concentration and ion exchange treatment in sequence.

[0033] In this invention, evaporation concentration includes triple-effect evaporation concentration; specifically, it includes:

[0034] (1) The by-product (initial concentration 5-8 wt%) is preheated to 60-70°C and then enters the first-effect evaporator; it is heated by low-pressure steam of 0.3-0.5 MPa at 100-110°C and -0.02--0.01 MPa.

[0035] (2) The byproducts after the first-effect concentration are directly fed into the second-effect evaporator; the temperature is 80-90℃ and the vacuum degree is -0.05--0.04MPa, and the secondary steam generated by the first-effect evaporation is used for heating;

[0036] (3) The byproducts after the second-effect concentration enter the third-effect evaporator; at 60-70℃ and -0.08--0.07MPa, the secondary steam generated by the second-effect evaporation is used for heating.

[0037] In this invention, a 001×7 type strong acid styrene-based cation exchange resin is used to perform ion exchange treatment on the product after evaporation and concentration. The 001×7 type strong acid styrene-based cation exchange resin has a crosslinking degree of 8% and a particle size of 0.3 to 1.2 mm.

[0038] The beneficial technical effects of the present invention through the above technical solution are as follows:

[0039] (1) The reaction of chlorine with sodium hydroxide was carried out by strictly controlling the ratio of chlorine to sodium hydroxide (1:1.15~1.25) and the water-to-chlorine ratio (1:4.5~5.5) to ensure the efficient generation of sodium hypochlorite. Excess sodium hydroxide not only promotes the complete conversion of chlorine and reduces chlorine residue, but also maintains the alkaline environment of the reaction system and prevents the decomposition of hypochlorous acid, thus providing a high-purity intermediate for subsequent steps. Urea and sodium hypochlorite undergo a redox reaction under the action of magnesium chloride-rare earth composite catalyst. The rare earth elements (such as cerium, lanthanum, etc.) in the catalyst act as Lewis acid sites, which can activate the carbonyl group and hypochlorite ion in the urea molecule, reduce the activation energy of the reaction, and accelerate the generation rate of hydrazine. Meanwhile, the segmented temperature-controlled static mixing tubular reactor matches the kinetic requirements of each stage of the reaction through precise temperature control of the inlet section (80-90℃), the middle section (110-115℃), and the outlet section (95-100℃): the inlet section promotes initial mixing and reaction initiation, the middle section increases the reaction rate, and the outlet section prevents the overheating and decomposition of hydrazine hydrate, thereby shortening the overall reaction time to 60-90 min and significantly improving the yield of hydrazine hydrate.

[0040] (2) The tail gas recovery system uses a two-stage series absorption tower. The first tower (35~40℃) absorbs most of the alkaline gases such as ammonia, while the second tower (5~15℃) condenses and recovers volatile organic compounds and hydrazine hydrate vapor. This temperature gradient design is based on the thermodynamic principle of gas absorption, maximizing recovery efficiency and reducing harmful gas emissions. By-product recovery is achieved through evaporation concentration and ion exchange. After evaporation concentration removes moisture, solid sodium chloride is obtained. Ion exchange further removes impurities, realizing the purification and resource utilization of by-products and reducing wastewater discharge. The entire process is designed in a closed loop, conforming to the principles of green chemistry. Through mechanistic optimization, common side reactions in traditional hydrazine hydrate synthesis (such as excessive oxidation to generate nitrogen) are suppressed to a minimum.

[0041] (3) The magnesium chloride-rare earth composite catalyst is prepared by forming a stable composite structure through an activation process (pH 5.5~6.5, 40~50℃, 1~1.5h). Magnesium chloride provides basic sites, while rare earth elements (such as cerium chloride) enhance electron transfer capabilities, synergistically promoting the selective reaction of urea and sodium hypochlorite and reducing the generation of byproducts such as chloramine or nitrogen. The d orbital holes of rare earth elements can selectively adsorb reaction intermediates, improving the selectivity of hydrazine hydrate to over 90%. At the same time, the catalyst can be reused, reducing waste generation.

[0042] (4) The segmented temperature-controlled reactor adopts a static mixing design, which enhances mass and heat transfer efficiency and reduces local overheating or cooling, thereby reducing energy consumption. Material ratio optimization ensures full conversion of reactants and reduces raw material waste. The overall process converts tail gas and by-products into useful resources through a recovery system, reducing raw material costs and waste treatment expenses.

[0043] In summary, this invention achieves high efficiency, greenness, and economy in the synthesis of hydrazine hydrate through mechanism-driven process design, providing a sustainable solution for industrial applications. Detailed Implementation

[0044] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0045] Preparation Example 1

[0046] The preparation of the catalyst includes the following steps:

[0047] (1) Add 8L of deionized water to a 20L constant temperature stirring tank, and then heat it to 30℃; add 95.21g of anhydrous MgCl2, and stir continuously for 30min until the solid is completely dissolved to obtain an aqueous solution of MgCl2;

[0048] (2) Take 1L of deionized water into a 5L beaker, add 18.57g of LaCl3·7H2O, and stir magnetically for 15min until completely dissolved to obtain La 3+ dilute solution;

[0049] (3) La 3+ Add the dilute solution to the MgCl2 aqueous solution and continue stirring for 60 minutes to obtain a mixed solution;

[0050] (4) Add 0.1 mol / L hydrochloric acid to the mixture until the pH of the solution reaches 5.5; raise the temperature of the stirring tank to 40°C and stir at 300 rpm for 1 h; and vacuum filter the obtained product through a 0.22 μm aqueous filter membrane (negative pressure -0.08 MPa) catalyst 1.

[0051] Preparation Example 2

[0052] The preparation of the catalyst includes the following steps:

[0053] (1) Add 7L of deionized water to a 20L constant temperature stirring tank, and then heat it to 35℃; add 95.21g of anhydrous MgCl2, and stir continuously for 30min until the solid is completely dissolved to obtain an aqueous solution of MgCl2;

[0054] (2) Take 1L of deionized water into a 5L beaker, add 37.26g of CeCl3·7H2O, and stir magnetically for 15min until completely dissolved to obtain CeCl3·7H2O. 3+ dilute solution;

[0055] (3) Ce 3+ Add the dilute solution to the MgCl2 aqueous solution and continue stirring for 60 minutes to obtain a mixed solution;

[0056] (4) Add 0.1 mol / L hydrochloric acid to the mixture until the pH of the solution reaches 5.5; raise the temperature of the stirring tank to 40°C and stir at 300 rpm for 1 h; and vacuum filter the obtained product through a 0.22 μm aqueous filter membrane (negative pressure -0.08 MPa) catalyst 2.

[0057] Preparation Example 3

[0058] The preparation of the catalyst includes the following steps:

[0059] (1) Add 7L of deionized water to a 20L constant temperature stirring tank, and then heat it to 35℃; add 95.21g of anhydrous MgCl2, and stir continuously for 30min until the solid is completely dissolved to obtain an aqueous solution of MgCl2;

[0060] (2) Take 1L of deionized water into a 5L beaker, add 37.26g of CeCl3·7H2O, and stir magnetically for 15min until completely dissolved to obtain CeCl3·7H2O.3+ dilute solution;

[0061] (3) Ce 3+ Add the dilute solution to the MgCl2 aqueous solution and continue stirring for 60 minutes to obtain a mixed solution;

[0062] (4) Add 0.1 mol / L hydrochloric acid to the mixture until the pH of the solution reaches 5.5; raise the temperature of the stirring tank to 50°C and stir at 300 rpm for 1 h; and vacuum filter the obtained product through a 0.22 μm aqueous filter membrane (negative pressure -0.08 MPa) catalyst 3.

[0063] Example 1

[0064] A method for the efficient and green synthesis of hydrazine hydrate includes the following steps:

[0065] (1) Add 500 kg of deionized water (chlorine to water mass ratio 1:5) to the reactor, start stirring (200 rpm), and slowly add 120 kg of sodium hydroxide (industrial grade, 98% purity), stirring until completely dissolved (the solution temperature naturally rises to 28℃). Control the chlorine (99.5% purity) flow rate at 10 kg / h using a rotor flow meter, and continue flowing for 10 h (total addition 100 kg, chlorine to sodium hydroxide mass ratio 1:1.2). During the reaction, stabilize the system temperature at 30℃ using cooling water, and continue the reaction for 45 min. After the reaction is completed, take a sample and test to obtain 715 kg of sodium hypochlorite solution, with an effective chlorine concentration of 10.7 wt% and a sodium hypochlorite content of 0.25 wt%.

[0066] (2) Dissolve 80 kg of urea (industrial grade, 99% purity) in 200 kg of deionized water to prepare a 28.6 wt% urea solution (the mass ratio of urea to sodium hydroxide in step 1 is 1:1.5). Pump this urea solution, the 682 kg sodium hypochlorite solution obtained in step 1, and 1.23 kg of magnesium chloride-lanthanum composite catalyst (prepared in preparation example 1) into a segmented temperature-controlled static mixing tubular reactor (made of 2205 duplex stainless steel, with built-in static mixing elements with a spacing of 50 mm and a helix angle of 30°, a total length of 10 m, and an inner diameter of 50 mm) using a metering pump.

[0067] (3) The tail gas produced by the reaction (containing about 3.2 kg of NH3, 0.5 kg of trace hydrazine, and about 12 kg of CO2) is treated by two-stage series absorption towers: the first tower (38℃) absorbs ammonia with 12.8 kg of deionized water to produce 16 kg of 20 wt% ammonia water; the second tower (10℃) absorbs trace hydrazine and CO2 with 50 kg of 5 wt% dilute hydrazine solution to obtain 62 kg of 8 wt% hydrazine recovery liquid; the remaining CO2 is absorbed by 25 wt% MDEA amine solution and desorbed to obtain 11.8 kg of CO2 (purity 99.95 wt%).

[0068] (4) The reaction byproduct is a mixed salt solution of NaCl / Na2CO3 (approximately 180 kg, initial concentration 6.5 wt%), which is then concentrated by triple-effect evaporation and treated by ion exchange.

[0069] The triple-effect evaporation process specifically includes: first effect (105℃, -0.015MPa, 0.4MPa low-pressure steam heating) to concentrate to 18wt%; second effect (85℃, -0.045MPa, first effect secondary steam heating) to concentrate to 23wt%; and third effect (65℃, -0.075MPa, second effect secondary steam heating) to concentrate to 28wt%, with a total residence time of 75min.

[0070] Ion exchange: After the concentrate is filtered through a 5μm filter, it enters an exchange column (inner diameter 300mm, height 1200mm) packed with 001×7 type resin (crosslinking degree 7%, particle size 0.3~1.2mm). The feed temperature is controlled at 35℃ and the empty column flow rate is 15m / h. After treatment, 42kg of NaCl solution (purity 99.6wt%) is obtained.

[0071] In this embodiment, the single-pass yield of hydrazine hydrate is 83.2%, the chlorine utilization rate is 98.5%, the by-product NaCl is 100% resource-based recovered, and the steam consumption is 3.4t / t of hydrazine hydrate, which is 36% lower than the energy consumption of traditional processes.

[0072] Example 2

[0073] A method for the efficient and green synthesis of hydrazine hydrate includes the following steps:

[0074] (1) Add 450 kg of deionized water (chlorine to water mass ratio 1:4.5) to the reactor, start stirring (200 rpm), and slowly add 115 kg of sodium hydroxide (industrial grade, 98% purity) until completely dissolved. Control the chlorine (99.5% purity) flow rate at 10 kg / h using a rotor flow meter, and continue flowing for 10 h (total addition 100 kg, chlorine to sodium hydroxide mass ratio 1:1.15). During the reaction, stabilize the system temperature at 25℃ using cooling water and continue the reaction for 30 min. After the reaction is completed, take a sample and test to obtain 660 kg of sodium hypochlorite solution, with an effective chlorine concentration of 10.2 wt% and a sodium chlorate content of 0.28 wt%.

[0075] (2) Dissolve 78 kg of urea (industrial grade, 99% purity) in 190 kg of deionized water to form a urea solution. Then, pump the urea solution, the sodium hypochlorite solution obtained in step 1, and 1.56 kg of magnesium chloride-cerium composite catalyst (obtained in Preparation Example 2) into a segmented temperature-controlled static mixing tubular reactor (made of 2205 duplex stainless steel, with internal static mixing elements spaced 50 mm apart and with a helix angle of 30°, total length 10 m, inner diameter 50 mm) using a metering pump.

[0076] (3) The tail gas produced by the reaction (containing about 3.2 kg of NH3, 0.5 kg of trace hydrazine, and about 12 kg of CO2) is treated by two-stage series absorption towers: the first tower (38℃) absorbs ammonia with 12.8 kg of deionized water to produce 16 kg of 20 wt% ammonia water; the second tower (10℃) absorbs trace hydrazine and CO2 with 50 kg of 5 wt% dilute hydrazine solution to obtain 62 kg of 8 wt% hydrazine recovery liquid; the remaining CO2 is absorbed by 25 wt% MDEA amine solution and desorbed to obtain 11.8 kg of CO2 (purity 99.95 wt%).

[0077] (4) The reaction byproduct is a mixed salt solution of NaCl / Na2CO3 (approximately 160 kg, initial concentration 5.8 wt%), which is then concentrated by triple-effect evaporation and treated by ion exchange.

[0078] The triple-effect evaporation process specifically includes: first effect (105℃, -0.015MPa, 0.4MPa low-pressure steam heating) to concentrate to 18wt%; second effect (85℃, -0.045MPa, first effect secondary steam heating) to concentrate to 23wt%; and third effect (65℃, -0.075MPa, second effect secondary steam heating) to concentrate to 28wt%, with a total residence time of 75min.

[0079] Ion exchange: After the concentrate is filtered through a 5μm filter, it enters an exchange column (inner diameter 300mm, height 1200mm) packed with 001×7 type resin (crosslinking degree 8%, particle size 0.3~1.2mm). The feed temperature is controlled at 35℃ and the empty column flow rate is 15m / h. After treatment, 33kg of NaCl solution (purity 99.5wt%) is obtained.

[0080] The single-pass yield of hydrazine hydrate is 82.0%, the chlorine utilization rate is 98.0%, the by-product NaCl recovery rate is 100%, the steam consumption is 3.5t / t of hydrazine hydrate, and the energy consumption is reduced by 35%.

[0081] Example 3

[0082] A method for the efficient and green synthesis of hydrazine hydrate includes the following steps:

[0083] (1) Add 550 kg of deionized water (chlorine to water mass ratio 1:5.5) to the reactor, start stirring (200 rpm), and slowly add 125 kg of sodium hydroxide (industrial grade, 98% purity), stirring until completely dissolved (the solution temperature naturally rises to 28℃). Control the chlorine (99.5% purity) flow rate at 10 kg / h using a rotor flow meter, and continue flowing for 10 h (total addition 100 kg, chlorine to sodium hydroxide mass ratio 1:1.2). During the reaction, stabilize the system temperature at 30℃ using cooling water, and continue the reaction for 45 min. After the reaction is completed, take a sample and test to obtain 770 kg of sodium hypochlorite solution, in which the effective chlorine concentration is 10.5 wt% and the sodium chlorate content is 0.22 wt%.

[0084] (2) Dissolve 78 kg of urea (industrial grade, 99% purity) in 200 kg of deionized water to prepare a 28.6 wt% urea solution (the mass ratio of urea to sodium hydroxide in step 1 is 1:1.6). Pump the urea solution, the sodium hypochlorite solution obtained in step 1, and 1.56 kg of magnesium chloride-cerium composite catalyst (prepared in preparation example 3) into a segmented temperature-controlled static mixing tubular reactor (made of 2205 duplex stainless steel, with built-in static mixing elements with a spacing of 50 mm and a helix angle of 30°, a total length of 10 m, and an inner diameter of 50 mm) using a metering pump.

[0085] (3) The tail gas produced by the reaction (containing about 3.2 kg of NH3, 0.5 kg of trace hydrazine, and about 12 kg of CO2) is treated by two-stage series absorption towers: the first tower (38℃) absorbs ammonia with 12.8 kg of deionized water to produce 16 kg of 20 wt% ammonia water; the second tower (10℃) absorbs trace hydrazine and CO2 with 50 kg of 5 wt% dilute hydrazine solution to obtain 62 kg of 8 wt% hydrazine recovery liquid; the remaining CO2 is absorbed by 25 wt% MDEA amine solution and desorbed to obtain 11.8 kg of CO2 (purity 99.95 wt%).

[0086] (4) The reaction byproduct is a mixed salt solution of NaCl / Na2CO3 (approximately 200 kg, initial concentration 7.2 wt%), which is successively concentrated by triple-effect evaporation and treated by ion exchange:

[0087] The triple-effect evaporation process specifically includes: first effect (105℃, -0.015MPa, 0.4MPa low-pressure steam heating) to concentrate to 18wt%; second effect (85℃, -0.045MPa, first effect secondary steam heating) to concentrate to 23wt%; and third effect (65℃, -0.075MPa, second effect secondary steam heating) to concentrate to 28wt%, with a total residence time of 75min.

[0088] Ion exchange: After the concentrate is filtered through a 5μm filter, it enters an exchange column (inner diameter 300mm, height 1200mm) packed with 001×7 type resin (crosslinking degree 8%, particle size 0.3~1.2mm). The feed temperature is controlled at 35℃ and the empty column flow rate is 15m / h. After treatment, 51kg of NaCl solution (purity 99.7wt%) is obtained.

[0089] The single-pass yield of hydrazine hydrate is 84.5%, the utilization rate of chlorine is 99.0%, the recovery rate of by-product NaCl is 100%, the steam consumption is 3.3t / t of hydrazine hydrate, and the energy consumption is reduced by 37%.

[0090] Comparative Example 1

[0091] A method for the efficient and green synthesis of hydrazine hydrate includes the following steps:

[0092] (1) Add 500 kg of water to the reactor, start stirring (150 rpm), add 105 kg of sodium hydroxide (industrial grade, 98% purity), stir until dissolved (solution temperature rises to 35℃), control the chlorine gas (99.5% purity) flow rate at 12 kg / h using a flow meter, and continue to flow for 8.3 h (total addition 100 kg, chlorine to sodium hydroxide mass ratio 1:1.05). During the reaction, the temperature is adjusted only by natural cooling, and the system temperature fluctuates between 35 and 42℃. Continue the reaction for 60 min. After the reaction is completed, take a sample and test to obtain 705 kg of sodium hypochlorite solution, in which the effective chlorine concentration is 8.8 wt% and the sodium hypochlorite content is 0.65 wt%.

[0093] (2) Dissolve 80 kg of urea (industrial grade, 99% purity) in 200 kg of tap water to prepare a 28.6 wt% urea solution (the mass ratio of urea to sodium hydroxide in step 1 is 1:1.31). Combine this urea solution, the 670 kg sodium hypochlorite solution prepared in step 1, and 1.23 kg of a single magnesium chloride catalyst (the MgCl2 concentration is the same as that in the composite catalyst of Example 1). 2+ (Concentration consistent) is pumped into a single-temperature zone tubular reactor (material: 304 stainless steel, no static mixing element, total length: 10m, inner diameter: 50mm) using a common centrifugal pump; the overall temperature of the reactor is controlled at 100℃ (no segmented temperature control), and the reaction time is 90min.

[0094] (3) The tail gas produced by the reaction (containing about 3.5 kg of NH3, 0.8 kg of trace hydrazine and about 12 kg of CO2) was treated by a single-stage water absorption tower (at a temperature of 25°C and absorbed by 200 kg of tap water) to produce only 28 kg of 12 wt% ammonia water; the unabsorbed trace hydrazine (about 0.5 kg) and CO2 (about 8 kg) were directly emitted (without the MDEA amine liquid absorption step), and the concentration of hydrazine in the tail gas exceeded the standard of the Integrated Emission Standard of Air Pollutants (GB16297-1996) by 3 times.

[0095] (4) The reaction byproduct is a mixed salt solution of NaCl / Na2CO3 (about 190 kg, initial concentration 5.8 wt%), which is concentrated to 28 wt% by single-effect evaporation (temperature 110℃, heated by 0.8 MPa high-pressure steam) with a total residence time of 120 min. Without ion exchange treatment, it is directly cooled and crystallized to obtain 13 kg of mixed salt (containing about 85% NaCl and about 15% Na2CO3), with a purity of only 85%, which cannot be reused in the chlor-alkali system and needs to be disposed of as solid waste.

[0096] In this comparative example, the single-pass yield of hydrazine hydrate was 74.5%, the chlorine utilization rate was 89% (9.5 percentage points lower than in Example 1), the by-product salt could not be recycled, the steam consumption was 5.2t / t hydrazine hydrate, the total energy consumption was 36% higher than in Example 1, and there was also the problem of excessive tail gas emissions.

[0097] Comparative Example 2

[0098] A method for the efficient and green synthesis of hydrazine hydrate includes the following steps:

[0099] (1) Add 500 kg of deionized water (chlorine to water mass ratio 1:5) to the reactor, start stirring (200 rpm), and slowly add 120 kg of sodium hydroxide (industrial grade, 98% purity), stirring until completely dissolved (the solution temperature naturally rises to 28℃). Control the chlorine (99.5% purity) flow rate at 10 kg / h using a rotor flow meter, and continue flowing for 10 h (total addition 100 kg, chlorine to sodium hydroxide mass ratio 1:1.2). During the reaction, stabilize the system temperature at 30℃ using cooling water, and continue the reaction for 45 min. After the reaction is completed, take a sample and test to obtain 682 kg of sodium hypochlorite solution, with an effective chlorine concentration of 11.2 wt% and a sodium chlorate content of 0.25 wt%.

[0100] (2) Dissolve 80 kg of urea (industrial grade, 99% purity) in 200 kg of deionized water to prepare a 28.6 wt% urea solution (the mass ratio of urea to sodium hydroxide in step 1 is 1:1.5). Pump this urea solution, 682 kg of sodium hypochlorite solution obtained in step 1, and 1.23 kg of magnesium chloride-lanthanum composite catalyst (prepared according to the aforementioned preparation example 1) into a segmented temperature-controlled static mixing tubular reactor (made of 2205 duplex stainless steel, with built-in static mixing elements with a spacing of 50 mm and a helix angle of 30°, a total length of 10 m, and an inner diameter of 50 mm) using a metering pump.

[0101] (3) The tail gas produced by the reaction (containing about 3.2 kg of NH3, 0.5 kg of trace hydrazine, and about 12 kg of CO2) is treated by two-stage series absorption towers: the first tower (38℃) absorbs ammonia with 12.8 kg of deionized water to produce 16 kg of 20 wt% ammonia water; the second tower (10℃) absorbs trace hydrazine and CO2 with 50 kg of 5 wt% dilute hydrazine solution to obtain 62 kg of 8 wt% hydrazine recovery liquid; the remaining CO2 is absorbed by 25 wt% MDEA amine solution and desorbed to obtain 11.8 kg of CO2 (purity 99.95 wt%).

[0102] (4) The reaction byproduct is a NaCl / Na2CO3 mixed salt solution (about 180 kg, initial concentration 6.5 wt%), which is concentrated by single-effect evaporation. The single-effect evaporation specifically includes heating with 0.8 MPa high-pressure steam, controlling the temperature at 115℃ and the vacuum at -0.03 MPa, concentrating to 28 wt%, with a total residence time of 130 min.

[0103] The concentrate was directly cooled to 25°C to crystallize, and centrifuged to obtain 13 kg of mixed salt (containing about 90% NaCl and about 10% Na2CO3), with a purity of only 90%. Due to the excessively high Na2CO3 content, it could not be reused in the chlor-alkali system.

[0104] In this comparative example, single-effect evaporation only utilizes primary live steam and has no secondary steam gradient utilization. Its energy utilization rate is more than 60% lower than that of triple-effect evaporation, resulting in a surge in steam consumption. Without ion exchange, it cannot remove Na2CO3 impurities, and the purity of the by-product salt is insufficient, losing its recycling value. At the same time, it increases the cost of solid waste disposal, which violates the goal of "green process".

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the efficient and green synthesis of hydrazine hydrate, characterized in that, Includes the following steps: (1) Chlorine gas, sodium hydroxide and water are mixed and reacted to obtain sodium hypochlorite solution; (2) Sodium hypochlorite solution, urea and catalyst are mixed and reacted to obtain hydrazine hydrate, tail gas and by-products. The catalyst includes magnesium chloride-rare earth composite catalyst. (3) Recover exhaust gas and by-products; The mass ratio of urea in step (2) to sodium hydroxide in step (1) is 1:1.4~1.6; In step (2), the mass ratio of urea to catalyst is 50~80:1; In step (2), the preparation of the magnesium chloride-rare earth composite catalyst includes: Magnesium chloride, rare earth chloride, and water were mixed and activated to obtain a magnesium chloride-rare earth composite catalyst. The molar ratio of rare earth elements in the magnesium chloride and the rare earth chloride is 10:0.5~1; The activation conditions are: pH 5.5-6.5, temperature 40-50℃, and time 1-1.5h.

2. The method for efficient and green synthesis of hydrazine hydrate according to claim 1, characterized in that, In step (1), the ratio of chlorine gas to sodium hydroxide is 1:1.15~1.25; In step (1), the mass ratio of chlorine gas to water is 1:4.5~5.

5.

3. The method for efficient and green synthesis of hydrazine hydrate according to claim 1, characterized in that, In step (1), the reaction temperature is 25~35℃.

4. The method for efficient and green synthesis of hydrazine hydrate according to claim 1, characterized in that, In step (2), the reaction process is as follows: In step (2), the mixed materials are placed in a segmented temperature-controlled static mixing tubular reactor for reaction; The reaction temperature is controlled in stages: 80-90℃ at the inlet, 110-115℃ in the middle, and 95-100℃ at the outlet. The reaction time is 60-90 minutes.

5. The method for efficient and green synthesis of hydrazine hydrate according to claim 1, characterized in that, In step (3), the exhaust gas recovery process includes: The exhaust gas is treated by a two-stage series absorption tower; The temperature of the first tower in the series absorption tower is 35~40℃, and the temperature of the second tower in the series absorption tower is 5~15℃.

6. The method for efficient and green synthesis of hydrazine hydrate according to claim 1, characterized in that, In step (3), the by-product recovery process includes: The byproducts were then subjected to evaporation concentration and ion exchange treatment in sequence.