Views:3 Author:Site Editor Publish Time: 2022-01-03 Origin:Site
There are four industrial production methods of hydrazine hydrate: lacey method, urea method, ketone nitrogen method and hydrogen peroxide method. At present, urea method is mainly used in China.
This process, first used in industrial production in 1906, produces hydrazine hydrate by reacting NaOCl with excess NH3. The mass fraction of NaOH used in the reaction is 8%. When Cl2 is used to produce NaOCl, The Excess NaOH is absorbed into aqueous NH3 solution with pure water. The mass ratio of NH3 to NaOCl solution is 20:1, and the reaction temperature is 170℃. The reaction can be carried out under pressure and completed in a few seconds.
The addition of gelatin to the reaction system helps to increase the yield. In addition to hydrazine hydrate, the distillate in the reaction column also contains NaCl and NaOH, unreacted ammonia and a small amount of by-products, which can be flash steamed under atmospheric pressure and separated from ammonia and the bottom liquid of the column by ammonia separation column. The bottom liquid enters the evaporation column, separates the sodium chloride and sodium hydroxide, and then concentrates the water from the top of the column, and the bottom of the column obtains hydrazine hydrate.
The hydrazine hydrate obtained by this method is a dilute aqueous solution of 1%-2%, the highest is not more than 4%, and the total synthesis rate is about 67%. A considerable amount of heat is required to extract hydrazine hydrate from a dilute solution, with 40-110kg of water required for every 1kg of hydrazine hydrate recovered. Due to the excessive use of ammonia, it is necessary to add a recovery device, which produces a large amount of NaCl and NH4Cl and other salts by side.
In actual production, there is a side reaction in which the hydrazine produced is further oxidized by chloramine. The presence of side reactions reduces the yield of hydrazine. In order to reduce side reactions, a large excess of raw ammonia is usually taken so that the product hydrazine is always at a low concentration (1%-2%wt) in the reaction solution. As a result, a large amount of ammonia water needs to be separated and recycled, and the distillation of hydrazine will consume more steam.
Compared with urea method, lacey method has lower raw material cost, but higher equipment investment and energy consumption. When the production scale is large, its total cost is lower than urea. Excerpted from Hydrazine Hydrate Technology and Market Research Report and Hydrazine Hydrate Investment Analysis Report of 6chem.com
Urea method, also known as Schestakoff method. At the beginning of the industrialization of Rasching, French chemists proposed the reaction of making hydrazine from urea.
Urea process is an improvement of Lacey process in essence. Urea is used instead of ammonia as nitrogen source. There is no problem of excessive reactants circulating in this process.
First, Cl2 reacts with 30% NaOH to generate NaOCl solution, and then oxidizes urea with NaOCl and NaOH solution under the action of oxidants such as KmnO4 and H2O2, and then evaporates, desalts and refines the finished product.
This process is simple and mature. When MgSO4 is used as catalyst, the reaction time is 1-2min, the temperature rises to 100℃ rapidly, and the yield is about 70%. This method uses urea instead of ammonia, the equipment is greatly simplified and the investment is saved.
But because the reactant NaOCl is a strong oxidant, the product is a strong reducing agent, there is a side reaction in the reaction process of hydrazine hydrate oxidation by NaOCl, and the side reaction is very intense, when the ingredients or improper operation will occur spray accident.
Therefore, the yield of urea oxidation method is low, generally 70%-80%. To curb the adverse event, it is necessary to maintain a low concentration of hydrazine (as mass fraction 2% 3%), 12 times by-product alkali amount of hydrazine, soda ash with freezing crystallization, evaporation in the mixing layer (5 cans) desalination and subsequent distillation carry strong hydrazine in consume large amounts of heat energy and mechanical energy, thus problems such as high energy consumption, high raw material costs and environmental constraints.
Almost all hydrazine hydrate enterprises in Our country adopt this method, has already realized continuous production. The most mature process technology: the technology is easy to master, the synthesis yield is higher than lasie method (more than 72%), every recovery of 1kg hydrazine hydrate steam out 20~25kg water. Urea method is used in most existing manufacturers, but only suitable for small-scale production.
In recent years, the technical improvement is: the production of sodium dichloride raw material in the packed absorption tower; Producing high concentration of sodium chlorite in sodium hypochlorite preparation process; The yield of hydrazine hydrate can be increased by changing the tank reactor to the tubular heating reactor. The intermittent evaporation of five-layer evaporator is changed to continuous evaporation of special new evaporator; The liquid phase intake column was changed to gas phase intake column to reduce the steam consumption. The crude solution of hydrazine hydrate is cooled to recover decahydrate sodium carbonate, and the by-product sodium chloride is recovered, so that the by-product can be comprehensively utilized to reduce production cost. By adopting advanced production equipment and optimizing production technology, the production cost of 80% hydrazine hydrate per ton can be further reduced to about 10,000 yuan.
In recent years, the purpose of improving the process is to inhibit side reaction and increase the yield of hydrazine hydrate. Additives can be added to the reaction medium, such as gelatin peptone KMNO4 MnSO4 and so on. KmnO4 and MnSO4 are widely used in China. However, these two additives dissolve in urea solution and are dark red, so it is difficult to control accurately in actual operation. At the same time, manganese oxide is generated due to the manganese salt reaction, which leads to pipe scaling and even blockage, and is easy to cause environmental pollution. Magnesium sulfate additive has been used to replace manganese salt. Excerpted from Hydrazine Hydrate Technology and Market Research Report and Hydrazine Hydrate Investment Analysis Report of 6chem.com.