Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C281/00—Derivatives of carbonic acid containing functional groups covered by groups C07C269/00 - C07C279/00 in which at least one nitrogen atom of these functional groups is further bound to another nitrogen atom not being part of a nitro or nitroso group
  • C07C281/06—Compounds containing any of the groups, e.g. semicarbazides

Definitions

• the present invention relates to a method and apparatus for preparing hydrazodicarbonamide with urea as a starting material, and more particularly to a method and apparatus for preparing hydrazodicarbonamide economically and environmentally desirably by producing biuret with urea, and reacting the obtained biuret with ammonia produced during the process of biuret synthesis.
• Hydrazodicarbonamide(HDCA) is a useful compound as a raw material for preparing azodicarbonamide which is widely used as a foaming agent. As shown in the following reaction Equation 1 , azodicarbonamide(2) can be obtained by oxidation of hydrazodicarbonamide (1 ) with proper oxidation agent.
• the conventional methods for preparing the hydrazodicarbonamide includes methods of ( i ) using hydrazine as a starting material, ( ii ) direct synthesis from urea, (iii) obtaining semicarbazide using urea, and then converting the obtained semicarbazide to hydrazodicarbonamide, and (iv) using biuret as starting material.
• reaction Equation 2 hydrazodicarbonamide is produced by reacting 1 mol of hydrazine(3) with 2 mol of urea(4), [Equation 2]
• the above-identified reaction has a merit in that the process is simple, but it has drawbacks in that the starting material, hydrazine is difficult to synthesis and expensive.
• the representative methods for preparing hydrazine includes Raschig process and method of using ketazine.
• hydrazine obtained by these methods needs concentration process and hydrolysis process. Therefore, the costs for energy and for utility are too high and accordingly the production cost is increasing.
• hydrazine can also be prepared by the urea process which reacts urea with sodium hypochlorite and sodium hydroxide. But, this method needs excess of sodium hydroxide, and the cost to remove sodium carbonate by-product is very high, and many chemicals are required to remove the by-product. Thus, this method is esteemed as uneconomical and environmentally undesirable.
• Equation 3 represents the direct synthetic method of hydrazodicarbonamide using urea.
• the reaction of 3 mol of urea with 4 mol of sodium hydroxide and 1 mol of chlorine produces 1 mol of hydrazodicarbonamide.
• this method also is improper because the production cost is high due to the requirement of excess reagents and the process is very complicated. And there is another important problem in that a lot of ammonia are formed as by-product, which is environmentally undesirable.
• Equation 3 n O O O
• Equation 4 shows another method of synthesizing hydrazodicarbonamide.
• the method comprises the steps of obtaining semicarbazide using urea, and subsequently converting the obtained semicarbazide to hydrazodicarbonamide.
• sodium monochlorourea salt is obtained by the reaction of urea with sodium hypochlorite, and the sodium monochlorourea salt reacts with excess ammonia in the presence of catalyst to produce the intermediate (semicarbazide), and then the obtained semicarbazide reacts with urea to produce the final product
• Equation 5 shows the method of synthesizing hydrazodicarbonamide using biuret (International Application PCT/KR00/ 00180). It comprises the steps of obtaining metal monohalobiuret salt by reacting biuret with metal hypohalogen (MOX), and subsequently reacting the obtained metal monohalobiuret with ammonia to obtain hydrazodicarbonamide.
• MOX metal hypohalogen
• the present invention provides a method for preparing hydrazodicarbonamide which comprises the steps of obtaining biuret of Formula 1 and ammonia by pyrolyzing urea, obtaining metal monohalobiuret salt of Formula 2 or 3 by reacting the obtained biuret with metal hypohalogen compound or with halogen and base, and reacting the obtained metal monohalobiuret salt with ammonia.
• M represents metal and X represents halogen.
• the urea pyrolysis temperature is 100 ⁇ 300°C, and the pyrolysis process is carried out while removing ammonia, and the removed ammonia reacts with the metal monohalobiuret salt.
• the present invention further provides an apparatus for preparing hydrazodicarbonamide which includes pyrolysis furnace to obtain biuret and ammonia by pyrolyzing urea; recrystallization reactor to purify the biuret obtained from the pyrolysis furnace; a first reactor to obtain an metal monohalobiuret salt by reacting the biuret with metal hypohalogen compound or with halogen and base; a second reactor to synthesize the hydrazodicarbonamide by reacting the metal monohalobiuret salt with ammonia; and an ammonia evaporator to separate the excess ammonia from hydrazodicarbonamide and to forward the separated ammonia to ammonia concentrator.
• an apparatus for preparing hydrazodicarbonamide which includes pyrolysis furnace to obtain biuret and ammonia by pyrolyzing urea; recrystallization reactor to purify the biuret obtained from the pyrolysis furnace; a first reactor to obtain an metal monohalobiuret salt by reacting the biuret with metal
• the ammonia concentrator is to concentrate the excess ammonia and ammonia obtained from the pyrolysis furnace, and to supply the concentrated ammonia to the second reactor.
• the pyrolysis furnace may include a gas injector for injecting inert gas, which does not react with isocyanic acid, into the pyrolysis furnace, and may include means for lowering pressure to remove ammonia from the pyrolysis furnace.
• Fig. 1 is a schematic diagram showing an apparatus to prepare hydrazodicarbonamide according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION
• biuret represented by Formula 1 and ammonia are produced by pyrolyzing urea at a temperature above the melting point of urea.
• biuret is widely used as a precursor of pharmaceuticals, weedicide and reagent for analysis, also used in large amount as feed for ruminants, and is applied in various field of plastic resins.
• the some derivatives of biuret works as physiological healing agent or chemical therapeutic agent.
• Equation 6 shows the biuret synthesis process by pyrolyzing urea. [Equation 6] o o o o o
• Equation 6 pyrolysis of 2 mol of urea gives biuret by elimination of ammonia. More precisely, as shown in the following Equation 7, it is presumed that isocyanic acid and ammonia is formed by pyrolysis of urea at first, and then the isocyanic acid reacts with another urea, which gives the target product biuret.
• the biuret synthesis by pyrolysis of urea has merits in that the reaction is
• cyanuric acid are formed due to reaction of biuret with isocyanic acid in the biuret
• the impurities like triuret, cyanuric
• temperature is preferably maintained at 100 ⁇ 300°C and more preferably is
• isocyanic acid is injected into the reactor, and/or the pressure of reactor is lowered,
• liquid phase organic compound which
• catalyst to increase the pyrolysis reaction rate can be any catalyst that can be used.
• inorganic acid catalyst such as nitric acid, hydrochloric acid,
• the preferable amount of catalyst is 0.001-0.5mol per 1 mol of urea, and more preferable amount is 0.01 ⁇ 0.3mol per 1 mol of urea.
• Metal monohalobiuret salt of the following Formula 2 or 3 can be produced by reacting the obtained biuret with metal hypohalogen compound or halogen and base.
• M represents metal and X represents halogen.
• Equation 8 The direct method of preparing metal monohalobiuret salt by reacting biuret with metal hypohalogen compound is shown in Equation 8, and the specific example is shown in Equation 9.
• Equation 9 n n 0 0 0
• biuret reacts with sodium hypochlorite to form sodium chlorobiuret salt. Because above reaction is exothermic, the reaction system preferably would be maintained at low temperature. But the obtained sodium chlorobiuret salt is stable against moderate heat, it can be prepared at
• reaction temperature is less than 60°C, and more preferably -10 ⁇ 60°C and most preferably -5 ⁇ 35°C.
• the reaction mol ratio of metal hypohalogen per 1 mole of urea is preferably between 0.1 and 2.
• the reaction mol ratio is less than 1 mol, the excess biuret can be recovered and can be reused.
• the reaction time would be too long. And if the reaction mol ratio is more than 2, the production cost increases and the side reaction may occur.
• the reaction temperature is more than 60°C, the produced metal monohalobiuret salt can be decomposed because it is unstable at high temperature.
• the sodium chlorobiuret salt obtained under above-mentioned condition can be used directly or can be stored for next reaction.
• Equation 10 A process of producing metal monohalobiuret salt of above Formula 2 or 3 by reacting biuret with halogen and base is shown in Equation 10. As shown in
• M represent metal and X represent halogen.
• the reaction temperature is maintained lower, specifically less than 60°C, preferably -10 ⁇ 60°C and most preferably -5 ⁇ 30°C for the proper reaction rate and the stability of reaction.
• metal monohalobiuret salt can be obtained by mixing metal hydroxide with biuret at first, and then reacting halogen with the obtained product. Because this reaction is also exothermic, the reaction temperature should be maintained lower, specifically to -10 - 60°C and more preferably -5 - 30°C. In above reaction, when the reaction temperature is less than 10°C, the reaction time would be too long, and when the reaction temperature is more than 60°C, the metal monohalobiuret salt can be decomposed because it is unstable against heat. As shown in Equation
• the obtained metal monohalobiuret salt can be metal 3-monohalobiuret salt(6) or metal 1 -monohalobiuret salt(7).
• metal monohalobiuret salt (8) unstable diaziridinone derivative (9) is formed by formation of nitrogen-nitrogen bond while metal halogen compound being eliminated.
• the diaziridinone derivative (9) readily reacts with highly reactive ammonia, and the hydrazodicarbonamide is prepared.
• metal monohalobiuret salt is converted to the compound which contains isocyanate group, and the converted isocyanate compound react with highly reactive ammonia to form hydrazodicarbonamide.
• reaction temperature is between 0 and 150 °C, more preferably between 30 and 150 °C.
• reaction temperature is less than 0°C, the reaction rate is too slow and the economically inefficient, and when above reaction temperature is more than 150°C, the equipment cost is increase because the equipment must be designed to endure the internal pressure caused by ammonia vaporization.
• ammonia can be used in either form of gaseous ammonia, or liquid ammonia or ammonium hydrate.
• Ammonia can be preferably used with excess amount to increase the reaction rate.
• the amount of ammonia can be between 1 and lOOOmol per 1mol of metal monohalobiuret salt, more preferably is between 2 and 500mol, most preferably between 5 and 100mol.
• the excess ammonia except 1mol of ammonia which react with 1 mol of metal monohalobiuret salt can be recovered and reused for next reaction.
• the pressure of the reaction system can be raised to prevent the vaporization of ammonia. This improves the reaction rate and efficiency, and the preferable range of the pressure is between 1 and 100 kgf/cm 2 .
• the catalyst includes at least one compound selected from the group consisting of sulfuric acid salt, chloride salt, carbonate salt or hydroxide salt of basic metal or amphoteric metal, and organic compounds including the metals.
• the preferable amount of the catalyst is between 0.001 and 1 mol, more preferably is 0.01 ⁇ 0.5mol per 1 mol of metal monohalobiuret salt.
• inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid can be added with the amount of 0.05 ⁇ 3.0mol per 1 mol of metal monohalobiuret salt.
• water can be used as a solvent of the reactant(biuret) or of entire reaction system.
• a second solvent at least one solvent selected from the group consisted with the polar solvent such as methanol, ethanol, propanol, isopropanol, tetrahydrofuran, acetonitrile, and the aprotic solvent such as dimethylformamide, dimethylsulfoxide, dimethylacetamide can be added.
• the amount of the second solvent is not limited particularly, but the preferable amount is between 0.1 and 50 times to the total weight of water, more preferable amount is 0.2-3.0.
• the second solvent can be introduced at the start of the reaction as a solvent for biuret or after mixing biuret solution with sodium hypochlorite solution.
• Equation 14 The reaction for preparing hydrazodicarbonamide using urea as a starting material according to the present invention is shown in Equation 14 as a whole.
• an apparatus to prepare hydrazodicarbonamide comprises pyrolysis furnace 10 to obtain biuret and gaseous ammonia by pyrolyzing urea.
• the pyrolysis furnace 10 preferably includes a gas injector 12 for injecting inert gas into the pyrolysis furnace 10, or may includes means (not shown) for lowering pressure of the furnace 10 to easily remove ammonia from the pyrolysis furnace 10.
• the non-limiting examples of the inert gas includes air, nitrogen, and liquid phase organic compound which changes into an inert gas in the pyrolysis furnace 10, which does not react with isocyanic acid.
• Ammonia removed from said pyrolysis furnace 10 is preferably supplied to ammonia concentrator 20, and the function of the ammonia concentrator 20 is concentrating the ammonia supplied from the pyrolysis furnace 10 and the excess ammonia remained after formation of hydrazodicarbonamide.
• the impurities, such as cyanuric acid and triuret, in biuret produced in the pyrolysis furnace 10 is separated by recrystallization means comprising recrystallization reactor 30 and dehydrator 32 such as a centrifuger, and then supplied to the first reactor 40.
• Purified biuret which is sent to the first reactor 40 reacts with metal hypohalogen compound (for example, NaOCI) or halogen (for example, chlorine) and base to produce metal monohalobiuret salt, and then the produced metal monohalobiuret salt is supplied to the second reactor 50.
• the metal monohalobiuret salt reacts with ammonia to produce hydrazodicarbonamide, and the ammonia is preferably supplied from the ammonia concentrator 20.
• the obtained hydrazodicarbonamide and excess ammonia are supplied to the ammonia evaporator 52.
• Ammonia evaporator 52 vaporizes the excess ammonia, and the vaporized ammonia is supplied to ammonia concentrator 20.
• the hydrazodicarbonamide separated from the excess ammonia is purified by dehydrator 54 such as filter.
• the hydrazodicarbonamide can be prepared in one continuous process from a starting material, urea. Because the entire process is carried out continuously, the efficiency of process can be improved. In addition, the production cost can be lowered by greatly reducing the required amount of the raw material due to the fact that metal monohalobiuret salt reacts with ammonia, which is produced as a byproduct in the process of biuret formation. Thus, hydrazodicarbonamide can be prepared environmentally desirably by using the environmentally undesirable by-product ammonia.
• a 2L glass reactor was charged with 423.1g(0.287mole) of slurry solution of 7% biuret, and cooled to 5 ° C with stirring.
• 223g (0.575mole) of aqueous solution of 10.3% sodium hydroxide was added, and 20.3g(0.287mole) of gaseous chlorine was added maintaining the reaction temperature of the system below 10 ° C .
• the reaction solution was analyzed by iodometry and by using liquid chromatography. The available chlorine was 3.0%. This corresponded to a yield of 98%.
• Example 10-18 Synthesis of hydrazodicarbonamide Reaction was carried out by the same method as Example 4 except that the 0.05 mole of various catalysts shown in Table 6 was added. After completion of reaction, unreacted ammonia was removed, and the reaction solution was filtered to get hydrazodicarbonamide insoluble to water and the yield of hydrazodicarbonamide was calculated and disclosed by the following Table 6. [Table 6]
• Example 28-36 Synthesis of hydrazodicarbonamide Reaction was carried out by the same method as Example 22 except that the 0.05 mole of various catalysts shown by following table 8 was added. After completion of reaction, unreacted ammonia was removed, and the reaction solution was filtered to get hydrazodicarbonamide insoluble to water and the yield of hydrazodicarbonamide was calculated and disclosed by the following Table 8. [Table 8]
• Example 46-54 Synthesis of hydrazodicarbonamide Reaction was carried out by the same method as Example 40 except that the 0.05 mole of various catalysts shown by following Table 10 was added. After completion of reaction, unreacted ammonia was removed, and the reaction solution was filtered to get hydrazodicarbonamide insoluble to water and the yield of hydrazodicarbonamide was calculated and disclosed by the following Table 10. [Table 10]
• Examples 55-58 Synthesis of hydrazodicarbonamide
• a 2L autoclave was charged with 593.1 g of sodium chlorobiuret salt obtained by the above Manufacturing Example 14, and cooled to 10 ° C with stirring. Maintaining the reaction temperature of solution below 10 ° C, aqueous ammonia solution was added while vigorously stirring for an hour at the amount shown by the following Table 11 . After completion of reaction, unreacted ammonia was removed, and the reaction solution was filtered to get hydrazodicarbonamide insoluble to water and the yield of hydrazodicarbonamide was calculated and disclosed by the following table 11. [Table 11]
• hydrazodicarbonamide can be synthesized from cheep and easily available urea as a starting material.
• hydrazodicarbonamide can be prepared economically and environmentally desirably due to the minimization of byproduct and input raw material, and with high efficiency from continuous process.

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