Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
  • C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
  • C07C273/14—Separation; Purification; Stabilisation; Use of additives
  • C07C273/16—Separation; Purification

Definitions

• the present invention is Ru Oh than also relates to a method of concentrating the aqueous urea solution purification step or these urea synthesis solution 9 9. 5 wt or more. Background technology
• the aqueous urea solution from the purification process usually contains 10 to 30 weight of water, so the water must be evaporated to make urea into a granular product. It is necessary to use a substantially anhydrous urea solution.
• the hydrolysis reaction of urea and the reaction of forming uretlets as shown in the following formula occur: NH 2 CONH 2 + H 20 ⁇ 2H 3 + C 0 2
• the uret is harmful to plants and degrades urea; hydrolysis reduces the overall efficiency of urine synthesis, and also helps to recover the ammonia and carbon dioxide produced. Due to problems, it is desirable to suppress the above reaction as much as possible.
• vacuum or hot air flow type evaporators have been used to concentrate urea aqueous solutions.
• a vacuum evaporator To concentrate to 99.5% or higher with a vacuum evaporator, a high vacuum of 20 to 30 baskets (absolute) is required, and the evaporating water is condensed under such pressure. To do this, cooling water at normal temperature cannot achieve its goal. Therefore, a chiller for cooling the cooling water
• An object of the present invention is to provide a method for concentrating a urea aqueous solution which consumes less steam and cooling water, and has an increase in the amount of pellets equal to or less than that of the conventional method.
• the purpose is.
• the method of concentrating an aqueous urea solution of the present invention the concentration 9 5 aqueous urea solution under vacuum - 9 a first step of 9% or in ⁇ , hot air flow and the direction of the first step or these urea solution at atmospheric pressure flow to the contacted by concentration of 9 9.5 weight?
• the feature is that it consists of a second step of concentrating more than one.
• the concentration of the urea solution at the outlet of the first stage is determined by condensing the steam in the second stage and the steam generated in the first stage by cooling water at a normal temperature.
• cormorants Ru considering the Oh Ru this by enabling 3 ⁇ 4 concentration reached under pressure 9 5 - 9 9 are by weight.
• outlet concentration in the first step within the above range, it is possible to reduce the rate of increase in the pellet, the rate of hydrolysis, and the specific unit of utility. it can .
• the drawing is a schematic diagram for explaining the present invention.
• the concentration of the aqueous urea solution supplied in the first stage is
• the degree is between 70 and 90 weight and the first stage pressure is preferably
• the concentration of the urea solution from the first stage is particularly preferably 90 to 99% by weight, and the temperature is higher than the saturation temperature of the urea solution in consideration of prevention of caking of molten urea in the granulation equipment. In order to minimize the amount of biuret formation and hydrolysis, it must be as low as possible. Therefore, the saturation temperature is usually 2 ° C to 5 ° C higher.
• the urea solution from the first stage is brought into countercurrent contact with a hot air stream and concentrated to a concentration of 99.5 weight or more, but the hot air stream has a temperature 135 °-200 ° C is preferred, with an airflow of 150 ° -170 ° C.
• Reference numeral 1 denotes a purification system for separating unreacted ammonia and carbon dioxide from the urea synthesis solution discharged from the urea synthesis tube to obtain an aqueous urea solution.
• the 70-90 weight urea aqueous solution from the purification system 1 is introduced into the vacuum evaporator 3 which is the first concentration step through the line 2.
• the vacuum evaporator 3 is heated by the steam coming out of the line 5]) and the line 5 coming out of the line.
• an arbitrary type such as a falling thin film type is used.
• the pressure is preferably between 40 and 300 m ⁇ .9 (absolute), especially between 60 and 120 mm.
• the urea liquid discharged from the bottom of the vacuum evaporator 3 via the line 6 weighs 95-99, preferably 98-99! ), Temperature is good Or 130-140 ° C.
• the water evaporated in the vacuum evaporator 3 enters the condenser 8 via the line 7 and is cooled and condensed by cooling water (usually 25-35 ° C).
• the condenser 8 is connected to a vacuum generator 10 via a line 9, and the urea liquid discharged via a line 6 is connected to a vacuum generator 10 via a line 12 by a pump 11, and is filled. It is drawn on the top of a hot air dryer 13 like this.
• the urea liquid supplied to the hot air dryer 13 flows down the packed bed and is brought into countercurrent contact with the hot air flow supplied from the line 14, for example, a hot air flow.
• the water contained is evaporated.
• the pressure of the hot air dryer 13 is kept substantially at atmospheric pressure.
• the temperature of the hot air flow is 135-200. C, especially 150-170 ° C is preferred.
• the temperature and volume of this hot air flow depend on the concentration of the urea solution at the inlet.]? If the concentration of the urea solution is low, the temperature of the air stream is high, and the amount is not large. It is not preferable because it causes the increase.
• the hot air stream is preferably dehumidified.
• Urea liquid having a temperature equal to or higher than the melting point of urea concentrated to 99.5 weight or more flowing down the packed bed is discharged from the line 15 and sent to the granulation tower for granulation. .
• the hot air stream used for concentrating the urine solution is discharged from line 16 and sent to the urea dust recovery system together with the exhaust gas from the granulation tower. Vacuum concentration and operate at relatively low vacuum (high absolute pressure and relatively low temperature).
• the urea aqueous solution is concentrated to a concentration of 95-99, and the second stage is concentrated by hot air flow to a concentration of 99.5 or more.
• Urea aqueous solution from urea purification system (concentration 83 wt.
• the 11-let content was 0.43 weight of urea, the temperature was 100 ° C.
• the pressure was supplied to a vacuum evaporator maintained at 80 mm E9- (absolute) at 119 tonnes. 3. 5 cd by heating vinegar team of G 9 9 ⁇ o or with you concentrated.
• the urea solution at a temperature of 133 ° C discharged from the vacuum evaporator is pumped into the top of the hot flash dryer. In this hot air dryer, the hot air flow at 170 ° C and 4300 Nm 3 Z comes into countercurrent contact with the urea liquid flowing down from the top, and the urea concentration becomes 99.7.
• Comparative Example 1 ′ The same urea aqueous solution as in Example 1 was concentrated in the first stage at 300 thighs (absolute) and 125 ° (at a concentration of 95% by weight). In two stages, it is supplied to a vacuum evaporator kept at 25 m (absolute) at 1338 ° C and concentrated to a concentration of 99.7 weights. The uret content is 0.83% by weight, and the hydration rate for this concentration is 0.4%.
• Example 2 The same urea aqueous solution as in Example 1 was supplied to a hot air flow type evaporator at 11.9 ton Z hours, and concentrated to a concentration of 99.7. Hot air flow
• the temperature is 150.
• the flow rate of hot air is 650 0 ⁇ ⁇ , and it is brought into countercurrent contact with the aqueous urine solution.
• the outlet temperature of the urea solution is 138.
• the urea solution at the outlet has a pipette content of 0.883% by weight and a hydrolysis rate of 0.5 upon concentration.
• Table 1 shows the basic unit of utility in Example 1 and Comparative Examples 1 and 2 described above.
• Example 2 The same aqueous urea solution as used in Example 1 is supplied to the concentrator used in Example 1, and concentrated to a concentration of 99.7 weight parts.
• Table 2 shows the operating conditions, the concentration of the pellets in the obtained urea solution, the hydrolysis rate of urea during the concentration, and the specific unit of utility.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1979
  • 1979-05-01 JP JP5251979A patent/JPS55145659A/ja active Pending
• 1980
  • 1980-04-25 WO PCT/JP1980/000088 patent/WO1980002425A1/ja not_active Ceased
  • 1980-04-25 GB GB8039154A patent/GB2061948B/en not_active Expired
  • 1980-05-12 IN IN565/CAL/80A patent/IN152760B/en unknown

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