Urea-Formaldehyde Slow-Release Nitrogen Fertilizer And Manufacturing Method Thereof

Abstract

A method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer includes steps of: mixing and heating urea and formaldehyde solution with a predetermined molar ratio of urea to formaldehyde; adjusting a PH value of hydroxymethylation reaction of urea and formaldehyde solution to 7.5-10.5; heating the hydroxymethylation reaction of urea and formaldehyde solution to the initial reaction temperature of 50° C.; adding a catalyst to start the hydroxymethylation reaction of urea and formaldehyde solution, and conducting hydroxymethylation reaction intermittently or continuously; heating cold urea-formaldehyde solution using the reaction heat of hydroxymethylation; adjusting the pH value of the methylenation reaction of urea and formaldehyde solution to 3.5-5.0; adding a catalyst; completing the methylenation reaction of urea and formaldehyde solution within 1 to 10 minutes; and performing spraying granulation of slurry after the methylenation reaction of urea and formaldehyde solution in the granulator to obtain a urea-formaldehyde slow-release nitrogen fertilizer.

Claims

1. A method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer, comprising steps of: (1) mixing urea and formaldehyde solution and heating, with a molar ratio of urea to formaldehyde at (1.5-2.5):1; (2) adjusting a PH value of hydroxymethylation reaction of urea and formaldehyde solution to 7.5-10.5; (3) heating the hydroxymethylation reaction of urea and formaldehyde solution to the initial reaction temperature of 50° C.; (4) adding a catalyst to start the hydroxymethylation reaction of urea and formaldehyde solution, and conducting hydroxymethylation reaction intermittently or continuously; (5) heating cold urea-formaldehyde solution using the reaction heat of hydroxymethylation, and heating appropriately if the temperature cannot reach the initial reaction temperature; (6) adjusting the pH value of the methylenation reaction of urea and formaldehyde solution to 3.5-5.0; (7) adding a catalyst, without controlling the temperature of materials for methylenation reaction; (8) completing the methylenation reaction of urea and formaldehyde solution in a reaction vessel within 1 min to 10 min; (9) directly performing spraying granulation of slurry after the methylenation reaction of urea and formaldehyde solution in the granulator, to obtain a urea-formaldehyde slow-release nitrogen fertilizer.

2. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the urea in step (1) is a solid urea, or a urea solution of intermediate product in the production process of a urea factory, and the concentration of the urea solution is >90%; the concentration of formaldehyde solution is 30% to 50%.

3. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the substance for adjusting the pH value is sodium hydroxide and solution thereof, or alkaline dissolved matter such as borax in step (2).

4. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the temperature of hydroxymethylation reaction of the urea and the formaldehyde solution in step (3) is between 50° C. and 75° C.

5. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the hydroxymethylation reaction of the urea and formaldehyde solution in step (4) is carried out in a reactor, and the reaction in the reactor can be performed intermittently one by one or continuously by reactors in series.

6. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein in the reaction of step (5), when the urea and formaldehyde solution react for the first time and restart reaction after suspension each time, the urea and formaldehyde solution are heated to the initial reaction temperature of 50° C., and not heated when reacting stably, or the heating intensity is reduced, and the heat released by the hydroxymethylation reaction is taken away by the cold urea-formaldehyde solution while heating the cold urea-formaldehyde solution.

7. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the pH value of methylenation reaction in step (6) is between 3.5 and 5.0, and the pH value is adjusted by acidic substances such as sulfuric acid, nitric acid, hydrochloric acid, acetic acid, and oxalic acid.

8. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the temperature of materials of methylenation reaction is not controlled and no cooling measures are taken in step (7), to make full use of the reaction heat and reduce the energy consumption for drying.

9. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the methylenation reaction of the urea and formaldehyde solution of step (8) is completed within 1 min to 10 min, with very short time.

10. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the methylenation reaction slurry of urea and formaldehyde solution in step (8) is directly spray-dried in a drying apparatus to obtain powdered urea-formaldehyde slow-release nitrogen fertilizer; or the methylenation reaction slurry is sprayed and granulated directly in a granulator to obtain granular urea-formaldehyde slow-release nitrogen fertilizer.

11. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 10, wherein the materials completed by the hydroxymethylation reaction are stored in a storage tank, and then methylenation is carried out according to production needs; or methylenation is carried out directly after hydroxymethylation.

12. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 1, wherein the methylenation reaction slurry in step (8) of claim 1 is added with raw materials containing other nutrient elements to produce a compound fertilizer.

13. The method for manufacturing a urea-formaldehyde slow-release nitrogen fertilizer according to claim 12, wherein the raw materials containing other nutrient elements are urea, ammonium nitrate, ammonium sulfate, ammonium chloride, liquid ammonia, molten urea liquid, powder urea-formaldehyde in nitrogen fertilizers, and a variety of calcium superphosphate, monoammonium or diammonium phosphate, calcium magnesium phosphate in phosphate fertilizers, and potassium sulfate, potassium chloride, potassium carbonate, and potassium hydrogen sulfate solution with sulfuric acid replacing potassium chloride in potash fertilizers; and the production apparatus is a drum granulator, a disc granulator.

Description

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0045] The present invention will be further described below in conjunction with specific embodiments.

Example 1

[0046] To a special reaction vessel, urea and 50% formaldehyde solution were evenly added at a molar ratio of 2.5:1, mixed to dissolve while heating, when the temperature reached 50° C., a catalyst and 25% sodium hydroxide solution were added to adjust the pH value to 7.5, then stirred continuously and cooled, to maintain the temperature at about 50° C. and stir for 35 minutes to carry out the hydroxymethylation reaction. Then the catalyst and 20% dilute sulfuric acid were added to adjust the PH value to 3.5, stirred for 1 minute for methylenation reaction, and then spray-dried to obtain pure slow-release urea-formaldehyde powder. Product indicators were as follows: total nitrogen 39.3%, of which cold water-soluble nitrogen (CWN) 11.9%, cold water insoluble nitrogen (CWIN) 27.6%, hot water insoluble nitrogen (HWIN) 12.7%, and activity coefficient (AI) 40%.

Example 2

[0047] To a special reaction vessel, urea and 30% formaldehyde solution were evenly added at a molar ratio of 1.5:1, dissolved while heating, and catalyst and 30% sodium hydroxide solution were added evenly, to control the material PH at 10.5, when the temperature reached 50° C., the control valve of the reaction vessel was opened, so that the materials reacted while flowing in the reaction vessel, and at the same time, urea, formaldehyde solution, catalyst, sodium hydroxide solution were added continuously according to a proportion. When the initially added material started to heat the later added material, the heating was reduced or stopped according to the temperature change, and the temperature was controlled at 75° C. for hydroxymethylation reaction. When the temperature of the initially added material started to decrease, the catalyst and 20% dilute sulfuric acid were added evenly according to the material flow rate and PH value from another feeding port, to control the PH value at 5, after methylenation reaction for 10 minutes, the slurry was sprayed to a granulation dryer to dry and granulate. The materials out of the granulator were sieved, and the sieved fine materials were sent back to the granulator again to continue granulation. The large materials were crushed to return to the granulator for re-granulation. The products with qualified particles were cooled and packed, to obtain qualified pure granular urea-formaldehyde slow-release nitrogen fertilizer. The indicators of pure granular urea-formaldehyde slow-release nitrogen fertilizers were as follows: total nitrogen 39.8%, of which cold water-soluble nitrogen (CWN) 17.0%, cold water insoluble nitrogen (CWIN) 22.7%, hot water insoluble nitrogen (HWIN) 9.7%, activity coefficient (AI) 65%.

Example 3

[0048] The following materials were mixed evenly and added to a spray granulating dryer evenly according to the amount added per hour: 1200 kg of potassium sulfate powder containing 50% potassium oxide, 680 kg of 11-44-0 monoammonium phosphate powder, 250 kg of urea with 46% nitrogen, 995 kg of dolomite powder, 50 kg of ferrous sulfate monohydrate, and 25 kg of zinc sulfate monohydrate). At the same time, the methylenation slurry produced in Example 2 was evenly sprayed into the spray granulation dryer at a rate of 3,000 kg/hour. Under the condition of continuous production, 5 tons of compound fertilizers containing urea-formaldehyde slow-release nitrogen with specification of 18-6-12 were produced per hour. In the 18% total nitrogen, there were ammonium nitrogen 1.5%, urea nitrogen 2.5%, urea-formaldehyde nitrogen 14.0% (of which cold water insoluble nitrogen 8.0%, hot water insoluble nitrogen 3.4%).

Example 4

[0049] To a special reaction vessel, urea and 40% formaldehyde solution were evenly added at a molar ratio of 2:1, at the same time, 30% sodium hydroxide solution and catalyst were added evenly to adjust PH at 9.8. The added amount of sodium hydroxide solution and catalyst was maintained stable and uniform, and the reaction temperature was controlled at 60° C. for hydroxymethylation reaction. When the hydroxymethylation reaction was basically completed, 20% dilute sulfuric acid and the catalyst were added to maintain the PH value of 4. After methylenation reaction for 10 minutes, the slurry was sprayed to a granulation dryer to dry and granulate. The materials out of the granulator were sieved, and the sieved fine materials were sent back to the granulator again to continue granulation. The large materials were crushed to return to the granulator for re-granulation. The products with qualified particles were cooled and packed, to obtain qualified pure granular urea-formaldehyde slow-release nitrogen fertilizer. The indicators of pure granular urea-formaldehyde slow-release nitrogen fertilizers were as follows: total nitrogen 38.7%, of which cold water-soluble nitrogen (CWN) 11.4%, cold water insoluble nitrogen (CWIN) 27.3%, hot water insoluble nitrogen (HWIN) 13.6%, activity coefficient (AI) 50.2%.

Example 5

[0050] To a two-ton reactor, 1,300 kg of urea particles and 950 kg of 50% formaldehyde solution were added, heated while stirring, and at the same time, a catalyst and 30% sodium hydroxide solution were added to adjust the pH to 9.5. When the temperature rose to 50° C., heating was stopped. After reaction started, the temperature was maintained at 65° C. for hydroxymethylation reaction. When the temperature was stable or started to drop, the slurry was introduced into the tubular reactor. At the same time, the catalyst and 20% sulfuric acid solution were added, to adjust PH to 4.2. After the methylenation reaction lasted 8 minutes, the slurry was sprayed into the spray dryer to obtain pure powdered urea-formaldehyde slow-release nitrogen fertilizer. The obtained product indicators were as follows: total nitrogen 38.3%, cold water insoluble nitrogen 25.6%, hot water insoluble nitrogen 14.4%, and activity coefficient 43.8%.

Example 6

[0051] The following materials were evenly placed into a drum granulator: 250 kg of powdered urea-formaldehyde slow-release nitrogen fertilizer produced in Example 5, 210 kg of granular urea, 250 kg of 60% potassium chloride powder, 225 kg of 11-44-0 monoammonium phosphate powder, 65 kg of dolomite powder, to produce a compound fertilizer containing urea-formaldehyde slow-release nitrogen with a specification of 20-10-15, of which, the cold water insoluble nitrogen was 6.4%, and hot water insoluble nitrogen was 3.6%.

Example 7

[0052] According to the traditional production process of sulfuric acid replacement of potassium chloride to produce sulfur-based compound fertilizer, urea-formaldehyde slow-release nitrogen was sprayed to produce sulfur-based urea-formaldehyde slow-release compound fertilizer. The specific method was as follows: concentrated sulfuric acid with a concentration of 98% was uniformly added to the reaction tank at a flow rate of 3.95 m.sup.3/h, and potassium chloride containing 60% potassium oxide was added to the reaction tank at an amount of 8 tons/hour to mix and stir, to produce potassium hydrogen sulfate slurry with a specific gravity of about 1.8 g/ml.

[0053] The previously prepared potassium hydrogen sulfate solution and 20% dilute phosphoric acid were mixed to produce mixed slurry, with a specific gravity of 1.4 g/ml. Then ammonia was added to neutralize, with a degree of neutralization of 1.2. The methylenation slurry prepared according to Example 5 and the neutralized mixed acid slurry were sprayed into the drum granulation dryer at the same time, to prepare the slow-release urea-formaldehyde compound fertilizer containing nitrogen, phosphorus and potassium. By changing the spraying ratio of mixed acid and methylenation slurry, compound fertilizers with different ratios of nitrogen, phosphorus and potassium could be produced.

[0054] Having described the invention by the description and illustrations above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Accordingly, the invention is not to be considered as limited by the foregoing description, but includes any equivalents.