JPH0474310B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a method for producing a slow-release nitrogen fertilizer containing a urea/formaldehyde condensate as an active ingredient, so-called formaldehyde-processed urea fertilizer as defined in the Fertilizer Control Law. Slow-release nitrogen fertilizers have a long-lasting effect, so they are widely used as base fertilizers or compounding ingredients for advanced chemical fertilizers. [Prior Art and Problems to be Solved by the Invention] Slow-release nitrogen fertilizers contain a urea/formaldehyde condensate as an active ingredient, and are usually produced by the following method. That is, an alkaline substance such as sodium hydroxide is added to an aqueous solution of urea and formaldehyde, and a methylolation reaction (addition reaction) is carried out at a neutral to alkaline pH range of 7 to 10.
Adding an acid such as sulfuric acid to the obtained methylol urea solution to lower the pH to 4 or less causes a methylenation reaction (condensation reaction) to solidify it, which is then dried, followed by processes such as crushing and sieving. It is manufactured using a method that obtains and commercializes it. In the above production method, the molar ratio of urea (U)/formaldehyde (F) (hereinafter referred to as U/F molar ratio) during the methylolation reaction is 1 or more, preferably 2 to 3. Also, the reaction temperature is 50 to 80
The reaction time is about 30 minutes to 1 hour. As mentioned above, the methylenation reaction is carried out by adding an acid to the solution in which the methylolation reaction has been completed, so the reaction temperature is about the same as that during the methylolation reaction, and after the addition of the acid, the methylolurea is condensed. It becomes methylene urea and solidifies in less than 30 minutes. The urea/formaldehyde condensate thus obtained consists of methylene urea whose general formula is represented by the following formula (1) and unreacted urea. H(NHCONHCH ₂ ) _o −NHCONH ₂
...(1) However, since the above methylenation reaction is a sequential competitive reaction, the resulting methylene urea, which is a urea/formaldehyde condensate, has n in the above formula (1), regardless of its production method. It is a mixture of numbers with different values. When the molar ratio of U/F is lowered, the proportion of compounds with a large number of n increases. Conversely, when the U/F molar ratio is increased, the proportion of compounds with a large number n decreases, but the proportion of unreacted urea and compounds with a small number n in the above formula (1) increases. As will be described later, it is well known that methylene urea exhibiting slow release properties as a nitrogen fertilizer is preferably one in which n is 2 to 3 in the above formula (1). As a measure of the solubility of nitrogen in water in slow-release fertilizers containing a urea/formaldehyde condensate as an active ingredient, the nitrogen content is divided into water-soluble nitrogen (hereinafter referred to as WN) and water-insoluble nitrogen (hereinafter referred to as WN). Hydrothermal soluble nitrogen (hereinafter referred to as HWN), hot water insoluble nitrogen (hereinafter referred to as HWIN). This classification is based on AOAC (Methods of Analysis of
According to the above analytical method,
WN (nitrogen soluble in water at 25 ± 2 ° C.) almost corresponds to the nitrogen contained in unreacted urea and methylene urea where n is 1 in the formula (1) above,
WIN (nitrogen insoluble in water at 25±2℃) almost corresponds to the nitrogen contained in methylene urea in which n is 2 or more in the above formula (1), and HWN (nitrogen at 100℃, PH
7.5 (nitrogen soluble in the buffer solution) corresponds to the nitrogen contained in methylene urea where n is 3 or less in the above formula (1), and HWIN (nitrogen insoluble in the above buffer solution) corresponds to ( Nitrogen contained in methylene urea in which the number n in formula 1) is 4 or more almost corresponds to this. In addition, the total nitrogen in the slow-release nitrogen fertilizer containing the above-mentioned urea/formaldehyde condensate as an active ingredient is TN,
Abbreviated as urea nitrogen and UN. In the above, WN is n in equation (1)
Since it is methylene urea nitrogen with a number of 1 and UN, it has high solubility in water and becomes mineralized in a short time, so it can be said to be a nitrogen fertilizer that is closer to fast-release than slow-release. In HWIN, the number n in formula (1) is large, condensation has progressed too much, and the mineralization rate is extremely slow, so it is said that it has virtually no fertilizer effect. On the other hand, methylene urea (WIN minus HWIN, hereinafter referred to as WIN−HWIN), where n is approximately 2 to 3 in formula (1) above, is better understood to be sparingly soluble in water than soluble in hot water. It is easy to mineralize and gradually becomes mineralized, so it has a long-term fertilizer effect. That is, this WIN-HWIN constitutes the active ingredient of slow-release nitrogen fertilizer. As an index showing the degree of slow release of nitrogen fertilizer, the nitrogen activity coefficient (Activity
Index (hereinafter referred to as AI) is used. AI[%]=[(WIN-HWIN)/WIN]×100...(2) As a slow-release nitrogen fertilizer, the higher the AI and the lower the WN content, the better. In addition, due to the revision of the Fertilizer Control Law at the end of 1986, slow-release nitrogen fertilizers, so-called formaldehyde-processed nitrogen fertilizers according to the Fertilizer Control Law, with a TN of 35% or more and a WN/TN of 50% or more are UN-approved.
Must be 20% or less. For things other than
AI must be 40% or higher. It was revised as follows. However, in slow-release nitrogen fertilizers obtained by conventional manufacturing methods, the value of n in equation (1) varies considerably, so in order to increase the AI value, the U/F molar ratio must be increased. As a result, unreacted urea increases. Conversely, in order to reduce the amount of unreacted urea, it is necessary to reduce the U/F molar ratio, but there is a contradictory problem in that reducing the U/F molar ratio lowers the AI value. Therefore, as a method to improve slow-release properties, (1) add 1 to 2 moles of urea to 1 mole of formaldehyde,
The addition reaction is carried out in a formaldehyde aqueous solution whose pH is adjusted to 8 to 10 at a temperature of 40 to 80°C, and the resulting addition reaction product has an acid dissociation constant pKa value (25
℃) is 4.5 to 5.5 (specifically organic acids such as citric acid, malic acid, phthalic acid, butyric acid, tartaric acid, propionic acid, acetic acid, etc.) to achieve a pH of 4.5 to 5.5.
6.5 and conduct a condensation reaction in a temperature range of 40 to 80°C (Japanese Unexamined Patent Publication No. 60-210585), (2) the molar ratio of urea/formaldehyde is 1.0 to 1.8,
Hexamethylenetetramine as an alkali catalyst,
A method is known in which one selected from ammonia, ammonium carbonate, ammonium bicarbonate, and monoethanolamine is used, and a carboxylic acid is used as the acid catalyst (Japanese Patent Laid-Open Publication No. 264384/1984). However, in method (1) above, the AI value is insufficient, probably because sodium borate or an alkali metal or alkaline earth metal hydroxide is used to adjust the pH during the addition reaction. Since the condensation reaction product is in the form of a cream or slurry, there are problems in that it is difficult to handle and the equipment and process are complicated because it is dried to produce a product. According to the results of the studies conducted by the present inventors, method (2) above does not necessarily have a satisfactory AI value, similar to method (1), and this method requires a condensation reaction to be carried out in a reaction tank. Therefore, it is thought that the condensation reaction product solidifies within the reaction tank. Therefore, like the method (1) above, there is a problem that the subsequent steps are complicated. [Means for Solving the Problem] In view of the above situation, the inventor has devised a method with a small WN and
As a result of extensive research aimed at developing a method to efficiently produce slow-release nitrogen fertilizer with a high AI value, we found two types of alkaline substances to be used for pH adjustment during the methylolation reaction (addition reaction). The inventors have discovered that the above object can be achieved by adding and using them in a specific order and carrying out the methylenation reaction at a specific pH on an endless rotating belt, and have completed the present invention. That is, in the present invention, an alkaline substance is added to an aqueous formaldehyde solution to cause a methylolation reaction in an alkaline environment, and then an acidic substance is added to the methylolation reaction in an acidic environment to form urea and formaldehyde. When producing slow-release nitrogen fertilizers made of condensates, the molar ratio of urea and formaldehyde (urea/formaldehyde) is set at 1.0 to 1.5.
As an alkaline substance, first add amines to 1 mole of formaldehyde in a range of 0.0005 to 0.005.
Then, add an inorganic hydroxide to adjust the initial pH during the methylolation reaction to 7.5 to 9.5, perform the methylolation reaction, and then add a mineral acid to adjust the pH. The present invention provides a method for producing a slow-release nitrogen fertilizer, which is characterized by adjusting the nitrogen concentration to 4.3 to 4.9 and carrying out the methylenation reaction on an endless rotating belt. [Detailed Disclosure of the Invention] The present invention will be described in more detail below. The method of the present invention is generally carried out as follows. That is, the present invention requires a reaction tank for carrying out the methylolation reaction. The reaction tank requires a stirrer and heating equipment, but it is convenient and preferred that the heating equipment is provided with a jacket outside the reaction tank, and heating is carried out by passing pressurized steam through this jacket. In the present invention, first, a formaldehyde aqueous solution and urea are mixed at a U/F molar ratio of 1.0 to 1.5, preferably 1.30 to
1.40 to the reaction tank, then add amines to the reactor while stirring and add 11 formaldehyde.
After adding 0.0005 to 0.005 mol (hereinafter, this molar ratio is abbreviated as amine/F molar ratio) to the mol, and further adding an inorganic hydroxide to adjust the pH to 7.9 to 9.5, preferably 8.0 to 8.5. , heat to completely dissolve the urea and carry out the methylolation reaction. In the present invention, the above-mentioned pH before heating and dissolution will be referred to as the initial pH during the methylolation reaction. In the present invention, the amines may be added to the mixture of formaldehyde and urea as described above, but they may also be added to the formaldehyde aqueous solution in advance, or at any stage before the urea is dissolved. In addition, the reaction temperature during the above methylolation reaction was 50°C.
Performed at ~70°C. If the reaction temperature is less than 50°C, not only will the reaction time be long, but the resulting slow-release nitrogen fertilizer (hereinafter abbreviated as the product) will be
This is not desirable because UN increases. Conversely, at temperatures exceeding 70℃, HWIN in the product increases.
This is also not desirable. The reaction is carried out until there is no unreacted formaldehyde, which takes 30 to 60 minutes at the above reaction temperature. In the present invention, the initial pH during the methylolation reaction is
It is important to adjust it to 7.5 to 9.5 as described above. In the methylolation reaction between formaldehyde and urea, the pH of the reaction solution gradually decreases as the reaction progresses, and if the reaction is continued, it may reach an acidic range. However, in the present invention, the initial PH during the methylolation reaction is adjusted using amines and inorganic hydroxides, so it is only necessary to adjust the initial PH to the above range, and even at the end of the methylolation reaction, the initial PH is Adjustment alone will not result in an acidic range. The amines used in the present invention are not particularly limited in type, but are usually methylamine, ethylamine, n-propylamine, iso-
Alkylamines such as propylamine; alkanolamines such as ethanolamine, n-propanolamine, and iso-propanolamine are used. The above amines include primary amines, secondary amines,
It may be either a primary amine or a tertiary amine. Also,
As the inorganic hydroxide, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; hydroxides of alkaline earth metals such as calcium hydroxide and magnesium hydroxide are usually used. In the present invention, two types of alkaline substances, various amines and inorganic hydroxides, are used to adjust the initial pH during the methylolation reaction, but the combination is not particularly limited, and amines and inorganic hydroxides are used. Any combination of hydroxides may be used. In the present invention, as described later, it is necessary to perform the methylenation reaction on an endless rotating belt and to dry the material solidified by the methylenation reaction, so it is desirable that the methylenation reaction solution has a high concentration. Therefore, the concentration of the raw material formaldehyde aqueous solution is preferably as high as possible within the range in which the methylolation reaction can be carried out in the form of an aqueous solution, and the formaldehyde aqueous solution usually used has a high concentration of about 40 to 55% by weight. The raw material urea is also used for the same reason as above. It is preferable to use granular or powdered ones as they are. The methylol urea aqueous solution thus obtained is continuously supplied to a mixing tank, where mineral acid is added to adjust the pH to a range of 4.3 to 4.9, preferably 4.5 to 4.9.
The pH is adjusted to a range of 4.7 (the pH at this time will be referred to as the initial pH of the methylenation reaction) and immediately sent onto an endless rotating belt. Note that sulfuric acid, hydrochloric acid, or the like is used as the mineral acid at this time, and is added to the methylol urea aqueous solution as an aqueous solution having a concentration of 10 to 20% by weight. As mentioned above, the pH of the methylol urea aqueous solution supplied onto the endless rotating belt is adjusted to 4.3 to 4.9, so it solidifies on the endless rotating belt in an extremely short period of 5 to 15 minutes, forming a plate-shaped cake. Form. The endless rotating belt used here may be a normal belt conveyor or the like installed horizontally, and there is no need to particularly consider its structure. The obtained cake contains about 25 to 35% water by weight, so the water content is reduced to 3% by weight.
After drying until the following is achieved, it undergoes a coarse crushing and classification process to produce granular and powder products. There is no particular limitation on the type of dryer, and any dryer may be used as long as it can dry solid materials, but a continuous dryer is preferred since the methylenation reaction step is continuous. In the present invention, the methylenation reaction is carried out on an endless rotating belt, so the cake obtained by solidification is plate-shaped and contains water as described above. Therefore, drying this cake as it is is a complicated operation, and the drying efficiency is also poor. Therefore, in the present invention, by providing the continuous crushing mechanism described in "Liquid Solidification Apparatus" (Utility Application No. 161593, 1983) devised by the present inventors on an endless rotating belt,
The plate-shaped cake can be easily crushed into small pieces, and the coarsely crushed cake can be easily dried. [Example] The present invention will be explained in more detail with reference to Examples below. In addition, below, % represents weight %. Example 1 After adding 3.1 ml of a 50% triethanolamine aqueous solution as an amine (amines/F molar ratio = 0.0018) to 830 g of a formaldehyde aqueous solution with a concentration of 43%, hydroxide with a concentration of 25% as an inorganic hydroxide was added. The initial pH value during the methylolation reaction was adjusted to 8.12 by adding an aqueous sodium solution. After adding 1000 g of granular urea to this formaldehyde aqueous solution, it was heated to carry out a methylolation reaction at a temperature of 60° C. for 30 minutes. After the methylolation reaction is complete, this reaction solution has a concentration of 15%.
sulfuric acid aqueous solution is added to the initial stage of the methylenation reaction.
The methylenation reaction was carried out by adjusting the pH value to 4.51. The time required for the reaction solution to solidify was 7 minutes. Immediately after the reaction solution solidified, it was crushed and dried at 120°C. The analysis results of the dried product were as shown in Table 2. Example 2 Example 2 Except for using only a 25% potassium hydroxide aqueous solution as the inorganic hydroxide as the methylolation reaction PH regulator, the initial PH value was set to 8.02, and the initial PH value during the methylation reaction was set to 4.63. As shown in Table 1, the methylolation reaction, methylenation reaction, and drying were carried out under the same conditions as in Example 1. The time required for solidification in the methylenation reaction was 10 minutes. The analysis results of the obtained product were as shown in Table 2. Examples 3 to 5 860 g of a formaldehyde aqueous solution with a concentration of 43% and 1000 g of granular urea (Example 3), 790 g of a formaldehyde aqueous solution with a concentration of 47% and 1000 g of granular urea (Example 4), and a formaldehyde aqueous solution with a concentration of 55%
Methylolation reaction, methylenation reaction and drying were carried out in the same manner as in Example 1 under the conditions shown in Table 1 using 683g of urea and 100g of granular urea (Example 5). The analysis results of the obtained product were as shown in Table 2. Example 6 760 kg of formaldehyde aqueous solution with a concentration of 47% was charged into a reaction tank equipped with a stirrer, and 3.0 kg of a triethanolamine aqueous solution with a concentration of 50% as amines was added to this.
(amines/F molar ratio = 0.0017), a 25% aqueous sodium hydroxide solution was added as an inorganic hydroxide, and the initial pH value during the methylolation reaction was adjusted to 8.00. Add granular urea to this formaldehyde aqueous solution.
After adding 1000 kg, the reaction solution was heated and methylolated at a temperature of 60°C for 45 minutes. After the methylolation reaction was completed, the reaction solution was
The mixture was continuously fed to a small overflow type mixer at a rate of 500/h, and an aqueous sulfuric acid solution with a concentration of 15% was continuously added to the mixer to adjust the initial pH value during the methylenation reaction to 4.60. Later, an endless rotating belt (liquid solidification device, Utility Application 1986) equipped with a coarse crushing mechanism was devised and filed by the inventors of the present invention.
-161593), and was solidified and coarsely crushed by a methylenation reaction. After that, it is dried in a continuous band dryer for 110 minutes.
Dry at a temperature of °C. The analysis results of the obtained product were as shown in Table 2.

【table】

[Table] Comparative Example 1 A sodium hydroxide aqueous solution with a concentration of 25% was added to 775 g of an aqueous formaldehyde solution with a concentration of 43%, and the initial PH value during the methylolization reaction was adjusted using only inorganic hydroxide. was set to 10.3. Add 1000% of granular urea to this formaldehyde aqueous solution.
Then, methylolation reaction, methylenation reaction and drying were carried out under the same conditions as in Example 1.
However, the initial pH value during the methylenation reaction was set to 4.57. The time required for solidification during the methylenation reaction was 7 minutes. The analysis results of the obtained product were as shown in Table 4. Comparative Example 2 The initial PH value during the methylolation reaction was adjusted by
The methylolation reaction and methylenation reaction were carried out under the same conditions as in Comparative Example 1, except that the initial PH value was adjusted to 8.11 by using only a 50% triethanolamine aqueous solution, and the initial PH value during the methylenation reaction was set to 4.51. and drying. The analysis results of the obtained product were as shown in Table 4. Comparative Example 3 The methylolation reaction, methylenation reaction, and drying were carried out under exactly the same conditions as in Example 1, except that the initial PH value during the methylenation reaction was 4.17. The analysis results of the obtained product were as shown in Table 4. Comparative Example 4 The methylolation reaction, methylenation reaction, and drying were carried out under exactly the same conditions as in Comparative Example 3, except that the initial PH value during the methylenation reaction was 5.05. The analysis results of the obtained product were as shown in Table 4. Comparative Example 5 The methylolation reaction, methylenation reaction, and drying were carried out under exactly the same conditions as in Example 1, except that the initial PH value during the methylolation reaction was set to 7.03, and the initial PH value during the methylenation reaction was set to 4.63. Ta. The analysis results of the obtained product were as shown in Table 4. Comparative Example 6 Except that the initial PH value during the methylolation reaction was 10.36 and the initial PH value during the methylenation reaction was 4.59.
Methylolation reaction, methylenation reaction and drying were carried out under exactly the same conditions as in Example 4. The analysis results of the obtained product were as shown in Table 4. Comparative Example 7 122 g of a formaldehyde aqueous solution with a concentration of 37% and 135 g of granular urea were mixed and stirred, the pH was adjusted to 10.00 by adding a sodium hydroxide aqueous solution with a concentration of 1% in a water bath at a temperature of 50°C, and the mixture was heated in a granular form for 30 minutes. The methylolation reaction was carried out by dissolving urea. Thereafter, an aqueous citric acid solution having a concentration of 50% was added thereto to adjust the initial pH value during the methylenation reaction to 5.00, and the methylenation reaction was carried out at 50° C. for 1 hour, followed by drying. The analysis results of the obtained product were as shown in Table 4. Incidentally, drying was carried out at a temperature of 80° C. for 5 hours. Comparative Example 8 After adding and dissolving 15.4 g of hexamethylenetetramine crystals with a purity of 99% in 773 g of a formaldehyde aqueous solution with a concentration of 37%, 798 g of granular urea was added thereto (U/F molar ratio = 1.30, The methylene group of methylenetetramine was converted into formaldehyde (added) and dissolved, and a methylolation reaction was performed at a temperature of 50°C for 30 minutes. In addition, the PH after the reaction
was 8.70. A citric acid aqueous solution with a concentration of 40% was added to this reaction solution to adjust the initial pH value during the methylenation reaction to 4.00, and the methylenation reaction was carried out at a temperature of 50°C to solidify, followed by drying. . The analysis results of the obtained product were as shown in Table 4. Note that the solidification time for the methylenation reaction required 15 minutes. Comparative Example 9 The methylolation reaction, methylenation reaction and drying were carried out under exactly the same conditions as in Comparative Example 8, except that the initial PH value during the methylenation reaction was carried out using a formic acid aqueous solution with a concentration of 40%. The analysis results of the obtained product were as shown in Table 4. Comparative Example 10 830g of formaldehyde aqueous solution with a concentration of 43%,
After adding 0.143 ml of a 25% NaOH aqueous solution, a 50% triethanolamine aqueous solution was added to adjust the pH value during the methylolation reaction to 8.1.
Using this formaldehyde aqueous solution, Example 1
The methylolation reaction was carried out under the same conditions as above, followed by the methylenation reaction. Immediately after the reaction solution solidified, it was crushed and dried at 120°C. As shown in Table 4, the analytical values of the obtained product were low in AI value and high in HWIN.

【table】

〔Effect of the invention〕

As explained in detail above, the method for producing a slow-release nitrogen fertilizer of the present invention includes setting the molar ratio of urea and formaldehyde (U/F molar ratio) in the range of 1.0 to 1.5,
After carrying out the methylolation reaction by using an amine and an inorganic hydroxide together as an alkaline substance for adjusting the pH during the methylolation reaction and adjusting the initial pH during the methylolation reaction within a limited range, This method involves adding a mineral acid to adjust the initial pH during the methylenation reaction to a specific range, and then carrying out the methylenation reaction on an endless rotating belt. Therefore, as understood from the examples, the slow-release nitrogen fertilizer obtained by the method of the present invention has a TN of 35%.
It is a slow-release fertilizer, with an AI value of more than 60%, which far exceeds the 40% or more standard under the Fertilizer Control Act, WN/TN of less than 50%, and extremely low WHIN. It is extremely suitable for this purpose. On the other hand, the initial PH during the methylolation reaction was adjusted using conventionally known methods such as using only inorganic hydroxide (Comparative Example 1) and using only amines (Comparative Example 2). AI value is low at 40% or less.
The one whose initial PH value during the methylenation reaction is lower than the range defined by the present invention (Comparative Example 3) has an AI value of 40% or more, but is much lower than that of the Examples. On the other hand, those with high initial PH values (Comparative Example 4) are WN/
TN exceeds 50%. In the case where the initial PH value during the methylolation reaction is lower than the range defined by the present invention (Comparative Example 5), the AI value is much lower than that in the Examples. On the other hand, in the case where the initial PH value is high (Comparative Example 6), WN/TN exceeds 50%. In addition, the product with a high initial PH value during the methylolization reaction (Comparative Example 7) has a satisfactory AI value, but
WN/TN exceeds 50%. The initial PH during the methylolation reaction was adjusted only with amines, and the PH during the methylenation reaction was adjusted with an organic acid (Comparative Examples 8 and 9), which has a HWIN of 10% or more, which is a problem. .

Claims (1)

[Claims] 1 After adding an alkaline substance to an aqueous solution of urea and formaldehyde to carry out a methylolation reaction under alkaline conditions, an acidic substance is added to this and a methylolation reaction is carried out under acidic conditions to form a urea/formaldehyde condensate. When producing slow-release nitrogen fertilizer, the molar ratio of urea and formaldehyde (urea/formaldehyde) is set in the range of 1.0 to 1.5,
First, amines are added as an alkaline substance in the range of 0.0005 to 0.005 mol per mol of formaldehyde, and then an inorganic hydroxide is added to adjust the initial pH during the methylolation reaction to 7.5 to 9.5, and the methylolation is carried out. After carrying out the reaction, add mineral acid to this
A method for producing a slow-release nitrogen fertilizer, which comprises adjusting the pH to 4.3 to 4.9 and carrying out a methylenation reaction on an endless rotating belt.