JPH0725620B2 - Method for producing slow-release nitrogen fertilizer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a slow-release nitrogen fertilizer.

More specifically, a urea-formaldehyde condensation system nitrogen having an excellent slow-release property, which is obtained by subjecting a methylolurea solution improved so as to suppress an increase in methylene compound during the reaction and during storage after the reaction, to a dehydration condensation reaction. The present invention relates to a fertilizer manufacturing method.

[Prior art]

Conventionally, the urea-formaldehyde condensation nitrogen fertilizer is manufactured as follows.

The molar ratio of urea to formaldehyde is 1: 1 to 3, and an alkaline agent is added to the reaction system to adjust the pH at the start of the reaction to 7
The addition reaction is performed at 30 to 90 ° C for tens of minutes to several hours. The obtained monomethylol urea, a methylol urea solution mainly composed of dimethylol urea is then subjected to a condensation reaction by adding an acid to adjust the solution to be acidic, that is, a condensation product mainly composed of a methylene compound, that is, a urea-formaldehyde condensation system. Get nitrogen fertilizer.

However, in general, when the substrate concentration is low, such as low-concentration urea aqueous solution and formaldehyde aqueous solution,
Since the concentration of the resulting methylol urea solution is low, the dehydration condensation reaction of the methylol urea solution has a low reaction rate, and the condensation product obtained as a precipitate must be separated by filtration from a large amount of water, and the operation of circulating the mother liquor is required. , The water content of the obtained condensate is 70
Since it is about% by weight, a great amount of drying time and cost are required, which is not industrially preferable.

On the other hand, since the concentration of the methylolurea solution obtained by the reaction of solid urea or a highly concentrated urea solution and an aqueous formaldehyde solution is high, the dehydration condensation reaction product using the methylolurea solution as a raw material is a complicated operation such as filtration separation. Is unnecessary,
It is economical and preferable that the water content of about 40% by weight need only be volatilized by drying.

On the other hand, as described above, when the addition reaction is carried out in an alkaline condition, the condensation reaction hardly occurs and the methylol urea production rate increases, so that the dehydration condensation reaction of the obtained methylol urea solution is easily controlled, and It has the advantage that the urea-formaldehyde condensate obtained is highly effective as a fertilizer.

However, when a caustic soda, ammonia, trisodium phosphate or the like, which is usually used as an alkaline agent for pH adjustment in methylolation, is used, methylolurea solution may be changed with time during the methylolation reaction and after the reaction is completed (for example, during storage). A drop in pH was observed, and this tendency was particularly remarkable when solid urea or a highly concentrated urea solution and a formaldehyde aqueous solution were converted to methylol. Such a decrease in pH is understood to be due to the fact that active formaldehyde released from methylolurea is oxidized by oxygen in the air to become formic acid, and that the Kanituaro reaction occurs, but the pH decreases, When it becomes 7.0 or less, the methylolurea solution deteriorates and becomes cloudy due to the start of dehydration condensation reaction.
When the reaction proceeds, the methylene compound precipitates, resulting in an extremely unfavorable handling situation during the production of fertilizer.

As a method for preventing alteration of the methylolurea solution due to a drop in pH, a method of adding an alkaline agent as needed with a drop in pH or a method of adding a large amount of an alkaline agent in advance can be considered. However, the former method is complicated in operation. Further, in the latter method, it is unavoidable that the pH in the initial stage of the reaction becomes high, particularly when the pH is 11 or higher, the production rate of dimethylolurea is high, and the precipitation of dimethylolurea tends to precipitate, which is not preferable in handling, or The high pH requires a large amount of acid when acidifying the methylolurea solution in the dehydration condensation reaction, and makes pH adjustment more difficult.

The methylol urea solution which has been deteriorated due to pH drop is not only difficult to handle, but also the urea-formaldehyde condensation nitrogen fertilizer produced using this as a raw material is inferior in slow release effect, which is not preferable.

Generally, the fertility of urea-aldehyde condensation nitrogen fertilizers in chemical analysis is determined by the AOAC method (ASSOCIATION OF OFFICIAL AN
Total nitrogen by ALYTICAL CHEMISTS (hereinafter abbreviated as TN)
Cold water soluble nitrogen (hereinafter abbreviated as WSN), cold water insoluble nitrogen (hereinafter abbreviated as WIN), thermal buffer solution insoluble nitrogen (hereinafter HWI)
N is abbreviated) and evaluated by the AI value (ratio of cold water-insoluble and heat buffer-soluble nitrogen in cold water-insoluble nitrogen) calculated according to the following formula.

Of the urea-formaldehyde condensates, methylene urea having a low degree of condensation is usually dissolved in water or a heat buffer solution and effectively absorbed as a nitrogen source in plants. Among them, water-soluble methylene urea is an inorganic substance. The rate of oxidization is relatively fast, and its slowing effect is not sufficient. On the other hand, methylene urea having a high degree of condensation, which does not dissolve in a thermal buffer solution, is extremely slow to be mineralized after fertilization and difficult to be used by plants.

Therefore, as a slow-release nitrogen fertilizer with particularly high fertility, WS
Low N content, high WIN content, and low HWIN content, in other words, high WIN content, and
Those with high AI values are desired.

However, when a methylolurea solution obtained by the conventional method is subjected to a methyleneation reaction under acidic conditions to produce a urea-formaldehyde condensed nitrogen fertilizer, the content of HWIN generally increases as the content of WIN increases. Is increasing,
The AI value drops rapidly, so the AI value is high and WIN
It is very difficult to obtain a slow-acting urea-formaldehyde condensed nitrogen fertilizer with a high content of.

[Problems to be solved by the invention]

Some of the inventors of the present invention compared with the conventional method for producing a methylol urea solution in the reaction and during the storage after the reaction.
We proposed a method for producing a stable methylolurea solution in which the fluctuation of pH is small and the increase of methylene compound is suppressed (Japanese Patent Application No. 60-261880).

As a result of further studies, the present inventors have found that the methylolurea solution thus obtained can be dehydrated and condensed to produce a urea-formaldehyde nitrogen fertilizer having excellent slow-release properties.

[Means for solving problems]

The gist of the present invention is to produce a methylol urea solution by subjecting urea and formaldehyde to an addition reaction in the presence of water and a condensed phosphate, followed by dehydration condensation, and drying the resulting condensate. It exists in the method of manufacturing organic nitrogen fertilizer.

Hereinafter, the present invention will be described in more detail.

In the present invention, first, urea and formaldehyde are reacted in the presence of water and an alkali to produce a methylol urea solution. Formaldehyde is usually used as an aqueous formaldehyde solution, and any concentration can be used. Generally, a 35% by weight or more formaldehyde aqueous solution is used. Further, the formaldehyde aqueous solution may contain a small amount of methanol. As urea, a high-concentration urea solution using water and an alcohol such as methanol as a solvent can be used, but solid urea is preferable.

In order to obtain a methylol urea solution which is a raw material for producing the urea-formaldehyde condensation nitrogen fertilizer of the present invention, the amount of urea used relative to formaldehyde is about 1 to 2 mole times,
It is preferable to use 1.1 to 1.6 mole times. The amount of water present in the reaction system in the present invention is not particularly limited and may be any amount greater than or equal to the amount introduced from the raw material formaldehyde aqueous solution. A stable methylol urea solution suitable for the production of effective nitrogen fertilizer can be obtained. In this case, the urea: formaldehyde: water (molar ratio) is about 1-2: 1: 1.3-4.5, preferably 1.1-1.6: 1: 1.5-3.

In the present invention, such an addition reaction between urea and an aqueous formaldehyde solution is carried out in the presence of condensed phosphate as an alkali.

As the condensed phosphate, alkali metal salts of phosphoric acid having various degrees of condensation can be used, but preferably, alkali metal salts such as pyrophosphoric acid and tripolyphosphoric acid are used. Particularly, sodium salts and potassium salts of tripolyphosphoric acid and pyrophosphoric acid are preferable. The condensed phosphate may be used in a crystalline form as it is, or may be dissolved in a solvent such as water in advance before use. The amount of the condensed phosphate used is usually such that the pH in the reaction system can be controlled to 7 to 10, preferably pH 7.5 to 10, and more preferably pH 8 to 10. Generally, it is appropriately selected from the range of 0.5% by weight or more and 9% by weight or less with respect to formaldehyde. The method of adding the condensed phosphate is not particularly limited, and it may be a method of adding it alone, a method of mixing it with urea, or the like. A method in which urea is mixed and dissolved in this is generally performed. The reaction temperature is any temperature from room temperature to 100 ° C, but usually room temperature to about 80 ° C, preferably 40 ° C.
To about 80 ° C., particularly preferably 40 to 60 ° C., and the reaction time is usually 15 minutes or longer, preferably about 30 to 60 minutes.

Although the unreacted urea and aldehyde usually remain in the methylol urea solution thus obtained, it can be used as a raw material for the dehydration condensation reaction without any special treatment. At that time, if necessary, urea and / or formaldehyde may be appropriately added to the methylol urea solution to be used as a raw material for the dehydration condensation reaction. The ratio of urea to formaldehyde in the methylolurea solution, which is the starting material for the reaction, is 1 to 2 times, and preferably 1.1 to 1.6 times. Also in that case, urea: formaldehyde: water (molar ratio) is 1 to 2: 1: 1.3 to 4.5, preferably 1.1 to 1.6:
It is 1: 1.5-3.

The dehydration condensation reaction is carried out by lowering the pH of the methylol urea solution to 3 to 7, preferably 4 to 7. As the pH adjuster in the dehydration condensation reaction, various acidic agents can be used, but usually, inorganic acids such as sulfuric acid and phosphoric acid, tartaric acid,
Organic acids such as citric acid may be mentioned. Among these, it is particularly preferable to use phosphoric acid or citric acid because the pH fluctuation during the dehydration condensation reaction is suppressed.

The amount of the pH adjuster used is not particularly limited as long as it can adjust the pH of the methylol urea solution to the above range.

The method of adding the pH adjuster is not particularly limited, but a method of adding a solution-like acidic substance to the methylol urea solution under stirring is generally performed.

The temperature and time of the dehydration condensation reaction, and the drying temperature and time of the obtained condensate are appropriately selected depending on the degree of condensation of the desired condensate, but the urea-formaldehyde condensate having a high degree of condensation is It is not soluble in a heat buffer solution and is not preferable as a slow-release fertilizer.

Therefore, the conditions for obtaining a urea-formaldehyde condensation-type nitrogen fertilizer with excellent slow release are reaction temperature, room temperature to
The temperature is about 120 ° C., preferably about 40 to 110 ° C., and the reaction time is 5 minutes or more, preferably about 10 to 2 hours. Also,
The drying temperature is usually about 60 to 300 ° C, preferably about 80 to 250 ° C, and the drying time is appropriately selected depending on the degree of condensation of the target urea-formaldehyde condensation nitrogen fertilizer and the water content, but Then, drying is performed for at least the time when the water content is 8% by weight or less.

Thus, the slow-release nitrogen fertilizer aimed at by the present application can be obtained.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1 When 122 g of 37% formalin heated in a 50 ° C water bath was added and dissolved with 2.2 g of sodium tripolyphosphate as an alkaline agent, the pH of the solution was 8.3. 135 g of crystalline urea in the solution
When the methylolation reaction was carried out for 60 minutes by adding and dissolving (the molar ratio of urea to formaldehyde was 1.5), the pH was 9.2. 4 in this methylol urea solution
The pH was adjusted to 5.0 by adding an aqueous solution of morpholinic acid, and the dehydration condensation reaction
The product was obtained by performing 0 minute and then drying at 80 ° C. for 4 hours.

Table 1 shows the results of analyzing the nitrogen content of the obtained product by the AOAC method.

Comparative Example 1 In Example 1, when 0.28 g of 10 wt% sodium hydroxide was used as the alkaline agent instead of sodium tripolyphosphate, the pH of the solution was 8.8. When the methylolation reaction was carried out for 60 minutes in the same manner as in Example 1, the pH was 6.6. To this methylol urea solution, add a phosphoric acid solution and adjust the pH.
Was set to 0.5, dehydration condensation reaction was carried out for 60 minutes, and then dried at 80 ° C. for 5 hours to obtain a product.

Table 1 shows the results of the same analysis as in Example 1.

Example 2 When 140 g of 37% formalin heated in a 50 ° C water bath was added and dissolved with 2.5 g of sodium tripolyphosphate as an alkaline agent, the pH of the solution became 8.4. To this solution, 135 g of crystalline urea (corresponding to a molar ratio of urea to formaldehyde of 1.3) was added and dissolved, and the methylolation reaction was carried out for 60 minutes.
Is 9.2. A 4 mol phosphoric acid aqueous solution was added to this methylol urea solution to adjust the pH to 5.0, and a dehydration condensation reaction was carried out for 60 minutes, followed by drying at 80 ° C. for 4 hours to obtain a product.

Table 1 shows the results of the same analysis as in Example 1.

Comparative Example 2 When 0.31 g of 10 wt% caustic soda was used as the alkaline agent in place of sodium tripolyphosphate in Example 2, the pH of the solution was 8.6. Thereafter, when a methylolation reaction was carried out for 60 minutes in the same manner as in Example 2, the pH was 6.4.
Tonatsuta. A 4 mol phosphoric acid aqueous solution was added to this methylol urea solution to adjust the pH to 4.0, dehydration condensation reaction was carried out for 60 minutes, and then dried at 80 ° C. for 4 hours to obtain a product.

Table 1 shows the results of the same analysis as in Example 1.

[Effect of the invention] As is clear from the results of Example 1 and Comparative Example 1, when the molar ratio of urea to formaldehyde is the same, the pH at the start of the dehydration condensation reaction is the same, and when a known alkali is used. In comparison, the nitrogen fertilizer of the present invention produced using methylolurea obtained by using condensed phosphate as an alkali is a nitrogen fertilizer having a large amount of WIN, a high AI value, and an excellent slow release effect.

Also, as is clear from the results of Example 2 and Comparative Example 2, when the molar ratio of urea to formaldehyde was the same and the pH at the start of the dehydration condensation reaction was changed so that the WIN of the product fertilizer was almost the same, a known alkali Compared with the case of using, the nitrogen fertilizer of the present invention produced from a methylol urea solution obtained by using a condensed phosphate as an alkali is AI
It is a nitrogen fertilizer with high value and excellent slow release.

According to the method for producing a slow-release nitrogen fertilizer according to the present invention, a methylolurea solution obtained by using a condensed phosphate as an alkali is subjected to a dehydration condensation reaction, thereby containing cold water-insoluble nitrogen in a urea-formaldehyde condensate. It is possible not only to increase the amount, but also to raise the AI value. Specifically, the urea-formaldehyde condensation nitrogen fertilizer produced according to the present invention has a ratio of urea to formaldehyde of 1 to 2 mole times, preferably 1.1 to 1.6 mole times.
C. Method TN 35-40%, WIN 12-28%, preferably 1
6-28%, WIN / TN 30-80%, preferably 40-80%,
Moreover, it is a nitrogen fertilizer having an AI value of 40 to 80, preferably 50 to 80, which is excellent in slow release.

Claims (4)

[Claims] 1. A mildly characterized in that urea and formaldehyde are subjected to an addition reaction in the presence of water and condensed phosphate to produce a methylol urea solution, which is then subjected to a dehydration condensation reaction and the resulting condensate is dried. Method for producing effective nitrogen fertilizer. 2. The method for producing a slow-acting nitrogen fertilizer according to claim 1, wherein the condensed phosphate is an alkali metal salt of pyrophosphoric acid and / or tripolyphosphoric acid. 3. The method for producing a slow-acting nitrogen fertilizer according to claim 1, wherein the dehydration condensation reaction is carried out in the presence of phosphoric acid and / or citric acid. 4. Urea: formaldehyde: water = 1 to 2: 1: 1.
The method for producing a slow-release nitrogenous fertilizer according to claim 1, characterized in that it is 3 to 4.5 (molar ratio).