DE887049C - Process for the production of nitrogenous fertilizers - Google Patents

Description

Process for the production of nitrogenous fertilizers The Invention relates to the production of nitrogenous fertilizers, in which the nitrogen in the soil is slowly available for plant nutrition will.

The nitrogen content of nitrogenous fertilizers is made available for plant nutrition through the activity of organisms in the soil. In many nitrogenous fertilizers, the nitrogen content becomes effective so quickly that soon after such fertilizer has been applied, more effective nitrogen is available in the soil than can currently be absorbed by the plants. For example, go 0 /, the nitrogen content of ammonium sulfate will be available in 2 or 3 weeks. It is therefore in many cases desirable to use a nitrogenous fertilizer in which the nitrogen becomes slowly available. According to an earlier proposal by the inventors, nitrogen-containing fertilizers were produced in which the nitrogen content becomes slowly available by reacting urea with formaldehyde in an aqueous solution in such a way that a thickened mixture is obtained which, on further treatment, becomes a solid Fertilizer yields.

According to the invention a method for the production of nitrogen-containing Suggested fertilizers in which the nitrogen content is slowly available and which method is characterized in that a substantially anhydrous Mixture of urea and paraformaldehyde heated to temperatures of 7o to i2o ' is obtained, a slurry is obtained, which hardens, crushed, dried and or or is granulated in order to obtain a product of the desired grain size, Although the heating is carried out up to a temperature within the above-mentioned range it has been found advantageous at a temperature of about ioo ' to work.

The mixture of urea and paraformaldehyde can be in any suitable one Reaction vessel are heated, this preferably being provided with devices by which the mixture is stirred or otherwise agitated. It was for cheap. found using a paddle mixer with a jacket, by the hot water or steam is directed. The length of time during which the mixture must be heated depends on the temperature actually used and only in to a small extent on the amounts of urea and paraformaldehyde used.

In the following table i of the results obtained, the second and third columns explain the effect of the temperature and the only slight effect of the amounts of urea and paraformaldehyde, expressed as the molar ratio of CO (NH,): H - CHO at the start of the reaction. The fourth column of the table shows the time that is still required for heating so that the pulp settles as a solid mass. Table i He- further Molar ratio to Urea warra- slurry production heating time, tempe- rature a fixed time required to obtain mass Formaldehyde Degrees minutes minutes I 8o 15 42 I go 13 20 I ioo 6 15 2 70 28 75 2 8o 16 40 2 go io 20 2 iio 4 9 2 120 3 9 Although the slurry can be solidified by prolonged heating as mentioned above, it is preferred to remove it from the heated reaction vessel while it is still sufficiently liquid and e.g. B. to cool in a suitable container or, as will be described, to further treat it in order to obtain a solid product.

The solid product can be broken or otherwise crushed and dried at a temperature not exceeding 13o '. The dried one Product can, if necessary, be further crushed to get particles of of desired size, or it can be powdered and then made into granules of desired size, e.g. B. by granulation with the addition of moisture, and, if desired, an inert diluent, e.g. B, anhydrite, plaster of paris, calcined Plaster of paris, chalk or starch.

If it is desired to use plaster of paris as a diluent, it can be added to the slurry while it is still in the heating vessel. However, the resulting pulp is not so easy to pour out of the heating vessel. The crushed and dried product or the product obtained by grinding can, if desired, be mixed with other fertilizers, e.g. B. with ground ammonium sulfate, mixed and granulated, ' In a preferred treatment of the pulp in order to obtain a solid product, the pulp is poured from the heating vessel onto a cooled or heated metal roller or plate in order to form a thin layer there, which are allowed to solidify so that they can then be broken up into flakes, which are dried at temperatures not exceeding 13o '. The dried flakes can be used as is, or they can be ground into particles of even smaller size and then granulated with or without the addition of other materials.

It has further been found that the hardening of the pulp after it has been poured out of the heating vessel can be accelerated considerably by adding a small amount of mineral acid, e.g. B. of nitric acid in amounts of approximately 0.02 to 0.05 percent by weight of the urea and paraformaldehyde used. Such an addition of acid takes place shortly before the slurry is poured out of the heating vessel.

The urea used in the method according to the invention should be preferred have a high degree of purity and can be in the usually crystalline, essentially dry form can be used, The proportions urea and paraformaldehyde can can be changed within a wide range. -Good results will be with. one Molar ratio of urea to formaldehyde of 1: 9, achieved.

Experiments have shown that fertilizers which have been produced by the process according to the present invention have a rate of saltpetre formation at which their nitrogen content becomes available in the vegetable diet over the course of several weeks. The rate of saltpetre formation depends on the molecular structure of the product, which in turn is influenced by the molecular ratio CO (NH,) ,: H - CHO. the lower this ratio, the slower the rate of saltpetre formation of the product.

Samples of fertilizers prepared according to the invention from different amounts of urea and paraformaldehyde with a grain size between 9.10 ß and 420µm were used for investigations after fertilization of the soil, and the results obtained are shown in Table 2 below . Table 2 Molar ratio percentage of the contained, to the nitrate nitrogen used by urea formation to formaldehyde 4 weeks 1 8 weeks 1 16 weeks I, 0 1 12.0 13.0 0 61, o 1.4 27: 9-43.0 1.8 43.0 63.0 8oo The invention is illustrated in the following examples: EXAMPLES 1. 252 g of dry crystalline urea were mixed with 10 g of dry paraformaldehyde in a jacketed pan mixer which was heated with steam to keep the temperature at about 100 '.

After the material was mixed for 2 minutes, it became damp. A wet slurry had formed after 6 minutes and a very thick slurry after ii minutes. When heated for a further 4 minutes, the material settles firmly.

A sample of the solid material, after being dried for 3 hours at 130 ', had a free urea content of 6.9 percent by weight.

A similar mass, in which the mixture initially contained about 1 percent by weight of water, showed similar results. After being dried at 130 for 24 hours, the product has a free urea content of 5.7 percent by weight.

2. 180 g of dry crystalline urea were mixed with 100 g of dry paraformaldehyde in a jacketed mixer according to Example 1, while the temperature was kept at about 100%. The reaction was over after 15 minutes, whereupon the product was comminuted and dried at 130 'for 6 hours.

3. 336 g of crystalline urea were mixed with 120 g of parafonnaldehyde in a paddle mixer which was steam-heated to 100%. After about 4 minutes a slurry had formed which was poured onto a metal plate. This was kept at a temperature of about 12o 'by blowing hot air over and around it. About 4 minutes after the pulp was poured out, it was hard enough to flake on the plate. After drying the flakes obtained in this way at 130 ° for 3 hours, a free urea content of 10.40% was found.

4. 336 g of dry urea were mixed in a paddle mixer according to Example 3 with 12o g of dry paraformaldehyde. When a slurry had formed, 40 cc of 0.350% nitric acid solution was added and mixing continued for about one minute. The slurry was then poured onto a chilled plate to form a 2 to 4 mm thick layer. This layer hardened very quickly and was hard to i '/, minutes enough to be crushed on the plate into flakes. The product was dried at 10 5 '. Thereafter, a free urea content of 11 % was found.

5. 168 g of urea were mixed with 60 g of paraformaldehyde in the manner indicated in the preceding examples in a steam-heated paddle mixer. A corresponding amount, that is 228 g, of plaster of paris was added to the paste formed after 5 minutes with constant stirring. The thick slurry so produced was removed from the mixer and spread on a metal plate, where it hardened to a nonplastic solid within 1 minute.

Claims (2)

PATENT CLAIMS: i. Process for the production of nitrogenous fertilizers with a nitrogen content that is slowly available for the plants, characterized in that . that essentially anhydrous mixtures of urea and paraformaldehyde are heated to temperatures of 7o to 12o ', in particular about 100', to form a paste which, after hardening, is comminuted, dried and / or granulated. 2. The method according to claim i, characterized in that the slurry is allowed to harden in the reaction vessel with prolonged heating. 3. The method according to claim i, characterized in that the slurry, if desired after adding mineral acid in an amount of about 0.02 to 0.05 percent by weight, poured from the heating vessel onto a cooled or heated metallic roller or plate, where it is hardens and is crushed into flakes. 4. Process according to Claims i to 3, characterized in that the hardened and comminuted product is dried at a temperature not exceeding 1300. 5. The method according to claims i to 4, characterized in that the dried product, preferably after comminution to a powder, is shaped into granules by granulation with the addition of moisture. 6. The method according to claims i to 5, characterized in that the dried product, preferably after being crushed to a powder, is granulated together with at least one other fertilizer.