Improved storage stability of urea particles comprising urea-formaldehyde condensation products and an inhibitor

Abstract

The invention relates to a method for producing fertilizer particles which as well as urea additionally contain urea-formaldehyde condensation products and at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, even more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT). The invention also relates to a plant for carrying out the method according to the invention, to the fertilizer particles produced according to the invention, and to the use thereof as fertilizers. The fertilizer particles according to the invention have a reduced content of urea-formaldehyde condensation products having reactive functional groups, which improves the storage stability, in particular with regard to the stability of the urease inhibitor and / or nitrification inhibitor.

Description

Improved storage stability of urea particles comprising urea-formaldehyde condensation products and an inhibitor

[0001] The priorities will be determined. - German patent application No. 10 2024 210 784.0 dated November 8, 2024; - the Luxembourg patent application No. LU103450 of 8 November 2024; - German patent application No. 10 2024 210 783.2 dated November 8, 2024; - the Luxembourg patent application No. LU 103449 of 8 November 2024; - German patent application No. 10 2025 105 782.6 dated February 17, 2025; - Belgian patent application No. BE 2025 / 5092 of 17 February 2025; - German patent application No. 10 2025 105 784.2 dated February 17, 2025; - Belgian patent application No. BE 2025 / 5093 of 17 February 2025; - Belgian patent application No. BE 2025 / 5108 of 24 February 2025; - German patent application No. 10 2025 106 835.6 dated February 24, 2025; and - claimed in German patent application No. 10 2025 137,495.3 dated September 17, 2025.

[0002] The invention relates to a process for producing fertilizer particles which, in addition to urea, contain urea-formaldehyde condensation products and at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT). The invention also relates to an apparatus for carrying out the process according to the invention, the fertilizer particles produced according to the invention, and their use as fertilizer. The fertilizer particles according to the invention have a reduced content of urea-formaldehyde reaction products with reactive functional groups, which improves storage stability, particularly with regard to the stability of the urease inhibitor and / or nitrification inhibitor.

[0003] In conventional methods for producing ham particles, such as granulation or prilling, formaldehyde-based additives, such as ham-formaldehyde solutions, are typically added to a ham melt solution shortly before solidification. Until now, in most cases, these additives were added approximately 8 to 40 seconds before solidification. These additives are needed to improve granulation or prilling and thus the quality of the ham particles.

[0004] Due to new regulations requiring higher nitrogen waste management efficiency and a reduction in ammonia and greenhouse gas emissions, the demand for stabilized urea is increasing and will be much higher in the future.

[0005] To produce stabilized urea, certain active ingredients must be added to the urea, particularly urease inhibitors, usually in the form of an inhibitor formulation. The most commonly used class of urease inhibitors are thiophosphoric triamides. Examples of commercially available thiophosphoric triamides are N-(n-butyl)thiophosphoric triamide (NBPT) and N-(n-propyl)thiophosphoric triamide (NPPT). Nitrification inhibitors are also frequently used. Generally, either urease inhibitors or nitrification inhibitors are used.

[0006] Nowadays, ham particles are mainly treated with inhibitor formulations by wholesalers, in small quantities as a separate treatment process in mixing stations / systems. The ham particles are coated with the inhibitor formulations. After application, inhibitors such as thiophosphoric triamides are relatively stable at a storage temperature of 20°C and show degradation rates of only 10-50% even after one year of storage.

[0007] For the nitrogen utilization efficiency of stabilized urea, a minimum concentration of the inhibitor in the urea particles must be ensured at the time of application in the field. In many applications, the potential to reduce nitrogen loss must be demonstrated / verified.

[0008] For the treatment of large quantities of urea with inhibitors, it is more economical to perform the treatment upstream in the value chain, specifically during granulation or prilling. For example, the urea can be treated with an inhibitor formulation as a melt / solution before entering the granulator / prilling tower, during the granulation process, or even during cooling.

[0009] However, if the ammonium particles are treated directly with the inhibitor during granulation or prilling, as described above, an unexpectedly strong degradation of the inhibitor itself is frequently observed even at storage temperatures as low as 20°C, especially of thiophosphoric triamides.

[0010] This observed rapid degradation of the inhibitor means that the required concentration of the inhibitor in the treated hemp product at the time of application in the field is neither economically nor practically achievable with this method. This would require the stabilized hemp product to be applied immediately after its production, i.e., without intermediate storage, which is logistically impossible. Alternatively, the inhibitor would have to be added in a very high concentration, which is neither economically nor ecologically justifiable.

[0011] WO 2015 027244 Al relates to a urea-nitrogen stabilizer composition and to processes, systems, and equipment for its production. The composition is incorporated into molten urea to obtain a composition containing less biuret, N-methyl-2-pyrrolidone (NMP), nitrogen stabilizer, and / or impurities, and yielding an effective solid fertilizer. These compositions are useful for odor control.

[0012] WO 2016 137815 Al relates to a urea granulate with an additive designated as a nitrogen stabilizer and a carrier system that is essentially homogeneously distributed throughout the entire granulate volume. Various methods for producing the urea granulate are described, including pricking, fluidized bed, and drum granulation. The nitrogen stabilizer may contain a urease inhibitor such as NBPT, with the NBPT purity ranging from 90% to 99%. The nitrogen stabilizer may also contain a nitrification inhibitor such as dicyandiamide (DCD).

[0013] WO 2017 019528 Al relates to a reaction product comprising an adduct formed from urea, formaldehyde and a urease inhibitor, which can be supplied in various forms.

[0014] WO 2018 134765 Al concerns a fertilizer composition comprising urea, one or more adducts of a urease inhibitor with urea, formaldehyde or both urea and formaldehyde, a particulate acid fertilizer and a basic component.

[0015] WO 2019 197183 Al relates to a process for the production of a fertilizer composition comprising at least one urea-containing fertilizer and at least one thiophosphoric triamide.

[0016] WO 2022 136360 A2 relates to a process for the production of a homogeneous, solid, particulate, urea-based composition comprising urea and one or more additives in a urea production plant.

[0017] WO 2023 057902 Al relates to an agricultural composition comprising paraformaldehyde, a nitrification inhibitor, urea, an ammonia source or a combination thereof and one or more reaction products prepared from paraformaldehyde, a nitrification inhibitor, urea, an ammonia source and optionally a solvent, wherein the one or more reaction products are present in an amount of at least 20% by weight of the total weight of the agricultural composition.

[0018] The known inhibitor particles are not satisfactory in every respect and there is a need for improvements, especially with regard to the inhibitor's long-term stability.

[0019] It is an object of the invention to provide hygroscopic particles containing formaldehyde-based additives as well as urease inhibitors, in particular thiophosphoric triamides, and / or nitrification inhibitors, and which are characterized by improved effervescence stability, particularly with regard to the inhibitor content. The hygroscopic particles should be easy and cost-effective to produce.

[0020] This problem is solved by the subject matter of the patent claims.

[0021] It was surprisingly found that the degradation of the inhibitor, especially thiophosphoric triamides, in urea-containing fertilizer particles can be significantly reduced, i.e., storage stability can be significantly improved, when a formaldehyde-based additive is added. The mixture obtained can react with urea in the form of a melt and / or solution for at least 50 seconds, preferably at a temperature of 105 °C to 150 °C, more preferably 115 °C to 140 °C, before being solidified together with further urea for the purpose of granulation or pricking. Intensive mixing of the formaldehyde-based additive with the urea also has a beneficial effect on storage stability.

[0022] Furthermore, it was surprisingly found that by storing the urea-containing fertilizer particles, possibly prior to treatment with the inhibitor, for at least 24 hours at a temperature of preferably at least 80°C, the degradation of the inhibitor is significantly reduced, i.e., the storage stability is significantly improved.

[0023] Without wishing to be bound to a scientific theory, there are indications that the degradation of the inhibitor, particularly thiophosphoric triamide, is caused by the reaction of the inhibitor with reactive functional groups of certain ham-formaldehyde reaction products, e.g., with methylol hams. The reactive functional groups, especially methylol groups, can be formed in the reaction of urea and formaldehyde, whereby the reaction forming the reactive functional groups is an addition, not a condensation. OO HjN L NH2* HLH Monomethylol urea Dimethylol urea Trimethylol urea

[0024] The compounds described above, or their mixtures and solutions, are commonly used as additives in urea granulation and pricking, e.g. as commercially available “Urea Formaldehyde Precondensate” (UFC or UF-85).

[0025] Surprisingly, the undesired reaction of the inhibitor, particularly thiophosphoric triamide, with the reactive functional groups of the ham-formaldehyde reaction products appears to occur predominantly in the solid fertilizer particles and hardly at all, if at all, in the melt. Thus, the degradation rate of the inhibitor in the fertilizer particles is apparently mainly determined by the concentration of ham-formaldehyde reaction products. The concentration of reactive functional groups and / or free formaldehyde determines the reaction products / addition products. The undesired reaction products / addition products with reactive functional groups are, in particular, methylol hams and low-molecular-weight methylol ham-based compounds, with the exception of polymeric or oligomeric methylol hams.

[0026] Measures to reduce the concentration of these urea-formaldehyde reaction products with reactive functional groups thus improve the stability of the inhibitor. These measures include processes that, prior to the solidification of the urea melt, promote the reaction of urea with formaldehyde to form urea-formaldehyde condensation products. Any reactive functional groups formed in the intermediate reaction may react further, so that ultimately no (or very few) reactive functional groups remain. The urea-formaldehyde condensation products thus formed then do not react with the inhibitors, or only to a small extent or at a slow rate, due to the lack of reactive functional groups.

[0027] According to the invention, a distinction is therefore made between ham-formaldehyde condensation products on the one hand and ham-formaldehyde reaction products with reactive functional groups on the other.

[0028] According to the invention, urea-formaldehyde condensation products are formed by the chemical reaction of at least one molecule of urea and at least one molecule of formaldehyde or formaldehyde equivalent with the elimination of water, wherein at least one newly formed covalent bond or functional group is not a methylol group (-NH-CH2-OH), preferably not a reactive functional group. Examples are methyleneham, methylenediham, and N-methylol-methylenediham. Preferably, several covalent bonds or functional groups newly formed during the chemical reaction are not methylol groups, preferably not reactive functional groups. More preferably, the urea-formaldehyde condensation products contain no methylol group at all, and even more preferably, no reactive functional groups at all.The formation of these urea-formaldehyde condensation products can proceed via intermediates, which in turn may contain reactive functional groups such as methylol groups, but preferably only temporarily. Urea-formaldehyde condensation products can themselves be intermediates, e.g., in the formation of higher urea-formaldehyde condensation products such as dimers, trimers, oligomers, and / or polymers. Urea-formaldehyde condensation products can be formed from urea, formaldehyde, and additionally from other molecules, in particular from those derived from urea or formaldehyde, e.g., biuret or monomethylol-urea compounds. Compounds in which an inhibitor, e.g., a thiophosphoric triamide such as NBPT, is covalently bound to a urea-formaldehyde condensation product, are preferably not urea-formaldehyde condensation products within the meaning of the invention.Hamse-formaldehyde condensation products preferably contain no covalent bond to inhibitors.

[0029] According to the invention, urea-formaldehyde reaction products with reactive functional groups are also formed by chemical reaction of at least one molecule of urea and at least one molecule of formaldehyde with elimination of water, but additionally contain reactive functional groups to a significant extent, preferably methylol groups.

[0030] For the purposes of the invention, reactive functional groups are chemical groups that react with the inhibitors at temperatures below the decomposition temperature of the inhibitors, in particular with thiophosphoric triamides, preferably at a maximum of 110°C, more preferably at a maximum of 100°C, even more preferably at a maximum of 80°C, and most preferably at a maximum of 60°C, most preferably in the solid state, particularly at typical storage temperatures such as room temperature to 50°C. Reactive functional groups are, in particular, methylol groups (-NH-CH2-OH).

[0031] Methylol groups and their compounds are analytically detectable and can be quantified. Suitable methods include HPLC with a suitable detector (e.g., HPLC-MS), the peroxide method for determining formaldehyde activity in ham-formaldehyde solutions, and other methods known to a competent person.

[0032] The required reaction progress is preferably achieved according to the invention by: - Feeding the formaldehyde-based additive upstream of the granulation or pricking unit, e.g. into a recirculation stream or into the evaporation zone; - Feeding the formaldehyde-based additive into a partial stream from the supply of freshly synthesized urea and recombining this partial stream with the supply of freshly synthesized urea after a suitable residence time (reaction time); - Reaction of the formaldehyde-based additive with a suitable amount of urea under suitable conditions in a separate reactor before feeding it into the supply of freshly synthesized urea; this can also be done in advance if necessary, which is why a commercial product can also be used; - Increase in temperature; and / or - Addition of a suitable catalyst.

[0033] Alternatively, the reaction between urea and formaldehyde can be carried out in a separate process before application in the granulation or prilling plant.

[0034] Instead of formaldehyde-ham solutions, non-reactive reaction products of urea and formaldehyde, such as methylenediham, can also be used. This has no discernible impact on other product quality criteria.

[0035] Alternatively, a comparatively small amount of formaldehyde-based additive can be used. However, this may negatively affect the other quality criteria of the product.

[0036] A first aspect of the invention relates to a process for producing fertilizer particles containing urea, urea-formaldehyde condensation products and at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), wherein the process comprises the steps of: (a) Adding a formaldehyde-based additive to a first starting material composition containing urea and in the form of a melt and / or solution, producing a precursor containing urea-formaldehyde condensation products and in the form of a melt and / or solution; (b) optional, combining the precursor with a composition containing at least one urease inhibitor and / or at least one nitrification inhibitor; (c) Mixing the precursor with a second reactant composition containing urea and in the form of a melt and / or solution, producing an intermediate containing urea and urea-formaldehyde condensation products and in the form of a melt and / or solution; (d) optional, combining the intermediate with a composition containing at least one urease inhibitor and / or at least one nitrification inhibitor; (e) Solidification of the intermediate product, producing particles; (f) optional, intermediate storage of the particles at elevated temperature; and (g) optional, combining the particles with a composition containing at least one urease inhibitor and / or at least one nitrification inhibitor; wherein the process includes at least one of the optional steps (b), (d) and (g); and wherein the solidification of the intermediate in step (e) takes place no earlier than 50 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0037] In step (a) of the process according to the invention, a precursor is produced, and in step (c) of the process according to the invention, an intermediate is produced. The precursor is produced in step (a) from urea and a formaldehyde-based additive and contains urea-formaldehyde condensation products. The intermediate is formed in step (c) from the precursor and urea.

[0038] According to the invention, the undesired degradation of the urease inhibitor is preferably prevented or at least reduced by one or more of the following measures: Contact of the first reactant composition with the formaldehyde-based additive for at least 50 seconds at a temperature in the range of 105°C to 150°C, preferably 115°C to 140°C; - Storing the particles for at least one day at elevated temperature, preferably above 80°C, before mixing, i.e. contacting, with the composition which contains at least one urease inhibitor and / or at least one nitrification inhibitor; - Production of particles which have at least 30 mol% fewer reactive functional groups (especially -NH-CH2-OH groups, hemiaminals) in ham-formaldehyde condensation products, compared to particles which are otherwise produced under identical conditions, but in which the solidification of the intermediate in step (e) takes place no later than 40 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0039] The segmented process flow with a first reactant composition and a second reactant composition has the advantage that, on the one hand, a sufficient reaction time can be ensured, allowing reactive functional groups to react (first reactant composition), and, on the other hand, not the entire amount of urea is exposed to the necessary reaction conditions, because otherwise other undesirable byproducts, in particular biuret, would be formed to a greater extent (second reactant composition). According to the invention, therefore, a segmented process flow with a first reactant composition and a second reactant composition is carried out, whereby further segmentation would also be possible in principle.

[0040] The residence time of the formaldehyde-based additive in the hygrotherm is preferably at least 60 seconds, more preferably at least 90 seconds, more preferably at least 120 seconds, even more preferably at least 150 seconds, most preferably at least 180 seconds, and in particular at least 210 seconds.

[0041] The residence time of the formaldehyde-based additive in the hygrotherm is preferably in the range of 60 to 600 seconds, more preferably 60 to 540 seconds, more preferably 60 to 480 seconds, even more preferably 60 to 420 seconds, most preferably 60 to 360 seconds, and particularly 60 to 300 seconds.

[0042] The process according to the invention can be carried out continuously, semi-continuously or in batch operation.

[0043] In continuous process operation, "before" means "upstream" in the direction of flow of a continuously moving material stream, and "after" means "downstream" in the direction of flow of a continuously moving material stream.

[0044] In continuous process operation, the time specifications refer to a section of a continuously moving material stream, which successively performs the steps of the process according to the invention. The flow of a continuously moving material stream is altered by the movement of the material. Suitable methods for determining the movement of such a section of this stream are familiar to qualified personnel. For example, tracers such as dyes can be used in routine tests.

[0045] Steps (a), (c), and (e) of the inventive procedure are mandatory.

[0046] Steps (b), (d), (f) (g) of the inventive method are in themselves independent of each other optional, however the method necessarily includes at least one of the optional steps (b), (d) and (g), preferably only one of the optional steps (b), (d) and (g).

[0047] Preferably, the method according to the invention comprises one of the two steps (b) and (d), in which case step (f) is less preferred.

[0048] In preferred embodiments, the method according to the invention comprises steps (a), (b), (c), and (e).

[0049] In other preferred embodiments, the method according to the invention comprises steps (a), (c), (d), and (e).

[0050] In further preferred embodiments, the method according to the invention comprises steps (a), (c), (e), (f) and (g); preferably (a), (c), (e) and (g).

[0051] The method according to the invention can comprise additional steps besides steps (a) to (g), which may optionally be carried out overlapping with one or more of steps (a) to (g). Preferably, steps (a) to (g) are carried out sequentially in alphabetical order.

[0052] For descriptive purposes, "essentially consisting of" means that the presence of other components in the mixture is not excluded, provided they do not significantly alter the essential characteristics of the mixture. Preferably, "essentially consisting of" means that the expressly listed components / ingredients of the mixture constitute at least 95% by weight of the total mass of the mixture, more preferably at least 96% by weight, even more preferably at least 97% by weight, most preferably at least 98% by weight, and particularly at least 99% by weight. Step (a) :

[0053] In step (a) of the inventive process, a formaldehyde-based additive is added to a first reactant composition containing urea, which is in the form of a melt and / or solution. For the purposes of description, "melt and / or solution" means that the composition exhibits properties of both a hydrated melt and a concentrated solution. Experts recognize that the transitions can be gradual and therefore a clear distinction between melt on the one hand and solution on the other is not useful. This process produces a precursor containing ammonium-formaldehyde condensation products, which is in the form of a melt and / or solution.

[0054] Preferably, in step (a), the formaldehyde-based additive is an aqueous concentrate which, in addition to water, contains or consists substantially of formaldehyde, urea, and optionally reaction products of formaldehyde and urea. Formaldehyde and urea reaction products can be ham-formaldehyde condensation products and / or ham-formaldehyde reaction products with reactive functional groups. Suitable additives are commercially available, for example, UF-85, Oman Formaldehyde Chemical Company LLC. Besides urea and formaldehyde, the additive can contain other components, in particular ham-formaldehyde reaction products with reactive functional groups, especially monomethylol ham, dimethylol ham, and / or trimethylol ham.

[0055] Preferably, step (a) is carried out at a temperature in the range of 105°C to 150°C, preferably 115°C to 140°C.

[0056] Preferably, in step (a), the formaldehyde-based additive is added in such an amount that the molar ratio of formaldehyde (or formaldehyde equivalents, i.e., the structural units formed from formaldehyde in methylol hams) and urea is at least 1:0.4, preferably at least 1:0.5, more preferably at least 1:0.6, even more preferably at least 1:0.8, most preferably at least 1:1, and particularly at least 1:1.2. This allows the number of reactive functional groups to be reduced even with comparatively small amounts of urea. This may then occur via the formation of polymer structures, which complicates handling and is therefore less preferred for practical reasons.

[0057] Preferably in step (a) the formaldehyde-based additive is added in such an amount that the molar ratio of formaldehyde (or formaldehyde equivalents, i.e. the structural units formed from formaldehyde in methylol hams) and urea is at least 1 : 1.5, preferably at least 1 : 2, more preferably at least 1 : 2.5, even more preferably at least 1 : 3, most preferably at least 1 : 3.5, and in particular at least 1 : 4.

[0058] Preferably, step (a) is carried out in a ham-formaldehyde reactor.

[0059] In preferred embodiments, the first reactant composition in step (a) contains or consists essentially of recovered urea.

[0060] In preferred embodiments, in step (a) the first reactant composition contains or consists essentially of freshly synthesized urea.

[0061] In preferred embodiments, recovered urea is additionally fed as a liquid urea-containing return stream to an evaporation unit of the urea synthesis unit, so that in such a case, after evaporation and after the combination of both streams, the first reactant composition contains not only the freshly synthesized urea but also recovered urea. The first starting material composition preferably contains freshly synthesized urea from the urea synthesis unit as well as recovered urea from the liquid urea-containing return stream. Preferably, the proportion of recovered urea is 1 to 9 wt.%, more preferably 3 to 7 wt.%, and even more preferably about 5 wt.%, in each case based on the total urea stream.

[0062] In preferred embodiments, in step (a) the urea content in the first reactant composition is at least 20 wt.%, preferably at least 30 wt.%, more preferably at least 40 wt.%, more preferably at least 50 wt.%, most preferably at least 60 wt.%, and in particular at least 70 wt.%, in each case based on the total mass of the first reactant composition.

[0063] In preferred embodiments, in step (a) the urea content in the first reactant composition is at least 80 wt.%, preferably at least 85 wt.%, more preferably at least 90 wt.%, more preferably at least 95 wt.%, most preferably at least 96 wt.%, and in particular at least 97 wt.%, in each case based on the total mass of the first reactant composition. Step (b):

[0064] In the optional step (b) of the process according to the invention, the precursor produced in step (a) is combined with a composition which contains an inhibitor, namely at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT).

[0065] If the inhibitor (or composition) contains at least one urease inhibitor, this inhibitor is preferably selected from the group consisting of N-(n-butyl)thiophosphoric triamide (NBPT), N-(n-propyl)thiophosphoric triamide (NPPT), hydroquinone, phosphorus triamide, ammonium thiosulfate, p-benzoquinone, cyclohexyl phosphate triamide, hexaamidocyclotrifosphazene, N-halogen-2-zoidrene, and N-dihalogen-2-zoidrene; preferably a thiophosphoric triamide; even more preferably N-(n-butyl)thiophosphoric triamide (NBPT) and / or N-(n-propyl)thiophosphoric triamide (NPPT). The inhibitor (or composition) may contain one urease inhibitor or two, three, or more urease inhibitors.

[0066] Provided that the inhibitor (or the composition) contains at least one nitrification inhibitor, this at least one nitrification inhibitor is preferably selected from the group consisting of nitrapyridine, dicyandiamide, 1-methylpyrazole-1-hydroxyamide, 3-methylpyrazole, ethyleneham, chlorazole, 4-aminotriazole, thioham, acetylene, 2-ethinylpyridine, sulfathiazole, amidinothioham, 1-amino-2,4-dimethylpyrazole phosphate, thiosulfates such as sodium thiosulfate or calcium thiosulfate, potassium azide, sodium azide, calcium carbide, 2,5-chloroaniline, 3-acetanilide, toluene, carbon sulfide, The inhibitor (or composition) may contain one nitrification inhibitor, or two, three, or more nitrification inhibitors. The inhibitor consists of phenylacetylene, 2-propyn-1-ol, ammoxidized lignin, and phenylphosphonium diamide.

[0067] The inhibitor (or composition) may also comprise combinations of at least one urease inhibitor with at least one nitrification inhibitor. The inhibitor (or composition) may also contain multiple urease inhibitors and / or multiple nitrification inhibitors.

[0068] The nitrification inhibitor can also be included in a separate composition, which is used separately from or simultaneously with the composition containing the urease inhibitor.

[0069] Preferably, step (b) is carried out upstream of a particulateation unit, e.g. a pricking unit or granulation unit, in particular a fluidized bed granulator.

[0070] Preferably, step (b) is performed downstream of a hemoglobin synthesis unit. Step (c) :

[0071] In step (c) of the inventive process, the precursor produced in step (a) and optionally combined in step (b) with at least one urease inhibitor and / or at least one nitrification inhibitor is mixed with a second reactant composition containing urea and present in the form of a melt and / or solution. This produces an intermediate containing urea and urea-formaldehyde condensation products, also present in the form of a melt and / or solution.

[0072] The composition (type and quantity of ingredients) of the second reactant composition can differ from the composition (type and quantity of ingredients) of the first reactant composition. However, it is also possible for the composition of the first and second reactant compositions to be identical. Preferably, the first and second reactant compositions differ with respect to the volume flows / quantities used. Thus, steps (a) and (c) of the process according to the invention can be carried out simultaneously (i.e., as a single step) or sequentially (i.e., as separate steps).

[0073] Preferably, step (c) is carried out at a temperature in the range of 105°C to 150°C, preferably 15°C to 140°C.

[0074] Preferably, the relative weight ratio of the second reactant composition used in step (c) to the first reactant composition used in step (a) is at least 2.0, preferably at least 2.5, more preferably at least 3.0, even more preferably at least 3.5, most preferably at least 4.0, and in particular at least 4.5.

[0075] Preferably, the relative weight ratio of the second reactant composition used in step (c) to the first reactant composition used in step (a) is at least 5.0, preferably at least 5.5, more preferably at least 6.0, even more preferably at least 6.5, most preferably at least 7.0, and in particular at least 7.5.

[0076] Preferably, the relative weight ratio of the second reactant composition used in step (c) to the first reactant composition used in step (a) is at least 10, preferably at least 12, more preferably at least 14, even more preferably at least 16, most preferably at least 18, and particularly at least 20. Up to a relative weight ratio of 20, not too much undesired byproduct, in particular biuret, is formed. Lower relative weight ratios are therefore preferred.

[0077] Preferably, in step (c), the second reactant composition contains or consists substantially of freshly synthesized urea. Like the first reactant composition, the second reactant composition also preferably contains freshly synthesized urea from the urea synthesis unit as well as recovered urea from the liquid urea-containing recirculation stream.

[0078] Preferably in step (c) the urea content in the second reactant composition is at least 80 wt.%, preferably at least 85 wt.%, more preferably at least 90 wt.%, even more preferably at least 95 wt.%, most preferably at least 96 wt.%, and in particular at least 97 wt.%, in each case based on the total mass of the second reactant composition.

[0079] Preferably, the mixing of the precursor with the second starting material composition to produce the intermediate in step (c) takes place no earlier than 50 seconds, preferably no earlier than 60 seconds, preferably no earlier than 90 seconds, more preferably no earlier than 120 seconds, even more preferably no earlier than 150 seconds, most preferably no earlier than 180 seconds, and in particular no earlier than 210 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0080] For the purpose of description, two time periods of different lengths can be distinguished, both of which begin with the addition of the formaldehyde-based additive to the first reactant composition in step (a). The longer of the two time periods ends with the solidification of the intermediate in step (e), at the earliest after 50 seconds. Within this time period lies the shorter of the two time periods, which ends with the mixing of the precursor with the second reactant composition to produce the intermediate in step (c).

[0081] Preferably, the mixing of the precursor with the second reactant composition to produce the intermediate in step (c) takes place no later than 660 seconds, preferably no later than 600 seconds, more preferably no later than 540 seconds, even more preferably no later than 480 seconds, most preferably no later than 420 seconds, and in particular no later than 360 seconds after the addition of the formaldehyde-based additive to the first reactant composition in step (a), but always before the solidification of the intermediate with the production of particles in step (e). Step (cl):

[0082] In the optional step (d) of the process according to the invention, the intermediate product produced in step (c) is combined with a composition containing an inhibitor, namely at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT).

[0083] The preferred urease inhibitors, nitrification inhibitors and combinations listed above in connection with optional step (b) are also analogously preferred for optional step (d).

[0084] Preferably, step (d) is carried out upstream of a particulate matter unit.

[0085] Preferably, step (d) is carried out downstream of a hemoglobin synthesis unit. Step(s):

[0086] In step (e) of the process according to the invention, the intermediate product generated in step (c) and optionally combined in step (d) with the at least one urease inhibitor and / or at least one nitrification inhibitor is solidified, producing particles, preferably by pricking or granulation, in particular by flow-bed granulation. The solidification of the intermediate product in step (e) takes place no earlier than 50 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0087] In continuous processes, this means that the corresponding portion of a continuously moving material stream, which came into contact with the formaldehyde-based additive in step (a) by adding it to the initial reactant composition, solidifies no sooner than 50 seconds later in step (e). Suitable methods for determining this time interval are familiar to qualified personnel. For example, tracers such as dyes can be used for this purpose in routine tests.

[0088] Preferably, the solidification of the intermediate product in step (e) takes place at the earliest 60 seconds, preferably at the earliest 90 seconds, preferably at the earliest 120 seconds, more preferably at the earliest 150 seconds, even more preferably at the earliest 180 seconds, most preferably at the earliest 210 seconds, and in particular at the earliest 240 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0089] The solidification of the intermediate in step (e) preferably takes place at the earliest 270 seconds, preferably at the earliest 300 seconds, more preferably at the earliest 330 seconds, even more preferably at the earliest 360 seconds, most preferably at the earliest 390 seconds, and in particular at the earliest 420 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0090] Longer time intervals between the addition of ingredients in step (a) and the solidification in step (e) increase the risk of significant amounts of undesirable byproducts forming, particularly biuret in the precursor and / or intermediate. Furthermore, longer time intervals require more complex equipment (longer pipelines / larger diameter pipelines, pressure vessels, etc.), which can be a disadvantage.

[0091] Preferably, the solidification of the intermediate product in step (e) takes place no later than 660 seconds, more preferably no later than 600 seconds, more preferably no later than 540 seconds, more preferably no later than 480 seconds, most preferably no later than 420 seconds, and in particular no later than 360 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

[0092] In preferred embodiments, the method according to the invention comprises, after step (e) and before step (f), one, several or all additional steps selected from - Pre-cooling of the particles; - Sieving and / or classifying the particles to obtain particle fractions; - Separating at least one of the particle fractions; and preferably returning this at least one separated particle fraction, e.g. as seed, to a granulation unit; and - Cooling of the remaining unseparated particles, i.e., the target product particle fraction obtained during sieving and / or classification. Step (f):

[0093] In the optional step (f) of the process according to the invention, the particles produced in step (e) are temporarily stored at an elevated temperature.

[0094] Preferably, the optional step (f) is performed for at least half a day, preferably at least one day, more preferably at least two days, more preferably at least three days, most preferably at least four days, and in particular at least five days.

[0095] Preferably, the optional step (f) is carried out at an elevated temperature of at least 40°C, more preferably at least 50°C, more preferably at least 60°C, even more preferably at least 70°C, most preferably at least 80°C, and particularly at least 90°C. Preferably, the temperature is higher than the local room temperature. Preferably, the temperature is actively increased, for example, by means of a heater.

[0096] As mentioned above, it was surprisingly found that storing the particles for, e.g., 24 hours at a temperature of preferably at least 80°C before treatment with the urease inhibitor significantly reduces the degradation of the urease inhibitor, i.e., significantly improves storage stability. Intensive mixing of the formaldehyde-based additive and the hygrothermal melt / solution also has a beneficial effect on storage stability. Step (g):

[0097] In the optional step (g) of the process according to the invention, the particles produced in step (e) and optionally temporarily stored in step (f) are combined with a composition which contains at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NB PT) or N-(n-propyl)thiophosphoric triamide (NPPT).

[0098] The preferred urease inhibitors, nitrification inhibitors and combinations listed above in connection with optional step (b) are also analogously preferred for optional step (g).

[0099] Preferably, the composition is non-aqueous. Preferably, the particles are coated with the composition, whereby any liquid present, preferably a non-aqueous organic solvent, is evaporated. Preferably, the particles are brought together by spraying with a non-aqueous solution of the inhibitor.

[0100] Preferably step (g) is carried out in a particulate matter unit or downstream of a particulate matter unit.

[0101] Preferably step (g) is carried out upstream of a precooling, in a precooling, or downstream of a precooling.

[0102] Preferably, step (g) is carried out upstream of an aftercooling system, in an aftercooling system, or downstream of an aftercooling system.

[0103] Preferably, step (g) is carried out upstream of a product storage area. Return:

[0104] In preferred embodiments, unreacted, excess and / or sorted-out material is separated from the fertilizer particles, optionally processed and recycled.

[0105] For descriptive purposes, the urea contained in the urea-containing recirculation stream is also referred to as 'recovered urea' to distinguish it from 'freshly synthesized urea' from a urea synthesis unit.

[0106] According to the invention, the recovered urea is preferably used as a component of the first reactant composition and / or the second reactant composition, preferably in each case in a mixture with freshly synthesized urea.

[0107] Particles separated by sieving because they are too small (undersized particles) or too large (oversized particles) are preferably returned to the granulation unit as seed material, with oversized particles preferably being crushed beforehand. Return is preferably in solid form.

[0108] Remaining, unreacted, excess, and / or rejected material, e.g., from particulate removal, the cooling section, or sieving, is preferably fed to a washing process, forming an aqueous urea-containing solution. This urea-containing solution is preferably recycled after storage in an intermediate tank. The liquid urea-containing return stream preferably contains residual amounts of the precursor, intermediate product, and other material streams, or consists essentially of them.

[0109] For the purpose of description, "unreacted, excess and / or sorted material" includes any material not contained in the fertilizer particles (e.g. dust) as well as material contained in fertilizers that do not meet certain requirements as rejects (e.g. under- or over-component), in particular residual urea, residual urea-formaldehyde condensation products, residual urease inhibitor or residual nitrification inhibitor, and mixtures thereof.

[0110] In preferred embodiments, the urea-containing recirculation stream is divided into a first partial stream and a second partial stream, and the first partial stream preferably contains or consists substantially of the first reactant composition. In this case, the formaldehyde-based additive is preferably added in step (a) to the first partial stream from the urea-containing recirculation stream, which provides the first reactant composition. Preferably, the first partial stream is smaller than the second partial stream.

[0111] If the recycled stream undergoes certain processing measures, e.g. cleaning by washing, intermediate storage and / or drying by evaporation of the liquid used for washing, preferably water, the division of the recycled stream into the first partial stream and the second partial stream can take place at different points or at different times.

[0112] Preferably, the stream is divided into the first partial stream and the second partial stream. - either downstream of an evaporation unit, which is preferably configured to dry the material by evaporating the liquid used for washing, preferably water; - or downstream of an intermediate storage unit and preferably upstream of an evaporation unit, which is preferably configured to dry the material by evaporating the liquid used for washing.

[0113] Preferably, the proportion of the first partial stream is at most 15 wt.% and the proportion of the second partial stream is at least 85 wt.%, based on the total amount of urea contained in the two partial streams.

[0114] Preferably, in step (c), the second reactant composition contains freshly synthesized urea and the second partial stream, or consists essentially of these. The second partial stream preferably contains recycled urea, so that the second reactant composition preferably contains recycled urea in addition to the freshly synthesized urea.

[0115] However, it is also possible that the second starting material composition contains only freshly synthesized urea, but no recycled urea.

[0116] In preferred embodiments, the urea-containing recirculated stream is returned to the urea synthesis unit for evaporation, into which an evaporation unit is preferably integrated. In this case, the second reactant composition is preferably a mixture of freshly synthesized urea and recovered urea.

[0117] Preferably, the second partial stream is combined with a stream of the precursor produced in step (a), preferably after step (a) and, depending on the process flow, before step (c) or possibly also as step (c). Preferably, the two streams add up to 100%, so that the combined streams preferably comprise all the recycled material, preferably all the unreacted, excess and / or rejected material.

[0118] In preferred embodiments, a reactant stream comprising freshly synthesized urea is divided into a first partial stream and a second partial stream. Preferably, the liquid urea-containing recirculated stream, which is preferably concentrated beforehand in an evaporation unit, is combined with the urea stream exiting the urea synthesis unit as a melt and / or solution. The reactant stream then preferably contains freshly synthesized urea from the urea synthesis unit as well as recovered urea from the liquid urea-containing recirculated stream. Preferably, the proportion of recovered urea is 1 to 9 wt.%, more preferably 3 to 7 wt.%, and even more preferably about 5 wt.%.

[0119] In step (a), the urea-based additive is added to the first partial stream as the first reactant composition. This partial stream, which contains urea as well as urea-formaldehyde condensation products, is then subsequently combined with the second partial stream as the second reactant composition and then fed to the solidification step (e). Introducing solid or liquid starting materials:

[0120] Preferably, solid starting materials, i.e., any solids to be introduced, such as solid additives, solid excipients, solid active ingredients, etc., are introduced, preferably independently of one another, either separately or as a mixture, using solid-liquid mixers. The solid starting material is then preferably contained within the fertilizer particles, preferably homogeneously distributed.

[0121] The solid starting material is preferably first introduced into a fluid. Preferably, the fluid is aqueous. Preferably, the fluid contains urea. Preferred fluids include water, aqueous urea solutions, urea melts, the first starting material composition, the precursor, the second starting material composition, the intermediate, and the composition containing at least one urease inhibitor and / or at least one nitrification inhibitor. Compared to using an aqueous solution of the solid starting material, direct introduction of the The amount of additional water that needs to be evaporated is reduced by the addition of solid feedstock to the fluid. Preferably, the fluid is generated in a plant for the production of fertilizer particles, for example, as process condensate, during the evaporation of fresh urea synthesis, during separate evaporation, in a tank, as a scrubbing solution for an exhaust gas scrubber, or in a pipeline. Optionally, the fluid is conveyed to the solid-liquid mixer by a feed pump, the feed pump being preferably arranged upstream of the solid-liquid mixer in the direction of fluid flow.

[0122] The solid feedstock to be introduced into the fluid is preferably stored in a reservoir (e.g., silo, big bag, hopper). Preferably, a defined quantity of the solid feedstock is fed to the solid-liquid mixer using a solid feed device. The feed can be, for example, gravimetric or volumetric. Examples of suitable solid feed devices are metering screws or rotary valves. Preferably, the solid feedstock has a particle size of < 1 mm.

[0123] In a solid-liquid mixer, the solid feedstock is mixed with the fluid. An example of a suitable solid-liquid mixer is the MHD2000 from IKA Werke GmbH. The resulting mixture can be a solution and / or a suspension. It can also be an emulsion, for example, if the melting point of the solid feedstock is below the temperature of the fluid or if a complex mixing ratio is present. The solid feedstock and the fluid are mixed in a defined ratio, which can be controlled and regulated using the optional feed pump and / or the solid dosing device. The ratio can be set manually or automatically controlled.

[0124] Optionally, the resulting mixture is then passed through a degassing unit, which may remove any gas that was previously introduced by the solid starting material or the solid-liquid mixer.

[0125] Optionally, the pressure of the generated mixture is subsequently increased using a pressure boosting device, preferably a pump. Such a pressure increase may be necessary if the back pressure downstream is higher than the outlet pressure of the solid-liquid mixer or the optional degassing unit. Since the generated mixture can be viscous, the pump is preferably suitable for pumping liquids of varying viscosities (e.g., a progressive cavity pump or a screw pump). The pump is also preferably suitable for pumping suspensions. The pump's delivery rate is preferably in a defined ratio to the outlet of the solid-liquid mixer. This ratio can be set manually or automatically controlled by means of a circuit.

[0126] The degassing unit and pressure boosting device can be separate or combined. Depending on the type of pressure boosting device, degassing and pressure boosting can be combined.

[0127] In preferred embodiments, the generated mixture is subsequently introduced into a concentrated hemp solution and / or melt, preferably at a feed point. The concentrated hemp solution and / or melt is preferably the main stream fed to the granulation or pricking unit. Preferably, the flow rate of the concentrated hemp solution and / or melt is greater than the flow rate of the generated mixture. The generated mixture is introduced into the concentrated hemp solution and / or melt in a defined ratio. This ratio can be set manually or automated by means of a circuit. Preferably, the distance between the solid-liquid mixer and the feed point is as short as possible. Preferably, the residence time of the mixture between the solid-liquid mixer and the feed point is as short as possible.The feed point is preferably located upstream of the granulation or pricking unit (e.g., fluidized bed granulation, pricking, drum granulator). Optionally, intensified mixing of the generated mixture and the concentrated ammonium solution and / or melt can take place downstream of the feed point and upstream of the granulation or pricking unit. A pump can be used for this mixing, particularly if the feed point is located upstream of a pump for the granulation or pricking unit. Alternatively, a static mixer, such as a filter, can be located downstream of the feed point and upstream of the granulation or pricking unit.

[0128] In other preferred embodiments, the generated mixture is subsequently introduced into a liquid composition obtained through evaporation or in a recycling system (e.g., exhaust gas scrubber). This liquid composition is preferably aqueous. The liquid composition preferably contains urea.

[0129] Preferably, liquid starting materials, i.e., any liquids to be introduced, such as liquid additives, liquid adjuvants, liquid active ingredients, etc., are introduced, preferably independently of one another, either separately or as a mixture, preferably with the aid of liquid-liquid mixtures. The liquid starting material is then preferably contained within the fertilizer particles, preferably homogeneously distributed.

[0130] For liquid starting material, an additional dosing device can optionally be provided.

[0131] In preferred embodiments, the liquid starting material is introduced upstream or downstream of the optional feed pump, downstream of the solid-liquid mixer, into or downstream of the degassing unit, upstream or downstream of the pressure increaser, upstream or downstream of the feed point, or directly upstream of the granulation or pricking unit. Attachment:

[0132] Another aspect of the invention relates to a system configured to carry out the inventive method described above.

[0133] The system according to the invention preferably comprises - a feed line, preferably a urea synthesis unit, configured to provide freshly synthesized urea, which preferably leaves the urea synthesis unit in the form of a melt and / or solution; - a device for adding a formaldehyde-based additive to a first starting material composition to produce a precursor; - a device for mixing the precursor with a second reactant composition to produce an intermediate product; - a particleization unit, preferably a granulation or pricking unit, in particular a fluidized bed granulator, which is configured to perform step (e), i.e. to solidify the intermediate produced in step (c) by generating particles; and - a product warehouse configured to store fertilizer particles.

[0134] Preferably, the system according to the invention comprises a device for controlling or regulating the time interval between the addition of the formaldehyde-based additive to the first reactant composition in step (a) and the solidification of the intermediate product in step (e) at the earliest after 50 seconds.

[0135] Preferably, the apparatus according to the invention comprises a ham-formaldehyde reactor, i.e., a reactor configured, i.e., set up and adapted, to react urea and formaldehyde (in particular, the formaldehyde-equivalent group of a methylol ham either with free urea or with the urea-equivalent group of a methylol ham). Preferably, the ham-formaldehyde reactor is configured to carry out step (a), i.e., to add a formaldehyde-based additive to a first reactant composition containing urea and present in the form of a melt and / or solution, generating a precursor containing ham-formaldehyde condensation products and present in the form of a melt and / or solution.

[0136] The system according to the invention can include, including the ham-formaldehyde reactor, any devices capable of extending the residence time of the formaldehyde-based additive in the melt and / or solution to the desired period of time.

[0137] For example, the urea-formaldehyde reactor as such may be a transport line with a larger diameter to slow down the mass flow compared to the main supply of urea from the urea synthesis unit; or a chemical reactor which may optionally include stirring or heating devices.

[0138] Preferably, the system according to the invention is configured such that, during the execution of the process according to the invention, the molar ratio of formaldehyde (or formaldehyde equivalent- The ratio of formaldehyde in the additive (the sulfur dioxide in the formaldehyde-based additive) to urea in the ham-formaldehyde reactor is at least 1:2 (mol formaldehyde : mol urea). The system according to the invention may optionally include a corresponding control or regulation system, or a specially designed pipeline for this purpose. Due to the high melting point of the ham-formaldehyde condensation product, it can be advantageous to add a larger excess of molten urea to maintain a liquid flow. The ham-formaldehyde condensation product preferably dissolves in the molten urea.

[0139] Preferably, the apparatus according to the invention comprises a sieve configured for sieving or classifying the particles generated in step (e). Preferably, a pre-cooling unit is arranged upstream of the sieve, configured to pre-cool the particles generated in step (e) before they are subsequently sieved or classified in the sieve and separated into at least two particle streams according to particle size. Preferably, a post-cooling unit is arranged downstream of the sieve, configured to post-cool the sieved or classified particles before they are optionally combined with the composition containing at least one urease inhibitor and / or at least one nitrification inhibitor and finally fed to the optional product storage.

[0140] Preferably, the system according to the invention comprises return lines which are configured to return unused, excess and / or sorted-out material to the cycle.

[0141] The system according to the invention preferably comprises several return lines. Particles separated by sieving because they are too small (undercomb) or too large (overcomb) are preferably returned as solids for particle formation via a return line, with overcomb preferably being comminuted beforehand. Unreacted, excess, and / or rejected material is preferably fed to a scrubber via one or more return lines and converted therein into a urea-containing solution. This urea-containing solution then forms a urea-containing return stream, which is preferably returned via a return line to an evaporation unit, which is either separate or integrated into the urea synthesis unit. From the evaporation unit, the optionallyThe concentrated return current is preferably routed via a return line to an injection point downstream of the urea synthesis unit and upstream of the preheating unit, where it is combined with a current of freshly synthesized urea.

[0142] The system according to the invention preferably includes a washing unit in the cycle, which is configured to wash the recycled material, preferably with water, more preferably with an aqueous urea solution. The washing unit preferably serves to remove urea-containing dust and ammonia from the process exhaust air, e.g., the fluidization air after granulation.

[0143] Preferably, the system according to the invention comprises an evaporation unit in the circuit, which is preferably arranged downstream of the laundry and which is configured to dry the material previously washed in the laundry. In preferred embodiments, the evaporation- The vaporization unit is integrated into the urea synthesis unit. In other preferred embodiments, the vaporization unit is separate from the urea synthesis unit. Preferably, the vaporization unit comprises a first vaporization stage and a second vaporization stage arranged downstream therefrom.

[0144] Preferably, the system according to the invention includes an intermediate storage unit in the cycle, which is configured to temporarily store recycled material, typically in the form of a solution or melt. The intermediate storage unit preferably contains recycled material in the form of a solution / melt. Preferably, no solids are temporarily stored. However, solids can be dissolved in this section. The solution or melt can also contain material that is generated elsewhere. Fertilizer particles:

[0145] A further aspect of the invention relates to fertilizer particles containing urea, ham-formaldehyde condensation products and at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), wherein the total content of methylol ham (preferably monomethylol ham, dimethylol ham and trimethylol ham) in the fertilizer particles is at most 0.10 wt.%, preferably at most 0.05 wt.%, more preferably at most 0.01 wt.%, more preferably at most 0.005 wt.%, most preferably at most 0.001 wt.%, and in particular at most 0.0005 wt.%, in each case based on the total mass of the fertilizer particles.

[0146] Preferably, the proportion of methylol hams (preferably monomethylol ham, dimethylol ham and trimethylol ham) is at most 30 mol%, preferably at most 20 mol%, more preferably at most 10 mol% and particularly preferably at most 5 mol%, in each case based on the amount of formaldehyde added in the additive (or the corresponding formaldehyde equivalents).

[0147] Preferably, the biuret content in the fertilizer particles is at most 2.0 wt.%, preferably at most 1.8 wt.%, more preferably at most 1.6 wt.%, even more preferably at most 1.4 wt.%, most preferably at most 1.2 wt.%, and in particular at most 1.0 wt.%, and most especially at most 0.8 wt.%, in each case based on the total mass of the fertilizer particles.

[0148] Preferably, the biuret content in the urea-containing composition increases by no more than 0.15 wt.% after leaving the urea synthesis unit and reaching the product storage area.

[0149] Preferably, the urease inhibitor is distributed at least substantially homogeneously throughout the volume of the fertilizer particles.

[0150] Preferably, the nitrification inhibitor is distributed at least essentially homogeneously over the volume of the fertilizer particles.

[0151] Preferably, the urea, urease inhibitor, and / or nitrification inhibitor are granulated or prilled and contained within the fertilizer particles. More preferably, the urea, urease inhibitor, and / or nitrification inhibitor are mixed and homogeneously distributed within the fertilizer particles. The fertilizer particles thus preferably do not exist in the form of core-shell particles, with the particle core comprising the urease inhibitor and / or the nitrification inhibitor and the particle shell comprising the urea.

[0152] In preferred embodiments, the fertilizer particles are not in the form of core-shell particles, i.e., not in the form of coated cores. Instead, the fertilizer particles preferably consist of a homogeneous mixture of all ingredients and components (monoliths).

[0153] In preferred embodiments, the fertilizer particles have a nucleus and a coating, wherein the nucleus of the fertilizer particles comprises a urease inhibitor and the coating of the fertilizer particles comprises a nitrification inhibitor.

[0154] In other preferred embodiments, the nucleus of the fertilizer particles comprises a nitrification inhibitor and the coating of the fertilizer particles comprises a urease inhibitor.

[0155] In other preferred embodiments, the fertilizer particles are in the form of core-shell particles, i.e., coated cores. In this case, preferably at least a subset, and more preferably the entire amount, of the urease inhibitor and / or the nitrification inhibitor is contained in the cores. If the coating contains any urease inhibitor and / or the nitrification inhibitor at all, then preferably only a subset thereof.

[0156] For the purposes of description, core-shell particles according to the invention have an inner core and a coating (shell) surrounding this inner core, the coating preferably completely surrounding the inner core. The chemical composition of the core differs from the chemical composition of the coating in at least one property, preferably in its chemical nature and / or in the weight fraction of at least one ingredient. Preferably, the core and the coating are each formed from chemical compositions that independently contain all of their respective ingredients in a homogeneous distribution. If the core and the coating have the same chemical composition, they are therefore not core-shell particles within the meaning of the invention.

[0157] In particularly preferred embodiments, the fertilizer particles are not in the form of core-shell particles.

[0158] In other particularly preferred embodiments, the fertilizer particles are in the form of core-shell particles, wherein the chemical composition of the core and the coating differs. The coating (shell) differs only by the weight fraction of the nitrification inhibitor and / or the urease inhibitor and / or their formulation.

[0159] In another preferred embodiment, the fertilizer particles are coated with a coating which retards the release of urea.

[0160] Preferably, the fertilizer particles are available according to the above-described, invention-based method.

[0161] Another aspect of the invention relates to the use of the fertilizer particles described above as fertilizer.

[0162] Preferred embodiments of the invention are explained below with reference to Figures 1 to 8. These embodiments are to be interpreted as examples and not as limiting.

[0163] Reference symbol list: 1: Hamster synthesis unit 2: Particular unit 3: Pre-cooling 4: Sieving 5: Post-cooling 6: Laundry 7: Cache 8: Evaporation unit 8a: first evaporation stage 8b: second evaporation stage 9: Ham-formaldehyde reactor 10: Product warehouse

[0164] Figure 1 schematically illustrates a preferred embodiment of the invention using a flow diagram, wherein urea is produced in a urea synthesis unit (1). The urea synthesis unit (1) may include an evaporation unit (not shown) in which a liquid urea-containing return stream from the intermediate storage (7) can be evaporated, particularly if, as in the embodiment according to Figure 1, no separate evaporation unit (8) is present.

[0165] The urea stream exiting the urea synthesis unit (1) as a melt and / or solution is split into a first partial stream and a second partial stream. The first partial stream is fed to a urea-formaldehyde reactor (9) and mixed with a formaldehyde-based additive, preferably UF-85 (urea-formaldehyde concentrate, 25 wt% urea, 60 wt% formaldehyde), to generate urea-formaldehyde condensation products. The first partial stream is then recombined with the second partial stream and subsequently fed to the particleization unit (2). To achieve the most homogeneous mixing possible of the first and second partial streams, it is preferred to combine these two partial streams as far upstream of the particleization unit (2) as possible.

[0166] The first partial stream, comprising ham-formaldehyde condensation products, requires a longer time within the ham-formaldehyde reactor (9) and after exiting it until reaching the particleization unit (2) (including the time after its merger with the second partial stream) than the second partial stream from the ham-formaldehyde synthesis unit (1) until reaching the particleization unit (2) (including the time after its merger with the first partial stream). If the first partial stream, comprising ham-formaldehyde condensation products, also temporarily contains ham-formaldehyde reaction products with reactive functional groups, these reactive functional groups can react with suitable reaction partners from the partial stream during the longer time period and are thus rendered harmless with regard to undesired reactions with the inhibitor.

[0167] The inventive system is preferably configured to realize different time periods or residence times, whereby the first partial flow is reached at the particulate unit. (2) can be delayed accordingly. This is possible, for example, by changing the length of the lines and / or changing the diameter of the lines. Preferred time intervals, dwell times, or delays according to the invention have been generally described above and apply analogously to all embodiments according to the figures.

[0168] Preferably, the particles produced in the particle generation unit (2) are pre-cooled. (3) pre-cooled, then sieved or classified in a sieving (4) and then further cooled in a post-cooling (5) before being fed into a product storage (10).

[0169] Particles that are separated during sieving (4) because they are too small (undercom) or too large (overcom) are preferentially fed as seed into the particle size distribution unit (2) (preferably granules- (Lilization unit) is recycled, with excess material preferably being comminuted beforehand. Recycling preferably takes place in solid form.

[0170] Remaining, unreacted, excess, and / or rejected material from the particulate unit (2), pre-cooling (3), sieving (4), and / or post-cooling (5) is preferably fed to a washing unit (6) and, if necessary, after storage in an intermediate storage tank (7), returned to the urea synthesis unit (1). For this purpose, urea-containing dust and ammonia-containing air are preferably introduced into the washing unit (6). Washing, preferably with water, optionally with an acidic washing stage, yields a liquid, urea-containing return stream, which is optionally temporarily stored in an intermediate storage tank (7).

[0171] The liquid urea-containing return stream is preferably concentrated in an evaporation unit, which is preferably integrated into the urea synthesis unit (1) (not shown), and subsequently combined with the urea stream formed as a melt and / or solution in the urea synthesis unit (1).

[0172] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, more preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particle collection unit (2) (preferably still in the melt), in the particle collection unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0173] Figure 2 schematically illustrates a preferred embodiment of the invention using a flowchart, which can be understood as a further development or variant of the embodiment according to Figure 1, which is why in Figure 2 - unless otherwise described - the elements shown in Figure 1 have the same meaning and function as described in connection with Figure 1 (this also applies to the other subsequent figures).

[0174] The unreacted, excess, and / or rejected material, possibly stored in intermediate storage (7), is first fed to an evaporation unit (8) and then combined with the urea stream leaving the urea synthesis unit (1) as a melt and / or solution. Preferably, water previously used in the washing unit (6) is evaporated in the evaporation unit (8). In contrast to the embodiment schematically illustrated in Figure 1, the embodiment schematically illustrated in Figure 2 does not use an evaporation unit integrated into the urea synthesis unit (1) to evaporate the liquid urea-containing return stream from the intermediate storage (7), but rather the separate evaporation unit (8).

[0175] Figure 3 schematically illustrates another preferred embodiment of the invention using a flow diagram, according to which the stream leaving the evaporation unit (8) is combined with the The ham stream exiting the evaporation unit (8) as a melt and / or solution is combined upstream of the particleization unit (2) (preferably still in the melt). The ham stream exiting the evaporation unit (8) as a melt and / or solution is thereby split into a first partial stream and a second partial stream. The first partial stream is fed to a ham-formaldehyde reactor (9) and treated therein with a formaldehyde-based additive to generate ham-formaldehyde condensation products, thus eliminating the need to split the mass stream downstream of the ham synthesis unit (1) and upstream of the particleization unit (2).

[0176] In a preferred embodiment, as shown in Figure 3, the first partial stream is recombined with the second partial stream, then combined with the hamsemium stream exiting the hamsemium synthesis unit (1) as a melt and / or solution, and subsequently fed to the particulateation unit (2). The first partial stream, comprising the hamsemium-formaldehyde condensation products, requires a longer time within the hamsemium-formaldehyde reactor (9) and after exiting it until reaching the particulateation unit (2) (including the time after its combination with the second partial stream and with the hamsemium stream exiting the hamsemium synthesis unit (1)) than the hamsemium stream exiting the hamsemium synthesis unit (1) until reaching the particulateation unit (2) (including the time after its combination with the previously combined first and second partial streams).

[0177] In another preferred embodiment (not shown), in modification of the embodiment shown in Figure 3, the first partial stream is first combined with the ham stream leaving the ham synthesis unit (1) as a melt and / or solution, only then combined with the second partial stream, and subsequently fed to the particleization unit (2). The first partial stream, comprising the ham-formaldehyde condensation products, requires a longer time within the ham-formaldehyde reactor (9) and after exiting it until reaching the particleization unit (2) (including the time after its combination with the ham stream leaving the ham synthesis unit (1) and with the second partial stream) than the ham stream leaving the ham synthesis unit (1) until reaching the particleization unit (2) (including the time after its combination with the first partial stream and with the second partial stream).

[0178] In order to achieve the most homogeneous mixing possible of the first partial stream, the second partial stream and the ham stream leaving the ham synthesis unit (1), it is preferred to combine these streams as far upstream as possible of the particulateation unit (2).

[0179] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particleization unit (2) (preferably while still in the melt). in the particle size distribution unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0180] Figure 4 schematically illustrates a preferred embodiment of the invention using a flow diagram, which can be understood as a further development or variant of the embodiment according to Figure 3. The stream entering the evaporation unit (8) from the intermediate storage unit (7) is split in the evaporation unit (8) into a first partial stream and a second partial stream. The first partial stream is fed to a ham-formaldehyde reactor (9) and mixed therein with a formaldehyde-based additive to generate ham-formaldehyde condensation products. Subsequently, the first partial stream is returned to the evaporation unit (8) and combined with the second partial stream. The two combined partial streams are then combined with the ham stream leaving the ham synthesis unit (1) and subsequently fed to the particulateation unit (2).

[0181] Alternatively, a ham-formaldehyde reactor (9) can be omitted (i.e., in deviation from the embodiment shown in Figure 4), and instead the formaldehyde-based additive can be added directly to the stream entering the evaporation unit (8). However, since this can lead to undesirable volatile organic compounds in the process condensate of the evaporation unit (8), this alternative is less preferred.

[0182] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, more preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particleization unit (2) (preferably still in the melt), in the particleization unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0183] Figure 5 schematically illustrates a preferred embodiment of the invention using a flowchart, which can also be understood as a further development or variant of the embodiments according to Figures 3 and 4.

[0184] The stream leaving the intermediate storage unit (7) is split into a first partial stream and a second partial stream. The first partial stream is fed to a ham-formaldehyde reactor (9) and treated with a formaldehyde-based additive to generate ham-formaldehyde condensation products. The first partial stream is then combined with the second partial stream. The two combined partial streams are then fed to the evaporation unit (8), where they are combined with the ham stream leaving the ham synthesis unit (1) and subsequently fed to the particulateation unit (2).

[0185] As already described in connection with Figure 4, the embodiment schematically illustrated in Figure 5 also allows for the omission of a urea-formaldehyde reactor (9) (i.e., in contrast to the embodiment shown in Figure 5), and instead, the formaldehyde-based additive can be added directly to the stream entering the evaporation unit (8). However, since this can also lead to undesirable volatile organic compounds in the process condensate of the evaporation unit (8), this alternative is also less preferred.

[0186] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, more preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particle collection unit (2) (preferably still in the melt), in the particle collection unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0187] Figure 6 schematically illustrates a preferred embodiment of the invention using a flow diagram. This embodiment can be understood as a further development or variant of the embodiments according to Figures 3 to 5. The current extracted from the laundry (6) is directed into the intermediate storage unit (7) and temporarily stored there. A current is diverted from the material temporarily stored in the intermediate storage unit (7) and fed to a hygrothermal-formaldehyde reactor (9). A formaldehyde-based additive is added to this reactor to produce a hygrothermal-formaldehyde condensation product. The current is then returned to the intermediate storage unit (7) and combined with the temporarily stored material. From there, a current is extracted and fed to the evaporation unit (8).Alternatively, another stream of temporarily stored material can be drawn off from the intermediate storage unit (7) and fed together with the stream coming from the ham-formaldehyde reactor (9) and then to the evaporation unit (8). The ham stream from the evaporation unit (8) is finally combined with the ham stream leaving the ham synthesis unit (1) and then fed to the particulate unit (2).

[0188] Alternatively, in this configuration, a ham-formaldehyde reactor (9) can be omitted (i.e., in deviation from the embodiment shown in Figure 6), and instead, the formaldehyde-based additive can be dosed directly into the intermediate storage tank (7). However, since this can also lead to undesirable volatile organic compounds that are found in the process condensate of the evaporation unit (8), this alternative is also less preferred.

[0189] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particleization unit (2) (preferably still in the melt), in the particleization unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0190] Figure 7 schematically illustrates, using a flow diagram, another preferred embodiment of the invention, in which the stream leaving the intermediate storage unit (7) is split into a first partial stream and a second partial stream. The first partial stream is fed to a urea-formaldehyde reactor (9) and mixed therein with a formaldehyde-based additive to generate urea-formaldehyde condensation products. The second partial stream is fed to an evaporation unit (8). The first partial stream leaving the urea-formaldehyde reactor (9) and the second partial stream leaving the evaporation unit (8) are combined, combined with the urea stream leaving the urea synthesis unit (1), and then fed to the particulateation unit (2).

[0191] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, more preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particle collection unit (2) (preferably still in the melt), in the particle collection unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0192] Figure 8 schematically illustrates, using a flow diagram, an additional preferred embodiment of the invention, in which the evaporation unit is designed as a two-stage unit, i.e., comprising a first evaporation stage (8a) and a second evaporation stage (8b). The stream leaving the intermediate storage tank (7) is fed to the first evaporation stage (8a) and subsequently, i.e., after leaving the evaporation stage (8a), split into a first partial stream and a second partial stream. The first partial stream is fed to a ham-formaldehyde reactor (9) and mixed therein with a formaldehyde-based additive to generate ham-formaldehyde condensation products. The second partial stream is fed to the second evaporation stage (8b).The first partial stream leaving the ham-formaldehyde reactor (9) and the second partial stream leaving the second evaporation stage (8b) are combined, combined with the ham stream leaving the ham synthesis unit (1) and then fed to the particulateation unit (2).

[0193] An inhibitor composition (not shown), which preferably comprises at least one urease inhibitor and / or at least one nitrification inhibitor, preferably at least one urease inhibitor, more preferably at least one thiophosphoric triamide, most preferably N-(n-butyl)thiophosphoric triamide (NBPT) or N-(n-propyl)thiophosphoric triamide (NPPT), is preferably added upstream of the particleization unit (2) (preferably still in the melt), in the particleization unit (2), immediately upstream of the pre-cooling unit (3), in the pre-cooling unit (3), immediately downstream of the pre-cooling unit (3), immediately upstream of the post-cooling unit (5), in the post-cooling unit (5) and / or immediately upstream of the product storage unit (10).

[0194] The following examples serve to illustrate preferred embodiments of the invention, but are not to be interpreted restrictively.

[0195] Comparative example 1:

[0196] An aqueous ham melt was treated with a formaldehyde-based additive and solidified / granulated in a conventional industrial plant. The formaldehyde-based additive was added to the aqueous ham melt at an injection point with a residence time of 30-40 seconds prior to solidification. Commercially available UF85 or UF80 was used as the additive. This is often described as UFC (urea-formaldehyde condensate or precondensate). It is a mixture containing primarily methylol hams, which are actually addition products, not condensation products. An inhibitor formulation was injected separately at a separate injection point.

[0197] Analysis conducted during the subsequent storage period showed a significant degradation of the inhibitor within a few weeks. The same degradation was observed when the inhibitor formulation was applied by spray coating.

[0198] Comparative example 2 and example 3 according to the invention:

[0199] An aqueous ham melt solution was treated with a formaldehyde-based additive and solidified / granulated in a batch-operated pilot plant. The formaldehyde-based additive (UF-85) was added to the aqueous ham melt at different time points to produce various samples. The samples were stored at room temperature before coating with an inhibitor formulation. Subsequently (at least three days later), the samples were coated with the inhibitor formulation. During the subsequent storage period, the degradation of the inhibitor in the different samples was analyzed several times over a period of months.

[0200] Comparison example 2 - short dwell time:

[0201] A formaldehyde-based additive (UF-85) was injected close to the granulation nozzle, resulting in the shortest possible reaction time before spraying and solidification. In this case, no additional mixing unit such as a pump or static mixer was used. The samples were stored at room temperature before coating. Afterwards (at least 3 days later), the samples were treated with the inhibitor- The formulation was coated. After storage of approximately one month, more than 40% of the applied inhibitor had already degraded.

[0202] Evaluation: The inhibitor degraded too quickly for commercial use.

[0203] Inventive example 3 - 260 seconds dwell time'.

[0204] A formaldehyde-based additive (UF-85) was added to a urea melt in a urea melter. The reaction time before spraying and solidification was at least one minute. The samples were stored at room temperature before coating. Subsequently (at least three days later), the samples were coated with the inhibitor formulation. In this example, even after two months of storage, less than 20% of the applied inhibitor had degraded.

[0205] Assessment: The degradation rate is well suited for commercial application.

[0206] The experimental results are shown in Figures 9 to 11. These figures illustrate the decrease in the percentage of inhibitor in the product over time, based on the amount present immediately after production, during storage.

[0207] Figure 9 shows the temporal development of the percentage of inhibitor present in the fertilizer particles with the duration of storage (based on the initial quantity in each case). The measurement curves shown differ with regard to the degradation rate of the inhibitor in fertilizer particles with a short UF-85 residence time and with a residence time of more than 50 seconds.

[0208] Figure 10 shows the temporal development of the percentage of inhibitor present in the fertilizer particles with the duration of storage (in each case based on the initial quantity). The measurement curves shown differ with regard to temperature when the fertilizer particles are stored before the inhibitor is absorbed.

[0209] Figure 11 shows the reaction (or lack thereof) between ham-formaldehyde and inhibitor in the melt.

Claims

Patent claims:

1. A process for producing fertilizer particles containing urea, ham-formaldehyde condensation products and at least one urease inhibitor and / or at least one nitrification inhibitor, the process comprising the steps of: (a) Adding a formaldehyde-based additive to a first starting material composition containing urea and in the form of a melt and / or solution, producing a precursor containing urea-formaldehyde condensation products and in the form of a melt and / or solution; (b) optional, combining the precursor with a composition containing at least one urease inhibitor and / or at least one nitrification inhibitor; (c) Mixing the precursor with a second reactant composition containing urea and in the form of a melt and / or solution, producing an intermediate containing urea and urea-formaldehyde condensation products and in the form of a melt and / or solution; (d) optional, combining the intermediate with a composition containing at least one urease inhibitor and / or at least one nitrification inhibitor; (e) Solidification of the intermediate product, producing particles; (f) optional, intermediate storage of the particles at elevated temperature; and (g) optional, combining the particles with a composition containing at least one urease inhibitor and / or at least one nitrification inhibitor; wherein the process includes at least one of the optional steps (b), (d) and (g); and wherein the solidification of the intermediate in step (e) takes place no earlier than 50 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

2. The method according to claim 1, wherein the solidification of the intermediate in step (e) takes place at the earliest 60 seconds, preferably at the earliest 90 seconds, preferably at the earliest 120 seconds, more preferably at the earliest 150 seconds, more preferably at the earliest 180 seconds, most preferably at the earliest 210 seconds, and in particular at the earliest 240 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

3. The method according to claim 1 or 2, wherein the mixing of the precursor with the second reactant composition to produce the intermediate in step (c) takes place at the earliest 50 seconds the, preferably at the earliest 60 seconds, preferably at the earliest 90 seconds, more preferably at the earliest 120 seconds, more preferably at the earliest 150 seconds, most preferably at the earliest 180 seconds, and in particular at the earliest 210 seconds after the addition of the formaldehyde-based additive to the first starting material composition in step (a).

4. The method according to any of the preceding claims, wherein the urease inhibitor is a thiophosphoric triamide or contains several thiophosphoric triamides.

5. The method according to any of the preceding claims, wherein the formaldehyde-based additive is an aqueous concentrate which, in addition to water, contains or essentially consists of formaldehyde, urea and optionally reaction products of formaldehyde and urea.

6. The method according to one of the preceding claims, wherein steps (a) and (c) are carried out independently of each other at a temperature in the range of 105°C to 150°C, preferably 115°C to 140°C.

7. The method according to one of the preceding claims, wherein in step (a) the additive based on formaldehyde is added in such an amount that the molar ratio of formaldehyde (or formaldehyde equivalents) and urea is at least 1 : 0.8, preferably at least 1 : 1, more preferably at least 1 : 1.5, more preferably at least 1 : 2, more preferably at least 1 : 2.5, even more preferably at least 1 : 3, most preferably at least 1 : 3.5, and in particular at least 1 :

4.

8. The method according to one of the preceding claims, wherein step (a) is carried out in a ham-formaldehyde reactor (9).

9. The method according to one of the preceding claims, wherein the relative weight ratio of the second reactant composition used in step (c) to the first reactant composition used in step (a) is at least 5.0, preferably at least 5.5, more preferably at least 6.0, more preferably at least 6.5, most preferably at least 7.0, and in particular at least 7.

5.

10. The method according to any of the preceding claims, wherein the first reactant composition and / or the second reactant composition contains or essentially consists of recovered urea and / or freshly synthesized urea.

11. The method according to one of the preceding claims, wherein the urea content in the first reactant composition is at least 80 wt.%, preferably at least 85 wt.%, more preferably at least 90 wt.%, more preferably at least 95 wt.%, most preferably at least 96 wt.%, and in particular at least 97 wt.%, in each case based on the total mass of the first reactant composition.

12. The method according to one of the preceding claims, wherein the urea content in the second reactant composition is at least 80 wt.%, preferably at least 85 wt.%, more preferably at least 90 wt.%, more preferably at least 95 wt.%, most preferably at least 96 wt.%, and in particular at least 97 wt.%, in each case based on the total mass of the second reactant composition.

13. The method according to one of the preceding claims, wherein step (f) is carried out at an elevated temperature of at least 40°C, preferably at least 50°C, more preferably at least 60°C, more preferably at least 70°C, most preferably at least 80°C, and in particular at least 90°C.

14. A system configured to carry out the method according to any of the preceding claims.

15. Fertilizer particles containing urea, methyl ol hams, formaldehyde condensation products and at least one urease inhibitor and / or at least one nitrification inhibitor, wherein the total content of methyl ol hams in the fertilizer particles is at most 0.10 wt.%, preferably at most 0.05 wt.%, more preferably at most 0.01 wt.%, even more preferably at most 0.005 wt.%, most preferably at most 0.001 wt.%, and in particular at most 0.0005 wt.%, in each case based on the total mass of the fertilizer particles.

16. The fertilizer particles according to claim 15, wherein the at least one urease inhibitor and / or at least one nitrification inhibitor is distributed at least substantially homogeneously over the volume of the fertilizer particles.

17. The fertilizer particles according to claim 15 or 16, comprising a nucleus and a coating, wherein (i) the nucleus of the fertilizer particles comprises a urease inhibitor and the coating of the fertilizer particles comprises a nitrification inhibitor; or (ii) the nucleus of the fertilizer particles comprises a nitrification inhibitor and the coating of the fertilizer particles comprises a urease inhibitor.

18. The fertilizer particles according to any one of claims 15 to 17, wherein the fertilizer particles are coated with a coating for retarding the urea release.

19. The fertilizer particles according to any one of claims 15 to 18, wherein the biuret content in the fertilizer particles is at most 2.0 wt.%, preferably at most 1.8 wt.%, more preferably at most 1.6 wt.%, even more preferably at most 1.4 wt.%, most preferably at most 1.2 wt.%, and in particular at most 1.0 wt.%, most especially at most 0.8 wt.%, in each case based on the total mass of the fertilizer particles.

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