Nitrogen-based fertilizer and method for producing same

Abstract

A first aspect of the invention relates to a method for producing a fertilizer. The method comprises adding (incorporating) a modified zeolite doped with sodium, calcium or potassium as a feedstock to a nitrogenous fertilizing substance. Another aspect of the invention relates to a fertilizer comprising a nitrogenous fertilizing substance supplemented with a modified zeolite doped with sodium, calcium and / or potassium.

Description

NITROGEN-BASED FERTILIZER AND PROCESS FOR ITS MANUFACTURE Technical Field

[0001] In general, the invention relates to a fertilizer composition for use in agriculture, viticulture, arboriculture, market gardening, horticulture and / or forestry. In a particular aspect, the invention relates to a fertilizer (e.g. in solid form, in powder, grain or granule form) containing urea or ammonium nitrate and a zeolite filler. Technological background

[0002] In the field of fertilizers (in English: "fertilizing product"), we can observe a growing effort of innovation, linked to the constant environmental and societal pressure that farmers are subjected to in relation to the use of synthetic products, but also to the awareness of the essential role of the relationships between soil microorganisms and plants: this is what we characterize as sustainable agriculture.

[0003] In the context of this document, the term "fertilizer" is used to refer to a substance or mixture of substances intended to be applied to plants or their rhizosphere, for the purpose of providing the plants with nutrients, the substance or mixture of substances comprising at least one fertilizer. The term "fertilizer" refers, in the context of this document, to a substance or mixture of substances intended to provide plants with nutrients, so as to improve their growth, increase the yield and / or quality of a crop. Different categories of nutrients are distinguished.

[0004] The macroelements (or macronutrients) are nitrogen (N), phosphorus (P) and potassium (K).

[0005] Secondary elements are considered to be calcium (Ca), sulfur (S) and magnesium (Mg).

[0006] Trace elements include iron (Fe), manganese (Mn), molybdenum (Mo), copper (Cu), boron (B), zinc (Zn) and others.

[0007] Fertilizers are also divided into different categories. Simple fertilizers are those fertilizers that provide only one of the three macronutrients (N, P, or K). Compound fertilizers contain several nutrients, including at least one macronutrient. So-called binary fertilizers combine two macronutrients (NP, NK, or PK fertilizers), and so-called ternary fertilizers combine all three macronutrients (NPK fertilizers).

[0008] Agriculture is the main source of nitrous oxide (N2O) emissions, mainly associated with the use of synthetic nitrogen fertilizers. Agricultural activities generate an average of 30 kg of surplus nitrogen per hectare of agricultural land per year. One of the major problems causing these surpluses appears to be the low efficiency of absorption and use of the nitrogen applied. Indeed, only about 50 to 60% of the nitrogen supplied by a fertilizer would, on average, be absorbed by the crop (Sylvester-Bradley R, Kindred DR. Analyzing nitrogen responses of cereals to prioritize routes to the improvement of nitrogen use efficiency. J Exp Bot. 2009;60(7): 1939-51. doi: 10.1093 / jxb / erp116. Epub 2009 Apr 23. PMID: 1939538). Some of it is lost through leaching, leading to pollution of surface water and groundwater.Another part is volatilized in the form of nitrous oxide (N2O), a greenhouse gas (GHG) with a radiative power 298 times stronger than CO2.

[0009] It is clear that there is potential for mitigating GHGs by reducing the use of synthetic fertilizers, combined on the one hand with rigorous reasoning regarding inputs, and on the other hand with the implementation of techniques likely to reduce nitrogen losses and increase the efficiency of nitrogen applied to crops.

[0010] Nitrogen in ammoniacal form can naturally be retained at the level of the clay-humic complex of the soil represented by its CEC (cation exchange capacity), which varies greatly depending on the soil.

[0011] However, the use of synthetic chemical fertilizers for decades, without parallel inputs of organic matter, has contributed to the depletion of humus in many soils, and therefore to a reduction in the clay-humic complex. This results in a net reduction in the CEC and an increase in the phenomenon of nitrogen loss through the mechanisms mentioned above.

[0012] In addition to economic losses, the 50% of nitrogen not used by plants causes serious environmental damage such as groundwater pollution and greenhouse gas (GHG) emissions.

[0013] It is therefore desirable to reduce nitrogen losses.

[0014] CN1078225A describes a compound of zeolite and ammonium nitrate. The zeolite content is 10-40% (mass) and the ammonium nitrate content is 60-90% (mass). The zeolite is ground into powder (particle size ranging from 0.15 mm to 0.28 mm) and mixed with ammonium nitrate in the desired mass ratio to produce granules in a granulator. Most of the granules (80%) are 1-4 mm in size. According to the document, the compound would reduce fertilizer costs by 15.6% without productivity losses.

[0015] EP1379558A1 relates to a zeolite-coated urea fertilizer. The mass ratio of zeolite to urea is between 6:1 and 0.5:1, preferably between 2.2:1 and 1.2:1. Preferred zeolites are analcime, chabazite, laumontite, phillipsite, faujasite, clinoptilolite and mordenite. According to EP1379558A1, bentonite may be added to the granules to improve the plasticity of the granules during granulation.

[0016] US5676729A describes urea particles containing a mineral filler, which may include zeolite, among other materials. According to the document, the mineral filler may be added to molten urea, and the resulting mixture is then formed into granules, prills, or pellets.

[0017] Zeolites are crystalline aluminosilicates with the general empirical formula: M x / n[(AIO2)x(SiO2)y].wH2O where M represents a cation with valence n, w is the number of water molecules, the ratio y / x represents the molar ratio between Si and Al and is greater than or equal to 1 and the part in brackets indicates the composition of the microporous skeleton. The presence of Al 3+ in the microporous skeleton (on sites that would otherwise be occupied by Si 4+ ) causes a negative charge which is compensated by the M cations in the interstices of the skeleton.

[0018] Natural zeolites have a variable adsorption capacity for ammonium ion, which can vary from approximately 3 to 30 mg / g. However, it should be noted that the adsorption rate of ammonium by natural zeolite decreases after heating it from 200°C, and decreases proportionally to the temperature to be reduced by almost half above 500°C. High temperature elevation can destroy adsorption sites by blocking pores through micropore aggregation and changing surface functional groups (Wang, S., Zhu, ZH, 2006. Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution. J. Hazard. Mater. 136 (3), 946-952, and Xu, Y., Liu, S., Guo, X. et al. Methane activation without using oxidants over Mo / HZSM-5 zeolite catalysts. Catal Lett 30, 135-149 (1994))) Since the synthesis reactions of various types of nitrogen fertilizers are exothermic, with temperatures up to 250°C, the zeolite used in nitrogen fertilizer synthesis will have its adsorption capacity for ammonium ion reduced.

[0019] Although the state of the art includes synthetic fertilizers based on ammonium nitrate or urea containing zeolite, the fertilizers in question are not effective in preventing losses of ammonium ion. General description of the invention

[0020] A first aspect of the invention relates to a method for manufacturing a fertilizer. The method comprises the addition (incorporation) of a modified zeolite, doped with sodium (in sodium ion Na + ), calcium (in calcium ion Ca 2+ ) or in potassium (in potassium ion K + ), as a filler to a nitrogen fertilizer.

[0021] Another aspect of the invention relates to a fertilizer comprising a nitrogen fertilizer added with a modified zeolite, doped with sodium, calcium or potassium. The modified zeolite may, in particular, be doped with sodium and calcium, sodium and potassium, calcium and potassium or sodium and calcium and potassium.

[0022] Zeolite modified by doping with sodium, calcium or potassium has an adsorption capacity for NH4 ions + higher, and faster, than the same zeolite before modification. The use of a modified zeolite, obtained by sodium doping, is particularly preferred, because it makes it possible in particular to compensate for the degradation of the adsorption capacity of the ammonium ion that an untreated zeolite undergoes if it is exposed to high temperatures.

[0023] The zeolite used can be in the form of a powder having a size (median diameter or diameter D50) of 1 pm to 1000 pm, preferably of 1 pm to 500 pm, more preferably from 20 pm to 500 pm, even more preferably from 50 pm to 400 pm, and most preferably from 100 pm to 200 pm. Unless expressly stated otherwise in this text, all particle size measurements (particle sizes, e.g., diameter D50) refer to measurements obtained by laser particle size analysis in accordance with ISO 13320:2020 based on the Fraunhofer diffraction pattern (diameters corresponding to equivalent spherical volumes). The micronization process of the zeolite can be dry or wet, by air jet mill, ball mill, or any other type.

[0024] The zeolite (before modification by doping) can be natural or synthetic. A zeolite is an aluminosilicate with a nanoporous structure. The empty spaces are connected to each other and are initially occupied by cations and water molecules. The cations and water molecules are mobile within the structure, which allows on the one hand ion exchanges, and on the other hand reversible partial dehydration. There are many zeolites classified into several families. Clinoptilolite (lamellar-monoclinic zeolite) and chabazite (hexagonal-cubic zeolite) are considered particularly effective in this context due to their content of exchangeable cations (Ca, K and Na) and their cation exchange capacities. There are also synthetic zeolites, but in the context of the invention, natural zeolites are preferred, in particular those from deposits selected for their purity. Preferably,the term "zeolite" means a natural zeolite selected from the analcime family such as analcime, pollucite, wairakite, bellbergite, bikitaite, boggsite and brewsterite; the chabazite family such as chabazite, willhendersonite, cowlesite, dachiardite, redingtonite, epistilbite, erionite, faujasite, ferrienite and herschelite; the gismondine family such as amicite, garronite, gismondine, gobbinsite, gmelinite, gonnardite and goosecreekite; the harmotome family such as harmotome, phillipsite and wellsite; the heulandite family such as clinoptilolite, heulandite, laumonite, levyne, mazzite, merlinoite, montesommaite, mordenite and maricopaite; the natrolite family such as mesolite, natrolite, scolecite, offretite, paranatrolite, paulingite and perlialite; the stilbite family such as barrerite, stilbite, stellerite,thomsonite, tschernichite and yugawaralite; sodium dachiardite; and tetranatrolite. More preferably, the term zeolite denotes clinoptilolite, chabazite, phillipsite, ferrierite, mordenite or erionite. Most preferably, the zeolite comprises or consists of clinoptilolite. It should be noted that the natural zeolite may contain impurities, e.g., contents of feldspar, illite or quartz. The natural zeolite preferably comprises at least 40% (mass / mass), and more preferably at least 60% (mass / mass) and even more preferably at least 80% (mass / mass) of pure zeolite.

[0025] The modified zeolite can represent between 2% and 98% by mass of the fertilizer, preferably 20 to 40% by mass of the fertilizer, even more preferably 30 to 40% by mass of the fertilizer, this to have a maximum effect of retention of the ammonium ion without reducing too much the nitrogen content of the fertilizer.

[0026] The nitrogen fertilizer may comprise, for example, ammonium nitrate, urea, ammonium sulfate or ammonium sulfonitrate. The nitrogen fertilizer may be a straight fertilizer. Alternatively, the nitrogen fertilizer is a compound fertilizer based on nitrogen and one or more elements selected from phosphorus, potassium, sulfur, magnesium and calcium, the presence of other nutrients not being excluded.

[0027] The addition step may include mixing the modified zeolite with an aqueous solution or melt of ammonium nitrate or urea.

[0028] The method may comprise forming an ammonium nitrate or urea prill and coating the prill with the ammonium nitrate or urea, with the modified zeolite and, optionally, one or more other adjuvants. The fertilizer may therefore be in the form of grains comprising ammonium nitrate or urea in their core (e.g., an ammonium nitrate or urea prill) and a coating of the mixture of the nitrogen fertilizer and the modified zeolite and, optionally, one or more other adjuvants.

[0029] The process may also include granulation of the nitrogen fertilizer with the modified zeolite added. The fertilizer may therefore be in the form of granules.

[0030] The method may comprise producing the modified zeolite. The modified zeolite may be produced by impregnating zeolite (natural or synthetic) with a solution containing sodium, calcium or potassium ions, e.g., a solution of sodium nitrate (NaNOs), sodium hydroxide (NaOH) and / or sodium chloride (NaCl), calcium nitrate (Ca(NOs)2) or potassium nitrate (KNO3).

[0031] Zeolite modification with impregnation of sodium, calcium or potassium based solution improves adsorption capacities and adsorption rates of NH4 ions + . Modification of the zeolite by impregnation with a sodium-based solution (preferably a sodium nitrate solution) improves the adsorption capacities of NH4 ions. +at high temperature, which is advantageous for nitrogen fertilizer manufacturing processes. Zeolite impregnation increases the cation exchange capacity and can also increase the volume ratio of zeolite mesopores, promoting the adsorption of ammonium ions NH4 + and improving its heat resistance.

[0032] Zeolite is formed from a microporous aluminosilicate skeleton; the valence electrons of the oxygen atoms are not balanced within the tetrahedron, making it negatively charged. Positively charged cations tend to be captured in the interstices of the microporous skeleton. These cations are weakly bound to the aluminosilicate and are therefore relatively easily exchanged. This cation exchange mechanism in zeolite plays an important role in the adsorption of ammonium, as the cations released by the zeolite are replaced by NH4 ions. + .

[0033] Different zeolites can have different selectivities for different cations. The selectivity of a zeolite for a cation M can be denoted a(M). Most natural zeolites have a(NH4 + ) > a(K + ) > a(Sr + ) > a(Na + ) > a(Ca 2+ ).

[0034] The modification of the zeolite (preferably it is initially a natural zeolite) involves doping it with sodium, calcium, or potassium ions, so that these are then exchanged for the benefit of the ammonium ion NH4 + for which the zeolite has a higher affinity than the ion with which it has been doped.

[0035] The doping cation is preferably selected based on the zeolite such that the selectivity of the zeolite for the ammonium ion NH4 +is greater than the selectivity for the doping cation. Depending on the type of zeolite chosen, the preference of the cation chosen for doping may vary between Na + , That 2+ , or K + .

[0036] Like Na ions + are normally the weakest bound to zeolite compared to K + , Mg 2+ , That 2+ and Cu 2+ , sodium doping is currently considered the most preferred.

[0037] When modifying the zeolite (during doping), cations naturally present in the interstices of the microporous skeleton of the zeolite are replaced by doping ions, e.g. by Na ions. + These can then be exchanged with ammonium ions NH4 + . It can be observed that the Na ions + , That 2+ and K +give the modified zeolite a higher ion exchange capacity and thus improve the adsorption of ammonium ion.

[0038] The production of the modified zeolite (preferably the production of the sodium-doped zeolite) optionally but preferably comprises drying and / or calcination of the zeolite after impregnation. The calcination can be carried out at a temperature in the range 300°C to 800°C. It is noted that calcination of unmodified zeolite (without doping) greatly reduces its adsorption capacities for ammonium ion. On the other hand, the modified zeolite, preferably zeolite modified by impregnation with a nitrate-based solution, e.g., based on sodium nitrate, calcium nitrate, or potassium nitrate, has improved capacities in the event of heat treatment, in particular calcination. The modified zeolite has good resistance to the heat of a calcination process and a synthetic fertilizer manufacturing process.

[0039] The mesoporous volume and specific surface area of ​​the zeolite are factors that may affect its ammonium adsorption capacity. It is known that nitrate salts (e.g., sodium nitrate, calcium nitrate, or potassium nitrate) can decompose and release oxygen gas at high temperatures. Such gas release can destroy some of the zeolite's micropores and create larger pores. The zeolite's pore structure may therefore be modified to benefit the NH4 ion adsorption capacity. + in particular by impregnation with NaNOs, followed by a calcination step.

[0040] Therefore, a sodium nitrate solution will preferably be chosen for doping the zeolite with sodium, because the heat treatments and / or high temperature reactions (which take place during the synthesis of fertilizers) will decompose the sodium nitrate, release oxygen and destroy part of the micropores of the zeolite and create larger pores. More particularly the Heat treatment of sodium nitrate-doped zeolite further increases the adsorption capacity and speed of NH4 ions + of zeolite if we compare to those of doped zeolite but without heat treatment.

[0041] The invention combines zeolite modified by doping with sodium, calcium or potassium and a nitrogen fertilizer in a fertilizer. It should be noted that the zeolite is present in the composition as an active filler. The zeolite cannot therefore be considered a simple excipient, but actively contributes to the effectiveness of the fertilizer. The combination of zeolite and nitrogen fertilizer effectively produces a synergistic effect in the fertilizer composition.

[0042] The use of fertilizer allows for a reduction in the amount of fertilizer applied to the soil or plants while avoiding a loss of crop yield. The presence of zeolite also helps reduce water requirements.

[0043] When applied to the soil, the zeolite in the fertilizer limits nitrogen leaching through reversible retention. The fertilizer helps retain nutrients, particularly nitrogen, near the roots by increasing the CEC, induced by the high CEC of the modified zeolite. As a result, the fertilizer also helps reduce nitrous oxide (N2O) emissions. Brief description of the drawings

[0044] Other features and characteristics of the invention will emerge from the detailed description of certain advantageous embodiments presented below, by way of illustration, with reference to the appended drawing which shows: Fig. 1: A schematic flowchart of a method for manufacturing a fertilizer according to one embodiment of the invention. Detailed description of the invention

[0045] In a preferred aspect, the present invention relates to the manufacture of a synthetic fertilizer comprising a nitrogen fertilizer and a zeolite modified by impregnation with a sodium, calcium or potassium based solution as a filler.

[0046] Zeolite modified by impregnation with a sodium-based solution can be calcined or not. Calcination of the zeolite after impregnation is preferably carried out in the temperature range from 300 to 550°C, e.g. at (approximately) 400°C.

[0047] The sodium-based solution may comprise an aqueous sodium nitrate (NaNOs) solution, an aqueous sodium hydroxide (NaOH) solution, or an aqueous sodium chloride solution. The concentration of the sodium-based solution is preferably in the range of 0.1 to 10 mol / l. A NaNOs solution at a concentration between 0.1 mol / l and 10 mol / l, preferably between 1 mol / l and 5 mol / l, e.g., 3 mol / l, has been found effective for impregnation. The duration of impregnation may depend on the concentration and temperature (room temperature is preferred) and is, e.g., between 2 and 48 hours.

[0048] The impregnation-modified zeolite has a higher and faster ammonium ion adsorption capacity than the zeolite (typically a natural zeolite) used as raw material.

[0049] The modification of zeolite by doping with sodium (sodium ions) improves the ammonium adsorption capacities at high temperatures, which is an advantage for mixing with a nitrogen fertilizer in the molten state. Doping the zeolite also increases the cation exchange capacity, promoting the adsorption of NH4 + .

[0050] The nitrogen fertilizer may comprise or consist of, e.g., ammonium nitrate (AN) or calcareous ammonium nitrate (CAN), urea, ammonium sulfate or ammonium sulfonitrate or another complex fertilizer.

[0051] The fertilizer can be presented in the form of granules with a homogeneous composition or in the form of grains comprising a core coated with the mixture comprising the nitrogen fertilizer and the modified zeolite.

[0052] The modified (sodium-doped) zeolite is compatible with common fertilizer and fertilizer manufacturing processes. The fertilizer can be made with a solution or melt of ammonium nitrate, ammonium sulfate, ammonium sulfonitrate, or urea, into which the modified zeolite is mixed as a filler. The mixture can then be granulated or used to coat a prill (e.g., urea or ammonium nitrate).

[0001] The manufacture of a modified, sodium-doped zeolite may comprise one or more of the following choices or operations: o the zeolite may comprise or consist of clinoptilolite; o the zeolite may be ground to a particle size of between 100 and 200 μm; o after grinding, the zeolite may be placed in a furnace at (approximately) 200°C for between 10 and 40 minutes, e.g., 20 minutes; o preparing a sodium nitrate (NaNOs) solution, e.g., at 3 mol / l; o impregnating the zeolite with a sodium nitrate solution at room temperature for between 10 and 72 hours, e.g., 24 hours; o the zeolite may then be collected by filtration and heat-treated, e.g., calcined at (approximately) 400°C in a furnace for 2 hours and then cooled to room temperature.

[0002] All operations can be carried out at neutral pH. The calcination temperature of the impregnated zeolite of (about) 400°C is considered advantageous, since sodium nitrate begins to decompose at about 380°C. Impregnation of a zeolite, in particular, clinoptilolite, as described above has been found to be a feasible method for significantly improving the efficiency of ammonium adsorption by the zeolite. Impregnation with a NaNOs solution, followed by calcination, also increases the sizes and volumes of the mesopores of the zeolite.

[0003] The method for manufacturing a fertilizer according to the invention may comprise one or more of the following operations: o production of a melt of ammonium nitrate or urea by any of the methods and incorporation of modified zeolite (doped with sodium), calcined or not, optionally followed by a granulation step; o manufacture of a prill of ammonium nitrate or urea followed by coating (in one or more layers) the prill with a mixture comprising a nitrogen fertilizer, modified zeolite and, optionally, one or more other adjuvants (e.g., binding agents, etc.); o Mixing ammonium nitrate or urea with a filler containing modified zeolite and, optionally, one or more other adjuvants (e.g., binding agents, etc.), followed by granulation in a granulator; o Mixture of ammonium nitrate or urea with one or more other macroelements (P and / or K) and / or with one or more secondary elements (Ca, Mg, S, Si, etc.) as well as with a filler containing modified zeolite and, optionally, one or more other additives (e.g., binding agents, etc.), followed by granulation in a granulator;

[0004] Various substances may be used as adjuvants, e.g. as a bonding agent for lignosulfites, molasses, resins, etc., as a binder for calcium bentonite, etc., during granulation or as a coating at the end of granulation to form a protective layer which will prevent moisture absorption and caking (lignosulfonates, etc.)

[0005] The manufacture of a synthetic nitrogen fertilizer is generally based on ammonia. This is obtained by combining nitrogen from the air and hydrogen from natural gas or, more recently, from the hydrolysis of water, and constitutes the basic raw material for the entire synthetic nitrogen fertilizer industry. Combined with carbon dioxide, ammonia makes it possible to obtain urea, while ammonium nitrate is obtained by reacting ammonia with nitric acid.

[0006] The manufacture of urea can be done using different processes (Stamicarbon, Snam Progetti, Chemico, Mitsui Toatsu, Montedison or CPI). The processes for the synthesis of urea (H2N-CO-NH2) use the same raw materials: ammonia and carbon dioxide. The finishing operations (granulation) are comparable for all processes and the quality of the granules depends on the quantity of impurities, in particular biuret (HN(CONH2)2), in the urea.

[0007] Ammonium nitrate (AN) and calcium ammonium nitrate (CAN) fertilizers can be produced from ammonium nitrate which is optionally mixed with a filler. There are several processes for the manufacture of ammonium nitrate (NH4NO3) (Kaltenbach, Stamicarbon, SBA, ICI, C and I, Montedison, Uhde, Fisons and Stengel) which employ various combinations of neutralization, evaporation, drying and finishing methods. Solid ammonium nitrate (AN) is produced in the form of pure grains, crystals or granules, or is mixed with one or more other fertilizers to form a complex fertilizer. Calcium ammonium nitrate (CAN), a mixture of limestone (CaCOs) or lime (CaO) and ammonium nitrate, is a nitrogen fertilizer with a nitrogen content of 20 to 30%, depending on the amount of calcium component added.

[0008] If a zeolite is used in its natural state, without modification, as a filler it will not perform well in terms of adsorption of the ammonium ion. The solutions or melts of ammonium nitrate or urea are at high temperatures (between 100°C and 200°C, or more) when the fillers are incorporated. At these temperatures, contact with a natural zeolite will reduce its adsorption rate of the NH4 ion. + , as described previously. The residual adsorption capacity may become insufficient to justify the use of zeolite as a filler.

[0009] It has been discovered that a sodium-doped zeolite has a higher adsorption capacity for ammonium ion and is more resistant to the high temperatures encountered during the manufacture of nitrogen fertilizers. Surprisingly, the modified zeolite, particularly the zeolite modified by impregnation with a sodium nitrate solution, even sees its adsorption capacity for ammonium ion improve when exposed to these temperatures, e.g., during a calcination step.

[0010] The modified zeolite can reversibly retain a higher number of cations supplied by a nitrogen fertilizer. In this way, it is possible to achieve a distribution of NH4 ions + more spread out over time and thus obtain more regular nitrification in NO 3-directly assimilated by plants. Nitrogen losses through leaching, denitrification and volatilization are reduced. In the context of the invention, the modified zeolite represents an active charge of the fertilizer in the sense that it actively contributes to cation exchange with plants and increases its effectiveness.

[0011] Since heat increases the adsorption capacities of the modified zeolite, in particular those of the zeolite modified by impregnation with a sodium nitrate solution, a calcination step at temperatures between 300°C and 800°C after sodium doping is considered advantageous. Calcination may further improve the performance of the impregnation-modified zeolite. The optimum calcination temperature may depend on the type of zeolite used. The high temperatures of calcination or nitrogen fertilizer melts may result in an increase in pore size and thus facilitate the diffusion of ammonium into the porous structure.

[0012] Zeolites particularly suitable for the invention are clinoptilolite and chabazite. The best results have been obtained with clinoptilolite, which has a high natural affinity for the ammonium ion and whose performance can be further improved by sodium doping (in particular by impregnation), followed, optionally, by a calcination step.

[0013] If the fertilizer contains an ammonium-based fertilizer, the ammonium must be converted into nitrate ions (NO 3- ) to be absorbed by plant roots. The modified zeolite fixes the ammonium ion and thus prevents excessively rapid nitrification leading to the loss of nitrate ions (very mobile) through leaching.

[0014] If the fertilizer contains a urea-based fertilizer, the urea must be hydrolyzed into ammonium by soil enzymes (ureases). The hydrolysis of urea temporarily induces a very strong increase in pH in the immediate vicinity of the fertilizer granule. The physicochemical balance between the ammonium in solution in the soil and the gaseous ammonia is shifted in favor of the latter and then results in nitrogen losses by ammonia volatilization. This volatilization will be mitigated by the modified zeolite which will have an effect not only on the reversible retention of the ammonium ion allowing for a progressive formation of nitric nitrogen by oxidation of the ammonium ion over time, but also to delay the hydrolysis of urea into ammonia. Example 1 (modified zeolite)

[0015] Clinoptilolite was impregnated with a NaNOs solution, after which the solids were collected by filtration and calcined.

[0016] Beforehand, the selected zeolite was ground to obtain a particle size of between 100 and 200 pm (D50 of approximately 150 pm), followed by a 20-minute passage in an oven at 200°C.

[0017] An aqueous solution of NaNOs at 3 mol / l (moles per liter) was prepared. The ground zeolite was impregnated with this solution at room temperature in a stirrer for 24 hours. The zeolite was then collected by filtration and calcined at 400°C (673 K) in a furnace for 2 hours, then cooled to room temperature. All operations took place at neutral pH. The calcination temperature of the impregnated zeolite was set at 400°C (673 K), because sodium nitrate begins to decompose at about 653 K. Tests to determine the NH4 adsorption capacity +natural zeolite and modified zeolite were carried out with a) a low-dose ammonium solution (200 mg / l - solution A) and b) a high-dose ammonium solution (> 1000 mg / l, solution B). In the example, it was observed with solution A that the mass NH4 + absorbed per unit mass of adsorbent was 14.4 mg / g for natural zeolite and increased to 20.6 mg / g after modification, an increase of 43%. With solution B, the mass NH4 + absorbed per unit mass of adsorbent was 23.9 mg / g for natural zeolite and increased to 32.5 mg / g after modification, an increase of 36%. It is noted that the tests to determine the adsorption capacity of NH4 +of natural zeolite and modified zeolite with a given ammonium solution are to be carried out under the same conditions of temperature, pH and incubation time for natural zeolite and for modified zeolite. It is noted that the adsorption rate of NH4 + of the modified zeolite is always significantly higher than that of the natural zeolite (for the same ammonium solution, and under the same conditions of temperature, pH and duration).

[0018] In another test, carried out with a natural zeolite of the chabazite type, impregnated in a 3 mol / l NaNOs solution and then heat-treated, the mass NH4 + absorbed per unit mass of adsorbent was 12 mg / g for natural zeolite. After treatment, the value increased to 16.3 mg / g, an increase of 35%.

[0019] The modified zeolite filler may be added directly to the molten urea or ammonium nitrate solution before granulation, or may be coated with a urea or ammonium nitrate prill during granulation. Example 2 (modified urea and zeolite granule)

[0020] Urea was produced from ammonia and carbon dioxide. The process included a first step of synthesis of ammonium carbamate and a second step of thermal decomposition of ammonium carbamate into urea. Both steps took place under a pressure of 140 to 250 bars.

[0021] The urea obtained was in the form of an aqueous solution with a concentration of approximately 70 to 80% (mass / mass). This was transformed by vacuum evaporation of the water into a mass called "molten urea".

[0022] Granulation of the molten urea was carried out in a rotating disc granulator, but other methods are also usable, e.g., fluidized bed granulation. The modified zeolite was added to the molten urea at the beginning of the granulation phase. The resulting granules can be directly bagged and / or stored in bulk.

[0023] A "horizontal thin-film dryer" can be used, in which the addition of the zeolite and any other additives can be done through an inlet separate from that which brings the urea. Liquid compounds can be injected through the rotor of the dryer. The components are mixed during their passage through the dryer to the final product. Example 3 (modified ammonium nitrate and zeolite granule)

[0024] Ammonium nitrate can be produced by neutralizing 45-65% by weight nitric acid with ammonia according to the reaction NH3+HNO3 NH4NO3. Neutralization is preferably carried out in stainless steel reactors. An ammonium nitrate solution reaching a concentration of 98 to 99.5% can be obtained. This concentrated ammonium nitrate solution can then be introduced into the granulator.

[0025] There are various processes for producing ammonium nitrate and granulating it, all of which may be implemented within the scope of this invention. Common granulating processes include high recycle processes (e.g., Pugmill, Spherodizer, Drum) and low recycle processes (e.g., Fluidized Bed, Pan, Fluidized Drum), where the recycle rate is defined as the amount of material returned to the granulator relative to the amount of product produced.

[0026] The modified zeolite filler and any other ingredients can then be incorporated into the ammonium nitrate. For this purpose, the concentrated ammonium nitrate melt can first be mixed with the zeolite filler and then granulated.

[0027] The proportion of the modified zeolite charge used according to the invention influences the spread over time of the release of the nitrogen contained in the fertilizer. The delay effect will be all the more significant as the proportion of modified zeolite is higher.

[0028] In Pugmill type installations, the molten ammonium nitrate and the modified zeolite filler can be added directly to the granulator in a fixed proportion or added in a mixing device before granulation, which makes it possible to increase or decrease the residence time of the molten ammonium nitrate and the filler before introduction into the granulator. This gives the possibility of adapting to changes in reactivity of the modified zeolite filler or to variable concentrations (always possible in the case of using natural raw materials).

[0029] The fertilizer containing ammonium nitrate and a modified zeolite filler may contain, e.g., 20 to 30% (mass / mass) nitrogen, depending on the amount of modified zeolite added. Example 4 (complex fertilizer and modified zeolite granule)

[0030] A nitrogen-based complex fertilizer comprises nitrogen and at least one other macro-element (P and / or K) and / or at least one other nutrient (e.g., Mg, Ca, S, B, Mn, ...)

[0031] All the nutrients are present in each granule, unlike blended fertilizers.

[0032] A complex fertilizer can be made from ammonium nitrate. The modified zeolite can be added along with the other nutrients to the ammonium nitrate solution before granulation. The mixing and granulation processes can be the same as in the previous examples.

[0033] Blended fertilizers, often based on urea, are manufactured by mixing granules of different compositions. One or more fertilizers according to the invention can be combined (possibly also with other fertilizers) to form a blended fertilizer. Example 5 (coated grain)

[0034] Prilling involves pumping a molten mass of ammonium nitrate or urea up a tower to release droplets that solidify as they fall. Prilling was once the preferred method for producing urea or ammonium nitrate fertilizers. However, the resulting grains may be small and / or have a low density.

[0035] To improve the quality, the "prills" obtained can be coated with a mixture of ammonium nitrate or urea with modified zeolite, or simply with modified zeolite. In this way, a grain with the desired nitrogen content can be obtained, having a diameter and density sufficient for quality spreading. The technique for coating a prill is known, but the application of a coating containing modified zeolite is not.

[0036] While particular embodiments have just been described in detail, those skilled in the art will appreciate that various modifications and alternatives thereto may be developed in light of the overall teaching provided by the present disclosure of the invention. Accordingly, the specific arrangements and / or methods described herein are intended to be given solely by way of illustration, without the intention of limiting the scope of the invention, which is determined by the scope of the appended claims.

Claims

Claims 1. Process for manufacturing a fertilizer, characterized by: the addition of a modified zeolite, doped with sodium, calcium or potassium, as a filler to a nitrogen fertilizer.

2. The method of claim 1, wherein the nitrogen fertilizer comprises ammonium nitrate or urea.

3. The method according to claim 1 or 2, wherein the nitrogen fertilizer is a compound fertilizer based on nitrogen and one or more elements chosen from phosphorus, potassium, sulfur, magnesium and calcium.

4. The method of any one of claims 1 to 3, wherein the adding step comprises mixing the modified zeolite with a melt of ammonium nitrate or urea.

5. The method according to any one of claims 1 to 4, comprising the formation of a prill of ammonium nitrate or urea and the coating of the prill with ammonium nitrate or urea, added with the modified zeolite and, optionally, one or more other adjuvants.

6. The method according to any one of claims 1 to 4, in which the nitrogen fertilizer added with the modified zeolite is subjected to granulation.

7. The process according to any one of claims 1 to 6, comprising producing the modified zeolite, the production of the modified zeolite comprising impregnating the zeolite with a solution containing sodium, calcium or potassium ions, e.g., a solution of sodium nitrate, sodium hydroxide and / or sodium chloride, calcium nitrate or potassium nitrate.

8. The method of claim 7, wherein producing the modified zeolite comprises drying the zeolite after impregnation.

9. The method of claim 7 or 8, wherein the production of the modified zeolite comprises calcination of the zeolite after impregnation.

10. The method of claim 9, wherein the calcination is carried out at a temperature in the range of 300°C to 800°C.

11. The method according to any one of claims 1 to 10, wherein the modified zeolite is a sodium-doped zeolite.

12. The method according to any one of claims 1 to 10, wherein the modified zeolite is a calcium-doped zeolite.

13. The method according to any one of claims 1 to 10, wherein the modified zeolite is a potassium-doped zeolite.

14. Fertilizer, characterized in that it comprises a nitrogen fertilizer added with a modified zeolite, doped with sodium, calcium or potassium.

15. The fertilizer of claim 14, wherein the nitrogen fertilizer comprises ammonium nitrate or urea.

16. The fertilizer according to claim 14 or 15, wherein the nitrogen fertilizer is a compound fertilizer based on nitrogen and one or more elements chosen from phosphorus, potassium, sulfur, magnesium and calcium.

17. The fertilizer according to any one of claims 14 to 16, in the form of grains comprising in their core a prill of ammonium nitrate or urea and a coating of ammonium nitrate or urea, added with modified zeolite and, optionally, one or more other adjuvants.

18. The fertilizer according to any one of claims 14 to 16, in the form of granules.

19. The fertilizer according to any one of claims 14 to 18, wherein the modified zeolite is a sodium-doped zeolite.

20. The fertilizer according to any one of claims 14 to 18, wherein the modified zeolite is a calcium-doped zeolite.

21. The fertilizer according to any one of claims 14 to 18, wherein the modified zeolite is a potassium-doped zeolite.

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