Coated fertilizer granules and manufacturing process for such granules

Abstract

The invention relates to a coated fertilizer granule (1) comprising: - a core (10) comprising a fertilizer, - a shell (11, 12) coating the core, the shell (11, 12) comprising phosphorylated cellulose. The invention also relates to a method for manufacturing coated fertilizer granules comprising the following steps: (a) phosphorylation of cellulose to obtain phosphorylated cellulose, (b) drying of fertilizer granules, (c) coating of the dried fertilizer granules with the phosphorylated cellulose, (d) drying of the coated fertilizer granules. Figure for the abstract: Figure 1A

Description

Title of the invention: Coated fertilizer granule and method of manufacturing such a granule Technical field

[0001] The invention relates to coated fertilizer granules and a method of manufacturing such granules. STATE OF THE ART

[0002] Water-soluble fertilizers are among the most widely used fertilizers for increasing crop yields. However, when water-soluble fertilizers are applied to soils, only a small portion of said fertilizers is actually used by the plant, while the residual amount undergoes chemical transformations and / or is eliminated by leaching. This amount of fertilizer not used by the plant therefore constitutes an economic loss and a waste of resources. In addition, it contributes significantly to environmental pollution.

[0003] One solution to this problem is the use of slow-release fertilizers. By controlling the kinetics of nutrient diffusion in the soil and matching the availability of these nutrients with the needs of the plant, slow-release fertilizers increase the efficiency of nutrient use.

[0004] Coating water-soluble fertilizers is an effective way to achieve the slow-release properties described above. Indeed, the coating provides a physical barrier that prevents nutrient losses through leaching and spreads out over time the availability of said nutrients that must diffuse through the physical barrier. Since the 1960s, various polymer-based coating materials have been developed, mainly non-biodegradable synthetic resins.

[0005] The major problem of fertilizers coated with non-biodegradable synthetic polymers lies in the accumulation of residues in the soil and the generation of toxic by-products. Therefore, biodegradable natural polymers can be advantageously used to replace non-biodegradable synthetic polymers.

[0006] The application of cellulose in the agricultural sector for the production of coated fertilizers is of great interest from an industrial point of view, due to the great availability of this resource. Indeed, it is the most abundant polymer on earth: cellulose is naturally produced by different living species every day in the biosphere, so that 7.5 xlO10 tonnes are extracted each year, of which approximately 1.8 xlO9 tonnes come from wood.

[0007] Cellulose also has very interesting chemical properties. Thus, cellulose is a biodegradable, renewable and recyclable polymer. In addition, when it degrades in the soil, it does not generate toxic by-elements. Finally, cellulose fibers are characterized by the presence of numerous hydroxyl groups in their chemical structure. Therefore, functionalization is a way to graft specific functional groups to the surface to target the desired properties.

[0008] As an example of the use of cellulose for the preparation of slow-release fertilizers based on coating technology, document CA2801614A1 describes the encapsulation of nutrients in wood cavities coated with a layer containing hydroxyapatite nanoparticles modified with cellulose. Document WO2015170217A1 also describes fertilizers coated with several biodegradable polymers, for example cellulose acetate or cellulose triacetate, the polymers being distributed over one or more coating layers.

[0009] Nevertheless, if the degradation products of the coating layers of such cellulose-based fertilizers do not constitute a source of soil pollution, the fact remains that they are ultimately not used by the plant. The coating layer therefore constitutes a limitation of the ratio of the mass of nutrients contained in the coated fertilizer to the total mass of the coated fertilizer.

[0010] Furthermore, it would be interesting to have coatings which not only slowly release nutrients, but also which contribute, during this release time, to improving the quality of the soil in which the plant grows. BRIEF DESCRIPTION OF THE INVENTION

[0011] An aim of the invention is to design a slow-release fertilizer based on the technology of coating with a biodegradable polymer, the biodegradable polymer being chosen so that the degradation of said biodegradable polymer constitutes an additional supply of nutrients for the plant.

[0012] Another object of the invention is to design a slow-release fertilizer which, in addition to the delayed supply of nutrients, also contributes to improving the quality of the soil in which the plant grows.

[0013] To this end, the invention provides a coated fertilizer granule comprising: - a heart including fertilizer, - a shell coating the core, the shell comprising phosphorylated cellulose.

[0014] After release of the fertilizer, the phosphorylated cellulose degrades and its biodegradation leads to the release of phosphate groups, which constitutes an additional source of nutrients provided to the plant.

[0015] Furthermore, being a three-dimensional network material, the phosphorylated cellulose gel has a very good water retention capacity, which makes the coating capable to delay the diffusion of nutrients and to conserve soil moisture near the plant and thus limit its drying out in the event of drought.

[0016] According to other optional but advantageous characteristics of said granule, possibly taken in combination:

[0017] - the diameter of the core is between 2.0 mm and 3.5 mm and the thickness of the shell is between 18+5 pm and 34+5 pm;

[0018] - the granule comprises, in mass percentage, between 2% and 3% of cellulose phos phorylated, said chemical composition being measured by the gravimetric method;

[0019] - the phosphorylation rate of the phosphorylated cellulose included in the shell is between 4860 mmol per kilogram of cellulose and 6200 mmol per kilogram of cellulose, the phosphorylation rate being measured by conductometric titration;

[0020] - the shell coating the core does not include any additives other than cellulose phosphorylated and / or the granule comprises a single shell coating the core;

[0021] - the fertilizer included in the core comprises phosphorus, nitrogen and / or potassium;

[0022] - the granule has a compressive strength of between 44 + 3.98 N and 62, 75 + 7.65 N, said resistance being measured by the mechanical compression test method.

[0023] Another object of the invention relates to the manufacture of coated fertilizer granules as described above.

[0024] Said method comprises the following steps: (a) phosphorylation of cellulose so as to obtain phosphorylated cellulose, (b) drying of fertilizer granules, (c) coating the dried fertilizer granules with phosphorylated cellulose, (d) drying of coated fertilizer granules.

[0025] According to other optional but advantageous characteristics of said method, possibly taken in combination:

[0026] - the method further comprises a step of extracting the cellulose from the biomass, said extraction step being carried out prior to step (a) of phosphorylation of the cellulose thus extracted;

[0027] - the biomass comprises Alfa fibers and the step of extracting the cellulose from from Alfa fibers includes the following sub-steps: (El) grinding, air drying then rinsing of the Alfa fibers, (E2) treatment of Alfa fibers with an aqueous solution comprising sodium hydroxide or potassium hydroxide so as to obtain a solid cellulosic residue without lignin and hemicellulose, (E3) treatment of the solid cellulosic residue without lignin and hemicellulose with a bleaching agent, so as to obtain pure cellulose;

[0028] - the bleaching agent comprises sodium chlorite, glacial acetic acid and sodium hydroxide;

[0029] - which step (a) of phosphorylation of cellulose comprises the sub-steps following:

[0030] (al) mixing cellulose with urea and diammonium phosphate in a mass ratio of 1:1:1 in distilled water at a mass concentration of between 10 and 20% at a temperature of between 25°C and 35°C for a period of between 6 h and 12 h.

[0031] (a2) drying the mixture at a temperature between 50°C and 60°C for a duration of between 6 hours and 14 hours in order to obtain a cellulose paste,

[0032] (a3) ​​heating the cellulose pulp to a temperature between 135°C and 160°C for a period of between 55 min and 65 min, so as to carry out the phosphorylation reaction of the cellulose pulp and to obtain a phosphorylated cellulose pulp,

[0033] (a4) dispersion of the phosphorylated cellulose pulp in suspension of fibers at a mass concentration between 1.5 and 2.25% in water and at a pH between 9 and 11, for a duration between 8 and 10 hours.

[0034] (a4) treatment of phosphorylated cellulose pulp using a microfluidizer high pressure;

[0035] - the fertilizer granule drying step (b) is carried out in a rotating drum at a temperature between 80°C and 100°C for a period of between 20 min and 30 min at atmospheric pressure;

[0036] - the step of coating the dried fertilizer granules with phosphorylated cellulose (c) includes the following sub-steps: (cl) preparation of an aqueous solution of the phosphorylated cellulose so as to obtain a coating solution, (c2) rotating the dried fertilizer granules in a drum, (c3) spraying the coating solution onto the fertilizer granules rotating in the drum;

[0037] - the viscosity of the coating solution is between 0.05 Pa.s and 0.1 Pa.s and / or wherein the phosphorylated cellulose concentration of the coating solution is between 0.20% and 0.50%;

[0038] - the rotation speed of the drum is between 6 rpm and 8 rpm, and / or the spray pressure is between 30000 Pa (0.3 bar) and 200000 Pa (2.0 bar);

[0039] - the step of drying the coated fertilizer granules (d) is carried out at a temperature between 80°C and 100°C at atmospheric pressure for a period of between 30 and 40 min, in a rotating drum. BRIEF DESCRIPTION OF THE FIGURES

[0040] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0041] - [Fig.lA] is a sectional view of a granule according to an embodiment of the invention; [Fig.lB] is a sectional view of a granule according to an alternative embodiment,

[0042] - [Fig.2] represents the curve of the conductometric titration by hydroxide of sodium phosphorylated cellulose used for coating triple superphosphate (TSP) fertilizer granules,

[0043] - [Fig.3] represents an infrared spectrum of the phosphorylated cellulose used for coating TSP fertilizer granules in a method according to the invention,

[0044] - Figures 4A to 4D represent images recorded under an electronic microscope scanning electron microscopy (SEM) of the surface (Figures 4A and 4C) and a cross-section (Figures 4B and 4D) of fertilizer granules before (Figures 4A and 4B) and after (Figures 4C and 4D) coating with phosphorylated cellulose,

[0045] - [Fig.5] represents the average resistance F to compression of granules of TSP fertilizers coated with phosphorylated cellulose (PCG-TSP) according to the invention measured by applying a compression force to 50 granules taken individually and calculating the average resistance, in comparison with the average compression resistance of said fertilizer granules without coating (TSP),

[0046] - [Fig.6] represents the phosphorus release profile in the soil from the granules of TSP fertilizers coated with phosphorylated cellulose according to the invention (PCG-TSP, in black) measured by column leaching, in comparison with the phosphorus release profile in the soil of said granules without coating (TSP, in gray),

[0047] - [Fig.7] represents the water retention capacity of TSP fertilizer granules coated with phosphorylated cellulose according to the invention by comparing the water retention of a soil comprising said granules (S / PCG-TSP) with a soil not comprising them (S), the water retention being measured by the method of loss of mass in water as a function of time.

[0048] For reasons of readability, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION OF EMBODIMENTS

[0049] The invention relates to a coated fertilizer granule comprising a core and a shell.

[0050] The core of the coated fertilizer granule according to the invention comprises a fertilizer. The fertilizer may comprise phosphorus, nitrogen and / or potassium. The fertilizer is for example TSP (triple superphosphate), NPK (nitrogen, phosphorus, potassium), DAP (diammonium phosphate) and / or MAP (monoammonium phosphate). The diameter of the core of the coated fertilizer granule is preferably between 2 mm and 3.5 mm. For example, the core of the coated fertilizer granule according to the invention may consist of a commercially available granule of TSP, NPK, DAP or MAP.

[0051] The shell of the coated fertilizer granule according to the invention comprises phosphorylated cellulose. Phosphorylated cellulose means cellulose in which all or part of the hydroxyl groups of the cellulose have been functionalized by phosphate groups.

[0052] In a particular embodiment of the invention, the phosphorylation rate of the phosphorylated cellulose included in the shell of the granule, defined as the rate of hydroxyl groups functionalized by a phosphate group in the cellulose, is between 4860 mmol / kg of cellulose and 6200 mmol / kg of cellulose, the phosphorylation rate being determined by conductometric titration. Briefly, 5 ml of 0.01 M NaCl was added to 0.3 g of phosphorylated fibers suspended in 85 ml of water. Then, hydrochloric acid (0.1 M) was added to the mixture to adjust the pH to 2.5. Finally, the mixture is titrated by adding NaOH solution (100 μl at 0.05 M) while monitoring the conductivity of the fiber suspension. The phosphorylation rate was determined from the midline of the curve showing electrical conductivity as a function of the volume of NaOH added.A phosphorylation rate between 4860 mmol / kg cellulose and 6200 mmol / kg cellulose facilitates the mechanical disintegration of phosphorylated cellulose to obtain the gel.

[0053] The thickness of the shell of the coated fertilizer granule according to the invention is preferably between 18+5 μm and 34+5 μm, said thickness being determined by scanning electron microscopy. Such a range of thicknesses advantageously makes it possible to obtain a shell that is sufficiently thick to very effectively delay the release of nutrients while maintaining a relatively low coating rate of the core.

[0054] Additionally or alternatively, the coated fertilizer granule preferably comprises, in mass percentage, between 2% and 3% of phosphorylated cellulose, said chemical composition being measured by gravimetry.

[0055] In a variant of the invention, illustrated in [Fig. 1A], the coated fertilizer granule 1 comprises a single shell 11 coating the core 10, said shell 11 comprising phosphorylated cellulose. Advantageously, a coated fertilizer granule comprising a single shell makes it possible to delay the release of nutrients with a minimal core coating rate.

[0056] In another variant of the invention, illustrated in [Fig.lB], the coated fertilizer granule 1 comprises at least two shells 11, 12, the first shell 11 coating the core 10 and each additional shell 12 coating the core and the innermost shells, such that at least one of the at least two shells 11, 12 comprises phosphorylated cellulose. For example, the coated fertilizer granule may comprise a first inner shell comprising phosphorylated cellulose and a second outer shell of the same composition. The second outer shell provides an additional barrier to delay the release of nutrients included in the core of the coated fertilizer granule even more effectively than the first inner shell alone.

[0057] According to a particular embodiment of the invention, the shell of the coated fertilizer granule comprising the phosphorylated cellulose does not comprise any additives other than the phosphorylated cellulose. For example, the shell does not comprise any plasticizers or non-biodegradable materials.

[0058] The coated fertilizer granule according to the invention preferably has a compressive strength of between 44 ± 3.98 N and 62.75 ± 7.65 N, measured by applying a compressive force to 50 copies of coated fertilizer granules taken individually (whose diameter is between 2.9 mm and 3.5 mm) using a compression machine, for example of the EZ Test EZ-X series from Shimadzu, and calculating the average strength over the 50 measurements. Such compressive strength is advantageously provided by the coating applied to the surface of the granules. Such compressive strength makes it possible to avoid mechanical degradation of the granules.

[0059] When such a coated fertilizer granule is placed in the soil, moisture penetrates into the granule through the phosphorylated cellulose shell, due to the porosity of said shell. Said moisture activates the release of the nutrients included in the core and the release of the fertilizer then extends over approximately three months. In addition, the phosphorylated cellulose shell thus ensures water retention in the vicinity of the plant, which contributes to further improving the quality of the soil and makes it possible to prevent the plant from drying out, even in periods of drought. When the release of the fertilizer is complete, the phosphorylated cellulose included in the shell degrades, thereby releasing phosphate groups which can themselves be assimilated by the plant, further extending the duration of nutrient release for said plant and limiting the amount of waste in the soil.

[0060] The invention also relates to a method for manufacturing coated fertilizer granules, said coated fertilizer granules comprising: - a heart including fertilizer, - a shell coating the core, the shell comprising phosphorylated cellulose.

[0061] In an optional step of the process, the extraction of non-functionalized cellulose is carried out from the biomass, preferably from Alfa fibers.

[0062] According to this embodiment, the extraction of cellulose from Alfa fibers may comprise a first step (El) of grinding, drying in the open air and then rinsing the plant material from the Alfa fibers, so as to eliminate the soluble constituents and impurities.

[0063] According to this same embodiment, the extraction of cellulose from the Alfa fibers comprises a second step (E2) of treating the Alfa fibers from step (E1) with an aqueous solution comprising sodium hydroxide or potassium hydroxide so as to obtain a solid cellulosic residue without lignin and without hemicellulose. The solution comprising sodium hydroxide or potassium hydroxide preferably has a sodium hydroxide or potassium hydroxide concentration of between 0.5 M and 2 M. The treatment of the Alfa fibers with the aqueous solution comprising sodium hydroxide or potassium hydroxide can be carried out in a stirred reactor at a temperature of between 60°C and 80°C, for a duration of between 1.5 h and 2.5 h. Preferably, said treatment is repeated several times, for example three times.Sodium hydroxide or potassium hydroxide can partially remove non-cellulose compounds such as lignin and hemicellulose. Repeating the treatment with sodium hydroxide or potassium hydroxide advantageously removes a maximum of lignin and hemicellulose.

[0064] Finally, the extraction of cellulose from Alfa fibers comprises a third step (E3) of treating the solid cellulosic residue without lignin and hemicellulose from step (E2) with a bleaching agent. For example, a mixture comprising sodium chlorite at a mass concentration of between 0.8 and 2%, preferably at a concentration of 1.7%, in an acetate buffer may be used. The acetate buffer ensures total solubility of the pigments present in the solid residue from step (E2). For example, the acetate buffer may be prepared by diluting 75 mL of glacial acetic acid and 27 g of sodium hydroxide NaOH in 1 L of distilled water.The solid residue may be added to the sodium chlorite - acetate mixture at a solid / liquid ratio preferably between 0.5 / 20 (g / mL) and 1.5 / 20 (g / mL), preferably a solid / liquid ratio of 1 / 20 (g / mL) for a period of between 1.5 and 2.5 hours, preferably a period of 2 hours, at a temperature which may be between 75°C and 90°C, preferably at a temperature of 80°C. This treatment may be repeated several times, for example three times. Alternatively, hydrogen peroxide may be used as a bleaching agent. Such a treatment makes it possible to obtain pure cellulose.

[0065] Alternatively, the cellulose used in the rest of the process comes from wood, hemp, coconut fiber, bagasse, wheat straw, corn straw, tomato plant residues, juncus and / or other cellulose-rich biomass. Alfa fibers have the advantage of being very available in Morocco.

[0066] In a step (a) of the process, the phosphorylation of the cellulose is carried out so as to obtain phosphorylated cellulose.

[0067] Preferably, the phosphorylation of the cellulose is carried out so as to obtain a phosphorylation rate of said cellulose of between 4860 mmol / kg of cellulose and 6200 mmol / kg of cellulose.

[0068] According to a particular embodiment of step (a) of phosphorylation of the cellulose, it is possible to mix in a step (al) cellulose, for example cellulose extracted from Alfa fibers, with urea and diammonium diphosphate.

[0069] By way of example, the mixture (a1) is implemented in a stirred reactor at a temperature which may be between 25°C and 35°C for a period of between 6 h and 12 h. A mixing period of between 6 h and 12 h advantageously allows the cellulose fibers to swell well and thus facilitate the subsequent phosphorylation reaction. By way of further example, the urea, diammonium phosphate and cellulose are mixed in a mass ratio of 1:1:1 in distilled water at a mass concentration which may be between 10 and 20%.

[0070] Then, in a step (a2), the mixture is dried for a period of between 6 h and 14 h at a temperature of between 50°C and 60°C, for example overnight, so as to obtain a cellulose paste and remove the water.

[0071] In a step (a3), the phosphorylation reaction of the cellulose pulp resulting from step (a2) is carried out, so as to obtain a phosphorylated cellulose pulp. For this purpose, the cellulose pulp can be heated to a temperature of between 135°C and 160°C for a period of time which can be between 55 min and 65 min.

[0072] Then, in a step (a4), the sample of phosphorylated cellulose pulp obtained at the end of step (a3) ​​is dispersed in a 2% fiber suspension and stirred for a period which may be between 8 and 10, for example overnight, after adjusting the pH to a value between 9 and 11, for example to a value of 10 using a base. For example, the pH can be adjusted using a NaOH solution (1 M). Step (a4) advantageously makes it suitable for the disintegration process.

[0073] Finally, in a step (a5) the phosphorylated cellulose pulp is treated using a high-pressure microfluidizer (the pressure is preferably set between 8E6 Pa and 1E7 Pa (between 80 and 100 bar) which allows the defibrillation of cellulose pulp, so as to obtain the phosphorylated cellulose in the form of a viscous gel of phosphorylated cellulose.

[0074] In a step (b) of the process, granules of the fertilizer that it is desired to coat with the phosphorylated cellulose are dried. Said fertilizer may comprise phosphorus, nitrogen and / or potassium. The fertilizer is for example TSP, NPK, DAP and / or MAP. The granules of said fertilizer have a diameter that can be between 2 mm and 3.5 mm.

[0075] The drying of the fertilizer granules can be carried out at a temperature between 80°C and 100°C for a period of between 20 min and 30 min, at atmospheric pressure in a rotating drum. Alternatively, the drying of the fertilizer granules can be carried out in an oven.

[0076] In a step (c) of the process, the fertilizer granules dried in step (b) are coated with phosphorylated cellulose from step (a), so as to obtain fertilizer granules coated with a shell comprising said phosphorylated cellulose. For example, the phosphorylated cellulose is in the form of a viscous gel of phosphorylated cellulose. The coating step (c) is preferably carried out so that the thickness of said shell is between 18 μm and 34 μm.

[0077] According to a particular embodiment of step (c) of coating the dried fertilizer granules, an aqueous solution of the phosphorylated cellulose is prepared in a step (cl) so as to obtain a coating solution whose concentration is preferably between 0.3% and 0.5%. Such a concentration range advantageously makes it possible to facilitate spraying during the subsequent coating step. Such a solution is for example obtained by diluting a viscous phosphorylated cellulose gel prepared as described in steps (al) to (a5).

[0078] According to a particular embodiment of the invention, the coating solution only comprises phosphorylated cellulose.

[0079] Preferably, the viscosity of the coating solution is between 0.05 Pa.s and 0.1 Pa.s in order to guarantee good spraying of said coating solution during the subsequent coating step, said viscosity being measured by a hybrid rheometer (Discovery HR-2, TA instrument, USA). Such a viscosity range corresponds to a concentration of phosphorylated cellulose in the coating solution of between 0.20% and 0.50% when the coating solution comprises only phosphorylated cellulose.

[0080] Then, in a step (c2), the dried fertilizer granules are rotated in a drum. The rotation speed of the drum is preferably between 6 rpm (rotations per minute, or revolutions per minute) and 8 rpm. A drum rotation speed of between 6 rpm and 8 rpm advantageously prevents agglomeration of the granules and promotes good homogenization of the coating.

[0081] Finally, in a step (c3), the coating solution is sprayed onto the fertilizer granules rotating in the drum, the spraying pressure being between 30000 Pa and 200000 Pa (between 0.3 bar and 2.0 bar).

[0082] In a final step (d) of the process for manufacturing coated fertilizer granules according to the invention, the coated fertilizer granules from step (c) are dried. coating. The step of drying the coated fertilizer granules (d) can, for example, be carried out at a temperature between 80 and 100°C for a period of between 30 and 40 min in a rotating drum at atmospheric pressure.

[0083] Optionally, the method may comprise additional steps (e) and (f) where (e) is a coating step and (f) a drying step, steps (e) and (f) being able to be carried out before or after steps (c) and (d) previously described, so that the coated fertilizer granule resulting from said manufacturing method comprises two shells.

[0084] For example, step (e) comprises forming a coating solution comprising the phosphorylated cellulose, rotating the fertilizer granules from step (b) or step (d) in a drum, and spraying the coating solution comprising the phosphorylated cellulose, such that the coated fertilizer granule comprises two shells of phosphorylated cellulose. Example

[0085] Extraction of cellulose from Alfa fibers

[0086] In a step (E1), the plant material from the Alfa fibers is coarsely ground, air-dried and treated in water. Then, in a step (E2), these fibers are treated three times with an aqueous solution of NaOH (4%) at 80°C for 2 hours. In a step (E3), the solid residue obtained in step (E2) is bleached using a mixture comprising sodium chlorite at 1.7% by mass in an acetate buffer, the acetate buffer being composed of 75 mL of glacial acetic acid and 27 g of NaOH diluted in 1 L of distilled water. Residue and mixture are introduced according to a fiber / liquid ratio of 1 / 20 (g / mL). The product obtained is bleached cellulose.

[0087] fa) Phosphorylation of cellulose extracted from Alfa fibers

[0088] In a step (al), the cellulose extracted from the Alfa fibers of the previous step is soaked in a mixture of urea, diammonium phosphate (DAP) and distilled water, the mass ratio cellulose:urea:DAP being 1:1:1. In a step (a2), the obtained cellulose pulp is dried overnight at a temperature between 50 °C and 60 °C. After complete drying, the phosphorylation reaction is carried out in a vacuum oven at 150 °C for 1 hour in a step (a3). Finally, in a step (a4), the obtained phosphorylated cellulose pulp is transformed into a viscous gel via mechanical treatment using a high-pressure microfluidizer (between 1200 psi and 1400 psi).

[0089] (b) Drying the fertilizer granules to be coated

[0090] In a step (b), the drying of the fertilizer granules that it is desired to coat is carried out in a rotating drum at a temperature of 100°C.

[0091] (c) coating the previously dried fertilizer granules

[0092] In a step (cl), a coating solution is prepared from the cellulose gel. phosphorylated (PCG) at a concentration of 0.5%. In step (c2), the dried fertilizer granules are rotated in a drum at a rotation speed of 8 rpm. In step (c3), the coating solution is sprayed onto the fertilizer granules rotating in the drum with a spray pressure of 200000+10000 Pa (2 ±0.1 bar). (d) drying of coated fertilizer granules

[0093] In a final step (d), the coated fertilizer granules from step (c) are dried at a temperature of 100°C for 30 min, at atmospheric pressure.

[0094] Column leaching of previously prepared coated fertilizer granules

[0095] The column leaching technique was used to determine the leached phosphorus rate as a function of time for coated and uncoated fertilizers. The PVC columns were equipped with a brass cycle valve and connected to a Tygon™ type flexible tube at the bottom to drain the water. Irrigation water under gravity drainage is collected at the lower end of each column in a container. Dry, sieved soil (200 g) was packed into the columns and then distilled water was added to moisten the soil to saturation. 2.5 g of coated and uncoated fertilizers were placed on the top surface of the soil and covered by an additional 50 g of soil as a top layer. The soil / fertilizer mixture was leached 3 times during the first week, followed by discontinuous leaching every 5 days for 3 months of incubation.The leaching solutions were collected for phosphorus content analysis using the Ammonium-Molybdate colorimetric method (AFNOR-T90-023). A control experiment (soil without fertilizer) was carried out and all tests were duplicated, and the average values ​​were considered. Results .

[0096] Analysis of the phosphorylated cellulose from step (a)

[0097] Conductometric titration was carried out to measure the charge content of the grafted phosphate groups. [Fig.2] represents the conductivity o measured as a function of the volume VNa0H of NaOH solution (0.05 M) poured. NaOH neutralizes the acid phosphate functions. This allows the charge content to be calculated, which is of the order of 5200 mmol / kg.

[0098] The IR spectrum of phosphorylated cellulose, shown in [Fig.3], reveals the appearance of peaks (compared to the FTIR spectra of cellulose microfibers) at around 1234 cm1, 902 cm 1 and 817 cm1, which are attributed to the P=O, P-OH and POC stretching vibrations, respectively. Therefore, the presence of these new bonds indicates that the phosphate groups have indeed been grafted to the molecular skeleton of cellulose.

[0099] Analysis of phosphorylated cellulose coated fertilizer granules from step (d)

[0100] Morphology of the surface of the coated granules High magnification SEM images shown in Figures 4A-4D show that the surface of uncoated granules is very rough and porous (see [Fig.4A]). However, after PCG coating, the surface becomes smoother and the pores disappear (see [Fig.4C]). Good coating adhesion to the granule surface can also be clearly observed ([Fig.4D]), probably due to their high chemical affinity with phosphate fertilizers.

[0101] Coating thickness The coating thickness of the fertilizer granules was determined from the SEM images of the cross-sections shown in [Fig.4D]. Ten measurements were considered giving an average thickness equal to 21+3 pm.

[0102] Elemental composition of the surface of the coated granule Analysis of the elemental composition of uncoated TSP fertilizer by X-ray microanalysis (EDAX) showed that it is composed mainly of phosphorus and calcium from its chemical structure (Ca(H2PO4)2). Once coated with PCG phosphorylated cellulose, carbon and oxygen were detected on the surface, indicating the deposition of an organic polymer layer. Phosphorus is also detected in the surface of PCG-TSP phosphorylated cellulose coated granules, which is normal since PCG phosphorylated cellulose contains phosphorus from the phosphorylation process.

[0103] Compressive strength The compressive strength of uncoated fertilizer, which was estimated to be 44.4 ± 3.98 N, was significantly increased after coating with phosphorylated cellulose (see [Fig.5]) and reached 59.14 ± 3.61 N.

[0104] Study of the slow release of phosphorus into the soil from coated fertilizer granules from step (d) by column leaching

[0105] In [Fig.6] is represented the rate of phosphorus released (in %) by the phosphorylated cellulose-coated PCG-TSP fertilizer granules (in black) in comparison with the rate of phosphorus released by the uncoated TSP granules (in gray) as a function of the number of days N. Said release curves show an interesting reduction in phosphorus leaching after coating the fertilizer granules with PCG. While the leached phosphate rate from the uncoated TSP fertilizer granules reaches 41.7% in the first week, and almost all of the phosphate from the said uncoated fertilizer granules is leached after 40 days of incubation, the phosphate release rate from the coated PCG-TSP fertilizer granules is about 20% after 40 days and at the end of the incubation period (3 months) it is only 40%.

[0106] Effect of coated fertilizer on soil water retention capacity

[0107] [Fig.7] compares the evolution of water retention R (H2O) measured as a function of the number of days N of a soil without fertilizer (S, in gray) and a soil comprising fertilizer granules coated with phosphorylated cellulose PCG-TSP (S / PCG-TSP, in black). A mixture of coated fertilizer (1g) with soil (100g) was placed in plastic cups and then saturated by adding water (50 mL). The water retention capacity of the soil was significantly improved by the presence of the coated fertilizer, which could be due to the water absorption capacity of phosphorylated cellulose due to its hydrophilic nature.

Claims

Claims

1. Coated fertilizer granule (1) comprising: - a core (10) comprising a fertilizer, - a shell (11,12) coating the core, the shell (11,12) comprising phosphorylated cellulose.

2. A coated fertilizer granule (1) according to claim 1, wherein the diameter of the core (10) is between 2.0 mm and 3.5 mm and the thickness of the shell (11,12) is between 18+5 pm and 34+5 pm.

3. Coated fertilizer granule (1) according to one of claims 1 or 2, comprising, in mass percentage, between 2% and 3% of phosphorylated cellulose.

4. Coated fertilizer granule (1) according to one of claims 1 to 3, wherein the phosphorylation rate of the phosphorylated cellulose included in the shell (11, 12) is between 4860 mmol per kilogram of cellulose and 6200 mmol per kilogram of cellulose.

5. Coated fertilizer granule (1) according to one of claims 1 to 4, wherein the shell (11, 12) coating the core does not comprise any additives other than phosphorylated cellulose and / or said granule comprises a single shell (11) coating the core (10).

6. A coated fertilizer granule (1) according to one of claims 1 to 5, wherein the fertilizer comprised in the core (10) comprises phosphorus, nitrogen and / or potassium.

7. Coated fertilizer granule (1) according to one of claims 1 to 6, having a compressive strength of between 44 + 3.98 N and 62.75 + 7.65 N.

8. A method of manufacturing coated fertilizer granules comprising the following steps: (a) phosphorylation of cellulose so as to obtain phosphorylated cellulose, (b) drying fertilizer granules, (c) coating the dried fertilizer granules with the phosphorylated cellulose, (d) drying the coated fertilizer granules.

9. A method of manufacturing coated fertilizer granules according to claim 8, further comprising a step of extracting cellulose from the biomass, said extraction step being carried out pre- possibly in step (a) of phosphorylation of the cellulose thus extracted.

10. A method of manufacturing coated fertilizer granules according to claim 9, wherein the biomass comprises Alfa fibers and the step of extracting cellulose from Alfa fibers comprises the following sub-steps: (E1) grinding, air drying and then rinsing the Alfa fibers, (E2) treating the Alfa fibers with an aqueous solution comprising sodium hydroxide or potassium hydroxide so as to obtain a solid cellulosic residue without lignin and hemicellulose, (E3) treating the solid cellulosic residue without lignin and hemicellulose with a bleaching agent, so as to obtain pure cellulose.

11. The method of claim 10, wherein the bleaching agent comprises sodium chlorite, glacial acetic acid and sodium hydroxide.

12. A method of manufacturing coated fertilizer granules according to one of claims 8 to 11, wherein step (a) of phosphorylation of the cellulose comprises the following sub-steps: (a1) mixing the cellulose with urea and diammonium phosphate in a mass ratio of 1:1:1 in distilled water at a mass concentration of between 10 and 20% at a temperature of between 25°C and 35°C for a period of between 6 h and 12 h.(a2) drying the mixture at a temperature between 50°C and 60°C for a period between 6 h and 14 h so as to obtain a cellulose pulp, (a3) ​​heating the cellulose pulp at a temperature between 135°C and 160°C for a period between 55 min and 65 min, so as to carry out the phosphorylation reaction of the cellulose pulp and to obtain a phosphorylated cellulose pulp, (a4) dispersing the phosphorylated cellulose pulp in a suspension of fibers at a mass concentration between 1.5 and 2.25% in water and at a pH between 9 and 11, for a period between 8 and 10 hours. (a4) treating the phosphorylated cellulose pulp using a high-pressure micro-fluidizer.

13. A method of manufacturing coated fertilizer granules according to one of claims 8 to 12, wherein the step of drying the granules of fertilizer (b) is carried out in a rotating drum at a temperature between 80°C and 100°C for a period of between 20 min and 30 min at atmospheric pressure.

14. A method of manufacturing coated fertilizer granules according to one of claims 8 to 13, wherein the step of coating the dried fertilizer granules with the phosphorylated cellulose (c) comprises the following substeps: (c1) preparing an aqueous solution of the phosphorylated cellulose so as to obtain a coating solution, (c2) rotating the dried fertilizer granules in a drum, (c3) spraying the coating solution onto the fertilizer granules rotating in the drum.

15. A method of manufacturing coated fertilizer granules according to claim 14, wherein the viscosity of the coating solution is between 0.05 Pa.s and 0.1 Pa.s and / or wherein the phosphorylated cellulose concentration of the coating solution is between 0.20% and 0.50%.

16. A method of manufacturing coated fertilizer granules according to one of claims 14 or 15, wherein the rotational speed of the drum is between 6 rpm and 8 rpm, and / or the spraying pressure is between 30000 Pa and 200000 Pa (between 0.3 bar and 2.0 bar).

17. A method of manufacturing coated fertilizer granules according to one of claims 8 to 16, wherein the step of drying the coated fertilizer granules (d) is carried out at a temperature of between 80°C and 100°C at atmospheric pressure for a period of between 30 and 40 min, in a rotating drum.

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