阅读说明：本技术 肥料涂覆方法 (Fertilizer coating method ) 是由 J·A·塞亚 J·T·小珀塞尔 S·M·布鲁克斯 L·罗伯逊二世 S·D·桑德斯 A·Z· 于 2019-06-04 设计创作，主要内容包括：本发明公开了一种用涂料涂覆肥料颗粒的方法,所述方法包括在涂覆单元中提供肥料颗粒,通过向所述涂覆单元中的所述肥料颗粒施加一种或多种涂料组分来施加涂层的一个或多个步骤,以及至少部分地固化或硬化所述涂层,其中所述固化或硬化涉及所述一种或多种涂料组分的化学反应,任选地在最终固化或硬化步骤之后从所述涂覆单元排出所涂覆的肥料颗粒,其中所述涂覆单元包括固定框架和至少两个能够移动的元件。(The present invention discloses a method for coating fertilizer granules with a coating, said method comprising one or more steps of providing fertilizer granules in a coating unit, applying a coating by applying one or more coating components to said fertilizer granules in said coating unit, and at least partially curing or hardening said coating, wherein said curing or hardening involves a chemical reaction of said one or more coating components, optionally discharging the coated fertilizer granules from said coating unit after a final curing or hardening step, wherein said coating unit comprises a stationary frame and at least two movable elements.)

1. A method of coating a fertilizer granule with a coating, wherein the method comprises:

a) the fertilizer granules are provided in a coating unit,

b) a step of applying a coating, the step comprising:

-applying one or more coating components to the fertilizer granules in the coating unit to provide coated fertilizer granules comprising a coating and the fertilizer granules,

-and at least partially curing or hardening the coating, wherein the curing or hardening involves a chemical reaction of the one or more coating components,

wherein step b) is carried out one or more times to provide coated fertilizer granules, and

c) discharging the coated fertilizer granules from the coating unit, or performing a final curing or hardening of the coated fertilizer granules in the coating unit and subsequently releasing the fertilizer granules from the coating unit, wherein the discharged fertilizer granules comprise the coating material,

wherein the coating material comprises a polymer, wherein the polymer is a polymer,

wherein the coating unit comprises a stationary frame and at least two movable elements, wherein the movable elements are independently movable with respect to the frame, and wherein the method comprises moving the at least two movable elements with respect to the frame during at least step b).

2. The method of claim 1, wherein a first of the movable elements is a container having walls and an inner space for containing fertilizer granules, wherein the method comprises rotating the container in a rotational motion around an axis of rotation while the container holds the fertilizer granules during at least step b).

3. The method according to claim 2, wherein a second of the movable elements is an agitation member arranged in the inner space of the container, and wherein the method comprises moving the agitation member while rotating the container during at least step b).

4. The method of claim 3, wherein the stirring member is a rotor, and wherein the method comprises rotating the rotor about a rotational axis of the rotor while rotating the vessel during at least step b).

5. The method of claim 4, wherein the rotational axis of the rotor and the rotational axis of the container are parallel to each other or have an included angle of less than 30 ° with each other, and wherein the rotational axis of the rotor and the rotational axis of the container are spaced apart from each other such that the rotor is eccentrically mounted in the interior space of the container.

6. The method of claim 5, wherein the rotor comprises a shaft and one or more vanes, wherein the shaft has a first end and a second end, wherein the first end is disposed in the interior space of the vessel, and wherein the second end is connected to an actuator, wherein the vanes are connected to the shaft and extend from the shaft in a direction perpendicular to a length of the shaft in the interior space of the vessel.

7. The method according to any one of claims 2 to 6, wherein the axis of rotation of the container is inclined with respect to a vertical axis, wherein the vertical axis is defined with respect to gravity.

8. The method according to any one of claims 2 to 7, wherein the container has a bottom and a wall, wherein the coating unit further comprises a scraper which is fixed relative to the frame during at least step b), wherein the scraper is arranged to scrape material off the wall and/or the bottom of the container.

9. The method of any preceding claim, wherein the coating of the ejected particles comprises a crosslinked polymer or a thermoset polymer.

10. The method according to claim 9, wherein in step b) a coating is applied in an amount of 0.50 to 4.0 wt. -%, based on the weight of the fertilizer granule to be coated without coating, and wherein step b) is performed within 10 to 600 seconds, preferably within 30 to 240 seconds,

and wherein said final curing of step c), if performed, is performed within 60 seconds to 15 minutes.

11. The method according to any one of the preceding claims, wherein steps a) and b) are performed at a temperature of at least 50 ℃ and wherein step c) comprises cooling the discharged particles from the temperature of at least 50 ℃ to a lower temperature.

12. The method of any one of claims 9 to 11, wherein the coating is a polyurethane coating, and wherein the coating component comprises a polyisocyanate component and a polyol.

13. The method of claim 4 or claim 5 or 6, wherein the coating is a polyurethane coating, and wherein step b) subsequently comprises:

B1) injecting a polyol into the bed of fertilizer granules within the container,

B2) mixing the polyol with the fertilizer granule for 5 to 120 seconds

B3) Injecting a polyisocyanate component into the bed of fertilizer granules within the container,

B4) rolling the fertilizer granules in the container for at least 10 to 300 seconds, thereby reacting the polyol and the polyisocyanate component with each other while the rotor is also rotating,

B5) injecting liquid wax into the fertilizer bed,

and optionally repeating said steps B1 to B5,

B6) optionally rolling the fertilizer in the container for at least 10 seconds, allowing the coating to further cure.

14. The method of any preceding claim, wherein the coating comprises a water-insoluble polymer.

15. A urea refining plant comprising:

a urea refining unit, such as a granulation unit or a prilling tower, wherein the urea refining unit has an inlet for a urea melt and an outlet for warm urea granules,

-a coating unit having an inlet connected to the outlet for warmed urea granules, the coating unit comprising a stationary frame and at least two movable elements, wherein the movable elements are independently movable with respect to the frame,

wherein a first of said movable elements is a container having walls and an inner space for containing fertilizer granules to be coated,

wherein a second of the movable elements is a stirring member arranged in the inner space of the container,

wherein the coating unit further comprises an outlet for coated urea particles,

-and a cooling unit having an inlet connected to the outlet for coated urea particles and further having an outlet for cooled coated urea particles, and preferably further having an inlet for cooling air and an outlet for exhaust gases.

Technical Field

The present invention relates to a method of coating granules, and in particular to a method of coating fertilizer granules.

Background

Many fertilizers are used as granular materials and are water soluble, such as, for example, urea-containing fertilizers. Controlled release fertilizers can be used to provide sustained release of the fertilizer from the granule. Sustained release can help to make more efficient use of the fertilizer. Such fertilizers can be made, for example, by applying a coating to the fertilizer granules. For example, US 2014/0033779 describes a method of coating a substrate, wherein a substrate material and a coating material are mixed and the coated mixture is cured in a separate reactor. The US 779 patent also mentions that the process of producing controlled release fertilizers using a single drum or reactor (i.e. batch processing) is functional and common, but is associated with several problems, such as the risk of producing lumps or balls of coated material.

US 5538531 describes a process for preparing a controlled release granular fertilizer which involves heating fertilizer granules, stirring the granules so that gentle mixing is maintained, adding a polyol, adding a polyisocyanate after the polyol component is spread evenly, reacting the components, and adding a wax.

Furthermore, existing fertilizer coating methods are relatively expensive, especially because the coating step adds a separate processing step to the production of the fertilizer. The coating step usually requires a long processing time and therefore involves large equipment, which results in high capital and operating costs. Although higher prices are acceptable for special coatings and horticulture, low cost is important for field crops such as corn (maize).

Thus, there is a need for a method for coating granules, in particular fertilizer granules. In particular, there is a need for a method of coating fertilizers at a competitive price to produce controlled release fertilizers suitable for effective fertilization of field commodity crops.

In one aspect, the object of the present invention is to provide a coating method that at least partially solves the above mentioned problems and desires.

Disclosure of Invention

In a first aspect, the present invention relates to a method of coating a fertilizer granule with a coating, wherein the method comprises:

a) the fertilizer granules are provided in a coating unit,

b) a step of applying a coating (step b), said step comprising:

applying one or more coating components to the fertilizer granules in a coating unit to provide coated fertilizer granules comprising a coating and the fertilizer granules,

and at least partially curing or hardening the coating, wherein said curing or hardening involves a chemical reaction of said one or more coating components,

wherein step b) is carried out one or more times to provide coated fertilizer granules, and

c) discharging the coated fertilizer granules from the coating unit, or performing a final curing or hardening of the coated fertilizer granules in the coating unit and subsequently releasing the fertilizer granules from the coating unit, wherein the discharged fertilizer granules comprise the coating material, wherein the coating material preferably comprises a water-insoluble polymer,

wherein the coating unit comprises a stationary frame and at least two movable elements, wherein the movable elements are independently movable with respect to the frame, and wherein the method comprises moving the at least two movable elements with respect to the frame during at least step b).

Drawings

Fig. 1 schematically shows an example coating unit that can be used in the method of the invention.

Fig. 2 shows experimentally obtained urea release rates of fertilizer granules prepared with the method according to the invention, wherein the coating compositions have different time values of reactivity.

Figure 3 shows the urea release time profiles obtained experimentally for two fertilizers coated according to the method of the invention and for two fertilizers coated with a drum coater according to the comparative method.

Detailed Description

The present invention broadly provides the judicious insight of combining a short residence time in a coating unit in which the particles to be coated are kept in motion with a coating unit comprising two movable elements, and preferably also with a coating composition having a short curing or hardening time.

The invention provides a method involving carrying out a chemical reaction of the one or more coating components in the coating unit while keeping the particles in motion in order to at least partially cure or harden the coating. Advantageously, this allows a high throughput and fast coating process without agglomerating the fertilizer granules and without forming solid deposits in the coating unit.

The present invention relates to a method of coating fertilizer granules. These fertilizer granules may also be referred to as granular fertilizers. The particles to be coated and/or the particles after coating have a particle size of, for example, 0.10mm to 20mm, such as 0.5mm to 15mm or 1.5mm to 5 mm. The particles may, for example, have a weight average particle size within this range, or, for example, wherein at least 90% by weight of the particles have a particle size within this range, wherein the size of the particles refers to, for example, the smallest size. These granules are, for example, granular or granulated fertilizers, or granulated, pastilled or compacted fertilizer materials. Optionally, the method comprises a step of solidifying the liquid fertilizer mass into fertilizer granules to be coated, such as with a prilling tower, a granulation unit (e.g. with a spouted bed or a fluidized bed), or with a granulator, especially if the fertilizer is a urea fertilizer or a urea-containing fertilizer. Preferably, in this solidification step, the melt (such as a urea melt) is cooled, for example using cooling air. Preferably, the particles are maintained at a temperature above 50 ℃ or above 60 ℃ between the solidifying step and the coating step.

The granules to be coated comprise (or consist of) a fertiliser material. The fertilizer material is, for example, a nitrogen fertilizer material and comprises nitrogen (on an N atom basis) in an amount of, for example, at least 10 wt.%, at least 20 wt.%, or at least 30 wt.%. The fertilizer material may for example comprise urea and/or ammonium salts, such as ammonium sulphate and ammonium nitrate, and comprise for example less than 10 wt% or less than 5 wt% of components other than urea and ammonium salts. Preferably, the fertilizer material comprises urea, such as at least 50 wt% urea, and preferably a urea fertilizer having at least 40 wt% N or at least 46 wt% N. The fertilizer material may also comprise K (potassium), Ca (calcium), P (phosphorus) and/or S (sulphur) (based on elemental composition), for example as sulphate and/or phosphate salts, optionally in combination with N, for example as urea and/or ammonia. The fertilizer material is typically water soluble such that when the fertilizer granules are applied to the ground, the fertilizer elements (such as N, P and S, K, Ca) are provided to the crop as dissolved material, and optionally in addition Zn and/or other micronutrients.

The method of the present invention involves coating fertilizer granules with a coating. Thus, the coated particles (as obtained after the coating process) comprise fertilizer particles and an outer layer of a coating substance partially or completely covering the fertilizer particles.

The coating provides for controlled release of, for example, a fertilizer material, especially when the fertilizer is applied to the ground (in the soil) and in contact with water. The coating may also provide slow release of the fertilizer material. In such embodiments, the fertilizer material is released from the particle, for example, by hydrolysis, by biodegradation, or by limited solubility, or by a combination thereof. Fertilizer material release refers to the release of nutrients available to the plant.

The coating preferably comprises a polymer, and more preferably a water insoluble polymer. The polymer has a solubility of less than 0.10g/L in deionized water, for example, at 100kPa and 20 ℃. Braun et al, "Practical Macromolecular Organic Chemistry" (CRC Press, 1984, page 73) that is insoluble in deionized water, for example, at 20 ℃, are used, wherein a sample of 30mg to 50mg of a finely divided polymer is placed in a small test tube with 1mL of liquid and allowed to stand for several hours.

The coating substance is, for example, water impermeable or semi-permeable. Preferably, the coating material protects the fertilizer inside the coating from the soil processes until released.

In some embodiments, water and solutes can permeate through the coating by diffusion. The time required for diffusion may provide a desired release rate of fertilizer nutrients from the coated particles into the soil. In this way, the coating can provide controlled release.

In some embodiments, the coating material is semi-permeable (e.g., water permeable but not permeable to a fertilizer material such as urea) and when applied to the ground, water enters through the coating due to permeation, causing the fertilizer material core to swell. This can lead to cracking of the coating and/or movement of the fertilizer material through the pores in the coating. In this way, a sustained and/or delayed release of the coating substance can be achieved.

The coating material amounts to, for example, at least 0.0010 wt.%, such as 0.10 wt.% to 10 wt.%, based on the total particle weight, and/or each coating layer is, for example, 0.2 wt.% to 5 wt.%, or 0.3 wt.% to 3.0 wt.%, or 0.3 wt.% to 1.5 wt.%, or 0.5 wt.% to 1.2 wt.%, such as 1.0 wt.% to 3 wt.% each coating layer. The total coating and/or the coating thickness of each coating is for example in the range of 1.0 μm to 50 μm, but other thicknesses are also possible.

The coating substance present in the coated granules is, for example, a polymer, and the coating composition applied to the fertilizer granules during the coating process is, for example, a resin.

Preferably, the coating of the particles released from the coating unit comprises a polymer. Preferably, the polymer is crosslinked. Preferably, the polymer is thermosetting, or thermoplastic.

The method involves providing fertilizer granules in a coating unit, e.g. feeding the granules into the coating unit, in particular into a rotating container. The coating unit is configured to receive fertilizer granules to be coated. The coating unit comprises, for example, a container for receiving and holding fertilizer granules. Such a container preferably has walls and an interior space, wherein the interior space is capable of receiving fertilizer granules.

The method may include screening the fertilizer granules to a desired size range prior to introducing the fertilizer granules into the coating unit.

The method may further comprise preheating the fertilizer particles prior to their introduction into the coating unit, such as to a temperature of at least 30 ℃, at least 40 ℃, at least 50 ℃ or at least 60 ℃ above ambient temperature, and/or to a temperature of at least 5 ℃, at least 10 ℃ or at least 20 ℃ above ambient temperature, and typically to a temperature of less than 100 ℃ or less than 80 ℃.

The method includes the step of applying a coating. This step may be performed one or more times to provide coated fertilizer granules having one or more coatings.

The step of applying the coating involves providing the fertilizer granule with the coating. This step includes applying one or more coating components to the fertilizer granules while the granules are in the coating unit. Further, other compounds such as solvents may be applied to the fertilizer particles during such steps of applying the coating, but in preferred embodiments no solvent is used. The method may also involve an additional step of applying an additional coating to the particles, such as a step in which a wax layer is applied. In a given step of applying the coating, the coating components and optional further compounds may be applied, for example simultaneously or subsequently. For example, at least two coating components are subsequently applied, such as stepwise, wherein the coating components have different compositions. Each coating component may also be a mixture of compounds. These coating components are typically applied as liquids (which may include, for example, emulsions, solutions and dispersions, and polymer melts), for example, by injection, such as by spraying the liquid. In this way, a fertilizer granule comprising a coating and the fertilizer granule as a core is provided. Thus, the applied coating component or components are present as (further) layers on the fertilizer granule.

In a preferred embodiment, at least one or all of the coating components, when applied, has a viscosity of less than 2000 mPa-s or less than 1000 mPa-s at 25 ℃, and typically a viscosity of more than 100 mPa-s at 25 ℃. The viscosity is measured, for example, according to ISO 3219: 1993.

Preferably, the one or more coating components are added to a bed of fertilizer granules, wherein the bed is provided by the movement of a movable element of the coating unit, in particular by a rolling action or by contact of the granules with the granules. Preferably, the bed is a lifted granule bed, wherein the fertilizer granules are lifted by the movement of the movable element. The coating unit is preferably operated such that all the substance in the inner space is kept in constant motion. Preferably, the coating unit is operated such that the airborne particles are continuously moving in a plurality of directions. In some embodiments, in an atmosphere other than air (e.g., an inert atmosphere, such as N)₂) In the middle of coatingAnd (5) carrying out the following steps. For example, the coating unit is operated such that at least some of the particles are "airborne" particles (e.g., airborne particles), and wherein the particles are generally continuously moving in multiple directions. This can help overcome gravitational effects and can offset particle size, shape, and density limitations to achieve uniform mixing of the coating components with the particles in a short mixing cycle.

The fertilizer granules are introduced into the container in an amount of, for example, more than 10 vol-% or more than 20 vol-% or more than 40 vol-% or more than 60 vol-% and/or less than 95 vol-% or less than 90 vol-% or less than 80 vol-%, such as from 60 vol-% to 90 vol-%, preferably from 75 vol-% to 90 vol-%, all volume of the inner space of the container, based on the bulk density of the material of the uncoated fertilizer granules. Volume fraction based on bulk density means the volume fraction of the interior space occupied by the bulk bed of uncoated particles (including void space in the bed). For example, 720kg/m can be used for urea granules or urea-containing granules³To 820kg/m³(e.g., 770 kg/m)³) The bulk density of (c). The filling rate is, for example, more than 10% or more than 20% or more than 30% and/or less than 60% or less than 50% of the volume of the inner space, based on the true density of the fertilizer material (without coating). This packing fraction can help to form an elevated bed during step b) and to facilitate a good distribution of the coating components.

Preferably, the coating component is solvent-free, e.g. comprises less than 5 wt% water, such as less than 1.0 wt% water, and less than 5 wt% or less than 1.0 wt% of an organic solvent, e.g. an organic compound having a boiling point below 120 ℃. Preferably, less than 1.0 wt% water and/or less than 1.0 wt% organic solvent is applied based on the weight of the uncoated fertilizer granule throughout the process. Preferably, the use of water is avoided, as many fertilizers are water soluble. Preferably, organic solvents are avoided to avoid emission risks and to comply with emission standards and other regulations.

Preferably, the coating component comprises less than 40 wt% or less than 20 wt% or less than 10 wt% of components other than reactants for the chemical reaction carried out during step b). Preferably, each coating component comprises more than 50% by weight or more than 80% by weight of reactants for carrying out the chemical reaction of curing or hardening. Preferably, each coating component comprises less than 10 wt% of compounds not contained in the coated fertilizer granule at discharge.

In embodiments where one or more of the coating components comprises or is a polymer, the polymer coating component is preferably applied as a liquid, such as a polymer melt, for example at a temperature sufficiently above the glass transition temperature of the polymer so that the polymer has a sufficiently low viscosity that it can be processed.

The method also involves at least partially curing or hardening the applied one or more coating components. This at least partial curing or hardening is carried out in the coating unit and, for example, ensures that the final coating comprises the preferred water-insoluble coating.

Curing or hardening involves a chemical reaction of the one or more coating components. The chemical reaction is carried out in the coating unit and, more specifically, while at least one of the movable elements is in motion. This chemical reaction, for example, increases the viscosity of the coating. In some embodiments, the chemical reaction involves the formation of a compound having a higher molecular weight than the reactants. The chemical reaction involves, for example, polymerization and/or crosslinking of the polymer.

In case of partial curing or hardening in step b), a final curing or hardening is subsequently performed before and/or after the coated fertilizer granules are discharged from the coating unit. The final curing is carried out, for example, in the coating unit used in step b).

Hardening and curing may include solidifying one or more liquid coating components added to the fertilizer granules into a solid coating substance by chemical reaction of the one or more coating components. In the case of curing, the chemical reaction includes, for example, a crosslinking reaction to give a thermosetting polymer. In the case of hardening, the chemical reaction does not generally involve crosslinking, and the chemical reaction generally produces a thermoplastic polymer. In embodiments where only one coating component is applied, that component may react with itself, for example in a polymerization reaction.

The one or more coating components include, for example, initiators and/or catalysts, such as polymerization initiators (e.g., free radical initiators or cationic initiators) and polymerization catalysts, depending on the reactive cure or hardening.

The coated fertilizer granules and/or the coating substance may comprise additional components. The additional components include, for example, one or more selected from the group consisting of wetting agents, surfactants, biocides, herbicides, insecticides, fungicides, antistatic agents, and micronutrients. The micronutrients are for example selected from the group consisting of Fe, Mn, Zn, Cu, Mo, Ni, Cl, Mg and B.

Such additional components are applied, for example, during the one or more steps of applying the coating, for example, as part of the one or more coating components or as additional components added during step b) and/or step c).

The coating may comprise wax, which is applied, for example, as a layer between coatings that are cured or hardened during step b) and/or as a final layer. The wax is, for example, an olefin wax, more preferably an alpha-olefin wax, such as a hydrocarbon (such as an alkane) having at least 20 or at least 30 carbon atoms, or, for example, having from 20 to 40 carbon atoms. The wax is, for example, a paraffin wax, a vaseline wax or a polyamide wax, and/or is, for example, a microcrystalline wax.

The method further comprises discharging the coated fertilizer granules from the coating unit, optionally after a final curing step or a final hardening step. The final hardening step may, for example, include evaporation or cooling of unreacted monomers, and/or a final hardening chemical reaction step. The optional final curing step may include allowing further reaction of the coating components present in the applied coating. The final curing step may involve crosslinking of the polymer coating material. The discharged fertilizer granules contain the coating material and the coating substance. An optional final hardening step is applied to subject the granules to a discharge condition, in particular the granules are non-tacky, having sufficient mechanical/crush strength for handling, packaging and storage.

The method optionally includes one or more steps after release of the coated fertilizer granules, such as a cooling step, a packaging step, a metering step, and/or a storage step. The cooling step uses, for example, cooling air. The coated fertilizer granules are suspended in cooling air, for example. The packaging step includes, for example, packaging the fertilizer granules in a bag or container. The metering step may involve dividing the coated fertilizer granule stream into quantitative batches, which may be transferred, for example, to a carrier or ship with or without packaging.

The coating process is carried out, for example, in a batch process or in a continuous process. The method is, for example, a batch process, for example, producing multiple coatings, wherein two or more steps of applying the coatings are performed in the same coating unit (e.g., in the same vessel). Also for a batch process, the one or more components may be added continuously, for example, for at least 10 seconds or at least 30 seconds. In one example process, two or more intermittent coating units are operated in parallel, wherein the parallel coating units each perform a different step from each other. In such embodiments, the process is carried out in a so-called batch-continuous or semi-continuous mode. For example, the method may involve filling a first coating unit with fertilizer granules while a second coating unit performs another step of the method than filling. In this way, with two or more coating units in parallel, a continuous feed of fertilizer granules can be processed at any time with at least one of the parallel coating units receiving uncoated fertilizer granules. In such embodiments, the method involves applying the total number of coatings to be applied (such as 1, 2, 3, or more layers) on the fertilizer granules, for example, in a single parallel coating unit.

In an example embodiment, wherein the method is performed as a continuous process, two or more coatings are applied in different coating units as described herein, each coating unit for example having a vessel and a rotor, arranged in series, wherein the method comprises transferring fertilizer granules from a first coating unit for applying a first coating to a second coating unit for applying a second coating. Such a transfer can be performed, for example, with a moving belt, or, for example, the coating units are placed on top of each other and transferred by gravity. The continuous process may involve continuously supplying fertilizer granules to a first coating unit and transferring the fertilizer granules with the coating from the first coating unit to a downstream second coating unit and withdrawing the fertilizer granules with the additional coating from the second coating unit. In further embodiments, the two or more coating units are used in series, wherein different coatings are applied stepwise in different ones of the coating units, and wherein the transferring involves transferring a batch of the coated fertilizer particles at least from a first coating unit to a downstream second coating unit.

The coating unit comprises a fixed frame and at least two movable elements, including a first movable element and a second movable element. The coating unit is capable of receiving fertilizer granules to be (additionally) coated. The movable element is configured to move the fertilizer granules during the coating process. The first movable element and the second movable element are each movable relative to the frame, and are typically movable in an independent manner relative to the frame. The method comprises moving the at least two movable elements relative to the frame during at least step b), preferably while in contact with the fertilizer granules. Preferably, the first and second movable elements are also moved relative to each other. The first and second movable elements move, for example, independently of each other and independently move in a rotational and/or reciprocating motion.

The movement of the movable element may cause the fertilizer granules to move during step b). This may help the added coating component or components mix well with each other and with the fertilizer granules. Moving the movable element may also avoid or prevent the formation of lumps, such as lumps of coating substance and fertilizer particles, during the coating process.

The fixed frame is used for mounting the movable element and, for example, an actuator such as a motor. The stationary frame may comprise a stationary housing.

Preferably, the first movable element comprises or is a container. The container has a wall and an interior space. The wall has, for example, a bottom portion and one or more side portions. The wall may be provided with a closable outlet opening, for example at the bottom, to discharge the coated fertilizer granules. The container is closed, for example at the top, with a cover plate as part of the coating unit. The cover plate may comprise an inlet opening for fertilizer granules and is for example provided with one or more spray nozzles for one or more coating components. The inlet opening may also be provided by an open tube. The open pipe is used, for example, to drip coating components into the particle bed. The inner space is used in a method for containing particles, for example by receiving and holding fertilizer particles in the free space of the inner space. During the method, the container is for example rotated and/or provided with a reciprocating movement, wherein the rotation or reciprocating movement is for example in a horizontal or vertical direction. The method involves rotating the container about an axis of rotation, for example, while the container holds fertilizer granules, in particular, within the interior space. Preferably, at least step b) is performed during said rotation. The rotation of the container provides for example a rolling of the fertilizer granules during step b). Preferably, the particles continue to remain in motion in the vessel (such as by rotating the vessel) until discharged.

The container is, for example, cylindrical and is, for example, a disc. The container has, for example, a circular cross-section in a plane perpendicular to the axis of rotation. The container is connected to a first actuator, such as a motor, for example. The first actuator is, for example, disposed in the frame and configured to move the container relative to the frame.

The coating unit may also comprise a doctor blade, which may be fixed with respect to the frame, for example, or may remain fixed with respect to the frame, for example, while the container is rotated. The scraper may be used to scrape solid matter from a rotating container wall. The scraper may also assist in agitating the particles during operation. The scraper is arranged near the container wall and/or the container bottom (e.g. a gap of 1 to 10mm, such as a gap of 1 to 5mm) and preferably on a preferably inclined upper side of the container. The scraper is movable relative to the vessel wall. In a preferred embodiment, the container has a bottom and side walls, wherein the coating unit further comprises a scraper which is fixed relative to the frame during at least step b), wherein the scraper is arranged for scraping off material from the side walls and/or from the bottom of the container.

In a preferred embodiment, the second movable element is or comprises a stirring member. The stirring element is arranged in the interior space of the container and is configured, for example, for rotating and/or reciprocating movement in the interior space. The method preferably comprises moving the stirring member continuously during at least step b) and while rotating the container and more preferably during step b). In this way, the stirring member is in contact with the fertilizer granules during step b) when the granules are provided with the one or more coating components. The stirring member is, for example, a mixing tool. The movement of the agitating member may assist in the mixing of the particles and/or help avoid the formation of agglomerates. In some embodiments, the stirring member is, for example, arranged to keep a substantial portion (e.g., more than 30% by number) or a majority of the particles suspended in air (not in contact with the container) at any given time during step b). During step b), the individual particles bounce, for example, to and from the container wall and the stirring member.

The stirring member is for example connected to an actuator, such as a second actuator provided in the frame for moving the stirring member relative to the frame, wherein the movement may be a rotation. The speed and movement of the stirring member can preferably be controlled independently of the speed and movement of the container.

More preferably, the stirring member is a rotor. The rotor includes, for example, a shaft and one or more blades. The blade may be configured as a paddle. The vanes or blades are preferably evenly spaced angularly about the shaft. The method comprises rotating the rotor about the axis of rotation of the rotor while rotating the container, for example during at least step b). One container may be provided with one or more rotors. The rotor preferably rotates about an axis. The axis of rotation of the rotor is, for example, substantially parallel (including parallel) to the axis of rotation of the vessel. The axis of rotation of the rotor has an angle of, for example, less than 30 °, or less than 20 °, or less than 5 ° (e.g. 0 °) with the axis of rotation of the vessel. The shaft may extend through an aperture in a cover plate of the container. For example, the rotor is mounted above and suspended in the container in a frame.

The container and rotor may rotate in the same or opposite rotational directions (at any given time), particularly if the shaft and axis of rotation are substantially parallel. The opposite direction of rotation is preferred. For example, the container may rotate in a clockwise direction and the rotor may rotate in a counter-clockwise direction, as seen from above with respect to gravity, or vice versa.

The vessel is rotated at a speed of, for example, at least 1rpm (revolutions per minute), typically less than 500rpm, preferably 5 to 100rpm, such as 10 to 60 rpm. The rotor is rotated, for example, at least 1rpm (revolutions per minute), typically less than 500rpm, preferably 5 to 100rpm, such as 10 to 60 rpm. The tip speed of the vessel is, for example, from 0.10m/s to 1m/s, preferably from 0.2m/s to 2.0m/s or from 0.5m/s to 2.0 m/s. The tip speed of the rotor is, for example, from 0.2 to 10m/s, preferably from 0.5 to 5.0m/s or from 1.0 to 2.5 m/s. The tip speed of the rotor is preferably higher than the tip speed of the vessel. These preferred speeds are particularly applicable to step b).

The rotational axis of the rotor is preferably spaced from the rotational axis of the vessel (at least in a plane perpendicular to the rotational axis of the vessel) such that the rotor is mounted eccentrically in the interior space of the vessel, particularly in embodiments wherein the rotational axis of the rotor is, for example, substantially parallel (including parallel) to the rotational axis of the vessel. The spacing is, for example, a distance of at least 2% or at least 5% of the diameter of the inner space in a plane perpendicular to the axis of rotation of the container. In some embodiments, a single vessel may optionally be provided with multiple rotors. The rotational axes of the rotors of the plurality of rotors are, for example, at the same distance or at different distances (in the radial direction) from the rotational axis of the vessel.

In a preferred embodiment, the rotor comprises a shaft and one or more blades. The shaft has a length in a length direction of a first end and a second end, wherein the first end is arranged in the inner space of the container. The blade is also disposed in the interior space. The second end is connected to an actuator, such as a second actuator, for example in a second motor. The blade is connected to the shaft and extends from the shaft in a direction perpendicular to the length of the shaft in said inner space of the vessel. The blade has a length in a direction perpendicular to the axis of at least 2% or at least 5% of the radius of the vessel, for example in a cross-section perpendicular to the axis of rotation of the vessel.

Preferably, the axis of rotation of the container is inclined with respect to the vertical, wherein the vertical is defined with respect to gravity. Preferably, the axis of rotation has an angle of at least 5 ° or at least 10 ° with respect to the vertical, and typically less than 30 °. The axis of rotation may also be vertical with respect to gravity. A vertical or slightly inclined orientation may provide a uniform (substantially angularly symmetrical about the axis of rotation) distribution of particles in the vessel, as compared to embodiments in which the axis of rotation is horizontal or nearly horizontal. In case of an inclined rotation axis, the frame comprises a housing, wherein the container is arranged on the support element such that the rotating container is inclined with respect to a horizontal plane, which is parallel to the bottom of the support element. Preferably, the container has a bottom wall provided by a flat plate (e.g. a cylindrical plate). Preferably, the bottom wall is mounted in the frame at an angle of at least 5 ° or at least 10 ° to the horizontal. For example, the cylindrical bottom wall may have a lowest point when at rest (not rotating). An outlet pipe for discharging the coated fertilizer granules is for example arranged at the lowest point or for example at the centre of the bottom wall. The oblique rotation may also contribute to better mixing of the fertilizer with the added one or more coating components.

In some embodiments, the coating unit comprises a plurality of coating devices arranged in series or parallel, wherein each coating device comprises a vessel and at least one rotor. For example, the coating unit comprises a plurality of coating devices arranged in series and connected to each other with a conveyor line (such as a moving belt or pipe) of coated fertilizer granules, wherein each coating device has one container. Each container has an inlet and an outlet for e.g. fertilizer granules (coated). Such a coating unit may for example be used in a process wherein step b) is performed two or more times. Each coating is applied, for example, in a different coating device (and in different containers), wherein, for example, no more than one coating is applied in each container. Fertilizer granules are supplied to and discharged from the most downstream coating device. The final coating device is used, for example, to perform final curing rather than to apply the coating. In another embodiment, the coating system is used with a plurality of coating units in parallel and with a common cooling stage downstream of the coating units.

According to the invention, the coating unit is, for example, an Eirich mixer, such as an R-type Eirich intensive mixer, or a plurality of such mixers, for example arranged in parallel or in series. According to the invention, the coating unit is a mixing device as described, for example, in US 4854715 or in US 9295109.

The coating unit may also be, for example, commercially available fromA company's horizontal mixing system, or, for example, an Eirich plow blender. The coating unit is, for example, a mixing device with a horizontal cylindrical tank and a solid horizontal shaft on which a wedge-shaped plow or an angled blade is mounted, such as an Eirich plow blender.

In a preferred embodiment, in step b) the coating is applied in an amount of from 0.10 to 6.0 wt. -%, more preferably from 0.50 to 4.0 wt. -%, even more preferably from 0.5 to 1.5 wt. -%, based on the weight of the fertilizer granule to be coated without coating. These amounts and times refer to one example of step b) if step b) is carried out two or more times, for example to obtain coatings with different compositions. For example, the total coating is from 1.0 wt% to 25 wt%, or from 1.0 wt% to 15 wt%, or for example from 1.5 wt% to 10 wt%, preferably from 1.5 wt% to 7.5 wt%, based on the weight of the fertilizer granule to be coated without any coating.

Preferably, step b) is performed (and completed) within 10 to 600 seconds, preferably within 30 to 240 seconds or 10 to 120 seconds, or 30 to 120 seconds, or 10 to 60 seconds, or 10 to 30 seconds or 30 to 90 seconds, especially for such amounts of coating substance. In some embodiments, the coating components are added to the container within 0.5s to 30s, or 1s to 10s, or 1s to 5s, and preferably the entire amount of such coating components, preferably each coating component, is added during this period. In some embodiments, the component is distributed on (i.e., mixed with) the fertilizer granule within 10s to 45s or 10s to 30 s. When used, such rapid mixing times are achieved, for example, by movement of the container and rotor.

These times refer to one example of step b) if step b) is carried out two or more times, for example to obtain coatings with different compositions. Preferably, the final curing of step c), if performed, is performed (and completed) within 60 seconds to 15 minutes, more preferably within 2 minutes to 10 minutes. Preferably, step b) involves the subsequent stepwise application of two or more coating components to the fertilizer granules while the container and rotor are rotating. Preferably, the coating component added first to the particles has a higher molecular weight (such as number average molecular weight) and/or a higher viscosity than the second coating component. Preferably, the first coating component is added to the particles and mixed for 2 to 120 seconds, such as 10 to 60 seconds, and then the second coating component is added. At the end of the mixing cycle and prior to the addition of the second coating component, the mixing of the first coating component preferably provides a uniform distribution of the coating component on the particles. Preferably, both coating components are injected as liquids (which may include both dripping and spraying), and preferably into the elevated particle bed. In a preferred embodiment, the elevated particle bed comprises a region in which the particles move fastest (e.g., near the rotor), and the coating component is added to that portion. This allows for a fast and uniform distribution of the coating components on the particles. In some embodiments, the first two coating components added will react with each other. After application of the one or more reactive coating components, the method may involve reacting the coating components with each other for a period of, for example, 10 to 300 seconds, such as 10 to 120 seconds, while the particles remain in motion. The advantage of the invention is that the reaction carried out in the coating unit allows the curing or hardening of the particles without agglomerating the coated particles.

It was found that carrying out the reaction in the coating unit, preferably in a rotating container with a rotor, leads to a rapid and complete distribution of the coating components. This distribution also allows complete encapsulation of the fertilizer particles with the coating. The rapid distribution also enables the use of coating compositions with faster reaction speeds, which at the same time are important for achieving high-quality coatings in such coating units. In particular, both too high a reaction rate and too low a reaction rate may result in too high a release rate of nutrients in the coated fertilizer granules. Furthermore, it was found that the formation of lumps in the coating unit is avoided by the movement of the movable elements (e.g. the container and the rotor).

After such a reaction time, one or more additional coating components, such as wax, preferably liquid wax injected into the fertilizer bed, may be added. Preferably, the wax is applied between the coatings. These steps are optionally repeated one or more times in the same vessel or in additional vessels in series, in order to obtain multiple coatings, and optionally followed by a final curing stage. The final curing stage is carried out (and completed) within, for example, 60 seconds to 15 minutes, such as 2 minutes to 10 minutes, preferably 2 minutes to 5 minutes, to ensure complete hardening or curing of the coating. Optionally, a final additional coating, such as a wax layer, is applied. The final curing can be performed in the same rotating vessel or in different parts of the coating unit. Final curing is typically stopped by discharging the coated fertilizer granules.

Preferably, steps a) and b) are performed at a temperature of at least 10 ℃, 30 ℃, at least 40 ℃, at least 50 ℃, at least 55 ℃ or at least 60 ℃ (typically less than 120 ℃ or less than 80 ℃, such as in the range of 40 ℃ to 120 ℃ or 50 ℃ to 100 ℃, more preferably in the range of 55 ℃ to 80 ℃). Preferably, the fertilizer granules are kept at such temperatures during the entire residence time in the coating unit. Preferably, the particles are at least 50 ℃ or at least 60 ℃ when discharged from the coating unit. The method may involve cooling the discharged particles from a temperature of at least 50 ℃ or at least 60 ℃ to a lower temperature, for example below 30 ℃. In some embodiments, the method includes a pre-heating step of the solid fertilizer particles. In some other embodiments, the method involves obtaining fertilizer granules as formed by curing at such temperatures (e.g., fertilizer granules as formed during granulation or prilling), and transferring the urea granules from the curing unit to the coating unit at such temperatures (e.g., above 50 ℃). Keeping the particles above 50 ℃ or above 60 ℃ in the coating unit, especially during the entire residence time, can contribute to a high-speed reactive curing or high-speed reactive hardening of the coating components, for example if polyurethane coatings are used. Other coating components may have reacted fast enough at lower temperatures, such as 10 ℃ to 50 ℃. Furthermore, if the coating contains additional components that are prone to degradation or undesirable side reactions at elevated temperatures, it may be beneficial to keep the particles below 80 ℃ or even below 60 ℃ or below 50 ℃. The coating unit is preferably operated at an absolute pressure of 0.010 bar to 10 bar, such as 0.5 bar to 2.0 bar or 0.5 bar to less than 1.0 bar (micro vacuum).

In a preferred embodiment, the coating is a polyurethane coating. Preferably, the coating component comprises a polyisocyanate and a polyol. Preferably, the polyisocyanate has 2 or more isocyanate groups per molecule. The polyisocyanates are, for example, aliphatic or aromatic, preferably aromatic. Polyisocyanates are, for example, diisocyanates having exactly two isocyanate groups. A particularly useful polyisocyanate is methylene diphenyl diisocyanate (MDI), such as 4,4' -MDI, another example being Toluene Diisocyanate (TDI). Aromatic polyisocyanates are used, for example, as blends of polymers and diisocyanates of isocyanates.

The polyol has at least 2 hydroxyl groups per molecule, preferably 2 to 5 hydroxyl groups, even more preferably 3 or 4 hydroxyl groups. The polyols are based, for example, on polyethers, polyesters or natural oils, and preferably on polyethers. The polyols have a hydroxyl number of, for example, 150 to 700, and an average functionality (number of isocyanate-reactive sites per molecule) of, for example, 3.

For example, polypropylene polyols or polyethylene polyols having a hydroxyl number of 150 to 700 and a functionality of 3 or 4 are used because they provide relatively short chain lengths (e.g., molecular weights of 300Da to 700 Da). Short chain lengths can help to reduce the viscosity of the polyol.

In a preferred embodiment, the polyol has a viscosity of less than 2000 mPa.s or less than 1000 mPa.s at 25 ℃ and typically more than 100 mPa.s at 25 ℃. The number of hydroxyl groups is measured, for example, according to ASTM D4274-99 or ISO 14900: 2017. Viscosity is measured, for example, according to ASTM D4878-15 (preferably method A) or ISO 3219: 1993.

The polyol is, for example, an aliphatic polyether polyol, such as formed from an initiator and a plurality of alkylene oxide units. The polyols are initiated, for example, by a compound having 3 hydroxyl groups, such as glycerol, or are initiated, for example, by an amine, or a combination thereof. The polyol is for example a polyethylene oxide or polypropylene oxide polyol or other polyether polyol. Polyester polyols may also be used. The number ratio of NCO to OH groups is, for example, in the range of 0.8:10 to 1.2: 10. However, many polyurethane coatings can be used.

The coating component comprises a polymerization catalyst, such as an organometallic catalyst, a tertiary amine, an organic base, or an inorganic base.

Preferably, the polyol and polyisocyanate cure in less than 2 minutes, at 25 ℃, at 70 ℃ and/or at the temperature at which the coating is applied, allowing for subsequent application at intervals of less than 2 minutes. The amount and type of catalyst can be adjusted accordingly for such cure times.

The reactivity of the coating component at room temperature is preferably between 25 seconds and 125 seconds (at least 50% of the time required for curing), and the reactivity at the operating temperature of the coating unit and/or at 55 ℃ is preferably between 10 seconds and 45 seconds. Preferably, the reactivity at room temperature is measured as described below in procedure a ("procedure for determining reactivity parameters (at 25 ℃) -cup reactivity"). Preferably, the reactivity at the operating temperature is measured as described below in procedure B ("procedure to determine the reactivity parameter at the desired curing temperature — hot plate reactivity").

In some embodiments, the coating is a polyester coating, more preferably a thermoset polyester coating. The coating component may comprise an unsaturated polyester (comprising carbon-carbon double bonds) and a vinyl monomer. The curing reaction of step b) may involve the copolymerization of a vinyl monomer and an unsaturated polyester. Unsaturated polymers are, for example, the reaction products of saturated dicarboxylic acids (or anhydrides), unsaturated dicarboxylic acids (or anhydrides) and polyhydric alcohols such as diols (glycols). The glycols are, for example, ethylene glycol, propylene glycol, 1, 3-butanediol or, for example, hydrogenated bisphenol A. The glycols are, for example, cyclic or acyclic and are, for example, aliphatic or aromatic. The glycols have, for example, 2 to 30C atoms. The vinyl monomer is, for example, styrene. The reaction during step b) may involve copolymerization of the unsaturated polyester and vinyl monomer in the presence of, for example, a free radical initiator and a catalyst. The unsaturated polyester is injected, for example, as a liquid mixture with the vinyl monomer, which also acts as a solvent for the polyester.

In another embodiment, the coating is a polyurea coating and the coating component comprises a polyisocyanate having 2 or more isocyanate groups per molecule and a polyamine having 2 or more amine groups per molecule, preferably 2 to 5 amine groups, more preferably 3 or 4 amine groups.

In another embodiment, the coating composition is a phenolic resin coating and the coating component comprises phenol and formaldehyde. The phenol component and the formaldehyde component can react in the coating unit to form a thermoset polymer.

In another embodiment, the coating composition is an epoxy coating, and the coating component comprises an epoxy component (having epoxy groups) and optionally a co-reactant having reactive groups such as amines, acids and anhydrides, phenols, alcohols, and thiols. The co-reactant typically has two or more of the reactive groups per molecule to provide for the formation of a thermoset polymer. The epoxy component can be crosslinked by homopolymerization in step b) or by reaction with an optional coreactant.

The operation of the coating unit described advantageously avoids the particles being crushed during coating, while the degree of mixing is greatly increased, such as compared to a drum coater. The coating unit allows for faster reaction times (such as between the polyol and polyisocyanate) providing a significantly shorter batch cycle time than the prior art. For example, the overall batch time for a three layer process may be 5 to 6 minutes, whereas 6 to 8 minutes may be required for each layer of the drum. The high intensity mixing and faster reaction time in the process of the present invention enables the coated fertilizer particles to be produced without agglomeration of the particles. In addition, the reaction rate can be used to optimize the fertilizer release rate by adjusting the type and amount of catalyst used. The coating method is particularly useful for preparing coated fertilizers for field crops such as corn (maize).

The reaction time of the one or more coating components, preferably at 25 ℃, is preferably from 30s to 250s, wherein the reaction time is the time required for hardening (optionally measured as procedure a — cup reactivity, described herein).

The one or more coating components preferably have a reaction time of 10 to 120 seconds, more preferably 10 to 60 seconds, at the coating temperature (such as at 70 ℃), where the reaction time is the time required for hardening (optionally measured as "hot plate reactivity" as described herein).

The reaction time can be achieved or adjusted by varying the amount and type of catalyst used for curing or hardening.

In a preferred embodiment, without limiting the invention, the coating unit comprises a container and a rotor, the coating is a polyurethane coating, and step b) subsequently (after each other, but optionally with further steps before, between and/or after) comprises:

B1) injecting a polyol into said bed of fertilizer granules within said vessel, preferably wherein the granules in said bed are lifted by the movement of the vessel and rotor, preferably wherein the injection utilizes open pipes or spray nozzles,

B2) mixing the polyol with the fertilizer granule for 5 to 120 seconds, preferably 10 to 60 seconds,

B3) injecting a polyisocyanate component into the bed of fertilizer granules within the container, preferably wherein the injection utilizes an open tube or spray nozzle,

B4) rolling the fertilizer granules in said container for at least 10 to 300 seconds, preferably 20 to 180 seconds, thereby reacting the polyol and polyisocyanate components with each other and at least partially curing the coating, while the rotor is also rotating,

B5) optionally injecting liquid wax into the fertilizer bed,

and optionally repeating said steps B1 to B5,

B6) the fertilizer is optionally rolled in the container for at least 10 seconds, allowing the coating to further cure.

In one variant, step B3 is performed before steps B1 and B2, so that the polyisocyanate is injected first. However, it is preferred to inject the polyol first, especially if the polyol is a polymeric compound. In some embodiments, for example in at least some of the optional repetitions of steps B1-B5, the wax injection step B5 is omitted. In some embodiments, steps B1 through B6 are performed with other coating components in addition to the polyisocyanate and the polyol to obtain different types of coatings. In steps B1 to B6, rolling the fertilizer may be performed by rotating the container and the rotor. It was found that this preferred embodiment provides particularly good coating results, wherein the fertilizer has a desired release rate when submerged in water.

The invention also relates to a urea refining plant comprising: a urea refining unit, such as a granulation unit or a prilling tower, wherein the urea refining unit has an inlet for urea melt and an outlet for warm urea granules; a coating unit having an inlet connected to the outlet for urea granules, preferably for warm urea granules, wherein the coating unit is as described above and comprises a frame and at least two movable elements, wherein the movable elements are independently movable with respect to the frame. Herein, "warm urea granules" refers to granules having a temperature above ambient temperature at the inlet of the coating unit, e.g. 30 ℃ to 95 ℃, preferably 50 ℃ to 85 ℃, more preferably 55 ℃ to 75 ℃. The connection between the inlet of the coating unit and the outlet of the refining unit preferably does not comprise a cooling unit between the urea refining unit and the inlet of the coating unit, in particular does not comprise a cooling unit using cooling air, such as a cooling unit comprising a blower or a fan for cooling air.

The movable element is preferably the container and the stirring member as described, more preferably a container having walls and an inner space for containing the fertilizer granules to be coated, and preferably a stirring member arranged in the inner space of the container. The stirring member is preferably said rotor. Furthermore, the coating unit comprises an outlet for the coated urea granules. The apparatus also includes a cooling unit. The cooling unit has an inlet connected to the outlet for coated urea granules and an outlet for cooled coated urea granules and preferably also an inlet for cooling air and an outlet for exhaust gases. This apparatus can be used to carry out the process of the invention. The process of the invention can also be carried out by obtaining fertilizer granules from a storage device and, if necessary, for example, preheating.

The invention also relates to fertilizer granules obtainable by the process of the invention. These fertilizer granules exhibit advantageous release rates. An example of a favorable release rate is given in example 3. The fertilizer granules obtainable with the method comprise, for example, urea, such as at least 50 wt% urea, based on the total weight of the coated fertilizer granules. The coating of the particles is for example a polyurethane coating. Preferably, the fertilizer granules obtainable with said method have a release rate of less than 40% after 20 days of immersion in water, such as measured according to procedure C as described herein. Preferably, the release rate at 7 days of immersion is also less than 20% by weight. The preferred use of water-insoluble polymers may advantageously assist in achieving such release rates. The total coating weight is, for example, 5 to 25 wt% or 10 to 20 wt%, based on the weight of the fertilizer granule to be coated without any coating. The number of coating layers is for example 1 to 12 layers, such as 4 to 8 layers, wherein the wax layer is counted as a separate layer. The particles comprise, for example, 3 layers of polyurethane and 3 layers of wax, for a total of 6 layers. The coating comprises, for example, 2 to 6 polyurethane layers, which are separated from one another, for example, by wax layers.

The present invention also relates to a coated fertilizer particle preferably comprising urea, more preferably at least 50 wt% urea based on the weight of the coated fertilizer particle, the coated fertilizer particle having a release rate of less than 40% after 20 days of immersion in water, such as measured according to procedure C ("procedure for determining the rate of release of nutrients from a controlled release fertilizer") as described herein. Preferably, the release rate at 7 days of immersion is also less than 20% by weight. The coating of the coated fertilizer granules is for example a polyurethane coating. The particles have, for example, a coating in the amounts and number of layers as described above.

Without being bound by theory, the coating process of the present invention can provide a uniform coating that is highly or completely covering the fertilizer particles.

Fig. 1 schematically shows an example coating unit that can be used in the method of the invention. The coating unit 1 comprises a frame 2, which is a housing, as well as a container 3 and a rotor 4. The rotor 4 is connected to a motor 5 for driving the rotor 4. The rotor 4 comprises a shaft 6 provided with blades 7. The container 3 is provided with a further motor 8 and has an axis of rotation 9. The axis of rotation 9 is parallel to and spaced from (the mid-line of) the shaft 6. The container 3 also has a scraper 10 near the container wall, but which may remain stationary while the container 3 rotates about the axis 9. The container 3 comprises a cover plate 14 and the shaft 6 extends through the cover plate. The container also has an inlet 11 for fertilizer granules and one or more inlets 12 for coating components. The inlet 12 is realized, for example, as an open pipe or as one or more spray nozzles, wherein each spray nozzle has, for example, a connection to a feed line for a particular coating composition. The container 3 also has an outlet 13 for the coated fertilizer granules, for example realized as a closable aperture in the bottom of the container 13.

The invention will now be further illustrated by the following examples, which do not limit the invention or the claimed subject matter.

Example 1

The mixer (with rotating vessel and rotating rotor) was preheated to about 75 ℃, and 4.08kg urea fertilizer granules were added and stirring was started. Once urea was confirmed to be at about 75 ℃, the first of 14.0g of three polyol charges was added and mixed for 30 seconds, followed by the first of 21.3g of three isocyanate charges. After 60 seconds of mixing, 10.2g of the first of two wax additions was added. The mass was allowed to mix for an additional 30 seconds. The polyol, isocyanate and wax addition steps and mixing times were repeated. Finally, a third addition of polyol and isocyanate is added with the appropriate mixing time.

Unlike the first two coatings, the addition of the wax layer was omitted after the third addition of the polyurethane component (polyol addition and isocyanate addition). Optionally, a wax layer may be applied over the third polyurethane coating. Free-flowing and lump-free or non-agglomerated urea is dispensed from the mixer for cooling. The total batch time for the three-layer process was 5.5 minutes; this is a significant reduction compared to the most recently reported batch times, which in the past typically required 6 to 8 minutes per layer. The paint weight was 3 wt%, and the final weight was 4.21kg, where the paint weight was 126 g. Only 2 layers of wax were applied at 0.5% and 3 coating steps were used. On visual inspection, the fertilizer granules were completely covered with the coating.

Example 2

Polyol formulations a through G were prepared by adding an organometallic catalyst or a tertiary amine catalyst to a polyether polyol with incremental amounts of catalyst as shown in table 1.

Table 1 shows the corresponding room temperature and high temperature reactivity of polyol blends when compounded with MDI based polyfunctional aromatic isocyanates. These samples were formulated to have reactivity ranging from a fast reaction time of 8 seconds to a very slow reaction time longer than 5 minutes. At a processing temperature of about 75 ℃, the reaction time is significantly faster. If the entry N/A is recorded, it means that the sample reacts during a mixing time of 20 seconds or substantially as soon as it is added to the hot plate.

The polyol was added to the preheated urea granules stirred in the mixer as described in example 1. The reaction parameters were a processing temperature of 71 ℃ (160 ° f), a total polyurethane coating weight of 3% (added via three separate layers, 1% per layer, polyol added first, then isocyanate added), and 0.5% total wax added via two separate layers after the first polyurethane coating and the second polyurethane coating.

TABLE 1

Figure 2 shows the urea release% (Y axis: 0 to 100%; measured according to procedure C) at 2 hours and at 1 day, 3 days and 7 days of impregnation for the different polyol blends of table 1 (polyol blend X axis for reactivity time in seconds according to room temperature). The desired slower release was achieved with polyol blends D, C and B, preferably with blends C and D. The release rate depends on the reactivity of the polyol blend modified by using different amounts and types of catalysts.

Example 3

In addition, polyol blends C and D were also applied to the fertilizer granules using a comparative drum mixer following the same order of addition and mixing time, but the material charge was reduced to reflect a lower charge of fertilizer granules. The release rate was determined according to procedure C.

Fig. 3 shows the urea release% (y-axis) at 2 hours and at 1 day, 3 days, 7 days, 14 days and 21 days (x-axis, time in days) of impregnation with the blends C and D applied with the coating units described (C1, D1) and with the comparative drums (C2, D2). The release rate of the mixer of the present invention is significantly better (slower) than that of a drum mixer. For C2 and D2, more than 60% of the urea was released in less than 3 days of immersion. For C1 and D1, less than 40% urea was released at 21 days of immersion. This indicates that faster reactivity is not beneficial for the comparative coated fertilizer produced with the comparative drum mixer process, but is very beneficial for the inventive process and the inventive urea granules.

Experimental procedures

In example 2, the following procedure was used.

Procedure a: procedure for determining reactivity parameters (at 25 ℃ C.) -cup reactivity

The required weight of the fully formulated components was added to reach 150 in a small cup. Immediately and simultaneously, a timer is started and mixing of the compounds is started. Mixing is continued for 20 seconds or until the substance solidifies (if less than 20 seconds).

To check the reaction time, periodically, a stainless steel spatula (or alternatively, a wooden spatula) was gently touched to the surface of the material. When the spatula encounters a hard or cured spot on the surface of the material, this is considered the reaction time. In example 2, a fully formulated isocyanate component (a-component) and a fully formulated polyol component (B-component), including any optional additives necessary to reach 150g, are added to a small cup. The chemical composition and equipment were initially at 25 ℃. The B component is first weighed into a mixing vessel in the appropriate component weight ratio, and then the a component is weighed.

Procedure B: procedure for determining reactivity parameters at desired curing temperature-Hot plate reactivity

A small mold capable of holding 2ml of the mixed mass was placed on a hot plate in a cavity 1/8 deep, and the mold was preheated to the desired temperature. Once the desired temperature was confirmed, the mixing procedure mentioned as procedure a-cup reactivity was followed, but now once the sample had been completely mixed, 2ml of the reaction mixture was poured into the cavity of the preheated mould. The timer is started immediately after the resin is added to the mold. Periodically contacting the surface of the material with a spatula; the reaction time is the time during which the resin solidifies into a hard substance.

Procedure C: procedure for determining the rate of release of nutrients from controlled release fertilizers

A nutrient solution prepared by dissolving a variety of known concentrations of nutrients in distilled water is prepared. A refractometer measures the refractive index at a known concentration and a calibration curve of refractive index versus concentration can be constructed. Then, 10g of the coated fertilizer granules were accurately weighed into a small jar and 90g of water was added. The sample was gently swirled and allowed to stand until the desired measurement time. Before each new measurement, the sample was gently swirled to ensure uniformity. A small sample of the solution was placed on a refractometer and the measurement was recorded. Comparison with the calibration curve yields the nutrient concentration in the solution. The percentage of nutrients released from the coated fertilizer granules was calculated. The experiment was performed at ambient temperature (e.g., 20 ℃).