Method for producing solid particles comprising urea, biuret, and n-containing compounds

Abstract

The present disclosure relates to method for producing solid particles comprising from 35 wt.% to 55 wt.% of urea, from 35 wt.% to 50 wt.% of biuret, and from 5.0 wt.% to 30 wt.% of N-containing compounds produced during a urea condensation process, or from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 2.0 wt.% to 15 wt.% of the N-containing compounds, and from 21 wt.% to 37 wt.% of a nitrate compound, with wt.% based on the total weight of the particles, wherein the method comprises the subsequent steps of adding a composition comprising urea, biuret, and N-containing compounds produced during a urea condensation process, in a container of a mixing device, mixing the content present in the container, thereby solidifying the composition thereby producing the solid particles, and removing the solid particles from the container (step c).

Description

METHOD FOR PRODUCING SOLID PARTICLES COMPRISING UREA, BIURET, AND N-CONTAINING COMPOUNDSTechnical field

[0001] The invention relates to a method for producing solid particles comprising urea, biuret, N-containing compounds produced during a urea condensation process, optionally further comprising a nitrate compound, using a mixing means or mixing device.Background

[0002] Urea is a chemical substance with the chemical formula CH4N2O. It contains a very high content (46 weight%) of nitrogen (N) and is used in a wide range of industries, including fertilizers, and animal feed.

[0003] It is known to produce urea particles such as granules, pellets, and any other known type, with a high amount of urea. However, a melt comprising substantial amounts of urea and biuret, such as between 5 wt.% and 60 wt.% of urea and between 2 wt.% and 60 wt.% of biuret, and a minor amount of other N-containing compounds produced during the condensation of urea, shows a much different solidification behaviour than (pure) urea. Such a melt only solidifies slowly, and exhibits a rather broad phase transition range instead of a well-defined solidification temperature, making the development of a particulation technology challenging.

[0004] Recently, a new feed composition for ruminants comprising urea, biuret and other compounds were found.

[0005] There is thus a need in the art for improved processes for producing particles from a composition comprising substantial amounts of urea and biuret, as well as minor amounts of N-containing compounds produced during the condensation of urea.Summary

[0006] The present disclosure generally provides a particulation technique, or stated differently, a method for the production of solid particles. The solid particles produced by the present technique comprise a substantial amount of urea and biuret, N- containing compounds produced during a urea condensation process, and optionally a nitrate compound.

[0007] In a first aspect, the present disclosure provides in a method for producing solid particles comprising urea, biuret, and N-containing compounds produced during a urea condensation process, wherein the solid particles comprise: from 35 wt.% to 55 wt.% of urea, from 35 wt.% to 50 wt.% of biuret, and from 5.0 wt.% to 30 wt.% of the N-containing compounds produced during a urea condensation process, and, optionally, from 0.1 wt.% to 5.0 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; or from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 2.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 21 wt.% to 37 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; with wt.% based on the total weight of the particles, wherein the method comprises the steps of a) adding a composition in the form of a melt or a combination of a melt and a solid, comprising urea, biuret, and N-containing compounds produced during a urea condensation process, in a container of a mixing device; b) mixing and, preferably, simultaneously actively cooling the composition present in the container, thereby solidifying the composition until the solid particles are formed; and c) removing the solid particles from the container.

[0008] In a particular method according to the present disclosure, step a is performed in(i) a static container and at least one rotating mixing element located inside the container which mixes the composition in the container, or(ii) a rotating container and a static mixing element located inside the container which mixes the composition in the container because of the rotational movement thereof,(iii) a rotating container and a rotating mixing element located inside the container which mixes the composition in the rotating container.The rotational movement of the container as well as that of the mixing element, whether or not in combination, takes care of the good mixing of the particles and provides a more uniform layer of the melt on each particle. This also helps better heat transfer in the system. The movement that is made by the container and the mixing element cause the impact of the particles to each other resulting in rounder shapes. Also, the mixing element rotation can break the large particles and agglomerates to make the average particle size smaller. Its rotational speed and the type of the mixing element can determine the final size and affect particle properties. If a combined rotational movement of the container and the mixing element takes place, the mixing is better, and the particles may get even rounder.

[0009] It is understood that actively cooling the composition during mixing accelerates the solidification process.

[0010] In a specific method according to the present disclosure, the container and / or the mixing element is rotated at a rotation speed of from 0.1 to 70 m / s.

[0011] In a particular method according to the present disclosure, the container is tiltable or tilted in view of the horizontal.

[0012] In a specific method according to the present disclosure, the composition is cooled to and subsequently maintained at a temperature of from 0°C to 100°C, such as from 10 °C to 70 °C, in the container using the cooling means.

[0013] In certain embodiments, the cooling means are configured as providing the container with a double wall wherein in between the walls a cooling medium is present.

[0014] In a particular method according to the present disclosure, the method comprises the step of scraping off the composition during solidification thereof fromthe inner wall of the container using a scraping tool located inside the container. This has the advantage that the accumulation of solids on the wall and / or the bottom of the container can be prevented. Removal of the accumulation of solids on the wall and / or bottom of the container by the scraping tool also contribute to a better mixing as well as a better cooling, as the accumulated solids do not have good heat transfer properties.

[0015] In a possible method according to the present disclosure, during the method, the composition solidifies into large agglomerates, wherein the method comprises the step of chopping the large agglomerates into smaller agglomerates using a chopping tool located inside the container. In certain embodiments, the mixing element may simultaneously function as a chopping tool.

[0016] In an optional method according to the present disclosure, the composition further comprises a nitrate compound, in particular a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof.

[0017] In a specific method according to the present disclosure, the solid particles produced in step b) have an average size of between 1.0 mm and 4.5 mm, in particular between 1.2 mm and 3.0 mm, more in particular between 1.5 mm and 2.5 mm, and even more in particular between 1.8 mm and 2.2 mm.

[0018] In certain embodiments, particular in the case wherein, in step (a), the composition is added in the form of a combination of a melt and a solid, comprising urea, biuret, and N-containing compounds produced during a urea condensation process, the solids are added before, during, or after adding the melt.

[0019] In an optional method according to the present disclosure, the composition comprising urea, biuret, and N-containing compounds produced during a urea condensation process, and optionally a nitrate compound, is added in different steps in the container during operation thereof.

[0020] More in particular, in the method according to the present disclosure, the composition is added to the container during operation thereof in at least a first step as a solid and in a subsequent step as a melt. In other words, the composition is added in two different physical forms. For example, the first addition of the composition may be done as a solid or powder, which acts as seed particles, whereas the one or moreother additions of the composition are done as a melt. This sequence may facilitate and / or accelerate the solidifications step, and / or provide particles with a narrower particle size distribution. In certain embodiments the composition is added to the container during operation thereof in at least a first step as a melt, and in a subsequent step when the melt has at least partially solidified again as a melt. For instance, the composition is first added to the container during operation thereof as a melt, which is subsequently solidified and broken to form seed particles. Next, the composition is further added to the container as a melt to enlarge and grow the seed particles.

[0021] In another aspect, the present disclosure provides the use of the solid particles produced by a method according to the present disclosure, as a non-protein nitrogen source for ruminants.Description of the figures

[0022] Figure 1 shows a schematic diagram of a high shear mixer as mixing device which can be used to perform the method according to the present disclosure.Figure 2 is a schematic cross-section of a container that can be used in a mixing device as shown in Figure 1.Detailed description

[0023] The present disclosure relates to a process for producing non-sticky solid particles comprising urea, biuret, and N-containing compounds produced during the urea condensation process, or, in other words, the production process of biuret out of urea. A urea condensation process is a process comprising heating urea above its melting point. When urea is heated above 132 °C, condensation reactions start to occur, and urea is partially converted into biuret, and, in addition, so-called “byproducts” in the form of N-containing compounds are formed. The main N-containing compounds that are formed during the condensation process of urea are ammelide, cyanuric acid and triuret.

[0024] In some embodiments, the N-containing compounds produced during a urea condensation process are selected from the group consisting of ammelide, cyanuric acid, triuret, and mixtures thereof. Ammelide is the compound with the chemicalformula: C3H4N4O2, and CAS number: 645-93-2, cyanuric acid is the compound with the chemical formula: C3H3N3O3, and CAS number: 108-80-5; and triuret is the compound with the chemical formula: C3H6N4O3, and CAS number: 556-99-0.

[0025] A melt comprising substantial amounts of urea and biuret, such as from 5.0 wt.% to 60 wt.% of urea, from 2.0 wt.% and 60 wt.% of biuret, and N-containing compounds produced during the condensation of urea, shows a much different solidification behaviour than compositions containing at least 90 wt.% of urea. Such a melt only solidifies slowly and exhibits a rather broad phase transition range instead of a well-defined solidification temperature, making the development of a granulation or particulation technology for this kind of melt challenging. Such a melt also displays an important supercooling effect, meaning that the melt can reach a temperature below its solidification temperature while staying in liquid phase.

[0026] It is essentially not possible to granulate a urea melt comprising at least 90 or 95 wt.% of urea in a fluidized bed granulator without any additive. Most modern urea production plants use urea formaldehyde, with a typical amount added to the urea melt being from 0.3 to 0.8 wt.%, as granulation additive.

[0027] Surprisingly, it was found that solid particles could be produced from compositions comprising urea, biuret, and N-containing compounds produced during a urea condensation process, in a mixing device without the addition of granulation or solidification additives to the composition. The method according to the present disclosure relates to the production of solid particles comprising either from 35 wt.% to 55 wt.% of urea, from 35 wt.% to 50 wt.% of biuret, and from 5.0 wt.% to 30 wt.% of the N-containing compounds produced during a urea condensation process, and, optionally, from 0.1 wt.% to 5.0 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, or from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 2.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 21 wt.% to 37 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, with wt.% based on the total weight of the particles, wherein the method comprises the steps of adding acomposition comprising urea, biuret, and N-containing compounds produced during a urea condensation process, in a container of a mixing device (step a), followed by mixing and, preferably, simultaneously actively cooling the composition present in the container, thereby solidifying the composition until the solid particles are formed (step b), and removing the solid particles from the container (step c).

[0028] During operation, the container of the mixing device contains the composition to be transformed into solid particles. The container should be in a material that does not react chemically with the composition to be transformed into solid particles. In some embodiments, the container is made of stainless steel.

[0029] Step a as mentioned above can be performed in different ways. A first possibility is that the container is static (does not rotate) and there is at least one mixing element which is located inside the (space in the) container and which mixes the composition in the container during rotation thereof. Another possibility is that the container rotates and the mixing element does not, or in other words is static. The composition will then anyway be mixed by the mixing element but because the container rotates. In a last possibility, the container as well as the mixing element rotate, providing the best mixing of the composition present inside the container. The container and the mixing element rotate more in particular around a central axis. The shape of the mixing element is not particularly limiting, as long as it is suitable for mixing the composition and for breaking up the aggregates formed during mixing or mixing and cooling. In certain embodiments, the mixing element may be in the form of a whisk, a beater, a cutter, a chopper, a spiral or a dough hook, a mixing screw, a ribbon, or in the shape of a paddle or a plow.

[0030] By subjecting the composition in a liquid form, also called a melt or a liquid and a solid form, present in the container to a continuous mixing action, the composition is gradually transformed into solid particles of variable sizes. The container and / or the mixing element more in particular rotate at a rotation speed of from 0.1 to 70 m / s and can rotate at a variable rotation speed.

[0031] It is also possible to configure the container in a tiltable way in view of the horizontal. Tilting the container during solidification or particulation increases the intensity of the mixing process. Without wishing to be bound by theory, by increasingthe angle, such as from about 0 degrees to about 30 degrees, the duration in which the material is impacted by the mixer is extended, resulting in a more intense mixing. Tilting the container causes the material to gather on one side of the container, thereby enhancing the mixing process. In certain embodiments, the container is tiltable to an angle between 0 degrees and 60 degrees, such as between 0 degrees and 50 degrees, between 0 degrees and 45 degrees, between 0 degrees and 40 degrees or between 0 degrees and 30 degrees. In certain embodiments, the method according to the present disclosure is performed with a container tilted at an angle ranging between 0 degrees and 60 degrees, such as between 0 degrees and 50 degrees, between 0 degrees and 45 degree, between 0 degrees and 40 degrees or between 0 degrees and 30 degrees, more particular with a container tilted at an angle ranging between 10 degrees or 20 degrees and 50 degrees, 45 degrees or 30 degrees, with respect to the horizontal.

[0032] In a possible method according to the present disclosure, the composition comprising urea, biuret, and N-containing compounds produced during a urea condensation process, and optionally a nitrate compound, is added gradually in more than one portion in the container during operation thereof. Alternatively, the composition is added in a continuous manner to the container during operation thereof.

[0033] In preferred embodiments, in step b, the composition present in the container is simultaneously subjected to mixing as well as to active cooling. The cooling may be done using a cooling means. The cooling step is in particular necessary for example in cases where the composition to be particulated has a low solidification point and / or displays a supercooling effect which complicates the solidification process.

[0034] In certain embodiments, the cooling process can be done by providing a double walled container wherein a cooling medium or cooling liquid is present between the walls of the container. Suitable cooling mediums or cooling liquids are known, including but not limited to water, glycol-water mixtures, brine solutions or thermal oils

[0035] . Alternatively, inert cooling agents, such as liquid nitrogen, may be added to the container for cooling purposes as well.

[0036] The composition is more in particular cooled to and subsequently maintained at a temperature of from 0 °C to 95 or 100 °C, such as between 5°C and 95 or 100°Cor between 10°C and 95 or 100°C, such as e.g. between 10 °C and 80°C or between 10 °C to 70 °C in the container using the cooling means. The temperature at which the cooling means maintain the content of the container during operation may depend on the chemical content of the composition used in the method and / or on the solidification temperature of the composition used in the method. The cooling means may be configured to maintain the composition in the container at a temperature below the solidification temperature of the composition to facilitate solidification and particulation of the composition. Step b may also be performed without any cooling, i.e. in the absence of any cooling or heating means. Generally, this will require longer mixing times for solidification and particulation of the composition.

[0037] The solid particles as produced in step b) more in particular have an average size of between 1.0 mm and 4.5 mm, in particular between 1.2 mm and 3.0 mm, more in particular between 1.5 mm and 2.5 mm, and even more in particular between 1.8 mm and 2.2 mm. The particle size may be determined by sieving or by image analysis of a sample.

[0038] The container may also comprise a chopping tool or a chopper. The chopping tool is configured to break up large agglomerates which may form during the solidification of the melt or the combination of the melt and the solid in the container. The chopping tool may be static or move during operation. The chopping tool may comprise blades or sharp elements to break up the formed agglomerates. In some embodiments, the chopping tool is mounted on a rotating shaft. The mixing means may be attached to the same rotating shaft of the chopping tool. Alternatively, the mixing device may comprise two rotating shafts, one mounted with the mixing means, and one mounted with a chopping tool. In certain embodiments, the mixing element also functions as the chopping tool: the mixing element and the chopping tool may thus be the same element.

[0039] In some embodiments, the mixing device is a mixer, a shear mixer, a ring-layer mix-pelletizer, a paddle mixer, a plow mixer, a conical mixer, a ribbon blender, a pugmill, a spiral mixer, or a planetary mixer.

[0040] A ring-layer mix-pelletizer is a device comprising a container, often a cylindrical container in horizontal position. The container comprises an internal axismounted with a plurality of mixing heads. The internal axis is configured to rotate inside the container, thereby mixing the content of the container with its mixing heads.

[0041] A paddle mixer is a device comprising a container, often a horizontal container, and a mixing means with the shape of a paddle, typically comprising two paddels.

[0042] A plow mixer is device comprising a container, often a horizontal container, and a mixing means with the shape of a plow.

[0043] A conical mixer is a mixing device, wherein the container has a conical shape. The mixing means may be a mixing screw, which is configured to mix the content and the container. The mixing screw can also act as a scraping tool if it is positioned on the edge of the container.

[0044] A ribbon mixer is a mixing device comprising a container, often a cylindrical container laid horizontally. A ribbon mixer comprises a shaft mounted with one or more ribbons. For ribbon mixers with two or more ribbons, the ribbons may be configured to rotate in different directions and / or at different speed to modify the mixing pattern.

[0045] A planetary mixer is a mixer wherein the bottom of the container is in a plane parallel to the ground. A spiral mixer is similar to a planetary mixer, but the container of a spiral mixer is rotatable. In some embodiments, the mixing means of a planetary mixer or of a spiral mixer is a hook which rotates around its own axis but also around another axis parallel to its own axis.

[0046] The mixing step of step b as mentioned above may have a range of consequences on the composition present in the container. For example, if the composition is added as a melt, the mixing action may transform the melt into a paste, large particles, or a powder, depending on factors, such as the mixing time, and the rotation speed of the mixing means. If a melt is added to a container containing a powder, the mixing action may agglomerate the small particles together with the melt or add a molten layer on top of the small particles to obtain larger particles. The rate of transformation of the melt into solid particles may depend on the temperature of the cooling means, if present, and the rotation speeds of the mixing means and the rotating speed and direction of the container, if the container is rotated.

[0047] Once the particles have reached the desired size, they are removed from the container in a step c as mentioned above.

[0048] The mixing device as used in a method according to the present disclosure may be operated in two different modes: a batch mode and a continuous mode. In batch mode, the mixing is stopped when the desired particles size is achieved, and all the content of the container is removed from the container. It may take a few runs of the method to achieve the desired particle size. A small sample may be removed from the container at regular time intervals and the particle size of the sample may be measured and compared versus the desired size. The batch mode includes operating the mixing device in semi -batch mode, wherein the composition, in particular the melt thereof, is added in a continuous manner, and wherein the particles removed batch wise, i.e. by removing all the content of the container. Some mixing devices are configured to operate in a continuous mode, wherein a continuous stream of composition is fed to the mixing device and a continuous stream of particles is removed from the mixing device. In continuous mode, a fraction of the particles removed from the mixing device is re-introduced into the container to act as seed particles. In some embodiments, the undersized particles, i.e., particles with a size lower than the desired size are reintroduced into the container. In some embodiments, the oversized particles, i.e., particles with a size greater than the desired size are crushed into smaller particles and re-introduced into the container.

[0049] In some embodiments, the composition comprising urea, biuret, and N- containing compounds produced during a urea condensation process is added sequentially, wherein at least one addition is done as a solid, and at least one addition is done as a melt.It is however also possible to add the composition sequentially as a melt or to add a second composition with a different composition. The first portion of melt may be mixed until it forms a powder or small particles, which can act as seed particles for the remainder of the melt, with the same or different composition. The remaining melt can be added in one portion or stepwise.

[0050] The rotational speed of the mixing means can be variable, such as according to the desired degree of mixing or the desired particle size. In some embodiments, therotation speed of the mixing means varies during the method. It may be an advantage to vary the rotation speed of the mixing means during the method, depending on the content of the container. For example, when a portion of melt or solid, in particular as a melt, is added to the container, a lower rotating speed may be preferred to distribute the added material evenly across the container. If the method is run as a batch method, it may be preferred to lower the rotating speed of the mixing means every time a new portion of melt or solid is added to the container.

[0051] In some embodiments, the mixing means is rotated at a speed of from 0.1 to 70 m / s or from 0.5 to 60 m / s, particularly at a speed between 1.0 and 60 m / s or between 1.0 and 50 m / s, such as from 5 to 50 m / s, from 10 to 40 m / s, from 10 to 20 m / s, or from 30 to 40 m / s. Converting the linear speed to a rotational speed is well known to the skilled person.

[0052] The chemical composition of the solid particles removed from the mixing device in step c) is substantially the same as the chemical composition of the composition added to the container.

[0053] More in particular, these particles comprise: from 35 wt.% to 55 wt.% of urea, from 35 wt.% to 50 wt.% of biuret, and from 5.0 wt.% to 30 wt.% of the N-containing compounds produced during a urea condensation process, and, optionally, from 0.1 wt.% to 5.0 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; or from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 2.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 21 wt.% to 37 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; with wt.% based on the total weight of the particles.

[0054] In some embodiments, the N-containing compounds produced during a urea condensation process are selected from the group consisting of ammelide, cyanuric acid, triuret, and mixtures thereof. Ammelide is the compound with the chemical formula: C3H4N4O2, and CAS number: 645-93-2, cyanuric acid is the compound withthe chemical formula: C3H3N3O3, and CAS number: 108-80-5; and triuret is the compound with the chemical formula: C3H6N4O3, and CAS number: 556-99-0.

[0055] In some embodiments, the N-containing compounds produced during a urea condensation process and comprised in the composition added to the container comprise from 2.5 wt.% to 15 wt.%, from 3.0 wt.% to 10 wt.%, from 3.0 wt.% to 8.0 wt.%, or from 5.0 wt.% to 8.0 wt.% of cyanuric acid. In some embodiments, the N-containing compounds produced during a urea condensation process and comprised in the composition added to the container comprise from 2.5 wt.% to 8.0 wt.%, or from 3.0 wt.% to 6.0 wt.% of triuret. In some embodiments, the N-containing compounds produced during a urea condensation process and comprised in the composition added to the container comprise from 0.1 wt.% to 5.0 wt.%, or from 0.5 wt.% to 3.0 wt.% of ammelide. In some embodiments, the N-containing compounds produced during a urea condensation process and comprised in the composition added to the container comprise (i) from 2.5 wt.% to 15 wt.%, from 3.0 wt.% to 10 wt.%, from 3.0 wt.% to 8.0 wt.% or from 5.0 wt.% to 8 wt.% of cyanuric acid; (ii) from 2.5 wt.% to 8.0 wt.%, or from 3.0 wt.% to 6 wt.% of triuret; and (iii) from 0.1 wt.% to 5.0 wt.%, or from 0.5 wt.% to 3.0 wt.% of ammelide. The composition added to the container may further comprise from 0.1 wt.% to 4.5 wt.%, or from 0.1 wt.% to 2.0 wt.% of moisture water.

[0056] When no nitrate compound(s) is (are) present in the solid particles produced by the present method or the concentration of the nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, is from 0 wt.% to 5.0 wt.%, the solid particles, hereafter referred to and abbreviated with “UB”, may comprise from 30 wt.% to 60 wt.% of urea, and from 30 wt.% to 60 wt.% of biuret, or from 35 wt.% to 55 wt.% of urea and from 35 wt.% and 50 wt.% of biuret, based on the total weight of the composition, the total weight% of the composition being 100 wt.%. UB compositions may further comprise from 5.0 wt.% to 30 wt.%, from 5.0 wt.% and 20 wt.% or from 6.0 wt.% to 16 wt.%, of the N-containing compounds produced during a urea condensation process. In some embodiments, the UB composition comprises, as N-containing compound, from 2.5 wt.% to 15 wt.%, from 3.0 wt.% and10 wt.%, or from 5.0 wt.% to 8.0 wt.% of cyanuric acid. In some embodiments, the UB composition comprises, as N-containing compound, from 0.1 wt.% to 5.0 wt.%, from 0.5 wt.% to 3.0 wt.%, or from 0.8 wt.% to 2.0 wt.% of ammelide. In some embodiments, the UB composition comprises, as N-containing compound, from2.5 wt.% to 8.0 wt.%, or from 3.0 wt.% and 6.0 wt.% of triuret. In some embodiments, the UB composition comprises, as N-containing compounds produced during a urea condensation process, (i) from 2.5 wt.% to 15 wt.%, from 3.0 wt.% and 10 wt.%, or from 5.0 wt.% to 8.0 wt.% of cyanuric acid; (ii) from 0.1 wt.% to 5.0 wt.%, from 0.5 wt.% to 3.0 wt.%, or from 0.8 wt.% to 2.0 wt.% of ammelide; and / or (iii) from2.5 wt.% to 8.0 wt.%, or from 3.0 wt.% and 6.0 wt.% of triuret. In some embodiments, the UB composition may comprise from 0.1 wt.% to 5.0 wt.%, or from 1.0 wt.% and4.5 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof.

[0057] In some embodiments, the solid particles may comprise at least 5.0 wt. of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof. Such solid particles, hereafter referred to as “UBN solid particles”, may comprise from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 4.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 20 wt.% to 40 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof. In some embodiments, the UBN solid particles may comprise from 25 wt.% to 35 wt.% of urea, from 25 wt.% to 35 wt.% of biuret, from 4.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 25 wt.% to 35 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, even more in particular between 29 wt.% and 33 wt.% of urea; between 29 wt.% and 33 wt.% of biuret, and between23.5 wt.% and 31.5 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, based on the total weight of the solid particles.

[0058] In some embodiments, the UBN solid particles comprises from 20 wt.% to 32 wt.%, from 22 wt.% to 30 wt.%, from 25 wt.% to 32 wt.%, or from 25 wt.% to 30 wt.% of calcium nitrate. In some embodiments, the UBN solid particles comprises ammonium nitrate. In some embodiments, the UBN solid particles comprises from 1.0 wt.% and 5.0 wt.%, or from 1.5 wt.% and 2.5 wt.% of ammonium nitrate. Some calcium nitrate compositions may comprise a small amount of ammonium nitrate due to the production process, such as in the nitro-phosphate process, also called Odda process.

[0059] In some embodiments, the UBN composition comprises from 6.0 wt.% to 16 wt.% of N-containing compounds produced during a urea condensation process. In some embodiments, the UBN composition comprises, as N-containing compounds produced during a urea condensation process, (i) from 1.0 wt.% to 5.0 wt.%, or from 1.5 wt.% to 3.0 wt.% of triuret, (ii) from 0.5 wt.% to 3.0 wt.%, or from 0.9 wt.% to 1.5 wt.% of ammelide; and / or (iii) from 3.0 wt.% to 15 wt.%, or from 3.0 wt.% and 7.0 wt.% of cyanuric acid.

[0060] In the context of the present disclosure, a “melt” of a compound or composition, such as a “melt of the composition comprising urea, biuret, and the N- containing compounds produced during a urea condensation process” refers to a composition in liquid form, i.e., above its melting temperature, containing at least 95 wt.% of the compound or composition and less than 5.0 wt.% water, preferably between 0.1 wt.% and 4.5 wt.%, or between 0.1 wt.% and 2.0 wt.% water. A melt (liquid feed) can be dosed to the container via a pressurized vessel or via a suitable pumping means. The temperature of the melt (Tfeed) can be maintained via a controlled heating system as known to the skilled person, for instance comprising a heating bath and a mantle, heating coils, or any other known alternatives.

[0061] In some embodiments, the melt added to the container comprises at least 0.1 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, the nitrate compound may be added, in particular as a solid, to the melt comprising urea, biuret, and N-containing compounds produced during a urea condensation process in a mixing device.

[0062] The solid particles removed from the reactor may have a semi-solid (or almost solid) or completely solid form. The solid particles may have a solid outer core, but a part of the inside of the particles may still be in a liquid form. This is not an issue as the particles may be further cooled down before being stored or bagged.

[0063] The diameter of the solid particles removed in step c) may be from 1.0 mm to 4.5 mm, from 1.2 mm to 3.0 mm, from 1.5 mm to 2.5 mm, or from 1.8 mm and 2.2 mm.

[0064] In some embodiments, the method further comprises, prior to step (a), the step of producing a composition comprising urea, biuret, and N-containing compounds produced during a urea condensation process, in particular in the form of a melt, wherein a urea melt is subjected to a heating process thereby converting the urea melt to the composition comprising urea, biuret, and N-containing compounds produced during a urea condensation process. Advantageously, the thus produced melt can be fed directly to the mixer and can be directly subjected to a granulation process according to the present disclosure, without any intermediate steps. The temperature and duration of the heating process may influence the chemical content of the composition produced by the heating process.

[0065] In some embodiments, the method comprises the step of directing a urea melt by suitable means, such as a pump, to a single reactor vessel or a series of different reactor vessels where the heating process and condensation of urea takes place. The urea melt directed to the one or more reactor vessels may comprise from 95 wt.% to 100 wt.% urea. The urea melt may be formed by melting solid urea particles, such as urea prills. Alternatively, the urea melt may be produced in a urea-producing plant by reacting ammonia and carbon dioxide in a reactor, thereby producing an aqueous solution comprising urea, which may be further processed to obtain a urea melt. This urea melt is then heated in the one or more reactor vessels using a heating device to a desired process temperature of between 140 °C and 180 °C. At this temperature, condensation reactions of urea occur and create biuret and other N-containing compound, such as ammelide, cyanuric acid and triuret. In some embodiments, the melt in the one or more reactor vessels is heated to a temperature of from 140 °C to 170 °C, or of 145 °C. Each of the reactor vessels has a top part with a headspace anda bottom part. Water present in the melt is evaporated and transported in the headspace of the reactor vessel.

[0066] During the heating process and the formation of the melt comprising urea, biuret, and N-containing compounds produced during a urea condensation process, gaseous by-products are produced as well. For example, it is known that ammonia (NH3) is liberated at temperatures above the melting point of urea, which is around 132 °C. Carbon dioxide and water vapor may also be formed during the condensation process. In order to increase the conversion of urea into biuret and other N-containing compounds produced during a urea condensation process, it is preferred to remove these gases from the melt and the reactor vessel. A first possibility to do so is to introduce a carrier gas in the melt present in the one or more reactor vessels which strips the gaseous by-products out of the melt. The carrier gas is thus mixed with the gaseous by-products resulting in a gas combination. A second possibility is to introduce a purging gas stream in the headspace of the one or more reactor vessels which mixes with the gaseous by-products, resulting in a gas combination. It is also possible to perform both options, either simultaneously or alternatingly. Introducing a carrier gas in the melt present in the one or more reactor vessels may be done using a sparger which is designed to bubble the carrier gas up into the melt from the bottom part of the respective reactor vessel(s). The carrier gas can be nitrogen gas, carbon dioxide, air, or mixtures thereof. Introducing a purging gas stream in the headspace of the one or more reactor vessels is more in particular done by applying a purging air stream. The resulting gas combinations as described above are then evacuated out of the respective reactor vessel via the top part thereof.[1] In some embodiments, those one or more reactor vessels are furthermore provided with a circulation loop which is arranged externally to the respective reactor vessel(s) and which is configured to let the melt circulate through it, wherein the melt flows from the reactor vessel to the circulation loop via an inlet opening of the circulation loop and flows back to the reactor via an outlet opening of the circulation loop. This allows mixing of the melt present in the one or more reactor vessels and aids in the mass transfer. The circulation loop is optionally heated to avoid plugging of the loop which could happen when the melt crystallizes in the loop. A suitablecirculation pumping means is provided. For instance, the circulation loop may be equipped with a suitable circulation pumping means, typically located close to the reactor vessel, to circulate the melt from the reactor vessel(s) through the circulation loop back to the reactor vessel(s). Advantageously, the circulation pumping means may be chosen or configured, as known to the skilled person, to have a capacity to ensure optimized or maximized mixing of the melt in the reactor vessel(s). Optionally, the circulation loop may be equipped with an eductor or ejector to further enhance the mixing of the melt in the reactor vessel(s). Advantageously, the circulation of the melt promotes the separation of the gaseous by-products via flashing. When the melt is circulated in the circulation loop via the circulation pumping means, the melt is pressurized. During the circulation process of the melt in the circulation loop, the melt reacts further to its autocondensation products because of the heat. When the melt flows back into the respective reactor vessel, the gases, amongst others ammonia, which are produced during the condensation reaction of the melt, are released because of the pressure drop effected when the melt passes through the outlet opening of the circulation loop in the reactor vessel. In an optional embodiment, the outlet opening of the circulation loop, i.e. where the circulation loop is connected to the reactor vessel and where the melt flows out of the circulation loop into the respective reactor vessel, may be arranged as a narrowed orifice to further promote the pressure build-up and thereafter expansion of the flow of the melt, providing in amongst others a better separation of gaseous by-products and melt, or in other words an improved flashing of the melt. Stated differently, in certain embodiments, the circulation loop has an inlet and an outlet opening, where the circulation loop is connected to the reactor vessel, wherein the outlet opening is arranged as a narrowed orifice, wherein the diameter of the inlet opening has the same size as the diameter of the circulation loop and wherein the diameter of the outlet opening is smaller than the diameter of the inlet opening and smaller than the diameter of the circulation loop. Accordingly, in particular embodiments, the separation of the gaseous by-products and the urea-containing melt also comprises flashing the urea-containing melt during the circulation process, wherein the urea-containing melt is circulated back to the respective reactor vessel viaan outlet opening of the circulation loop forming, said outlet opening adapted to form a constricted flow section in the circulation loop.

[0067] The chemical composition of the composition added to the container and the composition of the obtained solid particles are substantially the same. Typically, only the water content can be slightly decreased due to some evaporation inside the mixing device. However, in view of the low water content, typically less than 4.5 wt.%, or even less than 2.0 wt.%, such losses by evaporation are minimal.

[0068] Consequently, the method according to the present disclosure provides solid particles, comprising: from 35 wt.% to 55 wt.% of urea, from 35 wt.% to 50 wt.% of biuret, and from 5.0 wt.% to 30 wt.% of the N-containing compounds produced during a urea condensation process, and, optionally, from 0.5 wt.% to 5.0 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; or from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 2.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 21 wt.% to 37 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; with wt.% based on the total weight of the particle.

[0069] The solid particles comprising urea, biuret, and N-containing compounds produced during a condensation process of urea, optionally comprising a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof, according to the present disclosure as described above, can typically be used as a feed supplement for ruminants as aNon-Protein Nitrogen (NPN) source in their feed. Accordingly, another aspect of the present disclosure provides for the use of the solid particles according to the present disclosure as a non-protein nitrogen source for ruminants.

[0070] In the following paragraphs, an embodiment of a mixing device according to the present disclosure as described above will be discussed in more detail. It is emphasized that this is only an exemplary embodiment of a system according to thepresent disclosure which does not limit the scope of protection of the present disclosure.

[0071] Figure 1 is a schematic drawing of a high intensity shear mixing device 1 that may be used to perform the method according to the present disclosure. The device 1 comprises a base 4 on which sits a container 3. The base 4 is configured such that the container 3 can be inclined at different angles compared to the ground (not shown on Figure 1). The device 1 comprises a mixing means 2 for mixing the content of the container 3. Here, the mixing means l is a rotor. The device 1 comprises an electrical engine which is contained in a casing 5, wherein the electrical engine is configured to rotate the mixing device 2 and the container 3 simultaneously or separately during operation. The rotating speed of the mixing means 2 and the container 3 can be set independently from each other.

[0072] Figure 2 is a schematic drawing of a container 3 that can be used in a mixing device for the present method, for example in the mixing device shown in Figure 1. The container 3 comprises a double wall, i.e. an outer wall 6 and an inner wall 7. The container 3 is configured such that the composition to be particulated is to be placed inside the inner wall 7. The container 3 also comprises an inlet 8 for a cooling liquid and an outlet 9 for a cooling liquid. In operation, the cooling liquid is located between the outer wall 6 and the inner wall 7 and cools down the composition present in the container 3. The cooling liquid may simply be in the space between the two walls, or the space between the two walls may comprise pipes carrying the cooling liquid from the inlet 8 to the outlet 9 (not shown on Figure 1).

[0073] The present disclosure will now further be described in more detail referring to an example of a method for producing solid particles comprising urea, biuret, and N-containing compounds produced during a urea condensation process according to the present disclosure. It should be clear that these are only examples and are not limitative to the scope of the present disclosure.

[0074] ExampleInitially, 700 g of an UB composition as described above with a diameter of 0.9 mm as seed material was added to a high-shear mixer as shown in Figure 1 set at rotationspeed of 3000 rpm. A melt comprising biuret, urea and N-containing compounds produced out of the condensation reaction from urea to biuret, totaling approximately 1000 g (comprising about 55wt% urea, about 35 wt% biuret, about 3 wt% triuret, about 0.5 wt% ammelide, about 2.5 wt% cyanuric acid and about 6 wt% water), was gradually (stepwise) poured into the high shear mixer. The operation method was paused twice to collect samples and once more after completing the addition of the melt. The table shows the average diameter (Dp 50%) for both the initial material and the collected samples. Particle size was determined by image analysis. DP 50% represents the median particle size, or, stated differently, 50% of the particles in the sample are smaller than this size, and 50% are larger.This indicates that granulation is proceeding properly: as the mixing continues and as the process advances, the melt solidifies on smaller particles or serves as an agglomerator, thereby increasing particle size until the target dimension is achieved.

Claims

C L A I M S1. A method for producing solid particles comprising urea, biuret, and N-containing compounds produced during a urea condensation process, wherein the solid particles comprise: from 35 wt.% to 55 wt.% of urea, from 35 wt.% to 50 wt.% of biuret, and from 5.0 wt.% to 30 wt.% of the N-containing compounds produced during a urea condensation process, and, optionally, from 0.1 wt.% to 5.0 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; or from 20 wt.% to 40 wt.% of urea, from 20 wt.% to 40 wt.% of biuret, from 2.0 wt.% to 15 wt.% of the N-containing compounds produced during a urea condensation process, and from 21 wt.% to 37 wt.% of a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof; with wt.% based on the total weight of the particles. a) wherein the method comprises the steps of adding a composition in the form of a melt or a mixture of a melt and a solid comprising urea, biuret, and N-containing compounds produced during a urea condensation process, in a container of a mixing device; b) mixing and preferably simultaneously actively cooling the composition present in the container, thereby solidifying the composition until the solid particles are formed; and c) removing the solid particles from the container.

2. The method according to claim 1, wherein step a is performed in(j) a static container and at least one rotating mixing element located inside the container which mixes the composition in the container, or(ii) a rotating container and a static mixing element located inside the container which mixes the composition in the container because of the rotational movement thereof,(iii) a rotating container and a rotating mixing element located inside the container which mixes the composition in the rotating container.

3. The method according to claim 1 or 2, wherein the container and / or the mixing element is rotated at a speed of from 0.1 to 70 m / s.

4. The method according to any one of claims 1 to 3, wherein the container and / or the mixing element rotates at variable speed during operation thereof.

5. The method according to any one of claims 1 to 4, wherein the container is tiltable or tilted in view of the horizontal.

6. The method according to any one of claims 1 to 5, wherein the composition is cooled to and subsequently maintained at a temperature of from 0°C to 100 °C in the container using the cooling means.

7. The method according to claim 6, wherein the cooling means are configured as providing the container with a double wall wherein in between the walls a cooling medium is present.

8. The method according to any one of claims 1 to 7, wherein the method comprises the step of scraping off the composition during solidification thereof from the inner wall of the container using a scraping tool located inside the container.

9. The method according to any one of claims 1 to 8, wherein during the method, the composition solidifies into large agglomerates, wherein the method comprises the step of chopping the large agglomerates into smaller agglomerates using a chopping tool located inside the container.

10. The method according to any one of claims 1 to 9, wherein the composition comprising urea, biuret, and N-containing compounds produced during a urea condensation process, and optionally a nitrate compound, is added in different steps in the container during operation thereof.

11. The method according to claim 10, wherein the composition is added to the container during operation thereof in at least a first step as a solid and in a subsequent step as a melt.

12. The method according to claim 10, wherein the composition is added to the container during operation thereof in at least a first step as a melt, and in a subsequent step when the melt has at least partially solidified again as a melt.

13. The method according to any one of claims 1 to 12, wherein the composition further comprises a nitrate compound, in particular a nitrate compound selected from the group of calcium nitrate, potassium nitrate, ammonium nitrate, sodium nitrate, magnesium nitrate, and mixtures thereof.

14. The method according to any one of claims 1 to 13, wherein the solid particles produced in step b) have an average size of between 1.0 mm and 4.5 mm, in particular between 1.2 mm and 3.0 mm, more in particular between 1.5 mm and 2.5 mm, and even more in particular between 1.8 mm and 2.2 mm.

15. The method according to any one of claims 1 to 14, wherein the mixing device is a mixer, a shear mixer, a ring-layer mix-pelletizer, a paddle mixer, a plow mixer, a conical mixer, a ribbon blender, a pugmill, a spiral mixer, or a planetary mixer.

16. Use of the solid particles produced by the method according to any one of claims1 to 14, as a non -protein nitrogen source for ruminants.

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