D,L-Methionine with optimized particle size distribution

Abstract

The present invention relates to D,L-methionine, which contains, based on the total weight of the D,L-methionine, 15% by weight or more but less than 50% by weight of D,L-methionine having a particle size of more than 0 and less than 150 μm, 50% by weight or more but less than 90% by weight of D,L-methionine having a particle size of more than 0 and less than 300 μm, and 30% by weight or more but less than 80% by weight of D,L-methionine having a particle size in the range of 63 to 300 μm, and has a bulk density of at least 710 kg / m, as well as a method for preparing said methionine.

Description

[Technical Field]

[0001] The present invention relates to D,L-methionine with an optimized particle size distribution and to a method for preparing said D,L-methionine with an improved particle size distribution.

[0002] According to U.S. Patent No. 5,770,769, D,L-methionine (hereinafter simply referred to as methionine) is prepared by reacting 3-methylthiopropionaldehyde with hydrogen cyanide, ammonia, and carbon dioxide to obtain 5-(2-methylmercaptoethyl)-hydantoin, followed by hydrolysis of the hydantoin in the presence of an inorganic base, typically potassium carbonate, to obtain a salt of methionine. Finally, the methionine salt is neutralized by bubbling carbon dioxide into an aqueous solution of the methionine salt to provide methionine, which precipitates from the solution. The crude methionine thus obtained is then recrystallized to improve purity, as described, for example, in U.S. Patent Application Publication No. 2015 / 051421. The resulting methionine has a bulk density of only 500-580 g / L.

[0003] The term bulk density is synonymous with the term bulk weight and refers to the density per volume of a mixture of particulate solids, the so-called bulk material, and a continuous fluid, typically air, occupying the pores or cavities between the particles, in other words the mass of said mixture per volume. A high and reproducible bulk density therefore allows a specific volume, such as the volume of a shipping container or bag, to be filled with the greatest possible amount of product. The bulk density of a product is therefore an important key value in the production of organic compounds. 1.34 g / cm -3 or 1,340 g / l of methionine, the process of US Patent Application Publication No. 2015 / 051421 provides a significantly lower methionine bulk density of only 500-580 g / l.

[0004] When a methionine salt solution is neutralized with carbon dioxide for crystallization, foaming is an important factor affecting the results of neutralization and crystallization during the crystallization process. In most prior art, antifoaming agents, flocculants, and other additives are added during the crystallization process to avoid or reduce foaming. According to EP 3246310, some of these additives adhere to the surface of the methionine crystals and are carried away by them, while the rest remain in the mother liquor and are recycled together with the mother liquor. According to EP 3246310, recycling the latter additives together with the mother liquor will change the proportion of the additives in the mother liquor or transform them into unknown substances due to heat, thereby affecting the subsequent neutralization and crystallization processes and increasing instability in the neutralization and crystallization processes. This, among other things, will reduce the bulk density of methionine. According to EP 3246310 A1, the use of a DTB neutralization crystallizer with a gas phase neutralization section solves the problems of foaming and bulk density loss, and neutralization in the liquid phase, which is prone to foaming, is transferred to the gas phase to essentially eliminate the foaming problem in the neutralization process, while controlling the supersaturation in the crystallization process effectively controls the formation of crystal nuclei, thereby obtaining methionine with high bulk density.

[0005] EP 2 133 329 A1 discloses a method for producing methionine, which comprises the steps of hydrolyzing 5-[2-(methylthio)ethyl]imidazolidine-2,4-dione in the presence of a basic potassium compound in a first continuous non-agitated reaction vessel, and heat-treating the reaction solution after hydrolysis in a second reaction vessel. The method of EP 2 133 329 A1 enables the production of methionine with a higher bulk density.

[0006] In the process of WO 2013 / 139562, methionine crystals are separated from the mother liquor by a solid / liquid separation step, for example, using a vacuum belt filter or centrifugation. In the next step, the methionine particles are dried by steaming. Here, steam is applied to the methionine-containing filter cake at the end of the belt filter, evaporating the remaining mother liquor still adhering to the methionine particles. The methionine thus obtained has a bulk density of up to 650 g / l. Further experiments have shown that fine methionine particles (dust) are removed during drying in the steaming process. This is believed to have a negative impact on the bulk density of the methionine thus obtained.

[0007] The prior art method uses 680 kg / m 3 These methods result in methionine with a bulk density far below the desired bulk density or with a bulk density that can only be obtained by processes that are rather complicated and not suitable for industrial scale. Therefore, it has remained a problem to provide methionine with an optimized particle size distribution that provides methionine with increased bulk density.

[0008] According to the present invention, the object is to provide D,L-methionine, based on the total weight of D,L-methionine: 15% by weight or more and less than 50% by weight of D,L-methionine having a particle size greater than 0 and less than 150 μm; 50% to less than 90% by weight of D,L-methionine with a particle size greater than 0 and less than 300 μm, and 30% to less than 80% by weight of D,L-methionine with a particle size ranging from 63 to 300 μm This is resolved by D,L-methionine.

[0009] The D,L-methionine is at least 710 kg / m 3 It has a bulk density of

[0010] Therefore, an object of the present invention is to provide D,L-methionine, which, based on the total weight of D,L-methionine, 15% by weight or more and less than 50% by weight of D,L-methionine having a particle size greater than 0 and less than 150 μm; 50% to less than 90% by weight of D,L-methionine with a particle size greater than 0 and less than 300 μm, and 30% to less than 80% by weight of D,L-methionine with a particle size ranging from 63 to 300 μm Including, At least 710 kg / m 3 having a bulk density of D,L-methionine.

[0011] Any open-ended range is used in the context of this invention to represent a range where the lower endpoint not explicitly mentioned is always greater than 0. This applies to any open-ended range of proportions given in weight percent (wt%) and to any open-ended range of particle sizes given in μm.

[0012] All weight percentages (wt%) used in the context of the present invention are always based on the total weight of methionine. Deviations from the explicitly stated weight percentages are within the scope of the present invention, provided that they still provide the technical benefits of the present invention.

[0013] The D,L-methionine according to the invention always has a yield of at least 710 kg / m 3 , and even 740 kg / m 3 The D,L-methionine according to the present invention has a bulk density of up to 760 kg / m 3 The bulk density of the cellulose acylate may be 0.01 to 0.15.

[0014] Preferably, the upper limit for D,L-methionine having a particle size greater than 0 and less than 300 μm is 70% by weight.

[0015] In one embodiment, the D,L-methionine according to the present invention contains 50 to 70% by weight of D,L-methionine having a particle size of more than 0 μm and less than 300 μm.

[0016] Preferably, the lower limit of D,L-methionine having a particle size in the range of 63 to 300 μm is 30% by weight, and more preferably, the upper limit of methionine having a particle size in the range of 60 to 300 μm is 75% by weight.

[0017] In another embodiment, the D,L-methionine according to the present invention contains 30 to 75% by weight of D,L-methionine having a particle size in the range of 63 to 300 μm.

[0018] Preferably, the D,L-methionine according to the present invention contains 30 to 60 wt % or 30 to 65 wt % of D,L-methionine having a particle size in the range of 63 to 300 μm.

[0019] Preferably, the lower limit for methionine according to the present invention having particles greater than 0 and less than 150 μm is 15% by weight.

[0020] Preferably, the D,L-methionine according to the present invention is 15% by weight or more and less than 50% by weight of D,L-methionine having a particle size greater than 0 and less than 150 μm; 50% to 90% by weight or 50 to 70% by weight of D,L-methionine having a particle size of more than 0 and less than 300 μm, and 30% to 75% by weight of D,L-methionine with a particle size ranging from 63 to 300 μm include.

[0021] Preferably, D,L-methionine according to the present invention also includes D,L-methionine having a particle size greater than 300 μm, for example 300-500 μm, 500-710 μm, 710-1000 μm, and optionally greater than 1000 μm.

[0022] Preferably, the lower limit of D,L-methionine having a particle size of 300 to 500 μm is 10% by weight, and the upper limit of D,L-methionine having a particle size of 300 to 500 μm is 45% by weight or 50% by weight.

[0023] In a further embodiment of the D,L-methionine according to the invention, the D,L-methionine also comprises 10 to 45% by weight or 10 to 50% by weight of D,L-methionine having a particle size of 300 to 500 μm.

[0024] Preferably, the D,L-methionine according to the present invention also includes D,L-methionine having a particle size of 500 to 710 μm. Preferably, the lower limit of the D,L-methionine having a particle size of 500 to 710 μm is 1% by weight, and the upper limit of the D,L-methionine having a particle size of 500 to 710 μm is 20% by weight.

[0025] In a further embodiment, the D,L-methionine according to the invention also comprises 1 to 20% by weight of D,L-methionine having a particle size of 500 to 710 μm.

[0026] Preferably, the D,L-methionine according to the present invention also contains D,L-methionine having a particle size of 710 to 1000 μm. Preferably, the upper limit of the D,L-methionine having a particle size of 710 to 1000 μm is 10% by weight.

[0027] In yet another embodiment, the D,L-methionine according to the present invention also contains from greater than 0 to 10% by weight of D,L-methionine having a particle size of 710 to 1000 μm.

[0028] Preferably, the D,L-methionine according to the invention also comprises D,L-methionine having a particle size of more than 1000 μm. Preferably, the upper limit of D,L-methionine having a particle size of more than 1000 μm is 5% by weight, in particular 2% by weight.

[0029] In a further embodiment, the D,L-methionine according to the invention comprises up to 5% by weight of D,L-methionine having a particle size above 1000 μm.

[0030] The D,L-methionine according to the present invention is not limited with respect to the specific amounts of D,L-methionine having particles less than 32 μm, D,L-methionine having a particle size of 32-63 μm, D,L-methionine having a particle size of 63-100 μm, and D,L-methionine having a particle size of 100-150 μm, provided that the individual amounts of said particle size ranges meet the requirement that at least 15% but less than 50% by weight of the D,L-methionine has a particle size greater than 0 and less than 150 μm.

[0031] Nevertheless, it is preferred that the methionine according to the invention comprises from 0 to 20% by weight of methionine having a particle size of less than 32 μm, that the methionine according to the invention comprises from 0 to 20% by weight of methionine having a particle size in the range of 32-63 μm, that the methionine according to the invention comprises from 0 to 10% by weight of methionine having a particle size in the range of 63-100 μm, and / or that the methionine according to the invention comprises from 5 to 15% by weight of methionine having a particle size in the range of 100-150 μm.

[0032] In one embodiment, the D,L-methionine according to the present invention is up to 10% by weight of D,L-methionine with a particle size ranging from 63 to 100 μm, 20 to 50% by weight of D,L-methionine having a particle size greater than 0 and less than 150 μm, 50 to 70% by weight of D,L-methionine having a particle size greater than 0 and less than 300 μm, 30-75% by weight of D,L-methionine with a particle size ranging from 63 to 300 μm, 10 to 65% by weight of D,L-methionine with a particle size in the range of 300 to 500 μm, 1 to 20% by weight of D,L-methionine having a particle size in the range of 500 to 710 μm, from greater than 0 to 10% by weight of D,L-methionine having a particle size in the range of 710 to 1000 μm, and Up to 5% by weight of D,L-methionine with a particle size greater than 1000 μm include.

[0033] In another embodiment, the D,L-methionine according to the present invention is up to 10% by weight of D,L-methionine with a particle size ranging from 63 to 100 μm, 20 to 50% by weight of D,L-methionine having a particle size greater than 0 and less than 150 μm, 50 to 70% by weight of D,L-methionine having a particle size greater than 0 and less than 300 μm, 30-65% by weight of D,L-methionine with a particle size ranging from 63 to 300 μm, 10 to 45% by weight of D,L-methionine with a particle size in the range of 300 to 500 μm, 1 to 20% by weight of D,L-methionine having a particle size in the range of 500 to 710 μm, from greater than 0 to 10% by weight of D,L-methionine having a particle size of 710 to 1000 μm, and Up to 5% by weight of D,L-methionine with a particle size greater than 1000 μm include.

[0034] D,L-methionine, which has these characteristics, always has a viscosity of 710 kg / m 3 Ultra-high bulk density, specifically at least 720 kg / m 3 , and even up to 730 or 740 kg / m 3 It has ultra-high bulk density.

[0035] In yet another embodiment, the D,L-methionine according to the present invention contains 10 to 40% by weight of D,L-methionine having a particle size of 300 to 500 μm.

[0036] In a further embodiment, the D,L-methionine according to the invention comprises up to 2% by weight of D,L-methionine having a particle size above 1000 μm.

[0037] Preferably, the D,L-methionine according to the present invention is 15% by weight or more and less than 50% by weight of D,L-methionine having a particle size greater than 0 and less than 150 μm; 50 to 70% by weight of D,L-methionine having a particle size greater than 0 and less than 300 μm, 30-65% by weight of D,L-methionine with a particle size in the range of 63-300 μm, from greater than 0 to 20% by weight of D,L-methionine with a particle size of greater than 0 to 32 μm, from more than 0 to 15% by weight of D,L-methionine with a particle size in the range of 32 to 63 μm, from more than 0 to 10% by weight of D,L-methionine with a particle size in the range of 63 to 100 μm, 5 to 20% by weight of D,L-methionine with a particle size in the range of 100 to 150 μm, 5 to 20% by weight of D,L-methionine with a particle size in the range of 150 to 200 μm, 5 to 35% by weight of D,L-methionine with a particle size in the range of 200 to 300 μm, 10 to 45% by weight of D,L-methionine with a particle size in the range of 300 to 500 μm, from more than 0 to 20% by weight of D,L-methionine with a particle size in the range of 500 to 710 μm, from more than 0 to 10% by weight of D,L-methionine with a particle size of 710 to 1000 μm, D,L-methionine with a particle size of more than 1000 μm, up to 2% by weight include.

[0038] The present invention is not limited to any particular method for determining the individual weight percentages of D,L-methionine having a particular particle size. In the context of the present invention, it is preferred that D,L-methionine having the full spectrum of particle sizes be subjected to sieve analysis, preferably aerodynamic sieve analysis according to the following method:

[0039] The full spectrum of D,L-methionine particle size distribution was determined using an airflow sieving machine, such as the Hosokawa Alpine 200LS-N, equipped with a series of sieves (V2A type) with different mesh sizes. The series begins with a sieve with a mesh size greater than 1000 μm, followed by a series of increasingly smaller mesh sizes (710-1000 μm, 500-710 μm, 300-500 μm, 200-300 μm, 150-200 μm, 100-150 μm, 63-100 μm, and 32-63 μm), and ends with a sieve with a maximum mesh size of 32 μm. Because the material is moved through the different sieves solely by the airflow, particle attrition, which would otherwise affect the particle size distribution, is negligible. Specifically, a portion of the material to be analyzed, e.g., 25 g of the compound of interest, is accurately weighed and placed on the sieve with the finest mesh size. The sieve is placed in a sieving machine, the lid is closed, and sieving begins. After 3 minutes of sieving, the residue in the sieve is weighed and quantitatively transferred onto the next mesh size sieve using a brush, and this procedure is repeated. If static charging is a problem, an antistatic agent, such as alumina C, can be added to the sample at a rate of 0.5 to 1% based on the sample weight.

[0040] The sieve analysis is given as the percentage of the initial amount that passed through the sieve of each mesh size but was retained on the sieve of the smaller mesh size, which can be calculated using the following formula:

number

[0041] W = sample weight (g), R = sample residue on the sieve of each mesh size (g).

[0042] The amount of optionally added antistatic agent, e.g., alumina C, is so small that it can be ignored in the sieve analysis.

[0043] The bulk density is preferably determined in accordance with DIN ISO 697 and EN ISO 60. For example, the following procedure can be used.

[0044] A standard apparatus is used to determine bulk density. It includes a measuring cylinder (e.g., a 250 ml measuring cylinder), a tripod with a funnel whose volume is larger than the measuring cylinder's volume and whose outlet is designed to be flush with the cylinder's opening, a rotary dump, and a latch for the measuring cylinder. Before first use, the funnel must be adjusted to the same height as the measuring cylinder, and the rotary dump must be closed. Furthermore, the unfilled measuring cylinder is weighed on a laboratory balance (Sartorius LP4200S) and secured to the standard apparatus. The metal funnel is then completely filled with the test substance. Before this, the rotary dump is checked to ensure it is closed. The metal funnel is then completely filled with the test substance, and the rotary dump is then opened to allow the test substance to easily flow into the measuring cylinder. Because the funnel's volume is larger than that of the measuring cylinder, a small amount of test substance overflows. The small amount of overflow from the measuring cylinder is eliminated by completely closing the rotary dump, resulting in a consistent accurate volume of 250 ml. The filled graduated cylinder is then weighed on a laboratory balance. If necessary, the outside of the graduated cylinder is cleaned and smoothed. The bulk density (kg / m 3 ) can be calculated by multiplying the weight difference [g] by the factor required to reach a volume of 1000 ml. For a graduated cylinder with a volume of 250 ml, said factor is 4. The general formula for calculating bulk density is:

number

[0045] W = sample weight (g), V I = initial volume (ml).

[0046] In principle, the present invention is not limited with respect to the particular method for preparing methionine according to the present invention, however, air-flow delivery of methionine through hollow helices has been found to be particularly suitable for providing methionine according to the present invention.

[0047] It is believed that air conveying causes methionine particles to constantly move, causing collisions between the particles and with the circular inner and outer walls of the hollow spiral. These collisions have an abrasive effect on the particles. Therefore, one skilled in the art would expect that air conveying methionine through a hollow spiral would result in methionine that is predominantly or primarily made up of very fine particles, specifically dust. Such methionine would not have the appropriate mixture of fine, medium, and coarse particles that are beneficial for increasing the bulk density of methionine. It was therefore quite surprising that air conveying methionine through a hollow spiral resulted in methionine with the appropriate mixture of fine, medium, and coarse particles that are beneficial for increasing the bulk density of methionine. The methionine obtained from this preparation method still contains moisture, particularly water, and is therefore hereinafter also referred to as wet methionine. It has been found that moisture can be removed very efficiently from methionine by convective transfer of heat from a heat carrier to the methionine transported through the hollow spirals, such that said heat transfer and airflow transport of methionine through the hollow spirals occur simultaneously.

[0048] Therefore, another object of the present invention is a method for preparing D,L-methionine according to the invention, which comprises: i) a step of air-transporting D,L-methionine through a hollow helix (1); and ii) convectively transferring heat from a heat exchange medium to the D,L-methionine transported through the hollow spiral to remove water from the methionine. Including, Steps i) and ii) are carried out simultaneously; It is a method.

[0049] The process according to the invention can be considered as a post-treatment of D,L-methionine obtained from the process for its preparation.

[0050] The method for preparing D,L-methionine according to the present invention is preferably integrated into an overall method for preparing methionine, and is therefore part of an overall method for preparing methionine.

[0051] The term hollow spiral is used in the context of the present invention to describe a conveying unit that can be represented by a screw conveyor in a tube, the turns of which are tightly fitted together with the tube. From the outside, the hollow spiral appears as a tube with an opening at each end and an outlet side. The opening at the first end is where the conveyed methionine enters the hollow spiral, and the second opening at the other end is where the conveyed methionine exits the hollow spiral.

[0052] The terms "pneumatic transport" or "pneumatically transporting" are used in the context of the present invention to refer to the transport of methionine in step i) of the method by a gas stream, e.g., a stream of air. Thus, pneumatic transport can be achieved by applying an overpressure or pressure above atmospheric pressure at the opening side of the hollow spiral, thereby forcing methionine into and through the hollow spiral. Overpressure or pressure above atmospheric pressure is any type of pressure higher than atmospheric pressure. Alternatively, pneumatic transport can be achieved by applying a reduced pressure or subatmospheric pressure at the exit side of the hollow spiral, thereby drawing or sucking methionine into and through the hollow spiral. Subatmospheric pressure or pressure below atmospheric pressure is any type of pressure below atmospheric pressure. In either case, the overpressure or reduced pressure is the driving force for pneumatic transport of methionine through the hollow spiral. Therefore, regardless of whether overpressure or underpressure is used, it is always necessary to provide a pressure difference between the opening of the hollow spiral and the outlet side. For example, the pressure difference can range from about 0.1 bar to about 10 bar, with individual pressure differences of 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 bar. Under standard operating conditions, preferred pressure differences are up to about 1 bar, 700 mbar, or 600 mbar.

[0053] In one embodiment, the pneumatic conveying in step i) of the method according to the invention is achieved by superatmospheric pressure or by vacuum. Preferably, the pneumatic conveying in step i) of the method according to the invention is achieved by superatmospheric pressure.

[0054] In the simplest case, the overpressure is provided by a fan and the reduced pressure by a pump. Preferably, the fan or pump has an upstream cyclone filter or separator which separates any particles carried away from the environment, thereby keeping them out of the gas or air stream.

[0055] The hollow spiral (1) also includes a passage (2) extending through the axis of the hollow spiral, which contains a heat exchange medium. The hollow spiral (1) may also include a jacket (3) surrounding the hollow spiral, which also contains a heat exchange medium. In either case, heat transfer is always indirect from the heat exchange medium to the methionine transported in the airflow through the hollow spiral. Specifically, heat transfer occurs by heat conduction through a wall separating the hollow spiral from the surrounding jacket and / or by heat conduction through a wall separating the hollow spiral from the internal passage through the axis of the hollow spiral. Preferably, the hollow spiral (1) including the passage (2) through the axis of the hollow spiral and the surrounding jacket (3) is a thin film dryer or a swivel tube dryer.

[0056] According to this embodiment, water is removed from the methionine by heat transferred from the heat transfer medium. Because most processes for preparing methionine involve an aqueous reaction medium or recrystallization from crude methionine in some aqueous medium, the wet methionine used in this embodiment is likely to contain water. Even after separation from the aqueous medium and optional drying, the methionine thus obtained still contains residual moisture, essentially water. Therefore, when methionine is prepared in a non-aqueous medium and / or recrystallized from a non-aqueous medium, a temperature of at least 100°C, e.g., 110-140°C, is considered sufficient to completely remove water and all other solvents from the methionine, or at least as completely as possible. In principle, this embodiment is not limited to a specific heat exchange medium. Therefore, any type of heat exchange medium can be used, e.g., any type of fluid or fluid mixture, such as a liquid, a liquid mixture, a gas, e.g., steam or high-temperature steam, or a gas mixture. provided that the fluid or fluid mixture has a sufficient heat capacity to store the necessary heat to be transferred to the methionine, specifically a sufficient heat capacity to transfer heat of at least 100° C. to the methionine. The heat exchange medium is preferably fed through the passage (2) and jacket (3), preferably countercurrently to the pneumatically transported methionine.

[0057] In a preferred embodiment of the process according to the invention, the heat exchange medium supplied in step ii) has a temperature of at least 100°C.

[0058] In one embodiment of the method according to the present invention, wet methionine is conveyed through a hollow spiral (1) by airflow, while heat is convectively transferred from the heat exchange medium to the methionine being conveyed through the hollow spiral, thereby removing moisture from the methionine. A high residual moisture content in the methionine being subjected to the present invention can significantly adversely affect the progress of the process or the particle size distribution of the methionine. For example, methionine with an excessively high moisture content may aggregate during airflow conveyance through the hollow spiral. In the worst case, this can clog the hollow spiral or significantly reduce the efficiency of heat transfer from the heat exchange medium to the methionine. This can cause turbulence in the flow of the conveyed methionine, which is thought to result in excessive grinding of the methionine. However, this will shift the particle size distribution of the methionine to smaller particles. That is, the finer the particles, the greater the proportion of dust particles. As a result, the bulk density of the methionine will decrease. It has been found that methionine with a water content of up to 5% by weight can still be fed to the process according to the invention without clogging the hollow helices, disrupting the flow of pneumatically transported methionine, or other adverse effects, as determined after separating the methionine from the mother liquor in which it was precipitated.

[0059] Thus, in a preferred embodiment of the method according to the invention, the methionine provided in step i) has a water content of at most about 5% by weight.

[0060] The methionine having a water content of more than 5% by weight is mixed with dry methionine before being subjected to the process according to the invention. The mixing ratio of the methionine having a water content of more than 5% by weight to the dry methionine depends on the respective water content of the methionine.

[0061] The process according to the invention allows the preparation of D,L-methionine according to the invention, including all of the embodiments described above.

[0062] Another object of the invention is therefore also the D,L-methionine according to the invention, obtained and / or obtainable by the method according to the invention. [Brief explanation of the drawings]

[0063] [Figure 1] 1 is an exemplary diagram of a hollow spiral used in a method according to the present invention, where (1) is the hollow spiral, the hollow spiral (1) contains a passageway (2) therein, the path of which is shown by a thin dotted line, and (3) is a jacket surrounding the hollow spiral.

[0064] Working Example: 1. Sieve Analysis The particle size distribution of D,L-methionine was determined using an airflow sieving machine (Hosokawa Alpine, Model 200LS-N) equipped with a series of sieves (Model V2A) with different mesh sizes. The sieves began with a sieve with a mesh size greater than 1000 μm, followed by a series of increasingly smaller mesh sizes (710-1000 μm, 500-710 μm, 300-500 μm, 200-300 μm, 150-200 μm, 100-150 μm, 63-100 μm, and 32-63 μm), and ended with a sieve with a maximum mesh size of 32 μm. Because the material was moved through the different sieves solely by the airflow, particle attrition, which would affect the particle size distribution, was negligible. Specifically, a portion of the material to be analyzed, e.g., 25 g of the compound of interest, was accurately weighed and placed on the sieve with the finest mesh size. The sieve was placed in a sieving machine, the lid was closed, and sieving began. After 3 minutes of sieving, the residue in the sieve was weighed and quantitatively transferred onto the next mesh size sieve using a brush, and this procedure was repeated. If static charging was a problem, 0.5 to 1% of an antistatic agent, such as alumina C, based on the sample weight was added to the sample.

[0065] Sieve analysis is given as the percentage of the initial amount that passed through the sieve of each mesh size but was retained on the sieve of the smaller mesh size, which could be calculated using the following formula:

number

[0066] W = sample weight (g), R = sample residue on the sieve of each mesh size (g).

[0067] 2. Bulk density The bulk density of D,L-methionine was determined using the following procedure: A standard apparatus was used to determine bulk density. The apparatus included a measuring cylinder (e.g., a 250 ml measuring cylinder), a tripod with a funnel having a volume larger than the volume of the measuring cylinder and an outlet designed to be flush with the opening of the cylinder, a rotary dump, and a latch for the measuring cylinder. Prior to first use, the funnel was adjusted to the same height as the measuring cylinder, and the rotary dump was closed. Furthermore, the unfilled measuring cylinder was weighed on a laboratory balance (Sartorius LP4200S) and then secured to the standard apparatus. The rotary dump was then checked for closure. The metal funnel was then completely filled with the test substance, and the rotary dump was then opened to allow the test substance to easily flow into the measuring cylinder. Because the funnel's volume was larger than that of the measuring cylinder, a small amount of test substance spilled over. The slight spill from the measuring cylinder was eliminated by completely closing the rotary dump, resulting in a consistently accurate volume of 250 ml. The filled graduated cylinder was then weighed on a laboratory balance. If necessary, the outside of the graduated cylinder was then cleaned and smooth. Bulk density (kg / m 3 ) was calculated by multiplying the weight difference [g] by the factor required to reach a volume of 1000 ml. For a graduated cylinder with a volume of 250 ml, said factor was 4. The general formula for calculating bulk density is:

number

[0068] W = sample weight (g), V I= initial volume (ml).

[0069] 3. Comparative Example 1: In this example, three runs of methionine crystals from two crystallizers were separated from the mother liquor by a solid / liquid separation process using a pump and a vacuum belt filter. The filter cake thus obtained was washed and then dried by steam treatment at the end of the belt filter. Specifically, steam was applied to the filter cake from above to further dry it by evaporating the mother liquor that normally remains between the crystals. Sieve analysis and bulk density measurements were performed on the methionine thus obtained. Differences in bulk density were attributed to variations in crystallizer performance / operation. Table 1 shows the results of the sieve analysis and bulk density measurements, labeled C1–C3.

[0070] 4. Example 1: Comparative Example 1 was repeated for 10 runs, except that the D,L-methionine was subjected to a thin-film dryer instead of steam treatment. Sieve analysis and bulk density measurements were performed on the D,L-methionine thus obtained. Differences in bulk density were due to variations in crystallizer performance / operation and variations in thin-film dryer operating conditions. Table 1 shows the results of the sieve analysis and bulk density measurements, denoted as E1 to E10.

[0071] [Table 1]

Claims

1. 1. A method for preparing D,L-methionine, comprising the steps of: - 15% by weight or more and less than 50% by weight of the D,L-methionine having a particle size of more than 0 and less than 150 μm; - 50% to less than 90% by weight of the D,L-methionine having a particle size of greater than 0 and less than 300 μm; and 30% by weight or more and less than 80% by weight of the D,L-methionine having a particle size in the range of 63 to 300 μm Including, The D,L-methionine is at least 710 kg / m ３ and having a bulk density of i) air-transferring D,L-methionine through a hollow helix; and ii) convectively transferring heat from a heat exchange medium to the D,L-methionine transported through the hollow spiral to remove moisture from the D,L-methionine. Including, Steps i) and ii) are carried out simultaneously; method.

2. 2. The method of claim 1, wherein the D,L-methionine has a particle size of greater than 0 and less than 300 μm, and the content is 50 to 70% by weight.

3. 2. The method of claim 1, wherein the D,L-methionine has a particle size in the range of 63 to 300 μm and comprises 30 to 75% by weight.

4. 2. The method of claim 1, wherein the D,L-methionine has a particle size in the range of 63 to 300 μm and comprises 30 to 65% by weight.

5. 2. The method of claim 1, wherein the D,L-methionine has a particle size of 300 to 500 μm and is contained in an amount of 10 to 50% by weight.

6. 2. The method of claim 1, further comprising 1 to 20% by weight of said D,L-methionine having a particle size of 500 to 710 μm.

7. 2. The method of claim 1, further comprising from greater than 0 to 10% by weight of said D,L-methionine having a particle size of 710 to 1000 μm.

8. 2. The method of claim 1, wherein the D,L-methionine has a particle size of more than 1000 μm and contains up to 5% by weight of the D,L-methionine.

9. up to 10% by weight of said D,L-methionine having a particle size in the range of 63 to 100 μm; 20 to 50% by weight of said D,L-methionine having a particle size greater than 0 and less than 150 μm; 50 to 70% by weight of said D,L-methionine having a particle size greater than 0 and less than 300 μm; 30 to 75% by weight of said D,L-methionine having a particle size in the range of 63 to 300 μm; 10 to 65% by weight of said D,L-methionine having a particle size in the range of 300 to 500 μm; 1 to 20% by weight of said D,L-methionine having a particle size in the range of 500 to 710 μm; from greater than 0 to 10% by weight of said D,L-methionine having a particle size of 710 to 1000 μm, and up to 5% by weight of said D,L-methionine having a particle size of more than 1000 μm The method of claim 1 , comprising:

10. up to 10% by weight of said D,L-methionine having a particle size in the range of 63 to 100 μm; 20 to 50% by weight of said D,L-methionine having a particle size greater than 0 and less than 150 μm; 50 to 70% by weight of said D,L-methionine having a particle size greater than 0 and less than 300 μm; 30 to 65% by weight of said D,L-methionine having a particle size in the range of 63 to 300 μm; 10 to 45% by weight of said D,L-methionine having a particle size in the range of 300 to 500 μm; 1 to 20% by weight of said D,L-methionine having a particle size in the range of 500 to 710 μm; from greater than 0 to 10% by weight of said D,L-methionine having a particle size of 710 to 1000 μm, and up to 5% by weight of said D,L-methionine having a particle size of more than 1000 μm The method of claim 1 , comprising:

11. The method of claim 1, wherein the D,L-methionine has a bulk density of at least 720 kg / m 3 .

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