A process for obtaining an amino acid in crystalline form from a salt of said amino acid in aqueous solution

Abstract

The invention relates to a process for obtaining an amino acid in crystalline form, from a salt of said amino acid in aqueous solution, in the presence of carbon dioxide under pressure, said process being carried out in a forced circulation crystallizer (1), the latter comprising a chamber (2) having a lower part (3) and an upper part (4), the lower part (3) containing an aqueous liquid medium (6) comprising the amino acid and the upper part (4) containing carbon dioxide under pressure (7), and an external circuit (8) to this chamber (2) supplied with aqueous solution of said amino acid (5) and bringing it into the upper part (4) of the chamber (2), said external circuit (8) being connected to the chamber (2) from an outlet (9) located in the lower position of the chamber (2) to at least one inlet (10, 17) located in the upper position of the chamber (2), passing through a heat exchanger (11),said process comprising the following steps: the forced circulation crystallizer (1) is supplied with aqueous solution (5) of said salt, through at least one inlet (12, 12') in the external circuit (8) opening into the upper part (4) of the chamber (2) via the inlet (10); the aqueous solution (5) of said salt arriving in the upper part (4) of the chamber (2) from at least the inlet (10,17) by means of a distributor (13) emitting downward jets (14) towards the lower part (3) of the chamber (2); carbon dioxide is injected into the external circuit (8) and / or into the upper part (4) of the chamber (2) to obtain a pressurized carbon dioxide environment in the upper part (4) above the aqueous liquid medium (6); a juice containing the amino acid in crystalline form is collected at the bottom of the chamber (2) and conveyed to a purification module (15), and a juice substantially free of amino acid in crystalline form is drawn off and recirculated into the external circuit (8); and said amino acid is obtained in crystalline form in the purification module (15).

Description

Title of the invention: Process for obtaining an amino acid in crystalline form from a salt of said amino acid in aqueous solution

[0001] The invention relates to the manufacture of an amino acid and in particular its obtaining in crystalline form from an aqueous solution of a salt of said amino acid.

[0002] In the present text, the invention is described with reference to methionine, because its market size, which is major in animal nutrition, is enormous. It is indeed produced in the hundreds of thousands of tons per year.

[0003] The invention applies, however, to obtaining any other amino acid, the final stage of which is its purification from one of its salts.

[0004] Methionine is primarily manufactured by chemical synthesis, and its manufacturing processes are still the subject of much development. Methionine can be prepared by various processes involving different synthetic intermediates, and methionine salt, the salt of methionine and generally of an alkali metal such as sodium or potassium, is often the last. It is acidified (or neutralized) to methionine, which is then purified by crystallization.

[0005] One of the known chemical processes for obtaining methionine, see for example US2557920A, comprises a step of converting hydantoin from methionine, or 5-[2-methylthio)ethyl]-2,4-imidazolidinedione (also referred to as hydantoin in this text), by alkaline hydrolysis, or saponification, to the methionine salt, carried out in the presence of sodium hydroxide and / or sodium carbonate, in aqueous phase, under heat and pressure. This reaction is characterized by the simultaneous removal of carbon dioxide and ammonia, which are removed from the hydrolysis medium, for example, by filtration of the precipitated sodium carbonate and by stripping of the ammonia. The hydrolysis reaction medium containing the methionine is then acidified (or neutralized) with concentrated sulfuric acid to yield methionine. Methionine can then be purified by crystallization, by cooling, and then separated from the sodium sulfate formed by filtration.

[0006] The major drawback of this passage through the sodium methionate intermediate is the formation of large volumes of sodium sulfate, at the end of the neutralization, which cannot be recycled in the methionine manufacturing process and which are difficult to valorize.

[0007] Prior art provides some answers to this problem. Thus, according to the process described in WO2016 / 170252A1, a step of concentrating the hydrolysis reaction medium before neutralization is added, resulting in carbonate crystallization sodium, which limits the amount of sodium ions available to form sodium sulfate. Another solution involves saponifying hydantoin in the presence of a catalyst, such as a metal oxide, as illustrated in document US2004039228A1. However, these solutions have the drawback of complicating the industrial process for synthesizing methionine.

[0008] Document WO2016 / 127707A1 describes a process for continuously obtaining methionine crystals from potassium methionate in aqueous solution, comprising neutralizing the salt in the presence of carbon dioxide and crystallizing the methionine in a draft tube crystallizer (DTB type crystallizer for Draft Tube Baffle) equipped with an internal axial pump allowing homogenization of the crystals formed.

[0009] The invention provides a method which makes it possible to remedy the above problems and which, moreover, makes it possible to integrate the methionate neutralization step and the methionine crystallization step into a single unit, namely a forced recirculation crystallizer.

[0010] The process allows a stream of aqueous methionate solution to be treated to produce crystallized methionine of high purity, without forming unusable salts.

[0011] The crystallizer consists of an upper part in which methionine or a salt of another amino acid is sprayed and neutralized by carbon dioxide, and a lower part in which there is an aqueous liquid medium comprising methionine or any other amino acid, in salt form, in neutralized form and / or in crystallized form, this lower part ending in a constriction from which on the one hand the methionine crystals are recovered and on the other hand a juice of aqueous liquid medium essentially free of methionine crystals is recirculated to the upper part of the crystallizer.

[0012] The originality of the process of the invention lies in the simultaneous performance of the neutralization of the amino acid salt and the crystallization of the amino acid in the same environment, without requiring adjustment of parameters for neutralization and crystallization, respectively. The parameters of the process of the invention are defined for both steps.

[0013] Thus, the invention lies in a process for obtaining an amino acid in crystalline form, from a salt of said amino acid in aqueous solution, in the presence of carbon dioxide under pressure, said process being carried out in a forced circulation crystallizer, the latter comprising a chamber having a lower part and an upper part, the lower part containing an aqueous liquid medium comprising the amino acid and the upper part containing carbon dioxide under pressure, and an external circuit to this chamber supplied with aqueous solution of said amino acid and bringing it in the upper part of the crystallizer chamber, said external circuit being connected to said chamber from an outlet located in the lower position of the chamber to an inlet located in the upper position of the chamber, passing through a heat exchanger, said process comprising the following steps:

[0014] the forced circulation crystallizer is supplied with aqueous solution of said salt, via at least one inlet in the external circuit opening into the upper part of the chamber via the inlet;

[0015] the aqueous solution of said salt arriving in the upper part of the chamber from the inlet is dispersed by means of a distributor emitting downward jets towards the lower part of the chamber;

[0016] Carbon dioxide is injected into the external circuit and / or into the upper part of the chamber to obtain a carbon dioxide pressurized environment in the upper part above the aqueous liquid medium;

[0017] A juice containing the amino acid in crystalline form is collected at the bottom of the chamber and conveyed to a purification module, and a juice substantially free of amino acid in crystalline form is drawn off and recirculated in the external circuit; and

[0018] The amino acid is obtained in crystalline form in the purification module.

[0019] Before describing in more detail the characteristics and advantages of this process, certain terms used in this text are defined or clarified.

[0020] Amino acid crystals and amino acid in crystalline form have the same definition.

[0021] By crystalline methionine, also called methionine in powder form or in solid form, is meant methionine with a degree of purity of at least 85%, preferably at least 90%, or even at least 95%, which can go up to 99%, or even beyond.

[0022] An aqueous solution of methionine, or methionine in aqueous solution, may contain only methionine; it may contain unpurified or partially purified methionine as obtained from its synthesis. In this case, the aqueous solution of methionine will consist of a reaction medium resulting from the saponification of methionine hydantoin leading to methionine, which may contain molecules other than methionine. Methionine hydantoin may be obtained from 2-hydroxy-4-methylthio-butyronitrile (HMTBN). Preferably, it is not isolated from the reaction medium, and the latter is directly subjected to the saponification conditions.Thus, by other molecules present in the aqueous methionine solution, we mean molecules from the saponification medium of hydantoin from methionine to methionine, but also molecules that may come from previous stages of the methionine manufacturing process, and in particular from the hydantoin synthesis stage.

[0023] Methionate is a salt of methionine. Its nature results from the conditions of its synthesis. It can be a salt of an alkali metal, such as a sodium salt or a potassium salt. In the context of the present invention, it is preferably a salt of methionine and potassium, the potassium ion originating from the reaction medium for the saponification of hydantoin in the presence of potassium carbonate. The invention is, of course, not limited to such a salt, and the process is suitable for obtaining any amino acid in crystalline form from a corresponding salt, and in particular an amino acid salt and an alkali metal such as sodium or potassium.

[0024] Forced recirculation crystallization is a technique known to those skilled in the art. It is carried out in a crystallizer (or crystallizer) consisting of at least one tank, a circulation pump supplying the solution of the molecule to be crystallized at a flow rate suitable for operating the crystallizer under supersaturation conditions, and conduits connecting the constituent elements of the crystallizer. It may also include a heat exchanger located just downstream of the tank in the direction of fluid flow in the external circuit.

[0025] After discovering that the process as defined above led both to the neutralization (or acidification) of methionine to methionine and to the crystallization of methionine, the inventors of this invention extensively studied the various operating conditions of a process for optimizing this transformation. During their research, they observed that the manner in which gaseous carbon dioxide (or carbonic gas) is brought into contact with the methionine in aqueous solution was an important parameter. In doing so, they identified the following mechanism: the impact of jets of aqueous methionine solution on the surface of the aqueous liquid medium causes carbonic gas to be carried into said aqueous liquid medium beneath its surface.This gas entrainment produces a plume of gas bubbles in the aqueous liquid medium with a velocity close to the jet velocity upon impact with the surface, before reaching zero velocity at a certain depth due to current dispersion. Within this plume of bubbles trapped in the flow generated by the jets penetrating the aqueous liquid medium, each bubble develops a gas-liquid interface. The sum of these interfaces is very significant and sufficient for the transfer of gaseous CO2 to the aqueous liquid medium necessary for the neutralization of the methionate. The authors further observed that the impact of the aqueous methionate solution jets on the surface of the aqueous liquid medium contained in the lower part of the crystallizer causes the suction of any foams that might float on this aqueous liquid medium, thus limiting the risks of rock buildup and clogging of the equipment.

[0026] The methionine resulting from the neutralization of the methionate, being only slightly soluble in water, precipitates fairly rapidly in the lower part of the crystallizer and is recovered at the output of the latter. According to the process of the invention, methionine crystals having a d50 of at least 200 pm can be obtained. They can then be easily purified to recover the expected crystallized methionine.

[0027] The aqueous solution of the amino acid salt may be supplied, in whole or in part, directly or indirectly, to said distributor.

[0028] The aqueous solution can be supplied to the crystallizer using a pump that injects the aqueous solution under positive pressure through an ejector (for example, a venturi type or simple nozzles) which also draws in the carbon dioxide present in the air to create a mixture between the liquid and the carbon dioxide, resulting in a reaction over a large interfacial area between the two fluids. The mixing of the aqueous solution and the gas at the outlet of the ejector or nozzles allows for a significant portion of the neutralization of the amino acid salt.

[0029] The aqueous solution of the amino acid salt is also supplied, either continuously or temporarily, to the very top of the crystallizer through an inlet leading to spray nozzles located above the dispenser. The advantage of partially or fully supplying the dispenser and other equipment below it from the top is to use the feed stream as a cleaning solution. Indeed, the feed has a basic pH, which allows it to dissolve methionine solids that might accumulate in the upper part of the crystallizer. This contact between the feed and any solids that may have accumulated on the crystallizer walls (or other surfaces exposed by internal equipment) allows the reverse of the neutralization reaction, thus dissolving the amino acid solids.

[0030] Thus, according to one embodiment of the process of the invention, the aqueous solution is brought into the forced circulation crystallizer through a single inlet which opens into the upper part of the chamber, into spray nozzles placed above the distributor.

[0031] According to another mode, part of the aqueous solution is brought in through the inlet located in the upper position of the chamber and another part of the aqueous solution is brought in through another inlet opening into the upper part of the chamber, via spray nozzles placed above the distributor.

[0032] Due to their position at the top of the upper part of the chamber, the spray nozzles disperse the aqueous solution of the amino acid salt before its neutralization and have the ability to dissolve any solid deposit accumulated in the elements supplying said solution to the crystallizer and thus to clean them, which makes it possible to limit the number of interventions.

[0033] According to a variant that can be combined with either of the two modes above, a portion of the aqueous solution is further introduced into the forced circulation crystallizer via another inlet which opens into the upper part of The chamber is heated via ejectors located below the dispenser. Through the Venturi effect, the ejectors create an exchange surface between the carbon dioxide and the aqueous solution from the dispenser jets, thus promoting salt neutralization. Optionally, carbon dioxide is injected into the ejectors. Preferably, between 1 and 15 ejectors can be arranged in the upper part of the crystallizer chamber, in areas free from interaction with the jets produced by the dispenser(s). The jets produced by these ejectors help to suppress any foam that might form and accumulate on the surface of the aqueous liquid in the lower part of the crystallizer.

[0034] The amino acid in crystalline form is recovered from the aqueous liquid medium at the bottom of the chamber and the aqueous solution of said salt is recirculated from the aqueous liquid medium into the external circuit.

[0035] Other variations of a method of the invention are presented below; within the scope of the invention, they may be considered alone or in combination. Thus, features described for one embodiment of a step may or may not be combined with features described for a complementary embodiment of said step or with those described for an embodiment of another step.

[0036] In a variant of the process of the invention, the aqueous solution of the amino acid salt entering the crystallizer in forced circulation through any of the aforementioned inlets has a temperature of 20-90°C, preferably 30-40°C.

[0037] According to one aspect of the process, the purification module (15) includes a filter.

[0038] The amino acid can be chosen from methionine, selenomethionine, valine, isoleucine.

[0039] According to one variant, the process is continuous.

[0040] As previously stated, the feed rate is an important factor in crystallization by forced recirculation. According to one variant of the process, the amino acid is methionine, the amino acid salt is potassium methionate, and the mass flow rate of the aqueous potassium methionate solution in the external circuit ranges from 25 to 175 t / h, preferably from 70 to 130 t / h, said aqueous potassium methionate solution having a potassium methionate concentration of 19 to 30% (w / w), preferably from 20 to 25% (w / w) and even more preferably, from 22% (w / w).

[0041] According to a variant of the method, the diameter of the coverage of all the downward jets of aqueous solution on the surface of the aqueous liquid medium present in the lower part of the crystallizer covers at least 75% of this surface, preferably at least 85%.

[0042] The distance between the dispenser and the surface of the aqueous liquid medium in the lower part of the crystallizer chamber, or drop height, is determined based on the energy dissipated by the impact of the aqueous solution dispersion jets. However, this distance does not depend solely on the drop height; it also depends on the initial jet conditions. For example, the distance between the dispenser and the surface of the aqueous liquid medium in the lower part of the crystallizer chamber ranges from 1 to 3 m, preferably from 1.75 to 2.50 m. This distance may nevertheless change during the process depending on fluctuations in the liquid level in the crystallizer.

[0043] According to a variant of the process, the ratio of the cumulative cross-section expressed in m2 of all the jets and the square of the diameter of the crystallizer expressed in m2 ranges from 0.025 to 0.075, preferably from 0.04 to 0.06. The choice of this range of values ​​makes it possible to preserve the crystals formed by limiting their disintegration by attrition.

[0044] According to one embodiment of the process, each jet of the aqueous amino acid salt solution dispenser has an angle measured at the jet outlet ranging from 0° to 45° with respect to the vertical. The choice of the angle value is guided by a compromise between a homogeneous distribution of the jets over the entire free surface and a maximum reduction, or even an absence, of interactions between the fluid and the crystallizer wall.

[0045] According to one variant of the method, the number of jets of aqueous methionate solution emitted by the distributor ranges from 50 to 200 jets and each orifice producing jets with a diameter ranging from 50 to 200 mm, preferably from 100 to 175 mm.

[0046] Carbon dioxide is introduced into the crystallizer at a flow rate which must allow the stoichiometry of the neutralization of the methionate to be respected; for this purpose, the pressure of the carbon dioxide in the upper part of the chamber of the crystallizer is at a nominal value of 4 bars absolute and an actual value ranging from 2 to 10 bars absolute, for example from 3 to 6 bars absolute.

[0047] According to one variant, carbon dioxide is preferentially injected into the sky of the crystallizer in normal operation and into the external circuit upstream of the circulation pump of the aqueous solution of the amino acid salt in normal or transient operation in order to increase the dispersion of the gas in the aqueous liquid medium.

[0048] According to an alternative method, the excess carbon dioxide introduced into the upper part of the crystallizer chamber is collected via an outlet to be recycled to one and / or the other of the inlets in the external circuit and / or in the upper part of the chamber.

[0049] According to an embodiment of the process, the aqueous solution of the amino acid salt is an aqueous solution of methionine and is a reaction medium resulting from the saponification of methionine hydantoin. The reaction medium may be obtained from the saponification of methionine hydantoin in aqueous phase, under pressure, in the presence of potassium carbonate.

[0050] The invention also relates to a process for manufacturing methionine from methionine hydantoin, said process comprising the following steps:

[0051] Methionine hydantoin is saponified into potassium methionate, in aqueous solution, under pressure, hot, in the presence of potassium carbonate;

[0052] Optionally, the carbon dioxide and ammonia formed during saponification are removed until an aqueous methionate solution of at least 19% (w / w) is obtained; and

[0053] Potassium methionine is neutralized into methionine and the methionine is crystallized according to a process of the invention as defined above.

[0054] According to an advantageous embodiment, the carbon dioxide introduced into the crystallizer and excess is taken off for recycling at one and / or the other of the crystallizer feed and injection into the recirculation duct.

[0055] The prior removal of carbon dioxide and ammonia, if carried out, can be done under conditions known to those skilled in the art.

[0056] The reaction medium containing the methionate is at a temperature generally higher than the optimum temperature for the process of the invention. It is advantageously cooled before entering the crystallizer, to a temperature of 20-50°C, preferably 30-40°C, by means of a heat exchanger located upstream of the crystallizer and downstream of the carbon dioxide injection in the recirculation line of said aqueous liquid medium.

[0057] The invention and the advantages arising therefrom will become clear from the detailed description provided below with reference to the accompanying drawings as follows:

[0058] [Fig-1] represents a vertical cross-sectional view of a crystallizer and illustrates the implementation of the process in a variant in which the supply of the external circuit with aqueous solution of the amino acid salt is upstream of the heat exchanger and the solution is brought directly into the distributor placed in the upper part of the crystallizer chamber.

[0059] [Fig.2] represents a vertical cross-sectional view of a crystallizer and illustrates the setting in work of the process in one or more other variants in which the supply of the external circuit with aqueous solution of the amino acid salt is carried out by one or two inlets, one being upstream of the heat exchanger and the other downstream, and the solution is brought in by one, two or three inlets, one bringing it directly into the distributor, another bringing it into spray nozzles placed above the distributor and yet another bringing it into one or more ejectors. Example 1#:

[0060] For the implementation of the process according to the invention according to a variant as described in [Fig. 1], the parameters of the forced recirculation crystallizer 1 used are as follows:

[0061] diameter, 7.3 m

[0062] Recirculation flow rate of the aqueous solution of potassium methionate 5 in the external circuit 8, 16000 m3 / h

[0063] drop height 21 corresponding to the distance between the distributor 13 emitting the jets 14 of aqueous methionate solution 5 and the surface 20 of the aqueous liquid medium 6, 2 m minimum

[0064] diameter of the orifices producing the jets 14, 150 mm

[0065] number of jets 14 on distributor 13, 144.

[0066] An aqueous solution of potassium methionate at 22% (w / w) 5, having a pH of about 11.7, supplies an external circuit 8 of the forced recirculation crystallizer 1 above, by means of an unreferenced pump, through an inlet 12 located upstream of a heat exchanger 11 disposed on the external circuit 8 allowing the temperature of the solution 5 to be raised to about 20-90°C, preferably from 30-40°C. Solution 5 is brought into a distributor 13 arranged in the upper part 4 of the chamber 2 of the crystallizer 1, through an inlet 10, with a nominal flow rate of 99495 kg / h (120% of the nominal) under a CO2 pressure of 4 bar supplied into the upper part 4 of the chamber 2 of the crystallizer through an inlet 23. The distributor 13 emits jets 14 of solution 5 which reach the surface 20 of the aqueous liquid medium 6 contained in the lower part 3 of the chamber 2 of the crystallizer 1, where a foam forms.The neutralization process begins as soon as the jets 14 of solution 5 are emitted upon contact with pressurized CO2 in the upper part 4 of the chamber 2 of the crystallizer 1. It continues at the surface 20 of the aqueous liquid medium 6 and ends in said medium 6 where the crystallization of methionine begins. The methionine crystals fall towards the lower part of the crystallizer, which has a narrowed section. From this section, a stream of liquid containing the methionine crystals is drawn off and sent to a purification module 15. Through an outlet 9 located in the lower part of the crystallizer, the aqueous liquid medium is withdrawn through an outlet 9, in which a filter is provided to prevent the escape of methionine crystals, and is recirculated into the external circuit 8. Example 2#:

[0067] For another implementation of the process of the invention according to a variant as described in [Fig. 1], the parameters of the forced recirculation crystallizer 1 used are as follows:

[0068] diameter, 0.25 m

[0069] recirculation flow rate of the aqueous liquid medium 6.8 m³ / h

[0070] drop height 21 corresponding to the distance between the distributor 13 emitting the jets 14 of aqueous potassium methionate solution 5 and the surface 20 of the aqueous liquid medium 6, 0.3 m minimum

[0071] diameter of the orifice producing the jets 14.50 mm

[0072] number of jets 14 on distributor 13, 1.

[0073] An aqueous solution of potassium methionate at 22% (w / w) 5, having a pH of about 11.7, supplies an external circuit 8 of the above forced recirculating crystallizer, by means of an unreferenced pump, through an inlet 12 located upstream of a heat exchanger 11 disposed on the external circuit 8 allowing the temperature of the solution 5 to be raised to about 20-90°C, preferably from 30-40°C. Solution 5 is brought into a distributor 13 arranged in the upper part 4 of the chamber 2 of the crystallizer 1, by an inlet 10, with a nominal flow rate of 80 kg / h under a CO2 pressure of 4 bar supplied into the upper part 4 of the chamber 2 of the crystallizer by an inlet 23. The distributor 13 emits jets 14 of solution 5 which reach the surface 20 of the aqueous liquid medium 6 contained in the lower part 3 of the chamber 2 of the crystallizer 1, where a foam forms.The neutralization process begins as soon as the jets 14 of solution 5 come into contact with pressurized CO2 in the upper part 4 of the chamber 2 of the crystallizer 1. It continues at the surface 20 of the aqueous liquid medium 6 and ends in said medium 6 where the crystallization of methionine begins. The methionine crystals fall towards the lower part of the crystallizer, which has a narrowed section. From this section, a stream of liquid containing the methionine crystals is drawn off and sent to a purification module 15. The aqueous liquid medium is withdrawn through an outlet located in the lower part of the crystallizer, in which a filter is provided to prevent the escape of methionine crystals, and is recirculated in the external circuit 8. Example 3

[0074] Figure 2 illustrates several alternatives that can be carried out alone or in combination. These alternatives relate to supplying the external circuit 8 with aqueous solution of amino acid salt 5 and supplying the upper part 4 of the crystallizer chamber 2, as described below.

[0075] Thus, according to the process of the invention described in Examples 1 and 2 above, an external circuit 8 of the above forced recirculation crystallizer is supplied with an aqueous solution of amino acid salt 5, by means of an unreferenced pump, through an inlet 10 located upstream of a heat exchanger 11 disposed on the external circuit 8, allowing the temperature of the solution 5 to be raised to approximately 20-90°C, from Preferably 30-40°C. Solution 5 is brought into the distributor 13 arranged in the upper part 4 of the chamber 2 of the crystallizer 1, through the inlet 10.

[0076] According to a variant of the process of the invention described above, the external circuit 8 of the crystallizer 1 is further supplied with an aqueous solution of amino acid salt 5, by means of an unreferenced pump, through an inlet 12' located downstream of the heat exchanger 11. The solution 5 can be supplied to the distributor 13 located in the upper part 4 of the chamber 2 of the crystallizer 1, through the inlet 10. Alternatively, it can be supplied to one or more ejectors 19 supplied with CO2. This ejector or these ejectors will diffuse the aqueous solution of amino acid salt into the upper part 4 of the chamber to create, together with that emitted by the jets 14 of the distributor 13, a current that promotes the neutralization of the amino acid salt.

[0077] According to another embodiment of the process of the invention described above, shown in [Fig. 2], and which can be combined with the previous one, the external circuit 8 of the crystallizer 1 is further supplied with aqueous solution of amino acid salt 5, by means of a pump not shown, through an inlet 17 located at the top of the crystallizer 1. Through the inlet 17, the solution 5 is brought into hydraulic spray nozzles 16 which spray it into the distributor 13. Advantageously, the aqueous solution of amino acid salt 5 introduced through the inlet 17 does not come from the external circuit 8, but from the reaction medium not yet subjected to crystallization conditions; indeed, the presence of solids could damage the nozzles 16.

[0078] Regardless of the variant, the upper part 4 of the chamber 2 of the crystallizer 1 is under CO2 pressure supplied through inlet 23 located at the top of the crystallizer. This inlet can also be located at any other point in the walls of the upper part 4 of chamber 2 of the crystallizer. Distributor 13 emits jets 14 of solution 5 which reach the surface 20 of the aqueous liquid medium 6 contained in the lower part 3 of chamber 2 of the crystallizer 1, where foam forms. The neutralization process begins as soon as the jets 14 of solution 5 come into contact with the pressurized CO2 in the upper part 4 of chamber 2 of the crystallizer 1. It continues at the surface 20 of the aqueous liquid medium 6 and ends in said medium 6 where the crystallization of methionine begins. The methionine crystals fall towards the lower part of the crystallizer, which has a narrowed section. From this part, a stream of liquid containing methionine crystals is taken to be sent to purification module 15.Through outlet 9 located in the lower part of the crystallizer and in which a filter is provided to prevent the exit of methionine crystals, the aqueous liquid medium is withdrawn and put back into circulation in the external circuit 8.

Claims

1.

2. Demands A process for obtaining an amino acid in crystalline form from a salt of said amino acid in aqueous solution, in the presence of pressurized carbon dioxide, characterized in that the process is carried out in a forced circulation crystallizer (1), the latter comprising a chamber (2) having a lower part (3) and an upper part (4), the lower part (3) containing an aqueous liquid medium (6) comprising the amino acid and the upper part (4) containing pressurized carbon dioxide (7), and an external circuit (8) to this chamber (2) supplied with aqueous solution of said amino acid (5) and bringing it into the upper part (4) of the chamber (2), said external circuit (8) being connected to the chamber (2) from an outlet (9) located in the lower position of the chamber (2) to at least one inlet (10, 17) located in the upper position of the chamber (2), passing through a heat exchanger (11), said process comprising the following steps: the forced circulation crystallizer (1) is supplied with aqueous solution (5) of said salt, via at least one inlet (12, 12') in the external circuit (8) opening into the upper part (4) of the chamber (2) via at least one inlet (10, 17); the aqueous solution (5) of said salt arriving in the upper part (4) of the chamber (2) from the inlet (10) and / or (17) is dispersed by means of a distributor (13) emitting downward jets (14) towards the lower part (3) of the chamber (2); Carbon dioxide is injected into the external circuit (8) and / or into the upper part (4) of the chamber (2) to obtain a carbon dioxide pressurized environment in the upper part (4) above the aqueous liquid medium (6); A juice containing the amino acid in crystalline form is collected at the bottom of chamber (2) and conveyed to a purification module (15), and a juice substantially free of amino acid in crystalline form is drawn off and recirculated in the external circuit (8); and said amino acid is obtained in crystalline form in the purification module (15). A method according to claim 1, characterized in that the external circuit (8) is supplied with aqueous solution (5) via an inlet (12) located upstream of the heat exchanger (11) and / or by an inlet (12') located downstream of the heat exchanger (11).

3. Method according to claim 1 or 2, characterized in that all or part of the aqueous solution (5) is brought into the forced circulation crystallizer (1) the inlet (17), the latter opening into the upper part (4) of the chamber (2), into spray nozzles (16) placed above the distributor (13).

4. A method according to any one of claims 1 to 3, characterized in that a portion of the aqueous solution (5) is brought into the forced circulation crystallizer (1) via another inlet (18), the latter opening into the upper part (4) of the chamber (2), into one or more ejectors (19) supplied with CO2.

5. A method according to any one of claims 1 to 4, characterized in that the aqueous solution (5) of the amino acid salt entering the forced circulation crystallizer (1) through the inlet (10) and / or the inlet (17) and optionally the inlet (18) at a temperature of 20-90°C, preferably 30-40°C.

6. A method according to any one of claims 1 to 5, characterized in that the purification module (15) comprises a filter.

7. A method according to any one of claims 1 to 6, characterized in that the amino acid is selected from methionine, selenomethionine, valine, isoleucine.

8. A method according to any one of claims 1 to 7, characterized in that the amino acid salt is an alkali metal salt such as a sodium or potassium salt.

9. A method according to any one of claims 1 to 8, characterized in that it is continuous.

10. A process according to any one of claims 1 to 9, characterized in that the amino acid is methionine, the amino acid salt is potassium methionate, and the mass flow rate of supply of aqueous solution (5) of potassium methionate into the external circuit (8) is from 25 to 175 t / h, preferably from 70 to 130 t / h, said aqueous solution (5) of potassium methionate having a concentration of potassium methionate of 19 to 30% (w / w), preferably from 20 to 25% (w / w).

11. A method according to any one of claims 1 to 10, characterized in that the diameter of the coverage of the set of downward jets (14) of aqueous solution (5) at the surface (20) of the medium aqueous liquid (6) present in the lower part (3) of the crystallizer (1) covers at least 75% of this surface (20), preferably at least 85%.

12. A method according to any one of claims 1 to 11, characterized in that the distance (21) separating the distributor (13) and the surface (20) of the aqueous liquid medium (6) present in the lower part (3) of the chamber (2) of the crystallizer (1) goes from 1 to 3 m, preferably from 1.75 to 2.50 m.

13. A method according to any one of claims 1 to 12, characterized in that the ratio of the cumulative cross-section expressed in m2 of the set of jets (14) and the square of the diameter of the crystallizer (1) expressed in m2 goes from 0.025 to 0.075, preferably from 0.04 to 0.

06.

14. A method according to any one of claims 1 to 13, characterized in that each jet (14) has an angle measured at the exit of said jet of 0° to 25° with respect to the vertical.

15. A method according to any one of claims 1 to 14, characterized in that the carbon dioxide pressure in the upper part (4) of the chamber (2) is at a nominal value of 4 absolute bars and an actual value ranging from 3 to 6 absolute bars.

16. A method according to any one of claims 1 to 15, characterized in that the excess carbon dioxide introduced into the upper part (4) of the chamber (2) is taken up via an outlet (22) to be recycled to one and / or the other of the inlets in the external circuit (8) and / or in the upper part (4) of the chamber (2).

17. A process according to any one of claims 1 to 16, characterized in that the aqueous solution (5) of the amino acid salt is an aqueous solution of methionine and is a reaction medium resulting from the saponification of methionine hydantoin.

18. Process according to claim 17, characterized in that the reaction medium is obtained from the saponification of methionine hydantoin in aqueous phase, under pressure, in the presence of potassium carbonate.

19. A process for manufacturing methionine from methionine hydantoin, characterized in that it comprises the following steps: methionine hydantoin is saponified to potassium methionate, in aqueous solution, under pressure, hot, in the presence of potassium carbonate; The carbon dioxide and ammonia formed during saponification are removed until an aqueous methionate solution of at least 19% (w / w) is obtained; and Potassium methionine is neutralized to methionine and the methionine is crystallized according to a process as defined in any one of claims 1 to 18.

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