JP4948002B2 - Method and apparatus for producing 2-hydroxy-4-methylthiobutanoic acid - Google Patents

Description

  The present invention relates to a method for producing 2-hydroxy-4-methylthiobutanoic acid, and an apparatus for producing 2-hydroxy-4-methylthiobutanoic acid for producing 2-hydroxy-4-methylthiobutanoic acid by the production method. About.

2-hydroxy-4-methylthiobutanoic acid, which is useful as a feed additive, hydrolyzes 2-hydroxy-4-methylthiobutanenitrile and / or 2-hydroxy-4-methylthiobutanamide in the presence of an acid such as sulfuric acid. It is known to produce by reacting.
As a method for producing such 2-hydroxy-4-methylthiobutanoic acid, for example, a method including the following steps (A) to (E) has been proposed (for example, see Patent Document 1).

According to this method, 2-hydroxy-4-methylthiobutanoic acid can be efficiently and efficiently extracted from the reaction solution obtained by hydrolysis without using an organic solvent with good operability.
(A): 2-hydroxy-4-methylthiobutanenitrile and / or 2-hydroxy-4-methylthiobutanamide is hydrolyzed in the presence of sulfuric acid to obtain a reaction solution containing 2-hydroxy-4-methylthiobutanoic acid. Step, (B): Step of mixing the reaction solution obtained in (A) with a basic alkali metal compound, (C): Mixing the solution obtained in (B) with 2-hydroxy-4-methylthiobutanoic acid (D): the step of concentrating the oil layer obtained in (C), (E): the step of removing insolubles from the concentrated liquid obtained in (D).
JP 2001-226344 A

However, in the production method described in Patent Document 1, filtration and decantation are exemplified as means for removing insoluble matters from the concentrated liquid obtained in (D) in the step (E).
However, since the concentrated solution obtained in the step (D) and the insoluble matter removed in the step (E) are both high in viscosity and poor in fluidity, the insoluble matter is separated from the concentrated solution. It is difficult. For this reason, 2-hydroxy-4-methylthiobutanoic acid is likely to remain in the insoluble matter removed from the concentrated solution, which causes a reduction in production efficiency of 2-hydroxy-4-methylthiobutanoic acid.

  The object of the present invention is to efficiently and efficiently remove the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the production step from the organic phase obtained by phase separation and concentration. A process for producing 2-hydroxy-4-methylthiobutanoic acid capable of obtaining hydroxy-4-methylthiobutanoic acid, and 2-hydroxy-4-methylthiobutanoic acid for producing 2-hydroxy-4-methylthiobutanoic acid by the production process, An object of the present invention is to provide an apparatus for producing hydroxy-4-methylthiobutanoic acid.

  In order to achieve the above object, the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention comprises 2-hydroxy-4-methylthiobutanenitrile and / or 2-hydroxy-4-methylthiobutanamide, water and an acid. Is added to the reaction mixture containing 2-hydroxy-4-methylthiobutanoic acid and 2-hydroxy-4-methylthiobutanoic acid obtained in the above-mentioned generation step by adding alkali. Separating into an organic phase containing -4-methylthiobutanoic acid and an aqueous phase containing water and an inorganic salt, and separating the separated organic phase from the aqueous phase; The organic phase was heated at a temperature of 60 to 150 ° C. and a pressure of 1 to 20 kPa for 0.5 hour or more to remove water remaining in the organic phase, A concentration step for concentrating hydroxy-4-methylthiobutanoic acid, and a centrifugation step for separating, by centrifugation, a residue containing inorganic salts remaining in the organic phase from the organic phase concentrated in the concentration step; It is characterized by having.

  According to the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, grain growth of inorganic salt crystals can be promoted in the concentration step, and further, in the centrifugation step, the organic concentrated in the concentration step can be promoted. Since the phases are centrifuged, the efficiency of separating residues containing inorganic salts from the organic phase is improved. Therefore, the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the production step is efficiently and efficiently treated from the organic phase obtained by phase separation and concentration. Methylthiobutanoic acid can be purified.

  In the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, the production step comprises reacting 2-hydroxy-4-methylthiobutanenitrile with water in the presence of an acid catalyst to produce 2-hydroxy-4 -A hydration step for producing methylthiobutanamide, and water is added to the reaction solution containing 2-hydroxy-4-methylthiobutanamide obtained in the hydration step to produce 2-hydroxy-4-methylthiobutanoic acid. It is preferable to provide a hydrolysis step.

If the production process is divided into a hydration process and a hydrolysis process, hydration or hydrolysis can be carried out under the optimum conditions in each process, so that 2-hydroxy-4-methylthiobutanoic acid can be efficiently produced. Can do.
The apparatus for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention reacts 2-hydroxy-4-methylthiobutanenitrile and / or 2-hydroxy-4-methylthiobutanamide with water to give 2- A reaction vessel for producing hydroxy-4-methylthiobutanoic acid, a reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the reaction vessel, an organic phase containing 2-hydroxy-4-methylthiobutanoic acid; Separating the organic phase separated into the aqueous phase containing water and separating the separated organic phase from the aqueous phase, and the water remaining in the organic phase from the organic phase separated in the separating means. Removing and concentrating 2-hydroxy-4-methylthiobutanoic acid, and an inorganic salt remaining in the organic phase from the organic phase concentrated in the concentration means. Free residue, centrifugation is characterized by comprising a centrifugal separation means for removing.

  According to the apparatus for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, a residue containing an inorganic salt remaining in the organic phase is efficiently removed from the organic phase concentrated in the concentration means by the centrifugal separation means. It can be separated and removed, and the production efficiency of 2-hydroxy-4-methylthiobutanoic acid can be improved. Moreover, since the organic phase concentrated in the concentration means has a relatively high viscosity and low fluidity, in solid-liquid separation by natural sedimentation, a liquid component containing an organic phase and a solid component containing an inorganic salt (residue) However, the separation efficiency by centrifugation can improve the purification efficiency of 2-hydroxy-4-methylthiobutanoic acid.

In the apparatus for producing 2-hydroxy-4-methylthiobutanoic acid according to the present invention, it is preferable that the centrifuge is a decanter centrifuge.
Residues containing inorganic salts separated from the organic phase by centrifugation have poor fluidity. Therefore, when the organic phase concentrated in the concentration step is subjected to solid-liquid separation with a normal filter type centrifugal filter, Although there is a possibility that the load associated with the treatment may increase, the load associated with the treatment of the residue can be reduced by centrifuging using a decanter type centrifuge, and therefore 2-hydroxy-4-methylthio The production efficiency of butanoic acid can be improved.

  In the apparatus for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, the concentration means includes an evaporator for concentrating 2-hydroxy-4-methylthiobutanoic acid, and 2-hydroxy concentrated by the evaporator. Heating means for heating -4-methylthiobutanoic acid to a predetermined temperature and circulation for returning 2-hydroxy-4-methylthiobutanoic acid concentrated in the evaporator to the evaporator again via the heating means And a line.

  In this case, the concentrated solution concentrated in the evaporator is circulated in a circulation line for circulating it from the evaporator through the heating means to return to the evaporator again, thereby effectively reducing the residence time of the concentrated solution. Can be extended. As a result, grain growth of inorganic salt crystals can be promoted in the concentrated liquid, and the efficiency of separation and removal of the residue containing the inorganic salt from the organic phase by the centrifuge is improved. Therefore, 2-hydroxy-4-methylthiobutanoic acid can be efficiently purified with good operability from the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the production step.

  According to the method and apparatus for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the production step is subjected to phase separation and concentration. A residue containing an inorganic salt can be efficiently removed from the obtained organic phase with good operability. Therefore, it is possible to improve the purification efficiency of 2-hydroxy-4-methylthiobutanoic acid and improve the yield of 2-hydroxy-4-methylthiobutanoic acid.

  FIG. 1 is a schematic apparatus configuration diagram showing an embodiment of an apparatus for producing 2-hydroxy-4-methylthiobutanoic acid according to the present invention. FIG. 2 is an apparatus configuration diagram showing a specific example of the concentration tank 9 in FIG. 3 is an apparatus configuration diagram showing an example of a decanter centrifuge. Hereinafter, the manufacturing method of 2-hydroxy-4-methylthiobutanoic acid is demonstrated with the manufacturing apparatus 1 referring FIG.

In this method, first, 2-hydroxy-4-methylthiobutanenitrile (hereinafter abbreviated as HMTBN), water, and sulfuric acid are supplied to the hydration tank 2 to cause hydration reaction of HMTBN. Hydroxy-4-methylthiobutanamide is produced (hydration step).
HMTBN supplied to the hydration tank 2 is produced industrially, for example, by reacting acrolein and methyl mercaptan to obtain 3-methylthiopropionaldehyde and reacting this with hydrogen cyanide.

The hydration tank 2 only needs to be able to perform the above-described hydration reaction, and includes a known reaction tank.
And in the hydration tank 2, HMTBN, water, and a sulfuric acid are mixed. In addition, in the hydration tank 2, water is, for example, 20 to 70 parts by weight, preferably 25 to 50 parts by weight with respect to 100 parts by weight of HMTBN, and sulfuric acid is, for example, 1 mole of the above mixture. HMTBN, water, and sulfuric acid are supplied so that the total amount of sulfuric acid is 0.5 to 1 mol, preferably 0.6 to 0.8 mol.

In the hydration tank 2, water can be supplied to the hydration tank 2 in a state of being mixed with HMTBN and / or sulfuric acid in advance, that is, as an HMTBN aqueous solution and / or a sulfuric acid aqueous solution. Preferably, it supplies to the hydration tank 2 as sulfuric acid aqueous solution.
In the hydration tank 2, HMTBN hydrates with water in the presence of sulfuric acid to produce 2-hydroxy-4-methylthiobutanamide (hereinafter abbreviated as HMTBAA). The hydration reaction is performed, for example, in the range of 40 to 70 ° C. for 1 to 3 hours and aged after the reaction.

In this method, next, the reaction liquid containing HMTBAA obtained in the hydration tank 2 is supplied to the hydrolysis tank 4, and water is added to the reaction liquid in the hydrolysis tank 4, thereby hydrolyzing the HMTBAA. Then, 2-hydroxy-4-methylthiobutanoic acid (hereinafter abbreviated as HMTBA) is produced (hydrolysis step).
The hydrolysis tank 4 is connected to the hydration tank 2 via the connection line 3 and is composed of a known reaction tank or the like. Then, the reaction liquid containing HMTBAA obtained in the hydration tank 2 is supplied from the hydration tank 2 to the hydrolysis tank 4 through the connection line 3.

In the hydrolysis tank 4, the reaction solution is supplied, and water is supplied at a ratio of, for example, 100 to 200 parts by weight with respect to 100 parts by weight of the sulfuric acid aqueous solution in the reaction solution.
This water is supplied only from the reflux line 5 to be described later, or supplied from the reflux line 5 and supplied from a separately connected water supply line 6.
In the hydrolysis tank 4, HMTBAA is hydrolyzed with water and sulfuric acid to produce HMTBA, and ammonium bisulfate (NH ₄ HSO ₄ ) and ammonium sulfate ((NH ₄ ) ₂ SO ₄ are by-produced. For example, the hydrolysis reaction is carried out in a range of 90 to 130 ° C. and 2 to 6 hours after charging water and then raising the temperature.

In this method, after that, the reaction liquid containing HMTBA obtained in the hydrolysis tank 4 is supplied to the distillation column 7, and the reaction liquid is distilled in the distillation tower 7, whereby low boiling point components in the reaction liquid are removed. Remove.
The distillation column 7 is connected to the hydrolysis tank 4 via the connection line 3 and only needs to be able to remove low-boiling components in the reaction solution, and is constituted by a known evaporator or distiller. Then, the reaction liquid containing HMTBA generated by hydrolysis in the hydrolysis tank 4 is supplied from the hydrolysis tank 4 to the distillation column 7 through the connection line 3.

  In the distillation column 7, the reaction solution is supplied and distilled, for example, at 80 to 120 ° C. and 50 to 150 kPa. By this distillation, for example, malodorous components such as dimethyl sulfide and dimethyl disulfide by-produced by the above various reactions and corrosive components (low boiling point components) such as formic acid are added in an amount of 1 to 4 wt. % Is distilled off as distillate. The removed low boiling point components are subjected to waste water treatment after incineration.

Moreover, the reaction liquid containing HMTBA is supplied to the neutralization / separation tank 8 described below as a can liquid.
In this method, the reaction liquid from which the low-boiling-point components have been removed in the distillation column 7 is then supplied to the neutralization / separation tank 8 serving as a liquid separation means. The reaction solution is phase-separated into an organic phase containing HMTBA and an aqueous phase containing water and an inorganic salt (including ammonium bisulfate and ammonium sulfate) by neutralization by adding an alkali, and the phase-separated organic phase Is separated from the aqueous phase (separation step).

The neutralization / separation tank 8 is connected to the distillation column 7 via the connection line 3, and is only required to be able to perform the above-described neutralization and separation. For example, the stirring tank 8a and the separation tank 8b are set as one set. It consists of a mixer-settler type liquid-liquid extractor.
Then, the reaction liquid from which the low boiling point components have been removed in the distillation column 7 is supplied from the distillation column 7 to the neutralization / separation tank 8 through the connection line 3.

In the neutralization / separation tank 8, the reaction liquid is supplied to the stirring tank 8 a, and the alkali is, for example, 0.5 mol or more with respect to 1 mol of ammonium bisulfate in the reaction liquid. The amount is 6 mol or more, usually 1.2 mol or less, preferably 0.8 mol or less.
The amount of ammonium bisulfate contained in the reaction solution may be determined by analysis. However, sulfuric acid exceeds 0.5 mol and less than 1 mol with respect to 1 mol of HMTBN, and HMTBN reacts. Can be calculated according to the following formula.

Ammonium bisulfate (mol) = 2 × sulfuric acid (mol) −HMTBN (mol)
Moreover, the addition ratio of the alkali can also be managed by the hydrogen ion concentration (pH) of the reaction solution to which the alkali is added. Specifically, when 0.6 to 0.8 mol of sodium hydroxide is used per 1 mol of ammonium bisulfate, the pH of the reaction solution to which sodium hydroxide is added is about 1. 4 to about 1.9, and about 60 to about 1.9 to about 2.2.

  Examples of the alkali include sodium salts such as sodium hydroxide, sodium hydrogen carbonate, and sodium carbonate, and potassium salts such as potassium hydroxide, potassium hydrogen carbonate, and potassium carbonate, such as lithium hydroxide, lithium hydrogen carbonate, and lithium carbonate. And basic alkali metal compounds such as lithium salts. As needed, 1 type (s) or 2 or more types can also be used among the above. The basic alkali metal compound may be used as a solid or an aqueous solution. Preferably, sodium hydroxide is used.

  In the stirring tank 8a, the reaction solution is neutralized by the addition of alkali, and the reaction solution is phase-separated into an organic phase containing HMTBA and an aqueous phase containing water and an inorganic salt (including ammonium bisulfate). . The neutralization reaction is carried out, for example, at 15 to 120 ° C., preferably 30 to 110 ° C., for 0.1 to 3 hours, preferably 0.1 to 2 hours. In this neutralization reaction, heat of neutralization due to the reaction between ammonium bisulfate and alkali is generated, and when hydrogen carbonate or carbonate is used as the alkali, carbon dioxide gas may be generated, which is necessary. Depending on the heat removal and degassing.

Thereafter, the organic phase and the aqueous phase are allowed to stand in the separation tank 8b, and phase separation (separation) is performed so that the upper layer is the organic phase and the lower layer is the aqueous phase. And then taken out.
In the separation tank 8b, an inorganic salt may be precipitated in the aqueous phase, but in that case, it may be separated as it is, or it is separated after heating to dissolve the precipitated inorganic salt. You can also Furthermore, after removing the precipitated inorganic salt by filtration or decantation, it can also be separated. The temperature at the time of separation is, for example, in the range of 30 to 110 ° C.

The organic phase thus separated from the aqueous phase contains, for example, 40 to 60% by weight of HMTBA, 20 to 30% by weight of water, and 10 to 30% by weight of inorganic salt.
A water phase discharge line 15 for discharging the water phase is connected to the separation tank 8 b of the neutralization / separation tank 8. In the separation tank 8b, the aqueous phase separated from the organic phase is discharged from the separation tank 8b to the water phase discharge line 15. The aqueous phase discharge line 15 is connected to the liquid separation tank 14 via the solid discharge line 16. As will be described later, the aqueous phase discharged to the aqueous phase discharge line 15 is a solid component (residue made of a wet cake) containing inorganic salts discharged from the centrifuge 12 as a centrifugal separator through the solid discharge line 16. ) And supplied to the separation tank 14.

In the separation tank 14, the aqueous phase from the aqueous phase discharge line 15 and the solid component from the solid discharge line 16 are mixed, so that the aqueous phase dissolves and saturates the inorganic salt. The phases are separated (separated) into organic phases remaining in the solid component and in the aqueous phase. Mixing dissolution and phase separation in the separation tank 14 are performed in the range of 40 to 110 ° C., for example.
A waste line 17 and a recovered organic phase supply line 10 are connected to the separation tank 14. Then, the aqueous phase separated from the organic phase is discarded from the disposal line 17 in the separation tank 14. In the separation tank 14, the organic phase separated from the aqueous phase is recovered in the recovered organic phase supply line 10 as a recovered organic phase.

  In this method, the organic substance separated in the neutralization / separation tank 8 is then placed in a concentration tank 9 as a concentration means, specifically, an evaporator 19 (see FIG. 2) provided in the concentration tank 9. The phase is supplied, and in the concentration tank 9 (evaporator 19), the water remaining in the organic phase is removed by heating and staying at 60 to 150 ° C. for 0.5 hour or more to concentrate HMTBA. To be purified (concentration step).

The concentration tank 9 (evaporator 19) is connected to the neutralization / separation tank 8 via the connection line 3, and is only required to be able to concentrate as described above. For example, a known evaporator such as a centrifugal thin film type is used. It is done.
The organic phase separated in the neutralization / separation tank 8 is supplied from the separation tank 8 b of the neutralization / separation tank 8 to the concentration tank 9 via the connection line 3.

A recovered organic phase supply line 10 is connected in the middle of the connection line 3. The concentration tank 9 (evaporator 19) is supplied together with the organic phase separated in the neutralization / separation tank 8 and the recovered organic phase supplied from the recovered organic phase supply line 10 to the connection line 3.
In the concentration tank 9 (evaporator 19), the organic phase (including the recovered organic phase) is supplied, and is concentrated, for example, at a temperature of 60 to 150 ° C. and a pressure of 1 to 20 kPa for 0.5 hour or more. Thus, the water in the organic phase is concentrated so as to be, for example, 5% by weight or less, preferably 2% by weight or less, and more preferably 1% by weight or less. By concentrating in this way, it is possible to reduce the sulfate ion concentration in the product and the kinematic viscosity of the product, which will be described later.

  In addition, the organic phase is precipitated by this concentration, and an inorganic salt is precipitated to form a slurry. In the concentration tank 9 (evaporator 19), the organic phase is heated under the above heating conditions (temperature, pressure), and Since the residence time is long, the particle size of the inorganic salt precipitated in the organic phase becomes large. In the centrifugation step described later, solid (residue containing inorganic salt; solid component) and liquid (organic phase) The efficiency of the separation (solid-liquid separation) from the liquid component containing the liquid increases, and the inorganic salt can be easily removed.

On the other hand, in the concentration tank 9 (evaporator 19), when the heating condition (temperature, pressure) of the organic phase is out of the above range, or the organic phase stays for less than 0.5 hours, the organic phase Since the crystals of the inorganic salt precipitated therein are difficult to grow and the particle size is small, the efficiency of solid-liquid separation is lowered in the centrifugation step described later, and the removal of the inorganic salt becomes difficult.
In addition, for example, when the concentration process is performed at 80 ° C. in the concentration step, as described later, when the residence time in the organic phase concentration tank 9 (evaporator 19) is 0.1 hour, When the salt particle size is 20 μm, while the residence time in the organic phase concentration tank 9 (evaporator 19) is 3 hours, the particle size of the inorganic salt increases to 60 μm. .

In order to heat and heat the organic phase at a temperature of 60 to 150 ° C. and a pressure of 1 to 20 kPa for 0.5 hour or more in the concentration step, a concentration tank 9 shown in FIG. 2 is preferably used.
Hereinafter, the concentration tank 9 will be described with reference to FIG.
As shown in FIG. 2, the concentration tank 9 removes water remaining in the organic phase separated in the neutralization / separation tank 8 and concentrates it, and an evaporator 19 as a concentration means. In order to keep the temperature of the obtained concentrated liquid constant, it has a heater drum 21 as a heating / retaining means for heating the concentrated liquid. The evaporator 19 and the heater drum 21 are connected via a circulation line 22, and a circulation pump 20 is inserted in the circulation line 22 from the evaporator 19 to the heater drum 21. . For this reason, the concentrated liquid concentrated in the evaporator 19 is circulated through the evaporator 19 and the heater drum 21 via the circulation line 22 by the transport of the circulation pump 20, and is thereby retained in the concentration tank 9. . Thus, by providing a closed line through which the concentrate can circulate, the residence time can be extended efficiently.

In addition, by providing the heater drum 21 with a static mixer such as a static mixer, the concentrated liquid can be homogenized and circulated.
In such concentration, the residence time of the organic phase in the concentration tank 9 is set to 0.5 to 5 hours, whereby HMTBA is oligomerized (mainly a dimer, a small amount of trimer and 4 The concentration of the inorganic salt in the organic phase can be lowered by reducing the solubility of the inorganic salt in the organic phase.

The residence temperature, pressure, and residence time are preferably set so that the weight ratio of HMTBA monomer / oligomer is 4 or less, and more preferably 2 to 4. .
The residence time is particularly preferably in the range of 0.5 hours or more, preferably 0.5 to 5 hours, and the residence temperature is particularly preferably in the range of 60 to 150 ° C., preferably 80 to 100 ° C.

  Furthermore, the weight ratio of the HMTBA oligomer is preferably such that the HMTBA monomer / oligomer weight ratio is 2 or more with respect to the total weight of the concentrate. If it is less than 2, that is, if the oligomer of HMTBA is excessively produced, the water solubility of HMTBA as a product is reduced, and the components in the product may become non-uniform or the viscosity may increase. Yes, not preferred.

A reflux line 5 connected to the hydrolysis tank 4 is connected to the concentration tank 9 (evaporator 19) (see FIG. 1), and water distilled from the organic phase in the concentration tank 9 (concentrated waste water). Is supplied from the concentration tank 9 to the hydrolysis tank 4 via the reflux line 5.
In this case, the water distilled off from the organic phase in the concentration tank 9 is not drained as it is, but is supplied to the hydrolysis tank 4 via the reflux line 5, so that the concentration tank 9 (evaporator 19) is supplied. It is possible to eliminate the processing necessary for draining the water distilled from the water. As a result, HMTBA can be efficiently purified with good operability, while water used for production can be efficiently used to reduce production costs.

  Further, in the above case, the reaction liquid containing HMTBA obtained in the hydrolysis tank 4 is distilled in the distillation column 7 to remove low-boiling components in the reaction liquid, and then is added to the neutralization / separation tank 8. Since the water that is supplied and then distilled off from the concentration tank 9 is supplied to the hydrolysis tank 4 and recycled, the reduction of by-products (low-boiling components) accumulated in the system by water recycling is reduced. Can be planned.

  The low boiling point component may be removed in any step, and the low boiling point component may be removed by any method such as distillation or adsorption, and is determined as appropriate according to the specifications of the specific manufacturing apparatus. . For example, in the above case, the low boiling point component is removed in the distillation column 7, but equipment (process) for removing the low boiling point component can be provided again. In this case, for example, the adsorption tower 18 is interposed in the middle of the reflux line 5. In the adsorption tower 18, activated carbon is provided in a fixed bed or a fluidized bed, and low boiling point components are removed again from the water before being supplied to the hydrolysis tank 4.

Hereinafter, description will be given again with reference to FIG.
In this method, the slurry is then cooled in the cooling tower 11, and the slurry is separated into a liquid component containing the organic phase and a solid component (residue) containing the precipitated inorganic salt by the centrifugal separator 12 ( Centrifugation step).
The cooling tower 11 is connected to the concentrating tank 9 via the connection line 3 and only needs to be able to cool the slurry. For example, the cooling tower 11 includes a heat exchanger in which a refrigerant circulates. Then, the slurry concentrated in the concentration tank 9 is supplied from the concentration tank 9 to the cooling tower 11 via the connection line 3.

In the cooling tower 11, the said slurry is supplied and it cools at 60-120 degreeC, for example. By this cooling, the inorganic salt is sufficiently precipitated from the slurry.
Then, the slurry cooled in the cooling tower 11 is supplied from the cooling tower 11 to the centrifuge 12 via the connection line 3.
The centrifuge 12 is connected to the cooling tower 11 via the connection line 3 and separates the liquid component and the solid component from the slurry (solid-liquid separation).

Examples of the centrifuge include a cylindrical type, a separation plate type, and a decanter type. Among them, a decanter type centrifuge 23 shown in FIG. 3 is preferable.
The organic phase concentrated in the concentration step has a relatively high viscosity, low fluidity and liquid drainage, and a natural sedimentation rate of several mm / hr. According to solid-liquid separation by natural sedimentation, Productivity may be significantly reduced. However, since the decanter centrifuge 23 can process a suspension having a high concentration and a high viscosity, it is suitable for use in separating a liquid component and a solid component from the slurry.

In the decanter centrifuge 23, the slurry cooled in the cooling tower 11 enters the outer cylinder 24 from the hollow shaft 26 of the screw conveyor 25 that rotates about 0.1 to 2 s ^{−1 in the} same direction as the outer cylinder 24. And is separated into a liquid component containing an organic phase and a solid component containing a mineral salt (residue comprising a wet cake). The solid component accumulated in the outer cylinder 24 is conveyed to the conical bowl 27 side by the screw conveyor 25 and discharged from the one end 28 to the solid discharge line 16. Further, the liquid component overflows from the other side end portion 29.

Specifically, in the decanter centrifuge 23, the slurry is centrifuged at 60 to 120 ° C. and a centrifugal force of 10 to 4000 G, for example. The separated solid component contains 20 to 60% by weight of HMTBA.
In addition, since the organic phase concentrated in the concentration tank 9 has a long residence time in the concentration tank 9, the particle size of the inorganic salt precipitated in the organic phase is large. The efficiency of solid-liquid separation in the centrifugation step is high, and inorganic salts are easily removed.

  For example, using a centrifuge (cylindrical ball part inner diameter 180 mm, length 570 mm, screw differential rotation speed 30 rpm, centrifugal force 2500 G, supply speed 1.5 t / h, 80 ° C.) The inorganic salt particles in the slurry when the slurry concentrated in (1) is separated (solid-liquid separation) into a liquid component containing the organic phase and a solid component (residue consisting of a wet cake) containing the precipitated inorganic salt. The diameter (μm) and the concentration (% by weight) of HMTBA contained in the solid component after solid-liquid separation are shown in Table 1 depending on the concentration conditions in the concentration tank 9.

As shown in Table 1 above, when the residence time in the concentration tank 9 is 3 hours, the particle size of the inorganic salt in the slurry is increased, and the efficiency of solid-liquid separation is improved. The concentration of HMTBA contained in the later solid component could be reduced. Moreover, the inorganic salt remaining in the liquid component after the solid-liquid separation was about a trace.
On the other hand, when the residence time in the concentration tank 9 is 0.1 hour, the particle size of the inorganic salt in the slurry becomes small, and the efficiency of solid-liquid separation becomes insufficient, and after solid-liquid separation The concentration of HMTBA contained in the solid component could not be reduced. Further, the inorganic salt remaining in the liquid component after the solid-liquid separation was 0.54% by weight, and the degree of purification of HMTBA was lower than in the above case.

  The centrifuge 12 (decanter centrifuge 23) is connected to a solid discharge line 16 for discharging solid components, and the separated solid components are discharged from the centrifuge 12 to the solid discharge line 16. Is done. In the middle of the solid discharge line 16, an aqueous phase discharge line 15 is connected, and the solid component discharged to the solid discharge line 16 is mixed with the aqueous phase of the aqueous phase discharge line 15 and is supplied to the separation tank 14. Supplied.

In this method, the moisture is then adjusted in the adjustment tank 13 and then taken out as an HMTBA product.
The adjustment tank 13 is connected to the centrifuge 12 via the connection line 3 and only needs to be able to adjust HMTBA as a product. For example, the adjustment tank 13 includes a stirring tank. The organic phase that is a liquid component separated from the inorganic salt that is a solid component in the centrifugal separator 12 is supplied to the adjustment tank 13 via the connection line 3.

In the adjustment tank 13, water is supplied to the organic phase to adjust the water content.
Thereby, the organic phase is prepared as an HMTBA product containing 88 to 90% by weight of HMTBA (including oligomers produced during concentration), 10 to 12.5% by weight of water, and other trace components. This product is taken out from the adjusting tank 13 as appropriate.
If HMTBA is produced using the above-described apparatus for producing HMTBA, it is possible to promote grain growth of inorganic salt crystals in the concentration step, and further, in the centrifugation step, the concentrated organic phase is centrifuged. The separation efficiency of the residue containing inorganic salt from the organic phase is improved. Therefore, HMTBA can be purified efficiently and efficiently from the reaction solution containing HMTBA obtained in the production step, and the yield of HMTBA can be improved.

In the above-described method for producing HMTBA, a hydration step and a hydrolysis step were sequentially performed (in two steps) as a production step for producing HMTBA. For example, HMTBN and / or 2-hydroxy-4 It is also possible to carry out the hydration and hydrolysis reactions in one step (in one step) by adding water and sulfuric acid to methylthiobutanamide.
However, if the production process is divided into a hydration process and a hydrolysis process, in each process, hydration or hydrolysis can be carried out under respective optimum conditions, so that HMTBA can be efficiently produced.

  Further, the operation in each step described above may be any of batch, semi-continuous and continuous, and is appropriately selected according to specific apparatus conditions.

It is a schematic apparatus block diagram which shows one Embodiment of the manufacturing apparatus of 2-hydroxy-4-methylthiobutanoic acid of this invention. It is an apparatus block diagram which shows the specific example of the concentration tank 9 in FIG. It is an apparatus block diagram which shows an example of a decanter type centrifuge.

Explanation of symbols

2 Hydration tank 4 Hydrolysis tank 8 Neutralization / separation tank 9 Concentration tank 12 Centrifuge 23 Decanter centrifuge

Claims (2)

A production step of adding water and an acid to 2-hydroxy-4-methylthiobutanenitrile and / or 2-hydroxy-4-methylthiobutanamide to produce 2-hydroxy-4-methylthiobutanoic acid;
By adding a basic alkali metal compound to the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the production step, an organic phase containing 2-hydroxy-4-methylthiobutanoic acid, water and inorganic A liquid separation step of separating the phase into an aqueous phase containing a salt, and separating the phase separated organic phase from the aqueous phase;
The organic phase separated in the liquid separation step is heated for 0.5 hour or more under conditions of a temperature of 60 to 150 ° C. and a pressure of 1 to 20 kPa to remove water remaining in the organic phase, and 2-hydroxy A concentration step of concentrating -4-methylthiobutanoic acid;
From said organic phase which is enriched in the concentration step, the residue containing an inorganic salt remaining in the organic phase, the temperature 60 to 120 ° C., under the conditions of centrifugal force 10～4000G, centrifuging at decanter centrifuge A centrifugal separation step separated by
A process for producing 2-hydroxy-4-methylthiobutanoic acid.   The production step is obtained in a hydration step in which 2-hydroxy-4-methylthiobutanenitrile is reacted with water in the presence of an acid catalyst to produce 2-hydroxy-4-methylthiobutanamide, and in the hydration step. And a hydrolysis step of adding water to the reaction solution containing 2-hydroxy-4-methylthiobutanamide to produce 2-hydroxy-4-methylthiobutanoic acid. A process for producing 2-hydroxy-4-methylthiobutanoic acid as described in 1. above.

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