JP2007238555A - Method for producing 2-hydroxy-4-methylthiobutanoic acid and equipment for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing 2-hydroxy-4-methylthiobutanoic acid (HMTBA), by which HMTBA can efficiently be obtained in good operability from a reaction solution obtained in a production process. <P>SOLUTION: This method for producing HMTBA comprises adding an alkali to a HMTBA-containing reaction solution produced by adding water and an acid to 2-hydroxy-4-methylthiobutanenitrile and/or 2-hydrxy-4-methylthiobutaneamide, thereby phase-separating into an organic phase containing HMTBA and an aqueous phase containing water and an inorganic salt, separating the phase-separated organic phase from the aqueous phase, concentrating in a concentration tank 9, charging the concentrated organic phase into a centrifugal separator 12, separating inorganic salt-containing residues left in the organic phase, and then mixing the residues with the above-mentioned phase-separated aqueous phase to recover HMTBA left in the residues. <P>COPYRIGHT: (C)2007,JPO&INPIT

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, insoluble matter is removed from the concentrated liquid obtained in (D) in the step (E). -Methylthiobutanoic acid is included.
Therefore, Patent Document 1 describes that the insoluble matter removed in step (E) may be washed with water to elute 2-hydroxy-4-methylthiobutanoic acid and the resulting aqueous solution may be recycled. Has been. Moreover, as such recycling, although there is no specific illustration in patent document 1, normally, the basic aqueous-metal compound is mix | blended with the said aqueous solution, and the oil layer containing 2-hydroxy-4-methylthiobutanoic acid and It is a usual method to separate into an aqueous layer and concentrate the resulting oil layer.

However, in an industrial production process, the above-mentioned insoluble matter is washed, and water for eluting 2-hydroxy-4-methylthiobutanoic acid and basicity for separating the aqueous solution into an oil layer and an aqueous layer. An alkali metal compound is required, and the cost required for the recycling increases.
In addition, since 2-hydroxy-4-methylthiobutanoic acid is dissolved to some extent in the aqueous layer, in order to increase the recycling efficiency, for example, by dissolving a solid inorganic salt in the aqueous solution, When the inorganic salt is required to be in a saturated state, when dissolving the solid inorganic salt, it is necessary to take a long time for the dilution operation in consideration of the generated heat of dilution. Considering the dispersibility of inorganic salts, there is a problem that a strong stirring device is required.

  The object of the present invention is to improve the operability and efficiency from the residue removed by phase separation, concentration and solid-liquid separation of the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the production step. 2-hydroxy-4-methylthiobutane, which can recover 2-hydroxy-4-methylthiobutanoic acid while efficiently using the aqueous phase removed during the production. An object of the present invention is to provide an acid production method and an apparatus for producing 2-hydroxy-4-methylthiobutanoic acid for producing 2-hydroxy-4-methylthiobutanoic acid by the production method.

  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; Removing the water remaining in the organic phase from the organic phase and concentrating 2-hydroxy-4-methylthiobutanoic acid; and A solid-liquid separation step for separating a residue containing an inorganic salt remaining in the organic phase from the organic phase concentrated in the step, a residue removed in the solid-liquid separation step, and a phase separation in the liquid separation step. The organic phase containing 2-hydroxy-4-methylthiobutanoic acid and the aqueous phase containing water and an inorganic salt are separated, and the separated organic phase is separated from the aqueous phase. And a recovery step for recovery.

  The aqueous phase removed in the separation step usually does not reach saturation, but contains an inorganic salt at a relatively high concentration. Therefore, according to the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, by mixing the aqueous phase removed in the liquid separation step with the residue removed in the solid-liquid separation step, From the residue removed in the separation step, the organic phase containing 2-hydroxy-4-methylthiobutanoic acid and the aqueous phase containing water and an inorganic salt can be efficiently phase separated. Furthermore, since the aqueous phase removed in the liquid separation step is mixed with the residue removed in the solid-liquid separation step without being discarded, the production cost of 2-hydroxy-4-methylthiobutanoic acid is reduced. Can do.

In the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, in the concentration step, the organic phase recovered in the recovery step is mixed with the organic phase separated in the liquid separation step and concentrated. It is preferable to do.
The organic phase recovered from the residue removed in the solid-liquid separation step can be purified by mixing and concentrating the organic phase recovered in the recovery step with the organic phase separated in the liquid separation step. The production efficiency of 2-hydroxy-4-methylthiobutanoic acid can be improved.

Further, in the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, in the recovery step, the residue removed in the solid-liquid separation step and the aqueous phase phase-separated in the liquid separation step are mixed. Before, the water removed in the concentration step may be mixed with the aqueous phase phase-separated in the liquid separation step.
The aqueous phase removed in the liquid separation step usually does not reach a saturated state in the content of inorganic salt, but may reach a saturated state depending on the blending conditions of alkali in the liquid separation step. In such a case, the aqueous phase removed in the liquid separation step is difficult to dissolve the residue removed in the solid-liquid separation step, and the 2-hydroxy-4-methylthiobutanoic acid contained in the residue is It may become impossible to collect efficiently. Therefore, when the water phase removed in the liquid separation step is saturated with an inorganic salt, the water phase removed in the concentration step is mixed with the water phase phase-separated in the liquid separation step, and the water phase is mixed. Makes the residue efficiently dissolved, and 2-hydroxy-4-methylthiobutanoic acid can be efficiently recovered.

  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. In the solid-liquid separation means for separating the residue, the aqueous phase supply means for supplying the aqueous phase phase-separated in the liquid separation means to the residue separated in the solid-liquid separation means, and the solid-liquid separation means The separated residue and the aqueous phase phase-separated in the liquid separation means are mixed, and phase separation is performed by separating the liquid into an organic phase containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous phase containing water. And a recovery means for separating and recovering the phase-separated organic phase from the aqueous phase.

  According to the apparatus for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, the aqueous phase phase-separated in the liquid separation means is supplied to the residue removed in the solid-liquid separation means using the aqueous phase supply means. By separating the organic phase containing 2-hydroxy-4-methylthiobutanoic acid with good operability from the residue removed in the solid-liquid separation means, the 2-hydroxy-4-methylthiobutanoic acid is efficiently separated Can be recovered, and the production efficiency of 2-hydroxy-4-methylthiobutanoic acid can be improved. Moreover, since the aqueous phase phase-separated in the liquid separation means can be efficiently used in the solid-liquid separation means without being discarded as it is, the production cost of 2-hydroxy-4-methylthiobutanoic acid can be reduced. .

  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, concentration and solid-liquid. 2-hydroxy-4-methylthiobutanoic acid can be recovered from the residue removed by the separation while using the aqueous phase separated by the phase separation. Therefore, 2-hydroxy-4-methylthiobutanoic acid can be efficiently recovered from the residue by separating the organic phase containing 2-hydroxy-4-methylthiobutanoic acid with good operability. As a result, the production efficiency of 2-hydroxy-4-methylthiobutanoic acid can be improved and the production cost can be reduced.

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, and FIG. 2 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. 1 and 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 it 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.
Further, an aqueous phase discharge line 15 as an aqueous phase supply means for discharging the aqueous 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 a liquid separation tank 14 as a recovery means via a solid discharge line 16. As will be described later, the aqueous phase discharged to the aqueous phase discharge line 15 is a solid component (from the wet cake) containing inorganic salts discharged from the solid-liquid separator 12 serving as the solid-liquid separation means via the solid discharge line 16. To the separation tank 14.

In this method, thereafter, the organic phase separated in the neutralization / separation tank 8 is supplied to the concentration tank 9 as the concentration means, and water remaining in the organic phase is removed in the concentration tank 9, so that the HMTBA Is purified by concentration (concentration step).
The concentration tank 9 is connected to the neutralization / separation tank 8 via the connection line 3, and is only required to be able to perform the above-described concentration, and includes a known concentrator. 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 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, the said organic phase (a collection | recovery organic phase is included) is supplied, for example, it concentrates on the conditions of the temperature of 60-150 degreeC, and the pressure of 1-20 kPa. As a result, 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 the organic phase, an inorganic salt is precipitated by this concentration and becomes a slurry.

  Further, in such concentration, the residence time of the organic phase in the concentration tank 9 is further set to 0.5 hours or more, whereby the HMTBA is oligomerized (mainly a dimer, a small amount of trimer and A tetramer). This can reduce the solubility of the inorganic salt in the organic phase and reduce the concentration of the inorganic salt in the organic phase. Preferably, the temperature, pressure and residence time are set so that the weight ratio of HMTBA monomer / oligomer is about 2 to 4.

In such concentration, the concentration conditions are preferably a temperature of 60 to 150 ° C., a pressure of 1 to 20 kPa, a residence time of 0.5 hours or more, and more preferably 0.5 to 5 hours. By such concentration, the particle size of the inorganic salt precipitated in the organic phase is increased. Therefore, in the solid-liquid separation step described later, the efficiency of solid-liquid separation is increased and the inorganic salt can be easily removed.
Further, a reflux line 5 connected to the hydrolysis tank 4 is connected to the concentration tank 9, and water (concentrated waste water) distilled off from the organic phase in the concentration tank 9 passes through the reflux line 5. Then, it is supplied from the concentration tank 9 to the hydrolysis tank 4.

  In this case, in the concentration tank 9, the water distilled off from the organic phase is not drained as it is, but is supplied to the hydrolysis tank 4 through the reflux line 5. The treatment required for draining water can be made unnecessary. 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.

Further, as will be described later, a dilution water phase injection line 30 connected to the water phase discharge line 15 may be connected to the concentration tank 9, and in the concentration tank 9, water distilled from the organic phase ( The concentrated drainage) may be supplied from the concentration tank 9 to the aqueous phase discharge line 15 via the dilution aqueous phase injection line 30.
In this method, the slurry is then cooled in the cooling tower 11, and the slurry is converted into a liquid component containing an organic phase and a solid component containing a precipitated inorganic salt (by a solid-liquid separator 12 as solid-liquid separation means). Residue) (solid-liquid separation 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 solid-liquid separator 12 via the connection line 3.
The solid-liquid separator 12 is connected to the cooling tower 11 via the connection line 3, and a centrifuge is used to separate the liquid component and the solid component from the slurry.
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 filtration efficiency and liquid drainage, and has a natural sedimentation rate of several mm / hr, so that solid-liquid separation by natural sedimentation is difficult. 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 this method, next, the solid component from the solid discharge line 16 and the aqueous phase from the aqueous phase discharge line 15 are supplied to the separation tank 14, whereby the aqueous phase is saturated by dissolving the inorganic salt. Phase separation (separation) into an aqueous phase containing an inorganic salt and an organic phase remaining in the solid component and in the aqueous phase (recovery step).

Mixing dissolution and phase separation in the separation tank 14 are performed in the range of 40 to 110 ° C., for example.
A solid discharge line 16 for discharging a solid component is connected to the solid-liquid separator 12 (decanter centrifuge 23), and the separated solid component is supplied from the solid-liquid separator 12 to the solid discharge line 16. To be discharged. Further, an aqueous phase discharge line 15 is connected in the middle of the solid discharge line 16, and the solid component discharged to the solid discharge line 16 is mixed and dissolved with the aqueous phase of the aqueous phase discharge line 15, and separated. It is supplied to the liquid tank 14.

  The solid component (residue consisting of a wet cake) containing inorganic salts discharged from the solid-liquid separator 12 (decanter centrifuge 23) via the solid discharge line 16 contains 20 to 60% by weight of HMTBA. The fluidity is poor. Therefore, in order to supply the solid component as it is to the separation tank 14, although it has poor handling properties, it is mixed and dissolved with the aqueous phase of the aqueous phase discharge line 15. Smooth supply can be realized.

  Moreover, in order to collect | recover the organic phase containing HMTBA from the residue containing the inorganic salt discharged | emitted through the solid discharge line 16, water and an inorganic salt are mix | blended with respect to the residue containing an inorganic salt, and HMTBA is included. Phase separation between the organic phase and the aqueous phase saturated with the inorganic salt must be achieved, thus increasing the cost burden of the formulated water and inorganic salt. However, in this method, the water phase discharged to the water phase discharge line 15 in the separation tank 8 b of the neutralization / separation tank 8 is supplied through the water phase discharge line 15 and is normally discharged to the water phase discharge line 15. Although the water phase is not saturated with an inorganic salt, it is saturated by mixing with a residue containing an inorganic salt, and phase separation between an organic phase containing HMTBA and an aqueous phase saturated with an inorganic salt is efficiently performed. Can be achieved well.

  In the separation tank 8b of the neutralization / separation tank 8, the aqueous phase discharged to the aqueous phase discharge line 15 is usually unsaturated with inorganic salts, and the salting out effect is not sufficient. The amount is high. For this reason, if the aqueous phase is discarded as it is, the loss of the target compound, HMTBA, increases. When the water phase discharged to the water phase discharge line 15 is saturated with an inorganic salt, the HMTBA dissolved in the water phase is about 1 to 1.2% by weight. When the aqueous phase is unsaturated with an inorganic salt, the HMTBA dissolved in the aqueous phase is about 2 to 5% by weight.

  However, in this method, the water phase discharged from the water phase discharge line 15 is not discarded as it is, but is used in the recovery process through the water phase discharge line 15. Moreover, by mixing with the solid component containing the inorganic salt discharged through the solid discharge line 16, the inorganic salt becomes saturated and the salting out effect is maximized as described above, so that it dissolves in the aqueous phase. The amount of HMTBA that is running can be minimized.

For example, according to Example 3 described in JP-A No. 2001-226344, when the series of operations shown in the following (1) to (6) is repeated 7 times, HMTBA is 3.29% by weight. There are obtained 687.6 g of dissolved aqueous phase and 209.9 g of a residue (wet cake) containing 35.8% by weight of HMTBA.
(1): 85.0 g (0.7 mol) of an 85.2 wt% sulfuric acid aqueous solution was stirred with 165.0 g (1.0 mol) of a 79.2 wt% HMTBN aqueous solution at 50 ° C. After dripping over 30 minutes, it hold | maintained at 50 degreeC for 2 hours. To this, 120 g of water was added and stirred at 110 ° C. for 4 hours. (2): The filtration residue obtained in (5) below is added to the reaction solution obtained in (1) (except during the first operation), and a 48% by weight aqueous sodium hydroxide solution is stirred. Was added in the amount shown in Table 3 of the above publication. (3): The mixed liquid obtained in (2) was separated into an oil phase and an aqueous phase at 70 ° C. (4): The oil phase obtained in (3) was concentrated using an evaporator until the water content in the liquid phase part reached the value shown in Table 3 of the above publication. (5): The concentrate (slurry) obtained in (4) was filtered at 70 ° C. using a glass filter. (6): Water was added to the filtrate obtained in (5) so that the HMTBA content was 89.0 wt% (measured value by potentiometric titration).

When the aqueous phase and the residue thus obtained are mixed and dissolved, and then allowed to stand, 745.4 g of an aqueous phase in which 1.34 wt% of HMTBA is dissolved and 140 g of an organic phase having an HMTBA concentration of 62.2 wt% are obtained. . The liquid separation speed at this time was 7 m / hr, and the liquid separation property was good.
In the separation tank 8b of the neutralization / separation tank 8, the aqueous phase discharged to the water phase discharge line 15 is usually not saturated with an inorganic salt as described above. In some cases, the inorganic salt is saturated. In such a case, water (concentrated waste water) distilled from the organic phase in the concentration tank 9 is supplied to the aqueous phase discharge line 15 via the dilution aqueous phase injection line 30, and the water phase discharge line 15 The inorganic salt concentration of the aqueous phase may be adjusted as appropriate so that the aqueous phase of the aqueous phase becomes unsaturated with the inorganic salt. Thereby, when the residue removed in the solid-liquid separation step and the aqueous phase supplied from the aqueous phase discharge line 15 are mixed, the residue can be dissolved in the aqueous phase.

A drainage line 17 and a recovered organic phase supply line 10 are connected to the separation tank 14. And in the liquid separation tank 14, the water phase isolate | separated from the organic phase is drained from the drainage line 17 as waste_water | drain. 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 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 solid-liquid separator 12 (decanter centrifuge 23) via the connection line 3, and it is sufficient that HMTBA can be adjusted as a product. For example, the adjustment tank 13 includes a stirring tank. Then, the organic phase that is a liquid component separated from the inorganic salt that is a solid component in the solid-liquid 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 HMTBA production apparatus, the aqueous phase removed in the liquid separation step is mixed with the residue removed in the solid-liquid separation step without being discarded as it is. Since the organic phase containing HMTBA contained in the residue removed in the solid-liquid separation step is phase-separated and recovered, it is possible to improve the production efficiency of HMTBA and reduce the production cost. .

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 an example of a decanter type centrifuge.

Explanation of symbols

2 Hydration tank 4 Hydrolysis tank 8 Neutralization / separation tank 9 Concentration tank 12 Solid-liquid separator 14 Separation tank 15 Water phase discharge line 16 Solid discharge line 23 Decanter centrifuge

Claims (5)

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 an alkali to the reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the generating step, an organic phase containing 2-hydroxy-4-methylthiobutanoic acid, water containing water and an inorganic salt are added. A phase separation step of separating the organic phase separated from the aqueous phase,
A concentration step of removing 2-water-4-methylthiobutanoic acid by removing water remaining in the organic phase from the organic phase separated in the liquid separation step;
A solid-liquid separation step of separating a residue containing an inorganic salt remaining in the organic phase from the organic phase concentrated in the concentration step;
The residue removed in the solid-liquid separation step and the aqueous phase phase-separated in the liquid separation step are mixed, an organic phase containing 2-hydroxy-4-methylthiobutanoic acid, water containing water and an inorganic salt A recovery step in which the phase is separated into phases and the separated organic phase is separated from the aqueous phase and recovered;
A process for producing 2-hydroxy-4-methylthiobutanoic acid.   The 2-hydroxy-4- according to claim 1, wherein in the concentration step, the organic phase separated in the liquid separation step is mixed with the organic phase recovered in the recovery step and concentrated. A method for producing methylthiobutanoic acid.   In the recovery step, before mixing the residue removed in the solid-liquid separation step and the aqueous phase phase-separated in the liquid separation step, the water removed in the concentration step is phased in the liquid separation step. The method for producing 2-hydroxy-4-methylthiobutanoic acid according to claim 1 or 2, characterized by mixing with a separated aqueous phase.   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. The manufacturing method of 2-hydroxy-4-methylthiobutanoic acid in any one of -3. A reaction vessel in which 2-hydroxy-4-methylthiobutanenitrile and / or 2-hydroxy-4-methylthiobutanamide is reacted with water to produce 2-hydroxy-4-methylthiobutanoic acid;
The reaction solution containing 2-hydroxy-4-methylthiobutanoic acid obtained in the reaction vessel is phase-separated into an organic phase containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous phase containing water. Separating means for separating the organic phase from the aqueous phase;
Concentration means for removing water remaining in the organic phase from the organic phase separated in the liquid separation means and concentrating 2-hydroxy-4-methylthiobutanoic acid;
A solid-liquid separation means for separating a residue containing an inorganic salt remaining in the organic phase from the organic phase concentrated in the concentration means;
An aqueous phase supply means for supplying the aqueous phase separated in the liquid separation means to the residue separated in the solid-liquid separation means;
The residue separated in the solid-liquid separation means and the aqueous phase phase-separated in the liquid separation means are mixed, and an organic phase containing 2-hydroxy-4-methylthiobutanoic acid and water containing water are separated by liquid separation. Recovery means for phase-separating into phases and recovering the separated organic phase from the aqueous phase;
An apparatus for producing 2-hydroxy-4-methylthiobutanoic acid, comprising:

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