阅读说明：本技术 甲硫氨酸的制造方法 (Process for producing methionine ) 是由 山下大辅 古泉善行 于 2018-12-26 设计创作，主要内容包括：本发明的目的在于提供甲硫氨酸的制造方法,其能够从通过将母液浓缩而产生的气体中高效地回收氨并加以利用。该制造方法包括下述回收工序：将母液的浓缩工序中产生的气体导入使水循环的气体洗涤塔内,使该气体与水接触,从而将该气体所包含的氨回收；其中,以质量比计,水的流量相对于被导入上述气体洗涤塔中的气体的流量之比为2以上。优选的是,从气体洗涤塔排出的水在导入该气体洗涤塔中之前被冷却。(The purpose of the present invention is to provide a method for producing methionine, which can efficiently recover and utilize ammonia from a gas produced by concentrating a mother liquor. The manufacturing method comprises the following recovery steps: introducing a gas generated in the concentration step of the mother liquor into a gas scrubber circulating water, and bringing the gas into contact with water to recover ammonia contained in the gas; wherein the ratio of the flow rate of water to the flow rate of the gas introduced into the gas scrubber is 2 or more in terms of mass ratio. Preferably, the water discharged from the gas scrubber is cooled before being introduced into the gas scrubber.)

1. A method for producing methionine, comprising the steps of:

a hydantoinization step in which 3-methylthiopropanal and hydrocyanic acid are reacted with carbon dioxide and ammonia, or a compound obtained by reacting 3-methylthiopropanal and hydrocyanic acid is reacted with carbon dioxide and ammonia, thereby obtaining a liquid containing 5- (2-methylthioethyl) hydantoin;

a hydrolysis step of hydrolyzing the 5- (2-methylthioethyl) hydantoin;

a crystallization step of introducing carbon dioxide into the methionine salt-containing liquid obtained in the hydrolysis step to precipitate methionine;

a separation step of performing solid-liquid separation on the methionine slurry obtained in the crystallization step; and

a concentration step of concentrating the mother liquor obtained in the separation step,

the method further includes a recovery step of: introducing the gas generated in the concentration step into a gas scrubber for circulating water, and bringing the gas into contact with water to recover ammonia contained in the gas,

the ratio of the flow rate of water to the flow rate of the gas introduced into the gas scrubber is 2 or more in terms of mass ratio.

2. The process of claim 1, wherein the water discharged from the gas scrubber is cooled prior to introduction into the gas scrubber.

Technical Field

The present invention relates to a process for producing methionine.

Background

In the method for producing methionine, 5- (2-methylthioethyl) hydantoin (hereinafter, sometimes referred to as methionine hydantoin.) is prepared. The methionine hydantoin can be obtained, for example, by a method in which 3-methylthiopropanal cyanohydrin (hereinafter, sometimes referred to as methionine cyanohydrin) is reacted with carbon dioxide and ammonia in water. The methionine hydantoin can also be obtained by a method in which 3-methylthiopropanal (hereinafter, sometimes referred to as methionine aldehyde) is reacted with hydrocyanic acid, carbon dioxide and ammonia.

In this production method, methionine hydantoin is hydrolyzed. Thus, a liquid containing a methionine salt (hereinafter, sometimes referred to as a hydrolysis reaction liquid) was obtained. By introducing carbon dioxide into the hydrolysis reaction solution, methionine is precipitated to obtain a methionine slurry. The slurry is separated into methionine and mother liquor.

Methionine is dissolved in the mother liquor. In this production method, the mother liquor is heated and concentrated in order to recover the methionine. Carbon dioxide was introduced into the obtained concentrated solution to precipitate and recover methionine. Various studies have been made to improve the recovery rate of methionine from the mother liquor (for example, patent document 1).

In patent document 1, in order to improve the recovery rate of methionine, it is attempted to accurately control the hydrolysis temperature and the heat treatment temperature of the mother liquor to specific temperatures or lower.

Disclosure of Invention

Problems to be solved by the invention

In the reaction for obtaining methionine hydantoin (hereinafter, may be referred to as "hydantoination reaction"), an excess amount of ammonia is usually used. In the case where ammonia may remain in the mother liquor, the gas produced by concentrating the mother liquor may contain ammonia in addition to carbon dioxide. Ammonia affects not only the efficiency of methionine precipitation but also the yield and purity of the product methionine. Therefore, when carbon dioxide is recovered from a gas produced by concentrating the mother liquor and used, the amount of ammonia contained in the gas is preferably as small as possible.

Patent document 1 mentioned above shows: by concentrating the mother liquor, carbon dioxide can be distilled off from the mother liquor, and a recycle liquor favorable for the hydrolysis reaction can be obtained. However, patent document 1 does not disclose how to treat the gas generated by concentrating the mother liquor.

Considering the environmental impact, ammonia cannot be released directly into the atmosphere. Therefore, a method for producing methionine is strongly required to be environmentally friendly so that environmental damage due to ammonia emission does not occur.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing methionine, which can efficiently recover and utilize ammonia from a gas generated by concentrating a mother liquor.

Means for solving the problems

The present inventors have intensively studied an environmentally friendly technique focusing on the fact that ammonia is an essential component in the hydantoination reaction, and as a result, have found a technique capable of recycling ammonia contained in a gas generated by concentrating a mother liquor, thereby completing the present invention. That is, the method for producing methionine according to the present invention comprises the steps of:

a hydantoinization step of reacting 3-methylthiopropanal and hydrocyanic acid with carbon dioxide and ammonia, or reacting a compound obtained by reacting 3-methylthiopropanal and hydrocyanic acid with carbon dioxide and ammonia, thereby obtaining a liquid containing 5- (2-methylthioethyl) hydantoin;

a hydrolysis step of hydrolyzing the 5- (2-methylthioethyl) hydantoin;

a crystallization step of introducing carbon dioxide into the methionine salt-containing liquid obtained in the hydrolysis step to precipitate methionine;

a separation step of performing solid-liquid separation on the methionine slurry obtained in the crystallization step; and

a concentration step of concentrating the mother liquor obtained in the separation step,

the method further includes a recovery step of: introducing the gas generated in the concentration step into a gas scrubber for circulating water, and bringing the gas into contact with water to recover ammonia contained in the gas,

the ratio of the flow rate of water to the flow rate of the gas introduced into the gas scrubber is 2 or more in terms of mass ratio.

In this production method, ammonia is recovered from the gas generated in the concentration step (hereinafter, sometimes referred to as "concentration step off-gas") in the recovery step. In this production method, water is circulated and used, and therefore the amount of water used can be reduced. Further, since the ratio of the flow rate of water circulating through the gas scrubber to the flow rate of the concentration step off-gas introduced into the gas scrubber is 2 or more in terms of mass ratio, contact between the concentration step off-gas and water is promoted, and ammonia can be efficiently recovered from the concentration step off-gas. The recovered ammonia can be reused in the hydantoination step, for example. The production method can realize reduction of the amount of ammonia discharged from a methionine production facility. In this production method, production of methionine can be performed in consideration of environmental friendliness.

In the process for producing methionine, it is preferable that the water discharged from the gas scrubber is cooled before being introduced into the gas scrubber.

In this production method, the temperature of the exhaust gas from the concentration step is high. Therefore, when water is circulated and used in the gas scrubber, the temperature of the water increases, and the recovery rate of ammonia may decrease. However, in this production method, the water discharged from the gas scrubber is cooled before being introduced into the gas scrubber. Since the cooled water is introduced into the gas scrubber, the temperature of the water in the gas scrubber can be maintained appropriately even if the water is circulated and used. Since the dissolution of ammonia contained in the exhaust gas from the concentration step in water is promoted, the production method can efficiently recover ammonia from the exhaust gas from the concentration step.

ADVANTAGEOUS EFFECTS OF INVENTION

As is clear from the above description, the method for producing methionine of the present invention can efficiently recover and utilize ammonia from the exhaust gas of the concentration step. This production method can achieve a reduction in the amount of ammonia discharged. In this production method, production of methionine can be performed in consideration of environmental friendliness.

Drawings

FIG. 1 is a schematic view showing a part of an apparatus used in a method for producing methionine according to an embodiment of the present invention.

Detailed Description

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings as appropriate. In the present specification, the details of the conventionally known parts other than the parts necessary for explaining the present invention are omitted.

[ method for producing methionine ]

In the method for producing methionine according to one embodiment of the present invention, methionine is obtained using methionine aldehyde as a starting material. The production method comprises a hydantoinization step, a hydrolysis step, a crystallization step, a separation step, a concentration step and a recovery step. The formaldehyde methionine can be obtained, for example, by reacting methyl mercaptan with acrolein.

[ hydantoinization Process ]

In the hydantoinization step, methionine hydantoin-containing liquid (hereinafter, sometimes referred to as "hydantoin liquid") is obtained by reacting methionine aldehyde and hydrocyanic acid, or a compound obtained by reacting these components, for example, methionine cyanohydrin, with carbon dioxide and ammonia in the presence of water in a reaction tank. Specifically, examples of the method for obtaining the hydantoin solution include: a method of reacting thiamine aldehyde, hydrocyanic acid, carbon dioxide and ammonia; and a method of reacting methionine cyanohydrin, carbon dioxide and ammonia. In the present invention, carbon dioxide may be present in the form of carbonate ions and/or bicarbonate ions. Ammonia may also be present in the form of ammonium ions.

The reaction of methionine cyanohydrin to methionine hydantoin can be carried out by mixing methionine cyanohydrin with water containing dissolved carbon dioxide and ammonia and concentrating the mixture. The reaction temperature is usually 50 to 90 ℃. The reaction time is usually 0.5 to 6 hours.

In the reaction of methionine cyanohydrin to methionine hydantoin, the amount of water used is usually 3 to 4 times the amount of methionine cyanohydrin.

The amount of carbon dioxide used is usually 1 to 5 moles, preferably 1.5 to 3 moles, based on 1 mole of methionine cyanohydrin.

The amount of ammonia used is usually in excess of more than 2 moles, preferably 3 to 5 moles, based on 1 mole of methionine cyanohydrin.

When ammonium carbonate is used in place of carbon dioxide and ammonia, the amount of ammonium carbonate used is usually 0.7 to 3 times, preferably 0.9 to 2 times, the amount of methionine cyanohydrin.

The concentration of methionine hydantoin in the hydantoin solution is usually 1 to 50% by mass, preferably 10 to 20% by mass. In the present invention, the methionine hydantoin concentration may be determined by liquid chromatography.

In the hydantoination step, an excess amount of ammonia is generally used. Therefore, unreacted ammonia remains in the hydantoin solution. The hydantoin solution contains ammonia. The ammonia concentration of the hydantoin solution is usually 2 to 7 mass%, preferably 3 to 6 mass%. The amount of ammonia contained in the hydantoin solution is usually 1 to 4 moles, preferably 2 to 3 moles, based on 1 mole of methionine hydantoin. In the present invention, the ammonia concentration can be obtained by converting the amount of ammonium ions measured by ion chromatography into the amount of ammonia. The analytical conditions for determining the amount of ammonium ions are as follows.

(conditions for ion chromatography analysis)

Column: dionex IonPac CS12A

Column size: an inner diameter of 4mm and a length of 250mm

Eluent 20 mmol/L methanesulfonic acid

Hydantoin liquids typically contain carbon dioxide in addition to ammonia. The hydantoin solution usually has a carbon dioxide concentration of 2 to 7 mass%. The carbon dioxide concentration can be determined by gas chromatography.

[ hydrolysis step ]

In the hydrolysis step, methionine hydantoin may be hydrolyzed in the presence of a basic compound such as potassium hydroxide, sodium hydroxide, potassium carbonate, or potassium hydrogen carbonate. Thus, a liquid containing a methionine salt (hereinafter, sometimes referred to as a hydrolysis reaction liquid) can be obtained. In the hydrolysis step, the pressure is usually set in the range of about 0.5 to 1.0 MPaG. The temperature is set within the range of 150-200 ℃. The hydrolysis reaction liquid contains ammonia, and the ammonia concentration of the hydrolysis reaction liquid is usually 0.2 to 1 mass%. The ammonia concentration can be measured by the ion chromatography described above.

[ crystallization Process ]

In the crystallization step, carbon dioxide is introduced into the hydrolysis reaction liquid obtained in the hydrolysis step. Thus, methionine was precipitated, and a slurry of methionine was obtained. In the crystallization step, the crystallization temperature is usually 0 to 50 ℃, preferably 10 to 30 ℃. The crystallization time is usually 30 minutes to 24 hours based on the time until carbon dioxide is saturated in the reaction solution and methionine is sufficiently precipitated.

[ separation Process ]

In the separation step, the methionine slurry obtained in the crystallization step is solid-liquid separated into a cake (cake) of methionine as a solid component and a mother liquor as a liquid component by a solid-liquid separator such as a centrifugal separator. In this production method, the methionine cake obtained in the separation step is washed with washing water and purified, and then the cake is dried. Thus, a methionine powder as a product was obtained.

[ concentration step ]

Methionine and potassium hydrogencarbonate were dissolved in the mother liquor obtained in the separation step. In the production of methionine, methionine and potassium bicarbonate are valuable components. Therefore, in the concentration step, the mother liquor is concentrated to recover methionine and potassium hydrogencarbonate. The mother liquor is concentrated by heating the mother liquor to evaporate components such as water contained in the mother liquor. In the concentration step, the heating temperature of the mother liquor is usually 100 to 140 ℃.

As described above, in the concentration step, the components such as water contained in the mother liquor are evaporated by the concentration of the mother liquor. In other words, in the concentration step, a gas containing steam as a main component is generated. Since carbon dioxide is blown into the mother liquor in the crystallization step, carbon dioxide is contained in the mother liquor. As described above, the hydrolysis reaction solution contains ammonia. Therefore, a trace amount of ammonia remains in the mother liquor. Therefore, the exhaust gas from the concentration step contains carbon dioxide and a trace amount of ammonia. In this production method, in the next recovery step, the concentration step off-gas is brought into contact with water, thereby recovering ammonia contained in the concentration step off-gas.

[ recovering step ]

Fig. 1 shows a part of an apparatus 2 used in a method for producing methionine according to an embodiment of the present invention. In this production method, the treatment of the exhaust gas from the concentration step is performed using this facility 2. The apparatus 2 is provided with a gas scrubber 4, a pump 6 and a cooler 8. In this apparatus 2, the gas scrubber 4, the pump 6, and the cooler 8 are connected by liquid pipes 10 through which liquid flows.

In this production method, the concentration step off-gas is introduced into the gas scrubber 4 from below. The concentration step off-gas moves from the lower portion toward the upper portion in the gas scrubber 4 and is discharged from the top of the gas scrubber 4.

In this production method, water is introduced into the gas scrubber 4 from the upper part thereof. The water moves from the upper portion toward the lower portion in the gas scrubber 4 and is discharged from the bottom of the gas scrubber 4.

In this production method, the water introduced into the gas scrubber 4 is not particularly limited. Examples of the water include pure water, ion-exchanged water, tap water, and industrial water.

In the recovery step, the concentration step off-gas and water are introduced into the gas scrubber 4, and the concentration step off-gas and water are brought into contact with each other in the gas scrubber 4. Thereby, ammonia contained in the exhaust gas from the concentration step is dissolved in water. Therefore, the ammonia concentration of the gas discharged from the gas washing column 4 is lower than the ammonia concentration of the concentration step off-gas introduced into the gas washing column 4. The ammonia concentration of the water discharged from the gas washing tower 4 is higher than that of the water introduced into the gas washing tower 4. In this recovery step, ammonia contained in the exhaust gas from the concentration step is recovered in water in the gas scrubber 4.

In the recovery step, the water in which ammonia is dissolved by contact with the exhaust gas from the concentration step is discharged from the bottom of the gas scrubber 4. In the recovery step, water discharged from the bottom of the gas scrubber 4 is reintroduced into the gas scrubber 4 through the pump 6 and the cooler 8.

In this production method, water is circulated and used in the gas scrubber 4. In this production method, water repeatedly passes through the gas scrubber 4. For the sake of equilibrium, a part of the water is treated as wastewater, but at the time point when the ammonia concentration of the water becomes equal to or higher than a predetermined concentration, the ammonia-containing water is introduced into, for example, a storage tank in which an aqueous ammonium carbonate solution used in the hydantoination reaction is produced. Then, in order to stably maintain the amount of water in the gas washing column 4, water is reintroduced into the gas washing column 4 from the upper portion thereof.

In this production method, as described above, water discharged from the bottom of the gas scrubber 4 is introduced into the gas scrubber 4 via the pump 6 and the cooler 8. In this recovery step, the water discharged from the gas scrubber 4 is cooled in the cooler 8 before being introduced into the gas scrubber 4.

In this production method, the cooler 8 is not particularly limited as long as it can cool the water discharged from the gas scrubber 4. Although not shown, in this manufacturing method, the cooler 8 is configured as follows: cooling water flows through the inside of the gas scrubber, and the water discharged from the gas scrubber 4 can be cooled by heat exchange.

In this production method, ammonia is recovered from the exhaust gas from the concentration step in the recovery step.

In this production method, the amount of water used can be reduced because water is circulated and used. Further, since the ratio of the flow rate of water circulating through the gas scrubber 4 to the flow rate of the concentration step off-gas introduced into the gas scrubber 4 is 2 or more in terms of mass ratio, contact between the concentration step off-gas and water is promoted, and ammonia can be efficiently recovered from the concentration step off-gas. The recovered ammonia can be reused in the hydantoination step, for example. The production method can reduce the amount of ammonia discharged from methionine production equipment. In this production method, production of methionine can be performed in consideration of environmental friendliness.

In this production method, since the amount of the off gas in the concentration step is large, the amount of water used in the gas scrubber 4 is preferably large. From the viewpoint of enabling the ammonia to be recovered more efficiently from the concentration step off-gas, the ratio of the flow rate of the water circulating in the gas scrubber 4 to the flow rate of the concentration step off-gas introduced into the gas scrubber 4 is preferably 5 or more, 10 or more, 20 or more, 30 or more, 40 or more, or 50 or more in terms of a mass ratio. The upper limit of the ratio is determined by the facility-related restrictions (such as pressure loss) of the gas scrubber 4, and is usually 1000 or less.

In the production method, the temperature of the exhaust gas from the concentration step is, for example, 105 to 110 ℃. Therefore, when water is circulated and used, the temperature of water increases, and the recovery rate of ammonia may decrease. However, as described above, in this production method, the water discharged from the gas scrubber 4 is cooled before being introduced into the gas scrubber 4. Since the cooled water is introduced into the gas scrubber 4, the temperature of the water in the gas scrubber 4 can be maintained appropriately even if the water is circulated and used. Since the dissolution of ammonia contained in the exhaust gas from the concentration step in water is promoted, the production method can efficiently recover ammonia from the exhaust gas from the concentration step. Therefore, in this production method, from the viewpoint of efficiently recovering ammonia from the concentration step off-gas, it is preferable that the water discharged from the gas scrubber 4 is cooled before being introduced into the gas scrubber 4. From the viewpoint of improving the recovery rate of ammonia, the temperature of the water to be introduced into the gas scrubber 4 is more preferably 40 ℃.

As described above, in this production method, the water from which ammonia is recovered in the gas scrubber 4 is directly introduced into, for example, a storage tank in which an aqueous solution of ammonium carbonate used in the hydantoination reaction is produced. The concentration of ammonia contained in the water introduced into the storage tank from the gas scrubber 4 is preferably 0.1 mass% or more, from the viewpoint of effectively reducing the amount of water used and contributing to the production of the ammonium carbonate aqueous solution in the storage tank. In other words, the circulation of water in the gas scrubber 4 is preferably continued until the concentration of ammonia dissolved in the water becomes 0.1 mass% or more. The concentration of ammonia dissolved in the water is preferably 1 mass% or less.

As is clear from the above description, the method for producing methionine of the present invention can efficiently recover and utilize ammonia from the exhaust gas of the concentration step. This production method can achieve a reduction in the amount of ammonia discharged. In this production method, production of methionine can be performed in consideration of environmental friendliness.