Method for producing concentrated aqueous carbonate solution

Abstract

The present specification discloses a method for producing a concentrated aqueous carbonate solution. The present invention relates to a method for producing a concentrated aqueous carbonate solution, comprising a step for producing a concentrated aqueous bicarbonate solution by dehydrating an aqueous bicarbonate solution using a salt barrier film, in which the concentrated aqueous bicarbonate solution obtained in the previous step is heated to thermally decompose the bicarbonate into carbonate, carbon dioxide, and water, while evaporating water, and the concentrated aqueous carbonate solution is obtained. A concentrate of the carbonate aqueous solution is obtained.

Description

[0001] This invention application is a divisional application of PCT patent application PCT / JP2020 / 034580, filed on September 11, 2020, and entitled “Method for producing concentrated carbonate aqueous solution”. The application number of the parent application entering China is 202080064915.2. Technical Field

[0002] This patent application claims priority based on the Paris Convention of Japanese Patent Application No. 2019-168092 (filing date: September 17, 2019), which is hereby incorporated by reference into this specification in its entirety.

[0003] The present invention relates to a method for producing a concentrated carbonate aqueous solution, and more particularly, to a method for producing methionine using the method. Background Art

[0004] As a method for producing a compound that can be used as a feed additive, namely, methionine, there is known a method comprising the following steps: 5-(2-methylthio)hydantoin is hydrolyzed with an alkali metal carbonate and water to obtain an aqueous solution of an alkali metal salt of methionine, carbon dioxide is added to the solution, and the solution is separated into solid methionine and a mother liquor containing bicarbonate. It is known that the separated filtrate containing bicarbonate is heated, the bicarbonate is thermally decomposed into carbonate, carbon dioxide and water, and the water is evaporated to obtain a concentrate of a carbonate aqueous solution (carbonate concentration step), and the concentrated carbonate aqueous solution is used for the hydrolysis of hydantoin (see Patent Document 1). However, in the carbonate concentration step, since the latent heat of evaporation of water is large, the evaporation of water by heating may not be satisfactory in terms of energy efficiency.

[0005] As a common energy-saving dehydration technology, membrane separation technology such as RO membrane is known, and membrane elements are also commercially available. However, since the applicable range is generally below pH 9, the pH value of the concentrate exceeds 9 in the carbonate concentration process (for example, the carbonate concentration process in the methionine manufacturing process). Therefore, as an industrial manufacturing method, the application of membranes to carbonate concentration may cause problems.

[0006] Prior art literature

[0007] Patent Literature

[0008] Japanese Patent Application No. 2008-506520. Summary of the invention

[0009] Problems to be solved by the invention

[0010] The present invention provides a method for concentrating carbonates which improves energy efficiency by using membrane separation, and in particular provides a method for concentrating an aqueous carbonate solution which is suitable for a production process of methionine.

[0011] Means for solving problems

[0012] The present invention includes the following aspects.

[0013] 1. A method for producing a concentrated carbonate aqueous solution, comprising the step of dehydrating a bicarbonate aqueous solution using a salt barrier membrane to produce a concentrated bicarbonate aqueous solution, wherein the concentrated bicarbonate aqueous solution obtained in the above step is heated to thermally decompose the bicarbonate into carbonate, carbon dioxide and water, while evaporating the water to obtain a concentrate of the carbonate aqueous solution.

[0014] 2. The production method according to item 1, wherein the aqueous bicarbonate solution used for dehydration using the salt barrier membrane is an aqueous potassium bicarbonate solution or an aqueous sodium bicarbonate solution.

[0015] 3. The production method according to item 1 or 2, wherein the bicarbonate aqueous solution used for dehydration using the salt barrier membrane is a 1 to 34 wt % bicarbonate aqueous solution.

[0016] 4. The production method according to any one of items 1 to 3, wherein the salt barrier membrane is an RO membrane or a NF membrane.

[0017] 5. The production method according to any one of items 1 to 4, wherein the salt barrier film is an organic film.

[0018] 6. The production method according to any one of items 1 to 5, wherein the bicarbonate aqueous solution is a bicarbonate aqueous solution obtained by a methionine production process.

[0019] 7. The production method according to item 6, wherein the bicarbonate aqueous solution is a bicarbonate aqueous solution obtained by filtering out methionine.

[0020] 8. A method for producing methionine, comprising:

[0021] 1) Process for producing 5-(2-methylmercaptoethyl)-hydantoin by reacting 3-mercaptopropionaldehyde, hydrogen cyanide, ammonia and carbon dioxide or ammonium carbonate

[0022] 2) A step of hydrolyzing the generated 5-(2-methylmercaptoethyl)-hydantoin with potassium carbonate and water to obtain a potassium salt of methionine

[0023] 3) Step of introducing carbon dioxide into the hydrolysis reaction solution to precipitate methionine

[0024] A method for producing methionine, the method comprising:

[0025] 4) a step of filtering out methionine from the mixture of the potassium bicarbonate aqueous solution and methionine produced in the above step, and dehydrating the obtained potassium bicarbonate aqueous solution using a salt barrier membrane,

[0026] 5) a step of heating the membrane-concentrated potassium bicarbonate aqueous solution to thermally decompose the potassium bicarbonate into potassium carbonate and carbon dioxide while evaporating water to obtain a concentrated potassium carbonate aqueous solution,

[0027] 6) The obtained concentrated potassium carbonate aqueous solution is further subjected to the above-mentioned step 2).

[0028] Effects of the Invention

[0029] According to this method, the concentrated carbonate aqueous solution and by-produced carbon dioxide managed to a predetermined concentration can be recovered with better energy efficiency than before. DETAILED DESCRIPTION

[0030] A method for producing a concentrated carbonate aqueous solution is described. The method includes a step of dehydrating a bicarbonate aqueous solution using a salt barrier membrane to produce a concentrated bicarbonate aqueous solution, wherein the concentrated bicarbonate aqueous solution obtained in the aforementioned step is heated to thermally decompose the bicarbonate into carbonate, carbon dioxide and water, while evaporating the water to obtain a concentrate of the carbonate aqueous solution.

[0031] Bicarbonate is an amphoteric substance (HCO 3 - Relative to CO 3 2- It is an acid relative to H 2 CO 3 Therefore, if the pH of the solution is calculated by the dissociation constant, material balance and charge balance, the theoretical pH = (pKa1 + pKa2) / 2 ≈ 8.4. In addition, since the theoretical pH formula does not include the concentration term, the pH has the characteristic of being independent of the bicarbonate concentration, and the pH does not rise during the concentration using the membrane, so the concentration rate is not restricted by the pH rise.

[0032] 1) Dehydration process using membrane

[0033] Considering the solubility of bicarbonate at the suitable operating temperature of the membrane (usually below 45°C), the concentration of the bicarbonate aqueous solution concentrated by the salt barrier membrane is suitable for a concentration of 34wt% or less. As bicarbonate, sodium bicarbonate or potassium bicarbonate can be exemplified, and as carbonate after thermal decomposition, sodium carbonate and potassium carbonate can be exemplified. The pH of the bicarbonate aqueous solution provided for dehydration using the salt barrier membrane is typically about pH 9 or less. Concentration using the membrane is preferably carried out at a temperature below 50°C, and more preferably at a temperature below 45°C. The dehydration rate using the salt barrier membrane is preferably 5% or more, and more preferably 10% or more. The membrane supply pressure is preferably 1MPaG or more, and more preferably 3MPaG or more.

[0034] As a salt barrier membrane, a liquid separation membrane such as an RO membrane and a NF membrane that selectively allows the solvent to pass through by applying a pressure greater than the osmotic pressure difference between the solutions of the membrane that passes the solvent but not the solute on the high concentration side can be exemplified. As a membrane structure, polymer membranes such as asymmetric membranes and composite membranes can be cited. As a salt barrier membrane, an organic membrane can be exemplified, and as its raw materials, for example, polyamide raw materials such as aromatic polyamides, aliphatic polyamides, and their composite materials, cellulose raw materials such as cellulose acetate, etc. can be cited, but it is not limited to this. In addition, the form of the module (モジュール) is not particularly limited, and for example, a tubular membrane module, a flat membrane module, a spiral membrane module, a hollow fiber membrane module, etc. can be cited. As commercially available components of RO membranes and NF membranes, SU-820FA (made by Toray Industries, Ltd.) and CPA5-LD (made by Nitto Denko Corporation) can be cited. Among them, SU-600, NTR-729HF, NTR-7250, and NTR-7450 can be exemplified.

[0035] 2) Carbonate concentration process

[0036] The potassium bicarbonate aqueous solution concentrated by the membrane is heated to thermally decompose the bicarbonate into carbonate, carbon dioxide and water while evaporating the water to produce a concentrate of the potassium carbonate aqueous solution. In order to facilitate the evaporation of the water, the pressure is preferably 0.5 MPaG or less, more preferably 0.1 MPaG or less. The heating and gas-liquid separation can be poured into a gas-liquid separator after heating, or a distillation tower can be used. In addition, they can be concentrated to the target concentration in one stage, or multiple stages can be combined like a multi-effect tank.

[0037] As the aqueous hydrogen carbonate solution, an aqueous hydrogen carbonate solution obtained by a methionine production process can be exemplified. In the following scheme, the case where the hydrogen carbonate is composed of an alkali metal, a typical example of which is potassium, is shown as an example.

[0038]

[0039] Here, as shown in formula (2), after the hydantoin compound is hydrolyzed with a carbonate aqueous solution, carbon dioxide is blown into the reaction system to neutralize the alkali as shown in formula (3), and methionine is filtered out as a solid from the mother liquor containing the carbonate aqueous solution.

[0040] The bicarbonate aqueous solution obtained by filtration is concentrated by membrane, and then decomposed by heat treatment such as steam heating and evaporation of water as shown in the following flow to obtain a concentrated carbonate aqueous solution concentrated to a predetermined potassium ion concentration. The concentrated carbonate aqueous solution can be recycled to the step of formula (2), and the generated carbon dioxide can be recycled to the step of formula (3).

[0041] KHCO 3 →0.5K 2 CO 3 +0.5CO 2 +0.5H 2 O (4)

[0042] For the production process including the above formulae (1), (2), (3) and (4), for example, reference can be made to the descriptions of US2006016334 and US5770769.

[0043] As a method for producing methionine including the step of producing a concentrated carbonate aqueous solution, the following aspects can be exemplified.

[0044] A method for producing methionine, comprising:

[0045] 1) Process for producing 5-(2-methylmercaptoethyl)-hydantoin by reacting 3-methylmercaptopropionaldehyde, hydrogen cyanide, ammonia and carbon dioxide or ammonium carbonate

[0046] 2) A step of hydrolyzing the generated 5-(2-methylmercaptoethyl)-hydantoin with potassium carbonate to obtain a potassium salt of methionine

[0047] 3) A method for producing methionine comprising the step of introducing carbon dioxide into a hydrolysis reaction solution to precipitate methionine, the method comprising:

[0048] 4) a step of filtering out methionine from the mixture of the potassium bicarbonate aqueous solution and methionine produced in the previous step, and dehydrating the obtained potassium bicarbonate aqueous solution using a salt barrier membrane,

[0049] 5) a step of heating the membrane-concentrated potassium bicarbonate aqueous solution to thermally decompose the potassium bicarbonate into potassium carbonate, carbon dioxide and water, while evaporating the water to obtain a concentrated potassium carbonate aqueous solution,

[0050] 6) The obtained concentrated potassium carbonate aqueous solution is further subjected to the above-mentioned step 2).

[0051] Example

[0052] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples.

[0053] Example 1

[0054] The bicarbonate aqueous solution (hereinafter referred to as the stock solution) to be used for dehydration by membrane is set as an aqueous solution of 10 wt% potassium bicarbonate and 90 wt% water at 25°C under atmospheric pressure. The energy required to concentrate the potassium ion concentration to twice that of the stock solution through 1) a dehydration step by membrane and 2) a carbonate concentration step is calculated. Although it does not contribute to energy efficiency, for the convenience of calculation, the flow rate of the bicarbonate aqueous solution of the stock solution is set to 100 kg / h (potassium bicarbonate: 10 kg / h, water: 90 kg / h).

[0055] 1) Dehydration process using membrane (dehydration of bicarbonate aqueous solution using membrane separation)

[0056] The dehydration rate was set to 10%. Since the stock solution needed to be pressurized to a specified pressure, the pressurization energy was calculated using Aspen Plus (v10), and the pump efficiency used the default value of 71.27% in the same software. The membrane supply pressure required for dehydration was increased to the osmotic pressure difference of the membrane outlet benchmark with the highest osmotic pressure difference. The osmotic pressure was calculated using the ELECNRTL model of Aspen Plus (v10).

[0057] 2) Carbonate concentration process (thermal decomposition of bicarbonate and evaporation of water)

[0058] After the concentrated bicarbonate aqueous solution is reduced in pressure to atmospheric pressure, heating energy is applied to thermally decompose the bicarbonate into carbonate, carbon dioxide and water, and the water is evaporated to obtain a concentrate of the carbonate aqueous solution. At this time, heating energy is applied so that the potassium ion concentration in the concentrated carbonate aqueous solution reaches a predetermined concentration. Specifically, the concentrated bicarbonate aqueous solution is supplied to an atmospheric pressure distiller (stage 1), and a condition is obtained for making the potassium ion concentration in the bottom liquid reach a target concentration rate (2 times), and the heat energy applied by the distillation tower reboiler when the condition is met is set as the required heating energy.

[0059] (Calculation results)

[0060] The energy required for concentration by the steps 1), 2) and 3) was 85% of that in Comparative Example 1.

[0061] Example 2

[0062] In the method of Example 1, the dehydration rate by the membrane was set to 20% instead of 10%, and the same calculation was performed.

[0063] (Calculation results)

[0064] The energy required for concentration was 68% of that in Comparative Example 1.

[0065] Example 3

[0066] In the method of Example 1, the target concentration rate of potassium ion concentration was calculated by setting it to 3 times instead of 2 times.

[0067] (Calculation results)

[0068] The energy required for concentration was 88% of that in Comparative Example 2.

[0069] Example 4

[0070] In the method of Example 3, the dehydration rate by the membrane was set to 20% instead of 10%, and the same calculation was performed.

[0071] (Calculation results)

[0072] The energy required for the concentration is 75% of that in Comparative Example 2.

[0073] Comparative Example 1

[0074] The aqueous bicarbonate solution was thermally decomposed and concentrated without membrane concentration, and the potassium ion concentration was concentrated to twice that of the original solution.

[0075] Comparative Example 2

[0076] The aqueous bicarbonate solution was thermally decomposed and concentrated without membrane concentration, and the potassium ion concentration was concentrated to 3 times that of the original solution.

[0077] The results of Examples 1 to 4 and Comparative Examples 1 and 2 are summarized in Table 1.

[0078] [Table 1]

[0079]

[0080] Compared with the previous methods, the process of the present invention is shown to be an energy-saving process.

[0081] Industrial Applicability

[0082] A concentrated carbonate aqueous solution can be obtained efficiently.

Claims

1. A method for producing methionine, comprising: 1) a step of reacting 3-methylmercaptopropionaldehyde, hydrogen cyanide, ammonia and carbon dioxide or ammonium carbonate to produce 5-(2-methylmercaptoethyl)-hydantoin, 2) a step of hydrolyzing the generated 5-(2-methylmercaptoethyl)-hydantoin with potassium carbonate and water to obtain a potassium salt of methionine, 3) A method for producing methionine comprising the step of introducing carbon dioxide into the generated hydrolysis reaction solution to precipitate methionine, the method comprising: 4) a step of filtering out methionine from the mixture of the potassium bicarbonate aqueous solution and methionine produced in the above step, and dehydrating the obtained potassium bicarbonate aqueous solution using a salt barrier membrane, 5) a step of heating the membrane-concentrated potassium bicarbonate aqueous solution to thermally decompose the potassium bicarbonate into potassium carbonate, carbon dioxide and water, while evaporating the water to obtain a concentrated potassium carbonate aqueous solution, 6) The obtained concentrated potassium carbonate aqueous solution is further subjected to the above-mentioned step 2).

2. The manufacturing method according to claim 1, wherein: The salt barrier membrane is a RO membrane or a NF membrane.

3. The manufacturing method according to claim 1 or 2, wherein: Step 4) is a step of dehydrating the potassium bicarbonate aqueous solution using a salt barrier membrane until the dehydration rate reaches 10% or more.

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