JP2005154435A - Isolating process for monocarboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively isolating and collecting monocarboxylic acid from a mixture comprising the monocarboxylic acid and metal salt of monocarboxylic acid. <P>SOLUTION: The invention relates to the method for isolating and collecting the monocarboxylic acid as vapor by heating the mixture comprising the monocarboxylic acid and the metal salt of the monocarboxylic acid in the presence of an amide compound of the monocarboxylic acid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for separating and recovering a monocarboxylic acid from a mixture containing a monocarboxylic acid and a metal salt of a monocarboxylic acid. The present invention also relates to a method for separating and recovering monocarboxylic acid and ammonia from ammonium monocarboxylate. In particular, it decomposes ammonium monocarboxylate produced as a by-product in the production process of industrially important organic acids as various pharmaceuticals, agricultural chemicals, organic electronic materials, food additives, synthetic raw materials, or polyester raw materials. The present invention relates to a method for efficiently separating and recovering monocarboxylic acid and ammonia.

  In chemical processes using monocarboxylic acids and ammonia, ammonium monocarboxylate is often produced as a by-product. Such ammonium monocarboxylate is desired to be decomposed into monocarboxylic acid and ammonia and reused due to the influence on the environment and economic reasons for waste disposal.

  As a method for producing carboxylic acid from ammonium monocarboxylate, there is generally a method in which a monocarboxylic acid is isolated by adding a strong acid such as sulfuric acid. This method produces an ammonium salt of a strong acid such as ammonium sulfate. However, there is a problem that ammonia cannot be recovered at the same time.

  In order to solve this problem, a method of directly decomposing an ammonium salt of a heat-modified monocarboxylic acid using an ion exchange resin has been proposed (for example, see Patent Document 1). However, this method has a problem that when high-concentration ammonia is processed, the ion exchange resin is repeatedly expanded and contracted for resin regeneration, so that the deterioration is quick and the replacement cost of the ion exchange resin is high.

  A method of heating ammonium monocarboxylate in ether has also been proposed (see, for example, Patent Document 2). However, in particular, the process relating to the production of food additives and pharmaceuticals requires a sufficient attention to the mixing of the solvent and cannot be said to be preferable. Furthermore, this document does not specifically describe a method for regenerating a solvent and proposes steam stripping for the separation of high-boiling substances from the solvent. However, it is considered that the cost of steam increases.

Furthermore, a method of decomposing monocarboxylic acid ammonia salt using an alkali salt is also known (for example, see Patent Document 3). In this method, a metal salt of a monocarboxylic acid is produced, but the metal salt of a monocarboxylic acid forms a cluster with a monocarboxylic acid that should be free, and is difficult to separate. Therefore, in order to separate the monocarboxylic acid and the monocarboxylic acid metal salt and reuse them, a high temperature of 260 ° C. has been conventionally required.
Japanese Patent Laid-Open No. 62-238232 WO99 / 00350 pamphlet U.S. Pat. No. 2,090,947

  An object of the present invention is to provide a method for efficiently separating and recovering a monocarboxylic acid from a mixture containing a monocarboxylic acid and a monocarboxylic acid metal salt. Another object of the present invention is to provide a method for efficiently separating and recovering monocarboxylic acid and ammonia from monocarboxylic acid ammonium salt.

  The present inventor has intensively studied to solve the above problems. As a result, when separating and recovering the monocarboxylic acid from the mixture containing the monocarboxylic acid and the monocarboxylic acid metal salt, it becomes possible to handle the metal salt as a liquid substance by coexisting a sufficient amount of the amidated product, It has been found that monocarboxylic acids can be separated and recovered efficiently. Further, it has been found that by applying this method, the monocarboxylic acid and ammonia can be efficiently separated and recovered from the monocarboxylic acid ammonium salt. Thus, the present invention has been completed.

That is, the present invention is as follows.
(1) A method for separating and recovering a monocarboxylic acid from a mixture containing a monocarboxylic acid and a monocarboxylic acid metal salt, wherein the mixture is heated in the presence of an amidated monocarboxylic acid, and the monocarboxylic acid is used as a vapor. A method characterized by separating and collecting.
(2) The method of (1), wherein the amount of the amidated compound to be coexisted is 5% by weight or more of the monocarboxylic acid metal salt.
(3) The method of (1) or (2), wherein heating is performed at 140 ° C. or higher.
(4) The method according to any one of (1) to (3), wherein the heating is performed in a state where the pressure is reduced to 200 mmHg or less.
(5) The method according to any one of (1) to (4), wherein the monocarboxylic acid is acetic acid, propionic acid, or a mixture thereof.
(6) The method according to any one of (1) to (5), wherein the metal contained in the monocarboxylic acid metal salt is one or both of sodium and potassium.
(7) A method for separating and recovering monocarboxylic acid and ammonia from ammonium monocarboxylate, which comprises the following steps:
(A) heating a mixed liquid containing a monocarboxylic acid metal salt and a monocarboxylic acid amidated product together with ammonium monocarboxylic acid to separate and recover ammonia vapor; and (b) a residual liquid containing the monocarboxylic acid amidated product. A step of heating and separating and recovering the monocarboxylic acid as a vapor from the remaining liquid.

  By using the method of the present invention, a method for efficiently obtaining a monocarboxylic acid and ammonia from a monocarboxylic acid ammonium salt can be separated and recovered. Further, the monocarboxylic acid can be efficiently separated and recovered from the mixture of the monocarboxylic acid metal salt and the monocarboxylic acid, the recycle stream of the salt decomposition system can be reduced, and energy saving can be realized.

  The present invention relates to an invention relating to a method for separating and recovering a monocarboxylic acid from a mixture containing a monocarboxylic acid and a monocarboxylic acid metal salt (hereinafter referred to as the first invention), and from an ammonium monocarboxylate to a monocarboxylic acid. An invention relating to a method for separating and recovering ammonia (hereinafter referred to as a second invention) is provided. These inventions are described in detail below.

<1> Method for Separating and Recovering Monocarboxylic Acid from Mixture Containing Monocarboxylic Acid and Monocarboxylic Acid Metal Salt The first invention separates and recovers monocarboxylic acid from a mixture containing monocarboxylic acid and monocarboxylic acid metal salt And the mixture is heated in the presence of an amidated monocarboxylic acid to separate and recover the monocarboxylic acid as a vapor.

Although the kind of monocarboxylic acid is not specifically limited, Preferably an acetic acid or propionic acid is mentioned. Two or more monocarboxylic acids may be used.
The monocarboxylic acid metal salt contained in the mixture is preferably a salt formed by the same kind of carboxylic acid and metal as the monocarboxylic acid contained in the mixture. Examples of the metal forming the monocarboxylic acid metal salt include alkali metals and alkaline earth metals. The alkali metal is not particularly limited, but sodium or potassium is preferable in view of safety, economy, and ease of handling. On the other hand, examples of the alkaline earth metal include magnesium and calcium. However, alkaline earth metal monocarboxylic acid salt easily takes a cross-linked structure and may cause a problem of high viscosity and crystallization. Metal is more preferred. In addition, the metal which forms monocarboxylic acid metal salt may be 2 or more types.

  The mixture containing the monocarboxylic acid and the monocarboxylic acid metal salt is preferably a mixed solution containing water. In the mixed solution, the monocarboxylic acid metal salt may be ionized into ions. The amount of water in the mixed solution is appropriately selected depending on the type of monocarboxylic acid, the type and amount of metal, the structure of the reactor, the residence time distribution, etc. Generally, the content in the mixed solution is 15% by weight. To 70% by weight, more preferably 25% to 55% by weight. Further, the pH of the mixed solution is preferably 6.5 or more, and more preferably from 7 to 10.

  The amidated product to be coexisting is not particularly limited as long as the hydroxyl group of the monocarboxylic acid is substituted with an amino group, but for the simplification of the process, the same monocarboxylic acid as the monocarboxylic acid contained in the mixture is used. It is preferable to use those in which the hydroxyl group is substituted with an amino group. That is, for example, it is preferable to use acetamide when acetic acid is contained in the mixture, and to use propionamide when propionic acid is contained. The monocarboxylic acid amidation product is preferably added to a mixture containing a monocarboxylic acid and a metal salt of a monocarboxylic acid, but a by-product produced by heating ammonium monocarboxylate can also be used.

  The amidated compound is preferably 5% by weight or more and 200% by weight or less, more preferably 10% by weight or more and 150% by weight or less, and particularly preferably 20% by weight or more and 125% by weight, based on the weight of the monocarboxylic acid metal salt. Coexist in an amount of less than%.

  The heating of the mixture containing the monocarboxylic acid and the monocarboxylic acid metal salt in the presence of the amide compound is preferably performed at 140 ° C. or higher, more preferably 150 ° C. or higher. Furthermore, it is preferable to carry out pressure reduction to 200 mmHg or less. More preferably, it is 150 mmHg or less. The heating time varies depending on the amount of the mixture and the kind of the monocarboxylic acid metal salt and is not particularly limited, but is preferably 0.1 seconds to 60 minutes, more preferably 0.1 seconds to 10 minutes, and particularly preferably 0.1. Heat is applied in seconds to 5 minutes.

  Due to the coexistence of the amide compound, the alkali metal salt of monocarboxylic acid exists in the mixture as a liquid substance with little formation of clusters with the monocarboxylic acid. Therefore, by heating, the monocarboxylic acid can be specifically vaporized and separated from the mixture. The separated monocarboxylic acid may contain a monocarboxylic acid amidated product. In this case, for example, a high purity monocarboxylic acid is recovered by removing the amidated product using a distillation apparatus or the like. Can do.

<2> Method for Separating and Recovering Monocarboxylic Acid and Ammonia from Ammonium Monocarboxylate The second invention is a method for separating and recovering monocarboxylic acid and ammonia from ammonium monocarboxylate, and includes the following steps:
(A) heating a mixed liquid containing a monocarboxylic acid metal salt and a monocarboxylic acid amidated product together with ammonium monocarboxylic acid to separate and recover ammonia vapor; and (b) a residual liquid containing the monocarboxylic acid amidated product. The invention relates to a step of heating and separating and recovering monocarboxylic acid as a vapor from the remaining liquid.

  Although the kind of monocarboxylic acid contained in monocarboxylic acid ammonium, monocarboxylic acid metal salt, and monocarboxylic acid amidation is not specifically limited, Preferably it is an acetic acid or propionic acid. Two or more monocarboxylic acids may be used. However, it is preferable that the monocarboxylic acid contained in the ammonium monocarboxylic acid, the monocarboxylic acid metal salt, and the monocarboxylic acid amidated compound is the same. That is, when the monocarboxylic acid is acetic acid, the mixed solution used in the step (a) is preferably a mixed solution containing ammonium acetate, metal acetate and acetamide, and when the monocarboxylic acid is propionic acid, propionic acid is used. A mixed solution containing ammonium, propionic acid metal salt and propionamide is preferable.

  Examples of the metal contained in the monocarboxylic acid metal salt include alkali metals and alkaline earth metals. The alkali metal is not particularly limited, but sodium or potassium is preferable in view of safety, economy, and ease of handling. On the other hand, examples of the alkaline earth metal include magnesium and calcium. However, alkaline earth metal monocarboxylic acid salt easily takes a cross-linked structure and may cause a problem of high viscosity and crystallization. Metal is more preferred. Two or more metals may be used to form the monocarboxylic acid metal salt.

  The ratio of the monocarboxylic acid metal salt and the ammonium monocarboxylate in the mixed solution is not particularly limited, but the monocarboxylic acid metal salt is preferably 0.2 to 2 times the weight of the ammonium monocarboxylate, More preferably, it is 0.5 to 1.5 times the weight of ammonium. In the mixed solution, ammonium monocarboxylate and metal salt of monocarboxylic acid may be ionized into ions.

  The amount of the monocarboxylic acid amidated product in the mixed solution is preferably 5% by weight or more and 200% by weight or less, preferably 10% by weight or more and 150% by weight or less based on the weight of the monocarboxylic acid metal salt. Is more preferably 20% by weight or more and 150% by weight or less.

  A mixed solution containing ammonium monocarboxylate, monocarboxylic acid metal salt and monocarboxylic acid amidate is obtained, for example, by adding monocarboxylic acid amidate to a mixed solution containing monocarboxylic acid metal salt and ammonium monocarboxylate. be able to. The mixed liquid containing the monocarboxylic acid metal salt and the ammonium monocarboxylate in this case can be obtained, for example, by adding the monocarboxylic acid metal salt to the ammonium monocarboxylate solution. As the ammonium monocarboxylate solution, for example, in microbial fermentation production in which a microorganism is cultured in a culture solution containing ammonium ions and the like to produce an organic acid, the produced organic acid ammonium salt is replaced with a monocarboxylic acid such as acetic acid. Mention may be made of ammonium monocarboxylate solutions obtained by salt exchange and separation of the precipitated organic acid. In addition, in microbial fermentation production in which microorganisms are cultured in a culture solution containing metal ions to produce organic acids, the resulting organic acid metal salt is exchanged with ammonia, and the resulting organic acid ammonium salt is converted to acetic acid, etc. Examples thereof include an ammonium monocarboxylate solution obtained by salt exchange with a monocarboxylic acid, and separating a deposited organic acid.

  In a mixed solution containing ammonium monocarboxylate, metal monocarboxylic acid salt, and monocarboxylic acid amidate, the following equilibrium reaction occurs between the metal monocarboxylic acid salt and ammonium monocarboxylate. Note that these reaction formulas are described with an example where the monocarboxylic acid is acetic acid and the metal is sodium.

  This reaction is an equilibrium reaction, but in order to obtain ammonia by advancing the reaction in the right direction, the reaction is carried out in a pH range of preferably 6.5 to 10, more preferably 7 to 9. According to the reaction of the formula, ammonia is generated in the aqueous solution, so that the ammonia can be separated as vapor (gas) by heating. The heating is preferably performed at a temperature of 80 ° C. or higher and lower than both the melting point of ammonium monocarboxylate and the boiling point of monocarboxylic acid. That is, when ammonium monocarboxylate is ammonium acetate, it is preferably carried out at 80 ° C. or higher and 114 ° C. (melting point of ammonium acetate), and when ammonium propionate is used, it is preferably 80 ° C. or higher and 141 ° C. (boiling point of propionic acid) or lower. When taking the form of a distillation column as shown in WO03 / 95409, these temperature ranges are the temperature conditions at the top of the column. The heating time varies depending on the amount of the mixed solution and is not particularly limited, but is preferably 1 minute to 3 hours, more preferably 20 minutes to 1 hour. In addition, since monocarboxylic acid amidation has a high boiling point (for example, the boiling point of acetamide is 222 degreeC), it does not influence the said reaction and hardly reacts in process (a).

  The separated ammonia is preferably subjected to gas-liquid separation, gas-solid separation, or gas-liquid solid separation at a temperature not higher than the melting point of ammonium monocarboxylate under reduced pressure or normal pressure directly or after condensation. The separated ammonia can be carried out using a distillation apparatus as described later.

  Next, in step (b), the residual liquid from which ammonia has been separated in step (a) is heated to separate the monocarboxylic acid from the residual liquid. The residual liquid contains monocarboxylic acid, monocarboxylic acid metal salt (partially ionized into metal ion and monocarboxylic acid ion in aqueous solution), and monocarboxylic acid amidated product. Therefore, the mixture of monocarboxylic acid and monocarboxylic acid metal salt is heated in the coexistence of monocarboxylic acid amide by heating the residual liquid preferably at 140 ° C. or higher, more preferably 150 ° C. or higher. Monocarboxylic acid can be separated and obtained as a vapor. The residual liquid may contain an unreacted ammonium monocarboxylic acid salt. In this case, it is preferable that the heating time is short in order to prevent the ammonium salt from being amidated. The reaction conditions and the like in the step (b) are the same as in the first invention described above.

  Of the present invention, the second invention will be described below with reference to an embodiment. However, the second invention is not limited to the following modes.

Step (a) First, a liquid obtained by adding a monocarboxylic acid metal salt and a monocarboxylic acid amidated product to a mixed liquid of ammonium monocarboxylate and water (hereinafter sometimes referred to as “raw material liquid”) is heated. The gas of the basic aqueous solution (ammonia) generated in the raw material liquid is extracted. Hereinafter, this heating process may be referred to as “heating process (I)”, and this heating operation may be referred to as “heating operation (I)”.

  Then, after the extracted basic aqueous solution gas is directly or condensed, gas-liquid separation, gas-solid separation, or gas-liquid solid separation is performed at a temperature below the melting point of ammonium monocarboxylate under reduced pressure or normal pressure. Hereinafter, this separation step may be referred to as “heating step (b)”, and this separation operation may be referred to as “separation operation (b)”.

  The apparatus used in this heating step (A) may be any apparatus as long as it can perform a heating operation and can separate a gas phase and a liquid phase. The heating and gas-liquid separation may be separate devices, or a combination of a heat exchanger and a flash drum. If it is a kettle type heat exchanger, heating and gas-liquid separation can be performed with one apparatus. The heating mechanism is not particularly limited, and may be a flash drum provided with a jacket or a heat transfer coil, for example.

  A distillation column is most desirable for efficient gas-liquid separation with heating. The distillation column may be either a packed column or a plate column, and there are no particular restrictions on the structure, but a plate column is desirable for securing the residence time as described later. The reboiler may be a built-in type or an external type. In the case of using an external reboiler, a forced circulation reboiler, a thermosiphon reboiler, a kettle reboiler, and the like are conceivable, but are not limited thereto. In the present invention, an operation performed by combining a distillation column and a reboiler is regarded as a heating operation (ii).

  There is no restriction on the presence or absence of a condenser, and the condenser does not form part of the heating operation. Theoretically, a kettle heat exchanger and a flash drum with a heating device can also be regarded as a one-stage distillation column.

  Since the gas extracted in the heating step (a) contains ammonia and inevitably has a pH higher than 7, in the present invention, this is referred to as the heating step (a) for extracting the gas of the basic aqueous solution. .

  Among the apparatuses for performing the heating operation (ii) for extracting the gas of the basic aqueous solution, the most desirable one is a distillation column. Therefore, the heating step (ii) mainly using the distillation column will be described below.

  A distillation column is suitable for obtaining the effect of separating the monocarboxylic acid and water by the salt effect and simultaneously decomposing the monocarboxylic acid ammonium salt. That is, a predetermined residence time is required for this decomposition reaction. Therefore, in order to carry out the heating step (A) more efficiently, it is important to hold up the liquid. As a distillation column, even if it is a packed column, the liquid hold-up is not a little, but more reliably, it is possible to simultaneously obtain the separation effect of monocarboxylic acid and water by the salt effect and the decomposition effect of ammonium monocarboxylate simultaneously. It is desirable that it is a tray column rather than a packed column. As for the tray type of the tray tower, when considering the operating range at startup and shutdown, the sheave tray in which weeping easily occurs is inferior in practice. Even if the operation rate is slow or zero, a tray is preferred in which weeping hardly occurs and the liquid is reliably held on the tray. As an example of such a tray, there is a bubble bell tray. In the bubble bell tray, in order to improve gas-liquid contact on the tray, in addition to the downcomer weir, there is a weir in the gas hole on the tray on the mechanism of the bubble bell part, and the liquid depth can be maintained. Become. In addition, a tray of a type in which a hole on the tray is closed with a movable cap, such as a valve cap tray, is less likely to cause weeping and is preferable for application to the present invention.

  In order to obtain the separation effect of monocarboxylic acid and water due to the salt effect in the entire apparatus, in the case of a distillation column, it is preferable to carry out the raw material in the form of so-called extractive distillation, which is supplied from the upper part of the column. The supply stage is not particularly specified.

  The column pressure is not particularly limited, but at least the column bottom temperature is 80 ° C. or higher, preferably 115 ° C. or higher and 180 ° C. or lower for efficient decomposition of ammonium monocarboxylate. Furthermore, if the top of the column is lower than the higher of the melting point of the ammonium monocarboxylate (or the boiling point of the monocarboxylic acid), the top of the column can be regarded as a gas-liquid separation device in the subsequent separation step. The heating step (b) and the separation step (b) can be performed with one apparatus, and the number of apparatuses can be reduced, which is preferable in terms of investment cost. In this case, the temperature condition at the top of the column is 114 ° C. (melting point of ammonium acetate) or lower when ammonium monocarboxylate is ammonium acetate, and 141 ° C. (boiling point of propionic acid) or lower when ammonium monopropionate is used.

  The pressure conditions that satisfy the conditions at the top of the column vary depending on the type and amount of monocarboxylic acid and alkali (earth) metal used, the amount of water, the required degree of water / monocarboxylic acid separation, etc. Is 2.0 atm (0.2 MPa) or less, preferably normal pressure (1 atm (0.1 MPa)) or less. The pressure conditions that satisfy the above-mentioned conditions for the bottom of the column are the types of monocarboxylic acid and alkali (earth) metal and the amount used, the amount of water, the required degree of water / monocarboxylic acid separation, Although it varies depending on the pressure loss due to the tray and packing, it is usually 80 mmHg (10.6 kPa) or more, preferably 200 mmHg (26.7 kPa) or more.

  When supplying a raw material to a tower top part, monocarboxylic acid and a salt may be distilled off by the stripping effect and entrainment (entrainment entrainment). In that case, even if the conditions of the heating operation (b) and the separation operation (b) can be satisfied only with the distillation column, the gas-liquid separation corresponding to the separation operation (b) is aimed at the effect of removing the salt by stripping. It may be necessary to take measures such as installing the apparatus or lowering the supply stage.

  On the other hand, when separating the distillation column, which is one of the heating devices, and the gas-liquid separation device, the gas of the basic aqueous solution extracted from the top of the distillation column is once condensed by a condenser, You may supply to a liquid (gas-liquid solid, gas-solid) separation apparatus. In addition, the condenser may be a gas-liquid (gas-liquid solid, gas-solid) separation device by installing a pressure regulator in the extraction line from the top of the tower as necessary. In the former case, the supply to the gas-liquid separator is mainly liquid, but the gas-liquid may be supplied as it is. In the latter case, the supply to the gas-liquid separator is almost gas, although entrainment (entrainment) is present.

  The liquid, solid, or slurry extracted from the gas-liquid (gas-liquid solid, gas-solid) separation apparatus is a concentrated ammonium monocarboxylate distilled off mainly by the stripping effect. This is returned to the heating device for carrying out the heating step (a), or mixed with a newly supplied ammonium monocarboxylate aqueous solution or acetic acid aqueous solution and circulated until it is decomposed.

  The liquid extracted from the bottom of the tower, whether the distillation column in the heating step (ii) and the gas-liquid (gas-liquid solid, gas-solid) separation device in the separation step (b) are integrated or separate. Can be divided into monocarboxylic acid and alkali (earth) metal salt of monocarboxylic acid by a conventional method, for example, a thin film evaporator or an evaporator. Or you may extract gas from the collection | recovery part (collection stage) of the distillation column which is a heater.

Step (b) The solution obtained by separating ammonia as described above contains monocarboxylic acid, monocarboxylic acid metal salt, undecomposed ammonium monocarboxylate and monocarboxylic acid amidated product. By heating this solution in the presence of monocarboxylic amide, preferably at 140 ° C. or higher, more preferably at 150 ° C. or higher, the monocarboxylic acid metal salt and the monocarboxylic acid can be separated. As described above, ammonia can be separated from the monocarboxylic acid ammonium salt in the step (a) and the monocarboxylic acid can be separated in the step (b).

  Hereinafter, the present invention will be specifically described with reference to examples.

<Example 1>
Acetic acid 20.00 g Potassium acetate 10.00 g was placed in a 200 cc eggplant-shaped flask and placed on a rotary evaporator. The rotary evaporator was water-cooled, and a trap using ethanol cooled with dry ice was installed in front of the suction port of the vacuum pump to solidify the gas that could not be distilled off by water-cooling. The pressure was 60 mmHg, and the bath was gradually immersed in an oil bath heated to 180 ° C. It suddenly solidified in about 4 minutes and was immediately removed from the oil bath. The fraction (recovery by water cooling + solidification in the trap) was 10.9 g, and the residue was 15.92 g. Since there were only acetic acid and potassium acetate, and potassium acetate did not evaporate, it was found that potassium acetate occluded 5.5 g of acetic acid under these conditions.

<Example 2>
20.00 g of acetic acid 10.00 g of potassium acetate and 3.00 g of acetamide were placed in a 200 cc eggplant-shaped flask and placed in a rotary evaporator in the same manner. The pressure was 60 mmHg, and the bath was gradually immersed in an oil bath heated to 180 ° C. Precipitation occurred suddenly at about 18 minutes and solidified to complete. The fraction was 11.85 g and the residue was 16.32 g. Acetamide was not detected in the fraction. 15.7 wt% (equivalent to 2.41 g) was detected from the residue. As a result, it was found that acetic acid stored in potassium acetate was 3.3 g.

<Example 3>
Acetic acid 20.02 g Potassium acetate 10.00 g and acetamide 3.02 g were placed in a 200 cc eggplant-shaped flask and placed in a rotary evaporator in the same manner. The pressure was 60 mmHg, and the bath was gradually immersed in an oil bath heated to 160 ° C. Although it did not solidify, it ended after about 27 minutes. The fraction was 8.31 g and the residue was 21.50 g. Acetamide was not detected from the fraction. As a result, it was found that acetic acid stored in potassium acetate was 8.5 g.

<Example 4>
Acetic acid 20.02 g Potassium acetate 10.01 g and acetamide 3.01 g were placed in a 200 cc eggplant-shaped flask and similarly placed on a rotary evaporator. The pressure was 120 mmHg, and the bath was gradually immersed in an oil bath heated to 180 ° C. Although it did not solidify, it was finished after about 30 minutes. The fraction was 8.43 g and the residue was 21.70 g. From the fraction, 0.67 wt% (corresponding to 0.06 g) of acetamide was detected. As a result, it was found that acetic acid stored in potassium acetate was 8.7 g.

<Example 5>
20.01 g of acetic acid 10.00 g of potassium acetate and 2.00 g of acetamide were placed in a 200 cc eggplant-shaped flask and similarly placed on a rotary evaporator. The pressure was 60 mmHg, and the bath was gradually immersed in an oil bath heated to 180 ° C. Although it did not solidify, it was finished after about 31 minutes. The fraction was 13.33 g and the residue was 15.40 g. From the fraction, 0.55 wt% (corresponding to 0.07 g) of acetamide was detected. As a result, it was found that the acetic acid stored in potassium acetate was 3.5 g.

<Example 6>
Acetic acid 20.00 g Potassium acetate 10.00 g and acetamide 4.01 g were placed in a 200 cc eggplant-shaped flask and placed in a rotary evaporator in the same manner. The pressure was 120 mmHg, and the bath was gradually immersed in an oil bath heated to 180 ° C. Although it did not solidify, it was finished after about 33 minutes. The fraction was 12.47 g and the residue was 17.92 g. From the fraction, 0.78 wt% (corresponding to 0.1 g) of acetamide was detected. As a result, it was found that acetic acid stored in potassium acetate was 4.0 g.

  From Examples 2 to 4, it was found that acetic acid can be separated more efficiently under the conditions where the utility temperature is 180 ° C. and 60 mmHg. The results of Examples 1, 2, 5, and 6 are summarized in Table 1. According to this, it can be seen that the coexistence of acetamide significantly increases the separation efficiency of acetic acid.

In addition, a simple distillation experiment was conducted to verify the process temperature.
<Example 7>
A flask of a simple distillation apparatus was charged with 30 g of acetic acid, 5 g of ammonium acetate, 3.7 g of water, 32 g of potassium acetate, and 50 g of acetamide, and the pressure was reduced to 40 mmHg and gradually heated. The difference between the temperature in the flask and the temperature of the oil bath was maintained at 30 ° C. or higher and 40 ° C. or lower.
When the temperature in the flask reached 140 ° C., the flask was taken out from the oil bath, once the vacuum was broken, and 0.1 g of an analytical sample was collected from the remainder of the can. The analytical values of the residue at 140 ° C. were acetamide 49% by weight, acetic acid 39% by weight, potassium 16% by weight, and the molar ratio of acetic acid to potassium was 1.6. The temperature of the oil bath at this time was 170 ° C.
Furthermore, since precipitation was observed in the flask at 147 ° C., the experiment was stopped, and the can residue was analyzed. The analytical values of the can residue at the end of the experiment were 43% by weight of acetamide, 39% by weight of acetic acid and 20% by weight of potassium, and the molar ratio of acetic acid to potassium was 1.26. The temperature of the oil bath at this time was 186 ° C.
When the composition at the end of the experiment was adjusted to the ratio of potassium acetate to acetic acid, acetic acid was 0.26 mol per mol of potassium acetate, and it was found that the effect of sufficiently separating acetic acid was recognized. It was.

<Example 8>
A flask of a simple distillation apparatus was charged with 30 g of acetic acid, 5 g of ammonium acetate, 2 g of water, 32 g of potassium acetate, and 80 g of acetamide, and the pressure was reduced to 150 mmHg and gradually heated. The difference between the temperature in the flask and the temperature of the oil bath was maintained at 30 ° C. or higher and 40 ° C. or lower.
When the temperature in the flask reached 170 ° C., the flask was taken out from the oil bath, once the pressure reduction was broken, and 0.1 g of an analytical sample was collected from the remainder of the can. The analytical values of the residue at 170 ° C. were 61.6% by weight of acetamide, 29.7% by weight of acetic acid, 12.3% by weight of potassium, and the molar ratio of acetic acid to potassium was 1.56. The temperature of the oil bath at this time was 209 ° C.
Further, the can residue was similarly analyzed when the temperature in the flask reached 175 ° C. The temperature of the oil bath at this time was 210 ° C. The analytical values of the can residue were acetamide 59.2 wt%, acetic acid 28.2 wt%, potassium 15.3 wt%, and the molar ratio of acetic acid to potassium was 1.2. When the ratio of potassium acetate to acetic acid was adjusted, it was found that acetic acid was 0.2 mol per mol of potassium acetate, and it was found that the effect of sufficiently separating acetic acid was recognized.

<Example 9>
A flask of a simple distillation apparatus was charged with 30 g of acetic acid, 5 g of ammonium acetate, 2 g of water, 32 g of potassium acetate and 80 g of acetamide, and the pressure was reduced to 200 mmHg and gradually heated. The difference between the temperature in the flask and the temperature of the oil bath was maintained at 30 ° C. or higher and 40 ° C. or lower.
When the temperature in the flask reached 170 ° C., the flask was taken out from the oil bath, once the pressure reduction was broken, and 0.1 g of an analytical sample was collected from the remainder of the can. The analytical values of the residue at 170 ° C. were acetamide 59.9% by weight, acetic acid 34.0% by weight, potassium 9.9% by weight, and the molar ratio of acetic acid to potassium was 2.23. The temperature of the oil bath at this time was 205 ° C.
Furthermore, the can residue was similarly analyzed when the temperature in the flask reached 180 ° C. The temperature of the oil bath at this time was 210 ° C. The analytical values of the can residue were 64.5% by weight of acetamide, 27.1% by weight of acetic acid and 12.2% by weight of potassium, and the molar ratio of acetic acid to potassium was 1.45. When the ratio of potassium acetate to acetic acid is corrected, the amount of acetic acid is 0.45 mol per mol of potassium acetate, and it was found that some effect of separating acetic acid is recognized even under this condition.

From Examples 7, 8, and 9, it was found that acetic acid and potassium acetate can be sufficiently separated if the process temperature is 140 ° C. or higher by maintaining sufficient acetamide and sufficiently reducing the pressure. It was also found that acetic acid and potassium acetate could be separated at 175 ° C. when the pressure was 200 mmHg or less. From these, it was shown that the operation can be carried out at a remarkably gentle temperature as compared with the separation by heating at 260 ° C. or higher shown in US Pat. No. 2,090,947.

Claims (7)

A method for separating and recovering a monocarboxylic acid from a mixture containing a monocarboxylic acid and a metal salt of a monocarboxylic acid, wherein the mixture is heated in the presence of an amidated product of the monocarboxylic acid, and the monocarboxylic acid is separated and recovered as a vapor. A method characterized by that. The method according to claim 1, wherein the amount of the amidated compound to be coexisted is 5% by weight or more of the monocarboxylic acid metal salt. The method according to claim 1 or 2, wherein the heating is performed at 140 ° C or higher. The method according to any one of claims 1 to 3, wherein the heating is performed under a reduced pressure of 200 mmHg or less. The method according to any one of claims 1 to 4, wherein the monocarboxylic acid is acetic acid, propionic acid, or a mixture thereof. The method according to any one of claims 1 to 5, wherein the metal contained in the monocarboxylic acid metal salt is one or both of sodium and potassium. A method for separating and recovering monocarboxylic acid and ammonia from ammonium monocarboxylate, comprising the following steps:
(A) heating a mixed liquid containing a monocarboxylic acid metal salt and a monocarboxylic acid amidated product together with ammonium monocarboxylic acid to separate and recover ammonia vapor; and (b) a residual liquid containing the monocarboxylic acid amidated product. A step of heating and separating and recovering the monocarboxylic acid as a vapor from the remaining liquid.