JPH0796522B2 - Method for producing carboxylic acid from ammonium carboxylate aqueous solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering ammonia from an aqueous solution of ammonium carboxylate and producing carboxylic acid. Among carboxylic acids, acrylic acid and methacrylic acid are particularly useful as raw materials for various higher esters as well as synthetic raw materials for methyl acrylate and methyl methacrylate. Among the dicarboxylic acids, succinic acid and adipic acid are also useful as raw materials for the polymer.

(Prior Art) Conventionally, as a method of recovering a carboxylic acid from an aqueous solution of ammonium carboxylate, there is a method of isolating a carboxylic acid by adding an approximately theoretical amount of a strong acid. Ammonium salt was generated, and the cost associated with the treatment was large, which was economically problematic.

There is also a method of thermally decomposing a carboxylic acid ammonium salt to liberate ammonia to isolate the carboxylic acid,
Since this method is generally performed at a high temperature, a side reaction occurs and by-products such as amides and nitriles are easily generated.
In addition, the carboxylic acid ammonium salt having a double bond has a drawback when a polymerization reaction occurs.

As a countermeasure against this, in British Patent No. 967352, by adding a small amount of water to an unsaturated carboxylic acid ammonium salt, by heating while totally refluxing at a temperature of 80 ° C. or higher in an organic solvent such as a hydrocarbon, , There is a method of removing ammonia freely to obtain unsaturated carboxylic acid. However, when this method is applied to an aqueous solution of ammonium carboxylate, the aqueous solution must be once dried to dryness or concentrated, and the organic solvent is used while being totally refluxed, resulting in a large energy cost.

Further, in Japanese Examined Patent Publication No. 61-2055, an azeotropic distillation is carried out by adding an inert organic solvent which is azeotropic with water at a temperature of 60 to 100 ° C to an aqueous solution of an ammonium salt of acrylic acid or methacrylic acid, and water and liberated ammonia are released. A method for distilling off and obtaining acrylic acid or methacrylic acid has been reported. However, even in this method, a large amount of inert organic solvent has to be azeotropically distilled with water, resulting in high energy cost (problems to be solved by the invention) British Patent No. 967352 and Japanese Patent Publication No. 61-2055. It is worth noting that none of the methods described in No. 1 does not generate a strong acid or ammonium salt of a strong acid because no strong acid is used, but it is necessary to evaporate the organic solvent in a large excess with respect to the ammonium carboxylate aqueous solution. However, the energy cost is high and it is not an industrially satisfactory method.

(Means for Solving Problems) The present inventors aim to solve such problems,
As a result of earnest research on a method for producing a carboxylic acid from an aqueous solution of ammonium carboxylate, a method of recovering the carboxylic acid from the aqueous solution of ammonium carboxylate using an anion exchange resin and a specific organic solvent is extremely effective. Therefore, the present invention has been completed.

That is, the present invention is a method for separating carboxylic acid and ammonia from an aqueous solution of ammonium carboxylate, after adsorbing carboxylate ions on an anion exchange resin, alcohols, ketones, cyclic ethers, nitriles,
Carboxylates from ammonium carboxylate aqueous solution characterized by desorbing and recovering carboxylate ions adsorbed using at least one organic solvent selected from esters, pyrrolidones, dimethylsulfoxide, dimethylformamide, and dimethylacetamide as carboxylic acids. It is a method of producing an acid.

Any ammonium carboxylate used in the present invention can be used as long as it is soluble in water. Considering the desorption from the adsorption and anion exchange resin to anion exchange resin, acid dissociation constant in aqueous solution of a carboxylic acid that constitutes the ammonium carboxylate (25 ℃) (Ka) is 10 ^-2 to 10 ^- Those in the range of ⁷ (2 to 7 in pKa display) are suitable. For example, ammonium salicylate, ammonium benzoate, ammonium acetate, ammonium propionate, normal and ammonium isobutyrate, normal and ammonium isovalerate, ammonium acrylate, ammonium methacrylate, ammonium succinate, ammonium malonate, ammonium adipate, etc. Available. The higher the concentration of the ammonium carboxylate aqueous solution is, the more the carboxylate ions can be adsorbed on the anion exchange resin, which is advantageous, but the concentration is usually 0.1 to 70% by weight. Further, when handling an aqueous solution of ammonium carboxylate having a double bond such as ammonium acrylate or ammonium methacrylate, it is preferable to add a general polymerization inhibitor such as hydroquinone or methoxyhydroquinone because it is easily polymerized. The amount of polymerization inhibitor added is
Although it depends on the operating temperature and operating time, etc., it is usually 0.01 to 0.5% by weight.

The anion exchange resin to be used may be any resin as long as it can adsorb carboxylate ions, but in consideration of desorption of the carboxylic acid from the resin by the organic solvent, a weakly basic anion exchange resin is used. Resin is preferred. A resin having a functional group having a pKa value larger than the pKa value of NH ₄ ⁺ of 9.25 (25 ° C.) is preferable, and an anion exchange resin having a tertiary amine group is particularly suitable.

The organic solvent used for desorbing the carboxylate ion adsorbed to the resin as a carboxylic acid may be any organic solvent that does not react with the carboxylic acid, but in consideration of diffusion into the resin containing water. In this case, a hydrophilic organic solvent is desirable. Specific examples include alcohols such as methyl alcohol, ethyl alcohol, normal and isopropanol, glycols, ketones such as acetone and methyl ethyl ketone, tetrahydrofuran, 1,4
-Cyclic ethers such as dioxane, nitriles such as acetonitrile and acrylonitrile, and esters such as methyl acetate and ethyl acetate are mentioned, but dimethyl sulfoxide and dimethylformamide which are hydrophilic and have an affinity for resins. , Dimethylacetamide, pyrrolidones are particularly suitable.

The operating temperature is 0 ° C to 120 ° C in consideration of the adsorption rate of carboxylate ion to the anion exchange resin, the desorption rate of the adsorbed carboxylate ion as carboxylic acid, the heat resistant temperature of the resin, the coagulation temperature of the aqueous solution, and the like. The range of can be applied. However, considering the diffusion rate of the solution into the resin and the life of the resin, the range of 15 ° C to 90 ° C is preferable. More preferably, the temperature range of 15 ° C. to 70 ° C. is preferable when adsorbing carboxylate ions, and the temperature range of 50 ° C. to 90 ° C. is preferable when desorbing carboxylic acid with an organic solvent. Regarding the operating pressure, it can be carried out under any conditions of reduced pressure, normal pressure and increased pressure. When the vapor pressure of the organic solvent used is low, it is desirable to carry out the treatment with a pressurized system in order to prevent boiling. As a device to be used, any of a fluidized bed device, a fixed bed device and a continuous ion exchange device may be used, but from a practical point of view, a fixed bed device having a good contact efficiency between a solution and a resin. And continuous ion exchange equipment is suitable.

Thus, by contacting the ammonium carboxylate aqueous solution with the anion exchange resin and first adsorbing the carboxylate ion on the resin phase, the ammonia and the carboxylic acid can be separated. Next, the anion-exchange resin having adsorbed carboxylate ion is once washed with water and then washed with an organic solvent (hereinafter referred to as a desorption solvent), and the adsorbed carboxylate ion is desorbed from the resin as a carboxylic acid. A desorption solvent solution containing carboxylic acid is obtained. The target carboxylic acid can be recovered from this solution by a method such as distillation or crystallization. On the other hand, ammonium ions that are not adsorbed on the anion exchange resin are recovered as an aqueous ammonia solution, but by further distilling this aqueous solution, it is also possible to recover it as concentrated aqueous ammonia.

(Operation and effect) In the method of recovering ammonia from an aqueous solution of ammonium carboxylate and producing carboxylic acid, the decomposition rate into ammonia and carboxylic acid is low by simply heating the aqueous solution of ammonium carboxylate.

However, surprisingly, as in the present invention,
By using an anion exchange resin and an organic solvent capable of desorbing carboxylate ions adsorbed on the resin, the decomposition reaction of ammonium carboxylate can be carried out almost quantitatively at a low temperature, and furthermore, ammonia can be decomposed. It has also become possible to significantly improve the recovery rate of carboxylic acids. Further, the present invention, compared with the conventional method, by selecting a desorbing solvent having a higher boiling point than the target carboxylic acid, it is possible to significantly reduce the evaporation amount of water and organic solvent, the energy cost is low. It became an economically advantageous method. Furthermore, if a specific alcohol is selected as the elimination solvent, an alcohol solution of the desired carboxylic acid can be obtained, and direct esterification can be carried out from this, which is an economically advantageous method.

(Examples) Hereinafter, the present invention will be described more specifically.

Example 1 A glass column with a jacket (8φ × 1 m) was filled with a tertiary amine resin (DIATON WA-30 manufactured by Mitsubishi Kasei) having a dimethylamine group (CH ₃ ) ₂ N− as a functional group, and prepared in advance. An aqueous solution of 8.9% by weight of ammonium acrylate containing 0.1% by weight of hydroquinone was passed from the top of the column at 25 ° C. and normal pressure. Sampling the effluent by about 5 g each,
Analysis of ammonia and acrylic acid in each sample by gas chromatography showed that the total sampling amount was about 40.
At g, an aqueous solution having an ammonia odor started to flow out, and if about 20 g was sampled, acrylate ions started to flow out. The maximum concentration of the obtained aqueous ammonia was about 1.7% by weight, and the total amount of the obtained ammonia was 36 mmol as a result of titration with sulfuric acid. Next, water is poured into the column to replace the ammonium acrylate aqueous solution with water, and then the column jacket is
Hot water at ℃ was passed through, and ethanol was run as a desorbing solvent while maintaining the pressure inside the column at 5 kg / cm ² . About effluent
Sampling 5g each and analyzing ethanol and acrylic acid in each sample by gas chromatography,
Ethanol and acrylic acid flowed out when the total sampling amount was about 40 g. Further, when about 20 g was sampled, a 7.2 wt% acrylic acid ethanol solution was obtained. Sampling was performed until acrylic acid did not flow out, and acrylic acid of each sample obtained was added to obtain a total amount, which was 36.2 mmol.

Example 2 A secondary amine resin (DIATON WA-20 manufactured by Mitsubishi Kasei) having a —CH ₂ NHCH ₂ — group as a functional group was packed in the same apparatus as in Example 1, and a 15.4 wt% ammonium acetate aqueous solution was used as a column. The liquid was passed from the top under the conditions of 30 ° C. and normal pressure. The same operation as in Example 1 was performed except that 1,4-dioxane was used as the elimination solvent. As a result of analyzing ammonia, acetic acid and 1,4-dioxane in each effluent sample at the time of adsorbing acetate ions and desorbing acetic acid, the total amount of ammonia that could be recovered as aqueous ammonia was 39.1 mmol, and
The maximum concentration of the obtained ammonia water was 3.4% by weight. The total amount of acetic acid that could be desorbed from the resin by 1,4-dioxane was 39.2 mmol, and the maximum concentration in the effluent sample was 8.4% by weight.

Examples 3 to 10 Table 1 shows the results of an experiment in which carboxylic acid was recovered from various ammonium carboxylate aqueous solutions by the same operation as in Example 1.

Comparative Example 1 In a 500 ml flask equipped with a packed column (18φ × 150 mm) filled with helipack No. 2 and a reflux controller, 200 g of a 50 wt% aqueous solution of ammonium methacrylate and hydroquinone.
Distillation was carried out by adding 2 g, setting the reflux ratio to 5 by setting a timer, and setting the column top pressure to 375 mmHg. When the temperature of the liquid at the bottom of the column was raised to 88 ° C., the aqueous ammonia solution began to distill from the top of the column, and 5 hours after the start of distillation, the distillation was stopped when the temperature of the column bottom increased to 110 ° C. During that time, the amount of ammonia water obtained from the top of the column was 108 g, the concentration was 3.5% by weight, and the ammonia decomposition rate was 24% when the charged ammonium methacrylate was 100%. The conversion to methacrylamide was about 2%, and the conversion to polymer was about 1.
5% Atsuta.

Comparative Example 2 200 g of a 75 wt% aqueous solution of ammonium isobutyrate was distilled under the same apparatus and operating conditions as in Comparative Example 1. When the temperature of the liquid at the bottom of the column was raised to 112 ° C., the aqueous ammonia solution started to distill from the top of the column, and 5 hours after the start of distillation, the distillation was stopped when the temperature of the column bottom increased to 165 ° C.
During that time, the amount of ammonia water obtained from the top of the tower was 50 g, the concentration thereof was 16% by weight, and the charged isobutyric acid ammonia was 100%.
The ammonia decomposition rate was 32% when it was defined as%. However, about 20% of the conversion to isobutyric acid amide was observed.

Example 11 A glass column with a jacket (20φ, 1 m) was filled with a tertiary amine-based resin (organo IRA-94) having a dimethylamine group (CH ₃ ) ₂ N- as a functional group, and then the jacket portion was filled with 8
The temperature inside the column was kept at 80 ° C by pouring hot water at 4 ° C.
Next, a 10.3% by weight aqueous solution of ammonium methacrylate containing 0.1% by weight of methoxyhydroquinone was passed through the column through a preheater adjusted to 80 ° C, and the effluent was filtered to about 20%.
G was sampled. When ammonia and methacrylic acid in each sampling were analyzed by gas chromatography, ammonia started to be detected when the total sampling amount was about 250 g, and methacrylic acid ion started to be detected after further sampling about 120 g. Sampling was stopped when the concentration of methacrylate ions in the effluent sample reached 8.6% by weight, and the total amount of ammonia obtained up to that point was found to be 250 mmol as a result of sulfuric acid neutralization titration. The maximum concentration of the obtained ammonia water was 1.7% by weight. Next, when warm water of 80 ° C was poured from the upper part of the column to recover the ammonium methacrylate aqueous solution in the column, an ammonium methacrylate aqueous solution of 10% by weight was obtained (the recovery rate as ammonium methacrylate was 99% or more). . Next, while keeping the pressure in the column at 5 kg / cm ² , methanol was made to flow from the lower part of the column as a desorbing solvent through a preheater adjusted to 80 ° C. About 15 g of effluent was sampled from the upper part of the column, and when methanol and methacrylic acid in each sample were analyzed by gas chromatography, methanol and methacrylic acid began to be detected at a total sampling amount of about 220 g, and about 100 g was sampled. By the way 8.0
A methanol solution of methacrylic acid in weight% was obtained. Sampling was performed until methacrylic acid did not flow out, and methacrylic acid in each obtained sample was added to obtain a total amount, which was 249 mmol. Further, add 5 ml of concentrated sulfuric acid to the methanol solution of methacrylic acid,
When the reaction was carried out under reflux at 0 ° C. for 2 hours, 220 mmol of methyl methacrylate was obtained.

Example 12 A tertiary amine resin having a dimethylamine group (CH ₃ ) ₂ N- as a functional group (Organo IRA-94) was packed in the same packed column as in Example 11, and then warm water at 53 ° C. was placed in the jacket. To maintain the temperature inside the column at 50 ° C. A 20% by weight aqueous solution of ammonium methacrylate containing 0.1% by weight of hydroquinone was passed through the preheater adjusted to 50 ° C from the bottom of the column, and about 20 g of the effluent from the top of the column was passed.
Each was sampled. When ammonia and methacrylic acid in each sampling were analyzed by the same method as in Example 11, the total amount of ammonia obtained was 294 mmol, and the maximum concentration thereof was 3.3% by weight. Then from the top of the column 5
When hot water at 0 ° C was poured and the ammonium methacrylate aqueous solution in the column was extruded, a 19 wt% ammonium methacrylate aqueous solution could be recovered (the recovery rate as ammonium methacrylate was 99% or more). Then, 90 ° C. warm water was flown through the jacket to keep the internal temperature of the column at 86 ° C. Next, dimethyl sulfoxide, which had been preheated to 90 ° C. in advance, was made to flow from the upper part of the column as a desorption solvent. As a result of performing the same operation and analysis as in Example 11, the total amount of methacrylic acid obtained was 301 mmol, and the maximum concentration of methacrylic acid was 20% by weight. To the dimethylsulfoxide solution of methacrylic acid obtained here, 5 ml of concentrated sulfuric acid and 900 mmol of methanol were added, and the mixture was refluxed at 70 ° C. for 4 hours, whereby 210 mmol of methyl methacrylate was produced.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-14917 (JP, A) JP-A-61-550553 (JP, A) DIAION Manual of Ion Exchange Resins (2) [Revised Edition], Pages 29-30, Mitsubishi Kasei Co., Ltd. (1972)

Claims (1)

[Claims] 1. A method for separating carboxylic acid and ammonia from an aqueous solution of ammonium carboxylate, which comprises adsorbing a carboxylate ion on an anion exchange resin, and then alcohols, ketones, cyclic ethers, nitriles, esters, Production of carboxylic acid from ammonium carboxylate aqueous solution characterized by desorbing and recovering carboxylate ion adsorbed by using at least one organic solvent selected from pyrrolidones, dimethylsulfoxide, dimethylformamide and dimethylacetamide Law.