JP3310773B2 - Separation method of aliphatic carboxylic acid by extraction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating a carboxylic acid from an aqueous solution containing a carboxylic acid by extraction and a method for separating a carboxylic acid and an extractant by distilling the extract as a subsequent step. In particular, the present invention relates to an extractant for selectively extracting an aliphatic carboxylic acid from an aqueous solution containing the aliphatic carboxylic acid.

[0002]

2. Description of the Related Art
In the method of industrially extracting or extracting and extracting carboxylic acid from an aqueous solution containing carboxylic acid by extraction or extraction / distillation, aromatic compounds such as benzene and toluene are used as an extractant,
A wide variety of compounds such as ethers such as diisopropyl ether and diethyl ether, esters such as ethyl acetate and butyl acetate, higher alcohols such as decanol, amines, amides and paraffins have been studied and put to practical use. As a capacity condition necessary for such an extractant, the partition coefficient of the carboxylic acid to the extractant is large. The partition coefficient of water to the extractant is small. Low solubility in water. It is chemically stable under extraction conditions, and the extraction operation can be performed continuously and efficiently. As a subsequent step, separation of the extract and the carboxylic acid can be continuously and easily performed. Low toxicity. Inexpensive and easy to obtain. However, there are very few such ideal extractants. For example, ethyl acetate and butyl acetate are currently widely used industrially as carboxylic acid extractants.Ethyl acetate and butyl acetate have high carboxylic acid extraction ability but high solubility in water. However, it is not necessarily an industrially suitable extractant because of its chemical instability, such as the production of ethanol and butanol by hydrolysis. In addition, even if it was used as a mixed extractant prepared by mixing a hydrophobic compound with ethyl acetate and butyl acetate, it was often less than ideal. In addition, benzene and the like are chemically stable and have high hydrophobicity, but the distribution coefficient of carboxylic acid is small, and if an attempt is made to lower the acid concentration in the extraction column drainage, the amount of the extractant with respect to the charged liquid is significantly increased, The number of theoretical plates needs to be increased. Further, ketones have the highest performance as an extractant for acetic acid, but the solubility in water is so high that the loss of the extractant to the raffinate is very large. Taking diethyl ketone as an example, the solubility in water is about 7%, but those having smaller alkyl than diethyl ketone show higher solubility. As described above, ketones have such a value that the elution concentration in the raffinate is unbearable, and the amount of energy used to recover the extractant is considerable. On the other hand, ether is usually used as dicarboxylic ether (IPE) or diethyl ether as an extractant for carboxylic acid. However, although the hydrophobicity is large, the partition coefficient of carboxylic acid is small. Since it is necessary to always pay attention to the formation, it is hard to say that it is industrially preferable. Furthermore, recently, high-boiling-point extractants such as higher amines have been used with good extraction efficiency, and when the starting carboxylic acid contains high-boiling impurities, high-boiling impurities accumulate in the extracting agent, This separation requires a great deal of energy under high vacuum. Moreover, when an extractant having a lower boiling point than that of a carboxylic acid is used, a great deal of equipment cost is required for changing the process by using a high-boiling point extractant, so considerable risks must be prepared. As described above, there is no conventional extractant that satisfies all the conditions to be provided as an extractant, and in many cases, it is currently used as a mixed extractant according to each need.

[0003]

SUMMARY OF THE INVENTION The present inventors have developed a carboxylic acid extractant having the above-mentioned conditions, which has no hydrolyzability such as ester, high hydrophobicity, and non-toxic extract such as benzene. As a result of a search for a new ether-based extractant as an agent, methyl tertiary butyl ether (MT
BE), tertiary amyl methyl ether (TAM)
E) or ethyl tertiary butyl ether (ETB)
The extractant having one or more of E) as a main component has many advantages over the conventionally used ethyl acetate and the like, and is a substance that can sufficiently satisfy the capacity requirements as an extractant. The results were obtained, and the present invention was achieved. MTB
E, TAME, and ETBE are inexpensive ethers that can be easily obtained by reacting methanol or ethanol with isobutylene, which is a C4 fraction, or isoamylene, which is a C5 fraction, obtained in large quantities during petroleum refining. Also, regarding the production of peroxides which are problematic when industrially using ethers, it is difficult to generate peroxides for these ethers, and therefore, the use of gazoline additives as antiknock agents is known. It is.

That is, the present invention relates to an aqueous solution containing an aliphatic carboxylic acid using an extractant containing one or more selected from methyl tertiary butyl ether, tertiary amyl methyl ether and ethyl tertiary butyl ether as main components. More specifically, the present invention relates to a method for extracting an aliphatic carboxylic acid, which comprises selectively extracting an aliphatic carboxylic acid. Aliphatic carboxylic acids include formic acid, acetic acid and propionic acid. The extract obtained by the extraction method of the present invention is subjected to azeotropic distillation to extract the aliphatic carboxylic acid from the bottom of the column, and the extractant can be separated and recovered by distillation.

Hereinafter, the advantages of the present invention will be described in detail by taking as an example a case where acetic acid is extracted and distilled using MTBE as an extractant. In the case of MTBE, the partition coefficient for acetic acid is
It is 0.94, which is a considerably high value as a single component among extractants such as alcohols, esters, ethers and amines conventionally used industrially, and is comparable to diethyl ketone when compared with ketones. It can be seen that it has a very high partition coefficient as compared with 0.39 of IPE which is a representative of the same ether system. The solubility of MTBE in water is
2.4%, which is lower than that of the commonly used extractant. By the way, MTBE is 760mmHg with water, 52.6
It has the property of azeotropic at ℃. Since the boiling point of acetic acid is 118 ° C, when distilling the extract to separate the extractant and acetic acid,
Separation of the extractant and acetic acid is facilitated, and MTBE and water can be taken as the top solution and acetic acid with high purity can be taken as the bottom solution by controlling the reflux well. M
The boiling point of diethyl ketone of the same capacity as TBE is 1
At 02 ° C, the azeotrope with water is 82.9 ° C at 760 mmHg, making it difficult to distill the extract even when used as an extractant. Meanwhile, TA
ME and ETBE have a lower distribution of acetic acid than MTBE, but have an ability comparable to that of an extractant conventionally used industrially. The solubility in water was 1.9 for TAME.
%, ETBE is 0.7%, which is lower than MTBE. The azeotropic point with water is 73.8 ° C at 760 mmHg in TAME, ET
BE is 760 mmHg and 65.2 ° C. As well as MTBE, by controlling reflux well, TA
ME and water, or ETBE and water, and high-purity acetic acid as a bottom liquid can be taken out.

In implementing the present invention, MTBE, TAM
E and ETBE can be used alone or in combination of two or more. One or more of these may be mixed with a conventionally known extractant such as ethyl acetate or methyl isopropyl ketone.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

Example 1 An acetic acid extraction experiment was conducted from a 30% aqueous acetic acid solution using an MTBE-only extractant. For the experiment, a porcelain Raschig ring (outer diameter 5 mm, height 5 mm) was attached to a glass extraction tower (inner diameter 4 cm).
Countercurrent extraction using a packed tower filled with 100 cm at normal pressure and 40 ° C, under conditions of extractant amount / acid aqueous solution charge (S / F) 2.0 and charged acetic acid aqueous solution (30%) amount 5.3 kg / hr. As a result, the amount of water in the raffinate was 3.3 kg / hr, and the acetic acid concentration was 350 ppm. The concentration of MTBE in the raffinate is 2.4%, and the loss of the extractant is low. Further, this extract was subjected to distillation using an 40-stage Older Shaw tower, and distillation was performed to remove dry acetic acid as a bottom.The reflux ratio of the upper layer at the top of the column was 0.75, and water was 0.7% from the bottom of the column.
%, 99.3% pure acetic acid containing only 220 ppm MTBE. The amount of heat required in the dehydration step was 115 kcal per kg of water in the aqueous acetic acid solution charged in the extraction tower.

Comparative Example 1 An acetic acid extraction experiment was conducted in the case where diisopropyl ether (IPE) was used as a representative of the same ether system as the extractant. In the experiment, the packed tower used in Example 1 was used. At normal pressure and 40 ° C., the amount of acetic acid aqueous solution (30%) charged was 5.3.
When countercurrent extraction was carried out under the condition of kg / hr, the concentration of acetic acid in the raffinate finally reached 510 ppm when the amount of extractant / amount of acid solution charged (S / F) was 3.7. The concentration of IPE in the raffinate was 1.9%. Further, this extract was subjected to distillation using a 40-stage Oldershaw column, and distillation was performed in which dried acetic acid was removed as a bottom. When the reflux ratio of the upper layer at the top of the column was set to 0.2, water was 4 ppm from the bottom of the column. ,
Although acetic acid with a purity of 99.98% containing only 180 ppm of IPE was obtained, the amount of heat required in this experiment required 580 kcal / kg of water in the aqueous acetic acid solution charged to the extraction column, and IP in terms of dehydration was required.
Although E is effective, it requires a large amount of heat and is not industrially suitable.

Example 2 An acetic acid extraction experiment was carried out from a 30% acetic acid aqueous solution using an extractant of a single component of TAME. In the experiment, the amount of the extractant / the amount of the aqueous acid solution charged (S / F) was 1.6 and the amount of the aqueous acetic acid solution (30%) was charged at normal pressure and 40 ° C. using the packed tower used in Example 1.
When countercurrent extraction was performed under the condition of 5.3 kg / hr, the amount of water in the raffinate was 3.6 kg / hr, and the acetic acid concentration was 0.6%. In addition, the concentration of TAME in the raffinate is 1.9%, and the loss of the extractant is decreasing. Furthermore, the concentration of TAME in this extract is 1.9%, and the loss of the extractant is low. Further, this extract was subjected to distillation using a 40-stage Older Shaw tower, and distillation was performed to remove dry acetic acid as a bottom.
At 1.16, acetic acid with a purity of 99.0% containing 1.7 ppm of water and 0.98% of TAME was obtained from the bottom of the column. The amount of heat required in the dehydration process is 140 kC / kg of water in the aqueous acetic acid solution charged to the extraction tower.
al.

Example 3 The distribution coefficients of an extractant consisting solely of MTBE, TAME, ETBE and IPE and a mixed extractant of ethyl acetate (AE) and TAME in a weight ratio of 25:75 were measured. 33%
After adding 0.67 kg of extractant to 1 kg of acetic acid aqueous solution, stirring at 40 ° C. and allowing it to stand, the composition of the aqueous layer and the organic layer was analyzed.
The following results were obtained.

Acetic acid concentration in the organic layer (wt%) Partition coefficient MTBE 20.2 0.96 TAME 15.1 0.60 ETBE 11.1 0.41 IPE 10.8 0.39 AE / TAME 15.9 0.71 From these results, the extraction efficiency of MTBE, TAME and ETBE has been conventionally used. It turns out that it is higher than ether. It was also found that TAME to which AE was added at 25% was a very effective extractant.

Example 4 An acetic acid extraction experiment was performed using a mixed extractant in which MTBE and TAME were mixed at a weight ratio of 7: 3. Example 1 for the experiment
At normal pressure and 40 ° C., the amount of extractant / the amount of the acid aqueous solution charged (S / F) was 1.6, and the amount of the charged acetic acid aqueous solution (30
%), The amount of water in the raffinate was 3.4 kg / hr and the acetic acid concentration was 16 kg / hr.
It was 0 ppm. The concentration of TAME in the raffinate was 0.5
%, MTBE was 1.7%. In addition, this extract
Distillation was performed by an 40-stage Older Shaw tower, and distillation was performed to remove dry acetic acid as a bottom.The reflux ratio of the upper layer at the top of the tower was 0.83, water was 430 ppm from the bottom of the tower, and TAME was 75 ppm.
And 99.9% pure acetic acid containing only 30 ppb MTBE. The amount of heat required in the dehydration step was 110 kcal / kg of water in the aqueous acetic acid solution charged in the extraction tower.

Example 5 An acetic acid extraction experiment was performed using a mixed extractant in which ethyl acetate (AE) and TAME were mixed at a weight ratio of 25:75. In the experiment, the packed column used in Example 1 was used under the conditions of normal pressure and 40 ° C., the amount of the extractant / the amount of the acid aqueous solution (S / F) being 1.6 and the amount of the acetic acid aqueous solution (30%) being 5.3 kg / hr. As a result, the amount of water in the raffinate was 3.6 kg / hr, and the acetic acid concentration was 600 pm. The concentration of AE in the raffinate was 1.3%, and the content of TAME was 1.3%. Further, the extract was subjected to distillation using a 40-stage Older Shaw tower, and distillation was performed to remove dry acetic acid as a bottom. The reflux ratio of the upper layer at the top of the tower was 1.16, water was 5 ppm from the bottom of the tower, and AE850 p.
Acetic acid having a purity of 99.8% and containing only 950 ppm of pm and TAME was obtained. The amount of heat required in the dehydration step was 204 kcal / kg of water in the aqueous acetic acid solution charged in the extraction tower.

[0015]

As can be seen from the above Examples and Comparative Examples, the MTBE and TA of the present invention can be compared with a conventionally used ether-based carboxylic acid extractant such as IPE.
ME and ETBE have more conditions that the carboxylic acid extractant should have, and also exhibit excellent effects in the subsequent step of separating the extractant and the aliphatic carboxylic acid by distillation.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-156744 (JP, A) JP-A-59-5139 (JP, A) JP-A-60-25949 (JP, A) JP-A 53-156 149922 (JP, A) JP-B 46-1994 (JP, B1) JP-B 43-13041 (JP, B1) JP-B 28-1267 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 51/48 C07C 53/02 C07C 53/08 C07C 53/122

Claims (4)

(57) [Claims] 1. An aqueous solution containing an aliphatic carboxylic acid is extracted from an aqueous solution containing an aliphatic carboxylic acid by using an extractant containing one or more selected from methyl tertiary butyl ether, tertiary amyl methyl ether and ethyl tertiary butyl ether as main components. A method for extracting an aliphatic carboxylic acid, comprising selectively extracting an aliphatic carboxylic acid. 2. The method for extracting an aliphatic carboxylic acid according to claim 1, wherein the aliphatic carboxylic acid is formic acid, acetic acid or propionic acid. 3. The method of claim 1, wherein the aliphatic carboxylic acid is acetic acid.
A method for extracting an aliphatic carboxylic acid according to the above. 4. A method for separating an extract by distillation, wherein the extract obtained by the extraction method according to claim 1, 2 or 3 is subjected to azeotropic distillation to extract the aliphatic carboxylic acid from the bottom of the column.