JPH10298133A - Recovery of acetic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering acetic acid enabling the continuous measurement of the purity of the recovered acetic acid to monitor the quality and the easy performance of reflux ratio control when acetic acid is recovered by distillation. SOLUTION: The electroconductivity of the acetic acid recovered (as distillate) by distillation from an acetic acid-containing solution (e.g. the solution which is obtained by subjecting an acetic acid-containing waste generated from one of production process of aromatic carboxylic acids, aliphatic carboxylic acids, and their esters to pretreatment to treat components other than acetic acid, and preferably whose impurities have electroconductivities higher than 100 times that of acetic acid) is continuously measured, and the reflux ratio or heat supply of the distillation is controlled based on the measurements to enable the purification recovery of acetic acid sufficiently free from impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering acetic acid from an acetic acid-containing solution by a distillation operation. More specifically, the acetic acid-containing solution after distilling the acetic acid aqueous solution as it is, or adding an additive capable of forming an azeotrope with water and distilling or adding an extractant to remove water in advance and distilling the acetic acid-containing solution is removed. The present invention relates to a control method for purifying and recovering acetic acid.

[0002]

2. Description of the Related Art One of the methods for recovering acetic acid from an aqueous solution containing acetic acid is a distillation method. Further, as a method for efficiently separating acetic acid and water, an additive capable of forming an azeotrope with water is added and subjected to distillation and dehydration, or acetic acid is extracted with an extractant to separate from water, and thereafter, Methods for distilling acetic acid have been proposed. As such additives or extractants,
For example, ethyl acetate (Germany No. 3535583), benzene (India 150443), para-xylene (Japanese Unexamined Patent Publication No.
No. 3-16965), methyl isobutyl ketone (DE 3535583), butyl acetate (India 150443)
No.) is proposed. When these additives and extractants are used, those having a boiling point lower than that of acetic acid, such as benzene and ethyl acetate, are subjected to a distillate in the subsequent acetic acid distillation and purification step. And acetic acid is taken out as a residue. on the other hand,
For those having a higher boiling point than acetic acid, such as butyl acetate and methyl isobutyl ketone, acetic acid is taken out as a distillate.

By the way, the aqueous acetic acid solution to be recovered often contains, as impurities, lower aliphatic acid components such as formic acid in addition to water, and these impurities are contained in acetic acid after distillation and purification. If acetic acid is used, not only will the value of the product significantly decrease, but it may also cause corrosion of various devices. Therefore, it is important to sufficiently remove these impurities when purifying and recovering acetic acid.

Conventionally, intermittent methods such as gas chromatography analysis and melting point measurement have been adopted as a process analysis method for maintaining the quality of acetic acid taken out as a product. Therefore, the operation is performed with the reflux ratio at the time of distillation being excessive in consideration of the load fluctuation of the process, and there is a problem that a large amount of energy is consumed. Therefore, development of a method capable of continuously controlling the quality of purified and recovered acetic acid has been demanded.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned disadvantages of the prior art in recovering acetic acid from an acetic acid solution by a distillation method, and continuously measures the purity of acetic acid to be purified and recovered. It is an object of the present invention to provide a method capable of easily performing a refining operation such as a reflux ratio control, in addition to monitoring the flow rate.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, the purity of acetic acid can be detected by continuously measuring the conductivity of acetic acid purified and recovered. The present inventors have found that the purification operation factor can be immediately controlled according to the value, and have completed the present invention.

Thus, according to the present invention, "in recovering acetic acid from an acetic acid-containing solution by a distillation operation, the conductivity of the recovered acetic acid is continuously measured, and the reflux ratio or the amount of heating is controlled in accordance with the measured value. And a method for recovering acetic acid. "

[0008]

DETAILED DESCRIPTION OF THE INVENTION The acetic acid solution to which the present invention is directed is:
The concentration of the solvent and the acetic acid need not be particularly limited. However, it is preferable that the boiling point of the solvent differs from acetic acid by 20 ° C. or more, because the acetic acid can be easily separated. In the case where the acetic acid solution is an aqueous solution, if the concentration is 50% by weight or more, high-purity acetic acid can be recovered by a usual distillation method. And distilling in the presence of an additive capable of forming an azeotrope to separate a distillate consisting of the additive and water to obtain an acetic acid solution comprising acetic acid and the additive, and then distilling and separating acetic acid, or A method in which an extractant is added to collect acetic acid on the extractant side, and then a solution comprising acetic acid and the extractant is separated by distillation is preferably employed. In particular, impurities having a conductivity higher than that of acetic acid, such as aliphatic carboxylic acids (formic acid) lower than acetic acid, preferably 10
Acetic acid-containing wastewater containing 0 times or more impurities, for example, an acetic acid solution obtained by performing a pretreatment on an acetic acid-containing wastewater generated from a process for producing an aromatic carboxylic acid, an aliphatic carboxylic acid or an ester thereof is a recovered acetic acid described below. This is preferable because the accuracy of measuring the purity from the conductivity of the compound improves.

The additives used above include aliphatic ketones, aliphatic ethers and aliphatic esters having 6 to 10 carbon atoms. On the other hand, the extractant may have a lower boiling point or a higher boiling point than acetic acid, but is preferably an extractant that can be easily separated by distillation from acetic acid, for example, butyl acetate, methyl n-amyl ketone, ethyl acetate, and the like. Even if the extractant has a boiling point difference of less than 20 ° C. and is relatively difficult to separate from acetic acid, its conductivity with acetic acid is higher than that of acetic acid (2.4 μS /
Those which are 10 times or more, preferably 20 times or more, particularly preferably 100 times or more than m) are preferable because the acetic acid purity can be easily detected by the method described later.

In the present invention, when the solvent of the acetic acid solution has a higher boiling point than that of acetic acid, the recovered acetic acid is obtained as a distillate. Therefore, the conductivity of the distillate is measured continuously, The reflux ratio is adjusted according to the size. That is, when the conductivity increases due to the influence of impurities, the reflux ratio may be increased when the conductivity of the distillate increases. On the other hand, when the solvent has a lower boiling point than acetic acid, the recovered acetic acid is taken out as a bottom liquid, so the conductivity of the bottom liquid is continuously measured.
The heating amount of the distillation column is adjusted according to the magnitude of the value. In this case, the acetic acid recovered as the bottom residue may further contain high boiling point impurities. In such a case, acetic acid may be further distilled under conditions that can be taken out as a distillate, and collected as a distillate.

In order to measure the conductivity, it is important to properly select and set the accuracy depending on the conductivity of the impurities contained in the recovered acetic acid. The conductivity of the impurities is 100 times or less than that of acetic acid. In the case of, a conductivity meter having the highest sensitivity (0 to 10 μS / m) is used. On the other hand, when the conductivity of the impurity is 100 times or more that of acetic acid, a conductivity meter having low sensitivity may be used. In short, the conductivity of the recovered acetic acid is measured, and a conductivity meter having a sensitivity corresponding to the result may be used. In addition, the temperature at the time of conductivity measurement affects the measurement result, but usually a temperature correction mechanism is incorporated in the conductivity meter, so there is no particular problem if the temperature is below the maximum use temperature of the measurement cell of the conductivity meter. Absent.

When the concentration of the recovered acetic acid in the present invention is 95% by weight or more, preferably 99.5% by weight or more,
It is preferable because the effects of the present invention are maximized.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an apparatus used in one embodiment for distilling and purifying an acetic acid solution extracted and recovered using a high-boiling-point extractant.

First, acetic acid in acetic acid-containing wastewater from which wastewater from a dimethyl terephthalate production plant or the like has been pretreated to remove organic components other than acetic acid is dissolved on the extractant side by adding an extractant having a higher boiling point than acetic acid. Then, if necessary, an acetic acid-containing solution prepared by removing water from the extractant solution by, for example, azeotropic distillation or the like is introduced into the distillation column 1.
Here, the acetic acid is heated by the heater 8 and the acetic acid is removed from the condenser 2
And is taken out to the reflux tank 3 as a distillate. The obtained acetic acid is taken out as recovered acetic acid (product) 6. At this time, the conductivity of acetic acid is continuously measured by the conductivity meter 4, and the acetic acid is removed by the pipe 5 so that the quality of the recovered acetic acid becomes a reference value. Part is refluxed to the distillation column 1. The extractant 7 is withdrawn as a bottom liquid and reused for acetic acid extraction.

[0015]

The present invention will be described below in detail with reference to examples. In the examples, the conductivity and the purity were measured according to the following methods. <Conductivity> Toa Denki KK digital electric conductivity meter (CM
-40). <Purity> According to JIS K-1351 (freezing point method).

REFERENCE EXAMPLE The relationship between the conductivity and the acetic acid concentration when acetic acid contains formic acid and water as impurities was examined by randomly adding reagent grade formic acid and pure water to reagent grade acetic acid. Table 1 shows the results. The moisture concentration (% by weight) was measured using a Hiranuma Seisakusho Karl Fischer moisture analyzer, the formic acid concentration (% by weight) was measured using a Shimadzu isotachophoresis analyzer, and the acetic acid concentration (% by weight) was as follows. It was calculated from the equation. Acetic acid concentration = 100-formic acid concentration-water concentration

[0017]

[Table 1]

Example 1 Wastewater obtained at a dimethyl terephthalate production plant was pretreated to remove acetic acid and other organic components, and to remove acetic acid-containing wastewater (acetic acid 2.8% by weight, formic acid 0.1%).
Acetic acid as an extractant, ethyl acetate having a boiling point lower than that of acetic acid was added to extract the acetic acid to the ethyl acetate side, and the extract was first subjected to azeotropic distillation in a distillation column packed with 20 theoretical plates of Lab Pack. After removing the water, the ethyl acetate was distilled off to obtain an acetic acid solution as a residue in the kettle. At this time, the conductivity of the residue in the kettle was continuously measured, and the heating amount was adjusted so that the conductivity became 8.0 μS / m. The obtained acetic acid solution was introduced into a distillation column packed with a laboratory pack having 20 theoretical plates, and was subjected to heat distillation to obtain recovered acetic acid as a distillate. At this time, the reflux ratio is 1
The conductivity was set to 0, the conductivity of the recovered acetic acid was continuously measured, and the reflux ratio was finely adjusted so that the conductivity was as shown in Table 2.
Table 2 shows the results.

Example 2 Wastewater obtained at a dimethyl terephthalate production plant was pretreated to remove organic components other than acetic acid.
To the methyl n-amyl ketone as an extractant, the acetic acid was extracted to the methyl n-amyl ketone side, and the extract was first passed through a distillation column packed with a laboratory pack having 20 theoretical plates. Water was removed by azeotropic distillation. The obtained acetic acid-containing extractant solution (acetic acid, 2.18% by weight) was introduced into a distillation column packed with a lab pack having 38 theoretical plates and heated and distilled to obtain recovered acetic acid as a distillate. At this time, the reflux ratio was set to 30, the conductivity of the recovered acetic acid was continuously measured, and the reflux ratio was finely adjusted so that the conductivity was as shown in Table 2. The results are shown in Table 2. For reference, the conductivity and purity of industrial acetic acid are shown in Table 2.

[0020]

[Table 2]

[0021]

According to the method of the present invention, when acetic acid is recovered from an acetic acid solution by a distillation operation, the conductivity, which has a correlation with the purity, is continuously measured. In response to this, for example, it is possible to perform a purification operation such as reflux ratio control, and it is possible to use the purification device efficiently and to save energy, and its industrial value is extremely large. is there.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a process for distilling and purifying an acetic acid-containing extractant solution using a high-boiling extractant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Distillation tower 2 Condenser 3 Reflux tank 4 Conductivity meter 5 Reflux pipe 6 Product (recovered acetic acid) 7 Extractant 8 Reboiler

Claims (4)

[Claims] When recovering acetic acid from a solution containing acetic acid by distillation, the conductivity of the recovered acetic acid is continuously measured, and the reflux ratio or the amount of heating is controlled in accordance with the measured value. Collection method. 2. In recovering acetic acid as a distillate from a acetic acid-containing solution by distillation, the conductivity of the recovered acetic acid is continuously measured, and the reflux ratio is controlled according to the measured value. Acetic acid recovery method. 3. An acetic acid-containing solution obtained by pretreating an acetic acid-containing wastewater generated from any of a process for producing an aromatic carboxylic acid, an aliphatic carboxylic acid or an ester thereof to treat components other than acetic acid. The method for recovering acetic acid according to claim 1 or 2, which is a solution. 4. The method according to claim 1, wherein the impurities contained in the acetic acid-containing solution have a conductivity that is at least 100 times the conductivity of acetic acid.
The method for recovering acetic acid according to any one of the above.