KR20230154507A - The methods for recovering acetic acid and dimethylformamide by using pressure swing distillation - Google Patents

Abstract

The present invention relates to a method for separating and recovering acetic acid and dimethylformamide from waste solvents. Waste solvents containing water, acetic acid, and dimethylformamide are introduced into a weak vacuum distillation tower, and water is separated at the top of the weak vacuum distillation tower. and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of a weak vacuum distillation tower (S11); The mixture containing acetic acid and dimethylformamide is introduced into a high vacuum distillation tower, dimethylformamide is recovered at the top of the high vacuum distillation tower, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is added to the bottom of the high vacuum distillation tower. Obtaining step (S12); A mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is introduced into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and acetic acid, dimethylformamide, and acetic acid having a second azeotropic composition are added to the bottom of the atmospheric distillation column. and obtaining a mixture containing dimethylacetamide (S13); and acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained from the bottom of the atmospheric distillation tower so that the ratio of dimethylformamide/(dimethylformamide + dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9. It provides a method for recovering acetic acid and dimethylformamide, including a step (S14) of discharging a part of the mixture and circulating the remainder in the high vacuum distillation column or the weak vacuum distillation column.

Description

Method for recovering acetic acid and dimethylformamide using pressure swing distillation {THE METHODS FOR RECOVERING ACETIC ACID AND DIMETHYLFORMAMIDE BY USING PRESSURE SWING DISTILLATION}

The present invention relates to a method for recovering useful components from waste solvents, and more specifically, using the difference in azeotropic composition of acetic acid (AA), dimethylformamide (DMF), and dimethylacetamide (DMAc) under high vacuum conditions and normal pressure conditions. Thus, it relates to a method of recovering each component of acetic acid and dimethylformamide.

The components contained in the waste solvent (or DMF waste liquid) generated during polyimide film production and the typical composition of each component are shown in Table 1 below.

water AA
(acetic acid) 3MP
(3-methylpyridine) DMF
(Dimethyl formamide) Boiling point, ℃ 100 118 143-144 153 Composition cost, % 10 18 2 70

By putting the waste solvent into a distillation tower with a high number of stages, water and 3MP can be removed at the top of the tower, and a mixture of 20% acetic acid and 80% DMF can be obtained at the bottom of the tower.

AA and DMF form the maximum temperature azeotrope. According to the literature, the azeotrope temperature at normal pressure is 159°C, and the azeotrope composition at this time is 26% AA and 74% DMF.

Therefore, when the mixture of AA and DMF obtained at the bottom of the tower is put back into a conventional distillation column, part of the DMF is recovered at the top of the tower, and an azeotropic mixture of 26% AA and 74% DMF is obtained at the bottom of the tower. Even if the azeotropic mixture obtained in this way is re-injected into a general distillation column, an azeotropic mixture of the same composition is obtained at the top and bottom of the column.

Methods for separating azeotropic mixtures include Extractive Distillation, Azeotropic Distillation, and Pressure Swing Distillation. Depending on the characteristics of the azeotropic mixture, one of these methods is efficient. can be used to separate azeotropic mixtures by selecting . However, this choice is not possible in all cases, and even if separation of the azeotrope is possible with the selected method, it may not be economical.

In particular, as a technology for the separation of acetic acid and DMF, Japanese Patent Laid-Open No. 2002-363150 proposes a method of separating acetic acid and dimethylformamide using toluene, which is azeotropic with acetic acid but not with dimethylformamide, as an azeotrope. In addition, Korean Patent Publication No. 10-2010-0130219 proposes a method of removing carboxylic acid from a solution containing tertiary amide by contacting a solution containing carboxylic acid and tertiary amide with an extraction medium containing trilaurylamine, there is. However, the above-described prior art requires a third component, which results in low economic feasibility and the efficiency of the separation process is not sufficient, so a separation technology that complements this is needed.

Japanese Patent Publication No. 2002-363150 (published on December 18, 2002) Korean Patent Publication No. 10-2010-0130219 (published on December 10, 2010)

The method for recovering acetic acid and dimethylformamide of the present invention was devised to solve the above problems,

Injecting a waste solvent containing water, acetic acid, and dimethylformamide into a weak vacuum distillation tower, separating water at the top of the weak vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the weak vacuum distillation tower (S11);

The mixture containing acetic acid and dimethylformamide is introduced into a high vacuum distillation tower, dimethylformamide is recovered at the top of the high vacuum distillation tower, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is added to the bottom of the high vacuum distillation tower. Obtaining step (S12);

A mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is introduced into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and acetic acid, dimethylformamide, and acetic acid having a second azeotropic composition are added to the bottom of the atmospheric distillation column. and obtaining a mixture containing dimethylacetamide (S13); and

Acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained from the bottom of the atmospheric distillation tower so that the ratio of dimethylformamide / (dimethylformamide + dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9. The purpose is to provide a method for recovering acetic acid and dimethylformamide, including a step (S14) of discharging a part of the mixture and circulating the remainder in the high vacuum distillation column or the weak vacuum distillation column.

In addition to the clear objectives described above, the present invention may also aim to achieve other objectives that can be easily derived by a person skilled in the art from this objective and the overall description of the present specification.

The method for recovering acetic acid and dimethylformamide of the present invention is to achieve the objectives described above,

Injecting a waste solvent containing water, acetic acid, and dimethylformamide into a weak vacuum distillation tower, separating water at the top of the weak vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the weak vacuum distillation tower (S11);

The mixture containing acetic acid and dimethylformamide is introduced into a high vacuum distillation tower, dimethylformamide is recovered at the top of the high vacuum distillation tower, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is added to the bottom of the high vacuum distillation tower. Obtaining step (S12);

A mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is introduced into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and acetic acid, dimethylformamide, and acetic acid having a second azeotropic composition are added to the bottom of the atmospheric distillation column. and obtaining a mixture containing dimethylacetamide (S13); and

Acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained from the bottom of the atmospheric distillation tower so that the ratio of dimethylformamide / (dimethylformamide + dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9. A step (S14) of discharging a part of the mixture and injecting the remainder into the high vacuum distillation column or the weak vacuum distillation column for circulation.

And, in the second azeotropic composition, the ratio of dimethylformamide/(dimethylformamide + dimethylacetamide) may be 0.6 to 0.8.

Additionally, the waste solvent may include 3-methylpyridine.

Additionally, the bottom pressure of the weak vacuum distillation column may be 700 torr or less, 600 torr or less, or 500 torr or less.

Additionally, the bottom pressure of the high vacuum distillation column may be 200 torr or less, 150 torr or less, or 100 torr or less.

Additionally, the pressure at the bottom of the atmospheric distillation column may be 700 to 1200 torr, 700 to 1000 torr, or 700 to 900 torr.

In addition, the product recovered from the top of the high vacuum distillation tower may satisfy a purity of 99.5% or more with respect to dimethylformamide.

In addition, the water recovered from the top of the high vacuum distillation tower may have a moisture content of 200 ppm or less, 150 ppm or less, or 100 ppm or less.

In addition, the recovered product from the top of the high vacuum distillation tower may not contain acetic acid.

In addition, the recovered product from the top of the atmospheric distillation column may satisfy a purity of 99.5% or more with respect to acetic acid.

In addition, the atmospheric distillation tower top recovery may have a moisture content of 1 wt% or less, 0.8 wt% or less, or 0.6 wt% or less.

Additionally, the weak vacuum distillation column may be equipped with a forced circulation type reboiler.

Additionally, the atmospheric distillation column may be equipped with a forced circulation type reboiler.

According to the recovery method of acetic acid and dimethylformamide according to the present invention, high-purity dimethylformamide can be recovered from waste solvents through pressure swing distillation, and at the same time, acetic acid or acetic acid aqueous solution without dimethylformamide or impurities can be economically recovered. You can.

Figure 1 is a graph of changes in azeotropic composition according to pressure of AA and DMF and AA and DMAc.
Figure 2 is a graph of the boiling point change of DMAc and DMF according to pressure.
Figure 3 is a process diagram for recovering DMF from DMF waste liquid according to an embodiment of the present invention.
Figure 4 shows the results of measuring the DMF thermal decomposition reaction rate at each temperature according to residence time in the oil bath.
Figure 5 is a distillation experiment process diagram for removing water and 3-methylpyridine from DMF waste liquid according to an embodiment of the present invention.
Figure 6 is a distillation experiment process diagram linking a vacuum distillation column and an atmospheric distillation column according to an embodiment of the present invention.
Figure 7 shows a DMF yield prediction calculation tool reflecting the DMF thermal decomposition reaction rate.
Figure 8 shows the results of calculating the DMF recovery rate according to the ratio of DMF/(DMF+DMAc).

Hereinafter, preferred embodiments of the present invention will be described in detail.

However, the following is only a detailed description of specific embodiments, and since the present invention can be changed in various ways and have various forms, the present invention is not limited to the specific embodiments exemplified. The present invention should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

In addition, in the following description, many specific details, such as specific components, are provided, but this is provided to facilitate a more general understanding of the present invention, and it is known in the art that the present invention can be practiced without these specific details. It will be self-evident to those who have the knowledge. Additionally, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Additionally, the terms used in this application are only used to describe specific embodiments and are not intended to limit the present invention. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by a person of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless explicitly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

In this application, singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, the second component may also be named a first component without departing from the scope of the present invention.

In the present application, terms such as 'include', 'contain', or 'have' are intended to refer to the presence of features, components (or components), etc. described in the specification, but are not intended to indicate the presence of one or more other features or This does not mean that components, etc. do not exist or cannot be added.

In this specification, % may mean wt%.

Considering the composition ratio change characteristics of the azeotropic mixture of acetic acid (AA) and dimethylformamide (DMF) according to pressure as shown in Figure 1, the pressure at the bottom of the low-pressure distillation tower is 200 torr or less, and the pressure at the bottom of the high-pressure distillation tower is 700 torr. When operating at torr or higher, it can be expected that AA and DMF can be smoothly recovered by securing the difference in azeotropic composition (more than 5% based on AA) required for pressure swing distillation. Therefore, based on the concept of pressure swing distillation, a diagram of the recovery process of DMF and AA from DMF waste liquid can be derived as shown in FIG. 3.

However, when the AA and DMF mixture is put into a pressure swing distillation process to recover each useful component, the thermal decomposition of DMF occurs in the section where the temperature in the high-pressure distillation tower exceeds 155 ℃, and the thermal decomposition product, dimethylacetamide (DMAc) ) and the generation of moisture, it was unclear whether the DMF and AA recovered to the top met the product specifications and their economic recovery potential.

As shown in Figure 4, DMF, a heat-sensitive material, begins to thermally decompose at about 100°C, and as the temperature increases, thermal decomposition increases, and the degree of thermal decomposition tends to double with each 10°C increase in temperature. As shown in Scheme 1 below, DMF is thermally decomposed into dimethylamine (DMA) and carbon monoxide (CO), and dimethylamine combines with surrounding acetic acid to generate dimethylacetamide (DMAc) and moisture. At this time, the moisture production amount can be indirectly calculated as 18/87 = 20.7% of the DMAc production amount.

[Scheme 1]

The internal temperature of the high-vacuum distillation column is mostly below 110 ℃, so thermal decomposition of DMF rarely occurs, so there is little moisture generated. However, in the atmospheric distillation column, where the internal temperature is relatively high, the moisture generated by thermal decomposition is acetic acid recovered at the top of the atmospheric distillation column. In addition to increasing the moisture content of several thousand ppm, the moisture content of the atmospheric distillation tower bottom stream (circulating stream in FIG. 3) can also reach tens of ppm. Although the amount of moisture accompanying this circulating stream is small, it can be a major cause of the increase in moisture content of DMF recovered at the top of the high vacuum distillation column, making it difficult to meet the moisture specifications of DMF.

The present invention clearly identified the problems caused by thermal decomposition occurring in pressure swing distillation and at the same time derived ways to overcome them, and then developed DMF product specifications 'purity of 99.5% or more, moisture content' from DMF waste liquid including AA and DMF. A pressure swing distillation process that can recover DMF that satisfies ‘200 ppm or less’ and AA that satisfies ‘purity of 99.5% or more, moisture content of 1% or less’, which is also one of the AA product standards, at an economical and high yield. We would like to present the configuration and operating conditions and methods.

The recovery method of acetic acid and dimethylformamide of the present invention involves adding waste solvents containing water, acetic acid, and dimethylformamide to a weak vacuum distillation column, separating water at the top of the weak vacuum distillation column, and acetic acid and acetic acid at the bottom of the weak vacuum distillation column. Obtaining a mixture containing dimethylformamide (S11); The mixture containing acetic acid and dimethylformamide is introduced into a high vacuum distillation tower, dimethylformamide is recovered at the top of the high vacuum distillation tower, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is added to the bottom of the high vacuum distillation tower. Obtaining step (S12); A mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is introduced into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and acetic acid, dimethylformamide, and acetic acid having a second azeotropic composition are added to the bottom of the atmospheric distillation column. and obtaining a mixture containing dimethylacetamide (S13); and acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained from the bottom of the atmospheric distillation tower so that the ratio of dimethylformamide/(dimethylformamide + dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9. A step (S14) of discharging a part of the mixture contained therein and circulating the remainder by inputting it into the high vacuum distillation column or the weak vacuum distillation column.

Hereinafter, each step will be described in detail with reference to FIG. 3.

First, the waste solvent containing water, acetic acid, and dimethylformamide is introduced into a weak vacuum distillation tower, water is separated at the top of the weak vacuum distillation tower, and a mixture containing acetic acid and dimethylformamide is obtained at the bottom of the weak vacuum distillation tower (S11) .

The waste solvent to be treated in the present invention contains water, acetic acid, and dimethylformamide, and may further include 3-methylpyridine (3MP). For example, it may be a waste solvent generated during the manufacture of polyimide films for semiconductors and displays. .

Step S11 may be a step of removing substances other than carboxylic acid and amide compounds, which are the separation targets of the present invention. Specifically, before step S12, a waste solvent containing water, carboxylic acid, and amide compounds is added to the distillation tower, This may be a step of separating water and 3-methylpyridine at the top of the distillation tower and obtaining a mixture containing carboxylic acid and an amide compound at the bottom of the distillation tower.

At this time, the bottom pressure of the weak vacuum distillation column may be 700 torr or less, 600 torr or less, or 500 torr or less. Like the high vacuum distillation column, most of the moisture generated by thermal decomposition in the weak vacuum distillation column rises to the top of the column, but some is swept into the bottom stream and rises to the top of the high vacuum distillation column, which may affect the moisture content of DMF. When the bottom pressure is 700 torr or less or below the above bottom pressure range, the temperature of the bottom stream with a composition of 20% AA and 80% DMF does not exceed 150 ℃, so the moisture content in the bottom stream is 40 ppm or less, which results in a high vacuum distillation column. The increase in moisture content in DMF, the top stream, is less than 50 ppm, so it is within the range where it is possible to meet moisture standards.

Next, the mixture containing acetic acid and dimethylformamide recovered at the bottom of the weak vacuum distillation column in step S11 is introduced into the high vacuum distillation column, dimethylformamide is recovered at the top of the high vacuum distillation column, and a mixture having a first azeotropic composition is used at the bottom of the high vacuum distillation column. A mixture containing acetic acid, dimethylformamide, and dimethylacetamide is obtained (S12).

At this time, the bottom pressure of the high vacuum distillation column may be 200 torr or less, 150 torr or less, or 100 torr or less. The azeotropic composition ratio under pressure in the above range is sufficiently different from the azeotropic composition ratio under normal pressure to enable component separation by pressure swing distillation. The lower limit is not particularly limited, but the efficiency and economic feasibility of the process should be considered.

The recovered product from the top of the high vacuum distillation tower may satisfy a purity of 99.5% or more with respect to dimethylformamide. In addition, the water recovered from the top of the high vacuum distillation tower may have a moisture content of 200 ppm or less, 150 ppm or less, or 100 ppm or less, and the water recovered from the top of the high vacuum distillation tower may not contain acetic acid. Additionally, the high vacuum distillation tower top recovery may have a DMAc content of less than 0.5 wt%, less than 0.3 wt%, or less than 0.1 wt%.

At the bottom of the high vacuum distillation tower, a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is obtained. The composition ratio of the azeotrope containing all of acetic acid, dimethylformamide, and dimethylacetamide can be calculated from the graph of the DMF and AA azeotrope and the graph of the DMAc AA azeotrope shown in Figure 1. For example, at 100 torr, the acetic acid proportion of the DMF and AA azeotrope is 34% and the acetic acid proportion of the DMAc and AA azeotrope is 28%, and the acetic acid proportion of the DMF and DMAc azeotrope of 80:20 is ( 34x80+28x20)/100 = approximately 32.8%.

Next, a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is introduced into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and acetic acid and dimethyl having a second azeotropic composition are added to the bottom of the atmospheric distillation column. A mixture containing formamide and dimethylacetamide is obtained (S13).

At this time, the bottom pressure of the atmospheric distillation column may be 700 to 1200 torr, 700 to 1000 torr, or 700 to 900 torr. In the case of the normal pressure distillation column located after the high vacuum distillation column, the larger the column bottom pressure, the larger the pressure difference with the high vacuum distillation column, making it easier to separate acetic acid and dimethylformamide. However, when the column bottom pressure exceeds 1000 torr or the above range, as shown in Figure 2 Likewise, the boiling point of DMF is 165 ℃, and the azeotropic temperature of DMF and AA exceeds 170 ℃, and the thermal decomposition rate of DMF increases more than twice compared to normal pressure, and the moisture content of acetic acid recovered at the top of the normal pressure distillation column increases significantly, meeting the standard ( 1% or less) may be difficult to meet.

The atmospheric distillation tower top recovery may satisfy a purity of 99.5% or more with respect to acetic acid, may not contain dimethylformamide, and may have a moisture content of 1 wt% or less, 0.8 wt% or less, or 0.6 wt% or less.

At the bottom of the atmospheric distillation column, a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition is obtained. As shown in Figure 1, at normal pressure (760 torr), the acetic acid ratio of the azeotrope of DMF and AA is 26%, and the acetic acid ratio of the azeotrope of DMAc and AA is 21%, and the azeotrope of DMF and DMAc is 80:20. The proportion of acetic acid is about (26x80+21x20)/100 = 25.0%.

Next, acetic acid, dimethylformamide, and dimethylacet having a second azeotropic composition obtained from the bottom of the atmospheric distillation column so that the ratio of dimethylformamide/(dimethylformamide + dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9. A part of the mixture containing amide is discharged (discharge stream), and the remainder is circulated by inputting it into the high vacuum distillation column or the weak vacuum distillation column (circulating stream) (S14).

This is to recycle a part of the mixture having the second azeotropic composition obtained from the bottom of the atmospheric distillation tower by putting it into the high vacuum distillation tower or the weak vacuum distillation tower. Therefore, it may be mixed with the feed introduced into the distillation column in step S11 or S12. At this time, the second azeotropic composition can be adjusted according to the circulation ratio. In particular, the ratio of dimethylformamide/(dimethylformamide + dimethylacetamide) in the second azeotropic composition needs to be adjusted to be 0.4 to 0.9.

If the ratio of dimethylformamide/(dimethylformamide + dimethylacetamide) is less than the above range, the DMAc content in the DMF recovered at the top of the vacuum distillation tower increases, making it very difficult to meet the DMF purity standard (99.5% or more). On the other hand, when the ratio of dimethylformamide / (dimethylformamide + dimethylacetamide) exceeds the above range, the ratio of the normal pressure distillation tower bottom stream with the second azeotropic composition being discharged without being recycled increases, so that the DMF waste solution provider It is difficult to achieve the required DMF recovery rate target (over 90%).

Meanwhile, in the case of an atmospheric distillation column and a weak vacuum distillation column, a forced circulation type reboiler suitable for heat-sensitive materials such as DMF can be provided. Since these facilities can reduce the rate at which moisture generated as DMF is thermally decomposed in the reboiling section of the normal pressure distillation tower and the weak vacuum distillation tower cannot rise to the top of the tower and are swept away to the bottom stream, it is preferable to use a forced circulation type reboiler.

On the other hand, when the entire circulating stream is input into the high vacuum distillation column, the trace amount of moisture contained in the circulating stream goes to the top stream of the high vacuum distillation column. However, when part or all of the circulating stream is input into the weak vacuum distillation column, the circulating stream It can reduce the rate at which a trace amount of moisture contained in goes to the top of the high vacuum distillation tower. Therefore, it is desirable to inject part or all of the circulating stream into a weak vacuum distillation column to meet the moisture content specifications of DMF.

Hereinafter, embodiments of the present invention will be described.

[Example]

Preparation Examples 1-1 to 1-4: Confirmation of DMAc and moisture production due to thermal decomposition of DMF

After filling the water bath of the rotary evaporator with silicone oil, maintaining the bath temperature at 110 ℃, attach a 250 cc round flask filled with 100 g of mixed solution (26 g of AA acid, 74 g of DMF) to the rotary evaporator. , samples were collected at 30-minute intervals under 60 rpm conditions, and changes in the components of the mixed solution were analyzed (Preparation Example 1-1).

The same experiment was repeated at bath temperatures of 120°C (Preparation Example 1-2), 135°C (Preparation Example 1-3), and 150°C (Preparation Example 1-4), and the results are shown in FIG. 4. It can be seen that the ratio of DMAc increases rapidly as the temperature increases.

Preparation Example 2-1: Removal of water and 3-methylpyridine (3MP) from DMF waste solution

A 9600 Packed Column from B/R, USA, with a column inner diameter of 25 mm, number of theoretical plates, 45 stages, and a 5 liter heating flask was configured as shown in Figure 5, and a continuous distillation experiment was performed to remove water and 3MP from DMF waste liquid.

Actual DMF waste liquid (moisture 17.5%, AA 15.8%, DMF 64.8%, 3MP 1.8%, DMAc 0.1%) was introduced into the T2 position of the distillation device at a flow rate of 500 cc/h, the pressure was 450 torr, and the reflux ratio was ) was fixed at 4, and the load on the heating mantle was adjusted so that the 3MP content in the stream (water-free AA-DMF mixture) discharged to the bottom of the tower was maintained at about 500 ppm.

At 25 hours from the start of the injection of DMF waste liquid, the continuous distillation device reached a steady state. At this time, approximately 100 cc/h of 3MP wastewater was continuously discharged from the top of the tower, the tower bottom temperature (T5) was 150 ℃, and the tower bottom was about 400 cc/h of moisture 30 ppm and AA-DMF mixture (AA 19.1 %, DMF 80.1 %, 3MP 500 ppm, DMAc 0.7 %) were stably obtained.

Preparation Example 2-2: Removal of water and 3-methylpyridine (3MP) from DMF waste solution

It was operated in the same manner as Preparation Example 2-1, except that the vacuum pump of the distillation apparatus was turned off and the conditions were changed to normal pressure. A steady state was reached 10 hours after the pressure change. At this time, the temperature at the bottom of the tower (T5) was 160 ℃, about 400 cc/h of moisture at the bottom of the tower was 60 ppm, and the AA-DMF mixture (AA 18.8%, DMF 79.6%, 3MP 500 ppm, DMAc 1.5%) was reliably obtained. Through this, it was confirmed that as the bottom temperature of the distillation experiment device increases, both the DMAc content and the moisture content in the bottom stream tend to increase.

Preparation Example 3: Recovery of DMF and AA through vacuum and normal pressure coupled distillation experiment

Pressure swing to recover DMF and AA from an anhydrous AA-DMF mixture, respectively, by constructing two sets of 9600 Packed Columns of the US company B/R with a column inner diameter of 25 mm, number of theoretical plates, 45 stages, and a 5 liter heating flask as shown in Figure 6. Distillation experiments were performed.

Vacuum distillation of 30 ppm moisture and AA-DMF mixture (30 ppm moisture, 19.1 % AA, 80.1 % DMF, 500 ppm 3MP, 0.7 % DMAc) obtained as the bottom stream in Preparation Example 2-1 at a flow rate of 180 cc/h. It was put into the T3 position of the device, and the vacuum was set at 100 torr and the Reflux Ratio was fixed at 3. As long as the DMF stream discharged from the top does not contain AA, the stream discharged from the bottom (vacuum azeotrope) The load on the heating mantle was adjusted to keep the AA content as high as possible.

The vacuum azeotrope discharged from the bottom of the vacuum distillation device was introduced into the T2 position of the atmospheric distillation device, and the AA content in the stream discharged from the bottom of the column (atmospheric pressure azeotrope) was kept as low as possible while the Reflux Ratio was fixed at 8. The load on the heating mantle was adjusted to maintain.

Example 1: Change in recovery rate and purity according to DMF/(DMF+DMAc)

Of the bottom stream (atmospheric pressure azeotrope) of the atmospheric distillation apparatus according to Preparation Example 3, 260 cc/h was circulated to the T3 position of the vacuum distillation apparatus, and the remainder was discharged as an exhaust stream.

After 20 hours from the start of the experiment, DMF/(DMF+ DMAc)=0.84 in the normal pressure azeotrope, the amount of discharge stream was stabilized at 30 cc/h, and the top temperature (T1) of the vacuum distillation device was stabilized at 89 ℃. As a result, DMF that met the purity standards was recovered at the top of the tower at a flow rate of 125 cc/h, and the recovery rate of DMF was about 86%. Meanwhile, the top temperature (T1) of the atmospheric distillation device was stabilized at 114°C, and AA, which contained only water and did not contain DMF and met the purity standard, was recovered at a flow rate of 25 cc/h.

Example 2: Change in recovery rate and purity according to DMF/(DMF+DMAc)

Of the bottom stream (atmospheric pressure azeotrope) of the atmospheric distillation apparatus according to Preparation Example 3, the circulation amount to the T3 position of the vacuum distillation apparatus was adjusted to 310 cc/h, and the remainder was discharged as an exhaust stream.

After 17 hours from the time of circulation amount adjustment, DMF/(DMF+ DMAc=0.74 in the normal pressure azeotropic mixture, the amount of discharged stream was stabilized at 20 cc/h, and the top temperature (T1) of the vacuum distillation device continued to stabilize at 89 ℃. As a result, DMF that meets the purity standard was recovered at a flow rate of 130 cc/h to the top of the tower, and the recovery rate of DMF was about 91%. Meanwhile, the top temperature (T1) of the atmospheric distillation device continued to stabilize at 114 ℃ and was recovered to the top of the tower. AA, which contained only water and did not contain DMF and met the purity standard, was recovered at a flow rate of 30 cc/h.

Example 3: Change in recovery rate and purity according to DMF/(DMF+DMAc)

Of the bottom stream (atmospheric pressure azeotrope) of the atmospheric distillation apparatus according to Preparation Example 3, the circulation amount to the T3 position of the vacuum distillation apparatus was adjusted to 330 cc/h, and the remainder was discharged as an exhaust stream.

After 15 hours from the time of circulation amount adjustment, DMF/(DMF+ DMAc=0.60 in the normal pressure azeotropic mixture, the amount of discharged stream was stabilized at 10 cc/h, and the top temperature (T1) of the vacuum distillation device continued to stabilize at 89 ℃. DMF meeting the purity standards was recovered at the top of the tower at a flow rate of 140 cc/h, and the recovery rate of DMF was about 95%. Meanwhile, the top temperature (T1) of the atmospheric distillation device continued to stabilize at 115 ℃ and AA containing only water without DMF and meeting the purity standard was recovered at a flow rate of 30 cc/h.

Example 4: Change in recovery rate and purity according to DMF/(DMF+DMAc)

Of the bottom stream (atmospheric pressure azeotrope) of the atmospheric distillation apparatus according to Preparation Example 3, the circulation amount to the T3 position of the vacuum distillation apparatus was adjusted to 350 cc/h, and the remainder was discharged as an exhaust stream.

After 18 hours from the time of circulation amount adjustment, DMF/(DMF+ DMAc=0.39 in the normal pressure azeotropic mixture, the amount of discharged stream was stabilized at less than 10 cc/h, and the top temperature (T1) of the vacuum distillation device continued at 89 ℃. Although stabilized, DMF that did not meet the purity standard due to the increase in DMAc content at the top was recovered at a flow rate of 140 cc/h, and the recovery rate of DMF was about 97%. Meanwhile, the top temperature (T1) of the atmospheric distillation device was 115 ℃. As it continued to stabilize, AA containing only water and no DMF was recovered at a flow rate of 30 cc/h at the top.

The DMAc content in DMF, DMF recovery rate, and DMF content in AA according to DMF/(DMF+DMAc) in the normal pressure azeotropic mixtures according to Examples 1 to 4 are shown in Table 2.

Circulating amount DMF/(DMF+DMAc) During DMF
DMAc content DMF
recovery rate Among AA
DMF content Example 1 260 cc/h 0.84 Less than 0.1% 86% Not detected Example 2 310 cc/h 0.74 0.1% 91% Not detected Example 3 330 cc/h 0.60 0.3% 95% Not detected Example 4 350 cc/h 0.39 0.5% 97% Not detected

Through this, if the ratio of DMF/(DMF+DMAc) in the normal pressure azeotrope is low, there is an advantage of increasing the recovery rate of DMF, but there is a disadvantage of increasing the content of DMAc, especially when the ratio of DMF/(DMF+DMAc) is lowered. If it falls below 0.4, the DMF product specifications (purity of 99.5% or higher) are not met.

Example 5: Prediction of DMF recovery rate according to the ratio of DMF/(DMF+DMAc)

After modeling the acetic acid and dimethylformamide recovery process from DMF waste liquid as shown in Figure 3, a DMF yield prediction calculation tool was created in Microsoft Excel by reflecting the DMF thermal decomposition reaction rate, and its form is as shown in Figure 7. And using this tool, the DMF recovery rate was calculated according to the ratio of DMF/(DMF+DMAc), and the results are shown in Figure 8.

In the above, preferred embodiments of the present invention have been described, but the present invention is not limited to the specific embodiments described above, and various modifications can be made by those skilled in the art without departing from the gist of the present invention. Of course it is possible. Accordingly, the scope of the present invention should not be construed as limited to the above embodiments, but should be determined by the claims described below as well as equivalents to these claims.

Claims (9)

Injecting a waste solvent containing water, acetic acid, and dimethylformamide into a weak vacuum distillation tower, separating water at the top of the weak vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the weak vacuum distillation tower (S11);
The mixture containing acetic acid and dimethylformamide is introduced into a high vacuum distillation tower, dimethylformamide is recovered at the top of the high vacuum distillation tower, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is added to the bottom of the high vacuum distillation tower. Obtaining step (S12);
A mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is introduced into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and acetic acid, dimethylformamide, and acetic acid having a second azeotropic composition are added to the bottom of the atmospheric distillation column. and obtaining a mixture containing dimethylacetamide (S13); and
Acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained from the bottom of the atmospheric distillation tower so that the ratio of dimethylformamide / (dimethylformamide + dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9. A method for recovering acetic acid and dimethylformamide, comprising a step (S14) of discharging a part of the mixture and circulating the remainder in the high vacuum distillation column or the weak vacuum distillation column. In claim 1,
A method for recovering acetic acid and dimethylformamide, wherein the spent solvent contains 3-methylpyridine. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the bottom pressure of the weak vacuum distillation column is 700 torr or less. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the bottom pressure of the high vacuum distillation column is 200 torr or less. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the bottom pressure of the atmospheric distillation column is 700 to 1200 torr. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the recovered product from the top of the high vacuum distillation column satisfies a purity of 99.5% or more with respect to dimethylformamide. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the recovered product from the top of the atmospheric distillation column satisfies a purity of 99.5% or more with respect to acetic acid. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the weak vacuum distillation column is equipped with a forced circulation type reboiler. In claim 1,
A method for recovering acetic acid and dimethylformamide, characterized in that the atmospheric distillation column is equipped with a forced circulation type reboiler.