Recovery of acetic acid and dimethylformamide using pressure swing distillation

Abstract

The present invention relates to a method for separating and recovering acetic acid and dimethylformamide from a waste solvent, comprising the steps of: feeding a waste solvent containing water, acetic acid, and dimethylformamide into a low vacuum distillation tower, separating water at the top of the low vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the low vacuum distillation tower (S11); feeding the mixture containing acetic acid and dimethylformamide into a high vacuum distillation tower, recovering dimethylformamide at the top of the high vacuum distillation tower, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition at the bottom of the high vacuum distillation tower (S12); The present invention provides a method for recovering acetic acid and dimethylformamide, comprising the steps of: charging a mixture containing an amide into an atmospheric distillation column, recovering acetic acid at the top of the atmospheric distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition at the bottom of the atmospheric distillation column (S13); and discharging a portion of the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained at 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, and charging the remainder into the high vacuum distillation column or the low vacuum distillation column for circulation (S14).

Description

[Technical field]

[0001] The present invention relates to a method for recovering useful components from waste solvents, and more specifically, to a method for recovering the components acetic acid and dimethylformamide (DMF) by utilizing the difference in azeotropic composition between acetic acid (AA) and dimethylformamide (DMF) and dimethylacetamide (DMAc) under high vacuum and normal pressure conditions. [Background technology]

[0002] The components contained in the waste solvent (or DMF waste liquid) generated during the production of polyimide film and their typical composition are shown in Table 1 below. [Table 1]

[0003] The waste solvent is fed into a distillation tower with a large number of plates, and water and 3MP can be removed from the top of the tower, while a mixture of 20% acetic acid and 80% DMF can be obtained at the bottom of the tower.

[0004] AA and DMF form a maximum temperature azeotrope, and according to the literature, the azeotropic temperature is 159° C. under normal pressure conditions, and the azeotropic composition at this time is 26% AA and 74% DMF.

[0005] Therefore, when the mixture of AA and DMF obtained at the bottom of the column is fed back into a conventional distillation column, a portion of the DMF is recovered at the top of the column, and an azeotrope of 26% AA and 74% DMF is obtained at the bottom of the column. If the azeotrope thus obtained is fed back into a conventional distillation column, an azeotrope of the same composition is simply obtained at the top and bottom of the column.

[0006] Methods for separating azeotropes include extractive distillation, azeotropic distillation, and pressure swing distillation, and an efficient method can be selected from these depending on the characteristics of the azeotrope. However, such a selection is not possible in all cases, and even if the selected method can separate the azeotrope, it may not be economical.

[0007] In particular, as a technique for separating acetic acid and DMF, Patent Document 1 presents a method for separating acetic acid and dimethylformamide using toluene, which forms an azeotropic mixture with acetic acid but not with dimethylformamide, as an azeotropic agent, and Patent Document 2 presents a method for removing carboxylic acid from a tertiary amide-containing solution by contacting a solution containing carboxylic acid and tertiary amide with an extraction medium containing trilaurylamine. However, the above-mentioned conventional techniques require a third component, are less economical, and have insufficient efficiency in the separation process, so a complementary separation technique is needed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japan Patent No. 2002-363150 [Patent Document 2] Korea Patent No. 10-2010-0130219 Summary of the Invention [Problem to be solved by the invention]

[0009] The method for recovering acetic acid and dimethylformamide according to the present invention has been devised to solve the above-mentioned problems, A step (S11) of feeding a waste solvent containing water, acetic acid, and dimethylformamide into a low vacuum distillation tower, separating water at the top of the low vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the low vacuum distillation tower; a step (S12) of feeding the mixture containing acetic acid and dimethylformamide into a high vacuum distillation column, recovering dimethylformamide at the top of the high vacuum distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition at the bottom of the high vacuum distillation column; Feeding the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition into an atmospheric distillation column, recovering acetic acid at the top of the atmospheric distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition at the bottom of the atmospheric distillation column (S13); and The object of the present invention is to provide a method for recovering acetic acid and dimethylformamide, comprising: a step (S14) of discharging a part of a mixture containing acetic acid, dimethylformamide, and dimethylacetamide and having a second azeotropic composition obtained at 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, and feeding the remainder into the high vacuum distillation column or the low vacuum distillation column for circulation.

[0010] The present invention also has an object to achieve the above-mentioned clear objects, as well as other objects that can be easily conceived by a person skilled in the art from the general technology of the present specification. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the method for recovering acetic acid and dimethylformamide of the present invention comprises the steps of: A step (S11) of feeding a waste solvent containing water, acetic acid, and dimethylformamide into a low vacuum distillation tower, separating water at the top of the low vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the low vacuum distillation tower; a step (S12) of feeding the mixture containing acetic acid and dimethylformamide into a high vacuum distillation column, recovering dimethylformamide at the top of the high vacuum distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition at the bottom of the high vacuum distillation column; Feeding the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition into an atmospheric distillation column, recovering acetic acid at the top of the atmospheric distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition at the bottom of the atmospheric distillation column (S13); and The method includes a step (S14) of discharging a part of the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained at 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, and feeding the remainder into the high vacuum distillation column or the low vacuum distillation column for circulation.

[0012] In addition, in the second azeotropic composition, the ratio of dimethylformamide / (dimethylformamide+dimethylacetamide) may be 0.6 to 0.8.

[0013] The waste solvent may also contain 3-methylpyridine.

[0014] The low vacuum distillation column may have a bottom pressure of 700 torr or less, 600 torr or less, or 500 torr or less.

[0015] The bottom pressure of the high vacuum distillation column may be 200 torr or less, 150 torr or less, or 100 torr or less.

[0016] Furthermore, the bottom pressure of the atmospheric distillation column may be 700 to 1200 torr, 700 to 1000 torr, or 700 to 900 torr.

[0017] The product recovered from the top of the high vacuum distillation column may have a purity of 99.5% or more with respect to dimethylformamide.

[0018] The top recovery product 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.

[0019] The overhead recovery product of the high vacuum distillation column may be free of acetic acid.

[0020] The product recovered from the top of the atmospheric distillation column has a purity of 99.5% or more with respect to acetic acid.

[0021] The water content of the overhead recovery product of the atmospheric distillation tower may be 1 wt % or less, 0.8 wt % or less, or 0.6 wt % or less.

[0022] The low vacuum distillation column may also be equipped with a forced circulation reboiler.

[0023] The atmospheric distillation column may also be equipped with a forced circulation type reboiler. Effect of the Invention

[0024] According to the method for recovering acetic acid and dimethylformamide of the present invention, high-purity dimethylformamide can be recovered from waste solvent via pressure swing distillation, and at the same time, dimethylformamide or acetic acid or an aqueous solution of acetic acid that is free of impurities can be economically recovered. [Brief description of the drawings]

[0025] [Figure 1] 1 is a graph showing changes in the azeotropic composition of AA and DMF, and AA and DMAc depending on the pressure. [Diagram 2] 1 is a graph showing changes in boiling point of DMAc and DMF depending on pressure. [Diagram 3] FIG. 1 is a process diagram for recovering DMF from DMF waste liquid according to one embodiment of the present invention. [Figure 4]This is the result of measuring the DMF thermal decomposition reaction rate according to temperature and residence time in an oil bath. [Diagram 5] FIG. 2 is a distillation experimental process diagram for removing water and 3-methylpyridine from DMF waste liquid according to one embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing a distillation experiment using a vacuum distillation tower and an atmospheric distillation tower in combination according to an embodiment of the present invention. [Figure 7] FIG. 1 shows a prediction calculation tool for DMF yield reflecting the DMF thermal decomposition reaction rate. [Figure 8] This shows the results of calculating the DMF recovery rate based on the ratio of DMF / (DMF+DMAc). BEST MODE FOR CARRYING OUT THEINVENTION

[0026] Preferred embodiments of the present invention will now be described in detail.

[0027] However, the following will be described in detail by way of example of a specific embodiment, and since the present invention can be modified in various ways and can have various forms, the present invention is not limited to the specific embodiment exemplified. It should be understood that the present invention includes all modifications, equivalents, or alternatives falling within the spirit and technical scope of the present invention.

[0028] In the following description, many specific details such as specific components are described, but these are provided to facilitate a more comprehensive understanding of the present invention, and it will be obvious to those skilled in the art that the present invention can be implemented without these specific details. In describing the present invention, if a detailed description of related known functions or configurations is deemed to unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0029] In addition, the terms used in this application are merely used to describe a particular embodiment and are not intended to limit the present invention. Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by a person having ordinary knowledge in the technical field to which this invention belongs. Terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and unless expressly defined in this application, they should not be interpreted as ideal or overly formal.

[0030] In this application, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0031] In this application, terms such as first, second, etc. may be used to describe various components, but the components are not limited by the terms. The terms are used only to distinguish one component from another. For example, the first component may be named the second component, and the second component may be named the first component, without departing from the scope of the present invention.

[0032] In this application, terms such as "comprise," "contain," or "have" refer to the presence of features, components (or constituents), etc. described in the specification, but do not imply that one or more other features, components, etc. are not present or cannot be added.

[0033] In this specification, % may be wt %.

[0034] Considering the change in the composition ratio of the azeotropic mixture of acetic acid (AA) and dimethylformamide (DMF) due to pressure as shown in Figure 1, when the pressure at the bottom of the low-pressure distillation column is operated at 200 torr or less and the pressure at the bottom of the high-pressure distillation column is operated at 700 torr or more, it is expected that the difference between the azeotropic compositions required for pressure swing distillation (5% or more based on AA) will be secured and AA and DMF will be smoothly recovered. Therefore, based on the concept of pressure swing distillation, a diagram of the process for recovering DMF and AA from DMF waste liquid can be derived as shown in Figure 3.

[0035] However, when an attempt was made to feed a mixture of AA and DMF into a pressure swing distillation process to recover each of the useful components, thermal decomposition of DMF occurred in the section of the high-pressure distillation tower where the temperature reached 155°C or higher, and the thermal decomposition products dimethylacetamide (DMAc) and moisture were generated, making it uncertain whether the DMF and AA recovered at the top of the tower would meet their respective product specifications and whether it would be possible to economically recover them.

[0036] As shown in Figure 4, DMF, a heat-sensitive substance, begins to decompose at about 100°C, and the higher the temperature, the greater the decomposition, with the degree of decomposition tending to double for every 10°C increase in temperature. As shown in Reaction Scheme 1 below, DMF is thermally decomposed into dimethylamine (DMA) and carbon monoxide (CO), and dimethylamine combines again with the surrounding acetic acid to produce dimethylacetamide (DMAc) and water. At this time, the amount of water produced can be indirectly calculated as 18 / 87 = 20.7% of the amount of DMAc produced.

[0037] (Reaction Scheme 1) [ka]

[0038] The internal temperature of the high vacuum distillation tower is mostly below 110°C, so there is almost no thermal decomposition of DMF and almost no water generation, but the water generated by thermal decomposition in the atmospheric distillation tower, which has a relatively high internal temperature, not only increases the water content of the acetic acid recovered at the top of the atmospheric distillation tower by several thousand ppm, but the water content of the bottom stream of the atmospheric distillation tower (the recycle stream in Figure 3) can also reach several tens of ppm. Although the amount of water associated with such a recycle stream is small, it is the main cause of the increase in the water content of the DMF recovered at the top of the high vacuum distillation tower, and it may become difficult to meet the water content standard for DMF.

[0039] The present invention clearly identifies the problems caused by such thermal decomposition that occur during pressure swing distillation and derives a method for overcoming these problems. It then aims to present the configuration, operating conditions, and method of a pressure swing distillation process that can economically and at a high yield recover DMF that meets the DMF product standard of "purity of 99.5% or more, moisture content of 200 ppm or less" and AA that meets the AA product standard of "purity of 99.5% or more, moisture content of 1% or less" from DMF waste liquid containing AA and DMF.

[0040] The method for recovering acetic acid and dimethylformamide of the present invention includes the steps of: charging a waste solvent containing water, acetic acid, and dimethylformamide into a low vacuum distillation tower, separating water at the top of the low vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the low vacuum distillation tower (S11); charging the mixture containing acetic acid and dimethylformamide into a high vacuum distillation tower, recovering dimethylformamide at the top of the high vacuum distillation tower, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition at the bottom of the high vacuum distillation tower (S12); and a step (S14) of discharging a part of the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained at 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, and charging the remainder into the high vacuum distillation column or the low vacuum distillation column for circulation.

[0041] Each step will be described in detail below with reference to FIG.

[0042] First, waste solvent containing water, acetic acid, and dimethylformamide is charged into a low vacuum distillation column, water is separated at the top of the low vacuum distillation column, and a mixture containing acetic acid and dimethylformamide is obtained at the bottom of the low vacuum distillation column (S11).

[0043] The waste solvent to be treated in the present invention contains water, acetic acid, and dimethylformamide, and may further contain 3-methylpyridine (3MP), and may be, for example, a waste solvent generated during the production of polyimide films for semiconductors and displays.

[0044] Step (S11) may be a step of removing substances other than the carboxylic acid and the amide compound which are the target of separation in the present invention. Specifically, it may be a step of feeding a waste solvent containing water, a carboxylic acid, and an amide compound into a distillation column before step (S12), separating water and 3-methylpyridine at the top of the distillation column, and obtaining a mixture containing a carboxylic acid and an amide compound at the bottom of the distillation column.

[0045] At this time, the bottom pressure of the low vacuum distillation tower may be 700 torr or less, 600 torr or less, or 500 torr or less. As in the high vacuum distillation tower, most of the moisture generated by thermal decomposition in the low vacuum distillation tower rises to the top, but a part of it flows in the bottom stream and rises to the top of the high vacuum distillation tower, which may affect the moisture content of DMF. When the bottom pressure of the low vacuum distillation tower is 700 torr or less or in the above bottom pressure range, the temperature of the bottom stream having a composition of 20% AA and 80% DMF does not exceed 150°C, so the moisture content of the bottom stream is 40 ppm or less, and the increase in the moisture content of DMF, which is the top stream of the high vacuum distillation tower, is 50 ppm or less, which is within the range where the moisture standard can be met.

[0046] Next, the mixture containing acetic acid and dimethylformamide recovered at the bottom of the low vacuum distillation column in the above step (S11) is charged into a high vacuum distillation column, dimethylformamide is recovered at the top of the high vacuum distillation column, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is obtained at the bottom of the high vacuum distillation column (S12).

[0047] In this case, 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 the pressure in this range is sufficiently different from the azeotropic composition ratio under normal pressure, making it possible to separate components by pressure swing distillation. The lower limit is not particularly limited, but the efficiency and economy of the process should be taken into consideration.

[0048] The top recovery product of the high vacuum distillation tower may have a purity of 99.5% or more with respect to dimethylformamide. In addition, the top recovery product 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 may not contain acetic acid. In addition, the top recovery product of the high vacuum distillation tower may have a DMAc content of less than 0.5 wt%, less than 0.3 wt%, or less than 0.1 wt%.

[0049] A mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition is obtained at the bottom of the high vacuum distillation column. The composition ratio of the azeotropic mixture 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 ratio of the DMF and AA azeotrope is 34%, and the acetic acid ratio of the DMAc and AA azeotrope is 28%, but the acetic acid ratio of the azeotropic mixture in which the ratio of DMF and DMAc is 80:20 is about (34 x 80 + 28 x 20) / 100 = 32.8%.

[0050] Next, the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition is charged into an atmospheric distillation column, acetic acid is recovered at the top of the atmospheric distillation column, and a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition is obtained at the bottom of the atmospheric distillation column (S13).

[0051] At this time, the bottom pressure of the atmospheric distillation tower may be 700 to 1200 torr, 700 to 1000 torr, or 700 to 900 torr. In the case of the atmospheric distillation tower located next to the high vacuum distillation tower, the higher the bottom pressure, the greater the pressure difference with the high vacuum distillation tower, making it easier to separate acetic acid and dimethylformamide, but if the bottom pressure exceeds 1000 torr or the above range, as shown in Figure 2, the boiling point of DMF is 165 ° C, the azeotropic temperature of DMF and AA exceeds 170 ° C, the thermal decomposition rate of DMF increases by more than twice compared to atmospheric pressure, and the water content of acetic acid recovered at the top of the atmospheric distillation tower increases significantly, which may make it difficult to meet the standard (1% or less).

[0052] The overhead recovery product of the atmospheric distillation tower may have a purity of 99.5% or more with respect to acetic acid, may be free of dimethylformamide, and may have a water content of 1 wt% or less, 0.8 wt% or less, or 0.6 wt% or less.

[0053] 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 Fig. 1, the acetic acid ratio of the azeotropic mixture of DMF and AA at atmospheric pressure (760 torr) is 26%, and the acetic acid ratio of the azeotropic mixture of DMAc and AA is 21%, but the acetic acid ratio of the azeotropic mixture of DMF and DMAc with a ratio of 80:20 is about (26 x 80 + 21 x 20) / 100 = 25.0%.

[0054] Next, a part of the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained at the bottom of the atmospheric distillation column is discharged (discharge stream), and the remainder is charged into the high vacuum distillation column or the low vacuum distillation column (circulation stream) and circulated (S14) so ​​that the ratio of dimethylformamide / (dimethylformamide+dimethylacetamide) in the second azeotropic composition is 0.4 to 0.9.

[0055] In this method, a part of the mixture having the second azeotropic composition obtained at the bottom of the atmospheric distillation column is fed to the high vacuum distillation column or the low vacuum distillation column for recirculation. Therefore, it can be mixed and fed together with the feed fed to the distillation column in step (S11) or (S12). At this time, the second azeotropic composition can be adjusted according to the circulation ratio, and in particular, it is necessary to adjust the ratio of dimethylformamide / (dimethylformamide+dimethylacetamide) in the second azeotropic composition to 0.4 to 0.9.

[0056] 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, if the ratio of dimethylformamide / (dimethylformamide + dimethylacetamide) exceeds the above range, the proportion of the bottom stream of the atmospheric distillation tower having the second azeotropic composition that is discharged without being recycled increases, making it difficult to achieve the DMF recovery rate target (90% or more) required by the DMF waste liquid provider.

[0057] Meanwhile, atmospheric distillation towers and low vacuum distillation towers can be equipped with forced circulation reboilers suitable for heat-sensitive materials such as DMF. This type of equipment is preferable because it prevents the water generated by the thermal decomposition of DMF in the reboiling section of the atmospheric distillation tower and low vacuum distillation tower from rising to the top of the tower and reduces the amount of water that flows into the bottom stream.

[0058] On the other hand, when the entire amount of the circulating stream is fed to the high vacuum distillation tower, the trace amount of water contained in the circulating stream will go to the top stream of the high vacuum distillation tower, but when a part or all of the circulating stream is fed to the low vacuum distillation tower, the proportion of the trace amount of water contained in the circulating stream that goes to the top stream of the high vacuum distillation tower can be reduced. Therefore, it is preferable to feed a part or all of the circulating stream to the low vacuum distillation tower in order to meet the water content standard of DMF.

[0059] Examples of the present invention will now be described. Working Example Production Examples 1-1 to 1-4: Confirmation of the generation of DMAc and water by thermal decomposition of DMF After filling the water bath of the rotary evaporator with silicone oil, a 250 cc round-bottom flask filled with 100 g of the mixture (AA acid 26 g, DMF 74 g) was attached to the rotary evaporator while maintaining the bath temperature at 110°C. Samples were then taken at 30 minute intervals under 60 rpm conditions, and the compositional changes of the mixture were analyzed (Production Example 1-1).

[0060] The same experiment was repeated at bath temperatures of 120°C (Production Example 1-2), 135°C (Production Example 1-3), and 150°C (Production Example 1-4), and the results are shown in Figure 4. It can be seen that the proportion of DMAc increases rapidly as the temperature increases.

[0061] Production Example 2-1: Removal of water and 3-methylpyridine (3MP) from DMF waste liquid A 9600 Packed Column manufactured by B / R, USA, equipped with a column inner diameter of 25 mm, 45 theoretical plates, and a 5-liter heating flask, was configured as shown in Figure 5, and a continuous distillation experiment was conducted to remove water and 3MP from DMF waste liquid.

[0062] Actual DMF waste liquid (water content 17.5%, AA 15.8%, DMF 64.8%, 3MP 1.8%, DMAc 0.1%) was fed into the T2 position of the distillation apparatus at a flow rate of 500 cc / h, and with the pressure fixed at 450 torr and the reflux ratio fixed at 4, the load on the heating mantle was adjusted so that the 3MP content in the stream discharged to the bottom (anhydrous AA-DMF mixture) was maintained at approximately 500 ppm.

[0063] 25 hours after the start of the DMF waste liquid introduction, the continuous distillation apparatus reached a normal state. At this time, about 100 cc / h of 3MP waste water was continuously discharged from the top of the tower, the tower bottom temperature (T5) was 150°C, and about 400 cc / h of water with 30 ppm and AA-DMF mixture (AA 19.1%, DMF 80.1%, 3MP 500 ppm, DMAc 0.7%) were stably obtained from the bottom of the tower.

[0064] Production Example 2-2: Removal of water and 3-methylpyridine (3MP) from DMF waste liquid The operation was performed in the same manner as in Example 2-1, but the vacuum pump of the distillation apparatus was turned off and the conditions were changed to normal pressure. 10 hours after the pressure change, the normal state was reached, at which point the bottom temperature (T5) was 160°C, and about 400cc / h of water 60ppm and AA-DMF mixture (AA 18.8%, DMF 79.6%, 3MP 500ppm, DMAc 1.5%) were stably obtained at the bottom. This confirmed that the DMAc content and water content in the bottom stream tend to increase as the bottom temperature of the distillation experimental apparatus increases.

[0065] Production Example 3: Recovery of DMF and AA in a vacuum and atmospheric pressure combined distillation experiment Two sets of 9600 Packed Columns (manufactured by B / R, USA) equipped with a column inner diameter of 25 mm, 45 theoretical plates, and a 5-L heating flask were configured as shown in Figure 6, and a pressure swing distillation experiment was performed to recover DMF and AA from an anhydrous AA-DMF mixture.

[0066] In the above Production Example 2-1, the water content of 30 ppm obtained in the bottom stream and the AA-DMF mixture (water content 30 ppm, AA 19.1%, DMF 80.1%, 3MP 500 ppm, DMAc 0.7%) were fed into the T3 position of the vacuum distillation apparatus at a flow rate of 180 cc / h, and with the vacuum set at 100 torr and the reflux ratio fixed at 3, the load on the heating mantle was adjusted so that the DMF stream discharged to the top did not contain AA and the AA content in the stream discharged to the bottom (vacuum azeotrope) was kept as high as possible.

[0067] The vacuum azeotrope discharged to the bottom of the vacuum distillation apparatus was fed to the atmospheric distillation apparatus at position T2, and with the reflux ratio fixed at 8, the heating mantle load was adjusted so that the AA content in the stream discharged to the bottom (atmospheric azeotrope) was kept as low as possible.

[0068] Example 1: Changes in recovery rate and purity with DMF / (DMF+DMAc) Of the bottom stream (atmospheric azeotropic mixture) of the atmospheric distillation apparatus in Preparation Example 3, 260 cc / h was recycled to the T3 position of the vacuum distillation apparatus, and the remainder was discharged to the discharge stream.

[0069] After 20 hours had elapsed since the start of the experiment, the atmospheric azeotropic mixture had a DMF / (DMF+DMAc) ratio of 0.84, the amount of discharged stream was stabilized at 30cc / h, the top temperature (T1) of the vacuum distillation unit was stabilized at 89°C, DMF that met the purity standard was recovered at the top at a flow rate of 125cc / h, and the DMF recovery rate was approximately 86%. Meanwhile, the top temperature (T1) of the atmospheric distillation unit was stabilized at 114°C, and AA that did not contain DMF but only water and met the purity standard was recovered at a flow rate of 25cc / h.

[0070] Example 2: Changes in recovery rate and purity with DMF / (DMF+DMAc) Of the bottom stream (atmospheric azeotropic mixture) of the atmospheric distillation apparatus in Production Example 3, the amount recycled to the T3 position of the vacuum distillation apparatus was adjusted to 310 cc / h, and the remainder was discharged to the discharge stream.

[0071] After 17 hours had passed since the circulation rate was adjusted, the atmospheric azeotropic mixture had a DMF / (DMF+DMAc) ratio of 0.74, the discharge stream generation rate was stabilized at 20cc / h, the top temperature (T1) of the vacuum distillation apparatus continued to stabilize at 89°C, DMF that met the purity standard was recovered at the top at a flow rate of 130cc / h, and the DMF recovery rate was about 91%. Meanwhile, the top temperature (T1) of the atmospheric distillation apparatus continued to stabilize at 114°C, and AA that did not contain DMF but only water and met the purity standard was recovered at a flow rate of 30cc / h at the top.

[0072] Example 3: Changes in recovery rate and purity with DMF / (DMF+DMAc) Of the bottom stream (atmospheric azeotropic mixture) of the atmospheric distillation apparatus in Production Example 3, the amount recycled to the T3 position of the vacuum distillation apparatus was adjusted to 330 cc / h, and the remainder was discharged to the discharge stream.

[0073] After 15 hours had passed since the circulation rate was adjusted, the atmospheric azeotropic mixture had a DMF / (DMF+DMAc) ratio of 0.60, the discharge stream generation rate was stabilized at 10cc / h, the top temperature (T1) of the vacuum distillation apparatus continued to stabilize at 89°C, DMF that met the purity standard was recovered at the top at a flow rate of 140cc / h, and the DMF recovery rate was about 95%. Meanwhile, the top temperature (T1) of the atmospheric distillation apparatus continued to stabilize at 115°C, and AA that did not contain DMF but only water and met the purity standard was recovered at a flow rate of 30cc / h at the top.

[0074] Example 4: Changes in recovery rate and purity with DMF / (DMF+DMAc) Of the bottom stream (atmospheric azeotropic mixture) of the atmospheric distillation apparatus in Production Example 3, the amount recycled to the T3 position of the vacuum distillation apparatus was adjusted to 350 cc / h, and the remainder was discharged to the discharge stream.

[0075] After 18 hours had passed since the circulation rate was adjusted, the DMF / (DMF+DMAc) ratio in the atmospheric azeotrope was 0.39, the amount of discharged stream was stabilized at less than 10cc / h, and the top temperature (T1) of the vacuum distillation unit continued to stabilize at 89°C, but the DMAc content in the top increased, and DMF not meeting the purity standard was recovered at a flow rate of 140cc / h, with a DMF recovery rate of about 97%. Meanwhile, the top temperature (T1) of the atmospheric distillation unit continued to stabilize at 115°C, and AA containing only water, but not DMF, was recovered at a flow rate of 30cc / h.

[0076] The DMAc content in DMF, DMF recovery rate, and DMF content in AA of DMF / (DMF+DMAc) in the atmospheric pressure azeotropic mixture in Examples 1 to 4 are shown in Table 2. [Table 2]

[0077] As a result, when the DMF / (DMF+DMAc) ratio in the atmospheric pressure azeotrope is low, it has the advantage of increasing the DMF recovery rate, but it has the disadvantage of increasing the DMAc content. In particular, when the DMF / (DMF+DMAc) ratio is less than 0.4, it does not meet the DMF product specification (purity of 99.5% or more).

[0078] Example 5: Prediction of DMF recovery by DMF / (DMF+DMAc) ratio After modeling the process of recovering acetic acid and dimethylformamide from DMF waste liquid as shown in Figure 3, a DMF yield prediction calculation tool was created in Microsoft Excel reflecting the DMF thermal decomposition reaction rate, and its format is shown in Figure 7. Then, using this tool, the DMF recovery rate according to the ratio of DMF / (DMF+DMAc) was calculated, and the result is shown in Figure 8.

[0079] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the specific embodiment described above, and it is obvious that those skilled in the art can make various modifications without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited to the above embodiment, but should be determined not only by the claims described below, but also by equivalents to the claims.

Claims

1. Feeding the waste solvent containing water, acetic acid, and dimethylformamide into a low vacuum distillation tower, separating water at the top of the low vacuum distillation tower, and obtaining a mixture containing acetic acid and dimethylformamide at the bottom of the low vacuum distillation tower (S11); Feeding the mixture containing acetic acid and dimethylformamide into a high vacuum distillation column, recovering dimethylformamide at the top of the high vacuum distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a first azeotropic composition at the bottom of the high vacuum distillation column (S12); Feeding the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having the first azeotropic composition into an atmospheric distillation column, recovering acetic acid at the top of the atmospheric distillation column, and obtaining a mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition at the bottom of the atmospheric distillation column (S13); and A step (S14) of discharging a part of the mixture containing acetic acid, dimethylformamide, and dimethylacetamide having a second azeotropic composition obtained at 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, while charging the remainder into the high vacuum distillation column or the low vacuum distillation column for circulation; A method for recovering acetic acid and dimethylformamide comprising the steps of:

2. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the waste solvent contains 3-methylpyridine.

3. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the bottom pressure of the low vacuum distillation column is 700 torr or less.

4. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the bottom pressure of the high vacuum distillation column is 200 torr or less.

5. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the bottom pressure of the atmospheric distillation column is 700 to 1,200 torr.

6. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the top recovery product of the high vacuum distillation column has a purity of 99.5% or more with respect to dimethylformamide.

7. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the top recovery product of the atmospheric distillation column has a purity of 99.5% or more with respect to acetic acid.

8. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the low vacuum distillation column is equipped with a forced circulation type reboiler.

9. 2. The method for recovering acetic acid and dimethylformamide according to claim 1, wherein the atmospheric distillation column is equipped with a forced circulation type reboiler.

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