KR20050016671A - Purification of n,n-dimethylacetamide - Google Patents

Abstract

The present invention relates to a method for purifying N, N-dimethylacetamide (DMAc) from an aqueous solution containing acetic acid as an impurity. Two fractional distillation columns are arranged in series. A solution containing impurities is fed to the first column having a temperature gradient which causes the acetic acid to be distributed to the top water. The bottom residue of the first column is recycled to the first column or fed to the second column to recover DMAc free of acetic acid impurities, and the remaining DMAc and acetic acid are fed back to the first column for further separation. The process of the present invention does not require complex solvent extraction and / or chromatographic separation using standard fractional distillation methods and apparatus.

Description

Purification of N, N-dimethylacetamide {PURIFICATION OF N, N-DIMETHYLACETAMIDE}

The present invention relates to a continuous distillation process for purifying N, N-dimethylacetamide from a water-N, N-dimethylacetamide mixture in which acetic acid is present as an impurity.

Distillation, a method of separating the solution components, depends on the distribution of the components between the gas phase and the liquid phase. The gas phase is separated by evaporation in the liquid phase and new liquid phases with different constituents are produced by condensation from the gas phase.

Continuous distillation is a relatively simple and commonly used method for separating volatile components of a mixture by boiling point differences. Continuous distillation consists of a number of ideal distillation stages in which the liquid and gas phases come into contact together. The components of the liquid and gas phases are redistributed by condensation and evaporation, and the new liquid and gas phases of the other components leave the stage.

Although there is little component change in one step, many steps increase the overall component change and a pure component product can be formed.

Continuous distillation is performed using a column designed to facilitate contacting the liquid and gas phases by increasing the condensation surface. For example, the column can be combined with distillation components such as laminar plates, bubble caps, and tray valves to easily approach the ideal stage. Column incorporation, for example irregular filling or structural filling, does not have a clearly defined ideal step but is generally used for continuous distillation.

A common structure for a continuous distillation process is a distillation column with a single condenser above the column and a single reheater below the column. The raw material is fed into the middle of the column. The high boiling component is removed as bottom product in the reheating step. The low boiling component is removed with distillate in the condensation step. Part of the distillate returns back to the top of the column (ie reflux). The reflux liquid contacts the vapor from the reheater through the column to facilitate separation.

The design and size design of the apparatus for continuous distillation is known.

Each design is tailored to the individual components and their unique evaporation properties.

In the case of a mixture of N, N-dimethylacetamide (DMAc) and water, the separation of the two components is simple because of the large difference in boiling points. The boiling point of DMAc under atmospheric pressure is 166 ° C. and the boiling point of water under atmospheric pressure is 100 ° C. In the continuous distillation of water and DMAc mixture, water will collect as distillate in the condenser and DMAc will remain at the bottom of the heater.

Acetic acid is often present as an impurity in a mixture of DMAc and water. This is because acetic acid and dimethylamine (DMA) are formed when DMAc is decomposed. Alternatively, acetic acid can be used as a solvent for the synthesis of DMAc.

Although the boiling point of acetic acid is 118 ° C., which is sufficiently different from that of DMAc, it is not easy to separate acetic acid from DMAc. This is due to the effects of hydrogen bonds, which, when acetic acid is present, acts as a base and attracts acetic acid strongly. DMAc and acetic acid form a high boiling azeotropic mixture, defined as two or more liquids whose composition does not change by distillation. More specifically, the boiling point of the 21% acetic acid and 79% DMAc azeotropic mixture is about 171 ° C. under atmospheric pressure.

A typical continuous distillation structure cannot separate the mixture into two pure components from the azeotropic mixture. One of the products of the distillation column is close to the azeotropic mixture composition. The high-boiling azeotrope, if present, will gather into the bottom product of the reheater. The low boiling azeotrope will, if produced, collect in the distillate product of the condenser.

When a mixture of water, DMAc, and acetic acid is fed to a conventional distillation column structure, acetic acid forms azeotropic mixture of DMAc and high boiling point and thus separates down the column to contaminate DMAc.

Removing DMAc as lateral exhaust steam at or near the bottom of the column is not an effective solution. Acetic acid is concentrated near the bottom, close to the actual DMAc-acetic acid azeotrope. The vapor of the azeotrope moves over the column and contaminates the side-exhaust DMAc vapor. The acetic acid concentration at the bottom of the column can be well controlled to a lower concentration than the azeotrope by purging the column bottom. However, the large loss of DMAc results in undesirable results. When distilling the bottom DMAc product to remove DMAc as the top product in the second distillation column, the bottom of the second column must be purged again to lower the acetic acid below the azeotropic mixture composition, again resulting in significant loss of DMAc component.

French Patent No. 1,549,711 discloses a method for changing the composition of an azeotropic mixture by feeding DMAc and acetic acid, from which the bottom product of the second column, substantially the third component of water, is dried, to a third column and operated at different pressures. . However, this method requires additional cost and processing for the third column. In addition, this system has not been published for the separation of DMAc, water, and acetic acid.

Therefore, it is an object of the present invention to overcome the above problems.

1 is a schematic diagram of a system of the present invention.

     1A-1P illustrate various structures of the system of the invention of FIG.

2 is a temperature graph of each stage used in the system of the present invention.

The present invention relates to a method for separating N, N-dimethylacetamide (DMAc) from an aqueous N, N-dimethylacetamide (DMAc) solution containing acetic acid. The first distillation column includes a top and a bottom portion for the feed port. The bottom part is divided into upper, middle and lower bottom part. The solution is fed to the first distillation column through a side feed port located in the middle of the column.

The gradient of the column temperature is controlled such that the bottom bottom of the column is substantially dry and the top bottom of the column is substantially wet and acetic acid is distributed between the top distillate and bottom product. The bottom product of the first distillation column is fed to the feed port of the second distillation column so that purified DMAc is distilled to the stream above the column and DMAc and acetic acid remain as the bottom stream. The bottom stream from the second column is fed to the inlet port of the first column to distribute additional acetic acid from the DMAc and acetic acid mixture over the first column, so that substantially all of the acetic acid in the original feed is above the first column. Distilled to stream. Purified DMAc is recovered to the upper fraction of the second column.

In another embodiment, the present invention is directed to an apparatus for separating a fluid component into a raw material solution. The apparatus of the present invention has a first distillation column and a second distillation column connected thereto. The first distillation column has a supply port for the solution, a condenser for the distillation stream above the column, a reheater for the bottom stream, and an outlet port; The column includes a top and a bottom, and the bottom is divided into upper, middle and lower bottoms. The second distillation column comprises a feed port for the bottom stream of the first column, a condenser for the stream over the distilled column and a reheater for the bottom stream. The pump causes the bottom product stream from the second column to return to the feed port of the first column.

The reflux unit of the first column and the control unit on the first column reheater adjust the temperature gradient of the column so that the lowest boiling component is substantially free from the bottom of the bottom of the first column and the top of the top of the bottom of the first column. Make this low ingredient rich. The temperature gradient can be controlled by supplying a heat source to the reheater or by adjusting the flow rate of the reflux back to the column.

In another embodiment, the present invention relates to a process for separating and purifying DMAc from acetic acid in an aqueous solution, wherein the solution is first prepared under conditions sufficient to distill the acetic acid from the first column and form a dry, non-distilled bottom product. It consists of feeding to a distillation column. The bottom product of the first column is pumped back to the inlet port of the first column, and also the purified DMAc as distillate from the second column and the product of the non-distilled bottom of the second column containing DMAc and acetic acid It is fed back to the column and into the feed port of the second distillation column under conditions sufficient to be partitioned into aqueous acetic acid solution and DMAc. Returning the product of the second column bottom to the first column can also be done through the nominally middle feed port of the first column, the bottom reheater, or other inlet port. The product of the bottom pumped back to the first column can be fed to a supply port nominally located in the middle or to another inlet port located at the top or bottom of the first column. Purified DMAc is recovered as distillate from the second column.

The present invention also relates to a method for purifying a high boiling point component from a solution of a low boiling point component contaminated with a high boiling point component and a third component forming a high boiling point binary azeotropic mixture. The solution is substantially free of low boiling point components at the bottom of the column, rich in low boiling point components at the top of the first column and the first distillation column at a temperature gradient sufficient to distribute the third component to the distillate of the first column. The supply port is located in the nominal middle of the supply port. The product of the non-distilled bottom of the first column is fed from the second column to the second distillation column under conditions sufficient to distill the high boiling component into the pure component. The non-distilled bottoms product of the first column may also be fed to the feed port or other inlet port of the first column. The product of the non-distilled bottom of the second column comprises a mixture of the high boiling component and the third component and is fed to the feed port or other inlet port of the first column and partitioned into the low and high boiling components. The method of the present invention is generally applicable when the low boiling point component relaxes the azeotrope of the high boiling point component with the third component.

These and other embodiments of the invention are described in more detail by the following figures, detailed description and examples.

The method of the present invention is to separate acetic acid as an impurity from an aqueous N, N-dimethylacetamide (DMAc) solution. The process of the invention is a continuous distillation technique using a double column apparatus.

The method of the present invention is an effective, accurate and reproducible separation method that does not require complicated solvent extraction and / or chromatography or spectral separation and can separate DMAc components with high recovery and high purity.

In FIG. 1, the first 10 and second 20 fractional distillation columns are arranged one after the other. The first column 10 is divided into a top 12 and a bottom 16 and includes a feed port 17 and a discharge port 18. The exact location of feed port 17 is determined by the optimal design, as known to those skilled in the art, and need not be the middle of the column. Thus, feed port 17 is said to be located nominally in the middle of column 10. Bottom 16 is subdivided into top bottom 16a, mid-bottom 16b, and bottom bottom 16c. The number of steps that make up the top 12 and the bottom 16 depends on the particular column design and apparatus, as known to those skilled in the art. Examples of such parameters include raw material composition, reflux rate, and the like. The second column 20 is arranged such that the effluent of the first column 10 enters the feed port 27 of the second column 20. The product of the second column bottom is discharged to discharge port 28.

The first column 10 includes a condenser 11 above it and a reheater 13 below it. The second column 20 also includes a condenser 21 above it and a reheater 23 below it. The fluid flowing out of outlet port 18 of the first column 10 can be pumped directly to the feed port 27 of the second column 20. Alternatively, the fluid exiting the outlet port 18 of the first column 10 may pass through the reheater 23 into the second column 20. The fluid discharged from the outlet port 28 of the second column 20 is pumped back into the feed port 17 of the first column 10.

In general, the acetic acid introduced into DMAc-water feed 8 is controlled using a two column apparatus to control the moisture content of the upper bottom 16a of the first column 10 through the pumping circulation of the DMAc and acetic acid bottom products. Use both to purge. More specifically, in FIG. 1, the mixture of aqueous DMAc solution to be purified is introduced into the first distillation column 10 as raw material 8. The temperature of column 10 is controlled to contain water in the top bottom 16a of column 10 and the bottom bottom 16c of column 10 to be substantially dry to a higher temperature.

The temperature gradient required for effective separation is expressed as the percentage of the total temperature difference minus the top temperature of the column from the bottom temperature of the column. About 15% or less of the total column temperature difference occurs at the top 12 of the first column 10, about 15% or less of the column total temperature difference occurs at the top bottom 16a, and at least 70% of the column temperature difference is at the middle bottom 16b and Occurs at the bottom bottom 16c. The exact temperature relative to the percent temperature difference depends on the operating pressure of the first column 10.

The temperature is controlled by feeding a dimension to the first column reheater 13 or by adjusting the reflux rate of the distillate of the first column 10. The resulting temperature gradient causes the temperature to stabilize below the feed stage temperature such that the top bottom of the column contains substantially moisture. The water containing top bottom 16a is located below feed port 17 and allows acetic acid to be removed up as the distillate product 25 of the first column 10. The bottom product 30 of the first column 10 contains dry DMAc and acetic acid impurities and is fed back to the first column 10 through inlet port 15 which is part of the reheater 13 unit. The bottom product 30 of the first column 10 is also fed through the feed port 27 to the second column 20. Pure DMAc is distillation product 40 of the second column 20. The bottom product 45 of the second column 20 contains dry DMAc and acetic acid and is circulated to the feed port 17 of the first column 10. The pumping circulation stream 45 at the bottom flows through the bottom 16a with water, again the acetic acid portion is removed over the first column 10.

As the acetic acid in raw material 8 and bottom pumping circulation stream 45 is collected and removed, the amount of acetic acid removed as distillate 25 of the first column 10 is equal to the amount of acetic acid in raw material 8. Acetic acid (streams 30 and 45) in columns 10 and 20 is well below the concentration in the azeotropic mixture of DMAc and acetic acid, and pure DMAc can be produced as distillation product 40 in the second column 20.

Although a three-component system of DMAc, acetic acid, and water has been described, the invention can be used in any three-component system having the following characteristics: (a) The first component is a low boiling point component, i.e. Is present at a concentration of at least 25% or more; (b) the second component is a higher boiling component than the first component and is present in essential ingredients of the raw material, i.e. at least 5% or more; (c) the third component is present as a minor component, ie at a concentration of 5% or less, and forms a high boiling azeotropic mixture with the second component; (d) The first component removes, modulates or mitigates the azeotrope of the two components.

Within the scope of the present invention, first and second distillation columns of other structures are also possible. For example, the first column condenser may be a total system for removing liquid product as shown in FIG. 1A or a partial system for removing vapor product as shown in FIG. 1B. The second column condenser may be a total system for removing liquid product as shown in FIG. 1C or a partial system for removing vapor product as shown in FIG. 1D. In another example, the bottom product of the first column may be removed as liquid as in FIG. 1E, as a liquid / gas mixture using a conventional reheater as in FIG. 1F, or as lateral exhaust steam as in FIG. 1G. have. In another example, the bottom pumping circulation stream, when circulated to the first column, enters the feed port as shown in FIG. 1H or into the inlet port above the feed port as shown in FIG. 1I, or as shown in FIG. 1J. It can enter the inflow port in the part. In another example, the bottom pumping circulation stream may be obtained from the second column, as in FIG. 1K, or the pumping circulation stream of the first and second column bottoms may be circulated to the first column, as in FIG. 1L. In another example, the bottom pumping circulation stream eliminates the reheater on the second column and uses the reheater in common for the first and second columns, as shown in FIG. 1M, or by evacuating laterally as shown in FIG. To obtain a pumping circulation stream, or to the second column by side vapor discharge as shown in FIG. 1O and circulated back to the first column, or by using a reheater of a common bath tube as in FIG.

Example

A continuous distillation process with a temperature gradient of 26 steps was carried out as shown in the table below, so that the top bottom 16a of the first column 10 containing the reheater and the condenser contained water. In this example, the upper pressure of the first column 10 was 103 mm Hg, the lower pressure was 153 mmHg, and the pressure difference was 50 mmHg. However, the specific temperatures listed in the table below are a function of the pressure at which the first column is operated and do not require these specific temperatures or pressures. Thus, any temperature / pressure can be used that can substantially dry the bottom bottom of the column.

Table 1

Step number Temperature (℃) Pressure (mm Hg) One 42.1 Condenser with 103.0 bottom cooler 2 54.0 113.0 3 54.3 114.7 4 54.6 116.3 5 54.9 118.0 6 55.2 119.7 7 55.5 121.3 8 55.8 123.0 9 56.1 124.7 10 56.4 126.3 11 56.7 128.0 12 57.1 129.7 13 57.8 131.3 14 59.2 133.0 raw material 15 59.5 134.7 16 59.8 136.3 17 60.2 138.0 18 62.3 139.7 19 73.5 141.3 20 95.9 143.0 21 109.0 144.7 22 112.3 146.3 23 113.2 148.0 24 113.6 149.7 25 113.9 151.3 26 114.4 153.0 reheater

The total temperature difference in the column was calculated as follows.

Column bottom 114.4 ° C

Upper steam before condenser 54.O ℃

Total temperature difference 60.4 ℃

The temperature difference at the top of the column was calculated as follows.

Feed stage temperature 59.2 ℃

Upper steam before condenser 54.O ℃

Upper temperature difference 5.2 ℃

Calculated as a percentage of the total temperature difference, 5.2 / 60.4 = 8.6%.

The temperature difference of the top three steps of the top bottom of the column bottom 16 was calculated as follows.

Step 17 60.2 ° C

Feed stage temperature 59.2 ℃

Upper bottom temperature difference 1.0 ℃

Calculated as a percentage of the total temperature difference, 1.0 / 60.4 = 1.7%.

The temperature difference of the middle and lower bottoms was calculated as follows.

Column bottom 114.4 ° C

Step 17 60.2 ° C

54.2 ° C difference in middle and bottom floor temperatures

Calculating this as a percentage of the total temperature difference, 54.2 / 60.4 = 89.7%.

The temperature gradient shown in FIG. 2 represents the percent difference in temperature of the various parts of the column. This graph has a particular shape and the temperature at the top bottom 16a of column 10 (steps 15-17 in this example) shows a very moderate change (ie temperature stabilization). This characteristic shape appears regardless of the operating pressure of the column and is determined by the total temperature difference between the vapor before condensation and the liquid at the bottom. This temperature gradient creates a waterborne top bottom to remove acetic acid over the column. In the first column 10, there is a temperature difference of at least 70% in the upper bottom 16a and the middle bottom 16b (steps 15-20 in this example), a temperature difference of less than 15% in the lower bottom 16c, and a top 12 ( In this example, the temperature difference of 15% or less is also observed in steps 2-13). These conditions make the bottom bottom 16c of the first column substantially dry and the top bottom 16a of the first column substantially wet. Under this condition, acetic acid impurity is partitioned between stream 25 above column 10 and stream 30 below.

The effluent at the bottom 16c of the first column 10 and / or the effluent 45 from the second column is recycled to the feed port 17 of the first column 10 by the pumping circulation. This places virtually all acetic acid in water 25 above the first column 10.

The material of the bottom bottom 16c of the first column 10, which mainly contains DMAc and acetic acid, is fed to the second column 20 and redevaporated. The material can be supplied from the first column to the second column 20 as liquid or side discharge steam. Acetic acid is present at less than the concentration of the azeotrope, so it does not interfere with separating DMAc into pure component 40 and manipulating the second column 20.

Purification and analysis of DMAc twice independently using the system of the present invention showed the following parameters. The results were compared to fresh commercial DMAc with acetic acid concentration of about 80 mg / kg (0.008%).

TABLE 2

Analysis 1 Analysis 2 DMAc analysis 100% 99.7-99.8% Water content <0.01% <0.01% Acetic acid content <0.01% 0.2-0.3% color <5units <5units Dimethylamine Fraction in All Substrates 1-3mg / kg 1-3mg / kg

Thus, the method of the present invention allows the same DMAc as commercial DMAc.

The illustrated and described embodiments of the present invention are merely preferred embodiments and those skilled in the art can understand that the present invention is not limited thereto. For example, the process of the present invention may be used to recover low boiling product from high boiling contaminants to distillation product in the first column. Therefore, various modifications, changes and applications of these embodiments are possible within the spirit of the invention and the scope of the following claims.

Claims (27)

(a) a first distillation column having a supply port and an inlet port, consisting of an upper and a bottom part, which is divided into upper, middle, and lower parts of the bottom, the bottom of the column being substantially dry and The top bottom of the substrate is substantially water-containing and at a temperature sufficient to allow the acetic acid to be partitioned between the stream above the first column and the stream below, (b) feed the stream under the first column to the feed port of the second distillation column and distribute the purified DMAc to the stream above the column and DMAc and acetic acid to the stream below the column, (c) A process for separating DMAc from an aqueous DMAc solution comprising acetic acid consisting of partitioning additional acetic acid from the mixture of DMAc and acetic acid to the stream on the first column. The method of claim 1 further comprising recovering purified DMAc from the top of the second column. The method of claim 1 wherein the temperature gradient results in that no more than about 15% of the total temperature difference of the first column occurs at the top, no more than about 15% of the total temperature difference of the first column occurs at the top bottom, Wherein at least 70% of the total temperature difference occurs at the middle bottom and the bottom bottom. The method of claim 1, wherein the bottom stream of the second column is fed to the first column as a pumped circulation stream. The method of claim 1 wherein the bottom stream of the first column is fed to the second column as a liquid feed. The method of claim 1, wherein the bottom stream of the first column is fed to the second column as side vapor exhaust. The method of claim 1 wherein the bottom pumping circulation stream is fed to the feed port of the first column. The method of claim 1 wherein the bottom pumping circulation stream is fed to an inlet port located above the feed port of the first column. The method of claim 1 wherein the bottom pumping circulation stream is fed to the inlet port of the top bottom of the first column. 2. The process of claim 1, wherein the bottom stream of the second column contains less acetic acid than the azeotrope concentration. 4. The method of claim 3, wherein the temperature is a function of the pressure at which the first column is operated. The method of claim 1 wherein the acetic acid distributed in the top stream of the first column is recovered as a liquid. A process according to claim 1, wherein the acetic acid distributed in the top stream of the first column is recovered in the middle stage. The method of claim 2 wherein DMAc is recovered as a liquid from the top of the second column. 3. The process of claim 2 wherein DMAc is recovered as steam from the top of the second column. The method of claim 1, wherein the bottom stream of the first column is fed to the second distillation column in a physical state selected from the group consisting of liquid, gas, and liquid / gas mixture. The method of claim 1, wherein the additional portion of acetic acid is dispensed by feeding the bottom stream of the second column to the first column. The method of claim 1, wherein the additional portion of acetic acid is dispensed by circulating the bottom stream of the second column to the first column and then providing a pumped circulation stream of the bottom from the first column. 5. The method of claim 4, wherein the bottom pumping circulation stream is obtained by using a common reheater for the first and second columns. (a) a feed port for the solution, a condenser mounted above for distilled streams, a reheater for the bottom stream, a discharge port, comprising a top and a bottom, the bottom being the top, middle and bottom Broken down, first column (b) a second column subsequent to the first column, including a supply port for the bottom stream from the first column, a condenser mounted above for the distilled stream, an optional, reheater mounted below, and an outlet port , (c) a pump for circulating the product stream of the second column bottom to the first column, and (d) a control device for adjusting the temperature gradient such that the top bottom of the column is substantially wet and the bottom bottom of the column is substantially dry Apparatus for separating the fluid component in the raw material solution comprising a. 21. The control device of claim 20, wherein the control device has no more than about 15% of the total temperature difference of the first column occurring at the top, and no more than about 15% of the total temperature difference of the first column occurs at the top bottom and the entirety of the first column. And adjusting the temperature gradient of the first column between the distilled stream above the column and the stream below the column such that at least 70% of the temperature difference occurs at the middle bottom and the bottom bottom. 21. The device of claim 20, wherein the control device is located on the reheater of the first column. In the feed port of the first distillation column, the solution is supplied under conditions sufficient to distribute the aqueous acetic acid solution to the first column distillate. Feed the first column feed port and the second column feed port with the non-distilled bottom product of the first column under conditions sufficient to obtain purified DMAc as the distillate of the second column, Consisting of separating the acetic acid aqueous solution over the first column by feeding the non-distilled bottom product of the second column containing DMAc and acetic acid to the first column and separating DMAc under the first column A process for purifying N, N-dimethylacetamide (DMAc) from acetic acid in aqueous solution. 24. The method of claim 23, further comprising recovering pure DMAc as distillate from the second column. 24. The method of claim 23, wherein said condition comprises a temperature gradient sufficient to substantially dry the bottom bottom of the first column. 24. The method of claim 23, wherein the temperature gradient forms a temperature stabilized below the feed stage temperature such that the top bottom of the column contains substantially moisture.  (a) a first distillation column, having a supply port and an inlet port, consisting of an upper part and a lower part, wherein the bottom part is divided into upper, middle, and lower parts of the bottom part, wherein the bottom part of the column is substantially the first component. Supplying the solution at a temperature sufficient to ensure that the top bottom of the column is substantially rich in the first component and distributes the third component between the stream above the first column and the stream below it, (b) feeding the stream below the first column to the feed port of the second distillation column and distributing the purified second stream to the stream above the column and the mixture of the second and third components to the stream below the column, and (c) distributing the additional third component from the mixture of the second and third components to the stream on the first column. A method for purifying one or more components in a solution comprising a first low boiling point component, a second high boiling point component, and a third component forming an azeotrope with the second component, (i) the first component is a low boiling point compound present in the raw material at a concentration of at least 25%; (ii) the second component has a higher boiling point than the first component and is present at a concentration of at least 5% in the raw material; (iii) the third component is present in the raw material at a concentration of 5% or less and forms a high boiling point azeotrope with the second component; (iv) wherein the first component is capable of removing, adjusting or mitigating an azeotrope of two components.