TW201300356A - Process for separating monochloroacetic acid and dichloroacetic acid via extractive distillation - Google Patents

Abstract

The present invention pertains to a process for separating monochloroacetic acid and dichloroacetic acid from one another via extractive distillation, comprising the steps of (i) contacting a mixture comprising monochloroacetic acid and dichloroacetic acid with an extractive agent which is chemically stable and which hasa BF3 affinity of between 65 kJ/mole and 110 kJ/mole, (ii) distilling the mixture to obtain a monochloroacetic acid stream and a stream comprising dichloroacetic acid and the extractive agent, and (iii) regenerating the extractive agent.

Description

Method for separating monochloroacetic acid and dichloroacetic acid by extractive distillation

The present invention relates to a process for separating monochloroacetic acid and dichloroacetic acid from each other via extractive distillation.

The main industrial route for the production of monochloroacetic acid is by reaction of acetic acid with chlorine. This method is generally known and generally employs a reactor in which a mixture of liquid acetic acid (HAc) is reacted with chlorine under anhydrous conditions in the presence of a catalyst. In the reactor, monochloroacetic acid (MCA) and gaseous HCl and by-products such as dichloroacetic acid (DCA) and trichloroacetic acid (TCA) are formed.

After chlorination, the DCA is present in a substantial amount in the reaction product mixture containing MCA, typically from about 3 to 10 wt%. To reduce the amount of DCA in the MCA, the product mixture containing MCA/DCA should be subjected to a purification process. Purification methods are known to include (melting) crystallization and the use of hydrogen to reduce DCA in the presence of a hydrogenation catalyst. These methods can be performed on MCA/DCA streams that have been purified but still contain small amounts of DCA, or in streams containing a relatively high amount of DCA (DCA concentrations typically range between 50 ppm and 70 wt%). Implementation.

With melt crystallization, the one-stage recrystallization only reduces the concentration of dichloroacetic acid in the crude monochloroacetic acid feed to about 4, i.e., from 3% by weight to 0.7-0.8% by weight. Therefore, in order to produce pure monochloroacetic acid, the melt crystallization is repeated a plurality of times. After multiple crystallizations, the mother liquor still contains a mixture of monochloroacetic acid and dichloroacetic acid. Although this mother liquor still contains at least 30% by weight of one chloroacetic acid (depending on the cooling conditions), it cannot be converted into a saleable product by further crystallization. Product. Accordingly, there is a need in the art for an economically viable process for separating monochloroacetic acid and dichloroacetic acid from one another such that the mother liquor does not have to be discarded and the process can even eliminate the melt crystallization process.

Since the boiling points of monochloroacetic acid and dichloroacetic acid are very close (189 ° C and 194 ° C, respectively), they are not easily separated from each other by simple distillation because the volatility of the two components is almost the same, which makes it Evaporation at the same rate at almost the same temperature makes normal distillation impractical. However, it is known that components having a relative volatility value close to 1 in the mixture can be separated by extractive distillation. The extractive distillation is carried out by distillation in the presence of a third component (hereinafter referred to as extractant or EA) different from the interaction of the components of the mixture, thereby changing its relative volatility. This allows the new three-part mixture to be separated by normal distillation. The essence of extractive distillation has been, for example, by JFR Richardson, JH Harker and JR Backhurst, in Coulson and Richardson's Chemical Engineering , Vol. 2, 5th Ed. (2002), Butterworth-Heinemann, pp. 617-619 and by Hannsjörg Freund and Kai Sundmacher , explained in "Process Intensification, 4. Plant Level" (published online: July 15, 2011), page 22, Ullman's Encyclopedia of Industrial Chemistry: Extractive Distillation [187-190] .

A method of separating monochloroacetic acid and dichloroacetic acid from each other by extractive distillation is known from JP 47-30165. This patent states the use of sulfuric acid as an extractant. The addition of sulfuric acid to a mixture comprising monochloroacetic acid and dichloroacetic acid results in an increase in the difference in volatility. When distilling, dichloroacetic acid containing a small amount of monochloroacetic acid is distilled off on the top, while the bottom product is sulfuric acid and contains a very small amount of dichloroacetic acid. a mixture of chloroacetic acid. The bottom product is then distilled to obtain monochloroacetic acid and sulfuric acid. However, this method has the disadvantage that one of the chloroacetic acids thus obtained must be subjected to a crystallization step for purification. In addition, traces of sulfuric acid that may eventually be present in the top product of DCA will result in enhanced deactivation of the catalyst, which is used in the subsequent hydrogenation step to convert DCA to MCA.

JP 47-29886 discloses a similar process in which cyclobutanil is used as an extractant. Indeed, the use of cyclobutyl hydrazine as an extractant has the advantage that the extractant can be recovered and reused relatively easily. However, also in this case, there is still room for improvement in the degree of separation of monochloroacetic acid from dichloroacetic acid, which is due to the improvement in the relative volatility of the MCA/DCA system.

Accordingly, it is an object of the present invention to provide a process for separating monochloroacetic acid and dichloroacetic acid from each other via extractive distillation which is economically viable by achieving good separation and at the same time the extractant used can be regenerated relatively easily.

Surprisingly, it has been found that this can be achieved with the use of specific extractants.

More particularly, the present invention relates to a method for separating monochloroacetic acid and dichloroacetic acid from each other via extractive distillation, comprising the steps of: (i) contacting a mixture comprising monochloroacetic acid and dichloroacetic acid with an extractant, The extractant is chemically stable and has a BF ₃ affinity between 65 kJ/mol and 110 kJ/mol, (ii) the mixture is distilled to obtain a monochloroacetic acid stream and comprises dichloroacetic acid and an extractant. Streaming, and (iii) regenerating the extractant. It should be noted that a mixture comprising monochloroacetic acid and dichloroacetic acid is contacted with the extractant before and/or during the distillation step (ii). More specifically, in step (i), contacting a mixture comprising MCA and DCA with an extractant can be carried out inside a column for performing extractive distillation. However, it is also possible to bring the mixture comprising MCA and DCA into contact with the extractant before it enters the column for extractive distillation (ie, premix the mixture comprising MCA and DCA with the extractant and feed the resulting mixture to the column). To perform extractive distillation). A combination of these two techniques can also be used. It should be noted that it is preferred to contact the mixture comprising MCA and DCA with an extractant in an extractive distillation column. In this case, preferably, the extractant is fed to the column at a level higher than the stage at which the mixture comprising MCA and DCA is fed to the column, because in this case in the column At the higher end there will be excess extractant to capture any traces of DCA.

The term "extractant" as used throughout this specification is intended to mean any additive which is more complex with dichloroacetic acid (DCA) than the complex formed by monochloroacetic acid (MCA). By definition, the extractant is less volatile than the component to be separated.

The BF ₃ affinity of the extractant can be determined according to the test methods set forth below: Christian Laurence and Jean-Francois Gal, Lewis Basicity and Affinity Scales, Data and Measurement , 2010, John Wiley & Sons, ISBN 978-0-470- 74957-9, Chapters 3 and 7. A brief description of the test method is provided below.

BF ₃ (gas) + LB (CH ₂ Cl ₂ solution) LB-BF ₃ (CH ₂ Cl ₂ solution) (1) (where LB is Lewis Base, the extractant)

The heat generated in the mismatch reaction (1) was measured in a heat flux microcalorimeter whose temperature was adjusted at 298 K. The measurement unit contains a dilute solution of about 3 cm ^{3 of} Lewis base (ie, extractant) in CH ₂ Cl ₂ . The alkali concentration depends on its strength: it is usually in the range of 0.2 mol/L for a strong base to 1 mol/L for a weak base. An aliquot of gaseous BF _{3 in} the range of (1-3) 10 ^-4 moles was added to the alkaline solution by means of a vacuum line. Each time a certain amount of BF ₃ ( n mole) is added to produce a certain amount of heat Q. When the reaction is completed, the thermal enthalpy Δ H ^{o of} each mismatch is defined as the Q/n ratio. This method is equivalent to the base ₃ by continuous titration of acid BF. A titration provides a 6-8 △ H ^o value. Calculate the average and the corresponding confidence limits (usually at 95% level). The accuracy is quite good (0.2-0.5% in one group, 0.5-1% between groups) and the estimated accuracy is 1-2%.

It should be noted that it is necessary to use anhydrous solvents and reactants because trace amounts of moisture (and other impurities) are easily induced to generate additional heat of reaction. Moreover, boron trifluoride releases hydrogen fluoride by slow hydrolysis, which results in corrosion of the glass components of the system (see also Chapter 7.1.2 of the Laurence and Gal books mentioned above). It should also be noted that the calorimeter can be corrected by the Joule effect (see Chapter 7.1.3 of the book Laurence and Gal mentioned above).

The extractant of the present invention is chemically stable. To assess the stability of the extractant, the following tests can be performed. Dichloroacetic acid and extractant were added to a 10 mL vial at a 1:1 molar basis. The total amount of dichloroacetic acid and extractant mixture supplied to the vial was 2 mL. The vial containing the mixture was stored at a temperature of 160 ° C for 24 hours. Subsequently, a drop of the sample was added to 1.5 mL of acetone. A mixture of the sample and acetone was analyzed by GC-MS (gas chromatography-mass spectrometry) according to the following protocol: Equipment: Shimadzu GC-17A gas chromatograph + Shimadzu GC MS-QP5000 detector MS

Column: Chrompack VF-1ms 25 m ^* 0.25 mm ID DF=0.40 μm 100% dimethyl polyoxane

GC method: injection temperature: 300 ° C

Interface temperature: 250 ° C

Column inlet pressure: 24.5 kPa

Column flow: 0.8 mL/min

Linear speed: 35.5 cm/sec

Split ratio: 10

Carrier: Helium

Total flow: 9.4 mL/min

Carrier flow rate: 9.4 mL/min

Injection volume: 1 μL

Starting temperature: 50 ° C

Heating rate: 10 ° C / min

End temperature: 290 ° C (9 minutes hold time)

MS setting: start time: 1.4 min

End time: 33 min

Start m/z: 35 g/mole

Termination m/z: 400 g/mole

Scanning speed: 2,000

Interface temperature: 250 ° C

Acetone cut time: 1.4 min

Detector voltage: 1.3 kV

Threshold: 1,000

Interval: 0.2 seconds

The peak area ratio of the impurity to the extractant should be less than 0.3, preferably less than 0.1, and most preferably less than 0.05, and the extractant is considered to be chemically stable.

The peak area can be converted to a percentage of the denatured extractant based on the initial total amount of extractant used, using conventional correction techniques familiar to those skilled in the art. Therefore, the term "chemically stable" as used throughout the specification for an extractant indicates that when the extractant is held at 160 ° C for 24 hours in the presence of 1:1 molar ratio of dichloroacetic acid, there is less than 45% extraction. The agent (relative to the Mohr reference) is denatured. Preferably, it indicates that less than 15% of the extractant (relative to the molar reference) is denatured when the extractant is held at 160 ° C for 24 hours in the presence of 1:1 molar ratio of dichloroacetic acid. Most preferably, it indicates that less than 7.5% of the extractant (relative to the molar reference) is denatured when the extractant is held at 160 ° C for 24 hours in the presence of 1:1 molar ratio of dichloroacetic acid.

Preferably, the extractant is selected from the group consisting of phosphine oxides, aldehydes, ketones, ethers and decylamines which are chemically stable and have a BF ₃ affinity of between 65 kJ/mol and 110 kJ/mol. More preferably, the extractant is selected from the group consisting of aldehydes, ketones, ethers and guanamines which are chemically stable and have a BF ₃ affinity of between 65 kJ/mol and 110 kJ/mol. Most preferably, the extraction agent is selected from the group consisting of chemically stable and having a group consisting of BF interposed between the 65 kJ / mole and 110 kJ / mole and an ether ketone ₃ affinity.

As stated, the extractant of the present invention has a BF ₃ affinity of at least 65 kJ/mole. Preferably, however, it has a BF ₃ affinity of at least 70 kJ/mole and optimally at least 75 kJ/mole.

The extractant of the present invention has a BF ₃ affinity of up to 110 kJ/mol. Preferably, however, it has a BF ₃ affinity of at most 100 kJ/mol and, optimally, it has a BF ₃ affinity of at most 90 kJ/mole.

In a particularly preferred embodiment, the extractant is selected from the group consisting of tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, dihexyl ether, diethylene glycol dipentyl ether, and dihexyl ketone.

As described above, in the process of the present invention, a mixture comprising monochloroacetic acid and dichloroacetic acid is contacted with the extractant of the present invention. In addition to MCA and DCA, it may additionally comprise acetic acid. The mixture preferably comprises at least 50 ppm DCA, preferably at least 500 ppm DCA, and most preferably at least 5,000 ppm DCA. Preferably, it comprises no more than 70 wt% DCA, preferably no more than 60 wt% DCA, and most preferably no more than 50 wt% DCA.

Preferably, the extractant is used in the step such that the ratio of extractant to DCA is at least 0.5 (based on the molar basis), preferably at least 1.0 (based on the molar reference) and optimally at least 2.5 (based on the molar reference). (i) Medium. For the sake of clarity, the ratio of extractant to DCA is the total amount of extractant fed to the distillation column versus the total amount of DCA fed to the distillation column, both based on a molar reference. The extractant is preferably used in this amount such that the ratio of extractant to DCA is at most 50 (based on the molar reference), preferably at most 30 (based on the molar reference), and even more preferably at most 20 (based on the molar reference). And the best is at most 10 (based on the Mohr benchmark).

The mixture comprising MCA, DCA and extractant is distilled to obtain a monochloroacetic acid stream on the one hand and a stream comprising dichloroacetic acid and an extractant on the other hand. This extractive distillation step (step ii) is preferably carried out at a pressure below 500 mbar, preferably below 250 mbar and optimally below 100 mbar.

The extractive distillation step is preferably carried out at a temperature at the bottom of the distillation column of less than 453 K, preferably less than 433 K, even more preferably less than 413 K and most preferably less than 393 K.

In the next step, the extractant is regenerated by stripping or preferably by distilling a stream comprising dichloroacetic acid and an extractant. This step additionally produces dichloroacetic acid. Preferably, the regenerated extractant is recycled to step (i) of the process of the invention.

Step (iii) is preferably carried out at a pressure of less than 250 mbar, preferably less than 100 mbar, and most preferably less than 75 mbar.

In the case of the distillation step, the temperature at the bottom of the distillation column is preferably less than 493 K, preferably less than 473 K, still more preferably less than 453 K, and most preferably less than 433 K.

Those skilled in the art will appreciate that at the same pressure, the temperature at which step (iii) of the process of the invention is carried out is higher than the temperature at which extractive distillation of step (ii) is carried out.

Suitable equipment that can be used to carry out the extractive distillation step (step (ii)) of the present invention includes conventional distillation columns comprising a reboiler and a condenser. The regeneration step (step (iii)) can be carried out in a conventional stripping column or a conventional distillation column, with the latter being preferred.

In a preferred embodiment, at least a portion of the method of the invention is performed in a Petlyuk column or a dividing wall column. Petlyuk tubing and dividing wall tubing are conventionally known and are described, for example, by I. Dejanović, Lj. Matijašević and Ž. Olujić in Chemical Engineering and Processing 49, 2010, pages 559-580. The practice of carrying out the process of the invention using Petlyuk or a dividing wall column has the advantage of combining at least steps (ii) and (iii) of the process of the invention into one step. Preferably, however, steps (i), (ii) and (iii) are combined into a single step or unit operation by using a Petlyuk or dividing wall column.

The process of the invention can be used to further purify a stream comprising MCA and DCA that has been purified, for example, by a crystallization process, but still contains a small amount of DCA. It is also suitable for purifying crude streams containing a relatively high amount of DCA.

The DCA obtained via the process of the present invention can then be subjected to a hydrogenation step by contact with hydrogen in the presence of a hydrogenation catalyst (e.g., as disclosed in EP 557169) to produce MCA.

The method of the invention is further illustrated by the following non-limiting examples.

Example 1

This example illustrates the limited effect of cyclobutyl hydrazine on separation selectivity in extractive distillation of feeds containing monochloroacetic acid (MCA) / dichloroacetic acid (DCA).

To determine the effect of cyclobutyl hydrazine on the gas-liquid equilibrium of the MCA/DCA mixture, a boiling point meter (Fischer VLE 602D) was used. In this ebulliometer, the equilibrium vessel is equipped with a dynamic recirculating still of a Cottrel cycle pump. The heat capacity and pressure are controlled using a control unit (Fischer system M101). The vapor condensation rate is kept constant at 1 drop per second. The condenser was operated at 70 °C. The pressure was kept constant within a deviation of 0.02 kPa and the measured equilibrium temperature was 0.1 °C. After about 30 minutes to 45 minutes, equilibrium is reached when both the vapor temperature and the distillation rate are constant. A 30 μL sample of both the gas phase and the liquid phase was taken using a 500 μL syringe. The samples were diluted with 0.75 mL of acetonitrile and 0.75 mL of water. The concentration of the components was analyzed using high pressure liquid chromatography (HPLC, Varina Prostar). Grace Prevail ^TM-based silicon dioxide of an organic acid column (250 mm × 4.6 mm), wherein a particle size of 5 μm. For all measurements, the temperature of the column was kept constant at 313.2 K in an oven (Varian Prostar Model 510). Detection of MCA and DCA was performed at 210 nm using a UV detector (Varian Prostar Model 310). The concentration of the cyclic oxime was calculated by means of the mass balance of the sample. The flow rate of the eluent was 1 mL/min and consisted of acetonitrile (5 vol%) and an orthophosphoric acid solution (19 g/L) (95%) in Milli-Q water. The column was regenerated with pure acetonitrile after each injection. Each sample was injected twice. The molar fraction of the components in both the gas phase and the liquid phase was obtained with an accuracy of 0.001 (expressed in mole fraction).

MCA used in this example ( 99.0%) and DCA ( 99.0%) was obtained from Sigma-Aldrich.环丁碸 98%) was obtained from Fluka. All chemicals were used without further purification.

Prior to testing, approximately 100 mL of solution was prepared with a MCA/DCA ratio of 4/1 (based on the Mohr reference). Two cyclobutane/DCA ratios are used, namely 1/2 and 1/1 (based on the Mohr reference). All starting weights of the chemicals used in the gas-liquid equilibrium test are shown in Table 1. The gas-liquid equilibrium test was performed at pressures of 5 kPa, 7.5 kPa, and 10 kPa. One test was performed on a non-extractant basis to measure the relative volatility of DCA and MCA in the absence of extractant. In addition, a test was performed on the standard extractant ring guanidine. The relative volatility α presented in this example is calculated as follows: α = α _{MCA / DCA} = (y _MCA / y _DCA ) / (x _MCA / x _DCA ) where y _MCA and y _DCA are MCA and DCA in the gas phase The weight fraction, and x _MCA and x _DCA are the weight fractions of MCA and DCA in the liquid phase. The results of the gas-liquid equilibrium test are shown in Table 2. The data in Table 2 clearly shows that the addition of cyclobutanide limits the increase in relative volatility of MCA/DCA. Therefore, it has a slight (but limited) positive effect on the separation of MCA and DCA during distillation. However, for practical applications, this effect is too small to achieve acceptable separation.

Example 2

This example illustrates the benefits of various extractants to cyclobutyl hydrazine in an extractive distillation of a chloroacetic acid (MCA) / dichloroacetic acid (DCA) feed. As discussed above, the tests in this example were performed using the same equipment, pressure conditions, and extractant/DCA molar ratios used in Example 1.

To determine the effect of several extractants on the gas-liquid equilibrium of the MCA/DCA mixture, a boiling point meter (Fischer VLE 602D) was used. In this ebulliometer, the equilibrium vessel is equipped with a dynamic circulating still of a Cottrel cycle pump. The heat capacity and pressure are controlled using a control unit (Fischer system M101). The vapor condensation rate is kept constant at 1 drop per second. The condenser was operated at 70 °C. The pressure was kept constant within a deviation of 0.02 kPa and the measured equilibrium temperature was 0.1 °C. After about 30 minutes to 45 minutes, equilibrium is reached when both the vapor temperature and the distillation rate are constant. A 30 μL sample of both the gas phase and the liquid phase was taken using a 500 μL syringe. For the test using the extractants tetraethylene glycol dimethyl ether, succinonitrile, tri-n-butyl phosphate, tri-n-hexylamine and diethylene glycol dibutyl ether, the samples were used with 0.75 mL of acetonitrile and 0.75. Dilute with mL water. The concentration of the components was analyzed using high pressure liquid chromatography (HPLC, Varina Prostar). Grace Prevail ^TM-based silicon dioxide of an organic acid column (250 mm × 4.6 mm), wherein a particle size of 5 μm. For all measurements, the temperature of the column was kept constant at 313.2 K in an oven (Varian Prostar Model 510). Detection of MCA and DCA was performed at 210 nm using a UV detector (Varian Prostar Model 310). The concentration of the extractant is calculated by means of the mass balance of the sample. The flow rate of the eluent was 1 mL/min and consisted of 5 vol% acetonitrile and 95 vol% phosphoric acid solution (19 g/L) in Milli-Q water. The column was regenerated with pure acetonitrile after each injection. Each sample was injected twice. The molar fraction of the components in both the gas phase and the liquid phase was obtained with an accuracy of 0.001 (expressed in mole fraction).

For the tests using the extractants diethylene glycol dipentyl ether, dihexyl ketone, dihexyl ether and tri-n-octylphosphine oxide, the samples were diluted with 1.5 mL of acetonitrile. The concentration of the components was analyzed using high pressure liquid chromatography (HPLC, Varina Prostar). Grace Prevail ^TM-based silicon dioxide of an organic acid column (250 mm × 4.6 mm), wherein a particle size of 5 μm. For all measurements, the temperature of the column was kept constant at 313.2 K in an oven (Varian Prostar Model 510). Detection of MCA and DCA was performed at 210 nm using a UV detector (Varian Prostar Model 310). The concentration of the extractant is calculated by means of the mass balance of the sample. The flow rate of the eluent was 1 mL/min and consisted of 15% by volume of acetonitrile and 85% by volume of orthophosphoric acid solution (19 g/L) in Milli-Q water. The column was regenerated with pure acetonitrile after each injection. Each sample was injected twice. The molar fraction of the components in both the gas phase and the liquid phase was obtained with an accuracy of 0.001 (expressed in mole fraction).

MCA used in this example ( 99.0%) and DCA ( 99.0%) was obtained from Sigma-Aldrich. Tetraethylene glycol dimethyl ether 98.0%), succinonitrile ( 97.0%), tri-n-butyl phosphate ( 99%) and tri-n-octylphosphine oxide ( 97.0%) is obtained from Fluka and tri-n-hexylamine ( 96%), diethylene glycol dibutyl ether ( 99.0%), dihexyl ether ( 97.0%) and dihexyl ketone ( 97.0%) was obtained from Aldrich. Diethylene glycol dipentyl ether 99.0%) was obtained from Syncom. All chemicals are used without further purification

Prior to testing, approximately 100 mL of solution was prepared with a MCA/DCA ratio of 4/1 (based on the Mohr reference). Two EA/DCA ratios are utilized, namely 1/2 and 1/1 (based on the Mohr reference). All starting weights of the chemicals used in the gas-liquid equilibrium test are shown in Table 3. The gas-liquid equilibrium test was performed at pressures of 5 kPa, 7.5 kPa, and 10 kPa. The relative volatility α presented in this example is calculated as follows: α = α _{MCA / DCA} = (y _MCA / y _DCA ) / (x _MCA / x _DCA ) where y _MCA and y _DCA are MCA and DCA in the gas phase The weight fraction, and x _MCA and x _DCA are the weight fractions of MCA and DCA in the liquid phase. The results of the gas-liquid equilibrium test are shown in Table 4. The data in Table 4 clearly shows that all but one of the extractants outperformed cyclobutanide because of the considerable increase in relative volatility α _MCA/DCA compared to cyclobutanthine. More specifically, the BF ₃ affinity (indicating the Lewis basicity) of 60 kJ/mole of succinonitrile shows insufficient increase in relative volatility. Therefore, a suitable extractant for improving MCA and DCA by extractive distillation is an extractant having a BF ₃ affinity (declaring a Lewis basicity) of more than 65 kJ/mole (preferably more than 70 kJ/mole). The extractant exhibits a relative volatility of more than 1.8 and many even more than 2.0 at an EA/DCA molar ratio of 1/1. This is higher than the relative volatility obtained with cyclobutanil. Thus, it is shown that the extractant of the present invention exceeds the benefit of cyclobutyl hydrazine in an extractive distillation of a chloroacetic acid (MCA) / dichloroacetic acid (DCA) feed.

Example 3

To verify whether the extractant from Example 2 is regenerable, a gas-liquid equilibrium test was performed on the extractant in the presence of DCA. These regeneration tests were carried out using the same equipment, pressure conditions, analytical methods, and extractants used in Example 2.

Prior to the test, 100 mL of solution was prepared with an EA/DCA ratio of 1/1. This is the expected composition from the extractive distillation column. For some extractants that have been successfully regenerated for a 1/1 EA/DCA molar ratio, regeneration experiments for 5/1 and 9/1 EA/DCA molar ratios have also been performed. The contour EA/DCA composition is expected to be at the bottom of the regeneration column. The starting weights of all regeneration tests are shown in Table 5.

The relative volatility α presented in this example is calculated as follows: α = α _{DCA / EA} = (y _DCA / y _EA ) / (x _DCA / x _EA ) where in this example, y _DCA and y _EA are DCA and The weight fraction of EA in the gas phase, and x _DCA and x _EA are the weight fractions of DCA and EA in the liquid phase.

The results of the gas-liquid equilibrium test are shown in Table 6.

Table 6 shows that long chain ether diethylene glycol dibutyl ether, diethylene glycol dipentyl ether and tetraethylene glycol dimethyl ether can be regenerated. The same applies to dihexyl ether and dihexyl ketone. For tri-n-hexylamine, succinonitrile, tri-n-octylphosphine oxide and tri-n-butyl phosphate, the regeneration test was unsuccessful. For the extractants tri-n-hexylamine and tri-n-octylphosphine oxide, the complex formed with DCA is too strong and no gas phase is formed in the boiling point meter (this means that the extractant and DCA cannot be separated). Both succinonitrile and tri-n-butyl phosphate are unstable in a strong acid environment (as measured by the stability test mentioned in the description) and thus fail to meet the chemical stability criteria of suitable extractants. This example demonstrates that the stability of the extractant in a strong acid environment is a prerequisite for the suitability of the extractant for this process. In addition, it demonstrates that for proper regeneration of the extractant, an extractant having a BF ₃ affinity (describes a Lewis basicity) of less than 110 kJ/mole is required, since the extractant is at 1/1 of the extractant/ The relative volatility of over 2.0 was exhibited during DCA molar ratio regeneration. For extractives with a BF ₃ affinity between 65 kJ/mol and 110 kJ/mol and preferably between 70 kJ/mol and 100 kJ/mol, in extractive distillation (see Example 2) Good separation was obtained in both Table 4) and regeneration (see Table 6 in this example).

Claims (14)

A method for separating monochloroacetic acid and dichloroacetic acid from each other by extractive distillation, comprising the steps of: (i) contacting a mixture comprising monochloroacetic acid and dichloroacetic acid with an extracting agent, the extracting agent being chemically stable and having BF ₃ affinity between 65 kJ/mol and 110 kJ/mol, (ii) distillation of the mixture to obtain a monochloroacetic acid stream and a stream comprising dichloroacetic acid and the extractant, and (iii) The extractant is regenerated. The method of claim 1, wherein the extractant is selected from the group consisting of phosphine oxides, aldehydes, ketones, ethers, and decylamines. The method of claim 1 or 2, wherein the extractant has a BF ₃ affinity between 70 kJ/mol and 100 kJ/mol and preferably between 75 kJ/mol and 90 kJ/mol. . The method of claim 1 or 2, wherein the dichloroacetic acid is present in the mixture comprising monochloroacetic acid and dichloroacetic acid in an amount of at least 50 ppm, more preferably at least 500 ppm, and wherein the mixture optionally comprises acetic acid. . The method of claim 1 or 2, wherein the mixture comprising monochloroacetic acid and dichloroacetic acid is contacted with the extractant prior to and/or during step (ii). The method of claim 1 or 2, wherein the extractant is selected from the group consisting of tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, dihexyl ether, diethylene glycol dipentyl ether, and dihexyl ketone. Group. The method of claim 1 or 2, wherein the regenerant is recycled to step (i). The method of claim 1, wherein the step (ii) is carried out in a distillation column comprising a reboiler and a condenser. The method of claim 8, wherein the step (ii) is carried out at a pressure of less than 500 mbar and a temperature at the bottom of the distillation column of less than 453 K. The method of claim 1, wherein in the step (iii), the extractant is regenerated by stripping or distilling the stream comprising dichloroacetic acid and an extractant. The method of claim 10, wherein the recovered dichloroacetic acid is subsequently subjected to a hydrogenation step to produce MCA. The method of any one of clauses 8 to 11, wherein the step (iii) is carried out in a distillation column at a pressure of less than 250 mbar and a temperature at the bottom of the distillation column of less than 493 K. The method of claim 1 or 2, wherein the ratio between the extractant and the DCA in the step (i) is between 0.5 and 50 based on the molar reference. The method of claim 1 or 2, wherein at least steps (ii) and (iii) are carried out in a Petlyuk column or a dividing wall column.