Method for preparing dioxolane

Abstract

The present invention relates to a method for preparing dioxolane by reacting ethylene glycol with an aqueous formaldehyde solution in the presence of an acid catalyst. A crude product containing water, dioxolane and methanol is fed into a phase separation unit (20) in which an organic extractant is present. An organic fraction stream from the phase separation unit is transferred to the upper part of a purification tower (30), dioxolane is discharged from the purification tower as a bottom product, and a distillate stream from the purification tower is recycled to the phase separation unit. An aqueous fraction stream from the phase separation unit is transferred to a wastewater tower (40), a wastewater stream is discharged from the bottom of the wastewater tower, a side stream (42) is discharged from a section between a feed section and a reflux section of the wastewater tower, and the stream (42) is recycled to the phase separation unit, and a distillate stream (43) containing methanol is discharged from the wastewater tower.

Description

[0001] The present invention relates to a method for preparing dioxolane by reacting ethylene glycol with an aqueous formaldehyde solution in the presence of an acid catalyst.

[0002] 1,3-Dioxolane (hereinafter referred to as "dioxolane") is a derivative of ethylene glycol that is used industrially and can be prepared by reacting ethylene glycol with an aqueous formaldehyde solution in the presence of an acid catalyst such as sulfuric acid, boron trifluoride, zinc chloride, or an acidic ion exchanger. Pure dioxolane can be isolated from the reaction mixture using various separation methods, particularly by distillation or extraction.

[0003] EP 0 867 434 A1 discloses a process for producing dioxolanes, in which ethylene glycol is reacted with an aqueous formaldehyde solution in the presence of an acid catalyst. The reaction mixture is fed to a dehydration column, where water is removed as the bottoms product. At the top of the dehydration column, an azeotropic mixture consisting primarily of dioxolanes and water is discharged and fed to an azeotropic distillation column, where benzene is used to break the azeotrope. The dioxolane product obtained as the bottoms product from this column contains benzene, which must be removed in a further process step not disclosed in this document. Most of the added benzene is removed from the process and must be purified for further use or disposal.

[0004] German patent application DE 10 2005 042 505 A1 discloses a method for producing dioxolanes by reacting ethylene glycol with formaldehyde in an aqueous solution in the presence of a catalyst, wherein the reaction is carried out in a reactive distillation column. An azeotropic mixture consisting primarily of dioxolanes and water is discharged from the top of the column and fed to another distillation column operated at high pressure to obtain purified dioxolanes as the bottom product. The bottom stream of the reaction column is fed to another distillation column to separate the water and recycle the unreacted ethylene glycol. Even though this method does not require any extractant (e.g., benzene) in the previous process, a portion of the produced dioxolanes is lost due to the necessary discharge from the top of the dioxolane purification column.

[0005] The processes known in the art for preparing dioxolanes require relatively large amounts of extractants which have to be purified or discharged in further process steps and / or a portion of the valuable product dioxolanes is lost.

[0006] The object of the present invention is to provide a process for preparing dioxolanes which increases the yield of the product dioxolanes while reducing the amount of auxiliary substances and waste.

[0007] According to the invention, this object is achieved by a process for preparing dioxolanes. Advantageous embodiments and further developments of the invention are indicated in the appended claims.

[0008] According to the present invention, the method for preparing dioxolane comprises the following steps:

[0009] a) feeding a first feed stream comprising ethylene glycol and a second feed stream comprising formaldehyde and methanol in aqueous solution into a reactive distillation unit and reacting the ethylene glycol and formaldehyde in aqueous solution in the presence of at least one catalyst to obtain a crude product comprising water, dioxolane and methanol,

[0010] b) transferring the distillate stream comprising the crude product from the top of the reactive distillation apparatus to a phase separation unit, wherein an organic extractant is present in the phase separation unit,

[0011] c) transferring the organic fraction stream from the phase separation unit to the upper part of a purification column, discharging a bottom product stream comprising dioxolane from the purification column, and recycling the distillate stream from the purification column to the phase separation unit,

[0012] d) transferring the aqueous distillate stream from the phase separation unit to a wastewater column, withdrawing a wastewater stream from the bottom of the wastewater column, withdrawing a side stream from a section between the feed section and the reflux section of the wastewater column and recycling the stream to the phase separation unit, and withdrawing a distillate stream comprising methanol from the wastewater column.

[0013] It has been found that providing a phase separation unit between the reactive distillation apparatus and the two further columns, in combination with providing an organic extractant, simplifies the separation of the component mixture, increases the dioxolane purity, facilitates complete recycling of the extractant and minimizes losses of valuable products.

[0014] Preferably, the process of the present invention is a continuous process such that steps (a) to (d) above are performed simultaneously.

[0015] The reactive distillation apparatus used in step (a) can be any combination of reaction and distillation capable of reacting ethylene glycol and formaldehyde to produce dioxolane. In one embodiment, the reactive distillation apparatus is configured as a reactor directly connected to a distillation column. In another embodiment, the reactive distillation apparatus is configured as a reactive distillation column, wherein the catalyst is embedded on a plate or stage of the distillation column, preferably in the lower portion of the distillation column. In another embodiment, the reactive distillation apparatus is configured as a reactor directly connected to a reactive distillation column, wherein the catalyst is present in the reactor as well as in a portion of the distillation column.

[0016] Preferably, the mass fraction of methanol in the distillate stream from the reactive distillation unit is from 0.02% to 5% by weight.

[0017] It is further preferred that the mass fraction of methanol in the bottom product stream of the purification column is less than 0.5%, more preferably less than 0.1%, most preferably less than 0.05%, in particular less than 0.01%.

[0018] Methanol is often present in small amounts in the feed stream of aqueous formaldehyde solutions, primarily due to incomplete conversion of methanol during the formaldehyde production process. Furthermore, methanol acts as a stabilizer for the formalin solution. Despite its small presence in the feed stream, it has been found that complete water recirculation can lead to methanol accumulation and operational errors in long-term operation. This issue has not been addressed in the prior art. The present invention's technical solution, which removes a distillate stream containing methanol from the wastewater column, addresses this problem.

[0019] In a preferred embodiment, a side stream comprising additional methanol is discharged from a section below the feed section of the wastewater column. Depending on the operating conditions of the wastewater column, methanol accumulates in the middle region of the column. The additional side stream discharge is advantageous for removing methanol and thus stabilizing process operation.

[0020] In another preferred embodiment, a further stream comprising water is fed to the phase separation unit. Since water is a component of the distillate stream of the reactive distillation unit, it is transferred to the phase separation unit in step (b) of the process according to the invention. The largest part of the water is transferred to the wastewater column as the aqueous phase from the phase separation unit. At first glance, the addition of further water is counter-intuitive, as it would increase the load and thus the operating costs of the wastewater column. However, it has been found that the addition of further water increases the operability range of the phase separation unit and therefore has a positive effect on the stable operation of the process according to the invention.

[0021] Generally, there is no particular limitation on the composition of the organic extractant as long as it can separate dioxolane and water.

[0022] In a preferred embodiment, the organic extractant ("EA") is selected from the group consisting of:

[0023] (a) gamma_inf_298_(EA in water)+gamma_inf_298_(water in EA)>1600

[0024] (b) gamma_inf_298_(methanol in EA) / gamma_inf_298_(methanol in water)>1.5

[0025] (c) gamma_inf_335_(EA in dioxolane)>1

[0026] gamma_inf_335_(EA in water)>1

[0027] gamma_inf_335_(dioxolane in EA)>1

[0028] gamma_inf_335_(water in EA)>1

[0029] (d) and additionally

[0030] If P 0 DX >P 0 EA >P 0 W :

[0031] (P 0 DX gamma_inf_335_(dioxolane in EA) / P 0 EA -1)

[0032] (P 0 DX / P 0 EA / gamma_inf_335_(EA in dioxolane)-1)<0

[0033] Otherwise, if P 0 W >P 0 EA :

[0034] (P 0 DX gamma_inf_335_(dioxolane in EA) / P 0 EA -1)

[0035] (P 0 DX / P 0 EA / gamma_inf_335_(EA in dioxolane)-1)<0 and

[0036] (P 0 W gamma_inf_335_(water in EA) / P 0 EA -1)

[0037] (P 0 W / P 0 EA / gamma_inf_335_(EA in water)-1)<0

[0038] where “gamma_inf_<temperature>_(<solute> in <solvent>)” represents the limiting activity coefficient at 298.15 K (“298”) or 334.85 K (“335”) and infinite dilution of the solute in the solvent, respectively, and P 0 k represents the vapor pressure of pure component k, "DX" represents dioxolane, and "W" represents water.

[0039] Condition (a) ensures the presence of a miscibility gap in the phase separation unit, which enhances the separation of the organic and aqueous phases. Condition (b) ensures the enrichment of methanol in the aqueous fraction stream exiting the phase separation unit. Condition (c) ensures the absence of significant amounts of boiling azeotropes that would hinder separation into the pure components. Condition (d) depends on the vapor pressures of the pure components and favors azeotropic distillation. For condition (d), all pure component vapor pressures are calculated at a temperature of 334.85 K.

[0040] Methods and software tools for determining pure component vapor pressures and limiting activity coefficients are known in the art. For example, pure component vapor pressure data can be derived from the vapor pressure function of experimental data, and limiting activity coefficients (activity coefficients at infinite dilution) can be calculated using the quantum chemical continuum solvation model Cosmo-RS (COSMOthermX version C30_1702, developed and copyrighted by COSMOlogic GmbH & Co. KG, Imbacher Weg 46, 51379 Leverkusen, Germany) with parameterization BP_TZVP_C30_1701.

[0041] Preferably, the extractant is selected from pentane, cyclopentane, 2,2-dimethylbutane, 2,3-dimethylbutane, methyl isobutyl ether, 2-methylpentane, 3-methylpentane, propyl isopropyl ether, hexane, methylcyclopentane, 2,2-dimethylpentane, 2,4-dimethylpentane, cyclohexane, 3,3-dimethylpentane, 2-ethyl-3-methyl-1-butene, 1,1-dimethylcyclopentane, 2-methylhexane, di-n-propyl ether, (z)-1,3-dimethyl Cyclopentane, trans-1,2-dimethylcyclopentane, trans-1,3-dimethylcyclopentane, 3-methyl-hexane, 1-ethoxybutane, 3-ethylpentane, 2,2,4-trimethylpentane, n-heptane, isopropyl-isobutyl ether, (z)-1,2-dimethylcyclopentane, 2,2-dimethylhexane, 2,3-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 3,4-dimethylhexane, 2-methylheptane, octane.

[0042] Table 1 shows the values ​​of the vapor pressures of the pure components and the limiting activity coefficients calculated using the above-mentioned Cosmo-RS model.

[0043]

[0044]

[0045] More preferably, the extractant is selected from hexane (C6H 14 ). The isomers of hexane are n-hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane and 2,2-dimethylbutane. The extractant may contain a single isomer of hexane or a mixture of isomers. Other substances may be present in the extractant, such as other C6 hydrocarbons, such as cyclohexane or methylcyclopentane (C6H 12 ).

[0046] Even more preferably, the extractant comprises at least 80%, preferably at least 90%, more preferably at least 95%, and especially at least 99% by weight of n-hexane. Particularly preferred technically pure grades of hexane typically comprise 99% or more of n-hexane and up to 1% of a total amount of various C6 isomers, including cyclohexane and methylcyclopentane. High-purity n-hexane is preferred to avoid the accumulation of side components in the extractant.

[0047] In another preferred embodiment, a supplementary stream containing an organic extractant is fed into the phase separation unit. One advantage of the method according to the present invention compared to the prior art is that the extractant is completely recycled by design and therefore there is no loss of extractant. The extractant must be provided once at the beginning of the method. The extractant is then retained during the process. However, due to operational disturbances or failures, it may happen that the extractant is discharged from the method in the form of an effluent stream. Therefore, providing a supplementary stream of extractant is beneficial for the stable operation of the method. Generally, the supplementary stream can be fed into any process stream or process unit. Preferably, the supplementary stream is fed into the phase separation unit. More preferably, the supplementary stream is fed into the mixing device of the phase separation unit.

[0048] In a preferred embodiment of the method according to the present invention, the phase separation unit includes a mixer and a phase separator. The distillate stream from the reactive distillation device, the distillate stream from the purification tower, the side stream from the wastewater tower and optionally another stream comprising water and / or a supplementary stream comprising an organic extractant are fed to the mixer and mixed in the mixer. The outlet stream of the mixer is fed to the phase separator. The advantage of mixing the stream in the first step and separating each phase in the second step is that the mixture fed to the phase separator is more uniform, for example, in terms of droplet size, compared with the stream being directly fed to the phase separator without a mixing step. The mixer can be any type of mixing device that provides a thorough and uniform mixture. Preferably, the mixer is a static mixer. In another preferred embodiment, the mixed stream in the mixer outlet is fed to a cooling device, in which the temperature of the mixed stream is reduced before the mixed stream is fed to the phase separator. Reducing the temperature of the mixed stream is conducive to the stable operation of the phase separation.

[0049] The method according to the present invention offers several advantages over methods known in the prior art. Dioxolane is produced and provided in very high purity without significant product losses through other logistics. Side components, particularly methanol, are effectively removed. The extractant used can be recycled without causing material losses. The method can be operated in a stable and reliable manner on an industrial and commercial scale.

[0050] The invention will be described below with the aid of the accompanying drawings; the drawings are to be understood as schematic illustrations. They do not constitute any restrictions on the invention, for example with regard to specific dimensions or design variants of the components.

[0051] In the picture:

[0052] Figure 1 A block diagram of a first embodiment of the method according to the invention is shown.

[0053] Figure 2 A block diagram of a second embodiment of the method according to the invention is shown.

[0054] Figure 3 A preferred embodiment of the phase separation unit according to the invention is shown.

[0055] List of reference symbols used

[0056] 1...feed stream containing ethylene glycol

[0057] 2…feed stream containing formaldehyde and methanol in aqueous solution

[0058] 10…Reactive distillation unit

[0059] 11…Distillate stream from reactive distillation unit

[0060] 20…Phase separation unit

[0061] 21…Organic fraction logistics

[0062] 22…Aqueous fraction stream

[0063] 23…Logistics containing water

[0064] 24…Make-up flow of organic extractant

[0065] 25…Mixer

[0066] 26…Phase separator

[0067] 27…Cooling device

[0068] 30…Purification tower

[0069] 31…Bottom product stream of purification column

[0070] 32…Distillate stream from purification column

[0071] 40…wastewater tower

[0072] 41…Wastewater Logistics

[0073] 42…side stream from wastewater tower

[0074] 43…Distillate stream from wastewater tower

[0075] 44…side stream from wastewater column containing methanol

[0076] Figure 1 A block diagram of a first embodiment of the process according to the present invention is shown. The block diagram shows only the main operating units. Auxiliary equipment such as reboilers, condensers, pumps, valves and instrumentation are not shown. Figure 1 Depicted in.

[0077] In a continuous process for producing dioxolanes, a feed stream 1 comprising ethylene glycol and a feed stream 2 comprising formaldehyde and methanol in an aqueous solution are fed into the lower region of a reactive distillation apparatus 10. At least one catalyst is preferably present in the lower portion of the reactive distillation apparatus 10. The catalyst reacts the ethylene glycol and formaldehyde in the aqueous solution to form a crude reaction product comprising water, dioxolanes, and methanol. The crude product is removed from the top of the reactive distillation apparatus 10, a portion of which is condensed and recycled to the reactive distillation apparatus 10 in a reflux manner (not shown), and the remainder is transferred to a phase separation unit 20 as a distillate stream 11.

[0078] In phase separation unit 20, an organic extractant is present, which enhances the separation of the influent into an aqueous fraction and an organic fraction. The organic fraction is discharged from phase separation unit 20 as stream 21 and transferred to the upper portion of purification column 30. The aqueous fraction is discharged from phase separation unit 20 as stream 22 and transferred to wastewater column 40.

[0079] The purification column 30 is equipped with a reboiler (not shown) that vaporizes part of the material present at the bottom of the column so that the organic material fed as stream 21 and the vapor generated in the reboiler are in countercurrent within the column. The remaining portion of the material at the bottom of the purification column 30 is discharged as a dioxolane-rich bottom product stream 31. The upwardly flowing material is discharged from the purification column 30 as a distillate stream 32 and is recycled to the phase separation unit 20.

[0080] The aqueous fraction stream 22 from the phase separation unit 20 is fed to the middle section of the wastewater tower 40. The tower is equipped with a reboiler and a condenser (not shown) that can achieve a countercurrent state of liquid and vapor in the tower. Part of the liquid material at the bottom of the tower is discharged as a water-rich wastewater stream 41. The remainder is fed to the reboiler. The overhead stream leaving the top of the wastewater tower 40 is fed to the condenser. The main part of the condensed material is recycled to the tower in a reflux manner. The remainder is discharged as a distillate stream 43 containing methanol. A side stream 42 is discharged from the section between the feed section and the reflux section of the wastewater tower 40 and recycled to the phase separation unit 20. Optionally, an additional stream 23 containing water and / or a supplementary stream 24 containing an organic extractant is fed to the phase separation unit 20.

[0081] Figure 2 A block diagram of a second embodiment of the method according to the present invention is shown. Figure 1 The main difference is that an additional side stream 44 containing methanol is withdrawn from the section below the feed section of the wastewater column 40. An advantage of this embodiment is that the additional side stream 44 contains methanol, but only does not contain dioxolane. Figure 1 Compared to the first embodiment shown in , the methanol load in the upper portion of the wastewater column 40 is reduced, which results in a reduction in the distillate stream 43.

[0082] Figure 3A preferred embodiment of a phase separation unit 20 according to the present invention is shown. The phase separation unit 20 comprises a mixer 25 and a phase separator 26. The distillate stream 11 from the reactive distillation unit, the distillate stream 32 from the purification column, and the side stream 42 from the wastewater column are fed to the mixer 25. Optionally, an additional stream 23 comprising water and / or a make-up stream 24 comprising an organic extractant are also fed to the mixer 25. All streams are mixed in the mixer 25, the outlet stream of the mixer is fed to a cooling device 27, where the temperature of the mixed stream is reduced, and the outlet stream of the cooling device 27 is fed to the phase separator 26. Example

[0083] Under stable production conditions, according to Figure 1 The industrial-scale experiments in a continuous setup were operated over 9 days.

[0084] Reactive distillation apparatus 10 was configured as a reactor directly connected to a 30-tray distillation column. 145 kg / h of an aqueous solution containing 65 wt% formaldehyde and 0.6 wt% methanol was continuously fed into the reactor. 185 kg / h of ethylene glycol was continuously fed to the 10th tray (counted from the top) of the distillation column in a countercurrent flow to the crude dioxolane product flowing out of the reactor. Sulfuric acid was used as a catalyst at a concentration of 2 wt% relative to the reactor contents.

[0085] The distillate stream 11 containing the crude product is transferred from the top of the reactive distillation apparatus 10 to a phase separation unit 20. The phase separation unit comprises a static mixer 25 and a phase separator 26. An additional water stream 23 is fed to the reactor at a feed rate of 205 kg / h. During the startup process, n-hexane was charged into the apparatus as the organic extractant. The mass fraction of n-hexane in the organic extractant was 99%, and n-hexane (C6H 14 ) and C6H 12 The isomers of the components amounted to the remaining 1%.During the nine-day test run, it was not necessary to provide a make-up stream 24 comprising the extractant.

[0086] Regarding the selection criteria for a suitable extractant, the n-hexane used meets the following conditions:

[0087] (a) gamma_inf_298_(EA in water) + gamma_inf_298_(water in EA) = 72271 > 1600

[0088] (b) gamma_inf_298_(methanol in EA) / gamma_inf_298_(methanol in water) = 114.9 > 1.5

[0089] (c) gamma_inf_335_(EA in dioxolane) = 4.98 > 1

[0090] gamma_inf_335_(EA in water)=69637>1

[0091] gamma_inf_335_(dioxolane in EA)=4.1>1

[0092] gamma_inf_335_(water in EA)=202.14>1

[0093] Since the pure component vapor pressure of n-hexane (calculated at a temperature of 334.85K) is greater than the pure component vapor pressure of dioxolane (P 0 EA =1110.7hPa, P 0 DX =905.6hPa), so no other conditions need to be met.

[0094] Organic fraction stream 21 was transferred from phase separation unit 20 to the uppermost tray of purification column 30. Distillate stream 32 was recycled to mixer 25 of phase separation unit 20. Dioxolane having a purity of 99.9% by weight was removed from the bottom of the column at a rate of 190 kg / h as bottom product stream 31. The water content of the dioxolane product was 43 ppm. The methanol content was 69 ppm. No extractant (n-hexane) was detected in the dioxolane product.

[0095] Stream 22, which contains the aqueous fraction from the phase separator, is transferred to the 20th tray (30 trays total, counting from the top) of wastewater column 40. Wastewater stream 41 is discharged from the bottom of the column, having a water content of 98.3% by weight. Unreacted formaldehyde (1.6% by weight) is also discharged with wastewater stream 41.

[0096] A side stream 42 is removed from tray 10 of the wastewater column and recycled to mixer 25. Distillate stream 43 from the wastewater column is condensed and partially recycled to the top of the column as a reflux stream. The remainder of distillate stream 43 is removed from the wastewater column at a rate of 28.5 kg / h. This stream contains 85.5% by weight of dioxolane, 9.1% by weight of water, 0.9% by weight of methanol, and small amounts of formaldehyde and n-hexane.

[0097] In industrial-scale experiments, dioxolane was produced in excellent purity under stable production conditions. No extractant (n-hexane) was detected in the dioxolane product. During the 9 days of experimental operation, the wastewater quality always met the specifications. Some fluctuations in the side-cut flow from the wastewater column were observed, which led to further fluctuations of up to 10% by weight in the composition of the organic and aqueous phases in the phase separator. However, these fluctuations generally did not have an impact on the overall process, especially on the quality of the dioxolane product. Therefore, the method of the present invention proved to be very robust with respect to interferences.

[0098] Comparative Examples

[0099] The examples according to the invention were compared with Example 4 of document EP 0 867 434 A1. The main differences lie in the column sequence and the prior art column configuration lacking a phase separation unit, as well as in the choice of extractant.

[0100] In a comparative example, 85 g / h of formalin (60 wt% formaldehyde in aqueous solution) was fed to a reactor connected to a distillation column. 106 g / h of ethylene glycol was fed to the distillation column in a countercurrent flow to the crude dioxolane product exiting the reactor. A distillate stream containing 65.4 wt% dioxolane, 33.7 wt% water, and 0.1 wt% formaldehyde was discharged from the first distillation column at a rate of 191 g / h and fed to a dehydration column. In the dehydration column, water was discharged from the bottom, and a distillate stream containing an azeotropic mixture of 91.8 wt% dioxolane and 7.6 wt% water was discharged at a rate of 136 g / h and fed to a purification column. To break the azeotrope, benzene was added to the purification column as an extractant at a flow rate of 16 g / h. Dioxolane was obtained as a bottom product from the purification column at a flow rate of 135 g / h, wherein the benzene concentration in the dioxolane product stream was 11% by weight and the water content was 44 ppm.

[0101] Compared to this prior art example, the process according to the present invention provides the desired dioxolane product in significantly higher purity. As a further advantage of the process according to the present invention, the extractant is almost entirely recycled internally. In contrast to the prior art process, the process according to the present invention does not require expensive handling or processing of the extractant.

Claims

1. A method for preparing dioxolane, comprising the following steps: a) feeding a first feed stream (1) comprising ethylene glycol and a second feed stream (2) comprising formaldehyde and methanol in aqueous solution into a reactive distillation unit (10), and reacting ethylene glycol and formaldehyde in aqueous solution in the presence of at least one catalyst to obtain a crude product comprising water, dioxolane and methanol, b) transferring the distillate stream (11) comprising the crude product from the top of the reactive distillation apparatus (10) to a phase separation unit (20), wherein an organic extractant is present in the phase separation unit (20), c) transferring the organic fraction stream (21) from the phase separation unit (20) to the upper part of the purification column (30), discharging the bottom product stream (31) containing dioxolane from the purification column (30), and recycling the distillate stream (32) from the purification column (30) to the phase separation unit (20), d) transferring the aqueous fraction stream (22) from the phase separation unit (20) to a wastewater tower (40), discharging a wastewater stream (41) from the bottom of the wastewater tower (40), discharging a side stream (42) from a section between a feed section and a reflux section of the wastewater tower (40) and recycling the stream (42) to the phase separation unit (20), and discharging a distillate stream (43) containing methanol from the wastewater tower (40).

2. The method according to claim 1, wherein a side stream (44) containing methanol is discharged from a section below the feed section of the wastewater column (40).

3. The process according to claim 1, wherein a further stream (23) comprising water is fed to the phase separation unit (20).

4. The process according to any one of claims 1 to 3, wherein the extractant is selected from the group consisting of pentane, cyclopentane, 2,2-dimethylbutane, 2,3-dimethylbutane, methyl isobutyl ether, 2-methylpentane, 3-methylpentane, propyl isopropyl ether, hexane, methylcyclopentane, 2,2-dimethylpentane, 2,4-dimethylpentane, cyclohexane, 3,3-dimethylpentane, 2-ethyl-3-methyl-1-butene, 1,1-dimethylcyclopentane, 2-methylhexane, di-n-propyl ether, (z)-1,3-dimethylcyclopentane, trans-1,2-dimethylcyclopentane, trans-1,3-dimethylcyclopentane, 3-methyl-hexane, 1-ethoxybutane, 3-ethylpentane, 2,2,4-trimethylpentane, n-heptane, isopropyl-isobutyl ether, (z)-1,2-dimethylcyclopentane, 2,2-dimethylhexane, 2,3-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 3,4-dimethylhexane, 2-methylheptane, octane.

5. The process according to any one of claims 1 to 3, wherein the extractant is selected from the isomers of hexane.

6. The process according to any one of claims 1 to 3, wherein the extractant comprises n-hexane in a mass fraction of at least 80%.

7. The method according to claim 6, wherein the extractant comprises n-hexane in an amount of at least 90% by mass.

8. The process according to claim 7, wherein the extractant comprises n-hexane in an amount of at least 95% by mass.

9. The process according to claim 8, wherein the extractant comprises n-hexane in an amount of at least 99% by mass.

10. The process according to any one of claims 1 to 3, wherein a make-up stream (24) comprising an organic extractant is fed to the phase separation unit (20).

11. The method according to any one of claims 1 to 3, wherein the phase separation unit (20) comprises a mixer (25) and a phase separator (26), the distillate stream (11) from the reactive distillation apparatus (10), the distillate stream (32) from the purification tower (30), the side stream (42) from the wastewater tower (40), and optionally an additional stream (23) comprising water and / or a make-up stream (24) comprising an organic extractant are fed into the mixer (25) and mixed in the mixer (25), and the outlet stream of the mixer (25) is fed into the phase separator (26).

12. The process according to any one of claims 1 to 3, wherein the mass fraction of methanol in the distillate stream (11) from the reactive distillation unit (10) is from 0.02% to 5%.

13. The method according to any one of claims 1 to 3, wherein the mass fraction of methanol in the bottom product stream (31) of the purification tower (30) is less than 0.5%.

14. The method according to claim 13, wherein the mass fraction of methanol in the bottom product stream (31) of the purification tower (30) is less than 0.1%.

15. The method according to claim 14, wherein the mass fraction of methanol in the bottom product stream (31) of the purification tower (30) is less than 0.05%.

16. The method according to claim 15, wherein the mass fraction of methanol in the bottom product stream (31) of the purification tower (30) is less than 0.01%.

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