WO2024245763A1

WO2024245763A1 - Process for separating n-methylmorpholine (nmm) from a mixture com-prising nmm, water, trimethyl-ethylenediamine (trimethyl-eda) and tetra-methyl-ethylenediamine (tetramethyl-eda)

Info

Publication number: WO2024245763A1
Application number: PCT/EP2024/063462
Authority: WO
Inventors: Michael Joedecke; Joerg Pastre; Artur KOZICKI; Ralph Busch
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2023-05-26
Filing date: 2024-05-16
Publication date: 2024-12-05
Anticipated expiration: 2025-11-26

Abstract

Process for separating N-methyl morpholine (NMM) from a mixture comprising NMM, water, tri- methyl-ethylenediamine (Trimethyl-EDA) and tetramethyl-ethylenediamine (Tetramethyl-EDA), the process comprising the following steps: (1) subjecting the mixture to distillation to obtain a mixture (1) comprising NMM, water and Tetramethyl-EDA; (2) subjecting mixture (1) to dewatering to obtain a mixture (2) comprising NMM and Tetrame- thyl-EDA; and (3) subjecting mixture (2) to distillation to obtain a high purity NMM.

Description

PROCESS FOR SEPARATING N-M ETHYLMORPHOLINE (NMM) FROM A MIXTURE COMPRISING NMM, WATER, TRIMETHYL-ETHYLENEDIAMINE (TRIMETHYL-EDA) AND TETRA- METHYL-ETHYLENEDIAMINE (TETRAM ETHYL-EDA)

Description

TECHNICAL FIELD

This invention relates to a process for separating N-methylmorpholine (NMM) from a mixture comprising NMM, water, trimethyl-ethylenediamine (Trimethyl-EDA) and tetramethyl-ethylenedi- amine (Tetramethyl-EDA).

STATE OF THE ART

N-methylmorpholine (NMM) is used for instance in the production of N-methylmorpholine oxide (NMMO). The latter can be obtained by oxidation of NMM in the presence of H2O2. NMMO can be used as a solvent in the lyocell process to produce lyocell fibers. The production of NMMO and its use in the lyocell process as a cellulose solvent is for instance taught in DE 3618352 A1.

NMM can be obtained by the reaction of diethylene glycol and methylamine. It is further obtained as a by-product in the production of bis-[2-(N,N-dimethylamino)-ethyl]-ether (BDMAE) via the reaction of diethylene glycol and dimethylamine. Such process is for instance described in example 1 of WO 2010/031719 A1 (BASF). Upon purification of the BDMAE6 one obtains an NMM-rich mixture that predominantly contains water (about 50 wt.-%) and NMM (about 40 wt- %) but also small amounts of by-products such as Trimethyl-EDA and Tetramethyl-EDA. The boiling points of water, NMM, Trimethyl-EDA and Tetramethyl-EDA are very close to each other, namely 116°C (Trimethyl-EDA), 120 °C (Tetramethyl-EDA), 116 °C (NMM) and 100 °C (water), each at a pressure of 1 atm. Therefore, the separation of such mixture is technically challenging.

When starting the separation with the removal of water one obtains a mixture of NMM, Trimethyl-EDA and Tetramethyl-EDA. However, it has been observed that upon removal of water nor separation of Trimethyl-EDA and Tetramethyl-EDA from NMM is possible.

One object of this invention is to provide a process for separating NMM from a mixture comprising NMM, water, trimethyl-ethylenediamine and tetramethyl-ethylenediamine and obtaining NMM in high purity and high yield. SUMMARY OF THE INVENTION

Disclosed is a process for separating N-methylmorpholine (NMM) from a mixture comprising NMM, water, trimethyl-ethylenediamine (Trimethyl-EDA) and tetramethyl-ethylenediamine (Tet- ramethyl-EDA), the process comprising the following steps:

(1) subjecting the mixture to distillation to obtain a mixture (1) comprising NMM, water and Tetramethyl- EDA;

(2) subjecting mixture (1) to dewatering to obtain a mixture (2) comprising NMM and Tetrame- thyl-EDA; and

(3) subjecting mixture (2) to distillation to obtain high purity NMM.

DETAILED DESCRIPTION OF THE INVENTION

The mixture that is subjected to the process according to the present invention is simply referred to as “mixture” or “NMM-mixture”. Preferred compositions thereof are specified below.

In the context of this invention, high purity NMM preferably means NMM having a purity of > 96 wt.-%, more preferably > 98 wt.-%, even more preferably > 99 wt.-% or > 99.5 wt.-% (such as > 99.6 wt.-%). Such high purity NMM usually does not contain any Trimethyl-EDA or is substantially devoid thereof. In particular, the amount of Trimethyl-EDA in the high purity NMM is less than 0,001 wt.-%, preferably less than 10 wt.-ppm, more preferably less than 1 wt.-ppm or even less than 0.1 wt.-ppm. The amount of Tetramethyl -EDA in the high purity NMM may be less than 0,5 wt.-%, preferably less than 0.1 wt.-%.

It has been found that Trimethyl-EDA can only be separated from NMM before the separation of water. That means the presence of water in the separation of trimethyl-EDA is crucial. Moreover, it has been found, that on the other hand, the separation of Tetramethyl-EDA is not possible in the presence of water. Therefore, conducting steps (1) to (3) in their respective order is crucial for the efficient separation according to the present invention.

The process can be conducted either continuously or discontinuously.

Preferably, step (1) reads as follows:

(1) subjecting the mixture to distillation to obtain a mixture (1) comprising NMM, water and Tetramethyl-EDA and mixture (1a) comprising Trimethyl-EDA. Usually, NMM losses in step (1) cannot be avoided in which case mixture (1a) comprises Trime- thyl-EDA and NMM. Preferably it also comprises water. Preferred compositions of mixture (1) and (1a) are specified below.

Usually, mixture (1) is the lower boiling and mixture (1a) is the higher boiling fraction. In such case, mixture (1a) is obtained as a bottom product and mixture (1) constitutes the distillate. In case of a continuous operation of the process according to the invention, mixture (1) can be obtained at a side stream or at the top of the respective column (preferably at the top of the respective column). In case of a discontinuous operation of the process according to the invention, mixture (1) is obtained at the top of the respective column.

It has been found that Tetramethyl- EDA cannot be separated from the NMM in the presence of water. It is therefore crucial to dewater mixture (1) according to step (2) to obtain mixture (2) comprising NMM and Tetramethyl-EDA. Since NMM and water form an azeotrope, it is crucial to apply respective methods that allow for the separation of the NMM/water azeotrope. The dewatering pursuant to step (2) can for instance be accomplished by pressure swing distillation. Preferably, the dewatering pursuant to step (2) is carried out by extraction. As an extracting agent preferably an alkaline solution, particular preferably a solution of caustic soda, is used. Such solution of caustic soda preferably has a concentration of 40 to 60 wt.-%.

It has been found that, once the water is removed, Tetramethyl-EDA can be separated from NMM. This is accomplished by subjecting mixture (2) to distillation pursuant to step (3). Nonetheless, because the boiling points of NMM and Tetramethyl-EDA are very close, their separation is elaborate. The key point is therefore to provide for sufficient separation efficiency. In step (3) the Tetramethyl-EDA is usually obtained as a bottom product (i.e. step (3) preferably reads as: “subjecting mixture (2) to distillation to obtain a high purity NMM and a bottom product comprising Tetramethyl-EDA”). In principle, the separation can be conducted in one or two steps.

According to a first preferred embodiment, step (3) comprises the following steps:

(3i) subjecting mixture (2) to distillation to obtain a mixture (3a) comprising light boilers, a mixture (3) comprising NMM and a mixture (3b) comprising Tetramethyl-EDA, and

(3ii) subjecting mixture (3) to distillation to obtain high purity NMM and a bottom product comprising Tetramethyl-EDA.

An example for such embodiment is provided for in Fig. 1. Usually, NMM losses in step (3i) cannot be avoided in which case mixture (3a) comprises light boilers and NMM, and mixture (3b) comprises Tetramethyl-EDA and NMM. Preferred compositions of mixture (3a), (3) and (3b) are specified below.

In step (3i) mixture (3a) constitutes the low boiling fraction, followed by mixture (3) and mixture (3b) being the highest boiling fraction. Therefore, mixture (3b) is usually obtained as a bottom product. In case of a continuous operation of the process according to the invention, mixture (3a) can be obtained at the top of the respective column and mixture (3) as a side stream. In case of a discontinuous operation of the process according to the invention, mixture (3a) can be obtained as a first fraction and mixture (3) as a second fraction.

The mixture (3) obtained in step (3i) already provides for a high NMM purity. Nonetheless, it comprises small amounts of Tetramethyl-EDA. To further increase the purity of NMM, the mixture (3) obtained in step (3i) is subjected to distillation to obtain high purity NMM.

In step (3ii) usually a bottom product comprising Tetramethyl-EDA is obtained. Usually is also comprises NMM.

In case of a continuous operation of the process according to the invention, high purity NMM can be obtained as a side stream or at the top of the respective column (preferably at the top of the respective column). In case of a discontinuous operation of the process according to the invention, high purity NMM is obtained at the top of the respective column.

According to a second preferred embodiment step (3) comprises the following steps:

(3A) subjecting mixture (2) to distillation to obtain a mixture (3a) comprising light boilers and a mixture (3) comprising NMM as a bottom product, and

(3B) subjecting mixture (3) to distillation to obtain a to obtain high purity NMM and a bottom product comprising Tetramethyl-EDA.

This embodiment differs from the first preferred embodiment in the feature, that no mixture (3b) is obtained but the mixture (3) is obtained as a bottom product.

An example for such embodiment is provided for in Fig. 2.

Usually, NMM losses in step (3A) cannot be avoided in which case mixture (3a) comprises light boilers and NMM. Preferred compositions of mixture (3a) and (3) are specified below. In step (3A) mixture (3a) constitutes the low boiling fraction. Mixture (3) is obtained as a bottom product. In case of a continuous operation of the process according to the invention, mixture (3a) can be obtained at the top of the respective column and mixture (3) as a bottom stream. In case of a discontinuous operation of the process according to the invention, mixture (3a) can be obtained as a first fraction and mixture (3) in the bottom.

The mixture (3) obtained in step (3A) comprises the Tetramethyl-EDA. To remove the Tetrame- thyl-EDA from the NMM, mixture (3) as obtained in step (3A) is subjected to further distillation in step (3B). The Tetramethyl-EDA is obtained as a bottom product. It may further comprise NMM. High purity NMM is preferably obtained as a distillate (i.e. as a top stream in case of continuous distillation).

It is to be noted that the first and the second preferred embodiment uses two steps for the separation of NMM and Tetramethyl-EDA. This requires the use of columns providing for high separation efficiency. Nonetheless, it is also possible to conduct the separation in one step, which requires the use of a distillation columns that provides for an even higher separation efficiency.

Therefore, according to a third preferred embodiment, in step (3) mixture (2) is subjected to distillation using a column that provides for sufficient separation efficiency to obtain a mixture (3a) comprising light boilers, high purity NMM, and a bottom product comprising Tetramethyl-EDA.

An example for such embodiment is provided for in Fig. 3.

In such case, mixture (3a) is usually obtained as the first fraction, the high purity NMM as a second fraction (i.e. a side stream in case of a continuous distillation).

Preferably steps (1) and (3) (including steps (3i) and 3(ii) or (3A) and (3B), respectively) are conducted using a suitable distillation column(s) and step (2) using a suitable rectification columns) (in case of a continuous extraction) or a vessel (in case of a batch extraction). Any such columns are well known to the person having ordinary skill in the art. In step (1) a plate column or a packed column can be used. For step (2) any type of extraction column can be used. Preferred types of columns are plate columns and packed columns. Suitable columns that may be used in step (3) are preferably packed columns. The internals of any packed columns specified for steps (1) and (3) may be structured packings, mesh packings or random packings. . This applies to any of the three preferred embodiments specified above. Any pressure as referenced herein refers to the absolute pressure at the top of the respective column. The pressure in specified in bar or mbar using 1 bar = 1000 mbar = 10⁵ Pa = 100 kPa = 0.1 MPa.

Ranges for the top and the sump temperature in a column are always given under the proviso that the temperature in the sump is higher than the temperature at the top. Usually, the temperature in the sump is more than 1 °C, preferably more than 2 °C, or even more preferably more than 5 °C higher than the temperature at the top of a column.

The number of theoretical stages of a column used in step (1) is usually equal to or above 15, preferably in the range of 20 to 60. The pressure is preferably in the range of 0.1 to 3 bar, more preferably in the range of 0.8 to 2.5 bar. The top temperature is preferably in the range of 80 to 105 °C and the sump temperature is preferably in the range of 90 to 120 °C. The reflux ratio is preferably in the range of 0.1 to 10 or even more preferably 2 to 8.

The number of theoretical stages of a column used in step (2) is usually equal to or above 30, preferably in the range of 30 to 300 or even more preferably in the range of 30 to 200 or even 30 to 150. The temperature is preferably in the range of 20 to 70 °C. The extraction is typically conducted at ambient pressure. A preferred pressure is therefore in the range of 0.9 to 1.2 bar.

In case of the first and second embodiment (i.e. for steps (3i) and (3ii) or (3A) and (3B), respectively) the following applies:

The number of theoretical stages of a column used in step (3i) or (3A) is usually equal to or above 20, preferably in the range of 25 to 65. The pressure is preferably in the range of 50 to 600 mbar, more preferably in the range of 100 to 400 mbar. The top temperature is preferably in the range of 55 to 80 °C and the sump temperature is preferably in the range of 65 to 100 °C. The reflux ratio is preferably in the range of 0.1 to 15 or even more preferably 8 to 13.

The number of theoretical stages of a column used in step (3ii) or (3B) is usually equal to or above 10, preferably in the range of 15 to 100. The pressure is preferably in the range of 20 to 300 mbar, more preferably in the range of 50 to 200 mbar. The top temperature is preferably in the range of 35 to 65 °C and the sump temperature is preferably in the range of 50 to 100 °C. The reflux ratio is preferably in the range of 5 to 15 or even more preferably 9.9 to 15.

In case of the third embodiment the following applies with respect to step (3): The column that provides for sufficient separation efficiency is for instance a dividing wall column having preferably 10 to 50, more preferably 20 to 20 theoretical stages, or a column (having a side stream) having more than 80, preferably more than 90, more preferably in the range of 90 to 120 theoretical stages.

Preferably packed columns as specified above are used. This also applies in case of a dividing wall column.

The pressure is preferably in the range of 20 to 300 mbar, more preferably in the range of 50 to 200 mbar. The top temperature is preferably in the range of 30 to 80 °C and the sump temperature is preferably in the range of 150 to 200 °C. The reflux ratio is preferably in the range of 2 to 20 or even more preferably 5 to 10.

The overall distillation yield of NMM for steps (1) to (3) is typically in the range of 80 to 100 wt.- % (e.g. 85 to 98 wt.-%). The respective yield is determined by dividing the amount (mass) of NMM comprised in the high purity NMM, respectively, by the amount (mass) of NMM comprised in the NMM-mixture and multiplication with 100 wt.-%.

In the following, the compositions of all relevant mixtures are specified in more detail.

For any mixture specified herein, the amount of its respective components (including the specification of a “purity”) is specified in weight percent (wt.-%) based on the respective mixture.

The NMM-mixture comprises NMM, water Trimethyl-EDA and Tetramethyl-EDA. Typically, it comprises water in the range of 40 to 80 wt.-%, preferably 50 to 70 wt.-%, NMM in the range of 15 to 50 wt.-%, preferably 20 to 45 wt.-%, Trimethyl-EDA in the range of 0.01 to 3 to wt.-%, preferably 0.02 to 2 to wt.-%, and Tetramethyl-EDA in the range of 0.5 to 5 wt.-%, preferably 0.5 to 4 wt.-%. Preferably the cumulated amount of NMM, water Trimethyl-EDA and Tetramethyl-EDA in the NMM-mixture is > 80 wt.-%, preferably 85 wt.-%, more preferably > 90 wt.-%. Other components that may be present are for instance ethanol, dimethylamine, N,N-dimethyl ethylamine, morpholine, dioxane, 2-(dimethylamino)-ethan-1-ol (DMAE) and N-ethyl morpholine. These chemical compounds usually occur in the production of BDMAE as by-products.

The process according to the invention is suited to separate any mixture that comprises NMM, water Trimethyl-EDA and Tetramethyl-EDA. However, preferably the NMM-mixture results from a BDMAE production process, such process comprising the reaction of diethylene glycol (DEG) and dimethylamine (DMA) in the presence of hydrogen (H₂) and a heterogenous hydrogenation catalyst. BDMAE production can for instance be conducted as taught in WO 2011/067199 A1 or WO 2010/031719 A1 (BASF). The resulting raw BDMAE typically comprises NMM in a range of 8 to 15 wt.-%, based on the raw BDMAE. Usually, in such BDAMES production process, after the reaction of DEG and DMA, the raw BDMAE is subjected to distillation to obtain the NMM- mixture (for example as detailed in Figure 4).

In a preferred embodiment, the mixture (NMM-mixture) results from a continuous BDMAE production process, such process comprising the following steps:

(i) feeding diethylene glycol (DEG) and dimethylamine (DMA) into a reaction zone, where the DEG and the DMA are subjected to an alcohol amination reaction in the presence of hydrogen (H2) and a heterogenous hydrogenation catalyst to obtain a raw BDMAE stream comprising BDMAE, DMA, DEG, NMM, water, Trimethyl-EDA and Tetramethyl-EDA;

(ii) subjecting the raw BDMAE stream of step (i) to a distillation to remove DMA and to obtain a stream (ii) depleted in DMA;

(iii) optionally recycling the DMA obtained in step (ii) to the reaction zone of step (i);

(iv) subjecting the stream (ii) to a distillation to obtain the mixture and a stream (iv) comprising BDMAE and DEG;

(v) subjecting the stream (iv) to a distillation to obtain BDMAE and DEG; and

(vi) optionally recycling the DEG obtained in step (v) to the reaction zone of step (i).

Mixture (1) usually comprises water, NMM and Tetramethyl-EDA. Typically, it comprises water in the range of 10 to 40 wt.-%, preferably 15 to 35 wt.-%, NMM in the range of 40 to 80 wt.-%, preferably 45 to 75 wt.-% and Tetramethyl-EDA in the range of 0.1 to 10 wt.-%, preferably 1 to 8 wt.-%. Mixture (1) usually does not contain any Trimethyl-EDA or is substantially devoid thereof. In particular, the amount of Trimethyl-EDA in the mixture (1) is less than 0,001 wt.-%, preferably less than 10 wt.-ppm, more preferably less than 1 wt.-ppm or even less than 0.1 wt.-ppm. Mixture (1) may also comprise small amounts of ethanol, dimethylamine, dimethyl ethylamine, morpholine, dioxane, 2-(dimethylamino)-ethan-1-ol (DMAE) and N-ethyl morpholine, any of which preferably having a concentration of less than 0.5 wt.-ppm. The cumulated amount of water, NMM and Tetramethyl-EDA in mixture (1) is usually > 90 wt.-%, preferably > 95 wt.-%. Other components that may be present are for instance ethanol, dioxane and N-ethyl-morpholine.

Mixture (1a) usually comprises water, NMM and Trimethyl-EDA. Preferably, it comprises water in the range of 70 to 95 wt.-%, more preferably 80 to 90 wt.-%, NMM in the range of 1 to 20 wt- %, more preferably 3 to 15 wt.-%, and Trimethyl-EDA in the range of 0.01 to 10 wt.-%, more preferably 1 to 8 wt.-%. Mixture (2) usually comprises NMM and Tetramethyl-EDA. Depending on the dewatering efficiency it may also comprise small amounts of water. Typically, it comprises NMM in the range of 65 to 97 wt.-%, preferably 70 to 95 wt.-% and Tetramethyl-EDA in the range of 0.5 to 15 wt.-%, preferably 1 to 10 wt.-%. It may also comprise water in the range of 0.01 to 10 wt.-%, preferably 0.1 to 5 wt.-%. The cumulated amount of water, NMM and Tetramethyl-EDA in mixture (2) is usually > 85 wt.-%, preferably > 90 wt.-%. Other components that may be present are for instance dioxane, ethanol, N-ethyl morpholine, dimethylamine ethanol, 2-(dimethylamino)-ethan- 1-ol (DMAE) and dimethyl ethylamine.

Mixture (3) comprises NMM. Preferably mixture (3) (as obtained in step (3i)) comprises NMM in the range of 80 to 99 wt.-%, and Tetramethyl-EDA in the range of 0.1 to 10 wt.-%. The cumulated amount of NMM and Tetramethyl-EDA is preferably > 95 wt.-%, more preferably > 99 wt.- %. Preferably mixture (3) (as obtained in step (3A)) comprises NMM in the range of 75 to 98 wt- %, and Tetramethyl-EDA in the range of 0.5 to 15 wt.-%. The cumulated amount of NMM and Tetramethyl-EDA is preferably > 95 wt.-%, more preferably > 99 wt.-%.

Mixture (3a) (as obtained in any embodiment of step (3)) usually comprises low boilers and NMM. Low boilers are typically dioxane, ethanol, N-ethyl morpholine, dimethylamine ethanol, 2- (dimethylamino)-ethan-l-ol (DMAE) and dimethyl ethylamine. It may further comprise the remainder of the water not separated off in step (2). Mixture (3a) predominantly consists of NMM. Usually, the amount of NMM amounts to 60 to 95 wt.-% NMM.

Mixture (3b) (as obtained in step (3i)) comprises Tetramethyl-EDA and may further comprise NMM. It usually comprises NMM in the range of 10 to 50 wt.-% and Tetramethyl-EDA in the range of 20 to 80 wt.-%.

The bottom product obtained according to step (3ii) comprises Tetramethyl-EDA and may also comprise NMM. Usually it comprises NMM in the range of 70 to 95 wt.-% and Tetramethyl-EDA in the range of 5 to 20 wt.-%.

The N-methyl morpholine (NNM) being obtained in accordance with the process according to the present invention preferably has a purity of > 96 wt.-%, more preferably > 98 wt.-%, even more preferably > 99 wt.-% or > 99.5 wt.-% (such as > 99.6 wt.-%). Such NMM usually does not contain any Trimethyl-EDA or is substantially devoid thereof. In particular, the amount of Trime- thyl-EDA in the NMM is less than 0,001 wt.-%, preferably less than 10 wt.-ppm, more preferably less than 1 wt.-ppm or even less than 0.1 wt.-ppm. The amount of Tetramethyl -EDA in the NMM may be less than 0,5 wt.-%, preferably less than 0.1 wt.-%. Another aspect of the present invention is a process for the manufacture of BDMAE and high purity NMM, the process comprising the following steps:

(iv) subjecting the stream (ii) to a distillation to obtain a mixture, comprising NMM water, Tri- methyl-EDA, and Tetramethyl-EDA and a stream (iv) comprising BDMAE and DEG;

(v) subjecting the stream (iv) to a distillation to obtain BDMAE and DEG;

(vi) optionally recycling the DEG obtained in step (v) to the reaction zone of step (i); and

(vii) subjecting the mixture of step (iv) to a separation process in accordance with the present invention, including any and all preferred features and embodiments being taught herein, to obtain high-purity NMM.

Another aspect of the present invention is a process for the manufacture of N-methyl morpholine oxide (NMMO), wherein N-methyl morpholine (NMM) is obtained (preferably manufactured) by the process according to the present invention and said NMM being subjected to an oxidation reaction to obtain NMMO. Preferably the NMM is oxidized in the presence of H2O2 and CO2. Such oxidation reaction is for instance specified in more detail in EP application No.

22178338.4.

FIGURES

The following figures only serve for the purpose of the illustration of the present invention and shall therefore not limit it in whatsoever kind.

Figure 1 shows a typical set-up of a continuous operation mode of the process using two columns for the separation of NMM and Tetramethyl-EDA in step (3).

The NMM-mixture is fed to a first distillation column (1). Mixture (1) is withdrawn on top of column (1) and mixture (1a) as a bottom stream. Mixture (1) is fed into extraction column (2), wherein it is contacted with a caustic soda stream in a counter flow mode. A mixture (2) is obtained at the top of column (2) and fed into distillation column (3), wherein it is separated into three streams. This first stream (mixture (3a)) is withdrawn at the top of column (3), a second stream (mixture (3)) is withdrawn as a side stream and a third stream (mixture (3b)) is withdrawn as a bottom stream. Mixture (3) is fed into distillation column (4), where high purity NMM is withdrawn at the top of column (4) and a bottom product is withdrawn at the bottom.

Figure 2 shows a typical set-up of a continuous operation mode of the process using two columns for the separation of NMM and Tetramethyl-EDA in step (3).

The NMM-mixture is fed to a first distillation column (1). Mixture (1) is withdrawn on top of column (1) and mixture (1a) as a bottom stream. Mixture (1) is fed into extraction column (2), wherein it is contacted with a caustic soda stream in a counter flow mode. A mixture (2) is obtained at the top of column (2) and fed into distillation column (3), wherein it is separated into two streams. This first stream (mixture (3a)) is withdrawn at the top of column (3), a second stream (mixture (3)) is withdrawn as a bottom stream. Mixture (3) is fed into distillation column (4), where high purity NMM is withdrawn at the top of column (4) and a bottom product is withdrawn at the bottom.

Figure 3 shows a typical set-up of a continuous operation mode of the process using one column in step 3, such column providing for high separation efficiency.

The NMM-mixture is fed to a first distillation column (1). Mixture (1) is withdrawn on top of column (1) and mixture (1a) as a bottom stream. Mixture (1) is fed into extraction column (2), wherein it is contacted with a caustic soda stream in a counter flow mode. A mixture (2) is obtained at the top of column (2) and fed into distillation column (3), wherein it is separated into three streams. This first stream (mixture (3a)) is withdrawn at the top of column (3), a second stream (high purity NMM) is withdrawn as a side stream and a bottom product is withdrawn as a bottom stream.

Figure 4 shows a typical set-up of a BDMAE production including the separation of the NMM- mixture.

DMA and DEG are fed to a reaction zone to obtain a raw BDMAE stream comprising BDMAE, DMA, DEG, NMM, water, Trimethyl-EDA, and Tetramethyl-EDA. The raw BDMAE is fed to a distillation column (A), where DMA is distilled off and recycled to the reaction zone. The resulting stream depleted in DMA is fed to distillation column (B), where the NMM-mixture is distilled off. The resulting stream is fed to column (C), where high purity BDMAE is distilled off and DEG is obtained as a bottom stream which is recycled to the reaction zone.

EXAMPLES The following examples only serve for the purpose of the illustration of the present invention and shall therefore not limit it in whatsoever kind.

The experiments were conducted using an N MM -mixture obtained from BDAMEE production, having a composition as follows:

Water: 60 wt.-%

NMM: 32 wt.-%

Trimethyl-EDA: 0.25 wt.-%

Tetramethyl-EDA: 2,15 wt.-%

N.N-dimethyethylamine: 1 wt-%

Dioxan: 0,4 wt-%

Morpholine: 0,3 wt-%

DMAE: 3,5 wt-%

N-ethylmorpholine: 0,5 wt-%

The NMM-mixture was subjected to batch-distillation as follows:

Step 1:

In the first step an NMM-water azeotrope was distilled from water and trimethyl-EDA. The trime- thyl-EDA/water mixture contains the heavy boiling compounds of the raw material and is separated over the bottom of the tower.

The process conditions were:

• column efficiency: 25 - 30 theoretical steps

• top pressure: atmospheric pressure

• reflux ratio: ~5

• bottom temperature: ~100°C

• top temperature ~ 90°C

55 wt.-% of the feed (NMM-mixture) was removed over the bottom (mixture (1a)), 45 wt.-% over the top of the column (mixture (1)). Thus, most of the raw material (mainly water) is removed in the column bottom in this step. The trimethyl-EDA (0.25 wt.-% in the raw material) was separated completely from the NMM-water azeotrope. The concentration of NMM in the bottom was around 5.3 wt.-%. Thus, there is a small loss of NMM in this process step. The mixture (1) had a composition as follows: Water: 26 wt.-%

NMM: 66 wt.%

Tetramethyl-EDA: 5 wt.-%

Others: 3 wt.-%.

Others are in particular ethanol, dioxane and N-ethyl-morpholine.

Step 2:

The mixture obtained at the top of the column in step 1 was dewatered using caustic extraction. After the caustic extraction the water concentration of the resulting raw NMM (mixture (2)) was ~ 0.8%. The resulting raw NMM had a composition as follows:

NMM: 78 wt.-%

Tetramethyl-EDA: 3.6 wt.-%

Water: 1.42 wt.-%

Others: 5.02 wt.-%

Others are in particular ethanol, dioxane and N-ethyl morpholine.

Trimethyl-EDA was not detected anymore.

Step 3:

The third step was the purification of the raw NMM obtained in step 2.

The process conditions were:

• column efficiency: ~ 40 theoretical steps

• top pressure: 200 mbar

• reflux ratio: ~10

• bottom temperature: ~75°C

• top temperature: ~ 68°C

In this (third) step, the raw NMM obtained in step 2 was separated into 3 fractions. The light boiling fraction (11 wt.-% of the feed) included the remainder of the process water, light boilers and ~70 wt.-% of NMM. The second fraction (76 wt.-% of the feed) had an NMM-concentration of 99.01 wt.-% and 0.77 wt-% tetramethyl-EDA. The bottom fraction (remainder of the feed material) included 34 wt.-% of NMM and 56 wt.-% of tetramethyl-EDA. Step 4:

In this (fourth) step the NMM (mixture (3)) as obtained according to step 3 (i.e. fraction 2) is further purified.

The process conditions were:

• column efficiency: ~ 40 theoretical steps

• top pressure: 100 mbar

• reflux ratio: ~10 • bottom temperature: ~70°C

• top temperature: ~ 54°C

The NMM was purified to 99.7%. The bottom fraction included 7.1 wt.-% tetramethyl- EDA and

92.7 wt.-% NMM. The NMM distillation yield of both distillations was around 70%. Tetramethyl- EDA was detected in a very low amount (0.08 wt.-%). Such amount could be further reduced by applying for instance a column having more theoretical steps.

Claims

CLAIMS:

1. Process for separating N-methyl morpholine (NMM) from a mixture comprising NMM, water, trimethyl-ethylenediamine (Trimethyl-EDA) and tetramethyl-ethylenediamine (Tetra- methyl-EDA), the process comprising the following steps:

(1) subjecting the mixture to distillation to obtain a mixture (1) comprising NMM, water and Tetramethyl-EDA;

(2) subjecting mixture (1) to dewatering to obtain a mixture (2) comprising NMM and Tetramethyl-EDA; and

(3) subjecting mixture (2) to distillation to obtain a high purity NMM.

2. The process according to claim 1 , wherein step (1) reads as follows:

(1) subjecting the mixture to distillation to obtain a mixture (1) comprising NMM, water and Tetramethyl-EDA and mixture (1a) comprising Trimethyl-EDA.

3. The process according to any of the preceding claims, wherein step (2) is carried out by extraction, preferably using an alkaline solution as an extracting agent.

4. The process according to any of claims 1 to 3, wherein step (3) comprises the following steps:

(3ii) subjecting mixture (3) to distillation to obtain high purity NMM.

5. The process according to any of claims 1 to 3, wherein step (3) comprises the following steps:

6. The process according to any of the two preceding claims, wherein the pressure applied in step (3i) or (3A) respectively, is in the range of 50 to 600 mbar, preferably 100 to 400 mbar.

7. The process according to any of the three preceding claims, wherein the pressure applied in step (3ii) or (3B), respectively, is in the range of 20 to 300 mbar, preferably 50 to 200 mbar.

8. The process according to any of claims 1 to 3, wherein in step (3) mixture (2) is subjected to distillation using a column that provides for sufficient separation efficiency to obtain a mixture (3a) comprising light boilers, high purity NMM, and a bottom product comprising Tetramethyl-EDA.

9. The process according to the preceding claim, wherein the column that provides for sufficient separation efficiency is a dividing wall column or a column having more than 80, preferably more than 90, more preferably in the range of 90 to 120 theoretical stages.

10. The process according to any of the two preceding claims, wherein the pressure applied in step (3) is in the range of 20 to 300 mbar, preferably 50 to 200 mbar.

11. The process according to any of the preceding claims, wherein the pressure applied in step (1) is in the range of 0.1 to 3 bar, preferably 0.8 to 2.5 bar.

12. The process according to any of the preceding claims, wherein the pressure applied in step (2) is in the range of 0.9 to 1.2 bar.

13. The process according to any of the preceding claims, wherein the mixture comprises water in the range of 40 to 80 wt.-%, NMM in the range of 15 to 50 wt.-%, Trimethyl-EDA in the range of 0.1 to 3 to wt.-%, and Tetramethyl-EDA in the range of 0.5 to 5 wt.-%.

14. Process for the manufacture of BDMAE and high purity NMM, the process comprising the following steps:

(i) feeding diethylene glycol (DEG) and dimethylamine (DMA) into a reaction zone, where the DEG and the DMA are subjected to an alcohol amination reaction in the presence of hydrogen (H₂) and a heterogenous hydrogenation catalyst to obtain a raw BDMAE stream comprising BDMAE, DMA, DEG, NMM, water, Trimethyl-EDA and Tetramethyl-EDA;

(iv) subjecting the stream (ii) to a distillation to obtain a mixture, comprising NMM water, Trimethyl-EDA, and Tetramethyl-EDA and a stream (iv) comprising BDMAE and DEG;

(v) subjecting the stream (iv) to a distillation to obtain BDMAE and DEG;

(vii) subjecting the mixture of step (iv) to a separation process in accordance with any of claims 1 to 13 to obtain high-purity NMM.

15. Process for the manufacture of N-methyl morpholine oxide (NMMO), wherein N-methyl morpholine (NMM) is obtained by the process according to any of the preceding claims and said NMM being subjected to an oxidation reaction to obtain NMMO.