TECHNICAL FIELD

The invention relates to a process for the separation of a mixture comprising pyrrolidine, bis(pyrrolidino)butane and water.

STATE OF THE ART

The process products are used, inter alia, as intermediates in the production of fuel additives (USA-3,275,554; DE-A-21 25 039 and DE-A-36 11 230), surfactants, drugs and crop protection agents, hardeners for epoxy resins, catalysts for polyurethanes (WO2015/200408 A1 and WO2014/121959 A1), intermediates for the preparation of quaternary ammonium compounds, plasticizers, corrosion inhibitors, synthetic resins, ion exchangers, textile assistants, dyes, vulcanization accelerators and/or emulsifiers.

US 2014/0018547 A1 (BASF) refers to a process for the production of pyrrolidine and also teaches a process for the separation of the resulting reaction mixture (see paragraphs [0073] to [0084]). The formation of bis(pyrrolidino)butane is taught as an unwanted by-product (see paragraph [0079]). US 2014/0018547 A1 is silent on any further purification steps to obtain pure bis(pyrrolidino)butane.

DE 199 57 672 A1 (BASF) refers to a process for the purification of pyrrolidine, wherein pyrrolidine and water are separated by means of distillation at a pressure below 0.95 bar. DE 199 57672 A1 is silent on any further purification steps to obtain pure bis(pyrrolidino)butane.

Apart from the literature as cited above, it has been observed, that the further purification of bis(pyrrolidino)butane by distillation is problematic. The main problem arises from the fact, that a solid is formed in the feed (i.e. the respective pipe) and/or the bottom of the column in which the purification of the bis(pyrrolidino)butane is conducted. Such solid formation would either require extensive technical measure for the continuous removal of the solid or more frequent shutdowns of the respective plant for the purpose of removing the solid.

TECHNICAL PROBLEM

The technical problem to be solved by the present invention was to find an efficient process for the separation of a mixture comprising pyrrolidine, bis(pyrrolidino)butane and water and to obtain pyrrolidine and bis(pyrrolidino)butane with high purity. The technical problem was also to improve existing processes for separation of a mixture comprising pyrrolidine, bis(pyrrolidino)butane and water, and to remedy one or more disadvantages of the prior art. Surprisingly it has been found that the technical problem as specified above can be solved by a continuous process for the separation of a mixture comprising pyrrolidine, bis(pyrrolidino)butane and water, the process comprising the following steps:

A) separating a mixture stream (1) by distillation into a low-boiler stream (2) comprising pyrrolidine and water and a high-boiler stream (7) comprising bis(pyrrolidino)butane;

B) removal of a bis(pyrrolidino)butane stream (8) from stream (7) by distillation; and

C) removal of water from low-boiler stream (2) to obtain a pyrrolidine stream (6).

DETAILED DESCRIPTION OF THE INVENTION

The numbering of the streams in this patent application corresponds to the respective numbering in Fig. 1 or Fig. 2 respectively.

The respective pyrrolidine or bis(pyrrolidino)butane obtained in accordance with the present invention has a high purity.

Usually, the pyrrolidine obtained according to the present invention has a purity of equal to or more than 95 wt.-%, preferably equal to or more than 98 wt.-%, even more preferably equal to or more than 99 wt.-%. The water content is usually less than 2 wt.-%, preferably less than 1 wt.-%, even more preferably less than 0.5 wt.-%.

Usually, the bis(pyrrolidino)butane obtained according to the present invention has a purity of equal to or more than 90 wt.-%, preferably equal to or more than 93 wt.-%, even more preferably equal to or more than 95 wt.-%. The water content is usually less than 2 wt.-%, preferably less than 1 wt.- %, even more preferably less than 0.5 wt.-%.

Details regarding the mixture to be separated by the process according to the present invention, including its preferred composition and potential ways of its synthesis are outlined below.

Preferably, the removal of water and pyrrolidine according to step C) is achieved, by distillation or by extraction and subsequent distillation. Respective embodiments are discussed below in more detail.

Preferably the high-boiler stream (7) also comprises water.

Another aspect of the intention was also to find a preferred embodiment of the process to be performed in an efficient manner without the formation of a solid, the formation of which adversely affects the technical feasibility of the process.

In such preferred embodiment, the high-boiler stream (7) comprises equal to or less than 10% by weight of water. Any weight percentage for a certain stream refers to the total mass per hour of that stream. For example, the weight percentage of water in the high boiler stream (7) is based on total mass per hour of such stream (7). Weight percentage is denoted as “wt.-%” or “% by weight”, which are used synonymously.

It has been found that solid formation can be prevented when the water content in the high-boiler (7) stream is equal to or less than 10% by weight. It is to be emphasized, that there is no hint in the art, to realize such a low water content. US 2014/0018547 A1 discloses the removal of bis(pyrrolidino)butane as high boiler obtained in the bottom of the respective distillation column (see paragraph [0079]). Obviously, bis(pyrrolidino)butane is regarded here as an unwanted byproduct as no further purification of the bis(pyrrolidino)butane is taught. In such cases the resulting bottom stream is usually subjected to any kind of waste treatment. As the water removed in the work-up of the product is usually also subjected to such waste treatment, the person skilled in the art would have realized a considerable high amount of water (i.e. above 10 % by weight) in the bottom stream so it can be fed to the waste treatment together with bis(pyrrolidino)butane and the energy required for the evaporation of such water is saved.

Without wanting to be bound by any theory or limiting the scope of the present invention in whatsoever kind, it is believed that the solid formation can be attributed to the formation of a bis(pyrrolidino)butane hydrate, the formation of which depends on the water content. For example, the melting point of a mixture of 50% by weight water and 50% by weight bis(pyrrolidino)butane is 56°C, whereas a mixture of 5% by weight water and 95% by weight bis(pyrrolidino)butane remains liquid at 21 °C. For further details reference is made to Example 3 hereof.

Regarding a smooth operation of bis(pyrrolidino)butane distillation according to step B) it would therefore be necessary to ensure, that the temperature in the relevant parts of the plant is not below the melting point of the bis(pyrrolidino)butane/water hydrate. Otherwise the solid hydrate would form. Such requirement constitutes a serious task, particularly when the process according to the present invention is executed on an industrial scale. For example, a proper insulation of either the pipeline system or the respective distillation column can be hardly ensured throughout the entire operation. Moreover, with respect to the pipelines system, respective heating tracing of the latter could be required as well.

A water content of equal to or less than 10% by weight therefore significantly reduces unwanted hydrate formation and thus requires less efforts with respect to proper insulation and heating tracing. To further decrease unwanted hydrate formation, a smaller water content is even more preferred, for example a water content of equal to or less than 9% by weight, equal to or less than 8% by weight, equal to or less than 7% by weight, equal to or less than 6% by weight or equal to or less than 5% by weight. A water content of less than 5% by weight is also possible.

Any such low water content can be established by means well known in the art. For example, step A) can be conducted by using a column, that provides for sufficient separation efficiency. Separa- tion efficiency is mainly governed by the amount of theoretical stages and the reflux rate. I.e. the higher the amount of theoretical stages and the reflux rate, the higher is the separation efficiency.

As mentioned above, solid formation constitutes a serious problem particularly when the process according to the present invention is executed on an industrial scale. Thus, the amount of mixture to be subjected to the process according to the present invention is preferably considerably high. Preferably, the mixture (i.e. the mixture stream (1)) being fed into the process has a flow rate of equal to or greater than 10 kg/h, preferably equal to or greater than 500 kg/h. Even more preferably the mixture being fed into the process has a flow rate in the range from 10 to 4000 kg/h or 500 to 3000 kg/h.

Any distillation or extraction as referred to herein is preferably conducted in a suitable column. Suitable columns are for instance packed columns. The internals of such packed columns may be structured packings, mesh packings or random packings. Tray columns can also be used. The diameter of these columns is preferably in the range from 0.4 to 0.9 m. The packed height of these columns is preferably in the range from 8 to 25 m.

Any distillation pressure as referenced herein refers to the absolute pressure in the head of the respective column.

Any temperature ranges provided herein for the head and sump temperature of a certain column are always given under the proviso, that the sump temperature is higher than the head temperature.

Stream (2) resulting from step A) mainly consists of water and pyrrolidine. It may further contain small amounts of other compounds such as ammonia or tetrahydrofuran.

Preferably stream (2) is withdrawn overhead and stream (7) is withdrawn as a bottom stream.

Step A) is usually conducted in a column. The number of theoretical stages is usually equal to or above 15, preferably in the range from 15 to 60. Suitable types of columns are specified above. The pressure is preferably in the range from 1 to 5 bar. The head temperature is preferably in the range from 92 to 141 °C and the sump temperature is preferably in the range from 131 to 194 °C. The reflux ratio is preferably in the range from 0.1 to 10 or even more preferably 1 to 8.6.

In step B), the value product bis(pyrrolidino)butane is separated from the remaining water and other compounds. Usually bis(pyrrolidino)butane is withdrawn overhead or as a side stream. Usually water is withdrawn as a bottom stream.

The bis(pyrrolidino)butane stream (8) in step B) is preferably withdrawn as a side stream. Any compounds having a higher boiling point than bis(pyrrolidino)butane (for example 1-(4-(pyrrolidin- 1-yl)butyl)pyrrolidin-2-one) can be purged as bottom stream. In addition, a distillate stream can be withdrawn overhead. Such distillate stream can be used to purge compounds having a lower boiling than bis(pyrrolidino)butane (for example water, 1,4-butanediamine, or N-aminobutylpyrrolidine). Increasing the distillate stream in general helps to increase the purity of the bis(pyrrolidino)butane. On the other hand, it also reduces the bis(pyrrolidino)butane yield since bis(pyrrolidino)butane is also contained in the distillate stream. In order to increase the bis(pyrrolidino)butane yield a high reflux ratio can be realized in step B). Preferably the reflux ratio is in the range from 5 to 400 or even more preferably in the range from 24 to 180.

Step B) is usually conducted in a column. The number of theoretical stages is usually equal to or above 15, preferably in the range from 15 to 60, more preferably in the range from 30 to 60. Suitable types of columns are specified above. The pressure is preferably in the range from 0.01 to 0.60 bar. The head temperature is preferably in the range from 103 to 179 °C and the sump temperature is preferably in the range from 142 to 248 °C. Preferred reflux ratio ranges are given above.

Depending on the composition of the mixture, step C) may further comprise the removal of other compounds, in particular any compound that has not been removed via the high-boiler stream (7) in step A). This can be for example compounds having a lower boiling point than pyrrolidine (for example tetra hydrofuran).

The high boiler stream (7) usually comprises 50 to 95 wt.-% of bis(pyrrolidino)butane, preferably 55 to 90 wt.-% or even 55 to 80 wt.-%. Besides bis(pyrrolidino)butane and water such stream may also comprise other compounds, in particular N-propylpyrrolidine, N-butylpyrrolidine and N- aminobutylpyrrolidine.

With respect to step C) the removal of water and the pyrrolidine stream (6) from the low boiler stream (2) is for instance possible by subjecting the low boiler stream to low-pressure distillation, preferably below 0.95 bar, wherein the pyrrolidine stream (6) is withdrawn overhead. Preferably the pressure is below 0.5 bar. Even more preferably the pressure is in the range from 0.2 to 0.4 bar, particularly preferred in the range from 0.25 to 0.35 bar. Such low-pressure distillation is for instance taught in DE 199 57 672 A1 (BASF). The major drawback is, that pyrrolidine is obtained overhead and its liquefaction requires cooling at low temperature. If the available condensation temperature is not significantly low, the loss of pyrrolidine in the exhaust is significant. Since normal cooling water having a temperature of about 30 °C is usually not sufficient, this process is less favorable. Moreover, the process requires either technically complex columns having a considerably high amount of stages or a significantly increased reflux rate (the latter resulting in a larger reboiler and condenser equipment and utility consumption) to obtain high purity pyrrolidine overhead which has a considerable low amount of water.

Instead of for instance using the low-boiler distillation according to the preceding paragraph, it is preferred to conduct water removal and purification of pyrrolidine in two separate steps. Preferably, step C) comprises the following steps: C1) dewatering low-boiler stream (2) to form a stream (5) comprising the bulk of the pyrrolidine; and

C2) removal of a pyrrolidine stream (6) from stream (5) by distillation.

Dewatering of the low-boiler stream (2) as per step C1 can be conducted for instance by means of extraction or distillation. Preferred embodiments are detailed in connection with alternative I and II below.

Step C2 serves for the purification of pyrrolidine. In particular, remaining water and organic impurities (for example N-methyl-pyrrolidine) are removed, usually as a bottom stream.

Step C2 is usually conducted in a column. The number of theoretical stages is usually equal to or above 15, preferably in the range from 15 to 100 or even more preferably 45 to 85. Suitable types of columns are specified above. The pressure is preferably in the range from 1 to 5 bar. The head temperature is preferably in the range from 86 to 146 °C and the sump temperature is preferably in the range from 96 to 159 °C. The reflux ratio is preferably in the range from 0.1 to 50.

In step C2) stream (6) can be withdrawn overhead or as a side stream. Preferably, the pyrrolidine stream (6) in step C2 is withdrawn overhead. By means of overhead withdrawal it can be ensured, that the pyrrolidine is essentially free of respective mid- and high boilers. This is particularly preferred for alternative I (as further specified below), when a distillate stream is removed overhead in step Cl.I.b) or for alternative II (as further specified below), when distillate stream is removed overhead in step C1.II. a), since the respective distillate stream is used as a low boiler purge. In such cases, the amount of low boilers in stream (5) is already considerably low.

Preferably step C1 of the process according to the present invention comprises either steps Cl.I.a) to CI .I.c) according to alternative I or steps d .ll.a) to d .ll.c) according to alternative II as follows: alternative I:

Cl .I.a) removal of the bulk of water from low-boiler stream (2) by extraction to form a stream (41);

Cl .I.b) separating stream (41) by distillation into an overhead or side stream (91) comprising a water/pyrrolidine azeotrope and stream (5) as a bottom stream; and

CI .I.c) optionally but preferably recycling stream (9I) to step Cl .I.a); wherein, the distillation according to step Cl.I.b) is conducted at a pressure of > 1.5 bar. alternative II: d .ll.a) removal of the bulk of water from low-boiler stream (2) by distillation as a bottom stream to form an overhead or side stream (4); Cl.ll.b) separating stream (4II) by distillation into an overhead or side stream (9I) comprising a water/pyrrolidine azeotrope and stream (5) comprising pyrrolidine as a bottom stream; and

C1.II.C) optionally but preferably recycling stream (9) to step Cl.ll.a). wherein the distillation according to step d.ll.a) is conducted at a pressure of > 1.5 bar and the distillation according to step d .ll.b) is conducted at a pressure which is above, preferably at least 1 bar above the pressure of step d .Ila).

According to alternative I, the bulk of water is removed via extraction. The major advantage as compared to the low-pressure distillation as taught in DE 199 57672 A1 is, that according to step d .Lb), the bulk of the pyrrolidine can be removed as a bottom stream whereas the remaining water is removed as a water/pyrrolidine azeotrope. Thus, the process is less sensitive with respect to the separation efficiency of the respective column. Moreover, because of the higher pressure under which the distillation is conducted, the required condensation temperature is higher. Thus, usually normal cooling water suffices. Therefore, with respect to pyrrolidine quality, particularly with respect to the requirement of a low water content, the process according to alternative I constitutes more robust alterative as compared to the low-pressure distillation. Particularly with respect to a production on an industrial scale, the low-pressure distillation as taught in DE 199 57672 A1 is quite sensitive with respect to a not ideal operation conditions of the respective column which might for instance arise from slight deterioration of the column packing. In such case, the separation of water along the column is not sufficient, and an increased amount of water is contained in the pyrrolidine which is withdrawn at the head of the column. Thus, the risk of obtaining off-spec pyrrolidine, particularly in case of longer operation times, is quite high in case of the low-pressure distillation as taught in DE 199 57672 A1.

In step Cl.I.a) the bulk of water is usually withdrawn as a bottom stream. The bottom stream is usually subjected to any kind of wastewater treatment. Stream (41) is preferably withdrawn overhead. This is in particular preferable, when a distillate stream is withdrawn in step Cl .I.b).

Preferably, an alkaline solution, preferably a solution of caustic soda, is used as an extracting agent in step Cl.I.a). In case caustic soda is used, its concentration is preferably in the range from 40 to 60 wt.-%.

The extraction according to step Cl.I.a) is usually conducted in a column. The number of theoretical stages is usually equal to or above 1, preferably in the range from 1 to 10 or even more preferably in the range from 2 to 8 or even 3 to 5. Suitable types of columns are specified above. The pressure is preferably in the range from 0.5 to 3 bar and the temperature is preferably in the range from 20 to 70 °C.

The distillation according to step Cl .I.b) is usually conducted in a column. The number of theoretical stages is usually equal to or above 15, preferably in the range from 15 to 60 or even more pref- erably 40 to 60. Suitable types of columns are specified above. The pressure is preferably in the range from 1.75 to 5 bar. The head temperature is preferably in the range from 99 to 140 °C and the sump temperature is preferably in the range from 99 to 145 °C. The reflux ratio is preferably in the range from 10 to 1000.

In an optional but preferred step CI.I.c) stream (91) is recycled to step Cl.I.a). This can be achieved for example by feeding stream (2) and stream (91) into an appropriate mixing device, where both streams are mixed. The resulting stream (31) is then fed into step Cl .I.b). This is also shown in Fig. 1. Since stream (9I) also comprises pyrrolidine, the recycling increases the pyrrolidine yield.

With respect to step Cl.I.b) it is preferred to withdraw stream (91) as a side stream.

With respect to step Cl.I.b) it is even more preferred to withdraw stream (91) as a side stream and to withdraw a distillate stream overhead. The distillate stream works as a low boiler purge (a respective low boiler is for instance N-methylpyrrolidine). This is in particular advantages, in case the pyrrolidine stream (6) according to step C2) is withdrawn overhead, since there is no possibility to remove low-boilers in step C2), if the value product (pyrrolidine) is removed overhead. Moreover, this is in particular advantages, in case the stream (91) is recycled to step Cl.I.a) in accordance with step CI.I.c), since otherwise low-boilers would accumulate in steps Cl.I.a) and C1.IL b).

The implementation of a distillate stream including the advantages specified in the preceding paragraph are not taught in the art (e.g. US 2014/0018547 A1).

As compared to alternative I, alternative II further has the advantage that water is removed by distillation. The wastewater that is generated according to alternative II is the water removed from the mixture. To the contrary, extraction requires an additional amount of water being part of the extracting agent, thus more wastewater needs to be treated. Furthermore, the extracting agent is not only water but also contains a base, in particular caustic soda. Thus, not only the wastewater but also the base needs to be disposed. Moreover, also the production of respective bases such as caustic soda impacts the environment at least because of the CO2, that is generated thereby. All this will be of fundamental importance throughout the next decades because governmental provisions regarding environmental protection are becoming increasingly strict.

In addition to that, the process according to alternative II has also certain advantages as compared to the low-pressure distillation as taught in DE 199 57 672 A1. Particularly, according to step C1.IL b), the bulk of the pyrrolidine can be removed as a bottom stream whereas the remaining water is removed as a water/pyrrolidine azeotrope. Thus, the process is less sensitive with respect to the separation efficiency of the respective column. Therefore, with respect to pyrrolidine quality, particularly with respect to the requirement of a low water content, the process according to alternative II constitutes more robust alterative as compared to the low-pressure distillation as taught in DE 199 57672 A1. Moreover, because of the higher pressure under which the distillation is con- ducted, the required condensation temperature is higher. Thus, usually normal cooling water suffices.

For the person having ordinary skill in the art it was surprising that the separation of water according to steps d .ll.a) and d .ll.b) is possible when the distillation according to step d .ll.a) is conducted at a pressure of > 1.5 bar and the distillation according to step d .II. a) is conducted at a pressure which is above, preferably at least 1 bar, more preferably at least 5 bar or even at least

8.5 bar, above the pressure of step d.ll.a).

It has been found that a minimum pressure of 1.5 bar is required since below such pressure, pyrrolidine and water do not form an azeotrope. There is no hint in the art, that an azeotrope is formed at a pressure of > 1.5 bar and that the pressure-dependency of the concentration of the azeotrope allows for an effective separation. Furthermore, it has been found that a pressure difference of 1 bar is preferred in order to obtain sufficiently differing azeotrope compositions in steps d.ll.a) and d.ll.b). However, with respect to separation efficiency, higher pressure differences as specified above are preferred.

The key of the distillation according to steps d .ll.a) (low pressure azeotropic distillation) and d.ll.b) (high pressure azeotropic distillation) is to have an azeotropic concentration difference between these two steps. If the pressures for both stops are set in accordance with this invention, the water/pyrrolidine azeotrope formed in step d.ll.a) has a higher pyrrolidine concentration that the water/pyrrolidine azeotrope formed in step d.ll.b), consequently having a lower pyrrolidine concentration. The azeotropic point is overcome by feeding the low pressure azeotrope of step d.ll.a) into a high pressure distillation of step d.ll.b), where the azeotrope is lower in concentration. In addition to that, it has been found that the respective water/pyrrolidine azeotrope is a temperature-minimum azeotrope which means that both azeotropes will concentrate at the top of the column at the lower temperatures while the pure products such as water and pyrrolidine are being concentrated at the bottom of the columns. This is also explained in Example 4.2.7 for specific concentrations.

Preferably, the distillation according to step d.ll.a) is conducted at a pressure in the range from

1.5 to 2.5 bar and the distillation according to step d .ll.b) is conducted at a pressure in the range from 2.5 to 10 bar, wherein the pressure in step d .ll.b) is at least 1 bar, preferably at least 8.5 bar, above the pressure in step d.ll.a).

In a more preferred embodiment, the distillation according to step d.ll.a) is conducted at a pressure in the range from 1.5 to 1.75 bar and the distillation according to step d .ll.b) is conducted at a pressure in the range from 6.5 to 10 bar, wherein the pressure in step d.ll.b) is at least 5 bar, preferably at least 8.25 bar, above the pressure in step d.ll.a).

The low-pressure distillation according to step d.ll.a) is preferably conducted in a column. The number of theoretical stages is usually equal to or above 15, preferably in the range from 15 to 60 or even more preferably 40 to 60. Suitable types of columns are specified above. The head temperature is preferably in the range from 80 to 113 °C and the sump temperature is preferably in the range from 106 to 152 °C. The reflux ratio is preferably in the range from 500 to 3000.

The high-pressure distillation according to step C1 .IL b) is preferably conducted in a column. The number of theoretical stages is usually equal to or above 15, preferably in the range from 15 to 60 or even more preferably 40 to 60. Suitable types of columns are specified above. The head temperature is preferably in the range from 140 to 180 °C and the sump temperature is preferably in the range from 150 to 200 °C. The reflux ratio is preferably in the range from 0,5 to 50.

It is preferred, that in step C1 .II. a) stream (4II) is a side stream and a distillate stream is removed overhead. Such distillate stream usually contains tetra hydrofuran. If stream (4II) is withdrawn overhead, low-boilers (in particular tetrahydrofuran) can only be removed, if stream (9II) is not recycled. However, if stream (9II) is recycled, it is advantageous to realize such distillate stream because otherwise such low boilers (in particular tetrahydrofuran) would be circulated between steps Cl.ll.a) and Cl .ll.b).

It is also preferred, that in step Cl .ll.b) stream (911) is withdrawn overhead. This is in particular preferred, if a distillate stream in realized in step d .ll.a). That means, low-boilers (e.g. tetrahydrofuran) have already been purged in step d .ll.a). Thus steam (411) is essentially free of low-boilers and the overhead stream (911) is not contaminated with low-boilers, accordingly.

The process according to the present invention is particularly suited for those mixtures that contain a certain amount of water. Usually this water is formed in the synthesis of the pyrrolidine and bis(pyrrolidino)butane, respectively. Details regarding synthesis are presented below.

It is to be noted that any composition of the mixture given below refers to the mixture stream (1).

The mixture to be purified by the process according to the present invention preferably has a composition as follows:

20 to 90, preferably 20 to 85 % by weight of pyrrolidine;

1 to 70, preferably 5 to 70 % by weight of bis(pyrrolidino)butane;

5 to 45, preferably 9 to 40 or even 10 to 40 % by weight of water;

0 to 3 % by weight of ammonia; and

0 to 15 % by weight of others.

Compounds designated as “others” in the mixture specified above as well as any mixture specified below are for example tetrahydrofuran, 1 ,4-butanediamine, 4-amino-/4-hydroxybutylpyrrolidine, alkyl pyrrolidines (methyl-, propyl-, butyl-), compounds with a boiling point higher than bis(pyrrolidino)butane such as partially saturated bis(pyrrolidino)butane. Tetrahydrofuran for example is formed by intramolecular cyclization of 1 ,4-butanediol. 4-amino-/4-hydroxybutylpyrrolidine or alkyl pyrrolidines (methyl-, propyl-, butyl-) are for example obtained as by-products in the reaction of 1 ,4-butanediol with ammonia and/or pyrrolidine. It is to be noted, that the composition of the mixture, including the amount and type of the compounds designated as “others” depends on how the mixtures was obtained.

The amount of the above specified organic components can be analyzed by means of gas chromatography. The water content can be analyzed by means of Karl-Fischer titration.

Preferably, the mixture can be obtained either from i. the reaction of 1 ,4-butanediol with pyrrolidine in the presence of hydrogen and a hydrogenation catalyst, or ii. the reaction of 1 ,4-butanediol with ammonia or a mixture of ammonia and pyrrolidine in the presence of hydrogen and a hydrogenation catalyst and subsequent removal of unreacted ammonia from the resulting crude reaction product, preferably via distillation.

In the respective amination reactions according to the above options i. or ii., water is formed. Thus, the resulting mixture contains a considerable amount of water.

Such reactions are well described in the art, for instance in DE 10 2004 023 529 A1 (BASF AG).

The following preferred reaction parameters apply to both options.

Ammonia, pyrrolidine, or a respective mixture thereof can be used in a molar amount which is from 0.90 to 100 times that of the 1 ,4-butanediol. Preferably it is 1 to 30, particularly preferably 1.5 to 10 or even 2 to 8 times that of the 1 ,4-butanediol. For the avoidance of doubt, reference is made to the molar amount of entire 1 ,4-butanediol molecule; not the molar amount of two functional alcohol groups.

Fresh hydrogen is usually added in an amount of 100 to 1000, preferably 150 to 550 NL per (volume of catalyst in L and hour) with NL = standard liters = volume converted to STP. STP means standard conditions for temperature and pressure.

The reactions can be carried out at an absolute pressure in a range from 1 to 300 bar, preferably 10 to 50 bar, particularly preferably 10 to 30 bar or even 15 to 30 bar.

The reactions can be carried out at a temperature in a range from 80 to 300 °C, preferably 100 to 250 °C, particularly preferably 150 to 240 °C or even 170 to 230 °C. The reaction can be carried out adiabatically, isothermally or quasi isothermally (i.e. isoperibolically) provided in each case that the temperature in the reactor is within the respective range as per the preceding sentence. Preferably the reaction is carried out with an isoperibolic temperature profile to control the temperature of the reaction within borders of ±15 K, particularly preferably ±10 K. The conversion of 1 ,4-butanediol is preferably in the range from 80 to 100 %, more preferably 99 to 100% or even 99.5 to 100%.

The reactions are preferably conducted continuously. Preferably a fixed-bed reactor is used, in which case the liquid hourly space velocity is preferably in the range from 0.1 to 2.0 kg, preferably from 0.1 to 1.0 kg, particularly preferably from 0.2 to 0.6 kg, of 1 ,4-butanediol per litre of catalyst (bed volume) and hour.

In principal any hydrogenation catalyst suitable for alcohol amination reactions can be used. Catalysts which are particularly preferred are for instance taught in European Patent Application No.

21168407.1 on pages 5 to 10, which are herewith incorporated by reference.

In case of option i., the mixture preferably has a composition as follows:

10 to 50 % by weight of pyrrolidine

30 to 85 % by weight of bis(pyrrolidino)butane

5 to 30 % by weight of water

0 to 3 % by weight of ammonia 0 to 15 % by weight of others.

In case of option ii. the mixture (i.e. after the removal of ammonia from the respective crude reaction product) preferably has a composition as follows:

40 to 90 % by weight of pyrrolidine

1 to 30 % by weight of bis(pyrrolidino)butane

5 to 45, preferably 9 to 40 % by weight of water

0 to 3 % by weight of ammonia 0 to 15 % by weight of others.

Even more preferably it has a composition as follows:

40 to 70 % by weight of pyrrolidine

5 to 20 % by weight of bis(pyrrolidino)butane

10 to 40 or even 25 to 37 % by weight of water

0 to 3 % by weight of ammonia 0 to 10 % by weight of others.

In case of option ii., the reaction of 1 ,4-butanediol with ammonia is preferred. In particular, a continuous production process is used, which comprises reacting 1 ,4-butanediol with ammonia in the presence of hydrogen and a heterogeneous hydrogenation catalyst in the gas phase using a recycle gas mode, wherein the temperature in the pressure separator is > 20°C. Preferably the temperature in the pressure separator is > 21 °C or even > 25°C. Best results with respect to pyrrolidine and bis(pyrrolidino)butane selectivity can be obtained by realizing a temperature in the pressure separator which is > 30°C. Preferably the temperature in the pressure separator is in the range from 30 to 70°C, even more preferably from 30 to 60°C.

This process is described in detail in European Patent Application No. 21168407.1 on pages 2 to 13, which are herewith incorporated by reference.

As stated above, the removal of unreacted ammonia from the resulting crude reaction product is preferably conducted via distillation.

The distillation is preferably conducted in a column. The number of theoretical stages is usually equal to or above 5, preferably in the range from 5 to 30 or even more preferably 9 to 30. Suitable types of columns are specified above. The pressure is preferably in the range from 15 to 25 bar. The head temperature is preferably in the range from 30 to 60 °C and the sump temperature is preferably in the range from 180 to 210 °C. The reflux ratio is preferably in the range from 0,1 to 15.

Considerably preferred embodiments of the process according to the present invention are shown in Fig 1 (relating to alternative I) and Fig 2 (relating to alternative II).

As to Fig. 1:

A synthesis’ outlet (crude reaction product) is fed into the middle part of the ammonia removal column (C1). The synthesis can be conducted in accordance with option ii. as further specified above.

The resulting mixture stream (1) is withdrawn from the bottom of C1 and fed into the middle part of the high boiler removal column (C2), where the mixture is separated into the low-boiler stream (2) withdrawn at the top of column C2 and the high boiler stream (7) withdrawn at the bottom of C2 (corresponding to step A)).

Stream (7) is fed in the middle part of BPB purification column (C6) where a bis(pyrrolidino)butane stream (8) is withdrawn as a side stream (corresponding to step B)). Any high boilers may be purged in C6’s bottom draw. In operation the flow of the bottom draw can be adjusted in order to affect the specification of the BPB product. Furthermore, the distillate stream obtained at the head of column C6 might be used as light boiler purge but also contains the desired product BPB (light boilers are for instance 4-amino-/4-hydroxybutylpyrrolidine, alkyl pyrrolidines (methyl-, propyl-, butyl-)).

Streams (2) and (9I) are fed into a mixer and the resulting stream (3I) is fed to the middle part of extraction column C3, where caustic soda solution is fed above stream (3I), a wastewater stream is withdrawn at the bottom and stream (4I) is withdrawn overhead (corresponding to step Cl.I.a) and step CI.I.c) for the recycling). Stream (4I) is fed into a middle part of azeotropic column C4, where stream (9I) is obtained as a side stream and stream (5) is withdrawn from the bottom (corresponding to step C1 .Lb)). Moreover, C4 contains a distillate stream that works as low boiler purge (low boilers are for instance tetrahydrofuran and N-methylpyrrolidine). The flow of the distillate stream can be adjusted in order to adjust the product specifications or to decrease or increase pyrrolidine yield.

Stream (5) is fed into a middle part of pyrrolidine purification column C5, where a pyrrolidine stream (6) is withdrawn overhead (corresponding to step C2)).

As to Fig. 2:

A synthesis’ outlet is fed into the middle part of the ammonia removal column (C1). The synthesis can be conducted in accordance with option ii. as further specified above.

The resulting mixture stream (1) is withdrawn from the bottom of C1 and fed into the middle part of the high boiler removal column (C2), where the mixture is separated into the low-boiler stream (2) withdrawn at the top of column C2 and the high boiler stream (7) withdrawn at the bottom of C2 (corresponding to step A)).

Stream (7) is fed in the middle part of BPB purification column (C6) where a bis(pyrrolidino)butane stream (8) is withdrawn as a side stream (corresponding to step B)). Any high boilers may be purged in C6’s bottom draw. In operation the flow of the bottom draw can be adjusted in order to affect the specification of the BPB product. Furthermore, the distillate stream obtained at the head of column C6 might be used as light boiler purge but also contains the desired product BPB (light boilers are for instance 4-amino-/4-hydroxybutylpyrrolidine, alkyl pyrrolidines (methyl-, propyl-, butyl-)).

Streams (2) and (9II) are fed into a mixer and the resulting stream (3II) is fed to the middle part of low-pressure azeotropic column C3, where a wastewater stream is withdrawn at the bottom and stream (4II) is withdrawn as a side stream (corresponding to step Cl .I.a) and step CI .I.c) for the recycling). The distillate stream obtained at the head of column C3 might be used as light boiler purge (light boilers are for instance tetrahydrofuran and N-methylpyrrolidine)

Stream (411) is fed into a middle part of the high pressure azeotropic column C4, where stream (911) is obtained as an overhead stream and stream (5) is withdrawn from the bottom (corresponding to step Cl .I.b)).

Stream (5) is fed into a middle part of pyrrolidine purification column C5, where a pyrrolidine stream (6) is withdrawn overhead (corresponding to step C2)). The following examples only serve for the purpose of the illustration of the present invention and shall therefore not limit it in whatsoever kind.

EXAMPLES

The following Examples 1 and 2 show the manufacture of the mixture being subject to the process according to the present invention.

Example 1

For the preparation of a raw product mixture containing < 20 wt.-% bis(pyrrolidino)butane, 1 ,4- butanediol and ammonia were reacted over heterogeneous catalysts comprising copper and nickel.

The following example was carried out using a copper/nickel catalyst having the composition 45% by weight of CuO and 10% by weight of NiO, the remainder up to 100% is AI2O3, as described in DE 10 2004 023 52 (after its last heat treatment and before reduction with hydrogen). The shaped catalyst bodies were used in pellet form in sizes of 5x5 mm (i.e. 5 mm diameter and 5 mm height). Before commencement of the reaction, the catalyst was reduced (see below).

The experiment was carried out continuously in a gas phase furnace reactor through which the reactants flowed from the bottom upward in a 2.1 m long oil-heated double-walled tube which had an internal diameter of 4.8 cm and was filled from the bottom upward with 40 ml of ceramic spheres (2.5-3.5 mm), 1 liter of catalyst and 1.5 liters of inert material (ceramic spheres, 2.5- 3.5 mm). The reactor was operated at 20 bar. After installation in the reactor, the catalyst was activated at atmospheric pressure according to the following method: 12 h at 180° C (oil circuit reactor) with 20 NL/h and 400 NL/h of N ₂ , 12 hat 200° C. with 20 NL /h of 40 H ₂ and 400 NL /h of N ₂ , replace N ₂ by 200 NL /h of H ₂ over 6 h, 6 h at 240° C with 200 NL/h of H ₂ (NL = standard liters = volume converted to STP). Fresh hydrogen (160 NL/h), circulating gas (7 Nm ³ /h), ammonia (283 g/h) and 1 ,4-butanediol (500 g/h) were heated to 220 °C by means of a system comprising three coil heat exchangers. The third heat exchanger was regulated via a temperature sensor just before the reactor. The oil heating of the double-wall reactor was likewise set to reach a reactor outlet temperature of 209 °C. By means of two further coil heat exchangers, the reactor output was cooled firstly with river water and then heated to the desired temperature of the pressure separator (49 °C) using a cryostat and was fed to a pressure separator. The separation of liquid phase and gas phase occurred there. The liquid phase was depressurized in a low-pressure separator maintained at 45° C from where the released gases were discharged via the offgas (in particular hydrogen and the major part of unreacted ammonia) and the liquid was conveyed into the output drum. The gas phase from the pressure separator was recirculated in a defined amount via a circulating gas compressor and once again served as carrier gas for the starting materials. A pressure regulator ensured that excess gas was conveyed to the muffle furnace for incineration. Conversion and selectivity of the output were determined by gas-chromatographic analysis and are reported in corrected GC area%. The water content was determined by Karl-Fischer titration. Composition of the raw product mixture:

55.8 wt.-% pyrrolidine

32.9 wt.-% water

7.4 wt.-% bis(pyrrolidino)butane

1.2 wt.-% 4-amino-/4-hydroxybutylpyrrolidine

1.5 wt.-% alkyl pyrrolidines (methyl-, propyl-, butyl-)

0.3 wt.-% compounds with a boiling point higher than bis(pyrrolidino)butane 0.9 wt.-% rest

Example 2

For the preparation of a raw product mixture containing >45 wt.-% bis(pyrrolidino)butane, 1 ,4- butanediol and pyrrolidine were reacted over heterogeneous catalysts comprising copper.

For the following example a copper catalyst comprising 55% by weight of CuO and 45% of weight by AI2O3, as described in W02010/031719 A1 , was used. The shaped catalyst bodies were used in pellet form in sizes of 3x3 mm (i.e. 3 mm diameter and 3 mm height). Before commencement of the reaction, the catalyst was reduced (see below).

The experiments were carried out continuously in a steel reactor of 770 mm length, wall thickness 3 mm and inner diameter 12 mm with electric heating through which the reactants flowed from the bottom upward. The reactor was filled from top to bottom with 3 wire mesh rings, 10 mL glass sphere (diameters: 3 mm), 70 mL catalyst and 15 mL glass spheres (diameter: 3 mm) and 3 wire mesh rings. After installation in the reactor, the catalyst was activated at atmospheric pressure according to the following method: 150 to 200 °C starting with 50 NL/h 5% H2/95% N2 and replacing all N ₂ with H2 within 8 h, then 6 h at 200° C with 50 NL/h of H2. (NL = standard liters = volume converted to STP).

1 ,4-Butanediol and pyrrolidine were premixed in a molar ratio of 4 to 1 and were added via HPLC pump. The mixture (58 g/h) was evaporated using two oil heated coil heat exchangers operated at 220 °C. Hydrogen gas (30 NL/h) was introduced into the plant in front of the evaporator. The combined gas stream of 1 ,4-butanediol, pyrrolidine and hydrogen passed over the catalyst bed at 15 bar reactor pressure and a temperature of 200 °C. The outlet of the reactor was connected to a collecting container. Conversion and selectivity of the output were determined by gas- chromatographic analysis and are reported in corrected GC area%. The amount of water was determined by Karl-Fischer titration. Composition of the raw product mixture:

27.6 wt.-% pyrrolidine

48.8 wt.-% bis(pyrrolidino)butane 10.0 wt.-% water

6.0 wt.-% 4-amino-/4-hydroxybutylpyrrolidine

6.8 wt.-% compounds with a boiling point higher than bis(pyrrolidino)butane 0.8 wt.-% rest

Example 3 - Hydrate formation:

It was observed that the raw product mixture without light boilers, such as pyrrolidine, solidified. For example, a mixture of 30 wt.-% water, 64 wt.-% bis(pyrrolidino)butane, 6 wt.-% 4-amino/4- hydroxybutylpyrrolidine and 6 wt.-% high boilers solidified and had a melting point of 45 °C. It was hypothesized that bis(pyrrolidino)butane forms hydrates with water, which are solids. To verify this hypothesis, pure bis(pyrrolidino)butane was mixed with different amounts of water at 21 °C. Without water, pure bis(pyrrolidino)butane had a melting point of -20 °C and was liquid at room temperature. A mixture of 50 wt.-% water and 50 wt.-% bis(pyrrolidino)butane readily solidified under heat development. The melting point of this mixture was 56 °C. The amount of water was then systematically varied, and it was found that a mixture of 5 wt.-% water/95 wt.-% bis(pyrrolidino)butane remained still liquid at 21°C.

Example 4 - Simulation of the purification process according to the present invention.

The following examples are based on simulation results obtained with Aspen Plus software from Aspen Technology, Inc. The thermodynamic parameters used in the program for the individual components are based on published thermodynamic data or in-house measurements. The specification and the simulation of the specified distillation columns used were performed with the customary routines included in the software.

To optimize the simulation model, the simulated results were compared with experimental results, where available, and the simulation model was aligned with the experimental results so that a good agreement between simulation and experimental data was able to be achieved.

The following examples were computed using the optimized simulation model.

The simulation is based on production of pyrrolidine and bis(pyrrolidino)butane by reacting 1,4- butanediol and ammonia (for instance in accordance with Example 1). That means the reactions product contains unreacted ammonia what requires ammonia removal. In Example 1 ammonia removal already occurred in a low-pressure separator. When the process is conducted on an industrial scale a respective ammonia column as shown below in Example 4 is used instead of a low-pressure separator.

The simulation results correspond to a process that is operated on an industrial scale since the mixture stream (1) has a considerably high flow rate of 1305 kg/h. Example 4.1 : Simulation results for alternative I

A flow chart of the process according to alternative I is shown in Fig 1 .

4.1.1 Ammonia removal:

Following the synthesis section (S), the ammonia separation is set up by the ammonia column (C1). The liquid outlet of synthesis’ high pressure flash vessel (not shown in Fig. 1) feeds into the C1 whereas ammonia is separated from the residual product flow. This column operates at around

19.2 barabs with a head and sump temperature of about 48 °C and 195 °C, respectively. This results in a bottom draw (1) which is significant low in ammonia concentration. Such bottom draw (1) contains water (33.37 wt.-%), pyrrolidine (54.62 wt.-%), bis(pyrrolidino)butane (7.24 wt.-%), others (4.76 wt.-%).

4.1.2 High boiler removal:

Starting with the liquid outlet (1) of the ammonia column (C1), the high boiler column (C2) aims to separate high boilers such as bis(pyrrolidino)butane (BPB) and some water from the light boiler stream (2) mainly consisting of pyrrolidine and water. This column operates at about 3 barabs and a head and sump temperature of about 124 °C and 172 °C, respectively. The bottom draw (7) contains water (5 wt.-%), bis(pyrrolidino)butane (67.51 wt.-%), others (27.49 wt.-%). Such other components contained in stream (7) are in particular N-propylpyrrolidine, N-butylpyrrolidine and N- aminobutylpyrrolidine. The distillate stream (2) contains water (36.78 wt.-%), pyrrolidine (61.19 wt.- %), others (2.03 wt.-%) .

4.1.3 Water extraction:

After the separation of the high boilers, the C2’s distillate stream (2) is mixed (MIX) with the water-pyrrolidine temperature-minimum azeotrope side draw (9I) of the azeotropic column (C4). The resulting azeotropic mixture (3I) is then fed into the water extraction column (C3) which generates two phases, an aqueous and an organic phase, by adding 50 wt-% caustic soda (NaOH). The ratio of caustic feed to organic feed is set up to 0.35 mass caustic to mass organic. As a result, the organic outlet stream (4I) contains maximum 3 wt-% water. This way, the azeotrope has been dewatered via extraction. This extraction column operates at about 1.1 barabs and around 55 - 60 °C.

4.1.4 Azeotropic distillation:

Following the C3, the organic phase (4I) is fed to the azeotropic column (C4). This column operates at about 3 barabs and a head and sump temperature of around 103 °C and 124.9 °C, respectively. The side draw (9I) contains the azeotrope which is sent back in front of the water extraction column (C3). The side draw’s (9I) composition is close to the highest possible azeotropic concentration of a pure binary system with pyrrolidine and water at 3 barabs with 86 wt-% pyrrolidine and 14 wt-% water. With this setting the bottom draw (5) is significant low in water concentration to ensure less than 0.20 weight-% water in the product stream (6). The bottom draw (5) contains water (0.20 wt.-%) pyrrolidine (99.46 wt.-%) and others (0.35 wt.-%). 4.1.5 Pyrrolidine purification:

The purification column (C5) concentrates the light boiler pyrrolidine at the head. The column operates at around 3 barabs and a head and sump temperature of about 124 °C and 135 °C, respectively. Any high boilers dragged along since the high boiler column (C2) are purged in C5’s bottom draw. The product stream contains 99.6 weight-% pyrrolidine and 0.2 weight-% water.

4.1.6 Bis(pyrrolidino)butane (“BPB”) purifiction:

After the separation of the high boilers, the C2’s bottom draw (7) is fed to the BPB purification column (C6). This column operates at about 0.04 barabs and a head and sump temperature of about 121 °C and 170 °C, respectively. Any high boilers may be purged in C6’s bottom draw. The resulting product has purity of 95 wt.-% BPB.

Example 4.2: Simulation results for alternative II

A flow chart of the process according to alternative II is shown in Fig 2.

4.2.1 Ammonia removal:

Same as section 4.1.1 above.

4.2.2 High boiler removal:

Same as section 4.1.2 above.

4.2.3 Low pressure azeotropic column:

After the separation of the high boilers, the C2’s destillate stream (2) is mixed (MIX) with the high pressure water-pyrrolidine temperature-minimum azeotrope (9II) of the high pressure azeotropic column (C4) after the low pressure distillation column (C3). This azeotropic mixture (3II) is then fed into C3 operating at about 2 barabs and a head and sump temperature of about 95 °C and 120 °C, respectively. The bottom draw (WW) is significant low in pyrrolidine concentration used as high boiler purge. At the top, the vapor and distillate streams are used as light boiler purges. The low pressure azeotrope is drawn at the side (4II). The concentration is close to the highest possible azeotropic concentration of a pure binary system with pyrrolidine and water at 2 barabs with 91 weight-% pyrrolidine and 9 weight-% water.

4.2.4 High pressure azeotropic column:

Following the C3, the low pressure azeotrope (4II) is fed to the high pressure azeotropic column (C4). This column operates at about 10 barabs and a head and sump temperature of around 168 °C and 180 °C, respectively. In general, the reflux rate is kept low to keep the distillate stream (9II) low. The distillate stream’s (9II) composition is close to the highest possible azeotropic concentration of a pure binary system with pyrrolidine and water at 10 barabs with 76 weight-% pyrrolidine and 24 weight-% water. With this setting the bottom draw (5) is significant low in water concentration to ensure less than 0.20 weight-% water in the product stream (6). 4.2.5 Pyrrolidine purification:

Same as section 4.1.5 above. The product stream contains 99.6 weight-% pyrrolidine and 0.2 weight-% water.

4.2.6 bis(pyrrolidino)butane (“BPB”) purifaction:

Same as section 4.1.6 above. The resulting product has purity of 95 wt.-% BPB.

4.2.7 As to the azeotropic distillation in columns C3 and C4:

Concluding the idea is to have an azeotropic concentration difference between column C3 and column C4 due to the different azeotropic behavior at different pressures. In this example, the azeotrope at 2 barabs is around 91 weight-% pyrrolidine while the azeotrope at 10 barabs is around 76 weight-% pyrrolidine. Thus, the azeotropic point is overcome by feeding the low pressure azeotrope with around 91 weight-% pyrrolidine into a high pressure column where the azeotrope is lower in concentration at 76 weight-% pyrrolidine. In addition to that it is a temperature-minimum azeotrope which means that both azeotropes will concentrate at the top of the column at the lower temperatures while the pure products such as water and pyrrolidine are being concentrated at the bottom of the columns.