Purification process for obtaining vicinal toluenediamine

Abstract

A first aspect of the invention relates to a purification process for obtaining vicinal toluenediamine. In a second aspect, the invention is directed to vicinal TDA (vTDA) obtained or obtainable from a process of the first aspect of the invention, comprising less than 100 weight-ppm of a toluidine compound of formula (I). A third aspect of the invention is related to vicinal TDA (vTDA) having a purity in the range of at least 99 weight- % and comprising less than 100 weight-ppm of a toluidine compound of formula (I).

Description

[0001] Purification process for obtaining vicinal toluenediamine

[0002] A first aspect of the invention relates to a purification process for obtaining vicinal toluenediamine. In a second aspect, the invention is directed to vicinal TDA (vTDA) obtained or obtainable from a process of the first aspect of the invention, comprising less than 100 weight-ppm of a toluidine compound of formula (I). A third aspect of the invention is related to vicinal TDA (vTDA) having a purity in the range of at least 99 weight-% and comprising less than 100 weight-ppm of a toluidine compound of formula (I).

[0003] Processes for toluenediamine (TDA) preparation are known as well as methods for purification of the crude TDA (cTDA), which comprises meta TDA (mTDA) as well as vicinial TDA (vTDA).

[0004] TDA is produced on a technical scale by hydrogenation of dinitrotoluene (DNT) in a continuous liquid phase hydrogenation process. In that process, DNT is reacted with hydrogen in the presence of hydrogenation catalysts to form TDA and water. During hydrogenation, impurities of light components such as toluene, methylcyclohexylamine, aminotoluene (toluidine) may be formed due to the over hydrogenation reaction. Further, heavy-boiling components (Tar) are formed during hydrogenation and subsequent process steps. Moreover, the presence of ortho- and meta-isomers in the starting DNT results in the crude TDA produced by hydrogenation containing both ortho- and meta-isomers, namely vTDA and mTDA.

[0005] The mixture of TDA and water formed during the hydrogenation reaction is subsequently first separated from each other and the water is removed. The process is generally carried out by rectification. The crude TDA (cTDA) thus obtained contains vTDA and mTDA and traces of water, lighter boiling components and tar. For example, vTDA is ued for the production of rigid foams and corrosion inhibitors. The demand and the range of usability of vTDA however fluctuates greatly over time and is strongly dependent on the purity of the vTDA offered.

[0006] However, a major drawback with the vTDA obtained by such a process is that when used in polyol preparation, often the polyol properties such as viscosity and / or reactivity are unpredictable and can often not be controlled as desired.

[0007] The objective technical problem underlying the present invention was thus the provision of a purification process for crude toluenediamine (cTDA), which allows obtaining vicinal toluenediamine (vTDA) in a controllable purity.

[0008] 1staspect- Purification process

[0009] According to a first aspect of the present invention, the problem was solved by a purification process for obtaining vicinal toluenediamine comprising providing a first rectification column C1 and a second rectification column C2, providing a crude toluenediamine (cTDA) mixture comprising meta toluenediamine (mTDA) and vicinal toluenediamine (vTDA); wherein the process comprises feeding the cTDA mixture to the first rectification column C1 and subjecting the cTDA mixture to separation conditions in the rectification column C1; removing a top stream S1 from said rectification column C1, wherein S1 is enriched in vTDA compared to the cTDA mixture; splitting top stream S1 into a least a gaseous stream S1G and a liquid stream S1L, wherein S1L comprises vTDA and is enriched in vTDA compared to S1; wherein at least a part of stream S1 L is fed into the second rectification column C2, wherein C2 is operated under reflux with top vapor condensation, wherein a top stream S4 is removed from the second rectification column C2, passed through a condenser Vtop(C2)Jthereby obtaining a gaseous stream S4gand a liquid stream S4L, wherein S4L is split into at least two streams, wherein a first part stream is discarded (S4L<out)) and a second part stream is returned to the second rectification column C2 (S4L(in)), the reflux ratio of C2 being the mass based ratio of the second part stream returned into the second rectification column C2 (S4L(in)) to the discarded stream S4i_(out) R1 (S4L(in): S4L(Out)); wherein a stream S2L is removed from said second rectification column C2, said stream S2L preferably being enriched in vTDA compared to S1 L; the process further comprising

[0010] (a) removing at least a part of stream S2L, thereby obtaining a stream S2 yout) comprising vTDA and being enriched in vTDA compared to S1 L; and / or

[0011] (b) introducing at least a part of S2L into the first rectification column C1 or combining at least a part of S2L with the cTDA mixture fed to the first rectification column C1 , and

[0012] (c) optionally removing at least a part of liquid stream S1L from said stream S1 L before feeding at least a part of stream S1 L into the second rectification column, thereby obtaining a stream S1 L(out) comprising vTDA and being enriched in vTDA compared to S1; wherein

[0013] (I) the concentration of vTDA in stream S2L is monitored (C<VTDA)) and if C(VTDA> is

[0014] < 99 weight-%, step (a) is not conducted and step (b) is conducted; and

[0015] (ii) the content of a toluidine compound of formula (I) in stream S2L is monitored and only if the content of said toluidine compound of formula (I) in stream S2L is

[0016] < 100 weight-ppm, step (c) is optionally conducted; and if the content of said toluidine compound of formula (I) in stream S2L is >100 weight-ppm, the reflux ratio of the second rectification column C2 is adjusted to a reflux ratio R2 with R2 (S4L(in): S4i_(out)) R1 (S4L(in): S4i_(out)). "Monitoring the content of a toluidine compound of formula (I) in stream S2L” is done by sampling from stream S2L, wherein sampling is done in the range of from at least once per hour to at least once per month, preferably in the range of from once per hour to once per week, more preferably in the range of from once per hour to once per day, and analysis thereof by means known to the skilled person, for example, by gas chromatography. The same applies for "monitoring the concentration of vTDA in stream S2L”. Monitoring the content of a toluidine compound of formula (I) in stream S2L is equal to monitoring the content of a toluidine compound of formula (I) in stream S2 - as described herein below - or in stream S2i_(r) - as described herein below.

[0017] It had surprisingly been found that controlling the content of a toluidine compound of formula (I) in a respective vTDA stream enables an improved use of said vTDA in polyol preparation. vTDA is often used as starter molecule in polyol preparation and results in a four stranded branched structure of the resulting polyol, whereas the presence of toluidines in the vTDA results only in linear two stranded polyol chains. These linear two stranded polyol chains impair the product properties in that, for example, a desired viscosity and / or reactivity of the polyols cannot be achieved. Ensuring a content of toluidine compound of formula (I) of < 100 weight-ppm in vTDA enables achieving a desired viscosity and / or reactivity of the polyols prepared therefrom.

[0018] "A crude toluenediamine (cTDA) mixture preferably comprises meta toluenediamine (mTDA) and vicinal toluenediamine (vTDA)” in a molar ratio mTDA : vTDA in the range of from 20 to 35

[0019] "mTDA” is a mixture of toluene-2,4-diamine and toluene-2,6-diamine, preferably with a molar ratio of toluene-2,4-dia- mine to toluene-2,6-diamine in the range of from 3.5 to 4.5. In addition, cTDA further comprises heavy boilers. mTDA and vTDA have a boiling temperature range BTRTDA with a lower boiling temperature limit value TTDA<L) and an upper boiling temperature limit value TTDA<U) The boiling temperature range BTRTDA is thus a temperature range of from the lower boiling temperature limit value TTDA<L) to the upper boiling temperature limit value TTDA<U), wherein the lower boiling temperature limit value TTDA<L) and the upper boiling temperature limit value TTDA<U) are part of the range. As indicated above, boiling temperatures as well as boiling temperature ranges are indicated based on a pressure of 1013 hPa. Preferably, the lower boiling temperature limit value TTDA<L) are 255 °C, more preferably 260 °C. and the upper boiling temperature limit value TTDA<U) are 295 °C, more preferably 290 °C. A heavy boiling component XHI is a component having at 1013 hPa a boiling point of > TTDA<U), wherein preferably, the boiling point of each heavy boiling component XHI is < 400°C at 1013 hPa, more preferably, each heavy boiling component XHI has a boiling point in the range of from > TTDA(U) (O < 400°C at 1013 hPa. More preferably, each heavy boiling component XHI has a molecular weight of > 136 g / mol.

[0020] "vTDA” is a mixture of toluene-2,3-diamine and toluene-3,4-diamine, preferably with a molar ratio of toluene-2,3-dia- mine to toluene-3,4-diamine in the range of from 0.45 to 0.65.

[0021] From the stream S2L a part stream S2i_(r) is split of, wherein S2i_(r) is passed through a bottom reboiler of C2 (Vbot- tom(C2)) and reintroduced into C2, wherein only the remaining part of S2L is used for removing S2i_(out) and / or for the at least part of S2L, which is reintroduced into the first rectification column C1 or combined with the cTDA mixture fed to the first rectification column C1 .

[0022] According to step (ii), the content of a toluidine compound of formula (I) in stream S2L is monitored. In some preferred embodiments, if the content of said toluidine compound of formula (I) in stream S2L is < 100 weight-ppm, then step (a) is conducted, wherein the part of S2L removed as stream S2 yout) in step (a) represents in the range of from

[0023] 50 to 100 weight-% of stream S2L and the part of S2L introduced in step (b) into the first rectification column C1 or combined with the cTDA mixture fed to the first rectification column C1 is in the range of from 0 to 50 weight-% of stream S2L.

[0024] Preferably, R2 is > R1 , wherein more preferably the mass based reflux ratio R1 (S4L(in): S4i_(out)) is in the range of from 1 :1 to 500:1 and / or wherein the (adjusted) reflux ratio R2 (S^inj: S4i_(out)) is in the range of from 1 :1 to 500:1 with R2 > R1.

[0025] The mass based ratio S1i_: S4i_(out) is preferably in the range of from 5: 1 to 1000:1. Said ratio, as S4i_(out) mainly comprises toluidine compound of formula (I), relates to the amount thereof separated. The mass based ratio

[0026] 51 i_:S4i_(in) is preferably in the range of from 1 : 1 to 35:1.

[0027] Stream S2L, S2L(out)

[0028] According to step (a), at least a part of stream S2L is removed, thereby obtaining a stream S2 yout) comprising vTDA and being enriched in vTDA compared to S1 L. Preferably, stream S2i_(out) comprises at least 99 weight-%, more preferably at least 99.5 weight-%, more preferably at least 99.7 weight-%, vTDA, based on the total weight of stream S2i_(out) being 100 weight-%.

[0029] Stream S1L, Sl out)

[0030] As described herein above, at least a part of stream S1 L is fed into the second rectification column C2. According to step (a), optionally at least a part of liquid stream S1 L is removed from said stream S1 L before feeding at least a part of stream S1L into the second rectification column, thereby obtaining a stream Slyout) comprising vTDA and being enriched in vTDA compared to S1. Preferably, stream S1L and stream S1 L(out) respectively comprises at least 97 weight-%, more preferably at least 98 weight-%, more preferably at least 99 weight-%, vTDA, based on the total weight of stream S1L and stream S1 L(out) respectively being 100 weight-%. Also here, "vTDA” is a mixture of toluene- 2,3-diamine and toluene-3,4-diamine, preferably with a molar ratio of toluene-2,3-diamine to toluene-3,4-diamine in the range of from 3.5 to 4.5.

[0031] Preferably, stream S1L and stream S1 L(out) respectively comprises < 2 weight-% of said toluidine compound of formula (I) based on the total weight of stream S1 L and stream S1 L(out) respectively being 100 weight-%. Preferably, in the range of from 0 to 70 weight-% of stream S1 L are removed as stream S1 L(out) in step (c).

[0032] Condenser for stream S1L

[0033] As described herein above, a top stream S1 is removed from rectification column C1 , wherein S1 is enriched in vTDA compared to the cTDA mixture; splitting top stream S1 into a least a gaseous stream S1G and a liquid stream S1 L, wherein S1L comprises vTDA and is enriched in vTDA compared to S1 . Preferably, stream S1 is passed through a condenser, wherein the liquid stream S1L and a gaseous stream S1gare obtained, with the concentration of vTDA in liquid stream S1 L C(VTDA)SH > concentration of vTDA in stream S1 c(vTDA)si.

[0034] Sump recovery of mTDA from C1 by evaporation

[0035] As described herein above, the cTDA mixture is subjected to separation conditions in the rectification column C1 and a top stream S1 is removed from said rectification column C1.

[0036] According to a preferred embodiment, the process further comprises

[0037] (d) removal of a bottom stream S3 from the first rectification column C1 , wherein S3 comprises mTDA and heavy boilers, and passing at least a first part of bottom stream S3 (S3-1) into an evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-1 G, which is enriched in mTDA compared to S3, and a liquid stream S3-1 L, which is enriched in heavy boilers compared to S3 and has a higher viscosity than S3.

[0038] Viscosity is determined via a mass flow meter, preferably as online viscosity measurement.

[0039] Preferably, at least a part of vaporized stream S3-1 G, preferably S3-1G in total, is fed back into the first rectification column C1.

[0040] According to a preferred option of this preferred embodiment, at least a second part of bottom stream S3 (S3-2) is passed through a reboiler V2(C1 ), thereby obtaining a stream S3-2h having an elevated temperature compared to S3 and introducing at least a part of said stream S3-2h into the first rectification column C1. Preferably, bottom stream S3 is at least divided into two part streams S3-1 and S3-2, with a volume based ratio S3-1 to S3-2 in the range of from 0.0005 to 0.015. This set-up is schematically shown in Fig. 1.

[0041] According to another preferred option of this preferred embodiment, at least a second part of bottom stream S3 (S3- 2) is passed through a reboiler V2(C1 ) thereby obtaining a stream S3-2h having an elevated temperature compared to S3, wherein S3-2h is split into at least two streams S3-2.1 h and S3-2.2h and introducing at least a part of said stream S3-2.1h into the first rectification column C1. Preferably, stream S3-2.2h is passed into the evaporator Vi(C1), obtaining therefrom a vaporized stream S3-1GX, and a liquid stream S3-1LX. Preferably, the volume based ratio S3-1 to S3-2 is in the range of from 0:1 to 0.015:1 , and / or wherein the volume based ratio S3-2.1h to S3-2.2h is in the range of from 0.0005:1 to 0.015:1. This set-up is schematically shown in Fig. 2.

[0042] According to another preferred embodiment, the process comprises:

[0043] (d) removal of a bottom stream S3 from the first rectification column C1 , wherein S3 comprises mTDA and heavy boilers, and passing bottom stream S3 into a reboiler V2(C1 ), obtaining therefrom a stream S3h having an elevated temperature compared to S3.

[0044] Preferably, stream S3h is split into at least two streams S3-1 h and S3-2h, wherein at least a part of stream S3-1 h is fed into the first rectification column C1 and at least a part of S3-2h is is fed into an evaporator Vi(C1 ), obtaining therefrom a vaporized stream S3-2.2G, which is enriched in mTDA compared to S3, and a liquid stream S3-2.1 L, which is enriched in heavy boilers compared to S3-2h and has a higher viscosity than S3-2h. Preferably, the volume based ratio S3-1h to S3-2h is in the range of from 0.0005: 1 to 0.015: 1. This set-up is schematically shown in Fig. 3.

[0045] Overall, it is preferred that stream S3-1L or stream S3-1 LX or stream S3-2.1L, is mixed with at least a part of one or more of S1 L(out), S2(0Ut) and / or with an additional liquid stream Sx from another source, preferably with at least a part of S1 L(out), thereby obtaining a stream S6L, which has a lower viscosity than S3-1 L or S3-1LX or S3-2.1 L.

[0046] Liquid stream Sx is selected from the group consisting of aniline, aniline residue (aniline contains at least aminophenol, diaminobenzene, dipehenylamin, phenazine, N-phenyl-benzene diamine), organic solvent, fuel oil, water, and mixtures of two or more thereof.

[0047] Preferably, stream S6L is used for heating purposes, more preferably for thermal treatment and / or steam generation.

[0048] According to the process of the present invention, a second rectification column C2 is used, wherein the second rectification column C2 is preferably operated at a bottom pressure in the range of from 5 to 200 mbar(abs). Preferably, the second rectification column C2 is operated at a bottom temperature in the range of from 115 to 210 °C. Preferably, the second rectification column C2 has in the range of from 3 to 30, more preferably in the range of from 5 to 25 theoretical stages. Preferably, the feeding point for the part of stream S1L into the second rectification column C2 is between the 5thto the 28th, more preferably between the 6thto the 20th, theoretical stage of C2.

[0049] Preferably, a liquid bottoms stream S2 is removed from the second rectification column C2 and split into at least two liquid streams S2L and S2i_(r), wherein stream S2i_(r) is passed through a reboiler of C2, preferably a bottoms reboiler Vbottom(C2) and reintroduced into C2.

[0050] Removal of mTDA from C1

[0051] Preferably, the process further comprises: (e) removal of a, preferably side, stream S5 from the first rectification column C1, said stream S5 being enriched in mTDA compared to the cTDA mixture fed into C1 .

[0052] Preferably, the stream S5 comprises > 98 weight-% of mTDA and < 5000ppm vTDA, more preferably < 3000ppm, more preferably < lOOOppm vTDA, based on the total weight of stream S5 being 100 weight-%.

[0053] Toluidine compound of formula (I)

[0054] According to (ii), the content of a toluidine compound of formula (I) in stream S2L is monitored

[0055] Preferably, the toluidine compound of formula (I) comprises one or more compound(s) selected from the group consisting of 2-aminotoluene (ortho toluidine), 3-aminotoluene (meta toluidine) and 4-aminotoluene (para toluidine). At 1013 hPa, the toluidine compound of formula (I) has a boiling point in the range of from 200 to 203°C, i.e. is thus, compared to mTDA and vTDA, a "light boiler”.

[0056] Rectification column C1

[0057] The first rectification column C1 is preferably a dividing wall tower or comprises at least two rectification columns C1.1 and C1.2. Regarding a dividing wall tower as first rectification column C1 , said tower is preferably divided into four zones, namely an upper tower zone (UZ), a bottom tower zone (BZ), a feed tower zone (FZ) and a product zone (PZ). The feed zone (FZ) and the product zone (PZ) are preferably separated by a partition (P) and are not connected to each other.

[0058] The rectification column C1 is preferably equipped with liquid collectors, liquid distributors and trays and / or packings, wherein packings are structured packings or random packings. The number of theoretical stages in UZ is preferably in the range of from 1 to 20, more preferably in the range of from 3 to 15, the theoretical stages in BZ are preferably in the range of from 1 to 15, more preferably in the range of from 2 to 10. The number of theoretical stages in FZ is preferably in the range of from 5 to 40, more preferably in the range of from 10 to 35: preferably, the cTDA feed position is between the 2thand the 25ththeoretical stage, preferably between the 3thand the 20ththeoretical stage in FZ.

[0059] The number of theoretical stages in PZ is preferably in the range of from 5 to 40, more preferably in the range of from 10 to 35: The extraction position of the side stream S5 is between the 5thand the 30th, preferably between the 6thand the 25ththeoretical stage in PRZ. The rectification column C1 is preferably operated at a top pressure in the range of from 20 to 100 mbara, preferably in the range of from 30 to 80 mbara, and at a top temperature in the range of from 140 to 190°C, preferably in the range of from 160 to 180°C. Regarding the first rectification column C1 comprising at least two rectification columns C1.1 and C1.2, each of C1.1 and C1.2 is preferably equipped with liquid collectors, liquid distributors and trays and / or packings, wherein packings are structured packings or random packings. Each of C1 .1 and C1 .2 is preferably operated at a top pressure in the range of from 20 to 100 mbara, preferably in the range of from 30 to 80 mbara, and at a top temperature in the range of from 140 to 190°C, preferably in the range of from 160 to 180°C.

[0060] Regarding the arrangement, streams and connections in between C1.1 and C1.2, at least two options are:

[0061] (1) In a first option, rectification column C1.1 has in the range of from 20 to 60 theoretical stages and the (subsequent) rectification column C1 .2 has in the range of from 10 to 40 theoretical stages. The cTDA feed position is preferably i n the range of from theoretical stage 5 and 40 of C 1 .1 . 1 n C 1 .1 , vTD A is separated from mTD A and heavy boilers. A top stream S1 from is removed from C1.1, wherein S1 is enriched in vTDA compared to the cTDA mixture. Said top stream S1 is split into a least a gaseous stream S1 G and a liquid stream S1 L, wherein S1 L comprises vTDA and is enriched in vTDA compared to S1. At least a part of stream S1 L is fed into the second rectification column C2 as described herein above. A bottoms stream from C1.1, which is enriched in mTDA and heavy boilers compared to the feed stream cTDA, is at least partially, preferably after passing a reboiler, passed back into C1.1, wherein another part of said bottoms stream is passed into C1 .2, preferably in range of from theoretical stage 2 to 25of C1 .2. From C1.2, a, preferably top, stream is removed. Said top stream is passed into a condenser, from which a gaseous stream is taken off and a liquid stream is obtained, which is at least partially returned into C1 .2 and partially taken off as stream S5. Said stream S5 is enriched in mTDA compared to the cTDA mixture fed into C1.1. Stream S5 is handled as described in detail herein above. Furthermore, from C1.2, a, preferably bottom, stream S3 is removed, wherein S3 comprises mTDA and heavy boilers, which are enriched in S3 compared to the cTDA stream fed to C1.1 and also to the stream fed to C1.2. Stream S3 is handled as described in detail herein above. The first option is graphically shown in Fig. 4.

[0062] (2) In a second option, rectification column C1.1 has in the range of from 10 to 40 theoretical stages and the (subsequent) rectification column C1.2 has in the range of from 20 to 60 theoretical stages. The cTDA feed position is preferably in thethe range of from theoretical stage 2 to 25 of C1.1, wherein from C1.1, a, preferably top, stream comprising mTDA and vTDA is removed and a, preferably bottom, stream S3, which comprises the heavy boilers which are enriched in S3 compared to the cTDA stream fed to C1.1. Stream S3 is handled as described in detail herein above. The (top) stream from C1.1 is, preferably after passage through a condensor, from which a gaseous stream is taken off and a liquid stream is split into at least two parts, wherein a part is reintroduced into C1.1 and another part is fed into C1 .2, preferably in the range of from theoretical stage 5 to 40 of C1 .2. From C1 .2, a top stream S1 from is removed, wherein S1 is enriched in vTDA compared to the cTDA mixture. Said top stream S1 is split into a least a gaseous stream S1 G and a liquid stream S1 L, wherein S1 L comprises vTDA and is enriched in vTDA compared to S1 . At least a part of stream S1 L is fed into the second rectification column C2 as described herein in detail above. A, preferably bottom, stream from C1 .2, which is enriched in mTDA compared to the feed stream cTDA is at least partially, preferably after passing a reboiler, passed back into C.1 .2 wherein another part of said bottoms streams is the stream S5. Stream S5 is handled as described in detail herein above. The second option is graphically shown in Fig. 5. In case that C1 is operated with two columns C1.1 and C1.2, option (1) is preferred.

[0063] 2ndaspect - Vicinal TDA (Product-by-process)

[0064] A second aspect of the present invention is related to vicinal TDA (vTDA) obtained or obtainable from a process of the first aspect of the invention as described herein above, comprising less than 100 weight-ppm of a toluidine compound of formula (I). All details, embodiments and preferred embodiments (as well as options and preferred options) described herein above with respect to the process of the first aspect of the invention apply also to the second aspect of the present invention.

[0065] 3rdaspect - Vicinal TDA (Product)

[0066] In a third aspect, the invention is directed to vicinal TDA (vTDA) having a purity in the range of at least 99 weight-%, more preferably at least 99.5%, more preferably at least 99.7 weight% and comprising less than 100 weight-ppm of a toluidine compound of formula (I). All details, embodiments and preferred embodiments (as well as options and preferred options) described herein above with respect to the process of the first aspect of the invention and with respect to the vTDA of the second aspect of the present invention apply also to the third aspect of the invention.

[0067] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1, 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0068] 1 . A purification process for obtaining vicinal toluenediamine comprising providing a first rectification column C1 and a second rectification column C2, providing a crude toluenediamine (cTDA) mixture comprising meta toluenediamine (mTDA) and vicinal toluenediamine (vTDA); wherein the process comprises feeding the cTDA mixture to the first rectification column C1 and subjecting the cTDA mixture to separation conditions in the rectification column C1; removing a top stream S1 from said rectification column C1, wherein S1 is enriched in vTDA compared to the cTDA mixture; splitting top stream S1 into a least a gaseous stream S1G and a liquid stream S1 L, wherein S1 L comprises vTDA and is enriched in vTDA compared to S1; wherein at least a part of stream S1L is fed into the second rectification column C2, wherein C2 is operated under reflux with top vapor condensation, wherein a top stream S4 is removed from the second rectification column C2, passed through a condenser VtOp(C2), thereby obtaining a gaseous stream S4gand a liquid stream S4L, wherein S4L is split into at least two streams, wherein a first part stream is discarded (S4L<out)) and a second part stream is returned to the second rectification column C2 (S4L(in)), the reflux ratio of C2 being the mass based ratio of the second part stream returned into the second rectification column C2 (S4L(in)) to the discarded stream S4 (Out) R1 (S^inj: S4L(out)); wherein a stream S2L is removed from said second rectification column C2, said stream S2L preferably being enriched in vTDA compared to S1 L; the process further comprising

[0069] (a) removing at least a part of stream S2L, thereby obtaining a stream S2 yout) comprising vTDA and being enriched in vTDA compared to S1 L; and / or

[0070] (b) introducing at least a part of S2L into the first rectification column C1 or combining at least a part of S2L with the cTDA mixture fed to the first rectification column C1 , and

[0071] (c) optionally removing at least a part of liquid stream S1L from said stream S1 L before feeding at least a part of stream S1 L into the second rectification column, thereby obtaining a stream S1i_(out) comprising vTDA and being enriched in vTDA compared to S1; wherein

[0072] (ii) the concentration of vTDA in stream S2L is monitored (C<VTDA)) and if C(VTDA> is

[0073] < 99 weight-%, step (a) is not conducted and step (b) is conducted; and

[0074] (ii) the content of a toluidine compound of formula (I) in stream S2L is monitored and only if the content of said toluidine compound of formula (I) in stream S2L is

[0075] < 100 weight-ppm, step (c) is optionally conducted; and if the content of said toluidine compound of formula (I) in stream S2L is >100 weight-ppm, the reflux ratio of the second rectification column C2 is adjusted to a reflux ratio R2 with R2 (S4L(in): S4i_(out)) R1 (S4L(in): S4i_(out)). The process of embodiment 1 , wherein if the content of said toluidine compound of formula (I) in stream S2L is

[0076] < 100 weight-ppm, then step (a) is conducted, wherein the part of S2L removed as stream S2 yout) in step (a) represents in the range of from 50 to 100 weight-% of stream S2L and the part of S2L introduced in step (b) into the first rectification column C1 or combined with the cTDA mixture fed to the first rectification column C1 is in the range of from 0 to 50 weight-% of stream S2i_. 3. The process of embodiment 1 or 2, wherein R2 > R1 , wherein preferably the mass based reflux ratio R1 (S4L(in>: S4L(out>) is in the range of from 1 : 1 to 500:1 and / or wherein the (adjusted) reflux ratio R2 (S^inj: S4i_(out)) is in the range of from 1 :1 to 500:1 with R2 > R1.

[0077] 4. The process of any one of embodiments 1 to 3, wherein stream S2i_(0Ut) comprises at least 99 weight-%, preferably at least 99.5 weight-%, more preferably at least 99.7 weight-%, vTDA, based on the total weight of stream S2i_(out) being 100 weight-%.

[0078] 5. The process of any one of embodiments 1 to 4, wherein stream S1L and stream S1 L(out) respectively comprises at least 97 weight-%, preferably at least 98 weight-%, more preferably at least 99 weight-%, vTDA, based on the total weight of stream S1 L and stream Slyout) respectively being 100 weight-%.

[0079] 6. The process of any one of embodiments 1 to 5, wherein stream S1L and stream S1 L(out) respectively comprises < 2 weight-% of said toluidine compound of formula (I) based on the total weight of stream S1L and stream SlL(out) respectively being 100 weight-%.

[0080] 7. The process of any one of embodiments 1 to 6, wherein in the range of from 0 to 70 weight-% of stream S1 L are removed as stream Skfout) in step (c).

[0081] 8. The process of any one of embodiments 1 to 7, wherein stream S1 is passed through a condenser, wherein the liquid stream S1L and a gaseous stream S1gare obtained, with the concentration of vTDA in liquid stream S1L C(VTDA)SH > concentration of vTDA in stream S1 c(vTDA)si.

[0082] 9. The process of any one of embodiments 1 to 8 comprising

[0083] (d) removal of a bottom stream S3 from the first rectification column C1 , wherein S3 comprises mTDA and heavy boilers, and passing at least a first part of bottom stream S3 (S3-1) into an evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-1 G, which is enriched in mTDA compared to S3, and a liquid stream S3-1 L, which is enriched in heavy boilers compared to S3 and has a higher viscosity than S3.

[0084] 10. The process of embodiment 9 comprising feeding at least a part of vaporized stream S3-1 G, preferably S3-1G in total, back into the first rectification column C1.

[0085] 11 . The process of embodiments 9 or 10, wherein at least a second part of bottom stream S3 (S3-2) is passed through a reboiler V2(C1 ), thereby obtaining a stream S3-2h having an elevated temperature compared to S3 and introducing at least a part of said stream S3-2h into the first rectification column C1. 12. The process of any one of embodiments 9 to 11 , wherein bottom stream S3 is at least divided into two part streams S3-1 and S3-2, with a volume based ratio S3-1 to S3-2 in the range of from 0.0005 to 0.015.

[0086] 13. The process of embodiment 9 or 10, wherein at least a second part of bottom stream S3 (S3-2) is passed through a reboiler V2(C1) thereby obtaining a stream S3-2h having an elevated temperature compared to S3, wherein S3-2h is split into at least two streams S3-2.1 h and S3-2.2h and introducing at least a part of said stream S3-2.1h into the first rectification column C1.

[0087] 14. The process of embodiment 13, wherein stream S3-2.2h is passed into the evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-1GX, and a liquid stream S3-1LX.

[0088] 15. The process of embodiment 13 or 14, wherein the volume based ratio S3-1 to S3-2 is in the range of from 0:1 to 0.015:1 , and / or wherein the volume based ratio S3-2.1h to S3-2.2h is in the range of from 0.0005:1 to 0.015:1.

[0089] 16. The process of any one of embodiments 1 to 8, comprising

[0090] (d) removal of a bottom stream S3 from the first rectification column C1 , wherein S3 comprises mTDA and heavy boilers, and passing bottom stream S3 into a reboiler V2(C1 ), obtaining therefrom a stream S3h having an elevated temperature compared to S3.

[0091] 17. The process of embodiment 16, wherein stream S3h is split into at least two streams S3-1 h and S3-2h, wherein at least a part of stream S3-1 h is fed into the first rectification column C1 and at least a part of S3-2h is fed into an evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-2.2G, which is enriched in mTDA compared to S3, and a liquid stream S3-2.1 L, which is enriched in heavy boilers compared to S3 and has a higher viscosity than S3-2h.

[0092] 18. The process of embodiment 16 or 17, wherein the volume based ratio S3-1h to S3-2h is in the range of from 0.0005:1 to 0.015:1.

[0093] 19. The process of any one of embodiments 9 to 18, wherein stream S3-1L or stream S3-1 LX or stream S3-2.1L, is mixed with at least a part of one or more of S1 L(out), S2(0Ut) and / or with an additional liquid stream Sx from another source, preferably with at least a part of S1 L(out), thereby obtaining a stream S6L, which has a lower viscosity than S3-1 L or S3-1LX or S3-2.1 L.

[0094] 20. The process of any one of embodiments 11 to 19, wherein stream S6L is used for heating purposes, preferably for thermal treatment and / or steam generation. 21 . The process of any one of embodiments 1 to 20, wherein the second rectification column C2 is operated at a bottom pressure in the range of from 5 to 200 mbar(abs).

[0095] 22. The process of any one of embodiments 1 to 21 , wherein the second rectification column C2 is operated at a bottom temperature in the range of from 115 to 210 °C.

[0096] 23. The process of any one of embodiments 1 to 22, wherein the second rectification column C2 has in the range of from 3 to 30, preferably in the range of from 5 to 25 theoretical stages.

[0097] 24. The process of any one of embodiments 1 to 23, wherein the feeding point for the part of stream S1 L into the second rectification column C2 is between the 5thto the 28th, preferably between the 6thto the 20th, theoretical stage of C2.

[0098] 25. The process of any one of embodiments 1 to 24, wherein a liquid bottoms stream S2 is removed from the second rectification column C2 and split into at least two liquid streams S2L and S2i_(r), wherein stream S2i_(r) is passed through a reboiler of C2, preferably a bottoms reboiler Vbottom(C2) and reintroduced into C2.

[0099] 26. The process of any one of embodiments 1 to 25 comprising

[0100] (e) removal of a, preferably side, stream S5 from the first rectification column C1 , said stream S5 being enriched in mTDA compared to the cTDA mixture fed into C1.

[0101] 27. The process of embodiment 26, wherein the stream S5 comprises > 98 weight-% of mTDA and < 5000ppm vTDA, preferably < 3000ppm, more preferably < lOOOppm vTDA, based on the total weight of stream S5 being 100 weight-%.

[0102] 28. The process of any one of embodiments 1 to 27, wherein the toluidine compound of formula (I) comprises one or more compound(s) selected from the group consisting of 2-aminotoluene (ortho toluidine), 3-ami- notoluene (meta toluidine) and 4-aminotoluene (para toluidine).

[0103] 29. Vicinal TDA (vTDA) obtained or obtainable from a process of any one of embodiments 1 to 27, comprising less than 100 weight-ppm of a toluidine compound of formula (I).

[0104] 30. Vicinal TDA (vTDA) having a purity in the range of at least 99 weight-%, preferably at least 99.5%, more preferably at least 99.7 weight% and comprising less than 100 weight-ppm of a toluidine compound of formula (I).

[0105] The present invention is further illustrated by the following reference examples, comparative examples, and examples. Examples

[0106] Simulations

[0107] All simulations were done with the process simulation software ASPEN PLUS™ v.8.6. The components used in the process simulation and their characteristics respectively, were taken from the ASPEN PLUS™ v.8.6 PURE32 Database.

[0108] Pressures indicated in "bara”, "mbara” etc. are related to absolute pressure.

[0109] Example 1 : Purification of a crude toluenediamine (cTDA) mixture

[0110] A crude toluenediamine (cTDA) mixture comprising meta toluenediamine (mTDA) and vicinal toluenediamine (vTDA) was subjected to a purification process with a set-up as shown in Fig. 1 , wherein the rectification column C2 and the relevant streams around C2 were simulated.

[0111] The stream S1L from the first rectification column C1 to the second rectification column C2 and the part of the bottom stream S2L removed from C2 (bottom draw S2i_(out)) were set as follows:

[0112] Stream S1i : mTDA: < 1 ,5 weight-% vTDA: > 97 weight-% toluidine of formula (I): < 1 ,5 weight-% water: < 1000 weight-ppm

[0113] Bottom Draw S2L(0Un: mTDA: < 1 weight-% vTDA: > 99 weight-% toluidine of formula (I): < 100 weight-ppm water: < 100 weight-ppm

[0114] The first rectification column C1 was a divided wall column. The second rectification column C2 had 12 theoretical stages and was operated at a top pressure of 80 mbara and a bottoms pressure of about 87 mbara. The temperatures in C2 were set to be about 110°C at the top and about 181 -182°C at the bottom of C2.

[0115] A stream S1L was introduced into C2 with 1.5 weight-% toluidine at theoretical stage 9 of C2 as indicated in Table 1 with 699 kg / h (without any TDA). As stream S2L, a bottom stream was continuously removed from the bottom of C2, from which S2i_(out) was drawn, with a toluidine concentration of 10 weight-ppm and 650 kg / h.

[0116] The liquid stream S4i_(out) (purge) had 47.7 kg / h and a concentration of toluidine of 20 weight-%, the remainder up to 100 weight-% being 79.8 weight-% VTDA and traces of water, nitrogen and less than 0.1 weight of oxygen. Gaseous stream S4G (offgas) had 2.5 kg / h with 37 weight-% toluidine, 12 weight-% water the remainder up to 100 weight-% being other non-condensable (N2, O2).

[0117] The demand of heating steam at the sump reboiler of C2 was about 70 kg / h, which resulted in a reflux flow of about 99 kg / h. The concentration profile and the temperature profile are shown in Fig. 6.

[0118] Example 2: Variation of the reflux at the top of the second rectification column C2

[0119] Example 1 was repeated, wherein the number of theoretical stages of C2, the position of feeding stream S1 L and the amount and composition of S1L was kept as in Example 1 and the reflux S4i_(in) at the top of C2 were varied and the resulting mass fraction of toluidine in S2i_(0Ut) was monitored (x toluidine). The results are shown in Table 1 and are graphically depicted in Fig. 7 and Fig.8.

[0120] With increased reflux, a lower bottom toluidine concentration in stream S2i_(out) could be achieved. The demand of steam and cooling water increases with the higher reflux.

[0121] Table 1

[0122] Example 3: different toluidine concentrations in feed stream S1L to C2

[0123] Example 1 was repeated with different toluidine concentration in the feeding stream S1 L and the ratio S4i_(in):S4i_(out) was varied so that the resulting mass fraction of toluidine in S2i_(out) was stable at 10 ppm. The number of theoretical stages of rectification column C2 and the position of feeding stream S1L was kept as in Example 1 . The results are shown in Table 2 and are graphically depicted in Fig. 9, where it is shown the concentration profile of toluidine in the tower C2, respectively theoretical stages for different toluidine feed concentration in S1 L.

[0124] Table 2

[0125] It was found that a low toluidine concentration in S2i_(out) of 10ppm could be reached for all toluidine feed concentrations of S1 L by adjustment of the reflux ratio S4i_(in) to S4i_(out). In case of already low toluidine feed concentration in S1 L the reflux could be reduced to fullfil the needed bottom toluidine concentration in S2i_(out). By reducing the reflux ratio, steam and cooling demand at the reboiler and top condenser could be reduced.

[0126] Short description of the Figures

[0127] Fig. 1 shows the general setup with a first rectification column C1 being a dividing wall tower, said tower being divided into four zones, namely an upper tower zone (UZ), a bottom tower zone (BZ), a feed tower zone (FZ) and a product zone (PZ). The feed zone (FZ) and the product zone (PZ) are separated by a partition (P) and are not connected to each other. A crude TDA mixture (cTDA) is fed to the first rectification column C1 and subjected to separation conditions in the rectification column C1. A top stream S1 is removed from said rectification column C1, wherein S1 is enriched in vTDA compared to the cTDA mixture. The top stream S1 is split into a least a gaseous stream S1G and a liquid stream S1 L, wherein S1 L comprises vTDA and is enriched in vTDA compared to S1 , wherein at least a part of stream S1 L is fed into the second rectification column C2. The second rectification column C2 is operated under reflux with top vapor condensation, wherein a top stream S4 is removed from the second rectification column C2, passed through a condenser VtOp(C2), thereby obtaining a gaseous stream S4g, which is discarded, and a liquid stream S4L. The liquid stream S4L is split into at least two streams, wherein a first part stream is discarded (S4L<out)) and a second part stream is returned to the second rectification column C2 (S^nj), wherein the reflux ratio of C2 is the mass based ratio of the second part stream returned into the second rectification column C2 (S4L(in)) to the discarded stream S4i_(out) R1 (S^inj: S4L(out)). A bottoms stream S2, preferably being enriched in vTDA compared to S1 L, is removed from said second rectification column C2 and divided into two streams S2L and S2L(r), wherein S2i_(r) is passed through a bottom reboiler of C2 (Vbottom(C2)) and reintroduced into C2. The stream S2L, as the stream S2, is preferably enriched in vTDA compared to S1 L. Fig. 1 further shows the option that at least a part of stream S2L can be removed, thereby obtaining a stream S2 yout) comprising vTDA and being enriched in vTDA compared to S1 L. Additionally or alternatively (and / or) at least a part of S2L can be reintroduced into the first rectification column C1 or at least a part of S2L can be combined with the cTDA mixture and then be fed to the first rectification column C1 . Optionally, at least a part of liquid stream S1 L can be removed from stream S1 L before at least a part of stream S1 L is fed into the second rectification column, thereby obtaining a stream S1 L(out) comprising vTDA and being enriched in vTDA compared to S1. At the bottom of the first rectification column C1 , a bottom stream S3 is removed, wherein S3 comprises mTDA and heavy boilers.

[0128] Fig. 1 further shows that at least a first part of bottom stream S3 (S3-1) is passed into an evaporator Vi(C1), obtaining therefrom a vaporized stream S3-1G, which is enriched in mTDA compared to S3, and a liquid stream S3-1 L, which is enriched in heavy boilers compared to S3 and has a higher viscosity than S3. At least a part of vaporized stream S3-1 G is reintroduced back into the first rectification column C1 . At least a second part of bottom stream S3 (S3-2) is passed through a reboiler V2(C1 ), thereby obtaining a stream S3-2h having an elevated temperature compared to S3. At least a part of said stream S3-2h is reintroduced into the first rectification column C1.

[0129] Stream S3-1 L is optionally mixed with at least a part of one or more of S1 L(out), S2(0Ut) and / or with an additional liquid stream Sx from another source, preferably with at least a part of S1 L(out), thereby obtaining a stream S6L, which has a lower viscosity than S3L.

[0130] Fig. 2 shows the same setup as Fig. 1 with the deviation that the stream S3-2h is split into two streams S3-2.1 h and S3-2.2h, wherein stream S3-2.1 h is reintroduced into C1 and stream S3-2.2h is combined with stream S3-1 so that after passage through Vi(C1) a gaseous stream S3-1 GX and a liquid stream S3-1i_x are obtained, wherein gaseous stream S3-1 GX is reintroduced into C1. Stream S3-1LX is optionally mixed with at least a part of one or more of S1 L(out), S2(0Ut) and / or with an additional liquid stream Sx from another source, preferably with at least a part of S1 L(out), thereby obtaining a stream S6L, which has a lower viscosity than S3-1LX.

[0131] Fig. 3 shows the same setup as Fig. 1 with the deviation that the bottoms stream S3 from the first rectification column C1 is completely passed through reboiler V2(C1), thereby obtaining a stream S3h having an elevated temperature compared to S3. Stream S3h is split into at least two streams S3-1 h and S3-2h. At least a part of stream S3-2h is fed to the evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-2.2G, which is enriched in mTDA compared to S3, S3-2h, and a liquid stream S3-2.1 L, which is enriched in heavy boilers compared to S3, S3-2h and has a higher viscosity than S3, S3-2h. At least a part of vaporized stream S3-2.2G is reintroduced back into the first rectification column C1. Stream S3-2.1 L is optionally mixed with at least a part of one or more of S1 L(out), S2(0Ut) and / or with an additional liquid stream Sx from another source, preferably with at least a part of S1 L(out), thereby obtaining a stream S6L, which has a lower viscosity than S3-2.1 L.

[0132] Fig. 4 shows a detail how rectification column C1 is set up if build from two rectification columns C1 .1 and C1 .2, wherein C1.1 has more theoretical stages than C1.2.

[0133] Fig. 5 shows a detail how rectification column C1 is set up if build from two rectification columns C1 .1 and C1 .2, wherein C1.2 has more theoretical stages than C1.1.

[0134] Fig 6 shows the concentration profile of vTDA (2,3-TDA, 3,4-TDA), toluidine and the temperature profile in rectification column C2, respectively as a function of the theoretical stage according to Example 1 . The mass fraction of vTDA (2,3-TDA, 3,4-TDA) and toluidine x in (g / g) is shown on the upper x axis and the temperature on the bottom x axis in [°C], The theoretical stage is shown on the y axis, wherein stage 12 represents the top of C2 and stage zero represents the bottom of C2.

[0135] Fig 7 shows the toluidine concentration in S2i_(out) as a function of reflux S4i_(in) (feed stream S1 L toluidine concentration 1.5 weight-%) according to Example 2.

[0136] Fig 8 shows the concentration profile of toluidine according to Example 2 as a function of the theoretical stage. The mass fraction of toluidine x in (g / g) is shown on the bottom x axis and the theoretical stage is shown on the y axis, wherein stage 12 represents the top of C2 and stage zero represents the bottom of C2.

[0137] Fig. 9 shows the concentration profile of toluidine according to Example 3 as a function of the theoretical stage and varied toluidine concentration in feed stream S1 L. The mass fraction of toluidine x in (g / g) is shown on the bottom x axis and the theoretical stage is shown on the y axis, wherein stage 12 represents the top of C2 and stage zero represents the bottom of C2.

Claims

Claims1 . A purification process for obtaining vicinal toluenediamine comprising providing a first rectification column C1 and a second rectification column C2, providing a crude toluenediamine (cTDA) mixture comprising meta toluenediamine (mTDA) and vicinal toluenediamine (vTDA); wherein the process comprises feeding the cTDA mixture to the first rectification column C1 and subjecting the cTDA mixture to separation conditions in the rectification column C1; removing a top stream S1 from said rectification column C1, wherein S1 is enriched in vTDA compared to the cTDA mixture; splitting top stream S1 into a least a gaseous stream S1G and a liquid stream S1 L, wherein S1 L comprises vTDA and is enriched in vTDA compared to S1; wherein at least a part of stream S1 L is fed into the second rectification column C2, wherein C2 is operated under reflux with top vapor condensation, wherein a top stream S4 is removed from the second rectification column C2, passed through a condenser VtOp(C2), thereby obtaining a gaseous stream S4gand a liquid stream S4L, wherein S4L is split into at least two streams, wherein a first part stream is discarded (S4L<out)) and a second part stream is returned to the second rectification column C2 (S^nj), the reflux ratio of C2 being the mass based ratio of the second part stream returned into the second rectification column C2 (S4L(in)) to the discarded stream S4 (Out) R1 (S^inj: S4L(out)); wherein a stream S2L is removed from said second rectification column C2, said stream S2L preferably being enriched in vTDA compared to S1 L; the process further comprising(a) removing at least a part of stream S2L, thereby obtaining a stream S2 yout) comprising vTDA and being enriched in vTDA compared to S1 L; and / or(b) introducing at least a part of S2L into the first rectification column C1 or combining at least a part of S2L with the cTDA mixture fed to the first rectification column C1, and(c) optionally removing at least a part of liquid stream S1L from said stream S1 L before feeding at least a part of stream S1 L into the second rectification column, thereby obtaining a stream Slyout) comprising vTDA and being enriched in vTDA compared to S1; wherein(ill) the concentration of vTDA in stream S2L is monitored (C<VTDA)) and if C(VTDA> is< 99 weight-%, step (a) is not conducted and step (b) is conducted; and(ii) the content of a toluidine compound of formula (I) in stream S2L is monitoredand only if the content of said toluidine compound of formula (I) in stream S2L is< 100 weight-ppm, step (c) is optionally conducted; and if the content of said toluidine compound of formula (I) in stream S2L is >100 weight-ppm, the reflux ratio of the second rectification column C2 is adjusted to a reflux ratio R2 with R2 (S4L(in): S4i(out)) R1 (S4L(in): S4i_(out)).

2. The process of claim 1, wherein if the content of said toluidine compound of formula (I) in stream S2L is < 100 weight-ppm, then step (a) is conducted, wherein the part of S2L removed as stream S2 yout) in step (a) represents in the range of from 50 to 100 weight-% of stream S2L and the part of S2L introduced in step (b) into the first rectification column C1 or combined with the cTDA mixture fed to the first rectification column C1 is in the range of from 0 to 50 weight-% of stream S2L.

3. The process of claim 1 or 2, wherein R2 > R1, wherein preferably the mass based reflux ratio R1 (S4L(in): S4L(out>) is in the range of from 1 :1 to 500:1 and / or wherein the (adjusted) reflux ratio R2 (S^inj: S4i_(out)) is in the range of from 1 : 1 to 500: 1 with R2 > R1 .

4. The process of any one of claims 1 to 3, wherein stream S2i_(0Ut) comprises at least 99 weight-%, preferably at least 99.5 weight-%, more preferably at least 99.7 weight-%, vTDA, based on the total weight of stream S2i_(out) being 100 weight-%.

5. The process of any one of claims 1 to 4, wherein stream S1 L and stream Skfout) respectively comprises at least 97 weight-%, preferably at least 98 weight-%, more preferably at least 99 weight-%, vTDA, based on the total weight of stream S1L and stream S1 L(out) respectively being 100 weight-%.

6. The process of any one of claims 1 to 5, wherein stream S1 L and stream Slyout) respectively comprises < 2 weight-% of the toluidine compound of formula (I) based on the total weight of stream S1L and stream S1 L(out) respectively being 100 weight-%.

7. The process of any one of claims 1 to 6 comprising(d) removal of a bottom stream S3 from the first rectification column C1 , wherein S3 comprises mTDA and heavy boilers, and passing at least a first part of bottom stream S3 (S3-1) into an evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-1 G, which is enriched in mTDA compared to S3, and a liquid stream S3-1 L, which is enriched in heavy boilers compared to S3 and has a higher viscosity than S3.

8. The process of claim 7 comprising feeding at least a part of vaporized streamS3-1 G, preferably S3-1G in total, back into the first rectification column C1.

9. The process of claims 7 or 8, wherein at least a second part of bottom stream S3 (S3-2) is passed through a reboiler V2(C1 ), thereby obtaining a stream S3-2h having an elevated temperature compared to S3 and introducing at least a part of said stream S3-2h into the first rectification column C1 , wherein preferably, bottom stream S3 is at least divided into two part streams S3-1 and S3-2.

10. The process of claim 7 or 8, wherein at least a second part of bottom stream S3 (S3-2) is passed through a reboiler V2(C1) thereby obtaining a stream S3-2h having an elevated temperature compared to S3, wherein S3-2h is split into at least two streams S3-2.1 h and S3-2.2h and introducing at least a part of said stream S3- 2.1h into the first rectification column C1 , wherein preferably stream S3-2.2h is passed into the evaporator Vi(C1), obtaining therefrom a vaporized stream S3-1GX, and a liquid stream S3-1LX.11 . The process of any one of claims 1 to 7, comprising(d) removal of a bottom stream S3 from the first rectification column C1 , wherein S3 comprises mTDA and heavy boilers, and passing bottom stream S3 into a reboiler V2(C1 ), obtaining therefrom a stream S3h having an elevated temperature compared to S3; wherein preferably, stream S3h is split into at least two streams S3-1 h and S3-2h, wherein at least a part of stream S3-1 h is fed into the first rectification column C1 and at least a part of S3-2h is is fed into an evaporator Vi (C1 ), obtaining therefrom a vaporized stream S3-2.2G, which is enriched in mTDA compared to S3, and a liquid stream S3-2.1 L, which is enriched in heavy boilers compared to S3 and has a higher viscosity than S3-2h.

12. The process of any one of claims 7 to 11 , wherein stream S3-1L or stream S3-1 LX or stream S3-2.1L, is mixed with at least a part of one or more of S1 L(out), S2(0Ut) and / or with an additional liquid stream Sx from another source, preferably with at least a part of S1 L(out), thereby obtaining a stream S6L, which has a lower viscosity than S3-1 L or S3-1LX or S3-2.1L; wherein stream S6L is preferably used for heating purposes, more preferably for thermal treatment and / or steam generation.

13. The process of any one of claims 1 to 12 comprising(e) removal of a, preferably side, stream S5 from the first rectification column C1 , said stream S5 being enriched in mTDA compared to the cTDA mixture fed into C1.

14. Vicinal TDA (vTDA) obtained or obtainable from a process of any one of claims 1 to 13, comprising less than 100 weight-ppm of a toluidine compound of formula (I).

15. Vicinal TDA (vTDA) having a purity in the range of at least 99 weight-%, preferably at least 99.5%, more preferably at least 99.7 weight% and comprising less than 100 weight-ppm of a toluidine compound of formula (I).

Images