Mixture comprising toluene diamine and method for controlling a hydrogenation process for preparing toluene diamine

Abstract

A first aspect of the invention relates to a mixture comprising 2,4- toluene diamine and 2,6-toluene diamine and comprising less than 10 weight-ppm of an amino methyl cyclohexenone compound of formula (I) based on the total weight of the mixture being 100 weight-%. In a second aspect, the invention is directed to a method for controlling a hydrogenation process for preparing toluene diamine (TDA) from dinitrotoluene (DNT), said TDA having a boiling temperature range BTRTDA with a lower boiling temperature limit value TTDA(L) and an upper boiling temperature limit value TTDA(U). A third aspect relates to a mixture comprising at least 2,4- toluene diamine and 2,6-toluene diamine obtained or obtainable from the method according to the second aspect. A fourth aspect of the invention is directed to a use of the mixture according to the first aspect of the invention or of the mixture of the third aspect of the invention for the preparation of toluene diisocyanate (TDI). In a fifth aspect, the invention relates to a process for preparing toluene diisocyanate (TDI) comprising: (I) Providing a mixture according to the first aspect of the invention or of the mixture of the third aspect of the invention; and (II) Phosgenation of the mixture provided in (I), thereby obtaining TDI.

Description

[0001] Mixture comprising toluene diamine and method for controlling a hydrogenation process for preparing toluene diamine

[0002] A first aspect of the invention relates to a mixture comprising 2,4-toluene diamine and 2,6-tol uene diamine and comprising less than 10 weight-ppm of an amino methyl cyclohexenone compound of formula (I) based on the total weight of the mixture being 100 weight-%. In a second aspect, the invention is directed to a method for controlling a hydrogenation process for preparing toluene diamine (TDA) from dinitrotoluene (DNT), said TDA having a boiling temperature range BTRTDA with a lower boiling temperature limit value TTDA<L) and an upper boiling temperature limit value TTDA(U). A third aspect relates to a mixture comprising at least 2,4-toluene diamine and 2,6-tol uene diamine obtained or obtainable from the method according to the second aspect of the invention. A fourth aspect of the invention is directed to a use of the mixture according to the first aspect of the invention or of the mixture of the third aspect of the invention for the preparation of toluene diisocyanate (TD I) . In a fifth aspect, the invention relates to a process for preparing toluene diisocyanate (TD I ) comprising: (I) Providing a mixture according to the first aspect of the invention or of the mixture of the third aspect of the invention; and (II) Phosgenation of the mixture provided in (I), thereby obtaining TDI.

[0003] State of the art

[0004] Toluene diamine (TDA) is produced on a technical scale by hydrogenation of dinitrotoluene (DNT) in a continuous liquid phase hydrogenation process. DNT reacts with hydrogen using hydrogenation catalysts such as Pd / C, Pt / Ni, Pt / Fe, Raney nickel to form TDA and water, see, for example, Ullmann's Enzyklopadie der technischen Chemie, 4thedition, volume 7, page 393 ff, 1973, Verlag Chemie Weinheim / New York. In the course of the hydrogenation reaction, "light boiling” side products, i.e. side products having a boiling point below the TDA boiling range, are formed. For example, EP 2 905 273 B1 discloses that light boiling side products 2,4- and 2, 6-diamino-1 -methyl cyclohexanes are formed due to over hydrogenation. EP 1 864 969 B1 describes the formation of cyclic ketones in TDA preparation.

[0005] In the downstream distillation process to separate the TDA isomers, these light boiling side products might be incompletely removed from the respective TDA. So called meta TDA, which is normally a mixture mainly consisting of the 2,4- and 2,6-TDA isomers, is on large scale phosgenated to obtain toluene diisocyanate (TDI). Therein, light boiling side products are a source for product yield loss in the phosgenation process. Light boiling side products such as core hydrogenated compounds also have detrimental effects - if nothing else in that the yield of the desired products 2,4- and 2,6-TDA is reduced. Therefore, it is crucial that the generation of these light boiling side product is reduced already in the reaction section related to hydrogenation.

[0006] It was an object of the present invention to provide a process for TDA preparation which overcomes these drawbacks and which enables achieving TDA in high yield and high purity. The generation of the light boiling side products depends on several process-related aspects such as catalyst reactivity and the amount of catalyst in the reaction volume. The deactivation rate of the catalyst is depending on runtime, temperature, hydrogen gas content and moreover, the amount of catalyst in the reaction volume is influenced by losses of catalyst to downstream process steps. To compensate the deactivation and the losses of catalyst in the reaction volume, a dosing of fresh catalyst is necessary to keep a certain amount of active catalyst in the reaction volume and to guarantee an efficient hydrogenation and a high conversion from DNT to TDA.

[0007] It was surprisingly shown that an analysis of the light boiler side product concentration inside the reactor or downstream, for example, after catalyst separation, can be used as a control parameter for adjusting the dosage rate of fresh catalyst to the reactor to achieve, for example, a desired yield of 2,4-TDA and 2,6-TDA and / or a minimum content of unwanted side-products.

[0008] A first aspect of the invention is thus related to a mixture comprising 2,4- toluene diamine and 2,6-toluene diamine and comprising less than 10 weight-ppm of an amino methyl cyclohexenone compound of formula (I)

[0009] CH3

[0010] (I) based on the total weight of the mixture being 100 weight-%. The amino methyl cyclohexenone compound of formula (I) has a molecular weight of 125.17 g / mol. The amino methyl cyclohexenone compound of formula (I) can be one compound or a mixture of two or more isomers falling under formula (I).

[0011] In some preferred embodiments of the mixture, at least 98 weight-%, preferably at least 99 weight-%, of the mixture consist of 2,4- toluene diamine and 2,6-toluene diamine based on the total weight of the mixture being 100 weight-%.

[0012] In some preferred embodiments of the mixture, 2,4- toluene diamine and 2,6-toluene diamine are comprised in the mixture in a molar ratio 2,4- toluene diamine : 2,6- toluene diamine in the range of from 10:1 to 1 :10, preferably in the range of from 8:1 to 1 :1, more preferably in the range of from 6:1 to 2:1, more preferably in the range of from 5:1 to 3:1.

[0013] 2ndaspect - Method

[0014] In a second aspect, the invention relates to a method for controlling a hydrogenation process for preparing toluene diamine (TDA) from dinitrotoluene (DNT), said TDA having a boiling temperature range BTRiDAwith a lower boiling temperature limit value TTDA<L) and an upper boiling temperature limit value TTDA<U), wherein the hydrogenation process comprises

[0015] (I) providing a liquid aqueous mixture having a volume Viamin a hydrogenation reaction zone Z, the mixture comprising water, DNT, hydrogen (H2) and a heterogeneous hydrogenation catalyst, and converting the DNT comprised in the liquid aqueous mixture under nitro group hydrogenation conditions in the hydrogenation reaction zone Z; thereby obtaining in the hydrogenation reaction zone Z a liquid aqueous mixture comprising water, TDA and n hydrogenation reaction side products Xsi, wherein n is an integer with n>1 and i=1 ...n, each Xsi having a boiling point Txsi with Txsi < TTDA(L>;

[0016] (ii) introducing a hydrogenation catalyst into the liquid aqueous mixture in the hydrogenation reaction zone Z at a catalyst dosage rate De;

[0017] (ill) removing a liquid aqueous product stream SP from the hydrogenation reaction zone Z, the stream SP comprising water and the TDA; wherein the method for controlling the hydrogenation process comprises

[0018] (a) defining a maximum value cmax(Xsi) of the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SP, and / or in one or more subsequent product streams SP-I, wherein the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi S(c(Xsi)) is X”=i c( sr);

[0019] (b) at least periodically determining the sum of the concentration c(Xsi) of the side products Xsi S(c(Xsi)) and the TDA concentration c(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SP, and / or in one or more subsequent product streams SP-I;

[0020] (c) determining whether S(c(Xsi)) is equal to, larger, or smaller than cmax(Xsi); and

[0021] (c.1) if S(c(Xsi)) > cmax(Xsi),

[0022] Introducing the hydrogenation catalyst at a modified dosage Dem with

[0023] Dem < De;

[0024] (C.2) if S(c(Xsi)) — Cmax(Xsi),

[0025] Introducing the hydrogenation catalyst at a modified dosage Dem with Dem De

[0026] All details, embodiments and preferred embodiments described above in the section related to the first aspect of the invention also apply for the second aspect of the invention.

[0027] Each concentration c(Xsi) is indicated in weight-% based on ctotai being 100 weight-%, wherein ctotai is the sum of the concentrations c(Xsi) of all side products Xsi taken together with the concentrations of all TDA isomers c(TDA) and taken together with the sum of the concentrations C(XHI) of all m heavy boiling components XHI having a boiling point above TTDA(U>: 100 weight-%, wherein n is an integer with n>1 and 1=1 ... m, each Xsi having a boiling point Txsi with Txsi < TTDA(L> m is an integer with m>1 and j=1...m, each XHI having a boiling point TXHI with TXHI >TTDA<U), and c(TDA) is the sum of the concentrations of the isomers 2,3-TDA, 2,4-TDA, 2,6-TDA, 2,5-TDA, 3,4-TDA and 3,5-TDA, i.e. c(TDA) = c(2,3-TDA) + c(2,4-TDA) + c(2,6-TDA) + c(2,5-TDA) + c(3,4-TDA) + c(3,5-TDA). Determination of the concentrations c(Xsi) of the side products Xsi, as well as of the concentrations of the TDA isomers c(TDA) having a boiling point in the range of from TTDA<L) to TTDA<U) as well as of the concentrations C(XHI) of the heavy boiling component XHI is done by a method known in the art, for example, it can be done either using online gas chromatography (GC) or by taking a liquid sample from the reactor and / or after the reactor and determining the percentages of the components using GC. All boiling points and boiling point ranges are to be understood at 1013 hPa.

[0028] Side products Xsi are the so called light-boilers, which also include amino methyl cyclohexenone compounds of formula (I). Preferably, each side product Xsi, which has a boiling point at 1013 hPa of < TTDA<L), comprises at least one cyclic structure element based on carbon atoms, wherein a cyclic structure element based on carbon atoms is aromatic or cycloaliphatic. More preferably, each side product Xsi comprises at least one cyclic structure element with six C atoms. More preferably, each cyclic structure element with six C atoms has at least one functional substituent selected from the group consisting of =0 group, -OH group, -NH2 group, and -CH3 group.

[0029] Surprisingly, it was found that controlling the overall concentration of all hydrogenation reaction side products Xsi allowed to obtain a final product, i.e. a mixture comprising 2,4-TDA and 2,6-TDA, preferably after one or more further work-up step(s) as outlined herein in more detail below, which had less than 10 weight-ppm of an amino methyl cyclohexenone compound of formula (I), based on the total weight of the mixture being 100 weight-%.

[0030] A heavy boiling component XHI is, as indicated above, 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.

[0031] In some preferred embodiments of the method, if S(c(Xsi)) > cmax(Xsi), then the catalyst dosage rate is decreased so that 0.1 < Dcm / Dc^ 0.99, wherein preferably the difference Ac(Xsi) is determined by S(c(Xsi)) - cmax(Xsi), wherein if 0.5< Ac(Xsi) < 2, then the catalyst dosage rate is decreased so that 0.1 s Dcm / Dc- 0.9; if 0.3< Ac(Xsi) <0.5, then the catalyst dosage rate is decreased so that

[0032] 0.3 s Dcm / Dc- 0.95; if 0.1 < Ac(Xsi) <0.3, then the catalyst dosage rate is decreased so that

[0033] 0.6 < Dcm / Dc < 0.975; if 0.01 < Ac(Xsi) <0.1, then the catalyst dosage rate is decreased so that

[0034] 0.9 s Dcm / Dc- 0.98; if 0< Ac(Xsi) <0.01 , then the catalyst dosage rate is decreased so that 0.95 < Dcm / Dc< 0.99. In some preferred embodiments of the method cmax(Xsi) are 0.05 weight-% (500 weight-ppm), preferably 0.1 weight- % (1000 weight-ppm), more preferably 0.15 weight-% (1500 weight-ppm), more preferably 0.2 weight-% (2000 weight-ppm). As above, cmax(Xsi) is defined based on ctotai being 100 weight-%, wherein ctotai is as defined above.

[0035] Combined with TDA yield

[0036] In some preferred embodiments of the method, in the method for controlling the hydrogenation process,

[0037] (a) comprises a.1) defining a maximum value cmax(Xsi) of the sum S of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I, wherein the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi S(c(Xsi)) is ZF=i c( sr); a.2) defining a minimum value of the concentration of toluene diamine cmin(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I;

[0038] (b) comprises b.1 ) at least periodically determining the sum of the concentration of the side products Xsi S(c(Xsi)) and the TDA concentration c(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I; b.2) at least periodically determining the concentration c(TDA) of the TDA in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I; and

[0039] (c) comprises determining whether S(c(Xsi)) is equal to, larger, or smaller than cmax(Xsi) and determining whether c(TDA) is equal to, larger, or smaller than cmin(TDA) c.T) if S(c(Xsi)) > cmax(Xsi),

[0040] Introducing the hydrogenation catalyst at a modified dosage Dem with

[0041] Dem < De; c.2’) if S(c(Xsi)) Cmax(Xsi) and c(TDA) < cmin(TDA),

[0042] Introducing the hydrogenation catalyst at a modified dosage Dem with Dem > Dc;c.2”) if S(c(Xsi)) S Cmax(Xsi) and c(TDA) > cmin(TDA), Introducing the hydrogenation catalyst at a modified dosage Dem with Dem = De

[0043] Cmin(TDA) is, as Cmax(Xsi) above, based on ctotai being 100 weight-%, wherein ctotai is defined as above. Regarding c.T) the consequence that, if S(c(Xsi)) > cmax(Xsi), then the hydrogenation catalyst is introduced at a modified dosage Dem with Dem < De, applies regardless whether c(TDA) is larger, equal to or smaller than cmin(TDA). In some preferred embodiments of the method cmin(TDA) are 95 weight-%, preferably 96 weight-%, more preferably 97 weight-%, more preferably 98 weight-%, more preferably 99 weight-%.

[0044] In some preferred embodiments of the method Dem is in the range of from 0.01 to 950 g catalyst / (h m3• Viam), more preferably 50 to 650 g catalyst / (h m3• Viam), more preferably 100 to 400 g catalyst / (h m3• Viam).

[0045] In some preferred embodiments of the method the introducing of hydrogenation catalyst according to (II) is done with a catalyst dosage rate De in the range of from 0 to 1000 g catalyst / (h -m3Viam).

[0046] In some preferred embodiments of the method introducing the hydrogenation catalyst at the dosage rate De according to (ii) is done continuously or discontinuously (batch wise).

[0047] In some preferred embodiments of the method introducing the hydrogenation catalyst at the modified dosage rate Dem according to (c.1), (c.2), (c.1'), (c.2') and / or (.2”) is done continuously or discontinuously (batch wise).

[0048] A discontinuous introduction (a batch wise dosage) comprises dosage schemes with multiple dosage phases, including dosage phases where no catalyst is introduced in combination with a batch wise introduction and / or a continuous introduction during other dosage phases, provided that the overall dosage rate De or the respective modified dosage rate Dem in g of catalyst per m3Viamand per hour [g catalyst / (h -m3Viam)] is realized. A continuous introduction (continuous dosage) may be done with an, in average, continuous dosage but may also be done with dosage phases having a higher dosage and dosage phases having a lower dosage as long as the overall dosage rate De or the respective modified dosage rate Dem in g of catalyst per m3Viamper hour [g catalyst / (h -m3Viam)] is realized. De and Dem are both dosage rates averaged over time.

[0049] In some preferred embodiments of the method (i) comprises

[0050] (i.1 ) providing a liquid aqueous mixture in a hydrogenation reaction zone Z, the liquid aqueous mixture comprising water and heterogeneous hydrogenation catalyst;

[0051] (i.2) introducing DNT and a hydrogen (H2) containing gas into the liquid aqueous mixture provided in (i.1 ), thereby obtaining in the hydrogenation reaction zone Z a liquid aqueous mixture having a volume Viam, the mixture comprising water, DNT, hydrogen (H2) and a heterogeneous hydrogenation catalyst.

[0052] Introduction of DNT, H

[0053] In some preferred embodiments of the method the introduction of DNT and hydrogen containing gas according to (i.2) is done simultaneously or consecutively, wherein the consecutive introduction is done with or without overlap. In case of consecutive introduction of DNT and H2 containing gas, the introduction of DNT can be started first at a point in time ti and the introduction of H2 containing gas can be started at a point in time t2 thereafter, with or without overlap of DNT and H2 containing gas introduction, while it is also possible that the H2 containing gas introduction is started first at ti and the DNT introduction is started later at t2, also with or without overlap of DNT and H2 containing gas introduction. Also regarding a simultaneous introduction of DNT and H2 containing gas introduction, the starting points in time may differ slightly wherein it is irrespective which introduction is started first.

[0054] In some preferred embodiments of the method DNT is introduced in pure form or as a liquid aqueous mixture comprising DNT, wherein introduction in pure form is preferably done in molten state.

[0055] AMCHON

[0056] In some preferred embodiments of the method the side products Xsi comprise one or more amino methyl cyclohexenone compound(s) of formula (I)

[0057] CH3

[0058] (I)

[0059] The amino methyl cyclohexenone compound of formula (I) has a molecular weight of 125.17 g / mol. The amino methyl cyclohexenone compound of formula (I) can be one compound or a mixture of two or more isomers falling under formula (I). The number of amino methyl cyclohexenone compound(s) of formula (I), which are comprised by the n side products Xsi, is p, wherein p is an integer with p >1 ...n.

[0060] In some preferred embodiments of the method, preferably after one or more further work-up step(s) as outlined herein in more detail below, a mixture is thus obtained, which comprises 2,4- toluene diamine and 2,6-toluene diamine and comprising less than 10 weight-ppm of an amino methyl cyclohexenone compound of formula (I)

[0061] CH3

[0062] (I) based on the total weight of the mixture being 100 weight-%.

[0063] In some preferred embodiments of the method (b) and (c) are repeated at least once, preferably (b) and (c) are repeated periodically, over the duration of the hydrogenation process. In some preferred embodiments of the method at least (b) is carried out continuously (continuous monitoring).

[0064] In some preferred embodiments of the method the TDA obtained in (I) and the TDA comprised in the liquid aqueous product stream SP removed in (ill) comprises meta TDA, preferably 2,4-toluene diamine and 2,6-toluene diamine. In some preferred embodiments of the method the lower boiling temperature limit value TTDA<L) are 255 °C and the upper boiling temperature limit value TTDA<U) are 295 °C. 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 260 °C and the upper boiling temperature limit value TTDA<U) are 290 °C.

[0065] In some preferred embodiments of the method hydrogenation catalyst is introduced as dry material or as liquid aqueous mixture.

[0066] Water + optional alcohol

[0067] In some preferred embodiments of the method the liquid aqueous mixture provided in (i) comprises water and optionally one or more C1 to C5 mono alcohol(s), preferably selected from the group consisting of methanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or three thereof, more preferably at least isopropanol; and wherein preferably any liquid aqueous mixture introduced comprises water and optionally one or more C1 to C5 mono alcohol, wherein the C1 to C5 mono alcohol is more preferably selected from the group consisting of methanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or three thereof, more preferably any liquid aqueous mixture introduced comprises water and optionally at least iso-propanol. In some preferred embodiments, the liquid aqueous mixture provided in (i) additionally comprises one or more C1 to C5 mono alcohol(s), more preferably selected from the group consisting of methanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or more thereof, more preferably at least iso-propanol. In these preferred embodiments, in the range of from 95 to 100 weight-%, preferably in the range of from 98 to 100 weight-%, more preferably in the range of from 99 to 100 weight-%, more preferably in the range of from 99.5 to 100 weight-%, of the liquid aqueous mixture provided in (i) consist of hydrogen, heterogeneous hydrogenation catalyst, water, DNT and one or more C1 to C5 mono alcohol(s), based on the total weight of the liquid aqueous mixture being 100 weight-%. In some preferred embodiments, the liquid aqueous mixture provided in (i) is essentially free of one or more C1 to C5 mono alcohol(s). In these preferred embodiments, in the range of from 95 to 100 weight-%, preferably in the range of from 98 to 100 weight-%, more preferably in the range of from 99 to 100 weight-%, more preferably in the range of from 99.5 to 100 weight-%, of the liquid aqueous mixture provided in (i) consist of hydrogen, heterogeneous hydrogenation catalyst, water, and DNT, based on the total weight of the liquid aqueous mixture being 100 weight-%.

[0068] Hydrogen (H2)

[0069] In some preferred embodiments of the method hydrogen containing gas is introduced in (i) in that hydrogen containing gas is applied onto the liquid aqueous mixture in the hydrogenation zone with a pressure in the range of 5 to 100 bar, preferably in the range of from 10 to 50 bar, more preferably in the range of from 15 to 40 bar, more preferably in the range of from 20 to 30 bar. In some preferred embodiments of the method the hydrogen containing gas comprises at least 90 volume-%, preferably in the range of from 90 to 100 volume-%, of hydrogen, based on the total volume of the hydrogen containing gas being 100 volume-%.

[0070] In some preferred embodiments of the method the hydrogen containing gas comprises at least less than 0.1 volume- % of carbon monoxide, preferably less than 0.1 volume-% of carbon monoxide and less than 0.1 volume-% of oxygen, based on the total volume of the hydrogen containing gas being 100 volume-%.

[0071] Temperature

[0072] In some preferred embodiments of the method hydrogenation is done at a temperature in the hydrogenation reaction zone Z in the range of from 50 to 250 °C, preferably in the range of from 60 to 200 °C, more preferably in the range of from 70 to 180 °C.

[0073] Hydrogenation catalyst

[0074] In some preferred embodiments of the method the hydrogen catalyst of (i) and / or of (c) comprises at least one first metal of the I., II., V., VI. and / or VIII. subgroup of the periodic table of elements, preferably at least one metal of the I. and / or VIII. subgroup of the periodic table of the elements, more preferably at least one metal selected from the group consisting of nickel, platinum and palladium, optionally in combination with at least one second metal of the I., II., IV., V., VI. and / or VIII. subgroup of the periodic table of the elements, wherein the second metal is different from the first metal.

[0075] In some preferred embodiments of the method the hydrogen catalyst of (I) and / or of (c) comprises nickel, preferably nickel having an oxidation state 0, +1, +2, +3 and / or +4, wherein the hydrogenation catalyst more preferably comprises in the range of from 0.1 to 99% by weight, preferably in the range of from 1 to 90% by weight, more preferably in the range of from 25 to 85% by weight, more preferably in the range of from 60 and 80 % by weight, of Ni(0) and / or one or more nickel containing compounds, wherein the nickel has an oxidation state 0, +1, +2, +3 and / or +4, based on the total weight of the hydrogenation catalyst being 100 weight-%.

[0076] In some preferred embodiments of the method the second metal of the I., II., IV., V., VI. and / or VIII. subgroup of the Periodic Table is selected from the group consisting of palladium, platinum, rhodium, iron, cobalt, zinc, chromium, vanadium, copper, silver, zirconium, titanium, hafnium, and mixtures of two or more thereof.

[0077] In some preferred embodiments of the method the hydrogenation catalyst comprises a support which is preferably selected from the group consisting of activated carbon, carbon black, graphite, oxidic carrier component and mixtures of two or more thereof, wherein the oxidic carrier component is preferably selected from the group consisting of silicon dioxide, silicon carbide, kieselguhr, aluminum oxide, magnesium oxide, titanium dioxide, zirconium dioxide, hafnium dioxide and mixtures of two or more thereof, more preferably the oxidic carrier compound is selected from the group consisting of zirconium dioxide, silicon dioxide, hafnium dioxide and mixtures of two or more thereof, more preferably the oxidic carrier component comprises, more preferably is, zirconium dioxide and / or silicon dioxide.

[0078] Further steps

[0079] In some preferred embodiments of the method for controlling a hydrogenation process for preparing toluene diamine (TDA) from dinitrotoluene (DNT), the hydrogenation process further comprises

[0080] (iv) separating heterogenous hydrogenation catalyst from the liquid aqueous product stream SP removed in (ill); thereby obtaining a liquid aqueous product stream SR-I having a reduced content of heterogenous hydrogenation catalyst compared to the liquid aqueous product stream SP; and preferably determining the concentration c(Xsi) of the side product Xsi and of the TDA concentration c(TDA) in SP-I .

[0081] Preferably, the hydrogenation process further comprises

[0082] (v) separating TDA from the liquid aqueous product stream SP removed in (ill) or from liquid aqueous product stream SP-I obtained in (iv); thereby obtaining a product stream SP-2 comprising a crude TDA mixture comprising 2,4- toluene diamine, 2,6-toluene diamine, 2,3- toluene diamine, 3,4-toluene diamine and 2,5- toluene diamine and optionally 3,5- toluene diamine, SP-2 having a reduced water content compared to the liquid aqueous product stream SP or SP-I respectively.

[0083] In embodiments where the liquid aqueous mixture provided in (I) comprises water and one or more C1 to C5 mono alcohol(s), SP-2, aside from having a reduced water content compared to the liquid aqueous product stream SP or SP-I respectively, also has a reduced content of C1 to C5 mono alcohol(s) compared to the liquid aqueous product stream SP or Sp.i respectively.

[0084] Preferably, the hydrogenation process further comprises

[0085] (vi) separating the crude TDA mixture of product stream SP-2, preferably by distillation, thereby obtaining a first mixture comprising 2,4- toluene diamine and 2,6-toluene diamine and being depleted in 2,3- toluene diamine and 3,4-toluene diamine compared to Sp.2; and optionally a second mixture comprising 2,3- toluene diamine and 3,4-toluene diamine and being depleted in 2,4- toluene diamine and 2,6-toluene diamine compared to Sp.

[0086] 2.

[0087] 3rdaspect - Mixture

[0088] A third aspect of the invention is directed to a mixture comprising at least 2,4- toluene diamine and 2,6-toluene diamine obtained or obtainable from the method according to the second aspect, preferably after one or more further work-up step(s) as outlined herein above in more detail in the section related to the method of the second aspect of the invention, more preferably obtained or obtainable from (vi) of the method of the second aspect of the invention as outlined herein above in more detail in the section above, the mixture preferably comprising an amino methyl cyclohexenone compound of formula (I)

[0089] CH3

[0090] 0 in less than 10 weight-ppm, wherein the total weight of the mixture is 100 weight-%. The amino methyl cyclohexenone compound of formula (I) can be one compound or a mixture of two or more isomers falling under formula (I). All details, embodiments and preferred embodiments disclosed above in the section related to the first aspect of the invention and in the section related to the second aspect of the invention apply also to the third aspect of the invention.

[0091] 4thaspect - Use

[0092] In a fourth aspect, the invention relates to a use of the mixture according to the first aspect of the invention or of the mixture of the third aspect of the invention for the preparation of toluene diisocyanate (TDI).

[0093] All details, embodiments and preferred embodiments disclosed above in the section related to the first aspect of the invention, the section related to the second aspect of the invention and in the section related to the third aspect of the invention apply also to the fourth aspect of the invention.

[0094] 5thaspect - Process for preparing TDI

[0095] A fifth aspect of the invention is directed to a process for preparing toluene diisocyanate (TDI) comprising:

[0096] (I) Providing a mixture according to the first aspect of the invention or of the mixture of the third aspect of the invention;

[0097] (II) Phosgenation of the mixture provided in (I), thereby obtaining TDI.

[0098] All details, embodiments and preferred embodiments disclosed above in the section related to the first aspect of the invention, the section related to the second aspect of the invention, the section related to the third aspect of the invention, and in the section related to the fourth aspect of the invention apply also to the fifth aspect of the invention.

[0099] The hydrogenation process is carried out within a reaction vessel, which is preferably a reactor, wherein the hydrogenation reaction zone Z is preferably located at least partially within the reactor. The reactor is preferably selected from the group consisting of (multi)tubular reactor, stirred tank reactor and loop reactor, wherein the reaction vessel is preferably a loop reactor. The product stream SP is removed from the reactor continuously or discontinuously, preferably continuously, at any desired point, but preferably at a point in the lower region of the reactor at its base or in particular from the external loop flow via a catalyst separation unit or without one. This separation unit, used or usable for conduction step (i v), can be a gravity separator, for example a settler, a suitable filter, for example a cross-flow filter, or a centrifuge. The catalyst can be separated from the product and then the catalyst can be fed back into the reactor, preferably into the hydrogenation reaction zone Z, or discharged from the reactor and the hydrogenation reaction zone Z respectively. The separation of TDA from the liquid aqueous product stream SP removed in (ill) or from liquid aqueous product stream SR-I obtained in (iv), preferably from SR-I obtained in (iv), is then preferably done by distillation, wherein if an organic solvent such as an alcohol was part of the mixture, is done in one step or in at least two distillative steps. The separation of the crude TDA mixture of product stream SP-2 in (vi) is then again preferably done by distillation, wherein one or more rectification column(s) can be used. Suitable methods, conditions and apparatus are known to the skilled person and an overview is given, for example, in EP 1 746 083 B1.

[0100] 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 method 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 method 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.

[0101] Embodiment (1): Mixture comprising 2,4- toluene diamine and 2,6-toluene diamine and comprising less than 10 weight-ppm of an amino methyl cyclohexenone compound of formula (I)

[0102] CH3

[0103] (I) based on the total weight of the mixture being 100 weight-%.

[0104] Embodiment (2): Mixture according to embodiment (1), wherein at least 98 weight-%, preferably at least 99 weight- %, of the mixture consist of 2,4- toluene diamine and 2,6-toluene diamine based on the total weight of the mixture being 100 weight-%.

[0105] Embodiment (3): Mixture according to embodiment (1) or (2), wherein 2,4- toluene diamine and 2,6-toluene diamine are comprised in the mixture in a molar ratio 2,4- toluene diamine : 2,6- toluene diamine in the range of from 10:1 to 1 :10, preferably in the range of from 8:1 to 1 :1, more preferably in the range of from 6:1 to 2:1, more preferably in the range of from 5:1 to 3:1. Embodiment (4): A method for controlling a hydrogenation process for preparing toluene diamine (TDA) from dinitrotoluene (DNT), said TDA having a boiling temperature range BTRiDAwith a lower boiling temperature limit value TTDA(L) and an upper boiling temperature limit value TTDA(U), wherein the hydrogenation process comprises

[0106] (I) providing a liquid aqueous mixture having a volume Viamin a hydrogenation reaction zone Z, the mixture comprising water, DNT, hydrogen (H2) and a heterogeneous hydrogenation catalyst, and converting the DNT comprised in the liquid aqueous mixture under nitro group hydrogenation conditions in the hydrogenation reaction zone Z; thereby obtaining in the hydrogenation reaction zone Z a liquid aqueous mixture comprising water, TDA and n hydrogenation reaction side products Xsi, wherein n is an integer with n>1 and 1=1 ...n, each Xsi having a boiling point Txsi with Txsi < TTDA(L>;

[0107] (ii) introducing a hydrogenation catalyst into the liquid aqueous mixture in the hydrogenation reaction zone Z at a catalyst dosage rate De;

[0108] (ill) removing a liquid aqueous product stream SP from the hydrogenation reaction zone Z, the stream SP comprising water and the TDA; wherein the method for controlling the hydrogenation process comprises

[0109] (a) defining a maximum value cmax(Xsi) of the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SP, and / or in one or more subsequent product streams SP-I, wherein the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi S(c(Xsi)) is X”=i c( sr);

[0110] (b) at least periodically determining the sum of the concentration c(Xsi) of the side products Xsi S(c(Xsi)) and the TDA concentration c(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SP, and / or in one or more subsequent product streams SP-I;

[0111] (c) determining whether S(c(Xsi)) is equal to, larger, or smaller than cmax(Xsi); and

[0112] (c.1) if S(c(Xsi)) > Cmax (Xsi),

[0113] Introducing the hydrogenation catalyst at a modified dosage Dem with

[0114] Dem < De;

[0115] (C.2) if S(c(Xsi)) — Cmax(Xsi),

[0116] Introducing the hydrogenation catalyst at a modified dosage Dem with

[0117] Dem De

[0118] Embodiment (5): Method according to embodiment (4), wherein if S(c(Xsi)) > cmax(Xsi), then the catalyst dosage rate is decreased so that 0.1 < Dcm / Dc 0.99, wherein preferably the difference Ac(Xsi) is determined by S(c(Xsi)) - Cmax(Xsi), wherein if 0.5< Ac(Xsi) < 2, then the catalyst dosage rate is decreased so that

[0119] 0.1 s Dcm / Dc- 0.9; if 0.3< Ac(Xsi) <0.5, then the catalyst dosage rate is decreased so that

[0120] 0.3 s Dcm / Dc- 0.95; if 0.1 < Ac(Xsi) <0.3, then the catalyst dosage rate is decreased so that 0.6 < Dcm / Dc < 0.975; if 0.01 < Ac(Xsi) <0.1 , then the catalyst dosage rate is decreased so that

[0121] 0.9 s Dcm / Dc- 0.98; if 0< Ac(Xsi) <0.01 , then the catalyst dosage rate is decreased so that

[0122] 0.95 < Dcm / Dc< 0.99.

[0123] Embodiment (6): Method according to embodiment (4) or (5), wherein cmax(Xsi) are 0.05 weight-% (500 weight-ppm), preferably 0.1 weight-% (1000 weight-ppm), more preferably 0.15 weight-% (1500 weight-ppm), more preferably 0.2 weight-% (2000 weight-ppm).

[0124] Embodiment (7): Method according to any one of embodiments (4) to (6), wherein in the method for controlling the hydrogenation process,

[0125] (a) comprises a.1) defining a maximum value cmax(Xsi) of the sum S of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I, wherein the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi S(c(Xsi)) is X”=i c( sr); a.2) defining a minimum value of the concentration of toluene diamine cmin(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I;

[0126] (b) comprises b.1 ) at least periodically determining the sum of the concentration of the side products Xsi S(c(Xsi)) and the TDA concentration c(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I; b.2) at least periodically determining the concentration c(TDA) of the TDA in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I; and

[0127] (c) comprises determining whether S(c(Xsi)) is equal to, larger, or smaller than cmax(Xsi) and determining whether c(TDA) is equal to, larger, or smaller than cmin(TDA) c.T) if S(c(Xsi)) > Cmax (Xsi),

[0128] Introducing the hydrogenation catalyst at a modified dosage Dem with

[0129] Dem < De; c.2’) if S(c(Xsi)) S Cmax(Xsi) and c(TDA) < cmin(TDA),

[0130] Introducing the hydrogenation catalyst at a modified dosage Dem with Dem > Dc;c.2”) if S(c(Xsi)) S Cmax(Xsi) and c(TDA) > cmin(TDA),

[0131] Introducing the hydrogenation catalyst at a modified dosage Dem with Dem = De

[0132] Embodiment (8): Method according to embodiment (7), wherein cmin(TDA) are 95 weight-%, preferably 96 weight-%, more preferably 97 weight-%, more preferably 98 weight-%, more preferably 99 weight-%. Embodiment (9): Method according to any one of embodiments (4) to (8), wherein Dem is in the range of from 0.01 to 950 g catalyst / (h m3• Viam), more preferably 50 to 650 g catalyst / (h m3• Viam), more preferably 100 to 400 g catalyst / (h m3• Vi am)-

[0133] Embodiment (10): Method according to any one of embodiments (4) to (9), wherein the introducing of hydrogenation catalyst according to (ii) is done with a catalyst dosage rate De in the range of from 0 to 1000 g catalyst / (h -m3Viam).

[0134] Embodiment (11): Method according to any one of embodiments (4) to (10), wherein introducing the hydrogenation catalyst at the dosage rate De according to (ii) is done continuously or discontinuously (batch wise).

[0135] Embodiment (12): Method according to any one of embodiments (4) to (11), wherein introducing the hydrogenation catalyst at the modified dosage rate Dem according to (c.1 ), (c.2), (c.1'), (c.2') and / or (.2”) is done continuously or discontinuously (batch wise).

[0136] Embodiment (13): Method according to any one of embodiments (4) to (12), wherein (I) comprises

[0137] (1.1) providing a liquid aqueous mixture in a hydrogenation reaction zone Z, the liquid aqueous mixture comprising water and heterogeneous hydrogenation catalyst;

[0138] (1.2) introducing DNT and a hydrogen (H2) containing gas into the liquid aqueous mixture provided in (1.1), thereby obtaining in the hydrogenation reaction zone Z a liquid aqueous mixture having a volume Viam, the mixture comprising water, DNT, hydrogen (H2) and a heterogeneous hydrogenation catalyst.

[0139] Embodiment (14): Method according to embodiment (13=, wherein the introduction of DNT and hydrogen containing gas according to (1.2) is done simultaneously or consecutively, wherein the consecutive introduction is done with or without overlap.

[0140] Embodiment (15): Method according to any one of embodiments (4) to (14), wherein DNT is introduced in pure form or as a liquid aqueous mixture comprising DNT, wherein introduction in pure form is preferably done in molten state.

[0141] Embodiment (16): Method according to any one of embodiments (4) to (15), wherein the side products Xsi comprise one or more amino methyl cyclohexenone compound(s) of formula (I)

[0142] CH3

[0143] (I)

[0144] Embodiment (17): Method according to any one of embodiments (4) to (16), wherein (b) and (c) are repeated at least once, preferably (b) and (c) are repeated periodically, over the duration of the hydrogenation process. Embodiment (18): Method according to any one of embodiments (4) to (17), wherein at least (b) is carried out continuously (continuous monitoring).

[0145] Embodiment (19): Method according to any one of embodiments (4) to (18), wherein the TDA obtained in (i) and the TDA comprised in the liquid aqueous product stream SP removed in (ill) comprises meta TDA, preferably 2,4-toluene diamine and 2,6-toluene diamine.

[0146] Embodiment (20): Method according to any one of embodiments (4) to (19), wherein the lower boiling temperature limit value TTDA<L) are 255 °C and the upper boiling temperature limit value TTDA<U) are 295 °C.

[0147] Embodiment (21): Method according to any one of embodiments (1) to (20), wherein hydrogenation catalyst is introduced as dry material or as liquid aqueous mixture.

[0148] Embodiment (22): Method according to any one of embodiments (1) to (21), wherein the liquid aqueous mixture provided in (I) comprises water and optionally one or more C1 to C5 mono alcohol(s), preferably selected from the group consisting of methanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or three thereof, more preferably at least iso-propanol; and wherein preferably any liquid aqueous mixture introduced comprises water and optionally one or more C1 to C5 mono alcohol, wherein the C1 to C5 mono alcohol is more preferably selected from the group consisting of methanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or three thereof, more preferably any liquid aqueous mixture introduced comprises water and optionally at least iso-propanol.

[0149] Embodiment (23): Method according to any one of embodiments (4) to (22), wherein hydrogen containing gas is introduced in (I) in that hydrogen containing gas is applied onto the liquid aqueous mixture in the hydrogenation zone with a pressure in the range of 5 to 100 bar, preferably in the range of from 10 to 50 bar, more preferably in the range of from 15 to 40 bar, more preferably in the range of from 20 to 30 bar.

[0150] Embodiment (24): Method according to any one of embodiments (4) to (23), wherein the hydrogen containing gas comprises at least 90 volume-%, preferably in the range of from 90 to 100 volume-%, of hydrogen, based on the total volume of the hydrogen containing gas being 100 volume-%.

[0151] Embodiment (25): Method according to any one of embodiments (4) to (24), wherein the hydrogen containing gas comprises at least less than 0.1 volume-% of carbon monoxide, preferably less than 0.1 volume-% of carbon monoxide and less than 0.1 volume-% of oxygen, based on the total volume of the hydrogen containing gas being 100 volume-%. Embodiment (26): Method according to any one of embodiments (4) to (25), wherein hydrogenation is done at a temperature in the hydrogenation reaction zone Z in the range of from 50 to 250 °C, preferably in the range of from 60 to 200 °C, more preferably in the range of from 70 to 180 °C.

[0152] Embodiment (27): Method according to any one of embodiments (4) to (26), wherein the hydrogen catalyst of (I) and / or of (c) comprises at least one first metal of the I., II., V., VI. and / or VIII. subgroup of the periodic table of elements, preferably at least one metal of the I. and / or VIII. subgroup of the periodic table of the elements, more preferably at least one metal selected from the group consisting of nickel, platinum and palladium, optionally in combination with at least one second metal of the I., II., IV., V., VI. and / or VIII. subgroup of the periodic table of the elements, wherein the second metal is different from the first metal.

[0153] Embodiment (28): Method according to embodiment (27), wherein the hydrogen catalyst of (i) and / or of (c) comprises nickel, preferably nickel having an oxidation state 0, +1, +2, +3 and / or +4, wherein the hydrogenation catalyst more preferably comprises in the range of from 0.1 to 99% by weight, preferably in the range of from 1 to 90% by weight, more preferably in the range of from 25 to 85% by weight, more preferably in the range of from 60 and 80 % by weight, of Ni(0) and / or one or more nickel containing compounds, wherein the nickel has an oxidation state 0, +1, +2, +3 and / or +4, based on the total weight of the hydrogenation catalyst being 100 weight-%.

[0154] Embodiment (29): Method according to embodiment (27) or (28), wherein the second metal of the I., II., IV., V., VI. and / or VIII. subgroup of the Periodic Table is selected from the group consisting of palladium, platinum, rhodium, iron, cobalt, zinc, chromium, vanadium, copper, silver, zirconium, titanium, hafnium, and mixtures of two or more thereof.

[0155] Embodiment (30): Method according to any one of embodiments (27) to (29), wherein the hydrogenation catalyst comprises a support which is preferably selected from the group consisting of activated carbon, carbon black, graphite, oxidic carrier component and mixtures of two or more thereof, wherein the oxidic carrier component is preferably selected from the group consisting of silicon dioxide, silicon carbide, kieselguhr, aluminum oxide, magnesium oxide, titanium dioxide, zirconium dioxide, hafnium dioxide and mixtures of two or more thereof, more preferably the oxidic carrier compound is selected from the group consisting of zirconium dioxide, silicon dioxide, hafnium dioxide and mixtures of two or more thereof, more preferably the oxidic carrier component comprises, more preferably is, zirconium dioxide and / or silicon dioxide.

[0156] Embodiment (31): Method according to any one of embodiments (4) to (30), wherein the hydrogenation process further comprises

[0157] (iv) separating heterogenous hydrogenation catalyst from the liquid aqueous product stream SP removed in (ill); thereby obtaining a liquid aqueous product stream SR-I having a reduced content of heterogenous hydrogenation catalyst compared to the liquid aqueous product stream SP; and preferably determining the concentration c(Xsi) of the side product Xsi and of the TDA concentration c(TDA) in SP-I . Embodiment (32): Method according to any one of embodiments (4) to (31), wherein the hydrogenation process further comprises

[0158] (v) separating TDA from the liquid aqueous product stream SP removed in (iii) or from liquid aqueous product stream SR-I obtained in (iv); thereby obtaining a product stream SP-2 comprising a crude TDA mixture comprising 2,4- toluene diamine, 2,6-toluene diamine, 2,3- toluene diamine, 3,4-toluene diamine and 2,5- toluene diamine and optionally 3,5- toluene diamine, SP-2 having a reduced water content compared to the liquid aqueous product stream SP or SP-I respectively.

[0159] Embodiment (33): Method according to any one of embodiments (4) to (32), wherein the hydrogenation process further comprises

[0160] (vi) separating the crude TDA mixture of product stream SP-2, preferably by distillation, thereby obtaining a first mixture comprising 2,4- toluene diamine and 2,6-toluene diamine and being depleted in 2,3- toluene diamine and 3,4-toluene diamine compared to Sp.2; and optionally a second mixture comprising 2,3- toluene diamine and 3,4-toluene diamine and being depleted in 2,4- toluene diamine and 2,6-toluene diamine compared to Sp.

[0161] 2.

[0162] Embodiment (34): Mixture comprising at least 2,4- toluene diamine and 2,6-toluene diamine obtained or obtainable from the method according to any one of embodiments (4) to (33), preferably obtained from (vi), the mixture preferably comprising an amino methyl cyclohexenone compound of formula (I)

[0163] CH3

[0164] 0 in less than 10 weight-ppm, wherein the total weight of the mixture is 100 weight-%.

[0165] Embodiment (35): Use of the mixture according to any one of embodiments (1) to (3) or of the mixture of embodiment (34) for the preparation of toluene diisocyanate (TDI).

[0166] Embodiment (36): A process for preparing toluene diisocyanate (TDI) comprising:

[0167] (I) Providing a mixture according to any one of embodiments (1) to (3) or of the mixture of embodiment (34);

[0168] (II) Phosgenation of the mixture provided in (I), thereby obtaining TDI.

[0169] The invention is illustrated below by means of Examples.

[0170] Examples

[0171] Chemicals

[0172] * The supported catalyst was prepared as described in Example 2 of WO 2021 / 219796 A1 .

[0173] General setup: Miniplant with recycle flow used for hydrogenation

[0174] The miniplant with recycle flow used for the hydrogenation consisted of a jet loop reactor with internal draft tube (reaction zone). Pre-heated feed comprising DNT and H2 were dosed into the headspace of the reactor in close proximity to the recycle nozzle, which has been directed into the draft tube. Product stream was recycled from the reactor bottom outlet through a circulation pump and a (cross flow) filtration unit, where portions of the product stream were withdrawn and sampled by an online-gas chromatography (GC). Remaining product stream was recirculated via nozzle into the draft tube. Performance indicators have been time on stream (TOS) and GC-derived concentrations of heavy boilers, light boilers, 2,4-TDA, 2,6-TDA, 2,3-TDA, 3,4-TDA and 2,5-TDA and optionally 3,5- TDA - the TDA isomers summed-up as TDA. Additionally, the concentration of amino methyl cyclohexenone compound(s) of formula (I)

[0175] CH3

[0176] (I) which were / was part of the light boilers, was separately determined, wherein amino methyl cyclohexenone compounds of formula (I) were in the following abbreviated as AMCHON. The expression "TDA yield” in the following refers to TDA concentration c(TDA), "light boiler yield” refers to S(c(Xsi), "AMCHON yield” refers to the sum of the concentrations of all amino methyl cyclohexenone compound(s) of formula (I), all based on ctotai being 100 weight-%, wherein ctotai is as defined above.

[0177] Example 1 : hydrogenation with constant amounts of catalyst addition Cmax(Xsi) was set as 2000 weight-ppm, cmin(TDA) was set as 99 weight-%. In a typical miniplant hydrogenation, the miniplant as described above, was filled with water (5 1) and catalyst (141 g). Then, for fresh catalyst activation, the catalyst in water has been recirculated at 135°C and 25 bar (H2) for 3 h with 500 kg / h in the miniplant. Subsequently, 90°C preheated DNT (1 kg / h), corresponding to a weight hourly space velocity (WHSV) of 7 g(D NT) / g(cat.) / h, was dosed into the system. The liquid aqueous mixture in the miniplant had a volume Viam. The DNT was immediately converted in the initial section of the draft tube and formed the hydrogenation bath comprising catalyst, water, and TDA. The hydrogenation bath was further transferred through the circulation pump, via the cross flow filter (separation of product TDA and water equivalent to the DNT feed) and through the nozzle back into the draft tube, wherein this sequence was repeated over and over again. Typically, after 10-15 h time on stream (TOS), the catalyst could be operated for 24-48 h TOS before the simultaneous decrease of light boiler and TDA yield loss has occurred. After simultaneous decline of light boiler yield below about 0.2 weight-% and TDA yield below about 99 weight-%, a portion of suspended fresh catalyst in the range of 450-550 g / h / m3, wherein the m3were the volume Viamof the liquid aqueous mixture in the miniplant, was introduced into the reactor by a slice to counteract the yield losses. The catalyst addition was repeated over and over again, whenever the described conditions were fulfilled. After 106 hours TOS the hydrogenation was stopped without reaching the catalyst's end of lifetime.

[0178] The results for Example 1 are graphically shown in Fig. 1 and the product composition is shown below in Table 1 . It could be seen from Example 1 that controlling light boiler yield in combination with required TDA yield by fresh catalyst addition allowed maintaining continuous hydrogenation.

[0179] Table 1

[0180] Hydrogenation and batchwise catalyst dosage. n.a. = not analysed

[0181] A work-up of the resulting liquid aqueous mixture after separation from the catalyst including removal of water and optional alcohol, followed by work-up of the crude TDA resulted in a mixture, which comprised more than 98 weight- % of 2,4- toluene diamine and 2,6-toluene diamine and which comprised less than 10 weight-ppm of AMCHON based on the total weight of the mixture being 100 weight-%.

[0182] Example 2: hydrogenation with varied amounts of fresh catalyst addition

[0183] Cmax(Xsi) was set as 2000 weight-ppm, cmin(TDA) was set as 96 weight-%. The miniplant as described above, with recycle flow used for the hydrogenation with fresh catalyst addition was operated identically as described in Example 1 . However, in this experiment the threshold for TDA was reduced to 96 weight-% and the amount of added fresh catalyst was varied. At 72 h TOS the added fresh catalyst portion contained 450-550 g / h / m3, whereas, at 107 h TOS, a larger fresh catalyst portion in the range 900-1000 g / h / m3was added.

[0184] The results for Example 2 are graphically shown in Fig. 2. It could be seen from Example 2 that controlling light boiler yield in combination with required TDA yield by fresh catalyst addition allowed for maintaining continuous hydrogenation. Moreover, it was shown that the introduced amount of catalyst affected the duration in which the catalyst as capable to stay in the optimal operational window.

[0185] A work-up of the resulting liquid aqueous mixture after separation from the catalyst including removal of water and optional alcohol, followed by work-up of the crude TDA resulted in a mixture, which comprised more than 98 weight- % of 2,4- toluene diamine and 2,6-toluene diamine and which comprised less than 10 weight-ppm of AMCHON based on the total weight of the mixture being 100 weight-%.

[0186] Short description of the Figures

[0187] Fig. 1 shows the results for Example 1, wherein time on stream (TOS) in hours is indicated on the x axis wherein the points in time when catalyst was dosed are indicated at the top of the figure by arrows. The left y axis is related to the yield (Y) of all TDA isomers (2,3-TDA, 2,4-TDA, 2,6-TDA, 2,5-TDA, 3,4-TDA and 3,5-TDA) taken together in weight-%. The first y axis on the right is related to the concentration of all light boilers (including AMCHON) in weight-% and the second y axis on the right is related to AMCHON separately, also indicated in weight-%.

[0188] Fig. 2 shows the results for Example 2, wherein time on stream (TOS) in hours is indicated on the x axis wherein the points in time when catalyst was dosed are indicated at the top of the figure by arrows with the amount of catalyst indicated in addition. The left y axis is related to the yield (Y) of all TDA isomers (2,3-TDA, 2,4- TDA, 2,6-TDA, 2,5-TDA, 3,4-TDA and 3,5-TDA) taken together in weight-%. The first y axis on the right is related to the concentration of all light boilers (including AMCHON) in weight-% and the second y axis on the right is related to AMCHON separately, also indicated in weight-%.

[0189] Cited prior art Ullmann's Enzyklopadie der technischen Chemie, 4thedition, volume 7, page 393 ff, 1973, Verlag Chemie

[0190] Weinheim / New York

[0191] EP 2 905 273 B1

[0192] EP1 864 969 B1 EP 1 746 083 B1

[0193] WO 2021 / 219796 A1

Claims

Claims1 . A method for controlling a hydrogenation process for preparing toluene diamine (TDA) from dinitrotoluene (DNT), said TDA having a boiling temperature range BTRTDA with a lower boiling temperature limit value TTDA<L) and an upper boiling temperature limit value TTDA<U), wherein the hydrogenation process comprises(i) providing a liquid aqueous mixture having a volume Viamin a hydrogenation reaction zone Z, the mixture comprising water, DNT, hydrogen (H2) and a heterogeneous hydrogenation catalyst, and converting the DNT comprised in the liquid aqueous mixture under nitro group hydrogenation conditions in the hydrogenation reaction zone Z; thereby obtaining in the hydrogenation reaction zone Z a liquid aqueous mixture comprising water, TDA and n hydrogenation reaction side products Xsi, wherein n is an integer with n>1 and i=1 ...n, each Xsi having a boiling point Txsi with Txsi < TTDA(ii) introducing a hydrogenation catalyst into the liquid aqueous mixture in the hydrogenation reaction zone Z at a catalyst dosage rate De;(iii) removing a liquid aqueous product stream SP from the hydrogenation reaction zone Z, the stream SP comprising water and the TDA; wherein the method for controlling the hydrogenation process comprises(a) defining a maximum value cmax(Xsi) of the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SP, and / or in one or more subsequent product streams SP-I, wherein the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi S(c(Xsi)) is X”=i c( sr);(b) at least periodically determining the sum of the concentration c(Xsi) of the side products Xsi S(c(Xsi)) and the TDA concentration c(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SP, and / or in one or more subsequent product streams SP-I;(c) determining whether S(c(Xsi)) is equal to, larger, or smaller than cmax(Xsi); and(c.1) if S(c(Xsi)) > cmax(Xsi),Introducing the hydrogenation catalyst at a modified dosage Dem with Dem < De;(C.2) if S(c(Xsi)) — Cmax(Xsi),Introducing the hydrogenation catalyst at a modified dosage Dem with Dem De2. Method according to claim 1, wherein if S(c(Xsi)) > cmax(Xsi), then the catalyst dosage rate is decreased so that 0.1 < Dcm / Dc^ 0.99, wherein preferably the difference Ac(Xsi) is determined by S(c(Xsi)) - cmax(Xsi), wherein if 0.5< Ac(Xsi) < 2, then the catalyst dosage rate is decreased so that0.1 s Dcm / Dc- 0.9; if 0.3< Ac(Xsi) <0.5, then the catalyst dosage rate is decreased so that0.3 s Dcm / Dc- 0.95;if 0.1 < Ac(Xsi) <0.3, then the catalyst dosage rate is decreased so that0.6 < Dcm / Dc< 0.975; if 0.01 < Ac(Xsi) <0.1, then the catalyst dosage rate is decreased so that0.9 s Dcm / Dc- 0.98; if 0< Ac(Xsi) <0.01 , then the catalyst dosage rate is decreased so that 0.95 < Dcm / Dc< 0.99.

3. Method according to claim 1 or 2, wherein cmax(Xsi) are 0.05 weight-% (500 weight-ppm), preferably0.1 weight-% (1000 weight-ppm), more preferably 0.15 weight-% (1500 weight-ppm), more preferably 0.2 weight-% (2000 weight-ppm).

4. Method according to any one of claims 1 to 3, wherein in the method for controlling the hydrogenation process,(a) comprises a.1) defining a maximum value cmax(Xsi) of the sum S of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I, wherein the sum of the concentrations c(Xsi) of the n hydrogenation reaction side products Xsi S(c(Xsi)) is X”=i c( sr); a.2) defining a minimum value of the concentration of toluene diamine cmin(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I;(b) comprises b.1 ) at least periodically determining the sum of the concentration of the side products Xsi S(c(Xsi)) and theTDA concentration c(TDA) in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I; b.2) at least periodically determining the concentration c(TDA) of the TDA in the liquid aqueous mixture in the hydrogenation reaction zone Z, and / or in the product stream SR, and / or in one or more subsequent product streams SR-I; and(c) comprises determining whether S(c(Xsi)) is equal to, larger, or smaller than cmax(Xsi) and determining whether c(TDA) is equal to, larger, or smaller than cmin(TDA) c.T) if S(c(Xsi)) > cmax(Xsi),Introducing the hydrogenation catalyst at a modified dosage Dem withDem < De; c.2’) if S(c(Xsi)) Cmax(Xsi) and c(TDA) < cmin(TDA),Introducing the hydrogenation catalyst at a modified dosage Dem with Dem > Dc;c.2”) if S(c(Xsi)) S Cmax(Xsi) and c(TDA) > cmin(TDA),Introducing the hydrogenation catalyst at a modified dosage Dem with Dem = De5. Method according to claim 4, wherein cmin(TDA) are 95 weight-%, preferably 96 weight-%, more preferably 97 weight-%, more preferably 98 weight-%, more preferably 99 weight-%.

6. Method according to any one of claims 1 to 5, wherein Dem is in the range of from 0.01 to 950 g catalyst / (h m3• Viam), more preferably 50 to 650 g catalyst / (h m3• Viam), more preferably 100 to 400 g catalyst / (h m3• Viam).

7. Method according to any one of claims 1 to 6, wherein the introducing of hydrogenation catalyst according to(II) is done with a catalyst dosage rate De in the range of from 0 to 1000 g catalyst / (h -m3Viam).

8. Method according to any one of claims 1 to 7, wherein (I) comprises(1.1) providing a liquid aqueous mixture in a hydrogenation reaction zone Z, the liquid aqueous mixture comprising water and heterogeneous hydrogenation catalyst;(1.2) introducing DNT and a hydrogen (H2) containing gas into the liquid aqueous mixture provided in (1.1), thereby obtaining in the hydrogenation reaction zone Z a liquid aqueous mixture having a volume Viam, the mixture comprising water, DNT, hydrogen (H2) and a heterogeneous hydrogenation catalyst.

9. Method according to any one of claims 1 to 8, wherein the side products Xsi comprise one or more amino methyl cyclohexenone compound(s) of formula (I)CH3(I)10. Method according to any one of claims 1 to 9, thereby obtaining, preferably after one or more further work-up step(s), a mixture comprising 2,4- toluene diamine and 2,6-toluene diamine and comprising less than10 weight-ppm of an amino methyl cyclohexenone compound of formula (I)CH3(I) based on the total weight of the mixture being 100 weight-%.

11. Method according to any one of claims 1 to 10, wherein the lower boiling temperature limit value TTDA<L) are 255 °C and the upper boiling temperature limit value TTDA<U) are 295 °C.

12. Method according to any one of claims 1 to 11 , wherein the liquid aqueous mixture provided in (I) comprises water and optionally one or more C1 to C5 mono alcohol(s), preferably selected from the group consisting ofmethanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or three thereof, more preferably at least iso-propanol; and wherein preferably any liquid aqueous mixture introduced comprises water and optionally one or more C1 to C5 mono alcohol, wherein the C1 to C5 mono alcohol is more preferably selected from the group consisting of methanol, ethanol, propanol, including n-propanol and iso-propanol, and mixtures of two or three thereof, more preferably any liquid aqueous mixture introduced comprises water and optionally at least iso-propanol.

13. Mixture comprising at least 2,4- toluene diamine and 2,6-toluene diamine obtained or obtainable from the method according to any one of claims 1 to 12, preferably after one or more work-up step(s), the mixture preferably comprising an amino methyl cyclohexenone compound of formula (I)CH30 in less than 10 weight-ppm, wherein the total weight of the mixture is 100 weight-%.

14. Use of the mixture according to claim 13 for the preparation of toluene diisocyanate (TDI).

15. A process for preparing toluene diisocyanate (TDI) comprising:(I) Providing a mixture according to claim 13;(II) Phosgenation of the mixture provided in (I), thereby obtaining TDI.

Images