METHOD FOR PREPARING TOLUYLENE DIAMINE MIXTURES

Abstract

The invention relates to a method for preparing a toluylene diamine mixture which, along with toluylene diamine (TDA), also contains a high-boiling fraction, such as the high-boiling fraction which is accumulated as a sump flow in the distillative preparation of product mixtures obtained by hydrogenating dinitrotoluene. The method has a step (A), namely preparing a TDA mixture containing, based on the total mass of the mixture, (1) TDA in a range of 5 mass % to 80 mass % and (2) a high-boiling fraction in a range of 20 mass % to 95 mass %; a step (B), namely distilling TDA off from the TDA mixture, thereby obtaining a liquid TDA-depleted method product, containing (1) TDA in a range of 0 mass % to 38 mass % and (2) a high-boiling fraction in a range of 62 mass % to 100 mass %; and a step (C) namely mixing water into the TDA-depleted method product in a mixing chamber, thereby obtaining a mixture mixed with water, wherein the temperature and quantity of the water to be mixed into the mixture and the temperature and quantity of the TDA-depleted method product are matched such that the resulting temperature of the mixture mixed with water ranges from 110° C. to 250° C., and the mixture mixed with water is provided as a single phase. The mixing chamber is supplied with a pressure which is greater than or equal to the water vapor partial pressure at the resulting temperature.

Claims

1. A process for working upworkup of a tolylenediamine mixture containing tolylenediamine and compounds having boiling points higher than 2,4-tolylenediamine at 1013 mbar.sub.(abs.), comprising the steps of: (A) providing a tolylenediamine mixture containing (1) tolylenediamine in an amount of 5% by mass to 80% by mass and (2) compounds having boiling points higher than 2,4-tolylenediamine at 1013 mbar.sub.(abs.) in an amount of 20% by mass to 95% by mass, based on total mass of the tolylenediamine mixture; (B) distilling the tolylenediamine mixture to remove tolylenediamine therefrom and to obtain a liquid process product-depleted in tolylenediaminc containing (1) 0% by mass to 38% by mass of tolylenediamine, and (2) 62% by mass to 100% by mass of compounds having boiling points higher than 2,4-tolylenediamine at 1013 mbar.sub.(abs.) (high boilers), based on total mass of the liquid process product; C) incorporating water into the process product depleted in tolylenediamine in a mixing space to obtain a mixture admixed with water, wherein the temperature and amount of the water incorporated and the temperature and amount of the process product depleted in tolylenediamine are matched to one another to provide a temperature of the mixture admixed with water of 110° C. to 250° C. and the mixture admixed with water is monophasic, wherein a pressure which is greater than or equal to the water vapor partial pressure at the resulting temperature is established in the mixing space.

2. The process as claimed in claim 1 wherein in step (C) the pressure in the mixing space is established by introducing a gas selected from the group consisting of air, nitrogen, carbon dioxide, helium and argon and/or via a pressure control valve.

3. The process as claimed in claim 1, wherein the mass of the water incorporated in step (C) is 10% to 100% of the mass of the tolylenediamine distilled off in step (B).

4. The process as claimed in claim 1, further comprising: (D.I) preparing the mixture admixed with water for a use as material or for a thermal use comprising decompressing and cooling the mixture admixed with water to a temperature of 20° C. to 100° C. to obtain a decompressed and cooled mixture admixed with water; and (E) supplying the decompressed and cooled mixture admixed with water obtained in step (D) to a use as material or thermal use.

5. The process as claimed in claim 4, wherein the decompressed and cooled mixture admixed with water is, prior to its use as material or thermal use in step (E), stored and/or transported at a temperature of ambient temperature to the temperature to which it is cooled in step (D.I), wherein the storing and transporting altogether account for a period of 1 hour to 720 hours.

6. The process as claimed in claim 1, further comprising: (D.II) using the mixture admixed with water as a fuel.

7. The process as claimed in claim 1, wherein the tolylenediamine mixture in step (A) is provided by distillative workup of a meta-tolylenediamine-containing tolylenediamine isomer mixture, wherein a meta-tolylenediamine product fraction is obtained in addition to the tolylenediamine mixture.

8. The process as claimed in claim 7, wherein the distillative workup (1) comprises a distillation in a distillation column with an evaporator arranged downstream thereof, wherein the tolylenediamine mixture is withdrawn from a liquid bottoms stream from the evaporator or from a liquid bottoms stream obtained by further workup thereof and the meta-tolylenediamine product fraction is obtained as a distillate fraction from the evaporator; or wherein the distillative workup (2) comprises a distillation in a distillation column with an evaporator arranged upstream thereof, wherein the tolylenediamine mixture is withdrawn from a liquid bottoms stream from the evaporator or from a liquid bottoms stream obtained by further workup thereof and the meta-tolylenediamine product fraction is obtained as a liquid bottoms fraction from the distillation column; or wherein the distillative workup (3) comprises a distillation in a distillation column, wherein the tolylenediamine mixture is withdrawn from a liquid bottoms stream from the distillation column or from a liquid bottoms stream obtained by further workup thereof and the meta-tolylenediamine product fraction is obtained as a gaseous bottoms fraction from the distillation column; or wherein the distillative workup (4) comprises a distillation in a dividing wall column, wherein the tolylenediamine mixture is withdrawn from a liquid bottoms stream from the dividing wall column or from a liquid bottoms stream obtained by further workup thereof and the meta-tolylenediamine product fraction is obtained as a side draw fraction from the dividing wall column.

9. The process as claimed in claim 8, comprising one or more of the variants (1) to (3), but not variant (4), wherein the tolylenediamine mixture is withdrawn from a liquid bottoms stream obtained by further workup of the liquid bottoms stream from the evaporator or the distillation column, wherein the further workup comprises a stripping and a concentrating with addition of an ortho-tolylenediamine fraction distilled off in the distillation column.

10. The process as claimed in claim 9, wherein the toluenediamine distilled off in step (B) is used as a starter for polyether polyol production, as a dye additive, as a starting material for the production of a corrosion inhibitor or in an aminolysis reaction.

11. The process as claimed in claim 8, wherein the tolylenediamine mixture is withdrawn from the liquid bottoms stream from the evaporator or the distillation column or the dividing wall column.

12. The process as claimed in claim 11, wherein, in step (C), in addition to water, an amount of tolylenediamine smaller than that distilled off in step (B) is re-added, wherein the ratio of the tolylenediamine isomers to one another in the tolylenediamine distilled off on the one hand and in the tolylenediamine re-added on the other hand are selected such that molar ratio of ortho-tolylenediamine to meta-tolylenediamine in the mixture admixed with water is increased relative to the process product depleted in tolylenediamine.

13. The process as claimed in claim 11, wherein the tolylenediamine distilled off in step (B) is phosgenated to produce tolylene diisocyanate, and wherein a meta-tolylene diisocyanate product fraction is obtained by subsequent distillative workup.

14. The process as claimed in claim 7, wherein step (A) comprises: (AI) catalytic hydrogenation of dinitrotoluene, optionally in the presence of a solvent, to obtain, optionally after removal of the solvent, a crude product fraction of tolylenediamine which contains not only isomers of tolylenediamine but also organic impurities; (A.II) separation of water from the crude product fraction to obtain the meta-tolylenediamine-containing tolylenediamine isomer mixture; and (A.III) distillative workup of the meta-tolylenediamine-containing tolylenediamine isomer mixture to obtain the meta-tolylenediamine product fraction and the tolylenediamine mixture.

Description

EXAMPLES

Example 1

Discontinuous Mixing at Superatmospheric Pressure (Inventive)

[0084] A heatable stirred tank was filled with a mixture of ortho-TDA and TDA residue (mass ratio 1:1.5) that had been preheated to 80° C. using a water bath (step (A)) followed by heating of the mixture to 140° C. using thermal oil while simultaneously establishing a reduced pressure of 2 mbar.sub.(abs.) in the stirred tank. 70% of the mass of the ortho-TDA was then distilled off (Step (B)), condensed in an external condenser and collected. Subsequently, the tank contents having a temperature of 140° C. (containing 17% by mass of ortho TDA) were pressurized with nitrogen at a pressure of 4 bar.sub.(abs.) and water (33% of the mass of the ortho-TDA distilled off) having a temperature of 80° C. at a pressure of 4.5 bar.sub.(abs.) was injected into the container in stepwise fashion and mixed until a homogeneous phase was formed (step (C)). This homogeneous phase contained water in a mass fraction of 11.5% based on its total mass. This resulted in a mixing temperature of 135° C. was . After mixing, the vessel was cooled to 80° C. and decompressed to the atmosphere and the liquid mixture was discharged (step (D.I)). Compared to the starting mixture the obtained residue mixture had low-viscosity properties (144 mPa s instead of 326 mPa s) and remained stable over at least 4 weeks (even upon further cooling to room temperature).

Example 2

Discontinuous Mixing at Superatmospheric Pressure (Inventive)

[0085] A heatable stirred tank was filled with a mixture of ortho-TDA and TDA residue (mass ratio 1:1.5) that had been preheated to 80° C. using a water bath (step (A)) followed by heating of the mixture to 140° C. using thermal oil while simultaneously establishing a reduced pressure of 2 mbar.sub.(abs.) in the stirred tank. Subsequently 25% of the mass of the ortho-TDA was distilled off (Step (B)), condensed in an external condenser and collected. Subsequently, the tank contents having a temperature of 140° C. (containing 33% by mass of ortho TDA) were pressurized with nitrogen at a pressure of 4 bar.sub.(abs.) and water (100% of the mass of the ortho-TDA distilled off) having a temperature of 20° C. at a pressure of 4.5 bar.sub.(abs.) was injected into the container all at once and mixed until a homogeneous phase was formed (step (C)). This homogeneous phase contained water in a mass fraction of 15% based on its total mass. This resulted in a mixing temperature of 119° C. After mixing, the vessel was cooled to 80° C. and decompressed to the atmosphere and the liquid mixture was discharged (step (D.I)). Compared to the starting mixture the obtained residue mixture had low-viscosity properties (35 mPa s instead of 326 mPa s) and remained stable over at least 4 weeks (even upon further cooling to room temperature).

Example 3

Continuous Mixing at Superatmospheric Pressure (Simulation; Inventive)

[0086] The process comprises mixing a continuously obtained residue-rich waste stream (84% by mass of TDA residue and 16% by mass of ortho-TDA) obtained by distillative removal of TDA (step (B)) from a TDA mixture (containing 60% TDA residue and 40% ortho-TDA;

[0087] (step (A)) with water (step (C)) at superatmospheric pressure.

[0088] The process product depleted in TDA continuously obtained at 220° C. in the distillative removal of TDA in step (B) (containing 84% TDA residue and 16% ortho-TDA) is initially pre-cooled to 180° C. in a heat exchanger for performance of step (C). This is followed by addition of water having a temperature of 20° C. at a pressure of 6 bar.sub.(abs.) to obtain a mixture admixed with water having a temperature of 155° C., in which water is in the liquid state. The hot process product depleted in TDA may likewise be pre-cooled from 220° C. to 165° C. and an addition of water having a temperature of 90° C. at a pressure of 6 bar.sub.(abs.) performed to obtain an analogous mixture admixed with water having a temperature of 155° C. The mixture admixed with water is subsequently pumped through static mixers and then further decompressed to ambient pressure and cooled to a temperature in the range from 20° C. to 100° C. (step (D.I)), transported, stored and supplied to a further use as material (step (E)). The mixture admixed with water may also be incinerated (step (D.II)).

[0089] The example shows that the process according to the invention makes it possible to reduce the TDA content (here ortho-TDA) in the mixture admixed with water to 16% by mass while the obtained mixture admixed with water nevertheless remains processable, in particular pumpable at low temperatures. According to the teaching of WO 2018/140461 A1 the content of TDA in the TDA residue composition to be admixed with water is not less than 40% by mass.

Example 4

Discontinuous Mixing at Superatmospheric Pressure (Comparative—Excessively Low Temperature In Step (C))

[0090] A heatable stirred tank was filled with a mixture of ortho-TDA and TDA residue (mass ratio 1:1.5) that had been preheated to 80° C. using a water bath (step (A)) followed by heating of the mixture to 120° C. using thermal oil while simultaneously establishing a reduced pressure of 2 mbar.sub.(abs.) in the stirred tank. 70% of the mass of the ortho-TDA was then distilled off (Step (B)), condensed in an external condenser and collected. Subsequently, the tank contents having a temperature of 120° C. (containing 17% by mass of ortho TDA) were pressurized with nitrogen at a pressure of 4 bar.sub.(abs.) and water (33% of the mass of the ortho-TDA distilled off) having a temperature of 25° C. at a pressure of 4.5 bar.sub.(abs.) was injected into the container all at once and mixed (step (C)). The obtained mixture contained water in a mass fraction of 11.5% based on its total mass. The mixing temperature fell below 100° C. and the mixture was biphasic as a result. The temperature of the mixture was then increased to 140° C. with constant stirring. However, the mixture remained biphasic despite prolonged stirring.