CN-109134275-B - Method for treating a substance mixture containing aromatic amines, in particular crude aniline

CN109134275BCN 109134275 BCN109134275 BCN 109134275BCN-109134275-B

Abstract

The invention relates to a method for treating a substance mixture containing aromatic amines, in particular crude aniline. In particular, the invention relates to a method for treating a substance mixture comprising aromatic amines, wherein the aromatic amine is aniline or 2, 4-diaminotoluene, preferably aniline, wherein the substance mixture is a first substance mixture and comprises aromatic amines and compounds having a boiling point higher than the aromatic amines, comprising the steps of I) distillatively separating the first substance mixture in a first distillation unit (110,1130), at least partially separating the aromatic amines, whereby a first bottom product is additionally obtained, and discharging the first bottom product from the first distillation unit (110,1130). The bottom product from the first distillation unit (110,1130) is diluted after discharge with condensed top product from a distillation unit different from the first distillation unit and/or with a composition comprising methanol.

Inventors

MERKEL MICHAEL
T. KNAUF
C.A. Peters
T. SCHMIDT

Assignees

科思创德国股份有限公司
科思创德国股份有限公司

Dates

Publication Date: 20260421
Application Date: 20130429
Priority Date: 20130429

Claims (5)

1. A method for treating a substance mixture comprising aniline, wherein the substance mixture is a first substance mixture and comprises aniline and a compound having a boiling point higher than that of aniline, The method comprises the steps of: I) Separating the first substance mixture by distillation in a first distillation unit (110, 1130), at least partially separating aniline, thereby additionally obtaining a first bottom product, and withdrawing the first bottom product from the first distillation unit (110, 1130); it is characterized in that the method comprises the steps of, The bottom product from the first distillation unit (110, 1130) is diluted with a composition comprising methanol after discharge and incinerated after dilution, Wherein the aniline content in the bottom product from the first distillation unit (110, 1130) is from > 10 wt% to < 45 wt%, Wherein the composition comprising methanol comprises from 20% to 95% by weight methanol, Wherein the flow rate of the methanol-comprising composition is selected such that the calculated flow rate of pure methanol is not less than 30% by weight, based on the flow meter of the bottom product withdrawn from the first distillation unit (110, 1130), and Wherein the methanol-containing composition is a methanol-and water-containing composition obtained from a process for producing methylenediphenyl diamine.
2. A method according to claim 1, wherein the method comprises, It further comprises steps Ia) and Ib), wherein Ia) and Ib) are performed before I): ia) providing a second substance mixture, wherein the second substance mixture comprises aniline, a compound having a boiling point lower than that of aniline, and a compound having a boiling point higher than that of aniline, and the aniline content is different from the aniline content in the first substance mixture; Ib) separating off the second substance mixture by distillation in an upstream distillation unit, separating off compounds having a boiling point lower than that of aniline as top product, whereby aniline is additionally obtained as side stream and the first substance mixture as bottom product.
3. A method according to claim 1, wherein the method comprises, It furthermore comprises steps IIa), IIb) and III), wherein IIa) and IIb) are carried out before III), and III) is carried out before I): IIa) providing a second substance mixture, wherein the second substance mixture comprises aniline, compounds having a boiling point lower than aniline and compounds having a boiling point higher than aniline, and the aniline content is different from the aniline content in the first substance mixture; IIb) distillatively separating the second substance mixture in a second distillation unit (1110) to separate out compounds having a boiling point lower than that of aniline as an overhead product, whereby a bottom product comprising aniline is additionally obtained; III) distillatively separating the bottom product from the second distillation unit in a third distillation unit (1120), at least partially separating off aniline as top product, whereby the first substance mixture is additionally obtained as bottom product.
4. A process according to any one of claims 1 to 3, wherein the bottom product from the first distillation unit (110, 1130) is diluted with a composition comprising methanol after discharge such that the resulting mixture has a viscosity at 20 ℃ of from greater than or equal to 0.3 mPas to less than or equal to 1000 mPas.
5. A process according to any one of claims 1 to 3, wherein the bottom product from the first distillation unit (110, 1130) is diluted after discharge with only a composition comprising methanol.

Description

Method for treating a substance mixture containing aromatic amines, in particular crude aniline The patent application is a divisional application of the parent application with patent application number 201380023422.4 and application date of 2013, 4 and 29. Technical Field The invention relates to a method for treating a substance mixture containing aromatic amines, wherein the substance mixture is a first substance mixture and contains aromatic amines and compounds having a boiling point higher than that of the aromatic amines, comprising the steps of I) distillatively separating the first substance mixture in a first distillation unit, at least partially separating the aromatic amines, whereby a first bottom product is additionally obtained, and discharging this first bottom product from the first distillation unit. Such bottoms can then be diluted with waste material originally produced in the production run, thereby enabling the aromatic amine losses in the bottoms to be reduced. According to the invention, the aromatic amine is aniline or 2, 4-diaminotoluene, preferably aniline. Background Aromatic amines are important intermediates which must be produced inexpensively and on a large scale. Aromatic amine production plants are therefore commonly used to achieve great production capacity. High productivity of these devices is ensured by extremely long reaction cycles and a non-interfering operation between the start-up and shut-down processes for the hydrogenation of the hydrogenation catalyst used for regeneration. The main field of application of 2, 4-diaminotoluene is the production of Toluene Diisocyanate (TDI). It is industrially produced by hydrogenation of 2, 4-dinitrotoluene. The main field of application of aniline is the production of Methylenediphenyl Diamine (MDA), which is used to produce Methylenediphenyl Diisocyanate (MDI). Aniline is generally produced on an industrial scale by catalytic hydrogenation of nitrobenzene with hydrogen. Particularly preferred are the reaction modes described in EP 0 944 A2 (isothermal mode of operation) and EP 0 696 574 B1, EP 0 696 573 B1 and EP 1 882 681 A1 (adiabatic mode of operation). MDA production is described in a number of patents and publications (see, e.g., H.J. Twitchett, Chem. Soc. Rev. 3(2), 209 (1974), M.V. Moore in: Kirk-Othmer Encycl. Chem. Technol., , 3 rd edition, new York, 2, 338-348 (1978)). A common feature of the isothermal processes for the production of aniline is the vaporization of the raw material nitrobenzene at high temperature in a hydrogen stream. The reaction is generally carried out in such a way that the gaseous nitrobenzene/hydrogen mixture is fed into the hydrogenation reactor and reacted there over a fixed bed catalyst, optionally with the use of a subsequent make-up reactor (Nachreaktor), at elevated temperature and pressure. The released reaction heat is led out of the reactor via a heat exchanger and is generally used for producing heating steam. The reaction products aniline and water leave the reactor in gaseous form and are condensed from the hydrogen stream by multistage condensation. The excess hydrogen is introduced into the cycle by replenishing fresh hydrogen, vaporized with nitrobenzene and introduced as a mixture into the hydrogenation reactor. The hydrogen is loaded with gaseous impurities as a result of this cyclic mode of operation. To remove these impurities, a substream is taken from the hydrogen circuit and incinerated in a hot exhaust gas purge (Abluftreinigung). The condensed reaction product separates into an organic phase (crude aniline) and an aqueous phase (aniline-water), which are subjected to further processing, respectively. The crude aniline also contains water and organic by-products in dissolved form, which are separated by distillation. The low-boiling secondary components (e.g. cyclohexylamine, cyclohexanone, benzene) are first distilled off via the top of the column and water is distilled off in a side stream in the form of an aniline-water azeotrope. The side stream is two-phase and is returned to the phase separation. The low-boiling secondary components which also comprise aniline are taken off overhead and can be used directly in the incineration plant or are first condensed and subsequently incinerated with other residues. The bottom product (aniline + high boilers) is freed of high-boiling by-products (e.g.N-cyclohexylaniline, N-diphenylamine, phenol) in a second distillation column. Pure aniline was distilled off via the top of the column. The high boilers are enriched in the bottom and further concentrated in a third distillation column (residue column). Aniline is recovered at the top of the residue column and fed to the second column together with the bottom product of the first column. The bottoms of the residue column is transferred to a residue container. Here, the residual content of aniline acts as a solvent to maintain pumpability of the residue. In addition, the residue