DD229133A1 - PROCESS FOR PREPARING AROMATIC AMINONITRO COMPOUNDS - Google Patents

Abstract

The invention relates to a process for the preparation of nitrated aromatic amines from nitrohalocarbons by replacing the halogen with the amino group, preferably by reacting nitroaromatics with aqueous ammonia at pressures up to 25 MPa and temperatures up to 525 K in reactors, such as coiled tubing, autoclaves, autoclave cascades, continuous mixers etc. According to the inventive method, the space-time yield or the throughput of the reactor stage is increased by avoiding reaction-accelerating additives or without additional mixing devices that already reacted Aminonitroprodukt before the reaction stage and / or at one or more points of the reaction stage is added. According to the process of the invention, known compounds such as o-nitroaniline, p-nitroaniline and 4-chloro-2-nitroaniline can be prepared from o-nitrochlorobenzene, p-nitrochlorobenzene and 4-chloro-2-nitrobenzene by reaction with aqueous ammonia.

Description

VBB CHEMIEKOMBINAT BITTEHZSLD Bitterfeld, 17. 9 »1 <

2002

Process for the preparation of aromatic aminotrubber mixtures

Field of application of the invention

The invention relates to a process for the preparation of nitrated amines from aromatic nitrohalohydrocarbons by replacing the halogen with the amino group, preferably by reacting nitrohalobenzenes with aqueous ammonia at elevated pressure and elevated temperature.

Characteristic of the known technical solutions

Di3 production of aromatic amines by ammonolysis of Nitrohalogehbenzolen is usually carried out with 25 to 30% aqueous ammonia at pressures up to 4 ICPa and

- 2 - 2002

Temperatures up to 465 K in a batch autoclave process · The large-scale production of p-nitroaniline from p-iTitrochlorbenzol is carried out, for example, in 3200-1 cast steel autoclaves, which are provided with a conventional movement. For the reaction, 610 kg of p-methylchlorobenzene and 2200 l of 28 to 30% ammonia water are brought. By ^A ufheizen 435 E, the lower temperature threshold of the initial reaction is achieved. The released heat of reaction führt.zu heating of the autoclave at 460 E. The system pressure of 4 MPa initially reached falls at the end of the implementation to 3 to 3.3 MPa (cf.. Ullmann, 3rd Edition, Vol. 3, ^sec · 459 , Munich-Berlin, 1953).

From a safety point of view, the decisive factor for the discontinuous autoclave process is the correct adjustment of the quantitative ratio of hypochlorochlorobenzene to ammonia water, since the latter also serves as a heat store for the released energy of the exothermic amination reaction. Therefore, it is generally driven with an excess of ammonia in the molar ratio 1: 8 to 1:15.

At considerable lower dosage of ammonia water there is in accordance with the then low heat storage capacity of the reactor contents to an A _ns rise of the reaction temperature above 475 2 or to an analogous increase of the pressure in the autoclave. If even extremely high temperatures are reached with extremely incorrectly metered mixtures, then in addition to the thermal decomposition of the nitro compounds and the increase of undesired Febenreaktionen. The resulting decomposition gases cause an explosive increase in autoclave pressure, which is ultimately also

- 3 - 2002

facilities, such as rupture discs or safety valves can no longer safely divert, so that there is a destruction of the autoclave reactor. In order to limit the poles of an explosion to a great extent, continuous processes have been developed in the ear reactor (see Ullmann, Vol. 3, pp. 459 ff.) Although the starting point of a possible hazard, ie the underdosing of ammonia water, is the same, However, at the same productive capacity compared to the autoclave process, the critical reaction mass in the tubular reactor will be substantially lower. <br /><br/> Systems are known in which the reaction mixture is forced through a heat transfer tube, at which the system pressure is controlled by an expansion valve to about 20 MPa The reaction temperatures are generally between 475 and 515 K. By this process, o-nitroaniline, p-histoaniline and 4-chloro-2-nitroaniline are prepared using 27 to 60% aqueous ammonia, reaction times of from 30 to 50 The reaction mixture is usually decompressed into a vessel which is at a Temperature of 355 to 365 2 is maintained. At the head of the expansion vessel, a large part of the unreacted ammonia escapes, while water, ammonium chloride and nitroaniline are produced in the sump. The technology of the following stages depends on the type of nitroaniline produced. ^s o o-nitroaniline (solidification temperature 341.7 S) at about 355 to 365 K as a liquid nichtniischbare phase can be separated from the mother liquor, while z. B. p-JMitroanilin (solidification temperature 41954 2) obtained after relaxation as a crystal substance in the mother liquor and can be separated with suitable filtration or centrifuging. While maintaining the

- 4 - 2002

G-continuous rund.verfah.rens v / ground in the literature various ^A usführungen the reactor stage described. In DS-PS 540 001 an apparatus is described which consists essentially of 2 concentric reaction spaces. Here, molten p-chlorofluorobenzene and ammonia water are continuously metered. At pressures between 8 and 10 1, CPa and temperatures around 500 K, the average residence time in the reaction space is about 40 minutes. The p-nitroaniline produced under the given parameters is withdrawn continuously.

For a person skilled in the art, it is obvious that a stirred tank or a stirred tank cascade can also serve as a reactor stage for a continuous process. For example, DS-OS 1 768 518 describes autoclave reactors made of ^r i ^! itan who work intermittently or continuously.

In order to reduce residence times in the reactor, the use of catalysts, e.g. Copper (I) compounds, lime and potassium chlorate have been proposed, ie the use of reaction-accelerating additives has the disadvantage that, given incorrect metering of the catalyst, there is an increase in the already present danger of explosion. In addition, the separation, work-up and reactivation of the catalyst requires additional expenditure. It is known that nitrochlorobenzene is only sparingly soluble in aqueous ammonia solutions. So at the beginning of the reaction there are two separate phases.

5 - 2002

The Sealungszeiten in the continuous process are therefore crucially dependent on the mixing of the two phases. Conventional dynamic mixers, however, present great difficulty in sealing under the stated operating conditions of 10 to 20 MPa pressure and temperatures up to 515K. Special FüllkörperSachichtungen, as set forth in DE-PS 5 ^ 0 001, increase the risk of adding the reactor.

Object of the invention

The aim of the invention is to eliminate the mentioned disadvantages and to provide a process for the preparation of aromatic aminonitro compounds in which an increase in the space-time yield in the reactor stage is achieved without reaction-accelerating additives.

Explanation of the essence of the invention

According to the invention ^A is ASK achieved in that the ammonia water and the corresponding nitrohalogenobenzene be pressed by means of pumps in the optionally heated reactor and diverted part of the approximately fully reacted mixture before the expansion and by means of an additional pump at the reactor inlet and / or at one point or several points of the reactor is fed again. However, it is also possible for part of the still hot reaction product, which has formed after relaxation and phase separation, to be branched off and metered in by means of a pump at the inlet and / or at other points of the reactor stage.

- 6 - 2002

The reactor used for this purpose can be a coiled tube, a stirred autoclave or a cascade of autoclaves, an agitator cascade, a continuous mixer or another device known per se.

The presence of already formed reaction product already in the Startphs.se the reaction significantly improves the emulsion-like mixing or homogenization of the substances involved in the reaction over the known methods and shortens the average residence time of the reaction mixture in the reactor significantly. So it was found that z. B. in continuous operation by simultaneous feed of at temperatures above 425 K and a pressure above 5 MPa in ammonia water readily soluble 2-nitroaniline together with molten 2-xTitrochiorbenzol the reaction rate increases sharply and the flow rate per unit time is increased by more than 30 % . In batch autoclave operation, the reaction times are markedly shortened by the addition of 2-nitroaniline before addition of the reactants 2-M.trochlorbenzol and ammonia water.

embodiments

The invention will be illustrated by 2 examples.

- 7 - 2002

example 1

By iigur 1 a possible variant of the method according to the invention is shown. Liquefied p-lTitrochlorbenzol is conveyed by the pump 6 to the mixing device 7 from the heated container 3. From the tank 1 reaches 100% iEU with the pump 4 and from the container 2 27 fig ammonia water with the pump 5 also to the mixing device 7, so that behind this a dosing of p-Mtrochlorbenzol and 40% ammonia water in the molar ratio 1:15 to Rohrreäktor 8 passes. The ear reactor consists of parallel double-walled tubes, which are heated in the outer space by the liquid heat carrier W. The temperatures in the inner reaction tube reach up to 5 ^ 5 K ₅ the pressures are between 15 and 25 MPa. Tray Leaving the tubular reactor 8 is from the liquid divider 14, a partial flow of 50 to. 95 % of the reaction mixture, which consists of p-matoaniline, ammonia water, ammonium chloride and a little unreacted p-phtrochlorobenzene, branched off and fed with the pump 15 in front of the tubular reactor 8. The reaction-accelerating effect was determined by quantitative determination of the content of unreacted p-hypochlorochlorobenzene in the product stream prior to entering the liquid divider 14, wherein both the partial flow recycling and the amount of added starting materials were varied. It was found that with a partial flow recirculation of 50 %, a throughput increase of 20 % and a partial flow recirculation of 95 °, an increase in throughput of 50 % is possible, while the content of unreacted p-ITitrochlorbenzol was kept constant in the discharged reaction product.

8th - . 2002

The reaction mixture is released via the throttle valve 9 i the container 10, escapes from the excess ammonia A as a vapor. About the discharge screw 11 das.nach relaxation as a crystalline substance in the mother liquor resulting p-nitroaniline is promoted in the crystallizer 12. In the filtration device 13 · the finished end product P is separated from the mother liquor M.

Example 2

A further variant of the method according to the invention is illustrated in Figure 2. From the container 2, 4-0% ammonia water is fed to the mixing device 7 with the pump 5. Liquefied o-nitrocilorobenzene is likewise conveyed to the mixing device 7 by the pump 6, so that behind this is the molar ratio o-nitrochlorobenzene: ESo = 1: 12. The reaction stage is an autoclave channel 8.1, 8.2 and 8.3 · The finished reaction mixture is expanded via the throttle valve 9 into the container 10. This is heated to about 355 to 365 K so that the o-Iitroanilih (solidification temperature 34-1.7 K) remains liquid and can be deposited in the phase remover 16. A partial flow of 50 % of the separated from the mother liquor M o-nitroaniline is from the! Returned pump 15 and optionally fed into the mixing device 7 or at another stage of the autoclave cascade The capacity of the reaction stage can be increased by approx. 30 % . The finished product P leaves the liquid divider 14- in the free flow.

Claims (3)

9 - 2002 Invented by the Oruch 1. Process for the preparation of nitrated aromatic ¹ O Amines by reaction of nitrohalocarbons with aqueous ammonia at pressures up to 25 MPa and temperatures up to 525 K in reactors, such as coils, autoclaves, autoclave cascades, Durchlaufmisehern, characterized in that the reaction product before the reaction stage and / or at one or more points added to the reaction stage becomes. 2. The method according to item 1, characterized in that continuously diverted according to Figure 1, a partial stream of the reaction mixture upstream of the throttle valve (9) and with the pump (15) in the reactor (8) is fed. 3. The method according to item 1, characterized in that according to Figure 2, a portion of the reaction product formed after the separation of the aqueous phase is continuously diverted and fed with the pump (15) in the reactor system (8.1, 8.2, 8.3). Hie / 7ü._Jl