Process for the production of aromatic amines

Details Process for the production of aromatic amines Process for the production of aromatic amines

1998-08-21

2001-03-20

Killos, Paul J. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

Reexamination Certificate

active

06204411

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the production of aromatic amines, in particular aniline. More specifically, the present invention relates to an ammoxidation and/or an oxidative dehydrogenation/coupling reaction.
BACKGROUND OF THE INVENTION
Commonly used processes for the preparation of aromatic amines comprise two process stages: the aromatic hydrocarbon is first nitrated and then the nitrated aromatic hydrocarbon is hydrogenated to form the corresponding amine compound. Such processes have the drawback that they are energy and time consuming, require large amounts of reactants, and result in the production of considerable amounts of undesired by-products which need to be removed.
Accordingly there still remains a need for a process to produce aromatic amines directly from aromatic hydrocarbons resulting in a high yield and/or a substantially complete conversion.
Therefore, the present invention has the objective to provide a process for efficiently preparing aromatic amines, in particular aniline with high selectivity. A process with sufficiently high selectivity will improve the operating efficiency of the overall process by reducing the amount of unwanted end-products produced, allowing the process to be used on an industrial basis.
The process of the present invention is advantageous in its simplicity, use of operation, low capital and operating costs. The process can be run at a relatively low conversion of the feed hydrocarbon to the desired product due to the selectivity achieved. Selectivity is the amount of desired product divided by the total of all (desired and by-products) products. It will be appreciated that a process that runs at enhanced selectivity is highly advantageous even though the conversion may be low.
The selectivity achieved with the present process permits operation of the process at a relative low conversion, i.e. a change from the conventional objective of achieving the highest possible conversion. A substantial economic benefit is realised on an industrial scale even from increase in selectivity, which is achieved by the present invention, since the process retains and recycles a relative high percentage of unreacted aromatic hydrocarbon and ammonia.
The amount of unreacted aromatic hydrocarbon will depend on the percent per-pass conversion of the reactant aromatic hydrocarbon entering the ammoxidation reactor which is converted to products. Those skilled in the art will appreciate that factors such as specific choice of catalyst, specific operating temperature and the like can be adjusted to have the reactor operate at a desired conversion of the reactant aromatic hydrocarbon.
At lower operating conversion, there will be a greater amount of unreacted aromatic hydrocarbon and unreacted ammonia circulating in the process.
According to one embodiment of the present invention a process is provided for the production of aromatic amines by reacting an aromatic hydrocarbon with ammonia at a temperature of less than 500° C. and a pressure of less than 10 bara in the presence of a catalyst comprising at least one metal selected from the group consisting of the transition elements, lanthanides and actinides.
According to another embodiment of the present invention, the process of the present invention allows to recycle a high percentage of unreacted aromatic hydrocarbon and ammonia (FIG.
1
).
According to a preferred embodiment of the present invention, the aromatic hydrocarbon reacts with ammonia in the presence of an oxygen-containing gas.
More direct methods for the preparation of aromatic amines from aromatic hydrocarbons have been described in the prior art.
CA-A-553988 concerns a one-step process for the production of aromatic amines. In one embodiment a mixture of benzene, ammonia and oxygen is contacted in the vapour phase with a platinum catalyst at a temperature of about 1000° C. In another embodiment, a mixture of benzene and ammonia is contacted in the vapour phase with a reducible metal oxide at a temperature of about 100 to 1000IC.
GB-A-1463997 describes a process for the amination of an aromatic compound which is miscible with ammonia comprising reacting said compound with ammonia at an elevated temperature and at a superatmospheric pressure in the presence of a doped conditioned nickel
ickel oxide/zirconium catalyst system.
In GB-A-1327494 a process is described for converting aromatic compounds and ammonia to aromatic amines in the presence of a prereduced and conditioned nickel
ickel oxide catalyst composition at a temperature in the range of 150 to 500° C. and at a pressure in the range of 10 to 1000 atmospheres.
U.S. Pat. No. 2,948,755 discloses the preparation of aromatic amines by reacting an aromatic compound such as benzene with anhydrous ammonia in the presence of a group VI-B metal compound and a promoter consisting of an easily reducible metallic oxide at a temperature in the range from about 200 to 600° C.
JP-A 06/293715 describes a process for aminating and/or cyanating an aromatic compound in the presence of ammonia using a catalyst carrying a Group VIII-element. In an example a Fe-silica catalyst is used for amination of benzene at 400° C. The conversion rate of benzene was 0.85% and the selectivity rate for aniline was 97.3%.
None of the cited prior art documents disclose the features of the present process nor do these documents suggest the benefits associated with the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention thus provides a process for the production of aromatic amines by reacting an aromatic hydrocarbon with ammonia at a temperature of less than 500° C. and a pressure of less than 10 bara in the presence of a catalyst comprising at least one metal selected from the group consisting of the transition elements, lanthanides and actinides. Suitable aromatic hydrocarbons for use in the present invention include, for example, benzene, toluene, ethylbenzene, n-propylbenzene, isopropyl-benzene, n-butylbenzene, xylenes, diethylbenzenes, trimethylbenzene, ethyltoluene, naphthalene, anthracene, chrysene, phenanthrene and pyrene.
The preferred aromatic hydrocarbon is benzene, producing aniline in the process of the present invention.
While ammonia is preferred, it is anticipated that other amines such as methylamine may be used as the source of the amino-function substituted on the aromatic hydrocarbon.
The reaction is preferably carried out at a temperature between 300 and 450° C. and more preferably between 350 and 400° C.
It is preferred to employ pressures between 1 and 7 bara, more preferably between 2 and 5 bara. Typically an excess of ammonia over the stoichiometric amount is employed. Typically, the molar ratio of ammonia to hydrocarbon is from 1:1 to 10:1, preferably from 1:1 to 3:1.
The reaction time largely depends on the reaction conditions such as pressure and temperature, and on the type of catalyst used.
The metal used in the catalyst may be any transition element, a lanthanide or an actinide, or mixtures thereof Generally, Group I-B, IV-B, V-B, VI-B or VIII-metals are used.
The catalyst may comprise the metals in their pure form or oxides thereof Mixtures of metals with their oxides, or with oxides from other metals, are preferred for the purposes of the present invention. In accordance with the present invention, it has been found that selected catalysts, especially vanadium, when being present as oxides, enhances the selectivity.
The metals may be unsupported, for example in the form of alloys, or supported on a carrier.
Suitable carriers for supporting the metal or metal oxide include, for example, alumina, silica, aluminosilicate, carbon and other supports normally employed in supported heterogeneous catalyst systems.
Unsupported catalysts may be for example, in the form of a wire, sponge, particulate, sphere but are preferably present in the form of a wire gauze.
The catalyst may be in any suitable physical form including pellets and extrudates. The catalyst may be prepared by any method known to those skilled in the a

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