MXPA00003700A - Continuous method for producing aromatic amines - Google Patents

Abstract

The invention relates to a continuous method for producing aromatic diamines and/or polyamines by means of catalytic hydrogenation of corresponding aromatic dinitro and/or polynitro compounds with hydrogen. The invention is characterized in that in a reactor with a catalytic fixed bed or shower bed with a pressure ranging from 5 to 100 bar and at a reaction temperature ranging from 100 to 220°C, a) the aromatic dinitro and/or polynitro compounds are optionally introduced in the presence of a solvent in a product stream comprised of an essentially recycled hydrogenated product, water and hydrogen, and b) a part of the product stream is continuously withdrawn from the reactor system.

Description

Continuous process for obtaining aromatic amines Description of the invention; The invention relates to a continuous process for the preparation of aromatic diamines and polyamines by means of the catalytic hydrogenation of the corresponding dinitro and polynitro compounds at high temperatures and, where appropriate, the simultaneous removal of heat from the reaction mixture for the steam production with overpressure > 1.5 absolute bars in a stationary bed.

A large number of processes for obtaining aromatic amines by means of the catalytic hydrogenation of their corresponding nitro compounds are known (DE-A-2135155, DE-A-2106644, DE-A-4435839, EP-A-0696573 and WO 97/20804).

In general, industrial-scale catalytic hydrogenation of aromatic polynitro compounds is carried out in suspensions at low temperatures, since the hydrogenation of polynitro compounds at high temperatures has the danger of uncontrolled secondary reactions. These side reactions can lead to the formation of unwanted side products and therefore to yield decreases. Mention is made in this regard, for example, hydrogenations of the core, hydrogenolytic dissociations or formation of high molecular weight tarry products.

REF .: 119333 Explosive side reactions can also occur based on highly exothermic reaction courses of the nitro groups and their high reaction speed at high temperatures.

In the reaction of aromatic polynitro compounds with hydrogen, a considerable amount of heat is released. Hydrogenation processes are advantageous in which the increased energy of the reaction must not be dissipated at the expense of energy, but the energy of the reaction can be used economically in the form of steam production.

In the catalytic suspension process, silts and sediments are always observed. Therefore, it is often linked to polluting products, low hydrogenation yields and a high catalyst expenditure. The expense in purification and maintenance is considerable.

These disadvantages have been avoided by Thelen et al. (DE-A-2135154 and DE-A-2135155) by means of the description of a catalytic hydrogenation in a stationary bed. In spite of the advantageous distribution of the catalyst in a stationary bed, it is disadvantageous, however, that the heat is discharged into the reactor, since the dimensioning or construction of the reactor and the application of the spinel catalyst on the cooling tube are very costly. . The flow rate of polynitro aromatic compounds is low. The heat discharge is problematic and the reaction temperatures can only be controlled at a low level.

In WO 97/20804 (CHambost et al.) The catalytic hydrogenation of nitro aromatic compounds is described in a stationary bed in combination with two stationary bed reactors. The distribution of the product quantities after the first reactor with simultaneous gas separation is problematic and expensive. In the process described here, the use of two reactors and the low reaction temperatures of up to 120 ° C are disadvantageous. In addition, large quantities of solvents such as alcohols or ethers are used in part, whereby after the reaction has been carried out, the solvent must be separated and, if appropriate, the aromatic amines treated.

Therefore, the task has been to provide an improved process for obtaining amines by means of hydrogenation of aromatic nitro compounds which would also allow working at high temperatures without solvents or with only a small amount of solvent, without secondary reactions or reactions occurring. silts The subject of the invention is a continuous process for obtaining aromatic diamines and / or polyamines by means of catalytic hydrogenation of the corresponding aromatic dinitro and / or polynitro compounds with hydrogen, in which they are introduced into a reactor with a stationary bed or bed of catalytic irrigation at a pressure in the range of 5 to 100 bar and a reaction temperature in the range of 100 to 220 ° C, a) in a product stream, essentially composed of the feed-back hydrogenation product, water and hydrogen, the aromatic dinitro and / or polynitro compounds, where appropriate in the presence of a solvent and b) a part of the product stream is continuously removed from the reactor system.

It is preferred to keep a pressure of 210 to 80 bar and a temperature of 150 to 200 ° C in the reactor.

It is preferred that the reactor used has an external heat exchanger, so that the heat of reaction produced for obtaining steam can be used.

The discharge of the product can take place anywhere in the reactor system. It is preferred that the discharge occurs after the external heat exchanger and before the return pump. Preferably the product stream withdrawn from the reaction system is cooled to about 150 to 160 ° C.

Preferred examples of nitro aromatic compounds used are: 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene or technical mixtures of dinitrotoluenes essentially composed of the two isomers mentioned above.

It is particularly preferred to use 2,4-dinitrotoluene or its technical mixtures with up to 35% by weight, based on the total mixture, of 2,6-dinitrotoluene as aromatic nitro compounds. These technical mixtures can also contain secondary amounts, that is to say a maximum of 6% by weight, based on the total mixture, of 2,3-, 2,5- or 3,4-dinitrotoluene.

For the process according to the invention, the known hydrogenation catalysts for the nitro compounds are used. The catalysts can be arranged as heaps of molding bodies, fixed on supports, shelves, bundles or fabrics optionally arranged geometrically so that the pressure loss is as low as possible, the distribution on the catalyst bed is optimal and the mixing speed of the reaction is high enough to increase the heat of reaction. Suitable catalysts are especially the metals of the secondary group 8 of the periodic system of the elements, which use as support materials, for example, oxides of magnesium, aluminum, titanium and / or nickel, also Raney nickel. Nickel catalysts are preferably used. Noble metal catalysts are also used on suitable support materials, such as palladium on carbon. The catalysts are preferably in the form of compressed molding bodies, stacked on structural backings.

Preferably the process according to the invention is carried out so that, the circulation of the reaction mixture in the stationary bed or irrigation bed takes place so that the ratio by volume of mixture to nitro feed compound reaches 50 to 500, preferably 200 to 300, the hydrogen charge is self-breathing, that is, the hydrogen gas that is collected in the upper part of the reactor is mixed again with the reaction mixture by the energy of the circulating mixture, the operating pressure of the reactor system by loading new hydrogen from outside, the volumetric ratio of the hydrogen current drawn to the pumped mixture reaches from 0.1 to 7, extracting the necessary hydrogen is extracted from the gas space of the reactor and recharging the spent hydrogen in the reaction at any place in the system, the ratio of catalyst to nitro compound fed is < 20 kg / kg and preferably 5 to 14 kg / kg.

By mixing the aromatic nitro components with the re-fed hydrogenation product (product loop), an intensive mixing with the conventional process parameters and a partition on the catalyst bed is achieved. In this way, catalytic hydrogenation, possibly also without solvents, of diaromatic or polyaromatic compounds at high temperatures is possible, so that a heat evacuation from the system, at the same time as steam, can occur at more than 2 bar. overpressure. Secondary or similar reactions do not occur or only in a reduced form.

For the regeneration of the catalyst bed, the metering of the aromatic dinitro and / or polynitro compounds is interrupted if necessary. More simply, the catalyst can be regenerated by means of the fluid product stream, without a long interruption of the process being necessary for this.

If appropriate, the aromatic dinitro and / or polynitro compounds can also be metered in the solvent into the product stream. Suitable solvents are C, -C4 aliphatic alcohols, especially methanol, ethanol, isopropanol, tert-butanol or cyclic ethers, especially dioxane or tetrahydrofuran.

The process according to the invention can take place, for example, in a reaction system which is shown schematically in FIG. 1 (irrigation bed) or alternatively in FIG. 2 (stationary bed). In these figures the numbers have the following meanings: 1) Reactor 2) Catalyst bed 3) Pipe system, pump for the circular path of the reaction mixture 4) Heat exchanger for cooling the circulating reaction mixture ) Gas cooler 6) Aspiration of circulating hydrogen 7) Steam separator 8) Condensate The invention is explained in more detail by means of the following examples, without these limiting.

Examples Example 1 (see fig 1) 3 are pumped through the top of 1,000 1 / h of TDA / water mixture to an autoclave 1 (diameter 14 cm) with an irrigation bed (501 of compressed nickel-Ra catalyst, cubic molding bodies: from 3 to 4 mm in diameter, from 5 to 6 mm in height) through a heat exchanger 2. Chilled 5 gas containing hydrogen extracted from the reactor is pumped by means of the cooled liquid stream from 180 ° C to 155 ° C through the injector Four . Before the circulation of hydrogen, 5 kg / h of liquid dinitrotoluene (70 ° C) are added. The hydrogen used in the reaction is added via hydrogen in the same direction of flow through the top. Correspondingly to the dosage of the nitro compound, TDA isomers and water of reaction are obtained in a stoichiometric and selective manner with a yield > 99% Example 2 (See fig 2.) 1,000 l / h of TDA / water mixture is pumped under an autoclave 1 (diameter 14 cm) with a stationary bed (50 1 of catalyst as in example 1) through a heat exchanger 2. Pumped into gas 5 cooled containing hydrogen extracted from the reactor by means of a liquid stream cooled from 180 ° C to 155 ° C, through an injector 4. Before pumping 3, 5 kg / h of liquid dinitrotoluene (70 ° C) are dosed. The hydrogen used in the reaction is added by means of hydrogen in the same flow direction through the lower part. Correspondingly to the dosage of the nitro compound, TDA isomers and water of reaction are obtained in a stoichiometric and selective manner with a yield > 99.2%. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (1)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: . A continuous process for obtaining aromatic diamines and / or polyamines by means of catalytic hydrogenation of the corresponding aromatic dinitro and / or polynitro compounds with hydrogen, characterized in that they are introduced into a reactor with a stationary bed or a catalytic irrigation bed at a pressure of the range from 5 to 100 bar and a reaction temperature in the range of 100 to 220 ° C, a) in a product stream, essentially composed of the feed-back hydrogenation product, water and hydrogen, the aromatic dinitro or polynitro compounds, where appropriate in the presence of a solvent and b) a part of the product stream is continuously removed from the reactor system. A process according to claim 1, characterized in that the dinitro or aromatic polynitro compound is used in pure form as a mixture with the corresponding diamines or polyamines and water. A process according to claims 1 or 2, characterized in that 2,4-dinitrotoluene or its technical mixtures with 2,6-dinitrotoluene are used as dinitro aromatic compound. A process according to claims 1 to 3, characterized in that the volumetric ratio of the mixture pumped with fast flow to dinitro or polynitro compound reaches 50 to 500. A process according to claims 1 or 4, characterized in that the ratio of catalyst to nitro compound fed is < 20 kg / kg, preferably 5 to 14 kg / kg. A process according to claims 1 to 5, characterized in that the catalyst bed is driven from above or from below with the re-fed hydrogenation product. A process according to claims 1 to 6, characterized in that aliphatic alcohols C.-C, or cyclic ethers are used as solvents. A process according to claim 7, characterized in that the solvent is used in an amount of 0.1 to 40% by weight of the reaction mixture. A process according to claims 7 to 8, characterized in that the solvent is used in an amount of 1 to 10% by weight of the reaction mixture.