DE2214056C3 - Catalyst and process for the reduction of nitro compounds - Google Patents

Description

The invention relates to a particularly effective catalyst based on palladium together with metallic vanadium and / or vanadium compounds on spinels as a carrier material and the use this new catalyst / ur reduction of nitro compounds.

The reduction of nitro compounds is problematic because of the dangerousness involved in handling Nitro compounds, especially if they are dinitro or trinitro compounds. There's a lack of therefore not to literature about the most expedient way of reduction:

Basically the reduction is in the liquid phase, i. H. in a kettle or in a bubble column possible. The disadvantage of this process is that the catalyst must be suspended in the solution must and accordingly problems arise in the separation of the mostly pyrophoric catalyst. Man tried to circumvent these disadvantages by arranging the catalyst in a fixed bed and let the component to be reduced run over the catalyst in the Riesclphase. When using the Catalysts described hitherto also arise here difficulties, since the catalyst life is long is too short and the reaction is not selective enough. These disadvantages apply analogously to the Working in the gas phase over a fixed bed, with the nitro compound to be reduced in gaseous form the catalyst is passed. Usually, because of the safety risk in the gas phase, only with Mononitro compounds worked.

There has now been a process for reducing nitro compounds in the liquid or in the gas phase in a hydrogen atmosphere in the temperature range from 50 to 350 C in the presence of noble metal catalysts found on supports with particularly good yields, high selectivities, low Reaction temperatures and long catalyst life with good regenerative capacity of the Catalyst can be achieved and which is characterized in that catalysts are used the 0.1 to 10 weight percent palladium and 0.1 to 5.0 weight percent vanadium on alumina as Contain carrier which at least 20% has been converted into spinel.

The gas phase reaction is used for mononitro compounds preferred, while for the diniiro or trinitro compounds the liquid phase and especially the Trickle phase is preferred. With the reduction in the S liquid, the Rioselphase and the gas phase can basically with dilution by the resulting hydrogenated compound can be worked, but inert solvents - lower aliphatic ^ Alcohols such as B. methanol, saturated aliphatic

ίο Hydrocarbons etc. - are used.

The reaction temperature is in the range from 50 to 350 C. When working in the gas phase, one chooses the Range from 100 to 350 ° C, preferably 15 ° to 250 C, while when working in the liquid phase or in the trickle phase at 50 to 200 C, preferably 50 to 150 C, is worked. The hydrogenation can be either pressureless or under increased pressure be carried out, normally hydrogen Tn more a / s of the stoichiometrically required

ao mence is used and excess hydrogen can optionally also be recycled back into the reaction. At work under increased hydrogen pressure this is up to 100 bar, preferably 1 to 30 bar.

* 5 The highly effective catalysts according to the invention for the reduction of nitro compounds are obtained if the catalyst used is palladium in Presence of metallic vanadium and / or vanadium compounds and aluminum oxide as a carrier used, which has been completely or partially converted into spinel (hereinafter referred to as Pd-V spinel catalyst designated).

Such spinels are obtained by reacting aluminum ^; Umoxid with compounds of I- or bivalent metals, such as lithium, magnesium, cobalt, manganese or / ink (see Gmelin, System No. 35. Al, 1934 to 1935. pp. 26 to 28, and Ullmann's Enzyklopadie der technischen Chemie, 3rd ed. F 1955], Vol. 6, pp. 242 to 244). The use of

♦ ° formation of a lithium-aluminum spinel as a carrier. Through the use of preferably spherical aluminum oxide as the starting component, carriers with high mechanical strength are obtained in the spinel production, which also have optimal properties for the beds in the fixed bed due to the spherical shape. But you can of course also start from pulverulent Al ₂ O ₃ and then deform the catalyst support. The spinel formation should be at least 20 ″

Those carriers in which the aluminum oxide is practically completely in the form of spinel have proven to be very suitable. It is advantageous if, for the production of spinel, one starts out from highly active aluminum oxide in lump form, which has an inner surface area of 200 to 350 m ² g. All forms which still have sufficient absorbency and which form spinels during annealing in the presence of spinel-forming metal salts or oxides or hydroxides can be used as aluminum oxides. D'eses lumpy aluminum oxide, for example in the form of sausages, pills or preferably balls with dimensions of 2 to 10 mm, can be soaked with the solution or slurry of a compound (salt, hydroxide, oxide) of the spinel-forming metal to be used and dried. If you have soaked with salts, it is advisable, after possible conversion into the hydroxides, by heating to 250 to 650 C, if necessary with the addition of oxygenated

containing or steam-containing gases in oxides to chlorides in the production of the new catalyst

run over. Then it is done to bring about the one then washes it with water cblorid-

Spinel formation heating to 900 to 1300 C, e.g. B. free. Finally the catalyst is dried,

for a period of 1 to 6 hours. The catalysts prepared in this way are suitable for

stoichiometric swell formation can be achieved if 5 is particularly advantageous for the reduction of nitro compounds

the impregnation of the respective solution according to gene over a fixed in a tube furnace

intermediate drying and possible decomposition catalyst in the gas or trickle phase. All too

setting the salts several times. It is also possible in other technical embodiments of catalysis,

possible to produce mixing spindles by using _z . B. in the shaft furnace, stirred tank, bubble column or

of several spinel-forming metal compounds. io fluidized bed etc. come with the use of the

According to the invention for spin rope formation cobalt, catalysts according to the invention are basically in

Magnesium, nickel or zinc and particularly advantageous considerations.

Lithium applied. Duration of the annealing process The catalyst according to the invention can thus be used for the production of amines or spinels. The level of the glow temperature and its N-alkylation products due to the catalytic duration of the glow have an influence on the internal reduction of the corresponding nitro compounds. Surface area and pore diameter of the support. As nitro compounds, medium pore diameter-substituted aliphatic, araliphatic, aromatic blades of the catalyst supports of 200 to 800 Å as well as heterocyclic nitro compounds have been used which have internal surfaces of 20 to 120 m ² g. Turn 20. Aliphatic nitro compounds are sol-The further preparation of the novel catalyst with 1 to 12, preferably 1 to 4, carbon atoms to give a new catalyst takes place in a manner known per se. This also includes cycloaliphatic nitros by covering the carrier material (spinel), functional compounds with 5 to 7, preferably 6, carbon atoms, moderately by applying or soaking them in the ring system. Aromatic nitro compound solution of a vanadium compound as well as 25 compounds contain up to 14 carbon atoms in the aromatic nucleus, applied or soaked with a palladium / - in particular 12, preferably ό carbon atoms. Hetero solution. The amount of vanadium compound is such eye-ical nitro compounds are preferably 5 and measured that the finished catalyst contains 0.1 to 5.0 geo-membered heterocycles containing oxygen as the heteroatom, percent by weight, preferably 0.3 to 1.0 percent by weight, nitrogen or sulfur be able. Such a percentage, calculated as vanadium and based on the 3o heterocyclic compounds, may optionally contain a total amount of catalyst. The palladium 1- or 2-fold with an optionally partial hydrogenation should be fused in the finished catalyst in amounts of 0.1 to th benzene ring. Araliphatic ring contains 10 percent by weight, preferably from 0.5 to 5 systems, as aromatics, preferably the correct percent. Phenyl radical and in the aliphatic chain 1 to 4, before the impregnation of the carrier material with the salt 35 preferably 1 or 2 carbon atoms. At the same time, however, cycloaliphatic, araliphatic, aromatic and also one after the other can be used as substituents on the solutions of the two metals. As vanadium compounds of heterocyclic ring systems, all common ones come into consideration, apart from halos, namely genatoms, hydroxyl, mercapto, amino, sulfonic, as well as the solutions of the oxides (preferably vanadic acid, carboxyl and lower alkoxy and alkyl pentoxide) and salts (preferably Chloride), the 40 _{res) em} j _t | t, j _s 5, preferably 1 to 3 carbon atoms, ins vanadates (preferably alkali vanadates) or also special but methyl groups and organic vanadyl compounds (preferably oxalate, optionally one or even two further nitro formate, acetate). For reasons of expediency, groups. Apart from the alkyl radicals mentioned, those vanadium compounds are used which do not have the substituents listed and are only readily accessible, but rather alkyl radicals in particular in water. The solvents according to the invention or organic solvents (lower aliphatic catalysts of the present invention also for alcohols, ketones, benzene hydrocarbons known per se) can be used with readily soluble-reductive alkylation by being borrowed from the. You can fix the vanadium compound before the hydrogenation in the presence of an aldehyde or impregnation with Pd compounds according to conventional ketone works.

Methods, e.g. B. Precipitation. In the case of use, preferred starting compounds are nitrophes. An organic vanadium compound can, after nols, nitrochlorobenzenes, nitropropane, nitrodiphenyl, impregnation of the catalyst support with the orga- amine, but in particular nitrobenzene, dinitrobenzene vanadium compound to destroy the orga- zene, nitrotoluenes, dinitrotoluenes.
niche residues are tempered (heating to 200 to 500 C). The new Pd-V catalyst on spinel is suitable. The fixation can also be achieved by reduction, especially for the technically known reduction of aliphatic and aromatic substances which are optionally substituted together with the palladium salts. Unsubstituted mononitro compounds in the gas in principle come for the impregnation of the catalyst phase over a fixed catalyst. Since here the carrier of all commercially available palladium compounds reduction is possible at a ^{temperature which is relatively low for the gas phase reduction (preferably chlorides, palladium hydrochloric acid} , so that re and their salts) are possible. The normally long running time and very pure hydrogenation products are achieved by the subsequent reduction of the palladium salt (which can be achieved before, there is an advantage over the chloride) to the metal, for example, with conventional ver-formaldehyde or hydrazine in an alkaline solution, which work at higher temperatures.

or with hydrogen or ethylene, at elevated tem- ⁶ S It must also surprising as pronounced

temperature (100 to 200 ° C) can be carried out, but it should be considered that when using the catalyst

are all other known reduction methods sators of the invention, the reduction of Nitroverbin-

also possible. In the event of using fertilizer in the liquid phase over fixed

Catalyst at very low temperatures is possible. Other industrially customary, permanently arranged catalysts require higher temperatures for this, which, as described, leads to by-products and to shorter ones KataJysator runtimes leads.

The Niu ^ compound to be reduced can with the respective amine or another diluent are diluted to such an extent that an implementation the reduction is harmless and the heat of hydrogenation can be dissipated in an unproblematic manner.

The catalyst of the invention is not only distinguished from known hydrogenation catalysts an exceptionally long service life, but also shows compared to known catalysts Repeated regeneration by burning off (approx. 300 to 700 C) with air, optionally with additive of inert gas, such as. B. nitrogen or steam, a significantly better regenerability and constant high activity.

The amines obtainable by the process of the invention can be used in many ways, for example for the preparation of isocyanates and crop protection agents.

Examples

a) Manufacture of the catalysts:
Catalyst 1

2.86 l of spherical y-aluminum oxide with a diameter of 4 to 6 mm and an inner surface of about 250 m ² / g were soaked with 1 l of aqueous solution at 30 ° C., in successive 296 g of formic acid and 233 g of 54% aqueous lithium hydroxide solution had been given. The impregnated aluminum oxide was dried at 150.degree. C. in vacuo, impregnated again with the same solution and dried again at 150.degree. C. in vacuo. The carrier was then calcined to spinel at 1050 ° C. for 6 hours, as was determined by X-ray examination. The finished carrier had an inner surface of 25 m ² / g and an average pore size of 700 A. 4 l of the carrier material (lithium-aluminum spinel) produced as described above are mixed with a solution of 33 g of vanadium (V) oxide soaked in 1200 ml of a hot (about 70 to 90 C) aqueous 20gcwichtsprozentigen oxalic acid solution. After drying in a rotary evaporator (70 to 100 C / water jet vacuum), the remaining mass is impregnated with 1250 ml of a solution containing _{150 g of Na 2} PdCl _4. It is then treated with the aqueous solution of 20 percent by weight sodium hydroxide and 20 percent by weight formaldehyde for about 5 Ii. The remaining catalyst mass was then washed neutral and chloride-free with water and dried at 150 ° C. (normal pressure). According to analysis, the finished catalyst has a content of 1.8 percent by weight of palladium and 0.6 percent by weight of vanadium.

Catalyst 2

4 l of the Li-Al-Spin III used for catalyst I are soaked in a solution of 50 g of Na ₂ PdCl and 17 g of NaVO in 1350 ml of water. The impregnated catalyst is then treated with an aqueous solution of 20 percent by weight sodium hydroxide and 20 percent by weight formaldehyde for 4 hours. The catalyst is washed neutral and chloride-free with water and dried at 150 ° C. (under normal pressure). The finished catalyst contained 0.6 percent by weight palladium and 0.2 percent by weight vanadium.
5

Catalyst 3

4 liters of the Li-Al spinel used for catalyst 1 are impregnated _{with 1350 ml of an aqueous solution of 120 g of PdCl 2.} After reduction with an aqueous solution of 20 percent by weight sodium hydroxide and 20 percent by weight formaldehyde, the catalyst is washed neutral and free of chloride and dried at 150 ° C. (under normal pressure). The palladium catalyst was then with a solution of

¹ S 43 g of vanadium f V) oxide soaked in 1200 ml of a 70 to 90 C hot 20 weight percent oxalic acid, dried and then tempered at 400 C for 4 h. The finished catalyst contained 2.4 percent by weight palladium and 0.8 percent by weight vanadium.

Catalyst 4 (for comparison)

_{144 g of PdCl 2} in the form of an aqueous hydrochloric acid solution are applied to 4000 ml of a -aluminum oxide in the form of spheres of 4 to 6 mm and 30 ni ² / g specific surface area with intermediate drying. After the reduction with an aqueous solution of 20 percent by weight sodium hydroxide and 20 percent by weight formaldehyde, the KaIa-

- ₀ lyser washed neutral and chloride-free with water and dried. The finished catalyst contained 1.8 percent by weight palladium.

b) Examples of hydrogenation

The experiments in the trickle phase were carried out in a 6 m long reactor of 24 mm diameter and with 2.4 l catalyst carried out. The reaction tube was surrounded by a jacket tube, which was covered with Hcizodcr Cooling medium was flowed through. The liquid to be hydrogenated was from above at room temperature pumped onto the catalyst and trickled down over the catalyst into a separator from which part of the re-use as recirculation, the reactor was pumped. From the gas phase of the A portion of the reactor was depressurized in order to discharge the inerts from the system. The hydrogenation in the Trickle phase was carried out at about 50 bar hydrogen pressure, with the consumed hydrogen was automatically pressed in each case. Im IaIIe der Gas phase hydrogenation became the liquid to be hydrogenated converted into the gas phase in an evaporator with the hydrogen stream. The gas stream flowed through almost pressureless the one arranged in a 6 m long tubular reactor with a tube diameter of 40 mm Catalyst (3.7 l) from bottom to top. Your electricity leaving the reactor became that Ihdrierprodukt condenses.

Example I.

Add a 50% solution of nitrobenzene in aniline was with I kg / hli in the trickle phase through the with the catalyst 1 filled reactor passed. The reactor outlet temperature was 100 ° C. contained only 400 ppm impurities (200 ppm nitrobenzene and 200 ppm cyclohexylamine Hölicisicdcndc, unknown components could not be detected. The reduction could

operated for 2000 h without the catalyst losing activity.

Comparable results are achieved if one for the preparation of the catalyst 1 instead of Lithium is used as a spinel-forming metal cobalt, zinc, magnesium or nickel.

In a comparative experiment with catalyst 4, almost 200 ^° C. were necessary in order to reduce nitrobenzene. The hydrogenation product still contained 0.8 percent by weight nitrobenzene and 0.5 percent by weight cyclohexyl amine. In addition, higher-boiling condensation products were formed. The hydrogenation activity of the catalyst subsided after about 80 hours.

Example 2

A 30% strength methanolic solution of a mixture of 2,4-dinitrotoluene and 2,6-dinitrotoluene (in a ratio of 7: 3) was passed through the reactor filled with catalyst 2 at 1 kg / l · h in the trickle phase. The reactor outlet temperature was 110 ^° C. After a few days, the hydrogenation product was used in place of the methanol to dilute the nitro compound to be reduced. No more dinitrotoluene could be detected in the hydrogenation product; a 99.6% toluenediamine could be obtained. The reduction was carried out for 1000 hours without the catalyst having decayed.

Was reduced compared to 2,4-DinitrotoluoI under the same conditions with catalyst 4, the temperature to 180 ⁰ C had to be increased. After 100 hours of operation, the hydrogenation results deteriorated.

Example 3

A 5% methanolic solution of 2,4,6-trinitrotoluene became liquid at 1 kg / l · h through the with catalyst 3 filled reactor passed. The reactor outlet temperature was 90 ° C. From the It was possible to obtain hydrogenation product 2,4,6-triaminobenzoI with a yield of 93 °.

Example 4

A mixture of 30 weight percent o-nitro toluene and 70 percent by weight of o-toluidine was dissolved in dei trickle phase with 1 kg / I · h over the catalyst 2 be 100 ⁰ C starting temperature hydrogenated. The reduction could be operated for 800 hours with the original catalyst activity. o-Toluidine was obtained in a 99.7% yield. Of the by-products, 60 ppm of nuclear hydrogenated products and 400 ppm of high condensation products were formed.

Comparable results are achieved if mar instead of o-NitrotoluoI or o-toluidine as Ein substitute material o-nitrophenol, 2-nitropropane, p-nitro diphenylamine or a 50% solution of o-nitro chlorobenzene in o-chloroaniline is used.

Example p

Nitrobenzene was passed over catalyst 1 at 0.3 to 0.4 kg / l · h in the gas phase. The molar ratio of hydrogen to nitrobenzene was 11: 1. The temperature of the filled Diphyl Küh mantels was 210 ⁰ C. The hydrogenation enthiel only aniline, neither nitrobenzene nor kernhydrierti substances were detected. After 800 operating hours, the catalyst was regenerated in situ using air and steam at 300 to 500 ^° C. The regenerated catalyst showed the original activity.

In the comparative experiment with catalyst 4, the temperature had to be increased to 300 to 350 ^° C. in order to reduce nitrobenzene to aniline under the same conditions. Nevertheless, the conversion was only 99%. 1.5% ring-hydrogenated compounds occurred. The catalyst activity decreased sharply after 50 hours of operation.

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Claims (2)

Patent claims: 1. Process for the reduction of nitro compounds in the liquid or in the gas phase in one Hydrogen atmosphere in the temperature range from 50 to 350 C in the presence of noble metal catalysts on carriers, characterized that one uses catalysts, the 0.1 to IO weight percent palladium and 0.1 to Contain 5.0 percent by weight of vanadium on aluminum oxide as a carrier, which is at least 20% has been converted into spinel. 2. The method according to claim 1, characterized in that catalysts are used as Spinel-forming metals contain cobalt, magnesium, lithium, nickel or zinc.