DE2244401A1 - Alumina supported catalyst - for nitrobenzene reduction contains needles of aluminium-lithium - Google Patents

Abstract

Supported Pd catalyst for nitrobenzene reduction contains 0.1-10 pref. 1-8 wt.% of Pd and 0.1-5 pref. 0.6% V or a cpd. of V on an alumina >=20% of which has been converted to needles of Li-Al of internal surface 20-120 m2/g and pore size 200-800A. Reduction temp. is 100-350 pref. 200-300 degrees C at 1-100 bars pref. 1-20 bars with at least stoichiometric H2 (ratio H2: nitrobenzene =22:1). The support is prepd. from alumina (200-350 m2/g) impregnated with lithium soln. The needles are formed by calcination at 900-1300 degrees C pref. 1,000-1,200 degrees C for 6 hr. This catalyst lasts >1,000 hrs. increasing after regeneration compared with 260-280 hrs. for nickel sulphide.

Description

Catalyst and use of the catalyst for the reduction of nitrobenzene The invention relates to a particularly effective palladium-containing supported catalyst along with metallic vanadium or vanadium compounds on Li-Al spinel as Support and the use of this new catalyst for the reduction of nitrobenzene to aniline, For the reduction of nitrobenzene to aniline, both procedures are in the liquid phase as well as the gas phase. When working in the liquid or the bottom phase, the catalyst is suspended (DBP 951 930). Working in however, the bottom phase requires the application of relatively high pressure; Furthermore makes the handling of the suspended catalyst, which is introduced and must be filtered off again after the reduction, Difficultalten. It was because of that proposed to carry out the reaction in the gas phase. The Practice working with nickel sulfide as a catalyst prevailed. (USP 2 716 135, USP 2,822,397, USP 2,875,158). However, it has been found that nickel sulfide As a catalyst it can be regenerated, but that with each regeneration a decrease the activity is connected. It was therefore tried to address this disadvantage to fix (DAS 1 176 620), according to the aforementioned DAS is the average running time of a Nickel sulfide catalyst 130 hours and falls from original 260-280 hours multiple regeneration after a period of 50-60 hours from @@@ em on the other hand, the catalyst of the present invention shows run times of over 1000 Hours, with the same even increasing after regeneration and after the first regeneration already be 1175 hours.

Another great advantage when using the catalytic converter The present invention for the reduction of nitrobenzene to aniline is the high purity of the aniline obtained.

DAS 1 176 620 shows that aniline has a purity of 99.7 % is obtained with a nitrobenzene content of less than 0.1% (column 4, lines 5-15). So by-products have arisen, which usually require expensive post-cleaning do. When reworking the procedure of DAS 1 176 620 it turned out that it These by-products are essentially phenol, which is known brings with it particular difficulties in terms of wastewater treatment. Furthermore are due to azeotrope formation with the aniline formed in the catalytic hydrogenation it still contains 200-500 ppm phenol even after the fine distillation. In contrast is used in the use of the catalyst of the invention and in the case of the invention A method to obtain an aniline which is free from detectable amounts of phenol.

The new catalyst and the one with it in the reduction of nitrobenzene Excellent results that can be achieved with aniline must be extremely surprising be considered.

If one tries namely conventional hydrogenation catalysts based on noble metals such as palladium on aluminum oxide, be it with him or with lower Surface ider for example palladium on lithium-aluminum spinels for to use the reduction of nitrobenzene, as from the comparative examples apparent, unsatisfactory results with regard to the life of the catalyst and The purity of the aniline formed must therefore be extremely surprising be considered that in the catalytic reduction of nitrobenzene in the presence from hydrogen in the gas phase at an elevated temperature receives pure aniline, if a palladium-containing supported catalyst is used, which 0.1-10 wt .-% Palladium and 091 - 5% by weight vanadium or

Vanadium compounds on an aluminum oxide, which at least 20% were converted into Li-Al spinel. The new catalyst contains palladium in an amount of 0.1-10% by weight, preferably 25-5% by weight, around vanadium or Vanadium compound in an amount of 0.1-5% by weight, preferably 0.3-1% by weight. Of the The catalyst support is preferably a lithium-aluminum spinel, but can Spinel formation may only be up to 20 ß.

The specific surface of the Li-Al spinel used lies in the range of 20-120 m2 / g (BET method: BRUNAUER, EMMETT and TELLER, J.Amer. Chem. Soc. 60 (1938/309); the pore size is about 200 - 800 Å. (including RITTER and DRAKE, Int. Closely. chem., Anal. Ed. 17 (1945) 72-86; BARRETT et al., J. Amer. chem. Soc. 73 (1551) 373-80).

Such Spi-rello is obtained in a known manner by conversion of Aluminum oxide with compounds of lithium. Appropriately, it is from spherical Alumina assumed to be carriers with high mechanical strength and optimal To maintain properties for the bulk bed in the fixed bed.

Of course, you can also use all other Al2O3 types go out. The spinel formation should at least Be 20%, preferably almost 100%. It is beneficial if you go to spinel production of highly active Al2O3 emanates, which has a specific surface area of 200 to 350m³ /. Al2O3 is in the usual way with a solution or suspension of a lithium compound soaked. If one soaks with salts, it is advisable to do so first before brewing the hydroxide or oxide produced by treatment with T, eye or heating. The spinel is then formed in the usual way by annealing at 900 b @@@ l 300 ° C. The level of the annealing temperature and the duration of the annealing are decisive Influence on the specific surface of the carrier. It is therefore preferred between and and 120,000 over a period of 6 hours. In any case, you have to the conditions are set so that the finished Li-Al spinel carrier a specific surface area from 20 to 120 m2 / g and a pore diameter from 200 to 800 #.

The new catalyst according to the invention is now prepared likewise by customary methods by applying or soaking with a solution a vanadium compound and by applying or soaking with a palladium salt solution. The amount of palladium and vanadium or vanadium compounds is calculated in such a way that that the finished catalyst 0.1 to 10 wt .-%, preferably 0.1 to 5 wt .-% palladium and 0.1-5% by weight, preferably 0.3-1% by weight vanadium or vanadium compound (calculated as vanadium).

The impregnation of the Li-Al spinel carrier material with the salt solutions the two metals can be carried out simultaneously but also one after the other. As vanadium compounds all common ones come into consideration, both the solutions of the oxides (preferred Vanadium pentoxide) as well as salts (preferably Chlorides), the vanadates (preferably alkali vanadates) or organic vanadyl compounds (preferably Oxalate, formate, acetate). Such vanadium compounds are used for convenience use that are not only easily accessible, but especially in water or organic Solvents (lower aliphatic alcohols, ketones, benzene hydrocarbons) are readily soluble. The vanadium compounds can be used before the impregnation with Pd compounds fix according to the usual methods, e.g. Precipitation. In the case of using an organic Vanadium compound can be used after impregnating the catalyst support with the organic Temper the vanadium compound to destroy the organic residue (heat to 200-500 ° C). The fixation can also be carried out by reduction, if appropriate together with the palladium salts can be achieved.

In principle, for the impregnation of the catalyst support with Pd all commercially available palladium compounds (preferably chlorides, palladium hydrochloric acid and their salts). The normally subsequent reduction of the palladium salt to the metal, for example, with formaldehyde or hydrazine in an alkaline solution or carried out with hydrogen or ethylene at elevated temperature (100-2000C) however, all other known reduction methods are also possible. In the event that chlorides are used in the manufacture of the new catalyst it is then washed chloride-free with water. Finally, the catalyst dried.

The new catalyst is especially suitable for the reduction of nitrobenzene to aniline, although other nitro compounds such as dinitrobun: zc1e or dinitrotoluene are also used can advantageously be hydrogenated with the catalyst according to the invention. For the Carrying out the process of the invention is the new catalyst in a fixed bed arranged and the reduction in the temperature range of 100 - 350 ° C, preferably 200-300 ° C and a pressure in the range of 1-100 bar, preferably 1-20 Bar done. The catalytic reduction can be diluted with circulating Aniline or other diluents e.g. steam or nitrogen will. The hydrogen is at least in the stoichiometrically required amount, but preferably used in excess and expediently in proportion of about 20: 1, in particular in the range of 10: 1 and can optionally be circulated be guided. The reaction is carried out in the gas phase, preferably in a tube reactor, In principle, all embodiments are for gas phase reactions such as shaft furnace, fluidized bed, etc. possible. The considerable heat of reaction will preferably used to generate steam, the cooling being carried out directly by evaporating Water or else can be carried out through a secondary circuit.

Provided that the activity of the catalyst after more than 1000 hours of operation decreases, this can be done in the same reactor without changing the catalyst by simply burning it off (approx. 200-fj000C) with air or oxygen, if necessary with the addition of under inert gases, e.g. nitrogen or steam, are regenerated under the reaction conditions will. This easy and complete regenerability of the catalyst of the invention in eitu is a very significant advantage over the prior art Technology used nickel sulfide catalysts. During their regeneration a part of the sulfur content is always converted into sulfur dioxide, which leads to signs of corrosion leads in the hydrogenation apparatus. This catalyst is depleted by the formation of sulfur dioxide when regenerating continuously with sulfur and thereby loses activity.

As already mentioned at the beginning, the new catalytic converter shows after regeneration not only the same, but even an increased lifespan with constant activity and selectivity.

The method of the invention is explained below by way of example: Molten nitrobenzene is converted into the gas phase in an evaporator in a hydrogen stream convicted. The molar ratio of hydrogen to nitrobenzene is approx. 10: 1.

This gas mixture flows through with a catalyst loading of 0.2 - 0.6kg / leh, preferably 0.4kg / l.h, the fixed catalyst in the reactor tube from bottom to top at pressures in the range of 1-2 bar. The reaction tubes can 30-60 mm clear width have and are in general in industrial reactors 4-6 m long. The temperature of the cooling jacket filled with diphenyl or pressurized water is approx. 250 ° C. The diphenyl or pressurized water is passed through a heat exchanger out, in which secondary steam by cooling the pressurized water with evaporating Condensate is generated. The reaction product is obtained from the gas stream leaving the reactor (Aniline and water of reaction) condensed through heat exchange with the feedstock. The remaining residual gas is circulated via a fan.

In the event of a decrease in catalyst activity, Rana the catalyst can easily be regenerated in eit u, for this the catalyst is like at approx. 3500C described in the examples, one after the other with steam, nitrogen / air, nitrogen and treated with hydrogen. The catalyst is full again after approx. 10-20 hours active.

The aniline obtainable by the process can be used, for example, as an intermediate find use for the production of dyes.

Examples a) Preparation of the catalysts Catalyst No. 1,396 g Amic acid was mixed with 233 g of 45% strength by weight aqueous lithium hydroxide solution and then mixed with enough water that a solution with a total volume of 1 liter results. 2.86 1 # spherical alumina 4-6 mm in diameter and a specific surface of approx. 250 m were soaked with the aforementioned solution. The impregnated aluminum oxide was dried again at 150 ° C. in a water jet vacuum soaked with 1 liter of the above-mentioned solution and again at 1500 C in a water jet vacuum dried. The carrier mass formed was then calcined for 6 hours at 10500C, whereby - as was determined by X-ray examination - more than 50 - 'ige spinel formation took place. The finished carrier material had a specific surface of 25 m2 / g and a mean pore size of 700 #.

4 liters of this carrier material (lithium aluminum spinel) were used with a solution of 33 g vanadium (V) oxide in 1200 ml of a hot (approx. 70-900C) aqueous 20 wt .-% oxalic acid solution impregnated. After drying in a rotary evaporator (70-1000C / water jet vacuum) the remaining mass with 1250 ml of a 150 g aqueous solution containing Na2PdC14. Then the aqueous Solution of 20% by weight sodium hydroxide and 20% by weight formaldehyde for about 5 hours treated. The remaining catalyst mass then became neutral with water and washed free of chloride and dried at 1500C (normal pressure). The finished catalyst showed, according to analysis, the content of 1.5 wt .-% palladium and 0.6 wt .-% vanadium.

Catalyst No. 2 (for comparison) The catalyst used in DAS 1 176 620 described Ni sulfide catalyst used.

Catalyst # 3 (for comparison) 4 liters of spherical # alumina with 4-6 mm diameter, a specific surface of approx. 300 m and medium Pore values of approx. 100 i were obtained with the solution of 150 g Na2PdCl4lil'2000 ml of water soaked (required amount of water and thus absorbency was determined by preliminary test determined in the usual way and accordingly measured the amount of water so that the total amount was added to palladium salt solution). Then the catalyst mass as described for catalyst no. 1, reduced with formaldehyde solution, washed and dried. The finished catalyst contained 1.8% by weight of palladium catalyst No. 4 (for comparison) 3 liters of extruded alpha; -aluminum oxide of approx. 5x5 mm, one specific surface of approx. 15 m³ / g and mean pore values of approx. 700 i were treated as in the preparation of Catalyst No. 3 so that ultimately a catalyst containing 1.8% by weight of palladium was obtained.

Catalyst No. 5 (for comparison) 4 liters of the one used in manufacture Lithium-aluminum spinels described by catalyst # 1 were prepared as in US Pat Preparation of catalyst no. 3 described, with a 150 g Na2PdC14 in 1200 ml of water-containing solution soaked and as described there with formaldehyde solution reduced, washed and dried, so that a catalyst with 1.8 wt .-% Palladium was obtained.

b) Description of the experimental apparatus and the way in which the experiment was carried out The molten nitrobenzene was in an evaporator in a hydrogen stream in the Gas phase transferred. The gas stream flowed through that in a fixed bed with almost no pressure arranged catalyst from bottom to top.

The pipe length was 2.30 m, the pipe diameter 40 mm, the catalyst filling 2 liters. The hydrogenation product was formed from the gas stream leaving the reactor at the top (Aniline and water of reaction) condensed.

The nitrobenzene was with a catalyst loading of 0.3 to 0.4 kg / lxh passed over the respective catalyst in the gas phase. The molaro The ratio of hydrogen to nitrobenzene was 11.1. The temperature of the with Diphenyl-filled cooling jacket observation 230-250 ° C, c) Description of the in situ Regeneration The deactivated catalyst was heated to 320 to 350 ° C in the same reactor heated up; to this end, the addition of hydrogen and nitrobenzene was interrupted and then in approx. 4-5 hours with oa. Treated 10 kg of steam, so that the content of nitrobenzene and aniline in the condensate was # 0.02 wt%.

This was followed by 400 liters of nitrogen and 100 liters of air / h at 350 ° C regenerated until no more CO2 was detectable in the exhaust gas. Finally, the Air flow shut off and cooled to 200 C with 400 liters of nitrogen / h; after a two hours of flushing with 200 l of hydrogen / h, the catalyst was ready for use again.

The regeneration of NiS catalyst # 2 was similar, only occurred here before the C02 development completely failed to produce S02 by roasting, which on the one hand reduced the activity and on the other hand. to Caused corrosion phenomena, d) Comparison of the results obtained The results when using the various catalysts are shown in the table below put together; Catalyst 1 and 1 a according to the invention catalyst 2,2a, 3,4, and 5 for comparison.

(a denotes the regenerated contact in each case) Catalyst running time up to # conversion # selectivity # by-products No. Deactivation (h) Nitrobenzene based on% % Aniline 1 Pd / V Li-Al-Spi- 1007 100 100 none nell 1a Pd / V, Li-Al-1175 100 100 none Spinel lx regenerated 2 for comparison 550 100 99.4 0.4% phenol NiS 0.2% benzene 2a for cf. 400 100 99.3 0.5% phenol NiS regenerates 0.2% benzene 3z. Comparison 220 99.1 98.1 0.2% phenol Pd on # -Al2O3 0.8% benzene 4 for comparison Pd on 190 99.8 99.7 0.1% phenol α-Al2O3 5 for comparison Pd on Li-Al-118 99.0 98.8 0.1% phenol Spinel 0.1% benzene

Claims (7)

Patent claims: 1. Palladium-containing supported catalyst for reduction of nitrobenzene, characterized in that this 0.1 to 10 wt .-% palladium and 0.1 to 5 wt .-% vanadium or Contains vanadium compound on an alumina, which at least 20% has been converted into lithium aluminum spinel. 2. Catalyst according to claim 1, characterized in that the used Lithium-aluminum spinels inner surfaces from 20 to 120 m2 / g and average pore size from 200 to 800 #. 3. Catalyst according to Claims 1 and 2, characterized in that this palladium in amounts of 0.05 to 5% by weight and vanadium or vanadium compound contains in an amount of 0.3 to 1 wt .-%. 4, catalyst according to claims 1 to 3, characterized in that this is palladium in an amount of 1.8% by weight and vanadium or vanadium compounds in an amount of 0.6% by weight on lithium-aluminum spinel with an inner surface of 25 m2 / g and an average pore size of 700 #. 5. Use of the catalyst according to Claims 1 to 4 for reduction of nitrobenzene with hydrogen at an elevated temperature, characterized in that one arranges the catalyst in the fixed bed and the reduction in the temperature range from 100 to 3500C and a pressure of 1 to 100 bar with at least the stoichiometric required amount of hydrogen. 6. The method according to claim 5, characterized in that at 200 to 3000 C and a pressure of 1 to 20 bar works, with the ratio of Hydrogen to nitrobenzene is up to 20: 1. 7. Process according to Claims 5 and 6, characterized in that one works at 230-250 ° C. and a pressure of 1-2 bar, with the ratio from hydrogen to nitrobenzene is approx. 11: 1.