HK1027556B - Production of aromatic amines by means of novel hydrogenation catalysts - Google Patents

Description

Process for preparing aromatic amines using novel hydrogenation catalysts

The invention relates to a method for producing aromatic amines by catalytic hydrogenation of the corresponding aromatic nitro compounds in the gas phase using novel palladium-containing supported catalysts.

Processes for hydrogenating nitrobenzene to the corresponding aromatic amines in the gas phase over palladium catalysts fixed on ceramic supports are known. Such a process for reducing nitro compounds in the presence of a palladium-containing multicomponent supported catalyst in a cooled tubular reactor is described in DE-A2849002. alpha-Al per liter₂O₃The catalyst essentially comprises 1 to 20g of palladium, 1 to 20g of vanadium and 1 to 20g of lead. The disadvantage of the gas-phase hydrogenation process described in the above-mentioned patent document is the low loading capacity (unit load) of the catalyst. The known load capacities are approximately 0.4-0.5kg/l x h. The loading capacity is defined as the amount of nitroaromatic compound (in kg) reacted per liter of catalyst bed in 1 hour. The low loading capacity of the catalyst makes the space-time yield for the large-scale production of aromatic amines unsatisfactory. Furthermore, the selectivity in the initial operating phase is significantly lower than in the end phase, which is whyResulting in a decrease in yield and causing troubles in handling of the crude product.

The object of the present invention is to provide a process for preparing aromatic amines by catalytic hydrogenation of the corresponding aromatic nitro compounds, which can be carried out smoothly on a large scale, with which high space-time yields are obtained and with which the selectivity for the desired amine compounds is greater than or equal to 90%, even in the early stages of production.

The present invention accordingly provides a process for preparing aromatic amines by catalytic hydrogenation of the corresponding aromatic nitro compounds in the gas phase, which is characterized in that: the hydrogenation reaction is carried out in the presence of a catalyst at 180-500 ℃ in a catalyst bed with a molar ratio of hydrogen to nitro groups of 3: 1 to 30: 1, the catalyst being supported at a BET surface area of less than 40m²A ceramic support material which, in addition to palladium, vanadium and lead, also contains rhenium.

Aromatic nitro compounds which can be hydrogenated by the process according to the invention are in particular those corresponding to the structure of the formula:wherein R is¹And R²May be the same or different and represents hydrogen or C₁-C₄And n represents 1 or 2.

The process of the present invention preferably hydrogenates nitrobenzene or isomeric nitrotoluenes.

In general, suitable ceramic support materials for the catalysts of the invention include BET surface areas of less than 40m²In g, preferably less than 20m²In g, in particular less than 10m²Per g of all ceramic solids. The following compounds are particularly suitable ceramic solids: metal oxides and/or mixed metal oxides of magnesium, aluminum, silicon, germanium, zirconium and titanium, preferably alpha-alumina, are used as support material.

Surprisingly, it has now been found that those on the above-mentioned support materials, in particular on alpha-oxidationShell catalysts on aluminum, which contain Re in addition to palladium, vanadium and lead, are particularly stable, high loading and high selectivity catalysts. We therefore focus on a support material comprising a) from 1 to 50g of palladium, b) from 1 to 50g of vanadium, c) from 1 to 20g of lead and d) from 1 to 20g of rhenium per litre of oxide support material and having a surface area of less than 40m²In g, preferably less than 20m²A specific preference for a molar mass of less than 10m²Per g of catalyst. Particularly preferably used in alpha-Al₂O₃The catalyst contains 10-50g Pd, 10-50g V g Pb, 8-16g Re and 8-16g Re.

In general, methods for the preparation of noble metal supported catalysts are known. The invention has proven to be advantageous if the active components of the catalyst are deposited as closely as possible in the respective different layers on the support surface and the interior of the support material does not contain any metal. The support material may be prepared without pretreatment or with alkali. The support material is preferably pre-impregnated with a solution of an alkali or alkaline earth metal hydroxide prior to impregnation.

The metals may be supported on the support either individually or as a mixture of their salt solutions. Suitable salts are, for example, halides, acetates, carbonates, bicarbonates, sulfates, phosphates, oxalates, formates, oxides and hydroxides. After the respective impregnation and/or at the end of the above-described process, a reduction reaction is carried out using hydrogen, hydrazine and/or formic acid.

In general, the supported catalyst of the present invention may be in any shape, for example, spherical, rod-like, Raschig ring, granular or pellet-like. Catalyst shapes which form catalyst beds with low resistance to fluid flow and good gas-surface contact are preferably used, for example Raschig rings, saddles, castellations and/or spirals. The catalyst of the invention can be used neat or diluted with other inert filler materials, such as materials made of glass, ceramic or metal. The catalyst bed may consist of up to 90% by weight, preferably up to 75% by weight, particularly preferably up to 50% by weight, of inert packing or support material. In this connection, the catalyst bed can have a dilution gradient, the dilution decreasing in the flow direction. At the upstream surface, the catalyst bed may contain 50-90 wt% packing material, while at the discharge end, the catalyst bed may consist of 80-100 wt% pure supported catalyst.

In the process of the invention, the supported catalyst is used in an amount of 40 to 80%, preferably 50 to 70%, based on the total volume of the bed.

In the process of the present invention, the molar ratio of hydrogen to nitro compound (nitro group) is from 4: 1 to 20: 1, preferably from 5: 1 to 10: 1. In the present invention, the hydrogen concentration can be reduced by mixing an inert gas such as nitrogen, helium, argon and/or water vapor. The inert gas to be mixed is preferably nitrogen. An inert gas may be mixed in an amount of at most 10mol, preferably at most 3mol, particularly preferably at most 1mol, per mol of hydrogen.

Dilution with an inert carrier gas is preferably carried out at the beginning of the production using fresh catalyst, and then the catalyst is regenerated by burning out with air and reducing with hydrogen. The dilution with the inert gas is preferably carried out within the first 300 hours, more preferably within the first 200 hours, particularly preferably within the first 100 hours after the restart.

The deactivated catalyst bed is regenerated on the actual catalyst using a nitrogen/oxygen mixed gas at 200-400 deg.C, preferably at 250-350 deg.C. The process consists of₂A gas flow with a content of 90-99% is started and, during the burn-out, the oxygen content is gradually increased to the oxygen concentration in pure air. At the end of regeneration, the remaining carbides can be burned off with pure oxygen, if desired. Other inert carrier gases, such as helium, argon and/or water vapor, may also be used in place of nitrogen for incorporation into oxygen or air. The process of the invention is preferably carried out at temperatures of 200 ℃ and 460 ℃ and particularly preferably at temperatures of 220 ℃ and 440 ℃. It may be advantageous to continuously or gradually increase the temperature of the cooling medium in the process of the invention during the operating cycle.

In the process according to the invention, the hydrogen pressure is from 0.5 to 5 bar, preferably from 1 to 3 bar.

The loading capacity of the catalyst according to the invention on the aromatic nitro compound fed in must be increased continuously or stepwise from 0.01kg/l to 0.2kg/l to 0.5kg/l to 5.0kg/l, the maximum loading capacity being reached within 10 to 1000 hours.

For the catalyst of the invention, it is particularly advantageous for the loading capacity of the catalyst for the added aromatic nitro compound to be increased continuously or stepwise over a certain period of time to the desired loading capacity. Thus, it is preferred to increase the loading capacity of the catalyst continuously or stepwise from 0.01 kg/l.times.h to 0.5 kg/l.times.h, preferably from 0.1 kg/l.times.h to 0.4 kg/l.times.h, more preferably from 0.15 kg/l.times.h to 0.3 kg/l.times.h to 0.6 kg/l.times.h to 5.0 kg/l.times.h, preferably to 0.6 kg/l.times.h to 3.0 kg/l.times.h, most preferably to 0.6 kg/l.times.h to 2.0 kg/l.times.h, preferably within the first 500 hours, more preferably within the first 300 hours, most preferably within the first 200 hours.

The final high loading capacity is kept constant until unreacted educts appear. If the concentration of educt at the end of the reactor is too high, the temperature of the heating medium can be increased and/or the loading capacity of the catalyst for educts can be reduced in order to delay the interruption of the production for the regeneration of the catalyst.

The method of the present invention using a catalyst can be industrially carried out, for example, in the following manner. A recycle gas stream consisting essentially of hydrogen and a small amount of water is compressed to overcome the resistance to fluid flow in the apparatus. The gas stream is heated by counter-current heat exchange. Heat is removed from, for example, the recycle gas stream before the product condenses. The circulating gas stream is brought to the desired temperature. In the fresh hydrogen instead of the used hydrogen, the nitroaromatics subjected to the hydrogenation are vaporized and superheated, and the two gas streams are then mixed. The gas mixture is fed to a thermostatic reactor containing a fixed bed catalyst. The exothermic heat of reaction is removed from the reactor by a heat transfer medium. The product stream leaving the reactor is used to heat the recycle gas stream and is cooled to a temperature at which the aniline and water formed are condensed. The liquid and a small amount of recycle gas are removed to remove gases, such as nitrogen, which would otherwise accumulate. The recycle gas is then returned to the compressor.

In a preferred embodiment, the catalyst of the invention is introduced in the form of a bed into a linde-type (heat transfer medium flows through the interior of the reactor tubes, the catalyst is installed outside the reactor tubes with the heat transfer medium) reactor and the process of the invention is carried out as described above. Within the first few hours, fresh or freshly regenerated catalyst is activated with a nitrogen-hydrogen gas mixture. The advantage of this preferred mode of operation is that the catalyst has a high selectivity and the time between catalyst regenerations is long, even after multiple production cycles.

The reactor used in the process of the invention may be any known reactor using a cooled fixed catalyst bed and suitable for gas phase reactions. Suitable reactors include, for example, multitubular reactors in which the catalyst is located within a tube surrounded by a heat transfer medium and reactors in which the heat transfer medium flows counter-currently within the tube and the catalyst is located outside the tube. Reactors of this type are known, for example, from DE-A2848014 and 3007202.

Reactors in which the heat transfer medium flows through the tubes and the catalyst is located outside the tubes carrying the heat transfer medium (linde-type reactors) have proven to be particularly advantageous for the process of the invention. In these reactors, a fixed run time can be detected between catalyst regenerations during multiple regeneration cycles, in contrast to typical multitubular reactors.

In the process of the invention, the length of the catalyst bed in the direction of flow is from 0.5 to 20m, preferably from 1 to 10m, particularly preferably from 2 to 6 m.

The length of the bed can also optionally be achieved by connecting several reactors in series.

The invention also provides a hydrogenation catalyst supported on a BET surface area of less than 40m²A ceramic support which, in addition to palladium, vanadium and lead, contains rhenium, wherein the palladium content is from 1 to 50g, the vanadium content is from 1 to 50g and the lead content is from 1 to 50g per liter of ceramic support material1-20g and the total amount of rhenium is 1-20 g.

Suitable support materials are, in particular, the support materials mentioned above, in particular alpha-Al₂O₃。

The process of the present invention using the new catalyst is advantageous because of the high space time rate of the process and the reduced scale of equipment required and the significantly increased catalyst productivity. Thus, a significant increase in throughput can be achieved using existing equipment. Moreover, the process of the present invention is particularly advantageous because it has a particularly high selectivity towards hydrogenation products.

Examples Preparation of the catalyst Example 1 (comparative example)

1 liter of spherical alpha-Al is impregnated with 366ml of an aqueous solution containing 10.8g (equivalent to 0.27 gram equivalent) of sodium hydroxide₂O₃A support having a diameter of 3 to 5mm and a BET surface area of 9.8m²The absorption capacity per 100g of carrier can absorb 45.1ml of water and the bulk density is 812 g/l. The carrier can completely absorb the solution within a few minutes.

The wet carrier is dried in a hot, vigorous upward air stream. The time required to dry the support to constant weight was about 15 minutes. The residual moisture content after cooling was about 1% of the absorption capacity of the carrier.

The dried support pretreated as described above was impregnated with 366ml of an aqueous solution of palladium sodium tetrachloride containing 9g of palladium (equivalent to 0.169 gram equivalent) until the absorption capacity of the support was approached and left for 15 minutes. To reduce the palladium compound deposited on the support to metallic palladium, the support was covered with 400ml of 10% aqueous hydrazine hydrate solution and left to stand for 2 hours. The catalyst is then rinsed thoroughly with deionized water until no ions of the compound used to prepare the catalyst are detected in the rinsed water. This state is reached after about 10 hours.

The product was then dried to constant weight in a hot, vigorous ascending air stream.

The Pd-containing catalyst was then impregnated with 366ml of an aqueous solution of vanadium oxalate containing 9g of vanadium. As mentioned above, the carrier is dried in a hot air stream. The catalyst was then heat treated in a tube furnace at 300 c for 6 hours, during which the oxalate decomposed.

The catalyst was then impregnated with 366ml of an aqueous solution of lead acetate containing 3g of lead and dried in an ascending stream of air.

The catalyst prepared above contained 9g of palladium, 9g of vanadium and 3g of lead and was identical to the catalyst of DE-OS 2849002 in example 1.Example 2

1 liter of spherical alpha-Al is impregnated with 367ml of an aqueous solution containing 48g (equivalent to 1.2 gram equivalents) of sodium hydroxide₂O₃A support having a diameter of 3 to 5mm and a BET surface area of 9.8m²The absorption capacity is 45.1ml of water per 100g of carrier and the bulk density is 831 g/l. The carrier can completely absorb the solution within a few minutes.

The wet carrier is dried in a hot, vigorous upward air stream. The time required to dry the support to constant weight was about 15 minutes. The residual moisture content after cooling was about 1% of the absorption capacity of the carrier.

The dried support pretreated as described above was impregnated with 352ml of an aqueous solution of palladium sodium tetrachloride containing 40g of palladium (equivalent to 0.751 g eq.) until the absorption capacity of the support was approached and left for 24 hours. To reduce the palladium compound deposited on the support to metallic palladium, the support was covered with 400ml of 10% aqueous hydrazine hydrate solution and left to stand for 2 hours. The catalyst is then rinsed thoroughly with deionized water until no ions of the compound used to prepare the catalyst are detected in the rinsed water. This state is reached after about 10 hours.

The product was then dried to constant weight in a hot, vigorous ascending air stream.

The Pd-containing catalyst was then impregnated with 365ml of an aqueous solution of vanadium oxalate containing 40g of vanadium. As mentioned above, the carrier is dried in a hot air stream. The catalyst was then heat treated in a tube furnace at 300 c for 4 hours, during which the oxalate decomposed.

Then 365ml Re containing 14g of lead acetate and 14g of rhenium₂O₇Is impregnated with the catalyst and dried in an upward air stream.

The catalyst prepared above contained 40g of palladium, 40g of vanadium, 14g of lead and 14g of rhenium per liter of support. The catalyst was mixed homogeneously with 1 liter of untreated support material.Examples of hydrogenation of Nitrobenzene Example 3 (comparative example)

The catalyst bed (height 285cm) prepared in example 1 was placed in a reaction tube having an inner diameter of about 26mm, and the reaction tube was thermostatically controlled with oil. The catalyst was flushed with nitrogen and then hydrogen, and subsequently heated to 240 ℃ for 5 hours in a stream of hydrogen of about 1,528 NL/h. Nitrobenzene in the hydrogen stream then begins to vaporize. The nitrobenzene-hydrogen mixture reaches the surface of the catalyst bed at a temperature of about 230 c. The specific load of the catalyst increased from 0.2 kg/l.times.h to 1.05 kg/l.times.h within 80 hours, corresponding to a load per unit area of 2,994kg/m²Xh, i.e. an average load of 1.03kg/l Xh. It is important to ensure that the temperature at any point on the catalyst does not exceed 440 c throughout the process.

After approximately 700, 800 and 900 hours, the oil temperature rose from 240 ℃ to 300 ℃ in the amplitude of 20 ℃. The oil temperature along the reaction tube varied by about + -1 deg.C. The flow velocity of the oil at the surface of the tube was about 1.5 m/s.

The service life of the catalyst was about 1,050 hours, after which the nitrobenzene content in the condensate increased from 0 to about 300ppm, so that the catalyst had to be regenerated by burning off.

The average selectivity was 99.0%.

After the catalyst was regenerated, the performance of the catalyst was unchanged in the second run cycle, its lifetime was 990 hours and selectivity was 99.2%.Example 4

Mixing all the materialsThe catalyst bed prepared and diluted in example 2 (height 285cm) was placed in a reaction tube having an inner diameter of about 26mm, and the reaction tube was thermostatically controlled with oil. The catalyst was flushed with nitrogen and then hydrogen, and subsequently heated to 240 ℃ for 5 hours in a stream of hydrogen of about 1,528 NL/h. Nitrobenzene in the hydrogen stream then begins to vaporize. The nitrobenzene-hydrogen mixture reaches the surface of the catalyst bed at a temperature of about 230 c. The specific load of the catalyst increased from 0.2 kg/l.times.h to 1.07 kg/l.times.h in 50 hours, corresponding to a load per unit area of 3,051kg/m²Xh, i.e. an average load of 1.03kg/l Xh. It is important to ensure that the temperature at any point on the catalyst does not exceed 440 c throughout the process.

After about 266, 270, 293, 314, 317 and 362 hours, the oil temperature rose from 240 ℃ to 300 ℃ at a magnitude of 10 ℃. The oil temperature along the reaction tube varied by about + -1 deg.C. The flow velocity of the oil at the surface of the tube was about 1.5 m/s.

The service life of the catalyst was about 394 hours, after which the nitrobenzene content in the condensate increased from 0 to about 300ppm, with the result that the catalyst had to be regenerated by burning off.

The average selectivity was 99.78%.

After the catalyst is regenerated, the performance of the catalyst is unchanged in the second operation cycle, the service life of the catalyst is 876 hours, and the selectivity is 99.7%. The service life of the catalyst is significantly increased. This significant increase in service life was still sustained in the third and fourth cycles, 898 and 997 hours, respectively.

To further improve the good initial selectivity, N was used during the first 220 hours in the fourth cycle₂/H₂The mixture (see table 1).

TABLE 1 initial selectivity for nitrobenzene hydrogenation

Gas (es)	H2/N2	H2	H2
				Test catalyst	Example 4 a fourth run of example 2	Example 4 first run example 2	Example 3 first run example 1
Average selective service life	99.7％997h	99.7％394h	99.0％1052h
				Run time h	Load selectivity kg/l × h%	Load selectivity kg/l × h%	Load selectivity kg/l × h%
3.524487294	0.31 98.00.50 98.50.60 98.40.65 98.90.74 99.2	0.24 90.40.53 97.40.71 99.20.98 99.61.00 99.8	0.27 43.50.50 67.30.80 83.01.10 93.91.10 97.5

Ortho-nitrotolueneHydrogenation example (2) Example 5 (comparative example)

The catalyst bed prepared in example 1 (height 285cm) was placed in a reactor tube having an internal diameter of about 33mm and thermostatically controlled with oil. The catalyst was flushed with nitrogen and then hydrogen, and subsequently heated to 270 ℃ for 5 hours in a hydrogen stream of about 1,560 NL/h. The o-nitrotoluene in the hydrogen stream then begins to vaporize. The o-nitrotoluene-hydrogen mixture reaches the surface of the catalyst bed at a temperature of about 260 c. The specific load of the catalyst increased from 0.2 kg/l.times.h to 0.62 kg/l.times.h in 47 hours, corresponding to a load per unit area of 1,097kg/m²Xh, i.e. an average load of 0.58kg/l Xh. It is important to ensure that the temperature at any point on the catalyst does not exceed 440 c throughout the process.

The oil temperature along the reaction tube varied by about + -1 deg.C. The flow velocity of the oil along the surface of the tube was about 1.5 m/s.

The service life of the catalyst was about 216 hours, after which the ortho-nitrotoluene content in the condensate increased from 0 to about 300ppm, with the result that the catalyst had to be regenerated by burnout. The catalyst productivity is greater than about 125kg/l under the given boundary conditions.

The average selectivity was 99.85%.

After the catalyst was regenerated, the performance of the catalyst was nearly unchanged in the second cycle, with a lifetime of 198 hours and a selectivity of 99.85%.Example 6

The catalyst bed prepared in example 2 (height 285cm) was placed in a reactor tube having an internal diameter of about 33mm and thermostatically controlled with oil. The catalyst was flushed with nitrogen and then hydrogen, and subsequently heated to 270 ℃ for 5 hours in a hydrogen stream of about 1,560 NL/h. The o-nitrotoluene in the hydrogen stream then begins to vaporize. The o-nitrotoluene-hydrogen mixture reaches the surface of the catalyst bed at a temperature of about 260 c. The specific load of the catalyst increased from 0.13 kg/l.times.h to 0.689 kg/l.times.h within 50 hours, corresponding to a load per unit area of 1,219kg/m²xh, i.e. an average load of 0.644kg/l Xh. It is important to ensure that the temperature at any point on the catalyst does not exceed 440 c throughout the process.

The oil temperature along the reaction tube varied by about + -1 deg.C. The flow velocity of the oil along the surface of the tube was about 1.5 m/s.

The service life of the catalyst was about 239 hours, after which the ortho-nitrotoluene content in the condensate increased from 0 to about 300ppm, with the result that the catalyst had to be regenerated by burnout. The yield of the given catalyst is greater than about 154kg/l under the given boundary conditions.

The average selectivity was 99.82%.

After the catalyst is regenerated, the service life of the catalyst in the second circulation is 439 hours, and the selectivity is 99.87%; the service life of the catalyst is significantly increased. After the eleventh regeneration, the catalyst had a lifetime of 525 hours and an average selectivity of 99.9% in the twelfth cycle.

During the course of the study, the catalysts of the invention have a satisfactory service life and a high loading capacity after a number of regenerations.

Claims (3)

1. A process for the production of aromatic amines from aromatic nitro compounds of the formula,wherein R is¹And R²May be the same or different and represents hydrogen or C₁-C₄And N represents 1 or 2,

characterized in that the hydrogenation is carried out in a catalyst bed at a temperature of 180-500 ℃ in the presence of a catalyst in a molar ratio of hydrogen to nitro groups of 3: 1 to 30: 1, the catalyst being supported by BETSurface area less than 40m²A ceramic support which, in addition to palladium, vanadium and lead, contains rhenium.

2. The process of claim 1 wherein the aromatic nitro compound is nitrobenzene or ortho-nitrotoluene and the ceramic support is α -Al₂O₃。

3. A hydrogenation catalyst, which is loaded on a BET surface area of less than 40m²A/g ceramic support which, in addition to palladium, vanadium and lead, also contains rhenium and in which the palladium content per liter of ceramic support material is from 1 to 50g, the vanadium content is from 1 to 50g, the lead content is from 1 to 20g and the total content of rhenium is from 1 to 20 g.