Method for reactivating a noble metal-iron catalyst and carrying out a chemical reaction

Abstract

The catalytic activity of a spent precious metal-iron catalyst is restored by combining the spent catalyst with an iron(III) compound. This can be done by adding the iron(III) compound to a chemical reaction involving the spent precious metal-iron catalyst. No additional precious metal addition is required. This process is particularly useful in a continuous process for converting nitro compounds, such as nitrobenzene, to the corresponding amines.

Description

[Technical Field]

[0001] The present invention relates to a method for reactivating a precious metal-iron catalyst and to chemical reactions that use a precious metal-iron catalyst.

[0002] Noble metal catalysts are used industrially in a wide variety of chemical manufacturing processes, including the hydrogenation of organic nitro compounds such as nitrobenzene to the corresponding amines, the hydrogenation of organic aldehydes to the corresponding alcohols, the production of hydrogen peroxide via the anthraquinone process, and many others.

[0003] Noble metal catalysts may contain iron, which in some cases enhances catalytic performance. See, for example, U.S. Pat. No. 2,823,235; Underhill et al., JohnsonMathey Technol.Rev., 2018, 62, (4) 417; Chin et al., Applied Catalyst A: General 302(1) 2006 22-31; Kuroki et al., ACS Appl. Energy Mater. 2018, 1, 2, 324-330; and He et al., J. Hazardous Materials, 164(1), 2009, 126-132.

[0004] These catalysts tend to deactivate over time, which leads to a slowdown in reaction rate, especially in continuous processes, necessitating periodic catalyst replacement, which involves significant costs.

[0005] An alternative to catalyst replacement is catalyst reactivation. Various methods for achieving this have been mentioned. U.S. Pat. No. 3,959,382 describes a process in which a palladium hydrogenation catalyst is reactivated by treatment with alkali or alkaline earth metal compounds in a liquid medium. The process described in U.S. Pat. No. 4,999,326 involves contacting the deactivated catalyst with a polar solvent for naphthalene compounds. U.S. Pat. No. 5,143,872 and European Patent No. 1,853,292 describe contacting a spent catalyst with an aqueous alkaline solution. These methods have little or no effect when applied to precious metal-iron catalysts. Taninouchi et al., Metallurgical and Materials Transaction B49(4)2918 1781-1793, describes a method for recovering platinum group metals from spent automotive catalytic converters by treatment with FeCl vapor at a temperature of approximately 927°C. This forms an iron-precious metal alloy that can be recovered using magnetic means.

[0006] In one aspect, the present invention is a method for reactivating a spent precious metal-iron catalyst, the method comprising combining the spent precious metal-iron catalyst with an iron(III) compound while adding to the spent precious metal-iron catalyst up to 10 wt. % of the precious metal, based on the weight of iron in the added iron(III) compound.

[0007] Applicants have unexpectedly found that the activity of a spent precious metal-iron catalyst can be at least partially restored by combining it with an iron(III) compound. The iron(III) compound is not an additional amount of the precious metal-iron catalyst. In contrast, in this method, the addition of the iron compound alone is sufficient to restore catalytic activity, with little or no precious metal being combined with the spent catalyst. However, this process does not require the addition of more precious metal, whether in the form of the starting precious metal-iron catalyst or any other form.

[0008] Another unexpected advantage is that no special processing steps are required to obtain the desired increase in catalytic activity. Simply forming a physical mixture of the spent precious metal catalyst and the iron(III) compound is sufficient. Thus, the iron(III) compound in some embodiments can be added directly to a chemical manufacturing operation in which spent precious metal-iron catalyst is present, without the need to separately process the spent catalyst or to modify process conditions in any way (other than the addition of the iron(III) compound) to obtain the increased catalytic activity.

[0009] Accordingly, in a second aspect, the present invention provides a catalytic process for producing one or more chemical products, comprising: a) carrying out a chemical reaction by subjecting one or more starting compounds to reaction conditions in the presence of a noble metal-iron catalyst wherein the one or more starting compounds react to form one or more chemical products, wherein the reaction is continued for a time such that the noble metal-iron catalyst is at least partially spent; b) then adding an iron(III) compound to the reaction vessel one or more times while adding up to 10 wt. % of a noble metal based on the weight of iron in the added iron(III) compound, and thereafter continuing to carry out the chemical reaction in the presence of the at least partially spent noble metal-iron catalyst and the added iron(III) compound.

[0010] The present invention has particular significance for continuously operated hydrogenation processes for producing aromatic amines. In a third aspect, the present invention provides such a process, comprising: a) carrying out a continuous reduction reaction in the presence of a noble metal-iron catalyst by continuously or intermittently introducing a starting nitroaromatic compound and hydrogen into a reaction vessel and continuously or intermittently removing from the reaction vessel water and aromatic amines produced by the reaction of the starting nitroaromatic compound and hydrogen, wherein the reduction reaction is continued for a time such that the noble metal-iron catalyst is at least partially spent; b) thereafter, adding an iron(III) compound to the reaction vessel one or more times while adding up to 10 wt. % of the noble metal based on the weight of iron in the added iron(III) compound, and thereafter continuing to carry out the continuous reduction reaction in the presence of the at least partially spent noble metal-iron catalyst and the iron(III) compound.

[0011] A noble metal-iron catalyst is a composition containing at least one noble metal and iron. By "noble metal" is meant gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Of these, palladium and / or platinum are preferred.

[0012] The noble metal and iron in the catalyst may be present in metallic form as an alloy with one another, or in the form of a salt, oxide, or other compound. The noble metal and iron may be deposited together on a support. Such a support may be a fixed-bed support or a particulate support. The support may be any material that is inert under the conditions of the reaction. Examples of useful support materials include zeolites, molecular sieves, titanium dioxide, alumina, silica, other metal oxides and / or nitrides, and various forms of carbon, including carbon black, activated carbon (including activated charcoal and activated coke), graphite, charcoal, etc. Activated carbon has a surface area of ​​at least 3000 m as measured by gas adsorption. 2 / g porosity.

[0013] A virgin supported catalyst may contain, for example, 1-25 wt. % precious metal and 1-25 wt. % iron on a dry basis, based on the total weight of the supported catalyst. In some embodiments, the weights of the precious metal and iron each constitute at least 2%, at least 3%, or at least 4% of the total dry weight of the virgin supported catalyst, and up to 20%, up to 15%, up to 10%, or up to 7.5% of that weight. "Virgin" catalyst means one that has not been used previously.

[0014] In a particular embodiment, the catalyst is a carbon-supported palladium-iron or palladium-platinum-iron catalyst which, when fresh, contains 2 to 10%, in particular 3 to 7.5% by weight of palladium and / or platinum and a similar amount of iron, in each case based on the total dry weight of the fresh supported catalyst.

[0015] Methods for preparing noble metal-iron catalysts are described, for example, in U.S. Pat. No. 2,823,235; Berry et al., Applied Catalysis A: General 204(2) 2000 191-201; Underhill et al., JohnsonMathey Technol.Rev., 2018, 62, (4) 417; He et al., J. Hazardous Materials, 164(1), 2009, 126-132; Chin et al., Applied Catalyst A: General 302(1) 2006 22-31; and Kuroki et al., ACS Appl. Energy Mater. 2018, 1, 2, 324-330. Catalysts prepared according to any of these methods are suitable for use in the present invention.

[0016] Noble metal-iron catalysts are used to carry out chemical reactions. In a chemical reaction, one or more starting compounds are subjected to reaction conditions, including the presence of a catalyst, where the one or more starting compounds react to form one or more chemical products.

[0017] The chemical reaction can be, for example, an oxidation reaction such as the oxidation of phenol to form hydrogen peroxide or the oxidation of carbon monoxide, a dechlorination or dehydrochlorination reaction, a hydrodeoxygenation reaction, a reduction reaction, a hydrogenation reaction, or any other reaction in which a noble metal-iron catalyst is useful.

[0018] In some embodiments, the chemical reaction is the reduction (hydrogenation) of a nitro compound to the corresponding amine. The nitro compound can be a nitroaromatic compound in which one or more nitro groups are attached directly to a carbon atom of an aromatic ring. In certain embodiments, the nitro compound is nitrobenzene and the resulting amine is aniline.

[0019] A chemical reaction is carried out in the presence of a noble metal-iron catalyst for a time such that the noble metal-iron catalyst becomes at least partially spent. A catalyst is considered to be at least partially spent at the time, during, or after its use in a chemical reaction, and the catalyst exhibits a decrease in activity as indicated by a resulting decrease in the rate of the chemical reaction in the presence of the noble metal-iron catalyst itself (i.e., without added iron(III) compound). The decrease in activity can be measured in situ by periodically measuring the reaction rate or by recovering all or a portion of the catalyst and measuring its activity according to a suitable test.

[0020] Applicant has discovered that metals, particularly iron, in a catalyst can become depleted during use. Thus, the metal content, particularly iron content, of a catalyst changes during use from that of an unused catalyst. The change in metal content, particularly iron depletion, is believed to at least partially cause a decrease in catalytic activity and a resulting decrease in reaction rate. Thus, a catalyst is considered to be at least partially spent when it has lost all or a portion of its starting iron content (i.e., its iron content before use).

[0021] In the present invention, iron is replenished at least in part by combining a spent precious metal-iron catalyst with an iron(III) compound. This is done while adding 10 wt.% or less of the precious metal, based on the weight of iron in the added iron(III) compound, to the spent precious metal-iron catalyst. Preferably, any precious metal added during this combining step is added at a maximum impurity level in the iron(III) compound, e.g., 500 wt. ppm or less, 100 wt. ppm or less, or 10 wt. ppm or less, based on the weight of iron. In some embodiments, the precious metal is not added with the iron(III) compound, and thus the entire amount of the combined precious metal is provided by the spent precious metal-iron compound.

[0022] The additional precious metal, if added at all, may be added in the form of virgin precious metal-iron catalyst.

[0023] The iron(III) compound can be, for example, an iron(III) halide such as iron(III) fluoride, iron(III) chloride, or iron(III) bromide; iron(III) nitrate, iron(III) phosphate; iron(III) pyrophosphate, iron oxide (FeO); iron(III) basic carbonate, iron(III) carbonate, ferric hydroxide, iron(III) alkoxide; iron(III) aryloxide such as iron phenoxide; iron(III) carboxylate; iron(III) salicylate, iron(III) 3,5-di-t-butyl salicylate; iron(III) acetylacetonate; and iron(III) t-butyl acetylacetonate. Inorganic iron(III) compounds are preferred in some cases to avoid introducing foreign organic species into the reaction.

[0024] In some embodiments, the iron(III) compound may be solid under the conditions of the chemical reaction in which it is used, insoluble in the reaction mixture, and unreactive in the reaction mixture except for its catalytic activity. The solid and / or supported iron(III) compound may be in the physical form of, for example, a catalyst bed or particles. In particulate form, the solid and / or supported iron(III) compound (including the support, if present) may have a longest dimension of 10 nm to 10 mm or 25 nm to 100 μm.

[0025] The iron(III) compound may be supported on a support such as those described above for the noble metal-iron catalyst.

[0026] Particularly suitable iron(III) compounds for reduction and / or hydrogenation reactions, such as the reduction of organic nitro compounds to the corresponding amines (especially the hydrogenation of nitroaromatic compounds such as nitrobenzene to aromatic amines such as aniline), are ferric hydroxide or iron oxide, which may be supported on an inorganic support as described above, in particular a carbon support (such as an activated carbon support).

[0027] The spent noble metal-iron catalyst and iron(III) compound can be combined by simply mixing the materials to form a physical mixture. Generally, it is not necessary to process the physical mixture in any particular manner, such as to promote or cause a chemical reaction, fuse, alloy, or combine the starting materials. The physical mixture is often found to be catalytically active, just like unused noble metal-iron catalyst.

[0028] The mixing can be carried out, for example, by recovering all or a portion of an at least partially spent noble metal-iron catalyst from a chemical reaction and combining the recovered noble metal-iron catalyst with an iron(III) compound to form a physical mixture. The resulting physical mixture can be reintroduced into the chemical reaction of interest. By "recovering" it is meant that the catalyst is at least partially separated from the reactants of the chemical reaction. This can be done, for example, by removing the spent catalyst from the reaction vessel, by removing the reactants from the reaction vessel and leaving the spent catalyst in the reaction vessel, or by withdrawing a recycle stream containing all or a portion of the catalyst from the reaction vessel. Recycling spent catalyst, for example, by forming a mixture of an iron(III) compound with the spent catalyst recovered from the reaction vessel and reintroducing the resulting mixture into the reaction vessel, is not considered to be adding a noble metal for purposes of the present invention.

[0029] An unexpected advantage of the present invention is that the spent catalyst does not need to be recovered from the chemical reaction. As the chemical reaction proceeds, it can be combined with the iron(III) compound in the presence of the reactants to form a mixture of the spent catalyst and the iron(III) compound in situ. In such an embodiment, the iron(III) compound can simply be introduced into the reaction vessel as the reaction proceeds in the presence of the spent catalyst, and the chemical reaction is then carried out in the presence of both the spent catalyst and the iron(III) compound.

[0030] Generally, when the starting noble metal-iron catalyst becomes at least partially spent, a mixture of the at least partially spent noble metal-iron catalyst and iron(III) compounds is introduced into a chemical reaction. The decline in catalytic activity and the resulting decline in reaction rate can be monitored as needed using any suitable analytical method appropriate for the particular chemical reaction. For example, the conversion of one or more of the starting materials can be determined, with lower conversion indicating a loss of catalytic activity and a decline in reaction rate. Similarly, the consumption rate of one or more of the starting materials can be measured, with a drop in the consumption rate also indicating a decline in catalytic activity and reaction rate. The concentration and / or production rate of one or more products of the chemical reaction can be measured as an indication of a decline in catalytic activity and reaction rate. If desired, a sample of the noble metal-iron catalyst can be withdrawn from the chemical reaction and analyzed for iron content or evaluated for its catalytic activity.

[0031] Instead of, or in addition to, monitoring the chemical reaction, a general rate of decline in catalytic activity may be established empirically for any particular chemical reaction under a particular set of operating conditions. The empirical data is then used to estimate one or more times when catalytic activity and reaction rate decline such that an iron(III) compound should be provided to the reaction vessel. The experimental data can be used in this manner to establish a schedule for providing an iron(III) compound to the reaction. In such cases, the iron(III) compound can be added intermittently or continuously to maintain the desired catalytic activity and reaction rate.

[0032] The chemical reaction is then continued in the presence of both the spent noble metal-iron catalyst and the iron(III) compound.

[0033] The present invention is useful in continuous processes. In such continuous processes, one or more starting materials are continuously or intermittently introduced into a reaction vessel in the presence of a noble metal-iron catalyst, and one or more reaction products are continuously or intermittently removed from the reaction vessel. An iron(III) compound is continuously or intermittently added to the reaction vessel during continuous operation as the noble metal-iron catalyst becomes partially or completely spent, thereby increasing catalytic activity and the rate of the chemical reaction. The chemical reaction is then continued in the presence of the partially or completely spent noble metal-iron catalyst and iron(III) compound.

[0034] In certain embodiments, the chemical reaction is the reaction of a starting nitroaromatic compound with hydrogen to produce the corresponding aromatic amine. When the nitroaromatic compound is nitrobenzene, the amine product is aniline.

[0035] In a useful continuous process for producing aniline according to the present invention, nitrobenzene and hydrogen are intermittently or continuously introduced into the lower part of a reaction vessel operated at a temperature above the boiling point of aniline (at 1 atmosphere), such as 200-260°C. The pressure in the reaction vessel can be, for example, 10-30 atmospheres (1013-3040 kPa) gauge. The nitrobenzene and hydrogen react in the presence of a noble metal-iron catalyst in the reaction vessel to produce aniline and water. The aniline and water are continuously or intermittently removed in the vapor phase from the upper part of the reaction vessel for purification of the aniline. The reaction is continued for a period of time until the noble metal-iron catalyst is at least partially spent. An iron(III) compound is intermittently or periodically added to the reaction vessel during continuous operation, and the reaction is continued in the presence of the at least partially spent noble metal-iron catalyst and iron(III) compound after the addition of the iron(III) compound.

[0036] In a continuous process, a convenient mode of adding the iron(III) compound is to remove a recycle stream containing the spent noble metal-iron catalyst from the reaction vessel, combine the spent noble metal-iron catalyst with the iron(III) compound in all or a portion of the recycle stream, and then reintroduce that portion of the recycle stream containing the spent noble metal-iron catalyst and the added iron(III) compound into the reaction vessel. This can be done intermittently or continuously. The recycle stream typically contains a liquid phase that may include, for example, unreacted starting materials, solvent, and / or a certain amount of product. Some or all of the liquid phase can be removed from the recycle stream before it is reintroduced into the reaction vessel. For example, product can be recovered from the recycle stream before it is reintroduced into the reaction vessel. In the case of a nitroaromatic hydrogenation reaction, the recycle stream can contain a certain amount of product aromatic amine (aniline in the case of nitrobenzene hydrogenation). Some or all of the aromatic amine can be recovered from the recycle stream before it is reintroduced into the reaction vessel.

[0037] The following examples are provided to illustrate the present invention, but are not intended to limit the scope of the invention. All parts and percentages are by weight unless otherwise indicated. All molecular weights are number average unless otherwise indicated.

[0038] Examples 1 to 4 and Comparative Samples A and B Reaction time experiments are carried out in the general manner of charging a 300 mL autoclave (Autoclave Engineer Model ABA-300, steam jacketed and equipped with a stirrer) with 0.027-0.028 grams of palladium-iron catalyst as described below, 17.2 mL of nitrobenzene, 30 mL of methanol, and 50 mL of water. The reactor is sealed, purged with hydrogen, and then pressurized with nitrogen to 30 bar (3040 kPa) gauge pressure. The reactor contents are heated to 100°C by flowing steam through the jacket. The time at which the reactor contents reach 100°C is designated as time T0. The pressure within the reactor is continuously measured. The point at which the pressure becomes constant (T0) is determined to indicate completion of the reaction. c ) is judged. The reaction time is T c Calculate as -T0.

[0039] For Comparative Sample A, the palladium-iron catalyst is a virgin catalyst sample containing approximately 4.6 wt. % palladium, 0.4 wt. % platinum, and 5.15 wt. % iron (all on a dry weight basis by inductively coupled plasma-mass spectroscopy (ICP-MS)). The metals are supported on carbonaceous support particles. The palladium-iron catalyst is prepared according to the method described in U.S. Pat. No. 2,823,235.

[0040] For Comparative Sample B, the palladium-iron catalyst was a spent sample of the same palladium-iron catalyst obtained from a commercial aniline production plant.

[0041] The reaction times for Comparative Samples A and B are 7.1-7.2 minutes and 19.3-19.7 minutes, respectively. Thus, the used catalyst has approximately one-third the activity of the unused catalyst in this test.

[0042] ICP-MS analysis of the spent catalyst reveals that the palladium and platinum levels in the spent catalyst are substantially unchanged from those in the fresh catalyst, however, the iron content of the spent catalyst is found to be reduced by approximately 60%, to approximately 2.1% by weight of the catalyst.

[0043] Comparative Sample B was repeated four additional times, with ferric chloride (FeCl3 6H2O) added in each case as a physical mixture with the spent catalyst. In Example 1, sufficient ferric chloride was added to provide 1 part iron per 100 parts by weight of spent catalyst. In Examples 2-4, ferric chloride was added to provide 2, 3, and 4 parts iron per 100 parts of spent catalyst. The approximate total amount of iron (including that from the spent catalyst and ferric chloride) and reaction time, along with the results for Comparative Samples A and B, are shown in Table 1.

[0044] [Table 1] * It is not an embodiment of the present invention. 1 By weight of palladium-iron catalyst (used or unused).

[0045] As the data in Table 1 show, the addition of ferric chloride to the reaction results in a highly significant reduction in reaction time compared to used catalyst. When the iron content in the reaction mixture is increased to about that of virgin catalyst, the reaction time becomes essentially the same, if not faster, than the reaction time provided by virgin catalyst. Adding smaller amounts of iron(III) compound provides a smaller but significant advantage.

[0046] Example 5 and Comparative Sample C Although the addition of ferric chloride to the nitrobenzene reduction reaction described in the preceding example results in significantly improved reaction rates, the presence of chloride ions results in the formation of undesirable by-products in that particular reaction. Therefore, iron(III) compounds containing few, if any, halide ions are preferred for reducing nitro compounds to the corresponding amines.

[0047] Ferric chloride and activated carbon are combined in the presence of water in a 1:20 iron to carbon weight ratio. Sodium bicarbonate is added, which reacts with the ferric chloride to form ferric basic carbonate, which is precipitated onto the activated carbon and sodium chloride. The ferric carbonate activated carbon particles are separated from the liquid phase and heated to 80°C for 30 minutes to decompose the ferric carbonate into ferric hydroxide. The particles are then washed, filtered, and dried.

[0048] Comparative Sample C is run according to the general reaction time procedure described above. The catalyst is a spent palladium-iron catalyst from a commercial aniline production facility that was originally made according to the method described in U.S. Pat. No. 2,823,235.

[0049] In Example 5, the same mixture of spent catalyst and ferric hydroxide activated carbon particles is used. The mixture is formed by adding the spent catalyst and ferric hydroxide activated carbon particles separately to a reactor. Sufficient ferric hydroxide activated carbon particles are added to provide approximately 4 wt. % iron based on the weight of the spent catalyst particles. The total iron content in the combined spent catalyst and ferric hydroxide activated carbon particles is 5-6.25% of the weight of the spent catalyst particles. The results, along with those of Comparative Sample A, are shown in Table 2.

[0050] [Table 2] * It is not an embodiment of the present invention. 1 By weight of palladium-iron catalyst (used or unused).

[0051] As the data in Table 2 demonstrate, the addition of iron in the form of iron hydroxide supported on activated carbon restores catalytic activity to near that of virgin catalyst without the presence of undesirable reactive by-products. The present specification includes the following aspects. Section 1. 1. A method for reactivating a spent precious metal-iron catalyst, comprising combining the spent precious metal-iron catalyst with an iron(III) compound while adding to the spent precious metal-iron catalyst up to 10 wt. % of the precious metal, based on the weight of iron in the added iron(III) compound. Section 2. Item 10. The method according to Item 1, wherein the iron(III) compound is inorganic. Section 3. Item 3. The method according to Item 2, wherein the iron(III) compound is an iron(III) halide, iron oxide, basic iron(III) carbonate, iron(III) carbonate, or iron(III) hydroxide. Section 4. Item 4. The method according to any one of Items 1 to 3, wherein the noble metal is palladium, platinum, or a mixture of palladium and platinum. Section 5. Item 5. The method according to any one of Items 1 to 4, wherein the noble metal-iron catalyst is supported on a carbonaceous support. Section 6. 1. A catalytic process for producing one or more chemical products, comprising: a) carrying out a chemical reaction by subjecting one or more starting compounds to reaction conditions in the presence of a noble metal-iron catalyst wherein said one or more starting compounds react to form said one or more chemical products, said reaction being continued for a time such that said noble metal-iron catalyst is at least partially spent; b) thereafter, adding iron(III) compounds to the reaction vessel one or more times while adding up to 10 wt. % of a precious metal based on the weight of iron in the added iron(III) compounds, and thereafter continuing to carry out the chemical reaction in the presence of the at least partially spent precious metal-iron catalyst and the added iron(III) compounds. Section 7. Item 7. The catalytic process of item 6, wherein the iron(III) compound is inorganic. Section 8. Item 8. The catalytic process of item 7, wherein the iron(III) compound is an iron(III) halide, iron oxide, basic iron(III) carbonate, iron(III) carbonate, or iron(III) hydroxide. Section 9. Item 9. The catalytic process according to any one of items 6 to 8, wherein the noble metal is palladium, platinum, or a mixture of palladium and platinum. Section 10. Item 10. The catalytic process according to any one of items 6 to 9, wherein the noble metal-iron catalyst is supported on a carbonaceous support. Section 11. 20. The catalytic process according to any one of items 6 to 19, wherein the chemical reaction is one or more of an oxidation reaction, a dechlorination or dehydrochlorination reaction; a hydrodeoxygenation reaction; a reduction reaction, or a hydrogenation reaction. Section 12. 1. A process for producing an aromatic amine, comprising: a) carrying out a continuous reduction reaction in the presence of a noble metal-iron catalyst by continuously or intermittently introducing a starting nitroaromatic compound and hydrogen into a reaction vessel and continuously or intermittently removing from the reaction vessel water and aromatic amines produced by the reaction of the starting nitroaromatic compound and hydrogen, wherein the reduction reaction is continued for a time such that the noble metal-iron catalyst is at least partially spent; b) thereafter, adding an iron(III) compound to the reaction vessel one or more times, adding up to 10 wt. % of a noble metal based on the weight of iron in the iron(III) compound added, and thereafter continuing to carry out the continuous reduction reaction in the presence of the at least partially spent noble metal-iron catalyst and the iron(III) compound. Section 13. Item 13. The process according to item 12, wherein the iron(III) compound is an iron(III) halide, iron oxide, basic iron(III) carbonate, iron(III) carbonate, or iron(III) hydroxide. Section 14. 14. The process according to paragraph 12 or 13, wherein the noble metal is palladium, platinum, or a mixture of palladium and platinum. Section 15. 15. The process of any one of items 12 to 14, wherein the noble metal-iron catalyst is supported on a carbonaceous support.

Claims

1. 1. A process for producing an aromatic amine, comprising: a) carrying out a continuous reduction reaction in the presence of a noble metal-iron catalyst by continuously or intermittently introducing a starting nitroaromatic compound and hydrogen into a reaction vessel, and continuously or intermittently removing water and aromatic amines produced by the reaction of the starting nitroaromatic compound and hydrogen from the reaction vessel; b) thereafter adding an iron(III) compound to the reaction vessel one or more times, adding up to 10 wt. % of the noble metal based on the weight of iron in the added iron(III) compound, and thereafter continuing to carry out the continuous reduction reaction in the presence of the at least partially spent noble metal-iron catalyst and the iron(III) compound; the noble metal-iron catalyst is a palladium-iron catalyst or a palladium-platinum-iron catalyst; The process wherein the iron(III) compound is an iron(III) halide, iron oxide, basic iron(III) carbonate, iron(III) carbonate, or iron(III) hydroxide.

2. 10. The process of claim 1, wherein the noble metal is palladium, platinum, or a mixture of palladium and platinum.

3. 3. The process of claim 1 or 2, wherein the noble metal-iron catalyst is supported on a carbonaceous support.

4. The carbonaceous support has a porosity of at least 3000 m as measured by gas adsorption. ２ 4. The process of claim 3, comprising activated carbon having a % saturation of 0.15 to 0.25 g / g.

5. 5. The process of any one of claims 1 to 4, wherein the noble metal-iron catalyst is a carbon-supported palladium-iron catalyst or a palladium-platinum-iron catalyst that, when fresh, contains 3 to 7.5 wt. % palladium and / or platinum and an equal amount of iron, based on the total dry weight of the fresh supported catalyst.

6. the noble metal-iron catalyst is a palladium-iron catalyst; the iron(III) compound is ferric chloride or ferric hydroxide, and / or the iron(III) compound is added in an amount sufficient to provide 1 to 4 parts by weight of the spent palladium-iron catalyst; The process of claim 1.

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