HYDROGEN CATALYST REACTIVATION

Abstract

The present invention relates to a process for reactivating an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide, comprising at least one step of contacting said catalyst with an aqueous solution containing ammonia. The invention also relates to the use of an aqueous ammonia solution to reactivate an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide. Fig.: none

Description

Title of the invention: REACTIVATION OF HYDROGENATION CATALYST

[0001] The present invention relates to the field of catalysts and more particularly to the field of hydrogenation catalysts and more specifically to the field of anthraquinone hydrogenation catalysts used for the production of hydrogen peroxide.

[0002] More particularly, the present invention relates to a process for reactivating a hydrogenation catalyst used in the preparation of hydrogen peroxide, especially from anthraquinone, a preparation comprising the three main successive steps of hydrogenation, oxidation, and extraction. The preparation of hydrogen peroxide from anthraquinone (known as the "anthraquinone process") has been well known to those skilled in the art for many years and is extensively described in numerous publications, for example, in the Ullmann Encyclopedia (G. Goor et al., (April 15, 2007), https: / / doi.org / 10.1002 / 14356007.al3_443.pub2).

[0003] In this process for preparing hydrogen peroxide, known as the anthraquinone process, the first preparation step consists precisely of a catalytic hydrogenation of anthraquinone. The catalyst used is most often based on a noble metal, primarily palladium, platinum, or rhodium, which makes it an expensive catalyst. Thus, when the catalyst's activity decreases and no longer allows for the cost-effective preparation of hydrogen peroxide, it is desirable to regenerate (or reactivate) this catalyst, that is, to carry out a physicochemical treatment so that it regains sufficient activity for the needs of the anthraquinone hydrogenation reaction.

[0004] Prior art has for many years described techniques for regenerating or reactivating the anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide. For example, document GB787340 describes the regeneration of an anthraquinone hydrogenation catalyst by treatment with an alkaline solution at a pH greater than 12. The alkaline solution can be a sodium hydroxide solution, a solution of alkali metal carbonates or phosphates, and the treatment temperature can be, for example, 80°C with the sodium hydroxide solution. This document, however, indicates that certain types of supports, such as silicoaluminates, are damaged during this type of treatment.

[0005] Document EPI852392 describes a catalyst regeneration process hydrogenation comprising a treatment step with an alkaline solution at pH 10 or higher, then washing the treated catalyst with water or a second alkaline solution that is weaker than the first alkaline solution. However, the examples in this document show that, compared to the activity of the initial deactivated catalyst, only a slight increase in hydrogenation activity is observed, and this is starting from a pH value of 11.5.

[0006] Another technique described in US patent 3135699 involves catalyst regeneration by treatment with liquid ammonia at -80°C. US patent 3901822, on the other hand, mentions the use of aqueous ammonium hydroxide solutions of at least 1% for 0.1 to approximately 48 hours at a temperature between approximately 0°C and approximately 200°C, followed by post-treatment under an oxygen flow at a temperature between 250°C and the transition temperature of the catalyst's crystal structure for approximately 1 to 72 hours. Without post-treatment under an oxygen flow, and using only a 15% aqueous ammonium hydroxide solution, this patent indicates that the regenerated catalyst deactivates again very rapidly, particularly after four days of use.

[0007] Similar hydrogenation catalysts used in petroleum cracking have also been studied for regeneration. For example, US patent 3214385 describes the regeneration of a hydrogenation catalyst by treating it with a basic solution of an alkali metal hydroxide in concentrations ranging from 1% to 50%. US patent 3392111 describes the treatment of catalysts used in cracking with aqueous or solvent-based solutions of ammonia or amines.

[0008] US patent 3849293, also in the field of hydrocracking, teaches the treatment of palladium-type catalysts on zeolite (aluminosilicate) supports with aqueous ammonia solutions ranging from 0.1% to 30% containing a dissolved ammonium salt. These treatments are carried out under conditions such that the zeolite cations are at least partially exchanged while providing a desired redistribution of the Group VIII noble metal.

[0009] Prior art regeneration techniques, and in particular those described above, suffer from numerous disadvantages when it is desired to regenerate (or reactivate) an anthraquinone hydrogenation catalyst. Indeed, many of these regeneration techniques most often result in chemical and / or physical modifications of the catalyst, which then becomes unsuitable or inappropriate for future anthraquinone hydrogenation reactions.

[0010] For example, in a washing test of a palladium-type catalyst on a silico-aluminate support, using 10% or 20% ammonia at room temperature, a physical deterioration of the catalyst was observed, detrimental to the proper functioning of the filtration, due to clogging of the filters at the outlet of the hydrogenator, in due to the risk of formation of very fine catalyst particles passing through the filters.

[0011] It should be understood that the reactivation of the hydrogenation catalyst envisaged in the present invention can be carried out in situ, that is to say, in the very reactor where the hydrogenation of the anthraquinone takes place. It is therefore important that the reactivation operation does not result in any or minimal degradation of said catalyst into fine particles, which fine particles could then lead to a risk of violent decomposition of the hydrogen peroxide formed in the process during the oxidation and extraction steps.

[0012] An objective of the present invention is therefore to propose a catalyst reactivation process for the hydrogenation of anthraquinone for the preparation of hydrogen peroxide, said process allowing the reactivation of said catalyst, under appropriate conditions so that the catalyst does not undergo or undergoes few chemical and / or physical modifications, other than restoring in whole or at least in part the catalytic activity of said fresh catalyst.

[0013] Other objectives will appear in the following description of the invention. Unless otherwise indicated, percentages are expressed by weight.

[0014] Thus, and according to a first aspect, the present invention relates to the process for reactivating an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide, comprising at least the following successive steps: a) possible washing of the catalyst to be reactivated, b) possible drying or wringing of the catalyst to be reactivated, c) reactivation of the catalyst to be reactivated by contacting said catalyst with an aqueous solution comprising 0.01% to 1%, preferably 0.05% to 0.5%, and preferably still 0.1% to 0.2% of ammonia, inclusive, i.e. 0.06 to 0.12 moles L 1 of ammonia per liter of aqueous solution, d) possible washing of the reactivated catalyst, and e) drying or dewatering of said reactivated catalyst from step c) or step d).

[0015] The reactivation process according to the invention uses a very dilute ammonia solution. Despite this low concentration, the activity of the reactivated catalyst recovers to a level that, under the conditions of the industrial process for preparing hydrogen peroxide, restores a productivity close to that obtained with a new catalyst.

[0016] Furthermore, the process of the invention is carried out in a reaction medium with a pH below 12, thanks to the low concentration of ammonia, and preferably the pH of the aqueous ammonia solution is between 10 and 11, and advantageously between 10.5 and 10.8. One of the advantages of operating at this pH value is the reduced deterioration of the catalysts to be reactivated, and in particular of the supports, any particular- binding the silico-aluminate type supports.

[0017] Furthermore, the use of aqueous ammonia solution in the concentration described above differs from basic solutions containing alkali metals, such as sodium hydroxide solutions. Besides the fact that sodium hydroxide solutions, widely used in the prior art, have a detrimental effect on the catalysts to be regenerated, alkali metals, such as sodium, are detrimental to the hydrogen peroxide preparation process, particularly during the extraction step, because they make phase separation between the organic phase and the prepared aqueous phase of hydrogen peroxide difficult.

[0018] Another drawback associated with the use of alkaline bases, such as sodium hydroxide, is the risk of finding traces of alkali metals in the hydrogen peroxide preparation process, primarily during the hydrogenation step. Such traces of alkali metals pose a significant safety problem in the oxidation and extraction steps, where they can disrupt production, increase the pH of the aqueous hydrogen peroxide solution, and cause its destabilization or decomposition.

[0019] Such contaminants must therefore be avoided during catalyst reactivation. The process of the invention overcomes this drawback by using an aqueous ammonia solution, preferably and very advantageously free of alkali metals. The aqueous ammonia solution used in the process of the invention has the advantage of being easily removed, completely or at least largely, without leaving any traces during the drying and dewatering operations with steam or nitrogen, during catalyst regeneration.

[0020] Any residuals are generally easily removed, either in the hydrogen purges during hydrogenation or in the exhaust air exiting the oxidizer, before they can reach the extraction section. In contrast, residual sodium hydroxide or sodium carbonate will not be removed from the working solution and will therefore go directly and entirely into the extraction section, which presents a significant risk of process drift and hydrogen peroxide decomposition.

[0021] Thus, and as previously stated, the present invention relates to a method for reactivating the hydrogenation catalyst used in the industrial process, known as the anthraquinone process, for preparing hydrogen peroxide. The catalyst to be reactivated is generally extracted from the hydrogenation reactor for reactivation. In another embodiment, the catalyst can be reactivated in situ, that is, in the reactor used for the anthraquinone hydrogenation step.

[0022] The reactivation of the catalyst is then obtained by bringing the catalyst to be reactivated into contact with an aqueous ammonia solution with a concentration of between 0.01% and 1%, as previously stated. It was discovered, quite surprisingly, that this contact with the aforementioned aqueous ammonia solution allows the catalyst to regain a substantial intrinsic activity of approximately 50% to 70%, in a kinetic test, compared to a new catalyst. This reactivation, on the order of 50% to 70%, allows the catalyst to regain satisfactory productivity levels, close to those obtained with a new catalyst, during the hydrogenation stage of the industrial process.

[0023] Furthermore, it has been observed that this activity is durable over time and treatment with aqueous ammonia solution does not lead to a substantial change in selectivity during the hydrogenation step of anthraquinone.

[0024] Furthermore, and as previously stated, the catalyst reactivation process according to the invention can be implemented in situ or ex situ, and on all or only part of the catalyst to be reactivated. It is also possible to carry out this catalyst reactivation, in whole or in part, during operation, that is, during the operation of the industrial process for manufacturing hydrogen peroxide by hydrogenation of anthraquinone.

[0025] The reactivation process of the invention thus makes it easy to reactivate a catalyst used for the hydrogenation of anthraquinone in the industrial synthesis of hydrogen peroxide. The ease of implementation, whether on all or part of the catalyst to be reactivated, and the fact that this reactivation can be carried out in situ or ex situ, with or without stopping the hydrogen peroxide production unit, eliminates the need for downtime to replace the used catalyst, to clean up catalyst residues that have undergone chemical and / or physical deterioration, and thus substantially increases industrial hydrogen peroxide production yields.

[0026] Step a) of the process of the invention is an optional step of washing the catalyst to be reactivated (also called the deactivated catalyst). This step, if desired, includes contacting at least part or all of the catalyst to be reactivated with a solvent in order to remove residual quinones and hydroquinones, which can then be recovered and / or recycled.

[0027] According to a preferred embodiment of the invention, the solvent used in step a) of washing can be of any type well known to those skilled in the art, and advantageously the solvent is the same as that used in the industrial process for preparing hydrogen peroxide. This solvent can be of any type or even a mixture of solvents, and more advantageously a mixture of polar / nonpolar solvents, as for example described in Ullmann (G. Goor et al., op. cit.).

[0028] Step b) of drying or wringing, also an optional step, is mainly aimed at removing as much of the solvent potentially trapped in the pores of the catalyst. This drying or dewatering step can be carried out according to any classic method well known to those skilled in the art and includes, for example, the passage of an inert gas such as nitrogen or oxygen-depleted air or even steam over the catalyst to be dried or dewatered, steam treatment being preferred for this operation.

[0029] Step c) of contacting an aqueous ammonia solution, can be carried out according to any method well known in itself to a person skilled in the art, and for example, and without limitation, in a dedicated column or reactor, or can also be carried out on a filter, for example the filter which has been used previously in one or more steps a) and b), in particular during the extraction and / or washing of the catalyst with the solvent.

[0030] As previously stated, the concentration of the aqueous ammonia solution used is very low, ranging from 0.05% to 1%. Although it is possible to perform this catalyst reactivation operation with an ammonia concentration in water exceeding 1%, it is preferable not to exceed this recommendation in order to avoid damaging the catalyst and to prevent any risk of handling more concentrated ammonia solutions, which can produce harmful ammonia vapors.

[0031] The reactivation operation, step c) of the process of the present invention, can be carried out at any temperature. However, for obvious reasons of ease of implementation and treatment effectiveness, reactivation is most often performed at a temperature between 10°C and 80°C, preferably between 10°C and 40°C, even more preferably between 20°C and 30°C, and particularly advantageously at room temperature, i.e., around 25°C. It is possible, however, to carry out the reactivation operation at a temperature below 10°C, but at the expense of treatment effectiveness. Similarly, it is possible to carry out the reactivation operation at a temperature above 80°C, but at the risk of losing ammonia near the boiling point of water.

[0032] Step c) of reactivation can be carried out under atmospheric pressure, again for obvious reasons of ease of implementation, but it is possible to operate under a higher pressure, for example under slight overpressure, for example up to 2 to 3 bars (200 kPa to 300 kPa), in particular to facilitate the passage of the aqueous ammonia solution through the catalyst to be reactivated.

[0033] The quantities of ammonia solution relative to the catalyst can vary considerably, particularly depending on the nature and degree of fouling of the catalyst. However, it is preferable to operate in a ratio of between 1 and 20 parts, preferably between 1 and 10 parts by weight of ammonia solution to one part catalyst, and even more preferably between 2 and 5 parts of ammonia solution to one part catalyst, inclusive.

[0034] Following step c) of catalyst reactivation, one or more water washes (optional step d)) may be performed to remove as much of the aqueous ammonia solution as possible from the catalyst pores. This washing step may optionally be followed by a drying or spinning step (optional step e)) to remove all or part of the water from the catalyst pores, if desired. These two optional steps d) and e) may advantageously be carried out under conditions similar to those used in steps a) and b), respectively.

[0035] The catalyst thus reactivated at the end of the process of the present invention can then be reintroduced into the anthraquinone hydrogenation reactor, for the industrial synthesis of hydrogen peroxide.

[0036] The process of the present invention offers the advantage of being a simple operation to implement and carry out, and in addition with very low handling risks and environmental impact, in particular due to the low concentration of ammonia used, but also due to the absence of alkali metal ions, such as sodium, which can return to the hydrogen peroxide synthesis process.

[0037] Furthermore, and as previously indicated, the catalyst reactivation operation is carried out at pH values ​​below 12, typically between 10 and 11, i.e. in a range which presents little or no risk of deterioration of the catalyst support, for example compared to the same molar concentration of a basic agent such as sodium hydroxide.

[0038] The reactivation process can be carried out once or several times on all or part of the same catalyst that has already undergone one or more reactivation processes, depending on the nature of the catalyst, the degree of fouling of the catalyst, and the desired efficiency of said catalyst. Generally, the catalyst can thus be reactivated from 1 to 100 times, better from 1 to 50 times, even better from 1 to 20 times, and advantageously still from 1 to 10 times.

[0039] The reactivation process according to the invention can, if necessary or desired, be coupled with one or more other catalyst regeneration processes, such as, for example, those selected from steam regeneration, oxidation regeneration, noble metal reimpregnation, acid regeneration, and others.

[0040] The catalyst suitable for use in the process of the present invention can be of any type well known to those skilled in the art and is a suitable catalyst for the hydrogenation of anthraquinone. Generally, the catalyst used in the process of the invention comprises at least one noble metal, typically a metal chosen from those in columns 9, 10, and 11 of the Periodic Table of Elements, preferably from those in columns 9 and 10 of the Periodic Table of Elements, for example, a metal chosen from palladium, platinum, rhodium, iridium, silver, and gold, as well as than mixtures of said metals.

[0041] Catalysts comprising at least one metal selected from palladium, platinum, rhodium, iridium, and mixtures thereof, including with silver and / or gold, are particularly preferred, and preferably the metal is palladium, possibly in a mixture with silver or gold. Examples of catalysts usable in the process of the invention are those comprising as noble metals palladium, platinum, rhodium, iridium, a palladium / gold, palladium / silver, platinum / gold, platinum / silver, rhodium / gold, rhodium / silver, iridium / gold, or iridium / silver mixture.

[0042] The catalyst generally and most often comprises a support on which the noble metal(s) is / are deposited. The support generally comprises one or more oxides of metals or non-metals, alone or in mixtures, for example aluminium oxide, silica oxide, crystalline silico-aluminates (such as zeolites), and amorphous silico-aluminates.

[0043] Among silico-aluminates, and according to an embodiment of the invention, the support is a silico-aluminate, preferably an amorphous silico-aluminate, that is to say a non-crystalline silico-aluminate, for example an amorphous silico-aluminate containing sodium.

[0044] The most common and particularly suitable catalysts are chosen for example from, but not limited to, palladium on alumina support, palladium on amorphous silico-aluminate support, such as those marketed for example by Heraeus, under the trade name K-0290 N.

[0045] According to a second aspect, the invention relates to the use of an aqueous solution comprising 0.01% to 1%, preferably 0.05% to 0.5%, and even more preferably 0.1% to 0.2% of ammonia, by weight, including terminals, to reactivate an anthraquinone hydrogenation catalyst intended for the preparation of hydrogen peroxide.

[0046] The anthraquinone hydrogenation catalyst reactivation process of the present invention is particularly well suited for use in industrial hydrogen peroxide synthesis processes, commonly referred to as "anthraquinone processes." These processes usually comprise the following three main successive steps: hydrogenation, oxidation, and extraction. These processes are well known to those skilled in the art and are extensively described in the scientific literature, for example, in the Ullmann Encyclopedia (G. Goor et al., op. cit.).

[0047] The invention is now illustrated by means of the following examples, which in no way limit the invention, the scope of which is defined by the claims annexed to this description. Measurement of the "intrinsic" kinetic activity of the catalyst

[0048] The hydrogenation reactor is a glass-walled reactor with a capacity of one liter (1 L), equipped with a pressure sensor, capable of operating under pressures up to 10 bar absolute. It features a Rushton-type turbine with a hollow shaft, enabling efficient hydrogen dispersion through gas recirculation. The pressure in the reactor is maintained constant during the reaction by means of a pressure regulator connected to a hydrogen tank, compensating for hydrogen consumption during the reaction. Hydrogen consumption is measured by monitoring the pressure drop in the hydrogen tank over time. The reactor is equipped with a double-jacketed circulation system for heating or cooling.

[0049] 400 mL of the organic working solution are introduced into the reactor. The reactor is then pressurized to 3 bar (300 kPa) with nitrogen, and stirring is started at approximately 150 rpm. The double jacket circulation is started at a temperature of 65 °C. Once the temperature in the reactor has stabilized, the reactor is depressurized to atmospheric pressure, and then 3.2 g (expressed as dry weight, i.e., after drying in an oven at 110 °C for 24 hours) of a hydrogenation catalyst are introduced into the reactor. The reactor is closed, and stirring is stopped.

[0050] The reactor is then evacuated to approximately 0.1 bar absolute (10 kPa), then pressurized to 2 bar absolute (200 kPa) of nitrogen; the purging is repeated once. The reactor is again evacuated and then repressurized to 2 bar absolute (200 kPa) of hydrogen; this operation is also repeated once. The hydrogen pressure in the reactor is regulated by the hydrogen supply pressure regulator.

[0051] Stirring is then started at 1500 rpm, which disperses the hydrogen in the medium and initiates the reaction. Hydrogen consumption is monitored over time by the decrease in pressure (pressure and temperature are measured over time) in the hydrogen reservoir of known volume. When the desired hydrogenation level is reached, stirring is stopped and the reactor is purged. Two vacuum / argon cycles are then performed to remove the hydrogen. The hydrogenated working solution is then filtered and transferred under argon pressure into a receiving flask, which is itself under argon pressure. Heating is then stopped.

[0052] The quantities of hydrogen consumed over time are converted into hydrogen peroxide equivalent, knowing that one mole of hydrogen consumed is equivalent to one mole of potential hydrogen peroxide, i.e. 34 g in hydrogen peroxide equivalent, then brought back to the volume of working solution involved.

[0053] In order to compare the tests with each other, the time t(8), expressed in minutes, required to reach 8 g L 1 of hydrogen peroxide equivalent is taken as a basis. The activity of the catalyst is then defined as the rate: activity in g L 1 min 1 = 8 / 1(8).

[0054] The following abbreviations are used in the following: - TMB = 1,2,4-trimethylbenzene, - CIO = SHELSOLL A 150 N alkylaromatic derivative cut, - Sextate = 2-methylcyclohexyl acetate, - CAT = commercial catalyst K-0290 N from the company Heraeus, with 2% palladium on silico-aluminate. Examples of catalyst treatment (Examples Exl to Ex9)

[0055] A glass column equipped with sintered glass is used, into which 20 g of a catalyst to be treated is introduced, representing a bed of approximately 4 cm in height.

[0056] The solvent or aqueous ammonia solution is introduced into the column so as to wash the catalyst by gravity. The flow rate is regulated drop by drop by a tap located at the bottom of the column to ensure a flow rate of approximately 100 mL in 20-30 minutes.

[0057] Drying is carried out in an air oven at a temperature of 110°C for 24 hours. Three catalysts (CAT-1, CAT-2, and CAT-3) are tested; these catalysts are used for periods ranging from 6 to 18 months in a hydrogen peroxide production unit. A comparative "blank" test is performed with fresh catalyst. Examples 3, 5, and 7 are according to the present invention, and the other examples are comparative examples. The results are presented in the table below: [Tables 1] Exl Ex2 Ex3 Ex4 Ex5 Ex6 Ex7 Ex8 Ex9 Catalyst CAT-1 CAT-2 CAT-3 Fresh Catalyst Solvent TMB Wash 100 m L 100 m L 100 m L 100 m L 100 m L 100 m L 100 m L - - Solvent Methanol Wash - 200 m L 200 m L 200 m L 200 m L 200 m L 200 m L - - Drying yes yes yes yes yes yes yes yes yes Reactivation nNH3 0.2% - - 100 m L - 100 m L - 100 m L - 100 m L Methanol Wash - - 200 m L - 200 m L - 200 m L - 200 m L Drying no no yes no yes no yes no yes Activity 0.73 0.74 1.43 0.70 1.57 1.68 1.78 2.40 2.39

[0058] The particle size distribution of the catalyst was checked for examples 1 and 3, the results show that the catalyst does not undergo any degradation leading to a fracture of the catalyst beads or the formation of fines (see below, Table 5). Examples of catalyst treatment (Examples ExlO to Exl4)

[0059] In this second series of examples 10 to 14, the first washing of the catalyst is carried out with different solvents, or by omitting this step. The drying step before treatment with the aqueous ammonia solution has also been omitted. Finally, the last methanol wash is replaced by a simple water wash followed by drying.

[0060] Another catalyst (CAT-4) is tested, which is a catalyst used for a period of between 6 and 18 months in a hydrogen peroxide production unit. Examples 11, 12, and 13 are according to the present invention, and Examples 10 and 14 are comparative examples. The results are presented in the table below: [Tables 2] ExlO Exil Exl2 Exl3 Exl4 CAT-4 catalyst Solvent TMB 100 mL CIO 100 mL - Sextate 100 mL CIO 100 mL NH3 Reactivation 0.2% - 100 mL 100 mL 100 mL - Water wash - 200 mL 100 mL 200 mL 200 mL drying - yes yes yes yes activity 0.74 1.31 1.30 1.13 0.77

[0061] For example 12, the reactivation treatment with the ammonia solution was carried out in a bottle shaken laterally by about 20-30 swings per minute, so as not to cause attrition of the catalyst, and at 50°C.

[0062] These results show that treatment with an aqueous ammonia solution, even at low concentration, according to the process of the invention, allows in all cases a satisfactory reactivation of the catalyst. Examples 15-17: Catalyst reactivation and continuous reuse in the anthraquinone process

[0063] For these examples, a new K-0290 N catalyst from Heraeus (Exl5), 60 g of used CAT-5 catalyst from an industrial production unit containing approximately 50% of the working solution after simple filtration (Exl7) are used, and 60 g of used CAT-5 catalyst from an industrial production unit containing approximately 50% of the working solution after simple filtration (Exl7), subjected to the following treatments: - washing with 600 mL of methanol, - Rinse with 100 mL of demineralized water, - reactivation with 400 mL of 0.2% aqueous ammonia solution, - wash with 400 mL of demineralized water, and - Drying at 110°C for 24 hours.

[0064] The reactivation solution flow rates are set for a duration of approximately 40 to 60 minutes per treatment. This yields 33.5 g of reactivated dry catalyst, hereafter referred to as CAT-5 ttNH3. Catalyst evaluation

[0065] The catalysts of Examples 15 to 17 are implemented in a pilot plant operating continuously according to the anthraquinone process. The total volume of solution of The working volume in the installation is between 45 L and 55 L. The working solution flow rate is 16 L h1.

[0066] The reaction is carried out in a reactor stirred by a hollow shaft turbine allowing the hydrogen to be dispersed and the catalyst to be kept in suspension in the working solution.

[0067] The reactor level is regulated to maintain an average reaction volume of 7 L. Hydrogen is injected at a constant flow rate of 500 L h1. The pressure is regulated by a solenoid valve at 1.25 bar relative (226 kPa), with excess hydrogen being vented. The reaction temperature is maintained at 65°C. The hydrogen peroxide equivalent is controlled by catalyst additions.

[0068] The working solution is then filtered and sent to the oxidation reactor. Oxidation is carried out in a tubular reactor with an internal diameter of 7 cm and a height of 237 cm, operating in a counter-current flow. The working solution is injected at the top and air is injected at the bottom through a sintered stainless steel diffuser. The reactor is packed with packing material.

[0069] A solenoid valve located at the head of the oxidation reactor regulates the pressure to 1.8 bar relative (281 kPa). The air flow rate is 900 L h1. The reaction temperature is maintained on average in the reactor at 60°C.

[0070] The working solution is then injected into the extraction section, which consists of three tray columns arranged in series, each operating in a counter-current flow. Water is injected at the top, while the working solution is injected at the bottom. The water flow rate is set at 0.5 L / h. The working solution from the extraction step is separated from the water before being reintroduced into the hydrogenation reactor.

[0071] The quantity of catalyst used to achieve a hydrogenation rate corresponding to 9 g L 1 of hydrogen peroxide per liter of working solution (equivalents) at the outlet of the hydrogenator allows the efficiency of the catalysts to be compared.

[0072] Examples 15 and 16 are comparative, and Example 17 is according to the invention. The catalyst in Example 16 (Ex 16) is a CAT-5 catalyst washed with methanol and then dried, as described above. The pilot plant continuously produces hydrogen peroxide. The number of days elapsed until a loss of 1 g L⁻¹ of hydrogenation equivalents is recorded. The results are presented in the table below: [Tables 3] Exl5 Exl6 Exl7 New catalyst CAT-5 CAT-5_ttNH3 Amount of catalyst to reach 9 g L 1 15 to 20 g More than 50 g 20 to 25 g Number of days >15 days 7 days >15 days Analyses Analysis of a deactivated catalyst

[0073] The CAT-2 catalyst was analyzed before (Ex4) and after (Ex5) treatment with an ammonia solution, the resulting aqueous ammonia solution was then analyzed by proton NMR and carbon NMR.

[0074] NMR analysis of the ammonia solution obtained after treatment shows the predominant presence of 4-ethylbenzene-1,2-dicarboxylic acid (“ethylphthalic acid”), with the presence of oxalic acid and phthalic acid also noted. Without prejudice to the invention, it is believed that the ethylphthalic acid, resulting from secondary degradation reactions of ethyl-anthraquinone derivatives present in the working solution, binds to the catalyst by forming an insoluble carbon layer, clogging its pores and thus limiting its activity.

[0075] From the weight of the dry extract obtained on this solution, the quantity of ethylphthalic acid and oxalic acid that were fixed on the catalyst is estimated to be about 1% to 3%, relative to the dry catalyst.

[0076] Scanning electron microscopy (SEM) analysis of the catalyst surface clearly shows that ammonia treatment eliminates species that tend to form a layer on the catalyst.

[0077] Elemental composition analyses by X-ray fluorescence on the surface of grains show that the composition of the catalyst before and after regeneration with ammonia remains essentially the same. The sodium content is only slightly affected by treatment with a dilute ammonia solution. It is also observed that the ammonia treatment does not cause any change in the palladium content on the surface of the grains.

[0078] X-ray fluorescence analyses are performed using a JEOL JSM-IT500 LA scanning electron microscope. Samples are deposited on aluminum pads with carbon adhesive. Images are acquired at magnifications between 100x and 600x. EDX spectra and mapping are performed to determine the elemental composition of the catalyst grain surface. The results of the elemental composition analyses for Ex4 and Ex5 are shown in the table below: [Tables4] Spectrum No. Na Al Si Pd Ex4 6.7 - 6.6 8-7.9 19.7 - 19.2 Ex5 6.1-6.3 8.4-8.3 20-21 1.9-2 Particle size analysis of the treated catalysts (Examples 1 and 3)

[0079] Particle size measurement is performed using the wet laser diffraction technique with a Masterziser® S instrument sold by Malvem. The measurement is carried out by dispersing the catalyst powder in water in the presence of one drop of Igepal® surfactant (nonylphenol ethoxylate), at a speed of 2500 set on the instrument. The values ​​are recorded after 10 minutes of circulation in the measuring cell.

[0080] Diameter at 10-50 and 90% of the population (by volume)

[0081] The results are presented in the table below: [Tables 5] Sample 0 (0.1) in June 0 (0.5) in June 0 (0.9) in twin Ex3 82 118 171 Ex2 (Comp.) 88 119 161

[0082] It can be seen that treatment with a 0.2% ammonia solution does not significantly alter the particle size characteristics of the catalyst.

[0083] A similar palladium catalyst on a silico-aluminate support, treated in the same way and under the same conditions as in Example 5 but with a 20% ammonia solution, is, however, severely damaged: the catalyst grains are fractured by the treatment. Furthermore, the same effect was observed with a 10% ammonia solution.

Claims

Demands

1. A process for reactivating an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide, comprising at least the following successive steps: a) optional washing of the catalyst to be reactivated, b) optional drying or dewatering of the catalyst to be reactivated, c) reactivation of the catalyst to be reactivated by contacting said catalyst with an aqueous solution comprising 0.01% to 1%, preferably 0.05% to 0.5%, and preferably still 0.1% to 0.2% of ammonia, by weight, inclusive of terminals, d) optional washing of the reactivated catalyst, and e) drying or dewatering of said reactivated catalyst from step c) or step d).

2. A process according to claim 1, wherein the reaction temperature of step c) is between 10°C and 80°C, preferably between 10°C and 40°C, more preferably between 20°C and 30°C, and most advantageously at room temperature.

3. A method according to claim 1 or claim 2, wherein the reactivation step c) is carried out under atmospheric pressure or under overpressure up to 200 kPa to 300 kPa.

4. A method according to any one of the preceding claims, wherein the quantity of ammonia solution used in step c) of reactivation relative to the catalyst is in a ratio of between 1 part and 20 parts, preferably between 1 part and 10 parts by weight of ammonia solution for one part catalyst, preferably again between 2 parts and 5 parts of ammonia solution for one part catalyst, inclusive.

5. A method according to any one of the preceding claims, wherein the optional washing step of step a) includes contacting at least some or all of the catalyst to be reactivated with a solvent.

6. A method according to any one of the preceding claims, wherein the optional step b) of drying or spinning comprises passing an inert gas such as nitrogen or oxygen-depleted air or water vapor over the catalyst to be dried or spun.

7. A method according to any one of the preceding claims, coupled with one or more catalyst regeneration methods, selected including steam regeneration, oxidation regeneration, noble metal reimpregnation, acid regeneration, and others.

8. A method according to any one of the preceding claims, wherein the catalyst comprises at least one noble metal, selected from those in columns 9, 10 and 11 of the Periodic Table of Elements, preferably from those in columns 9 and 10 of the Periodic Table of Elements, for example a metal selected from palladium, platinum, rhodium, iridium, silver and gold, as well as mixtures of said metals.

9. A method according to any one of the preceding claims, wherein the catalyst comprises a support, said support comprising one or more oxides of metals or non-metals, alone or in mixtures, preferably aluminium oxide, silica oxide, crystalline silico-aluminates, amorphous silico-aluminates.

10. Use of an aqueous solution comprising 0.01% to 1%, preferably 0.05% to 0.5%, and even more preferably 0.1% to 0.2% of ammonia, by weight, including terminals, for reactivating an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide.