REACTIVATION OF A HYDROGENATION CATALYST

Abstract

The present invention relates to a method for reactivating an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide, comprising at least one step of bringing said catalyst into contact with an aqueous solution comprising ammonia. The invention also relates to the use of an aqueous ammonia solution for reactivating an anthraquinone hydrogenation catalyst for the preparation of hydrogen peroxide.

Claims

1-10. (canceled)

11. A process for the reactivation of an anthraquinone hydrogenation catalyst in the preparation of hydrogen peroxide, comprising at least the following successive stages: a) optional washing of the catalyst to be reactivated, b) optional drying or draining of the catalyst to be reactivated, c) reactivation of the catalyst to be reactivated by bringing said catalyst into contact with an aqueous solution comprising from 0.01% to 1%, of ammonia, by weight, limits included, d) optional washing of the reactivated catalyst, and e) drying or draining of said reactivated catalyst resulting from stage c) or from stage d).

12. The process as claimed in claim 11, in which the reaction temperature of stage c) is between 10 C. and 80 C.

13. The process as claimed in claim 11, in which the reactivation stage c) is carried out at atmospheric pressure or under an excess pressure up to 200 kPa to 300 kPa.

14. The process as claimed in claim 11, in which the amount of ammonia solution employed in the reactivation stage c), with respect to the catalyst, is in a ratio of between 1 part and 20 parts, by weight of ammonia solution per one catalyst part, limits included.

15. The process as claimed in claim 11, in which the optional washing stage of stage a) comprises bringing at least a part or the whole of the catalyst to be reactivated into contact with a solvent.

16. The process as claimed in claim 11, in which the optional drying or draining stage b) comprises passing an inert gas over the catalyst to be dried or to be drained.

17. The process as claimed in claim 11, coupled with one or more other catalyst regeneration processes, selected from the group consisting of steam regeneration, oxidative regeneration, noble metal reimpregnation, and regeneration by an acid.

18. The process as claimed in claim 11, in which the catalyst comprises at least one noble metal, chosen from columns 9, 10, and 11 of the Periodic Table of the Elements, and also mixtures of said metals.

19. The process as claimed in claim 11, in which the catalyst comprises a support, said support comprising one or more metal or nonmetal oxides, alone or as mixtures.

Description

EXAMPLES OF TREATMENT OF A CATALYST (EXAMPLES EX1 TO EX9)

[0070] A glass column equipped with a glass frit is used, into which 20 g of a catalyst to be treated, representing a bed approximately 4 cm in height, are introduced.

[0071] The solvent or the aqueous ammonia solution is introduced into the column so as to wash the catalyst by gravity. The flow rate is adjusted dropwise by a valve located at the bottom of the column in order to ensure a flow rate of approximately 100 ml in 20-30 minutes.

[0072] The drying operations are carried out in an oven under air at a temperature of 110 C. for 24 hours. 3 catalysts (Cat-1, Cat-2 and Cat-3), which are catalysts used for a period of time of between 6 and 18 months in a hydrogen peroxide production unit, are tested. A comparative blank test is carried out 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:

TABLE-US-00001 TABLE 1 Ex1 Ex2 Ex3 Ex4 Ex5 Ex6 Ex7 Ex8 Ex9 Catalyst CAT-1 CAT-2 CAT-3 Fresh catalyst Solvent 100 ml 100 ml 100 ml 100 ml 100 ml 100 ml 100 ml TMB washing Solvent 200 ml 200 ml 200 ml 200 ml 200 ml 200 ml methanol washing Drying yes yes yes yes yes yes yes yes yes 0.2% NH.sub.3 100 ml 100 ml 100 ml 100 ml reactivation Methanol 200 ml 200 ml 200 ml 200 ml washing 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

[0073] The particle size dispersion of the catalyst was checked for examples 1 and 3. The results show that the catalyst does not undergo any degradation resulting in fracturing of the catalyst beads or the formation of fines (see Table 5 below).

[0074] The comparison of examples 8 and 9 shows that the reactivated catalyst exhibits an activity comparable to the fresh catalyst. It is deduced therefrom that the dispersion of the catalyst is not modified.

EXAMPLES OF TREATMENT OF A CATALYST (EXAMPLES EX10 TO EX14)

[0075] In this second series of examples 10 to 14, the first washing of the catalyst is carried out with different solvents, or while omitting this stage. The drying stage before the treatment with the aqueous ammonia solution was also omitted. Finally, the last washing with methanol is replaced by simple washing with water, followed by drying.

[0076] Another catalyst (Cat-4), which is a catalyst used for a period of time of between 6 and 18 months in a hydrogen peroxide production unit, is tested. 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:

TABLE-US-00002 TABLE 2 Ex10 Ex11 Ex12 Ex13 Ex14 Catalyst CAT-4 Solvent TMB C10 Sextate C10 100 ml 100 ml 100 ml 100 ml 0.2% NH.sub.3 100 ml 100 ml 100 ml reactivation Washing with water 200 ml 100 ml 200 ml 200 ml Drying yes yes yes yes Activity 0.74 1.31 1.30 1.13 0.77

[0077] For example 12, the reactivation treatment with the ammonia solution was carried out in a flask stirred laterally by approximately 20-30 swings per minute, so as not to cause attrition of the catalyst, and at 50 C.

[0078] These results show that the treatment with an aqueous ammonia solution, even at low concentration, according to the process of the invention, makes possible in all cases a satisfactory reactivation of the catalyst.

EXAMPLES 15-17: REACTIVATION OF CATALYST AND REUSE CONTINUOUSLY IN THE ANTHRAQUINONE PROCESS

[0079] For these examples, a new catalyst K-0290 N from Heraeus (Ex15), 60 g of used catalyst Cat-5, resulting from an industrial production unit and containing approximately 50% of working solution after simple filtration (Ex16), and 60 g of used catalyst Cat-5, resulting from an industrial production unit and containing approximately 50% of working solution after simple filtration (Ex17), are used, which catalysts are subjected to the following treatments: [0080] washing with 600 ml of methanol, [0081] rinsing with 100 ml of demineralized water, [0082] reactivation with 400 ml of 0.2% aqueous ammonia solution, [0083] washing with 400 ml of demineralized water, and [0084] drying at 110 C., for 24 hours.

[0085] The flow rates of reactivation solution are regulated for a duration of approximately 40 minutes to 60 minutes per treatment. 33.5 g of dry reactivated catalyst, subsequently referred to as Cat-5 ttNH.sub.3, are thus recovered.

Evaluation of the Catalyst

[0086] The catalysts of examples 15 to 17 are employed in a pilot plant operating continuously according to the anthraquinone process. The total volume of working solution in the plant is of between 45 l and 55 l. The flow rate of working solution is 16 l.Math.h.sup.1.

[0087] The reaction is carried out in a reactor stirred by a turbine having a hollow shaft making it possible to disperse the hydrogen and to keep the catalyst in suspension in the working solution.

[0088] The level of the reactor is regulated so as to maintain a mean reaction volume of 7 l. The hydrogen is injected with a constant flow rate of 500 l.Math.h.sup.1. The pressure is adjusted by a solenoid valve to 1.25 bar relative (226 kPa), the excess hydrogen being removed through a vent. The reaction temperature is maintained at 65 C. The hydrogen peroxide equivalent is controlled by additions of catalyst.

[0089] The working solution is subsequently filtered and then 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 countercurrentwise. The working solution is injected at the top and air is injected at the bottom through a sintered stainless steel diffuser. The reactor is filled with packing.

[0090] A solenoid valve placed at the top of the oxidation reactor makes it possible to adjust the pressure to 1.8 bar relative (281 kPa). The air flow rate is 900 l.Math.h.sup.1. The reaction temperature is maintained on average in the reactor at 60 C.

[0091] The working solution is subsequently injected into the extraction section, consisting of 3 plate columns, placed in series, each operating countercurrentwise. Water is injected at the top, while the working solution is injected at the bottom. The water flow rate is fixed at 0.5 l.Math.h.sup.1. The working solution resulting from the extraction stage is separated from the water before being reintroduced into the hydrogenation reactor.

[0092] The amount of catalyst deployed to reach a degree of hydrogenation corresponding to 9 g.Math.l.sup.1 of hydrogen peroxide per liter of working solution (equivalents) at the hydrogenator outlet makes it possible to compare the effectivenesses of the catalysts.

[0093] Examples 15 and 16 are comparative and example 17 is according to the invention. The catalyst of example 16 (Ex16) is a catalyst Cat-5 washed with methanol and then dried, as indicated above. The pilot plant continuously produces hydrogen peroxide. The number of days elapsed up to a loss in the number of hydrogenation equivalents of 1 g.Math.l.sup.1 is recorded. The results are presented in the table below:

TABLE-US-00003 TABLE 3 Ex15 Ex16 Ex17 New catalyst CAT-5 Cat-5_ttNH.sub.3 Amount of catalyst to 15 to 20 g more than 50 g 20 to 25 g reach 9 g .Math. 1.sup.1 Number of days >15 days 7 days >15 days

Analyses

Analyses of a Deactivated Catalyst

[0094] The catalyst Cat-2 was analyzed before (Ex4) and after (Ex5) treatment with an ammonia solution. The resulting aqueous ammonia solution is then analyzed by proton NMR and carbon-13 NMR.

[0095] NMR analysis of the ammonia solution obtained after treatment shows the predominant presence of 4-ethylbenzene-1,2-dicarboxylic acid (ethylphthalic acid). The presence of oxalic acid and phthalic acid is also recorded. Without prejudice to the invention, it is thought that the ethylphthalic acid, originating from degradation side reactions of ethylanthraquinone derivatives present in the working solution, becomes fixed with the formation of an insoluble carbon-based layer at the surface of the catalyst, obstructing the pores of the catalyst and thus limiting its activity.

[0096] From the weight of the dry extract obtained with regard to this solution, the amount of ethylphthalic acid and of oxalic acid which were fixed to the catalyst is estimated at approximately 1% to 3%, with respect to the dry catalyst.

[0097] Scanning electron microscope (SEM) analysis of the catalyst surface clearly shows that the ammonia treatment makes it possible to remove entities tending to form a layer on the catalyst.

[0098] The analyses of elemental composition by X-ray fluorescence at the surface of grains show that the composition of the catalyst before and after regeneration by ammonia remains substantially identical. The sodium content is not greatly impacted by the treatment with a dilute ammonia solution. It is also seen that the operation of treatment with ammonia does not cause a change in the palladium content at the surface of the grains.

[0099] The X-ray fluorescence analyses are carried out with a JSM-IT500 LA scanning electron microscope from Jeol. The samples are deposited on aluminum studs provided with carbon adhesives. Images are recorded at magnifications of between 100 and 600. EDX spectra and maps are produced to determine the elemental composition of the surface of the grains of catalysts. The results of the analyses of elemental compositions for Ex4 and Ex5 are presented in the table below:

TABLE-US-00004 TABLE 4 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 ANALYSES OF THE TREATED CATALYSTS (EXAMPLES 1 AND 3)

[0100] The particle size measurement is carried out according to the wet laser diffraction technique using a Masterziser S appliance sold by Malvern. The measurement is carried out by dispersing the catalyst powder in water in the presence of a drop of Igepal (ethoxylated nonylphenol) surfactant, rate 2500 adjusted on the appliance. The values are recorded after 10 minutes of circulation in the measurement cell.

[0101] Diameter at 10%, 50% and 90% of the population (by volume)

[0102] The results are presented in the table below:

TABLE-US-00005 TABLE 5 Sample (0.1) in m (0.5) in m (0.9) in m Ex3 82 118 171 Ex2 (Comp.) 88 119 161

[0103] It is seen that the treatment with a 0.2% ammonia solution does not significantly modify the particle size characteristics of the catalyst.

[0104] A similar palladium on aluminosilicate support catalyst treated in the same way and conditions as in example 5 but with a 20% ammonia solution is for its part highly damaged: the catalyst grains are fractured by the treatment. In addition, the same effect was observed with a 10% ammonia solution.