EP0862494A1

EP0862494A1 - Process for preparing a hydrogenation catalyst

Info

Publication number: EP0862494A1
Application number: EP96933397A
Authority: EP
Inventors: Daniel Heineke; Christopher William Rieker; Jozef Oostvogels; Dany Postelmans; Heinz-Walter Schneider; Alfred Thome; Günther Achhammer
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1995-10-04
Filing date: 1996-09-26
Publication date: 1998-09-09
Also published as: CA2231536A1; CN1198686A; MX9802151A; DE19536777C1; WO1997012673A1; JPH11513302A

Abstract

The invention relates to a hydrogenation catalyst by the reduction from platinum in the stage of oxidation of +4 (Pt (IV)) with a selective reducing agent in an acidic aqueous medium in the presence of a carbon-containing carrier to platinum in the stage of oxidation +2 (Pt (II)), subsequent poisoning of the platinum thus obtained with a sulphur-containing selective reducing agent, and subsequent reduction of the platinum thus partially poisoned to form metallic platinum (Pt(0)) and subsequent processing as known per se in that (a) Pt (II) is partially poisoned with a sulphur-containing selective reducing agent, wherein the sulphur-containing selective reduction agent is used in an amount which corresponds to from 15 to 70 mol % of the amount of the sulphur-containing selective reducing agent which might be needed to reduce Pt(IV) to Pt (II), provided that the amount of Pt (IV) corresponds to the amount of Pt (II) used and to be poisoned, and subsequently the partially poisoned Pt (II) is reduced with an alkali metal formate to Pt (0); or (b) platinum in the stage of oxidation of greater than +2 is partially poisoned and subsequently or simultaneously reduced with an alkali metal formate to Pt (0). The invention also relates to a hydrogenation catalyst, use of the hydrogenation catalyst for preparing hydroxylammonium salts, a process for the preparation of hydroxylammonium salts, and a process for regenerating platinum-containing hydrogenation catalysts.

Description

Process for the preparation of a hydrogenation catalyst

Description 5

The present invention relates to an improved process for the preparation of a hydrogenation catalyst by reduction of platinum in the oxidation state of +4 with a selective reducing agent in an acidic aqueous medium in the presence of a

10 carbon-containing carrier to platinum in the oxidation state +2, subsequent poisoning of the platinum thus obtained with a sulfur-containing selective reducing agent, and then reduction of the partially poisoned platinum to metallic platinum and subsequent processing in a known manner

15 wise.

The invention further relates to the use of alkali metal formates for the preparation of hydrogenation catalysts, hydrogenation catalysts produced according to the invention, a process for the preparation of hydroxylammonium salts and a process for the regeneration of hydrogenation catalysts based on platinum.

Precious metals such as palladium, platinum or ruthenium, which are applied to various supports such as silicon dioxide, aluminum oxide, graphite or activated carbon, are suitable for the hydrogenation of organic and inorganic compounds 25, as from "Catalytic hydrogenations in the organic chemical laboratory", F. Zimalkowski , Ferdinand Enke Verlag, Stuttgart (1965) is known. 30

The high dispersion of the noble metal on the catalyst support is essential for the activity of these catalysts. Technically disadvantageous is the fact (see "Structure of Metallic Catalyst", JR Anderson, Academic Press (1975), pages 35 164ff) that under reaction conditions agglomeration increases the particle size of the applied precious metal, the dispersion decreases, and that elemental precious metal is detached from the carrier mass.

40 DE-PS 1,088,037 describes a process for the preparation and regeneration of a special catalyst for the production of hydroxylamine by first platinum in the oxidation state of +4 with a selective reducing agent in an acidic aqueous medium in the presence of a carbon-containing carrier to platinum

45 reduced in the oxidation state +2, then partially poisoned the platinum thus obtained with a sulfur-containing selective reducing agent, and then the reduction of the so partially poisoned platinum is carried out to form metallic platinum with a formate and is then worked up in a manner known per se.

Disadvantages of this process are the insufficient selectivity with respect to hydroxylamine, the excessive accumulation of ammonia and nitrous oxide, the insufficient conversion of nitrogen monoxide and the unsatisfactory space-time yield.

DE-C 40 22 853 describes that by using platinum-graphite supported catalysts with a grain size of the graphite between 1-600 μm, the selectivity with respect to hydroxylamine in the hydrogenation of nitrogen monoxide can be increased.

From DE-PS 956038 platinum-graphite support catalysts are already known which are obtained by precipitating platinum on suspended graphite supports, optionally with the addition of poisoning agents such as sulfur, selenium, arsenic or tellurium compounds. Such catalysts are suitable for the catalytic hydrogenation of nitrogen monoxide. These catalysts have the disadvantage that the reactivity and selectivity decrease rapidly with prolonged use.

DE-C 40 22 851 describes that in the production of hydroxylamine by hydrogenation of nitrogen monoxide in the presence of platinum-graphite supported catalysts, the selectivity is related to the apparent density, the compressive strength and porosity of the graphite support.

The catalysts used in the processes of the aforementioned German patent documents have the disadvantage that only relatively short service lives of the catalysts can be achieved due to agglomeration of the active components.

DE-A 43 11 420 describes the preparation of a hydrogenation catalyst which can be obtained by treating a platinum metal salt with finely divided sulfur in the presence of a dispersant and then reducing the platinum metal salt to metallic platinum metal. Sodium formate is also mentioned as the reducing agent, but according to the teaching of DE-A 43 11 420 formic acid is particularly preferred. Tests with sodium formate were not carried out in the corresponding DE document. There is also no indication that the particle size of the platinum has a decisive role in the stability of the catalyst, the selectivity and the by-product spectrum. The object of the present invention was therefore to provide an improved process for the preparation of hydrogenation catalysts which ensures longer service lives of the catalysts used with at least the same selectivity and high space-time yield. Furthermore, a minimization of the by-products, in particular dinitrogen monoxide and ammonia, should be achieved.

Accordingly, an improved process for the preparation of a hydrogenation catalyst by reduction of platinum in the oxidation stage of +4 (Pt (IV)) with a selective reducing agent in an acidic aqueous medium in the presence of a carbon-containing carrier to platinum in the oxidation stage +2 (Pt (II)), subsequent poisoning of the platinum thus obtained with a sulfur-containing selective reducing agent, and then reduction of the partially poisoned platinum to metallic platinum (Pt (0)) and subsequent workup in a manner known per se by:

(a) Pt (II) partially poisoned with a sulfur-containing selective reducing agent, the sulfur-containing selective reducing agent being used in an amount which corresponds to from 15 to 70 mol% of the amount of a selective reducing agent which was required in order to use Pt (IV) to Pt (II), provided the amount of Pt (IV) corresponds to the amount of Pt (II) to be poisoned, and then the partially poisoned Pt (II) with an alkali metal formate Pt (0) reduced, or

(b) Partially poisoned platinum in an oxidation state greater than +2 and subsequently or simultaneously reduced to Pt (0) with an alkali metal formate.

Furthermore, the use of alkali metal formates for the preparation of hydrogenation catalysts, hydrogenation catalysts prepared according to the invention, a process for the preparation of hydroxylammonium salts and a process for the regeneration of hydrogenation catalysts based on platinum were found.

According to the invention poisoned in variant (a) platinum in an oxidation state of +2 with a sulfur-selective Re ^¬ duktionsmittel in an acidic aqueous medium in the presence of a carbonaceous wearer. The platinum thus partially poisoned is then reduced to metallic platinum with an alkali metal formate and is then worked up in a manner known per se. The amount of the sulfur-containing selective reducing agent is chosen so that it is used in an amount which corresponds to from 15 to 70, preferably from 20 to 65, mol% of the amount of a selective reducing agent which is required in order to use Pt (IV) to reduce to Pt (II), under the condition that the amount of Pt (IV) corresponds to the amount of Pt (II) to be poisoned.

In variant (b), according to the invention, platinum is poisoned in an oxidation state greater than +2 and then reduced to Pt (0) or simultaneously with an alkali metal formate.

According to the invention, alkali metal formates, preferably lithium formate, sodium formate and kaiium formate, particularly preferably sodium formate, are used.

In a particular embodiment, variant (a) uses platinum in the oxidation state +2, which can be obtained by reducing platinum with an oxidation number greater than +2, particularly preferably Pt (IV), with a selective reducing agent.

As selective reducing agent can be the sulfoxyl acid, in particular the well-known under the name Rongalit ^® Ein¬ effective product of formaldehyde on hyposulfite, sulfur dioxide and sulphites use, typically dithionites, especially sodium (Blankit ^®) derivatives.

In general, the selective reducing agent is used in an amount equivalent to the dissolved platinum with an oxidation state greater than 2, preferably +4, equivalent.

When using a sulfur-containing selective reducing agent as a poisoning agent in variant (a), which is capable of converting platinum in the oxidation state +4 to platinum in the

To reduce oxidation level +2 (eg Blankit ^® ), the reduction is first carried out according to the invention only up to the level of platinum in oxidation level +2. According to previous observations, the end point of this reaction can be recognized from a strong change in the potential which is measured during the reduction. The partial poisoning then takes place according to the invention subsequently by adding a certain amount, which is required beyond the reduction of Pt (> II), preferably Pt (IV), to Pt (II), from 15 to 70, preferably from 20 to 65 mol % corresponds to the amount used to reduce Pt (IV) to Pt (II). The reduction with the alkali metal formate then takes place according to the invention. If a compound is used as the poisoning agent which is not able to reduce platinum in an oxidation state of greater than +2, in particular Pt (IV), to Pt (II), variant (b), then according to the invention the platinum is first poisoned and then, or simultaneously with an alkali metal formate as reducing agent, it reduces to platinum (0) (metallic platinum).

Such poisoning agents are customary poisoning agents based on sulfur, selenium, arsenic or tellurium such as sodium dithionite, alkali thiosulfates, hydrogen sulfide, alkali sulfide, alkali polysulfides, thiourea, telluric acid or arsenic acid or combinations thereof. Elemental sulfur, in particular network sulfur, which has a particle size of less than 500 μm, preferably less than 50 μm, is particularly preferably used.

The molar ratio of platinum to sulfur, selenium, arsenic or tellurium to be poisoned is usually chosen in the range from 20: 1 to 3: 1, preferably from 10: 1 to 5: 1.

The partial poisoning is usually carried out according to methods known per se, as described, for example, in DE-C 40 22 853.

Preferably after the partial poisoning has been carried out, the reduction with alkali metal formate to metallic platinum is carried out.

The platinum (IV) compound used is, in particular, the waterless compounds such as hexachloroplatinic acid and their alkali metal and ammonium salts, such as disodium, dipotassium and diammonium hexachloroplatinate.

The molar ratio of platinum used to the alkali metal formate is usually chosen in the range from 1000: 1 to 10: 1, preferably from 100: 1 to 20: 1.

Suspended graphite or activated carbons, in particular electrographite grades, are generally used as the carbon-containing carrier, particularly preferably those electrographite grades that have a grain size in the range from 0.5 to 600 μm, preferably from 1 to 70, particularly preferably from 2 to 50 μm. The amount of platinum is generally from 0.2 to 2, preferably from 0.5 to 1 wt .-%, based on the total mass of platinum-graphite carrier catalyst. The reduction of the platinum is carried out according to the invention in an aqueous solution, the weight ratio of water to platinum generally being selected from 1000: 1 to 100: 1, preferably from 500: 1 to 100: 1.

The reduction is also carried out in slightly acidic form, the pH usually being from 4.5 to less than 7, preferably from 5 to 6. The pH is generally adjusted by adding buffer salts such as alkali metal acetate, in particular sodium acetate.

In a preferred embodiment of variant (a) is used as the selective reducing agent Blankit ^® (sodium dithionite). Thereby it is usually just enough to Blankit ^®, that the measured with a glass electrode potential of the solution in the range of 420 to 500 mV, preferably amounts of 440 mV to 480 mV. After reduction of the platinum (IV) to platinum (II), which is recognizable by recent observations of a strong change of the potential, it is a benotigte via the reduction of platinum (IV) to platinum (II) addition amount of Blankit ^® to to

Achievement of a certain desired potential. This potential characterizes the poisoning state of the catalyst and is usually in the range from 440 mV to 200 mV, preferably from 270 mV to 340 mV.

The molar ratio of alkali metal formate to platinum is generally chosen in the range from 1000: 1 to 10: 1, preferably

The temperature during the reduction is generally chosen in the range from 50 to 95 ° C., preferably from 60 to 90 ° C.

Furthermore, it is convenient to work under atmospheric pressure.

The pH after reduction to metallic platinum essentially depends on the type of reducing agent chosen and is usually in the range from pH 5 to 8, particularly preferably from 5 to 6.5.

When the reduction has ended, the catalyst is operated in the

Usually as usual, for example by filtering it off from the reaction mixture and washing it appropriately with water, preferably until the wash water is neutral. The particle size of the platinum particles produced according to the invention has generally not been greater than 3.5 nm according to previous observations by determining the line width at half the height by means of X-ray diffraction.

According to the observations made to date, the catalysts obtained by the process according to the invention are suitable both for the hydrogenation of organic and of inorganic compounds.

The catalysts according to the invention are preferably used for the hydrogenation of olefinically or acetylenically unsaturated compounds, furthermore for the hydrogenation of carboxylic acids, aldehydes or ketones to the corresponding alcohols or of nitriles to the corresponding amines. Furthermore, the catalysts according to the invention are suitable for the hydrogenation of inorganic substances such as oxygen, but in particular for the production of hydroxylammonium salts by hydrogenation of nitrogen monoxide in aqueous mineral acids.

In the preparation of hydroxylammonium salts, a molar ratio of hydrogen to nitrogen monoxide of 1.5: 1 to 6: 1, preferably from 3.5 to 5: 1, is generally maintained. According to the previous observations, particularly good results are obtained if it is ensured that a molar ratio of hydrogen to nitrogen monoxide of 3.5: 1 to 5: 1 is maintained in the reaction zone.

Strong mineral acids such as nitric acid, sulfuric acid or phosphoric acid or aliphatic Ci-Cs-monocarboxylic acids such as formic, acetic, propionic, butteric and valeric acid, preferably formic acid and acetic acid, are advantageously used as acids. Acidic salts such as ammonium bisulfate are also suitable. As a rule, 4 to 6 normal aqueous acids are used and the acid concentration is usually not allowed to drop below 0.2 in the course of the reaction.

The hydrogenation of nitrogen monoxide is generally carried out at a temperature from 30 to 80, preferably from 35 to 60 ° C. Furthermore, the pressure during the hydrogenation is usually chosen in the range from 1 to 30, preferably 1 to 20, bar (absolute).

The ratio of mineral acid to catalyst essentially depends on the platinum metal and the reactor pressure and, in the case of platinum, is generally in the range from 1 to 100. preferably 30 to 80 g of platinum-graphite catalyst per liter of mineral acid.

In a further preferred embodiment, in particular in the preparation of hydroxylammonium salts, the catalyst is treated in an acidic solution before the hydrogenation, expediently in the mineral acid in which the hydrogenation is to be carried out with hydrogen (“activation”).

Used platinum metal catalysts can be regenerated with the aid of the process according to the invention by usually dissolving the platinum metal of the catalyst using an acid or an acid mixture and, if appropriate, removing insoluble constituents. The platinum metal salt solution obtained is then neutralized, and the platinum metal salt is then treated by the process according to the invention described above.

According to the observations made to date, the catalysts according to the invention are superior to known catalysts for the same purpose in terms of activity, selectivity and service life.

Examples

The particle size of the graphite particles was determined using a MALVERN master sizer (see also Process Engineering 24 (1990) p. 36ff). Fraunhofer diffraction was measured at a wavelength of 633 nm. By choosing an attachment lens with a focal length of f = 300 nm, the particle size distribution was determined in a range from 1 to 600 μm.

For the measurement, a spatula tip of the powder to be examined was placed in one liter of a 0.1% by weight aqueous Nekanil 910 solution (BASF AG; Nekanil 910 is a nonylphenol reacted with 9 to 10 mol ethylene oxide; properties: water-clear, viscous Liquid; non-ionic, density at 20 ° C: 1.04 g / cm ³ ; pour point: below -10 ° C; pH of a 1% by weight solution (6.5 to 8.5). Before the measurement, the mixture to be examined thus obtained was subjected to an ultrasound treatment for 1 min.

The particle size of the platinum particles was determined by means of X-ray diffraction by determining the line width at half the height. example 1

a) 40 g of a graphite from Becker-Pennrich with a particle size of 28 to 50 μm and 0.5310 g of hexachloroplate IV acid 6-hydrate were mixed with 40 ml of an aqueous solution, the 3.87 ml of concentrated hydrochloric acid and 0 , 87 ml of concentrated nitric acid, stirred at 80 ° C. overnight. The suspension obtained was mixed with sodium carbonate until a pH of 2.75 was reached. Then 2.5 g of sodium acetate were added for buffering. Then a 4.58% by weight aqueous sodium dithionite solution was added until platm ^{4+ was} reduced to platinum ^{2 "1"} (recognizable by a strong change in the potential at 460 mV).

To poison the catalyst with sulfur, the same sodium dithionite solution used to reduce platinum ⁴ " ¹ " to platinum ^{2 "1" was} used in an amount equal to 60 mol% of that used to reduce Pt ⁴⁺ was used to Pt ²⁺ added. The potential of the solution obtained afterwards, determined with a glass electrode, was 355 mV.

14.1 g of a 40% by weight aqueous sodium formate solution (83 mmol) were then added to the suspension thus obtained and the mixture was stirred at 80 ° C. for 4 hours. After this time, no more platinum was detectable with hydrazine hydrate (giving a black precipitate in alkaline solution in the presence of platinum).

The catalyst prepared in this way was separated from the reaction mixture by filtration through a glass frit and washed with distilled water until the pH of the wash water was no longer in the acidic range. The dried catalyst contained 0.5% by weight of platinum.

b) 4.8 g of the catalyst prepared under a) were suspended in 120 ml of 4.3 N sulfuric acid and at 40 ° C with vigorous

Ruhren (3500 rpm) per hour 7.75 l of a mixture of 35 vol .-% nitrogen monoxide and 65 vol .-% hydrogen. After 4 hours, the catalyst was separated off and the liquid phase was analyzed. The separated catalyst was then mixed with 120 ml of 4.3 N sulfuric acid and the reaction was continued. This process was repeated every four hours. The reaction was stopped after the selectivity to dinitrogen monoxide formed exceeded the upper limit of 10%. The test results are shown in the table below. Comparative Example 1

The procedure was as in Example 1, with the differences that 56 mol% of sodium dithionite, based on the amount used for the reduction to platinum (II), was used for poisoning, and that 6.25 ml was used to precipitate the platinum to zero conc. Formic acid were used. The results are shown in the table below.

Example 2

a) 40 g of a graphite from Becker-Pennrich with one

Particle sizes of 28 to 50 mm and 0.5310 g of hexachloroplate IV acid 6-hydrate were mixed with 40 ml of an aqueous solution containing 3.87 ml of concentrated hydrochloric acid and 0.87 ml of concentrated nitric acid at 80 ° C. overnight touched. Sodium carbonate was added to the suspension obtained until a pH of 2.75 was reached. Then 2.5 g of sodium acetate were added for buffering. Then 6.25 mg of elemental sulfur was added and, after a waiting time of 2 minutes, 14.1 g of a 40% by weight aqueous sodium formate solution (83 mmol) were added to the suspension thus obtained and the mixture was stirred at 80 ° C. for 4 hours. After this time, no more platinum was detectable with hydrazine hydrate (which gives a black precipitate in alkaline solution in the presence of platinum).

The catalyst thus prepared was separated from the reaction mixture by filtration through a glass frit and washed with distilled water until the pH of the

Wash water was no longer in the acidic range. The dried catalyst contained 0.5% by weight of platinum.

b) The catalyst was tested as described under lb).

Comparative Example 2 - analogous to DE-A 43 11 420

The procedure was as in Example 2 with the difference that 6.25 mg of elemental sulfur for poisoning, and that 6.25 ml of conc. Formic acid were used. The results are shown in the table below.

Claims

claims

1. Process for the preparation of a hydrogenation catalyst by reduction of PTatin in the oxidation state of +4

(Pt (IV)) with a selective reducing agent in an acidic aqueous medium in the presence of a carbon-containing carrier to platinum in the oxidation state +2 (Pt (II)), subsequent poisoning of the platinum thus obtained with a sulfur-containing selective reducing agent, and then Reduction of the partially poisoned platinum to metallic platinum (Pt (0)) and subsequent processing in a manner known per se, characterized in that

(a) Pt (II) partially poisoned with a sulfur-containing selective reducing agent, the sulfur-containing selective reducing agent being used in an amount which corresponds to from 15 to 70 mol% of the amount of a selective reducing agent which was needed in order to

To reduce Pt (IV) to Pt (II), provided the amount of Pt (IV) corresponds to the amount of Pt (II) to be poisoned, and then the partially poisoned Pt (II) with an alkali metal formate to Pt (0) reduced, or

2. The method according to claim 1, characterized in that the Pt (II) in variant (a) is obtained by reducing platinum in an oxidation number of greater than +2 with a selective reducing agent.

3. Use of formates for the preparation of a hydrogenation catalyst by reduction of Pt (IV) with a selective reducing agent in an acidic aqueous medium in the presence of a carbon-containing carrier to Pt (II), subsequent poisoning of the platinum thus obtained with a sulfur-containing selective Reducing agent, and then reduction of the partially poisoned platinum to metallic platinum (Pt (0)) and subsequent workup in a manner known per se, characterized in that (a) Pt (II) is partially poisoned with a sulfur-containing selective reducing agent , using the sulfur-containing selective reducing agent in an amount which from 15 to 70 mol% of the amount of a selective reducing agent required to reduce Pt (IV) to Pt (II), provided the amount of Pt (IV) corresponds to the amount of poisoned Pt (II) used, and then the partially poisoned Pt (II) is reduced to Pt (0) with an alkali metal formate, or

(b) Partially poisoned platinum with an oxidation state greater than +2 and subsequently or simultaneously reduced to Pt (0) with an alkali metal formate.

4. The method according to claims 1 or 2, characterized gekenn¬ characterized in that one uses in variant (a) as a selective reducing agent sodium dithionite.

5. Process according to claims 1, 2 or 4, characterized in that sodium formate is used as the alkali metal formate.

6. The method according to claims 1, 2, 4 or 5, characterized in that the particle size of the platinum particles is not greater than 3.5 nm.

7. hydrogenation catalyst, obtainable by one of the processes according to claims 1, 2 or 4 to 6.

8. Use of the hydrogenation catalyst according to claim 7 or prepared by a process according to claims 1, 2 or 4 to 6 for the preparation of hydroxylammonium salts.

9. A process for the preparation of hydroxylammonium salts by reduction of nitrogen monoxide with hydrogen in the presence of a hydrogenation catalyst, characterized in that the hydrogenation catalyst used is a hydrogenation catalyst according to claim 7 or prepared by a process according to claims 1, 2 or 4 to 6.

10. A process for the regeneration of a hydrogenation catalyst based on platinum in a manner known per se, characterized in that Pt (IV) is reduced to Pt (II) with a selective reducing agent in an acidic aqueous medium in the presence of a carbon-containing carrier, then partially poisoned the platinum thus obtained with a sulfur-containing selective reducing agent, and then the platinum thus partially poisoned to metallic Platinum (Pt (0)) reduced and then worked up in a manner known per se, wherein

(a) Partially poisoning Pt (II) with a sulfur-containing selective reducing agent by using the sulfur-containing selective reducing agent in an amount which corresponds to from 15 to 70 mol% of the amount of a selective reducing agent which was needed thus reducing Pt (IV) to Pt (II), provided the amount of Pt (IV) corresponds to the amount of Pt (II) to be poisoned, and then the partially poisoned Pt (II) with an alkali metal formate Pt (0) reduced, or

(b) Partially poisoned platinum in the oxidation state greater than +2 and subsequently or simultaneously reduced to Pt (0) with an alkali metal formate.