Method for producing ruthenium/iron/carbon carrier catalysts

Abstract

The present invention relates to a process for producing iron-doped ruthenium-carbon support catalysts and also their use for the selective liquid-phase hydrogenation of carbonyl compounds to the corresponding alcohols, in particular for the hydrogenation of citral to geraniol or nerol or of citronellal to citronellal.

Claims

1. A process for producing a ruthenium-iron-carbon support catalyst comprising from 0.1 to 5% by weight of iron in addition to from 0.1 to 10% by weight of ruthenium on a carbon support by a) introducing a support into water b) simultaneously adding the catalytically active components ruthenium and iron in the form of solutions of their metal salts c) coprecipitating the catalytically active components on the support by addition of a base d) separating the catalyst from the aqueous phase of the support suspension e) drying the catalyst f) reducing the catalyst in a stream of hydrogen at from 100 to less than 400 C. in a reduction reactor g) removing the catalyst from the reduction reactor under liquids having a flashpoint of greater than 80 C. or passivating the catalyst by passing a diluted oxygen stream over it or passivating the catalyst by passing a diluted oxygen stream over it and removal of the catalyst from the reduction reactor under liquids having a flashpoint of greater than 80 C.

2. The process according to claim 1, wherein the catalyst produced is a suspended catalyst.

3. The process according to claim 1, wherein the catalyst produced is a fixed-bed catalyst.

4. The process according to claim 1, wherein steps (b) and (c) are carried out at a temperature of from 50 to 95 C.

5. The process according to claim 1, wherein steps (b) and (c) are carried out either simultaneously or successively.

6. The process according to claim 1, wherein the catalytically active components are used in the form of their chlorides, nitrates, nitrosyl nitrates, acetates, oxides, hydroxides or acetylacetonates.

7. The process according to claim 1, wherein the carbon support is pretreated by oxidation by means of HNO.sub.3, oxygen, hydrogen peroxide or hydrochloric acid.

8. The process according to claim 1, wherein Na.sub.2CO.sub.3, NaHCO.sub.3, (NH.sub.4).sub.2CO.sub.3, NH.sub.3, urea, NaOH, KOH or LiOH is used as base for precipitation of the catalytically active components onto the support.

9. The process according to claim 1, wherein NaOH is used for precipitation of the catalytically active components.

10. A process comprising selective liquid-phase hydrogenating carbonyl compounds of the general formula I ##STR00003## where R.sup.1, R.sup.2 are, independently of one another, identical or different and are each hydrogen or a saturated or a monounsaturated or polyunsaturated straight-chain or branched, optionally substituted, C.sub.1-C.sub.20-alkyl radical, an optionally substituted aryl radical or an optionally substituted heterocyclic group, to the corresponding alcohols of the general formula II ##STR00004## where R.sup.1, R.sup.2 are as defined above; where the hydrogenation occurs over a catalyst produced by the process according to claim 1.

11. The process according to claim 10, wherein the carbonyl compound is an alpha,beta-unsaturated carbonyl compound.

12. The process according to claim 10, wherein the carbonyl compound is citral.

13. The process according to claim 10, wherein the carbonyl compound is citronellal.

14. The process according to claim 10 as suspended catalyst or fixed-bed catalyst.

15. The process according to claim 1, wherein the reduction in step f) is carried out at from 120 to 300 C.

16. The process according to claim 1, wherein the reduction in step f) is carried out at from 150 to 250 C.

17. The process according to claim 1, wherein the reduction in step f) is carried out at from 180 to 220 C.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1:

(2) This figure shows catalyst recycling for a catalyst according to the invention, reduced at 200 C. (produced as per example 3).

(3) This catalyst is active enough to achieve complete conversion even in the fourth cycle after 360 minutes (FIG. 1, bottom). In the first cycle, complete conversion was achieved after 100 minutes (FIG. 1, top).

(4) FIG. 2:

(5) This figure shows catalyst recycling for a catalyst according to EP 1 317 959, reduced at 500 C. (produced as per comparative example 2).

(6) When using the catalyst reduced at 500 C., no complete conversion was achieved in the fourth cycle after 360 minutes (FIG. 2, bottom). In the first cycle, complete conversion was achieved only after 120 minutes (FIG. 2, top).

(7) The invention will now be illustrated with reference to the following nonlimiting examples.

EXAMPLES

Example 1 (Analogous to Examples 1A to 1C of EP 1 317 959)

(8) A) 100 g of activated carbon were admixed with 500 ml of concentrated HNO.sub.3 and stirred at 80 C. for 6 hours in a 1 liter flask. After cooling, the mixture was filtered and the filter cake was washed with 10 liters of distilled water.

(9) The moist carbon was returned to the stirred vessel, suspended in 2.5 liters of water and heated to 80 C. under reflux. A solution of 13.11 g of ruthenium chloride and 5.15 g of iron chloride in 375 ml of water was then added dropwise over a period of 120 minutes while stirring. After addition of the metal salt solution, the pH of the suspension was 1.4. The pH was then increased to 9 by slow dropwise addition of 1 M sodium hydroxide solution; about 400 ml of NaOH were consumed here. The mixture was subsequently stirred for another 1 hour and then cooled. The catalyst was transferred to a glass suction filter, washed with a total of 40 liters of water and dried at 80 C. for 6 hours in a vacuum drying oven. The dried powder was then reduced in a stream of 70% of H.sub.2 and 30% of N.sub.2 at 200 C. in a rotary bulb oven for 3 hours. After the reduction was complete, the powder was cooled under nitrogen and passivated by means of a gas mixture composed of 1% of oxygen in nitrogen. The finished catalyst had a chloride content of less than 0.05% by weight. Furthermore, the following contents (% by weight) were determined: Na: 2.8, Ru: 5.2, Fe: 1.1.

(10) B) The procedure as described in A was repeated, using ruthenium nitrosyl nitrate and iron(III) nitrate instead of ruthenium chloride and iron chloride. The finished catalyst had a ruthenium content of 5.1% by weight, an iron content of 1.1% by weight, a nitrate content of <0.01% by weight and an Na content of 2.1% by weight.

(11) C) The procedure as described in A was repeated, but lower ruthenium and iron contents were applied to the activated carbon. The finished catalyst had a ruthenium content of 2.8% by weight, an iron content of 0.54% by weight, a chloride content of 0.02% by weight and an Na content of 3.8% by weight.

(12) D) 110 g of the activated carbon Norit SX Plus were, without further pretreatment, introduced into a stirred flask with 2 liters of water, suspended and heated to 80 C. under reflux. The pH was then increased to 9 by addition of aqueous NaOH (1 mol/l). 300 ml of a solution of ruthenium nitrosyl nitrate and iron nitrate (concentralion corresponding to 5.85 g of Ru and 1.17 g of Fe) was then added dropwise at 80 C. over a period of one hour, with the pH being kept at about 9 at the same time by simultaneous addition of aqueous NaOH. The mixture was stirred at 80 C. for another one hour and then cooled. The cold suspension was filtered and the solid was washed with 40 liters of water, then dried at 80 C. for 16 hours in a vacuum drying oven and reduced and passivated as described under A. The catalyst had an Ru content of 5.0% by weight, an Fe content of 1.0% by weight and an Na content of 0.036% by weight.

Example 2 (Analogous to Example 2 of EP 1 317 959)

(13) 62 g of activated carbon extrudates (Supersorbon SX 30 from Lurgi, diameter 3 mm, surface area about 1000 m.sup.2/g) were placed together with 400 ml of deionized water in a stirred vessel and heated to 80 C. with gentle stirring and under reflux. A solution of 8.13 g of ruthenium chloride and 3.19 g of iron chloride was added dropwise at 80 C. over a period of 60 minutes. The pH was then increased to 9 by addition of 1 M sodium hydroxide solution and the mixture was stirred for another one hour. The catalyst was transferred to a glass suction filter, washed with 10 liters of deionized water and subsequently dried at 80 C. for 6 hours in a vacuum drying oven. The catalyst was then reduced in a gas mixture of hydrogen and nitrogen (4/50) at 200 C. for 3 hours in a reduction oven, cooled to room temperature and passivated by means of a gas mixture composed of 1% of oxygen in nitrogen.

Example 3 (Analogous to Example 1D of EP 1 317 959)

(14) 50 g of Norit carbon SX plus were stirred up in 300 ml of distilled water and heated to 80 C. Iron nitrate and ruthenium nitrosyl nitrate in water were then introduced at a pH of 9.0 (maintained by addition of NaOH, 1.5 molar) over a period of about 70 minutes. After stirring for another 1 hour, the carbon was filtered off and washed with about 16 l of water. The catalyst was then dried at 100 C. for 10 hours in a vacuum drying oven. The reduction was carried out in a rotary tube oven into which the catalyst was firstly introduced, after which the oven was heated to 180 C. in a stream of N.sub.2, maintained at 180 C. in the stream of N.sub.2 (35 standard l/h) for 2 hours then heated under 30 standard l/h of N.sub.2 and 4 standard l/h of H.sub.2 to 200 C. and maintained at this temperature for 2 hours and cooled, likewise under 30/4 standard l/h of N.sub.2/H.sub.2. Passivation was carried out in the same apparatus at room temperature. A stream of pure N.sub.2 (30 standard l/h) was firstly passed over the catalyst, and, taking account of the temperature, this stream was slowly reduced to 0, while in parallel to this air was slowly fed in until at the end 10 standard l/h of air were fed in at room temperature for 60 minutes. The catalyst was then removed from the reduction reactor in water.

Example 4

(15) The procedure of example 3 was repeated, but passivation was not carried out after the reduction at 200 C., but the catalyst was instead introduced directly into water. The resulting catalyst displayed equally good properties compared to that of example 3.

Comparative Example 1 (Catalyst According to Example 2 of EP 1 317 959)

(16) A catalyst was produced as described in example 2, but the reduction was carried out at 500 C.

Comparative Example 2 (Catalyst According to Example 1D of EP 1 317 959)

(17) The procedure of example 3 was repeated, except that the reduction was carried out according to the prior art at 500 C., i.e. the catalyst was heated to 180 C. in a stream of nitrogen, held for 2 hours (35 standard l/h), then heated under 30 standard l/h of N.sub.2 and 4 standard l/h of H.sub.2 to 500 C. and held for 2 hours and cooled (likewise under 30/4 standard l/h of N.sub.2/H.sub.2).

(18) Testing

(19) To compare the catalysts, the reaction of citral was in each case carried out using a catalyst as per example 3 or comparative example 2 according to the following method:

(20) About 3 g of water-moist catalyst according to the invention (FIG. 1reduction at 200 C.) or according to the prior art (FIG. 2reduction at 500 C.) (corresponds to about 1.5 g of dry catalyst) were placed in a pressure-rated autoclave (300 ml volume). 105 ml of citral-N and a mixture of 37.4 ml of methanol and 7.5 ml of trimethylamine were in each case added thereto. The autoclave was closed, made inert and pressurized with 30 bar of H.sub.2 and heated to 80 C. with the stirrer rotating. During the first hour, a sample was taken via a frit every 15 minutes, and thereafter every hour. After about 6 hours, the experiment was stopped, and the autoclave was depressurized, cooled, and flushed with nitrogen before opening. The samples were analyzed in a gas chromatograph.

(21) Result:

(22) The catalyst which had been reduced at 200 C. according to the present invention is active enough to achieve complete conversion even in the fourth cycle after 360 minutes. In the first cycle, complete conversion was already achieved after 100 minutes.

(23) In comparison, no complete conversion could be achieved in the fourth cycle after 360 minutes when using the catalyst of the comparative example (i.e. according to EP 1 317 959). Even in the first cycle, complete conversion was achieved only after 120 minutes.

(24) The formation of by-products is approximately the same for both catalysts. The selectivity rose during the experiments: in the fourth cycle, neither citronellol nor citronellal is formed.

(25) In summary, it can be said that the catalyst according to the present invention displayed higher stability and activity than the catalyst according to EP 1 317 959 with otherwise equally good properties.