Process for the regeneration of a supported noble metal catalyst

Abstract

A process for the regeneration of a supported noble metal catalyst comprising contacting the catalyst with a liquid aqueous system at a temperature in the range of from 90 to 160 C., wherein the pH of the aqueous system is outside the range of from 6 to 8, separating the aqueous system from catalyst; and subjecting the catalyst to calcination.

Claims

1. A process for regenerating a supported noble metal catalyst, the process comprising (a) separating the catalyst from a mixture (A) to obtain a separated catalyst (I); (b) contacting the separated catalyst (I) with a liquid aqueous system at a temperature in a range of from 90 to 160 C. in a closed system under autogenous pressure, wherein a pH of the aqueous system is outside a range of from 6 to 8; (c) separating the liquid aqueous system from the separated catalyst (I) to obtain a separated catalyst (II); and (d) subjecting the separated catalyst (II) to calcination, wherein the catalyst has been used in a process comprising (i) providing a mixture comprising water, an organic solvent, and a hydroperoxypropanol; and (ii) treating the mixture provided in (i) in a reactor under reducing conditions with hydrogen in the presence of the catalyst to obtain the mixture (A) comprising water, the organic solvent, and propylene glycol.

2. The process of claim 1, wherein the mixture provided in (i) comprises the hydroperoxypropanol in an amount of from 0.1 to 1 weight-% based on a weight of the mixture.

3. The process of claim 1, wherein the mixture provided in (i) further comprises an oxygenate in an amount of from 0.1 to 1 weight-% based on a weight of the mixture.

4. The process of claim 1, wherein the mixture provided in (i) comprises water in an amount of from 10 to 40 weight-% and the organic solvent in an amount of from 55 to 85 weight-%, based on a weight of the mixture.

5. The process of claim 1, wherein the organic solvent in the mixture provided in (i) is selected from the group consisting of methanol and acetonitrile.

6. The process of claim 1, wherein the noble metal of the supported noble metal catalyst is selected from the group consisting of palladium, platinum, rhodium, iridium, osmium and a combination of two or more thereof.

7. The process of claim 1, wherein the treating (ii) is carried out at a temperature in a range of from 25 to 120 C. and a pressure in a range of from 1 to 100 bar.sub.abs.

8. The process of claim 1, wherein the contacting (b) is performed in the reactor of (ii) comprising the separated catalyst (I).

9. The process of claim 1, wherein the contacting (b) is performed for a period of time in a range of from 0.1 to 10 h.

10. The process of claim 1, wherein the pH of the liquid aqueous system in (b) is in a range of from 0 to 5.5.

11. The process of claim 1, wherein the pH of the liquid aqueous system in (b) is in a range of from 8.5 to 14.

12. The process of claim 1, wherein the separating (a) is performed by filtration, centrifugation, decantation, evaporation, or a combination of two or more thereof, and wherein the separating (c) is performed by filtration, centrifugation, decantation, evaporation, or a combination of two or more thereof.

13. The process of claim 12, wherein the separating (c) further comprises washing the separated catalyst (I).

14. The process of claim 1, wherein in (d), the separated catalyst (II) is subjected to the calcination at a temperature in a range of from 200 to 700 C.

15. The process of claim 1, further comprising (e) activating the catalyst obtained from (d).

16. The process of claim 1, wherein the mixture provided in (i) is obtained by a process for epoxidizing propene comprising reacting propene with hydrogen peroxide in the presence of the organic solvent and a titanium zeolite catalyst to obtain an epoxidation reaction mixture, and separating propylene oxide from the epoxidation reaction mixture to obtain the mixture provided in (i).

17. The process of claim 1, comprising employing the catalyst obtained from (d) as a catalyst in a process comprising (ii).

Description

EXAMPLES

(1) A Regeneration of a Catalyst Used in the Hydrogenation of a Hydroperoxypropanol in a Mixture Further Containing Acetonitrile and Water

(2) The deactivated catalyst used in Comparative Example A1 and further in Examples A1 and A2 originated from a process for the epoxidation of propene to yield propylene oxide. The epoxidation was carried out in the presence of a catalyst comprising a TiMWW zeolite. As solvent, acetonitrile was employed. An aqueous hydrogen peroxide solution was employed as epoxidation agent. Propene as starting material was used as a mixture of propene and propane. The reaction mixture obtained was subjected to a separation stage where unreacted propene and propane were separated off by distillation as low boilers.

(3) The resulting mixture comprising acetonitrile, water, and propylene oxide was subjected to a downstream separation stage where propylene oxide was distilled off as low boiler. The thus obtained liquid mixture contained acetonitrile (81 weight-%), water (18 weight-%) and hydroperoxypropanol (0.5 weight-%) and traces of further oxygenates including acetaldehyde, propylenoxide, propionaldehyde, acetamide, acetone, 1-(2-hydroxypropoxy)propan-2-ol, tripropyleneglycol, propylene glycol, hydroxyacetone, formaldehyde, 2,4-dimethyl-4,5-dihydrooxazole, 2,5-dimethyl-4,5-dihydrooxazole, acetoxyacetone, cis- and trans-2-ethyl-4-methyl-1,3-dioxolane, 2-pentanone, 2-hexanone, pentanenitrile, 2,6-dimethyl-4-heptanone, 4,6-dimethyl-2-heptanol, butanone, 1-nitropropane, 2-nitropropane, 4-methyl-1,3-dioxolane, 2-propanol, 2-pentanol, 3-methylbutanenitrile. This liquid mixture was used as starting mixture subjected to hydrogenation.

(4) The hydrogenation catalyst consisted of 0.3 weight-% palladium supported on alpha-alumina (0.3% Pd/Al.sub.2O.sub.3). The catalyst was used in the form of strands having a diameter of 4 mm. Before starting a hydrogenation reaction, the fresh catalyst was activated in the reactor at 115 C. and 15 bar for 18 hours in a gas stream comprising a mixture of hydrogen (25 Nl/min) and nitrogen (10 Nl/min) (Nl=norm liter).

(5) The hydrogenation catalyst was in use for 3787 hours. After said 3787 hours, the deactivated catalyst was removed from the reactor. Portions of the deactivated catalyst were subjected to different regeneration processes, followed by determination of the respective catalytic activity.

Comparative Example A1

Regeneration of the Deactivated Catalyst by Activation with Hydrogen Only

(6) For comparative Example A1, 25 g of the deactivated Pd/Al.sub.2O.sub.3 were transferred into a technical scale reactor. The reactor comprised four tubes of 1.5 m length having an inner diameter of 5 mm equipped with heating means. The activation of the deactivated catalyst was carried out in the reactor at 115 C. and 15 bar for 18 hours in a gas stream comprising a mixture of hydrogen (25 Nl/min) and nitrogen (10 Nl/min) (Nl=norm liter) (Sample 1).

Example A1

Regeneration of the Deactivated Catalyst by Contacting with a Liquid Basic Aqueous System

(7) 30 g of the deactivated Pd/Al.sub.2O.sub.3 catalyst were submitted to regeneration in an alkaline aqueous medium according to the invention. The catalyst was immersed in ammonia solution (10 weight-% in water, having a pH of 10.5 at 80 C.) and heated in an autoclave under autogenous pressure for 4 hours at 120 C. Following the alkaline treatment, the catalyst was washed with water to a neutral pH and dried for 16 hours at 120 C. in air. After completed drying, the catalyst was calcinated for 2 hours at 250 C. in air.

(8) 25 g of the thus treated catalyst were transferred in the technical scale reactor and activated as described in Comparative Example A1 (Sample 2).

Example A2

Regeneration of the Deactivated Catalyst by Contacting with a Liquid Acidic Aqueous System

(9) 30 g of the deactivated Pd/Al.sub.2O.sub.3 catalyst were submitted to regeneration in an acidic aqueous medium according to the invention. The catalyst was immersed in oxalic acid solution (5 weight-% in water, having a pH of 1.0 at 82 C.) and heated in an autoclave under autogenous pressure for 4 hours at 120 C. Following the acidic treatment, the catalyst was washed with water to a neutral pH and dried for 16 hours at 120 C. in air. After completed drying, the catalyst was calcinated for 2 hours at 250 C. in air.

(10) 25 g of the regenerated catalyst were transferred in the technical scale reactor and activated as described in Comparative Example A1 (Sample 3).

Example A3

Catalytic Activity of the Regenerated Catalysts

(11) The regenerated catalysts of Comparative Example A1 and of Examples A1 and A2 (Samples 1 to 3) were used in a hydrogenation reaction performed at technical scale in the reactor described in Comparative Example 1. For further comparison, a hydrogenation of hydroperoxypropanol was performed with 25 g of fresh Pd/Al.sub.2O.sub.3 catalyst which had been activated prior to hydrogenation in a reactor as described in Comparative Example A1 (Sample 4).

(12) The liquid mixture described above, containing acetonitrile, water, hydroperoxypropanol and the oxygenate traces was continuously fed into the technical scale reactor with a WHSV (weight hourly space velocity) of 16 h.sup.1.

(13) A mixture of hydrogen and nitrogen was also introduced into the reactor (5 Nl/h H.sub.2 and 5 Nl/h N.sub.2). The reduction of hydroperoxypropanol was performed at a temperature of 70 C. and a pressure of 15 bar. The hydroperoxypropanol content was determined iodometrically according to DIN EN ISO 3960 from which the hydroperoxypropanol conversion rate was calculated.

(14) The individual operating times and conversion rates based on hydroperoxypropanol for the individual catalyst samples are summarized in Table 1 below.

(15) TABLE-US-00001 TABLE 1 The results according to Example A Hydroperoxy- Hydroperoxy- Differential propanol propanol conversion rate conversion rate conversion rate based on Operating (%) (%) averaged conversion Catalyst time at end of operating averaged over rate condition (hours) time operating time (% points) Sample 1 deactivated/ 370 67 70 19 activated Sample 2 deactivated/ 370 85 85 4 regenerated/ activated Sample 3 deactivated/ 370 89 92 0 regenerated/ activated Sample 4 fresh/ 361 89 89 activated

(16) It is evident from Table 1 that a deactivated catalyst which has been activated only (Sample 1) exhibits an unfavorable hydroperoxypropanol conversion rate of only 67% at the end of an operation time of 370 hours. The hydroperoxypropanol conversion rate averaged over these 370 hours was 70%.

(17) On the other hand, the catalysts which are regenerated according to the process of the present invention (Sample 2 and Sample 3) show a hydroperoxypropanol conversion rate of 85% and 89%, respectively, at the end of the running time of 370 hours, which corresponds to an averaged conversion rate of 85% and 92%. The catalytic activity of the supported noble metal catalyst regenerated according to the process of the present invention is therefore in the range or equal to the catalytic activity of fresh catalyst (Sample 4), for which a hydroperoxypropanol conversion rate of 89% at the end of the running time and also an average conversion rate of 89% was determined. For the consideration of the average conversion rate of Samples 1 to 4, it was disregarded that the overall running time for Sample 4 was 361 hours instead of 370 hours.

(18) From the average conversion rates, further the differential conversion rates of Samples 1 to 3 relative to Sample 4 representing fresh catalyst were determined (right column of Table 1). Favorably, the average conversion rates of Samples 2 and 3 regenerated according to the process of the invention deviate by only 4 and 0% points from the average conversion rate of Sample 4. In contrast, the average conversion rate of comparative Sample 1 deviated from the average conversion rate of Sample 4 by 19% points.

(19) B Regeneration of a Catalyst Used in the Hydrogenation of Hydroperoxypropanol in a Mixture Further Containing Methanol and Water

(20) The deactivated catalyst used in Comparative Example B1 and further in Example B1 and B2 originated from a process for the epoxidation of propene to yield propylene oxide. The epoxidation was carried out in the presence of a catalyst comprising a TS-1 zeolite. As solvent, methanol was employed. An aqueous hydrogen peroxide solution was employed as epoxidation agent. Propene as starting material was used as a mixture of propene and propane. The reaction mixture obtained was subjected to a separation stage where unreacted propene and propane were separated off by distillation as low boilers.

(21) The resulting mixture comprising methanol, water, and propylene oxide was subjected to a downstream separation stage where propylene oxide was distilled off as low boiler. The resulting liquid mixture contained methanol (75 weight-%), water (22 weight-%) and hydroperoxypropanol (0.5 weight.-%) and traces of further oxygenates including ethanol, acetaldehyde, methylformiate, isopropanol, dimethoxymethane, propyleneoxide, 2-propenol, n-propanol, propionaldehyde, methylacetate, 1,1-dimethoxyethane, acetone, 1-butanol, 1,1-dimethoxypropane, 2,4-dimethyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxypropane, 1-methoxy-2-propanol, 2-methoxy-1-propanol, propylene glycol, hydroxyacetone, 2-methylvaleraldehyd, 2-hexanone, 2-methylcyclohexanol, 2,6-dimethyl-4-heptanone, dipropylglycolmethylether, dipropyleneglycol, tripropyleneglycol. This liquid mixture was used as starting mixture subjected to hydrogenation.

(22) The hydrogenation catalyst consisted of 0.3 weight-% palladium supported on alpha-alumina (0.3% Pd/Al.sub.2O.sub.3). The catalyst was used in the form of strands having a diameter of 4 mm. Before starting a hydrogenation reaction, the fresh catalyst was activated in the reactor at 115 C. and 15 bar for 18 hours in a gas stream comprising a mixture of hydrogen (25 Nl/min) and nitrogen (10 Nl/min) (Nl=norm liter).

(23) The hydrogenation catalyst was in use until the conversion rate with respect to hydroperoxypropanol dropped below 80% relative to the respective conversion rate of the fresh catalyst. Portions of the deactivated catalyst were subjected to different regeneration processes, followed by determination of the respective catalytic activity.

Comparative Example B1

Regeneration of the Deactivated Catalyst by Activation with Hydrogen Only

(24) For Comparative Example B1, 25 g of the deactivated Pd/Al.sub.2O.sub.3 were transferred into the technical scale reactor already described in Comparative Example A1. The activation of the deactivated catalyst was carried out in the reactor at 115 C. and 15 bar for 18 hours in a gas stream comprising a mixture of hydrogen (25 Nl/min) and nitrogen (10 Nl/min) (Nl=norm liter) (Sample 5).

Example B1

Regeneration of the Deactivated Catalyst by Contacting with a Liquid Basic Aqueous System

(25) 30 g of the deactivated Pd/Al.sub.2O.sub.3 catalyst were submitted to regeneration in an alkaline aqueous medium according to the invention. The catalyst was immersed in ammonia solution (10 weight-% in water, having a pH of 10.5 at 80 C.) and heated in an autoclave under autogenous pressure for 4 hours at 120 C. Following the alkaline treatment, the catalyst was washed with water to a neutral pH and dried for 16 hours at 120 C. in air. After completed drying, the catalyst was calcinated for 2 hours at 450 C. in air.

(26) 25 g of the regenerated catalyst were transferred in the technical scale reactor and activated as described in Comparative Example A1 (Sample 6).

Example B2

Regeneration of the Deactivated Catalyst by Contacting with a Liquid Acidic Aqueous System

(27) 30 g of the deactivated Pd/Al.sub.2O.sub.3 catalyst were submitted to regeneration in an acidic aqueous medium according to the invention. The catalyst was immersed in oxalic acid solution (5 weight-% in water, having a pH of 1.0 at 82 C.) and heated in an autoclave under autogenous pressure for 4 hours at 120 C. Following the acidic treatment, the catalyst was washed with water to a neutral pH and dried for 16 hours at 120 C. in air. After completed drying, the catalyst was calcinated for 2 hours at 450 C. in air.

(28) 25 g of the regenerated catalyst were transferred in the technical scale reactor and activated as described in Comparative Example A1 (Sample 7).

Example B3

Catalytic Activity of the Regenerated Catalysts

(29) The regenerated catalysts of Comparative Example B1 and of Examples B1 and B2 (Samples 5 to 7) were used in a hydrogenation reaction performed at technical scale in the reactor described in Comparative Example 1. For further comparison, a hydrogenation of hydroperoxypropanol was also performed with 25 g fresh Pd/Al.sub.2O.sub.3 catalyst (Sample 8) which had been activated before in a reactor as described in Comparative Example A1.

(30) The liquid mixture described above, containing methanol, water, hydroperoxypropanol and the oxygenate traces was continuously fed into the technical scale reactor with a WHSV of 16 h.sup.1. A mixture of hydrogen and nitrogen was also introduced into the reactor (5 Nl/h H.sub.2 and 5 Nl/h N.sub.2). The reduction of hydroperoxypropanol was performed at a temperature of 55 C. and a pressure of 15 bar. The hydroperoxypropanol content was determined iodometrically according to DIN EN ISO 3960 from which the hydroperoxypropanol conversion rate was calculated.

(31) The individual operating times and conversion rates based on hydroperoxypropanol for the individual catalyst samples are summarized in Table 2 below.

(32) TABLE-US-00002 TABLE 2 The results according to Example B Operating Hydroperoxypropanol Average hydroperoxypropanol Catalyst time conversion rate (%) conversion rate (%) condition (hours) at end of operating time over operating time Sample 5 deactivated/ 191 87 88 activated Sample 6 deactivated/ 1160 94 96 regenerated/ activated Sample 7 deactivated/ 404 93 93 regenerated/ activated Sample 8 fresh/ 914 95 95 activated

(33) The results in Table 2 clearly show that deactivated catalyst which has been only activated has a hydroperoxypropanol conversion rate of merely 87% after 191 hours of operating time (Sample 5). The average hydroperoxypropanol conversion rate over the operating time of 191 hours was determined to be 88%.

(34) Surprisingly, the catalysts which have been regenerated according to the process of the present invention (Sample 6 and Sample 7), show a significantly increased hydroperoxypropanol conversion rate of 94% and 93%, respectively, relative to the catalyst which has been activated only (Sample 5) following 1160 and 404 hours operating time. The catalytic activity of the supported noble metal catalyst regenerated according to the process of the present invention is therefore in the range of the catalytic activity of fresh catalyst (Sample 8), for which a hydroperoxypropanol conversion rate of 95% was determined after 914 hours running time. It is further noted that like Sample 8, the average conversion rates of Samples 6 and 7 (96% and 93%) differed only slightly or not at all from the conversion rates at the end of their respective operating times (94% and 93%), indicating a stable catalytic performance.

CITED LITERATURE

(35) WO 02/062779 A WO 2007/074101 A EP 0 200 260 A Ullmann's Encycolpedia of Industrial Chemistry, 5th edition, volume 3 (1989) pages 447-457