CATALYST FOR ETHANE ODH

Abstract

A catalyst for oxidative dehydrogenation (ODH) of ethane with an empirical formula Mo—V—Te—Nb—Pd—O produced using a process comprising impregnation of the Pd component on the surface of the catalyst following a calcination step using a Pd compound free of halogens. The resulting catalyst can be used in both diluted and undiluted ODH processes and shows higher than expected activity without any loss of selectivity.

Claims

1. A process for preparing an oxidative dehydrogenation catalyst comprising a mixed metal oxide having the empirical formula
Mo.sub.aV.sub.bTe.sub.cNb.sub.dPd.sub.eO.sub.f wherein a, b, c, d, e and f are the relative atomic amounts of the elements Mo, V, Te, Nb, Pd and O, respectively; and when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, 0.001<e≦0.10 and f is dependent on the oxidation state of the other elements; the process comprising: i) admixing compounds of elements Mo, V, Te, and Nb, in a solvent comprising water to produce a first mixture; ii) heating said first mixture in a first pressurized vessel at a temperature of from 100° C. to 200° C., for from 6 hours to 240 hours; iii) recovering first insoluble material from said first pressurized vessel; iv) subjecting said first recovered insoluble material to a calcining under an inert atmosphere to produce a calcined product; v) then, impregnating said calcined product from iv) with an aqueous solution of a Pd compound free of halogens to form second mixture; vi) subjecting said second mixture to drying at a temperature of from 50° C. to 150° C., for from 1 hour to 48 hours; and vii) recovering second insoluble material from vi) to obtain a catalyst.

2. The process of claim 1 wherein the step ii) heating of said first mixture in said first pressurized vessel is done at a temperature of from 160° C. to 185° C.

3. The process of claim 1 wherein the step vi) drying temperature is from 120° C. to 130° C.

4. The process of claim 1 wherein b equals from 0.1 to 0.5.

5. The process of claim 1 wherein b equals from 0.2 to 0.4.

6. The process of claim 1 wherein c equals from 0.05 to 0.4.

7. The process of claim 1 wherein c equals from 0.08 to 0.3.

8. The process of claim 1 wherein d equals from 0.05 to 0.4.

9. The process of claim 1 wherein d equals from 0.08 to 0.3.

10. The process of claim 1 wherein d equals from 0.10 to 0.25.

11. The process of claim 1 wherein e equals from 0.005 to 0.10.

12. The process of claim 1 wherein e equals from 0.01 to 0.05.

13. The process of claim 1 wherein e equals from 0.015 to 0.03.

14. The process of claim 1 wherein the inert atmosphere comprises gaseous nitrogen.

15. The process of claim 1 wherein the said first recovered insoluble material is calcined at a temperature of from 500° C. to 700° C., (preferably from 550° C. to 650° C., most preferably from 580° C. to 620° C.), for from 1 hours to 8 hours.

16. The process of claim 1 wherein the said first recovered insoluble material is calcined by ramping temperature from at or about room temperature to at or about 600° C. over a period of 4 to 7 hours, followed by holding at or about 600° C. for from 1 hour to 4 hours.

17. The process of claim 1 wherein the Pd compound free of halogens is selected from [Pd(NH.sub.3).sub.4](NO.sub.3).sub.2, Pd(HCO.sub.3).sub.2, Pd(CH.sub.3COO).sub.2 and an analogous Pd containing salt.

18. The process of claim 1 wherein impregnation of said calcined product is accomplished by admixing an aqueous solution of a Pd compound free of halogens.

19. An oxidative dehydrogenation catalyst comprising a mixed metal oxide having the empirical formula
Mo.sub.aV.sub.bTe.sub.cNb.sub.dPd.sub.eO.sub.f wherein a, b, c, d, e and f are the relative atomic amounts of the elements Mo, V, Te, Nb, Pd and O, respectively; and when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, 0.001<e≦0.10 and f is dependent on the oxidation state of the other elements; prepared by a process comprising: i) admixing compounds of elements Mo, V, Te, and Nb, in a solvent comprising water to produce a first mixture; ii) heating said first mixture in a first pressurized vessel at a temperature of from 100° C. to 200° C., for from 6 hours to 240 hours; iii) recovering first insoluble material from said first pressurized vessel; iv) subjecting said first recovered insoluble material to a calcining under an inert atmosphere to produce a calcined product; v) then, impregnating said calcined product from iv) with an aqueous solution of a Pd compound free of halogens to form second mixture; vi) subjecting said second mixture to drying at a temperature of from 50° C. to 150° C., for from 1 hour to 48 hours; and vii) recovering second insoluble material from vi) to obtain a catalyst.

20. The process of claim 19 wherein impregnation of said calcined product is accomplished by admixing an aqueous solution of a Pd compound free of halogens.

Description

EXAMPLES

Comparative Example 1

(No Pd Component)

[0039] 2.65 g of ammonium heptamolybdate (tetrahydrate) and 0.575 g of telluric acid were dissolved in 19.5 g of distilled water at 80° C. and the pH adjusted to 7.5 using a 25% aqueous solution of ammonium hydroxide. The water was evaporated by stirring at 80° C., and the solid precipitate dried at 90° C. 3.0 g of the precipitate was suspended in water (21.3 g) at 80° C. and 0.9 g of vanadyl sulfate and 1.039 g of niobium oxalate were added. The mixture was stirred for 10 min and then transferred to an autoclave with a Teflon® (tetrafluoroethylene) lining. Air in the autoclave was substituted with argon, the autoclave was pressurized and heated to 175° C. for 60 hours. The solid formed was filtered, washed with distilled water and dried at 80° C. to produce an active catalyst phase that was calcined at 600° C. (2 h) in a flow of argon. The temperature for calcination was ramped from room temperature to 600° C. at 1.67° C./min. The resulting powder was pressed and the required mesh size particles were collected. The resulting catalyst comprised an atomic element ratio (oxygen not included) of Mo.sub.1.0V.sub.0.31Te.sub.0.17Nb.sub.0.16.—calculated by molar ratio stoichiometry of reagents.

Comparative Example 2

(Impregnation with PdCl.SUB.2.)

[0040] The catalyst was prepared according to Comparative Example 1 with the exception that after calcining the sample at 600° C., the catalyst was ground in a mortar with a small amount of water (about 5 ml per gram of the catalyst) for 20 min. The suspension of the catalyst in water was transferred into a glass beaker (volume 50 ml) and then a solution containing 0.1 mmol of PdCl.sub.2 in 10 ml of water was added to the suspension. The beaker content was stirred by a magnetic stirrer with a low rate for 2 h. The beaker was placed in a water bath at a temperature of 80° C. and the content was stirred until the liquid in the beaker was fully removed. The beaker with the catalyst was transferred into a drying box and was dried overnight at 120° C. The catalyst obtained was ground in a mortar and pressed into tablets that were crashed into particles 0.8-1.0 mm. The resulting catalyst comprised an atomic element ratio (oxygen not included) of Mo.sub.1.0V.sub.0.31Te.sub.0.17Nb.sub.0.16Pd.sub.0.02.—calculated by molar ratio stoichiometry of reagents.

Comparative Example 3

(Direct Pd Incorporation)

[0041] 2.65 g of ammonium heptamolybdate (tetrahydrate) and 0.575 g of telluric acid were dissolved in 19.5 g of distilled water at 80° C. and the pH adjusted to 7.5 with a 25% aqueous solution of ammonium hydroxide. Water was evaporated by stirring at 80° C. The solid precipitate was dried at 90° C. 3.0 g of the precipitate was suspended in water (21.3 g) at 80° C. and 0.9 g of vanadyl sulfate and 1.039 g of niobium oxalate were added together with palladium in the form of [Pd(NH.sub.3).sub.4](NO.sub.3).sub.2] in amounts to produce an atomic element ratio (oxygen not included) of Mo.sub.1.0V.sub.0.31Te.sub.0.17Nb.sub.0.16Pd.sub.0.02. The catalyst was calcined at 600° C. (2 h) in a flow of argon, where the temperature was ramped from room temperature to 600° C. at 1.67° C./min. The powder was pressed and the required mesh size particles were collected.

Example 1

(Pd Nitrate Incorporation)

[0042] The catalyst was prepared according to Comparative Example 1 with the exception that after calcining the sample at 600° C., the catalyst was ground in a mortar with a small amount of water (about 5 ml per gram of the catalyst) for 20 min. The suspension of the catalyst in water was transferred into a glass beaker (volume 50 ml) and then a solution containing 0.1 mmol of [Pd(NH.sub.3).sub.4](NO.sub.3).sub.2] in 10 ml of water was added to the suspension. The beaker content was stirred by a magnetic stirrer at a low rate for 2 h. The beaker was placed in a water bath at a temperature of 80° C. and the content was stirred until the liquid in the beaker had evaporated completely. The beaker with the catalyst was transferred into a drying box and was dried overnight at 120° C. The resulting catalyst was ground in a mortar and pressed into tablets that were crushed into particles 0.8-1.0 mm. The resulting catalyst comprised an atomic element ratio (oxygen not included) of Mo.sub.1.0V.sub.0.31Te.sub.0.17Nb.sub.0.16Pd.sub.0.02.

Example 2

(Pd Carbonate Incorporation)

[0043] The catalyst was prepared according to Example 1 with the exception that after calcining the sample at 600° C., the catalyst was treated with an aqueous solution of Pd(HCO.sub.3).sub.2 to introduce the amount of palladium corresponding to a final atomic element ratio (oxygen not included) of M.sub.1.0V.sub.0.31Te.sub.0.17Nb.sub.0.16Pd.sub.0.02.

Example 3

(Pd Acetate Incorporation)

[0044] The catalyst was prepared according to Example 1 with the exception that after calcining the sample at 600° C., the catalyst was treated with an aqueous solution of Pd(CH.sub.3COO).sub.2 to introduce the amount of palladium corresponding to a final atomic element ration (oxygen not included) of Mo.sub.1.0V.sub.0.31Te.sub.0.17Nb.sub.0.16Pd.sub.0.02.

ODH Testing Conditions

[0045] All catalysts were tested for ability to catalyze oxidative dehydrogenation of ethane using a gas mixture O.sub.2/C.sub.2H.sub.6 with an O.sub.2 content of 25% (outside the explosive limit). The mixture was fed into a plug-flow reactor with a gas hourly space velocity of 4500 h.sup.−1 at a pressure of 1 atm, and a temperature that ranged from 320-440° C. (or for example at 420° C.). The amount of catalyst loading ranged from 0.13-1.3 g; fraction 0.25-0.5 mm, a flow type reactor with a stationary catalyst bed was used. The catalyst was heated to 360° C. in the reaction mixture and the catalytic activity was measured at 420° C. The data are presented in Table 1.

TABLE-US-00001 TABLE 1 Summary of results Space-time yield of ethylene Ethane Oxygen (Productivity). Ethylene conversion, conversion, mmol/h per Selectivity Example % % g of catalyst % 1 33 56 60 97.5 (Compar- ative) 2 6 17 — 96 (Compar- ative) 3 31 53 55 97 (Compar- ative) 1 49 83 94 98 2 48 81 91 98 3 46 80 88 98