Catalyst for ethane ODH

Abstract

A catalyst for oxidative dehydrogenation (ODH) of ethane with an empirical formula MoVTeNbPdO 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=0.02 to 0.4, c=0.08 to 0.3, d=0.01 to 0.25, 0.015<e0.03 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 at a temperature of from 500 C. to 700 C., for from 1 hour to 8 hours 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: wherein the process excludes calcination after the impregnation of Pd in step v).

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 the inert atmosphere comprises gaseous nitrogen.

5. 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.

6. 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.

7. 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.

Description

EXAMPLES

Comparative Example 1

No Pd Component

(1) 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 PdCl2

(2) 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

(3) 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

(4) 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

(5) 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

(6) 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.

(7) ODH Testing Conditions

(8) 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.

(9) 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