Alkane dehydrogenation catalyst and process for its preparation

Abstract

The invention relates to a catalyst composition comprising (a) a metal M selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), rhenium (Re), ruthenium (Ru) and iridium (Ir), (b) tin (Sn), (c) zinc (Zn), (d) alkaline earth metal and (e) a porous metal oxide catalyst support, wherein the amount of each of elements (a), (b) and (d) is independently chosen in the range of from 0.1 to 5 wt. % based on the porous metal oxide catalyst support and wherein the amount of element (c) is chosen in the range of from 0.1 to 2 wt. % based on the porous metal oxide catalyst support. Furthermore, the invention also relates to a process for the preparation of said catalyst composition and its use in non-oxidative dehydrogenation of an alkane, preferably propane.

Claims

1. A catalyst composition comprising: (a) a metal M selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), rhenium (Re), ruthenium (Ru) and iridium (Ir); (b) tin (Sn); (c) zinc (Zn); (d) alkaline earth metal; and (e) a porous metal oxide catalyst support; wherein the amount of each of elements (a), (b) and (d) is independently chosen in the range of from 0.1 to 5 wt. % based on the porous metal oxide catalyst support and wherein the amount of element (c) is chosen in the range of from 0.1 to 2 wt. % based on the porous metal oxide catalyst support.

2. The catalyst composition according to claim 1, wherein the alkaline earth metal is selected from the group consisting of magnesium (Mg), calcium (Ca) and strontium (Sr).

3. The catalyst composition according to claim 1, wherein the metal M is platinum (Pt).

4. The catalyst composition according to claim 1, wherein the porous metal oxide catalyst support is selected from the group of γ-alumina (γ-Al.sub.2O.sub.3), titania (TiO.sub.2), ceria (CeO.sub.2), zirconia (ZrO.sub.2) and mixtures thereof.

5. The catalyst composition according to claim 4, wherein the porous metal oxide catalyst support is γ-alumina (γ-Al.sub.2O.sub.3).

6. The catalyst composition according to claim 1, wherein the porous metal oxide catalyst support has a BET surface area of 50-500 m.sup.2/g.

7. A process for the preparation of a catalyst composition according to claim 1 comprising: (a) depositing the metal M, Sn, Zn and the alkaline earth metal on the porous metal oxide catalyst support to obtain a catalyst precursor; and (b) subjecting the catalyst precursor to calcination in an environment comprising oxygen to obtain a catalyst, wherein step (a) comprises (a1) contacting the porous metal oxide catalyst support with a solution comprising a salt of the metal M, a salt of tin (Sn), a salt of zinc (Zn) and a salt of the alkaline earth metal, and subsequently; (a2) evaporating the liquid in said solution to prepare a modified slurry; and optionally (a3) washing the modified slurry with a solvent to obtain the catalyst precursor.

8. The process according to claim 7, wherein step (a) comprises: (a1) contacting the porous metal oxide catalyst support with a solution comprising a salt of the metal M, a salt of tin (Sn), a salt of zinc (Zn) and a salt of the alkaline earth metal, and subsequently; (a2) evaporating the liquid in said solution to prepare a modified slurry; and (a3) washing the modified slurry with a solvent to obtain the catalyst precursor.

9. The process according to claim 7, wherein calcination is performed at a temperature of 400 to 650° C. for 1 to 6 hours.

10. The process according to claim 7, wherein the solution has a pH in the range from 4 to 7.5.

11. The catalyst composition according to claim 1, wherein the alkaline earth metal is calcium (Ca).

12. The catalyst composition according to claim 1, wherein the amount of each of elements (a), (b) and (d) is independently chosen in the range of 0.5 to 2 wt %, based on the porous metal oxide catalyst support.

13. A catalyst composition, comprising: (a) a metal M selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), rhenium (Re), ruthenium (Ru) and iridium (Ir); (b) tin (Sn); (c) zinc (Zn); (d) alkaline earth metal; and (e) a porous metal oxide catalyst support; wherein the amount of each of elements (a), (b) and (d) is independently chosen in the range of from 0.1 to 5 wt. % based on the porous metal oxide catalyst support and wherein the amount of element (c) is chosen in the range of from 0.1 to 2 wt. % based on the porous metal oxide catalyst support; wherein the catalyst composition is obtained by a process comprising (a) depositing the metal M, Sn, Zn and the alkaline earth metal on the porous metal oxide catalyst support to obtain a catalyst precursor; and (b) subjecting the catalyst precursor to calcination in an environment comprising oxygen to obtain a catalyst; wherein step (a) comprises the steps of (a1) contacting the porous metal oxide catalyst support with a solution comprising a salt of the metal M, a salt of tin (Sn), a salt of zinc (Zn) and a salt of the alkaline earth metal, and subsequently; (a2) evaporating the liquid in said solution to prepare a modified slurry; and optionally (a3) washing the modified slurry with a solvent to obtain the catalyst precursor.

14. A process for producing an alkene by non-oxidative dehydrogenation of an alkane comprising the step of contacting a feed stream comprising the alkane with the catalyst composition of claim 1 to form the alkene.

15. The process according to claim 14, wherein the alkane is propane.

16. The process according to claim 14, wherein the non-oxidative dehydrogenation is performed at a temperature of from 400 to 650° C., a weight hourly space velocity of 0.1-1 hour.sup.−1 and/or a pressure of 0.01-0.3 MPa.

17. A process for producing an alkene by non-oxidative dehydrogenation of an alkane comprising the step of contacting a feed stream comprising the alkane with the catalyst composition of claim 13 to form the alkene.

18. The catalyst composition according to claim 13, wherein the solution has a pH in the range from 4 to 7.5.

Description

EXAMPLES

Example 1

Preparation of Pt—Sn—Ca—Zn/γ-Al2O3 Catalyst (Catalyst A)

(1) 5 g of γ-Al.sub.2O.sub.3 was dried at 120° C. for 2 hours. 0.0885 g of PtCl.sub.4 was dissolved in 20 ml of deionized (DI) water. 0.0965 g of SnCl.sub.2 was dissolved in 15 ml ethanol. 0.1450 g of CaCl.sub.2 was dissolved in 10 ml of DI water. 0.1041 g of ZnCl.sub.2 was dissolved in 10 ml of DI water. It was assured that the solutions of all salts were transparent and that there was no suspension at all.

(2) The temperature of the water bath was set to 65° C. The evaporating flask of Rotavapor was filled up with DI water in a volume of 200 ml minus the volume of the salt solutions. When the temperature became stable at 65° C., all solutions prepared were added to the evaporating flask to obtain a total solution volume of 200 ml. The preheated support (γ-Al.sub.2O.sub.3 at a temperature of about 65° C.) was added to the flask and the solution was kept on rotation at 65° C. for 3.5 hours. Then the solution was evaporated under vacuum until only solid slurry was left.

(3) The slurry was then dried for 2 hours at 120° C. in the oven. The dried catalyst mass was then washed with hot water to remove chloride ions. An AgNO.sub.3 test was used to ensure the complete removal of chlorides. The washed catalyst was again dried for 2 hours at 120° C. and was then calcined at a temperature of 600° C. for 6 hours. The calcination temperature was achieved at a ramp rate of 10° C./minute.

Example 2

Preparation of Pt—Sn—Sr—Zn/γ-Al2O3 Catalyst (Catalyst B)

(4) A Pt—Sn—Sr—Zn/γ-Al.sub.2O.sub.3 catalyst was prepared in a manner similar to example 1, with the difference that instead of dissolving 0.1450 g of CaCl.sub.2, 0.1521 g of SrCl.sub.2 was dissolved in 10 ml of DI water.

Example 3

Preparation of Catalysts for the Comparative Examples

(5) A Pt—Sn/γ-Al.sub.2O.sub.3 catalyst (comparative catalyst C), Pt—Sn—Ca/γ-Al.sub.2O.sub.3 catalyst (comparative catalyst D), Pt—Sn—Zn/γ-Al.sub.2O.sub.3 catalyst (comparative catalyst E) were prepared in the same way as in example 1 with the difference that for comparative catalyst C, the solutions of CaCl.sub.2 and ZnCl.sub.2 were not used for comparative catalyst D, the solution of ZnCl.sub.2 was not used for comparative catalyst E, the solution of CaCl.sub.2 was not used.

Example 4

Preparation of Pt—Sn—Ca—Zn/ZSM-5 Catalyst

(6) A Pt—Sn—Ca—Zn catalyst was prepared in a manner similar to example 1, with the difference that instead of γ-Al.sub.2O.sub.3, 5 g of a ZSM-5 zeolite support was used. The resulting Pt—Sn—Ca—Zn/ZSM-5 catalyst is hereafter referred to as comparative catalyst F.

Example 5

Testing of the Catalytic Activity of Catalysts A, B and Comparative Catalysts C, D, E and F

(7) The catalytic activity of the catalysts A, B and comparative catalysts C, D, E and F in propane dehydrogenation was measured in a quartz flow reactor having an internal diameter of 10 mm. To this end, 0.25-1.0 g catalyst was mixed with 1.0 g quartz sand (mesh size 12-25) and added to the quartz flow reactor. The reaction temperature was kept at 575° C. as measured by a thermocouple located in the catalyst bed. The feed stream contained H.sub.2:propane:N.sub.2 in a volume ratio of 1:1:5. The gas hourly space velocity (GHSV) of the feed stream was 3800.h.sup.−1. The flow rate of the feed stream was controlled by mass flow controllers at the reactor inlet.

(8) Before use, the catalysts were reduced in the reactor at a temperature of 575° C. for 2 hours.

(9) The inlet and outlet composition of the reactants was analyzed by gas chromatograph SRI8610C (USA) with PID and HWD detectors. The reaction products were separated on a 2 m column filled with alkalinized alumina using nitrogen as a carrier gas.

(10) The results of example 5 are presented in Table 1 below; wherein Conv (%) is the conversion of propane in %. Sel (%) is the selectivity of the catalyst towards propylene in the feed stream in % Yield (%) is the selectivity towards propylene multiplied by the conversion of propane.

(11) Carbon is the amount of carbon that is formed on the catalyst in mg/(g.Math.h) as measured using TGA (thermogravimetric analysis).

(12) TABLE-US-00001 TABLE 1 Catalytic activity data of from catalytic tests at feed composition of H.sub.2:C.sub.3H.sub.8:N2 = 1:1:5, a GHSV of 3800 h.sup.−1 and a temperature 575° C. Cata- Conv Sel Yield Product composition (mole %) lyst (%) (%) (%) Cokes.sup.1 C.sub.3H.sub.8 CH.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.4 C.sub.3H.sub.6 A 43.9 95.8 36.0 7.1 58.4 2.9 0.2 2.3 36.2 B 34.8 96.8 30.1 8.0 67.7 0.6 0.4 0.1 31.3 C 42.1 92.1 19.8 15.4 72.9 0.8 1.2 0.1 25.0 D 49.8 60.5 30.7 13.2 49.7 13.0 5.6 1.3 30.4 E 45.0 96.5 21.2 12.7 71.05 0.35 0.63 0.05 27.93 F 62.0 27.1 12.2 33.2 45.7 18.4 17.2 4.0 14.7 .sup.1The amount of cokes formed on the catalyst is given in mg .Math. g cat.sup.−1 .Math. h.sup.−1.

(13) As can be seen from Table 1 above, propene is formed in a high yield when using the catalysts of the invention (catalysts A and B) as compared to comparative catalysts C—F. Also, the catalysts of the invention show a high selectivity towards propane. Furthermore, the amount of coke formed on the catalysts of the invention is lower.

(14) This demonstrates the catalyst composition of the invention is capable of catalyzing the conversion of propane to propene in a non-oxidative dehydrogenation process in a high yield and with a high selectivity. It also demonstrates that the amount of coke formed on the catalyst in the catalyst composition of the invention may be lower. Also, the catalyst composition of the invention may be more stable for a longer Time on Stream (TOS).

(15) Catalyst A has the further advantage that as a byproduct, relatively more ethylene is formed. This demonstrates that the total amount of valuable products that may be obtained in a non-oxidative dehydrogenation of propane is higher when using the catalyst according to the second special embodiment of the invention.

(16) Set forth below are some embodiments of the catalyst composition, methods for making and using the catalyst composition.

(17) Embodiment 1: A catalyst composition comprising: (a) a metal M selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), rhenium (Re), ruthenium (Ru) and iridium (Ir); (b) tin (Sn); (c) zinc (Zn); (d) alkaline earth metal; and (e) a porous metal oxide catalyst support; wherein the amount of each of elements (a), (b) and (d) is independently chosen in the range of from 0.1 to 5 wt. % based on the porous metal oxide catalyst support and wherein the amount of element (c) is chosen in the range of from 0.1 to 2 wt. % based on the porous metal oxide catalyst support.

(18) Embodiment 2: The catalyst composition according to Embodiment 1, wherein the alkaline earth metal is selected from the group consisting of magnesium (Mg), calcium (Ca) and strontium (Sr), preferably calcium (Ca).

(19) Embodiment 3: The catalyst composition according to Embodiment 1 or Embodiment 2, wherein the metal M is platinum (Pt).

(20) Embodiment 4: The catalyst composition according to any one of Embodiments 1-3, wherein the porous metal oxide catalyst support is selected from the group of γ-alumina (γ-Al.sub.2O.sub.3), titania (TiO.sub.2), ceria (CeO.sub.2), zirconia (ZrO.sub.2) and mixtures thereof, preferably γ-alumina (γ-Al.sub.2O.sub.3).

(21) Embodiment 5: The catalyst composition according to any one of Embodiments 1-4, wherein the porous metal oxide catalyst support has a BET surface area of 50-500 m.sup.2/g.

(22) Embodiment 6: The process for the preparation of a catalyst composition according to any one of Embodiments 1-5 comprising: (a) depositing the metal M, Sn, Zn and the alkaline earth metal on the porous metal oxide catalyst support to obtain a catalyst precursor; and (b) subjecting the catalyst precursor to calcination in an environment comprising oxygen to obtain a catalyst.

(23) Embodiment 7: The process according to Embodiment 6, wherein step (a) comprises: (a1) contacting the porous metal oxide catalyst support with a solution comprising a salt of the metal M, a salt of tin (Sn), a salt of zinc (Zn) and a salt of the alkaline earth metal, and subsequently; (a2) evaporating the liquid in said solution to prepare a modified slurry; and (a3) washing the modified slurry with a solvent to obtain the catalyst precursor.

(24) Embodiment 8: The process according to Embodiment 6 or 7, wherein calcination is performed at a temperature of 400 to 650° C. for 1 to 6 hours.

(25) Embodiment 9: A catalyst composition, comprising: (a) a metal M selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), rhenium (Re), ruthenium (Ru) and iridium (Ir); (b) tin (Sn); (c) zinc (Zn); (d) alkaline earth metal; and (e) a porous metal oxide catalyst support; wherein the amount of each of elements (a), (b) and (d) is independently chosen in the range of from 0.1 to 5 wt. % based on the porous metal oxide catalyst support and wherein the amount of element (c) is chosen in the range of from 0.1 to 2 wt. % based on the porous metal oxide catalyst support; wherein the catalyst composition is obtained or obtainable by a process comprising (a) depositing the metal M, Sn, Zn and the alkaline earth metal on the porous metal oxide catalyst support to obtain a catalyst precursor; and (b) subjecting the catalyst precursor to calcination in an environment comprising oxygen to obtain a catalyst; wherein step (a) comprises the steps of (a1) contacting the porous metal oxide catalyst support with a solution comprising a salt of the metal M, a salt of tin (Sn), a salt of zinc (Zn) and a salt of the alkaline earth metal, and subsequently; (a2) evaporating the liquid in said solution to prepare a modified slurry; and optionally (a3) washing the modified slurry with a solvent to obtain the catalyst precursor.

(26) Embodiment 10: A process for producing an alkene by non-oxidative dehydrogenation of an alkane comprising the step of contacting a feed stream comprising the alkane with the catalyst composition of any one of Embodiments 1-5 and 9, to form the alkene.

(27) Embodiment 11: The process according to Embodiment 10, wherein the alkane is propane.

(28) Embodiment 12: The process according to Embodiment 10 or 11, wherein the non-oxidative dehydrogenation is performed at a temperature of from 400 to 650° C., a weight hourly space velocity of 0.1-1 hour.sup.−1 and/or a pressure of 0.01-0.3 MPa.

(29) Embodiment 13: A use of the catalyst composition of any one of Embodiments 1-5 or of Embodiment 9 in a non-oxidative dehydrogenation of an alkane.