Catalyst composition for the dehydrogenation of alkanes

Abstract

The invention relates to a catalyst composition suitable for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms comprising silico-zinc aluminate, wherein the relative molar ratios of the elements comprised in said composition are represented by Si.sub.xZn.sub.1-xAl.sub.2O.sub.4, wherein x stands for a number in the range from 0.003 to 0.76. The invention also relates to a process for the preparation of said catalyst composition, to a process for the non-oxidative dehydrogenation of alkanes, preferably isobutane using said catalyst and to the use of said catalyst in a process for the non-oxidative dehydrogenation of alkanes.

Claims

1. A catalyst composition suitable for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms comprising silico-zinc aluminate, wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1)
Si.sub.xZn.sub.1-xAl.sub.2O.sub.4(1) wherein x stands for a number in the range from 0.05 to 0.76.

2. The catalyst composition according to claim 1, wherein the catalyst composition further comprises zinc aluminate and/or an oxide of silicon and/or an oxide of aluminum and/or an oxide of zinc.

3. The catalyst composition according to claim 1, wherein said catalyst composition is essentially platinum free.

4. The catalyst composition according to claim 1, wherein the silico-zinc aluminate has a spinel structure.

5. The catalyst composition according to claim 1, wherein the catalyst composition additionally comprises M, wherein M is selected from the group of alkali, alkaline earth metals, 3-5d elements and mixtures thereof, wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1a)
M/Si.sub.xZn.sub.1-xAl.sub.2O.sub.4(1a) wherein x is as defined above.

6. The catalyst composition according to claim 5, wherein M is selected from the group of sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), strontium (Sr), barium (Ba), magnesium (Mg), calcium (Ca), gallium (Ga), germanium (Ge), tin (Sn), copper (Cu), zirconium (Zr), cobalt (Co), manganese (Mn), molybdenum (Mo), tungsten (W) and mixtures comprising at least one of the foregoing.

7. The catalyst composition according to claim 5, wherein M is present in an amount from 0.01 to 5 wt % based on the silico-zinc aluminate.

8. Process for the preparation of a catalyst composition according to claim 1 comprising: (a) preparing a solution and/or suspension comprising silicon, zinc and aluminum to form a silicon- and zinc- and aluminum-comprising solution and/or suspension, (b) admixing a basic solution, preferably ammonia, to the silicon- and zinc- and aluminum-comprising solution and/or suspension to co-precipitate mixed hydroxides and/or oxides of zinc, aluminum and silicon, and (c) calcining the co-precipitate obtained in step (b).

9. The process according to claim 8, wherein the silicon- and zinc- and aluminum-comprising solution and/or suspension further comprises M before admixing the basic solution in step (b), or wherein the silico-zinc aluminate formed in step (c) is contacted with an M-comprising salt solution, wherein M is as defined above.

10. The process according to claim 8 wherein one or more of the salts in the silicon- and zinc- and aluminum-comprising solution and/or suspension or at least one of the salts in the M-comprising salt solution or the silicon- and zinc- and aluminum solution and/or suspension further comprising M or in the M-comprising salt solution is a nitrate salt.

11. The process according to claim 8, wherein the silico-zinc aluminate is calcined at 500-1100 C. for 2-24 hours in an oxygen containing atmosphere.

12. The process according to claim 8, further comprising (d) contacting the catalyst composition obtained in step (c) with a reducing agent.

13. The process for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms comprising contacting said alkanes with the catalyst composition of claim 1.

14. The process according to claim 13, wherein the process is performed at a reaction temperature of 500-600 C., a weight hourly space velocity (WHSV) of 0.1-1 h.sup.1 and a pressure of 0.01-0.3 MPa.

15. A catalyst composition suitable for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms comprising silico-zinc aluminate, wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1)
Si.sub.xZn.sub.1-xAl.sub.2O.sub.4(1) wherein x stands for a number in the range from 0.05 to 0.76; wherein said catalyst composition is essentially platinum free; and wherein the silico-zinc aluminate has a spinel structure.

16. The catalyst composition according to claim 15, wherein the catalyst composition additionally comprises M, wherein M is selected from the group of alkali, alkaline earth metals, 3-5d elements and mixtures thereof, wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1a)
M/Si.sub.xZn.sub.1-xAl.sub.2O.sub.4(1a) wherein x is as defined above.

17. The catalyst composition according to claim 16, wherein M is selected from the group of sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), strontium (Sr), barium (Ba), magnesium (Mg), calcium (Ca), gallium (Ga), germanium (Ge), tin (Sn), copper (Cu), zirconium (Zr), cobalt (Co), manganese (Mn), molybdenum (Mo), tungsten (W) and mixtures comprising at least one of the foregoing.

18. The catalyst composition according to claim 16, wherein M is present in an amount from 0.01 to 5 wt % based on the silico-zinc aluminate.

19. The catalyst composition according to claim 15, wherein the catalyst composition further comprises zinc aluminate and/or an oxide of silicon and/or an oxide of aluminum and/or an oxide of zinc.

Description

EXAMPLES

Example 1

Preparation of Silico-Zinc Aluminate

(1) 27.63 g zinc nitrate hexahydrate was dissolved in 60 ml demineralised water. 69.68 g of aluminum nitrate nonahydrate was dissolved in 230 ml of demineralised (DM) water. 1.0 g silica gel was mixed in 20 ml of DM water. All three solutions/mixtures were mixed in a four-necked round bottom flask (1000 ml) equipped with dropping funnel, reflux condenser and thermometer. The mixture was slowly heated to 80 C. Then aqueous ammonia solution (10 wt %) was added drop wise to the mixture with continuous stilling. The addition was stopped when the pH of the hot mixture in the 4-neck flask was measured 7.0-8.0. This mixture was further digested at 80 C. for 2 hours. Then the hot slurry formed was filtered under vacuum and washed with DM water up to the pH of the filtrate was reached 7.0. Then the wet cake was dried at 100 C. in an air oven for 4 hours. The dried solid was, then, calcined in a muffle furnace at 800 C. for 4 hours in presence of air.

Example 2

Preparation of Catalyst Particles

(2) A number of catalyst compositions comprising different silico-zinc aluminates and binder or diluents (alpha alumina) were prepared in particle form by mixing the silico-zinc aluminate and the binder support thoroughly in a 1:1 weight ratio. The mixture was pressed at 10 ton pressure to make pellets. The pressed catalyst compositions were crushed and sieved. The fraction containing particles from 0.5 to 1.0 mm were selected for further use. The particles of the active silico-zinc aluminate component, and binder were also prepared separately after which the two components (in particle forms) were mixed in a 1:1 ratio (wt/wt) to prepare the final catalyst composition and perform the catalytic testing.

Example 3

Catalyst Testing

(3) Five grams catalyst particles (particle size 0.5-1.0 mm) were loaded in a down flow fixed bed micro catalytic reactor and pre-treated in the following way:

(4) Step 1: Exposed for 10-60 min to nitrogen at the flow rate of 100 ml/min at 550 C.

(5) Step 2: Exposed for 5-60 min to hydrogen at the flow rate of 100 ml/min at 550 C.

(6) After the pre-treatment, isobutane was fed to the reactor at 19 ml/min. The temperature of the catalyst bed before start of isobutane flow was maintained at 550 C. Pure isobutane was used as feed-stream. The Weight Hourly Space Velocity (WHSV) was 0.54 h.sup.1. The product stream coming out of the reactor was analyzed by an on-line Gas Chromatograph with a plot Al.sub.2O.sub.3/Na.sub.2SO.sub.4 column using a Flame Ionization Detector (FID).

(7) After the reaction, the catalyst was regenerated in the following way:

(8) Step 1: Exposed for 10 min to air at the flow rate of 100 ml/min at 550-560 C.

(9) Step 2: Exposed for 10 min to nitrogen at the flow rate of 100 ml/min at 550-560 C.

(10) Step 3: Exposed for 5 min to hydrogen at the flow rate of 100 ml/min at 550-560 C.

(11) After the regeneration of the catalyst, isobutane was fed to the bed at 19 ml/min and the dehydrogenation reaction was continued.

(12) Results

(13) Table 1 provides the catalytic performance (isobutane conversion and isobutene selectivity) study for isobutane dehydrogenation (Reaction temperature=550 C., Pressure=1 atmosphere, WHSV=0.54 h.sup.1). Reactions were conducted for 8 min. The catalyst used was silico-zinc aluminate (prepared using 1 wt % of silica or equivalent molar amount of different silica sources); alpha-alumina was taken as diluent/binder. Active component to binder ratio was considered as 1:1 (wt/wt) for the final catalyst composition.

(14) Table 2 provides the catalytic performance (isobutane conversion and isobutene selectivity) study of many cycles and catalyst's stability for isobutane dehydrogenation (Reaction temperature=550 C., Pressure=1 atmosphere, WHSV=0.54 h.sup.1). Reaction was conducted for 8 min and then the catalyst was regenerated. The catalyst used was silico-zinc aluminate (prepared using 5 wt % of silica gel); alpha-alumina was taken as diluent/binder. Active component to binder ratio was considered as 1:1 (wt/wt) for the final catalyst composition.

(15) Table 3 provides the catalytic performance (isobutane conversion and isobutene selectivity) study for different catalyst batches for isobutane dehydrogenation (Reaction temperature=550 C., Pressure=1 atmosphere, WHSV=0.54 h.sup.1). Reactions were conducted for 50 min. The catalyst used was silico-zinc aluminate (prepared using 5 wt % of silica gel); alpha-alumina was taken as diluent/binder. Active component to binder ratio was considered as 1:1 (wt/wt) for the final catalyst composition.

(16) As can be seen from Table 1, catalysts of the invention showed a good isobutane conversion and isobutene selectivity for isobutane dehydrogenation reaction screened with different silico-zinc aluminate catalysts prepared using different silica sources. Moreover, catalysts of the invention show a high selectivity for isobutene (see entry 1-4 in Table 1).

(17) As can be seen from Table 2, catalyst of the invention showed a good and reproducible isobutane conversion and high selectivity for isobutane dehydrogenation reaction for many reaction-regeneration catalytic cycles. Moreover, catalyst of the invention showed a high stability (see entry 1-6 in Table 2) up to 500 cycles. This shows that catalysts of the invention maintain their activity over long periods of time.

(18) As can be seen from Table 3, the catalyst of the invention showed a reproducible isobutane conversion and high selectivity for isobutane dehydrogenation reaction for different catalyst synthesis batches. This shows that catalysts of the invention show reproducible catalytic performance from different catalyst batches.

(19) TABLE-US-00001 TABLE 1 Table 1: Comparison of catalytic performance studies for isobutane dehydrogenation reaction using catalyst composition comprising Si.sub.xZn.sub.1xAl.sub.2O.sub.4 (x = 0.036) + alpha-alumina (1:1) as principal components. The conversion and selectivity given in this table were collected after 8 min of reaction. Isobutane Isobutene Silica Source Conversion (%) Selectivity (%) Silica gel 51.4 89.0 Colloidal silica 48.3 97.0 Sodium silicate 49.3 95.8 Silicic acid 54.5 94.2

(20) TABLE-US-00002 TABLE 2 Table 2: Catalytic performance studies over several reaction cycles for isobutane dehydrogenation reaction using catalyst composition comprising Si.sub.xZn.sub.1xAl.sub.2O.sub.4 (x = 0.18) + alpha-alumina (1:1) as principal components. The conversion and selectivity given in this table were collected after 8 min of reaction. The catalyst was regenerated after 8 min of reaction. No of Isobutane Isobutene Cycles Conversion (%) Selectivity (%) 1 53.5 90.9 103 48.6 92.8 201 48.6 92.7 299 48.6 92.5 404 48.7 91.7 497 47.1 91.2

(21) TABLE-US-00003 TABLE 3 Table 3: Catalytic performance studies of different catalyst batches for isobutane dehydrogenation reaction using catalyst composition comprising Si.sub.xZn.sub.1xAl.sub.2O.sub.4 (x = 0.18) + alpha-alumina (1:1) as principal components. The conversion and selectivity given in this table were collected after 50 min of reaction. No of Isobutane Isobutene Batches Conversion (%) Selectivity (%) 1 52.8 93.4 2 52.1 91.8 3 50.5 89.1 4 49.7 92.8 5 49.5 89.2

(22) Set forth below are some embodiments of the catalyst and processes disclosed herein.

Embodiment 1

(23) A catalyst composition suitable for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms comprising silico-zinc aluminate (e.g., silico-zinc aluminate spinel), wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1)
Si.sub.xZn.sub.1-xAl.sub.2O.sub.4(1)
wherein x stands for a number in the range from 0.003 to 0.76.

Embodiment 2

(24) A catalyst composition suitable for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms comprising silico-zinc aluminate (e.g., silico-zinc aluminate spinel), wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1)
Si.sub.xZnAl.sub.2O.sub.4(1)
wherein x stands for a number in the range from 0.003 to 0.76.

Embodiment 3

(25) The catalyst composition according to Embodiment 1 or Embodiment 2, wherein said catalyst composition is essentially platinum free.

Embodiment 4

(26) The catalyst composition according to any one of Embodiments 1-3, wherein the silico-zinc aluminate has a spinel structure.

Embodiment 5

(27) The catalyst composition according to any one of Embodiments 1-4, wherein the catalyst composition additionally comprises M, wherein M is selected from the group of alkali, alkaline earth metals, 3-5 d elements and mixtures thereof, wherein the relative molar ratios of the elements comprised in said composition are represented by formula (1a)
M/Si.sub.xZn.sub.1-xAl.sub.2O.sub.4(1a)
wherein x is as defined above.

Embodiment 6

(28) The catalyst composition according to Embodiment 5, wherein M is selected from the group of sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), strontium (Sr), barium (Ba), magnesium (Mg), calcium (Ca), gallium (Ga), germanium (Ge), tin (Sn), copper (Cu), zirconium (Zr), cobalt (Co), manganese (Mn), molybdenum (Mo), tungsten (W) and mixtures comprising at least one of the foregoing.

Embodiment 7

(29) The catalyst composition according to Embodiment 5 or Embodiment 6, wherein M is present in an amount from 0.01 to 5 wt % based on the silico-zinc aluminate.

Embodiment 8

(30) The catalyst composition according to Embodiment 7, wherein M is present in an amount from 0.01 to 1.5 wt % based on the silico-zinc aluminate.

Embodiment 9

(31) The catalyst composition according to Embodiment 8, wherein M is present in an amount from 0.01-0.1 wt % based on the silico-zinc aluminate.

Embodiment 10

(32) The catalyst composition according to any one of Embodiments 1-9, wherein the catalyst composition further comprises zinc aluminate and/or an oxide of silicon and/or an oxide of aluminum and/or an oxide of zinc.

Embodiment 11

(33) Process for the preparation of a catalyst composition according to any one of Embodiments 1-10 comprising:

(34) (a) preparing a solution and/or suspension comprising silicon, zinc and aluminum to form a silicon- and zinc- and aluminum-comprising solution and/or suspension,

(35) (b) admixing a basic solution, preferably ammonia, to the silicon- and zinc- and aluminum-comprising solution and/or suspension to co-precipitate mixed hydroxides and/or oxides of zinc, aluminum and silicon, and

(36) (c) calcining the co-precipitate obtained in step (b).

Embodiment 12

(37) The process according to Embodiment 11, wherein the silicon- and zinc- and aluminum-comprising solution and/or suspension further comprises M before admixing the basic solution in step (b).

Embodiment 13

(38) The process according to Embodiment 11, wherein the silico-zinc aluminate formed in step (c) is contacted with an M-comprising salt solution.

Embodiment 14

(39) The process according to any one of Embodiments 11-13, wherein one or more of the salts in the silicon- and zinc- and aluminum-comprising solution and/or suspension or at least one of the salts in the M-comprising salt solution or the silicon- and zinc- and aluminum solution and/or suspension further comprising M or in the M-comprising salt solution is a nitrate salt.

Embodiment 15

(40) The process according to any one of Embodiments 11-14, wherein one or more of the salts in the silicon- and zinc- and aluminum-comprising solution and/or suspension is a nitrate salt.

Embodiment 16

(41) The process according to any one of Embodiments 11-14, wherein at least one of the salts in the M-comprising salt solution is a nitrate salt.

Embodiment 17

(42) The process according to any one of Embodiments 11-14, wherein the silicon- and zinc- and aluminum solution and/or suspension further comprising M is a nitrate salt.

Embodiment 18

(43) The process according to any one of Embodiments 11-17, wherein the silico-zinc aluminate is calcined at 500-1100 C. for 2-24 hours in an oxygen containing atmosphere.

Embodiment 19

(44) The process according to any one of Embodiments 11-18, wherein the silico-zinc aluminate is calcined at 600-900 C. for 2-24 hours in an oxygen containing atmosphere.

Embodiment 20

(45) The process according to any one of Embodiments 11-19, wherein the silico-zinc aluminate is calcined at 700-800 C. for 2-24 hours in an oxygen containing atmosphere.

Embodiment 21

(46) The process according to any one of Embodiments 18-20 wherein the oxygen containing atmosphere is air.

Embodiment 22

(47) The process according to any one of Embodiments 11-21, further comprising (d) contacting the catalyst composition obtained in step (c) with a reducing agent.

Embodiment 23

(48) The process according to Embodiment 22, wherein the reducing agent is selected from the group of hydrogen (H.sub.2) and hydrocarbons having 2 to 5 carbon atoms per molecule.

Embodiment 24

(49) The catalyst composition obtained or obtainable by the process of any one of Embodiments 11-23.

Embodiment 25

(50) The process for the non-oxidative dehydrogenation of alkanes having 2-8 carbon atoms, preferably isobutane, comprising the step of contacting said alkanes with the catalyst composition of any one of Embodiments 1-10 or 24.

Embodiment 26

(51) The process according to Embodiment 25, wherein the alkane comprises isobutane.

Embodiment 27

(52) The process according to any one of Embodiments 25-26, wherein the process is performed at a reaction temperature of 500-600 C., a weight hourly space velocity (WHSV) of 0.1-1 h.sup.1 and a pressure of 0.01-0.3 MPa.