Heterogeneous alkane dehydrogenation catalyst

Abstract

A heterogeneous catalyst suitable for use in alkane dehydrogenation has an active layer that includes alumina and gallia. The active layer is dispersed on a support such as alumina or silica-modified alumina.

Claims

1. A heterogeneous alkane dehydrogenation catalyst consisting of a combination of aluminum oxide and gallium oxide dispersed as an active layer on a silica-modified alumina support.

2. The catalyst of claim 1, wherein the aluminum and the gallium in the active layer are present in a molar ratio of gallium to aluminum that is within a range of from greater than 0.5:1 to less than 15:1.

3. The catalyst of claim 2, wherein the molar ratio is within a range of from 1:1 to 10:1.

4. The catalyst of claim 1, wherein the aluminum oxide in the active layer is present in an amount within a range of from 0.05 percent by weight to 14 percent by weight and the gallium oxide in the active layer is present in an amount within a range of from greater than 0 percent by weight to less than fourteen by weight, each weight percent being based upon total catalyst weight.

5. The catalyst of claim 4, wherein the amount of aluminum oxide is within a range of from 0.05 percent by weight to 5 percent by weight and the gallium oxide is present in an amount within a range of from greater than 0 percent by weight to less than seven percent by weight, each weight percent being based upon total catalyst weight.

6. The catalyst of claim 1, comprising the silica-modified alumina support comprising from 0.1 wt. % to 10 wt. % silica based on the total weight of the support.

7. A heterogeneous alkane dehydrogenation catalyst consisting of a combination of aluminum oxide and gallium oxide dispersed as an active layer on an alumina support or a silica-modified alumina support, wherein the aluminum and the gallium in the active layer are present in a molar ratio of gallium to aluminum that is within a range of from greater than 0.5:1 to less than 15:1.

8. The catalyst of claim 7, wherein the molar ratio is within a range of from 1:1 to 10:1.

9. The catalyst of claim 7, wherein the aluminum oxide in the active layer is present in an amount within a range of from 0.05 percent by weight to 14 percent by weight and the gallium oxide in the active layer is present in an amount within a range of from greater than 0 percent by weight to less than fourteen by weight, each weight percent being based upon total catalyst weight.

10. The catalyst of claim 9, wherein the amount of aluminum oxide is within a range of from 0.05 percent by weight to 5 percent by weight and the gallium oxide is present in an amount within a range of from greater than 0 percent by weight to less than seven percent by weight, each weight percent being based upon total catalyst weight.

11. A catalyst comprising a support and an active layer dispersed on the support, the active layer comprising aluminum oxide and gallium oxide, wherein a molar ratio of gallium to aluminum in the active layer is from 0.5:1 to 15:1.

12. The catalyst of claim 11, wherein the support is an inactive support.

13. The catalyst of claim 11, wherein the support is an alumina support or a silica-modified alumina support.

14. The catalyst of claim 13, wherein the support is a silica-modified alumina support comprising from 0.1 wt. % to 10 wt. % silica based on the total weight of the support.

Description

COMPARATIVE EXAMPLES (CEX) A THROUGH C

(1) In a replication of work presented by Chen et al. in the 2008 Journal of Catalysis article noted above, mix together concentrated aqueous ammonia (28 wt % ammonia, Aldrich, Catalogue No. 221228, based upon total weight of concentrated aqueous ammonia) and ethanol in a 50:50 volume ratio. Add this mixture dropwise to an ethanol solution of gallium nitrate hydrate (99.9 percent purity, Aldrich, Catalogue No. 289892) and aluminum nitrate hydrate (at least 98 percent purity, Aldrich, Catalogue No. 237973) until solution pH reaches 8.5 and no further visible precipitation is observed. The ethanol solutions each contain 15 grams (g) of gallium nitrate hydrate and varying amounts of aluminum nitrate hydrate, with CEx A containing 13.2 g, CEx B containing 6.6 g, and CEx C containing 3.3 g. Filter gel from the solution and wash the gel with ethanol before drying it overnight at 373° Kelvin (100° C.) and then calcining it at 773° K (500° C.) for six hours.

EX 1-5 AND CEX D-E

(2) Use aqueous incipient wetness impregnation to prepare a supported catalyst using 20 g of SIRALOX™ 1.5/70 (Sasol, 1.5 wt % silica, based on total weight of the support, and a surface area (S.A.) of 79 square meters per gram (m.sup.2/g) as a catalyst support. Pre-dry the catalyst support at a temperature of 350° C. for a period of two hours. Spray a solution with a targeted amount of metal precursor (gallium nitrate hydrate and aluminum nitrate as in CEx A-C and potassium nitrate (at least 99% purity, Aldrich, Catalogue No. 221295) and solution volume sufficient to match 95% pore volume (PV) (0.25 milliliters per gram (mL/g) onto the pre-dried support. Age the sprayed support at ambient temperature for two hours before drying it in an electric muffle furnace at 175° C. for one hour and then calcining it at 750° C. for one hour. Metal precursor amounts are as follows: Ex 1—1.72 g gallium nitrate hydrate, 1.53 g aluminum nitrate hydrate and 0.13 g potassium nitrate; Ex 2—1.72 g gallium nitrate hydrate, 0.76 g aluminum nitrate hydrate and 0.13 g potassium nitrate; Ex 3—1.72 g gallium nitrate hydrate, 0.38 g aluminum nitrate hydrate and 0.13 g potassium nitrate; Ex 4—1.72 g gallium nitrate hydrate, 0.18 g aluminum nitrate hydrate and 0.13 g potassium nitrate; Ex 5—12.06 g gallium nitrate hydrate, 3.11 g aluminum nitrate hydrate and 0.15 g potassium nitrate; CEx D—1.72 g gallium nitrate hydrate and 0.13 g potassium nitrate; and CEx E—11.87 g gallium nitrate hydrate and 0.15 g potassium nitrate.

EX 6-8 AND CEX F

(3) Replicate Ex 1-5 and CEx D-E with changes to prepare four catalysts using high purity Al.sub.2O.sub.3 (at least 99.5% pure, CATALOX™ 5/70, Sasol) as the support. Metal precursor amounts are as follows: Ex 6—1.72 g gallium nitrate hydrate, 1.78 g aluminum nitrate hydrate and 0.13 g potassium nitrate; Ex 7—1.72 g gallium nitrate hydrate, 0.89 g aluminum nitrate hydrate and 0.13 g potassium nitrate; Ex 8—1.72 g gallium nitrate hydrate, 0.44 g aluminum nitrate hydrate and 0.13 g potassium nitrate; and CEx F—1.72 g gallium nitrate hydrate and 0.13 g potassium nitrate.

EX 9-10

(4) Replicate Ex 2-3 with changes to prepare two catalysts by sequentially loading first the gallium nitrate hydrate and potassium nitrate and second the aluminum nitrate hydrate precursors. After the first loading step with gallium and potassium precursors, age the obtained material for two hours at ambient temperature, dry the aged at 175° C. for one hr, and then calcine the dried material at 750° C. for 1 hour before loading the aluminum nitrate hydrate precursor. After completing the aluminum precursor loading, dry the material and calcine it in the same manner as after the first loading step.

(5) TABLE-US-00001 TABLE 1 Metal oxide loading on catalyst Weight % on Catalyst* Ga:Al** Ga.sub.2O.sub.3 Al.sub.2O.sub.3 K.sub.2O (mol/mol) Bulk metal oxide catalysts) CEx A 68.3% 31.7% 0.0% 1.2 CEx B 81.2% 18.8% 0.0% 2.3 CEx C 89.6% 10.4% 0.0% 4.7 Supported catalysts using silica containing aluminum as a support (Siralox) Ex1 2.1% 1.0% 0.3% 1.2 Ex2 2.2% 0.5% 0.3% 2.3 Ex3 2.2% 0.3% 0.3% 4.7 Ex4 2.2% 0.1% 0.3% 9.8 Ex5 13.2% 1.8% 0.3% 4.0 CEx D 2.2% 0.0% 0.3% — CEx E 13.2% 0.0% 0.3% — Supported catalysts using high purity aluminum as a support (Catalox) Ex6 2.1% 1.2% 0.3% 1.0 Ex7 2.1% 0.6% 0.3% 2.0 Ex8 2.2% 0.3% 0.3% 4.0 CEx F 2.2% 0.0% 0.3% — Sequential loading Supported catalysts using silica containing aluminum as a support (Siralox) Ex9 2.2% 0.5% 0.3% 2.3 Ex10 2.2% 0.3% 0.3% 4.7 *Based upon combined weight of Ga.sub.2O.sub.3, Al.sub.2O.sub.3, K.sub.2O. When the support is present, the stated amounts of Ga.sub.2O.sub.3, Al.sub.2O.sub.3, K.sub.2O are those deposited on the support, with the support contributing the balance of the catalyst up to 100 wt %. **Ratio excluding contribution from the support where present
Catalyst Testing

(6) Admix 0.5 g of each catalyst with 1.0 g silicon carbide, then subject the catalyst to a number of dehydrogenation reaction/catalyst reactivation/catalyst rejuvenation cycles as detailed below. In the dehydrogenation reaction step, pass a feed stream (95 mole percent (mol %) propane and 5 mol % nitrogen through a catalyst for a period of 60 seconds at a temperature of 625° C. and a propane weight hourly space velocity (WHSV) of 8 reciprocal hours (hr.sup.−1) under ambient pressure (e.g. one atmosphere). Collect data for propane conversion and propane selectivity approximately 6 seconds after initiating contact between the feed stream and the catalyst. After the 60 second period lapses, ramp reactor temperature to 730° C. at a rate of 20° C. per minute in the presence of helium (He) flowing through the catalyst at a rate of 120 standard cubic centimeters per minute (sccm). Maintain the temperature at 730° C. while contacting the catalyst with a simulated CH.sub.4 combustion products stream (4 mol % oxygen, 8 mol % carbon dioxide, 16 mol % water vapor and 72 mol % He) at a flow rate of 150 sccm for a period of three minutes. Subsequent to treatment with the simulated combustion products stream, pass 100% air through the catalyst at a flow rate of 150 sccm for a period of 15 minutes. After air treatment and before starting another PDH reaction cycle, cool the reactor to the reaction temperature (625° C.) and stabililze the temperature of the system over a period of 20 min under flowing He (flow rate of 120 sccm) to effect stripping of labile oxygen from the catalyst and make the temperature of the catalyst bed substantially uniform before the next reaction/regeneration cycle.

(7) Summarize catalyst test results for catalysts prepared in CEx A-C after 15, 30 and 50 cycles in terms of % propane (C.sub.3H.sub.8) conversion, % propylene (C.sub.3H.sub.6) selectivity and product % selectivity for propylene (C.sub.3H.sub.6 in Table 2 below. In Tables 3A-3C below, do the same for Ex 1-5, 9, 10, CEx D and CEx E.

(8) The conversion, selectivity and yield are all based on mol %.

(9) TABLE-US-00002 TABLE 2 Cat/Cycle % C.sub.3H.sub.8 % C.sub.3H.sub.6 No Conversion Selectivity % C.sub.3H.sub.6 Yield A/15 40.3 71.5 28.8 A/30 38.9 72.5 28.2 A/50 38.0 72.9 27.7 B/15 34.5 79.2 27.4 B/30 32.6 80.1 26.1 B/50 31.0 80.7 25.0 C/15 37.2 78.2 29.1 C/30 34.9 79.5 27.8 C/50 32.7 83.9 27.4

(10) TABLE-US-00003 TABLE 3A Cat/ % C.sub.3H.sub.8 % C.sub.3H.sub.6 Cycle Con- Se- % C.sub.3H.sub.6 Ga:Al* Weight % on Catalyst* No version lectivity Yield (mol/mol) Ga.sub.2O.sub.3 Al.sub.2O.sub.3 K.sub.2O 1/15 42.2 94.0 39.7 1.2 2.1% 1.0% 0.3% 1/30 40.4 93.7 37.9 1/50 37.7 93.2 35.1 2/15 52.1 95.0 49.5 2.3 2.2% 0.5% 0.3% 2/30 51.1 94.9 48.5 2/50 49.1 94.8 46.6 3/15 43.6 93.8 40.9 4.7 2.2% 0.3% 0.3% 3/30 45.6 94.0 42.9 3/50 45.6 94.0 42.9 4/15 39.7 94.7 37.6 9.8 2.2% 0.1% 0.3% 4/30 41.2 94.8 39.1 4/50 40.9 94.7 38.8 *Refers to the amount of Ga, Al, K added to the support.

(11) TABLE-US-00004 TABLE 3B Cat/ % C.sub.3H.sub.8 % C.sub.3H.sub.6 Cycle Con- Se- % C.sub.3H.sub.6 Ga:Al* Weight % on Catalyst* No version lectivity Yield (mol/mol) Ga.sub.2O.sub.3 Al.sub.2O.sub.3 K.sub.2O  5/15 29.6 87.8 26.0 4.0 13.2% 1.8% 0.3%  5/30 28.4 88.0 25.0  5/50 27.2 87.8 23.9  6/15 42.4 93.3 39.5 1.0 2.1% 1.2% 0.3%  6/30 44.0 93.5 41.2  6/50 44.4 93.6 41.5  7/15 42.2 93.7 39.5 2.0 2.1% 0.6% 0.3%  7/30 44.1 93.9 41.4  7/50 45.4 94.1 42.8  8/15 39.0 93.3 36.4 4.0 2.2% 0.3% 0.3%  8/30 40.0 93.4 37.4  9/15 37.4 93.4 35.0 2.3 2.2% 0.5% 0.3%  9/30 38.9 93.5 36.4  9/50 38.2 93.5 35.7 10/15 39.8 94.7 37.7 4.7 2.2% 0.3% 0.3% 10/30 41.8 94.8 39.6 10/50 43.3 94.8 41.1 *Refers to the amount of Ga, Al, K added to the support.

(12) TABLE-US-00005 TABLE 3C Cat/ % C.sub.3H.sub.8 % C.sub.3H.sub.6 Cycle Con- Se- % C.sub.3H.sub.6 Ga:Al* Weight % on Catalyst* No version lectivity Yield (mol/mol) Ga.sub.2O.sub.3 Al.sub.2O.sub.3 K.sub.2O D/15 29.4 91.8 27.0 — 2.2% 0.0% 0.3% D/30 28.8 91.7 26.4 D/50 27.6 91.3 25.2 E/15 26.1 88.3 23.1 — 13.2% 0.0% 0.3% E/30 26.5 88.7 23.5 E/50 26.2 89.3 23.4 F/15 33.5 92.2 30.9 — 2.2% 0.0% 0.3% F/30 35.7 92.1 32.9 F/50 37.2 92.4 34.4 *Refer to the amount of Ga, Al, K added to the support.

(13) The data presented in Tables 2 and 3A through 3C provide support for a number of observations. First, as shown in Table 2, bulk mixed metal oxides, even with Ga.sub.2O.sub.3 loadings in excess of 65 wt % (see Table 1 for CEx A-C), provide a propane conversion of no more than 40.3% (Table 2, CEx A, 15 cycles). Second, also as shown in Table 2, the maximum selectivity to propylene for bulk mixed metal oxides is 83.9% (Table 2, CEx C, 50 cycles). Third, Table 3C shows that propane conversion, propylene selectivity and propylene yield are somewhat higher for a relatively low Ga.sub.2O.sub.3 loading (2.2 wt % for CEx D) than for a relatively higher Ga.sub.2O.sub.3 loading (13.2 wt % for CEx E). Fourth, addition of Al.sub.2O.sub.3 to the active layer (along with the Ga.sub.2O.sub.3), either in a one-step procedure (Ex 1-5) or a sequential procedure (Ex 9-10), leads to a marked increase in propylene selectivity relative to what one can obtain with bulk mixed metal oxides where the same oxides are used but with Ga.sub.2O.sub.3 loadings significantly lower for the supported catalysts than for the bulk mixed metal oxides. Fifth, the amount of Al.sub.2O.sub.3 included in the active layer also affects catalyst performance, with a Ga/Al molar ratio preferred to range from greater than 0.5:1 to less than 15:1, and more preferably 1:1 to less than 10:1, and most preferably 1.5:1 to 5:1. For catalyst to have good activity and selectivity, gallium oxides loading is preferably to be greater 0 wt % and lower than 14 wt %, and more preferably be greater 0 wt % and lower than 10 wt %, and most preferably greater 0 wt % and lower than 5 wt %.