Method of producing compound comprising alkenyl group

Abstract

A method of producing at least one compound comprising an alkenyl group from at least one compound comprising an alkyl group having two or more carbon atoms, the method comprising: (i) Providing a mixture comprising carbon dioxide and at least one compound comprising an alkyl group having two or more carbon atoms; and (ii) Contacting said mixture with a catalyst comprising one or both of palladium and platinum and one or more lanthanide, thereby converting at least a portion of the at least one compound comprising an alkyl group having two or more carbon atoms into a compound comprising an alkenyl group, the total of the weight of the palladium and/or platinum being more than 0.1 wt % of the catalyst.

Claims

1. A method of producing at least one compound comprising an alkenyl group from at least one compound comprising an alkyl group having two or more carbon atoms, the method comprising: (i) Providing a mixture comprising carbon dioxide and at least one compound comprising an alkyl group having two or more carbon atoms, the mixture comprising at least 5 mol % carbon dioxide; and (ii) Contacting said mixture with a catalyst comprising (a) one or both of palladium and platinum, and (b) one or more of the lanthanide series of elements, thereby converting at least a portion of the at least one compound comprising an alkyl group having two or more carbon atoms into a compound comprising an alkenyl group, wherein the catalyst comprises at least 2.0 mol % and up to 15.0 mol % palladium, platinum or combination thereof based on a total for palladium and/or platinum relative to total catalyst, wherein a molar ratio of the one or more of the lanthanide series of elements to the one or both of palladium and platinum is from 1:1 to 15:1 in the catalyst, and wherein the contacting in step (ii) is conducted at a temperature of at least 300° C. and up to 600° C.

2. The method according to claim 1 in which the step (ii) takes place in the absence of steam, oxygen and/or hydrogen.

3. The method according to claim 1 in which the compound(s) comprising the alkyl group having two or more carbon atoms is a C.sub.2-C.sub.2 alkane or an alkyl aryl compound.

4. The method according to claim 1 in which the step (ii) is conducted at a temperature of at least 450° C. and up to 600° C.

5. The method according to claim 1 in which the mixture comprises from 25-40 mol % carbon dioxide.

6. The method according to claim 1 in which the mixture comprises from 25-40 mol % of the at least one compound comprising an alkyl group having two or more carbon atoms.

7. The method according to claim 1 in which a molar ratio of carbon dioxide to the at least one compound comprising an alkyl group having two or more carbon atoms is from 0.3:1 to 3:1.

8. The method according to claim 1 in which the mixture comprises up to 40 mol % of one or more inert component.

9. The method according to claim 1 further comprising a step of contacting at least a portion of the mixture with the catalyst more than once.

10. The method according to claim 1 further comprising passing a treated portion of the mixture from a position downstream of the catalyst to the catalyst.

11. The method according to claim 1 in which the catalyst comprises at least 2.0 mol % and up to 15.0 mol % of the one or more of the lanthanide series of elements.

12. The method according to claim 1 in which the one or more of the lanthanide series of elements is selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, terbium, and combinations thereof.

13. The method according to claim 1 in which the one or more of the lanthanide series of elements is cerium.

14. The method according to claim 1 in which the catalyst further comprises a thermal stabiliser for stabilising the one or more of the lanthanide series of elements.

15. The method according to claim 14 in which the thermal stabiliser comprises zirconium.

16. The method according to claim 15 in which a molar ratio of the zirconium to the one or more of the lanthanide series of elements is at least 1:4 and no more than 2:1.

17. The method according to claim 15 in which the catalyst comprises at least 2.0 mol % zirconium, and up to 12.0 mol % zirconium.

18. The method according to claim 1 in which the catalyst comprises at least 4.0 mol % and up to 20.0 mol % aluminum.

19. The method according to claim 1 in which the catalyst comprises aluminum and in which a molar ratio of the aluminum to the one or more of the lanthanide series of elements is from 1:2 to 3:1.

20. The method according to claim 1 in which the catalyst comprises at least 1.0 mol % of the one or more of the lanthanide series of elements.

21. The method according to claim 1 in which the catalyst comprises at least 3.0 mol % and up to 15.0 mol % palladium, platinum or combination thereof based on a total for palladium and platinum relative to total catalyst.

Description

DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

(2) FIG. 1 shows how the conversion % of carbon dioxide and propane, and the amount of carbon dioxide involved in the reaction varies with the relative amounts of carbon dioxide and propane in an embodiment of the method of the present invention;

(3) FIG. 2 shows how the conversion % of propane varies with temperature in a in a further example of an embodiment of the present invention;

(4) FIG. 3 shows how the selectivity % for propene varies with temperature in a further example of an embodiment of the present invention; and

(5) FIG. 4 shows how the conversion of carbon dioxide and propane varies with the GHSV in a further example of an embodiment of the present invention.

DETAILED DESCRIPTION

(6) Method of Making Catalysts

(7) Requisite amounts of Ce (acac).sub.3 (and Al(acac).sub.3 and/or Zr(acac).sub.4 if Al and/or Zr are to be incorporated into the catalyst) were added together and ground thoroughly for period of 10 mins using mortar and pestle to form a homogenous powder. The powder was heat treated in flowing air at 300° C. for 2 h, heating rate 5° C./min. Once the powder had been calcined, it was ground again for 30 sec. This process provided the support comprising Ce (and optionally Al and Zr).

(8) Pd was wet impregnated onto the calcined support as will now be described. Requisite amount of support was added to an aqueous solution of a Pd-containing precursor (Pd (NH.sub.3).sub.4 (NO.sub.3).sub.2 (10% wt in H.sub.2O, Sigma Aldrich), under vigorous stirring at room temperature. A few drops of HPLC water were added to this mixture to enable better mixing of powder with Pd solution. The solution was agitated in this way until it formed a paste, which was dried at room temperature overnight and further ground again using mortar and pestle for minimum 1 min to obtain homogeneous powder. Catalyst was further calcined using following conditions: flowing air, T=500° C., heating rate 10° C./min, t=4 hrs.

(9) Catalyst 1

(10) Catalyst 1 comprised palladium loaded at 5 mol % onto a CeO.sub.2 support, and was made using the general method described above.

(11) Catalyst 2

(12) Catalyst 2 comprised 5% Pd/CeZrAl.sub.2O.sub.7, and was made using the general method described above. The elemental composition of Catalyst 2 was investigated using transmission electron microscope energy dispersive x-ray spectroscopy (TEM EDX), and was determined to be 68.0% 0, 10.3% Al, 6.9% Zr, 5.2% Pd and 9.6% Ce. The values determined by EDX were reasonably consistent with the values determined by the amounts of starting material used. The catalyst was determined to have a surface area of 82 m.sup.2/g by BET analysis. This compares with 100 m.sup.2/g for CeZrO.sub.x and 104 m.sup.2/g for CeZrAlO.sub.x.

(13) X-ray photelectron spectroscopy (XPS) analysis of Catalyst 2 indicated that the Pd(0) content of the surface palladium was initially 0%, with a Pd.sup.2+ content of 100%, and that the Ce.sup.3+ content was 27% of the Ce, with a Ce.sup.4+ content of 73%. After use of the catalyst, XPS indicated that the Pd(0) content of the surface palladium was 100%, with a Pd.sup.2+ content of 0%, and that the Ce.sup.3+ content was 37% of the Ce, with a Ce.sup.4+ content of 63%. X-ray absorption near edge structure spectroscopy (XANES) indicates that the particle size in the used catalyst is greater than that of the virgin, unused catalyst.

(14) The catalysts mentioned above were used in exemplary embodiments of the method of the present invention, as will now be described by way of example only.

(15) General Method

(16) Catalytic measurements were performed using a fixed bed laboratory micro reactor at atmospheric pressure, keeping GHSV at 6000 h.sup.−1 and total flow rate of 15 mL min.sup.−1. Catalyst (0.2 g) was loaded into a stainless steel reactor tube (length 30 cm, diameter 1.2 cm) and placed between 2 quartz wool portions. Before commencing the reaction, catalyst was pre-treated inside the reactor tube in the flow of helium (10 ml/min) at temperature of 110° C. for period of 30 mins to remove any impurities. The catalyst was then heated to the desired temperature and the catalyst was exposed to the reaction mixture. The reaction mixture comprised He, CO.sub.2 and C.sub.3H.sub.8, with 26% He, and the rest being CO.sub.2 and C.sub.3H.sub.8. The reactants and products were analysed by a Varian 3800 online gas chromatograph using Porapak Q and Molsieve columns with TCD and FID detectors.

Example 1

(17) The method as generally described above was performed with Catalyst 1. Catalyst 1 was placed in the microreactor which was then heated to 500° C. The reaction mixture comprised a 9:1 mixture of carbon dioxide:propane. The GHSV was 6385.7/h. After 30 min of reaction, the conversion % of carbon dioxide was about 16% and the conversion % of propane was about 33%.

Example 2

(18) The method of Example 1 was repeated using Catalyst 2 instead of Catalyst 1. The conversion % of carbon dioxide was about 17% and the conversion % of propane was about 34%.

Comparative Example 1

(19) The method of Example 1 was repeated using CeO.sub.2 catalyst instead of Catalyst 1. The conversion % of carbon dioxide was about 3.5% and the conversion % of propane was about 5%.

(20) The data of Examples 1, 2 and Comparative Example 1 indicate that the presence of palladium is advantageous. Furthermore, Catalyst 2 was found to be more stable than Catalyst 1, being attributable to the ZrO.sub.2 in Catalyst 2 providing a thermal stabiliser for CeO.sub.2 to inhibit sintering of CeO.sub.2.

Further Examples

(21) The effect of the ratio of carbon dioxide:propane on the respective conversion % of carbon dioxide and propane was investigated using Catalyst 2 using the method of Example 2, with a variation in the ratio of carbon dioxide:propane. The results are shown in FIG. 1, with filled squares denoting the conversion of propane, open squares denoting the conversion of carbon dioxide and filled circles denoting the percentage of the carbon dioxide involved in the oxidative dehydrogenation reaction. FIG. 1 indicates that for Catalyst 2, a molar ratio of 1:1 for the carbon dioxide:propane resulted in the highest conversion of both the oxidant and the substrate.

(22) Effect of Catalyst Temperature

(23) Applicant investigated how catalyst temperature affected the reaction in relation to Catalyst 2 by varying the catalyst temperature between 400 and 600° C. It was found that at temperatures lower than 500° C., the activity of the catalyst is relatively poor, whereas temperatures higher than 550° C. the fragmentation of propane is significant. A temperature of about 500° C. proved to be effective because it facilitates the formation of propene, but reduces the risk of coking, and of the fragmentation of propane. Furthermore, use of this temperature reduces the risk of damaging the CeO.sub.2 catalyst compared to higher temperatures.

(24) The effect of catalyst temperature was further studied by examining % conversion of propane and % selectivity for propene as a function of temperature using the General Method set-out above. The conditions were: Catalyst 2, total flow rate—15 ml/min, 26% He, 37% CO.sub.2, 37% propane, GHSV—6000 h.sup.−1. The results are shown in FIGS. 2 and 3. The results show that as the temperature increases, the % conversion of propane increases, but that selectivity for propene drops-off significantly at temperatures above 550° C.

(25) Effect of GHSV

(26) The effect of GHSV on % conversion for both carbon dioxide and propane was studied using Catalyst 2 and the General Method described above, with the catalyst maintained at 500° C. The conditions were: 26% He, 37% CO.sub.2, 37% propane. The results are shown in FIG. 4. FIG. 4 indicates that for Catalyst 2, the % conversion for both carbon dioxide and propane decreases as GHSV increases over the range of GHSV studied.

(27) Deactivation and Regeneration of Catalyst 2

(28) Catalyst 2 is observed to deactivate over time when exposed to the mixture comprising carbon dioxide and propane. The conversion % of propane is seen to drop over time to a “steady state” value of about 4%. This deactivation is associated with the reduction of the catalyst. Without wishing to be found by theory, it is believed that palladium may be reduced from a +2 oxidation state to a 0 oxidation state, and an increased proportion of the cerium is at a lower oxidation state. It was observed that the catalyst could be regenerated by exposing the catalyst to an oxidant at elevated temperature (e.g. 6 mL/min. flow of carbon dioxide at 500° C. for about 2 hours). It was found that Catalyst 2 could be regenerated twice using carbon dioxide. It was also observed that Catalyst 2 could be regenerated using oxygen gas. It was also observed that heating the catalyst to 500° C. in an inert atmosphere did not lead to any significant regeneration of the catalyst.

(29) Proposed Reaction Scheme

(30) Without wishing to be bound by theory, applicant believes that carbon dioxide is disassociating on the catalyst to form carbon monoxide and an oxygen species. The oxygen species reacts with the propane to form propene and water. The hypothesis that carbon dioxide is forming carbon monoxide is supported by observations made when catalysts are exposed to pulses of carbon dioxide. In this connection, when virgin Catalyst 2 at 455° C. is exposed to pulses of carbon dioxide, then carbon monoxide is produced (as detected by mass spectrometry using Temporal Analysis of Product (TAP)). When used Catalyst 2 at 455° C. is exposed to carbon dioxide, then carbon dioxide is still produced, but in smaller quantities. These effects were observed not only in relation to Catalyst 2, but also in relation to Pd/CeZrAl.

(31) Applicant has demonstrated that it is possible to perform oxidative dehydrogenation of alkanes using carbon dioxide at a relatively low temperature by using a catalyst comprising palladium and/or platinum at more than a trace level (i.e. more than 0.1 wt %) and one or more lanthanide (for example cerium).

(32) The examples above illustrate the use of the catalysts to facilitate oxidative dehydrogenation of propane. Those skilled in the art will realise that other substrates may be treated using the same catalysts, such as any alkane, in particular C.sub.2-C.sub.12 alkanes. Furthermore, other species comprising alkyl groups comprising at least 2 carbon atoms may be treated, for example, ethyl benzene to form styrene.

(33) The examples above demonstrate the use of 5 mol % palladium. Those skilled in the art will realise that different loadings of palladium/platinum may be used.

(34) The examples above illustrate the passage of a gas over a static catalyst. Those skilled in the art will realise that other arrangements may be used, for example, a fluidised bed arrangement.

(35) The examples above disclose the use of an inert gas. An inert gas need not be used. Furthermore, if an inert gas is used, an alternative gas to helium may be used, such as nitrogen.

(36) The examples above illustrate the use of palladium in conjunction with cerium. Platinum may be used instead of, or in conjunction with, the palladium. Furthermore, one or more lanthanides other than, or in addition to, cerium may be used.

(37) The examples above illustrate how cerium may be used as part of a support. Those skilled in the art will realise that cerium may be loaded onto a support which does not initially comprise cerium.

(38) Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

(39) Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.