Catalyst and Process for Olefin Metathesis Reaction

Abstract

The present invention relates to the use of magnesium oxide (MgO) as catalyst for isomerisation of olefins with defined physical properties, a catalyst for olefin metathesis comprising said MgO and a process for olefin metathesis using said catalyst.

Claims

1. A catalyst for conversion of olefins comprising a mixture of: at least one first catalyst component comprising a metathesis catalyst, and at least one second catalyst component comprising a magnesium oxide (MgO) as a catalyst for double bond isomerisation, wherein the magnesium oxide (MgO) comprises: a specific surface area BET of 105 to 300 m.sup.2/g; a crystallite size of 5 to 25 nm; a total pore volume of 0.1 to 0.5 cm.sup.3/g; and a maximum of pore size distribution of 5 to 15 nm, wherein the magnesium oxide (MgO) is free of a structure stabilizing agent; and wherein the magnesium oxide is obtained from magnesium carbonate hydroxide of the formula (MgCO.sub.3).sub.4.Mg(OH).sub.2.5H.sub.2O by calcination in the presence of an oxygen-containing gas.

2. The catalyst according to claim 1, wherein the catalyst comprises the MgO as isomerisation catalyst component and the at least one metathesis catalyst component in a weight ratio between 5:1 and 1:1.

3. The catalyst according to claim 1, wherein the catalyst comprises the MgO as isomerisation catalyst component and the at least one metathesis catalyst component in a weight ratio between 4:1 and 2:1.

4. The catalyst according to claim 1, wherein the catalyst comprises the MgO as isomerisation catalyst component and the at least one metathesis catalyst component in a weight ratio of 3:1.

5. The catalyst according to claim 1, wherein the metathesis catalyst comprises oxides of metals of the 6.sup.th and 7.sup.th group of the periodic system of the elements (PSE), in particular at least one of tungsten oxide, molybdenum oxide or a precursor thereof, deposited on at least one inorganic carrier.

6. The catalyst according to claim 1, wherein the magnesium oxide is additionally arranged as a pre-bed upstream of the catalyst mixture of metathesis catalyst and isomerisation catalyst.

7. The catalyst according to claim 6, characterized in that the mass ratio of the pre-bed and the main catalyst bed being a mixture of metathesis catalyst and isomerisation catalyst is between 1:10 and 3:1

8. The catalyst according to claim 6, characterized in that the mass ratio of the pre-bed and the main catalyst bed being a mixture of metathesis catalyst and isomerisation catalyst is between 1:6 and 2:1.

9. The catalyst according to claim 6, characterized in that the mass ratio of the pre-bed and the main catalyst bed being a mixture of metathesis catalyst and isomerisation catalyst is between 1:4 and 1:2.

10. The catalyst according to claim 1, wherein the catalyst is activated in a process comprising the steps of: heating the catalyst in an inert gas atmosphere to a temperature between 300 C. and 500 C.; oxidizing the catalyst in an oxygen containing atmosphere at temperatures between 400 C. and 600 C.; reducing the catalyst in a hydrogen containing atmosphere at temperatures between 300 C. and 500 C.; heating the catalyst in an inert gas atmosphere at temperatures between 400 C. and 600 C.; and subsequently cooling down the catalyst in an inert gas atmosphere.

11. The catalyst of claim 1, wherein the specific surface area BET of magnesium oxide is 105 to 150 m.sup.2/g.

12. The catalyst of claim 1, wherein the specific surface area BET of magnesium oxide is 105 to 120 m.sup.2/g.

13. The catalyst of claim 1, wherein the specific surface area BET of magnesium oxide is 105 to 115 m.sup.2/g.

14. The catalyst according to claim 1, wherein the crystallite size of magnesium oxide is 10 to 20 nm.

15. The catalyst according to claim 1, wherein the crystallite size of magnesium oxide is 10 to 15 nm.

16. The catalyst according to claim 1, wherein the total pore volume of magnesium oxide is 0.2 to 0.4 cm.sup.3/g.

17. The catalyst according to claim 1, wherein the total pore volume of magnesium oxide is 0.3 to 0.4 cm.sup.3/g.

18. The catalyst according to claim 1, wherein the maximum of pore size distribution of magnesium oxide is 7 to 10 nm.

19. The catalyst according to claim 1, wherein the maximum of pore size distribution of magnesium oxide is 8 to 9 nm.

20. A process for obtaining an olefin, in particular propene, comprising the steps of: feeding at least two olefins as starting material, to a reactor, in particular a fixed-bed reactor, comprising at least one catalyst for conversion of olefins comprising a mixture of: at least one first catalyst component comprising a metathesis catalyst; and at least one second catalyst component comprising a magnesium oxide (MgO) as a catalyst for double bond isomerisation, wherein the magnesium oxide (MgO) comprises: a specific surface area BET of 105 to 300 m.sup.2/g; a crystallite size of 5 to 25 nm; a total pore volume of 0.1 to 0.5 cm.sup.3/g; and a maximum of pore size distribution of 5 to 15 nm, wherein the magnesium oxide (MgO) is free of a structure stabilizing agent; and wherein the magnesium oxide is obtained from magnesium carbonate hydroxide of the formula (MgCO.sub.3).sub.4.Mg(OH).sub.2.5H.sub.2O by calcination in the presence of an oxygen-containing gas; and, converting the at least two olefin gases at a pressure between 1 to 50 bar and a temperature between 100 and 600 C. to obtain at least one new olefin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention is further explained in more detail by the means of the following examples with reference to the Figure. It shows:

[0064] FIG. 1: a diagram illustrating the time-on-stream a) conversion of n-butene and b) yield of propene in ethene and 2-butene metathesis for an embodiment of a catalyst according to the invention;

[0065] FIG. 2: a diagram illustrating the time-on-stream a) conversion of n-butene and b) yield of propene in ethene and 2-butene metathesis using a catalyst containing MgO prepared from Mg(OH).sub.2;

[0066] FIG. 3: a diagram illustrating the time-on-stream a) conversion of n-butene and b) yield of propene in ethene and 2-butene metathesis using a catalyst containing commercial MgO; and

[0067] FIG. 4: a diagram illustrating the time-on-stream mol fractions of a) 1-butene and b) cis-2-butene obtained under standard reaction conditions using MgO according to the invention (labelled as MgO.sub.L1); MgO prepared from Mg(OH).sub.2 (labelled as MgO.sub.L2) and commercial MgO (labelled as MgO.sub.c).

DETAILED DESCRIPTION OF THE INVENTION

Example 1: Inventive Example

[0068] MgO.sub.L1 (MgO according to the invention) was prepared by calcination of (MgCO.sub.3).sub.4.Mg(OH).sub.2.5H.sub.2O at 550 C. for 16 h in an air flow. The results of MgOL.sub.1 characterisation by BET and XRD are given in Table 2 below.

[0069] (WO.sub.x/SiO.sub.2).sub.L1 was prepared by wet impregnation of SiO.sub.2 (Aerolyst 3038, Evonik) with a solution of ammonium metatungstate hydrate (Aldrich 99.99%, trace metals basis) and potassium hydroxide (Merck). The tungsten (calculated for WO.sub.3) and potassium (calculated for K.sub.2O) loadings were set to approximately 7 and 0.2 wt. %, respectively, as described in U.S. Pat. No. 4,575,575. The dried catalyst precursors were calcinated in a muffle oven with circulating air flow at 538 C. for 8 h.

[0070] The calcined (WO.sub.x/SiO.sub.2).sub.L1 and MgO.sub.L1 powders were then pressed, crushed and sieved to obtain particles of 315-710 m.

[0071] The catalyst was then activated according to activation steps as outlined in Table 1.

TABLE-US-00001 TABLE 1 activation procedure for catalyst T.sub.start/ T.sub.end/ Heating rate/ Holding time Activation steps C. C. C./min at T.sub.end/h Heating in N.sub.2 from room 25 400 5 2 temperature Oxidation in air 400 525 5 2 Cooling down in N.sub.2 525 400 2 0.5 Reduction in N.sub.2/H.sub.2 = 70/30 400 400 0.5 Purge with N.sub.2 400 400 0.5 Desorption in N.sub.2 400 550 5 16 Cooling down in N.sub.2 550 300

[0072] Pure MgO.sub.L1 was tested for trans-2-butene isomerization in presence of ethene at 300 C. The cross-metathesis of ethene and trans-2-butene was also investigated at 300 C. but using a catalysts bed consisting of MgO.sub.L1 pre-bed and a mixture of MgO.sub.L1 and (WO.sub.x/SiO.sub.2).sub.L1, i.e. MgO.sub.pre-bed/(MgO:(WO.sub.x/SiO.sub.2)=3:1)=0.25. Ethene and trans-2-butene were extra purified using molsieve 3A. An additional triple gas filter cartridge (Oxygen, Moisture and Hydrocarbon trap, Restek) was used to remove oxygen, moisture and hydrocarbons form nitrogen, hydrogen, and hydrogen mixtures. A standard reaction feed consisted of C.sub.2H.sub.4, trans-2-C.sub.4H.sub.8, and N.sub.2 (10 vol. %) with a C.sub.2H.sub.4/trans-2-C.sub.4H.sub.8 ratio of 2.5. The weight hourly space velocity (WHSV related to the main catalyst bed, namely MgO/WO.sub.xSiO.sub.2-mix mass) was set to 1.9 h.sup.1 with respect to co-fed trans-2-butene (standard reaction conditions).

[0073] The results of metathesis and isomerization tests are shown in FIG. 1. The diagram in FIG. 1 shows the time-on-stream (a) conversion of n-butenes and (b) yield of propene over MgO.sub.L1/(MgO.sub.L1:(WO.sub.x/SiO.sub.2).sub.L1)=0.25) under standard reaction conditions. As deducible from the diagrams of FIG. 1 it becomes apparent that MgO.sub.L1 prepared from (MgCO.sub.3).sub.4.Mg(OH).sub.2.5H.sub.2O by calcination in air shows a very good time-on stream stability.

Example 2: Comparative Example

[0074] MgO.sub.L2 was prepared by calcination of Mg(OH).sub.2 at 550 C. for 16 h in an air flow. The results of MgO.sub.L2 characterisation by BET and XRD are provided in Table 2 below.

[0075] (WO.sub.x/SiO.sub.2).sub.L2 was prepared similarly to (WO.sub.x/SiO.sub.2).sub.L1 (see Example 1) but using SiO.sub.2 (Davisil, Aldrich) instead of SiO.sub.2 (Aerolyst 3038, Evonik). Both catalytic materials were tested as described in Example 1. It should be noted that the two support materials Aerolyst 3038 and Davisil have the same surface properties and texture.

[0076] The results of metathesis and isomerization tests using this catalytic preparation are shown in FIG. 2. The diagrams of FIG. 2 show that the overall stability of MgO.sub.L2 is dramatically reduced in comparison to experiment with MgO.sub.L1.

Example 3: Comparative Example

[0077] Commercial MgO and WO.sub.x/SiO.sub.2, were used. They are denoted as MgO.sub.c and (WO.sub.x/SiO.sub.2).sub.C, respectively. The results of MgO.sub.C the characterization by BET and XRD are provided in Table 2 below. Both catalytic materials were tested as described in Example 2.

[0078] The results of metathesis and isomerization tests are shown in FIG. 3. The diagrams of FIG. 3 reveal that the overall stability of a commercial available MgO.sub.c is lower than of MgO.sub.L1.

[0079] FIG. 4 shows time on stream profiles of the effluent molar fractions of 1-butene and cis-2-butene formed over MgO.sub.L1 according to the invention, MgO.sub.L2 obtained from Mg(OH).sub.2 and commercial MgO.sub.c. This direct comparison and supports the results shown in FIGS. 1-3. It is apparent that the amount of butene converted over time are dramatically improved when using the more stable MgO.sub.L1.

Example 4: Bulk and Surface Properties of Differently Originated MgO

[0080]

TABLE-US-00002 TABLE 2 List of referenced types of MgO including bulk and surface properties Max. of Total pore pore size MgO BET volume distribution Crystallite denotation Precursor [m.sup.2/g] [cm.sup.3/g] [nm] size [nm] MgO.sub.c commercial 34 0.151 4.4-5 17.9 MgO.sub.L1 (MgCO.sub.3).sub.4Mg(OH).sub.25H.sub.2O 109 0.356 8-8.4 13.3 (CAS No 39409-82-0), Acros Organics MgO.sub.L2 Mg(OH).sub.2 (CAS No 1309- 15.5 0.189 n.d. >100 42-8), Fluka

[0081] It becomes clear from the above results shown in FIGS. 1-4 that MgO.sub.L1 is the best promoter or co-catalyst for the metathesis catalyst WO.sub.3SiO.sub.2. Especially the time-on-stream stability which is characterised by the conversion after e.g. 150 hours is clearly improved. The material has also a better isomerisation activity. The outstanding promoter properties are a result of the combination of the higher specific BET surface area, the higher maximal pore size and the low crystallite size.

[0082] The methods used for determining the catalyst properties are standard methods.

S.SUB.BET.Specific Surface Area

[0083] Nitrogen physisorption at 196 C. on BELSORP-mini II setup (BEL Japan, Inc.) was employed to determine specific surface areas (SBET). The pore size distribution and total pore volume were obtained using the BJH method. The samples were exposed to vacuum (2 Pa) and then heated at 250 C. for 2 h before the measurements.

[0084] X-Ray Diffraction (XRD)Crystallite Size

[0085] X-ray diffractograms of freshly calcined MgO were recorded in the Bragg angle (2) range from 5 to 65 at a rate of 0.01 s1 on a STOE Stadi P setup using Cu K radiation (=0.154 nm). The phase identification was carried out basing on the ICDD database.