Catalyst bed configuration for olefin conversion and process for obtaining olefins

Abstract

The present invention relates to a catalyst bed configuration for conversion of olefins comprising i) at least one main catalyst bed comprising a) at least one first catalyst component comprising a metathesis catalyst, and b) at least one second catalyst component comprising a catalyst for double bond isomerization, and ii) at least one catalyst pre-bed arranged upstream of the at least one main catalyst bed comprising at least one compound selected from the group of alkaline earth oxides. The at least one compound used as catalyst pre-bed and selected from the group of alkaline earth oxides is subjected to a pre-treatment before arranging said at least one compound used as catalyst pre-bed upstream of the at least one main catalyst bed, wherein the pre-treatment comprises at least one cycle comprising successive treatment in an oxidizing and reducing atmosphere.

Claims

1. A catalyst system for conversion of olefins comprising at least one main catalyst bed comprising a) at least one first catalyst component comprising a metathesis catalyst, and b) at least one second catalyst component comprising a catalyst for double bond isomerisation, and at least one thermally pre-treated (pre-aged) catalyst pre-bed that is arranged upstream of the at least one main catalyst bed, wherein the at least one thermally pre-treated (pre-aged) catalyst pre-bed comprises at least one compound selected from the group of alkaline earth oxides, wherein the at least one compound forming the catalyst pre-bed was thermally pre-treated in at least one cycle comprising a successive treatment in an oxidizing and reducing atmosphere carried out at temperatures between 300 C. and 800 C., and wherein the at least one compound is arranged after said successive treatment in catalyst pre-bed upstream of the at least one main catalyst bed.

2. The catalyst system according to claim 1, wherein the pre-treatment of the at least one compound of the catalyst pre-bed comprises the steps: a) heating the at least one compound in an inert gas atmosphere to a temperature between 300 C. and 500 C.; b) treating the at least one compound in an oxygen containing atmosphere at temperatures between 400 C. and 600 C.; c) treating the at least one compound in a hydrogen containing atmosphere at temperatures between 300 C. and 500 C.; d) flushing the at least one compound with an inert gas at temperatures between 400 C. and 600 C.; and e) subsequently cooling down the at least one compound.

3. The catalyst system according to claim 2, wherein the inert gas is selected from a group consisting of argon, nitrogen or methane.

4. The catalyst system according to claim 1, wherein the pre-treatment of the at least one compound of the catalyst pre-bed comprises the steps: a) heating the at least one compound in an inert gas atmosphere to 400 C.; b) treating the at least one compound in an oxygen containing atmosphere at temperatures between 500 C. and 550 C.; c) treating the at least one compound in a hydrogen containing atmosphere at 400 C., d) flushing the at least one compound with an inert gas at temperatures between 400 C. and 550 C.; and e) subsequently cooling down the at least one compound to a temperature between 200 C. and 350 C.

5. The catalyst system according to claim 1, wherein the pre-treatment of the at least one compound if the catalyst pre-bed comprises the steps: a) heating the at least one compound in an inert gas atmosphere to 400 C.; b) replacing the inert gas atmosphere by an oxygen containing gas atmosphere and simultaneous temperature increase to 500 C. to 550 C. and treating the at least one compound in said oxygen containing flow; b1) cooling the at least one compound to 400 C., in an inert gas atmosphere; c) treating the at least one compound in a hydrogen containing gas atmosphere at 400 C., d) flushing the at least one compound with an inert gas and increasing the temperature simultaneously to 500 C. to 600 C.; and e) subsequently cooling down the at least one compound to a temperature between 200 C. and 350 C.

6. The catalyst system according to claim 1, wherein the pre-treatment cycle is repeated at least twice.

7. The catalyst system according to claim 6, wherein the pre-treatment cycle is repeated at least 5 times.

8. The catalyst system according to claim 1, wherein the main catalyst bed comprises the at least isomerisation catalyst component and the at least one metathesis catalyst component in a ratio between 5:1 and 1:1.

9. The catalyst system according to claim 1, wherein the metathesis catalyst comprises oxides of metals of the 6th and 7th group of the PSE deposited on at least one inorganic carrier.

10. The catalyst system according to claim 9, wherein the metathesis catalyst comprises tungsten oxide, molybdenum oxide, and/or a precursor thereof deposited on at least one inorganic carrier.

11. The catalyst system according to claim 1, wherein said second catalyst component for double bound isomerisation of the main catalyst bed comprises Group 2 metal oxides.

12. The catalyst system according to claim 11, wherein said second catalyst component for double bond isomerisation of the main catalyst bed comprises magnesium oxide, calcium oxide, barium oxide, strontium oxide, or mixtures thereof.

13. The catalyst system according to claim 1, wherein the mass ratio of the pre-bed and the catalyst mixture of metathesis catalyst and isomerisation catalyst is between 1:10 and 3:1.

14. The catalyst system according to claim 1, wherein said at least one compound of the catalyst pre-bed comprises an oxide selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide, barium oxide or mixtures thereof.

15. The catalyst system according to claim 1, wherein said at least one compound of the catalyst pre-bed comprises magnesium oxide.

16. The catalyst system according to claim 1, wherein the isomerisation catalyst of the main catalyst bed underwent a pre-treatment.

17. The catalyst system according to claim 16, wherein the isomerisation catalyst of the main catalyst bed underwent the same pre-treatment as the alkaline earth oxide of the catalyst pre-bed.

18. The catalyst system according to claim 1, wherein the at least one main catalyst bed and the at least one catalyst pre-bed comprising the at least one pre-treated compound are activated in a process comprising the steps of a) heating the catalyst bed and the catalyst pre-bed in an inert gas atmosphere to a temperature between 300 C. and 500 C.; b) treating the catalyst bed and the catalyst pre-bed in an oxygen containing atmosphere at temperatures between 400 C. and 600 C.; c) treating the catalyst bed and the catalyst pre-bed in a hydrogen containing atmosphere at temperatures between 300 C. and 500 C.; d) heating the catalyst bed and the catalyst pre-bed in an inert gas atmosphere at temperatures between 400 C. and 600 C.; and e) subsequently cooling down the catalyst bed and the catalyst pre-bed in an inert gas atmosphere.

19. A process for obtaining an olefin by metathesis comprising the steps of feeding at least two olefins as starting material to a reactor comprising a catalyst system according to claim 1; and converting the at least two olefin gases at a pressure between 1 to 50 bar at a temperature between 100 C. and 600 C. to at least one new olefin.

20. The process for obtaining an olefin according to claim 19, wherein the reactor is a fixed-bed reactor.

21. The catalyst system according to claim 1, wherein the at least one compound of the catalyst pre-bed was thermally pre-treated at temperatures between 300 C. and 600 C.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention is further explained in more detail by the means of the following examples.

Example 1: Catalyst Preparation and Pre-Aging Procedure

(2) The WO.sub.x/SiO.sub.2 catalyst has been prepared according to U.S. Pat. No. 4,575,575 (see example 1, catalyst component C). Commercial MgO has been used.

(3) In order to prove if MgO loses its improving effect on propene production over several metathesis/regeneration cycles, MgO was pre-aged according to the standard procedure of catalyst treatment described below without exposure to olefin feed.

(4) Pre-Treatment (Pre-Aging) Procedure

(5) MgO was initially heated in a continuous flow reactor using a flow of pure nitrogen up to 400 C. with a heating rate of 5 K.Math.min.sup.1. The temperature was held constant for 2 h. Hereafter, the nitrogen flow was replaced by an air flow with a simultaneous increase in temperature to 525 C. with a heating rate of 5 K.Math.min.sup.1. After 2 hours in this flow at the final temperature, the reactor was cooled to 400 C. (2 K.Math.min.sup.1) in a flow of pure nitrogen. The temperature was held constant for 0.5 h followed by feeding an H.sub.2:N.sub.2=30:70 (mol/mol) flow for 0.5 h. Then, the reactor was flushed with a flow of pure nitrogen and heated in the same flow up to 550 C. with a heating rate of 5 K.Math.min.sup.1. The temperature was held constant for 16 h. Finally, the reactor was cooled down to 300 C. After finishing this cycle the above procedure was additionally repeated for 5 times. Such treated MgO is called pre-aged MgO.

Example 2: Catalytic Testing

(6) Catalytic tests were performed in a reactor system equipped with 16 continuous-flow fixed-bed quartz reactors operating in parallel under identical conditions, i.e. total pressure of 1.4 bar, reaction temperature of 300 C. and a C.sub.2H.sub.4:trans-2-C.sub.4H.sub.8:N.sub.2=64.3:25.7:10 feed. The total gas flow in each reactor was 14.9 ml (STP).Math.min.sup.1 yielding a WHSV (weight hourly space velocity) of 1.9 h.sup.1 related to trans-2-C.sub.4H.sub.8. One reactor was always empty and used for by-pass measurements. C.sub.2H.sub.4 (Linde, purity>99.95%), trans-2-C.sub.4H.sub.8 (Linde, purity>99.0%) were extra purified with molsieve 3 A, while oxysorb and molsieve 3 A were applied for purifying N.sub.2 (Air Liquide, purity>99.999%). The main catalyst bed is a physical mixture of MgO (0.3-0.7 mm) and WO.sub.x/SiO.sub.2 (0.3-0.7 mm) with a weight ratio of 3. MgO (0.3-0.7 mm) was additionally used as a pre-bed arranged upstream. Both beds were packed within the isothermal zone of the reactor. The reactor is heated by an electrical furnace, which is located inside a box pre-heated to 120 C. Up- and downstream lines to the reactor are also inside this box.

Example 3: Embodiment According to the Invention

(7) 300 mg of main catalyst bed (see example 2) and 300 mg of pre-aged MgO pre-bed (see example 1) arranged upstream the main bed were loaded in a quartz reactor and used over 9 metathesis cycles and 8 regeneration cycles. The reaction conditions are defined in example 2.

Example 4: Comparative Example

(8) For comparative purposes, a metathesis reaction as described in example 3 was performed, however, using freshly prepared MgO instead of the pre-aged one; i.e. 300 mg main catalyst bed (see example 2) and 300 mg of freshly prepared MgO pre-bed.

(9) It should be mentioned that the tests in examples 3 and 4 were simultaneously carried out in the same set-up (see example 2). This means that the differently composed catalysts were analysed under identical conditions. The duration of selected metathesis cycles and selected catalytic performance at the cycle end are given in Table 1.

(10) Activation Procedure

(11) Before each metathesis cycle, the reactor filled with the whole catalyst bed was heated in a flow of pure nitrogen up to 400 C. with a heating rate of 5 K.Math.min.sup.1. The temperature was held constant for 2 h. Hereafter, an air flow was fed to the reactor followed by temperature rising to 525 C. with a heating rate of 5 K.Math.min.sup.1. After 2 hours in this flow at the final temperature, the reactor was cooled to 400 C. (2 K.Math.min.sup.1) in a flow of pure nitrogen. The temperature was held constant for 0.5 h followed by feeding an H.sub.2:N.sub.2=30:70 (mol/mol) flow for 0.5 h. Then, the reactor was flushed with a flow of pure nitrogen and heated in the same flow up to 550 C. with a heating rate of 5 K.Math.min.sup.1. The temperature was held constant for 16 h. Finally, the reactor was cooled down to 300 C., where the metathesis reaction was started.

(12) Regeneration Procedure

(13) After completing each metathesis cycle the catalyst was heated in an O.sub.2 (1 vol. % in N.sub.2) flow up to 420 C. followed by increasing O.sub.2 concentration to 3 vol. % with a simultaneous rise in reaction temperature to 480 C. Hereafter, these both parameters were again increased to 6 vol. % and 525 C., respectively. Finally, pure air was fed to the reactor at 525 C. for 3 hours followed by cooling down to 400 C. in a nitrogen flow. Then, the above activation procedure was repeated before starting next metathesis cycle. The duration of selected metathesis cycles and selected catalytic performance at the cycle end are given in Table 1.

(14) TABLE-US-00001 TABLE 1 Conversion of n-butenes (X(n-butenes)) and propene selectivity (S(C.sub.3H.sub.6)) at the end of metathesis cycle as described in examples 3 and 4. n(C.sub.3H.sub.6) represents an overall amount of propene formed during each cycle. Cycle Time on X(n-butenes)/ S(C.sub.3H.sub.6)/ n(C.sub.3H.sub.6)/mol number stream/h Example 3 Example 4 Example 3 Example 4 Example 3 Example 4 1 186 0.72 0.51 0.996 0.996 3.17 3.03 2 140 0.57 0.34 0.997 0.997 2.13 1.94 9 140 0.48 0.20 0.995 0.999 2.26 2.11

(15) It was expected that the pre-aging of the magnesium oxide would negatively influence its on-stream activity. Surprisingly, the results in table 1 clearly demonstrate that a simple oxidative thermal treatment combined with a hydrogen reduction step is beneficial for on-stream propene production. This is valid both for short and long metathesis cycles with the highest being achieved for industrially attractive long time on stream tests.