Process for obtaining olefins by metathesis

Abstract

The present invention relates to a process for obtaining an olefin by metathesis comprising feeding at least one stream comprising at least one olefin as starting material to at least one reactor 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 isomerization, whereby the first and second catalyst are physically mixed with each other, wherein the at least one stream comprising at least one olefin as starting material is co-fed with hydrogen gas in a concentration range between 0.01 Vol % and 0.2 Vol % in respect to the total gas amount in the stream, and the metathesis process is conducted in the at least one reactor at a pressure between 0.1 MPa and 3.0 MPa and at a temperature between 250 C. and 300 C.

Claims

1. A process for obtaining an olefin by metathesis comprising feeding at least one stream comprising at least one olefin as starting material and hydrogen gas in a concentration range between 0.01 vol % and 0.2 vol % in respect to the total gas amount in the stream to at least one reactor comprising at least one main catalyst bed, the 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, whereby the first and second catalyst are physically mixed with each other, and conducting a metathesis process in the at least one reactor at a pressure between 0.1 MPa and 3.0 MPa and at a temperature between 250 C. and 300 C.

2. The process according to claim 1, wherein the hydrogen gas is co-fed in a concentration range between 0.05 vol % and 0.2 vol %, in respect to the total gas amount in the stream.

3. The process according to claim 1, wherein the reaction pressure is between 0.12 MPa and 2.5 MPa.

4. The process according to claim 1, wherein the reaction temperature is between 270 C. and 300 C.

5. The process according to claim 1, wherein at least two olefins are fed as starting material.

6. The process according to claim 5, wherein a first of the at least two olefins used as starting material comprises at least two carbon atoms (C2-compound) and a second of the at least two olefins used as starting material comprises at least four carbon atoms (C4-compound).

7. The process according to claim 6, wherein the ratio of the C2-compound and the C4-compound is 20:1.

8. The process 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 process according to claim 1, wherein the metathesis catalyst comprises oxides of metals of the 6th and 7th group of the Periodic Table of the Elements deposited on at least one inorganic carrier.

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

11. The process according to claim 1, wherein at least one catalyst pre-bed comprising at least one compound selected from the group of alkaline earth oxides is arranged upstream of the at least one main catalyst bed.

12. The process according to claim 11, wherein the mass ratio of the catalyst in the pre-bed and the catalyst mixture of metathesis catalyst and isomerisation catalyst in the main catalyst bed is between 1:10 and 3:1.

13. The process according to claim 11, wherein said compound comprises magnesium oxide, calcium oxide, strontium oxide, barium oxide or a mixture thereof.

14. The process according to claim 1, wherein the isomerisation catalyst of the main catalyst bed and/or the catalyst pre-bed are subjected to a pre-treatment before use, wherein the pre-treatment comprises at least one cycle comprising a successive treatment in an oxidizing and reducing atmosphere.

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

16. The process according to claim 2, wherein the hydrogen gas is co-fed in a concentration range between 0.05 vol % and 0.1 vol % in respect to the total gas amount in the stream.

17. The process according to claim 3, wherein the reaction pressure is between 1.0 MPa and 2.0 MPa.

18. The process according to claim 4, wherein the reaction temperature is between 280 C. and 300 C.

19. The process according to claim 6, wherein the C2-compound is ethene and the C4-compound is 2-butene.

20. The process according to claim 7, wherein the ratio of the C2-compound and the C4-compound is 2.5:1.

21. The process according to claim 1, wherein the reaction pressure is between 2.0 and 3.0 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is further explained in more detail by the means of the following examples with reference to the Figures. It shows:

(2) FIG. 1 a diagram illustrating the initial time on stream yield of propene obtained by ethen-2-butene metathesis co-fed with hydrogen at different concentrations; and

(3) FIG. 2 a further diagram illustrating the initial time on stream yield of propene obtained by ethen-2-butene metathesis co-fed with hydrogen at different concentrations.

DETAILED DESCRIPTION OF THE INVENTION

Example 1: A First Standard Reactor Configuration without Hydrogen (Comparative Example)

(4) Catalytic tests were performed in a tubular (4 mm i.d.) continuous-flow fixed-bed reactor made of quartz at 1.4 bar and 300 C. using a C.sub.2H.sub.4:trans-2-C.sub.4H.sub.8:N.sub.2=64.3:25.7:10 feed. 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 3A, while oxysorb (Resteck) and molsieve 3A were applied for purifying N.sub.2 (Air Liquide, purity>99.999%). The main catalyst 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 3.0. The MgO (0.3-0.7 mm) was additionally used as a pre-bed arranged upstream. Both beds were placed within the isothermal zone of the reactor. The weight hourly space velocity (WHSV) was of 1.9 h.sup.1 related to trans-2-C.sub.4H.sub.8 and the main catalyst.

(5) Before catalytic testing, the following pre-treatment was performed. The reactor 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) gas mixture 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 studied.

(6) FIG. 1 shows the yield of propene (equation 1) as a function of time on stream.
Y.sub.C.sub.3.sub.H.sub.6=S.sub.C.sub.3.sub.H.sub.6H.sub.n-butenes(1),

(7) where S.sub.C.sub.3.sub.H.sub.6 is propene selectivity calculated according to

(8) $\begin{array}{cc}{S}_{C_3{H}_6}=\frac{m_{C_3{H}_6}^{\mathrm{outlet}}}{m_{C_3{H}_6}^{\mathrm{outlet}}+.Math.m_{C_5}^{\mathrm{outlet}}+.Math.m_{C_6}^{\mathrm{outlet}}},& \left(2\right)\end{array}$

(9) where m.sup.outlet is mass flow of C.sub.3H.sub.6, C.sub.5 and C.sub.6 olefins, respectively X.sub.n-butenes is conversion of n-butenes, calculated according to

(10) $\begin{array}{cc}{X}_{n\text{-}\mathrm{butenes}}=\left(1-\frac{X_{t\text{-}2\text{-}{C}_4{H}_8}^{\mathrm{outlet}}+X_{1\text{-}{C}_4{H}_8}^{\mathrm{outlet}}+X_{\mathrm{cis}\text{-}2\text{-}{C}_4{H}_8}^{\mathrm{outlet}}}{X_{t\text{-}2\text{-}{C}_4{H}_8}^{\mathrm{inlet}}}\right)& \left(3\right)\end{array}$

(11) where x.sub.i.sup.inlet and x.sub.i.sup.outlet represent mole fractions of 1- or 2-butenes at the reactor inlet and outlet, respectively.

Example 2: First Standard Reactor Configuration with 0.1 Vol % Hydrogen (Inventive Example)

(12) The test was carried out as described in Example 1 but using the standard feed additionally containing 0.1 vol % H.sub.2.

Example 3: Second Standard Reactor Configuration and Technical Conditions Without Hydrogen (Comparative Example)

(13) A liquid technical C4 stream containing 82 wt % 2-butene, 1 wt % 1-butene, 1 wt % iso-butene and 16 wt % n-butane was fed over a treatment tower filled in flow direction with 90 vol. % Selexsorb CD and 10 vol. % Selexsorb COS into a metering tank. The tank is connected over a cooler with a HPLC pump. The cooler was kept at a temperature of 3 C. A C4 flow of 3.6 g/min was fed by means of the pump to an evaporator which was operated at 215 C. The evaporator has two inlets, one at the bottom and a second in the middle of the tube (volume 450 ml). The C4 entered the evaporator at the bottom and was evaporated. In a second stream 5.73 NI/min ethene was fed by means of a flow controller and entered the evaporator at the middle inlet. The mixed feed passed a static mixer and entered the metathesis reactor at the top flange, past the catalyst bed and left the reactor at the bottom. The inlet and outlet feed composition was analyzed with an Agilent 7890 gas chromatograph using a HP Al/S column.

(14) The reactor had an internal diameter of 38 mm and a length of 900 mm. For the preparation of the catalyst bed MgO and WO.sub.3SiO.sub.2 pellets with a size of 2-4 mm were physically mixed in a mass ratio of 3:1. 113.2 g of the mixture was placed in the reactor as main-bed. Upstream to the main-bed 28.3 g MgO were introduced as pre-bed. The catalyst beds were placed in the middle of the reactor in an isothermal zone and the space between reactor bottom and catalyst bed as well as that above the bed was filled with alumina bed support balls with a size of inch. The temperature of the bed was adjusted to 280 C. and was kept constant over the whole time on stream. The reaction pressure was 25 bar, the E/B mole ratio 4.0 and the WHSV was 1.6 h.sup.1.

(15) Before catalytic testing, the following pre-treatment was performed. The reactor was heated in a flow of pure nitrogen up to 300 C. with heating rate of 0.2 K.Math.min.sup.1 at a pressure of 3 bar. Hereafter, an oxygen stream was added to adjust an oxygen content of 5 vol %. The temperature was kept constant for 2 hours. After that the temperature was raised to 400 C. with a heating rate of 0.2 K.Math.min.sup.1 and the oxygen content was increased to 10 vol %. The temperature was kept constant for 2 further hours. After treatment at 400 C. the temperature was raised to 525 C. with the above mentioned heating rate. Pure synthetic air was used for the final oxidation step.

(16) After 2 hours in this flow at the final temperature, the reactor was cooled to 400 C. (0.7 K.Math.min.sup.1) in a flow of pure nitrogen. The temperature was held constant for 0.5 h followed by feeding a hydrogen flow of 0.9 NI/h 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 0.2 K.Math.min.sup.1. The temperature was held constant for 16 h. Finally, the reactor was cooled down to 280 C., where the metathesis reaction was started.

(17) The conversion increased during the first 116 hours from 81% to a maximum of 87%, was constant for further 184 hours and decreased afterwards. The conversion after 400 hours was 84%.

Example 4: Second Standard Reactor Configuration Technical Conditions with 0.2 Vol % Hydrogen in the Feed (Inventive Example)

(18) The experiment was carried out in the same way as described in example 3. In addition to the olefin feed 0.2 vol % hydrogen were fed to the evaporator.

(19) The conversion increased after 2 hours to 88% and stayed constant over a time of 400 hours.

Example 5: First Standard Reactor Configuration with 0.5 Volume % Hydrogen (Comparative Example)

(20) The test was carried out as described in Example 1 but using the standard feed additionally containing 0.5 vol % H.sub.2.

Example 6: First Standard Reactor Configuration with 2 Vol % Hydrogen (Comparative Example)

(21) The test was carried out as described in Example 1 but using the standard feed additionally containing 2 volume % H.sub.2.

Example 7: First Standard Reactor Configuration with 0.001 Vol. % Hydrogen

(22) The test was carried out as described in Example 1 but using the standard feed additionally containing 0.001 vol. % H.sub.2.

(23) The results of the conversion using the first standard reactor configuration with different amounts of hydrogen are depicted in the diagram of FIG. 1.

(24) FIG. 1 shows the time on-stream yield of propene in ethylene-2-butene metathesis to propene over standard catalyst at 300 C. a C.sub.2H.sub.4:trans-2-C.sub.4H.sub.8:N.sub.2:H.sub.2=64.3:25.7:(10-x):x feed at a reaction pressure of 1.2 bar in a time on stream range of up to 80 h.

(25) FIG. 1 depicts the time on stream yield using different concentrations of co-fed hydrogen, namely 0 vol % H.sub.2, 0.001 vol % H.sub.2, 0.1 vol % H.sub.2, 0.5 vol % H.sub.2 and 2 vol % H.sub.2.

(26) The results clearly indicate that the total amount of propene in the conversion range above 60% is higher at a hydrogen concentration about 0.1 Vol %. In particular the results show that the initial time-on-stream yield of propene (that means within the first 80 hours reaction time) is increased when co-feeding hydrogen compared to no-co-feeding of hydrogen.

(27) In addition, the results also show that the time-on-stream yield is further influenced by the amount of hydrogen co-fed. Co-feeding 0.1 vol % hydrogen improved the propene yield over an extended period of time (up to 80 hours) while the propene yield using a concentration of 0.5 vol % hydrogen dropped rapidly after about 40 h time on stream and was even worse compared to the olefin fed without hydrogen. Co-feeding only 0.001 vol % hydrogen on the other hand showed no influence on the time-on-stream yield in respect to the standard condition without hydrogen.

(28) The massive beneficial influence of small amounts of hydrogen on the initial time on stream yield was in view of the prior art surprising and not to be expected.

Example 8: First Standard Reactor Configuration Technical Conditions with 0.2 vol % Hydrogen in the Feed (Inventive Example)

(29) The test was carried out as described in Example 1 but using the standard feed additionally containing 0.2 vol % H.sub.2.

Example 9: First Standard Reactor Configuration with 0.3 Volume % Hydrogen (Comparative Example)

(30) The test was carried out as described in Example 1 but using the standard feed additionally containing 0.3 vol % H.sub.2.

(31) The results of the conversion of example 8 and 9 using the first standard reactor configuration with different amounts of hydrogen are depicted in the diagram of FIG. 2.

(32) FIG. 2 shows the time on-stream yield of propene in ethylene-2-butene metathesis to propene over standard catalyst at 300 C. a C.sub.2H.sub.4:trans-2-C.sub.4H.sub.8:N.sub.2:H.sub.2=64.3:25.7:(10-x):x feed at a reaction pressure of 1.2 bar in a time on stream range of up to 80 h.

(33) FIG. 2 depicts the time on stream yield using different concentrations of co-fed hydrogen, namely 0 vol % H.sub.2, 0.1 vol % H.sub.2, 0.2 vol % H.sub.2, 0.3 vol % H.sub.2 and 0.5 vol % H.sub.2.

(34) The results clearly indicate that the total amount of propene in the conversion range above 60% is higher at a hydrogen concentration about 0.1 and 0.2 Vol %. In particular the results show that the initial time-on-stream yield of propene (that means within the first 80 hours reaction time) is increased when co-feeding hydrogen compared to no-co-feeding of hydrogen.

(35) In addition, the results also show that the time-on-stream yield is further influenced by the amount of hydrogen co-fed. Co-feeding up to 0.2 vol % hydrogen improved the propene yield over an extended period of time (up to 80 hours) while the propene yield using a concentration of >/=0.3 vol % hydrogen dropped rapidly after about 45 h time on stream and was even worse compared to the olefin fed without hydrogen.