Process for olefin production by metathesis and reactor system therefor

Abstract

The present invention relates to a process for obtaining an olefin by metathesis including the steps of i) feeding at least one stream with at least one olefin as starting material to at least one first reactor with at least one pre-bed having at least one compound selected from the group of alkaline earth oxides and ii) feeding the stream leaving the at least one first reactor to at least one second reactor downstream to the at least one first reactor including at least one main bed having a) at least one first catalyst component and b) at least one second catalyst component. The first and second catalyst are physically mixed with each other. The operational temperature of the at least one first reactor is lower than the operational temperature of the at least one second reactor.

Claims

1. A process for obtaining propene by metathesis comprising the steps of feeding at least one stream comprising ethene and 2-butene, wherein 2-butene is supplied as a technical 2-butene stream containing 1 butene, as starting material to at least one first reactor with at least one pre-bed comprising at least one compound selected from the group consisting of alkaline earth metal oxides, wherein the at least one first reactor is operated at an operational temperature T1, and feeding at least one stream leaving the at least one first reactor to at least one second reactor downstream of and separate from the at least one first reactor comprising at least one main bed comprising a) at least one first catalyst component comprising a metathesis catalyst, and b) at least one second catalyst component comprising an isomerisation catalyst for double bond isomerisation, wherein the at least one first catalyst and the at least one second catalyst are physically mixed with each other, wherein the at least one second reactor is operated at an operational temperature T2, wherein the operational temperature T1 of the at least one first reactor is in a range between 150 C. and 280 C. and the operational temperature T2 of the at least one second reactor is in a range between 290 C. and 350 C., and wherein the operational temperature T1 of the at least one first reactor is at least 40 C. lower than the operational temperature T2 of the at least one second reactor.

2. The process according to claim 1, wherein the operational temperature T1 of the at least one first reactor is in a range between 200 C. and 280 C.

3. The process according to claim 1, wherein the operational temperature T2 of the at least one second reactor is in a range between 290 C. and 330 C.

4. The process according to claim 1, wherein a stream comprising one first olefin is fed to the at least one first reactor, is mixed with at least one third olefin after leaving the at least one first reactor forming a mixture of the effluent resulted from the at least one first reactor and the at least one third olefin which is subsequently fed to the at least one second reactor.

5. The process according to claim 1, wherein a stream comprising at least two olefins as starting materials for metathesis is fed into the at least one first reactor and subsequently after leaving the at least one first reactor is fed to the at least one second reactor.

6. The process according to claim 1, wherein a pressure in the at least one first reactor and the at least one second reactor is between 1 to 50 bar.

7. The process according to claim 1, wherein a pressure in the at least one first reactor is higher or equal to a pressure in the at least one second reactor.

8. The process according to claim 1, wherein a mass ratio of the at least one pre-bed in the at least one first reactor and the at least one main bed in the at least one second reactor is between 1:10 and 3:1.

9. The process according to claim 1, wherein the at least one main bed comprises the isomerisation catalyst and the metathesis catalyst component in a mass ratio of the isomerization catalyst to the metathesis catalyst between 5:1 and 1:1.

10. The process according to claim 1, wherein the metathesis catalyst comprises oxides of metals of the Group VIB and VIIB of the Periodic Table of Elements (PSE) deposited on at least one inorganic carrier and the at least one second catalyst component comprises oxides of metals of the Group IIA of the Periodic Table of Elements.

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

12. The process according to claim 1, wherein a metathesis reaction is performed in the at least one second reactor at a Weight Hourly Space Velocity (WHSV) in a range between 1 and 100 h.sup.1.

13. The process according to claim 1, wherein the operational temperature T1 of the at least one first reactor is at least 100 C. lower than the operational temperature T2 of the at least one second reactor.

14. The process according to claim 10, wherein the metathesis catalyst comprises oxides selected from the group consisting of tungsten oxide, molybdenum oxide, or a precursor thereof.

15. The process according to claim 10, wherein the at least one second catalyst component comprises oxides of metals of the Group IIA of the Periodic Table of Elements selected from the group consisting of magnesium oxide, calcium oxide, barium oxide, strontium oxide, or mixtures thereof.

16. The process according to claim 3, wherein the operational temperature T2 of the at least one second reactor is in a range between 290 C. and 310 C.

17. The process according to claim 6, wherein the pressure in the at least one first reactor and the at least one second reactor is between 10 to 30 bar.

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 FIGURE. It shows:

(2) FIGURE: a diagram illustrating the propylene selectivity in dependency on the time-on-stream in ethene-2-butene metathesis for a first embodiment of the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1: Catalyst Preparation

(3) The WO.sub.x/SiO.sub.2 catalyst was prepared according to U.S. Pat. No. 4,575,575, example 1, catalyst component C. Commercial magnesium oxide powder was used, which was pelletized and crushed to receive the necessary particle size of 0.3 to 0.7 mm.

Example 2: Standard Reactor Configuration, Comparative Example

(4) A conventional metathesis reactor (2) was loaded with 600 mg of main bed (a physical mixture of MgO and WO.sub.3/SiO.sub.2 powder particles with a diameter of 0.3 to 0.7 mm in the mass ratio of 3:1) and with 150 mg of pure MgO (pre-bed) arranged upstream. The mass ratio between the pre-bed and main bed was 1 to 4. The reactor was operated at 300 C. The catalytic results are summarised in table 1.

Example 3: Dual Reactor Configuration, T (MgO Pre-Bed)=300 C.

(5) The metathesis reactor (2) was loaded with 712 mg of main bed. Another separate reactor, the so-called pre-bed reactor (1) arranged upstream of reactor (2) contained 150 mg of pure MgO. Both reactors (1, 2) were operated at 300 C. The catalytic results are summarised in table 1.

Example 4: Dual Reactor Configuration T (MgO Pre-Bed)=250 C.

(6) The metathesis reactor (2) was loaded with 712 mg of main bed and operated at 300 C. The amount of MgO pre-bed in the upstream pre-bed reactor (1) was 150 mg. Its temperature was 250 C. The catalytic results are summarised in table 1.

Example 5: Dual Reactor Configuration T (MgO Pre-Bed)=400 C.

(7) The metathesis reactor (2) was loaded with 712 mg of main bed and operated at 300 C. The amount of MgO pre-bed in the upstream pre-bed reactor (1) was 150 mg. Its temperature was 400 C. The catalytic results are summarised in table 1.

(8) TABLE-US-00001 TABLE 1 Reactor configuration, reaction conditions and selected catalytic results (conversion of t-2-butene - X(t-2-C.sub.4H.sub.8), propene selectivity - S(C.sub.3H.sub.6) and propene yield - Y(C.sub.3H.sub.6)) after 2, 50 and 100 hours on metathesis stream. T.sub.1/ T.sub.2/ X(t-2-C.sub.4H.sub.8)/% S(C.sub.3H.sub.6)/% Y(C.sub.3H.sub.6)/% Ex Reactor C. C. 2 h 50 h 100 h 2 h 50 h 100 h 2 h 50 h 100 h 2 Standard 300 300 86.3 88.2 86.5 90.2 92.2 93.0 77.8 81.3 80.5 3 Dual bed 300 300 87.2 87.6 81.2 91.2 92.9 93.5 79.6 81.5 76.0 4 Dual bed 300 250 87.7 88.1 87.1 91.3 92.6 93.2 80.0 81.6 81.2 5 Dual bed 300 400 86.2 88.8 86.4 87.0 89.0 89.1 75.0 79.1 77.1 T.sub.1 is the reaction temperature of MgO:(WO.sub.x/SiO.sub.2) = 3:1 main-bed metathesis reactor T.sub.2 is the reaction temperature of MgO pre-bed isomerisation reactor

(9) The conversion of t-2-C.sub.4H.sub.8 was calculated on the basis of its inlet and outlet mole fractions (equation 1). The product selectivity was calculated on a molar basis (equation 2). 1-C.sub.4H.sub.8 and cis-2-C.sub.4H.sub.8 were considered as reaction products. The propene yield is a product of the propene selectivity and the t-2-butene conversion (equation 3).

(10) $\begin{array}{cc}{X}_{t\text{-}2C_4{H}_8}=\left(1-\frac{x_{t\text{-}2C_4{H}_8}^{\mathrm{outlet}}}{x_{t\text{-}2C_4{H}_8}^{\mathrm{inlet}}}\right)100\%& \left(1\right)\end{array}$
where x is mole fraction of t-2-butene.

(11) $\begin{array}{cc}{S}_{C_3{H}_6}=\frac{n_{C_3{H}_6}^{\mathrm{outlet}}}{n_{C_3{H}_6}^{\mathrm{outlet}}+n_{1\text{-}{C}_4{H}_8}^{\mathrm{outlet}}+n_{\mathrm{cis}\text{-}2C_4{H}_8}^{\mathrm{outlet}}+n_{C_5}^{\mathrm{outlet}}+n_{C_6}^{\mathrm{outlet}}}100\%& \left(2\right)\end{array}$
where n.sub.i.sup.outlet is number of moles of propylene, 1-butene, cis-2-buetene, pentenes (C.sub.5) and hexenes (C.sub.6) at the reactor outlet.
Y.sub.C.sub.3.sub.H.sub.6=S.sub.C.sub.3.sub.H.sub.6X.sub.t-2-C.sub.4.sub.H.sub.8100%(3),
where S.sub.C.sub.3.sub.H.sub.6 is propene selectivity and X.sub.t-2-C4H8 is conversion of t-2-butene calculated according to equations 1 and 2, respectively.

(12) The examples in Table 1 as wells as in the diagram of the FIGURE clearly demonstrate that catalytic properties such as conversion, propene selectivity and yield can be improved if the metathesis process is carried out using MgO pre-bed and MgO(WO.sub.xSiO.sub.2) catalyst main bed in two separate reactors, which operate in a temperature range between 250 and 300 C.