Catalyst and method for the selective hydrogenation of unsaturated c4 hydrocarbons

Abstract

The invention relates to a catalyst for the selective hydrogenation of molecules having at least one double bond, in particular unsaturated C4 compounds such as butenes, butadienes or C4 acetylenes. The catalyst comprises a support material and the two catalytically active metals platinum and silver, in each case in a quantity of 0.01 to 1 wt.%. The invention further relates to a method for the selective hydrogenation of molecules having at least one double bond, in particular unsaturated C4 compounds such as butenes, butadienes or C4 acetylenes, in at least one reactor with the addition of hydrogen and using the catalyst according to the invention.

Description

[0001] Catalyst and process for the selective hydrogenation of unsaturated C4 hydrocarbons

[0002] The present invention relates to a catalyst for the selective hydrogenation of molecules having at least one double bond, in particular unsaturated C4 compounds such as butenes, butadienes, or C4 acetylenes. The catalyst comprises a support material and the two catalytically active metals platinum and silver, each in an amount of 0.01 to 1 wt.%. The present invention further relates to a process for the selective hydrogenation of molecules having at least one double bond, in particular unsaturated C4 compounds such as butenes, butadienes, or C4 acetylenes, in at least one reactor with the addition of hydrogen and using the catalyst according to the invention.

[0003] Selective hydrogenation is a process in which specific molecules with at least one double bond, such as olefins or acetylenes, are selectively hydrogenated in the presence of other substances or compounds with at least one double bond, while the other substances or compounds are not or only slightly hydrogenated. Such processes have been known in the petrochemical industry for many years.

[0004] Palladium-containing heterogeneous catalysts are used in known processes for the selective hydrogenation of molecules with at least one double bond. Palladium (Pd) is typically the active metal that catalyzes the actual hydrogenation reaction. Such processes are described, for example, in EP 0 081 041 A1 or WO 2012 / 004081 A1. Sufficient selectivities are generally achieved with palladium catalysts, even in selective hydrogenation. A further improvement in selectivity can be achieved, if necessary, by moderating the activity of the palladium-containing catalyst through the addition of carbon monoxide (CO).

[0005] In recent years, the price of palladium has risen steadily. This steady increase has also led to a steady rise in the price of palladium-containing catalysts for use in selective hydrogenation. These catalysts are therefore becoming increasingly unattractive from an economic perspective. Various hydrogenation-active metals, such as nickel, are known as alternatives to palladium. However, the problem with known catalysts containing other hydrogenation-active metals is their lack of selectivity, which makes their use in selective hydrogenation difficult.

[0006] The object of the present invention was therefore to provide a catalyst for the selective hydrogenation of molecules containing at least one double bond, preferably unsaturated C4 compounds such as butenes, butadienes, or C4 acetylenes, which does not exhibit the known problems. The catalyst should be economically attractive while simultaneously exhibiting high selectivity in the selective hydrogenation.

[0007] Surprisingly, it was discovered that the selectivity of platinum catalysts can be significantly increased by adding another metal. Experiments have shown that catalysts containing silver and platinum exhibit higher and thus better selectivity than catalysts containing only platinum. This allows these comparatively less expensive catalysts to also be used in selective hydrogenation.

[0008] The present invention thus relates to a heterogeneous catalyst for the selective hydrogenation of molecules having at least one double bond, preferably unsaturated C4 compounds such as butenes, butadienes or C4 acetylenes, which comprises a support material which is selected from the group consisting of silicon dioxide, aluminosilicate, aluminum oxide, silica gel, activated carbon, titanium dioxide and mixtures thereof, preferably from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide and mixtures thereof and two different catalytically active metals, wherein the one catalytically active metal is platinum in an amount of 0.01 to 1 wt.%, preferably 0.05 to 0.5 wt.%, particularly preferably 0.1 to 0.3 wt.%, based on the total weight of the catalyst, and wherein the other catalytically active metal is silver in an amount of 0.01 to 1 wt.%, preferably 0.05 to 0.5 % by weight, particularly preferably 0.1 to 0.3 wt.-%, based on the total weight of the catalyst. The catalyst preferably consists of catalyst particles, in particular as granules, in the form of extrudates, or in the form of spheres, and is therefore not a monolithic material.

[0009] If the catalyst is in the form of granules, the particle size (length of the longest edge) of the granules is preferably in the range of 0.5 to 5 mm, preferably in the range of 1 to 4 mm. If the catalyst is in the form of extrudates, the particle size (length of the longest edge) of the extrudates is preferably in the range of 0.5 to 2.5 mm, preferably in the range of 1 to 2 mm. The particle size can be determined using known methods. The particles can also have a spherical shape, i.e., a ball shape. In this case, the diameter is preferably 0.5 to 5 mm, particularly preferably 2 to 4 mm.

[0010] Platinum and silver, as hydrogenation-active metals, are preferably present in the catalyst particles of the catalyst according to the invention in an outer peripheral zone, the peripheral zone thickness preferably being less than 500 μm, particularly preferably less than 250 μm. The metals can be deposited in the outer peripheral zone thermally or by chemical precipitation onto the support material. It is particularly preferred according to the invention if platinum and silver are the only hydrogenation-active metals in the catalyst according to the invention. In particular, the catalyst is free of palladium, ie, the catalyst contains less than 0.001 wt. % palladium, based on the total weight of the catalyst.

[0011] For catalysts which are intended to selectively hydrogenate small amounts (<10 wt.% of the hydrocarbon stream, preferably <3 wt.% of the hydrocarbon stream, based in each case on the total weight of the hydrocarbon stream) of dienes or acetylene-containing components to olefins, supports with a high BET surface area are preferably used, BET > 100 m 2 / g, particularly preferably > 150 m 2 / g to achieve the highest possible dispersion of the precious metal components. At higher concentrations of dienes or acetylene-containing components (> 10 wt.% of the hydrocarbon stream, preferably > 20 wt.% of the hydrocarbon stream, each based on the total weight of the hydrocarbon stream), supports with a small BET surface area are preferred, with BET < 100 m 2 / g. Low BET surface areas generally indicate low acidity of the support material, thus reducing the tendency for polymer formation on the support.

[0012] The present invention further provides a process for the selective hydrogenation of olefins, preferably unsaturated C4 compounds such as butenes, butadienes or C4 acetylenes, wherein the process is carried out in at least one reactor with the addition of hydrogen, characterized in that the heterogeneous catalyst is used in the process which comprises a support material which is selected from the group consisting of silicon dioxide, aluminosilicate, aluminum oxide, silica gel, activated carbon, titanium dioxide and mixtures thereof, preferably from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide and mixtures thereof and two different catalytically active metals, wherein the one catalytically active metal is platinum in an amount of 0.01 to 1 wt.%, preferably 0.05 to 0.5 wt.%, particularly preferably 0.1 to 0.3 wt.-%, based on the total weight of the catalyst, and wherein the other catalytically active metal, silver, is present in an amount of 0.01 to 1 wt.%, preferably 0.05 to 0.5 wt.%, particularly preferably 0.1 to 0.3 wt.%, based on the total weight of the catalyst. The catalyst preferably consists of catalyst particles, in particular as granules, in the form of extrudates, or in the form of spheres, and is thus not a monolithic material.

[0013] According to a preferred embodiment, the process is a selective hydrogenation of butenes, butadiene, or C4 acetylene. For the selective hydrogenation of these molecules, typically no pure streams are used, but rather industrially available C4 hydrocarbon streams (e.g., cracked C4 streams, raffinates, or the like) in which, in addition to the substances to be hydrogenated, additional C4 hydrocarbons having at least one double bond are present. These additional C4 hydrocarbons having at least one double bond are not hydrogenated, or are only hydrogenated to a very limited extent, during the selective hydrogenation, but remain largely unchanged, i.e., based on their original fraction in the C4 hydrocarbon stream used, >95%, preferably >98%.

[0014] In the selective hydrogenation according to the invention, the hydrogen is preferably added in a slight molar excess relative to the number of moles of double bonds to be hydrogenated, preferably in an amount of 1.0 to 1.5 mol of hydrogen per mole of double bond to be hydrogenated, and particularly preferably in an amount of 1.0 to 1.3 mol of hydrogen per mole of double bond to be hydrogenated. The minimal excess of hydrogen is intended to prevent side reactions and / or the other hydrocarbons from reacting due to an excessive excess of hydrogen.

[0015] Selective hydrogenation can be carried out over a wide temperature range and depends, for example, on the molecular mass of the molecules. The selective hydrogenation according to the invention is preferably carried out at a temperature between 20 and 300°C, more preferably between 25 and 250°C, and particularly preferably between 30 and 200°C. The pressure during the selective hydrogenation should not exceed 50 bar, preferably 30 bar, and particularly preferably 20 bar. Increasing the pressure beyond that required to achieve sufficient hydrogen solubility normally has no influence on the process. The pressure could therefore, in principle, also be higher, but would require greater equipment complexity without having a significant effect on the reaction. The selective hydrogenation according to the invention can be carried out in the gas phase or in the liquid phase, but is furthermore preferably a liquid-phase hydrogenation.In this case, the temperature must of course be selected so that the hydrocarbon stream to be processed is in the liquid phase.

[0016] The selective hydrogenation process of the present invention can be carried out in any suitable reactor, for example in a trickle-bed reactor, in a circulation reactor with a downstream finisher reactor, or in a pulse-flow reactor. Such reactors are known to those skilled in the art. In a preferred embodiment of the present invention, the selective hydrogenation is carried out in at least two reactors, particularly preferably in at least one circulation reactor and in at least one reactor operated in a straight-pass mode. Preferably, the circulation reactor is the first reactor, and the reactor operated in a straight-pass mode is the second reactor.

[0017] The reaction mixture obtained by selective hydrogenation can then be processed by thermal separation, in particular by distillation.

Claims

Patent claims 1. Heterogeneous catalyst for the selective hydrogenation of molecules having at least one double bond, preferably unsaturated C4 compounds such as butenes, butadienes or C4 acetylenes, which catalyst comprises a support material selected from the group consisting of silicon dioxide, aluminosilicate, aluminum oxide, silica gel, activated carbon, titanium dioxide and mixtures thereof, preferably from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide and mixtures thereof, and two different catalytically active metals, one catalytically active metal being platinum and present in an amount of 0.01 to 1 wt. %, based on the total weight of the catalyst, and the other catalytically active metal being silver and present in an amount of 0.01 to 1 wt. %, based on the total weight of the catalyst.

2. Heterogeneous catalyst according to claim 1, wherein the one catalytically active metal platinum is present in an amount of 0.05 to 0.5 wt.%, preferably 0.1 to 0.3 wt.%, in each case based on the total weight of the catalyst.

3. Heterogeneous catalyst according to claim 1 or 2, wherein the other catalytically active metal silver is present in an amount of 0.05 to 0.5 wt.%, preferably 0.1 to 0.3 wt.%, in each case based on the total weight of the catalyst 4. Heterogeneous catalyst according to one of claims 1 to 3, wherein platinum and silver are present in the catalyst particles in an outer edge zone, wherein the edge zone thickness is preferably less than 500 pm, particularly preferably less than 250 pm.

5. Heterogeneous catalyst according to one of claims 1 to 4, wherein the catalyst is free of palladium, that is to say palladium is contained in the catalyst in an amount of less than 0.001 wt.% based on the total weight of the catalyst.

6. A process for the selective hydrogenation of olefins, preferably unsaturated C4 compounds such as butenes, butadienes or C4 acetylenes, wherein the process is carried out in at least one reactor with the addition of hydrogen, characterized in that the heterogeneous catalyst is used in the process which comprises a support material selected from the group consisting of silicon dioxide, aluminosilicate, aluminum oxide, silica gel, activated carbon, titanium dioxide and mixtures thereof, preferably from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide and mixtures thereof, and comprises two different catalytically active metals, wherein one catalytically active metal is platinum and is present in an amount of 0.01 to 1 wt.%, based on the total weight of the catalyst, and wherein the other catalytically active metal is silver and is present in an amount of 0.01 to 1 wt.%, based on the total weight of the catalyst.

7. Process according to claim 6, characterized in that the process is a selective hydrogenation of butenes, butadiene or C4-acetylene, in which, in addition to the substances to be hydrogenated, additional hydrocarbons having at least one double bond are present.

8. The process according to claim 7, wherein the hydrogen is added in a slight molar excess, preferably in an amount of 1.0 to 1.5 mol of hydrogen per mol of double bond to be hydrogenated, more preferably in an amount of 1.0 to 1.3 mol of hydrogen per mol of double bond to be hydrogenated.

9. Process according to one of the preceding claims, wherein the selective hydrogenation is carried out at a temperature between 20 and 300 °C, preferably between 25 and 250 °C, particularly preferably between 30 and 200 °C.

10. Process according to one of the preceding claims, wherein the selective hydrogenation is carried out as liquid phase hydrogenation.

11. Process according to one of the preceding claims, wherein the process is carried out in at least two reactors, preferably in at least one circulation reactor and in at least one reactor operated in a straight pass.

12. Process according to one of the preceding claims, wherein the one catalytically active metal platinum is present in an amount of 0.05 to 0.5 wt.%, preferably 0.1 to 0.3 wt.%, in each case based on the total weight of the catalyst.

13. A process according to any one of the preceding claims, wherein the other catalytically active metal, silver, is present in an amount of 0.05 to 0.5 wt.%, preferably 0.1 to 0.3 wt.%, in each case based on the total weight of the catalyst.

14. A process according to any one of the preceding claims, wherein the catalyst is free of palladium, i.e. palladium is contained in the catalyst in an amount of less than 0.001% by weight based on the total weight of the catalyst.

15. The process according to any one of the preceding claims, wherein platinum and silver are present in the catalyst particles in an outer peripheral zone, the peripheral zone thickness preferably being less than 500 pm, particularly preferably less than 250 pm.