Olefin isomerization process

Abstract

The subject of the present invention is a process for isomerizing C4 to C9 olefins having terminal double bonds to the corresponding olefins having internal double bonds, wherein a heterogeneous catalyst comprising a silicon-aluminum mixed oxide composition is used.

Description

[0001] The present invention relates to a process for isomerizing C4 to C9 olefins having terminal double bonds to the corresponding olefins having internal double bonds, using a heterogeneous catalyst comprising a silica-alumina mixed oxide composition.

[0002] In isomerization (also called "rearrangement" in the case of intramolecular processes), the starting molecule is converted into a molecule in which the molecular formula remains unchanged but the atomic order, atomic arrangement or bond arrangement is changed. Isomers generally have similar bond energies and can therefore be relatively freely converted into each other. A distinction is made according to the type of conversion, such as bond isomerization, in which double bonds are rearranged, for example between CC bonds (however, many bond isomerizations involving heteroatoms (such as O, N, P and S) are also known to those skilled in the art); skeletal isomerization, in which straight-chain compounds are rearranged into branched compounds; hydroisomerization, in which alkanes are converted into isoalkanes via olefin intermediates in the presence of hydrogen; or cis / trans isomerization, in which the substituents of the double bonds are rearranged. Isomerization is usually accelerated by acidic / basic catalysts. The nature of the catalyst (such as the strength of the acid / base center) essentially determines which isomerization occurs in the molecule. The isomerization required in this article is a bond isomerization.

[0003] The corresponding olefins with terminal or internal double bonds can be provided by various methods, such as cracking methods. Another possibility is the catalytic isomerization of olefins with terminal double bonds to corresponding olefins with internal double bonds. The degree of conversion is limited by thermodynamic equilibrium in each case. For example, the catalytic isomerization of olefins with terminal double bonds is known from EP 3822244 A1.

[0004] A general problem with isomerization reactions is that, since the olefins to be isomerized have double bonds and are therefore reactive molecules, side reactions may occur. One example is oligomerization, which can occur on acidic catalyst systems and occurs as a side reaction in isomerization when corresponding acidic catalysts are used. In order to prevent oligomerization of olefins during isomerization to olefins with terminal double bonds, it is more likely to use basic catalyst systems or catalysts doped with alkali metals or alkaline earth metals.

[0005] A disadvantage of the catalyst systems known hitherto is that they have only been described for the isomerization of olefins having internal double bonds to olefins having terminal double bonds.

[0006] The object of the present invention is therefore to provide a process in which olefins with terminal double bonds are preferably isomerized to olefins with internal double bonds, in particular 1-butene is isomerized to 2-butene. From an economic point of view, the isomerization should be able to be carried out at low temperatures, with the shortest possible residence time, with high selectivity and high conversion. The catalysts used here should also have long-term stability and promote side reactions such as oligomerization as little as possible.

[0007] Surprisingly, it has been found that, in contrast thereto, it is also possible to use (weakly) acidic SiO2-based catalysts with a certain aluminum oxide content, i.e. catalysts based on the silicon-aluminum mixed oxide compositions described herein, which provide high activity and good product selectivity for the isomerization. In addition, oligomerization as a side reaction does not occur or hardly occurs.

[0008] Thus, the process of the present invention is a process for isomerizing C4 to C9 reactant olefins having terminal double bonds to product olefins having internal double bonds, wherein a hydrocarbon mixture comprising at least the reactant olefins to be isomerized and the product olefins is contacted with a heterogeneous catalyst, wherein the heterogeneous catalyst is an X-ray amorphous silicon-aluminum mixed oxide composition having the following composition:

[0009] a) 96% to 99.99% by weight of silicon oxide (calculated as SiO2); and

[0010] b) 0.01 to 4% by weight of aluminum oxide (calculated as Al2O3).

[0011] The X-ray amorphous silicon-aluminum mixed oxide compositions used as catalysts can be prepared by flame hydrolysis, in particular according to the methods disclosed in DE 19847161 A1 or EP 0850876 A1. In this so-called "co-fumed process", volatile silicon compounds and aluminum compounds (e.g. silicon tetrachloride and aluminum trichloride) are sprayed into a hydrogen-oxygen flame consisting of hydrogen and oxygen or air, whereby the silicon compounds and aluminum compounds are hydrolyzed by the water formed in the hydrogen-oxygen flame and a mixed oxide composition is formed.

[0012] An alternative method also disclosed in the above-mentioned document is the so-called doping method. In this method, on the one hand, an oxide (in this case silicon oxide) is generated from its volatile compounds (for example silicon tetrachloride) by flame hydrolysis in a hydrogen-oxygen flame, and on the other hand, an aerosol in which a salt of the element to be doped (in this case aluminum) is present is introduced into the hydrogen-oxygen flame, so that the corresponding mixed oxide is formed. The silicon-aluminum mixed oxide composition thus generated by flame hydrolysis is mainly or completely amorphous.

[0013] The X-ray amorphous silicon-aluminum mixed oxide composition produced by the preparation process mentioned by way of example is characterized by its high chemical purity and has the following composition:

[0014] a) 96% to 99.99% by weight of silicon oxide, preferably 98.5% to 99.95% by weight of silicon oxide (calculated as SiO2); and

[0015] b) 0.01 to 4% by weight of aluminum oxide, preferably 0.05 to 1.5% by weight of aluminum oxide (calculated as Al2O3).

[0016] In a preferred embodiment of the present invention, the silicon-aluminum mixed oxide composition also contains alkali metal oxides and / or alkaline earth metal oxides, particularly preferably in an amount of up to 1% by weight, based on the total composition. In order to introduce alkali metal oxides or alkaline earth metal oxides, the mixed oxide composition prepared by flame hydrolysis can be treated with an aqueous solution of an alkali metal hydroxide or an alkaline earth metal hydroxide. This can be achieved, for example, by wetting or impregnating the mixed oxide composition prepared by flame hydrolysis with a solution of an alkali metal salt and / or an alkaline earth metal salt. The treated mixed oxide composition is then washed with water, dried at 100°C to 150°C, and calcined at 300°C to 600°C, preferably 450°C to 550°C. The silicon oxide and aluminum oxide themselves may already contain traces of alkali metals or alkaline earth metals, but these are not considered here.

[0017] The silicon-aluminum mixed oxide composition of the present invention can also be treated with an acidic aqueous solution containing a phosphorus source. The phosphorus source used can be phosphoric acid, phosphonic acid, phosphinic acid, polyphosphoric acid or dihydrogen phosphate, preferably phosphoric acid. To this end, the mixed oxide composition is first suspended in water, and then the phosphorus source is added to the resulting suspension, preferably so that the pH value is 0 to 6, further preferably 1 to 2.5, and particularly preferably 2 to 2.5. The treated mixed oxide composition is then washed with water, dried at 100°C to 150°C, and calcined at 300°C to 600°C, preferably 450°C to 550°C.

[0018] In a preferred embodiment, the silicon-aluminium mixed oxide composition according to the invention is present predominantly (ie >70%) or entirely in the form of aggregated primary particles. The silicon-aluminium mixed oxide composition here is characterized in particular in that the weight ratio of the primary particles in the near-surface region (Al2O3 / SiO2) is 表面 Less than the weight ratio of the entire primary particle (Al2O3 / SiO2) 整个 The term "near-surface region" herein refers to the region from the surface to a depth of up to 5 nm. The difference in weight ratio means that the concentration of alumina at the surface is lower than in the entire composition. The entire primary particle includes silica and alumina portions in the near-surface region.

[0019] Preference is therefore given to silicon-aluminium mixed oxide compositions which are present predominantly or entirely in the form of aggregated primary particles, wherein

[0020] I) (Al2O3 / SiO2) in the entire primary particle 整个 The weight ratio of is 0.002 to 0.05, preferably 0.003 to 0.015, particularly preferably 0.005 to 0.01; and

[0021] II) Weight ratio of primary particles in a near-surface layer with a thickness of 5 nm (Al2O3 / SiO2) 表面 Smaller than the entire primary particle.

[0022] Weight ratio of primary particles at the surface (Al2O3 / SiO2) 表面 It can be determined, for example, by X-ray induced photoelectron spectroscopy (XPS analysis) of the powder. Further information on the surface composition can be determined by energy dispersive X-ray analysis of the individual primary particles (TEM-EDX analysis). The weight ratio (Al2O3 / SiO2) in the entire primary particle 整个 It can be determined by chemical or physicochemical methods of the powder, for example by X-ray fluorescence analysis.

[0023] The silicon-aluminum mixed oxide composition used as a catalyst in the present invention is X-ray amorphous. "X-ray amorphous" in the present invention means that the X-ray amorphous material does not show a crystal structure in an X-ray diffraction pattern as low as a detection limit of 5 nm.

[0024] The silicon-aluminum mixed oxide composition of the present invention, in particular the silicon-aluminum mixed oxide composition having the above composition, in particular the silicon-aluminum mixed oxide composition having the above weight ratio (Al2O3 / SiO2) preferably has 50 to 250 m 2 / g, preferably 100 to 200 m 2 The BET surface area of ​​1,4-dimethoxy-1,4-dB is 1,4-dimethoxy-1,4-dB (determined according to DIN ISO 9277 (version: 2014-01)).

[0025] In addition, it may be advantageous that the silicon-aluminum mixed oxide composition has a dibutyl phthalate value of 300 to 350 (in g dibutyl phthalate (DBP) / 100g mixed composition). The DBP value is a measure of aggregate structure. Low values ​​correspond to low structures, and high values ​​correspond to high structures. For mixed oxide compositions according to the present invention, the range of 300 to 350 corresponds to high structures. In the case of DBP absorption, the force absorption or torque (in Nm) of the rotating blades of the DBP measuring device is measured when a specific amount of DBP is added. For silicon-aluminum mixed oxide compositions, this preferably gives a well-defined maximum value, which is subsequently reduced when a specific amount of DBP is added. Dibutyl phthalate absorption can be measured with the RHEOCORD 90 device of the Haake company of Karlsruhe, for example. For this reason, 12g silicon-aluminum mixed oxide powder is put into a kneading chamber sealed with a lid, and dibutyl phthalate is metered in at a predetermined metering rate of 0.0667ml / s through the hole in the lid. The kneader was operated at a motor speed of 25 revolutions per minute. After reaching the maximum torque, the kneader and the DBP metering were automatically switched off. The amount of DBP consumed and the amount of granules metered in were used to calculate the DBP absorption according to the following formula: DBP value (g / 100 g) = (DBP consumption (in g) / powder weighed in weight (in g)) x 100.

[0026] For industrial isomerization using a catalyst comprising a silicon-aluminum mixed oxide composition, the reaction is preferably carried out in one or more fixed bed reactors. For liquid phase reactions, a slurry reactor or a trickle bed reactor may also be used. Other types of reactors may also be used, such as a fluidized bed reactor or a moving bed reactor. For this reason, it is necessary to shape the above-mentioned mixed oxide composition made by flame hydrolysis or pyrolysis with the addition of a binder by a molding method known to those skilled in the art, in particular to shape it into particles, pellets or molded bodies, such as tablets, cylinders, spheres, strip extrudates or rings. Suitable binders are known to those skilled in the art; for example, aluminum oxide, ceramic clay, colloids or amorphous zeolites are used.

[0027] For shaping, 1% to 20% by weight of the silicon-aluminum mixed oxide composition is first mixed with one of the above-mentioned binders and additionally with temporary auxiliaries, for example water, aqueous solutions, water substitutes, for example ethylene glycol and polyethylene glycol, and optionally further auxiliaries, for example fixatives, for example cellulose ethers, and / or plasticizers, for example polysaccharides, and / or pressing aids, for example nonionic wax dispersions. This process can be carried out in apparatuses known to those skilled in the art, for example in kneaders or intensive mixers. The actual shaping is then carried out by a shaping method, for example granulation, extrusion or dry pressing. Before being installed in the one or more fixed bed reactors, the shapes or shaped bodies are calcined at a temperature in the range of 200° C. to 700° C., so that at least the temporary auxiliaries are removed.

[0028] The silicon-aluminum mixed oxide composition can be applied to a support that is inert to the isomerization, such as a metal, plastic or ceramic support. If the silicon-aluminum mixed oxide composition is applied to an inert support, the mass and composition of the inert support are not taken into account when determining the composition of the silicon-aluminum mixed oxide composition.

[0029] The method of the present invention is carried out by using the above-mentioned silicon-aluminum mixed oxide composition as a catalyst to isomerize C4 to C9 reactant olefins having a terminal double bond, preferably C4 to C8 reactant olefins having a terminal double bond, further preferably C4 to C6 reactant olefins having a terminal double bond, and particularly preferably C4 reactant olefins having a terminal double bond into product olefins having an internal double bond.

[0030] The olefins are not necessarily used in pure form, but in the form of industrially available hydrocarbon mixtures. Thus, the content of product olefins in the hydrocarbon mixture is increased by isomerization, while the content of reactant olefins is reduced.

[0031] C5 olefins are contained in the light gasoline fraction of a refinery or cracking plant. Industrial mixtures containing linear C4 olefins include the light gasoline fraction of a refinery, the C4 fraction of a FC cracker or steam cracker, mixtures from Fischer-Tropsch synthesis, mixtures from butane dehydrogenation, and mixtures formed by metathesis or other industrial processes.

[0032] Preferably, the linear butene mixture suitable for the process according to the invention can be obtained from the C4 fraction of a steam cracker. 1,3-Butadiene can be removed in a preliminary step. This can be achieved by extracting (or extractive distilling) butadiene or by selective hydrogenation thereof. In both cases, a C4 fraction which is almost free of butadiene, the so-called raffinate 1, can be obtained. The C4 fraction which is now free of butadiene, the so-called raffinate I, contains isobutene, linear butenes and optionally butane.

[0033] According to the present invention, reactant olefin is an olefin with a terminal double bond, which is at least partially converted into product olefins by isomerization, i.e., an olefin with an internal double bond. In a preferred embodiment, reactant olefin is 1-butylene or a hydrocarbon mixture comprising 1-butylene, which is converted into cis- and / or trans-2-butylene by isomerization according to the present invention. This makes the 2-butylene enrichment, to promote the isobutylene distillation separation. Such an advantage is that energy can be saved and, when using the same equipment, significantly higher throughput can be achieved. 2-butylene can be oligomerized into C8 olefins subsequently, and then can be prepared by it Plasticizer alcohol.

[0034] The lower limit of the conversion of the reactant olefins into the product olefins is limited, inter alia, by the temperature-dependent position of the chemical equilibrium of the isomerization reaction. The advantage of using the catalyst according to the invention is that the conversion corresponds to the thermodynamic equilibrium conversion over a wider temperature range or is only slightly below this value. This also applies to the isomerization of 1-butene to 2-butene, which is limited by the thermodynamic equilibrium of the n-butene isomers. High temperatures shift the thermodynamic equilibrium of a mixture comprising 2-butene and 1-butene in the direction of 1-butene. The thermodynamic equilibrium of 1-butene at a temperature of 25° C. is about 3%, and the thermodynamic equilibrium at a temperature of 500° C. is about 29%.

[0035] For the isomerization process of the present invention, it is preferred to use at least one fixed bed reactor. Other types of reactors may also be used, such as a fluidized bed reactor, a moving bed reactor, a slurry reactor or a trickle bed reactor.

[0036] The process of the invention can be carried out at atmospheric pressure. However, higher reaction pressures can also be used. For example, operating under pressure in the process of the invention is useful when the product olefins from the isomerization process of the invention are also fed to a separation stage that is also operated under pressure.

[0037] According to the invention, the isomerization of olefins having terminal double bonds into olefins having internal double bonds, in particular the isomerization of 1-butene into 2-butene, is preferably carried out at a temperature of 20° C. to 250° C., more preferably 35° C. to 200° C., particularly preferably 45° C. to 160° C. The gas hourly space velocity (GHSV) may be 5 to 500 h -1 , preferably 10 to 250h -1 The selectivity of the olefins in the isomerized product of the present invention is preferably greater than 85%, more preferably greater than 90%, and particularly preferably greater than or equal to 95%.

[0038] If the activity and selectivity of the catalyst according to the invention decrease due to carbon deposits on the catalyst, the catalyst can advantageously be regenerated. An advantageous method for regenerating the catalyst is to burn off the carbon deposits on the deactivated catalyst in an oxygen-containing gas, preferably in air. It may be advantageous to dilute the air with nitrogen here. The catalyst regeneration is generally carried out at temperatures of 350° C. to 600° C., preferably at 400° C. to 450° C. This generally allows the initial activity and initial selectivity of the catalyst according to the invention to be restored in a simple manner.

[0039] The present invention also provides a process for the distillative separation of isobutene from a C4 hydrocarbon stream comprising at least isobutene, 1-butene and 2-butene, wherein the process comprises the following steps:

[0040] 1) isomerizing a C4 hydrocarbon stream to at least partially convert 1-butene in the C4 hydrocarbon stream into 2-butene, wherein the C4 hydrocarbon stream is contacted with a heterogeneous catalyst, wherein the heterogeneous catalyst is a silicon-aluminum mixed oxide composition having the following composition:

[0041] a) 96% to 99.99% by weight, preferably 98.5% to 99.95% by weight, of silicon oxide (calculated as SiO2); and

[0042] b) 0.01 to 4% by weight, preferably 0.15 to 1.5% by weight, of aluminium oxide (calculated as Al2O3); and

[0043] 2) Distillation separation is performed to separate isobutylene from the C4 hydrocarbon stream.

[0044] The distillative separation of isobutene from a C4 hydrocarbon stream is known in principle to the person skilled in the art. The distillation in step 2) is preferably carried out at a pressure of 1-10 bar, preferably 2 to 8 bar. The distillation temperature in step 2) is preferably 20° C. to 80° C., particularly preferably 25° C. to 70° C. In addition, the distillation in step 2) can be carried out using a known distillation column. The column may comprise a plurality of trays and / or separation stages.

[0045] The invention also relates to a two-stage isomerization with an intermediate distillation. In the first stage, the above-mentioned isomerization is carried out, i.e. C4 to C9 reactant olefins with terminal double bonds, preferably C4 olefins, preferably 1-butene, are isomerized into product olefins with internal double bonds, preferably 2-butene, wherein a hydrocarbon mixture comprising at least the reactant olefins to be isomerized and the product olefins is contacted with a heterogeneous catalyst, wherein the heterogeneous catalyst is a silicon-aluminum mixed oxide composition having the following composition:

[0046] a) 96% to 99.99% by weight, preferably 98.5% to 99.95% by weight, of silicon oxide (calculated as SiO2); and

[0047] b) 0.01 to 4% by weight, preferably 0.15 to 1.5% by weight, of aluminum oxide (calculated as Al2O3).

[0048] The isomerization is followed by a distillation in which the separated reactant olefins with terminal double bonds, preferably 1-butene, are separated together with isobutene from the product olefins with internal double bonds, preferably 2-butene. The person skilled in the art is familiar with the corresponding methods and the respective conditions.

[0049] The separated reactant olefin, preferably a mixture of 1-butene and isobutene obtained by separation, is then further isomerized in the second step. The catalyst used can be the silicon-aluminum mixed oxide composition also used in the first step, which has the following composition:

[0050] a) 96% to 99.99% by weight, preferably 98.5% to 99.95% by weight, of silicon oxide (calculated as SiO2); and

[0051] b) 0.01 to 4% by weight, preferably 0.15 to 1.5% by weight, of aluminum oxide (calculated as Al2O3).

[0052] In the second step, in addition to the isomerization, further reactions may also occur, such as dimerization of the olefins present. In the case of C4 olefins, isobutene in particular can dimerize to form diisobutene, which can however also subsequently be easily separated and sold.

[0053] The present invention is described below by way of examples, which are only for illustrative purposes and do not constitute a limitation of the subject matter of the present invention.

[0054] Example 1

[0055] 11.7 g of the catalyst according to the present invention ( MOX170, about 1 wt% alumina, BET surface area 140 to 200 m 2 / g) and glass beads were introduced into a tubular reactor with a diameter of 1 cm at a dilution of 1:1. 1-Butene (>99%) was charged into the reactor. The 1-Butene was conducted through the reactor at different volume flow rates. The isomerization was carried out at a temperature of 80°C to 140°C and ambient pressure. In the reaction, the conversion of 1-Butene and the formation of 2-Butene were determined.

[0056] The analysis was performed by gas chromatography. The peak areas were estimated according to an external calibration method.

[0057]

[0058] a The experimental time exceeded 500 hours.

[0059] The results show that the catalyst according to the invention is very suitable for isomerization. It can also be seen that almost no side reactions occur; on the contrary, a high selectivity for 2-butene can be achieved. This also applies to long-term experiments with an experimental time of more than 500 hours.

Claims

1. A process for isomerizing C4 to C9 reactant olefins having terminal double bonds to product olefins having internal double bonds, wherein a hydrocarbon mixture comprising at least the reactant olefins to be isomerized and the product olefins is contacted with a heterogeneous catalyst, wherein the heterogeneous catalyst is an X-ray amorphous silicon-aluminum mixed oxide composition having the following composition: a) 96% to 99.99% by weight of silicon oxide (calculated as SiO2); and b) 0.01 to 4% by weight of aluminum oxide (calculated as Al2O3).

2. The method according to claim 1, wherein the silicon-aluminum mixed oxide composition used as a heterogeneous catalyst has the following composition: a) 98.5% to 99.95% by weight of silicon oxide (calculated as SiO2); and b) 0.05% to 1.5% by weight of aluminum oxide (calculated as Al2O3).

3. The process according to claim 1 or 2, wherein the silicon-aluminum mixed oxide composition used as a heterogeneous catalyst has a molecular weight of 50 to 250 m 2 / g, preferably 100 to 220m 2 / g of BET surface area. 4 . The process according to claim 1 , wherein the heterogeneous catalyst consists of a shaped body which is produced from a silicon-aluminium mixed oxide composition in a shaping process by adding a binder and at least a temporary auxiliary.

5. The process according to any one of claims 1 to 4, wherein the content of product olefins in the hydrocarbon mixture is increased due to the isomerization.

6. The process according to any one of claims 1 to 5, wherein the isomerization is carried out at a temperature of 20°C to 250°C, further preferably 35°C to 200°C, particularly preferably 45°C to 160°C.

7. The process according to any one of claims 1 to 6, wherein the gas hourly space velocity during the isomerization process is 5 to 500 h -1 , preferably 10 to 250h -1 .

8. The process according to any one of claims 1 to 7, wherein the reactant olefin used is a C4 to C8 reactant olefin having a terminal double bond, preferably a C4 to C6 reactant olefin having a terminal double bond, particularly preferably a C4 reactant olefin having a terminal double bond.

9. The process according to claim 8, wherein the reactant olefin used is 1-butene or a hydrocarbon mixture comprising 1-butene, and the product olefin having an internal double bond is cis- and / or trans-2-butene.

10. The method according to any one of claims 1 to 9, wherein the silicon-aluminium mixed oxide composition is present mainly or entirely in the form of aggregated primary particles.

11. The method according to claim 10, wherein the silicon-aluminum mixed oxide composition is characterized by a weight ratio of primary particles (Al2O3 / SiO2) in the near-surface region: 表面 Less than the weight ratio of the entire primary particle (Al2O3 / SiO2) 整个 .

12. The method according to claim 10 or 11, wherein the silicon-aluminum mixed oxide composition is mainly or entirely in the form of aggregated primary particles, wherein I) Weight ratio in the entire primary particle (Al2O3 / SiO2) 整个 0.002 to 0.05, preferably 0.003 to 0.015, particularly preferably 0.005 to 0.01; and II) Weight ratio of primary particles in a near-surface layer with a thickness of 5 nm (Al2O3 / SiO2) 表面 Smaller than the entire primary particle.

13. A process for separating isobutene by distillation from a C4 hydrocarbon stream comprising at least isobutene, 1-butene and 2-butene, wherein the process comprises the following steps: 1) carrying out an isomerization according to any one of claims 1 to 13, thereby at least partially converting 1-butene in a C4 hydrocarbon stream into 2-butene; 2) Distillation separation is performed to separate isobutylene and 1-butene from the C4 hydrocarbon stream.

14. The process according to claim 13, wherein the isomerization is carried out in two stages, wherein after the distillation in step 2), the mixture of 1-butene and isobutene obtained by separation is further isomerized in a second step.

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