Method for producing isobutene, catalyst for producing isobutene, and isobutene production system

Abstract

To provide a method for generating isobutene, for use in isomerizing normal butene to isobutene, in which the generation of by-products can be minimized, and a high yield of isobutene can be achieved.SOLUTION: A method for generating isobutene includes the step of isomerizing normal butene to isobutene. In the isomerizing step, the normal butene is brought into contact with a zeolite. It is preferable that the reaction temperature in the isomerizing step should range 25°C to 249°C.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for producing isobutene, a catalyst for producing isobutene, and an isobutene production system.

Background Art

[0002] Conventionally, efforts aimed at mitigating or reducing the impact of climate change have continued, and research and development related to reducing carbon dioxide emissions have been conducted to achieve this. For example, technologies for recovering carbon dioxide from exhaust gas or the atmosphere and electrochemically reducing it to obtain valuable substances are known. The above technologies are promising technologies that have the potential to achieve carbon neutrality.

[0003] By electrochemically reducing carbon dioxide, ethylene is produced. By subjecting ethylene to a polymerization reaction in the presence of a polymerization catalyst, olefins such as 1-butene are produced. Incidentally, isobutene, which is a structural isomer of normal butene containing 1-butene, is an industrially important hydrocarbon and has various uses as a synthetic intermediate. For example, by subjecting isobutene to an addition reaction with methanol or ethanol, MTBE or ETBE used as a gasoline additive can be obtained. Further, by dimerizing and alkylating isobutene, isooctane added to gasoline can be obtained. Therefore, technologies related to catalysts that promote the isomerization reaction of normal butene to isobutene have been proposed (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Non-Patent Document 1 shows that high yields of isobutene can be obtained by isomerizing normal butene to isobutene in the presence of a zeolite catalyst such as the FER type. On the other hand, in the isomerization reaction disclosed in Non-Patent Document 1, by-products having 3 or 5 carbon atoms are generated at a fairly high rate. Therefore, it has been difficult to separate and recover unreacted normal butene after the isomerization reaction. Further, even if unreacted normal butene could be separated and recovered, since by-products are generated, the yield of isobutene could not be made equal to or higher than a predetermined yield. From the above, in the method of isomerizing normal butene to isobutene, a technique for further improving the yield of isobutene has been demanded.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a method for producing isobutene, which can suppress the generation of by-products as much as possible and obtain a high yield of isobutene in the method of isomerizing normal butene to isobutene.

Means for Solving the Problems

[0007] (1) The present invention relates to a method for producing isobutene, including an isomerization step of isomerizing normal butene to isobutene, wherein in the isomerization step, the normal butene is contacted with a zeolite, and the reaction temperature in the isomerization step is in the range of 25 to 249°C.

[0008] (1) According to the invention of (1), in the method for producing isobutene by isomerizing normal butene to isobutene, it is possible to provide a method for producing isobutene in which the generation of by-products can be suppressed as much as possible and a high yield of isobutene can be obtained.

[0009] (2) The SiO 2 / Al 2 O 3 ratio of the zeolite is 2 to 1500, and the method for producing isobutene according to (1).

[0010] According to the invention of (2), it is possible to provide a method for producing isobutene that can suppress the production of by-products as much as possible and obtain a higher yield of isobutene.

[0011] (3) Further, the present invention relates to a catalyst for producing isobutene that promotes an isomerization reaction for producing isobutene by isomerizing normal butene. The catalyst for producing isobutene is zeolite, and the SiO 2 / Al 2 O 3 ratio is 2 to 1500.

[0012] (3) According to the invention, as a catalyst that promotes an isomerization reaction for producing isobutene by isomerizing normal butene to isobutene, it is possible to provide a catalyst for producing isobutene that can suppress the production of by-products as much as possible and obtain a high yield of isobutene.

[0013] (4) Further, the present invention includes an electrolyzer that produces ethylene by electrolyzing carbon dioxide, a dimerizer that produces normal butene by dimerizing the ethylene, and an isomerizer that produces isobutene by isomerizing the normal butene. The isomerizer includes a catalyst with which the normal butene comes into contact, and the catalyst is zeolite of any one of FAU type, MFI type, BEA type, and MOR type. The SiO 2 / Al 2 O 3 ratio is 2 to 1500.

[0014] (4) According to the invention, since it is possible to recover carbon dioxide in exhaust gas or the atmosphere and produce isobutene, which is an industrially important hydrocarbon, it can contribute to the achievement of carbon neutrality. Also, in the isomerization reaction for producing isobutene by isomerizing normal butene to isobutene, it is possible to provide an isobutene production system that can suppress the production of by-products as much as possible and obtain a high yield of isobutene.

[0015] (5) Further comprising a hydration reaction device, the hydration reaction device separates the normal butene from a mixture containing the normal butene and the isobutene generated from the isomerization device, and the normal butene separated by the hydration reaction device is returned to the isomerization device. The isobutene production system according to (4).

[0016] According to the invention of (5), the yield of isobutene in the isomerization device of the isobutene production system can be theoretically close to 100%.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0018] <Catalyst for Isobutene Production> The catalyst for isobutene production according to the present embodiment is a catalyst that promotes an isomerization reaction that isomerizes normal butene to isobutene. In this specification, normal butene means an equilibrium mixture in which the structural isomers 1-butene, cis-2-butene, and trans-2-butene exist in an equilibrium state.

[0019] The catalyst for isobutene production according to this embodiment is zeolite. The zeolite is not particularly limited, and examples include zeolites such as FAU type, MFI type, BEA type, MOR type, FER type, and CHA type. FAU type, MFI type, BEA type, MOR type, FER type, and CHA type are codes defined by the International Zeolite Association (IZA) and indicate the framework structure of the zeolite. For example, the maximum ring size of FAU type zeolite is 10. The intrinsic pore diameter of FAU type zeolite is about 7.4 Å. Since the molecular diameter of the target substance, isobutene, is about 5.0 Å, the intrinsic pore diameter of FAU type zeolite is considered to be a suitable diameter for the isomerization reaction of normal butene to isobutene.

[0020] The zeolite according to this embodiment has an SiO 2 / Al 2 O 3 ratio (molar ratio) preferably in the range of 2 to 1500. In the isomerization reaction of normal butene to isobutene, by using a zeolite having an SiO 2 / Al 2 O 3 ratio within the above range as a catalyst, the yield of isobutene can be improved. Also, the formation of by-products can be suppressed as much as possible. Although the reason for the above is not clear, it is considered that by setting the SiO 2 / Al 2 O 3 ratio within the above range, the amount and distribution of acid sites on the zeolite surface become conditions particularly suitable for the isomerization reaction of normal butene to isobutene. From the above viewpoints, the SiO 2 / Al 2 O 3 ratio is more preferably 500 to 1500. Also, the zeolite according to this embodiment is preferably a Y-type zeolite.

[0021] The zeolite as described above may be prepared by hydrothermal synthesis or may be a commercially available product (for example, manufactured by Tosoh Corporation; HSZ-390HUA, etc.).

[0022] The zeolite according to this embodiment is preferably a proton-type zeolite. The proton-type zeolite can be obtained by a known protonation treatment.

[0023] The acid strength of the zeolite according to this embodiment is preferably less than 140E NH 3 / kJmol -1 This can suppress the generation of by-products such as hydrocarbons having 3 or 5 carbon atoms, which are generated by the cracking of hydrocarbons having 8 carbon atoms. The acid strength of the zeolite in this specification is obtained by calculating the heat of adsorption of ammonia adsorbed on the acidic sites of the zeolite by a quantum chemical calculation called density functional theory (DFT) calculation.

[0024] <Method for Producing Isobutene> The method for producing isobutene according to this embodiment includes an isomerization step of bringing normal butene, which is a raw material substance, into contact with the above zeolite, which is a catalyst for promoting the isomerization reaction. The isomerization reaction of normal butene in the above isomerization step is represented by the following formula (1).

[0025]

Chemical formula

[0026] In the above formula (1), normal butene (n-Butene) is described as 1-butene for convenience, but normal butene is actually an equilibrium mixture in which 1-butene, cis-2-butene, and trans-2-butene exist in an equilibrium state. "i-Butene" in the above formula (1) means isobutene. "Unreactive n-Butene" in the above formula (1) means normal butene that is not isomerized by the isomerization reaction and remains unreacted. In the above formula (1), isobutene and normal butene are described as products, but in addition to the above products, trace amounts of by-products may be generated by the isomerization reaction represented by the above formula (1).

[0027] In the isomerization step, the reaction temperature is in the range of 25 to 249 °C. The reaction temperature is preferably 25 to 200 °C, more preferably 25 to 150 °C, and even more preferably 25 to 100 °C. By using the catalyst for isobutene production according to the present embodiment, not only can the isomerization step be carried out at a lower temperature and the cost required for the isomerization step be reduced, but also a more preferable isobutene yield can be obtained by lowering the reaction temperature.

[0028] In the isomerization step, the space velocity GHSV (gas hourly space velocity) of the raw material gas containing normal butene is 20000 to 80000 ml·g -1 ·h -1 is preferable. Also, the contact time (W / F) is preferably 0.0008 to 0.0031 g·min·ml -1 is preferable. Thereby, the conversion rate of normal butene can be improved. The conversion rate of the above normal butene is represented by the following formula (2).

[0029] Normal butene conversion rate (%) = ((amount of substance of normal butene in the raw material gas) - (amount of substance of normal butene in the product gas)) / (amount of substance of normal butene in the raw material gas) × 100 (2)

[0030] The selectivity of the above isobutene is represented by the following formula (3), and the yield of the above isobutene is represented by the following formula (4).

[0031] Isobutene selectivity (%) = (amount of substance of isobutene in the product gas) / (amount of substance of normal butene in the raw material gas) × 100 (3)

[0032] Isobutene yield (%) = (isobutene selectivity (%)) × (normal butene conversion rate (%)) ÷ 100 (4)

[0033] The method for producing isobutene according to the present embodiment may include steps other than the above isomerization step. For example, isobutene is N 2The method may include a step of preparing a raw material gas by diluting it with a gas to a predetermined dilution ratio. Further, the method may include a step of separating unreacted normal butene from the product gas, and may further include a step of recycling the separated normal butene as a raw material gas. Since the method for producing isobutene according to the present embodiment can suppress the generation of by-products as much as possible, unreacted normal butene can be easily separated from the product gas. Further, by recycling the normal butene separated from the product gas as a raw material gas, the theoretical yield of isobutene can be improved to nearly 100%.

[0034] The step of separating unreacted normal butene from the product gas can be realized, for example, by a hydration reaction (hydration addition reaction) represented by the following formula (5).

[0035] [Chemical formula] Formula (5)

[0036] By the hydration reaction in the above formula (5), only isobutene can be converted into TBA (tert-butyl alcohol) which is liquid or solid at room temperature, so that normal butene which is gas at room temperature can be easily separated from the product gas. As a specific method, for example, a known method such as a method using an aqueous solution containing a heteropoly acid having at least one element selected from Mo, W and V as a condensed coordination element and reacting at a temperature below 100 °C can be used. Note that TBA can be effectively utilized by converting it into isooctane by known dimerization techniques and hydrogenation techniques, etc. This is because isooctane can be used as a base material for gasoline, etc.

[0037] <Isobutene production system> As shown in FIG. 1, the isobutene production system 1 according to the present embodiment includes an electrolysis device 10, a dimerization device 20, an isomerization device 30, a hydration reaction device 40, and flow paths F1 to F4 connecting the devices.

[0038] The electrolysis device 10 is a device that electrochemically reduces carbon dioxide (CO 2 ) to produce ethylene (C 2 H 4 ). The electrolysis device 10 reduces carbon dioxide by an electrolytic cell that reduces carbon dioxide. Examples of the electrolytic cell include an electrolytic cell having at least a cathode and an anode. The cathode electrochemically reduces carbon dioxide to produce hydrocarbons such as ethylene (C 2 H 4 ) and also reduces water to produce hydrogen. The anode oxidizes hydroxide ions to produce oxygen. The ethylene (C 2 H 4 ) produced by the electrolysis device 10 is supplied to the dimerization device 20 via the flow path F1.

[0039] The source of the carbon dioxide (CO 2 ) supplied to the electrolysis device 10 is not particularly limited and may be separated and recovered from the air or may be separated and recovered from the exhaust gas discharged from combustion facilities such as boilers.

[0040] The dimerization device 20 dimerizes the ethylene (C 2 H 4 ) supplied via the flow path F1 by a dimerization reaction to produce normal butene (n-C 4 H 8 ). The dimerization device 20 has a reactor 21 and a cooling separator 22. The dimerization device 20 can produce normal butene (n-C 4 H 8 ) at a yield of, for example, 80% or more.

[0041] The reactor 21, for example, performs a polymerization reaction of ethylene in the presence of an olefin polymerization catalyst to produce carbon-increased olefins such as normal butene (n-C 4 H 8 ), 1-hexene, and 1-octene. The olefin polymerization catalyst is, for example, a solid acid catalyst using silica alumina or zeolite as a carrier, a transition metal complex compound, or the like. Examples of the metal atom supported on the carrier include Ni.

[0042] The cooling separator 22 performs gas-liquid separation on the product gas after the polymerization reaction in the reactor 21. Since the carbonized olefins contained in the product gas have a boiling point that increases with the increase in the number of carbon atoms, by setting the temperature of the cooling separator 22 to be equal to or higher than the boiling point of the target substance, normal butene (n-C 4 H 8 ), and lower than the boiling point of other olefins having 6 or more carbon atoms, normal butene (n-C 4 H 8 ) and other olefins having 6 or more carbon atoms can be easily separated by gas-liquid separation. The normal butene (n-C 4 H 8 ) separated by the cooling separator 22 is supplied to the isomerization device 30 through the flow path F2. The other olefins having 6 or more carbon atoms separated by the cooling separator 22 are separated and discharged as a liquid fraction.

[0043] The isomerization device 30 is a device that generates isobutene (i-C 4 H 8 ) from the normal butene (n-C 4 H 8 ) supplied through the flow path F2. The isomerization device 30 has the above-mentioned zeolite. The zeolite is filled, for example, in the catalyst layer of the fixed-bed reactor provided in the isomerization device 30. When a gas containing normal butene (n-C 4 H 8 ) flows through the catalyst layer, normal butene (n-C 4 H 8 ) comes into contact with the zeolite, and the isomerization reaction is promoted. In addition to the above, the isomerization device 30 may be provided with a dilution device that dilutes normal butene (n-C 4 H 8 ) with N 2 gas to a predetermined dilution ratio. Further, it may be provided with a known device capable of adjusting the flow rate of the gas containing normal butene (n-C 4 H 8 ), as well as the temperature and pressure of the fixed-bed reactor. The isobutene (i-C 4 H 8 ) generated by the isomerization device 30 and the unreacted normal butene (n-C4 H 8 ) and the mixture containing the same are supplied to the hydration reactor 40 through the flow path F3.

[0044] The hydration reactor 40 is a device that separates unreacted normal butene (n-C 4 H 8 ) from the mixture containing isobutene (i-C 4 H 8 ) and unreacted normal butene (n-C 4 H 8 ) by the hydration reaction in the above formula (5). By the hydration reactor 40, only isobutene (i-C 4 H 8 ) is converted to TBA (tert-butyl alcohol) by the hydration reaction and separated from normal butene (n-C 4 H 8 ) by gas-liquid separation. The TBA (tert-butyl alcohol) separated by the hydration reactor 40 is converted to isooctane or the like by existing techniques and used. The unreacted normal butene (n-C 4 H 8 ) separated by the hydration reactor 40 is returned to the isomerization device 30 through the flow path F4 as a return flow path. The flow path F4 may be connected in the middle of the flow path F2 or may be connected to the isomerization device 30.

[0045] According to the isobutene production system 1 having the above configuration, the following effects are achieved. Since the isobutene production system 1 has the isomerization device 30 having zeolite, isobutene (i-C 4 H 8 ), which is the target substance, can be obtained in a high yield, and the generation of by-products can be suppressed as much as possible. Further, the isobutene production system 1 includes a hydration reactor 40 that separates the mixture of isobutene (i-C 4 H 8 ) generated by the isomerization device 30 and unreacted normal butene (n-C 4 H 8 ), and the unreacted normal butene (n-C 4 H8 ) is provided with a flow path F4 as a return flow path for returning to the isomerization device 30. Thereby, in the isomerization device 30, the yield of isobutene (i-C 4 H 8 ) with respect to normal butene, which is a raw material substance, can be made close to 100% in theory.

[0046] In addition, since the isobutene generation system 1 can recover exhaust gas and carbon dioxide in the atmosphere and generate isobutene, which is an industrially important hydrocarbon, it contributes to the achievement of carbon neutrality.

[0047] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

[0048] In the above embodiment, the isobutene generation system 1 has been described as being directly connected between the devices by the flow paths F1 to F4. It is not limited to the above. Each device may store the product in a storage tank such as a cylinder, and the product may be supplied to other devices by transporting the storage tank.

Example

[0049] Hereinafter, the present invention will be described in detail using examples. However, the present invention is not limited to these examples.

[0050] [Relationship between isobutene yield and circulation time (reaction time)] High silica H + -Y zeolite (SiO 2 / Al 2 O 3 =500, 390HUA, Tosoh Corporation) was used, and normal butene (n-C 4 H 8 ): 15 ml / min, N 2The reaction gas was passed through at a flow rate of 50 ml / min for isomerization reaction. The reaction conditions were temperature: 100 °C, pressure: 0.1 MPa, and catalyst amount: 0.2 g. For each different gas flow time (reaction time), the product gas generated by the isomerization reaction was quantitatively analyzed by gas chromatography. The measurement conditions of the gas chromatography are as shown below. The results are shown in Figure 2. In the graph of Figure 2, the vertical axis represents the isobutene yield (%), and the horizontal axis represents the gas flow time (reaction time) (min).

[0051] (Measurement conditions) Measuring device: GC-2014 (manufactured by Shimadzu Corporation) Column: Rtx-1 (RESTEK, length 60 m, inner diameter 0.25 mm, film thickness 0.5 mm) Carrier gas: N 2 (Total flow rate 50 ml / min, purge flow rate 3.0 ml / min) Split ratio: 66.1 (column flow rate 0.70 ml / min) Injection: 250 °C Detection: 280 °C Analysis: 40 °C for 10 min, then heated to 250 °C at 20 °C / min, then 250 °C for 9.5 min (total 30 min)

[0052] As shown in Figure 2, it is clear that by using a zeolite with an SiO 2 / Al 2 O 3 ratio of 500 and setting the reaction temperature at 100 °C, a favorable isobutene yield can be obtained. Also, it is clear that the yield of the by-product 2-C 4 H 8 is also suppressed.

[0053] [Relationship between reaction temperature and isobutene yield] As catalysts, the catalysts shown in Table 1 and Table 2 below were used respectively, and at each reaction temperature shown in Table 1 and Table 2 below, normal butene (n-C 4 H 8) was subjected to an isomerization reaction. The reaction conditions were the same as those in Figure 2 except for the reaction temperature. The results are shown in Tables 1 and 2. Note that "Yield / % iso-C 4 H 8 " in Tables 1 and 2 indicates the isobutene yield.

[0054]

Table 1

[0055]

Table 2

[0056] The details of the catalysts in Tables 1 and 2 are as follows. · Ferrierite (manufactured by Tosoh Corporation, 760HOA, FER (silica / alumina ratio 58)) · MOR type zeolite (manufactured by Tosoh Corporation, 690HOA, MOR (silica / alumina ratio 240)) · FAU type (Y type) zeolite (manufactured by Tosoh Corporation, 390HUA, Y (silica / alumina ratio 500)) · MFI type zeolite (manufactured by Zeolyst, CBV28014, ZSM-5 (silica / alumina ratio 280)) · MFI type zeolite (manufactured by Tosoh Corporation, 890HOA, ZSM-5 (silica / alumina ratio 1500)) · BEA type zeolite (manufactured by Zeolyst, CP811E-150, β (silica / alumina ratio 150))

[0057] As shown in Tables 1 and 2, it is clear that a high isobutene yield can be obtained by performing the isomerization reaction of normal butene using zeolite. Also, as the type of zeolite, it is clear that a higher isobutene yield can be obtained as the temperature becomes lower, especially in the temperature range below 250 °C, by using any one of FAU type, MFI type, BEA type, and MOR type zeolites.

[0058] [Relationship between Zeolite Type and Isobutene Yield] Using each catalyst shown in Table 3 below, normal butene (n-C 4 H 8 ): 15 ml / min, N 2 : The reaction gas was passed through at a flow rate of 50 ml / min for isomerization reaction. The reaction conditions were temperature: 200 °C, pressure: 0.1 MPa, reaction time: 40 min, and catalyst amount: 0.2 g.

[0059]

Table 3

[0060] <Gas chromatography> The product gas generated by the isomerization reaction using each catalyst shown in Table 3 was quantitatively analyzed by gas chromatography under the same conditions as those in Figure 2. Based on the analysis results obtained by gas chromatography, the yield of isobutene was determined, and the results are shown in the graph of Figure 3.

Explanation of symbols

[0061] 1 Isobutene production system 10 Electrolysis device 20 Dimerization device 30 Isomerization device 40 Hydration reaction device

Claims

1. A method for producing isobutene, comprising an isomerization step of isomerizing normal butene to isobutene, wherein in the isomerization step, the normal butene is contacted with a zeolite, and the reaction temperature in the isomerization step is in the range of 65 to 150 °C. A method for producing isobutene.

2. The SiO of the zeolite ２ / Al ２ O ３ ratio is 2 to 1500, and the method for producing isobutene according to claim 1.

3. A catalyst for promoting an isomerization reaction for producing isobutene by isomerizing normal butene, which is used in the method for producing isobutene according to Claim 1, wherein the catalyst for producing isobutene is a zeolite. The SiO of the zeolite ２ / Al ２ O ３ ratio is 2 to 1500, and it is a catalyst for isobutene production.

4. An isobutene production system, which is used in the method for producing isobutene according to Claim 1, wherein an electrolyzer for generating ethylene by electrolyzing carbon dioxide, a dimerization device for generating normal butene by dimerizing the ethylene, and an isomerization device for generating isobutene by isomerizing the normal butene, and the isomerization device includes a catalyst with which the normal butene comes into contact, and the catalyst is a zeolite. The SiO of the zeolite ２ / Al ２ O ３ ratio is 2 to 1500, an isobutene production system.

5. further comprising a hydration reactor, the hydration reactor separates the normal butene from a mixture containing the normal butene and the isobutene generated from the isomerization device, and the normal butene separated by the hydration reactor is returned to the isomerization device. The isobutene production system according to Claim 4.

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