JP7672103B2 - Method for producing cyclopentadiene - Google Patents

Description

The present invention relates to a method for producing cyclopentadiene.

Various uses for hydrocarbons with a carbon number of 5 have been proposed. For example, cyclopentadiene is widely used industrially as a synthetic raw material for agricultural chemicals, insecticides, and various resin plasticizers. Cyclopentadiene can be obtained, for example, by recovering C5 fractions, which are mainly composed of hydrocarbons with a carbon number of 5 and are by-produced during the production of ethylene by liquid feed steam cracking (e.g., naphtha and heavier feedstocks), through a dimerization process and a distillation process. However, the cyclopentadiene content in the C5 fraction is low, and existing liquid feed steam cracking units are shifting to lighter feedstocks than naphtha, so it is expected that the supply amount will not be sufficient to meet the demand for cyclopentadiene. Therefore, a method for producing cyclopentadiene that is not restricted by the supply limit of existing manufacturing methods is being considered.

For example, Non-Patent Document 1 describes a method for producing cyclopentadiene from n-pentane, n-pentene, and 1,3-pentadiene using a Pt/ _SiO2 catalyst. The yields to cyclopentadiene are as high as 21%, 35%, and 53% for the conversion of n-pentane, n-pentene, and 1,3-pentadiene at 600°C, respectively, indicating that olefins are favored in the conversion to cyclopentadiene.

V. Sh. Fel’dblyum et al., Doklady Chemistry, 424(2), 27-30 (2009)

However, it has been reported in the document that the catalyst deteriorates in a short time (for example, within 15 minutes) in the method described in Non-Patent Document 1. This is thought to be because when olefins are dehydrogenated, coke is likely to be produced during the reaction, and the produced coke accumulates on the catalyst surface, deactivating the catalyst. For this reason, in conventional methods for producing cyclopentadiene, there has not been sufficient research into stably producing cyclopentadiene at a high yield over a long period of time in the presence of olefins, and there is still room for improvement.

The present invention aims to provide a new method for producing cyclopentadiene, which uses a zeolite catalyst in the coexistence of an olefin to produce cyclopentadiene stably over a long period of time with a high yield.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that by using a specific zeolite catalyst, cyclopentadiene can be produced stably over a long period of time at a high yield from a raw material composition containing an olefin having a carbon number of 5, and thus completed the present invention.

One aspect of the present invention relates to a method for producing cyclopentadiene, comprising a cyclization/dehydrogenation step in which a raw material composition containing an olefin having a carbon number of 5 is contacted with a zeolite catalyst having an MFI structure to obtain a reaction product containing cyclopentadiene. In this production method, the zeolite catalyst contains at least one metal atom selected from transition metals or post-transition metals in the zeolite framework, and has Lewis acidity and strong solid basicity.

In one embodiment, the raw material composition may contain a diolefin having 5 carbon atoms.

In one embodiment, the content of the diolefin having 5 carbon atoms in the raw material composition may be 5% by mass or more.

In one embodiment, the metal atoms are one or more selected from Zn atoms, Fe atoms, and Ni atoms, and the content of the metal atoms may be 1 to 15 atom% relative to the Si atoms.

In one embodiment, the zeolite catalyst may contain no alkali metal or may contain 1 atom% or less of alkali metal relative to the Si atoms of the zeolite framework.

In one embodiment, the zeolite catalyst may be one that supports Pt.

In one embodiment, in the cyclization dehydrogenation step, the gas flow rate (ml/min) ratio of the raw material composition to molecular hydrogen supplied to the reaction system may be 1:0.001 to 1:3.

The present invention provides a new method for producing cyclopentadiene, which uses a zeolite catalyst in the presence of an olefin to produce cyclopentadiene stably over a long period of time with a high yield.

FIG. 2 shows the results of synchrotron XRD analysis of the zeolite catalyst and the Zn-impregnated supported catalyst according to the examples. FIG. 2 is a diagram showing the results of ²⁹ Si MAS NMR measurement of a zeolite catalyst according to an example. FIG. 1 is a diagram showing the results of FT-IR analysis of a zeolite catalyst, ZnO crystals, and a Zn-impregnated supported catalyst according to an embodiment. FIG. 1 is a diagram showing the results of FT-IR analysis of the zeolite catalyst, ZnO crystals, and Zn-impregnated supported catalyst according to the examples, with pyridine adsorbed thereon. FIG. 2 is a diagram showing the results of CO ₂ -TPD analysis of the zeolite catalyst and the Zn-impregnated supported catalyst according to the examples. FIG. 2 is a diagram showing the results of NH ₃ -TPD analysis of the zeolite catalyst and the Zn-impregnated supported catalyst according to the examples. FIG. 1 is a diagram showing the results of UV-vis analysis of a zeolite catalyst and ZnO crystals according to an embodiment.

The manufacturing method of the present invention will be described in detail below, but the explanation of the constituent elements described below is one example (representative example) of one embodiment of the present invention, and is not limited to these contents.

The method for producing cyclopentadiene according to this embodiment includes a cyclization/dehydrogenation step of contacting a raw material composition containing an olefin having a carbon number of 5 with a zeolite catalyst having an MFI structure to obtain a reaction product containing cyclopentadiene.
According to the production method of this embodiment, by using a specific zeolite catalyst, cyclopentadiene can be produced stably over a long period of time with a high yield.

(Zeolite catalyst)
The zeolite catalyst according to this embodiment contains at least one metal atom selected from transition metals or post-transition metals in the zeolite framework, and has Lewis acidity and strong solid basicity.

The zeolite catalyst according to this embodiment contains almost no Bronsted acid, and only Lewis acid. It is generally known that the amount of by-products produced in the cyclization dehydrogenation reaction increases or decreases depending on the presence of Bronsted acid. However, since the zeolite catalyst according to this embodiment contains almost no Bronsted acid, it is possible to control side reactions and suppress the generation of by-products. By using the zeolite catalyst according to this embodiment for the production of cyclopentadiene, for example, side reactions are suppressed and the cyclopentadiene selectivity is improved, and the generation of coke due to polymerization of cracking by-products is suppressed, and thus cyclopentadiene can be produced stably for a long period of time. Furthermore, since the zeolite catalyst according to this embodiment has Lewis acid sites that can be active sites for the cyclization dehydrogenation reaction highly dispersed, cyclopentadiene can be produced in high yield by using the zeolite catalyst according to this embodiment for the production of cyclopentadiene.

Here, zeolite means a crystalline substance in which _four TO units (T is a central atom) having a tetrahedral structure are three-dimensionally linked by sharing O atoms to form regular micropores.

The transition metal means a metal belonging to Groups 3 to 12 of the long-form periodic table of elements based on the provisions of the International Union of Pure and Applied Chemistry (IUPAC).
The post-transition metal refers to a base metal having an atomic number later than the transition metals in the fourth, fifth, and sixth periods of the periodic table.

The inclusion of metal atoms in the zeolite framework means that metal atoms, similar to silicon (Si), have been introduced into the zeolite framework by, for example, mixing a compound containing the target metal atom as a raw material for hydrothermal synthesis. The state in which metal atoms are included in the zeolite framework can be ascertained by various measurement methods, such as XRD (X-ray Diffraction), NMR (Nuclear Magnetic Resonance spectroscopy), FT-IR (Fourier Transform Infrared Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and ESCA (Electron Spectroscopy for Chemical Analysis).

Lewis acidity means a property capable of accepting an unshared electron pair, and for example, means that when pyridine is adsorbed on a zeolite catalyst and analyzed by FT-IR, an absorption band is detected near 1450 cm ^-1 .

"Solid basicity" means that the surface of the zeolite catalyst exhibits basicity. "Strong solid basicity" means that the surface of the zeolite catalyst is strongly basic, and for example, means that when a CO ₂ -TPD analysis is performed using a TPD (Temperature Programmed Desorption) analyzer, a desorption peak of CO ₂ adsorbed on the zeolite catalyst is detected in the high temperature range of 500°C or higher.

The zeolite catalyst according to the present embodiment is a zeolite with a 10-membered ring structure, and has an MFI structure. The zeolite with an MFI structure is not particularly limited, but is preferably a crystalline metallosilicate. The zeolite with an MFI structure means a zeolite that corresponds to MFI in the structure code databased by the International Zeolite Association.
Whether a zeolite has a 10-membered ring structure, particularly an MFI structure, can be confirmed by, for example, X-ray diffraction.

The metal atoms contained in the zeolite framework are not particularly limited as long as they are transition metal atoms or post-transition metal atoms, and examples of such metal atoms that can be used include titanium (Ti), vanadium (V), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), zirconium (Zr), and indium (In). Among these, zinc (Zn), nickel (Ni), and iron (Fe) are preferred from the viewpoint of excellent reactivity in the cyclization dehydrogenation reaction. The metal atoms contained in the zeolite framework may be of one type alone or two or more types.

The content of metal atoms contained in the zeolite skeleton is not particularly limited, but is preferably 1 to 15 atom% relative to silicon (Si) atoms, more preferably 1 to 10 atom%, and even more preferably 1 to 3 atom%. If the content of metal atoms contained in the zeolite skeleton is equal to or greater than the lower limit of the above range, the zeolite catalyst has more solid base sites and tends to have excellent reactivity in the cyclization dehydrogenation reaction. If the content of metal atoms contained in the zeolite skeleton is equal to or less than the upper limit of the above range, the reaction efficiency of the cyclization dehydrogenation reaction of the raw material relative to the metal content tends to be excellent.

The content of alkali metals contained in the zeolite catalyst is preferably zero or 1 atom% or less relative to the Si atoms, and more preferably 0.1 atom% or less. If it is less than the above upper limit, there is a tendency to maintain high reactivity of the cyclization dehydrogenation reaction while maintaining promotion of zeolite crystallization.

From the viewpoint of improving moldability, the zeolite catalyst may further contain a molding aid within the scope of the present invention. The molding aid may be, for example, at least one selected from the group consisting of a thickener, a surfactant, a water retention agent, a plasticizer, a binder raw material, etc. The molding process for molding the zeolite catalyst may be performed at an appropriate stage in the manufacturing process of the zeolite catalyst, taking into account the reactivity of the molding aid.

The zeolite catalyst may be a catalyst in which platinum is supported on a carrier using a platinum (Pt) source. Examples of the platinum source include tetraammineplatinum (II) acid, tetraammineplatinum (II) acid salts (e.g., nitrates, etc.), tetraammineplatinum (II) acid hydroxide solution, dinitrodiammineplatinum (II) nitric acid solution, hexahydroxoplatinum (IV) acid nitric acid solution, and hexahydroxoplatinum (IV) acid ethanolamine solution. It is preferable to use a metal source that does not contain chlorine atoms as the platinum source. By using a metal source that does not contain chlorine atoms, corrosion of the device can be suppressed and the cyclization dehydrogenation reaction can be performed more efficiently.

When platinum is supported on the zeolite catalyst, the platinum content in the zeolite-supported platinum catalyst is preferably 0.05 mass% or more, and more preferably 0.1 mass% or more, based on the total amount of the zeolite-supported platinum catalyst. The platinum content is preferably 3.0 mass% or less, and more preferably 2.5 mass% or less, based on the total amount of the zeolite-supported platinum catalyst. When the platinum content in the zeolite-supported platinum catalyst is within the above range, the platinum surface area per unit platinum weight is large, and therefore a more efficient reaction system tends to be realized.

The zeolite catalyst used may be one that has been subjected to a reduction treatment as a pretreatment. The reduction treatment may be performed, for example, by holding the zeolite catalyst at 40 to 600°C in an atmosphere of a reducing gas. The holding time may be, for example, 0.05 to 24 hours. The reducing gas may contain, for example, hydrogen, carbon monoxide, etc. By using a zeolite catalyst that has been subjected to a reduction treatment, the initial induction period of the cyclization dehydrogenation reaction can be shortened. The initial induction period of the cyclization dehydrogenation reaction refers to a state in which very little of the supported metals in the zeolite catalyst are reduced to an active state, and the activity of the catalyst is low.

<Method for preparing zeolite catalyst>
The zeolite catalyst according to the present embodiment can be prepared by combining a silica gel aging step, a hydrothermal synthesis step, and a calcination step, thereby making it possible to prepare the zeolite catalyst without using an alkali metal, boron, or aluminum.

An example of a suitable preparation example of the zeolite catalyst according to this embodiment includes mixing a silica source, an organic structure directing agent (OSDA), and water, aging (stirring) the mixture at 100° C. or less for 10 hours or more, and then mixing a transition metal atom or a post-transition metal atom as a metal source, followed by hydrothermal synthesis at 100° C. or more, and then calcining the mixture at 500° C. or more for 5 hours or more.
When platinum is supported on the zeolite catalyst, the method for supporting platinum is not particularly limited, and for example, an impregnation method, a deposition method, a coprecipitation method, a kneading method, an ion exchange method, a pore filling method, or the like can be used.

As the silica source, for example, silicon alcoholates, silanes, silicon tetrachloride, water glass, and other hydrolyzable silicon compounds can be used.
The organic structure-directing agent is not particularly limited as long as it can obtain a zeolite having an MFI structure, and for example, a quaternary alkyl ammonium salt, an amine, etc. The organic structure-directing agent may be used alone or in combination of two or more kinds.

As an example of a suitable preparation example of the zeolite catalyst according to this embodiment, it is preferable to further include a step of washing the synthesized product with water before calcining the synthesized product obtained after hydrothermal synthesis. By including a water washing step, it is possible to reduce the effect of alkali such as sodium on the zeolite catalyst.

The above method is an example of a suitable preparation example for preparing a zeolite catalyst without using an alkali metal, boron, or aluminum, but the preparation method of this embodiment does not limit the use of an alkali metal, boron, or aluminum as long as it does not deviate from the spirit of the present invention. For example, an alkali metal may be mixed during hydrothermal synthesis as long as it does not deviate from the spirit of the present invention. By mixing an alkali metal, the promotion of crystallization of the zeolite is maintained, and it tends to be easy to obtain a zeolite catalyst with an MFI structure in which a transition metal atom or a post-transition metal atom is introduced into the zeolite framework.
Examples of the alkali metal include sodium (Na), potassium (K), and rubidium (Rb). Among these, sodium (Na) is preferable. As described above, the amount of the alkali metal to be mixed is preferably 1 atom % or less relative to the Si atoms in the zeolite catalyst.

By the method described above, transition metal atoms or post-transition metal atoms can be introduced into the zeolite framework, and a zeolite catalyst with highly dispersed active sites can be obtained. Furthermore, a zeolite catalyst with strong solid basicity, in which there is almost no Bronsted acid and only Lewis acid, can be obtained.

(Method for producing cyclopentadiene)
In the production method according to the present embodiment, in the cyclization dehydrogenation step, a raw material composition containing an olefin having a carbon number of 5 is contacted with the above-mentioned zeolite catalyst, whereby a cyclization dehydrogenation reaction of the olefin having a carbon number of 5 occurs, and a reaction product containing cyclopentadiene is obtained.

<Raw Material Composition>
The raw material composition may contain an olefin having at least 5 carbon atoms. An olefin having 5 carbon atoms is an organic compound having one or more carbon-carbon double bonds in the molecule, usually having no functional groups, and means a linear and/or branched hydrocarbon having 5 carbon atoms. The olefin having 5 carbon atoms according to this embodiment is preferably a monoolefin and/or diolefin having 5 carbon atoms.

A monoolefin having 5 carbon atoms is an organic compound having only one carbon-carbon double bond in the molecule and usually having no functional groups, and refers to a linear and/or branched hydrocarbon having 5 carbon atoms.
Examples of the monoolefin having 5 carbon atoms according to the present embodiment include 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and among these, it is preferable to use 1-pentene. The monoolefin having 5 carbon atoms may be one of the above alone or a mixture containing two or more of them.

A diolefin having 5 carbon atoms is an organic compound having two or more carbon-carbon double bonds in the molecule and usually having no functional groups, and means a linear and/or branched hydrocarbon having 5 carbon atoms.
Examples of the diolefin having 5 carbon atoms according to the present embodiment include 1,3-pentadiene and 1,4-pentadiene, and among these, it is preferable to use 1,3-pentadiene. The diolefin having 5 carbon atoms may be one of the above alone or a mixture containing two or more of them.

The raw material composition may further contain compounds other than olefins having a carbon number of 5, within the scope of the present invention. For example, the raw material composition may contain a C5 fraction mainly composed of hydrocarbons having a carbon number of 5 obtained in a naphtha pyrolysis furnace or the like. The raw material composition may be used as it is in a state in which compounds other than olefins having a carbon number of 5 are arbitrarily mixed due to the production method, or may be used after purification.
The content of the olefin having 5 carbon atoms in the raw material composition is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, particularly preferably 90% by mass or more, and may be 100% by mass.

The content of monoolefins having 5 carbon atoms in the raw material composition is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, and may be 100% by mass.

The content of the diolefin having 5 carbon atoms in the raw material composition is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more. The content is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and particularly preferably 70% by mass or less.
When the diolefin content is equal to or greater than the lower limit, the yield of cyclopentadiene tends to be high. When the diolefin content is equal to or less than the upper limit, coke formation in the cyclization dehydrogenation reaction tends to be efficiently suppressed.

The olefin having 5 carbon atoms may be a mixture of a monoolefin having 5 carbon atoms and a diolefin having 5 carbon atoms. The mixing ratio (mass ratio) of the monoolefin having 5 carbon atoms and the diolefin having 5 carbon atoms is not particularly limited and may depend on the ratio resulting from the production method. The mixing ratio (mass ratio) of the monoolefin having 5 carbon atoms and the diolefin having 5 carbon atoms is preferably 20:80 to 95:5, more preferably 25:75 to 90:10, and even more preferably 30:70 to 85:15.

<Cyclization dehydrogenation step>
In the cyclization dehydrogenation step, for example, a reactor filled with a zeolite catalyst may be used, and the raw material composition may be passed through the reactor to carry out the cyclization dehydrogenation reaction. As the reactor, various reactors used in gas phase reactions using solid catalysts may be used. As the reactor, for example, a fixed bed adiabatic reactor, a radial flow reactor, a tubular reactor, etc. may be mentioned.

The reaction format of the cyclization dehydrogenation reaction is a continuous reaction format in which the raw material composition is continuously supplied, and may be, for example, a fixed bed type, a moving bed type, or a fluidized bed type. Of these, the fixed bed type is preferred from the viewpoint of equipment costs.

From the viewpoint of reaction efficiency, the temperature at which the raw material composition is contacted with the zeolite catalyst (which can also be referred to as the reaction temperature of the cyclization dehydrogenation reaction or the temperature inside the reactor) is preferably 350 to 800°C, more preferably 400 to 700°C, and even more preferably 450°C to 650°C. If the reaction temperature is equal to or higher than the lower limit, the yield of cyclopentadiene tends to be further improved. If the reaction temperature is equal to or lower than the upper limit, the rate of coke production is suppressed, and the high cyclization dehydrogenation activity of the zeolite catalyst tends to be maintained for a longer period.

The pressure when the raw material composition is brought into contact with the zeolite catalyst (which can also be called the reaction pressure of the cyclization-dehydrogenation reaction, or the pressure inside the reactor) is preferably 0.01 to 4.0 MPa, more preferably 0.03 to 0.5 MPa, and even more preferably 0.05 to 0.3 MPa. If the reaction pressure is within the above range, the cyclization-dehydrogenation reaction tends to proceed more easily, and even better reaction efficiency tends to be obtained.

The raw material composition supplied to the reaction system is preferably a gas. When the raw material composition is a gas, it can be mixed with a gas other than the raw material composition and supplied to the reaction system as a gas containing the raw material composition. The gas other than the raw material composition may be any gas that is substantially inert under the cyclization dehydrogenation reaction conditions. Examples of gases that are substantially inert under the cyclization dehydrogenation reaction conditions include molecular hydrogen, nitrogen, argon, neon, carbon dioxide, helium, and steam. In addition to the gas other than the raw material composition, any diluent that is substantially inert under the cyclization dehydrogenation reaction conditions may be supplied to the reaction system.

When the cyclization dehydrogenation step is carried out in a continuous reaction format in which the raw materials are continuously supplied, the gas flow rate (ml/min) ratio between the raw material composition supplied to the reaction system and the gas substantially inert under the cyclization dehydrogenation reaction conditions is preferably 1:0.1 to 1:20, and more preferably 1:0.5 to 1:10. In particular, when molecular hydrogen is used among the gases substantially inert under the cyclization dehydrogenation reaction conditions, the gas flow rate (ml/min) ratio between the raw material composition supplied to the reaction system and the molecular hydrogen is preferably 1:0.001 to 1:3, and more preferably 1:0.001 to 1:0.5.
In the dehydrogenation reaction using a solid acid catalyst, molecular hydrogen is usually supplied to the reaction system to suppress deactivation of the catalyst due to coke generation. However, in the production method of this embodiment, as shown in the examples described later, catalyst deactivation is hardly observed even if molecular hydrogen is not supplied to the reaction system. Therefore, in the production method of this embodiment, molecular hydrogen does not need to be substantially supplied to the reaction system. In this specification, "substantially not supplying molecular hydrogen to the reaction system" means that molecular hydrogen is not intentionally supplied to the reaction system, and for example, the gas flow rate (ml/min) ratio of the raw material composition to molecular hydrogen supplied to the reaction system is less than 1:0.001. This makes it possible to reduce the production cost of cyclopentadiene, which is industrially useful.

When the cyclization dehydrogenation step is carried out in a continuous reaction format in which the raw material is continuously supplied, the mass hourly space velocity (hereinafter sometimes referred to as "WHSV") is preferably 0.01 h ^-1 or more, more preferably 0.1 h ^-1 or more, from the viewpoint of improving the conversion rate of the raw material. In addition, the WHSV is preferably 100 h ^-1 or less, more preferably 20 h ^-1 or less, from the viewpoint of reducing the reactor size.
Here, WHSV is the ratio (F/W) of the feed rate (feed amount/time) F of the raw material to the mass W of the zeolite catalyst in a continuous reaction apparatus. The amounts of the raw material composition and catalyst used may be appropriately selected within more preferable ranges depending on the reaction conditions, catalyst activity, etc., and the WHSV is not limited to the above range.

The method for separating and purifying cyclopentadiene from the reaction product obtained by the cyclization dehydrogenation step is not particularly limited, and purification can be performed by known distillation operations, etc. In addition, unreacted raw materials may be recovered from the reaction product after separation of cyclopentadiene, and the recovered raw materials may be mixed with new raw materials and reused.

As described above, the production method according to this embodiment uses a specific zeolite catalyst, making it possible to stably produce cyclopentadiene from a raw material composition containing an olefin having five carbon atoms at a high yield over a long period of time.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[Catalyst Preparation Example 1]
<Preparation of Pt/[Zn]-MFI catalyst>
(1) Aging step 20.0 g of tetraethyl orthosilicate (TEOS) and 20.3 g of a 25% by mass aqueous solution of tetrapropylammonium hydroxide (TPAOH, organic structure directing agent) were added to a stainless steel pressure vessel, sealed, and stirred (aged) for 24 hours at 80° C. The mixture after stirring was in a liquid state.

(2) Hydrothermal synthesis step 2.2 g of zinc nitrate hexahydrate was dissolved in 4.7 g of ion-exchanged water. Then, the mixture obtained in the aging step was added and stirred at room temperature (25 to 30°C) until it was homogenized. The mixture after stirring was placed in an autoclave and hydrothermal synthesis was carried out at 175°C for 24 hours while rotating at 20 rpm.

(3) Calcination step: The mixture after the hydrothermal synthesis step was placed in a centrifuge tube and centrifuged to obtain a gel sample. The gel sample was then washed with ion-exchanged water.
The washing was carried out by adding ion-exchanged water to the gel sample, washing it, and then centrifuging it. The pH of the supernatant after centrifugation was measured, and washing and centrifugation were repeated until the pH was in the range of 7 to 8.
The washed gel sample was dried overnight at 90° C. The dried sample was placed in a muffle furnace and calcined in an air environment at 550° C. for 8 hours to remove organic matter (tetrapropylammonium ions (cations)) and obtain a zeolite catalyst ([Zn]-MFI catalyst).

The obtained zeolite catalyst was subjected to the following measurements.
(a) Synchrotron XRD Analysis XRD analysis was carried out using a synchrotron XRD device.
(b) Solid-state NMR Analysis ²⁹ Si MAS NMR measurement was carried out using an NMR (ECA-600, manufactured by JEOL Ltd.).
(c) FT-IR Analysis The structure was analyzed by FT-IR (FT/IR-4600, manufactured by JASCO Corporation). At this time, as a pretreatment, the sample was evacuated to a vacuum at 450° C. for 1 hour.
(d) CO ₂ -TPD analysis CO ₂ -TPD analysis was performed using a TPD analyzer (Microtrack Bell, BELCAT II). About 30 mg of zeolite catalyst was pretreated at 500°C for 1 hour while flowing helium gas at a flow rate of 50 mL/min. After that, it was cooled to less than 40°C, 1 vol% CO ₂ /He gas was flowed at a flow rate of 50 mL/min to adsorb CO ₂ to the zeolite catalyst, and then helium gas was flowed at a flow rate of 50 mL/min for 5 minutes. Then, while flowing helium gas at 30 mL/min, the temperature was raised to 800°C at a heating rate of 10°C/min, and the release of CO ₂ was analyzed using a TCD (Thermal Conductivity Detector) and MASS. For the MASS, BELMass, manufactured by Microtrack Bell, was used.
The amount of base was measured by calculation from the peak area measured by CO ₂ -TPD.
(e) NH ₃ -TPD analysis NH ₃ -TPD analysis was performed using a TPD analyzer (Microtrack Bell, BELCAT II). About 30 mg of zeolite catalyst was pretreated at 500°C for 1 hour while flowing helium gas at a flow rate of 50 mL/min. After that, it was cooled to 100°C, 1 vol% NH ₃ /He gas was flowed at a flow rate of 50 mL/min to adsorb NH ₃ on the zeolite catalyst, and then helium gas was flowed at a flow rate of 50 mL/min for 15 minutes. After that, while flowing helium gas at 30 mL/min, the temperature was raised to 700°C at a heating rate of 10°C/min, and the desorption of NH ₃ was analyzed by TCD and MASS. For the MASS, BELMass, manufactured by Microtrack Bell, was used.
The amount of Lewis acid was measured by calculation from the peak area measured by NH ₃ -TPD.
(f) UV-vis analysis UV-vis analysis was carried out using an ultraviolet-visible-near infrared spectrophotometer (V-660, manufactured by JASCO Corporation). The measurement method was a diffuse reflectance method, and the analysis was carried out at room temperature.

(a) Synchrotron XRD Analysis The results of synchrotron XRD analysis are shown in Figure 1. In the Zn/[Si]-MFI catalyst shown in Catalyst Preparation Example 2 described later, a peak due to ZnO crystals was observed at the position indicated by the dotted line, but in the [Zn]-MFI catalyst, no peak due to ZnO crystals was observed.
(b) Solid-state NMR analysis
The results of the ²⁹ Si MAS NMR analysis are shown in Figure 2. When a zeolite composed of Si, O, and Zn is measured by ²⁹ Si MAS NMR, if the four bonds of the Si atom are only -O-Si, a peak appears at -110 to -120 ppm, and if at least one of the four bonds of the Si atom is -O-Zn, a peak appears around -100 ppm ("Synthesis and Characterization OF Zincosilicates with the SOD Topology" M.A. Cambroer, R.F. Lobe, H. Koller, M.E. Davis, Chemistry of Materials, 6, P.2193-2199 (1994)). In the case of the [Zn]-MFI catalyst, this peak at -100 ppm was observed.
(c) FT-IR analysis The results of FT-IR analysis at room temperature after pretreatment by evacuation at 450°C for 1 hour are shown in Figure 3. If Zn exists close to each other, it will become Zn-O-Zn by pretreatment. ZnO crystals and Zn-impregnated supported catalysts do not have an absorption band in the region of 3600 to 3700 cm ^-1 in FT-IR analysis. However, in the [Zn]-MFI catalyst, an absorption band is observed near 3640 cm ^-1 due to the Zn-OH vibration of Zn, and it is considered that Zn is taken up into the zeolite framework and is isolated from each other.
In addition, after the pretreatment, the catalyst was cooled to 150°C, pyridine was introduced, and the temperature was raised to 250°C while evacuating to a vacuum, after which FT-IR analysis was performed. The results are shown in Figure 4. It is known that when pyridine is adsorbed on a zeolite catalyst in the presence of a Brønsted acid and then measured by FT-IR, an absorption band resulting from the vibration of C ₆ H ₅ N-H is observed near 1560 cm ^-1 . However, this absorption band was not observed in the case of the [Zn]-MFI catalyst.
It is known that when a Lewis acid is present, an absorption band is observed near 1450 cm ^-1 when pyridine is adsorbed on a zeolite catalyst and the catalyst is measured by FT-IR. In the case of the [Zn]-MFI catalyst, an absorption band was observed near 1450 cm ^-1 . This demonstrated that the [Zn]-MFI catalyst does not have a Bronsted acid, but only has a Lewis acid.
(d) CO ₂ -TPD Analysis The results of the CO ₂ -TPD analysis are shown in FIG. 5. In the CO ₂ -TPD analysis, a typical aluminum-containing zeolite catalyst exhibits a peak in the low temperature range around 100°C, but no peak is observed in the high temperature range of 500°C or higher. In addition, a peak is observed only in the vicinity of 100°C in the Zn-impregnated supported catalyst. However, in the [Zn]-MFI catalyst, a peak is observed even in the high temperature range of 500°C or higher, confirming that the solid basicity of this zeolite catalyst is strong. The amount of solid base calculated from the peak area in the high temperature range of 500°C or higher by CO ₂ -TPD was 0.001 to 0.035 mmol/g.
(e) NH ₃ -TPD Analysis The results of NH ₃ -TPD analysis are shown in FIG. 6. In the NH ₃ -TPD analysis, a broad peak was observed around 200°C for the Zn-impregnated supported catalyst. On the other hand, a large broad peak was observed from 150°C to 500°C for the [Zn]-MFI catalyst. In the FT-IR analysis, it was confirmed that the [Zn]-MFI catalyst does not have a Bronsted acid, but only a Lewis acid, and therefore this peak is considered to be derived from the release of NH ₃ adsorbed to the Lewis acid. In addition, the amount of acid calculated from the peak area was 0.01 to 0.2 mmol/g.
(f) UV-vis analysis The results of the UV-vis analysis are shown in Figure 7. In the UV-vis analysis, the peak of ZnO crystals is assigned to 255-322 nm, and the peak of ZnO clusters in the zeolite pores is assigned to 240 nm. No peaks of ZnO crystals or ZnO crystals in the zeolite pores were confirmed in the [Zn]-MFI catalyst, and it is considered that Zn atoms are highly dispersed in the zeolite framework.

These results confirm that the obtained [Zn]-MFI catalyst is a zeolite catalyst with an MFI structure that does not have any Brønsted acids, has only Lewis acids, and has strong solid basicity.

(4) Platinum Supporting Step Next, a dinitrodiamine platinum (II) nitric acid solution (manufactured by Tanaka Kikinzoku Kogyo, [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] / HNO ₃ ) having a platinum content of 4.557% by mass was added to 1 g of the calcined zeolite catalyst, and platinum was impregnated and supported so that the platinum supporting amounts were 0.2 mass%, 0.5 mass%, 1.0 mass%, and 2.0 mass%, respectively. Then, the catalyst was dried overnight at 130 ° C. and calcined in air at 550 ° C. for 3 h to prepare Pt / [Zn]-MFI catalysts, which are zeolite-supported platinum catalysts supporting 0.2 mass%, 0.5 mass%, 1.0 mass%, and 2.0 mass% platinum, respectively.

[Catalyst Preparation Example 2]
<Preparation of Zn/[Si]-MFI catalyst>
A gel prepared by mixing sodium hydroxide, tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH), and ion-exchanged water (TEOS:TPAOH:ion-exchanged water=1:0.12:70 (molar ratio)) was stirred (aged) at 80°C for 24 hours. The resulting mixture was subjected to hydrothermal synthesis at 175°C for 24 hours, and then repeatedly washed with water. Then, it was dried overnight at 130°C and baked at 550°C for 3 hours. This resulted in a silicalite that does not contain aluminum. It was confirmed that the obtained silicalite had an MFI structure by X-ray diffraction measurement (X-ray source: CuKα, device: Rigaku Corporation, RINT 2500). Next, zinc was impregnated and supported using an aqueous solution of 1M zinc nitrate hexahydrate so that the amount of zinc supported was 10.0 mass%, dried overnight at 130°C, and baked at 550°C for 3 hours to prepare a Zn/[Si]-MFI catalyst.

[Catalyst Preparation Example 3]
<Preparation of Pt/ _{MgAl2O4 catalyst} >
10.0 g of commercially available γ-alumina (Neo Bead GB-13, Mizusawa Chemical Industry Co., Ltd.) was mixed with an aqueous solution in which 12.5 g of magnesium nitrate hexahydrate (Mg(NO ₃ ) _{2.6H 2} O, Wako Pure Chemical Industries, Ltd.) was dissolved in 100 mL of water. The resulting mixture was stirred at 50° C. for 180 minutes using an evaporator, and then water was removed under reduced pressure. The mixture was then dried overnight at 130° C., and fired at 550° C. for 3 hours, and then fired at 800° C. for 3 hours. This resulted in an alumina-magnesia carrier having a spinel structure. The resulting alumina-magnesia carrier was confirmed to have diffraction peaks attributable to Mg spinel at 2θ = 36.9, 44.8, 59.4, and 65.3 deg by X-ray diffraction measurement (X-ray source: CuKα, device: Rigaku Corporation, RINT 2500).
Next, a dinitrodiammine platinum (II) nitric acid solution (Tanaka Kikinzoku Kogyo Co., Ltd., [P
The catalyst was impregnated with platinum using a 1.0 mass% mixture of 1.0% by mass of MgAlAlO2 and 1.0% by mass of t( _NH3 ) ₂ ( _NO2 ) ₂ / _HNO3 , dried overnight at 130°C, and calcined at 550°C for ₃ hours to prepare a Pt/ _MgAlAl2O4 catalyst.

[Production of cyclopentadiene]
Using the catalysts obtained in Catalyst Preparation Examples 1 and 3, cyclopentadiene was produced.

Example 1
A tubular reactor was filled with 0.1 g of Pt/[Zn]-MFI catalyst carrying 1.0 mass% platinum, and the tubular reactor was connected to a fixed-bed flow reactor. The tubular reactor was heated to 550° C. while flowing molecular hydrogen at 30 mL/min, and then held at that temperature for 1.0 h. Then, an olefin having a carbon number of 5 (1-pentene:1,3-pentadiene=50:50 (mass ratio)) and nitrogen were each supplied to the tubular reactor as a raw material composition, and a cyclization dehydrogenation reaction was carried out at a reaction temperature of 500° C. and normal pressure. The WHSV was 1.1 h ⁻¹ . The gas flow rate (mL/min) ratio was raw material composition:nitrogen (N ₂ )=1:12.

At 0.5, 2.5, 4.5, and 6.5 hours after the start of the reaction, the products of the cyclization dehydrogenation reaction were analyzed using a gas chromatograph (FID-GC) equipped with a hydrogen flame detector. Based on the gas chromatogram, each component (unit: mass%) of the collected reaction product was quantified, and the total conversion rate of the raw materials (sum of the conversion rates of each raw material, unit: mass%) and the cyclopentadiene yield (yield relative to the amount of olefin with a carbon number of 5 used as the raw material, mass%) were calculated. The results are shown in Table 1. The total conversion rate was calculated using the following formula (1).

Total conversion rate (mass%) = (1 - (C _{product 1-pentene} + C _{product 1,3-pentadiene} ) / (C _{raw material 1-pentene} + C _{raw material 1,3-pentadiene} )) x 100 (1)
In formula (1), C _{raw material 1-pentene} and C _{raw material 1,3-pentadiene} are the mass% of 1-pentene and 1,3-pentadiene contained in the raw material, and C _{product 1-pentene} and C _{product 1,3-pentadiene} are the mass% of 1-pentene and 1,3-pentadiene contained in the product.

(Examples 2 to 11)
The yield of cyclopentadiene was calculated in the same manner as in Example 1, except that the raw material composition, catalyst, WHSV, and gas flow rate ratio in Example 1 were changed as shown in Tables 2 to 5. The yield ratio of cyclopentadiene (yield of cyclopentadiene in a reaction time of 6.5 hours/yield of cyclopentadiene in a reaction time of 2.5 hours) was calculated from the yield of cyclopentadiene obtained. The results are shown in Tables 2 to 5.

(Examples 12 and 13 and Comparative Examples 1 to 3)
The raw material conversion rate or the total raw material conversion rate, and the cyclopentadiene yield were calculated in the same manner as in Example 1, except that the raw material composition, catalyst, WHSV, and gas flow rate ratio in Example 1 were changed as shown in Tables 1 and 6. The results are shown in Tables 1 and 6.

As shown in Table 1, when a reaction was carried out using a catalyst in which a precious metal was supported on the zeolite catalyst in which a transition metal was introduced into the zeolite framework in Example 1, the total conversion rate of the raw materials and the yield of cyclopentadiene tended to be higher than those in Comparative Example 1, in which a supported precious metal catalyst was not used as a support for a crystalline metallosilicate.
Furthermore, with the catalyst of Example 1, the yield of cyclopentadiene was maintained high even after 6.5 hours had elapsed, and stable production of cyclopentadiene over reaction time was observed. On the other hand, the catalyst of Comparative Example 1 was deactivated by coke deterioration immediately after the start of the reaction, and the cyclopentadiene yield tended to remain low.

Table 2 shows the effect of platinum content in the zeolite catalyst on the yield ratio of cyclopentadiene.
As shown in Table 2, even when the platinum content in the zeolite catalyst was 0.2 mass %, stable production of cyclopentadiene was observed over the reaction time.

Table 3 shows the effect of WHSV on the specific yield of cyclopentadiene.
As shown in Table 3, stable production of cyclopentadiene over the reaction time was observed over a wide range of WHSV from 0.5 to 5.0 h ⁻¹ .

Example 1 in Table 1 and Example 8 in Table 4 show the effect of the content of the diolefin having 5 carbon atoms in the raw material composition on the yield ratio of cyclopentadiene.
Here, the yield ratio of cyclopentadiene in Example 1 (6.5 hr/2.5 hr) was 1.09.
As shown in Example 1 of Table 1 and Example 8 of Table 4, even when the contents of the diolefin having 5 carbon atoms in the raw material composition were 33% by mass and 50% by mass, stable production of cyclopentadiene was observed over the course of reaction time.

Example 1 in Table 1 and Examples 9 to 11 in Table 5 show the effect of the flow rate ratio of gases supplied to the reaction system on the yield ratio of cyclopentadiene.
As shown in Example 1 in Table 1 and Examples 9 to 11 in Table 5, even when molecular hydrogen was not supplied to the reaction system, stable production of cyclopentadiene was observed over the course of reaction time.

As shown in Examples 12 and 13 in Table 6, even in the case of Example 1 in which only a monoolefin having a carbon number of 5 was used as the raw material composition, the raw material conversion rate and the cyclopentadiene yield were high, and stable production of cyclopentadiene was observed over the course of the reaction time.
On the other hand, the methods of Comparative Examples 2 and 3 in Table 6 did not achieve such high raw material conversion and cyclopentadiene yield as those of Examples 12 and 13, and in particular, the method of Comparative Example 3 showed a decrease in cyclopentadiene yield over time.

Claims (7)

a cyclization/dehydrogenation step of contacting a raw material composition containing an olefin having a carbon number of 5 with a zeolite catalyst having an MFI structure to obtain a reaction product containing cyclopentadiene,
The zeolite catalyst contains Zn atoms in the zeolite framework and has Lewis acidity and strong solid basicity.
A method for producing cyclopentadiene. The method for producing cyclopentadiene according to claim 1, wherein the raw material composition contains a diolefin having 5 carbon atoms. The method for producing cyclopentadiene according to claim 2, wherein the content of the diolefin having 5 carbon atoms in the raw material composition is 5 mass% or more. The method for producing cyclopentadiene according to any one of claims 1 to 3, wherein the content of Zn atoms is 1 to 15 atom% relative to Si atoms. The method for producing cyclopentadiene according to any one of claims 1 to 4, wherein the zeolite catalyst does not contain an alkali metal or contains an alkali metal in an amount of 1 atom% or less relative to the Si atoms of the zeolite framework. The method for producing cyclopentadiene according to any one of claims 1 to 5, wherein the zeolite catalyst is supported with Pt. The method for producing cyclopentadiene according to any one of claims 1 to 6, wherein in the cyclization dehydrogenation step, the gas flow rate (ml/min) ratio between the raw material composition and molecular hydrogen supplied to the reaction system is 1:0.001 to 1:3.