JP7724166B2 - Method for producing lower olefins - Google Patents

Description

The present invention relates to a method for producing lower olefins using a catalyst containing DDR-type zeolite.

Conventional methods for producing lower olefins such as ethylene, propylene, and butene include steam cracking of naphtha and fluid catalytic cracking of vacuum gas oil. In recent years, metathesis reactions using ethylene and 2-butene as feedstocks and the MTO (methanol to olefins) process using methanol and/or dimethyl ether as feedstocks have become well known.

For example, Non-Patent Documents 1 to 3 disclose that by using methanol as a raw material and a zeolite with a DDR structure (Sigma-1, ZSM-58 zeolite) as a catalyst, it is possible to suppress the by-production of hydrocarbon components of C5 or more, and produce ethylene and propylene in high yields.

Catal. Sci. Technol. , 6, 2663-2678 (2016) ACS Catal. , 7, 4033-4046 (2017) ACS Catal. , 10, 3009-3017 (2020)

Non-Patent Document 1 reports the ethylene yield when the reaction temperature of a DDR zeolite having a particle size of 2.4 μm and an Si/Al ₂ ratio (value calculated from NH ₃ -TPD) of 315 is varied from 380°C to 475°C. The results show that the ethylene yield increases as the reaction temperature increases, with the maximum ethylene yield reaching approximately 45% at a reaction temperature of 475°C. It can be seen that the ethylene yield increases significantly when the reaction temperature is increased from 380°C to 450°C, but does not change significantly between 450°C and 475°C.
Furthermore, Non-Patent Document 2 reports the ethylene yield when the reaction temperature of a DDR-type zeolite with Si/Al=50 and a particle size of about 500-1000 nm is varied from 350°C to 450°C, and the maximum ethylene yield at a reaction temperature of 450°C is about 48%.
However, the reaction temperature for increasing the yield of ethylene has not been sufficiently studied. Generally, when the reaction temperature is increased, the amount of olefin components with small carbon numbers tends to increase at equilibrium, but on the other hand, the amount of by-products such as methane, which has the smallest carbon number, increases. Therefore, as mentioned above, the reaction temperature has not been increased to a temperature higher than 475°C.

The present invention aims to solve the above problems and provide a method for producing lower olefins that can achieve a high ethylene yield.

The inventors conducted research to solve the above-mentioned problems and discovered that a method for producing lower olefins comprising a step of contacting a raw material containing methanol and/or dimethyl ether with a DDR-type zeolite can be provided, which can achieve a high yield of ethylene by setting the reaction temperature at a certain temperature or higher, and thus completed the present invention. In this specification, lower olefins refer to ethylene, propylene, and butene. In other words, they are olefins having 2 to 4 carbon atoms.

The present invention includes the following aspects.
[1] A method for producing lower olefins, comprising a step of contacting a raw material containing methanol and/or dimethyl ether with a DDR-type zeolite, wherein the reaction temperature is 490°C or higher and 600°C or lower.
[2] The method for producing lower olefins according to the above [1], wherein the average primary particle diameter of the DDR type zeolite is 2000 nm or less.
[3] The method for producing lower olefins according to the above [1] or [2], wherein the DDR type zeolite is a DDR type zeolite that has been treated under alkaline conditions in the presence of a surfactant.
[4] The DDR type zeolite contains silicon (Si) and aluminum (Al) as constituent elements, and the molar ratio of silicon (Si) to aluminum (Al) (Si/Al) is 25 or more and 500 or less. [1] - [3] The method for producing lower olefins according to any one of the above.

The present invention provides a method for producing lower olefins that can achieve a high ethylene yield.

FIG. 1 is a diagram showing the results of powder X-ray diffraction of DDR zeolite (as-made type) according to samples A to E. 1 shows scanning electron microscope (SEM) images of DDR type zeolite (as-made type) according to samples A to E. 1 is a graph showing the transition of methanol conversion and selectivity in the production of lower olefins using the DDR zeolites according to Examples 1 to 5 and Comparative Examples 1 to 5 as catalysts.

The present invention will be described in detail below. However, the following description of the constituent elements is one example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents, and various modifications can be made within the scope of the gist of the invention.

[DDR type zeolite]
DDR-type zeolite is a zeolite with a two-dimensional pore structure in which two eight-membered ring structures intersect as its structural units. According to the IZA database, the pore size is 3.6 x 4.4 Å, which is a narrower pore structure compared to CHA-type zeolites (3.8 x 3.8 Å) such as SAPO-34, which is industrially used as an MTO catalyst. This is thought to be why the by-production of hydrocarbon components of C5 or higher can be suppressed.

The composition of the DDR-type zeolite of this embodiment is not particularly limited, but preferably contains silicon (Si) and aluminum (Al) as constituent elements. When elements other than Si and Al are contained, the other elements are not particularly limited, but examples include one or more selected from boron (B), titanium (Ti), vanadium (V), iron (Fe), zinc (Zn), gallium (Ga), germanium (Ge), zirconium (Zr), and tin (Sn).

Specific examples of preferred zeolites include crystalline aluminosilicates containing Si and Al as constituent elements, as well as crystalline galloaluminosilicates containing Ga. These zeolites have excellent catalytic activity because the Al and Ga in the zeolite framework act as acid sites and act as active sites for catalytic reactions.

In the case of the crystalline aluminosilicate, the Si/Al molar ratio is preferably 25 or more, more preferably 50 or more, even more preferably 60 or more, particularly preferably 70 or more, and especially preferably 80 or more, and is preferably 500 or less, more preferably 250 or less, and even more preferably 150 or less. It is especially preferably 140 or less, and especially preferably 130 or less. By setting the Si/Al molar ratio within this range, a zeolite catalyst can be obtained that has sufficient catalytic activity and further improves the catalyst life.
In the case of the crystalline gallosilicate, the ratio of its constituent elements is not particularly limited, but the Si/Ga molar ratio is usually 5 or more, preferably 10 or more, more preferably 25 or more, even more preferably 50 or more, particularly preferably 100 or more, and especially preferably 200 or more, and is usually 5000 or less, preferably 1000 or less, and more preferably 500 or less. By setting the Si/Ga molar ratio within this range, a zeolite catalyst can be obtained that has sufficient catalytic activity and further improved catalyst life.

The contents of Si, Al, Ga, B, etc. in the DDR zeolite of this embodiment are typically values measured for the manufactured DDR zeolite using inductively coupled plasma atomic emission spectroscopy (ICP-AES) or similar, and are not the ratios of the raw material loadings.

The ion exchange sites of the DDR-type zeolite of this embodiment are not particularly limited and may be H-type or may be exchanged with metal ions. Here, specific examples of metal ions include alkali metal ions, alkaline earth metal ions, cerium, tungsten, manganese, and iron.

[Ratio of BET specific surface area (A2) to external surface area (A1)]
The external surface area (A1) of the DDR zeolite of this embodiment is usually 5 m ² /g or more, preferably 10 m ² /g or more, more preferably 15 m ² /g or more, and even more preferably 20 m ² /g or more, and is usually 500 m ² /g or less, preferably 300 m ² /g or less, and more preferably 200 m ² /g or less.
The BET specific surface area (A2) of the DDR zeolite of this embodiment is not particularly limited, but is usually 150 m ² /g or more, preferably 200 m ² /g or more, more preferably 250 m ² /g or more, and even more preferably 300 m ² /g or more, and is usually 800 m ² /g or less, preferably 700 m ² /g or less, and more preferably 600 m ² /g or less.
In this embodiment, the ratio (A2/A1) of the BET specific surface area (A2) to the external surface area (A1) is preferably 20 or less. When A2/A1 is 20 or less, it is thought that the diffusion of the reaction product out of the pores is improved, and coking can be suppressed. From the above viewpoints, A2/A1 is more preferably 18 or less, even more preferably 17 or less, still more preferably 16 or less, and particularly preferably 15 or less. On the other hand, the lower limit is not particularly limited, but is usually 2 or more.
The micropore volume (A3) of the DDR zeolite of the present embodiment is not particularly limited, and is usually 0.05 ml/g or more, preferably 0.075 ml/g or more, more preferably 0.10 ml/g or more, and is usually 3 ml/g or less, preferably 2 ml/g or less.
The external surface area (A1), BET specific surface area (A2), and micropore volume (A3) can be calculated from nitrogen adsorption/desorption measurements, for example, using a Belsorp-mini II manufactured by Microtrac-Bell. Data analysis can be performed using analysis software BELMaster manufactured by Microtrac-Bell. The BET specific surface area (A2) can be calculated by BET plotting measurement data at relative pressures (P/P0) of 0.002 to 0.06. The external surface area (A1) and micropore volume (A3) can be calculated by t-plotting data at relative pressures (P/P0) of 0.20 to 0.42. The Harkins-Jura isotherm is used as the standard isotherm.

The average primary particle size of the DDR zeolite of the present embodiment is not particularly limited, and is usually 3 μm (3000 nm) or less, preferably 2 μm (2000 nm) or less, more preferably 1 μm (1000 nm) or less, even more preferably 800 nm or less, still more preferably 700 nm or less, and particularly preferably 600 nm or less. Also, it is usually 20 nm or more, preferably 40 nm or more.
The average primary particle size of DDR type zeolite can be determined using a scanning electron microscope (SEM).

As described above, the "primary particle size" and the "average primary particle size" can both be calculated using a scanning electron microscope (SEM).
Here, "primary particles" refer to the smallest particles for which no grain boundaries are observed. In the present invention, an SEM image of the zeolite catalyst is obtained, and the smallest particles that correspond to the zeolite contained in the SEM image and for which no grain boundaries are observed are determined to be "primary particles." In the present invention, the primary particles do not have to exist as single particles, and may form secondary particles by aggregation or the like. Even if secondary particles are formed, it is possible to distinguish the primary particles on the surfaces of the secondary particles in the SEM image. Note that although cracks-like things may be seen on the surface of DDR-type zeolite, these are not considered to be grain boundaries.
The "average primary particle diameter" is measured as follows. That is, 50 primary particles contained in an SEM image of a zeolite catalyst are randomly selected, and the major axis (the length of the longest straight line when connecting one end of a primary particle with the other end of a primary particle) of each of the selected 50 primary particles is measured, and the arithmetic mean of the major axes of the 50 measured particles is defined as the "average primary particle diameter." However, if the entire zeolite catalyst contains fewer than 50 primary particles, the major axis of each of all primary particles contained in the zeolite catalyst is measured, and the average value thereof is defined as the "average primary particle diameter."

[Method for producing DDR type zeolite]
Hereinafter, a method for producing the DDR type zeolite of this embodiment will be described.

DDR-type zeolite can generally be prepared by hydrothermal synthesis. For example, an alkali source and an organic structure-directing agent, preferably 1-adamantylamine, methyltropinium iodide, or quinuclidinium hydroxide, are added to water and stirred. An aluminum source, a gallium source, a boron source, a silica source, or the like is then added to form a uniform gel. The resulting raw gel is then crystallized by holding it at 100 to 220°C in a pressurized, heated vessel such as an autoclave. Seed crystals may be added as needed during crystallization, but adding seed crystals is preferred because it facilitates crystallization of DDR-type zeolite. It is preferable to use DDR-type zeolite as the seed crystals. It is preferable to use pulverized zeolite as the seed crystals. Using pulverized seed crystals makes it easier to obtain DDR-type zeolite with a small particle size.

After the raw gel crystallizes, the crystallized raw gel is filtered and washed, and the solids are dried at 100-200°C and then calcined at 400-900°C to obtain zeolite powder.

The silica source used in preparing the raw gel may be one or more of silicates such as fumed silica, silica sol, silica gel, silicon dioxide, and water glass, silicon alkoxides such as tetraethoxyorthosilicate and tetramethoxysilane, and silicon halides.
As the aluminum source, one or more of aluminum sulfate, aluminum nitrate, pseudoboehmite, aluminum alkoxide, aluminum hydroxide, alumina sol, sodium aluminate, etc. can be used.
As the gallium source, one or more of gallium nitrate, gallium sulfate, gallium phosphate, gallium chloride, gallium bromide, gallium hydroxide, etc. can be used.
As the boron source, one or more of boric acid, sodium borate, boron oxide, etc. can be used.

There are no particular restrictions on the molar ratio (Si/Al) of silicon (Si) to aluminum (Al) in the DDR-type zeolite used as seed crystals, but it is preferably in the range of 25 to 10,000. It is also preferable to use approximately 1 to 20 mass% of the seed crystals relative to the silica source added.

DDR-type zeolite can adjust the amount of metals it contains by adjusting the amount of constituent elements (Si, Al, Ga, B, etc.) during synthesis. It is also possible to use zeolites in which the content is adjusted by removing some of the constituent elements through steaming, acid treatment, etc.

In this embodiment, the DDR zeolite prepared by hydrothermal synthesis may be subjected to an alkali treatment in the presence of a surfactant. The alkali treatment improves the ethylene yield.
The surfactant used in the alkali treatment step may be a cationic surfactant, anionic surfactant, nonionic surfactant, amphoteric surfactant, or the like, which may be used alone or in combination. Suitable examples include cationic surfactants such as hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyltrimethylammonium hydroxide.
The concentration of the surfactant in the alkali treatment step is not particularly limited, and it can be contained in the treatment liquid at about 0.1 to 10% by mass.

The alkali for the alkali treatment is not particularly limited, and an ammonia solution, a sodium hydroxide solution, or the like can be used. The level of alkalinity is also not particularly limited, and the pH may be, for example, about 9 to 12.
The alkali treatment can be carried out by bringing DDR zeolite into contact with an alkali, or by stirring it in an alkali solution containing a surfactant. The temperature of the alkali treatment is not particularly limited, and may be, for example, about 100 to 200°C. The time for the alkali treatment is also not particularly limited, and the zeolite may be immersed in the alkali solution containing a surfactant for 0.1 to 24 hours.
After the alkali treatment, it is desirable to dry the product and then calcinate it again to remove the incorporated surfactant for use as a catalyst.

[catalyst]
The DDR zeolite of this embodiment is useful as a catalyst used in a reaction for producing lower olefins.

The DDR-type zeolite of this embodiment may be used directly as a catalyst in the reaction of the present invention, or may be used as a mixture with other substances inert to the reaction, such as alkaline earth metals or silicon-containing compounds. It may also be granulated or molded using a binder and used in the reaction. Examples of substances or binders inert to the reaction include alumina or alumina sol, silica, silica gel, silicate, quartz, and mixtures thereof. Among these, silica is preferred because it is expected to have excellent strength and catalytic performance as an industrial catalyst. Mixing with these substances is also effective in reducing the overall cost of the catalyst, increasing the density of the catalyst, and increasing the catalyst strength.

[Method for producing lower olefins]
In the method for producing lower olefins using a catalyst containing a DDR zeolite of this embodiment, methanol or dimethyl ether is used as a raw material. Alternatively, a mixture of methanol and dimethyl ether may be used.

A method for producing lower olefins, which is an embodiment of the present invention, includes a step of contacting a feedstock containing methanol and/or dimethyl ether with a catalyst containing the above-mentioned DDR-type zeolite.

The origin of the methanol and dimethyl ether used as raw materials is not particularly limited. Examples include those obtained by the hydrogenation reaction of a hydrogen/CO mixed gas derived from coal, natural gas, and a by-product of the steel industry, those obtained by the reforming reaction of plant-derived alcohols, those obtained by fermentation, those obtained from organic substances such as recycled plastics and urban waste, and those obtained by a methanol synthesis reaction using carbon dioxide as a raw material. In this case, a mixture of compounds other than methanol and dimethyl ether resulting from each production method may be used as is, or a purified product may be used.
As the reaction raw material, only methanol or only dimethyl ether may be used, or a mixture of these may be used. When a mixture of methanol and dimethyl ether is used, there is no limitation on the mixing ratio.

The reaction mode in this embodiment is not particularly limited as long as the methanol and/or dimethyl ether feedstock is in the gas phase in the reaction zone, and a known gas-phase reaction process using a fluidized bed reactor, a moving bed reactor, or a fixed bed reactor can be applied. The use of a fluidized bed reactor enables operation even with a catalyst having a short one-pass life.
The process may be carried out in any of a batch system, a semi-continuous system, or a continuous system, but is preferably carried out in a continuous system, and the process may use a single reactor or a plurality of reactors arranged in series or parallel.

When the fixed-bed reactor is packed with the catalyst, in order to minimize the temperature distribution in the catalyst layer, granular materials inert to the reaction, such as quartz sand, alumina, silica, or silica-alumina, may be mixed with the catalyst and packed. In this case, there are no particular restrictions on the amount of granular materials inert to the reaction, such as quartz sand, used. In order to ensure uniform mixing with the catalyst, it is preferable that the granular materials have a particle size similar to that of the catalyst.
Furthermore, the reaction substrates (reaction raw materials) may be supplied to the reactor in divided portions for the purpose of dispersing the heat generated by the reaction.

The total concentration (substrate concentration) of methanol and dimethyl ether in all the components fed to the reactor is not particularly limited, but the sum of methanol and dimethyl ether is preferably 90 mol % or less, more preferably 10 mol % or more and 70 mol % or less, of all the components fed.
The above range is preferable in terms of the reaction rate and the yield of low olefins.

In addition to methanol and/or dimethyl ether, the reactor may contain gases inert to the reaction (hereinafter also referred to as "diluents"), such as helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, paraffins, hydrocarbons such as methane, aromatic compounds, and mixtures thereof. Among these, the coexistence of water (water vapor) is preferred because it allows for good separation.
As such a diluent, impurities contained in the reaction raw materials may be used as they are, or a separately prepared diluent may be mixed with the reaction raw materials. In addition, the diluent may be mixed with the reaction raw materials before being charged into the reactor, or may be supplied to the reactor separately from the reaction raw materials.

In the present invention, the reaction temperature is 490°C or higher and 600°C or lower. The lower limit of the reaction temperature is preferably 495°C or higher, more preferably 500°C or higher, and the upper limit of the reaction temperature is preferably 560°C or lower, more preferably 540°C or lower. If the reaction temperature is too low, the yield of olefins other than ethylene will increase and the yield of ethylene will decrease. On the other hand, if the reaction temperature is too high, the yield of paraffins such as methane will increase and the yield of ethylene will decrease. In addition, coking of the catalyst will become severe, making it impossible to produce olefins stably over a long period of time. Note that the reaction temperature here refers to the temperature at the outlet of the catalyst layer.

The upper limit of the reaction pressure is preferably 5 MPa (absolute pressure, hereinafter) or less, more preferably 2 MPa or less, even more preferably 1 MPa or less, even more preferably 0.7 MPa or less, and particularly preferably 0.4 MPa or less. There is no particular restriction on the lower limit of the reaction pressure, but it is usually 0.1 kPa or more, preferably 7 kPa or more, and more preferably 50 kPa or more. When the reaction pressure is below the upper limit, the amount of undesirable by-products such as paraffins and aromatic compounds produced is suppressed, and the yield of lower olefins is increased. On the other hand, when the reaction pressure is above the lower limit, a sufficient reaction rate is obtained.

The weight hourly space velocity of the reaction raw materials is preferably 0.1 hr ^-1 or more, more preferably 0.5 hr ^-1 or more. On the other hand, the weight hourly space velocity is preferably 10 hr ^-1 or less, more preferably 5 hr ^-1 or less. When the weight hourly space velocity is within this range, the yield of light olefins is improved while maintaining a high conversion.

The reactor outlet gas (reactor effluent) is a mixed gas containing lower olefins as the reaction product, by-products, and a diluent. The concentration of lower olefins in the mixed gas is usually 5 to 95 mass %.
Depending on the reaction conditions, the reaction product may contain methanol and/or dimethyl ether as unreacted raw materials. However, it is preferable to carry out the reaction under conditions that result in a high conversion of methanol and/or dimethyl ether. This facilitates separation of the reaction product from the unreacted raw materials. In particular, carrying out the reaction under reaction conditions that result in a 100% conversion of methanol and/or dimethyl ether is preferable, as this eliminates the need for separation of the reaction product from the unreacted raw materials.

The reactor outlet gas, a mixed gas containing the reaction product lower olefins, unreacted raw materials, by-products, and diluent, is introduced into known separation and purification equipment, where each component can be recovered, purified, recycled, or discharged according to its composition.

The present invention will be explained in more detail below using examples, but the scope of the present invention is not limited to the following examples.

Production Example 1
3.63 g of a 1 M aqueous solution of sodium hydroxide, 0.30 g of 1-adamantylamine as an organic structure-directing agent, and 9.62 g of water were mixed, and 0.062 g of aluminum sulfate was added to the mixture and stirred, and then 3.95 g of Cataloid SI-30 (manufactured by JGC Catalysts and Chemicals Co., Ltd.) as a silica source was added and thoroughly stirred. Furthermore, 0.072 g of pulverized DDR-type zeolite was added as seed crystals, and the mixture was stirred to prepare a raw material gel.

The resulting raw gel was placed in an autoclave and heated at 160°C for one day. The product was filtered, washed with water, and then dried at 100°C to obtain an as-made white powder. The X-ray diffraction (XRD) pattern of the product confirmed that the resulting product was DDR-type zeolite. Note that "as-made" refers to the state after drying and before calcination of the organic structure-directing agent.

The resulting zeolite powder was calcined in an air atmosphere at 600°C for 6 hours to obtain sodium-type zeolite powder. The resulting powder was subjected to ion exchange in a 1N ammonium nitrate aqueous solution at 80°C for 1 hour and then filtered. The filtered powder was again subjected to ion exchange in a 1N ammonium nitrate aqueous solution at 80°C for 1 hour, then filtered and dried to obtain ammonium-type zeolite powder. This was then calcined in an air atmosphere at 500°C for 6 hours to obtain proton-type zeolite. This zeolite is designated Sample A.

Production Example 2
3.61 g of a 1 M aqueous sodium hydroxide solution, 0.60 g of 1-adamantylamine, and 9.64 g of water were mixed, and 0.060 g of aluminum sulfate was added to the mixture and stirred. Then, 3.97 g of Cataloid SI-30 (manufactured by JGC Catalysts and Chemicals) was added as a silica source and stirred thoroughly. Furthermore, 0.073 g of pulverized DDR-type zeolite was added as seed crystals and stirred to prepare a raw gel. The obtained raw gel was heated and post-treated in the same manner as in Production Example 1, and a proton-type zeolite powder was obtained.
0.400 g of the obtained proton-type zeolite, 0.280 g of hexadecyltrimethylammonium bromide, 23.98 g of demineralized water, and 1.63 g of 10% aqueous ammonia were mixed and thoroughly stirred. The obtained slurry was charged into an autoclave and heated at 150°C for 7 hours while standing. The product was filtered, washed with water, and then dried at 100°C to obtain a white powder. After drying, the product was calcined in an air atmosphere at 600°C for 6 hours to obtain a zeolite powder. This zeolite was designated Sample B.

Production Example 3
A raw gel was prepared by mixing 8.37 g of a 1 M aqueous sodium hydroxide solution, 0.61 g of 1-adamantylamine, and 23.73 g of water, adding 0.124 g of aluminum sulfate and stirring, and then adding 2.40 g of aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.) as a silica source and stirring thoroughly. The obtained raw gel was heated and post-treated in the same manner as in Production Example 1, except that it was heated at 160°C for 5 days, to obtain a proton-type zeolite powder. This zeolite is designated Sample C.

Production Example 4
3.65 g of a 1 M aqueous sodium hydroxide solution, 0.30 g of 1-adamantylamine, and 9.61 g of water were mixed, and 0.125 g of aluminum sulfate was added thereto and stirred. Then, 3.96 g of Cataloid SI-30 (manufactured by JGC Catalysts and Chemicals) was added as a silica source and stirred thoroughly. Furthermore, 0.072 g of pulverized DDR-type zeolite was added as seed crystals and stirred to prepare a raw gel. The obtained raw gel was heated and post-treated in the same manner as in Production Example 1, to obtain a proton-type zeolite powder. This zeolite is designated Sample D.

Production Example 5
3.62 g of a 1 M aqueous sodium hydroxide solution, 0.30 g of 1-adamantylamine, and 9.61 g of water were mixed, and 0.015 g of aluminum sulfate was added thereto and stirred. Then, 3.95 g of Cataloid SI-30 (manufactured by JGC Catalysts and Chemicals) was added as a silica source and stirred thoroughly. Furthermore, 0.072 g of pulverized DDR-type zeolite was added as seed crystals and stirred to prepare a raw gel. The obtained raw gel was heated and post-treated in the same manner as in Production Example 1, to obtain a proton-type zeolite powder. This zeolite is designated Sample E.

The synthesis conditions for samples A to E are summarized in Table 1.

[Evaluation of Zeolite]
The zeolites of Samples A to E were evaluated as follows.

<X-ray diffraction measurement>
X-ray diffraction (XRD) measurements of the synthesized zeolites were carried out using a "D2PHASER" manufactured by BRUKER. The XRD patterns obtained by the measurements are shown in Figure 1. From Figure 1, it was confirmed that all of the zeolites related to samples A to E had a DDR type structure.

<Elemental analysis>
Elemental analysis was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The zeolites of Samples A to E were measured using an iCAP7600Duo manufactured by Thermo Fisher Scientific. The Si/Al molar ratios of the synthesized zeolites are shown in Table 1.

<Scanning electron microscope>
Scanning electron microscope (SEM) measurements for samples A, D, and E were performed using an "ULTRA55" manufactured by Zeiss. SEM measurements for samples B and C were performed using an "S-4800" manufactured by Hitachi High-Technologies Corporation. Figure 2 shows SEM images of the zeolite catalysts for samples A to E. Note that Figure 2 is an image magnified 10,000 times. Fifty primary particles were randomly extracted from the obtained SEM image, and the major axis of the particles was measured to determine the particle size. (Note that for sample C, the particle size was measured using an image magnified 4,000 times, as the particle size was large.) The arithmetic mean of the determined particle sizes was determined as the average primary particle size. The results are shown in Table 1.

<Nitrogen adsorption/desorption measurement>
Nitrogen adsorption and desorption measurements of the synthesized zeolite were performed using a Microtrac-Bell "Belsorp-mini II." For the measurements, the zeolite was heated and dried at 400°C under vacuum for 2 hours, and then nitrogen adsorption and desorption measurements were performed at liquid nitrogen temperature. Data analysis was performed using Microtrac-Bell's analysis software, BELMaster. The BET specific surface area (A2) was calculated by BET plotting the measurement data for relative pressures (P/P0) of 0.002 to 0.06. The external surface area (A1) and micropore volume (A3) were calculated by t-plotting the data for relative pressures (P/P0) of 0.20 to 0.42. Harkins-Jura was used as the standard isotherm.

<Production of lower olefins>
[Example 1]
Lower olefins were produced using zeolite sample A. A fixed-bed flow reactor was used for the reaction, and a quartz reactor tube with an inner diameter of 6 mm was filled with 100 mg of premixed proton-type zeolite powder and 400 mg of quartz sand. A mixed gas of 50 mol% methanol and 50 mol% nitrogen was supplied to the reactor so that the weight hourly space velocity of methanol was 1 hr ^-1 , and the reaction was carried out at 500°C and 0.1 MPa (absolute pressure). The products were analyzed by gas chromatography every hour from the start of the reaction. Figure 3 shows a graph showing the changes in methanol conversion and selectivity. Table 1 shows the methanol conversion (%), ethylene yield (C-mol%), propylene yield (C-mol%), and butene yield (C-mol%) after 3 hours from the start of the reaction. The methanol conversion rate (%), ethylene yield (C-mol%), propylene yield (C-mol%), and butene yield (C-mol%) are also shown as average values from 2 hours to 4 hours after the reaction.

[Example 2]
Lower olefins were produced in the same manner as in Example 1, except that Sample B was used as the catalyst. Table 1 shows the results of catalyst evaluation.

[Example 3]
Lower olefins were produced in the same manner as in Example 1, except that Sample C was used as the catalyst. Table 1 shows the results of catalyst evaluation.

[Example 4]
Lower olefins were produced in the same manner as in Example 1, except that Sample D was used as the catalyst. Table 1 shows the results of catalyst evaluation.

[Example 5]
Lower olefins were produced in the same manner as in Example 1, except that Sample E was used as the catalyst. Table 1 shows the results of catalyst evaluation.

[Comparative Example 1]
Lower olefins were produced in the same manner as in Example 1, except that the reaction temperature was changed to 450° C. Table 1 shows the results of catalyst evaluation.

[Comparative Example 2]
Lower olefins were produced in the same manner as in Example 2, except that the reaction temperature was changed to 450° C. Table 1 shows the results of catalyst evaluation.

[Comparative Example 3]
Lower olefins were produced in the same manner as in Example 3, except that the reaction temperature was changed to 450° C. Table 1 shows the results of catalyst evaluation.

[Comparative Example 4]
Lower olefins were produced in the same manner as in Example 4, except that the reaction temperature was 450° C. Table 1 shows the catalyst evaluation results.

[Comparative Example 5]
Lower olefins were produced in the same manner as in Example 5, except that the reaction temperature was 450° C. Table 1 shows the results of catalyst evaluation.

The values shown for methanol conversion (%), ethylene yield (C-mol%), propylene yield (C-mol%), and butene yield (C-mol%) indicate the values three hours after the start of the reaction, and the "average" values are the average of the values measured every hour after two to four hours have elapsed.

As shown in Table 1, when comparing Examples 1 to 5, in which the reaction temperature was 500°C, with Comparative Examples 1 to 5, in which the reaction temperature was 450°C, it can be seen that for each zeolite, Examples 1 to 5 exhibited a higher ethylene yield. Furthermore, the DDR-type zeolites of Examples 1, 2, 4, and 5, which had an average primary particle size of 2000 nm or less, exhibited an ethylene yield exceeding 55%, a particularly high ethylene yield. Furthermore, the DDR-type zeolite of Example 2, which was subjected to alkali treatment, exhibited the highest ethylene yield.

Claims (4)

A method for producing lower olefins, comprising a step of contacting a raw material containing methanol and/or dimethyl ether with a DDR type zeolite,
A method for producing lower olefins, characterized in that the reaction temperature is 490°C or higher and 600°C or lower , and the average primary particle size of the DDR-type zeolite is 2000 nm or less . 2. The method for producing lower olefins according to claim 1, wherein the DDR type zeolite is a DDR type zeolite treated under alkaline conditions in the presence of a surfactant. 3. The method for producing lower olefins according to claim 1 or 2, wherein the DDR zeolite contains silicon (Si) and aluminum (Al) as constituent elements, and the molar ratio of silicon (Si) to aluminum (Al) (Si/Al) is 25 or more and 500 or less. The method for producing lower olefins according to any one of claims 1 to 3, wherein the ratio (A2/A1) of the BET specific surface area (A2) to the external surface area (A1) of the DDR zeolite is 20 or less.