Method for producing lower olefins

Abstract

To provide a method for producing a lower olefin capable of achieving a high yield of ethylene.SOLUTION: There is provided a method for producing a lower olefin which comprises a step of bringing a DDR zeolite into contact with a raw material, wherein the DDR zeolite is a DDR zeolite subjected to silylation treatment.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process for producing lower olefins using a catalyst containing a DDR type zeolite. [Background technology]

[0002] Conventional methods for producing lower olefins such as ethylene, propylene, and butene have been steam cracking of naphtha and fluid catalytic cracking of vacuum gas oil, but in recent years, metathesis reactions using ethylene and 2-butene as raw materials and the MTO (methanol to olefins) process using methanol and / or dimethyl ether as raw materials have become well known.

[0003] For example, Non-Patent Documents 1 to 3 disclose that by using methanol as a raw material and a zeolite having 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 to produce ethylene and propylene in high yields.

[0004] Patent Document 1 reports that silylation treatment of CHA-type zeolite to reduce the amount of acid on the outer surface improves the selectivity of propylene in the production of propylene from ethylene as a raw material. However, silylation treatment of DDR-type zeolite has not been carried out, and there is no mention of its effect on the production of lower olefins from methanol and / or dimethyl ether. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2010 / 128644 [Non-patent literature]

[0006] [Non-Patent Document 1] Catal.Sci.Technol.,6,2663-2678(2016) [Non-patent document 2] ACS Catal.,7,4033-4046(2017) [Non-patent document 3] ACS Catal.,10,3009-3017(2020) Summary of the Invention [Problem to be solved by the invention]

[0007] Non-Patent Document 1 reports the ethylene yield when the Si / Al2 ratio (calculated from NH3-TPD) of a DDR-type zeolite having a particle size of approximately 2.5 μm is varied from 120 to 415. The results show that the ethylene yield increases as the Si / Al2 ratio increases, with the maximum ethylene yield reaching approximately 43%. Furthermore, the ethylene yield when the particle size is varied is reported for a sample with a Si / Al2 ratio of 315, and the ethylene yield tends to be higher in samples with smaller particle sizes, with the maximum ethylene yield reaching approximately 46%. Furthermore, Non-Patent Document 2 lists the reaction evaluation results of DDR-type zeolite with Si / Al=50 and a particle size of about 500-1000 nm, and the maximum ethylene yield is about 48%. Furthermore, Non-Patent Document 3 reports the results of a performance comparison of DDR-type zeolites with particle sizes of several μm and Si / Al ratios of 22 to 172. The comparison is made in the methanol conversion range of 45-55%, and the ethylene selectivity reaches its maximum at Si / Al=22, showing a value of about 37%. However, while there is a demand for DDR-type zeolites to further improve ethylene yield, the use of additional DDR-type zeolites to increase ethylene yield has not been investigated.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a process for producing lower olefins that can achieve a high ethylene yield. [Means for solving the problem]

[0009] The present inventors have conducted studies to solve the above-mentioned problems, and have found that, for example, in a process for producing light olefins comprising a step of contacting a raw material containing methanol and / or dimethyl ether with a DDR zeolite catalyst, light olefins can be produced with a high ethylene yield by subjecting the DDR zeolite to a silylation treatment, thereby completing the present invention.

[0010] The present invention includes the following aspects. [1] A method for producing lower olefins, comprising a step of contacting a raw material with a DDR-type zeolite, wherein the DDR-type zeolite is a DDR-type zeolite that has been subjected to a silylation treatment. [2] The method for producing lower olefins according to the above [1], wherein the raw material contains methanol and / or dimethyl ether. [3] The method for producing lower olefins according to the above [1] or [2], wherein the average primary particle size of the DDR-type zeolite is 2000 nm or less. [4] The method for producing lower olefins according to any one of [1] to [3] above, wherein 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. [5] The reaction temperature is 200°C or higher and 750°C or lower, the reaction pressure is 0.1kPa or higher and 2MPa or lower, and the weight space velocity is 0.1hr -1 More than 10 hours -1 The method for producing a lower olefin according to any one of the above [1] to [4], wherein the method is as follows: [Effects of the Invention]

[0011] According to the present invention, there is provided a method for producing lower olefins that can achieve a high yield of ethylene. In this specification, lower olefins refer to ethylene, propylene, and butene. In other words, lower olefins are olefins having 2 to 4 carbon atoms. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the transition of methanol conversion and selectivity in the production of lower olefins using the DDR-type zeolites of Example 1 and Comparative Example 1 as catalysts. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various modifications within the scope of its gist.

[0014] [DDR type zeolite] DDR-type zeolites are zeolites with a two-dimensional pore structure in which two eight-membered ring structures intersect as their structural units. According to the IZA database, the pore size is 3.6 x 4.4 Å, which is a narrower pore structure than 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.

[0015] The composition of the DDR 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 thereof include one or more elements selected from the group consisting of boron (B), titanium (Ti), vanadium (V), iron (Fe), zinc (Zn), gallium (Ga), germanium (Ge), zirconium (Zr), and tin (Sn).

[0016] Specifically, 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 become acid sites and act as active sites for catalytic reactions.

[0017] 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.

[0018] The contents of Si, Al, Ga, B, and the like in the DDR zeolite of the present embodiment are generally values ​​measured for the produced DDR zeolite by inductively coupled plasma atomic emission spectroscopy (ICP-AES) or the like, and are not the ratios of the raw materials charged.

[0019] The ion exchange sites of the DDR zeolite of this embodiment are not particularly limited, and may be H-type or may be exchanged with metal ions, specifically, alkali metal ions, alkaline earth metal ions, cerium, tungsten, manganese, iron, etc.

[0020] [Ratio of BET specific surface area (A2) to external surface area (A1)] The outer surface area (A1) of the DDR zeolite of this embodiment is usually 5 m 2 / g or more, preferably 10m 2 / g or more, more preferably 15m 2 / g or more, more preferably 20m 2 / g or more, usually 500m 2 / g or less, preferably 300m 2 / g or less, more preferably 200m 2 / g or less. The BET specific surface area (A2) of the DDR zeolite of this embodiment is not particularly limited and is usually 150 m 2 / g or more, preferably 200m 2 / g or more, more preferably 250m 2 / g or more, more preferably 300m 2 / g or more, usually 800m 2 / g or less, preferably 700m 2 / g or less, more preferably 600m 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 reaction products 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 this embodiment is not particularly limited, but 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, using, for example, a Microtrac-Bell Belsorp-mini II. Data analysis can be performed using Microtrac-Bell's BELMaster analysis software. The BET specific surface area (A2) can be calculated by plotting the measured data for relative pressures (P / P0) of 0.002 to 0.06. The external surface area (A1) and micropore volume (A3) can be calculated by plotting the data for relative pressures (P / P0) of 0.20 to 0.42. The Harkins-Jura isotherm is used as the standard.

[0021] The average primary particle size of the DDR zeolite of this embodiment is not particularly limited, but 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 the DDR zeolite can be determined using a scanning electron microscope (SEM).

[0022] As mentioned 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 a zeolite catalyst is acquired, 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, primary particles do not have to exist as individual particles, and may form secondary particles by aggregation or the like. Even if secondary particles are formed, primary particles on the surfaces of the secondary particles can be identified in the SEM image. Note that, although cracks-like structures may be seen on the surface of DDR-type zeolites, these are not considered to be grain boundaries. The "average primary particle diameter" is measured as follows: 50 primary particles are randomly selected from an SEM image of the zeolite catalyst, and the major axis (the length of the longest straight line drawn between one end of a primary particle and 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 taken 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 is taken as the "average primary particle diameter."

[0023] [Method of manufacturing DDR-type zeolite] Hereinafter, a method for producing the DDR zeolite of this embodiment will be described.

[0024] DDR zeolites 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 maintaining it at 100 to 220°C in a pressurized, heated vessel such as an autoclave. Seed crystals may be added as needed during crystallization, and the addition of seed crystals is preferred because it facilitates crystallization of the DDR zeolite. It is preferable to use DDR zeolite as the seed crystals. It is preferable to use pulverized zeolite as the seed crystals. The use of pulverized seed crystals makes it easier to obtain DDR zeolites with small particle sizes.

[0025] After the raw gel is crystallized, the crystallized raw gel is filtered and washed, and then the solid content is dried at 100 to 200°C and subsequently calcined at 400 to 900°C, thereby obtaining zeolite powder.

[0026] The silica source used to prepare the raw gel can 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, and the like can be used. As the boron source, one or more of boric acid, sodium borate, boron oxide, etc. can be used.

[0027] There are no particular restrictions on the molar ratio (Si / Al) of silicon (Si) to aluminum (Al) in the DDR zeolite used as seed crystals, but it is preferably in the range of 25 to 10000. In addition, it is preferable to use about 1 to 20 mass% of the seed crystals relative to the silica source to be added.

[0028] The amount of metal contained in DDR-type zeolite can be adjusted 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 by steaming, acid treatment, etc.

[0029] The process for producing lower olefins of the present invention is characterized by the silylation treatment of the DDR zeolite obtained as described above. By subjecting the zeolite to silylation treatment, the acid sites on the outer surface of the zeolite are reduced, and the effective pore size near the outer surface is narrowed, which is presumably responsible for improving the ethylene yield. The silylation method is not particularly limited, but can be liquid-phase silylation using alkoxysilanes or gas-phase silylation using chlorosilanes, for example.

[0030] The silylating agent is not particularly limited, but examples of alkoxysilanes include quaternary alkoxysilanes such as tetramethoxysilane and tetraethoxysilane, tertiary alkoxysilanes such as trimethoxymethylsilane and triethoxymethylsilane, secondary alkoxysilanes such as dimethoxydimethylsilane and diethoxydimethylsilane, and primary alkoxysilanes such as methoxytrimethylsilane and ethoxytrimethylsilane. As the chlorosilane, tetrachlorosilane, dimethyldichlorosilane, trimethylchlorosilane, etc. can be used. Among these, tetraethoxysilane is preferred as an alkoxysilane, and tetrachlorosilane is preferred as a chlorosilane.

[0031] In the liquid phase silylation method, a solvent can be used as appropriate. The solvent to be used is not particularly limited, but organic solvents such as benzene, toluene, and hexamethyldisiloxane, or water can be used. In the liquid-phase silylation method, the molar ratio of the silylating agent to the zeolite in the treatment solution is not particularly limited, but is usually preferably 5 or less, more preferably 3 or less. It is also usually 0.005 or more, preferably 0.1 or more. When this value is equal to or less than the upper limit, adequate silylation can be achieved, and pores will not be blocked. When the value is equal to or greater than the lower limit, sufficient silylation can be achieved, and the acid sites on the outer surface can be adequately covered.

[0032] The silylation temperature can be adjusted appropriately depending on the type of silylating agent and solvent, and is not limited, but is usually 140°C or lower, preferably 120°C or lower. It is also usually 20°C or higher, preferably 40°C or higher. When the temperature is below the upper limit, the silylating agent does not evaporate, and silylation can be carried out efficiently. On the other hand, when the temperature is above the lower limit, a sufficient reaction rate of silylation can be obtained. The treatment time is not particularly limited as long as silylation occurs, but is usually 0.5 hours or more, preferably 2 hours or more, and usually 48 hours or less, preferably 24 hours or less. If the treatment time is equal to or greater than the lower limit, silylation occurs sufficiently, and the acid sites are sufficiently covered. On the other hand, if the treatment time is equal to or less than the upper limit, silylation can be carried out efficiently.

[0033] The vapor-phase silylation treatment is usually carried out so that the mass of silica vapor-deposited relative to the zeolite is 20% by mass or less, and more preferably 18% by mass or less. There is no particular lower limit, but usually 0.1% by mass or more is preferred, and more preferably 1% by mass or more. When the amount is below the upper limit, moderate silylation can be achieved and pores will not be blocked. On the other hand, when the amount is above the lower limit, sufficient silylation can be achieved, and the acid sites on the outer surface can be covered. The temperature for the vapor-phase silylation can be adjusted appropriately depending on the silylating agent, and is not limited to any particular value, but is usually 20° C. or higher, preferably 100° C. or higher. The temperature is usually 500° C. or lower, preferably 400° C. or lower. If the temperature is below the upper limit, there is no risk of decomposition of the silylating agent or collapse of the zeolite framework, while if the temperature is above the lower limit, the silylation reaction proceeds sufficiently.

[0034] [catalyst] The DDR zeolite of this embodiment is useful as a catalyst used in a reaction for producing lower olefins.

[0035] The DDR zeolite of this embodiment may be used in the reaction as a catalyst in the present invention as is, or may be used as a mixture with other substances inert to the reaction, such as compounds containing alkaline earth metals or silicon. The DDR zeolite may also be used in the reaction after granulation or molding using a binder. Examples of the substances and 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.

[0036] [Production method of lower olefins] In the method for producing lower olefins using a catalyst containing the DDR zeolite of this embodiment, raw materials include, but are not limited to, methanol and dimethyl ether, and can be appropriately selected depending on the type of target olefin.

[0037] The process for producing lower olefins using the above catalyst will be described below by taking as an example the case where the raw material is methanol and / or dimethyl ether.

[0038] A method for producing lower olefins according to 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-described DDR zeolite.

[0039] 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 steelmaking industry, those obtained by the reforming reaction of plant-derived alcohols, those obtained by fermentation, those obtained from organic materials 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.

[0040] The reaction method 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.

[0041] 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.

[0042] 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.

[0043] 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. The diluent may also be mixed with the reaction raw materials before being introduced into the reactor, or may be supplied to the reactor separately from the reaction raw materials.

[0044] The lower limit of the reaction temperature is usually about 200°C or higher, preferably 250°C or higher, more preferably 300°C or higher, and particularly preferably 400°C or higher, and the upper limit of the reaction temperature is usually 750°C or lower, preferably 700°C or lower, and more preferably 600°C or lower. If the reaction temperature is too low, the reaction rate will be low, a large amount of unreacted raw material will tend to remain, and the yield of lower olefins will also decrease. On the other hand, if the reaction temperature is too high, it will be difficult to achieve stable catalyst activity, and the yield of lower olefins will decrease significantly. Here, the reaction temperature refers to the temperature at the outlet of the catalyst layer.

[0045] The upper limit of the reaction pressure is usually preferably 5 MPa (absolute pressure, hereinafter the same) 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. The lower limit of the reaction pressure is not particularly limited, but 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 above 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 above lower limit, a sufficient reaction rate is obtained.

[0046] The weight space velocity of the reactant is 0.1 hr -1 It is preferable that the time is 0.5 hours or more. -1 On the other hand, it is more preferable that the weight hourly space velocity is 10 hr or more. -1 It is preferable that it is less than 5 hours. -1 When the weight hourly space velocity is within this range, the yield of lower olefins is improved.

[0047] 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 to separate the reaction product from the unreacted raw materials. By-products include olefins having 5 or more carbon atoms, paraffins, aromatic compounds and water.

[0048] The reactor outlet gas is a mixed gas containing lower olefins (reaction products), unreacted raw materials, by-products, and diluents. It is then introduced into a known separation and purification facility, where each component can be recovered, purified, recycled, or discharged according to its composition. [Example]

[0049] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the following examples.

[0050] [Example 1] 3.63 g of 1 M sodium hydroxide solution, 0.30 g of 1-adamantylamine (organic structure directing agent), and 9.61 g of water were mixed, and 0.062 g of aluminum sulfate was added and stirred, followed by 3.96 g of Cataloid SI-30 (manufactured by JGC Catalysts and Chemicals) as a silica source and thorough stirring. 0.072 g of crushed DDR-type zeolite was then added as seed crystals and stirred to prepare a raw gel.

[0051] 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 a DDR-type zeolite. The term "as-made" refers to the state after drying and before calcination of the organic structure-directing agent.

[0052] The obtained zeolite powder was calcined in an air atmosphere at 600°C for 6 hours to obtain a sodium-type zeolite powder. The obtained 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 an ammonium-type zeolite powder. This was then calcined in an air atmosphere at 500°C for 6 hours to obtain a proton-type zeolite powder (hereinafter referred to as zeolite powder (A)). To 0.25 g of the obtained proton-type zeolite, 1.25 mL of tetraethoxysilane and 5.0 mL of toluene were added, and silylation treatment was carried out by heating and stirring at 100 °C for 2 hours. Then, filtration and drying were performed to obtain the zeolite powder of Example 1.

[0053] [Comparative Example 1] The above zeolite powder (A) was used as the zeolite powder of Comparative Example 1. The synthesis conditions in Example 1 and Comparative Example 1 were summarized in Table 1.

[0054] [Evaluation of Zeolite] The following evaluations were performed on the zeolites according to Example 1 and Comparative Example 1.

[0055] [X-ray Diffraction Measurement] The X-ray diffraction (XRD) measurement of the synthesized zeolite was carried out using "D2 PHASER" manufactured by BRUKER.

[0056] [Elemental Analysis] Elemental analysis was performed by inductively coupled plasma atomic emission spectrometry (ICP-AES). "iCAP7600 Duo" manufactured by Thermo Fisher Scientific was used for the measurement of the synthesized zeolite. The Si / Al molar ratio of the synthesized zeolite is shown in Table 1.

[0057] [Scanning Electron Microscope] The scanning electron microscope (SEM) measurement of the synthesized zeolite was carried out using "S-4800" manufactured by Hitachi High-Technologies Corporation. 50 primary particles were randomly extracted from the obtained SEM image, and the major axis of the particles was measured as the particle size. The arithmetic mean of the obtained particle sizes was taken as the average primary particle size. The results are shown in Table 1.

[0058] [[ID=三十六]][Production of Lower Olefins] The zeolites obtained in Example 1 and Comparative Example 1 were used to produce lower olefins. A fixed-bed flow reactor was used for the reaction, and a quartz reaction 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 introduced at a weight hourly space velocity of 1 hr -1 The mixture was fed to the reactor so that the reaction temperature was 450°C and 0.1 MPa (absolute pressure). The products were analyzed by gas chromatography every hour from the start of the reaction. Figure 1 shows a graph illustrating 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%) three hours after the start of the reaction. Table 1 also shows the average values ​​for methanol conversion (%), ethylene yield (C-mol%), propylene yield (C-mol%), and butene yield (C-mol%) from two to four hours after the start of the reaction.

[0059] [Table 1]

[0060] As shown in Table 1, it can be seen that the zeolite of Example 1 exhibits a high ethylene yield.

Claims

1. A method for producing lower olefins, comprising a step of contacting a raw material with DDR type zeolite, wherein the DDR type zeolite is silylation-treated DDR type zeolite, the average primary particle diameter of the DDR type zeolite is 2000 nm or less, and the raw material contains methanol and / or dimethyl ether.

2. 2. The method for producing lower olefins according to claim 1, 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.

3. The reaction temperature is 200°C or higher and 750°C or lower, the reaction pressure is 0.1 kPa or higher and 2 MPa or lower, and the weight hourly space velocity is 0.1 hr －１ Over 10 hours －１ 3. The method for producing lower olefins according to claim 1 or 2, wherein the following is true:

4. 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.

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