Process 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 containing methanol and / or dimethyl ether, wherein the reaction temperature is 490°C or mor and 600°C or less.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. [Prior art documents] [Non-patent literature]

[0004] [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]

[0005] Non-Patent Document 1 reports the ethylene yield when the reaction temperature of a DDR zeolite with a particle size of 2.4 μm and a Si / Al2 ratio (calculated from NH3-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 approximately 500-1000 nm is varied from 350°C to 450°C, and the maximum ethylene yield at a reaction temperature of 450°C is approximately 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 at the same time, by-products such as methane, which has the smallest carbon number, increase. Therefore, as mentioned above, the reaction temperature has not been raised above 475°C.

[0006] 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]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems and have found that a method for producing lower olefins, which includes a step of contacting a raw material containing methanol and / or dimethyl ether with a DDR zeolite, can achieve a high ethylene yield by maintaining the reaction temperature at a certain temperature or higher, and have thus completed the present invention. In this specification, lower olefins refer to ethylene, propylene, and butene. In other words, lower olefins are olefins having 2 to 4 carbon atoms.

[0008] 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, characterized in that the reaction temperature is 490°C or higher and 600°C or lower. [2] The method for producing lower olefins according to [1] above, wherein the DDR-type zeolite has an average primary particle size of 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 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. [Effects of the Invention]

[0009] According to the present invention, a method for producing lower olefins that can achieve a high yield of ethylene can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the results of powder X-ray diffraction of DDR-type zeolites (as-made) according to samples A to E. [Figure 2] 1 shows scanning electron microscope (SEM) images of DDR-type zeolites (as-made type) according to samples A to E. [Figure 3] 1 is a graph showing the transition of methanol conversion and selectivity in the production of lower olefins using the DDR-type zeolites according to Examples 1 to 5 and Comparative Examples 1 to 5 as catalysts. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] [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.

[0013] 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).

[0014] 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.

[0015] 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.

[0016] The contents of Si, Al, Ga, B, and the like in the DDR zeolite of the present embodiment are usually 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.

[0017] 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.

[0018] [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.

[0019] 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).

[0020] 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."

[0021] [Method of manufacturing DDR-type zeolite] Hereinafter, a method for producing the DDR zeolite of this embodiment will be described.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] In this embodiment, the DDR zeolite prepared by hydrothermal synthesis may be subjected to an alkali treatment in the presence of a surfactant, which 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.

[0028] 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 it is sufficient that the pH is about 9 to 12, for example. The alkali treatment can be carried out by contacting the DDR zeolite with an alkali, or by stirring the DDR zeolite 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 duration of the alkali treatment is also not particularly limited, and the DDR 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.

[0029] [catalyst] The DDR zeolite of this embodiment is useful as a catalyst used in a reaction for producing lower olefins.

[0030] 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.

[0031] [Production method of lower olefins] In the method for producing lower olefins using a catalyst containing a DDR zeolite of this embodiment, methanol and dimethyl ether are used as raw materials. Alternatively, a mixture of methanol and dimethyl ether may be used.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 for a long period of time. Here, the reaction temperature refers to the temperature at the outlet of the catalyst layer.

[0039] 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.

[0040] 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 light olefins is improved while maintaining a high conversion rate.

[0041] 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.

[0042] 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]

[0043] 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.

[0044] Manufacturing Example 1 3.63 g of 1 M sodium hydroxide solution, 0.30 g of 1-adamantylamine (organic structure directing agent), and 9.62 g of water were mixed, and 0.062 g of aluminum sulfate was added and stirred, followed by the addition of 3.95 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.

[0045] 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.

[0046] The obtained zeolite powder was calcined in an air atmosphere at 600°C for 6 hours to obtain 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 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.

[0047] Manufacturing Example 2 3.61 g of 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 and stirred. 3.97 g of Cataloid SI-30 (manufactured by JGC Catalysts and Chemicals) was then added as a silica source and stirred thoroughly. 0.073 g of crushed DDR-type zeolite was then added as seed crystals and stirred to prepare a raw gel. The resulting raw gel was heated and post-treated in the same manner as in Production Example 1, yielding a proton-type zeolite powder. 0.400 g of the resulting 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 resulting slurry was placed in 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.

[0048] Manufacturing Example 3 A raw gel was prepared by mixing 8.37 g of a 1 M aqueous solution of sodium hydroxide, 0.61 g of 1-adamantylamine, and 23.73 g of water, adding 0.124 g of aluminum sulfate and stirring, followed by 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.

[0049] Manufacturing Example 4 3.65 g of 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 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. 0.072 g of crushed 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.

[0050] Production Example 5 3.62 g of 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 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. 0.072 g of crushed 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.

[0051] The synthesis conditions for Samples A to E are summarized in Table 1.

[0052] [Evaluation of Zeolite] The zeolites of Samples A to E were evaluated as follows.

[0053] <X-ray Diffraction Measurement> The X-ray diffraction (XRD) measurement of the synthesized zeolite was performed using a "D2 PHASER" manufactured by BRUKER. The XRD pattern obtained by the measurement is shown in Fig. 1. From Fig. 1, it was confirmed that the zeolites related to Samples A to E all have a DDR-type structure.

[0054] <Elemental Analysis> Elemental analysis was performed by inductively coupled plasma atomic emission spectrometry (ICP-AES). For the measurement of the zeolites of Samples A to E, an "iCAP 7600 Duo" manufactured by Thermo Fisher Scientific was used. The Si / Al molar ratios of the synthesized zeolites are shown in Table 1.

[0055] <Scanning Electron Microscope> The scanning electron microscope (SEM) measurement for Samples A, D, and E was performed using an "ULTRA 55" manufactured by Zeiss. Also, the SEM measurement for Samples B and C was performed using an "S-4800" manufactured by Hitachi High-Technologies. Fig. 2 shows the SEM images of the zeolite catalysts related to Samples A to E. Note that Fig. 2 is an image at 10,000 times magnification. 50 primary particles were randomly extracted from the obtained SEM images, and the major axis of the particles was measured and taken as the particle size. (For Sample C, since the particle size was large, an image at 4,000 times magnification was used to measure 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.

[0056] <Nitrogen Adsorption-Desorption Measurement> Nitrogen adsorption and desorption measurements of the synthesized zeolites were performed using a Microtrac-Bell "Belsorp-mini II." The zeolites were heated and dried under vacuum at 400°C for 2 hours, and then nitrogen adsorption and desorption measurements were performed at liquid nitrogen temperature. Data analysis was performed using Microtrac-Bell's BELMaster software. The BET specific surface area (A2) was 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) were calculated by plotting the data for relative pressures (P / P0) of 0.20 to 0.42. The Harkins-Jura isotherm was used as the standard.

[0057] <Production of lower olefins> [Example 1] Using the zeolite sample A, lower olefins were produced. A fixed-bed flow reactor was used for the reaction. 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 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%) three hours after the start of the reaction. The average values for the 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 are also shown.

[0058] [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.

[0059] [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.

[0060] [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.

[0061] [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 catalyst evaluation results.

[0062] [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 catalyst evaluation results.

[0063] Comparative Example 2 Lower olefins were produced in the same manner as in Example 2, except that the reaction temperature was 450° C. Table 1 shows the catalyst evaluation results.

[0064] Comparative Example 3 Lower olefins were produced in the same manner as in Example 3, except that the reaction temperature was 450° C. Table 1 shows the catalyst evaluation results.

[0065] 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.

[0066] Comparative Example 5 Lower olefins were produced in the same manner as in Example 5, except that the reaction temperature was changed to 450° C. Table 1 shows the catalyst evaluation results.

[0067] [Table 1]

[0068] The methanol conversion rate (%), 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 averages are the averages of the values taken every hour after two to four hours have elapsed.

[0069] As shown in Table 1, when Examples 1 to 5, in which the reaction temperature was 500°C, are compared with Comparative Examples 1 to 5, in which the reaction temperature was 450°C, it is found that for each zeolite, Examples 1 to 5 exhibited a higher ethylene yield. Furthermore, the DDR zeolites of Examples 1, 2, 4, and 5, each having an average primary particle size of 2000 nm or less, exhibited an ethylene yield exceeding 55%, a particularly high ethylene yield. Furthermore, the DDR zeolite of Example 2, which was subjected to an alkali treatment, exhibited the highest ethylene yield.

Claims

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, 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. 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. 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.

4. A method for producing lower olefins described in 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 type zeolite is 20 or less.

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