Zeolite catalyst

Abstract

One aspect of the present invention relates to an MFI-type zeolite catalyst containing chromium that contains hexavalent chromium.

Description

Zeolite catalyst

[0001] The present invention relates to a zeolite catalyst.

[0002] In recent years, carbon dioxide materialization has been attracting attention as an alternative production method to fossil fuels. Specifically, research is being conducted into technologies for producing chemical raw materials by reacting carbon dioxide with hydrogen, etc. For example, it is known that carbon dioxide can be converted into benzene, methanol, ethylene, xylene, etc.

[0003] Known methods for producing aromatic compounds such as xylene include those that use crystalline aluminosilicate or crystalline gallosilicate as a catalyst to produce xylene from alcohols, olefins, or paraffins. However, in these production methods using catalysts, xylene is obtained as a mixture of para-, meta-, and ortho-isomers, and special separation equipment is required to separate paraxylene from these isomers. Therefore, there is a need for a production method that can selectively produce paraxylene from among xylenes.

[0004] To date, a method for producing aromatic hydrocarbons has been reported as a technology capable of obtaining an aromatic hydrocarbon mixture containing a high ratio of para-xylene among xylene isomers, in which aromatic hydrocarbons are synthesized from at least one compound selected from alcohols, olefins, and paraffins, and the reaction is carried out in the presence of a catalyst containing a compound in which a silicate selected from crystalline aluminosilicates and crystalline gallosilicates is modified with silica (Patent Document 1).

[0005] Among the catalysts described in Patent Document 1, MFI zeolite catalysts, in particular, are believed to be capable of producing an aromatic hydrocarbon mixture containing a high ratio of para-xylene among xylene isomers. However, it has been found that when an MFI zeolite catalyst is used to synthesize para-xylene, coke by-products accumulate on the catalyst surface and inside in a relatively short period of time, causing a decrease in catalyst performance. As such, MFI zeolite catalysts, which have a relatively short catalyst life, require regeneration treatment.

[0006] However, the temperature for the regeneration treatment of the MFI zeolite catalyst is higher than the temperature during paraxylene synthesis using the MFI zeolite catalyst, and the temperature must be raised to regenerate the catalyst. Therefore, each time paraxylene synthesis and catalyst regeneration are repeated, the temperature must be raised to a high temperature, resulting in a problem of time and energy losses.

[0007] Therefore, a main object of the present invention is to provide an MFI zeolite catalyst capable of regenerating catalytic performance at a lower temperature than conventional catalysts.

[0008] JP 2010-208948 A

[0009] One aspect of the present invention relates to a chromium-containing MFI-type zeolite catalyst, including hexavalent chromium.

[0010] Fig. 1 is a graph showing the regeneration rate of a zeolite catalyst composed of only a core in an example. Fig. 2 is a graph showing the regeneration rate of a core-shell type zeolite catalyst in an example.

[0011] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to these.

[0012] [Zeolite Catalyst] The zeolite catalyst of the present embodiment is an MFI zeolite catalyst (ZSM-5 zeolite catalyst), which is an aluminosilicate zeolite, and contains chromium including hexavalent chromium. With this configuration, it is possible to provide an MFI zeolite catalyst that can regenerate catalytic performance at a lower temperature than conventional ones.

[0013] It is known that the temperature required for the synthesis of aromatic compounds such as paraxylene using an MFI zeolite catalyst is approximately 400°C. When aromatic compound synthesis continues using a zeolite catalyst, coke, a by-product, accumulates on the surface and inside of the catalyst, causing a decline in catalytic performance. To regenerate the catalytic performance, it is necessary to stop the supply of raw materials for aromatic compound synthesis, introduce air, and raise the temperature to approximately 500°C to burn the coke.

[0014] However, the zeolite catalyst of the present embodiment contains chromium, including hexavalent chromium, which suppresses coke deposition on the catalyst surface and inside, and allows the catalyst to be regenerated at a lower temperature than conventional catalysts, i.e., at a temperature approximately the same as that used for aromatic compound synthesis. This reduces the time and energy loss required for temperature increase and decrease each time aromatic compound synthesis using the zeolite catalyst and catalyst regeneration treatment are repeated, and makes catalyst regeneration easy and inexpensive.

[0015] The zeolite catalyst of the present embodiment is not particularly limited as long as it is an MFI zeolite catalyst containing chromium, including hexavalent chromium. The chromium contained in the MFI zeolite catalyst is not particularly limited as long as it contains hexavalent chromium, and may contain divalent chromium, trivalent chromium, or the like in addition to hexavalent chromium.

[0016] The chromium content of the zeolite catalyst of this embodiment is preferably 0.1 wt % or more and 10.0 wt % or less relative to the total amount of the zeolite catalyst. Furthermore, the amount of chromium contained in the zeolite catalyst as hexavalent chromium varies depending on the amount of Si—OH groups present on the surface and inside the zeolite catalyst. The Si—OH groups present on the surface of the MFI zeolite catalyst used in this embodiment are relatively low compared to other zeolite catalysts. Therefore, when the chromium content is approximately 1.0 to 3.0 wt %, the amount of chromium contained in the zeolite catalyst as hexavalent chromium is thought to saturate. Therefore, when the chromium content exceeds 3.0 wt %, the amount of hexavalent chromium contained in the zeolite catalyst does not increase any further, and the proportion of chromium other than hexavalent chromium, such as trivalent chromium, increases.

[0017] In a preferred embodiment, the zeolite catalyst of the present embodiment further contains zinc. The zinc-supported MFI zeolite catalyst is a catalyst that can selectively synthesize paraxylene, which is particularly useful among aromatic compounds.

[0018] The zeolite catalyst of this embodiment may also be a zeolite catalyst with a core-shell structure. Specifically, it may have an MFI zeolite catalyst as the core and a silica coating as the shell. This has the advantage of increasing the yield in the synthesis of paraxylene using the zeolite catalyst of this embodiment. The silica coating is preferably a crystalline silica coating, and in particular, a porous silicalite coating is preferred from the viewpoint of the diffusibility of reactants (molecules) and products (molecules).

[0019] In the case of a zeolite catalyst having a core-shell structure, the chromium may be contained in the MFI zeolite catalyst core or in the silica coating shell. In addition, in the case where the zeolite catalyst contains zinc, it is preferable that the zinc be contained in the MFI zeolite catalyst core.

[0020] From the viewpoint of para-xylene selectivity, the zeolite catalyst of this embodiment is preferably a zinc-added zeolite catalyst having a silica coating (hereinafter also referred to simply as a "silica-coated zeolite catalyst"). The silica coating is preferably a thin film, which is thought to increase the zeolite catalytic activity and improve the yield in the production of aromatic compounds using the catalyst.

[0021] Specifically, the thickness of the silica coating in the silica (silicalite)-coated zeolite catalyst of this embodiment is preferably 500 nm or less. By having a silica coating with a thickness of 500 nm or less, the zeolite catalyst can improve not only high isomer selectivity but also yield. There is no need to particularly limit the lower limit of the thickness of the silica coating, but from the viewpoint of maintaining high isomer selectivity, it is usually 1 nm or more. The thickness of the silica coating is more preferably 5 nm or more and 50 nm or less.

[0022] Furthermore, in the silica-coated zeolite catalyst of this embodiment, the amount of the silica coating is preferably 1 part by mass or more and 100 parts by mass or less relative to 100 parts by mass of the zinc-added zeolite core catalyst. If the amount of the silica coating exceeds 100 parts by mass, the yield when producing an aromatic compound using the zeolite catalyst may be insufficient. In a more preferred embodiment, the amount of the silica coating is more preferably 3 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the zinc-added zeolite core catalyst. The amount of the silica coating can be determined from the rate of weight increase before and after the formation of the silica coating.

[0023] [Uses of Zeolite Catalyst] The zeolite catalyst of this embodiment can be suitably used for producing aromatic compounds. Examples of aromatic compounds include aromatic hydrocarbons having a substituent such as benzene, toluene, xylene, and ethylbenzene. The zeolite catalyst of this embodiment is particularly suitable for producing paraxylene. Paraxylene is a starting material for terephthalic acid, which is a raw material for polyethylene terephthalate. The catalyst of this embodiment can produce paraxylene with high selectivity and high yield, and can also be easily regenerated, making it extremely useful for industrial applications.

[0024] There are no particular limitations on the method for producing paraxylene using the zeolite catalyst of the present embodiment. For example, paraxylene can be produced by reacting raw materials such as methanol, lower olefins, alkanes, and / or aromatic hydrocarbons with a methylating agent in the presence of the zeolite catalyst of the present embodiment.

[0025] Examples of the aromatic hydrocarbon raw material include benzene, alkylbenzene, etc. Examples of the methylating agent include methanol, dimethyl ether, dimethyl carbonate, and methane.

[0026] [Method for producing zeolite catalyst] A method for producing the zeolite catalyst of this embodiment will be described. In this embodiment, MFI zeolite is used as the zeolite catalyst. As the MFI zeolite, commercially available zeolite can be used, but it can also be synthesized by a known method.

[0027] There are no particular limitations on the method for adding chromium containing hexavalent chromium to the MFI zeolite catalyst. For example, a chromium source and MFI zeolite are mixed, and the hexavalent chromium can be added to the zeolite by, for example, evaporating to dryness.

[0028] The chromium source is not particularly limited, but examples thereof include chromium nitrate, chromium chloride, and hydrates thereof.

[0029] Specifically, the evaporation to dryness method is a method in which a catalyst is impregnated in an aqueous solution containing a metal source, dried, and then calcined.

[0030] As the MFI zeolite catalyst, as described above, commercially available catalysts or catalysts obtained by known production methods can be used as they are, but it is preferable to use a silica-coated zeolite catalyst obtained by the following method.

[0031] Specifically, a method for producing a zeolite catalyst having a silica coating is carried out, which includes at least mixing a zinc source with an MFI zeolite to obtain a zinc-added zeolite, preparing a mixed solution containing a structure-directing agent containing tetraethylammonium, a silica source, and water, and adding the mixed solution to the surface of the zinc-added zeolite to perform hydrothermal synthesis.

[0032] By using such a production method, a zeolite catalyst having a thin silica coating can be obtained.

[0033] In the production method, first, a zinc source and MFI zeolite are mixed to obtain zinc-added zeolite.

[0034] The zinc source that can be used in this embodiment is not particularly limited as long as it can add zinc ions to the zeolite, and examples thereof include zinc nitrate, zinc acetate, zinc chloride, zinc sulfate, etc. Among these, zinc nitrate, zinc chloride, etc. are preferably used from the viewpoint of solubility in aqueous solution. Hydrates of the above-mentioned zinc sources can also be used.

[0035] The mixing ratio of the zinc source and the MFI zeolite is not particularly limited, but for example, they are preferably mixed so that the weight ratio of MFI zeolite to zinc source is about 100:1 to 1:10, and more preferably so that the weight ratio of MFI zeolite to zinc source is about 20:1 to 1:2.

[0036] When mixing, for example, the MFI zeolite is added to the aqueous solution containing the zinc source, and the mixture is stirred at a temperature of 20 to 100° C. for about 1 to 24 hours.

[0037] The resulting mixture is then filtered, washed, dried, and then calcined to obtain zinc-doped zeolite. There are no particular limitations on the methods for filtering, washing, and drying, and any known method can be used. After drying, the mixture is calcined at approximately 400 to 600°C for 1 to 24 hours.

[0038] Next, a mixed liquid containing a structure directing agent containing tetraethylammonium, a silica source, and water is prepared.

[0039] The structure-directing agent used in this embodiment contains at least tetraethylammonium. By using a structure-directing agent containing tetraethylammonium, the crystal growth rate when forming a silica coating on the catalyst surface can be suppressed, making it possible to coat the catalyst with a more uniform and thinner silica coating than with conventional methods. As a result, it is believed that the zeolite catalytic activity is increased, and the yield in synthesis and production using this catalyst is improved.

[0040] The structure-directing agent of this embodiment may further contain a structure-directing agent other than the tetraethylammonium, and may also contain, for example, tetrapropylammonium, triethylamine, ethylenediamine, or the like.

[0041] The silica source used in this embodiment is not particularly limited as long as it can coat the zinc-added zeolite, and can be appropriately selected depending on the composition of the desired silica coating. Specific examples include tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, colloidal silica, and fumed silica.

[0042] The silica coating is preferably a crystalline silica coating, particularly a porous silicalite coating, and therefore tetraethyl orthosilicate, colloidal silica, fumed silica, etc. can be suitably used as the silica source.

[0043] The mixed solution containing the structure-directing agent containing tetraethylammonium, the silica source, and water is used as a raw material solution for forming a silica coating on zinc-added zeolite. The solvent contained in the mixed solution may be water alone, but in order to increase the solubility of the silica source, the mixed solution may also contain a water-soluble organic solvent such as ethanol, propanol, or glycerin in addition to water.

[0044] The amounts of the tetraethylammonium and the silica source in the mixed solution are not particularly limited, and may be appropriately adjusted within a range that allows a silica coating to be formed on the zinc-added zeolite.

[0045] The amount of tetraethylammonium in the mixed solution is preferably adjusted so that the molar ratio of silica source to tetraethylammonium is about 100:1 to 1:1, and more preferably, the molar ratio of silica source to tetraethylammonium is about 10:1 to 2:1.

[0046] The amount of the silica source in the mixed solution is preferably adjusted so that the weight ratio of the zinc-added zeolite to the silica source is about 20:1 to 1:5, and more preferably, the amount of the zinc-added zeolite to the silica source is about 5:1 to 1:2.

[0047] Next, the mixed liquid containing the structure-directing agent containing tetraethylammonium, the silica source, and water is added to the surface of the zinc-added zeolite. The method of addition is not particularly limited, and the zinc-added zeolite may be immersed in the mixed liquid containing the silica source and the structure-directing agent, or the mixed liquid may be applied to the surface of the zinc-added zeolite.

[0048] Thereafter, hydrothermal synthesis is carried out. In this embodiment, the means for hydrothermal synthesis is not particularly limited, and for example, a rotary autoclave, a stirring autoclave, a static (unstirred) autoclave, or the like can be used. Specifically, the zinc-added zeolite can be immersed in the mixed solution and placed in the autoclave to carry out hydrothermal synthesis, or the zinc-added zeolite, the surface of which has been coated with the mixed solution, can be placed in hot water in the autoclave to carry out hydrothermal synthesis.

[0049] The temperature of the hydrothermal synthesis is preferably about 100 to 200° C., more preferably 150 to 190° C. The reaction time of the hydrothermal synthesis is preferably about 1 to 200 hours, more preferably about 4 to 48 hours.

[0050] After hydrothermal synthesis, the resulting product is washed and dried, and then calcined to obtain a zeolite catalyst having a silica coating. There are no particular limitations on the washing and drying methods, and any known method can be used as appropriate. After drying, the silica coating is calcined at approximately 400 to 600°C for 1 to 24 hours.

[0051] The above steps can produce the zeolite catalyst of the present embodiment having a silica coating. The obtained silica-coated zeolite catalyst can be used as is after adding chromium containing hexavalent chromium by the above-mentioned method, or the particle size can be adjusted by a known granulation method or the like, as necessary.

[0052] As described above, this specification discloses various aspects of the technology, but the main technologies among them are summarized below.

[0053] The zeolite catalyst according to the first aspect of the present invention is an MFI zeolite catalyst containing chromium, including hexavalent chromium. With this configuration, it is possible to provide a zeolite catalyst whose catalytic performance can be regenerated at a lower temperature than conventional zeolite catalysts.

[0054] The zeolite catalyst according to the second embodiment is the zeolite catalyst according to the first embodiment, further containing zinc.

[0055] The zeolite catalyst according to a third embodiment is the zeolite catalyst according to the first or second embodiment, wherein the chromium content is 0.1% by weight or more and 10.0% by weight or less relative to the total amount of the zeolite catalyst.

[0056] The zeolite catalyst in a fourth embodiment is the zeolite catalyst of any one of the first to third embodiments, which has a silica coating.

[0057] The zeolite catalyst in a fifth embodiment is the zeolite catalyst in the fourth embodiment, wherein the silica coating is a silicalite coating.

[0058] The zeolite catalyst in a sixth embodiment is the zeolite catalyst of any one of the first to fifth embodiments, which is a catalyst for producing paraxylene.

[0059] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0060] <Production of Zeolite Catalyst> (Example 1) Preparation of Zinc-Doped Zeolite 1 g of zeolite "HSZ-840HOA" (ZSM-5 (MFI type zeolite), particle size 3 μm) manufactured by Tosoh Corporation as a core catalyst, 2 g of zinc nitrate hexahydrate manufactured by Nacalai Tesque Inc. as a zinc source, and 66.5 g of distilled water were mixed and stirred at 80°C overnight. Thereafter, the mixed liquid was suction filtered and washed with 1 L of distilled water. Then, it was dried overnight in a dryer at 90°C until the liquid disappeared. The obtained dried product was calcined at 550°C for 5 hours to obtain zinc-doped zeolite. At that time, the temperature was increased at a rate of 5°C / min and decreased by natural cooling.

[0061] Chromium addition: Chromium nitrate nonahydrate was added as a chromium source to the zinc-doped zeolite obtained above so that the weight of chromium was 0.1 wt% relative to the total amount of zinc-doped zeolite, and zinc-doped zeolite containing chromium was obtained by evaporation to dryness. Specifically, chromium nitrate nonahydrate and water were first mixed to achieve the above ratio to prepare an aqueous chromium nitrate solution. 0.8 ml of the prepared aqueous solution was added dropwise to the zinc-doped zeolite. The resulting mixture was dried at 90°C for 24 hours and then calcined at 550°C for 5 hours in an air atmosphere to obtain a chromium-containing zinc-doped zeolite.

[0062] The obtained chromium-containing zinc-added zeolite was subjected to ultraviolet-visible absorption measurement, and it was confirmed that the added chromium contained hexavalent chromium.

[0063] Examples 2 to 4 Chromium-containing zinc-doped zeolite catalysts were obtained in the same manner as in Example 1, except that the amount of the chromium source added was changed to 1.0, 3.0, or 10.0 wt % relative to the total amount of the zinc-doped zeolite. It was confirmed that the chromium added to the zeolite catalysts of Examples 2 to 4 in the same manner as in Example 1 contained hexavalent chromium.

[0064] Comparative Example 1 The zinc-added zeolite obtained in Example 1 was used as a zeolite catalyst of Comparative Example 1 (without chromium addition) without adding chromium.

[0065] (Example 5) A silica coating was formed on the chromium-containing, zinc-added zeolite obtained in Example 2 by the following method. Formation of Silica Coating 0.693 g of tetraethyl orthosilicate (TEOS) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. as the silica source, 0.28 g of a 35 wt % aqueous solution of tetraethylammonium hydroxide (TEAOH) manufactured by SIGMA-ALDRICH as the structure-directing agent, and 5.28 g of distilled water were placed in a Teflon (registered trademark) inner tube and stirred at room temperature for 1 hour to obtain a mixed solution containing the silica source, the structure-directing agent, and water.

[0066] 0.3 g of the zinc-added zeolite obtained above was added to the resulting mixed solution, and hydrothermal synthesis was carried out for 24 hours using a rotary autoclave (manufactured by HIRO COMPANY, "Hydrothermal Synthesis Reaction Apparatus (apparatus name)") at a temperature of 180°C and 10 rpm.

[0067] After that, the supernatant was discarded, water was added, and the mixture was centrifuged for 10 minutes. This procedure was repeated three times for washing, and then the mixture was dried in a dryer at 90°C overnight until the liquid was completely removed.

[0068] The dried product was calcined at 550° C. for 5 hours to obtain a zeolite catalyst (core-shell catalyst) having a silica coating. The temperature was increased at a rate of 5° C. / min and decreased by natural cooling.

[0069] Example 6 A silica coating was formed in the same manner as in Example 5 on the zinc-added zeolite obtained in Example 1 before adding chromium.

[0070] Thereafter, chromium was added to the silica coating in the same manner as in the "chromium addition" described in Example 1. At this time, chromium was added so that the weight of chromium was 1.0 wt % relative to the total weight of the silica-coated zeolite catalyst.

[0071] Comparative Example 2 A silica coating was formed on the zinc-added zeolite obtained in Example 1, without adding chromium, in the same manner as in Example 5. The resulting zeolite catalyst having a silica coating and no chromium added was used as the catalyst of Comparative Example 2.

[0072] <Evaluation Method> (Catalyst Regeneration Rate) Synthesis of Paraxylene A fixed-bed reactor was packed with 0.05 g of each of the zeolite catalysts of Examples 1 to 6 and Comparative Examples 1 and 2, and methanol gas was supplied thereto at atmospheric pressure and 400° C. to carry out a synthesis reaction for 3 hours.

[0073] Thereafter, the amount of coke deposited on the catalyst due to the synthesis reaction was measured by thermogravimetry (TG-DTA) to evaluate the regeneration rate of the catalyst. Specifically, the supply of methanol gas to the reactor was stopped, and air was supplied instead to combust the coke, thereby regenerating the catalyst. The weight loss of the coke during regeneration treatment at temperatures from 300°C to 700°C was set as 100, and the temperature at which 50% of that weight loss was observed was set as the "50% regeneration temperature," and the regeneration rate of the catalyst for each example and comparative example was evaluated.

[0074] The measurement conditions for thermogravimetry (TG-DTA) in this test were as follows: Atmospheric gas: air Gas flow rate: 0 mL / min Sample amount: 10 mg Heating rate: 5°C / min Hold temperature: 800°C

[0075] The results are shown in Table 1 (core-only catalyst) and Table 2 (core-shell catalyst). The results in Tables 1 and 2 are also shown graphically in Figures 1 and 2.

[0076]

[0077]

[0078] (Discussion) From the results of Tables 1 and 2 and Figures 1 and 2, it was confirmed that the catalysts of the examples containing chromium, including hexavalent chromium, all had a 50% lower regeneration temperature than the comparative example catalysts not containing chromium. In other words, it was found that the MFI zeolite catalyst of the present embodiment can be regenerated at a lower temperature than conventional catalysts.

[0079] Furthermore, the results of Comparative Example 2 show that the core-shell zeolite catalyst has a higher 50% regeneration temperature than the zeolite catalyst consisting of only a core without a shell (Comparative Example 1). However, the 50% regeneration temperatures of the zeolite catalysts of Examples 5 and 6, which contain chromium including hexavalent chromium, were both lower than the 50% regeneration temperature of Comparative Example 2. Therefore, it was confirmed that the MFI zeolite catalyst can be regenerated at low temperatures whether the chromium is contained in the core or the shell.

[0080] This application is based on Japanese Patent Application No. 2024-042025 filed on March 18, 2024, the contents of which are incorporated herein by reference.

[0081] In order to express the present invention, the present invention has been properly and sufficiently described above through embodiments with reference to specific examples, etc. However, it should be recognized that those skilled in the art can easily change and / or improve the above-described embodiments. Therefore, unless changes or improvements made by those skilled in the art deviate from the scope of the claims set forth in the claims, such changes or improvements are construed as being encompassed within the scope of the claims.

Claims

1. MFI-type zeolite catalyst containing chromium, including hexavalent chromium.

2. The zeolite catalyst according to claim 1, which contains zinc.

3. The zeolite catalyst according to claim 1, wherein the chromium content is 0.1% by weight or more and 10.0% by weight or less based on the total amount of the zeolite catalyst.

4. The zeolite catalyst of claim 1 having a silica coating.

5. The zeolite catalyst of claim 4, wherein the silica coating is a silicalite coating.

6. The zeolite catalyst according to any one of claims 1 to 5, which is a catalyst for producing paraxylene.

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