Method for regenerating zeolite catalyst

Abstract

[Problem] To provide a method for regenerating a reaction catalyst including a zeolite catalyst, wherein catalytic activity, including conversion rate and selection rate, is sufficiently restored. [Solution] A method for regenerating a zeolite catalyst used in a reaction step for obtaining a reaction product including an olefin or an aromatic compound by bringing a raw material gas mixture including carbon dioxide or carbon monoxide, or a mixed gas of both and hydrogen into contact with a reaction catalyst including the zeolite catalyst, the method characterized in that the zeolite catalyst is brought into contact with a gas containing hydrogen.

Description

Method for regenerating zeolite catalysts

[0001] The present invention relates to a method for regenerating zeolite catalysts, and more particularly to a method for regenerating zeolite catalysts used in a reaction process to obtain reaction products containing olefins and aromatic compounds from a raw material gas mixture containing carbon dioxide, carbon monoxide, or both, and hydrogen.

[0002] Lower olefins such as ethylene and propylene are important raw materials for various chemical products, and among aromatic compounds, paraxylene, in particular, which is useful as a raw material for polyester fibers and polyethylene terephthalate (PET) resin, has seen a remarkable increase in demand in recent years. Conventionally, olefins and aromatic compounds have been produced in petrochemical complexes by the reforming reaction of naphtha, but this method requires fossil (petroleum) resources and emits large amounts of carbon dioxide during the manufacturing process.

[0003] As a method for producing olefins and aromatic compounds without using fossil resources, a method using a mixed gas containing carbon dioxide or carbon monoxide and hydrogen as a raw material has already been proposed (Non-Patent Document 1, Patent Document 1). This method is based on the principle of converting the above mixed gas into methanol using a metal oxide catalyst, and then converting methanol into olefins and aromatic compounds using a zeolite catalyst. The use of a mixture of metal oxide catalyst and zeolite catalyst is also disclosed in the prior art documents mentioned above.

[0004] Patent Document 2 discloses that in a reaction to produce lower olefins from raw materials containing methanol and / or dimethyl ether, the light-boiling hydrocarbon components in a zeolite catalyst with increased hydrocarbon content can be effectively stripped by treating it with a hydrogen-containing gas, and furthermore, catalytic activity can be significantly restored by coke removal. In particular, a technology for the synthesis of lower olefins is disclosed that can restore catalytic activity without causing permanent degradation of the zeolite catalyst due to water vapor or the like.

[0005] Japanese Patent Publication No. 2019-205969 Japanese Patent Publication No. 2018-183773

[0006] Peipei Zhang et al., Chemical Science, The Royal Society of Chemistry, October 2017, Volume 8, Pages 7941-7946

[0007] The methods described in Patent Document 1 and Non-Patent Document 1 are commendable in that they enable the synthesis of olefins and aromatic compounds in a single reaction step from a mixed gas of carbon monoxide or carbon dioxide and hydrogen. However, the zeolite catalyst contained in the mixed catalyst deteriorates (deactivates) over time due to the deposition of coke (carbon) as it is used, making periodic regeneration of the catalyst, including the zeolite catalyst, essential. Conventionally, this regeneration of the catalyst after use involved removing the carbon deposited on the surface by oxidation using an oxygen-containing gas such as air. However, it has been confirmed that while the conversion rate of carbon monoxide and carbon dioxide is restored by regeneration of the catalyst with an oxygen-containing gas, the aromatic selectivity (the proportion of aromatic compounds in the reaction product) and the liquid selectivity (the proportion of components that are liquid at room temperature and pressure in the reaction product) are not sufficiently restored. This is thought to be because the water generated during regeneration with oxygen causes dealuminization of the zeolite catalyst, thereby structurally degrading the zeolite catalyst.

[0008] The present invention provides a method for regenerating a zeolite catalyst used in a reaction step to obtain a reaction product containing an olefin or an aromatic compound by contacting the zeolite catalyst with a raw material gas mixture containing carbon dioxide, carbon monoxide, or a mixed gas of both and hydrogen, characterized in that the zeolite catalyst is contacted with a gas containing hydrogen, thereby solving the above-mentioned problems.

[0009] According to the present invention, since no water is generated when regenerating a reaction catalyst containing a zeolite catalyst, degradation due to dealuminization of the zeolite catalyst does not occur, and catalytic activity, including conversion rate and selectivity, is fully restored.

[0010] This is a schematic diagram illustrating an example of implementing the regeneration method according to the present invention.

[0011] The present invention relates to a method for regenerating a zeolite catalyst used in a reaction step for obtaining a reaction product containing an olefin or an aromatic compound by bringing a raw material gas mixture containing a mixed gas of carbon dioxide, carbon monoxide, or both, and hydrogen into contact with a reaction catalyst containing a zeolite catalyst. The above reaction step will be described in more detail as follows. Carbon dioxide or carbon monoxide and hydrogen in the raw material gas mixture react as shown in the following formula (1) or (2) in the presence of a metal oxide catalyst to produce methanol or dimethyl ether (methanol synthesis reaction). 2CO ２ + 6H ２ ⇒ 2CH ３ OH + 2H ２ O (⇔ CH ３ OCH ３ + 3H ２ O) (1) 2CO + 4H ２ ⇒ 2CH ３ OH (⇔ CH ３ OCH ３ + H ２ O) (2) Then, the methanol and dimethyl ether produced in the above methanol synthesis reaction produce lower olefins such as ethylene and propylene and aromatic hydrocarbons such as BTX in the presence of a zeolite catalyst (olefin / aromatic synthesis reaction). Although the mechanism of this reaction is not yet fully understood, a model is assumed in which ethylene is produced from dimethyl ether generated by dehydration of methanol, and three ethylene molecules bond to form a benzene ring.

[0012] The reaction catalyst used in the above reaction step has the advantage of shifting the equilibrium of the methanol synthesis reaction towards methanol production and increasing the reaction rate by allowing the methanol synthesis reaction and the subsequent olefin / aromatic synthesis reaction to proceed continuously or in parallel in the same reactor. For this reason, it is preferable to use a mixed catalyst that includes a metal oxide catalyst that converts the above raw material gas mixture (mixed gas) into methanol and a zeolite catalyst that converts the produced methanol into olefins or aromatic compounds. However, the zeolite catalyst that is the target of regeneration by the method of the present invention is not necessarily limited to constituting such a mixed catalyst. For example, the above reaction step is a two-stage process consisting of a preliminary step that converts the mixed gas into methanol and a subsequent step that converts methanol into olefins or aromatic compounds, and the zeolite catalyst that is the target of the method of the present invention may be a catalyst used alone in the subsequent step.

[0013] The zeolite catalyst described above does not transform into other substances during the reaction process, and by devising the composition of the mixed catalyst, it is possible to extend the catalyst life to withstand hundreds of hours of continuous operation. However, in any case, continuous use in the reaction will cause the zeolite catalyst to deteriorate and become inactive. The main cause of this deterioration is thought to be that when the olefin / aromatic synthesis reaction proceeds on the surface of the zeolite catalyst, carbonaceous substances such as coke adhere to the catalyst surface and cover the catalyst's active sites (acid sites). For this reason, the zeolite catalyst needs to be regenerated (activated) periodically. While it is common to remove carbon adhering to the catalyst surface by oxidation (combustion) with oxygen, in this invention, it is removed by reduction with hydrogen. In oxidation regeneration with oxygen, water is produced along with carbon dioxide when carbonaceous substances are oxidized, but in reduction regeneration with hydrogen, lower hydrocarbons are produced instead of carbon dioxide and water, thus preventing deterioration of the zeolite catalyst caused by dealuminization by water. Furthermore, as will be discussed later, since hydrogen is also a gas contained in the raw material gas mixture, there is the advantage that it is not necessary to temporarily replace the space filled with catalyst particles with an inert gas when switching between the reaction process and the regeneration process.

[0014] To carry out the above reaction step, a raw material gas mixture containing carbon dioxide, carbon monoxide, or a mixture of both with hydrogen is sequentially or simultaneously brought into contact with a metal oxide catalyst and a zeolite catalyst contained in a reactor. At this time, a preferred method is to place the reaction catalyst consisting of the aforementioned metal oxide catalyst and zeolite catalyst as a fixed bed in the reactor and to flow the raw material gas mixture supplied to the reactor while keeping it in contact with the reaction catalyst. In this way, lower olefins such as ethylene and propylene can be produced from the raw material gas mixture via a methanol synthesis reaction, and further reaction products containing useful aromatic compounds such as paraxylene can be produced via the lower olefins, or gasoline can be produced directly from methanol. Therefore, the zeolite catalyst regenerated by the regeneration method of the present invention can be used in the manufacture of olefin products, aromatic compound products, or liquid fuel products.

[0015] Since one of the objectives of the present invention is to contribute to reducing the concentration of carbon dioxide in the atmosphere, it is preferable to use carbon dioxide separated from exhaust gas from equipment that burns fuels that generate carbon dioxide, such as thermal power plants and various heating furnaces, carbon dioxide separated in ammonia production equipment, ethylene glycol production equipment and hydrogen production equipment, carbon dioxide separated from product gases of coal, biomass and waste gasification furnaces, carbon dioxide separated from blast furnaces in steel mills, or carbon dioxide separated from air in the atmosphere as the carbon dioxide that constitutes the raw material gas mixture in the above reaction process.

[0016] Furthermore, it is preferable to use hydrogen produced by electrolyzing water using renewable energy such as solar power, wind power, hydropower, geothermal energy, biomass, or electricity generated by nuclear power as the hydrogen used in the regeneration method and reaction steps of the present invention.

[0017] In particular, it is preferable to use synthesis gas produced by a gasification furnace, off-gas discharged from a blast furnace at a steel mill, off-gas separated in a hydrogen production device, synthesis gas produced by co-electrolysis of water and carbon dioxide, or synthesis gas produced by a reverse shift reaction of hydrogen and carbon dioxide as the raw material gas mixture for the above reaction step.

[0018] The type of reactor used in the above reaction process is not particularly limited as long as it allows for gas-solid contact between the raw material gas mixture (gas) and the reaction catalyst (solid) and can maintain the desired temperature and pressure (fixed bed, moving bed, fluidized bed, etc.). However, a fixed bed reactor filled with catalyst particles is preferred because it offers good contact efficiency, is less prone to channeling, and causes less mechanical damage to the catalyst particles. The catalyst packing amount and gas flow rate can be set as appropriate, but in the case of a fixed bed reactor, the space velocity (SV) can be expressed on an empty tower basis or on a catalyst mass basis. In this specification, using the catalyst mass basis, the catalyst packing amount and gas flow rate can be set so that the space velocity (SV) is, for example, about 500 to 50,000 mL / g-cat / h, preferably about 1,000 to 20,000 mL / g-cat / h.

[0019] To regenerate the catalyst used in the above reaction process, particularly the zeolite catalyst, an appropriate method can be used depending on the type of gas-solid contact means used in the reaction process to bring it into contact with a regeneration fluid (in this invention, a gas containing hydrogen). For example, when using a fixed-bed reactor, the flow of the raw material gas mixture can be stopped while the reactor is filled with catalyst particles, and the gas flowing through the reactor can be switched to a hydrogen-containing gas for regeneration. At that time, it is also necessary to switch the operating conditions (temperature, pressure, gas flow rate, etc.) in the reaction process to the operating conditions in the regeneration process. Therefore, if one reactor is considered, its operation will alternate between the reaction process and the regeneration process. However, if multiple reactors are arranged in parallel and configured so that some reactors are performing the regeneration process while others are performing the reaction process, the reaction process can be carried out continuously as a whole. In contrast, when using a moving bed or fluidized bed reactor, catalyst particles are intermittently or continuously removed from the reactor and transferred to a separate regeneration container for regeneration. Therefore, if there is only one set of reactor and regeneration container, the reaction process can be carried out continuously (however, if catalyst particles are transferred intermittently in a moving bed reactor, the reaction process will be stopped during the transfer).

[0020] In methods for producing olefins and aromatic compounds using a mixed gas containing carbon dioxide or carbon monoxide and hydrogen as a raw material, metal oxide catalysts for methanol synthesis and zeolite catalysts for olefin / aromatic synthesis are used, as described above. Examples of metal oxide catalysts include ZnZrO ｘ Catalysts, AlZnZrO ｘ Catalyst, CrZnZrO ｘ Catalysts are one example. However, since the last catalyst mentioned contains harmful chromium, the first two, which do not contain chromium, are preferable from a safety standpoint.

[0021] Zeolites are a general term for crystalline aluminosilicates, and have a skeletal structure consisting of Al, Si, and O (SiO ４ and AlO ４ Zeolites have a tetrahedral structure and contain cations as counterions between their lattice. Zeolites have pores formed by their skeletal structure, and since only molecules smaller than their diameter can enter these pores, they function as molecular sieves. Furthermore, proton-type (H-type) zeolites have acid sites and are therefore used as catalysts. There are various types of zeolite catalysts, and the pore size and cations they possess differ depending on the type, so it is necessary to select an appropriate one depending on the reactants in the reaction process. The zeolite catalyst that can be regenerated by the method of the present invention is not particularly limited as long as it is a zeolite catalyst that can be used in a reaction process to obtain a reaction product containing an olefin or aromatic compound. For example, zeolite catalysts such as H-ZSM-5, SAPO-34, beta-type, ferrielite-type, and mordenite-type zeolites can be used, but the present invention is particularly preferred for the regeneration of H-ZSM-5.

[0022] A known method for regenerating zeolite catalysts involves supplying oxygen-containing gas to the reactor and burning off carbonaceous substances such as coke that have precipitated on the zeolite catalyst. However, as mentioned above, it has been found that while regenerating zeolite catalysts using oxygen restores the conversion rate in the reaction process, it reduces the selectivity for the intended target components (aromatic compounds, etc.). This is thought to be because water is generated during the regeneration process using oxygen, causing dealuminization and degradation of the zeolite catalyst.

[0023] A key feature of this invention is the use of a hydrogen-containing gas instead of oxygen in the zeolite catalyst regeneration process. Otherwise, the process can be the same as in conventional regeneration processes. When the reaction catalyst includes both a metal oxide catalyst and a zeolite catalyst, the zeolite catalyst may be separated and regenerated, or it may be regenerated in a mixed state. In the hydrogen-containing gas, the hydrogen concentration is preferably 80 mol% or higher, and more preferably 90 mol% or higher. Examples of components other than hydrogen in the hydrogen-containing gas include methane.

[0024] In this invention, by using hydrogen to regenerate the zeolite catalyst, water is not generated during the regeneration process, and lower paraffins are mainly produced. Because water is not generated, dealuminization does not occur, and the degradation of the zeolite catalyst is suppressed. Furthermore, in the regeneration process using hydrogen, regeneration progresses more from the outer surface of the catalyst to the inside of the pores, so the selectivity of the intended target component is improved compared to before the regeneration process.

[0025] By combining the regeneration step according to the present invention with a reaction step in which a raw material gas mixture containing carbon dioxide, carbon monoxide, or both, and hydrogen is brought into contact with a reaction catalyst containing a zeolite catalyst, a preferred process for obtaining a reaction product containing an olefin or aromatic compound can be constructed. For example, the process can be constructed such that the reaction step is carried out by circulating the raw material gas mixture through a reactor having a fixed bed filled with a reaction catalyst, and then the regeneration step is carried out by circulating a gas containing hydrogen through the reactor after the reaction step has been completed, thereby performing the regeneration step according to the present invention.

[0026] In the process described above, the temperature inside the reactor during the reaction step is preferably 300°C to 400°C, and more preferably 320°C to 400°C. Furthermore, the temperature inside the reactor during the regeneration step is preferably 400°C to 600°C, and more preferably 450°C to 550°C.

[0027] Furthermore, in the process described above, the pressure can be arbitrarily set depending on the target product, but it is preferable that the pressure P1 in the reactor during the reaction step and the pressure P2 in the reactor during the regeneration step satisfy the relationship 0.5 ≤ P2 / P1 ≤ 1.5. It is even more preferable that the relationship 0.8 ≤ P2 / P1 ≤ 1.2 is satisfied. The pressure in the reactor during the reaction step is not particularly limited, but for example it can be 4.0 MPaG or more and 10.0 MPaG or less, and it is preferable that it be 5.0 MPaG or more and 8.0 MPaG or less. When the pressure in the reactor during the reaction step is 5.0 to 8.0 MPaG, the pressure in the reactor during the regeneration step can be 4.0 to 9.6 MPaG.

[0028] The regeneration method of the present invention allows the regeneration process to be carried out at high pressure, and the regeneration process can be performed at a pressure close to that of the reaction process. Therefore, by simply switching the gas introduced into the reactor and making the necessary adjustments to the temperature and pressure inside the reactor, the reaction process and the regeneration process can be smoothly switched in a short time using the same reactor, and energy loss can be reduced. Furthermore, as shown in Figure 1, by arranging multiple reactors in parallel and carrying out the reaction process in at least one reactor (for example, the first fixed-bed reactor 1), it is possible to carry out continuous operation as a whole by carrying out the regeneration process in another at least one reactor (for example, the second fixed-bed reactor 2) while the reaction process is being carried out in at least one other reactor. In this case, by introducing at least a portion of the exhaust gas discharged from the reactor carrying out the regeneration process into the inlet side of the reactor carrying out the reaction process, the reaction process and the regeneration process can be efficiently carried out while switching between multiple reactors. Here, hydrogen may be separated from the exhaust gas discharged from the reactor carrying out the regeneration process by membrane separation or pressure swing adsorption, and the separated hydrogen may be introduced into the inlet side of the reactor carrying out the reaction process. By recycling the gas produced in the regeneration process back into the reaction process, hydrogen can be utilized more effectively (hydrogen loss is reduced).

[0029] Furthermore, as mentioned above, if the reaction process is a two-stage process consisting of a preliminary step that converts the mixed gas to methanol and a subsequent step that converts methanol to olefins or aromatic compounds, and the zeolite catalyst is used alone in the subsequent step, it is also possible to prepare a reactor with the metal oxide catalyst and the zeolite catalyst separated into two stages, and in the regeneration step, hydrogen gas is brought into contact only with the zeolite catalyst.

[0030] Furthermore, according to the regeneration method of the present invention, since a gas containing hydrogen is used in both the reaction step and the regeneration step, it is possible to avoid the need for replacement with a third gas when switching between the reaction step and the regeneration step. Here, the third gas is a gas that is inert in both the reaction step and the regeneration step, such as steam or nitrogen. If, for example, oxygen is used in the regeneration step, there is a concern that residual hydrogen from the reaction step may cause heat generation or explosion due to the combustion reaction between the hydrogen and oxygen, so replacement with a third gas is necessary. However, since the regeneration method of the present invention does not use oxygen, replacement is not required. This reduces the cost of nitrogen or steam required for replacement and the time spent on replacement, allowing more time to be allocated to the reaction step. For example, when performing the regeneration step, only hydrogen gas can be introduced into the reactor, and when performing the reaction step, carbon monoxide gas or carbon dioxide gas, or both, can be added.

[0031] By performing the regeneration method described above, the olefin selectivity and aromatic selectivity that have decreased due to the reaction process can be restored to the olefin selectivity and aromatic selectivity at the start of the reaction. To confirm whether the regeneration process is being carried out as intended, it can be evaluated by the recovery rate of aromatic selectivity before and after regeneration. This recovery rate can be calculated by dividing the aromatic selectivity after the regeneration process by the aromatic selectivity before the regeneration process. From the perspective of comparing the recovery rate with that of the conventional oxygen gas regeneration method, for example, 0.90 or higher is one guideline. On the other hand, from the perspective of observing the degree of improvement before and after regeneration, it is preferable for the recovery rate to exceed 1.00, and it is even more preferable if it is 1.08 or higher, 1.12 or higher, and even 1.15 or higher. There is no particular upper limit specified, but it is usually 1.25 or lower.

[0032] <Example 1> A raw material gas composed of carbon dioxide and hydrogen (volume flow rate of hydrogen:volume flow rate of carbon dioxide = 2.6:1) was introduced into a reactor provided with a fixed bed filled with a reaction catalyst composed of a metal oxide catalyst and a zeolite catalyst H-ZSM-5, and the reaction step was carried out under the conditions of a pressure of 6 MPaG and an SV of 2000 mL / g-cat / h. Next, hydrogen gas was introduced into the reactor, and a regeneration step was performed for 120 hours at a pressure of 6 MPaG and a catalyst layer temperature of 500°C. After that, the reaction step was carried out again. In the regeneration step, hydrogen gas was appropriately supplemented so that the hydrogen concentration in the reactor did not fall below 90 mol%. For the reaction products before and after the regeneration step, after removing water, the products were injected into gas chromatography (manufactured by Shimadzu Corporation: GC-8A) and analyzed by a flame ionization detector (FID: Flame Ionization Detector). The proportion of aromatic compounds in the reaction product was measured as the aromatic selectivity (%) based on carbon moles. In addition, a value obtained by dividing the aromatic selectivity after the regeneration step by the aromatic selectivity before the regeneration step was calculated as the recovery rate of aromatic selectivity before and after regeneration.

[0033] <Example 2> The reaction step and the regeneration step were carried out in the same manner as in Example 1, except that in the regeneration step, the temperature of the catalyst layer was switched to 520°C after 72 hours had elapsed, and the regeneration step was further carried out for 24 hours.

[0034] <Comparative Example 1> The reaction step and the regeneration step were carried out in the same manner as in Example 1, except that oxygen gas was introduced instead of hydrogen gas in the regeneration step.

[0035] Table 1 shows the recovery rate of aromatic selectivity before and after the regeneration step (aromatic selectivity after regeneration ÷ aromatic selectivity before regeneration) in each of the examples and the comparative example. As shown in Table 1, compared with Comparative Example 1 in which the regeneration step according to the present invention was not carried out, Examples 1 and 2 in which the regeneration step according to the present invention was carried out had a higher recovery rate of aromatic selectivity before and after regeneration. It was confirmed that the regeneration method according to the present invention prevents deterioration of the reaction catalyst and improves the aromatic selectivity.

[0036]

[0037] 1 First fixed-bed reactor 2 Second fixed-bed reactor

Claims

1. A method for regenerating a zeolite catalyst used in a reaction step to obtain a reaction product containing an olefin or an aromatic compound by contacting the zeolite catalyst with a raw material gas mixture containing carbon dioxide or carbon monoxide or a mixed gas of both and hydrogen, characterized in that the zeolite catalyst is contacted with a gas containing hydrogen.

2. A method for producing the reaction product, comprising: carrying out the reaction step by circulating the raw material gas mixture through a reactor having a fixed bed filled with the reaction catalyst; and carrying out the regeneration step by circulating the hydrogen-containing gas through the reactor after the reaction step has been completed using the regeneration method described in claim 1.

3. A method for regenerating a zeolite catalyst according to claim 1, wherein the aromatic selectivity that was reduced in the reaction step is restored or improved by contacting the zeolite catalyst with a gas containing hydrogen.

4. The method according to claim 2, wherein the temperature inside the reactor in the regeneration step is 400 to 600°C.

5. The method according to claim 2, wherein the pressure P1 in the reactor during the reaction step and the pressure P2 in the reactor during the regeneration step satisfy the relationship 0.5 ≤ P2 / P1 ≤ 1.

5.

6. The method according to claim 2, wherein a plurality of reactors are arranged in parallel, and when the regeneration process is being carried out in at least one reactor, the reaction process is carried out in at least one other reactor.

7. The method according to claim 6, wherein at least a portion of the exhaust gas discharged from the reactor carrying out the regeneration process is introduced into the inlet side of the reactor carrying out the reaction process.

8. The method according to claim 2, wherein no substitution operation with a third gas is performed when switching between the reaction step and the regeneration step.

9. The method according to claim 1 or 2, wherein the reaction product is used in the manufacture of an olefin product, an aromatic compound product, or a liquid fuel product.

10. The method according to claim 1 or 2, wherein the reaction product is used to produce paraxylene, and the zeolite catalyst is H-ZSM-5.

11. The method according to claim 1 or 2, wherein the reaction catalyst is a mixed catalyst containing a metal oxide catalyst and a zeolite catalyst.

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