JP2014024007A - Zeolite catalyst, process for producing zeolite catalyst and process for producing lower olefin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zeolite catalyst which can, when producing lower olefins from low-boiling hydrocarbon raw materials such as light naphtha, promote a reaction at as low a temperature as possible, increase a yield of propylene relative to ethylene, and be long lived.SOLUTION: This zeolite catalyst is used when producing lower olefins by feeding low-boiling hydrocarbon raw materials such as light naphtha with dilution with steam. The zeolite catalyst is a crystalline aluminosilicate having an MFI structure containing an iron element and its molar composition ratio of iron to a total of the iron element and aluminum element is set in a range of 0.5 to 0.6. This zeolite catalyst enables improvement of propylene yield, lowering of reaction temperature, and prolongation of catalyst life.

Description

  The present invention relates to a zeolite catalyst for producing a lower olefin used when producing a lower olefin from a low-boiling hydrocarbon raw material such as light naphtha, a method for producing the zeolite catalyst, and a method for producing a lower olefin using the zeolite catalyst. .

  Lower olefins (ethylene and propylene), which are important basic raw materials in petrochemistry, are expected to continue to be in strong demand, and are currently produced mainly by the naphtha steam cracking method. However, since this method is catalyst-free, the decomposition requires a high temperature of 800 to 900 ° C. and is a process that requires a large amount of energy.

  In addition, since the main product of the above technology is ethylene and propylene is a by-product (the production ratio is almost fixed at ethylene / propylene = 2/1), supply can catch up with the expansion of demand for propylene. There may be no situation. In view of the above, there is a strong demand for a low energy consumption alternative process for producing propylene in high yield from naphtha raw materials.

Currently, research and development of a naphtha catalytic cracking method using a zeolitic solid acid catalyst typified by ZSM-5 (Al-MFI type zeolite) is being actively developed.
For example, a ZSM-5 having an MFI structure as a zeolite-based solid acid catalyst and a raw material mixture containing a layered compound such as bentonite, silicon dioxide, phosphorus pentoxide, aluminum oxide and boron oxide are subjected to crosslinking in water. There has been proposed an aqueous slurry containing a liquefied product and pelletizing the aqueous slurry into a solid acid catalyst (see, for example, Patent Document 1). For example, it has been proposed to produce ethylene and propylene as a lower olefin (light olefin) from full-range naphtha using this solid acid catalyst.

Special table 2008-512236 gazette

  By the way, even if a zeolite-based solid acid catalyst is used, a high temperature of about 650 ° C. is still necessary to obtain a high propylene yield. Moreover, the present condition is that the catalyst system which has the level which can be applied to a fixed bed process is not discovered regarding a catalyst lifetime.

As a cause of the short catalyst life, catalyst deterioration accompanying coke generation can be mentioned.
In addition, the amount of aromatic hydrocarbons that cause coke formation during the production of lower olefins becomes a problem, and suppressing the generation of aromatic hydrocarbons is an important key in developing zeolite-based catalysts that have a long lifetime. Become.

In order to suppress this catalyst deterioration, there is a method of supplying steam as a diluent to the hydrocarbon of the raw material, but steam is a dealumination phenomenon (the aluminum element in the zeolite skeleton is desorbed by exposure to water vapor). There is a problem that it is easy to cause non-renewable catalyst deterioration due to the collapse of the structure.
Accordingly, there is a need for a catalyst capable of maintaining a stable high propylene yield in a mild temperature range of about 550 ° C. when producing a lower olefin from a low-boiling hydrocarbon raw material diluted with steam.

  The present invention was made in view of the above circumstances, and when producing a lower olefin from a low-boiling hydrocarbon raw material such as light naphtha, the reaction proceeds at the lowest possible temperature, and as a lower olefin, An object of the present invention is to provide a zeolite catalyst that can increase the yield of propylene and has a longer life, and a method for producing the zeolite catalyst and a method for producing a lower olefin using the zeolite catalyst.

  In order to solve the above-mentioned problems, the zeolite catalyst of the present invention is a zeolite catalyst for producing a lower olefin, which is used when a low-boiling hydrocarbon raw material such as light naphtha is supplied together with water vapor as a diluent to produce a lower olefin. A crystalline aluminosilicate having an MFI type structure containing iron, and a composition ratio of the number of moles of iron element to the sum of the number of moles of iron element and aluminum element is in the range of 0.5 to 0.6 It is characterized by being.

  According to such a configuration, the zeolite catalyst used when producing the lower olefin from light naphtha diluted with water vapor is a crystalline aluminosilicate having an MFI type structure containing iron element, As the composition ratio of the number of moles of iron element with respect to the sum of the number of moles with aluminum element is in the range of 0.5 to 0.6, as a lower olefin, the production amount of propylene can be made higher than ethylene, The production of aromatic hydrocarbons that cause coke formation can be suppressed, and low-boiling hydrocarbon raw materials can be produced at relatively low temperatures to produce lower olefins. It is possible to extend the catalyst life by suppressing the above-described catalyst deterioration due to water vapor.

  In order to obtain the above-described effects using a raw material diluted with water vapor as a low-boiling hydrocarbon material, the composition ratio of the number of moles of iron element needs to be in the range of 0.5 to 0.6. . That is, when the composition ratio of the iron element is smaller than 0.5 or larger than 0.6, the production amount of propylene at the above-described relatively low temperature decreases, or the lower the combined amount of ethylene and propylene. The production amount of olefin is reduced, and it is difficult to suppress the above-described catalyst deterioration in the presence of water vapor.

  Naphtha (full-range naphtha) is a product having a boiling range of about 35 to 180 (200) ° C. among products obtained by distilling and separating crude oil using an atmospheric distillation apparatus. Among these naphtha, those having a boiling range of about 35-80 (100) ° C. are called light (light) naphtha, and those having a boiling range of about 80 (100) -180 (200) ° C. are called heavy (heavy) naphtha. . Light naphtha corresponds to a fraction mainly composed of pentane having 5 carbon atoms and hexane having 6 carbon atoms.

  In addition, the low boiling point hydrocarbon raw material is basically light naphtha, but may include, for example, part of heavy naphtha or full range naphtha. Further, the low boiling point hydrocarbon raw material may be other than naphtha, for example, natural gas other than petroleum or other hydrocarbon material, basically a fraction corresponding to light naphtha.

  The lower olefin may be defined to include, for example, ethylene, propylene, butene and olefins having more carbon atoms (for example, 5 to 8 carbon atoms) as olefins having a small number of carbon atoms. Here, the lower olefin includes ethylene having 2 carbon atoms and propylene having 3 carbon atoms.

The MFI type is one of the structural codes indicating the framework structure of zeolite, and the MFI type includes, for example, aluminosilicate ZSM-5. The structure coat is made into a database by the International Zeolite Society and consists of three uppercase letters. This structure code designates only the geometric structure of the framework of the zeolite, and is included in the same structure code if the geometric structure is the same even if the composition and lattice constant are different.
The acid density described later in the crystalline aluminosilicate is, for example, the composition ratio of the number of moles of silicon element to the number of moles of aluminum element, that is, silicon element (Si) / aluminum element (Al). It further contains iron element or iron element and gallium element. In addition, when the value as a composition ratio of the number of moles of silicon element to the sum of the number of moles of aluminum element, iron element, or aluminum element, iron element and gallium element contained in crystalline aluminosilicate is reduced, the amount of acid When the value increases and the value increases, the acid amount decreases.

  In the above configuration of the present invention, the acid density as a composition ratio of the number of moles of silicon element to the sum of the number of moles of iron element and aluminum element is preferably in the range of 25.0 to 45.0.

  According to such a structure, while making an acid density into the range of 25.0-45.0, as above-mentioned, while being able to make the production amount of propylene higher than ethylene as a lower olefin, It is possible to produce a lower olefin by suppressing catalyst deterioration which is considered to be based on the dealumination phenomenon due to coexistence, and cracking a low-boiling hydrocarbon raw material at a relatively low temperature.

  Further, in the above structure of the present invention, the composite is obtained by molding a crystalline aluminosilicate having an MFI type structure containing an iron element and a binder, or is crystalline having an MFI type structure containing an iron element. A composite obtained by molding an aluminosilicate and a binder previously loaded with gallium is preferred.

According to such a configuration, when a zeolite catalyst is used industrially by forming a composite obtained by molding an aluminosilicate having a MFI structure containing iron and a binder, the mechanical properties can be improved. Loss can be reduced.
Further, in a composite obtained by molding a crystalline aluminosilicate having an MFI type structure containing iron and a binder by supporting gallium on the binder, when the hydrocarbon as a raw material comes into contact, gallium Can promote the dehydrogenation of alkanes and contribute to the production of lower olefins.

  Further, in the above configuration of the present invention, the crystalline aluminosilicate having an MFI type structure containing a gallium element in addition to the iron element, and the mole of the iron element with respect to the sum of the number of moles of the iron element, the gallium element, and the aluminum element The composition ratio of the number of moles of gallium to the sum of the moles of iron, gallium and aluminum is in the range of 0.1 to 0.4. Preferably there is.

  According to such a configuration, in addition to the iron element having the action of weakening the acid strength, the gallium element having the action of promoting dehydrogenation of the hydrocarbon raw material (alkane) is included in the MFI type aluminosilicate, and As described above, the composition ratio of the number of moles of iron element is in the range of 0.2 to 0.6, and the composition ratio of the number of moles of gallium element is in the range of 0.1 to 0.4. As a lower olefin, the production amount of propylene can be made higher than that of ethylene, catalyst deterioration due to coexistence of water vapor can be suppressed, and low boiling point hydrocarbon raw materials can be decomposed at a relatively low temperature. Lower olefins can be produced.

  In the above configuration of the present invention, the acid density as a composition ratio of the number of moles of silicon element to the sum of the number of moles of iron element, gallium element, and aluminum element is in the range of 25.0 to 40.0. preferable.

  According to such a configuration, when the acid density is in the range of 25.0 to 40.0, as described above, it is possible to increase the production amount of propylene as compared with ethylene as a lower olefin, and to coexist with water vapor. The lower olefin can be produced by suppressing the catalyst deterioration due to the lower temperature and decomposing the low-boiling hydrocarbon raw material at a relatively low temperature.

  In addition, the present invention is a method for producing a zeolite catalyst having the above structure, and includes a hydrothermal synthesis step, a molding step, and an ion exchange step.

  According to such a configuration, the above-described zeolite catalyst having the above-described effects can be produced.

  The present invention also relates to a method for producing a lower olefin, which comprises producing a lower olefin from a hydrocarbon raw material using the zeolite catalyst having the above structure, wherein the low boiling point hydrocarbon raw material is diluted with steam and supplied, and the zeolite catalyst The reaction for producing the lower olefin from the low-boiling hydrocarbon raw material proceeds in the reaction temperature range of 525 ° C. to 575 ° C.

  According to such a configuration, by producing a lower olefin from a low-boiling hydrocarbon raw material using the above-mentioned zeolite catalyst, as described above, the production amount of propylene can be made higher than ethylene as the lower olefin. At the same time, catalyst deterioration due to coexistence of water vapor can be suppressed, and low-boiling hydrocarbon raw materials can be decomposed at a relatively low temperature to produce lower olefins, particularly propylene.

  According to the zeolite catalyst of the present invention, it is possible to mainly promote the production of propylene as a lower olefin from a low-boiling hydrocarbon raw material at a relatively low reaction temperature, and to suppress the deterioration of the zeolite catalyst and thereby increase the catalyst life. Can be long.

It is a graph for demonstrating the experimental result in the Example of this invention.

Embodiments of the present invention will be described below.
In this embodiment, a zeolite catalyst for efficiently producing a lower olefin such as propylene, a method for producing the zeolite catalyst, and a method for producing a lower olefin using the zeolite catalyst will be described.

  The zeolite catalyst of this embodiment is an MFI type crystalline aluminosilicate containing iron element (Fe) and is suitable for the production of lower olefins under conditions using steam as a diluent. It is a produced catalyst. The zeolite catalyst is preferably a composite obtained by molding with a binder (binder). In this case, the gallium element may be supported on the binder, and the gallium element may be included in the composite.

  This zeolite catalyst includes an MFI type zeolite catalyst which is a crystalline aluminosilicate containing a gallium element (Ga) having an action of promoting an alkane dehydrogenation reaction in addition to an iron element (Fe) that suppresses acid strength. It is.

  In a zeolite catalyst that is an MFI type crystalline aluminosilicate containing iron element (not containing gallium element), the elemental molar composition of iron element (iron element / (iron element + aluminum element (Al))) is 0.5 It is preferable that it is -0.6.

  Further, in an MFI type zeolite catalyst containing an iron element (not containing a gallium element), the acid density (ratio of silicon element (Si) / (iron element + aluminum element)) is 25.0 to 45.0. It is preferable. The element ratio is a composition ratio based on the number of moles of each element described above.

  Further, in the MFI type zeolite catalyst containing iron element and gallium element, the elemental molar composition of iron element (iron element / (iron element + gallium element + aluminum element)) is preferably 0.2 to 0.6. Furthermore, it is more preferable that it is 0.3-0.5.

  Further, in the zeolite catalyst which is an MFI type crystalline aluminosilicate containing iron element and gallium element, the elemental molar composition of gallium element (gallium element / (iron element + gallium element + aluminum element)) is 0.1-0. .4, more preferably 0.2 to 0.4.

  Further, in the MFI type zeolite catalyst containing iron element and gallium element, the acid density (ratio of silicon element / (iron element + gallium element + aluminum element) element) is preferably 25.0 to 40.0, Furthermore, it is more preferable that it is 25.0-35.0.

  As described above, by using the zeolite catalyst of this embodiment which is an MFI type crystalline aluminosilicate containing iron element, the acid strength can be adjusted from the content of iron element and the acid density, By adding gallium element, the promoting action of dehydrogenation of alkane can be improved.

  Thereby, by making the above-mentioned composition ratio of the number of moles of the above-mentioned iron element, the composition ratio of the number of moles of gallium element, and the acid density into the above-mentioned ranges, for example, at a reaction temperature in the range of 525 ° C. to 575 ° C. In addition to improving the yield of propylene, it is possible to suppress catalyst deterioration that is considered to be due to dealumination due to coexistence of water vapor.

  In the case where gallium is supported on a binder and calcined as described above, the composition ratio of the number of moles of gallium element is preferably substantially the same as that of the above-described zeolite catalyst containing gallium element. In this case, the number of moles of aluminum does not include the binder alumina.

  Zeolite as such a solid acid catalyst (zeolite catalyst) is roughly classified as follows: 1. Hydrothermal synthesis process 2. ion exchange process; Manufactured through three molding steps.

1. Hydrothermal synthesis process "Hydrothermal synthesis method" is a general term for the synthesis of substances performed in the presence of high-temperature and high-pressure water, and many zeolites as crystalline aluminosilicates are produced by this hydrothermal synthesis method. Synthesized. The raw materials used in the synthesis include silica sources (sodium silicate, colloidal silica, fumed silica, etc.), alumina sources (aluminum hydroxide, sodium aluminate, etc.), structure directing agents (amines, etc.), mineralizers ( Alkali metal hydroxides) and water are common.

  In the zeolite catalyst of this embodiment, an iron source (for example, iron nitrate) is added to the raw material. Furthermore, it is preferable to add a gallium source (for example, gallium nitrate). Note that, as described above, the gallium source may be supported on a binder instead of being added to the raw material of the MFI type crystalline aluminosilicate.

  These are mixed to prepare a highly reactive amorphous hydrogel (mother gel), filled in an autoclave, which is a pressure-resistant reactor, and heated at about 150 to 250 ° C. for a predetermined time to synthesize zeolite. . After the hydrothermal synthesis reaction, powdered zeolite is obtained through steps such as product separation, water washing, drying, and calcination (performed to decompose and remove the structure-directing agent).

In addition, the above-mentioned raw material includes mother liquor gel A composed of colloidal silica having a particle size of 8 to 11 nm as fine silica as a silicon source and pH-adjusting sodium hydroxide (NaOH), and Al ₂ (as an aluminum source). SO ₄ ) -nH ₂ O, Ga (NO ₃ ) ₃ -nH ₂ O as the gallium source, Fe (NO ₃ ) ₃ -nH ₂ O as the iron source, and tetrapropylammonium bromide ( Mother liquor gel B containing TPrABr). In addition, it is preferable to reduce the addition amount of TPrABr as a structure directing agent.

  Next, these mother liquor A and mother liquor B are stirred and mixed (for example, 15 minutes). As a result, a highly reactive amorphous hydrogel is prepared. Next, the mixed and stirred mother liquor gel is aged (eg, overnight at 60 ° C.). Next, as the hydrothermal synthesis described above, stirring is performed at 120 ° C. to 150 ° C. and at a rotational speed of 150 rpm to 300 rpm. That is, crystallization is performed at high temperature and pressure. However, the reaction temperature is relatively low, and the generation of coarse particles is suppressed by nucleating at a low temperature. Further, the stirring speed is relatively high and the amount of nuclei generated is increased. Under these conditions, for example, stirring is performed for 24 hours to obtain crystals. The obtained crystal is washed with water, and dehydration is performed by centrifugation. Thereafter, the crystal is dried, for example, at 120 ° C. for 3 hours and fired at 550 ° C. for 3 hours to remove TPrABr. When gallium is not included, no gallium source is added to the mother liquor gel B.

2. Ion exchange process Many of the chemical reactions that use zeolite as a catalyst are based on the properties of a solid acid. This property of an acid is obtained by introducing an acidic OH group (Bronsted acid point) into the zeolite. To express.

In order to express this acid property, an ion exchange reaction is generally applied. Usually, the zeolite obtained by the hydrothermal synthesis method contains a sodium cation (Na ⁺ ) in order to maintain the balance of electric charges, but this is replaced with protons (H ⁺ ) by ion exchange. In some cases, a method may be adopted in which ion exchange is performed with ammonium ions (NH4 ⁺ ) once in an NH ₄ NO ₃ solution, followed by drying and baking to remove ammonia to convert it into protons (H ⁺ ).

3. In general, when zeolite is used industrially as a catalyst, it is often used after being molded into a cylindrical shape from the viewpoint of improving mechanical properties and reducing pressure loss. This process mainly includes steps such as kneading, molding, drying and firing with a binder (binder) such as alumina powder. In molding, for example, an extrusion molding method or the like is used.

  For example, alumina (aluminum oxide) is added as a binder to the powdered zeolite obtained through the hydrothermal synthesis process (or ion exchange process) described above, and kneading and molding (for example, a thin cylindrical shape of φ1.0 mm For example, it is dried at 120 ° C. for 3 hours. Thereafter, it is calcined at 550 ° C. for 3 hours to obtain a zeolite catalyst as a composite of the above-mentioned MFI type zeolite containing iron element (and gallium element) and aluminum oxide. In addition, although a shaping | molding process may be performed after an ion exchange process or an ion exchange process may be performed after a shaping | molding process, it is preferable to perform an ion exchange process after a shaping | molding process.

  For example, as a production method for producing a lower olefin from light naphtha using such a zeolite catalyst, a hydrocarbon raw material is supplied to a reactor in a state diluted with water vapor as a diluent. That is, the hydrocarbon raw material is allowed to react with the catalyst in the presence of water vapor. Moreover, the above-mentioned zeolite catalyst is arrange | positioned as a fixed bed in a reactor, and the method of allowing the raw material gas supplied in a reactor to pass through making it contact with a zeolite catalyst is used. At this time, the reaction is allowed to proceed in a moderate temperature range of 525 ° C. to 575 ° C., preferably 540 ° C. to 575 ° C., to produce ethylene and propylene.

  In such a zeolite catalyst, a method for producing a zeolite catalyst, and a method for producing a lower olefin, it is possible to achieve propylene production by an energy-saving naphtha catalytic cracking method in a low temperature range of about 525 to 575 ° C. In addition, since the reaction proceeds at a relatively low temperature, there is an advantage that renewable energy such as solar heat and various unused exhaust heat can be used for the heat source. In addition, the zeolite catalyst of this embodiment works stably even in the presence of steam and significantly reduces the selectivity of the aromatic compound (suppresses the formation of the aromatic compound). It can be greatly suppressed.

Next, examples of the present invention will be described.
In this example, Examples 1 to 3 shown in Table 1 and Table 2 below were experimentally produced as zeolite catalysts to be Comparative Example 1, and compared with the produced zeolite catalysts of Examples 1 to 3. The lower olefin was produced using the zeolite catalyst of Example 1. Example 1 is a zeolite catalyst according to the above-described embodiment that contains an iron element and does not contain a gallium element, and Example 2 is a zeolite catalyst according to the above-described embodiment that includes both an iron element and a gallium element. Example 3 is the zeolite catalyst according to the above-described embodiment using an MFI type crystalline aluminosilicate containing an iron element and not containing a gallium element, in which the gallium element is supported on alumina as a binder.

  Each of Examples 1 to 3 is a zeolite catalyst as a composite fired using a binder. Further, the number of moles of iron element, the number of moles of gallium element and the number of moles of aluminum element contained in the crystalline aluminosilicate of the zeolite catalyst of Example 2, and the crystalline aluminosilicate of Example 3 The total number of moles of iron element and the number of moles of aluminum element (not including the aluminum element in the binder) plus the number of moles of gallium element contained in the binder is approximately equal. Yes.

Comparative Example 1 is an MFI type crystalline aluminosilicate containing neither iron element nor gallium element (for example, ZSM-5 which is an Al-MFI type zeolite).
Below, each Example and a comparative example are demonstrated.

Example 1
A method for synthesizing the FeAl-MFI zeolite in Example 1 will be described.
Colloidal silica: 58.9 g (SiO ₂ : 30.6 wt%, Na ₂ O: 0.4 wt%, H ₂ O: 69.0 wt%), sodium hydroxide: 2.25 g solution A solution, aluminum sulfate -A solution consisting of n-hydrate: 1.14 g, iron nitrate.9-hydrate: 0.98 g, tetrapropylammonium bromide: 4.65 g, water: 187.1 g was designated as solution B.

  The liquid A and the liquid B were gradually mixed with stirring at room temperature, and then vigorously stirred for 15 minutes in a mixer. The mixed solution was kept at 60 ° C. and allowed to stand overnight, and then a hydrothermal synthesis reaction was performed in an autoclave under self-pressure at 150 ° C. for 24 hours at 300 rpm. After cooling, it was thoroughly washed with purified water (a centrifuge was used to separate the solid and aqueous solution).

After that, it was dried at 120 ° C for 3 hours and calcined in an air stream at 550 ° C for 3 hours to synthesize a powdery Na-type MFI zeolite containing Fe and Al (hereinafter abbreviated as FeAl-MFI zeolite). did. The elemental molar composition of the zeolite was Si / (Fe + Al) = 30.5, Fe / (Fe + Al) = 0.5, and Al / (Fe + Al) = 0.5 (see Table 1).

Next, a method for preparing a FeAl-MFI zeolite / alumina composite catalyst will be described.
Powdered Na-type FeAl-MFI zeolite (moisture content: 4.0 wt%) and alumina powder (JGC Catalysts & Chemicals Co., Ltd., Cataloid AP-1, Al ₂ O ₃ content: 71.7 wt.) Synthesized according to the above procedure %) And kneaded while adding an appropriate amount of purified water to make a soot-like zeolite / alumina mixture, processed into a cylindrical shape (1.0 mmφ) with an extruder, dried at 120 ° C. for 3 hours, under air flow Was calcined at 550 ° C. for 3 hours to obtain a FeAl-MFI zeolite / alumina composite.

  The composite was subjected to ion exchange with a 2.2 mol / L aqueous ammonium nitrate solution under boiling reflux and subsequent water washing four times (one ion exchange was performed for 2 hours, and each time a new 2.2 mol / L was added). It was replaced with an aqueous ammonium nitrate solution), dried at 120 ° C. for 3 hours, and calcined at 550 ° C. for 3 hours in an air stream to obtain a proton-type FeAl-MFI zeolite / composite catalyst. The composite catalyst had a weight composition of zeolite / alumina = 65 wt% / 35 wt% (see Table 1).

Next, a performance evaluation test method for the FeAl-MFI zeolite / alumina composite catalyst will be described.
A catalyst sample for performance evaluation was prepared by adjusting the size of a cylindrical FeAl-MFI zeolite / alumina composite prepared according to the above procedure. In the reaction test, n-hexane catalytic cracking reaction was carried out in a fixed bed flow type reactor. 1.0 mL of catalyst is filled in a stainless steel reaction tube (made of SUS316) having an inner diameter of 8.0 mm so that the layer height of the catalyst layer is about 20 mm, glass wool is placed before and after the catalyst layer, and glass beads are placed before and after the catalyst layer. Filled.

The reaction conditions were a reaction temperature of 550 ° C., a total pressure of 0.1 MPa, an n-hexane flow rate of 1.31 g / h (LHSV based on n-hexane (Liquid Hourly Space Velocity) 2.0 h ⁻¹ ), purification. The water flow rate was 1.37 g / h (H ₂ O / n-hexane = 5 mol / mol), and the n-hexane catalytic decomposition reaction was performed for 5 hours in the presence of steam. The reaction product is analyzed by gas chromatography at regular intervals to determine the reaction conversion rate (wt%) and the yield of lower olefins (ethylene, propylene) and aromatic hydrocarbons (wt%). did. The catalyst performance 1.5 hours after the start of the reaction is shown in Table 2, and the change over time in the reaction conversion rate is shown in FIG.

(Example 2)
A method for synthesizing FeGaAl-MFI zeolite in Example 2 will be described.
Aluminum sulfate.n hydrate: 0.76 g, Gallium nitrate.n hydrate: 0.44 g, Iron nitrate.9 hydrate: 0.98 g, Tetrapropylammonium bromide: 4.65 g, Water: 187. A powdery Na-type FeGaAl-MFI zeolite was synthesized in exactly the same manner as in Example 1 except that the solution consisting of 2 g was changed to the solution B.

  The elemental molar composition of this FeGaAl-MFI zeolite is Si / (Fe + Ga + Al) = 31.3 (acid density), Fe / (Fe + Ga + Al) = 0.4, Ga / (Fe + Ga + Al) = 0.3, Al / (Fe + Ga + Al) = 0.3 (see Table 1).

Next, a method for preparing the FeGaAl-MFI zeolite / alumina composite catalyst will be described.
Using the powdered Na-type FeGaAl-MFI zeolite and alumina powder synthesized in accordance with the above procedure, it was shaped and ion-exchanged in the same manner as in Example 1 to obtain a cylindrical proton-type FeGaAl-MFI. A zeolite / composite catalyst was obtained. The composite catalyst had a weight composition of zeolite / alumina = 65 wt% / 35 wt% (see Table 1).

  Next, the performance evaluation test method of the FeGaAl-MFI zeolite / alumina composite catalyst will be described. A reaction test was carried out in the same manner as in Example 1, using a cylindrical FeGaAl-MFI zeolite / alumina composite prepared in accordance with the above-mentioned procedure as a catalyst sample for performance evaluation. The catalyst performance 1.5 hours after the start of the reaction is shown in Table 2, and the change over time in the reaction conversion rate is shown in FIG.

(Example 3)
A method for synthesizing FeAl-MFI zeolite in Example 3 will be described.
Except that the solution consisting of aluminum sulfate / n hydrate: 0.76 g, iron nitrate / 9 hydrate: 0.98 g, tetrapropylammonium bromide: 3.26 g, water: 187.2 g was used as solution B In exactly the same manner as in Example 1, a powdery Na-type FeAl-MFI zeolite was synthesized.

The elemental molar composition of this FeAl-MFI zeolite was Si / (Fe + Al) = 44.7 (acid density), Fe / (Fe + Al) = 0.57, and Al / (Fe + Al) = 0.43 (see Table 1). ).

Next, a method for preparing a FeAl-MFI zeolite / gallium-containing alumina composite catalyst will be described.
Using powdered Na-type FeAl-MFI zeolite synthesized in accordance with the above procedure and alumina powder previously loaded with gallium (the gallium content in this example is the same as the FeGaAl-MFI zeolite of Example 2). The total number of (Fe + Ga + Al) moles contained in the zeolite component of Example 2 ≈ the total number of (Fe + Al) moles contained in the zeolite of this example and the number of Ga moles contained in the alumina binder. And was molded and ion-exchanged in the same manner as in Example 1 to obtain a cylindrical proton-type FeAl-MFI zeolite / gallium-containing alumina composite catalyst.

The weight composition of this composite catalyst was zeolite / (gallium + alumina) = 65 wt% / 35 wt% (see Table 1).
Next, a performance evaluation test method for the FeAl-MFI zeolite / gallium-containing alumina composite catalyst will be described.
A reaction test was carried out in exactly the same manner as in Example 1, using a cylindrical FeAl-MFI zeolite / gallium-containing alumina composite prepared according to the above procedure as a catalyst sample for performance evaluation. . The catalyst performance 1.5 hours after the start of the reaction is shown in Table 2, and the change over time in the reaction conversion rate is shown in FIG.

(Comparative Example 1)
A method for synthesizing the Al-MFI zeolite in Comparative Example 1 will be described.
Na-type Al in the same manner as in Example 1 except that the solution consisting of aluminum sulfate n-hydrate: 1.90 g, tetrapropylammonium bromide: 4.65 g, and water: 187.2 g was used as solution B. -MFI zeolite was synthesized. The elemental molar composition of this Al-MFI zeolite was Si / Al = 30.7 (see Table 1).

Next, a method for preparing an Al-MFI zeolite / alumina composite catalyst will be described.
Using powdered Na-type Al-MFI zeolite and alumina powder synthesized in accordance with the above procedure, molding and ion exchange were carried out in the same manner as in Example 1, and cylindrical proton-type Al- An MFI zeolite / composite catalyst was obtained.

  The composite catalyst had a weight composition of zeolite / alumina = 65 wt% / 35 wt% (see Table 1).

Next, a performance evaluation test method for the Al-MFI zeolite / alumina composite catalyst will be described.
A reaction test was carried out in the same manner as in Example 1, using a cylindrical sample of Al-MFI zeolite / alumina composite prepared according to the above procedure as a catalyst sample for performance evaluation. The catalyst performance 1.5 hours after the start of the reaction is shown in Table 2, and the change over time in the reaction conversion rate is shown in FIG.

Next, experimental results will be described with reference to Table 2 and FIG.
As shown in Table 2, although the generation of aromatic hydrocarbons was suppressed in the presence of water vapor, the conventional Al-MFI zeolite (Comparative Example 1) was clearly shown from the change over time in FIG. The deterioration of the catalyst was observed within a few hours, and it was found that there was a problem with the stability of the catalyst under water vapor. Since the yield of aromatic hydrocarbons has been reduced to 2 wt% or less, it is suggested that there is a higher possibility of the zeolite structure collapsing / degrading due to the dealumination phenomenon peculiar to the steam atmosphere rather than deterioration due to coke formation. The

  On the other hand, FeAl-MFI zeolite containing iron having an action of weakening acid strength (Example 1), FeGaAl-MFI zeolite containing both iron having an action of weakening acid strength and gallium having an action of promoting dehydrogenation of alkane In (Example 2 and Example 3), it was confirmed that not only the yield of propylene was improved, but also the catalyst performance was stably maintained even under steam (see FIG. 1).

For the sample of Example 2, the space-time yield of propylene (in the present invention, defined as the weight of propylene that can be produced per unit weight of zeolite per unit weight. Optimal reaction conditions depending on the type of diluent used. Is adopted as one standard for evaluating the catalyst performance) is about 0.78 (g-propylene / g-zeolite · h), which is nearly twice the value shown by this sample in the presence of nitrogen. became. Furthermore, as can be seen from the comparison between Example 2 and Example 3 (see Table 2), gallium is improved in propylene yield and stability regardless of whether it is contained in the zeolite or in the binder. Was confirmed to have the same effect.

Claims (7)

A zeolite catalyst for producing a lower olefin used when producing a lower olefin by supplying a low-boiling hydrocarbon raw material such as light naphtha together with steam as a diluent,
A crystalline aluminosilicate having an MFI type structure containing an iron element, and the composition ratio of the number of moles of iron element to the sum of the number of moles of iron element and aluminum element is in the range of 0.5 to 0.6.
A zeolite catalyst characterized by the above. The zeolite catalyst according to claim 1, wherein
The acid density as a composition ratio of the number of moles of silicon element to the sum of the number of moles of iron element and aluminum element is in the range of 25.0 to 45.0.
A zeolite catalyst characterized by the above. A zeolite catalyst according to claim 1 or claim 2,
It is a composite obtained by molding a crystalline aluminosilicate having an MFI type structure containing an iron element and a binder, or a crystalline aluminosilicate having an MFI type structure containing an iron element and gallium previously supported A composite obtained by molding with a binder,
A zeolite catalyst characterized by the above. The zeolite catalyst according to claim 1, wherein
It is a crystalline aluminosilicate having an MFI type structure containing a gallium element in addition to an iron element, and the composition ratio of the number of moles of iron element to the sum of the number of moles of iron element, gallium element and aluminum element is 0.2 to In the range of 0.6, the composition ratio of the number of moles of gallium element to the sum of the number of moles of iron element, gallium element and aluminum element is in the range of 0.1 to 0.4.
A zeolite catalyst characterized by the above. A zeolite catalyst according to claim 4,
The acid density as a composition ratio of the number of moles of silicon element to the sum of the number of moles of iron element, gallium element and aluminum element is in the range of 25.0 to 40.0.
A zeolite catalyst characterized by the above. A method for producing a zeolite catalyst according to any one of claims 1 to 5,
Including hydrothermal synthesis process, molding process, ion exchange process,
A method for producing a zeolite catalyst. A method for producing a lower olefin, which comprises producing a lower olefin from a low-boiling hydrocarbon raw material using the zeolite catalyst according to any one of claims 1 to 5,
The low boiling point hydrocarbon raw material is diluted with steam and supplied.
In the presence of the zeolite catalyst, the reaction for producing the lower olefin from the low-boiling hydrocarbon raw material proceeds in a reaction temperature range of 525 ° C. to 575 ° C.,
A process for producing a lower olefin, characterized in that

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