JPS6248649B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for isomerizing xylenes. More specifically, the present invention relates to a method for isomerizing a mixture of xylene isomers in which at least one of the xylene isomers has a concentration below the thermodynamic equilibrium concentration. In particular, the present invention provides p-xylene by isomerizing a xylene isomer mixture in which the concentration composition of p-xylene is below the thermodynamic equilibrium concentration.
- Concerning a method for obtaining a composition with a high xylene concentration. Conventionally, it is a well-known method to isomerize a xylene mixture in which at least one component has a concentration below the thermodynamic equilibrium concentration by contacting it with, for example, a silica-alumina catalyst to obtain a mixture having a certain equilibrium composition. be. and p as a xylene isomer mixture
-There are three isomer mixtures of xylene, m-xylene and o-xylene, and isomer mixtures containing other alkylbenzenes, and it is known that these mixtures each form a thermodynamic equilibrium composition. ing. For example, it is known that the equilibrium composition of a mixture of three isomers at 427°C is as follows in terms of molar ratio. p-xylene m-xylene o-xylene 23.4% 52.1% 24.5% (The chemical Thermodynamics of
Organic Compounds by STULL, WESTRUM
and SINKE JOhn Wiley and Sons, 1969) On the other hand, the isomerization of xylenes is industrially divided into the isomerization reaction process of xylenes, the separation process of xylene isomers from the isomerization reaction mixture, and the process of separating xylene isomers from the isomerization reaction mixture. A suitable combination of steps for recycling the residual composition mixture is carried out. In this case, bringing the composition in the isomerization reaction closer to the thermodynamic equilibrium composition and suppressing side reactions such as decomposition of xylenes and disproportionation reactions have a great influence on its industrial value. In many conventional methods for isomerizing xylenes, research has focused on improving and developing catalysts, mainly silica-alumina catalysts, and improving isomerization conditions, and many proposals have been made regarding this. In particular, much research has been carried out on methods of changing the shape and structure of the silica/alumina catalyst itself, methods of processing it, and methods of adding various components to silica/alumina. However, there are very few silica-alumina catalysts that satisfy the conditions of having excellent isomerization reaction activity and suppressing undesirable side reactions as much as possible. On the other hand, the present inventors have previously proposed that crystalline aluminosilicate prepared using a certain cation source is a new zeolite. As a catalyst, it has excellent activity, with little deterioration of activity even after long-term use, and little side reactions.What is especially surprising is that the equilibrium composition of xylenes in the isomerization reaction mixture was previously unknown. It was found that the composition of p-xylene showed a much higher value than the equilibrium attainment rate mentioned above. As a result of further research into the isomerization characteristics of xylenes in the above-mentioned new zeolite, the present inventors found that the ratio of sodium cations to the cation sites influences side reactions other than isomerization. It has been shown that when a proportion of zeolite of at least 10% is used as a catalyst, the isomerization activity is still maintained at a high level, and undesirable side reactions (e.g. disproportionation reactions, transalkylation reactions, etc.) are further suppressed. Heading The present invention has been arrived at. That is, _the present invention _is based on _the following formula ₍ ) ion alkali metal ion, alkaline earth metal ion, group metal ion of the periodic table or rare earth metal ion, n
indicates the valence of the ion. x ranges from 0.5 to 4; y indicates a value of at least 10; ] and has the following lattice spacing dÅ relative strength : 11.2±0.5 Moderate to strong 9.9±0.5 Moderate to strong 4.67±0.1 Moderate 4.33±0.1 Very strong 4.02±0.05 Strong to very strong 3.83±0.05 Medium 3.72±0.05 Weak to Medium 3.44±0.04 Weak to Strong 3.33±0.04 Weak to Strong 3.28±0.03 Neutral A crystalline aluminosilicate having an X-ray lattice spacing substantially represented by the value of A catalyst containing a zeolite in which at least 10% of the total cation sites of the zeolite are occupied by sodium ions is contacted with a raw material mixture containing xylene isomers, at least one of which has a thermodynamic equilibrium concentration or less, in the gas phase. This is an isomerization method for xylenes that is characterized by the following. The method of the present invention will be explained in more detail below. The zeolite used in the method of the present invention and its manufacturing method were discovered by the present inventors as explained above, and
(submitted November 4, 1981) and December 1981
These are explained in detail in the specification of the patent application filed on the 21st, and these will be explained next. As mentioned above, the zeolite used in the present invention is a zeolite with a high silica content, that is, a zeolite with a SiO ₂ /Al ₂ O ₃ molar ratio of 10 or more. , ZSM-12,
ZSM-based zeolites such as ZSM-38 and Zeta 3
(Zeta3) Zeolite is a zeolite with a novel crystal structure that exhibits an X-ray diffraction pattern completely different from that of high-silica-containing zeolites such as zeolite, and is hereinafter referred to as "zeolite TPZ-3" in this specification. In the method of the present invention, the above-mentioned patent application No. 55-155017
As stated in the specification, zeolite M
is a hydrogen ion, an alkali metal ion, an alkaline earth metal ion, a group metal ion of the periodic table or a rare earth metal ion, and at least 10% of its total cation sites are sodium ions, preferably sodium ions. It is unique in that it uses zeolite, which is 20% composed of sodium ions, as a catalyst. The above zeolite TPZ-3 was prepared using a water-soluble alkali metal compound, N,N,N,N',N',N'-hexamethyl-1,6-hexanediammonium compound, under reaction conditions (hydrothermal reaction conditions described below). A mixture containing a compound that provides silica (hereinafter referred to as silica source), a compound that provides alumina (hereinafter referred to as alumina source) under reaction conditions (hydrothermal reaction conditions described below), and water is heated at a temperature of at least 80°C to form crystals. It can be produced by a method comprising maintaining the zeolite for a sufficient period of time to produce it, and subjecting the produced zeolite to an ion exchange reaction with other cations as necessary. In this case, in addition to a water-soluble alkali metal compound, a N,N,N,N',N',N'-hexamethyl-1,6-hexanediammonium compound is used as a cation source constituting the cation portion of the zeolite. be done. In the above method, the above-mentioned starting materials are mixed in such a proportion as to give the following molar ratio in terms of the molar ratio of the following components in the reaction mixture after mixing these raw materials. _SiO2 / _Al2O3 =10~ ₂₀₀₀ , preferably 10~
500, more preferably 20 to 250; R/(Si+Al)=1×10 ^-4 to 1, preferably 5
×10 ⁻⁴ to 0.5, more preferably 1×10 ⁻³
~1×10 ⁻¹ ; OH ⁻ /(Si+Al)=1×10 ⁻⁴ ~1.5, preferably 1×10 ⁻³ ~1, more preferably 5×10 ⁻³
~0.4; _H2O /(Si+Al)=5~100, preferably 10~
50, more preferably 15 to 40; OH ^- /H ₂ O = 1 x 10 ^-5 to 1 x 10 ^-1 , preferably 1 x 10 ^-4 to 1 x 10 ^-1, more preferably 1 x
10 ^-4 ~1×10 ^-2 ; [However, R is N, N, N, N', N', N'-hexamethyl-1.6-he, xanediammonium ion [(CH ₃ ) ₃ N-(CH ₂ ) ₆ - N(CH ₃ ) ₃ ]. ] In the above formula, OH ^- quantitatively represents the degree of alkalinity in the above mixture, and its value is calculated from the total number of moles of hydroxyl groups brought into the mixture by the starting materials other than water. This value is calculated by subtracting the number of moles of hydroxyl groups consumed by the neutralization reaction with the acid radicals in the molecule. Next, each starting material will be described in more detail. (A) As a silica source, any of those commonly used in zeolite production can be used, such as silica powder, colloidal silica, water-soluble silicon compounds, silicic acid, etc. Specific examples of these are explained in detail. Then, as silica powder,
Precipitated silica produced by a precipitation method from an alkali metal silicate such as aerosil silica, fumed silica, and silica gel is suitable, and as colloidal silica, those having various particle sizes, e.g.
A particle size of 50 microns is available. Also, water-soluble silicon compounds include Na ₂ O or K ₂ O1
Examples include water glass, alkali metal silicates, etc. containing ₁ to 5 moles, especially 2 to 4 moles, of SiO 2 per mole, and colloidal silica or water glass is particularly preferred as the silica source. (B) As an alumina source, any of those commonly used in the production of zeolites can be used, including salts of aluminum such as chlorides, nitrates, and sulfates; for example, colloidal alumina, pseudoboehmite, Alumina in a hydrated or hydrateable state such as boehmite, γ-alumina, α-alumina, β-alumina trihydrate; examples include sodium aluminate, among which sodium aluminate or aluminum salts are preferred. It is also possible to use aluminosilicate compounds such as naturally occurring feldspathic kaolin, acid clay, bentonite, montmorillonite, etc. as a source of both silica and alumina, and these aluminosilicates can be used as sources for the above-mentioned alumina. Some or all of the silica sources and/or silica sources may be replaced. The blending ratio of the silica source and the alumina source in the raw material mixture of the present invention is SiO ₂ and Al ₂ O ₃ , respectively.
Expressed as SiO ₂ /Al ₂ O ₃ (molar ratio) is 10~
It is preferable that the number is in the range of 2000, preferably in the range of 10 to 500, and more preferably in the range of 20 to 250. (C) On the other hand, as water-soluble alkali metal compounds,
Water-soluble alkali metal salts and alkali metal hydroxides are suitable, in particular alkali metal chlorides, carbonates, such as sodium chloride, sodium carbonate, potassium carbonate, etc., or sodium hydroxide, potassium hydroxide. Alkali metal hydroxides such as Furthermore, alkali metal silicates such as sodium silicate and potassium silicate, and alkali metal aluminates such as sodium aluminate and potassium aluminate can also be used as a silica source or an alumina source. Particularly suitable alkali metal compounds include sodium hydroxide, sodium silicate, sodium aluminate and the like. (D) The N,N,N,N',N',N'-hexamethyl-1.6-hexanediammonium compound used together with the above water-soluble alkali metal compound has the following formula Y.(CH ₃ ) ₃₃ N-(CH ₂ ) ₆ -N(CH ₆ ) ₃・
Y (wherein Y represents an anion such as a halogen ion, OH ^- ion, 1/2SO ₄ ^--ion, etc.), and this compound can be mixed with other starting materials in this form. or in situ in a mixture, e.g.
It may also be formed by reacting N'-tetramethyl-1,6-hexamethylene diamine with a methyl halide, such as methyl iodide. Such a diammonium compound has an amount of 1×10 ^{−4 to} ₁ per 1 mole of Si and Al in total, converted to the total number of moles of Si and Al in the silica source and alumina source.
It can be used in an amount of mol, preferably 5 x 10 ^-4 to 0.5 mol, more preferably 1 x 10 ^-3 to 1 x 10 ^-1 mol. Furthermore, it is necessary that at least a certain amount of OH ^- ions be present in the raw material mixture, and therefore, at least one of the starting materials other than water used must be one that dissociates OH ^- ions. Such OH ^- ions must be supplied into the mixture by the alkali metal compounds and/or diammonium compounds mentioned above. Therefore, OH ^- ions are contained in the mixture in an amount of 1 x 10 ^-4 to 1.5 mol, preferably 1 x 10 - per 1 mol of Si and Al total in terms of the number of moles of Si and Al in the silica source and alumina source ^. It can be present in an amount of ³ to 1 mol, more preferably 5 x 10 ^-3 to 1.4 mol. Furthermore, the OH ^- ion is present in an amount of 1×10 ⁻⁵ to 1× per 1 mole of water, based on the amount of water in the mixture.
It can be present in an amount of 10 ^-1 mol, preferably 1 x ¹⁰ _-4 to 1 x 10 ^-1 mol, more preferably 1 x 10 ^-4 _to 1 x 10 ^-2 mol. (E) Furthermore, in the raw material mixture, water is (Si
+Al) in a molar ratio of 5 to 100, preferably 10 to 50, particularly 15
A range of ~40 has been found to have favorable results. Alkali metal compounds as described above, N, N,
N,N',N',N'-hexamethyl-1.6-hexanediammonium compound, silica source, alumina source, and water are mixed in the proportions described above, and the resulting mixture is heated at a temperature and for a time sufficient to form zeolite. The desired zeolite can be produced by maintaining heating (that is, subjecting it to a hydrothermal reaction), but the reaction temperature at that time is 80°C.
℃ or higher, particularly preferably within the range of 100 to 200℃. The reaction time is usually 5 hours to 100 days, preferably 10 hours to 50 days, particularly preferably 1 day to 7 days.
Autogenous pressure or higher pressure is applied, and it is generally carried out under autogenous pressure in an autoclave, but if necessary, it is carried out under an inert gas atmosphere such as nitrogen gas. Good too. The zeolite formation reaction is continued by heating the raw mixture to the desired temperature and, if used, under stirring until the zeolite is formed. After crystals have thus formed, the reaction mixture is cooled to room temperature and filtered, preferably so that the ionic conductivity of the washings is generally
50μ/cm or less, preferably 25μ/cm or less,
More preferably, it is thoroughly washed with water until it becomes 15 μ/cm or less, and dried if necessary. Drying of the crystals can be carried out at room temperature or under heating up to about 150°C, and may also be carried out at normal pressure or reduced pressure, for example, at normal pressure of about 50 - 130°C for 5 - 24°C.
It is preferable to do this for about an hour. Note that, if powder particles of zeolite TPZ-3, which is the target product, are made to exist in the raw material mixture before carrying out the above-mentioned zeolite formation reaction, the zeolite formation reaction rate may be increased. Therefore, the desired zeolite is present in the raw material mixture.
Incorporation of small amounts of TPZ-3 powder particles as seeds often provides favorable results. Furthermore, a quaternary ammonium compound and/or a water-soluble amine having a smaller molecular weight than the diammonium compound may be added to the raw material mixture, thereby increasing the reaction rate of zeolite formation. Examples of quaternary ammonium compounds that can be used for this purpose include tetramethylammonium and tetraethylammonium. The amine or ammonium compound has N,
For 1 mole of N,N,N',N',N'-hexamethyl-1.6-hexanediammonium compound
It can be added in a proportion of 0.1 to 10 mol, preferably 0.1 to 5 mol. The thus obtained zeolite TPZ-3 has cations containing alkali metal ions and N, N,
It contains N,N',N',N'-hexamethyl-1.6-hexanediammonium ion, and for example, it can be ion-exchanged by reacting with NH ₄ Cl aqueous solution to replace the cation site with ammonium ion. . The crystals thus obtained are heated at about 100 to about 600℃,
Preferably at a temperature of about 300 to about 500°C, about 8 to about
Calcination may be performed for 24 hours, preferably from about 8 to about 16 hours, thereby removing organic cations and/or ammonium ions from the cation sites, such that the cation sites are substantially alkali metal. Zeolite TPZ-3 consisting of ions and/or hydrogen ions can be obtained. Zeolite produced as described above
TPZ-3 has a characteristic X-ray diffraction pattern, and is clearly distinguished from conventional high-silica-containing zeolites by having at least the following characteristic peaks. For example, as is clear from the table below, a very strong peak at 4.33±0.1 Å is observed in zeolite TPZ-3, but no such peak is observed in the known zeolite ZSM-5. In addition, 4.02±0.05Å for zeolite TPZ-3
A strong peak is observed in zeolite ZSM.
-12, only a relatively weak peak is observed at 4.02±0.05Å. Surface lattice spacing dÅ Relative strength 11.2±0.5 Moderate to strong 9.9±0.5 Moderate to strong 4.67±0.1 Moderate 4.33±0.1 Very strong 4.02±0.05 Strong to very strong 3.83±0.05 Moderate 3.72±0.05 Weak Moderate 3.44±0.04 Weak to strong 3.33±0.04 Weak to strong 3.28±0.03 Moderate These characteristic peaks of the X-ray lattice spacing are based on the type of cation M in the formula () showing the chemical composition of zeolite TPZ-3. It is understood that, although there may be a slight shift in the lattice spacing and/or a slight change in the relative strength due to the Should. Note that the value of the lattice spacing dÅ in the X-ray diffraction patterns described in this invention was determined by standard techniques. That is, the irradiation beam was a copper Kα twin beam, and a self-recording scintillation counting spectrophotometer was used. Peak optical height () and 2θ (θ
(Brang angle) was read from the chart of the spectrophotometer. From this, the relative intensity is 100×/ ₀ ( ₀
was the height of the strongest line or peak) and d, the lattice spacing in Angstroms corresponding to the recorded line. Note that the relative strength is 100 to 60, which is very strong, and 60
~40 is strong, 40-20 is medium, and 20-10 is weak. As long as the zeolite TPZ-3 exhibits the characteristic peak of the above-mentioned X-ray lattice spacing,
It is to be understood that all are included whether or not there are peaks elsewhere. However, in some cases, in addition to the above-mentioned characteristic peaks, a strong peak near 20 Å may be observed in the X-ray diffraction pattern of zeolite TPZ-3, but the presence or absence of this peak essentially depends on the
-3 does not affect the identification. Zeolite TPZ-3 is chemically expressed in the form of an oxide in an anhydrous state by the following general formula () xM ₂ /nO・Al ₂ O ₃・ySiO ₂ ... () [In the formula, M, n, x and y have the meanings given above. ] It has the following composition. In the above formula (), x is an indicator of the amount of cations bonded to the zeolite, and in the case of the zeolite TPZ-3 of the present invention, it can be in the range of 0.5 to 4, preferably 0.9 to 3. . Zeolites, or crystalline aluminosilicates, are basically made up of a combination of silica tetrahedra and alumina tetrahedra, and the charge on the alumina tetrahedra is positively distributed within the crystal. It has a neutralized structure due to the presence of ions. Therefore, in the above formula () representing zeolite, "X" representing the amount of cation is theoretically equal to the amount of alumina, that is, 1, but in reality, zeolite in the synthetic state has It is common for cation precursors that cannot be removed by ordinary washing to be included, and it is rather rare for x to be 1 in actual analytical data of synthesized zeolites. Thus,
"x" in the above formula () represents the amount (number of moles) of the total cations in the purified synthetic zeolite, including the cations of the encapsulated cation precursors that cannot be removed by normal washing. shall be. Further, y, which is an index of silica content, is at least 10, preferably 10 to 2000, and more preferably 10
A range of 500 to 500 is advantageous, and a range of 20 to 250 is particularly preferred because a zeolite with excellent properties can be obtained. Zeolite TPZ-3 has shape selectivity as one of its properties, and this property can be expressed by the cyclohexane/n-hexane adsorption ratio. This adsorption ratio indicates the size of the pores present in the zeolite, and is defined as the ratio of the weight of cyclohexane to the weight of n-hexane adsorbed per unit weight of zeolite under constant temperature and pressure. The fact that this ratio is small means that molecules with a large molecular cross-section, such as cyclohexane, have difficulty diffusing into the pores of the zeolite.
From the viewpoint of catalytic reactions, this leads to improved selectivity.
The adsorption amount of cyclohexane or n-hexane per unit weight of zeolite is determined by weighing a certain amount of zeolite that has been dried by calcining it at 450°C for 8 hours in an electric furnace, and then weighing it at 25°C and 120 + 20 mmH.
The weighed zeolite was kept in a saturated gas atmosphere of g of cyclohexane or n-hexane for 6 hours, and the zeolite was further kept at 25°C and 120±20 mmHg for 2 hours in the absence of cyclohexane or n-hexane, and then cyclohexane or n-hexane was added to the zeolite. It can be determined by weighing the zeolite to which n-hexane has been adsorbed and determining the difference in weight between the zeolite before and after the adsorption operation. Zeolite TPZ-3 generally does not exceed 0.95,
It preferably has a cyclohexane/n-hexane adsorption ratio within the range of 0.1 to 0.95. The zeolite TPZ-3 is also unique in that it has far superior cracking activity compared to commercially available highly active silica-alumina cracking catalysts. This cracking activity can be expressed as a "cracking index" (hereinafter referred to as CI). This CI is expressed as a temperature that gives a constant reaction rate constant in the cracking reaction of hexane, and is specifically measured as follows. After calcining the zeolite or silica-alumina catalyst shaped into 10 to 20 meshes in electricity at 450°C for 8 hours, it was charged into a quartz glass reactor, and then nitrogen gas saturated with hexane was heated at 25°C. Feed the hexane into the reaction tube, measure the conversion rate of hexane, calculate the reaction rate constant at each reaction temperature, and estimate the reaction temperature at which the reaction rate constant becomes 0.5. The CI of zeolite TPZ-3 varies depending on the type and amount of cations present in the cation site, and representative examples are as follows. 300 or less for hydrogen ion type; approximately 300 for beryllium ion type (BeO/Al ₂ O ₃ molar ratio = 0.97)
300; in the case of strontium ion type (SrO/Al ₂ O ₃ molar ratio = 0.95), it was 400. Furthermore, zeolite TPZ-3 has extremely excellent thermal stability; for example, even if it is heat-treated at 800°C for 12 hours or more, the above-mentioned X-ray diffraction pattern does not substantially change. It is understood that it is extremely stable. In the xylenes isomerization method of the present invention, a zeolite TPZ-3 containing at least 10% of the total cation sites is occupied by sodium ions is used. Here, the total cation sites are zeolite TPZ-3.
-3 refers to the number of all cations present (theoretically corresponds approximately to the number of aluminum atoms), of which at least 10%, preferably at least 20%, are cations due to sodium ions. That's fine. A particularly preferred proportion of sodium ions is at least 25%. On the other hand, it is not preferable for the purpose of the present invention that all cation sites be occupied by sodium ions, and the upper limit of the proportion of sodium ions is preferably 99% or less, preferably 95% or less. In the isomerization catalyst of the present invention, in addition to keeping the proportion of sodium ions within a certain range as described above, cations other than sodium ions are ions that exhibit acidity under the isomerization reaction conditions, such as hydrogen ions, ammonium ions, polyvalent ions, etc. It is desirable that it contains metal ions. The zeolite TPZ-3 containing a certain proportion of sodium ions has the following characteristics compared to a zeolite whose cation sites are substantially composed of hydrogen ions. One of them is that the shape selectivity of the pore size of the zeolite TPZ-3 is improved, and therefore the above-mentioned cyclohexane/n-hexane adsorption ratio is greatly improved. The other one is that it contains sodium ions, so acid sites, especially relatively strong acid sites, can be neutralized and the content can be reduced, and the acid strength can also be adjusted. It is possible to control CI (cracking index) to a desired level. Zeolite TPZ of the present invention having such characteristics
-3 is used for the isomerization of xylenes, TPZ
An excellent industrial advantage is obtained in that undesirable side reactions such as xylene and ethylbenzene disproportionation reactions and transalkylation reactions can be reduced to lower values while maintaining the high isomerization activity inherent in -3. Another advantage of the catalyst of the present invention is that such side reactions are suppressed to a relatively low level from the initial stage of the isomerization reaction of xylenes. Zeolite TPZ-3 containing a certain proportion of sodium ions, which is the catalyst of the present invention, can be prepared by various methods as long as the proportion of sodium ions to all cation sites is within the above range. For example, zeolite TPZ-3 obtained according to the production method described above can be used as is, as long as its sodium ions are within the scope of the present invention. In addition, zeolite TPZ, which does not substantially contain or has a low content of sodium ions such as hydrogen ion type and ammonium ion type,
3 may be prepared in advance, and a desired proportion of sodium ions may be introduced therein according to a commonly known ion exchange method. Furthermore, it is also possible to prepare zeolite TPZ-3 in which substantially all cations are composed of sodium ions, and then replace some of the sodium ions with other cations to obtain the desired zeolite TPZ-3 of the present invention. can. When the zeolite TPZ-3 is used in the isomerization reaction of the present invention, the zeolite TPZ-3 may be in the form of a fine powder or, if necessary, in various desired shapes, such as pellets, as is commonly used. Alternatively, it can be formed into a tablet shape and then subjected to such a reaction. When molding zeolite TPZ-3, zeolite TPZ-3 is prepared using a synthetic or natural refractory inorganic oxide, such as silica, alumina, or silica-alumina, which is normally used as a binder for zeolite catalysts. After mixing with , kaolin, silica-magnesia, etc., it can be molded into a desired shape and then baked to harden. The amount of zeolite TPZ-3, which is a catalytically active component, in such a molded product is generally 1 to 100% by weight, preferably 10 to 100% by weight, based on the weight of the molded product.
Advantageously, it is 90% by weight. Upon use, the catalyst thus prepared is heated under a reducing atmosphere, such as in hydrogen gas, for 200 min.
It is also possible to process at temperatures of up to 600°C, preferably between 250 and 550°C. Next, according to the method of the present invention, the sodium cation-containing zeolite TPZ-
A method for isomerizing xylenes using No. 3 as a catalyst will be explained. As the raw material mixture, one containing at least one xylene isomer having a concentration below the thermodynamic equilibrium concentration is used, and one in which the concentration composition of p-xylene is below the thermodynamic equilibrium concentration is particularly advantageously used. Ru. The raw material mixture may be, for example, a mixture of three isomers of p-xylene, m-xylene, and o-xylene, or a mixture of four isomers in which ethylbenzene is included. . These xylene isomer mixtures are mixed into the zeolite (TPZ-3) in the gas phase.
brought into contact with a catalyst. In the isomerization reaction of the present invention, hydrogen may or may not be present in the raw material mixture. However, it is generally preferable to use hydrogen. In this case, hydrogen is desirably used in an amount of 1 to 100 moles per mole of hydrocarbon. Furthermore, in the isomerization of the present invention, non-aromatic hydrocarbons such as ethylcyclohexane, alkyl-substituted cyclopentane, paraffin, and naphthene with a normal pressure boiling point of 50 to 150°C, particularly 120 to 150°C, are used. It can also be carried out by adding. In the isomerization reaction, the weight hourly space velocity (WHSV) is
0.1~200, preferably 0.1~50, and the reaction temperature is 280~500℃, preferably 300℃.
It is appropriate to carry out the reaction at a temperature in the range of ~450°C. Further, the reaction of the present invention is desirably carried out in a pressure range of normal pressure to 30 kg/cm ² G, preferably normal pressure to 25 kg/cm ² G. As described above, according to the present invention, it is possible to obtain a xylene mixture in which the equilibrium attainment rate of p-xylene is extremely high, and the active life of the catalyst is long, so that it is industrially advantageous.
-Can produce xylene. In particular, when the zeolite catalyst is used in the method of the present invention, a unique phenomenon is observed in which a high p-xylene (PX) equilibrium attainment rate can be maintained for several days under normal pressure without using a carrier gas. Furthermore, according to the method of the present invention, side reactions such as disproportionation reactions and transalkylation reactions of xylene and ethylbenzene other than the target isomerization reaction of xylenes are relatively suppressed, and therefore the loss of xylene is also small. This advantage is obtained, and this advantage persists even when the catalyst is used for a long time. The method of the present invention will be described in detail below with reference to Examples. Example 1 Water glass (Wako Pure Chemical Industries, Ltd.) as a silica source
SiO ² 36.24wt%, Na ₂ O 17.30wt%, H ₂ O 46.46wt
%) 3315g, aluminum sulfate as alumina source
266 g of 18 hydrate, 668 g of sulfuric acid as a neutralizing agent, 500 g of sodium chloride as a mineralizing agent, 339 g of N,N,N',N'-tetramethyl-1,6-hexanediamine as an organic ammonium source, 567 g of methyl iodide, and pure water. The gel was prepared from 10. The composition of this product is expressed in molar ratios: SiO ₂ /Al ₂ O ₃ = 50 ammonium salt/Si + Al = 0.096 OH ^- /Si + Al = 0.10 H ₂ O / Si + Al = 30.9 OH ^- /H ₂ O = 3.3 x 10 ^-3. It was hot. This gel was placed in a 200 volume stainless steel autoclave, and reacted for one week at 160° C. under autogenous pressure while being gently stirred. After removing and separating the reactants, wash the washing solution with pure water at 50%
It was washed until it became less than μ/cm and dried at 60°C overnight. This product weighed 1.2 kg, and from the X-ray diffraction diagram shown in Figure 1 and Table 1, it was found to be TPZ-3. The composition of this zeolite, expressed as a molar ratio of oxides, is 1.26RO; 0.21Na ₂ O; Al ₂ O ₃ ; 42.03SiO ₂ ;
4.75H ₂ O and the detected C to N ratio is 0.167
(Theoretical value 0.194).

[Table] Example 2 After baking 315 g of TPZ obtained in Example 1 at 500°C for 6 hours, 100 ml of 10% ammonium chloride aqueous solution was added.
ion exchange under reflux to form ammonium form,
This ion exchange operation was repeated three times. After filtering this, it was thoroughly washed, dried again, and then fired in a Matsufuru furnace at 500°C for 6 hours to obtain hydrogen type TPZ-3.
This will be referred to as Hz hereafter. Table 2 shows the sodium content after ion exchange.
As shown in the figure, the ion exchange rate is extremely low, indicating that ion exchange is almost complete. Also, this H ⁺ -TPZ
The X-ray diffraction of -3 was essentially the same as that before ion exchange, and remained unchanged even after heat treatment at 800°C. Furthermore, 15 g of the thus obtained Hz was ion-exchanged with 100 ml of a 10% aqueous solution of sodium chloride under reflux. This ion exchange operation was repeated three times. After filtering this, it was thoroughly washed, dried again, and fired in an electric Matsufuru furnace at 500°C for 6 hours to obtain NaZ-1. The sodium content is shown in Table 2. As a comparative example, the results of ZSM-5 synthesized according to Japanese Patent Publication No. 46-10064 are also described. Furthermore, using Hz5g, the concentration of the sodium chloride aqueous solution and the number of ion exchange operations were changed, and contact was carried out at 70℃, and various amounts of alkali were introduced.
7 was adjusted. The results are shown in Table-2. Next, NaZ-16g was brought into contact with ammonium chloride aqueous solutions of various concentrations at 70°C.
1 was adjusted. Similarly, using 15g of NaZ, we mixed it with hydrochloric acid of various concentrations.
NaZ-12-15 was prepared by contacting at 70°C. The results are summarized in Table 2.

[Table] Example 3 Various powdered H-TPZ- obtained in Example 2
3. Na-TPZ-3 at 450°C to remove adhering moisture.
After baking in an electric Matsufuru furnace under an air atmosphere for 8 hours, about 1 g was weighed into a weighing bottle. Next, the weighed zeolite was placed in a desiccator containing the adsorbed solvent at 25°C under a reduced pressure of 120 ± 20 mmHg for 6 hours.
By leaving it for a certain period of time, the adsorbed substance was saturated and adsorbed. Next, the adsorbed solvent in the desiccator was removed and further heated at 25°C under reduced pressure of 120±20mmHg for 2 hours.
Evacuated for an hour and weighed again. The adsorption amount of zeolite to the adsorbed substance is determined as follows. V=W ₂ -W ₁ /W ₁ ×100 (%) Here, V (%) is defined as the amount of adsorption per unit amount of zeolite, and W ₁ and W ₂ represent the weight of zeolite before and after adsorption, respectively. The adsorption amounts obtained for H ₂ O, EB, PX, OX, n-hexane, and cyclohexane and the adsorption ratio of n-hexane and cyclohexane (V-cyclohexane/Vn-hexane) are summarized in Table 3 together with comparative examples. Melt.

[Table] From the above results, by introducing sodium ions, molecules with large molecular diameters become difficult to diffuse into the pores, and adsorption selectivity can be significantly improved. Example 4 A mixture of the various zeolites obtained in Example 2 and an equal weight of alumina gel for chromatography was made into pellets, and the particle size was adjusted to 10 to 20 meshes. 450
After baking at ℃ for 8 hours, it was filled into a glass reaction tube. A saturated gas stream (hexane partial pressure = 0.2 atm) after passing nitrogen gas through hexane at 25° C. in an absorption pin was then fed to the catalyst bed. The reaction temperature was adjusted so that the conversion of hexane was in the range of 5 to 40%. Here, the hexane conversion rate is defined as follows. However, the fed hexane is _C6 paraffin containing at least 80% n-hexane. Hexane conversion rate (ε) = 1-hexane concentration in product (%)/10
0 The product was sampled between 10 and 20 minutes after the start of the feed and analyzed using gas chromatography. The reaction rate constant at each reaction temperature was calculated as follows. K=(1/τ)ln1/1−ε where K(sec ^-1 ); rate constant γ(sec); contact time [catalyst volume (ml)/
Feed gas flow rate (ml/sec)] ε; Hexane conversion rate The above hexane conversion rate is determined at a reaction temperature of 150° to 550°.
℃ and a contact time of 1 to 20 seconds. As an index of the cracking activity of the catalyst, the cracking index expressed as the temperature at which the above reaction rate constant becomes 0.5 is summarized in Table 4.

[Table] Cracking activity can be adjusted by controlling the amount of sodium ions introduced into the zeolite. Example 5 A catalyst obtained in the same manner as in Example 4 was activated in an electric Matsufuru furnace at 450° C. in an air atmosphere for 8 hours.
5g of this catalyst was packed into a 16mmφ glass reaction tube into which a thermocouple was inserted, heated from the surrounding area using a nichrome wire heater, and mixed xylene was fed at the desired temperature under normal pressure using hydrogen gas as a carrier, resulting in a xylene isomerization reaction. I did this. The mixed xylene to be fed contained 0.5 wt% toluene, 15 wt% ethylbenzene (EB), 8 wt% paraxylene (PX), and 73.5 wt% metaxylene + ortho-xylene. Table 5 shows the results obtained under the conditions of 450°C, WHSV4 (zeolite standard), and H ₂ /xylene molar ratio of 1. Na-TPZ- which contains a lot of sodium ions
Compared to H-TPZ-3, the rate of deterioration of both the EB disappearance rate and the Xyl loss is slower in the case of 3. Furthermore, it can be seen that NaZ-1, which has the highest sodium content, has significantly improved both conditions.

【table】

[Table]
Table 6 summarizes the Xyl loss for 48 hours under the conditions of 350° C., WHSV4 (zeolite standard), and H ₂ /xylene molar ratio of 1. Although some changes are observed depending on the method of introducing and removing sodium ions, it can be seen that in general, Na-TPZ-3 with 50% or more introduced has Xyl loss suppressed to less than half that of H-TPZ-3. Here, PX equilibrium attainment rate (%) = PX concentration in xylene of product - PX concentration in xylene of feed / PX equilibrium concentration in xylene - PX concentration in xylene of feed x 100 Xyl loss (%) = in feed xylene concentration - xylene concentration in the product / xylene concentration in the feed x 100 EB disappearance rate (%) = EB concentration in the feed - EB concentration in the product / EB concentration in the feed x 100 However, each concentration in the formula is Represents weight percentage.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 shows the TPZ obtained in Example 1 of the present invention.
3 shows the X-ray diffraction diagram of No. 3.

Claims (1)

_{[ Claims ]} 1 _The following formula () represents a hydrogen ion, an alkali metal ion, an alkaline earth metal ion, a group metal ion of the periodic table, or a rare earth metal ion,
n indicates the valence of the ion. x ranges from 0.5 to 4 and y represents a value of at least 10. ] and has the following lattice spacing dÅ relative strength : 11.2±0.5 Moderate to strong 9.9±0.5 Moderate to strong 4.67±0.1 Moderate 4.33±0.1 Very strong 4.02±0.05 Strong to very strong 3.83±0.05 Medium 3.72±0.05 Weak to Medium 3.44±0.04 Weak to Strong 3.33±0.04 Weak to Strong 3.28±0.03 Medium hand,
at least 10 of the total cation sites of the zeolite
Xylenes, characterized in that a catalyst containing zeolite in which % of sodium ions is occupied is brought into contact with a raw material mixture containing xylene isomers, at least one of which has a thermodynamic equilibrium concentration or less, in the gas phase. isomerization method. 2. The catalyst contains at least 20% of the total cation sites.
2. The method for isomerizing xylenes according to claim 1, wherein the method contains a zeolite in which the zeolite is occupied by sodium ions.