JPS623131B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating p-xylene from a mixture of _C8 aromatic hydrocarbon isomers. More specifically, a _C8 aromatic hydrocarbon isomer mixture is brought into contact with a specific zeolite adsorbent to selectively adsorb aromatic hydrocarbon isomers other than p-xylene contained therein, and then p-
This invention relates to a method for concentrating and separating xylene. Conventionally, adsorption methods, extraction methods, cryogenic separation methods, and the like are known as methods for recovering p-xylene from a _C8 aromatic hydrocarbon isomer mixture containing p-xylene. In general, adsorption methods include selective adsorption of a specific component from a mixture, and conversely, a method of concentrating a specific component by selectively adsorbing and removing other components other than the specific component. There is. Regarding the so-called former method, which is a method of selectively adsorbing and separating only specific components from a _C8 aromatic hydrocarbon isomer mixture, for example, in the case of p-xylene separation,
Special Publication No. 52-936, No. 937, No. 20455, No. 29300
No. 29730 and No. 31328, in the case of ethylbenzene separation, JP-A-49-87636, and m.
- In the case of xylene separation, proposals have been made in Japanese Patent Publications No. 52-933, No. 934, etc. On the other hand, regarding the latter method, that is, a method of selectively adsorbing and removing components other than the specific components and concentrating the specific components, p-xylene is described in Japanese Patent Publication No. 37-5155 and US Pat. No. 3,126,425, and ethylbenzene is described in Japanese Patent Publication It is reported in No. 10223/1983 (US Patent No. 3,917,734). This method is a method for concentrating p-xylene from two or three components containing p-xylene out of a mixture of four isomers of _C8 aromatic hydrocarbons. That is, the method of US Pat. No. 3,126,425 uses
This method uses MS-13A (Ca type) to selectively adsorb and remove m-xylene in the gas phase.
The method of No. 37-5155 uses MS-10X (Ca
m- in the gas phase using MS-13X (Na type) and MS-13X (Na type).
This is a method for selectively adsorbing and removing xylene and o-xylene. However, these methods
It is extremely difficult to selectively concentrate and separate p-xylene from a mixture containing four isomers of _C8 aromatic hydrocarbons. The present inventors have conducted intensive research on an adsorbent that can selectively adsorb the other three isomers excluding p-xylene among the four isomer mixtures of _C8 aromatic hydrocarbons, and can substantially concentrate and separate p-xylene. As a result, it was proposed that L-type zeolite, especially L-type zeolite containing alkali metals, alkaline earth metals, or thallium, is excellent as a selective adsorbent. Therefore, the present inventors conducted research on improving the performance of such adsorbents and found that (a) cesium and
(b) L-type zeolite containing a combination of at least one alkali metal selected from the group consisting of sodium, lithium, and potassium has the ability to selectively adsorb _C8 aromatic hydrocarbon isomers other than p-xylene. The inventors have discovered that these metals are far superior to L-type zeolites containing only these metals, and have thus arrived at the present invention. That is, the present invention provides a C ₈ aromatic hydrocarbon isomer mixture containing p-xylene, (a) cesium, (a
component) and (b) at least one alkali metal selected from the group consisting of sodium, lithium and potassium (component b) in a ratio of component a:component b of 1:1 to 1000:1 by weight. C ₈ aromatic hydrocarbon isomers other than p-xylene are selectively adsorbed on the adsorbent by contacting with an adsorbent made of L-type zeolite containing p-xylene from the isomer mixture. This is a separation method. According to the present invention, when a C ₈ aromatic hydrocarbon isomer mixture containing p-xylene is brought into contact with an adsorbent made of L-type zeolite containing the components (a) and (b), Components other than p-xylene are selectively adsorbed by the adsorbent, and p-xylene can be obtained in high concentration or high purity by separating the adsorbent that has adsorbed components other than p-xylene. The L-type zeolite used in the present invention is preferably one represented by the following formula (1). (However, in the formula, M is the metal of component a and component b, n is the valence of the metal, w is 6.4 ± 0.5, and x is a value of 0 to 7.) As the alkali metal of component (b), Particular preference is given to lithium or potassium. The L-type zeolite can be synthesized by a commonly known method, for example, by adding a raw material mixture containing a silica source such as sodium silicate or silica gel, an alumina source such as sodium aluminate, caustic soda, and water to crystalline zeolite. can be adjusted by heating until . A method for producing L-type zeolite is described, for example, in Japanese Patent Publication No. 36-3675. Commercial products can be used as the L-type zeolite described above, but these are generally of the alkali metal type or alkaline earth metal type. Therefore, the conversion to L-type zeolite used in the method of the present invention involves converting the alkali metal or alkaline earth metal contained in the L-type zeolite to cesium (component a) and a metal selected from the group consisting of sodium, lithium, and potassium. Ion exchange may be performed with at least one type of alkali metal (component b). This ion exchange can be performed by a method commonly used for zeolite ion exchange. That is, it can be carried out by contacting the L-type zeolite with an aqueous solution of chloride, nitrate, etc. containing ions of the metal to be exchanged. At this time, the concentration of salt can be arbitrarily selected, but in the case of an aqueous solution, it is 1 to 20% by weight, especially 5 to 10% by weight.
A weight percent range is preferred. Although ion exchange proceeds satisfactorily at room temperature, it is desirable to raise the temperature to increase the exchange reaction. Further, when direct exchange from an alkali metal or alkaline earth metal results in a low exchange rate, it is also possible to carry out contact treatment with an ammonium compound in advance to exchange ammonium ions, and then carry out ion exchange. Such contact treatment with ammonium compounds can be carried out using various ammonium salts (e.g. ammonium chloride, nitrate,
An aqueous solution of sulfate, carbonate, etc.) is brought into contact with the L-type zeolite and then calcined to convert it into a hydrogen (H) form, which is then ion-exchanged. In that case, the firing temperature is 200-700
C, preferably in the range from 300 to 600C. Ion exchange can also be carried out by contacting the L-type zeolite with the ions of component (a) and ions of component (b) at the same time, but the ions of component (a) are exchanged in advance, and then the ions of component (b) are It is also possible to exchange the ions of component (b) and then exchange the ions of component (a).
It is also possible to exchange component ions. In short, it contains (a) component and (b) component, and (a) component: (b)
Ion exchange may be performed such that the ratio of the components is in the range of 1:1 to 1000:1, preferably 2:1 to 700:1, by weight. In particular, if the L-type zeolite originally contains sodium, lithium, or calicum metal ions, these are also metals of component (b), so simply replacing cesium (a) to achieve the above ratio. Therefore, it is also possible to prepare the L-type zeolite of the present invention. The ion exchange method may be a continuous method or a batch method. When using the batch method, the solid-liquid ratio is 1 to 10.
It is preferable to repeat the treatment about 1 to 10 times depending on the degree. Since the adsorbent that has undergone ion exchange contains a large amount of water, it is desirable to perform dehydration activation treatment. Such activation is carried out by heat treating the zeolite. The treatment temperature can be 100℃ or higher and lower than the decomposition temperature of zeolite, but especially 200℃
The appropriate time is 1 hour to 10 hours under normal pressure or vacuum at a temperature in the range of .degree. C. to 500.degree. The raw material mixture used in the method of the present invention may have a content of p-xylene in any range as long as it is a C ₈ aromatic hydrocarbon isomer mixture containing p-xylene. For example, petroleum-based or tar-based xylene mixtures, or xylene fractions obtained by hydroforming of gasoline fractions can be used as the raw material mixture. The feed stream in the process of the invention can also consist of an effluent stream from the process in which one or more xylene isomers have been removed in various ways. By way of example, at least ethylbenzene and/or
Alternatively, o-xylene is previously removed from a raw material mixture containing xylene isomers by fractional distillation.
Ethylbenzene has a boiling point about 2°C lower than the boiling point of the other nearest C ₈ aromatic hydrocarbon (p-xylene), while o-xylene has a boiling point lower than that of the other nearest C ₈ aromatic hydrocarbon (m-xylene). Approximately 3℃ below boiling point
Since it has a high boiling point, ethylbenzene can be removed from the top and o-xylene from the bottom. Alternatively, components other than p-xylene are removed in advance from a raw material mixture containing xylene isomers by fractional crystallization. In this case, the concentration of p-xylene in the effluent fed as a feed stream to the process of the present invention is high, and the concentrations of other components are low, so the amount of adsorbent used is small, and high purity p-xylene can be produced. It is effective for The combination with this separation crystallization method will be explained next by giving a specific example. A two-stage purification method is generally used to separate and purify p-xylene from a C ₈ aromatic hydrocarbon isomer mixture by a fractional crystallization method. This two-stage purification method is a method in which the purity of p-xylene is increased and separated in the first stage crystallizer, and then the second stage crystallizer is introduced to obtain p-xylene with a high purity of 99% or more. In the stage purification method, p-
By obtaining a mixture containing xylene at a concentration of 75 to 85% and subjecting this mixture to the adsorption treatment of the present invention, a larger amount of high-purity p-xylene can be separated than based on the capacity of the first stage crystallizer. can do. As described above, by combining the fractional crystallization method and the adsorption method of the present invention, it is possible to increase the production amount and provide a method for separating p-xylene. Furthermore, the present invention uses p-xylene-rich _C8 aromatic hydrocarbons obtained by other methods, such as methylation reaction of toluene, disproportionation reaction, and cyclodehydrogenation reaction of olefins such as isobutylene, as a raw material. It is advantageous to combine the adsorption methods. Methods for synthesizing p-xylene-rich _C8 aromatic hydrocarbons by alkylation and disproportionation reactions of toluene are described, for example, in Japanese Patent Publications Nos. 1577-1977, 6652-1982 and 6652-1982, and JP-A-52
-120292, and also describes the cyclodehydrogenation reaction of _C4 olefins, for example, in Japanese Patent Publication No. 41-4577.
No. 52-12179 and No. 52-27723. According to these methods, p-xylene concentration is high in C ₈ aromatic hydrocarbons and ethylbenzene is theoretically absent, so p-xylene can be purified by selective adsorption of other C ₈ aromatic hydrocarbons except p-xylene. It becomes easier. In carrying out the method of the present invention, commonly used contact methods and adsorption devices can be used as the contact method and contact device for bringing the adsorbent and the adsorbed liquid together. Adsorption operations such as catalytic overadsorption, fixed bed adsorption, moving bed adsorption, and fluidized bed adsorption are advantageously used as the adsorption operation. The adsorption equipment may be a stirred tank adsorption equipment for catalytic hyperadsorption, a tower filled with an adsorbent for fixed bed adsorption, a hypersorption equipment or percolation equipment for moving bed adsorption, or a percolation equipment or percolation equipment for fluidized bed adsorption. A tower or the like in which an adsorbent is dispersed in a fluid is used. Further, these adsorption operations can be performed either batchwise or continuously. The contact between the adsorbent and the adsorbing fluid may be in cocurrent or countercurrent, and the fluid may be in a liquid phase or a gaseous phase. The optimum particle size or particle shape of the adsorbent used in the method of the present invention is determined depending on the adsorption operation. When synthetic zeolite is used, for example, in a fixed bed adsorption tank, it usually has fine crystals of several microns, so
When filling the packed tower, it is preferable to add a viscosity agent as a binder and form it into a suitable pellet or bead shape. However, when used in a moving bed or fluidized bed adsorption bed, zeolite crystals may be used as they are, or they may be formed as described above. Methods for desorbing the adsorbed components adsorbed on zeolite by the method of the present invention from the adsorbent include, for example, a thermal desorption method, a method using an exchange fluid, and a method that only reduces the pressure inside the column without heating. In the method using a replacement fluid, the adsorbent containing the adsorbed component is brought into contact with the replacement fluid to desorb the adsorbed component. The replacement fluid may be any fluid as long as it can be replaced and does not adversely affect the adsorption/separation characteristics of the feedstock, especially one that allows easy separation of adsorbed components or feedstock from the replacement fluid. is desirable. Such exchange fluids include, for example, benzene, alkylbenzenes other than the adsorbed _C6 component, halogen-substituted benzenes,
Examples include halogen-substituted alkylbenzene. The temperature at which the adsorption is carried out may be any temperature within a range where the zeolite used does not substantially lose its adsorption ability and selectivity, and which maintains the material to be treated in a liquid or gaseous state. The preferred temperature is room temperature to 350°C, and the particularly preferred temperature is 10 to 250°C. The pressure used in the method of the present invention can be advantageously reduced, normal pressure, or increased pressure, but at extremely low pressures (for example, below 1 mmHg absolute pressure), the equilibrium adsorption amount of adsorbates on zeolite decreases significantly. Since it is undesirable, and it is generally uneconomical to increase the pressure, a pressure of 100 mmHg absolute pressure or more and 50 atmospheres or less is usually preferable. A separation coefficient is usually used to indicate the adsorption separation ability of an adsorbent.
For example, the adsorption selectivity α in the adsorption of a mixture of two components A and B is expressed by the formula α=molar ratio of adsorbed layer (A/B)/molar ratio of non-adsorbed phase (A/B). When the thread is in equilibrium, if α = 1, there is no selectivity of the adsorbent, and if the value of α is significantly greater than 1 or very close to zero, there is no selectivity of the adsorbent. is extremely excellent. Hereinafter, according to the present invention, other _C8 components can be selectively adsorbed and removed from a _C8 aromatic hydrocarbon isomer mixture, particularly a mixture having a p-xylene content of 50% by weight or more, especially 70% by weight or more. Therefore, highly pure p-xylene can be easily separated. The method of the present invention will be described in detail below with reference to Examples. Example 1 10 parts by weight of a 1 mol ammonium chloride aqueous solution was added to 1 part by weight of a commercially available L-type crystalline aluminosilicate (manufactured by Union Carbide, USA, trade name: Molecular Sieve SK-45) at 80°C or above. 2
Stir for more than an hour to exchange sodium form for ammonium form. After repeating this operation three times, the zeolite is thoroughly washed with deionized water until no chloride ions are detected during the washing process. Subsequently, it is dried at 120°C or higher to remove adhering water, and then fired at about 500°C to convert the ammonium-substituted portion into a hydrogen type. Add 10 parts by weight of a 2 mol lithium chloride aqueous solution to 1 part by weight of the L-type zeolite converted to hydrogen form.
Stir on a water bath at 80°C or higher for 2 hours or more to convert at least 50% of the cation exchange sites into lithium. Next, the zeolite is filtered, and 10 parts by weight of a 2 mol cesium chloride aqueous solution is added thereto, followed by stirring on a water bath at 80°C or above for 2 hours or more. After repeating the treatment with an aqueous cesium chloride solution twice or more to perform ion exchange to a predetermined ratio, the zeolite is separated and thoroughly washed with deionized water. This cation exchange treatment removes at least the potassium and sodium ions of commercially available L-type zeolite.
Converts more than 80% to cesium and lithium ions. The other combinations of cation species listed in Table 1 below are treated in the same manner. The cation-exchanged zeolite is dried at 120°C or above to remove moisture, and then activated by firing at approximately 500°C for several hours. p for 2g of cation-exchanged L-type zeolite
- Add 10 ml of a solution of a _C8 aromatic hydrocarbon mixture containing approximately 80% by weight of xylene and approximately equal amounts of ethylbenzene, m-xylene, and o-xylene mixed with i-octane in a volume ratio of 1:3 to achieve adsorption equilibrium at room temperature. Leave it to stand, stirring occasionally, until it becomes . The composition of _C8 aromatic hydrocarbons in the liquid phase and adsorption phase was measured by gas chromatography. Table 1 shows the adsorption selectivity of other _C8 aromatic hydrocarbon isomers to p-xylene.

【table】

[Table] As is clear from this table, by ion-exchanging L-type zeolite containing cesium with a combination of potassium and lithium, the average selective adsorption rate of other C ₈ aromatic hydrocarbon isomers to p-xylene can be improved. It can be seen that it is highly effective compared to other comparative examples. Example 2 Commercially available powder crystal L-type zeolite (trade name: Molecular Sieve SK- manufactured by Union Carbide Company, USA)
45) was preliminarily calcined at about 500°C, 100ml of a 2 mol cesium chloride aqueous solution was added per 10g of the mixture, and the mixture was stirred for 2 hours on a water bath at 80°C or higher. After repeating this process twice, the zeolite was separated and washed with deionized water until no chloride ions were detected in the solution. The moisture adhering to the zeolite surface was dried at about 120°C or higher, and the zeolite was activated by firing at 500°C for about 3 hours. The results of measuring the cation concentration and adsorption performance of the activated zeolite on a weight basis are shown in Table 2 below.

【table】

Claims (1)

[Claims] 1 A C ₈ aromatic hydrocarbon isomer mixture containing p-xylene is mixed with (a) cesium (component a) and (b) at least one alkali metal selected from the group consisting of sodium, lithium and potassium (component b). )
and the ratio of component a to component b is 1:1 to 1 by weight.
The isomer mixture is brought into contact with an adsorbent made of L-type zeolite containing at a ratio of 1000:1, and C ₈ aromatic hydrocarbon isomers other than p-xylene are selectively adsorbed on the adsorbent. p-
How to separate xylene.