JPS623130B2 - - 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-13Å (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 discovered and proposed that X-type zeolite, especially X-type zeolite containing zinc, lithium, cobalt, cadmium, and magnesium, is excellent as a selective adsorbent. As a result of research into improving the performance of such adsorbents, the present inventors found that (a) cadmium and (b) at least one member selected from the group consisting of sodium, lithium, calcium, and zinc. It was discovered that type X zeolite containing a combination of these metals has a much superior selective adsorption ability for _C8 aromatic hydrocarbon isomers other than p-xylene compared to type X zeolite containing these metals alone. The invention has been achieved. That is, the present invention converts a C ₈ aromatic hydrocarbon isomer mixture containing p-xylene into (a) cadmium (a
component), and (b) at least one member selected from the group consisting of sodium, lithium, calcium, and zinc (component b) in a ratio of component a:component b of 1:1 to 1000:1 by weight. By contacting with an adsorbent made of type X zeolite containing p-xylene,
A method for separating p-xylene from the isomer mixture, characterized in that the _C8 aromatic hydrocarbon isomer is selectively adsorbed onto the adsorbent. According to the present invention, a mixture of _C8 aromatic hydrocarbon isomers containing p-xylene is brought into contact with an adsorbent made of type X zeolite containing the components (a) and (b). Then, 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 type X 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 1 to 3, and X is 0 to 9.) Particularly preferred is W in the formula (1). is 2-3
is within the range of As component (b), lithium, calcium or zinc is particularly suitable. The method for synthesizing the X-type zeolite includes heating 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 until crystalline zeolite is formed. It can be adjusted by Regarding the production method of X-type zeolite, for example, Japanese Patent Publications No. 32-6712, No. 33-5722, No. 44-12016
No. 44-23986, No. 42-20387, No. 40-5054
No. 42-845, No. 40-746, No. 38-5806,
It is described in No. 38-5807, No. 44-30611, No. 38-3659, and No. 44-12016. The X-type zeolite mentioned above is a fauziasite type zeolite, and commercially available products can be used, but these are generally alkali metal type or alkaline earth metal type. Therefore, in the conversion to type X zeolite used in the method of the present invention, the alkali metal or alkaline earth metal contained in the type X zeolite is selected from the group consisting of cadmium (component a), sodium, lithium, calcium, and zinc. It is sufficient if at least one type (component b) is used for ion exchange. This ion exchange can be performed by a method commonly used for zeolite ion exchange. That is, it can be carried out by bringing an aqueous solution of chloride, nitrate, etc. containing ions of the metal to be exchanged into contact with the X-type zeolite. 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, followed by ion exchange. Such contact treatment with an ammonium compound involves bringing an aqueous solution of various ammonium salts (for example, ammonium chloride, nitrate, sulfate, carbonate, etc.) into contact with the X-type zeolite and then calcining it to convert it into a hydrogen (H) form. Then perform ion exchange. In that case, the firing temperature is
A range of 200-700°C, preferably 300-600°C is advantageous. Ion exchange can also be carried out by contacting the X-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, the X-type zeolite originally contains lithium,
If it contains sodium or calcium metal ions, these are also the metals in component (b), so the type It is also possible to prepare 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
The appropriate time is 1 hour to 10 hours under normal pressure or vacuum at a temperature in the range of 200°C to 500°C. 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 a process in which one or more xylene isomers have been removed in various ways. By way of example, at least ethylbenzene and/or o-xylene are 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). Ethylbenzene has a boiling point about 3°C higher than the boiling point, and therefore ethylbenzene is
The o-xylene can be removed from the bottom of the column. 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 fractional 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 p-xylene is sent to the second stage crystallizer to obtain p-xylene with a high purity of 99% or more. In the two-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 based on the capacity of the first stage crystallizer. be able to. 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 the cyclodehydrogenation reaction of _C4 olefins is described in, for example, 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 contact filtration adsorption, fixed bed adsorption, moving bed adsorption, and fluidized bed adsorption are advantageously used as the adsorption operation. As adsorption equipment, for contact filtration adsorption, for example, a stirred tank adsorption equipment, for fixed bed adsorption, for example, a column filled with an adsorbent, for moving bed adsorption, for example, a hypersorption equipment or percolation equipment, and for fluidized bed adsorption, for example, 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 adsorption 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 desirable to add a viscosity agent as a binder and form it into a suitable pellet or beet 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 exchanged 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. As such exchange fluid,
Examples include benzene, alkylbenzenes other than the adsorbed _C8 component, halogen-substituted benzenes, and halogen-substituted alkylbenzenes. The adsorption temperature 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. A preferred temperature is room temperature to 350°C, and a particularly preferred temperature is 10 to 250°C. The pressure used in the method of the present invention can be advantageously reduced pressure, normal pressure, or increased pressure, but extremely low pressure (for example, 1 mm
A pressure of 100 mmHg absolute pressure or less and 50 atm or less is undesirable because the amount of adsorbate adsorbed on the zeolite decreases significantly, and increasing the pressure is generally uneconomical. 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 phase (A/B)/molar ratio of non-adsorbed phase (A/B). When the system 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 X-type crystalline aluminosilicate (manufactured by Union Carbide, USA, trade name: Molecular Sieve 13X) and heated on a water bath at 80°C or higher for 2 hours. Stir as above to exchange the sodium form into the ammonium form. After repeating the exchange to the sodium type twice or more, the zeolite is filtered off and thoroughly washed with deionized water until no chloride ions are detected. Subsequently, it is dried at 120°C or higher to remove adhering water, and then fired at about 500°C. The calcination process converts the zeolite into the hydrogen form. Add 10 parts by weight of a 2 mol calcium chloride aqueous solution to 1 part by weight of X-type zeolite converted to hydrogen form.
Stir on a water bath at 80°C or higher for 2 hours or more to convert hydrogen form into calcium form. The zeolite in which at least some of the cation exchange sites have been converted to calcium cations is filtered, washed with deionized water, and then added to 10 parts by weight of a 2 molar cadmium chloride aqueous solution and stirred on a water bath of 80°C or higher for 2 hours or more. After repeating the ion exchange with cadmium twice, the zeolite is decomposed and thoroughly washed with deionized water. By the above cation exchange treatment, X-type sodium ions are exchanged with calcium and cadmium cations. Combinations of other cationic species are treated in the same manner. This zeolite is dried at 120°C or above to remove moisture, and then activated by firing at about 500°C. Approximately 80% by weight of p-xylene, ethylbenzene, m-
Add 10 ml of a mixture of _C8 aromatic hydrocarbon containing approximately xylene and o-xylene and i-octane in a volume ratio of 1:3, and leave to stand at about 50° C. with occasional stirring until adsorption equilibrium is reached. 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 hydrocarbons with respect to p-xylene. Comparative Example 1 A single cation-exchanged zeolite was prepared by heating with 10 parts by weight of an aqueous solution containing 2 moles of cation per 1 part by weight of the zeolite converted to the hydrogen form by the same treatment as in Example 1. For p-xylene in the same manner as in Example 1.
The results of measuring the adsorption selectivity of _C8 aromatic hydrocarbons are shown in Table 1 as a comparative example.

[Table] Comparative example (1) is a commercially available molecular sieve 13X that is simply calcined and contains primary sodium at the cation exchange site in the zeolite. (2) to (5) are single cation exchanged. Combinations of cadmium and sodium, lithium, calcium, and zinc had improved selective adsorption rates and excellent synergistic effects compared to those containing each cation alone. Example 2 Commercially available powder crystalline X-type zeolite (U.S. Union
Manufactured by Carbide, trade name Molecular Sieve
13X) at about 500℃ in advance, and 2
100 ml of molar calcium chloride aqueous solution was added, and the mixture was stirred for 2 hours at a temperature of 80°C or higher. After repeating this process twice, it was filtered and thoroughly washed with deionized water. Further, 100 ml of a 2 mol cadmium chloride aqueous solution was added and stirred for 2 hours at a temperature of 80°C or higher. After repeating this process twice, it was filtered and washed with deionized water until no chlorine ions were detected. Dry adhering moisture at approximately 120℃ or higher, and then dry at 500℃
Activated by firing for an hour. Table 2 shows the results of measuring the cation concentration in the zeolite based on the calcined weight. Furthermore, the results of measuring the adsorption selectivity of _C8 aromatic hydrocarbon isomer to p-xylene in the same manner as in Example 1 are shown.

[Table] Example 3 Commercially available powder crystalline X-type zeolite (U.S. Union
Manufactured by Carbide, trade name Molecular Sieve
13X) was preliminarily calcined at about 500°C, 100ml of a 2 mol cadmium chloride aqueous solution was added per 10g, and the mixture was stirred for 2 hours on a water bath at 80°C or higher. After repeating this process twice, it was filtered and thoroughly washed with deionized water. 2 more
100 ml of molar calcium chloride aqueous solution was added, and the mixture was stirred for 2 hours at a temperature of 80°C or higher. After repeating this process twice, it was filtered and washed with deionized water until no chlorine ions were detected. The cation concentration in the zeolite and the adsorption selectivity of the _C8 aromatic hydrocarbon isomer to p-xylene were measured in the same manner as in Example 2. The results are shown in Table 3.

[Table] Example 4 Using a commercially available X-type crystalline aluminosilicate (manufactured by Union Carbide, USA, trade name: Molecular Sieve 13X), two types of cations were exchanged simultaneously with an aqueous solution containing a mixture of cadmium and calcium chlorides. I did it. That is, 10 g of zeolite and 100 ml of a 2 molar aqueous solution containing cadmium chloride and calcium chloride in an arbitrary ratio were stirred on a water bath at about 80° C. or higher for more than 2 hours. After repeating this process twice, it was filtered and washed with deionized water until no chlorine ions were detected. The zeolite was treated in the same manner as in Example 2, and the cation concentration in the zeolite and the adsorption selectivity of the _C8 aromatic hydrocarbon isomer to p-xylene were measured. Table 4 shows the results.

【table】

Claims (1)

[Claims] 1. A C ₈ aromatic hydrocarbon isomer mixture containing p-xylene is mixed with (a) cadmium (component a) and (b) at least one member selected from the group consisting of sodium, lithium, calcium and zinc (component b). and the ratio of component a to component b is 1:1 to 1000 by weight.
The isomer mixture is brought into contact with an adsorbent made of X-type zeolite in a ratio of 1 to 1 to selectively adsorb C ₈ aromatic hydrocarbon isomers other than p-xylene to the adsorbent. A method for separating p-xylene.