JP2002302461A - Method for producing para-xylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the production of p-xylene with a small investment to reduce the production cost. SOLUTION: This method for producing p-xylene from mixed xylene containing ethylbenzene contains the following five steps. (1) A step to recover p-xylene; (2) a step to isomerize o-xylene and m-xylene to p-xylene; (3) a step to increase the concentration of p-xylene by membrane separation; (4) a step to remove ethylbenzene; and (5) a step to remove low-boiling components and high-boiling components from the xylenes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing para-xylene, which is a raw material for polyester, from mixed xylene containing ethylbenzene. The present invention relates to a method for producing para-xylene more efficiently than the current production process.

[0002]

2. Description of the Related Art Generally, a method for producing para-xylene from mixed xylene containing ethylbenzene comprises a step of separating and recovering para-xylene from a mixed xylene containing ethylbenzene and a step of isomerizing ortho-xylene and meta-xylene to para-xylene. .

[0003] Paraxylene is separated and recovered by a crystallization separation method (cryogenic crystallization separation method) utilizing the fact that para-xylene has a higher melting point than other isomers or an adsorption separation method based on the principle of liquid chromatography. It is practiced industrially.

Above all, the adsorptive separation method is currently the most widely practiced method, in which xylene as a raw material moves in an adsorber packed with an adsorbent while para-xylene has a stronger adsorbing power than other isomers. Is adsorbed and separated from other isomers. Next, para-xylene is extracted out of the system by a desorbing agent, and is separated from a desorbing liquid by distillation after desorption. The actual process includes the UOP PAREX method and Toray's A
The ROMAX method is exemplified. The recovery of para-xylene is 1
More than 90% by pass and the purity of para-xylene is 99.5%. This adsorption separation method is an excellent process in which the recovery and purity of para-xylene are higher than those of other separation methods, and the operation cost is low. The use of special rotary valves and sequence control solenoid valves, as well as the use of special zeolites as adsorbents, make the equipment extremely expensive to construct.

[0005] Ethylbenzene contained in the raw material is removed by dealkylation in the isomerization step or isomerization to xylene via 5-membered ring naphthene to prevent the accumulation of ethylbenzene in the system.

[0006]

As described above, since the construction of the adsorption / separation apparatus is extremely expensive, it is desirable to maximize the capacity of the adsorption / separation apparatus when producing para-xylene. However, xylene passed through the adsorption separation is a mixture of four isomers of ethylbenzene, para-xylene, meta-xylene, and ortho-xylene, and the para-xylene concentration does not exceed the thermodynamic equilibrium value. Has become. On the other hand, even if paraxylene is separated and the remaining components are isomerized and recycled to the separation and recovery step, they are not isomerized to para-xylene beyond the thermodynamic equilibrium value and are recycled. The para-xylene concentration of the isomerized xylene is also less than 24%. That is, in the adsorption / separation apparatus, adsorption and desorption operations are performed together with the remaining 76% or more of ethylbenzene, ortho-xylene, and meta-xylene in order to adsorb and separate less than 24% of para-xylene.

[0007] If the concentration of para-xylene in xylene passing through the adsorption separation apparatus is increased, the production efficiency of para-xylene is greatly improved. In order to solve this, WO97 / 27162 proposes to incorporate a step of passing the isomerized mixed xylene through a molecular sieve membrane to increase the paraxylene concentration into the paraxylene production process. This proposes to increase the para-xylene concentration by taking advantage of the fact that para-xylene having the smallest minimum molecular size is more likely to pass through a molecular sieve membrane than ortho-xylene and meta-xylene. However, the minimum molecular size of ethylbenzene contained in the xylene raw material is the same as that of para-xylene, which should inhibit the passage of para-xylene in the molecular sieve membrane.In the present invention, the coexisting ethylbenzene is the molecular sieve membrane. Is supplied to In the process of the present invention,
It is postulated that ethylbenzene and benzene, naphthene, and ethane converted from ethylbenzene in the isomerization step are inhibiting membrane permeation of para-xylene.

An object of the present invention is to provide a process for minimizing the introduction of ethylbenzene in the step of increasing the paraxylene concentration by membrane separation.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to achieve this object, and as a result, have reached the present invention. The present invention is a method for producing para-xylene from mixed xylene containing ethylbenzene, which comprises the following five steps. (1) Step of separating and recovering para-xylene (2) Step of isomerizing ortho-xylene and meta-xylene to para-xylene (3) Step of increasing para-xylene concentration by membrane separation (4) Step of removing ethylbenzene (5) A step of removing low-boiling and high-boiling compounds from xylenes.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method for producing para-xylene of the present invention will be described in detail.

The feedstock supplied to the process of the present invention is a mixed xylene containing ethylbenzene. In general, xylene raw materials used industrially are obtained by improving naphtha, followed by aromatic extraction and reforming oil-based xylene obtained by aromatic extraction and fractionation, or cracked gasoline by-produced by thermal decomposition of naphtha. Crude oil-based xylene obtained by fractional distillation. A characteristic feature of the cracked oil-based xylene is that the concentration of ethylbenzene is more than twice as high as that of the reformed oil-based. The typical composition is shown in Table 1.

[0012]

[Table 1]

In the process of the present invention, the mixed xylene containing ethylbenzene as described above is used as a raw material, and five steps are essential for efficiently producing para-xylene.

The first step is a step of separating and recovering para-xylene. That is, this is a step of separating only para-xylene from the xylene component. A typical industrially practiced method for separating para-xylene is a crystallization separation method utilizing the fact that para-xylene has a higher freezing point than other xylene components, and a difference in adsorption power to a solid such as zeolite. This is an adsorption separation method utilizing

[0015] The crystallization separation method is a method that has been practiced from the earliest, and a process having a difference in crystallization conditions, crystal separation method, and the like has been put to practical use. However, compared with the adsorption separation, there are problems such as a lower recovery rate of para-xylene in one-pass treatment and a lower purity of para-xylene, and the number of new constructions is reduced.

In the present invention, it is preferable to use an adsorption separation method as a method for separating and recovering para-xylene. As the raw xylene moves through the adsorption tower filled with the adsorbent, para-xylene having a higher adsorptivity than other isomers is adsorbed and separated from other isomers. Next, para-xylene is extracted out of the system by a desorbing agent, and is separated from a desorbing liquid by distillation after desorption. As a desorbing agent, para-diethylbenzene is preferably used. As the adsorbent, faujasite zeolite exchanged with potassium or barium ions is preferably used. Actual processes include the UOP PAREX method and the Toray AROMAX method. The para-xylene concentration in xylene of the liquid introduced into this step is 2 in ordinary para-xylene production.
Although it is about 0%, in the present invention, it is preferably at least 25%. The higher the concentration of para-xylene, the greater the amount of para-xylene recovered in one pass, which is preferable from the viewpoint of energy saving and reduction of fixed cost. The relationship between the para-xylene concentration in the liquid introduced into this step and the para-xylene productivity differs depending on the adsorbent, desorbent, and operating conditions in this step. Here, the productivity refers to the amount of para-xylene product relative to the total amount of liquid introduced into the present process per unit time. For example, if the para-xylene concentration doubles, the productivity increases 1.5 to 2 times. Also,
If the paraxylene concentration is tripled, the productivity will be double to triple.

The second step is a step of isomerizing ortho-xylene and meta-xylene to para-xylene. In the isomerization step of a normal para-xylene production process, ortho-xylene and meta-xylene containing ethylbenzene are isomerized.
At that time, it is essential that ethylbenzene be hydrodeethylated to benzene and ethane, or converted to xylene via naphthene. However, in the process of the present invention, since there is another step of removing ethylbenzene, the function of converting ethylbenzene may not necessarily be added in the isomerization step. In the present invention, it is preferable that the liquid passing through the xylene isomerization step contains little ethylbenzene. The concentration of ethylbenzene in the oil passing liquid is preferably 2% by weight or less, more preferably 1% by weight or less. This step may have the function of removing ethylbenzene, but if a large amount of ethylbenzene is present, the ethylbenzene is deethylated and converted to benzene, and after the isomerization step, ethane or It is necessary to provide a process for removing benzene so that ethane and benzene do not go to the third process as much as possible. The catalyst used here is not particularly limited, but is preferably an acid-type zeolite. Particularly preferred are MFI-type zeolites. The reaction system is preferably a stationary phase flow reaction system, and may be a liquid phase or a gas phase.
In the case of the liquid phase, the yield of the isomerization reaction is high, which is preferable.

The third step is a step of increasing the para-xylene concentration by membrane separation. This step is a step of increasing the concentration of para-xylene using a molecular sieve membrane that transmits para-xylene having the smallest molecular size from a mixture of para-xylene, ortho-xylene, and meta-xylene. Ethylbenzene and benzene, which are molecules of the same size as para-xylene, penetrate the membrane to the same extent as para-xylene, and it is not preferable that such molecules coexist.
In the process of the present invention, fourth and fifth steps are provided in order to lower the concentration of ethylbenzene or benzene having the same minimum molecular size as paraxylene in the liquid passing through this step. The greatest feature of the present invention is that the concentration of ethylbenzene and benzene in the liquid passed through the third step is low, and it is preferable that the concentration be 1% by weight or less. The combination of the second step and the third step is preferably performed. In the third step, the concentration of para-xylene in the liquid supplied to the film is preferably higher. Therefore, it is most preferable to separate only para-xylene while isomerizing. In addition, the xylene isomerization reaction is an equilibrium reaction, and the concentration of para-xylene does not exceed the equilibrium composition, so it is a membrane from which para-xylene can be selectively extracted out of the system.
Isomerization while removing para-xylene is preferable because the efficiency of the isomerization reaction to para-xylene increases.

The membrane used for membrane separation is preferably a zeolite membrane. Among the zeolite membranes, an MFI type membrane is preferably used. The method of forming the zeolite membrane is not particularly limited, but a generally known method can be applied. For example, when a zeolite or zeolite analog membrane is coated on a support, a method of subjecting the support to a precursor gel for synthesizing zeolite or a zeolite analog and performing a hydrothermal treatment (eg, 63-291809), and the support is previously provided with a seed crystal of zeolite or a zeolite analog.
A method of coating and then immersing the precursor gel in hydrothermal treatment (eg, JP-A-7-109116, Microporous and Meso
Porous Materials 38 (2000) 61-73), a method in which a precursor gel is coated on the surface of a support, dried, and then treated with steam (eg, JP-A-7-89714), or zeolite or zeolite-like fine particles are used as they are. Method such as coating method (Japanese Patent Publication No. 5-50331)
Can be applied. The method for coating the support with the seed crystal of zeolite or zeolite analog, the precursor gel of zeolite or zeolite analog, or the zeolite or zeolite analog fine particles is not particularly limited, and any known method can be applied. For example, a method in which a support is immersed in a slurry and then pulled up as it is, a method of applying, a method in which one side of the support is brought into contact with the slurry and the pressure is reduced from the other side, and a method in which the slurry is pressed from one side of the support by applying pressure. Can be considered. The coating of the zeolite membrane may be performed twice or more. Further, it is preferable to perform the measurement twice or more in terms of denseness. After the zeolite or zeolite-like membrane is formed, the membrane may be subjected to treatments such as washing with water, drying and baking.
Whether or not a zeolite membrane has been formed can be confirmed using an X-ray diffractometer for a thin film.

The fourth step is a step for removing ethylbenzene. The method for removing ethylbenzene is not particularly limited, but (1) a method in which ethylbenzene is dealkylated to benzene, (2) a method in which paraxylene is removed in a separation and recovery step, and then a membrane separation is performed;
For example, adsorption separation of ethylbenzene can be considered. The most preferred method is the method (1). Specifically, in the presence of hydrogen, xylenes containing ethylbenzene are passed through a catalyst layer containing zeolite and a hydrogenated metal, and highly dealkylated ethylbenzene without losing xylene as much as possible to form benzene and ethane. It is a conversion. Specifically, the technique of Japanese Patent Publication No. 5-87054 can be used. As the dealkylation catalyst, an acid type MFI type catalyst is used. In the present invention, it is preferable to remove the ethylbenzene in this step until the concentration of ethylbenzene becomes 1% or less of the whole.

The fifth step is a step of removing low-boiling compounds and high-boiling compounds that can be duplicated in the second step and the fourth step, and usually employs a distillation process or gas-liquid separation.

Hereinafter, the process of the present invention will be specifically described with reference to the drawings.

(Comparative Process: Current) FIG. 1 shows a normal para-xylene production process. 1 is a separation and recovery step of para-xylene. Either adsorption separation or cryogenic separation may be used. Adsorption separation is preferred, and the adsorption separation will be described as an example. Toray's AROMAX method, UOP's PAREX
Law can be used. The recovery of para-xylene in these adsorptive separations can be 97% and the purity of para-xylene can be 99.9%. The liquid from which para-xylene has been removed is sent to the isomerization step 3. The ethylbenzene contained in the feed is converted here. Methods for converting ethylbenzene include a method of isomerizing ethylbenzene to xylene via naphthene (modified xylene isomerization) and a method of dealkylating ethylbenzene (dealkylated xylene isomerization). Here, a method of dealkylating ethylbenzene and converting it to benzene will be described as an example. UOP I-100, Mobil MHAI, M as catalysts
Although HTI is used, Toray's ISOLENE catalyst is preferably used because it has the least loss of xylene. The reaction conditions and the like are not particularly limited, but the isomerization is usually performed at a high temperature (300 ° C. to 400 ° C.) and a high pressure (0.5 to 1.5 MPa) in the presence of hydrogen with a catalyst based on acidic zeolite. In this step, ethylbenzene is converted to 65%. Xylene is isomerized to an equilibrium composition. The xylene loss in this step can be between 1.5 and 2.0 if the catalyst and operating conditions are optimized.
%. Increasing the conversion of ethylbenzene increases xylene loss, and lowering the conversion results in accumulation of ethylbenzene in the system. The para-xylene concentration in the total xylene after isomerization is 23 to 24%. The second step is a step of separating a substance other than the C8 aromatic produced in the third step by a distillation operation or gas-liquid separation. The raw material xylene usually contains 15 to 18% of ethylbenzene. Since the para-xylene concentration is only 23% in the isomerization step, it is necessary to pass through the isomerization step about four times before the raw xylene is converted to para-xylene, and the loss of xylene is 6 to 8%.
Becomes Further, the concentration of paraxylene supplied to the paraxylene recovery step is about 21%, does not exceed 24% in theory, and there is no method for increasing the production except for building a new process.

(Process 1 of the Present Invention) FIG. 2 shows an example of the process of the present invention. In step 3, an ethylbenzene dealkylation step can be used as an ethylbenzene removal step. In this step, the technique disclosed in Japanese Patent Publication No. 5-87054 can be used. In this process, 99% of ethylbenzene
After the above conversion, the amount of ethylbenzene is reduced to 1% by weight or less, a xylene mixture containing only 1% by weight or less of ethylbenzene is supplied to a circulation system for isomerization, membrane separation, and adsorption separation. Step 2 is a distillation process and a gas-liquid separation process, in which low-boiling components such as ethane, benzene, and toluene and C9
+ This is a step of removing high boiling components such as aromatics. The removal by the gas-liquid separation in the step 2 is preferably provided immediately after the steps 3 and 4. In this case, only the distillation column is located at the place of Step 2. The xylene mixture from which the low-boiling components and high-boiling components have been removed goes to a para-xylene recovery step (step 1), where para-xylene is recovered. As the para-xylene recovery step, the adsorption separation process mentioned in the comparative process can be preferably used. Step 4 is an isomerization step of converting the xylene mixture having a small amount of para-xylene from the separation and recovery step of para-xylene (step 1) into xylene having an equilibrium composition. The catalyst used in this step can be the same as that used in the comparison process described above. Since the remaining small amount of ethylbenzene is further dealkylated, it does not accumulate in the system, the amount of ethylbenzene is small, and does not significantly inhibit the membrane permeation of para-xylene in step 5. A part of the xylene mixture which has reached the equilibrium composition in Step 4 goes to Step 5, but a part does not pass through Step 5, but is passed through Step 2 together with the high-concentration para-xylene coming out of Step 5. By-products from side reactions in the isomerization step, especially C9
+ A part of the mixture is passed to step 2 to prevent high boiling compounds such as aromatics from accumulating in the isomerization / membrane separation system. Step 5 is
This is a step of concentrating para-xylene using a zeolite membrane. The mixed xylene from step 4 is concentrated by the molecular sieve membrane through which para-xylene with the smallest minimum molecular diameter selectively permeates. Specifically, the molecular sieve membrane is a zeolite membrane having pores having a uniform molecular size. The high-concentration para-xylene that has passed through the membrane is supplied to step 2, and the low-concentration para-xylene after the selective permeation of para-xylene is supplied again to step 4, where it is isomerized to xylene having an equilibrium composition. From step 5, mixed xylene having a paraxylene concentration of 24% or more is mixed with mixed xylene having a paraxylene concentration of 23% from step 4, and mixed xylene having a paraxylene concentration of 23% from step 3 is added. Since the concentration of para-xylene in xylene supplied to the reactor becomes higher than 24%, the production can be finally increased by the same adsorption separation equipment.

(Process 2 of the Present Invention) The process shown in FIG. 3 is a case where the isomerization step 4 is filled with a catalyst having only the function of isomerizing ability without having the dealkylating ability of ethylbenzene. For example, there is a case where isomerization is performed under mild conditions in a liquid phase. In this case, ethylbenzene accumulates in the system because the cycle of isomerization / adsorption separation has no function of dealkylating ethylbenzene. Therefore, before supplying the raw materials to the isomerization step, a part is supplied to the step 3 so that the ethylbenzene concentration is kept constant in the system. Step 3
Since the dealkylation step also has the ability to isomerize xylene, xylene supplied from step 1 having a low para-xylene concentration can not only remove ethylbenzene, but also
Para-xylene can also be regenerated. The advantage of this process is that the loss of xylene in the isomerization step 4 can be reduced because the isomerization reaction can be performed under mild conditions.

(Process 3 of the Present Invention) The process shown in FIG. 4 is a case where the step 3 for removing ethylbenzene is provided after the step for recovering para-xylene. In this case, since the para-xylene concentration in the liquid passed through the deethylbenzene step is low, using a membrane similar to the membrane for separating para-xylene,
Ethylbenzene can be removed. Of course, a dealkylation catalyst may be used as in the above-described method. In the dealkylation reaction, para-xylene is most disproportionated, so xylene loss in step 3 can be reduced by dealkylating at a low para-xylene concentration. In this step, it is preferable to remove 90% or more of ethylbenzene. After removing ethylbenzene, isomerization step 4
Isomerizes xylene to an equilibrium composition. At this stage,
Since high-boiling products and low-boiling products generated in the steps 3 and 4 are contained, they are removed in the distillation step 2. The mixed xylene substantially containing only the C8 component is supplied to the membrane separation step 5 to improve the para-xylene concentration. Xylene having a low para-xylene concentration after the permeation of para-xylene is returned to step 3 or 4. Whether to return to step 3 or to return to step 4 depends on the dealkylation ability in step 4 and the ability to remove ethylbenzene in step 3. 100% in step 3
If ethylbenzene can be removed, return to 4
If the dealkylation ability is not sufficient in the step 4 and the liquid from the step 3 contains ethylbenzene,
It is necessary to return to step 3 to avoid accumulation of ethylbenzene. Since isomerization catalysts that are commonly used also have the ability to dealkylate ethylbenzene, steps 3 and 4 involve:
It may be one process. Separating the catalyst component having high dealkylation ability and the component having high isomerization ability in a commonly used isomerization catalyst to prepare a catalyst and separately charging the catalysts in Steps 3 and 4 reduces xylene loss. Excellent in point. In any case, it is important to highly dealkylate ethylbenzene to remove 90% or more of ethylbenzene.

(Process 4 of the Present Invention) The process shown in FIG. 5 is the same as the process of FIG. 4 except that mixed xylene containing ethylbenzene as a raw material is directly supplied to the deethylbenzene step 3. In this case, since the concentration of para-xylene in the xylene supplied to the step 3 is higher than that in the case of FIG. 4, it is not preferable to remove ethylbenzene by membrane separation. In the deethylbenzene step, it is preferable to convert 90% or more of ethylbenzene. If the ordinary dealkylation type isomerization catalyst is packed by combining the steps 3 and 4, the membrane separation step 5 can be simply added to the conventional paraxylene production facility, and the capital investment can be minimized. However, also in this case, it is important that ethylbenzene be highly dealkylated and removed.

(Process 5 of the Present Invention) The process shown in FIG. 6 is basically the same as the process of FIG. 2, but illustrates the step 4 of the membrane reactor system in which the membrane separation and the isomerization steps are combined. This is a case where it is installed in place of Steps 4 and 5 of Step 2. This reactor is characterized in that it isomerizes while removing para-xylene as a product, so that it can be isomerized very efficiently. By controlling the permeation rate and isomerization rate of para-xylene, it is preferable that the liquid permeating through the membrane has a high concentration of para-xylene, and the xylene which has not permeated and exits from the reactor outlet has an equilibrium composition. In order to operate this membrane reactor efficiently,
It is important that ethylbenzene in the raw material mixed xylene be removed to a high degree in Step 3.

[0029]

The process of the present invention will be described more specifically with reference to the following examples.

Example 1 Ethylbenzene hydrodeethylation step 1, paraxylene recovery step 2 by simulated moving bed adsorption separation, isomerization step 3, paraxylene membrane separation step 4 using zeolite membrane, and xylene Steps 5 to 7 for separating and removing low-boiling and high-boiling compounds were combined to form a para-xylene production facility as shown in FIG. The operating conditions of each step are shown below. The molar ratio of ethylbenzene / xylene in the raw material mixed xylene was 0.17.

(1) Hydrodeethylation step of ethylbenzene Method: fixed bed gas phase flow reaction method Catalyst: Japanese Patent Publication No. 5-87054 Catalyst described in Example 3 Ethylbenzene conversion: 99% (2) Para-xylene recovery step : Liquid phase simulated moving bed adsorption separation method Adsorbent: AROMAX adsorbent Desorbent: para-diethylbenzene Product para-xylene purity: 99.4% (3) Xylene isomerization step Method: Stationary phase gas phase flow reaction system Catalyst: Toray ISOLENE Catalyst Para-xylene / xylene after isomerization reaction = 23.0% Ethylbenzene conversion: 50 to 65% (4) Membrane separation process Method: Membrane separation method Membrane: MFI type zeolite membrane (on a tubular α-alumina porous support) An MFI-type zeolite membrane was grown on the membrane.) Paraxylene / xylene concentration 50% after passing through the membrane. That by varying the ratio of the amount of liquid fed from the liquid amount and the step 3 to the gas-liquid separation step 5 directly, it is possible to change the paraxylene concentration entering the paraxylene recovery process. When the liquid volume ratio was 10: 1, the para-xylene concentration in the para-xylene recovery step was about 30%. About 25
% Para-xylene can be increased.

(Example 2) Ethylbenzene hydrodeethylation step 1, paraxylene recovery step 2 by simulated moving bed adsorption separation, membrane reactor step 3 in which membrane separation and isomerization steps are combined, and xylene Steps 4 to 6 for separating and removing compounds having a lower boiling point and a higher boiling point were combined to constitute a para-xylene production facility as shown in FIG. The operating conditions of each step are shown below. The molar ratio of ethylbenzene / xylene in the raw material mixed xylene is 0.1.
It was 17.

(1) Hydrodeethylation step of ethylbenzene Method: fixed bed gas phase flow reaction method Catalyst: Japanese Patent Publication No. 5-87054 Catalyst described in Example 3 Ethylbenzene conversion: 99% (2) Para-xylene recovery step : Liquid phase simulated moving bed adsorption separation method Adsorbent: AROMAX adsorbent Desorbent: para-diethylbenzene Product para-xylene purity: 99.4% (3) Xylene isomerization and membrane separation (membrane reactor) process Method: stationary phase gas phase flow Reaction system Catalyst: Toray's ISOLENE catalyst Paraxylene / xylene after isomerization reaction = 23.0% Ethylbenzene conversion: 50 to 65% Membrane: MFI type zeolite membrane (MFI type on a tubular alumina-alumina porous support, (A zeolite membrane is grown.) After passing through the membrane, para-xylene / xylene 50% N'yori low boiling after removal by distillation of high-boiling compounds were introduced into the adsorption separation process. It is possible to increase paraxylene production by about 100%.

[0034]

As is clear from the above-described embodiments, according to the method for producing para-xylene of the present invention, it is possible not only to increase the production of para-xylene with little capital investment but also to reduce the influence of ethylbenzene on membrane separation. It can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a current paraxylene production process.

FIG. 2 is a schematic view showing an example of a process flow suitable for performing the method for producing para-xylene of the present invention.

FIG. 3 is a schematic view showing an example of a process flow suitable for performing the method for producing para-xylene of the present invention.

FIG. 4 is a schematic view showing an example of a process flow suitable for performing the method for producing para-xylene of the present invention.

FIG. 5 is a schematic view showing an example of a process flow suitable for performing the method for producing para-xylene of the present invention.

FIG. 6 is a schematic view showing an example of a process flow suitable for performing the method for producing para-xylene of the present invention.

FIG. 7 is a diagram illustrating a process flow according to the first embodiment.

FIG. 8 is a diagram illustrating a process flow according to a second embodiment.

Claims (3)

[Claims] 1. A method comprising the following five steps:
A method for producing para-xylene from mixed xylene containing ethylbenzene. (1) Step of recovering para-xylene (2) Step of isomerizing ortho-xylene and meta-xylene to para-xylene (3) Step of increasing para-xylene concentration by membrane separation (4) Step of removing ethylbenzene (5) Xylene For removing low-boiling and high-boiling compounds from water 2. The method for producing para-xylene according to claim 1, wherein the step of removing ethylbenzene is a step of hydrodealkylating ethylbenzene by 90% or more to form benzene and ethane. 3. The method for producing para-xylene according to claim 1, wherein the step of recovering para-xylene is performed by an adsorption separation method.