JPH10212251A - Production of metaxylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process of m-xylene by isomerization of o-xylene in which the catalyst does not cause deterioration in its catalytic activity even in the case that the regeneration of the catalyst is repeated. SOLUTION: A catalyst containing ZSM-4 and/or ω-zeolite, a kind of crystalline aluminosilicate zeolite, is used to isomerize o-xylene in the vapor or liquid phase to produce m-xylene. In this case, the catalyst of which isomerization activity is deteriorated is regenerated in an oxygen-containing gas at a temperature of <=400 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing meta-xylene from ortho-xylene.

[0002]

BACKGROUND OF THE INVENTION Xylene isomers consist of para-xylene, meta-xylene, ortho-xylene and ethylbenzene,
Para-xylene is used as a raw material for polyester fibers, polyester films, etc., meta-xylene is used as a raw material for heat-resistant aramid fibers, alkyd resins, etc., ortho-xylene is used as a raw material for plasticizers, etc., and ethylbenzene is used as a raw material for polystyrene, etc., respectively. It is an important chemical. Among them, meta-xylene has recently been significantly increased in demand as a raw material for heat-resistant fibers obtained by subjecting it to isophthalic chloride by a condensation polymerization reaction with meta-phenylenediamine.

Conventionally, meta-xylene has been produced by selectively extracting meta-xylene by complex formation from mixed xylene containing the aforementioned xylene isomer as a main component. This manufacturing method is characterized in that the reaction can be carried out at a low temperature and a low pressure, so that the equipment can be made compact.

[0004] However, this production method is a liquid phase homogeneous reaction using a highly corrosive hydrogen fluoride-boron trifluoride complex in the extraction step and the isomerization step, and requires a step of recovering the catalyst. From the point that the equipment cost is high, furthermore, when using normal mixed xylene, a precision distillation step for removing ethylbenzene is required, and when not producing para-xylene or ortho-xylene together, the process is There is a significant drawback in that the amount of internal circulation is significantly increased and requires a large amount of energy.

On the other hand, mixed xylene obtained from petroleum reformate or cracked gasoline contains meta-xylene in an amount close to the thermodynamic equilibrium composition. However, it is extremely difficult to separate meta-xylene from these raw materials by a distillation method or a crystallization method in view of the numerical value of the boiling point / melting point between xylene isomers.

That is, in the distillation method, ortho-xylene (boiling point: 144.41 ° C.) and ethylbenzene (boiling point: 1
Although it is possible to separate meta-xylene from 36.19 ° C.), it is difficult to separate meta-xylene (boiling point 139.10 ° C.) and para-xylene (boiling point 138.35 ° C.). Ortho-xylene (melting point −25.17 ° C.)
The mixture of para-xylene (melting point: 13.26 ° C.) and meta-xylene (melting point: −47.87 ° C.) after the separation of ethylbenzene (melting point: −94.98 ° C.) is cooled to crystallize para-xylene at a high concentration. However, it is difficult to recover high-purity meta-xylene from the remaining filtrate.

[0007] As another production method for solving such a problem, the selective isomerization of ortho-xylene to meta-xylene is performed by using at least one crystalline alumina silicate selected from the group consisting of ZSM-4, omega, and faujasite. A method has been proposed in which the contact is carried out in a gas phase or a liquid phase in the presence of a zeolite-containing catalyst (Japanese Patent Publication No. 6-62456). According to this method, ortho-xylene and light / heavy components are separated by distilling and separating the product brought into contact with the catalyst to obtain meta-xylene containing a small amount of para-xylene. High purity meta-xylene can be obtained by the method.

According to this method, ortho-xylene isomerized to meta-xylene at a high conversion rate, and the production of para-xylene by secondary isomerization of meta-xylene can be extremely suppressed. It is possible to provide a process with low energy cost and equipment cost because the catalyst can be produced in a high yield, the catalyst is not corrosive, and a recovery process is unnecessary.

[0009] However, the present method is intended to provide a method for isomerizing ortho-xylene using a catalyst in which the cation site of ZSM-4 or omega zeolite is replaced with a proton, for example.
There is a problem that a heavy substance generated as time elapses, that is, coke, accumulates on the catalyst, and the conversion of ortho-xylene decreases with time. For this reason, after a certain period of time, it is necessary to regenerate the catalyst by treating the catalyst whose activity has been reduced at a high temperature in an oxygen-containing atmosphere.

However, it has been found that if the regeneration of the catalyst is repeated many times, the catalyst is damaged, so that the catalyst activity after the regeneration of the catalyst gradually decreases, and finally a low orthoxylene conversion can be obtained. It is necessary to replace the catalyst whose activity has been reduced in this way, and the replacement of the catalyst has a large effect on the operation rate and the catalyst cost.

The reduction in catalytic activity due to catalyst regeneration is a common problem not only in the isomerization of ortho-xylene, but also in the construction of a catalytic process using zeolite, and several methods for improving this are disclosed.

For example, JP-A-64-80443 discloses that a hydrogen-type zeolite catalyst having reduced activity is brought into contact with an aqueous ammonium salt solution, then washed, dried, heated and dehydrated, and further calcined at 400 to 650 ° C. A catalyst regeneration method characterized by the above is disclosed.

[0013] Also, Japanese Patent Application Laid-Open No. H5-15784 discloses that
In the regeneration of the used crystalline silicate catalyst, a dry oxygen-containing gas having a water content of 0.2 vol% or less
A method characterized by contacting with a catalyst under the condition of 00 ° C. is disclosed.

However, in the former method, it is necessary to once withdraw the catalyst filled in the reactor, or to flow an aqueous solution of ammonium salt having high corrosivity through the reactor, and in addition, the operation is complicated. .

Further, when the latter method was carried out in the orthoxylene isomerization reaction with omega zeolite,
It was still found that the activity gradually decreased as the regeneration was performed.

As described above, in the orthoxylene isomerization reaction with omega zeolite, no effective catalyst regeneration method has been found.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and one of its objects is to provide a method for selectively producing high-purity meta-xylene in a high yield. is there. Still another object of the present invention is to provide a method for producing meta-xylene which is inexpensive in terms of equipment and energy. Still another object of the present invention is to provide
An object of the present invention is to provide a method for producing meta-xylene, which can achieve an improvement in operation rate and a reduction in catalyst cost by using a catalyst for a long period of time.

[0018]

SUMMARY OF THE INVENTION The present invention provides a method for producing meta-xylene by isomerizing orthoxylene in a gas or liquid phase using a catalyst containing ZSM-4 and / or omega zeolite. A method for producing meta-xylene, characterized in that the catalyst having reduced isomerization activity is treated in an oxygen-containing gas at 400 ° C. or lower to regenerate it.

The present invention will be described in detail below. The catalyst in the method of the present invention contains ZSM-4, which is a kind of crystalline aluminosilicate zeolite, and / or omega zeolite.

ZSM-4 and omega zeolites are structurally similar and naturally occur as mazzite. These syntheses are detailed in GB 1,117,568 and GB 1,178,186 and are usually synthesized in the presence of sodium and tetramethylammonium ions. The structure consists of a gmelinite cage tied along the C-axis, and the aperture diameter of the channel system parallel to the C-axis has a size of 0.75 nm. Usually, when using a crystalline aluminosilicate zeolite as the active component of the catalyst, AlO ₂ is a component of the zeolite to increase its function as a catalyst ^- proton cation sites derived from the (H
⁺ ) Is being replaced. As the method, the synthesized zeolite is converted to a proton source hydrochloric acid,
After contacting with a mineral acid aqueous solution such as nitric acid, or contacting with an ammonium cation supply source such as ammonium chloride and aqueous ammonia, drying and calcination desorb ammonia to generate protons at the cation sites. A known method is used. In the present invention, the proton occupancy based on the cation site of ZSM-4 and / or omega zeolite is preferably 70% or more, more preferably 90% or more. The remaining cation sites may be occupied by alkali metal ions, alkaline earth metal ions, transition metal ions, lanthanide metal ions, and the like.

The catalyst in the present invention may have any shape, but is preferably a molded product from a practical viewpoint. When molding, it is preferable to use a binder such as clay, alumina and silica.

The reaction temperature of the isomerization reaction used in the present invention is preferably 50 to 400 ° C., and 100 to 300 ° C.
Is more preferred. If the reaction temperature is lower than 50 ° C., the conversion of the raw materials is not sufficient, while if the reaction temperature is higher than 400 ° C., xylene is disproportionated to toluene and trimethylbenzene by sequential isomerization and disproportionation. Since the xylene concentration increases, the yield of meta-xylene decreases.

In the present invention, the contact between the catalyst and the starting orthoxylene can be carried out arbitrarily in a gas phase or a liquid phase. The weight hourly space velocity (WHSV) can be set in the range of 0.01 to 10 hr ^-1 .

The reaction pressure may be any of reduced pressure, normal pressure and pressurized pressure, but it is usually preferable to carry out the reaction at a gauge pressure of 0 to 5 MPa. In particular, when the reaction is carried out in a liquid phase, it is preferable to pressurize the reaction vessel according to the reaction temperature.
As a method for pressurizing the reaction vessel, a method using a pressurized gas is preferable, and as the kind of the pressurized gas, a gas inert to the isomerization reaction such as hydrogen, nitrogen, helium, or argon is preferably used.

Using ortho-xylene as a raw material, the products obtained as described above include light aromatic hydrocarbons such as benzene and toluene, unreacted ortho-xylene, meta-xylene produced as a result of the isomerization reaction, and some para-xylene. And heavy aromatic hydrocarbons such as trimethylbenzene. To separate meta-xylene from the product,
As described in Japanese Patent No. 2456, this can be achieved by further distilling and separating the remaining liquid after distilling and separating the light fraction, and further purifying by a method such as adsorption depending on the required purity of meta-xylene.

In the catalyst regenerating method of the present invention, a catalyst containing used ZSM-4 and / or omega zeolite to which coke is attached (hereinafter may be simply referred to as used catalyst) and an oxygen-containing gas are used. The contact is performed at a temperature of 400 ° C. or less. The oxygen concentration in the oxygen-containing gas is arbitrary, but from the viewpoint of burning the coke to such an extent that the catalyst bed temperature can be controlled to 400 ° C. or less, 0.5
-30% by volume is preferred. As a component other than oxygen in the oxygen-containing gas, an inert gas such as nitrogen, argon, carbon dioxide, and helium is preferable. Such an oxygen-containing gas is
It can be obtained as air, a gas obtained by diluting an appropriate amount of air with an inert gas, or a gas obtained by mixing an appropriate amount of an inert gas with an oxygen gas. The processing pressure in the regeneration of the used catalyst can be arbitrarily selected.

In the present invention, it is preferable to apply the above-mentioned catalyst regeneration method without taking out the used catalyst in the isomerization reactor. However, the used catalyst is taken out from the isomerization reactor, and this is separated into another. It is also possible to charge the combustion reactor to regenerate the catalyst, and then charge the isomerization reactor again.

[0028]

Next, the present invention will be described specifically with reference to examples.

[Example 1] 50 g of omega zeolite (manufactured by Tosoh Corporation) was added to a 10% aqueous ammonium chloride solution 5
The mixture was charged into 00 ml, and kept under reflux for one day to perform ion exchange. After repeating this operation three more times, the mixture was filtered and washed with water, and the obtained powder was dried at 90 ° C. overnight to obtain a hydrogenated omega zeolite.

To the obtained hydrogen-type omega zeolite was added an equal weight of gel-like γ-alumina (ACP-1 manufactured by Catalyst Chemicals Co., Ltd.), and the mixture was sufficiently mixed and molded into a size of 10 to 20 mesh. The molded product is fired in an electric furnace at 500 ° C. under air flow,
5 g of this was filled in an upflow glass vertical reaction tube. While flowing hydrogen under normal pressure, the catalyst bed temperature was raised to 14
After the temperature was reduced to 0 ° C., ortho-xylene was supplied at a flow rate of 2.5 g / hr to carry out an isomerization reaction of ortho-xylene. The product obtained 240 hours after oil passing was collected and analyzed for components.

Subsequently, after passing the oil for 480 hours, the flow of ortho-xylene was stopped. After purging with hydrogen and organic matter by flowing nitrogen, air is blown at 20 ml / mi at normal pressure.
n, and gradually raise the catalyst bed temperature to 350
° C and the catalyst was regenerated by flowing at 350 ° C for 48 hours.

After the regeneration of the catalyst, the inside of the system was replaced with hydrogen, and the same orthoxylene isomerization reaction was carried out again for 480 hours.

By repeating the above operation, the reaction was repeated 5 times and the catalyst was regenerated 4 times, and the analysis values of the products after 240 hours were compared. Table 1 shows the results.

Comparative Example 1 An orthoxylene isomerization reaction and catalyst regeneration were carried out in the same manner as in Example 1 except that the catalyst regeneration temperature was set at 500 ° C. Table 1 shows the results. According to the results in Table 1. It is clear that the activity gradually decreases as the catalyst regeneration is repeated.

[0035]

[Table 1]

[0036]

According to the present invention described above, it becomes possible to produce high-purity meta-xylene while exhibiting stable performance for a long time.

Claims (2)

[Claims] 1. A process for producing meta-xylene by isomerizing ortho-xylene in a gas phase or a liquid phase using a catalyst containing ZSM-4 and / or omega zeolite, wherein the activity of the isomerization reaction is reduced. A method for producing meta-xylene, comprising regenerating the catalyst by treating the catalyst in an oxygen-containing gas at 400 ° C. or lower. 2. The method for producing meta-xylene according to claim 1, wherein the isomerization reaction is performed at a temperature in the range of 100 ° C. to 300 ° C.