JP6350259B2 - Process for producing aromatic compound isomers - Google Patents

Description

  The present invention relates to a method for industrially advantageously producing an aromatic isomer from an aromatic isomer mixture.

  Specifically, it is a production method in which two isomers are produced together from a mixture of isomers of aromatic compounds substituted with at least two alkyl groups and / or halogen groups.

  A technique for extracting a target isomer with high efficiency from a halogenated and / or alkylated aromatic compound having a plurality of isomers has been studied.

  For example, in Patent Document 1, when producing paraxylene from a xylene mixture, the pressure swing adsorption method is combined with paraxylene purification technology using crystallization separation or simulated moving bed adsorption separation to improve the recovery rate of paraxylene in the purification process. Technology to make it reported. In a typical embodiment of Document 1, after separation of product para-xylene by crystallization separation, the residual liquid is recycled to the isomerization step. In order to perform isomerization efficiently, the paraxylene concentration in the residual liquid needs to be made sufficiently low. However, the paraxylene recovery rate that can be achieved by crystallization separation has a limit due to the eutectic point.

  In Patent Document 2, when producing paradichlorobenzene (hereinafter p-DCB), m-DCB, which is a by-product that is difficult to separate, is transchlorinated and reduced to monochlorobenzene to be reused as a reaction raw material. And the technique which improves a yield is proposed. Thus, it is desired to develop a process for efficiently converting a target isomer other than the target isomer to be extracted as a product.

JP-T-2004-502746 Japanese Patent Laid-Open No. 10-218807

  However, in the production method as in Patent Document 1, the proportion of para-xylene in the reaction solution obtained from the isomerization step is at most about 22% by mass, and the remaining about 80% does not become the target product. Circulating the separation process. For this reason, the facilities are large and inefficient in terms of energy. Similarly, in the production method as in Patent Document 2, the ratio of p-DCB in the reaction solution obtained from the isomerization step is about 28% by mass at the maximum, and the production efficiency is poor.

In order to solve the above problems, the present invention provides the following method as a method for obtaining two or more isomers from aromatic compound isomers.
A process for producing an aromatic compound isomer by separating at least two isomers from a mixture of aromatic compound isomers substituted with at least two alkyl groups and / or halogen groups, the aromatic compound isomer mixture comprising: A reaction step for increasing the concentration of a target component in the isomerization reaction, a first separation for separating a first flow containing a large amount of the target component from a reaction solution obtained from the reaction step and a second flow containing a non-target component as a main component. Steps obtained from the second separation step and the second separation step for separating the first flow obtained in the step, the first separation step into a third flow containing the first target component and a fourth flow containing the second target component The second stream obtained in the first separation process is separated from the fourth stream containing the second target component from the fourth stream, the third separation step for separating the sixth stream containing the non-target component and / or the first target component. Recycle to the chemical reaction process Step two types of method for producing an aromatic compound isomer which comprises a step of circulating the sixth stream obtained from the third separation step in the first separation step.

  In the method for producing two kinds of aromatic compound isomers of the present invention, by reducing the target component in the stream circulating to the isomerization reaction step, the amount of the target component generated in the equilibrium reaction occurring in the reaction step is increased. High productivity can be achieved. Moreover, in this process using two isomers as the target components, the pass-through rate of the reaction raw materials to the target components is extremely high, and it is possible to produce with small-scale equipment and utility amount compared to the production amount. . Furthermore, also in the separation step, high separation efficiency can be achieved by separating the non-target components first.

FIG. 3 is a process flow diagram illustrating an exemplary embodiment of the present invention. It is a process flow figure showing a typical embodiment in case distillation separation is used for the 1st separation process. 2 is a process flow diagram of Example 1. FIG. 6 is a process flow diagram of Comparative Example 1. FIG. 6 is a process flow diagram of Example 2. FIG. 10 is a process flow diagram of Comparative Example 2. FIG.

  The aromatic compound to be produced in the present invention is an aromatic compound substituted with at least two alkyl groups and / or halogen. As the substituent, C1 to C3 or halogen is preferable. As the aromatic compound, those substituted with two substituents are preferable, and are particularly suitable for DCB, diethylbenzene, and xylene. Such an aromatic compound has three or more isomers, an isomerization step for increasing the proportion of the target component in the reaction solution by an isomerization reaction, and a separation step for separating the target component from the mixture of isomers. Often a manufacturing process consisting of

  The production method of the present invention includes a production method in which m-DCB is separated from a DCB isomer mixture as a first target component and p-DCB is separated as a second target component, or a first target component from a xylene isomer mixture. It is particularly suitable for a production method in which m-xylene is separated and p-xylene is separated as the second target component.

(Representative embodiment)
Hereinafter, a representative embodiment of the present invention will be described using DCB as an example. FIG. 1 shows a process flow diagram of a representative embodiment.

  This is a process of supplying a mixture of o-DCB, m-DCB and p-DCB as raw materials to the isomerization step to produce m-DCB as the first target component and p-DCB as the second target component.

(Isomerization process)
In this invention, the ratio of the target component in a reaction liquid is raised by isomerization reaction. The isomerization reaction is an equilibrium reaction, and in the isomerization process, using a catalyst, the supplied raw material is brought close to the equilibrium composition, and the proportion of the target component in the reaction solution is increased, thereby increasing the proportion of the target component in the supply solution and the reaction solution. The target component is generated by the difference between the target component concentrations. When DCB is used as the aromatic compound, for example, a zeolite catalyst described in JP-A-11-319573 can be used as a catalyst for isomerization.

  Details of the isomerization catalyst will be described. A suitable catalyst for the isomerization of DCB is a zeolite whose main cavity inlet is composed of a 10-membered oxygen ring. Such a zeolite is known as a so-called pentasil-type zeolite. Moreover, ZSM-5 zeolite whose crystal structure is described in Nature 271, 30 March, 437 (1978) and zeolite considered to belong to the same series are preferably used. Specifically, for example, in addition to ZSM-5, ZSM-8 described in British Patent 1334243, ZSM-11 described in Japanese Patent Publication No. 53-23280, US Pat. No. 4,001346, ZSM-21 described in JP-A-53-144500, ZSM-35 described in JP-A-51-67299, Zeolite Zeta 1 described in JP-A-51-67299, and JP-A-51-67298 Examples thereof include zeolite zeta 3 described in the publication. Of course, any zeolite can be used as long as it is a zeolite having a structural characteristic in which the entrance of the main cavity is a 10-membered oxygen ring.

  Various methods have been disclosed so far for producing a pentasil-type zeolite. For example, JP-A-52-115800, JP-A-53-134798, JP-A-57-123815 and the like can be mentioned. The silica / alumina molar ratio constituting such zeolite is preferably 10 to 100. More preferably, it is 18 to 50. A silica / alumina molar ratio in the range of 10 to 100 is preferred in terms of catalytic activity.

  When the zeolite is in a powder state, it must be molded for industrial use as a catalyst. There are various molding methods such as a compression molding method, a kneading method, an oil drop method, and the kneading method is preferably used. As a kneading method, a binder is generally required, and inorganic oxides and / or clays are used.

  Examples of the binder preferably used include alumina sol and alumina gel. The amount of the binder is 5 to 30 parts by weight, preferably 10 to 20 parts by weight, based on 100 parts by weight of zeolite, on the basis of absolutely dry. When moldability is poor, it is effective to add alkali metal salts such as sodium chloride, magnesium chloride, and barium chloride, alkaline earth metal salts, and surfactants such as polyvinyl alcohol, span, and rhodol during kneading. . The compact is then dried at 50 to 200 ° C. and then fired at 350 to 600 ° C. to increase the strength of the compact.

  In the catalyst molded body, zeolite aggregates primary crystallites to form secondary particles. The secondary particle diameter in the catalyst molded body can be easily examined with a scanning electron microscope (SEM). The secondary particle diameter of zeolite having a 10-membered oxygen ring at the entrance of the main cavity in the catalyst molded body is suitable as an isomerization catalyst with a maximum of 5 microns or less. When the raw material zeolite is uniformly mixed with inorganic oxide and / or clay and molded, the secondary particles are partially broken and dispersed, but the inlet of the main cavity in the catalyst molded body consists of a 10-membered oxygen ring. It is preferable that the secondary particles of the zeolite are sufficiently small and highly dispersed because the catalyst effectiveness is improved and the catalytic activity of the isomerization reaction of the aromatic compound is improved. The secondary particle diameter during catalyst molding is controlled by the molding conditions and the secondary particle diameter of the raw zeolite powder. As the molding conditions, the mixing time and moisture content of the raw material zeolite and the inorganic oxide and / or clay are important. For example, the longer the kneading time, the smaller the secondary particle size in the catalyst molded body is preferable. The secondary particle size of the raw material zeolite powder can be controlled by the reaction mixture composition ratio at the time of synthesis, the crystallization time, the stirring conditions, the drying method, etc. Must be selected. According to the knowledge so far, when the alkalinity in the reaction mixture at the time of synthesis is lowered or the crystallization time is shortened, the secondary particle diameter tends to be reduced.

  When used as an isomerization catalyst, it is preferable to convert the zeolite having a 10-membered oxygen ring at the inlet of the main cavity contained in the catalyst molded body into an acid form. In the case of ammonium form or organic cation which is an acid form or a hydrogen ion precursor before molding, it is not always necessary to carry out a new treatment for acid form, but alkali metal ions, alkaline earth metal ions, etc. When it contains, an ion exchange treatment for converting it to an acid form is performed. In the ion exchange treatment, when an acid form is directly formed with an aqueous solution such as an inorganic acid or an organic acid, ion exchange is performed with an aqueous solution such as ammonium chloride or ammonium nitrate, ammonium ions are introduced, and then calcined to be converted into hydrogen ions. There is a method to make an acid form. When ion exchange is performed with an aqueous acid solution, dealumination of the zeolite is likely to occur. Therefore, ion exchange is preferably performed with an aqueous ammonium salt solution. The catalyst composition thus prepared is dried at 50 to 200 ° C., then calcined at 350 to 600 ° C. and subjected to an isomerization reaction of a halogenated aromatic compound.

The isomerization reaction of a halogenated aromatic compound such as DCB can be carried out according to various conventionally known isomerization operations, and good results are obtained in both gas phase reaction and liquid phase reaction. As the isomerization reaction method, any of a fixed bed, a moving bed, and a fluidized bed can be used, but a fixed bed flow reaction method is particularly preferable because of ease of operation. The reaction temperature is 200 to 550 ° C, preferably 250 to 500 ° C. The reaction pressure is not particularly limited. Needless to say, in the case of a liquid phase reaction, the reaction pressure must be set in order to keep the reaction system in a liquid phase state. Also, coexistence of hydrogen, aromatic compounds, or polyhalogenated aromatic compounds different from the feedstock during the isomerization reaction is often effective in reducing side reactions and extending catalyst life. The weight hourly space velocity (WHSV) is 0.05 to 30 Hr ⁻¹ , preferably 0.1 to 20 Hr ⁻¹ .

(Low high boiling cut)
The reaction solution obtained in the isomerization process contains low-boiling components produced as a by-product of the reaction, and when directly supplied to the isomerization process or separation process, the isomerization catalyst and the adsorbent used in the separation process There is a possibility of degrading performance. Therefore, it is desirable to remove low boiling components and high boiling components from the reaction solution obtained in the isomerization step by distillation or the like.

(First separation step)
In the present invention, the target component and the non-target component are separated in the first separation step. Although any method can be applied as the separation method, distillation is preferable in the case of DCB. When the first target component is m-DCB and the second target component is p-DCB, o-DCB, which is a non-target component, is separated as a bottoms and supplied as a second stream to the isomerization step. The first stream supplied to the second separation step contains m-DCB and p-DSC as target components, and the o-DCB concentration of non-target components is 0.1% by mass or more and 15.0% by mass or less. The m-DCB concentration is preferably 40.0 mass% or more and 80.0 mass% or less, and the p-DCB concentration is 20.0 mass% or more and 60 mass% or less. 0.0 mass% or less is preferable.

  The o-DCB concentration in the second flow is 70.0% by mass or more and 99.9% or less, preferably 95.0% by mass or more and 99.0% by mass or less, and the m-DCB concentration is 0.1% by mass or more and 30% by mass or less. The mass is preferably not more than mass%, and the p-DCB concentration is preferably not less than 0.1 mass% and not more than 20 mass%.

(Second separation step)
In the present invention, in the second separation step, the first target component and the second target component contained in the first flow are separated. Although any method can be applied as the separation method, in this embodiment, adsorption separation is preferably employed, and simulated moving bed adsorption separation, pressure swing adsorption separation, and the like are preferred. When using simulated moving bed adsorption separation, for example, a separation method as disclosed in JP-A-4-330025 can be applied.

When adsorption separation is employed in the second separation step, Y-type zeolite can be used as the adsorbent. The Y-type zeolites referred to herein, consists of a molar ratio of oxide A crystalline aluminosilicate belonging to the faujasite type zeolite represented by _{M n / 2 O · Al 2} O 3 · xSiO 2 · yH 2 O Is done. Here, M is a metal cation or proton, and n is the valence of the metal M or proton. X is a silica / alumina ratio and is usually in the range of 4.5 to 6.0. y varies depending on the degree of hydration. M preferably contains potassium ions and lead ions. The ratio of potassium and lead in all cations is usually preferably 80 mol% or more, more preferably 90 mol% or more as (PbO + K ₂ O) / M _{n / 2} O. The ratio of potassium ion to the lead ion ^is preferably in the range of 10 to 80 mol% ^{Pb 2+ / (Pb 2+ 2K +} ), more preferably from 20 to 50 mol%.

  The desorbent used for the adsorption separation has characteristics such as that the separation ability of the adsorbent is not impaired in the presence of the desorbent, that the DCB adsorbed to the adsorbent can be efficiently desorbed, and can be easily separated from the DCB. Required. As the desorbing agent satisfying such characteristics, various alkyl-substituted or halogen-substituted benzene derivatives can be used, among which 3,4-dichlorotoluene is particularly preferable. As operation conditions for the adsorption separation, the temperature is from room temperature to 350 ° C., preferably from 50 to 250 ° C., and the pressure is from atmospheric pressure to 5.0 MPaG (gauge pressure), preferably from atmospheric pressure to 4.0 MPaG (gauge pressure). It is. Adsorption separation can be carried out either in the gas phase or in the liquid phase, but is preferably carried out in the liquid phase in order to reduce the operating temperature and reduce undesirable side reactions of the feedstock or desorbent.

  The purity of the first target component obtained by the second separation step is preferably 99.6% by mass or more. The upper limit is usually 99.9% by mass or less. In addition, the o-DCB concentration in the remaining fourth flow separated from the first target component by the second separation step is 1% by mass to 50% by mass, the m-DCB concentration is 1% by mass to 50% by mass, The p-DCB concentration is preferably 50% by mass or more and 90% by mass or less.

(Third separation step)
In the present invention, the remaining fourth stream obtained by separating the first target component in the second separation step is subjected to the third separation step to separate the second target component. Although any method can be applied as the separation method in the third separation step, in the case of DCB, crystallization separation or simulated moving bed adsorption separation is desirable.

  When the third separation step is separated by crystallization separation, the eutectic point of p-DCB and m-DCB, p-DCB and o-DCB is about −20 ° C., and p− The DCB concentration is 13% by mass. The melting point of p-DCB is about 53 ° C., and the operation temperature of the crystallization tank is preferably −15 ° C. to 30 ° C. Further, depending on the required purity of p-DCB, a crystal refining device disclosed in Japanese Patent Publication No. 47-40621 may be combined.

  In this embodiment, the purity of the second target component can be 99.90% by mass or more. The upper limit is usually 99.99% by mass or less. In addition, the o-DCB concentration in the sixth flow after the second target component is separated in the third separation step is preferably 1% by mass to 50% by mass, and the m-DCB concentration is 1% by mass to 50% by mass. The p-DCB concentration is preferably 15% by mass or more and 50% by mass or less.

(6th flow circulation)
As shown in JP-T-2004-502746, etc., conventionally, the residual liquid after removing the target component has been generally re-supplied to the isomerization step. However, in the case of xylene, the proportion of paraxylene in the reaction solution obtained from the isomerization step is at most about 22% by mass. Paraxylene production efficiency is greatly impaired. Therefore, for separation of paraxylene, it was necessary to input a large amount of energy using a large-scale facility and recover paraxylene as much as possible. Similarly, in dichlorobenzene, the proportion of p-DCB in the reaction solution obtained from the isomerization step is at most about 28% by mass, and it is necessary to reduce the concentration of p-DCB supplied to the isomerization step. .

  Furthermore, in the crystallization separation often used for separation of paraxylene and p-DCB, the paraxylene concentration that can be achieved in the crystallization residual liquid is 7% and the p-DCB concentration is 13% by mass due to the restriction due to the eutectic point. It is the lower limit, and it is difficult to collect more than that. Paraxylene and p-DCB contained in the crystallization residual liquid are re-supplied to the isomerization step, thereby deteriorating the production efficiency.

  In the present invention, the residual liquid obtained from the third separation step is circulated as the sixth flow to the first separation step. Since the non-target component separated from the first separation step is supplied to the isomerization step, it is possible to keep the concentration of the target component re-supplied to the isomerization step low regardless of the restriction due to the eutectic point. The amount of the target component produced by isomerization can be increased. In addition, by aiming at a process for producing two target components, it is possible to achieve efficient production with a facility smaller than the production amount.

  Furthermore, when the concentration of the target component contained in the raw material is high, efficient production can be performed without increasing the target component flowing into the isomerization step by supplying the raw material to the first separation step. it can. Therefore, it can be said that the process proposed by the present invention can flexibly cope with fluctuations in the raw material composition.

  The removal of the low-boiling components generated in the isomerization step may be carried out from any of the reaction solution, the first stream, or the second stream. However, when distillation separation is used in the first separation step, Since the components are contained in the first flow and the high-boiling components are contained in the second flow in a large amount, the low-boiling components are prevented from accumulating in the circulating flow returning from the first separation step through the third separation step to the sixth flow. From the viewpoint, it is preferable to separate the low boiling point component from the first stream, and from the viewpoint of reducing the load applied to the separation, it is preferable to separate the high boiling point component from the second stream. A typical embodiment in the case of using distillation separation in the first separation step is shown in FIG.

  Next, the present invention will be described in more detail with reference to examples.

Example 1
FIG. 3 shows a block flow diagram of the first embodiment. A mix-DCB solution containing 90% o-DCB and 10% p-DCB as raw materials is supplied to the isomerization process. m-DCB was obtained, and p-DCB was obtained as a product through a crystallization step. The crystallization residue was recycled to the o-DCB rectification column, and the bottom of the o-DCB purification column was recycled to the isomerization step. Details of each process are as follows.

As an isomerization catalyst, a pentasil type zeolite prepared by the same method as in Example 1 of JP-A-11-319573 was used. The temperature of the isomerization reaction column was about 330 ° C., and the pressure was 2.9 MPaG (gauge pressure). WHSV was set to 0.4 Hr ⁻¹ .

  For adsorption separation, a scaled-up version of the simulated moving bed apparatus described in the examples of JP-A-4-33025 was used. As the adsorbent, a zeolite adsorbent for separating m-DCB prepared by the method described in Examples 1 to 4 of JP-A-4-33025 was used. Table 1 shows the operating conditions of the adsorption tower.

  For crystallization separation, a melt crystallizer was used in addition to two crystallizers. The operating temperature of the crystallization tank was 29 ° C. and 13 ° C., respectively, and the reflux ratio in the melt crystallizer was 1. The results are shown in Table 2.

(Comparative Example 1)
FIG. 4 shows a block flow diagram of the first comparative example. The same procedure as in Example 1 was performed except that the crystallization residual liquid was recycled to the isomerization step. The results are shown in Table 3.

  In Example 1 in which the crystallization residual liquid was recycled to the isomerization step, m-DCB and p-DCB produced by isomerization increased as compared with Comparative Example 1, so that m-CB and p- obtained in 10 and 12 were obtained. The flow rate of DCB increased.

(Example 2)
FIG. 5 shows a block flow diagram of the second embodiment. The same procedure as in Example 1 was performed, except that a mix-DCB solution containing 80% o-DCB and 20% p-DCB as raw materials was supplied to the o-DCB rectification column. The results are shown in Table 4.

(Comparative Example 2)
FIG. 6 shows a block flow diagram of the second comparative example. The same procedure as in Example 2 was performed except that the crystallization residual liquid was recycled to the isomerization step. The results are shown in Table 5.

  In Example 2 in which the crystallization residual liquid was recycled to the isomerization step, m-DCB and p-DCB produced by isomerization increased as compared with Comparative Example 2, so that m-CB and p- obtained in 10 and 12 were obtained. The flow rate of DCB increased.

  By the method of the present invention, at least two kinds of isomers can be efficiently separated and recovered from a mixture of aromatic isomers such as dichlorobenzene and xylene.

DESCRIPTION OF SYMBOLS 1 1st flow 2 2nd flow 3 3rd flow 4 4th flow 5 5th flow 6 6th flow 7 Raw material 8 Reaction liquid 9 2nd flow (non-target component: o-DCB)
10 Third flow (first target component: m-DCB)
11 Fourth flow (with crystallization)
12 5th flow (2nd target component: p-DCB)
13 Sixth flow (crystallization residual liquid)

Claims (9)

A process for producing an aromatic compound isomer by separating at least two isomers from a mixture of aromatic compound isomers substituted with at least two alkyl groups and / or halogen groups, the aromatic compound isomer mixture comprising: A reaction step for increasing the concentration of a target component in the isomerization reaction, a first separation step for separating a first stream containing a target component from a reaction solution obtained from the reaction step and a second flow containing a non-target component; The second flow separating the first flow obtained in the separation step into the third flow containing the first target component and the fourth flow containing the second target component, and the fourth flow obtained from the second separation step. A third separation step for separating the fifth stream containing the two target components and the sixth stream containing the non-target components and / or the first target component, and the second stream obtained in the first separation step to the isomerization reaction step Circulating process, 3rd Two method for producing an aromatic compound isomer which comprises a step of circulating the sixth stream obtained from the isolation step to a first separation step. The method for producing an aromatic compound isomer according to claim 1, wherein the first separation step is distillation separation. The method for producing an aromatic compound isomer according to claim 2, wherein low boiling components are removed from the first stream which is a distillate of distillation separation. The method for producing an aromatic compound isomer according to claim 2, wherein a high-boiling component is removed from the second stream which is the bottoms of distillation separation. The method for producing an aromatic compound isomer according to any one of claims 1 to 4, wherein the second separation step is adsorption separation. The method for producing an aromatic compound isomer according to any one of claims 1 to 5, wherein the third separation step is crystallization separation or adsorption separation. The aromatic compound isomer according to any one of 1 to 6, wherein the concentration of the non-target component of the second stream obtained in the first separation step circulating to the isomerization reaction step is 70% by mass or more. Production method. The method for producing an aromatic compound isomer according to any one of claims 1 to 7, wherein the concentration of the second target component in the fourth stream obtained from the second separation step is 50% by mass or more. The method for producing an aromatic compound isomer according to any one of claims 1 to 8, wherein the aromatic compound is dichlorobenzene or xylene.

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