JPH06107574A - Reduction of m-dichlorobenzene and production of p-and o-dichlorobenzene taking advantage of the reduction - Google Patents

Abstract

PURPOSE:To efficiently obtain benzene in high yield by catalytic treatment within a specified temperature range of a dichlorobenzene isomer mixture containing a specified amount of m-dichlorobenzene to reduce the m- dichlorobenzene. CONSTITUTION:A dichlorobenzene isomer mixture containing 5-40mol% of m-dichlorobenzene and 20-90mol% of o-dichlorobenzene is put to catalytic treatment at 200-400 deg.C to reduce the m-dichlorobenzene, thus affording benzene. And, (monochloro)benzene is chlorinated to produce a dichlorobenzene isomer mixture, and p-dichlorobenzene is crystallized and separated from said mixture and o-dichlorobenzene is separated by distillation of the liquor left after separating the p-dichlorobenzene; o-dichlorobenzene is then added to the rest of the isomer mixture so as to be >=20mol% in the o-dichlorobenzene content followed by reduction with hydrogen to produce benzene; thus affording the objective p- and o-diehlorobenzenes.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for reducing dichlorobenzene (DCB) containing metadichlorobenzene (MDCB), which has a low utility value, to benzene, and paradichlorobenzene (PDCB) and orthodichlorobenzene (ODCB) using the method. The present invention relates to a method for producing with high purity.

[0002]

BACKGROUND OF THE INVENTION Paradichlorobenzene is highly useful as an insect repellent and a raw material for high-performance engineering plastics, and orthodichlorobenzene is useful as an intermediate for medicines and agricultural chemicals or as a solvent. The chlorination of benzene or chlorobenzene to produce PDCB and ODCB is para-
Ortho-oriented, the main products are PDCB and O
Although it is DCB, it is unavoidable that a small amount of MDCB is produced as a by-product. However, it has been difficult to separate a small amount of MDCB with high purity.

For example, as a method for separating a small amount of MDCB from a mixture of DCB isomers, a method of adsorbing and separating MDCB on zeolite is known (Japanese Patent Laid-Open No. 24974/1992).
No. 0). However, in this method, the adsorbent is greatly deteriorated due to the presence of a trace amount of water, and it is necessary to dehydrate the water to 10 ppm or less, and it is expensive to dehydrate, and it takes energy to desorb the adsorbed MDCB and to regenerate the adsorbent. Not economical. Further, when the concentration of MDCB is low, the effect is essentially small. Therefore, in order to prevent the accumulation of MDCB in the reaction system, it was necessary to extract it as a DCB isomer mixture containing MDCB. That is the loss.

On the other hand, in recent years, P has been used as a raw material for high-performance engineering plastics.
The utility value of DCB has increased, and attention has been paid to a method for producing DCB having a large proportion of PDCB. Therefore PDCB
A chlorination method using a zeolite catalyst having a large / ODCB ratio (JP-A-59-163329) or a chlorination method using a zeolite catalyst and a solvent in combination (JP-A-4-253929) has been proposed. However, although these methods increase the PDCB / ODCB ratio, they also increase the byproduct ratio of MDCB.

Regarding reduction of polychlorinated benzene to return to benzene, a method of reducing tetrachlorobenzene to trichlorobenzene using a Pd, Pt catalyst (US Pat. No. 2,826,817), ODCB is used. Report of becoming monochlorobenzene and benzene under high temperature and pressure of 11MPa at 275-375 ℃ under NiMo / γ-Al ₂ O ₃ catalyst (AICh.E.Journ
al Vol 36 (5) 773 (1990)), etc., but industrial P
The catalyst life was not sufficient to combine it with the production method of DCB and ODCB.

[0006]

Under the above circumstances, PDCB and ODCB which do not dispose of MDCB, which is unavoidable as a by-product during the production of PDCB and ODCB, in the form of an isomer mixture. Is required. For this purpose, PDCB and ODCB can be reduced to benzene with sufficient catalyst life and incorporated into the production process of PDCB and ODCB.
It aims at providing the manufacturing method of.

[0007]

According to the study of the present inventors, when benzene is chlorinated to produce PDCB and ODCB, P is better than that of DCB isomer mixture of chlorinated products.
The isomer mixture containing MDCB after high-purity separation of DCB and ODCB was 20% by mol of ODCB.
By catalytic reduction under the above conditions, MDCB
That is, the present invention has reached to the present invention. That is, the structural feature of the present invention is to catalytically reduce a DCB isomer mixture containing 5 to 40 mol% MDCB and 20 to 90 mol% ODCB at 200 to 400 ° C. to obtain benzene. MDC
B reduction method, a chlorination step of chlorinating benzene or monochlorobenzene to obtain a DCB isomer mixture, a step of crystallizing and separating PDCB from the isomer mixture, and a step of distilling and separating ODCB from the PDCB separated liquid And a method of producing PDCB and ODCB, which comprises a reduction step of adding ODCB to the remaining isomer mixture in an amount of 20 mol% or more and reducing with hydrogen to return to benzene.

The present invention will be described in detail below.

For chlorination of benzene or monochlorobenzene, ferric chloride or aluminum chloride is used as a catalyst, or sulfur or selenium is used as a co-catalyst with them, or a number of acid catalysts such as silica-alumina and zeolite are used. It can be carried out in the presence of a known chlorination catalyst such as use. The chlorination reaction may be in a liquid phase or a gas phase, but is preferably chlorinated in a liquid phase at 30 ° C. or higher using ferric chloride and sulfur as a catalyst or benzene is chlorinated in a zeolite-solvent system.

A more preferred chlorination method is that benzene is chlorinated with ferric chloride-sulfur catalyst to give monochlorobenzene, and the obtained monochlorobenzene is chlorinated with a zeolite-solvent system to obtain DCB. It is a method of chlorination.

As the zeolite catalyst, L-type, Y-type, mordenite-type and offretite-erionite-type can be used, but preferably partially cation-exchanged zeolite, for example, KL-type containing 8 to 20% by weight of potassium as K2O. It is a zeolite. As the solvent, one or a mixture of ethane or a propane halide such as 1,2-dichloroethane, 1,2-dibromoethane, 1,2,3-trichloropropane, and 1,2-dichloropropane can be used. The use ratio of the solvent to the benzene compound is 0.5 to 15 volume ratio, preferably 1 to 10 volume ratio.

As described above, PDCB and ODC
When benzene is chlorinated to obtain B, DCB containing MDCB in an amount of 0.1 to 1 mol% is slightly different depending on chlorination conditions.
It is inevitable that an isomer mixture is obtained and MDCB is produced.

From this mixture, PDCB was converted to O by crystallization.
DCB can be separated into high purity by distillation, but M
DCB exists as a mixture of isomers in a concentrated state after separating PDCB and ODCB.

20 mol% of ODCB was added to this isomer mixture.
By adding the above amount and catalytically reducing the MDC
B can be returned to benzene, and MDCB can be effectively used without disposal. However, the conventionally proposed reduction method has a short catalyst life and cannot be an industrial method incorporated into a process for producing PDCB and ODCB.

The main causes of the deterioration of the reduction catalyst are considered to be carbon precipitation and catalytic metal sintering.
According to the studies by the present inventors regarding the reduction rate of each DCB isomer and the catalyst deterioration, the reduction rate of each isomer is in the order of meta> para >> ortho, while the catalyst life is conversely ortho >>para> meta. It was in order. As a result of further studying the catalyst life, it was found that OD was found in MDCB, PDCB or a mixture thereof.
When CB is added in an amount of 15 mol% or more, preferably 20 mol% or more, the reaction can be performed with the same catalyst life as in the case of reducing ODCB alone.

The composition of DCB used in the reduction reaction is MDC.
B is present in an amount of 5 mol% or more, preferably 10 mol%.
To this end, PDCB and OD were better than the crude DCB isomers.
CB is separated into high purity to increase the MDCB concentration.
When the MDCB concentration is lower than 5 mol%, the efficiency is poor and it is not preferable. The upper limit of the concentration of MDCB is about 40 mol% because it is difficult to separate it from PDCB and the presence of 15 mol% or more of ODCB is required. Also ODCB
Is present in an amount of 15 to 90 mol%, preferably 20 to 80 mol%. ODC added to increase the ODCB concentration
B does not have to be ODCB separated in high purity, and may be a filtrate obtained by crystallizing and separating PDCB from a chlorinated product.

As the reduction catalyst, Pd, Pt, Ag, Cu, Ni
At least one selected from the above, especially Pd and Pt are preferable. These are usually used by dispersing carbon, alumina, silica or the like as a carrier. The reaction is in the gas phase at 200-400 ℃
Done in. Below 200 ° C, not only the reaction is slow, but also unfavorable hydrogenation reaction of the aromatic ring increases. At 400 ° C or higher, the catalyst deteriorates significantly. The molar ratio of hydrogen to DCB is 0.
It is 2 to 4, preferably 0.5 to 2.5.

The DCB content of the liquid supplied to this reduction step is 90% by weight or more, MDCB is 5 to 40 mol%, and ODC is
B20 to 90 mol% is sufficient, and other polychlorinated benzene such as trichlorobenzene or a solvent used for chlorination may be used. The water content is preferably 400 ppm or less.

Next, a method for producing PDCB and ODCB incorporating the method for reducing the mixture of DCB isomers containing MDCB will be described.

First, benzene or monochlorobenzene is chlorinated under the above conditions to obtain a DCB isomer mixture.

The chlorination reaction ends when the degree of chlorination (average degree of chlorine bonded to the benzene ring) reaches 1.7 to 1.9,
Unreacted benzene and monochlorobenzene are recovered by distillation and returned to the chlorination process. When the solvent is used, the solvent is also recovered by distillation and reused. D obtained in the chlorination process
The CB mixture is cooled to crystallize out PDCB. (This is called the first crystallization). The crystallized and separated PDCB can be purified by recrystallization, but industrially, for example, JP-B-47-40621
According to the continuous crystallizer described in the publication, PDCB having a purity of 99.9% or more can be obtained.

The residual liquid after separating most of the PDCB is
Although it contains polychlorinated compounds such as ODCB, PDCB, MDCB and a small amount of trichlorobenzene, the remaining PDCB and MDCB are distilled by utilizing the boiling point difference, and the distillate is cooled again to crystallize. (Referred to as second crystallization), the crude PDCB is recovered and supplied to the first crystallization to increase the recovery rate of PDCB. OD including polychlorinated compounds
ODCB can be separated into high purity by subjecting the above-mentioned distillation residual liquid mainly containing CB to further distillation.

The residual liquid of the second crystallization is MDCB and PDC.
Although B is the main component, ODCB is added thereto in an amount of 20 mol% or more to catalytically reduce DCB back to benzene, thereby effectively utilizing MDCB without discarding it.

The present invention will be specifically described below with reference to examples.

[0025]

[Example 1] An inner diameter equipped with a glass tube having an outer diameter of 10 mm for inserting a hydrogen introducing tube, a DCB vaporizer and a thermocouple
Using a 30 mm vertical glass double reactor, 0.5
20 ml of pelletized carbon carrying% palladium
(8.6g) filled.

The temperature was raised to 300 ° C. while flowing nitrogen, and then switched to 15 liter / H of hydrogen. Next, the DCB isomer mixture (meta: 21.5 mol%, para: 58.4 mol%, ortho: 20.1 mol%) was vaporized at 30 ml / H and then fed to the reactor. The product was collected by a cold trap, and after removing hydrogen chloride, analyzed by gas chromatography.

After 10 hours from the start of the reaction, the DCB conversion was 98% or more, and the composition of the reaction product at the time of 8.6 kg treatment (221 hours) corresponding to 1000 times the catalyst weight is shown in Table 1. Thus, the DCB conversion rate remained at 72%.

[0028]

Example 2 DCB (meta: different composition from Example 1)
The reduction reaction was performed in the same manner as in Example 1 using 10.0 mol%, para: 59.8 mol%, ortho: 30.2 mol%). The DCB conversion rate after the lapse of 10 hours from the start of the reaction was 98% or more, and the conversion rate after 221 hours was 79%. The composition of the reaction product after 221 hours has passed is shown in Table 1.

[0029]

Comparative Example A DCB isomer mixture having 10% ODCB content (meta: 19.7 mol%, para: 70.3 mol%, ortho: 10.0 mol%) was subjected to a reduction reaction in the same manner as in Example 1. Reaction start 1
The DCB conversion rate at the time of 0 hours was 98% or more.
After 1 hour, the DCB conversion rate has dropped to 30%,
The deterioration of the catalyst was large. The composition of the reaction product after 221 hours has passed is shown in Table 1.

[0030]

[Table 1]

[0031]

[Embodiment 3] FIG. 1 is a diagram showing the flow of substances in this embodiment.

54 mol / H of benzene and 46 mol of benzene recovered from the benzene separator 2 were combined in the first chlorination reactor 1,
Introducing 100 mol / H benzene and 60.9 mol / H chlorine, FeC
It was chlorinated to a degree of chlorination of 0.6 at 50 ° C in the presence of 0.06% by weight of a catalyst consisting of l ₃ and sulfur. The chlorinated liquid after the catalyst separation is unreacted benzene 44.5 mol / H, monochlorobenzene 50.2 mol / H,
It contained DCB 5.3 mol / H and trichlorobenzene 0.02 mol / H.

Benzene 1. from the reduction reactor 10 was added to this liquid.
5 mol / H, monochlorobenzene 0.4 mol / H and DCB 0.3 mol / H
H was added and benzene was recovered in the benzene separation column 2.

To the effluent of the benzene separation column 2, 12.6 mol / H of monochlorobenzene from the monochlorobenzene separation column 4 and 60 mol / H of 1,2-dichloroethane as a chlorinated solvent were added and supplied to the second chlorination reactor. . In the second chlorination reactor, L-type zeolite containing 12% by weight of potassium as K ₂ O was chlorinated at 75 ° C to a chlorination degree of 1.8 while introducing 50.6 mol / H of chlorine in the presence of 4% with respect to the liquid weight. . The second chlorination reaction solution was unreacted monochlorobenzene 12.6 mol / H, DCB 56.1 mol / H (meta: 0.4%, para: 90.0%, ortho: 9.7%), trichlorobenzene 0.08 mol / H and 1, 2 -Dichloroethane was 60 mol / H.

Then, this liquid is supplied to the monochlorobenzene separation column 4 to recover the monochlorobenzene and the solvent, and the bottom liquid is 4.2 mol / H of crude PDCB from the second crystallizer 9.
(Meta: 1.0%, para: 97.6%, ortho: 1.4%) together with the first crystallizer 5 and the crystal refiner 6, PDCB having a purity of 99% or more was obtained at 49.1 mol / H.

The filtrate from the first crystallizer and the crystal refiner consisted of DCB 11.2 mol / H (meta: 2.2%, para: 48.8%, ortho: 49.1%) and trichlorobenzene 0.08 mol / H, and had a low content. It was supplied to the boiling point separation tower 7. Low boiling point separation tower 7 The top liquid is 6.0 mol / H (meta: 4.0%, para: 91.0%, ortho: 5
%) And was fed to the second crystallizer 9 to recover crude PDCB.

The filtrate of the second crystallizer 9 is DCB 1.8 mol / H.
(Meta: 10.9%, para: 75.6%, ortho: 13.5%), from which a part of the bottom liquid of the low boiling point separation column 7 is ODC
BOD 0.4 mol / H was added to raise the ODCB content to 29% and fed to the reduction reactor 10 at 2.2 mol / H.

In the reduction reactor 10, carbon pellets loaded with 0.5% of Pd were filled as a catalyst, and LHSV (liquid hourly space velocity) of 1.0 Hr ^-1 and hydrogen of 5.5 mol / H at a temperature of 260 ° C. were supplied for reduction. Product 2.2 mol / H (benzene: 69.8%, monochlorobenzene: 17.4%, MDCB: 0.2%, PDC
B: 2.9%, ODCB: 9.7%) were obtained and returned to the benzene separation column. MDCB was reduced by 0.2 mol / H by this reduction reaction, and accumulation of MDCB 0.2 mol / H produced in the chlorination step did not occur even after 500 hours from the start of operation.

The balance of the bottom liquid of the low boiling point separation column 7 is ODCB.
The ODCB having a purity of 99% or more is supplied to the separation tower 8 from the top of the tower.
Obtained at 4.8 mol / H.

When the reduction reaction is not carried out, the DCB isomer pair mixture having low utility value (meta: 10.9%, para: 75.
6%, ortho: 13.5%) will be discharged out of the system at 1.8 mol / H.

[0041]

According to the method of the present invention, MDCB, which is produced in a small amount and is difficult to separate, can be reduced to benzene as a mixture of isomers with a sufficient catalyst life. Therefore, the reduction reaction can be incorporated into the production process of chlorinating benzene or monochlorobenzene and separating PDCB and ODCB with high purity, and MDCB can be returned to benzene and effectively used.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a manufacturing process of PDCB and ODCB according to the present invention.

[Explanation of symbols]

 1: First Chlorination Reactor 2: Benzene Separation Tower 3: Second Chlorination Reactor 4: Monochlorobenzene Separation Tower 5: First Crystallizer 6: Crystal Refining Device 7: Low Boiling Separation Tower 8: ODCB Separation Tower 9: Second crystallizer 10: Reduction reactor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C07C 1/26 15/04 9280-4H 17/12 9280-4H // C07B 61/00 300

Claims (2)

[Claims] 1. A method for reducing metadichlorobenzene, which comprises catalytically reducing a dichlorobenzene isomer mixture containing 5 to 40 mol% of metadichlorobenzene and 20 to 90 mol% of orthodichlorobenzene at 200 to 400 ° C. to obtain benzene. . 2. A chlorination step of chlorinating benzene or monochlorobenzene to obtain a dichlorobenzene isomer mixture, a step of crystallizing and separating paradichlorobenzene from the isomer mixture, and a step of distilling and separating orthodichlorobenzene from a paradichlorobenzene separated liquid. And a reduction step of adding orthodichlorobenzene to the residual isomer mixture in an amount of 20 mol% or more and reducing with hydrogen to return to benzene.