JP2009102275A - METHOD FOR PRODUCING p-DICHLOROBENZENE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably produce p-dichlorobenzene by appropriately suppressing the temperature rise in the intensive exothermic reaction of chlorination, thereby keeping the operation temperature within a proper range. <P>SOLUTION: The p-Dichlorobenzene is produced by using at least one of benzene and monochlorobenzene as a raw material and chlorinating with chlorine gas. In the production process, benzene 1 and chlorine gas 2 are introduced into a reactor 10 containing a zeolite catalyst 18, at least one of cooling medium selected from chloromethane 3 and chloroethane is introduced into the reactor 10, and the cooling medium is evaporated to suppress the temperature rise in the chlorination reaction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing paradichlorobenzene, in particular, using at least one of benzene and monochlorobenzene as a raw material, using zeolite as a catalyst and chlorinating with chlorine gas to produce paradichlorobenzene (hereinafter also referred to as “p-DCB” or “PDCB”). It relates to a method of manufacturing.

p-DCB is a compound with extremely high industrial value as a raw material for pharmaceuticals and agricultural chemicals, itself as an insecticide and insect repellent, and as a raw material for polyphenylene sulfide (PPS).
Conventionally, p-DCB has been known to be a liquid phase chlorination of benzene and / or monochlorobenzene using a Lewis acid such as ferric chloride or antimony pentachloride as a catalyst. Ferric chloride has a high activity, the chlorine conversion rate reaches 99.99% or more, and a very small amount of unreacted chlorine in the by-produced hydrochloric acid gas remains. However, the selectivity of the desired para-substituted product is at most about 60% with the catalyst alone, and is increased to about 75% by adding a cocatalyst.
In recent years, as a method for producing p-DCB with a selectivity of 90% or more, as shown in Patent Document 1, Patent Document 2, and the like, a method using L-type zeolite as a catalyst has been disclosed.
However, the methods using zeolite as a catalyst are all laboratory-level, and are not considered to be specific enough to operate as an actual apparatus. Incidentally, since the chlorination reaction in the present invention is a vigorous exothermic reaction, in an actual apparatus, it is very important to appropriately suppress the temperature rise and maintain the operation within a certain temperature range. The prior art does not teach an effective solution to this point.
Japanese Examined Patent Publication No. 63-12450 JP 2001-213815 A

Therefore, the main problem to be solved by the present invention is that although the chlorination reaction is a violent exothermic reaction, the temperature rise can be appropriately suppressed and the operation can be maintained within a certain temperature range. The object is to provide a method capable of stable operation.
Other issues will become apparent from the following description.

The present invention that has solved this problem is as follows.
[Invention of Claim 1]
In a method for producing paradichlorobenzene by chlorinating with chlorine gas using at least one of benzene and monochlorobenzene as a raw material,
While guiding the raw material and the chlorine gas to a reactor equipped with a zeolite catalyst,
A method for producing paradichlorobenzene, wherein at least one cooling medium of chloromethane and chloroethane is introduced into the reactor, and the cooling medium is evaporated to suppress a temperature rise in the chlorination reaction.

[Invention of Claim 2]
The method for producing paradichlorobenzene according to claim 1, wherein the zeolite catalyst is a molded body, and the zeolite catalyst is built in the reactor as a fixed bed, and the raw material, chlorine gas, and cooling medium are circulated in a down flow.

[Invention of Claim 3]
The method for producing paradichlorobenzene according to claim 1 or 2, wherein the evaporated gas content of the cooling medium is condensed outside the reactor, and the condensed liquid is reused as the cooling medium.

[Invention of Claim 4]
The method for producing paradichlorobenzene according to claim 1 or 2, wherein the chlorination reaction is carried out at a temperature of 40 to 130 ° C and a pressure of 10 atm or less.

[Invention of Claim 5]
The reactor has a plurality of stages, the raw material, chlorine gas and cooling medium are supplied to the first stage reactor, the reaction product of the previous stage is supplied to the reactor of the next stage, and the reactor after the next stage is supplied to the reactor. The method for producing paradichlorobenzene according to claim 1 or 2, wherein chlorine gas and a cooling medium are supplied in parallel to obtain paradichlorobenzene from the final reaction product.

  According to the present invention, although the chlorination reaction is a violently exothermic reaction, the temperature rise can be appropriately suppressed and the operation can be maintained within a certain temperature range, thereby enabling a stable operation. .

(Basic idea of the invention)
In the present invention, as described above, a homogeneous catalyst such as ferric chloride not only has low p-DCB selectivity, but also increases the burden on the apparatus for separation and recovery of the catalyst. Therefore, by using a zeolite catalyst, the selectivity of p-DCB is increased, and by using it as a solid catalyst, it can be reused.

  Further, as described above, the chlorination reaction is a violent exothermic reaction. Incidentally, if the heat is not removed, the temperature is easily raised to 400 to 500 ° C. Therefore, it is necessary to appropriately suppress the temperature rise and maintain the operation within a certain temperature range. If the temperature is too low, the viscosity increases and the pressure loss increases. On the other hand, when the temperature is high, the chlorine dissolution rate is controlled and the reaction is suppressed. Further, the boiling point of benzene is 80.1 ° C., and naturally the reaction is suppressed under the condition that benzene evaporates. It is also necessary to determine the reaction pressure so that an appropriate reaction temperature (reaction rate) can be maintained.

As a method for suppressing an exothermic reaction, a method in which a reactor such as a jacket or a coil is provided with a cooling part, a method for suppressing a temperature rise by using a large amount of solvent (1.2 dichloroethane and MCB are considered as solvent candidates. )), And a method using a cooling part and a solvent in combination. However, under suitable reaction conditions (40 to 130 ° C., 10 atm or less), a gas-liquid mixed phase is obtained, but the overall heat transfer rate of the reaction part-metal part-cooling part is overwhelmed with the liquid phase volume. Therefore, the heat transfer rate in the reaction section becomes dominant, and the overall heat transfer coefficient is only about 10 to 30 kcal / m ² hr ° C. Under this condition, a huge heat transfer area is required, and as a reactor It becomes difficult to materialize.

  Therefore, the present invention proposes a direct cooling method using the latent heat of vaporization of the cooling solvent. It is possible to absorb the enormous reaction heat generated by transferring the latent heat of vaporization caused by the evaporation of the compound to the compound by having a compound having the same boiling point as the reaction conditions in the reaction system. It becomes.

Evaporated compounds can be condensed and reused. When condensing, a general-purpose external heat exchanger such as a shell and tube that can secure a general heat transfer coefficient of 600 to 1100 kcal / m ² hr ° C. can be used. It is.

  Such a compound that can be directly used as a cooling medium is required not to react, and suitable for the chlorination reaction of p-DCB synthesis is dichloromethane (Tb 40.2 ° C.), trichloromethane (Tb 61.1 ° C.), tetra Chloromethanes such as chloromethane (Tb 76.8 ° C.), 1.1-dichloroethane (Tb 57. ° C.), 1.1.1-trichloroethane (Tb 73.9 ° C.), and chloroethanes. Stable temperature control is possible by selecting a suitable pressure condition in consideration of the desired reaction temperature and the boiling point of benzene and the direct cooling medium.

  In the process described below, an example using trichloromethane (also known as chloroform) having an atmospheric pressure boiling point of 61 ° C. will be described, but the use of other chloromethanes and chloroethanes described above is also possible. It has been confirmed that more than one can be used.

By the way, the present invention uses benzene and chlorine gas and the direct cooling medium (chloroform in the following example). This is summarized as follows.
1) Raw materials and raw material impurities: benzene, chlorine 2) Solvents / utilities and their impurities: chloroform, water 3) Reaction products: monochlorobenzene, dichlorobenzene, trichlorobenzene, hydrogen chloride Separation means are combined to obtain paradichlorobenzene for the purpose.

An example of the reaction formula is as follows.
Bz (C ₆ H ₆ ) → MCB (C ₆ H ₅ Cl) → PDCB, MDCB, ODCB (p-C ₆ H ₄ Cl ₂ , o-C ₆ H ₄ Cl ₂ , m-C ₆ H ₄ Cl ₂ → TCB (C ₆ H ₃ Cl ₃ )
PDCB synthesis reaction system:
C ₆ H ₆ + Cl ₂ → C ₆ H ₅ Cl + HCl (1)
C ₆ H ₅ Cl + Cl ₂ → p-C ₆ H ₄ Cl ₂ + HCl (2)
C ₆ H ₅ Cl + Cl ₂ → o-C ₆ H ₄ Cl ₂ + HCl (3)
C ₆ H ₅ Cl + Cl ₂ → m-C ₆ H ₄ Cl ₂ + HCl (4)
p-C ₆ H ₄ Cl ₂ + Cl ₂ → C ₆ H ₃ Cl ₃ + HCl (5)
o-C ₆ H ₄ Cl ₂ + Cl ₂ → C ₆ H ₃ Cl ₃ + HCl (6)
C ₆ H ₃ Cl ₃ + Cl ₂ → C ₆ H ₃ Cl ₄ + HCl (7)

  In the present invention, a zeolite catalyst is used. Examples of the zeolite include L-type, Y-type, ZSM-5, offretite, erionite, ferrierite, X-type, omega, and mordenite, and any of them can be used. These zeolites may be ion-exchanged with alkali metals such as Li, K, and Na, alkaline earth metals such as Mg and Ca, and the like by a known method. Among these zeolites, L-type and KL-type zeolites can also be used because of high p-DCB selectivity.

  However, the present inventor selected five kinds of zeolites (MFI, MWW, BEA, MOR, FAU: the pore diameters increased in this order) that were expected to be effective, and their activity and para-body selectivity. As a result, the results shown in FIG. 2 were obtained. BEA zeolite is highly active and MWW zeolite is highly selective. In this respect, BEA zeolite has been found to be optimal.

  Furthermore, in the case of a homogeneous catalyst, the reaction proceeds sequentially and concurrently, whereas in the case of a zeolite catalyst, the reaction proceeds almost 100% as shown in FIG. It was. Contrary to the heterogeneous catalyst, this is considered to be due to the fact that the zeolite catalyst has a resistance to diffusion, so that the reaction proceeds sequentially in the order of diffusing with benzene, Mono, Di, and Tetra.

In the present invention, the zeolite catalyst is installed in the reactor. It is desirable to use the reactor in multiple stages (minimum of two stages) and use them interchangeably because of the deterioration of the zeolite catalyst.
The zeolite catalyst is preferably used as a fixed bed and the raw material, chlorine gas and cooling medium are circulated in a down flow.

  In this case, it is desirable to ensure the dispersion of the gas phase centered on chlorine gas and the uniform flow of the liquid phase, and to eliminate backmixing. The flow pattern of the gas-liquid multiphase flow changes depending on the diameter of the reactor used. The flow pattern to be adopted is pulsating flow (Fulsing and Foaming Flow) or perfusion flow (Gas-continuous or Trickling Flow), preferably perfusion flow. Pulsating flow is a state where large and small portions of liquid hold-up alternate, and irrigation flow causes liquid to flow down on the catalyst particles in the form of a film by gravity, and gas flows as a continuous phase in that space. State. As the flow velocity of the gas-liquid multiphase flow increases, the flow pattern changes from pulsating flow to perfusion flow.

  Further, the number of stages of the reactor fixed bed may be one, but three is preferable. In many cases, the solid catalyst is deteriorated due to the loss of active sites due to the inflow of the deterioration-causing substance from the inlet. As countermeasures against this, it is possible to connect each fixed floor in a series of 3 independent tanks and replace the connections when they are deteriorated to operate cyclically. By adding multiple amounts of chloroform, it can be reused and the amount of chloroform circulating in the system can be suppressed.

  As the reaction temperature, when the temperature is too low, the viscosity increases and the pressure loss increases. On the other hand, when the temperature is high, the chlorine dissolution rate is controlled and the reaction is suppressed. Therefore, as reaction temperature, it is 40-130 degreeC, More preferably, it is 55-90 degreeC.

  The reaction pressure is preferably 950 to 1450 Torr (within a range of 55 to 90 ° C.) from the correlation between the amount of chloroform added and the PDCB liquid phase recovery rate as shown in FIG. Same if any).

  The following can be seen from FIG. (1) When the operating pressure increases, the reaction temperature cannot be maintained unless the chloroform / benzene ratio is increased. (2) Above the pressure at a certain operating temperature, the chloroform does not evaporate and the temperature is maintained. In addition, an enormous amount of chloroform is required. (3) Conversely, at a pressure below a certain operating temperature, the chloroform is completely evaporated. At this time, PDCB is similarly evaporated. (4) Therefore, the conditions under which chloroform and PDCB remain at the bottom of the reactor are appropriate, and the recovery of chloroform and PDCB is not greatly affected by the chloroform / benzene ratio. It is preferable to operate in a region where the chloroform / benzene ratio is 16 to 20 and the PDCB recovery rate is 90 to 95%.

  After the reaction, the adiabatic evaporated chloroform and the reaction product are recovered and cooled for reuse in the next stage. For condensation cooling of chloroform, a general-purpose external heat exchanger such as a shell and tube can be used.

  Although PDCB also vaporizes, since the melting point of PDCB is 53 ° C., it cannot be reduced to 53 ° C. or lower in an environment where PDCB condenses alone. However, since chloroform functions as a solvent for PDCB, it has been experimentally confirmed that if chloroform is present, precipitation of PDCB does not occur even at around room temperature. It is not impossible to lower the temperature below 40 ° C.

  The direct cooling medium trichloromethane (chloroform) reacts with chlorine and is converted to tetrachloromethane. As a result, it is desirable to separate tetrachloromethane from trichloromethane and remove it from the system so that tetrachloromethane does not accumulate in the trichloromethane circulation system.

Next, operations desirable for process construction will be supplementarily described.
By-products (hydrocarbon compounds) and hydrogen chloride are contained in the reaction product in the reactor. Since the boiling point of hydrogen chloride is -85 ° C. and liquid recovery is extremely difficult, it is recovered as an aqueous solution. The concentration of hydrogen chloride to be recovered is preferably as high as possible, but if it is about 35% HCl, it can be easily recovered.

  That is, the reaction product in the reactor is sent to the hydrogen chloride removal tower, hydrogen chloride and the hydrocarbon compound accompanying it are separated from the top of the hydrogen chloride removal tower, and this is sent to the cooling tower. In addition, the aqueous phase cooled by the attached condenser is sprayed into the tower and cooled, so that the aqueous phase and the chloroform phase are separated at the bottom of the cooling tower, and 35% HCl aqueous solution is used as the separated aqueous phase. obtain. The cooling medium from the final stage of the reactor can be cooled by a condenser, led to a mixer, and used for supplying new chloroform. Part of the chloroform from the mixer is fed into the cooling tower and separated into an aqueous phase and a chloroform phase at the bottom of the cooling tower as described above. The chloroform phase is separated into water and chloroform by a subsequent separation tower, and the chloroform is reused.

The reaction product collected at the bottom of the hydrogen chloride removing column can be commercialized by crystallizing the desired p-DCB while removing TCB, m-DCB and o-DCB.
The liquid in the system can be returned to an appropriate position in the process and reused.

(Embodiment)
Next, an embodiment of the present invention will be described.
FIG. 1 shows a preferred embodiment of the present invention.
Reference numeral 10 denotes a reactor, which has a three-stage configuration in the embodiment. The benzene 1 as a raw material is supplied from the top of the first-stage reactor 10 after moisture is removed beforehand by a moisture removing means (not shown) if necessary.

  The chlorine gas 2 is supplied from the tops of the reactors 10, 10, 10 in each stage in parallel. Capacitors 12, 12, 12 are attached to each reactor 10, 10, 10. Chloroform (cooling medium) 3 is sent from the storage tank to the mixer 14, and is supplied from the top to the first stage reactor 10 by the pump 16. Further, the recovered chloroform 3A recovered in the subsequent step of the processing flow not shown in detail is supplied together with benzene 1 from the top of the first stage reactor 10. The mixer 14 is also supplied with recovered chloroform 3B recovered in a subsequent step of the processing flow, the details of which are not shown.

  In each of the reactors 10, 10, and 10, a zeolite catalyst 18 (molded body) is provided as a fixed bed, and raw materials (benzene), chlorine gas, and a cooling medium are circulated in a down flow. A cooling jacket 11 is provided on the peripheral wall of the reactor 10 and is cooled by a cooling medium such as water.

  The reaction product is sequentially led to the next reactors 10 and 10 by the pumps 20 and 20. In the reactor 10, the evaporation component (mainly the cooling medium) is condensed by the condensers 12, 12, 12 and then sent to the reactors 10, 10 and the mixer 14 in the next stage. A part of a small amount of the reaction product which has not been condensed and chloroform are sent to the cooling tower 24.

  The bottom component of the reactor 10 in the final stage is sent to the hydrogen chloride removal tower 22, and by lower heating, hydrogen chloride and the hydrocarbon compounds accompanying it are separated from the top of the hydrogen chloride removal tower 22, and this is separated. The cooling water is sent to the cooling tower 24, and the water phase cooled by the attached condenser 26 is sprayed into the cooling tower 24 and cooled by the pump 28, whereby the cooling tower 24 separates the water phase and the chloroform phase. And a 35% aqueous HCl solution is obtained as the separated aqueous phase. The chloroform phase collected in the precipitation tank 30 provided at the bottom of the bottom of the cooling tower 24 is separated into water and chloroform by a subsequent separation tower (not shown), and the chloroform is reused.

  The cooling medium from the final stage of the reactor 10 is cooled by the condenser 12 and then led to the mixer 14 and can be used for supplying new chloroform.

  The reaction product collected at the bottom of the hydrogen chloride removal tower 22 is then crystallized from the target p-DCB while removing TCB, m-DCB and o-DCB using an appropriate treatment means. Can be commercialized. Reference numeral 32 denotes a decompression pump.

(Example)
According to the flow in FIG. 1, paradichlorobenzene was produced by chlorination with chlorobenzene using benzene as a raw material. A silica compact of BEA zeolite catalyst was installed as a fixed bed in the reactor.
The chlorination reaction was carried out under conditions of a reaction temperature of 80 ° C. and a pressure of 1.8 kg / cm ² . The degree of chlorination was about 2.0.
The selectivity of the obtained p-DCB was 72.1%, and p-DCB could be stably produced with high selectivity.

(Comparative example)
The comparative example using the homogeneous catalyst ferric chloride FeCl ₃ which is a conventional method is shown. As a reaction apparatus, as shown in FIG. 5, a fully mixed reactor 50 with a jacket 51 and a stirrer 52 is used, to which chlorine is supplied from a blower, benzene and FeCl ₃ are supplied, and a cooling water unit 53 supplies a jacket. The reaction is conducted while cooling through 51. The reaction product from the bottom was stored in the liquid storage tank 54 after cooling, and the gas liquid component from the top was stored in the gas liquid storage tank 55 after cooling.

The reaction conditions are as follows.
○ Catalyst FeCl ₃ concentration: 0.0088 catalyst mol / benzene mol
○ Raw material chlorine gas supply rate: 0.850.0088 mol / benzene mol
○ Reaction temperature: 80 ℃

FIG. 6 shows the change in the product of chlorination of benzene in this reaction process as the reaction progress (chlorination degree).
It can be seen from FIG. 6 that the homogeneous catalyst proceeds in a sequential and concurrent manner. This is probably because the homogeneous catalyst has no resistance to diffusion, and benzene and the Mono isomer, or the Mono isomer and the Di isomer reacted at the same time. Therefore, the Di body selectivity in the reaction remains at a maximum of 80%.

  FIG. 7 shows the change in the selectivity of PDCB in DCB accompanying the DCB yield, and FIG. 8 shows the change in the PDCB yield accompanying chlorination. Since the homogeneous catalyst has no steric hindrance in the ortho-para orientation, the para-body selectivity is as low as 60% as shown in FIG. Further, since the Di-isomer selectivity remains at a maximum of 80%, the maximum Para-isomer yield in the reaction is 50% as shown in FIG.

  The experiment was conducted by reducing the reaction temperature from 80 ° C. under standard conditions to 70 ° C. The results are shown in FIG. It can be seen that the para-isomer selectivity does not change even when the reaction temperature is lowered.

  Next, the catalyst amount was changed from 0.0181 g-cat / g-Bz (0.0088 catalyst mol / benzene mol) to about 1/20 0.0010 g-cat / g-Bz (0.00049 catalyst mol / benzene). As a result, the activity was not changed, and it was clarified that the selectivity was not changed as shown in FIG.

  As described above, it has been clarified that p-DCB cannot be produced with high selectivity as long as a homogeneous catalyst is used.

  According to the present invention, a compound having an extremely high industrial value can be continuously obtained as a raw material for PPS.

It is a flow sheet of an embodiment of the invention. It is a graph of the para selectivity by a zeolite catalyst kind. It is a graph of reaction progress in the case of using a zeolite catalyst. It is an explanatory graph showing a recovery rate and the like in relation to pressure and chloroform / benzene ratio under the conditions of a reaction temperature of 80 ° C. and a liquid phase cooling temperature of 58 ° C. It is a general | schematic block diagram of the reaction apparatus of a prior art example (comparative example: use of a homogeneous catalyst). It is a composition change graph of each substance in a conventional example (use of a homogeneous catalyst). It is a graph of the selectivity of p-DCB in a conventional example (using a homogeneous catalyst). It is a graph of the p-DCB yield accompanying chlorination in a conventional example (use of a homogeneous catalyst). It is a graph which shows the influence of the reaction temperature of the selectivity in a prior art example (use of a homogeneous catalyst). It is a graph which shows the influence of the catalyst amount of the selectivity in a prior art example (use of a homogeneous catalyst).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Benzene, 2 ... Chlorine gas, 3 ... Chloroform (cooling medium), 10 ... Reactor, 11 ... Jacket, 12 ... Condenser, 14 ... Mixer, 18 ... Zeolite catalyst, 22 ... Hydrogen chloride removal tower, 30 ... Precipitation Tank, 32 ... decompression pump.

Claims (5)

In a method for producing paradichlorobenzene by chlorinating with chlorine gas using at least one of benzene and monochlorobenzene as a raw material,
While guiding the raw material and the chlorine gas to a reactor equipped with a zeolite catalyst,
A method for producing paradichlorobenzene, wherein at least one cooling medium of chloromethane and chloroethane is introduced into the reactor, and the cooling medium is evaporated to suppress a temperature rise in the chlorination reaction.   The method for producing paradichlorobenzene according to claim 1, wherein the zeolite catalyst is a molded body, and the zeolite catalyst is built in the reactor as a fixed bed, and the raw material, chlorine gas, and cooling medium are circulated in a down flow.   The method for producing paradichlorobenzene according to claim 1 or 2, wherein the evaporated gas content of the cooling medium is condensed outside the reactor, and the condensed liquid is reused as the cooling medium.   The method for producing paradichlorobenzene according to claim 1 or 2, wherein the chlorination reaction is carried out at a temperature of 40 to 130 ° C and a pressure of 10 atm or less.   The reactor has a plurality of stages, the raw material, chlorine gas and cooling medium are supplied to the first stage reactor, the reaction product of the previous stage is supplied to the reactor of the next stage, and the reactor after the next stage is supplied to the reactor. The method for producing paradichlorobenzene according to claim 1 or 2, wherein chlorine gas and a cooling medium are supplied in parallel to obtain paradichlorobenzene from the final reaction product.

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