JP2002020351A - Method for recovering heat in production of diaryl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently and stably recovering heat in the production of a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound. SOLUTION: This method for recovering the heat on the production of the diaryl carbonate from the dialkyl carbonate and the aromatic hydroxy compound by a transesterification reaction and a disproportionation reaction by a batch method, comprising generating steam with the distillation tower overhead condenser of a reactor, characterized by using two or more reactors equipped with distillation towers, respectively, and controlling the reaction time of each reactor and calorie necessary on the reaction to generate the process steam and smooth the recovered calorie.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering heat used in producing a diaryl carbonate. Diaryl carbonate is a compound useful as a raw material for transesterification polycarbonate.

[0002]

2. Description of the Related Art Diaryl carbonates are conventionally produced by reacting an aromatic hydroxy compound with phosgene. However, phosgene is highly toxic,
Since the apparatus is highly corrosive and a large amount of alkali is required to neutralize hydrogen chloride as a by-product, a method that does not use phosgene has been demanded, and several attempts have been made.

[0003] Among them, the present inventors have disclosed in Japanese Patent Laid-Open No.
At 52455, producing a dialkyl carbonate from urea and an alkyl alcohol having 3 to 6 carbon atoms, further transesterifying the dialkyl carbonate with an aromatic hydroxy compound to obtain an alkylaryl carbonate, and further disproportionating the alkylaryl carbonate. Has proposed a method for producing diaryl carbonate. In this production method, if the by-produced alkyl alcohol is reused again as a raw material for the dialkyl carbonate, the diaryl carbonate can be produced from inexpensive urea and aromatic hydroxy compound.

[0004] The reaction of forming a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound in the process can be divided into a transesterification reaction and a disproportionation reaction, and these reactions are all equilibrium reactions.
The reaction is carried out using a reactor equipped with a distillation column, and the reaction proceeds by distilling off the reaction product having a low boiling point from the top of the distillation column. At this time, since a large amount of heat is required, it is indispensable to recover heat for commercialization. As a method for performing heat recovery, it is general to generate steam using the exchange heat of the condenser at the top of the distillation column.

[0005] In an equilibrium reaction such as the present reaction, the reaction proceeds more rapidly in a batchwise reaction than in a continuous method in which raw materials are continuously supplied to a reactor. However, when the reaction is carried out by a batch method, steam cannot be generated since the reaction is not carried out at the time of charging and withdrawing the reaction solution. In general, the amount of heat required in the transesterification and the disproportionation reaction is designed so that the steam load in the distillation column section becomes equal. However, the amount of heat required per unit time to be added to the reaction and the amount of heat recovered per unit time as steam from the condenser are different between the transesterification reaction and the disproportionation reaction. Therefore, in order to recover steam stably and use the recovered steam effectively, it is necessary to generate steam while the steam cannot be recovered by the condenser.Therefore, a compensating boiler is required to supplement this. there were. Further, since the amount of heat required for the reactor fluctuates, heating equipment such as a steam generating boiler and a heating medium heating furnace also need to have a large capacity according to the peak.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a method for efficiently and stably recovering heat when producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound. To provide.

[0007]

Means for Solving the Problems The present inventors have solved the above-mentioned problems in a heat recovery method for producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound by a transesterification reaction and a disproportionation reaction. We studied diligently. As a result, by using two or more reactors equipped with a distillation column, the reaction timing was adjusted so that the reaction was performed in another reactor while one reactor was extracting and charging the reaction solution. Further, they have found that the amount of heat recovered can be smoothed by adjusting the amount of heat required for the transesterification reaction and the disproportionation reaction, thereby completing the present invention.

That is, the present invention relates to a process for producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound by a transesterification reaction and a disproportionation reaction in a batch process, wherein steam is produced in a condenser at the top of a distillation column of a reactor. When performing heat recovery by generating heat, two or more reactors equipped with a distillation column are used, and the reaction time of each reactor and the amount of heat required during the reaction are adjusted to generate process steam, thereby smoothing the recovered heat. This is a heat recovery method for

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to a case where a reaction for producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound by a transesterification reaction and a disproportionation reaction is performed in a batch reactor equipped with a distillation column. Is done.

The transesterification reaction is a reaction for producing an alkylaryl carbonate and an alkyl alcohol from a dialkyl carbonate and an aromatic hydroxy compound, and the disproportionation reaction is a reaction for converting a diaryl carbonate and a dialkyl carbonate from 2 mol of the alkylaryl carbonate. This is a reaction for producing one mole. Since both the transesterification reaction and the disproportionation reaction are equilibrium reactions, the reaction proceeds by distilling off the alkyl alcohol in the transesterification reaction and dialkyl carbonate in the disproportionation reaction.

The present invention is practiced by using two or more reactors equipped with a distillation column and adjusting the reaction time of each reactor and the amount of heat required during the reaction. As a specific example,
As shown in FIG. 2, two reactors are arranged in parallel, the transesterification reaction and the disproportionation reaction are performed in the same reactor, and the amount of heat required per unit time in the transesterification reaction and the disproportionation reaction is reduced. A method in which the reaction step and the reaction liquid withdrawing and charging steps are alternately performed, as shown in FIG.
Groups are arranged in parallel, transesterification and disproportionation are carried out in the same reactor, and the amount of heat required per unit time is adjusted so that the transesterification and disproportionation reaction times are equal. A method in which transesterification, disproportionation, withdrawal and charging are performed in a reactor, and each step of transesterification, disproportionation, withdrawing and charging is sequentially performed,
As shown in FIG. 4, two reactors are arranged in series, transesterification and disproportionation are performed in separate reactors, a buffer tank is provided in the middle, and the transesterification and disproportionation reactors are provided. A method in which the necessary heat amount per unit time is equalized, and the reaction step and the withdrawal and charging steps of the reaction solution are alternately performed, and a transesterification reactor as shown in FIG.
Disproportionation reactors A and B are arranged in series, the required amount of heat per unit time of each reactor is made equal, disproportionation reactor A is withdrawn while the transesterification reactor is conducting the reaction,
The disproportionation reactor B is charged, the disproportionation reactor B starts the reaction as soon as the transesterification reaction is completed, the transesterification reactor is withdrawn, and the disproportionation reactor A is charged. As described above, there is a method of sequentially performing the steps. Of course, a method of adjusting the reaction schedule by providing four or more reactors is also possible.

With the above method, the amount of heat recovered can be smoothed. Although there is no particular limitation on the method of heat recovery, it is appropriate to recover heat by generating steam from a condenser of a distillation column provided in the upper part of the reactor.

The dialkyl carbonate used as a raw material is not particularly limited, but is preferably a dialkyl carbonate having an alkyl group having 3 to 6 carbon atoms. Specifically, various isomers of dipropyl carbonate, dibutyl carbonate, dipentyl carbonate, and dihexyl carbonate are exemplified.

The other raw material, the aromatic hydroxy compound, is also not particularly limited, but may be phenol or phenol substituted with an alkyl group, an alkoxy group and halogen, specifically phenol, cresol (each isomer), Xylenol (each isomer), ethylphenol (each isomer), methoxyphenol (each isomer), fluorophenol (each isomer), or chlorophenol (each isomer) is preferred. Furthermore, phenol is particularly preferred in view of the usefulness of the produced diaryl carbonate.

The catalyst used in the reaction may be any one which is generally known as a transesterification catalyst. In particular, alkoxides, metals of metals selected from titanium, aluminum, gallium, tin and yttrium may be used.
Preferred are any of aryl oxides, alkyl-substituted oxides, and acetylacetonates, or adducts of these compounds with other compounds.

Among the above catalysts, particularly, Ti (OX) ₄
(X represents an alkyl group having 3 to 6 carbon atoms or an aryl group.)
X) It is preferable to use an adduct of a titanium compound represented by ₄ · XOH (X represents an alkyl group or an aryl group having 3 to 6 carbon atoms). The amount of the catalyst is 0.01 to 10 based on the dialkyl carbonate used as the raw material.
Molar% is appropriate.

The transesterification reaction is usually carried out at a reaction temperature of 160
２５０250 ° C. and a reaction pressure of 0.01-1 MPa. The disproportionation reaction is usually performed at a reaction temperature of 160 to 250 ° C. and a reaction pressure of 0.001 to 0.5 MPa.

[0018]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Comparative Example 1 A 1640 kg raw material containing 46% by weight of dibutyl carbonate, 50% by weight of phenol and 4% by weight of titanium tetraphenoxide was charged into a 2000-liter reactor equipped with a distillation column at the top shown in FIG. The reaction was repeated batchwise with a 4 hour cycle. The transesterification reaction was carried out at normal pressure, and the disproportionation reaction was carried out under reduced pressure from normal pressure to 100 torr. During the reaction, heating is performed so that the vapor load of the distillation column is equal, transesterification is 115,800 kcal / hr heat input per unit time for 1 hour, and disproportionation reaction is 91,600 kcal / hr input unit time. The reaction was carried out for 2 hours at a calorific value. After the reaction, a crude diphenyl carbonate solution containing 65% by weight of diphenyl carbonate was obtained. In addition to the reaction, one hour was required for charging the raw materials and extracting the reaction solution. The amount of heat recovered as steam at 110 ° C from the condenser provided at the top of the distillation column was 115,80 during the transesterification reaction.
0 kcal / hr, 91,600 kcal / hr at the time of disproportionation reaction, and 0 at the time of preparation and extraction. The amount of heat that can be reused is always 115,80
It was necessary to install a compensating boiler so that the pressure became 0 kcal / hr. Further, the equipment for heating the reactor also required a capacity of 115,800 kcal / hr. The operating schedule and results of the reactor and compensation boiler are shown in Tables 1 and 6.

[0020]

[Table 1]

Example 1 As shown in FIG. 2, a capacity of 1000 with a distillation column
L reactors A and B were installed in parallel. 46 in reactor A
8% by weight of dibutyl carbonate, 50% by weight of phenol and 4% by weight of titanium tetraphenoxide
After charging 20 kg of the raw material, a transesterification reaction of 45 minutes followed by a disproportionation reaction of 75 minutes was carried out at a heat input of 75,000 kcal / hr. During the transesterification and disproportionation operation in the reactor A, the crude diphenyl carbonate solution containing 65% by weight of diphenyl carbonate produced in the previous reaction was withdrawn in the reactor B, and the raw material for the next reaction was converted into the reactor A. After the disproportionation reaction of the reactor A is completed, the transesterification reaction is started immediately after the same composition and the same amount are charged. By repeating the above operation, a crude diphenyl carbonate liquid was obtained at the same production rate as in Comparative Example 1. In addition, this allows the condenser provided at the top of the distillation column to always generate steam using the process steam heat, and stably recovers 75,000 kcal / hr of heat without using a compensation boiler. Was completed. Also, the heating equipment for the reactor is 75,000 kcal
/ hr capability was sufficient. The operating schedule and results for each reactor are shown in Tables 2 and 6.

[0022]

[Table 2]

Example 2 As shown in FIG. 3, a capacity of 700 L equipped with a distillation column at the top
Of reactors A, B, and C were installed in parallel. After charging 550 kg of a raw material containing 46% by weight of dibutyl carbonate, 50% by weight of phenol and 4% by weight of titanium tetraphenoxide in reactor A, transesterification 8
Zero minutes was performed at a heat input of 29,000 kcal / hr, followed by a disproportionation reaction of 80 minutes at a heat input of 46,000 kcal / hr. Reactor B
The transesterification and disproportionation reaction was carried out with a delay of 80 minutes. The transesterification and disproportionation reaction in reactor C
I went further 80 minutes later. Withdrawal and charging of each reactor was performed in the remaining 80 minutes. By repeating the above operation, a crude diphenyl carbonate solution was obtained at the same production rate as in Comparative Example 1. In addition, this allows the condenser provided at the top of the distillation column to always generate steam using the process steam heat, and to stably recover 75,000 kcal / hr of heat without using a compensation boiler. Was completed. In addition, the reactor heating equipment required a capacity of 75,000 kcal / hr. The operating schedule and results for each reactor are shown in Tables 3 and 6.

[0024]

[Table 3]

Example 3 As shown in FIG.
L reactor A and reactor B were installed in series via a buffer tank. After charging 1640 kg of a raw material containing 46% by weight of dibutyl carbonate, 50% by weight of phenol, and 4% by weight of titanium tetraphenoxide in reactor A, the transesterification reaction was conducted for 90 minutes and the heat input was 75,000 kcal.
/ hr, and the remaining 150 minutes were withdrawn from the buffer tank and waited. Meanwhile, in the reactor B, the disproportionation reaction 1
Fifty minutes were performed with a heat input of 75,000 kcal / hr. By repeating the above operation, a crude diphenyl carbonate solution was obtained at the same production rate as in Comparative Example 1. In addition, this allows the condenser provided at the top of the distillation column to always generate steam using the process steam heat, and to stably recover 75,000 kcal / hr of heat without using a compensation boiler. Was completed. The equipment for heating the reactor is also 75,000kc
al / hr capacity was sufficient. The operating schedule and results for each reactor are shown in Tables 4 and 6.

[0026]

[Table 4]

Example 4 As shown in FIG. 5, a capacity of 2000 with a distillation column
L transesterification reactor, volume 2 with distillation column on top
A 2,000 L disproportionation reactor A and a 1000 L disproportionation reactor B equipped with a distillation column on top were installed in series.
After feeding 1640 kg of a raw material containing 46% by weight of dibutyl carbonate, 50% by weight of phenol and 4% by weight of titanium tetraphenoxide to a transesterification reactor, a transesterification reaction was conducted for 90 minutes at a heat input of 75,000 kcal / hr. The kettle liquid was discharged to the disproportionation reactor A in 75 minutes, and after waiting for 45 minutes, the raw materials were charged in 30 minutes. On the other hand, in the disproportionation reactor A, the disproportionation reaction was performed at a heat input of 75,000 kcal / hr for 75 minutes after the completion of the charging. Thereafter, the pot liquid of the disproportionation reactor A was charged into the disproportionation reactor B for 90 minutes, and the disproportionation reaction was performed in the disproportionation reactor B for 75 minutes at a heat input of 75,000 kcal / hr. By repeating the above operation, a crude diphenyl carbonate solution was obtained at the same production rate as in Comparative Example 1. In addition, the condenser provided at the top of the distillation column can always generate steam using the process steam heat, and can stably generate 75,000 kC without using a compensation boiler.
al / hr of heat was recovered. In addition, the reactor heating equipment required a capacity of 75,000 kcal / hr. Tables 5 and 6 show the operation schedule and results of each reactor.

[0028]

[Table 5]

[0029]

[Table 6]

[0030]

According to the method of the present invention, when diphenyl carbonate is produced from a dialkyl carbonate and an aromatic hydroxy compound by a batch method, heat can be recovered stably and the amount of heat consumed for heating can be smoothed. Can be Therefore, as compared with the conventional heat recovery method, a compensating boiler is not required, and the capacity of the heating device of the reactor can be reduced, so that the cost of the auxiliary equipment can be reduced. Furthermore, since there is no need to generate steam by the compensation boiler, the operating cost can be reduced.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration diagram of a conventional single batch reactor.

FIG. 2 is a schematic configuration diagram when two units are arranged in parallel.

FIG. 3 is a schematic configuration diagram when three units are arranged in parallel.

FIG. 4 is a schematic configuration diagram when two units are arranged in series.

FIG. 5 shows a schematic configuration diagram when three units are arranged in series.

[Explanation of symbols]

 1: Raw material feed line 2: Reactor distillation section 3: Reactor tank section 4: Circulation pump 5: Reboiler 6: Product extraction line 7: Supply water for steam generation 8: Condenser / steam generator 9: Generation steam extraction line 10: Low-boiling product take-out line 11: Steam generator for compensation 12: Buffer tank 13: Transesterification reactor 14: Disproportionation reactor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B01J 19/00 B01J 19/00 E

Claims (1)

[Claims] 1. A method for producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound by a transesterification reaction and a disproportionation reaction by a batch method, wherein steam is generated in a condenser at the top of a distillation column of a reactor. When performing heat recovery, it is necessary to use two or more reactors equipped with a distillation column and adjust the reaction time of each reactor and the amount of heat required during the reaction to generate process steam and smooth the recovered heat. Characterized heat recovery method.