JPS5826742B2 - Transesterification reaction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved industrial transesterification process for obtaining bis-β-hydroxyethyl terephthalate and/or its low polymers by transesterification of dimethyl terephthalate and ethylene glycol. .

More specifically, the present invention relates to a method of carrying out a transesterification reaction between dimethyl terephthalate and ethylene glycol in the presence of a specific amount of a specific compound.

Dimethyl terephthalate (hereinafter referred to as DMT) and ethylene glycol (hereinafter referred to as EG) are reacted to form bis-β.
- In the usual transesterification method for obtaining hydroxyethyl terephthalate and/or its low polymer (hereinafter referred to as BHT), there is a problem that a large amount of DMT vapor is generated, which slows down the transesterification reaction rate. There is.

In other words, it is a rectification column that generates a large amount of DMT vapor and removes methanol generated from the reaction solution. DMT condenses and solidifies especially at the bottom of the rectification column, clogging the rectification column and causing damage to the reaction vessel. Extremely unfavorable phenomena occur during operation, such as an abnormal pressure rise and bumping of the reaction liquid.

And this phenomenon occurs, for example, when a mixture with a low reaction rate (50% or less) is converted into 19% in a batch transesterification method.
This is particularly noticeable at the early stage of the reaction when heating is performed at a high temperature of 0°C or higher.

Therefore, in a relatively low reaction rate region of 50% or less, D
It is necessary to set the temperature increase rate so slow that only clogging of the rectification column occurs due to MT, and in the low reaction rate region, the temperature must be kept below the boiling point of EG.

Therefore, in the conventional batch transesterification method, the reaction rate is slow and it is difficult to improve the productivity of BHT.

In order to solve the problems of the above-mentioned batch transesterification method of DMT and EG, we have developed a method in which the entire amount of EG is first supplied to the reaction vessel before the reaction, and then DMT is supplied at a specific ratio for reaction ( Special Publication No. 5O-15785) has been proposed.

Compared to the conventional method in which a predetermined amount of DMT and the entire amount of EG are supplied to the reaction vessel before the reaction, the DMT at the initial stage of the reaction is
Since the proportion of MT present is small, less DMT rises to the rectification column as vapor.

Therefore, only clogging of the rectification column occurs, and the reaction can be carried out at a temperature close to the boiling point of EC from the initial stage of the reaction, making it possible to increase the reaction rate relatively.

However, in this method where DMT is continuously supplied after supplying the entire amount of EG before the reaction, the etherification reaction proceeds due to the presence of a large amount of free EC at high temperatures except in the latter half of the reaction, and diethylene glycol (hereinafter referred to as DEG) ), which has the disadvantage of lowering the softening point of the polymer obtained from HT.

Furthermore, the reaction rate is still insufficient due to the low concentration of DMT at the initial stage of the reaction, and there is a need for an improved method to carry out the reaction at an even higher reaction rate.

The object of the present invention is to improve the drawbacks of the conventionally known transesterification reaction of DMT and EG.

That is, the first object of the present invention is to provide a method for producing HT that has a good transesterification reaction rate and good productivity, and the second object is to provide a method for producing HT that can reduce the clogging of the rectification column due to condensation and solidification of DMT. An object of the present invention is to provide a transesterification reaction method that enables stable operational management without bumping of a reaction solution.

A third object is to provide a method for economically producing high-grade BHT by using conventionally used batch or continuous reactors as they are.

As a result of intensive research to achieve the above object, the present inventors have discovered that the reaction rate can be improved by making a small amount of a specific compound present during the transesterification reaction between DMT and EG, and have arrived at the present invention.

That is, in the present invention, when reacting DMT and EG, the transesterification reaction is carried out at 50 to 20,000 p, P, m (
This is a transesterification method characterized in that it is carried out in the presence of methyl ethyl terelentalate (hereinafter referred to as MET) and/or diethyl terephthalate (hereinafter referred to as DET) of dimethyl terephthalate.

The abundance of MET and/or DET should be in the range of 50 to 20000 p, plm relative to DMT,
The range of 150 to 8000 p, p, m is more preferable.

By setting the abundance of MET and/or DET in the range of 50 to 20000 p, plm relative to DMT,
Even when the temperature increase rate is increased in the transesterification reaction of DMT and EG, the condensation and solidification phenomenon of DMT in the rectification column can be suppressed or eliminated.

The reason for this is unclear, but MET and /' or D
The presence of ET suppresses the vaporization rate of DMT, or the vaporized DMT is condensed in the rectification column and knocked down into the reaction liquid in a liquefied state, reducing the proportion of solidification in the rectification column. This is thought to be due to factors such as.

Therefore, in the method of the present invention, the reaction temperature can be set high, and as a result, the reaction rate can be increased.

If the amount of MET and/or DET relative to DMT is less than 50 p, p1m, the DMT in the above-mentioned rectification column is
The effect of suppressing the condensation and solidification phenomenon is expressed, and 20
If it exceeds 000p, pom, the transesterification reaction will be inhibited.

As a means for making MET and/or DET exist in the reaction system, they may be added to the mixed system of DMT and EG before the reaction or the system at the initial stage of the reaction, or they may be allowed to exist uniformly in the DMT before the reaction.

When MET and/or DET are homogeneously present in DMT before reaction, the mixture is heated to 140 to 18
Melt storage may be carried out at a temperature of 0° C. for 0.5 to 720 hours.

The transesterification reaction temperature is preferably in the range of 140 to 280°C.

Also, the reaction pressure is -500mRHg~3, Okg/cv
Although the pressure can be set to tG pressure, it is preferably set to 0.02 to 0.30 kg/cntG pressure under atmospheric pressure, including the pressure outside the pressure loss of the rectification column.

The molar ratio of EG/DMT used in the reaction is preferably in the range of 1.2 to 2.0, more preferably in the range of 1.35 to 1.80.

Any method may be used to supply DMT and EG to the transesterification reactor, such as (1) a method in which m and DMT are simultaneously supplied before the reaction, (2) a method in which EG is supplied before the reaction and DMT - Continuous supply method during reaction (3) A part of EG is supplied before the reaction, and the remaining EG and DM
(4) A method in which a portion of BHT is stored before the reaction, and EG and DMT are reacted by continuously supplying T during the reaction.
(5) complete mixing tank continuous transesterification method; (6)
A known method such as a column-type continuous transesterification method can be employed.

Methanol and ethanol generated in the transesterification reaction are fractionated from DMT, EG, etc. in a rectification column, distilled from the top of the column, and then cooled and taken out in a total condenser.

As the transesterification catalyst used in the method of the present invention, known compounds can be used, but manganese acetate, zinc acetate, cobalt acetate, calcium acetate, magnesium acetate, antimony dioxide, etc. alone or in combination are preferred.

Additives include titanium oxide, kaolinite, talc,
Known external particles such as clay, silica, alumina, etc. can be added to the reaction product before the transesterification reaction, at any stage during the reaction, or after the reaction is complete.

Moreover, known phosphorus compounds such as phosphoric acid, trimethyl phosphate, and phosphorous acid can be added as anti-fouling agents at any stage from during the transesterification reaction to after the completion of the reaction.

Due to the subsequent polycondensation reaction, the BHT obtained by the method of the present invention has low DEG content and no decrease in softening point, and can be made into polyethylene terephthalate, which is excellent for molding fibers, films, and resins.

Note that after the transesterification reaction, it is desirable to perform initial polymerization in order to increase the degree of polymerization.

The method of the present invention can of course be applied to transesterification methods using not more than 25 mol % of copolymer components in addition to DMT and EG.

The copolymerization components include isophthalic acid dimethyl ester, 5-sulfosodium isophthalic acid dimethyl ester,
Dicarboxylic acids such as phthalic acid dimethyl ester, isophthalic acid diethyl ester, phthalic acid diethyl ester, 2,6-naphthalic acid dimethyl ester, 1,4-cyclohexane dimetatool, rosehydroxybenzoic acid methyl ester, adipic acid, sebacic acid, etc. ester and/or
Alternatively, there are dicarboxylic acids, noalkylene glycols such as (1).4-butanediol, propylene glycol, and 1.6-hexanediol.

The excellent effects obtained by the present invention are listed below.

(1) Clogging of the rectification column caused by condensation and solidification of DMT during the reaction can be avoided, and stable operational management can be achieved.

(2) The temperature of the reaction solution at the initial stage of the reaction can be set high, and the reaction rate can be increased.

(3) Since the reaction time is shortened, the by-product of DEC is reduced, and HT, which is useful for obtaining high-grade polyester, can be obtained with high productivity.

The present invention will be explained in detail with reference to Examples below.

Example 1 Using the experimental apparatus shown in FIG. 1, 300 Sl' of DMT and 1632 E of
G (molar ratio to DMT 1.70), cobalt acetate tetrahydrate 0
．． A predetermined amount of MET was added to 075P1 calcium acetate monohydrate 0, 06 P, and DMT as shown in Table 1 to obtain reaction solution 12.

Stirring was carried out using a half-moon type tool by driving the motor 3 and rotating the stirring shaft 11.

Reaction temperature is 22.5℃/hr from 145℃ to 235℃
The temperature controller 5 was operated at a rate of 1, and the temperature was raised at a constant rate by heating with the mantle heater 2 for 4 hours.

Methanol and a small amount of ethanol generated from the reaction system are rectified in a glass rectification column (packed column) 6, distilled off from the top of the column, and sent to a water-cooled decentralizer-equipped distributor (arrow indicates cooling water flow) γ. A portion was refluxed and a portion was distilled off.

The distilled methanol was cooled in a total condenser 8 (the arrow indicates a cooling water flow) and collected in a graduated cylinder 9.

The temperature of the reaction liquid is measured by the recorder 4, while the temperature of the rectifying column is measured by the lower stage.
Recordings were made using a recorder 10 for each part of the middle stage and the top of the column, and the reflux amount was controlled by a distributor γ so that the temperature of the top of the column was maintained at the boiling point of methanol, 65°C.

The reflux ratio in this case was approximately 1.0.

During the transesterification reaction, clogging of the rectification tower due to condensation and solidification of DMT was evaluated by observing the state of condensation and solidification of DMT in the lower part of flask 1 and rectification tower 6, as shown in Figure 2. .

Figure 2 A shows the degree to which DMT is slightly condensed and adhered to a part of the inner surface of the glass, B shows the degree to which DMT condenses and adheres to a part of the filling and about half of the inner surface of the glass, and C shows a part of the filling. and D indicates the degree to which DMT condenses and adheres to the entire inner surface of the glass, and D indicates the degree to which DMT condenses and solidifies on the entire inner surface of the glass, the entire filling, and below the filling, and the rectification column is mostly clogged. The preferred range for the invention is A
and B.

The clogging of the rectification column with NaoriMT was evaluated by observing the state when DMT was most condensed and solidified during the transesterification reaction and ranking according to Figure 2.

In addition, the reaction rate determined from the amount of methanol distilled at that time,
Table 1 shows the temperature at the bottom of the rectification column, as well as the reaction rate at the end of the reaction and the DEG content of the produced HT.

Experiment number 1.2.11 in Table 1 is a comparison level for clarifying the effect of the method of the present invention.

The end point of the reaction was determined after reaching 235°C and keeping the reaction solution at the same temperature for 15 minutes**.

From the results of this experiment, 50 to 20,000 for DMT.
In the transesterification reaction in which ppm of MET is added, the rank is A-B even when the bottom of the rectification tower is clogged.
, and the temperature at the bottom of the rectification column at this time is 70 to 75°C.
This allowed the rectification operation to be carried out stably.

Moreover, the reaction rate at the end of the reaction was 97.1% to 99.1%, and there was no problem.

On the other hand, in Experiments Nos. 1 and 2, the amount of MET added to DMT was less than 50 ppm, so the clogging of the rectification column was poor at rank C, and the temperature at the bottom of the rectification column was high at 92-94℃, resulting in a decrease in rectification efficiency. This resulted in unstable rectification operation.

In other words, most of the rectification column is blocked (rank D)
There was little margin for this, and the temperature increase rate was close to its limit.

Furthermore, in Experiment No. 11, since the amount of MET added to DMT exceeded 20,000 ppm, reaction inhibition occurred and the reaction rate reached at the end of the reaction was as low as 95.1%.

Example 2 MET and/or DET under the same equipment conditions as Example 1
Table 2 shows the results of experiments conducted with different amounts added and evaluated in the same manner as in Example 1.

Experiment No. 12 in Table 2 shows a comparative level below the lower limit of the amount of MET and/or DET added according to the present invention.

From this experiment result, in experiment numbers 13 to 18, the amount of MET and/or DET added to DMT was 50 to 20,000 ppm in total of both compounds, so the clogging state of the rectification column was rank A-B. The temperature at the bottom of the rectifying column was also as low as 70 to 74°C, allowing stable rectification.

In Experiment No. 12, the amount of MET and/or DET added to DMT was as small as 40 ppm, so the clogging of the rectification column was poor at rank C, and the temperature at the bottom of the rectification column was as high as 92°C, resulting in a low rectification efficiency. The temperature increase rate was close to its limit.

Example 3 MET 11 for DMT using the same equipment as Example 1
The reaction was carried out under the same conditions as in Example 1, except that 00 ppm was present, the reaction initiation temperature was 160°C, and the temperature was raised at a constant rate of 25°C/h to reach 235°C in 3 hours.

45 minutes after the start of the reaction, when the reaction temperature was 179°C, the most likely cause was clogging of the DMT rectification column, but the rank was B in Figure 2.
At this time, the temperature at the bottom of the rectification column was 74°C, and the reaction rate was 39.
%Met.

After the reaction temperature reached 235°C, it was maintained at the same temperature for 15 minutes,
The reaction was completed.

The reaction rate of the obtained BHT was 98.2%, and the DEC content was 0.
．． It was 22% by weight.

Comparative Example I When carried out using the same equipment and conditions as in Example 3 without adding MET, 53 minutes after the start of the reaction, the reaction temperature was 182°C,
When the reaction rate was 42% and the temperature at the bottom of the rectification tower was 96°C, the rectification tower was clogged to the second level due to condensation and solidification of DMT, and most of the lower part of the rectification tower was blocked, making the experiment dangerous. Canceled.

Example 4 600 ppm of MET was present in DMT20001y,
It was melted and stored in advance at 150° C. for 1 hour before being supplied to the transesterification reactor.

Next, 1.151 kg of EG preheated to 150°C (molar ratio to DMT 1.8), cobalt acetate tetrahydrate 0.01% by weight/DMT, manganese acetate tetrahydrate 0.03% by weight/D
MT and 0.03% by weight of antimony trioxide/DMT were added and stirred to start the reaction.

The reaction initiation temperature was 150°C, and the temperature was increased to 233°C for 3 hours.
The temperature was controlled to increase at a constant rate in minutes, and after reaching 233°C, the reaction was completed by holding for 15 minutes.

Methanol and a small amount of ethanol generated from the reaction system were rectified in a rectification column, passed through a total condenser, and distributed so that one part was refluxed and the other part was distilled out.

Note that the reflux ratio was approximately 1.0. Throughout the reaction, the pressure inside the reactor was constant at approximately 0.1 kg/critG pressure, and no particular abnormality was observed.

The reaction completed in 3 hours and 55 minutes, and the reaction rate of HT produced was 98.
．． 9%, and the DEG content was 0.29% by weight.

Comparative Example 2 A reaction was carried out under the same conditions as in Example 4 except that MET was not present in DMT.

One hour after the start of temperature rise, reaction temperature was 175°C, reaction rate was 42%.
, the pressure inside the tank is highest when the temperature at the lower stage of the rectifying column is 103°C,
The pressure was 0.3kg/ff1G.

This is presumed to be due to the phenomenon of partial blockage of the rectification column due to MT, as shown in the second diagram.

Comparative Example 3 A reaction was carried out without the presence of MET in DMT while maintaining the same internal pressure as in Example 4, ie, 0.1 kg/crit and G pressure.

In order to maintain the pressure while the reaction progresses, the temperature must be 150°C.
It took 4 hours and 20 minutes to raise the temperature from 233°C to 233°C, and if you add the time to hold the temperature at 233°C for 15 minutes at the end of the reaction, it took 4 hours and 35 minutes, so compared to Example 4, the reaction time was 40 minutes. Minutes late.

Example 5 The experiment was carried out using the same equipment and conditions as in Example 4, except that DET was present at 19,000 ppm relative to DMT.

The DMT clogging state of the rectification column was rank A in Figure 2, and the temperature at the bottom of the rectification column at this point was 73°C.

After the reaction temperature reached 233°C, the temperature was maintained for 15 minutes to complete the reaction.

The reaction rate of the obtained BHT was 97.0%, and the DEC content was 0.
．． It was 31% by weight.

Comparative Example 4 The experiment was carried out using the same equipment and conditions as in Example 4, except that DET was present at 21,000 ppm relative to DMT. Although the temperature was stable at 72° C., the reaction rate at a reaction time of 3 hours and 55 minutes was as low as 94.5%.

In order to increase the reaction rate, the reaction temperature was kept at 233℃ for 3
When the reaction time was extended for 5 minutes, the reaction rate reached 97.0% and the reaction was terminated.

Total reaction time was 4 hours and 30 minutes.

The DEC content of the obtained BHT was as high as 0.46% by weight.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of a transesterification reaction apparatus in a flask used in an example of the present invention. FIG. 2 is a diagram showing the rank of DMT clogging in the rectification column. 1: Three-necked flask 2: Mantle heater, 3: Stirring motor, 4, 10: Recorder, 5: Temperature controller, 6: Rectifier, 7: Distributor, 8: Total condenser, 12: Reaction liquid.

Claims (1)

[Claims] 1 When dimethyl terephthalate and ethylene glycol are reacted to obtain bis-β-hydroxyethyl terephthalate and/or its low polymer, the transesterification reaction is performed with methyl ethyl of 50 to 200001), P, m (vs. dimethyl terephthalate). A transesterification method characterized in that it is carried out in the presence of terephthalate and/or diethyl terephthalate.