JP3404825B2 - Method for producing 2-hydroxycarboxylic acid oligomer - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lactide characterized by efficiently distilling only water using a partial condenser.
The present invention relates to a method for producing a 2-hydroxycarboxylic acid oligomer useful as a precursor for producing a 2-hydroxycarboxylic acid cyclic dimer such as glycolide.

BACKGROUND OF THE INVENTION 2-Hydroxycarboxylic acid-based oligomers are produced by dehydrating 2-hydroxycarboxylic acids such as lactic acid and glycolic acid, and are precursors for producing 2-hydroxycarboxylic acid cyclic dimers such as lactide and glycolide. Used as. BACKGROUND OF THE INVENTION 2-Hydroxycarboxylic acid cyclic dimers have attracted attention as raw materials for biodegradable polymers, and a highly efficient production method of 2-hydroxycarboxylic acid oligomers is required.

Conventionally, 2-hydroxycarboxylic acid oligomers have been produced by directly dehydrating 2-hydroxycarboxylic acids from a kettle without using a partial condenser. However, in this method, as the dehydration progresses, the raw material 2-hydroxycarboxylic acids are distilled out together with water, and the 2-hydroxycarboxylic acids are recovered from the distillate and recycled, so that another separation facility is required.

In this method, when recovering 2-hydroxycarboxylic acids, it is necessary to distill off a large amount of water in order to recover a small amount of 2-hydroxycarboxylic acids. Considering the high latent heat of vaporization of water, it is considered utility. Not only is it disadvantageous, but also at this time the problem of distilling 2-hydroxycarboxylic acids with dehydration occurs again.

A method (US Pat. No. 5,196,551) of adding a highly toxic co-solvent such as ortho-dichlorobenzene to 2-hydroxycarboxylic acids and dehydrating the mixture using a partial condenser has been known. In the subsequent step, only the co-solvent is distilled off under reduced pressure and then recovered, which is a separation operation. Moreover, due to the toxicity of the solvent, the solvent is not allowed to remain in the product, and strict process control is required.

In addition to the problems of safety, these not only complicate the oligomer production operation, but also decrease the yield and production efficiency of the 2-hydroxycarboxylic acid type oligomer as a whole, leading to an increase in oligomer cost. It had drawbacks.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, the problem to be solved by the present invention is to selectively distill off only water with a simple production facility, and to obtain a high yield of 2- It is to provide a method for producing a hydroxycarboxylic acid-based oligomer.

[0006]

As a result of earnest studies, the present inventors have found that a 2-hydroxycarboxylic acid oligomer can be efficiently produced by using a condensation device equipped with a partial condenser. Came to complete.

That is, the present invention is characterized in that 2-hydroxycarboxylic acid is dehydrated and condensed by using a reactor equipped with a partial condenser, and has a weight average molecular weight of 500 to 100.
No. 00 2-hydroxycarboxylic acid oligomer.

Further, the present invention relates to a method for producing an oligomer in which 2-hydroxycarboxylic acid is lactic acid, and more specifically, the partial condenser is 0.2 in number of stages measured by a chlorobenzene / ethylbenzene system under normal pressure. A method for producing an oligomer, which is a packed column having 10 to 10 stages.

The present invention is also characterized in that the method for producing an oligomer is characterized by dehydration under a reduced pressure of 25 to 400 Torr, and a batch type and continuous type reaction apparatus equipped with a partial condenser. It includes a method for producing an oligomer.

Next, the present invention will be described in detail. The 2-hydroxycarboxylic acid-based oligomer in the present invention means an oligomer having a weight average molecular weight of 500 to 10,000 formed by dehydration condensation of 2-hydroxycarboxylic acids such as lactic acid and glycolic acid.

The 2-hydroxycarboxylic acid type oligomer containing lactic acid as a main constituent (pre-dehydration component) may be referred to as a lactic acid type oligomer. The lactic acid referred to in the present invention also includes L-lactic acid, D-lactic acid, racemic lactic acid, and mixtures thereof. Further, the lactides referred to in the present invention include, among the 2-hydroxycarboxylic acid cyclic dimers, a cyclic dimer having lactic acid as a constituent element,
That is, it means giractide.

In the dehydration condensation reaction of the present invention, a condensation catalyst is not particularly required, but tin, zinc, antimony,
The reaction may be carried out after adding lead, alkali metal, and a mixture thereof. Further, the 2-hydroxycarboxylic acids used as the condensation raw material may have a concentration in the range of 5 to 95% by weight, and commercially available 2-hydroxycarboxylic acids can be used.

The 2-hydroxycarboxylic acid oligomer obtained by the production method of the present invention is a colorless resinous substance having a water content of 1% or less, usually 0.4 to 0.5% by weight.
Is. Moreover, the residual monomer in the oligomer has a concentration below the detection limit by gel permeation chromatography.

With these low water contents obtained according to the invention,
Also, the monomer content is low, and the weight average molecular weight is 1500.
The oligomers of up to 6000 are particularly suitable as a raw material for producing 2-hydroxycarboxylic acid cyclic dimers such as lactide and glycolide by a thermal decomposition reaction in the presence of a catalyst.

The dephlegmator in the present invention is provided at the distillate outlet when the 2-hydroxycarboxylic acid oligomer is produced by dehydration condensation, and removes dehydrated water through the dephlegmator. That is, 2-hydroxycarboxylic acid, an oligomer having a weight average molecular weight of 500 or less, and 2-hydroxycarboxylic acid are selected from the vapors produced when a 2-hydroxycarboxylic acid-based oligomer is produced by dehydration condensation of 2-hydroxycarboxylic acid. This is a device in which only cyclic dimers are condensed and returned into the reaction device, and only water is passed in the form of steam.

[0016] Usually, the dephlegmator is equipped with a device for efficiently performing gas-liquid contact in the tower and causing sufficient turbulence in the flow of both gas phase and liquid phase. As the partial condenser to be used, any type such as a perforated plate tower, a bubble cap tower and a packed tower can be used, but the one using the packed tower has less pressure loss and can increase the production amount per unit time. It is particularly preferable in that it can be obtained.

In the present invention, the packed column refers to a column packed with packing, and either a packed packing with regular packing or a packed packing with irregular packing can be used. I can. For example, as regular packing, Sulzer packing, Good roll packing, Techno pack, etc.
Examples of the irregular packing include Raschig ring, McMahon packing, Dixon packing and the like.

The number of stages of the packed tower is chlorobenzene /
The number of stages of 0.2 or more and 10 or less as measured by ethylbenzene at atmospheric pressure can be particularly preferably used. The 0.2 step mentioned here is the minimum value obtained from the actual test data, and does not mean the limit value of the present invention.

When the number of stages is 0.2 or less, the separation efficiency of water from 2-hydroxycarboxylic acids and 2-hydroxycarboxylic acid cyclic dimers is not sufficient, and a large amount of 2-
Hydroxycarboxylic acids are mixed in. Further, 10 stages or more are usually unnecessary from the viewpoint of thermal efficiency and separation efficiency.

As a method for determining the number of plates, a two-component standard solution can be used to perform a total reflux test. As standard solutions, chlorobenzene / ethylbenzene system, cis-
Decalin / trans-decalin system, cyclohexane / heptane system, etc. are used. Further, as the material of the packed tower and the packing, those having a property of being corroded or deteriorated by an acid are not preferable, and glass, ceramics, or SUS is preferable.
It is necessary to use a metal having an acid resistance of 316 or higher.

The condensation reaction device equipped with a partial condenser in the present invention may be either a batch type or a continuous type, and any of a batch reactor, a multi-chamber evaporator, a continuous tank type reactor and a switch type reactor. However, it can be preferably used. The batch reactor is a single kettle-type reactor, and an oligomer is usually produced by a batch operation after charging raw materials.

The multi-chamber evaporation device is a device in which one kettle-shaped reactor is vertically divided into partition plates and holes corresponding to the flow rate are formed in the partition plates from the inlet to the outlet. By feeding 2-hydroxycarboxylic acid as a raw material continuously to the first chamber, an oligomer can be continuously produced from the last chamber. In the continuous tank reactor, several batch reactors are connected in series, the starting 2-hydroxycarboxylic acid is continuously supplied to the first reactor, and the 2-hydroxycarboxylic acid is continuously supplied from the last reactor. It is a reactor that can obtain a system oligomer.

The reactor is characterized in that a dephlegmator is installed in each reactor and dehydration is performed through the dephlegmator. In the switch type reactor, several batch reactors are connected in parallel, each reactor is equipped with a partial condenser, and dehydration is performed through the partial condenser. This is an apparatus in which the timing of each reactor is shifted and as a result, a 2-hydroxycarboxylic acid oligomer is continuously obtained.

The operating pressure of the apparatus is not particularly limited, but dehydration can be preferably performed under reduced pressure of 25 to 400 Torr. Below 25 Torr, the boiling point of water is 26
Since it becomes below ℃, it becomes difficult to completely condense and recover water due to the problem of cooling efficiency of cooling water. Also 400To
Above rr, the distillation rate of water becomes extremely slow, which makes practical application difficult.

The temperature of the condensation reaction can be easily controlled by heating the reactor at a temperature of the top of the partial condenser at a temperature not higher than the boiling point of water at the operating pressure. Further, the internal temperature of the reactor rises as the dehydration reaction proceeds, but if the internal temperature of the reactor is raised to 200 ° C. or higher, the coloring phenomenon of the 2-hydroxycarboxylic acid oligomer may occur. It is preferable to keep the temperature low.

[0026]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
In this example,% represents weight percentage unless otherwise specified. In addition, the concentration of the raw material lactic acid represents the weight percentage in terms of monomer.

The number of stages was measured with a chlorobenzene / ethylbenzene system at atmospheric pressure. More specifically, the area ratio of both components was calculated by a gas chromatography method, converted into a molar ratio, and then the obtained molar fraction was substituted into the Fenske's formula to obtain.

The composition of the distillate was determined by high performance liquid chromatography using tartaric acid as an internal standard, and the molecular weight of the lactic acid oligomer was determined by gel permeation chromatography.

(Example 1) Commercially available 90% L-lactic acid 15
1.5 g was charged as a dephlegmator into a 4-necked flask equipped with 20 mmφ × 300 mmH filled with 6 mm McMahon packing, and dehydration condensation was performed under reduced pressure while stirring. The manufacturing results are shown in the following table.

[0030]

The weight of the obtained oligomer was 108.5.
g, Mw of oligomer molecular weight = 3.11 × 10 ³ .

The number of stages of the demultiplexer was calculated as follows. That is, from the gas chromatographic analysis of the fractionated liquid obtained in the total reflux test, the mole fractions of top and bottom chlorobenzene, 0.5076 and 0.3756, were substituted into the Fenceke's formula, and converted into the number of stages n. I asked. The subsequent examples were also obtained by the same method.

N + 1 = log (0.5076 / (1.0-0.5076) x (1.0
-0.3756) /0.3756) / log (1.130) Here, 1.130 is a constant unique to the chlorobenzene / ethylbenzene system. Therefore, the number of demultiplexer stages is n = 5.4

From the composition analysis in the distillate, it is found that the distillate contains almost no lactic acid or lactide and only water is distilled.

Example 2 Commercially available 90% L-lactic acid 15
While charging 1.9 g into a four-necked flask and stirring,
Dehydration was performed under reduced pressure. As the demultiplexer, a 20 mmφ × 103 mmH one filled with 6 mm Dickson packing was used. (Number of demultiplexer stages = 2.1 stages) The results are shown below.

Top temperature (° C): 47 Bottom temperature (℃): Room temperature to 191 Weight (g): 37.4 Pressure (Torr): 100 Collection time (min): 180 Lactic acid monomer to lactic acid tetramer: 0.0

The weight of the obtained oligomer was 108.9.
g, the molecular weight of the oligomer was Mw = 3.80 × 10 ³ . From the composition analysis in the distillate, it is found that lactic acid or lactide is not contained and only water is distilled.

(Example 3) Commercially available 90% L-lactic acid 15
2.4 g was charged into a four-necked flask and stirred,
Dehydration was performed under reduced pressure. As the demultiplexer, a 20 mmφ × 85 mmH one filled with 6 mm McMahon packing was used. (Number of demultiplexer stages = 0.5 stages) The results are shown below.

Top temperature (° C): 47 Bottom temperature (℃): Room temperature to 191 Weight (g): 36.6 Pressure (Torr): 100 Collection time (min): 180 Lactic acid monomer (%): 0.3 Lactic acid dimer to tetramer (%): 0.0

Obtained oligomer weight (g) = 109.
8 g, oligomer molecular weight Mw = 3.45 × 10 ³ .

(Example 4) Commercially available 90% L-lactic acid 15
2.4 g was charged into a four-necked flask and stirred,
Dehydration was performed under reduced pressure. The decompressor used was a 20 mmφ × 85 mmH filled with a 6 mm Raschig ring. (Number of demultiplexer stages = 0.2) The results are shown below.

Top temperature (° C.): 47 Bottom temperature (℃): Room temperature to 191 Weight (g): 39.3 Pressure (Torr): 100 Collection time (min): 90 Lactic acid monomer (%): 0.4 Lactic acid dimer to tetramer (%): 0.0

Obtained oligomer weight (g) = 109.
9 g, oligomer molecular weight Mw = 4.28 × 10 ³ .

Comparative Example 1 Commercially available 90% L-lactic acid 15
1.5 g was placed in a four-necked flask without using a partial condenser, and dehydrated under reduced pressure with stirring. The results are shown in the table below.

[0045]

Weight of oligomer obtained (g) = 102.
0 g, oligomer molecular weight Mw = 1.7 × 10 ³ . It can be seen that, in addition to water, a large amount of components such as lactic acid are found in the distillate, and the weight of the oligomer is small due to the loss of the active ingredient in the distillate.

[0047]

INDUSTRIAL APPLICABILITY The present invention can provide a method for producing a high-yield 2-hydroxycarboxylic acid oligomer by selectively distilling off only water with a simple production facility.

Claims (4)

(57) [Claims] 1. A method for producing a 2-hydroxycarboxylic acid-based oligomer having a weight average molecular weight of 500 to 10,000, which comprises dehydrating and condensing 2-hydroxycarboxylic acid using a reactor equipped with a partial condenser. . 2. The method according to claim 1, wherein the 2-hydroxycarboxylic acid is lactic acid. 3. The production method according to claim 1, wherein the dephlegmator is a packed column having 0.2 or more and 10 or less plates as measured by a chlorobenzene / ethylbenzene system at atmospheric pressure. 4. The production method according to claim 1, wherein dehydration is performed under a reduced pressure of 25 to 400 Torr.