JPH08333359A - Production of ester cyclic dimer - Google Patents

Abstract

PURPOSE: To obtain the subject highly optically pure cyclic dimer in high efficiency by depolymerizing a polymer or an oligomer of an α-hydroxycarboxylic acid in the presence of a depolymerization catalyst in a molten state in a specific reactor, taking out the depolymerized substance in a vapor phase outside the reaction system. CONSTITUTION: (A) A polymer or an oligomer of an α-hydroxycarboxlic acid is depolymerized in the presence of (B) a depolymerization catalyst in a method state in a reactor having a built-in sheetlike stirrer having >=200cm<2> , preferably >=400cm<2> evaporation area based on 11 of a reaction substance to form a cyclic dimer. The dimer is taken out in a vapor phase from the reaction system. Preferably the lower part of the reactor is packed with the reaction substance, a space is made at the upper part and a stirring element is alternately passed through the reaction substance at the lower part and upper space by revolution of a horizontally set driving shaft. The stirring element is preferably obtained by equipping a disc or a petal like form element with a hole, a groove, etc., and has function of sending the reaction substance by rotation movement of at least part of the stirring element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved process for producing a cyclic dimer which is a raw material for polymerizing polylactic acid, polyglycolic acid and other poly .alpha.-hydroxycarboxylic acids.

[0002]

2. Description of the Related Art Polymers that are biodegradable or that decompose in a natural environment have attracted attention from the viewpoint of environmental protection. In particular, polylactic acid, polyglycolic acid and the like are excellent in degradability and physical properties, and their early commercialization is desired. One of the conditions necessary for practical application and industrialization is that the raw material is supplied with high efficiency and low cost. From lactide and glycolide, which are cyclic dimers of lactic acid and glycolic acid, polylactic acid and polyglycolic acid can be obtained with high efficiency by ring-opening polymerization. Therefore, high efficiency of these cyclic (6-membered ring) dimers can be obtained. A manufacturing method is desired.

Cyclic dimers of α-hydroxycarboxylic acids such as lactic acid and glycolic acid are produced by heating their (crude) polymers or oligomers in the presence of a catalyst to depolymerize them. That is, rather than purifying and polymerizing lactic acid or glycolic acid, a low-purity raw material is once polymerized into an oligomer or polymer, and then depolymerized to obtain a high-purity 2
Polymerization of the monomer gives higher efficiency and higher molecular weight polymer, and this method is considered as a shortcut to industrialization.

As a method for producing an ester cyclic dimer by depolymerization of polylactic acid or polyglycolic acid, a method in which a reaction and separation of the formed dimer are carried out by using a thin film distiller is disclosed in Japanese Patent Publication No. HEI-7 / 7. No. -500091. In this publication, as a conventional technique, the method shown in European Patent Application Publication No. 264926 using a twin-screw mixing extruder is introduced, and if a thin film distiller is applied, it is possible to produce a ring 2 with high efficiency in a shorter time than that. It is said that it can manufacture a quantity.

However, a detailed examination of the technique disclosed in the above-mentioned publication discloses that the crude lactide obtained has an unsatisfactory low optical purity as shown in the examples. That is, in all of the examples, the L-form ratio of the obtained lactide was 90.8-92.5% (average 91.6%), and the meso-lactide (L / D mixture) as an impurity was averaged 7.6%. Similarly, it also contains D-lactide on average 0.8%. That is, the racemization proceeds considerably strongly in the depolymerization process.

[0006]

Needless to say, lactide or the like having a high optical purity is desirable. In order to obtain a homopolymer having excellent crystallinity and heat resistance, the optical purity of lactide or the like is preferably 98% (99% by weight). Even in the case of copolymerization, in order to stably obtain a product of constant quality, the raw material should have a high purity (eg 99% by weight or more).
It is desirable that Crude lactide having a low L-form ratio has a problem in that the efficiency and yield in the refining process are low and the cost is disadvantageous. An object of the present invention is to provide an improved new method capable of producing an ester cyclic dimer having high optical purity with high efficiency.

[0007]

The object of the present invention is to depolymerize an α-hydroxycarboxylic acid (eg lactic acid or glycolic acid) polymer or oligomer in the molten state in the presence of a depolymerization catalyst. In the method of producing a cyclic dimer and taking it out of the reaction system in a gas phase, the production of the dimer by depolymerization includes a planar stirrer having an evaporation area of 200 cm ² or more per 1 liter of a reactant. It is achieved by performing the reaction under reduced pressure in a reaction container.

In the present invention, the molecular weight of the raw material poly α-hydroxycarboxylic acid is not particularly limited. In the conventional method, it is necessary to use one having a low melt viscosity, and usually one having a molecular weight of about 500 to 3000 is used. In the examples of the above-mentioned publication, an oligomer having a polymerization degree of 10 to 20 (molecular weight of about 740 to 1300) is used. This is because a thin film distillation method is difficult to handle if it has a high viscosity. In the method of the present invention, the raw material polymer may be an oligomer having a molecular weight of about 500 to 3,000, and a higher molecular weight one, for example, one having a molecular weight of about 30,000 or more can be used, and the applicable range of the raw material is wide. This is because the thin film distillation method does not have a stirrer, but the present invention uses a reaction vessel having a stirrer.

A feature of the present invention is to use a reaction vessel (reactor) having a large-area evaporating area and a built-in planar stirrer. In order to provide the stirring device with a large evaporation surface, the planar stirring element having a large surface area may alternately pass through both the liquid of the reactant and the space for evaporation by the rotational movement of the drive shaft. . The device used in the present invention will be described below with reference to the drawings.

1 and 2 are explanatory views showing a concrete example of a reaction apparatus suitable for the present invention. FIG. 1 is a cross-sectional view of a reaction apparatus, in which a reaction vessel 1 is provided with disk-shaped stirring elements 4 and 5 which are rotated by two drive shafts 2 and 3. The lower half of the container 1 contains the reactant 6, and the upper half of the container is the space 7. Reference numeral 8 is a hole for supplying an inert gas or connecting to an exhaust (vacuum) system. Although not shown in the figure, the container 1 and the like are heated by a suitable heating means, for example, electric heat, steam, or other heat medium of gas or liquid. Due to the rotational movement of the drive shafts 2 and 3, the disk-shaped stirring elements 4 and 5 are rotated, and the reactant 6
And alternately pass through the space 7. Stirring elements 4 and 5
Is (1) acceleration of the reaction by stirring the reactant 6, (2)
The heat from the heated reaction vessel 1 is effectively taken into the reaction substance by stirring, and (3) the reaction substance is moved in the upper space 7 in a state of being attached in a film form on its surface to It acts to evaporate volatile components (such as lactide). By repeating the movement in the reaction substance 6 and in the upper space 7, the volatile components in the reaction substance 6 are evaporated and guided to an external recovery device having, for example, a rectification device or a condenser by an external vacuum system, and lactide. It is recovered as a cyclic dimer such as or glycolide. If the recovery device has a high-performance multi-stage distillation (rectification) device, a product of considerably high purity can be obtained, and if not, crude lactide or the like can be obtained, and further purified by a recrystallization method or the like in the purification step. Become a product.

FIG. 2 is a plan view of the device of FIG. Two drive shafts 2 and 3 are attached to the container 1, and the disk-shaped stirring elements 4 and 5 and the screw-shaped stirring elements and liquid feeding elements 9 and 10 are rotated. 11 is the inlet of the reactant,
12 is an exit. The screws 9 and 10 serve to stir the reactants and to send them from the inlet to the outlet. These may be omitted, but the inside of the reaction vessel 1 is depressurized, and in order to take out the reaction product from the outlet 12 by, for example, a pump, some sort of liquid feeding mechanism or pressurization that applies back pressure to the pump. A mechanism is needed. In the closed system in which the outlet 12 is closed, such a liquid feeding mechanism is unnecessary. That is, even if the outlet is closed, the cyclic dimer and the like produced by the reaction are taken out of the system by the vacuum device. Therefore, if the amount of the raw material commensurate with the amount taken out is supplied from the inlet, the reaction system will be in a steady state. The reaction proceeds in a stable manner.

On the other hand, when a part of the reaction material is taken out at an appropriate rate and supplied again to the inlet of the reaction apparatus, the reaction system becomes a circulation system, and the reaction is carried out more uniformly and steadily,
Wider range of applications is possible. In such a circulatory system,
There is also an advantage that depolymerization catalysts and additives are repeatedly used, and the consumption of them is small. In a closed system, impurities in the reactants accumulate in the reaction vessel, so long-term continuous operation cannot be performed.However, if the reaction residue is continuously or intermittently taken out from the outlet of the reaction vessel, long-term continuous operation is possible. Is possible. It is also possible to improve the fluidity, reactivity, stability, etc. by adding an appropriate solvent or diluent (eg polyethylene glycol), stabilizer (eg antioxidant) to the reaction system. Is advantageous.

The stirring device may be a single shaft, but as shown in FIGS. 1 and 2, a two-shaft or multi-shaft stirring device in which a plurality of stirring elements are arranged on two driving shafts so as to overlap or mesh with each other is a container. Has a self-cleaning function that constantly scrapes off the substances adhering to the inner surface of the
It is particularly preferable for the purpose of the present invention because it has a feature that the device is less contaminated by deposits and can be operated stably for a long period of time. The thin-film distillation apparatus does not have such a mechanical self-cleaning action and may cause a problem in long-term continuous operation. In the depolymerization step, a considerable amount of heat of evaporation is required because the produced cyclic dimer is evaporated and taken out of the system. The main sources of this heat are conduction and infrared radiation from the container 1 and heat generation by stirring the reactants. Therefore, in order to improve the efficiency of stirring and conduction, it is also preferable to appropriately provide fins and irregularities on the stirring element. Of course, by increasing the rotation speed of the stirrer, more heat can be supplied to the reactants, and the method of the present invention has a wider range of application.

One of the differences between the apparatus shown in FIGS. 1 and 2 and the cylindrical twin-screw extruder is that the volume of the reaction vessel can be made extremely large. Therefore, the reaction product 6 can be reacted at a relatively slow and mild condition, that is, at a low temperature, and a large-capacity apparatus suitable for industrial production can be obtained at a relatively low cost. The second difference is that
That is, the stirring element is planar. Therefore, the stirring element has a large surface area as compared with its weight, and the reaction device has a large evaporation area and high efficiency and low cost.

For the purposes of the present invention, the reaction (depolymerization)
Must be carried out at a temperature as low as possible within a certain short time. This is because racemization occurs earlier at higher temperatures.
Of course, the deterioration of the reaction material (oxidation, coloring, etc.) is more likely to occur at higher temperatures. For example, in the synthesis by depolymerization of polylactic acid, racemization occurs at 160 ° C or higher and 220 ° C.
The above becomes remarkable. Therefore, the reaction temperature is preferably 220 ° C or lower, particularly preferably 210 ° C or lower, and most preferably 200 ° C or lower. In the thin-film distillation method, the reaction time is extremely short (within 1 minute), so that the reaction temperature has to be set to a high temperature of 220 ° C. or higher, which leads to progress of racemization and deterioration of optical purity of the product. In the example of the above-mentioned publication, the temperature of the thin film distiller is as high as 260 ° C, and as a result, the L-body ratio of the product is about 92% by weight on average.
And low.

The reaction time need not be so short as long as the temperature is low to some extent. The average reaction time depends on the evaporation area, but it is 30 minutes or less at 220 ° C, especially 1
It is preferably 0 minutes or less, 2 hours or less at 210 ° C, particularly 1 hour or less, and 5 hours or less, particularly 3 hours or less at 200 ° C.

The larger the surface area of the stirrer, the greater the evaporation capacity, which is desirable. The evaporation area can be approximated by the sum of 1/2 of the surface area of the stirrer and the horizontal cross-sectional area in the middle of the reaction container when the lower half of the reaction container is filled with the reactant. The ratio between the evaporation area and the volume of the reactant (unit: liter) is hereinafter referred to as the effective evaporation area. For highly efficient reaction, an effective evaporation area of 200 cm ² / l or more is required.
cm ² / l or more is preferable, and 600 cm ² / l or more is most preferable. The planar stirrer, that is, the planar stirrer, the curved stirrer, and those with appropriate irregularities or deformations can obtain a larger evaporation area with a relatively simple structure as compared with the twin-screw extruder. For example, 2 cm for a flat disc-shaped stirrer
If they are arranged at intervals, the evaporation area can be 500 cm ² / l or more. If, for example, corrugated, grooved, spherical, fin-shaped or other unevenness is provided on the surface of a flat or curved element,
Further, the evaporation area can be increased to 1.5 times or more of the flat surface.

The shape of the stirrer or the element thereof is arbitrary, but for example, a disc, a petal shape, a multilobe shape, a screw shape, or those provided with appropriate holes, grooves, fins or irregularities are preferably used. The screw type has various applications such as a screw conveyor type as shown in FIG. 2 and a propeller of a ship or a fan blade of a fan, etc. It has a liquid function. FIG. 2 shows an example in which the two shafts rotate in the same direction, but in the case of reverse rotation, screws in opposite directions may be combined.

FIG. 3 is a system diagram showing an embodiment of the present invention. Although lactic acid will be described below as an example, the same applies to α-hydroxycarboxylic acids other than lactic acid. The lactic acid aqueous solution as a raw material is supplied from the tank 21 to the concentrating device 23 by the pump 22. Tanks 24 and 26 are for additives (antioxidants, catalysts, solvents, etc.), which are supplied by pumps 25 and 27 as needed. The concentrating device 23 evaporates the water content of the raw material and sends it out of the system, and 28 is the extracted water content. This concentration step is usually 100-1
It is carried out at 50 ° C. and normal pressure, but it may be carried out under reduced pressure.
Lactic acid that has been concentrated and has almost zero water content is supplied to the first polymerization reaction device 31 through a filter 30 by a pump 29 in a molten state. In the reactor 31, for example, 300
150 to 16 under slightly weak decompression of about 100 Torr
Lactic acid is dehydrated and condensed at 0 ° C to form an oligomer. A vacuum (exhaust) device 32 is composed of a condenser or a trap and a vacuum pump. What was polymerized in the reactor 31 is
It is sent to the second polymerization device 34 by the pump 33. The second reactor 34 is almost the same as the first reactor, but the degree of vacuum is slightly high at 1 to 100 Torr. Reference numeral 35 is a vacuum device.

Although FIG. 3 shows an example in which the polymerization is continuously carried out by two reactors connected in series, it goes without saying that three or more reaction vessels may be used in multiple stages and one reactor may be used. The intermittent operation may be performed in a batch system. In this polymerization step, an oligomer having a molecular weight of polylactic acid of about 500 to 3000 is often produced. This is because when the molecular weight is large, the melt viscosity is high and it becomes difficult to handle at low temperatures. In the polymerization step, a polymerization catalyst may be used, but an oligomer can be obtained without a catalyst. The presence of a catalyst may promote racemization, so it is preferable not to use a catalyst. Further, in order to prevent the molecular weight from becoming excessive in this polymerization step, a polymerization inhibitor or a terminating agent may be used. That is, a monocarboxylic acid or monoalcohol having a boiling point of 100 ° C, particularly 150 ° C or higher,
The degree of polymerization can be suppressed to 100 to 10 by adding, for example, 1 to 10 mol% of dicarboxylic acid, diol, hydroxide or carbonate of an alkali metal to lactic acid.

The oligomer obtained in the reaction device 34 is sent to the first depolymerization device 37 by the pump 36. As the depolymerization device 37, for example, a reaction container having a planar stirrer shown in FIGS. 1 and 2 is used, and a depolymerization catalyst in a tank 38 is supplied by a pump 39. In the depolymerization device 37, the orycomer or polymer of lactic acid reacts (depolymerizes) in the presence of a catalyst at a temperature of 180 to 220 ° C. and a vacuum degree of 10 to 100 Torr to form a cyclic dimer, which evaporates to the outside of the reaction system. After passing through the rectification tower 40 provided, it is condensed in a condenser 41 and recovered as a lactide 43. 42 is a vacuum (exhaust) device, and 44 is a high boiling point component, which is discarded or returned to a previous polymerization step or the like. The reaction material of the depolymerization device 37 is sent to the second depolymerization device 46 by the pump 45. The second depolymerization apparatus 46 is almost the same as the first depolymerization apparatus 37, and the degree of vacuum is set high, for example, 1 to 10 Torr.
47 is a rectification column, 48 is a condenser, 49 is a vacuum device,
50 is the recovered lactide and 51 is the high boiling point material.

Although FIG. 3 shows an example in which two depolymerization reaction vessels 37 and 46 are connected in series, the number of reaction vessels may be one, or three or more may be arranged in series. A part of the reaction substance in the reaction container 46 is taken out by the pump 52, and when the valve 53 is closed and the valve 55 is opened, it is returned to the reaction container 37 at the previous stage to form a circulation system. If the valve 55 is closed and the valve 53 is opened, the reaction residue 54
Is taken out. If the pump 52 is stopped, the reaction container 46
Is a closed system.

Liquid feed pump 2 for connecting each process and reaction device
Although 9, 33, 36, 45, and 52 may be continuous operation or intermittent operation, continuous operation is preferable in terms of steadiness. It is also desirable to adjust and control the liquid-sending rate of those pumps or the like so as to keep the amount of the reaction substance in each reaction container constant. In addition, a storage tank can be provided between the steps of concentrating the raw materials, polymerization, and depolymerization, if necessary.

The average residence time (reaction time) of the reactants in the reactors 37 and 46 may be a little longer when the reaction temperature is low as described above, but of course, a shorter residence time prevents racemization. It is also preferable in terms of production efficiency. Factors that govern the depolymerization rate are the type and amount of catalyst, temperature, stirring rate of reactants, heat transfer rate, vacuum degree and effective evaporation area. In the present invention, the stirring rate, the heat transfer rate and the effective evaporation area can be made sufficiently large, and therefore the reaction temperature can be made relatively low and the reaction rate can be made relatively large.
High quality products can be obtained with high efficiency. Polymerization and depolymerization are equilibrium reactions, and it is considered that the same catalyst works for both reactions. The catalyst is not particularly limited, and known ones or effective ones may be used, but metal tin, tin oxide, tin chloride, tin salts of organic acids such as tin octylate are preferably used, and the catalyst is For example, about 0.01 to 3%, especially about 0.1 to 1% is often used. The reactor shown in FIGS. 1 and 2 can also be preferably used for the concentration and polymerization of raw materials. In the apparatus of FIG. 3, the reaction is continued in a state where the pump 36 is stopped and the supply of the oligomer and the like is stopped at regular intervals (for example, 10 days), and most of the oligomer and the like in the reaction vessels 37 and 46 are lactide. After the conversion and distillation, the valve 55 is closed and the valve 53 is opened, the residue of the depolymerization reaction is taken out of the system, and a new catalyst or a fluidity improving agent (for example, polyethylene glycol) is replenished.

The method of the present invention can be applied to the recovery and reuse (recycling) of a cyclic dimer from a molded product such as polylactic acid or polyglycolic acid or scraps after use. That is, after removing the collected dust such as molded articles, it is crushed into fine pieces and melted by, for example, a screw extruder,
It may be supplied to the polymerization step or the depolymerization step. By adjusting the water content of the polymer pieces before melting, the molecular weight of the polymer after melting can be arbitrarily controlled, and the polymer can be made suitable for the reaction in those steps.

[0026]

EXAMPLES In the following examples,% and parts are weight ratios unless otherwise specified.

[Example 1] L having an optical purity of 99.5% or more
-About 300 liters of a 90% aqueous solution of lactic acid is supplied to a tank type reaction vessel having an anchor type stirrer and a capacity of 800 liters, heated and concentrated under atmospheric pressure at 135 ° C for 3 hours, and stored in a storage tank. These two tanks correspond to the concentrating device 23 in FIG. The concentrated lactic acid solution was supplied to a polymerization device in which two reaction devices as shown in FIGS. The reactor was equipped with 35 disc-type stirring elements with a diameter of 60 cm at 2 cm intervals on one side (70 sheets in total) and screw-type elements (feeding 5c).
m, 2 rotations) are arranged at two places on the inlet side and the outlet side, and correspond to 31 and 34 in FIG. The effective volume of the lower half of the reactor is about 190 l, and the effective evaporation area when the reactant is filled therein is about 600 cm ² / l. First
The reactor has a temperature of 150 ° C and a vacuum degree of 100 Torr, and the second reactor has a temperature of 155 ° C and a vacuum degree of 20Tor.
The rotation speeds of rr and the stirrer are both 15 rpm. The average molecular weight of the oligomer after polymerization was 2200 and was continuously supplied to the next depolymerization step.

The depolymerization device is a device in which two devices having the same biaxial planar stirring device as the above-mentioned polymerization device are connected in series and correspond to the reaction devices 37 and 46 in FIG. The first depolymerization reactor has a temperature of 200 ° C., a vacuum degree of 20 Torr,
The second depolymerization reactor has a temperature of 200 ° C and a vacuum degree of 10To.
The rotation speeds of rr and the stirrer are both 30 rpm. Second
A part of the reactant in the reactor is taken out by the pump 52 as in FIG. 3 and returned to the first reactor at a rate of 10 l / min. The speeds of the pumps 36 and 45 are adjusted so that the liquid levels of the reactants of the two depolymerization reaction devices are respectively 3 cm below the center of the stirring shaft. The catalyst used tin octylate as the reactant. The amount of the oligomer supplied to the depolymerization apparatus was 3.32 l / min on average, and the average residence time of the reaction substance inside the reaction vessel was about 2 hours. The conversion rate of lactide obtained from the two condensers to the raw material lactic acid was 93.1% of the theoretical value, and the L-form ratio was 98.5 (optical purity of 97.
It was 0)%. This is far superior to the L-form ratio of lactide of about 92% in the example of the above-mentioned publication. According to the knowledge of the present inventors, when the L-form ratio is 97.5% or more, a high-purity lactide having an L-form ratio of 99.5% or more can be easily obtained in the purification step by the recrystallization method. However, if the L-form ratio is 95% or less, it is extremely difficult to increase the L-form ratio by a recrystallization method using a solvent or the like.

[Embodiment 2] An experiment similar to that of Embodiment 1 is carried out.
The depolymerization apparatus having different surface areas of the stirring elements was used. The stirrer is disk-shaped and has grooves with a semi-circular cross section with a width of 1.6 mm and a depth of 0.8 mm on the surface of the stirrer with concentric intervals of 2 mm
, The surface area is 1.46 times that of a flat disc, and further flat fins with a width of 6 mm, a length of 10 mm and a thickness of 3 mm are radially welded to the tip of the disc at intervals of 60 ° to remove the oligomer on the inner surface of the reaction vessel. By scraping (clearance 5 mm), heat transfer and stirring efficiency were enhanced. The effective evaporation area of the reactor was about 880 cm ² / l, and the rotation speed was 40.
rpm. The temperature and pressure of the reaction vessel are the same as in Example 1. As a result, the oligomer supply rate to the depolymerization apparatus was 4.35 l / min, and the depolymerization reaction rate was about 1.31 times that of Example 1. The conversion rate to lactide was 93.3% and the L-form ratio was 98.5%, which were almost the same as in Example 1. The molecular weight of the oligomer supplied from the polymerization step to the depolymerization step was 1960, which decreased slightly due to the increase in the supply amount, but there is no particular problem.

[0030]

INDUSTRIAL APPLICABILITY According to the present invention, a cyclic dimer having a high optical purity can be easily produced with high efficiency from an oligomer or polymer of poly α-hydroxycarboxylic acid. Further, the reactor used in the present invention has the following major features: high efficiency, relatively simple structure, easy size increase, low manufacturing cost, wide range of application of raw materials, and stable operation. For this reason, the cost of the produced lactide, glycolide, etc. was further reduced, and the possibility of practical application of the biodegradable polymer was further enhanced.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of a reaction device incorporating a biaxial stirring device suitable for the present invention.

FIG. 2 is a plan view of the apparatus shown in FIG.

FIG. 3 is a system diagram of an apparatus for continuously producing an ester cyclic dimer showing an example of the present invention.

[Explanation of symbols]

1 reaction vessel 2 drive shaft
3 Drive shaft 4 Stirring element 5 Stirring element
6 Reactant 7 Space 8 Air supply / exhaust hole
9 screw type element 10 screw type element 11 reactant inlet
12 Reactant outlet 21 Raw material (lactic acid etc.) tank 22 Metering pump
23 Concentrator 24 Additive Tank (1) 25 Metering Pump
26 additive tank (2) 27 weighing feeder 28 steam
29 Liquid Delivery Pump 30 Filter 31 Polymerization Reaction Device (1)
32 exhaust device 33 liquid feed pump 34 polymerization reaction device (2)
35 Exhaust Device 36 Liquid Delivery Pump 37 Depolymerization Device (1)
38 catalyst tank 39 metering pump 40 rectification tower
41 condenser 42 vacuum pump 43 products (lactide, etc.)
44 high boiling point substance 45 liquid feed pump 46 depolymerization device (2)
47 Fractionation tower 48 Condenser 49 Vacuum pump
50 products (lactide, etc.) 51 high boiling substances 52 liquid feed pump
53 valves 54 residues 55 valves
56 filters

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiichi Koseki 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto City Stock Company Shimadzu Sanjo Factory

Claims (5)

[Claims] 1. A method of depolymerizing an α-hydroxycarboxylic acid polymer or oligomer in a molten state in the presence of a depolymerization catalyst to form a cyclic dimer, which is taken out of the reaction system in a gas phase. A method for producing an ester cyclic dimer, characterized in that the formation of the dimer by polymerization is carried out in a reaction vessel containing a planar stirrer having an evaporation area of 200 cm ² or more per 1 liter of a reactant. 2. The method according to claim 1, wherein the evaporation area is 400 cm ² / liter or more and the reaction temperature is 220 ° C. or less. 3. The reaction container is filled below with a reaction substance to form a space above, and the stirring element is alternately passed through the reaction substance below and the space above by the rotation of a horizontally provided drive shaft. The method according to 1-2. 4. The stirring element is at least one selected from the group of "disc, petal, leaflet, screw, and those provided with holes, grooves, fins and / or various irregularities".
A seed, and at least a part of which has a function of sending a reactant by rotational movement.
The described method. 5. The method according to claim 1, wherein the plurality of stirring elements are provided on the two drive shafts so as to overlap with each other or mesh with each other, and rotate in the same direction or opposite directions to each other.