JP3443265B2 - Method for producing biodegradable polyester - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biodegradable polyester, and more particularly to a method for producing a biodegradable polyester having a small amount of impurities resulting from a catalyst or a catalyst diluent.

[0002]

2. Description of the Related Art Polylactic acid has been used in the medical field because it is a polymer that is decomposed in vivo and has excellent mechanical properties. However, it is decomposed by microorganisms even in the natural environment. From the viewpoint of environmental protection, it is expected to expand to various industrial and consumer applications.

As a method for producing a biodegradable polyester, for example, a cyclic ester compound such as lactide or glycolide is used as a raw material monomer, heated to a predetermined temperature condition, and polylactic acid is added in the presence of a catalyst such as stannous octylate. A common method is to produce polyglycolic acid or the like. However, biodegradable polyester is required not to pollute the environment after decomposition, especially when used in bioabsorbable materials for medical purposes, the purity of the polymer is important, and the amount of catalyst added is as small as possible. Is desirable.

However, no commercially available catalyst injecting device is capable of continuously injecting a very small amount (for example, about 100 ppm) of the catalyst, and it is difficult to continuously supply an extremely small amount of the catalyst to the reactor. there were.

Further, when the amount of the catalyst is very small, if the catalyst is directly injected into the polymerization tank without being diluted, the catalyst is likely to adhere to the agitator or the wall surface of the polymerization tank or be deposited, and the catalyst is uniformly dispersed. Therefore, it was not possible to carry out a stable polymerization reaction over the entire polymerization tank.

Therefore, it is possible to inject the catalyst into the raw material monomer feed line for supplying the raw material monomer to the polymerization reaction tank, but when the polymerization is started in the raw material monomer feed line, clogging easily occurs at the entrance to the polymerization tank. .

Therefore, in the conventional production method, it was indispensable to use various catalyst diluents such as toluene. However, the use of a catalytic diluent as an impurity is not desirable due to the properties required of the biodegradable polymer as described above.

[0008]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a biodegradable polyester having a small amount of impurities resulting from a catalyst or a catalyst diluent. Is.

[0009]

Means for Solving the Problems The present invention, which has solved the above problems, is a method for producing a biodegradable polyester in which a trace amount of a catalyst is added to a raw material for polymerization to carry out polymerization. The gist is to dilute the catalyst with a molten raw material for polymerization heated to a temperature lower than the polymerization initiation temperature and add it to the reaction system. INDUSTRIAL APPLICABILITY The present invention can be suitably used in a production method in which the raw material for polymerization is lactide and the biodegradable polyester is polylactic acid.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have taken up polylactic acid as a biodegradable polyester as a representative, and have conducted extensive studies on a method of adding a catalyst in the production process thereof, and have obtained the following findings. That is, the present invention has been accomplished by finding out that ring-opening polymerization reaction does not occur even if molten lactide is at a temperature near the melting point (for example, 100 ° C.). Therefore, in the present invention, a catalyst may be added to the raw material monomer to dilute it at a temperature equal to or higher than the melting point and lower than the substantial polymerization initiation temperature.

Incidentally, lactide has optical isomers, and its melting point is 97 in the case of D-lactide and L-lactide.
C., 125.5 ° C. in the case of D, L-mesolactide
Is. In the case of an oligomer, the melting point tends to increase as the molecular weight increases. As described above, the melting point of the raw material for polymerization varies depending on the type of lactide used, but in the present invention, a raw material for polymerization mainly containing lactide may be used, and heating may be performed according to the melting point. It may be.

The polymerization initiation temperature also changes depending on the type and amount of polymerization raw materials and catalyst. For example, JP-A-5-9
No. 3050 discloses a method for producing polylactic acid, which comprises adding a monomer mixture of 1000 ppm or more and then adding 1
A method of polymerizing in a temperature range of 50 to 250 ° C. is shown. When the polymerization reaction proceeds at 150 ° C. or higher as described above, the catalyst may be diluted by heating and melting the raw material for polymerization in the temperature range of the melting point or higher and lower than 150 ° C.

The present invention is not limited by the kind of the catalyst, and a general catalyst may be used as a catalyst for promoting ring-opening polymerization. For example, stannous chloride, stannous bromide,
Stannous iodide, stannous sulfate, stannic oxide, tin octylate, tetraphenyl tin, titanium tetrachloride, ethyl titanate, butyl titanate, propyl titanate, glycol titanate, zinc chloride, zinc oxide, Zinc acetate, antimony trioxide, antimony trifluoride, antimony acetate, lead oxide, aluminum oxide, iron oxide, manganese carbonate, manganese acetate and the like can be used.

The present invention is not limited by the amount of the catalyst, but is preferably as small as possible from the viewpoint of product quality, and it can be applied at 1000 ppm or less or 100 ppm or less. Further, in the present invention, it is not necessary to have a desired concentration in the catalyst diluting tank. For example, when the polymerization reaction is to be carried out at a catalyst concentration of 100 ppm, the catalyst is first diluted to 1000 ppm with the molten raw material for polymerization. ,
Then, when it is injected into the feed line for polymerization raw material, it can be diluted to 100 ppm by supplying it so that the amount of the diluted catalyst becomes 1/10 of the raw material for polymerization.

In the present invention, the diluted catalyst may be directly charged into the polymerization tank, but when the catalyst is injected into the raw material monomer feed line, the catalyst is first mixed and dispersed in the catalyst diluting step, and then the raw material monomer feed line. Since the catalyst is mixed and dispersed even when it is injected into the reactor, it is desirable for ensuring the dispersion of the catalyst and performing a uniform and stable polymerization reaction.

FIG. 1 is an explanatory view showing a representative example of the catalyst supply method of the present invention. The raw material monomer for polymerization is quantitatively sent to the raw material monomer feed line L1 by the pump 1 and sent to the polymerization reactor. The raw material monomer for catalyst dilution is supplied from the raw material monomer feed line L1 to the diluted monomer line L2.
Is supplied to the catalyst dilution tank 6 after being measured by the flow meter 2. The supply of the diluting raw material monomer is stopped by closing the on / off valve 3 when the amount of the monomer to be diluted into the catalyst diluting tank 6 reaches a predetermined amount. A predetermined amount of the catalyst is injected into the catalyst dilution tank 6 from the catalyst metering injection device 4 (batch measurement, batch injection) arranged in the catalyst dilution tank 6.

The supply of the diluting raw material monomer is restarted by opening the on / off valve 3. At the same time or with a delay of several seconds, the measured catalyst is put into the catalyst diluting tank 6. These operations are repeated at regular intervals according to the setting of the timer 5, and the liquid amount in the diluting tank 6 is maintained within a predetermined range by monitoring the liquid level gauge 7.

A stirring device is incorporated in the diluting tank 6 to uniformly disperse the catalyst. A predetermined amount of the diluted catalyst is measured by the control pump 8 according to the dilution rate, and the diluted catalyst is continuously or intermittently injected into the raw material monomer supply line L1. Further, if the mixing nozzle 9 is installed in the raw material monomer feed line L1 after the catalyst is injected and mixing is performed, the catalyst can be more uniformly dispersed. Automatic control is possible by controlling the ratio between the pump 1 and the control pump 8 as shown in the figure (as indicated by the chain line).

It is desirable that the inside of the diluting tank is completely shielded from the outside air by N ₂ gas. A temperature adjusting means such as a jacket is provided on the outer surface of the diluting tank so that the temperature in the diluting tank can be controlled by adjusting the temperature of the raw material monomer. The temperature is controlled to be higher than the melting point and lower than the temperature at which the polymerization reaction does not start. The capacity of the diluting tank 6 may be appropriately determined according to the catalyst dilution rate, the cycle time, etc., but it is desirable to determine it based on the range in which the accuracy of the catalyst metering and injecting device 4 is good.

According to the method of the present invention, the amount of catalyst to be charged into the diluting tank is increased by collecting the amount of catalyst to be charged within a predetermined cycle time. Can also reduce the error during weighing. Also, it is extremely difficult to control the injection amount of a very small amount of catalyst with a control pump, but if the amount of injection is increased by diluting in this way, even a very small amount of catalyst can be injected stably. It will be possible.

In the above system, the concentration of the catalyst injected by the control pump 8 temporarily fluctuates immediately after supplying the diluting monomer or immediately after introducing the catalyst. However, since there is a sufficient residence time in the post-polymerization apparatus, Instantaneous fluctuations in catalyst concentration are not a problem.

However, if there is a case where the residence time in the polymerization apparatus is very short in the subsequent step and even an instantaneous fluctuation of the catalyst concentration is not desirable, two dilution tanks are installed side by side or two dilution systems are installed. The diluting tanks can be switched and used by installing them as a set, and the switching operation in this case can be automatically operated by using the liquid level signal of the diluting tanks.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any modification of the present invention can be made in view of the gist of the preceding and the following. Are included in the technical scope of.

[0024]

FIG. 2 is a schematic explanatory view showing a typical example of the manufacturing process of the present invention. In FIG. 2, 1 is a pump and 2, 1
2, 22 are flow meters, 3, 10, 13, 20 are on / off valves, 4, 14 are catalyst metering injection devices, 6, 16 are catalyst dilution tanks, 7 and 17 are liquid level gauges, 8 is a control pump, 9 is The mixing nozzle 21 indicates a flow control valve, respectively.

L-lactide (melting point 97 ° C.) was used as the raw material, and tin octylate was used as the catalyst. Catalyst dilution tank 6,1
The volume of 6 was 4 liters, and the temperature in the tank and the feed line was maintained at 110 ° C.

First, the flow rate of the flow meter 22 is set to 19 kg / h,
The flow rate of the control pump 8 was set to 1 kg / h, and the pump 1 started feeding the raw material. On-off valve 3
Was opened, the raw material monomer was supplied to the catalyst dilution tank 6, and when the supply amount reached 1999.8 g, the on / off valve 3 was closed and the supply of the raw material was stopped. At that time, 0.2 g of the catalyst (100 ppm in the catalyst diluting tank) in the catalyst metering device 4
Equivalent to) was injected. When the catalyst was ready, the on / off valve 10 was opened, the mixture was passed through the mixing nozzle 9, mixed with the raw material monomer, and supplied to the downstream polymerization reactor.
The catalyst concentration in the polymerization reactor was about 5 ppm.

Further, at the same time when the on / off valve 10 is opened, the on / off valve 13 is opened to supply the raw material monomer to the catalyst diluting tank 16, and when the supply amount reaches 1999.8 g, the on / off valve 13 is closed and the catalyst is 0.2 g of the catalyst was injected by the metering injection device 14 to set it in a standby state.

At the time when the remaining amount display of the liquid level gauge 7 becomes 0, the on / off valve 10 is closed, and at the same time, the on / off valve 3 is opened to supply the raw material monomer to the catalyst dilution tank 6, and the on / off valve 20 is opened. The catalyst supply from the dilution tank 16 was started. When the supply amount to the catalyst diluting tank 6 reached 1999.8g, the on / off valve 3 was closed, and 0.2g of the catalyst was injected by the catalyst metering injection device 4 to put it in a standby state. When the remaining amount display of the liquid level gauge 17 became 0, the on / off valve 20 was closed, the on / off valves 10 and 13 were opened, and the supply of the catalyst in the catalyst dilution tank 6 was started. In this way, the catalyst diluting tanks 6 and 16 were sequentially switched, and the catalyst was continuously supplied to the downstream polymerization reactor without being cut off. As a result, the polymerization reaction could be stably performed in the downstream polymerization reactor, and the raw material monomer feed line was not clogged.

[0029]

EFFECTS OF THE INVENTION Since the present invention is constituted as described above, it is possible to provide a method for producing a biodegradable polyester in which the amount of impurities caused by a catalyst or a catalyst diluent is small.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a typical example of a catalyst supply system of the present invention.

FIG. 2 is a schematic explanatory view showing another typical example of the catalyst supply system of the present invention.

[Explanation of symbols]

1 pump 2 Flow meter 3 on-off valve 4 Catalyst metering device 5 timer 6 catalyst dilution tank 7 Level gauge 8 control pump 9 mixing nozzles 10 on-off valve 12 Flowmeter 13 on-off valve 14 Catalyst metering device 16 Catalyst dilution tank 17 Level gauge 20 on-off valve 21 Flow control valve 22 Flow meter

─────────────────────────────────────────────────── ─── Continuation of front page (72) Kazuhisa Fujisawa 1-5-5 Takatsukadai, Nishi-ku, Kobe City Kobe Steel Research Institute, Kobe Steel Co., Ltd. (72) Koji Yamamoto 1-5, Takatsukadai, Nishi-ku, Kobe No. 5 inside Kobe Steel Research Institute, Kobe Steel, Ltd. (56) Reference JP-A-8-3292 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08G 63/00- 63/91

Claims (4)

(57) [Claims] 1. Continuous addition of a trace amount of catalyst to a raw material for polymerization
In the method for producing a biodegradable polyester, the catalyst is diluted with a molten raw material for polymerization which is heated to a temperature equal to or higher than the melting point and lower than the substantial polymerization initiation temperature, and continuously added to the reaction system.
A method for producing a biodegradable polyester , which comprises adding continuously or intermittently . 2. The production method according to claim 1, wherein the raw material for polymerization is lactide, and the biodegradable polyester is polylactic acid. 3. Biodegradation by adding a trace amount of catalyst to the monomer
When performing the polymerization of water-soluble polyester, the temperature above the melting point
Monomer in the molten state heated below the typical polymerization initiation temperature
Catalyst supply for diluting the catalyst by the method and adding it to the reaction system
A system for feeding a monomer for a polymerization raw material to a polymerization reactor.
The monomer for the polymerization raw material is fixed on the nomer feed line and the feed monomer feed line.
A pump for feeding a fixed amount of liquid, and a raw material monomer for diluting the catalyst from the raw material monomer feed line.
Dilution monomer line into which the mer is introduced , and raw material monomer for catalyst dilution from the dilution monomer line
Was supplied to uniformly disperse the raw material monomer and the catalyst.
For the catalyst dilution tank and the amount of raw material monomer input to the catalyst dilution tank for catalyst dilution
On / off to suspend the feeding when the specified amount is reached
A valve and a catalyst metering device for injecting the catalyst into the catalyst dilution tank.
And the catalyst diluted with the raw material monomer in the catalyst dilution tank
To feed the raw material monomer feed line.
Catalyst supply system characterized by having a roll pump
Mu. 4. The diluted monomer line and the catalyst diluent.
From the tank, the on / off valve, and the catalyst metering device
It consists of two sets of configured dilution systems.
The catalyst supply system according to claim 3, wherein