JPH1060101A - Continuous production of biodegradable polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for preparing a biodegradable polyester which can remove the heat generated in ring-opening polymn. to regulate the temp. in the reaction system, can react a high-viscosity polymer and can stably prepare a high-mol.wt. biodegradable polyester free from coloring. SOLUTION: At least one dimer cyclic ester of a hydroxycarboxylic acid and/or at least one lactone are continuously fed from one end of a tubular reactor provided with a jacket to conduct ring-opening polymn., while the resultant polymer is withdrawn from the other end of the reactor. A heat transfer medium for the regulation of the temp. is passed through the jacket. Pref., initial polynm. is carried out in an agitation tank type reactor provided with an agitating element, and the resultant polymn. mixture is introduced into the tubular reactor to further conduct the polymn. A multi-tubular heat exchanger is pref. as the tubular reactor. This process is suitable for the preparation of a polylactic acid by ring-opening polymn. of a lactide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for continuously producing a biodegradable polyester, and more particularly, to a method for producing a ring-opening polymerization reaction system having excellent temperature control.

[0002]

2. Description of the Related Art In recent years, polyethylene, polypropylene,
A huge amount of plastic products such as polystyrene, polyethylene terephthalate, and vinyl chloride are used,
These waste treatments have been highlighted as one of the environmental problems. That is, the current waste treatment is incineration or burial treatment. For example, incineration of polyethylene or the like results in high burned calories, which damages the incinerator and shortens its life. Further, when polyvinyl chloride or the like is incinerated, harmful gases are generated. On the other hand, land is limited for burying plastic products. Further, when disposed in a natural environment, the chemical stability thereof is extremely high, and there is almost no biological decomposition by microorganisms and the substance remains almost semi-permanently. For this reason, the landscape is damaged, and in addition, there is a problem that the living environment of marine life is polluted.

In order to solve these problems, development of a polymer which is biodegradable or decomposes in a natural environment has been developed for conventional plastics. In particular, aliphatic polyesters such as polyglycolic acid, polylactic acid, and poly-ε-caprolactone are excellent in melt moldability and physical properties of molded articles, and early commercialization thereof is desired. Among them, polylactic acid and lactic acid-based polymers having lactic acid units as main constituent units are excellent in decomposability, physical properties and melt moldability, and are expected to reduce the cost of raw materials in the future, and have been put to practical use in various fields. Most expected.

There are two conventional methods for synthesizing these aliphatic polyesters. That is, a method of directly dehydrating and condensing the corresponding hydroxycarboxylic acid monomer, and a method of ring-opening polymerization of the corresponding dimeric cyclic ester of hydroxycarboxylic acid or the corresponding lactone. According to the ring-opening polymerization method, there is an advantage that a polymer having a high molecular weight can be obtained, and it is suitable for obtaining a block copolymer.

However, ring-opening polymerization is an exothermic reaction, and it is difficult to control the temperature of the reaction system. Further, as the polymerization proceeds, the viscosity of the reaction system increases and stirring becomes difficult. Temperature control was difficult. An increase in temperature leads to a decrease in the molecular weight of the obtained polymer, coloring of the polymer, and the like.

For example, Japanese Unexamined Patent Publication No. Hei 3-502115,
JP-A-7-53684, JP-A-7-126358
Japanese Patent Application Laid-Open Publication No. H11-216, describes that a twin-screw extruder is used to react a high-viscosity polymer in the production of polyester by ring-opening polymerization. However, in the methods described in these publications, since the stirring is carried out vigorously, there is a considerable rise in temperature due to shear heat generation, and it has been difficult to control the temperature.

[0007] Also, Japanese Patent Application Laid-Open No. Hei 7-26001 discloses that
It is described that ring-opening polymerization is performed using a static mixer to uniformly mix a high-viscosity polymer. However, in the method described in the same publication, the high-viscosity polymer is passed through a reactor equipped with a static mixer,
The pressure was increased by the static mixer, and the temperature increased due to the heat generated by shearing, making it difficult to control the temperature.
Further, there is a problem that the static mixer is expensive as equipment.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to continuously produce biodegradable polyester by a ring-opening polymerization reaction. Is to provide a production method capable of controlling the temperature of the reaction system by removing heat, reacting a high-viscosity polymer, and stably obtaining a high-molecular-weight polymer without coloring.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the temperature of a polymerization reaction system can be controlled by using a tubular reactor having a jacket as a polymerization reaction apparatus. We have found that we can achieve this and have completed the present invention.

That is, the continuous production method of the biodegradable polyester of the present invention is characterized in that the biodegradable polyester is obtained by ring-opening polymerization using at least one kind of dimeric cyclic ester of hydroxycarboxylic acid and / or at least one kind of lactone as a main raw material. In the method for producing polyester, a tubular reactor having a jacket is used as a reactor, a heat transfer medium for temperature control is passed through the jacket, and the polymer is continuously fed from one end of the tubular reactor. And a polymerization reaction is carried out, and a polymer is taken out from the other end. Hereinafter, the present invention will be described in detail.

In the present invention, a tubular reactor having an outer jacket is used as a polymerization reactor, and a heat transfer medium for controlling temperature is passed through the outer jacket. The heat transfer medium may be any as long as it can remove the heat generated from the reactants flowing in the tube, and examples thereof include dibenzyltoluene, triphenyl hydroxide, paraffinic mineral oil, alkylnaphthalene, alkylbenzene, and diphenyldiphenylether. be able to.

The tube of the tube type reactor may have any shape such as a straight tube, a U-shaped curved tube, and a coil shape. The polymer is continuously supplied from one end of the tube, and polymerized from the other end. What is necessary is just to be able to take out the thing.

The tubular reactor may be constituted by a single tube, but may be constituted by a plurality of tubes arranged in parallel. When a large amount of the polymer is continuously supplied, it is preferable to use a tubular reactor having the latter configuration. That is, when a large amount of a polymer is continuously supplied to a tubular reactor constituted by one tube, the pressure increases,
This is because the flowability of the high-viscosity reactant deteriorates, and when the pipe is thickened to reduce the pressure, the heat transfer efficiency deteriorates, and it becomes difficult to remove the reaction heat.

In the present invention, a double-tube heat exchanger or a multi-tube heat exchanger can be used as the tube reactor.

The double-pipe heat exchanger comprises an inner pipe and an outer pipe, and allows a reactant to flow through the inner pipe and a heat transfer medium to flow through the outer pipe. The reactants in the inner tube and the heat transfer medium in the outer tube may be co-current, but are generally circulated in countercurrent. Also, to increase the heat transfer area outside the inner tube,
It is also preferable to use a finned tube having fins formed on the outer peripheral surface of the inner tube as the inner tube. The fin includes a vertical fin and a spiral fin. In the present invention, the double tube heat exchanger is preferably used when the flow rate of the polymer to be treated is small.

The multi-tube heat exchanger is of a so-called shell-and-tube type in which a tube bundle composed of a plurality of tubes arranged in parallel is usually housed in a cylindrical body, and a reactant is passed through the tubes. The heat transfer medium is passed through the gap between the body and the tube bundle.
The multi-tube heat exchanger includes a fixed tube plate type, a U-tube type, a floating head type and the like, and any of them can be used. The heat transfer area can be changed depending on the number, diameter, length, and the like of the tubes. The multi-tube heat exchanger can process a large amount of material to be polymerized by increasing the number of tubes, and has excellent heat removal (temperature control) performance by increasing the heat transfer area. Most preferable because it is small and inexpensive. The length, diameter, and number of tubes of the multitubular heat exchanger are not limited, but are, for example, lengths 1 to 10
m, diameter 0.5 to 10 inches, number 2 to 100.

These tubular reactors may be installed in any of a horizontal state, a vertical state, and an oblique state.

As described above, in the present invention, since a tubular reactor having an outer jacket is used as the reactor, the flow of the reactant is close to the flow of the piston, and the reactor is suitable as a reactor for a high-viscosity reactant. Further, since a heat transfer medium for temperature control is circulated through the jacket, the heat removal performance of the ring-opening polymerization heat of the reactant is excellent, and the temperature can be controlled.

In the present invention, a dimeric cyclic ester of hydroxycarboxylic acid and / or lactone is used as a main raw material of the biodegradable polyester.

Examples of the dimeric cyclic ester of hydroxycarboxylic acid include, for example, glycolide which is a dimeric cyclic ester of glycolic acid, lactide which is a dimeric cyclic ester of lactic acid, other 2-hydroxybutyric acid, 2-hydroxyisobutyric acid Dimeric cyclic esters such as butyric acid, 2-hydroxyvaleric acid, 2-hydroxyisovaleric acid and 2-hydroxy-2-ethylbutyric acid can be exemplified. Of these, those having an asymmetric carbon may be any of the D-form, L-form, meso-form, and mixtures thereof. For example, in the case of lactide, any lactide of L-lactide, D-lactide, meso-lactide, or a mixture thereof may be used.

Examples of the lactone include aliphatic lactones such as ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and δ-valerolactone. .

A homopolymer can be obtained by ring-opening polymerization using only one of these dimeric cyclic esters of hydroxycarboxylic acid or lactone. Further, depending on the use of the polymer, a copolymer can be obtained by ring-opening polymerization using two or more of these dimeric cyclic esters of hydroxycarboxylic acid and lactone. In this case, the copolymerization ratio of each monomer can be appropriately selected according to the use and physical properties of the polymer.

In the present invention, in addition to the dimeric cyclic ester or lactone of the hydroxycarboxylic acid, other components copolymerizable therewith, that is, a dicarboxylic acid having two or more ester bond-forming functional groups. Acids, polyhydric alcohols and the like can also be used.

Examples of such a dicarboxylic acid include succinic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid.

Examples of the polyhydric alcohol include aromatic polyhydric alcohols such as those obtained by adding ethylene oxide to bisphenol, ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neomethyl Examples include aliphatic polyhydric alcohols such as pentyl glycol and ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol.

These other copolymerizable components can be used alone or in combination of two or more. The copolymer component is also preferably one having biodegradability.

Further, in the present invention, copolymerization with an aliphatic polyester can be carried out. Here, the aliphatic polyesters include (1) glycolic acid, lactic acid, hydroxycarboxylic acid such as hydroxybutyl carboxylic acid, (2) glycolide, lactide, ε-caprolactone glycolide, ε-caprolactone, β-propio Lactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, aliphatic lactones such as δ-valerolactone, (3) aliphatic glycols such as ethylene glycol, propylene glycol, butanediol, hexanediol, etc. 4) oligomers of polyalkylene ethers such as diethylene glycol, triethylene glycol, ethylene / propylene glycol, dihydroxydiethylbutane, etc., polyethylene glycol,
Polypropylene glycol, polyalkylene glycol such as polybutylene ether, (5) polypropylene carbonate, polyalkylene carbonate glycol such as polybutylene carbonate, and oligomers thereof,
(6) succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as decanedicarboxylic acid, aliphatic polyesters derived from the like,
The aliphatic polyester may be a homopolymer or a copolymer.

Examples of the aliphatic polyesters include block copolymers of the above aliphatic polyesters with other components, for example, aromatic polyesters, polyethers, polycarbonates, polyamides, polyureas, polyurethanes, polyorganosiloxanes, and the like. It may be a random copolymer. Alternatively, a mixture of the aliphatic polyester and the other components may be used.

In the present invention, a polymerization catalyst can be used for the polymerization reaction. Although the polymerization catalyst is not particularly limited, it is generally a group IA, a group IIIA, a group IVA,
A catalyst comprising a metal or a metal compound selected from the group consisting of Group IIB, Group IVB and Group VA can be used.

The compounds belonging to Group IA include, for example, hydroxides of alkali metals (eg, sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.) and salts of alkali metals and weak acids (eg, sodium lactate, sodium acetate). , Sodium carbonate, sodium octylate, sodium stearate, potassium lactate, potassium acetate, potassium carbonate, potassium octylate, etc., and alkoxides of alkali metals (eg, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, etc.) )
And the like.

As a member belonging to the group IIIA, for example,
Examples thereof include aluminum ethoxide, aluminum isopropoxide, aluminum oxide, and aluminum chloride.

Examples of those belonging to the IVA group include organotin-based catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate, α-tin). Tin naphthoate, β-tin tin naphthoate, tin octylate, etc.)
In addition, tin powder, tin oxide and the like can be mentioned.

Examples of those belonging to Group IIB include zinc dust, zinc halide, zinc oxide, and organic zinc compounds.

The compounds belonging to the group IVB include, for example, titanium compounds such as tetrapropyl titanate and zirconium compounds such as zirconium isopropoxide.

The compounds belonging to the VA group include, for example, antimony compounds such as antimony trioxide and bismuth oxide.
And bismuth compounds such as (III).

Of these, a catalyst comprising tin or a tin compound is particularly preferred from the viewpoint of activity.

The amount of these catalysts used is about 0.0001 to 5% by weight based on the dimer cyclic ester and / or lactone of hydroxycarboxylic acid as the main raw material.

Further, the polymerization reaction may be carried out using a suitable organic solvent. Suitable organic solvents include toluene,
Examples thereof include xylene, chlorobenzene, acetophenone, benzophenone, dibutylbenzene, and anisole. By using an organic solvent, the viscosity of the reaction system can be reduced.

In the present invention, from the beginning of the polymerization reaction,
A tubular reactor provided with a jacket may be used as the reactor. That is, the polymerization reaction may be carried out by continuously supplying the dimeric cyclic ester of hydroxycarboxylic acid and / or the lactone monomer directly to the tubular reactor.

However, in a more preferred embodiment,
The initial polymerization reaction is performed in a stirred tank reactor having a stirring blade, and the obtained polymerization reaction mixture is continuously introduced into a tubular reactor to further perform the polymerization reaction. That is, at the beginning of the polymerization reaction, there is not much increase in viscosity,
Even when the reaction is carried out by stirring in a stirred tank reactor, the temperature can be controlled with little heat generation due to shearing due to stirring. Then, the polymerization reaction product is introduced into the tubular reactor before the viscosity increases, and the latter stage of the polymerization reaction is performed. In a tubular reactor, the flow of the polymerization reactant is close to the piston flow and there is no shear heating. Further, since a heat transfer medium for temperature control is circulated through the jacket, it is possible to remove the heat of ring-opening polymerization of the reactant and control the temperature.

The initial polymerization reaction is generally carried out under an inert gas stream such as nitrogen gas or argon gas at a melting temperature of the raw material monomer of 2 to 2.
It can be performed at a temperature of 50 ° C, preferably 150 to 200 ° C. For example, in the case of ring-opening polymerization of lactide, 17
The temperature is about 0 to 190 ° C. Although the time of the initial polymerization reaction depends on the raw material monomers, the time is such that the viscosity does not increase so much and it can be taken out from the stirred tank reactor sufficiently.
Generally, the viscosity of the reaction system is between 1000 poise and less as the melt viscosity at the polymerization temperature. Alternatively, the conversion of the raw material monomer is about 20 to 60%.

Subsequently, the polymerization reaction mixture obtained in the initial polymerization reaction is continuously introduced into a tubular reactor to perform a late polymerization reaction. The late polymerization reaction is carried out under an inert gas stream or under reduced pressure.
Polymer melting temperature to 250 ° C, preferably 160 to 2
It can be performed at a temperature of 10 ° C. For example, in the case of polylactic acid, the temperature is about 180 to 210 ° C. In general, the latter polymerization reaction is preferably performed until the conversion of the raw material monomer becomes 90% or more.

In the present invention, it is preferable to add a catalyst deactivator at a later stage of the polymerization reaction or after the completion of the polymerization reaction to deactivate the catalyst. Examples of the catalyst deactivator include aluminum compounds such as a phosphate aluminum compound and aluminum oxide; monostearyl acid phosphate, distearyl acid phosphate, trimethyl phosphate, tri-n-butyl phosphate, triphenyl phosphate, and phosphorous acid Phosphoric esters such as triphenyl, diethyl phosphite, dibutyl phosphite, trimethyl phosphite, tributyl phosphite; sodium dihydrogen phosphate, potassium pyrophosphate, bis (3,5-di-t-butyl) Phosphoric acid-based metal salts such as -4-ethyl cohydroxybenzylphosphonate) calcium;
An oxidizing agent such as dibenzoyl peroxide; a mixture thereof; The addition amount of the catalyst deactivator is about 0.5 to 20% by weight based on the amount of the catalyst used.

In addition, the catalyst is deactivated at a later stage of the polymerization reaction or after the polymerization reaction is completed, and the pressure of the polymerization reaction product is reduced in a molten state to remove unreacted monomers (for example, lactide) and low molecular compounds such as lactic acid. It is preferred to reduce these contents in the resulting polymer. For example, the lactide content in the polymer may be 0.1% by weight or less,
It is desirable from the viewpoint of product quality (decomposition stability, etc.). For example, a late-stage polymerization reaction product from a tubular reactor is supplied to a twin-screw extruder,
It can be performed by introducing it to a finisher such as a glasses type or a lattice type.

In the present invention, a stabilizer such as calcium stearate, a plasticizer such as phthalic acid ester, a coloring agent such as red-mouthed graphite and titanium oxide may be used in the latter stage of the polymerization reaction or after the completion of the polymerization reaction, if necessary. Can be added.

According to the method of the present invention, since a tubular reactor equipped with a jacket is used as the reactor, the flow of the reactant is close to the flow of the piston and does not generate shear heat. Are suitable. Further, since a heat transfer medium for temperature control is circulated through the jacket, the heat removal performance of the ring-opening polymerization heat of the reactant is excellent, and the temperature can be controlled.

[0047]

The present invention will be described more specifically with reference to the following examples.

The analysis was performed as follows. <Weight average molecular weight of polymer> It was measured by GPC (gel permeation chromatography) under the following conditions. Detector: RID-6A, Pump: LC-9A, Column oven: GT
O-6A, Column: Shim-pack GPC-801C, -804C, -806C, -8
025C in series (manufactured by Shimadzu Corporation) Mobile phase: chloroform, flow rate: 1 ml / min, sample amount: 200 μl (dissolved in chloroform so that the sample concentration becomes 0.5 w / w%), column temperature: 40
° C.

<Conversion rate of raw material> A predetermined amount was sampled from the reaction system, and the conversion rate (%) was determined from the area ratio of the polymer to the monomer in the chromatogram obtained by GPC analysis under the above conditions.

Example 1 L-lactide (manufactured by Shimadzu Corporation) was supplied at a rate of 10 kg / h to a dissolution tank (100 L).
L-lactide was dissolved at 110 ° C. in a dissolving tank, and a vertical reaction tank (1) equipped with a stirring blade at 10 kg / h by a gear pump was used.
35L). As a catalyst, tin octylate was supplied to the vertical reaction tank at a rate of 0.1 g / h.
An initial polymerization reaction was performed at 80 ° C. The reaction mixture was discharged by a gear pump so that the average residence time in the vertical reaction tank was 10 hours, and this was continuously introduced into a tubular reactor.
The conversion of the raw material at the outlet of the vertical reactor was 35%.

As a tubular reactor, length 6 m, diameter 300
Using a fixed tube plate type multi-tube heat exchanger provided with seven inner tubes of 2 inches in diameter in a cylindrical outer jacket of 2 mm, dibenzyltoluene as a heat transfer medium was circulated in the outer jacket, and the outlet of the tubular reactor The late-stage polymerization reaction was performed by controlling the temperature of the polymer to 200 ° C. The conversion of the raw material at the outlet of the tubular reactor was 90%.

This polymer was continuously introduced into a twin-screw extruder having a diameter of 30 mm and a barrel number of 7. Extruder internal temperature 22
While maintaining the molten state of the reactant at 0 ° C., vacuum was drawn from the second, fourth and sixth barrels of the extruder at 10 Torr to vaporize unreacted lactide. The product obtained at the outlet of the extruder was made into a strand, cooled in a water bath, and then pelletized with a pelletizer.

When the obtained pellet was measured by GPC, it was found to be poly-L-lactic acid having a weight average molecular weight of 240,000 and 960 ppm by weight of unreacted lactide.

Example 2 The stirring blades of the vertical reaction tank were changed to high-viscosity stirring blades.
Poly L-lactic acid was produced in the same manner as in Example 1 except that the residence time was changed. Operating temperature of 200 in a vertical reactor
An initial polymerization reaction was carried out at a temperature of 8 ° C. and an average residence time of 8 hours, and this was continuously introduced into a tubular reactor. The conversion of the raw material at the outlet of the vertical reactor was 59%.

This was continuously introduced into a tubular reactor controlled at a temperature of 200 ° C. in the same manner as in Example 1 to perform a late polymerization reaction. The raw material conversion at the outlet of the tubular reactor was 93
%Met.

This polymer was continuously introduced into a twin-screw extruder under the same conditions as in Example 1. The product obtained at the outlet of the extruder was made into a strand, cooled in a water bath, and pelletized with a pelletizer.

When the obtained pellet was measured by GPC, it was found to be poly-L-lactic acid having a weight average molecular weight of 240,000 and 720 ppm by weight of unreacted lactide.

[0058]

According to the continuous production method of the present invention, as described above, a tube-type reactor having a jacket is used as a reactor, and a heat transfer medium for temperature control is circulated through the jacket. The flow of the material is close to the flow of the piston and there is no shearing heat, so that the high-viscosity reactant can be further reacted, and the heat of the ring-opening polymerization heat of the reaction system is excellently removed, and appropriate temperature control can be performed. As a result, a high-molecular-weight biodegradable polyester without coloring can be stably and continuously produced. Further, the tubular reactor is a low-cost facility and is economically excellent.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Fujii 1 Nishinokyo Kuwaharacho, Nakagyo-ku, Kyoto-shi, Kyoto Inside Shimadzu Sanjo Works Co., Ltd. (72) Inventor Masahiro Ito 1 Nishinokyo-kuwaharacho, Nakagyo-ku, Kyoto, Kyoto Inside Shimadzu Sanjo Plant (72) Inventor Hiroshi Maeda 4-1-1, Bingo-cho, Chuo-ku, Osaka-shi Kobe Steel, Ltd.Osaka branch office (72) Inventor Kunihiko Shimizu 4-3-1, Bingo-cho, Chuo-ku, Osaka-shi No. Kobe Steel, Ltd. Osaka Branch Office (72) Inventor Hiroshi Miyagawa 4-3-1, Bingo-cho, Chuo-ku, Osaka City Kobe Steel Ltd. Osaka Branch Office

Claims (4)

[Claims] 1. A method for producing a biodegradable polyester by ring-opening polymerization using at least one kind of a dimeric cyclic ester of a hydroxycarboxylic acid and / or at least one kind of a lactone as a main raw material, comprising a jacket as a reactor. Using a tubular reactor, a heat transfer medium for temperature control is circulated through the jacket, and a polymerization reaction is carried out by continuously supplying a substance to be polymerized from one end of the tubular reactor and polymerizing from the other end. A method for continuously producing biodegradable polyester. 2. The method for continuously producing biodegradable polyester according to claim 1, wherein the tubular reactor is a reactor constituted by a plurality of tubes arranged in parallel. 3. The continuous method for producing a biodegradable polyester according to claim 1, wherein the tubular reactor is a double-tube heat exchanger or a multi-tube heat exchanger. 4. The polymerization reaction according to claim 1, wherein the initial polymerization reaction is carried out in a stirred tank reactor having stirring blades, the obtained polymerization reaction mixture is introduced into a tubular reactor, and the polymerization reaction is further carried out. The continuous production method of the biodegradable polyester according to any one of the above.