JPH10114769A - Production of lactide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a lactide having a high optical purity. SOLUTION: This method for producing a lactide having a high optical purity containing processes of (i) a process of heating lactic acid for concentrating the acid, (ii) a process of dehydrating the concentrated lactic acid while refluxint the same for forming a lactic acid oligomer, (iii) a process of removing lactic acid by depolymerization of the lactic acid oligomer in the presence of a catalyst, is constituted by performing the process (ii) under the following temperature conditions of 1st-3rd steps consecutively. the 1st step: liquid temperature 135±3 deg.C, the 2nd step: liquid temperature 150±3 deg.C, the 3rd step: liquid temperature 160±3 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optically pure L-
Alternatively, the present invention relates to a method for producing D-lactide.

[0002]

2. Description of the Related Art Lactide is a cyclic diester formed by dehydration of two molecules of lactic acid, and is a raw material for polylactic acid. As a method for producing lactide, for example, JP-A-63-101378
In the publication, first, lactic acid is dehydrated and concentrated to obtain an intermediate oligomer, to which a tin-based catalyst is added, which is heated to about 200 ° C. in a high vacuum to decompose and cyclically dimerize lactide. Is described.

[0003]

Embedded image However, in such a production method, a large amount of a low-polymerization degree linear oligomer is contained in the reaction solution in addition to the cyclic dimer lactide. For this reason, at the time of distilling out lactide, these oligomers are distilled out together with lactide, and the optical purity and yield of the product lactide are reduced. On the other hand, to prevent this,
When the degree of dehydration and concentration of lactic acid is increased, lactic acid is distilled out during concentration, the yield of lactide is reduced, and the optical purity is also reduced.

An object of the present invention is to provide a method for producing lactide having high optical purity in a high yield.

[0005]

Means for Solving the Problems The present invention provides the following (i) to
Step (iii): (i) heating and concentrating the lactic acid, (ii) dehydrating the concentrated lactic acid while refluxing to produce a lactic acid oligomer, and (iii) converting the lactic acid oligomer into a catalyst. It is intended to provide a process for producing lactide, which comprises a step of depolymerizing and distilling off in the presence of lactide. Next, each of these steps will be described in detail.

(I) Concentration Step In the first step of the present invention, lactic acid is concentrated to produce an oligomer. The lactic acid used may be either L-lactic acid or D-lactic acid. As such lactic acid, any one produced by a conventionally known method is used,
In particular, a purity of at least 80% and an optical purity of 9 produced by a fermentation method.
It is preferably at least 9%. Such lactic acid is heated at a temperature of 130 to 140 ° C. under normal pressure to perform simple distillation, and water is distilled off until no gas is generated.

(Ii) Refluxing step The mixture containing the oligomer of lactic acid obtained in the above step (i) as a main component is preferably refluxed under reduced pressure while dehydrating. The reduced pressure is preferably 10 to 100 Torr. The reflux is performed at a temperature of 130 to 170 ° C. for 3 to 4 hours. It is preferable that the temperature of the reflux is gradually increased in steps. For example, it is preferable that the first stage is 135 ± 3 ° C., the second stage is 150 ± 3 ° C., and the third stage is 160 ± 3 ° C. By such a reflux, lactic acid becomes a 6- to 10-mer linear oligomer, which has a large difference in boiling point from lactide, thereby facilitating separation. The reflux step may be further performed in multiple stages, or the temperature may be gradually increased continuously and heating may be performed until reflux is stopped. Lactide is a needle-like crystal having a melting point of 95 to 100 ° C.
Keep warm to a degree.

(Iii) Distillation Step Next, the high-purity oligomer obtained in the step (ii) is cyclically dimerized. That is, a cyclic dimerization (transesterification reaction) catalyst is added, and the lactide is distilled off preferably by heating under reduced pressure. As the catalyst used here, any conventionally known catalyst can be used, and for example, any of tin octylate, antimony trioxide, zinc oxide and the like can be used. Heating is performed under reduced pressure of 10 to 50 Torr, preferably 1
Perform at 90-210 ° C. In addition, the use of a high-vacuum, high-temperature apparatus further improves the yield of lactide.

As described above, if the step of refluxing at a predetermined temperature and dehydrating is added between the conventional two steps of lactic acid concentration and distilling out of lactide, the amount of oligomers having a high degree of polymerization increases and the isolation of lactide is facilitated. It became. In the present invention, lactic acid distillation can be prevented by concentrating and refluxing lactic acid, and the optical purity of lactide does not decrease, thereby improving the yield of lactide.

[0010]

Next, the present invention will be described more specifically based on examples.

[Example 1] L- having an optical purity of 99% or more
L-lactide was synthesized from lactic acid (90% by weight) as follows.

35 kg of a raw material was charged into a glass reactor (50 L), the lactic acid raw material was heated to a liquid temperature of 135 ° C., subjected to simple distillation at normal pressure, and concentrated for 30 minutes. Then, under reduced pressure (13-7
(0 Torr). The liquid temperature was set in the following three stages, and the process proceeded to the next stage as soon as it was within each stage.

The first step: setting the liquid temperature to 135 ° C. The second step: setting the liquid temperature to 150 ° C. The third step: setting the liquid temperature to 160 ° C.
Lactide was distilled off by simple distillation at a liquid temperature of 200 ° C. at 35 Torr. The condenser temperature was set at 105 ° C. to prevent pipe clogging. During the above operation, stirring at 300 rpm was continued. Table 1 shows the results.

Example 2 L- with an optical purity of 99% or more
L-lactide was synthesized from lactic acid (90% by weight) as follows.

35 kg of a raw material was charged into a glass reactor (50 L), and the raw lactic acid was heated to a liquid temperature of 135 ° C., subjected to simple distillation at normal pressure, and concentrated for 30 minutes. Then, under reduced pressure (20-7
(0 Torr) The temperature of the solution was set to 200 ° C., and total reflux was performed.
Then, a catalyst of tin octylate was charged and the pressure was reduced (10 to 10).
Lactide was distilled off by simple distillation at a liquid temperature of 200 ° C. at 25 Torr. The condenser temperature was set at 105 ° C. to prevent pipe clogging. During the above operation, stirring at 300 rpm was continued. Table 1 shows the results.

[Example 3] L- having an optical purity of 99% or more
L-lactide was synthesized from lactic acid (90% by weight) as follows.

35 kg of the raw material was charged into a glass reactor (50 L), and the raw lactic acid was heated to a liquid temperature of 135 ° C., subjected to simple distillation at normal pressure, and concentrated for 30 minutes. Then, under reduced pressure (30-6
(0 Torr) The temperature of the solution was set at 160 ° C., and total reflux was performed.
Then, a catalyst of tin octylate was charged and the pressure was reduced (10 to 10).
Lactide was distilled off by simple distillation at a liquid temperature of 200 ° C. at 20 Torr. The condenser temperature was set at 105 ° C. to prevent pipe clogging. During the above operation, stirring at 300 rpm was continued. Table 1 shows the results.

[Table 1] Test No Purity (%) Yield (%) Optical purity (%) Example 1 80.4 77.7 99.1 Example 2 85.9 82.9 99.2 Example 3 85.5 86.0 99 As is clear from Table 1, according to the production method of the present invention, L-lactic acid having an optical purity of 99% or more (90% by weight) is converted to an optical purity of 9%.
9.0% or more of L-lactide is obtained in a high yield of 70% or more of the theoretical yield.

[0019]

According to the production method of the present invention, lactide having high optical purity can be obtained in high yield.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitomi Ohara No. 1 Kuwabaracho, Nishinokyo, Nakagyo-ku, Kyoto Inside Shimazu Works Sanjo Plant

Claims (1)

[Claims] (1) a step of heating and concentrating lactic acid;
i) a method of producing lactide comprising the steps of: dehydrating the concentrated lactic acid while refluxing to produce a lactic acid oligomer; and (iii) depolymerizing and distilling the lactic acid oligomer in the presence of a catalyst. , And step (ii) is sequentially performed under the following first to third stage temperature conditions. First stage: liquid temperature 135 ± 3 ° C Second stage: liquid temperature 150 ± 3 ° C Third stage: liquid temperature 160 ± 3 ° C