JP3069297B2 - Polyester production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyester, and more particularly to a method for producing a polyester useful as a sorbic acid precursor obtained by reacting crotonaldehyde with ketene.

[0002]

BACKGROUND OF THE INVENTION Sorbic acid and its salts (particularly potassium salts) have a preservative action and a fungicide action and are therefore useful as food additives.
Sorbic acid is highly soluble in solvents and fats,
As a preservative for butter, cheese and the like, potassium sorbate has a high water solubility and is used as a preservative for miso, jam, wine and the like. Sorbic acid is usually produced by subjecting a polyester obtained by the reaction between crotonaldehyde and ketene to hydrolysis such as hydrochloric acid decomposition, alkali decomposition and thermal decomposition.

In general, the higher the average degree of polymerization of the polyester, the higher the efficiency of sorbic acid production. A polyester having an average degree of polymerization of about 30 to 40 has conventionally been used. However, since the polyester having the average degree of polymerization has a high viscosity, there is a problem that the transfer, storage, and decomposition of the polyester are hindered. Similar problems have been encountered with other polyesters obtained by the reaction of aldehyde compounds other than crotonaldehyde with ketene. Therefore, particularly in the production of sorbic acid, a polyester having a degree of polymerization that can improve the production efficiency and the process operability such as transfer, storage, and decomposition has been desired.

[0004]

The polyester is prepared by, for example, reacting an aldehyde compound with ketene under an appropriate catalyst to synthesize β-lactone, and then continuously polymerizing the β-lactone while opening the ring. Water and acetic acid produced in the reaction system and present in the reaction system block the molecular terminals of the polyester. The present inventors have conducted intensive studies to solve the above problems in this production method, and as a result, the content ratio of acetic acid and water in the reaction system was set to a specific range, that is, the acetic acid to ketene mole number, By setting the ratio of the sum of the number of moles and the number of moles of water to a specific range, the production efficiency is good,
In addition, it has been found that a polyester having a good degree of polymerization can be produced with good process operability such as transfer, storage and decomposition. Heretofore, in this reaction, the effects of acetic acid and water present in the reaction system have not been studied so far.

That is, the present invention relates to (1) a method for producing a polyester by reacting an aldehyde compound with ketene, wherein the ratio of the sum of the moles of acetic acid and water to the moles of ketene is 0. A method for producing a polyester, characterized in that the reaction is carried out under a condition of 0.01 to 1.0. The preferred embodiment is as follows. (2) The method for producing a polyester according to the above (1), wherein the aldehyde compound is crotonaldehyde. (3) The method for producing a polyester according to (1), wherein the ratio of the sum of the number of moles of acetic acid and the number of moles of water to the number of moles of ketene is 0.03 to 0.20. (4) The method for producing a polyester according to (1), wherein the reaction is carried out under the condition that the ratio of the number of moles of water to the number of moles of ketene is 0.5 or less. (5) The ratio of the number of moles of acetic acid to the number of moles of ketene is 0.0
1 to 1.0, the ratio of the number of moles of water to the number of moles of ketene is 0.5 or less, and the ratio of the sum of the number of moles of acetic acid and the number of moles of water to the number of moles of ketene is 0.01 to 1 The method for producing a polyester according to (1), wherein the reaction is carried out under a condition of 0.0. (6) The obtained polyester has a polymerization degree of 4 to 27.
(2) A method for producing a polyester. (7) The viscosity of the obtained polyester at 80 ° C. is 40
(2) The method for producing a polyester according to (2), wherein

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the method for producing the polyester of the present invention, taking crotonaldehyde as a raw material as an example, as shown in the following formula (I), crotonaldehyde and ketene are reacted in the presence of a catalyst to convert β-lactone. The β-lactone is synthesized, and the β-lactone is subsequently ring-opened and polymerized continuously without isolation of the β-lactone.

[0007]

Embedded image

(Wherein, m and n each represent an integer of 4 to 27)

The aldehyde compound used in the present invention is not particularly limited as long as it can form β-lactone. Specific examples include aldehydes such as crotonaldehyde, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde. Among them, crotonaldehyde is useful for producing a polyester which is a precursor of sorbic acid.

Since the reactivity of ketene is high, the aldehyde compound is usually charged in excess with respect to the ketene charge, but usually 1.0 to 4.0 mol, preferably 1 to 4.0 mol, per mol of ketene. Is 1.5 to 3.0 mol.

Ketene usually contains water and acetic acid. Ketene easily reacts with water and acetic acid, and becomes acetic acid and acetic anhydride, respectively, as shown in the following formula.

[0012]

Embedded image

The production method of the present invention is usually carried out in the presence of a catalyst. Examples of the catalyst include those usually used in the synthesis of β-lactone, such as zinc isovalerate,
Fatty acid zinc salts such as zinc acetate, zinc isobutyrate, zinc chloride,
Examples thereof include zinc compounds such as zinc oxide, and zinc powder. These catalysts are usually used in an amount of 0.0005 to 0.02 mol, preferably 0.001 to 0.02 mol as Zn per mol of ketene.
0.01 mol.

After synthesis of the β-lactone, the polyester is obtained by successively polymerizing the β-lactone after the ring opening, and usually by reacting at 25 to 40 ° C. to obtain the β-lactone. Then, polymerization proceeds.
During this polymerization, depending on the amount of acetic acid and water present in the reaction system,
The degree of polymerization of the resulting polyester is determined. That is, when the number of moles of acetic acid and water is large, the molecular terminals of the polyester are easily sealed, and a polyester having a low degree of polymerization can be obtained. Further, if the molar numbers of acetic acid and water are too large, ketene is wasted as in the above formula, and the desired polyester cannot be obtained. Conversely, when the amounts of acetic acid and water present in the reaction system are small, the degree of polymerization of the obtained polyester increases. Therefore, in order to obtain a polyester having a desired degree of polymerization, it is necessary to limit the amounts of acetic acid and water to a specific range. Not.

In the production method of the present invention, the ratio of the sum of the mole number A of acetic acid and the mole number H of water to the mole number K of ketene, that is, (A + H) / K is 0.01 to 1.0, preferably Is 0.03 to 0.20, more preferably 0.04 to 0.2.
The reaction is carried out under the conditions that give 14. When (A + H) / K is less than 0.01, the degree of polymerization of the obtained polyester is increased and the viscosity thereof becomes too high, which hinders the steps of transferring, storing and decomposing the polyester. Conversely, when (A + H) / K exceeds 1.0, the reaction as shown in the above formula occurs mainly and ketene is wasted and the desired polyester cannot be obtained. In this reaction system, the case where acetic acid does not exist or the case where water does not exist are also within the scope of the present invention.

As can be seen from the above equation, in the method of the present invention, water consumes a large amount of ketene wastefully. In order to prevent this, in the above reaction system, the ratio of the mole number H of water to the mole number K of ketene, that is, H / K is preferably 0.5 or less, particularly preferably 0.3 or less.

In a particularly preferred embodiment, A / K is 0.0
1 to 1.0, H / K is 0.5 or less, and (A + H) / K
Is to be reacted under the condition of 0.01 to 1.0.

The above (A + H) / K, A / K, H / K
Can be adjusted to the above range by a method such as removing acetic acid and water contained in ketene to some extent in advance, or adding acetic acid and water to the reaction system. Acetic acid and water contained in ketene are measured by gas chromatography (TCD) analysis of ketene gas.

The above β-lactone is synthesized at a reaction temperature of 2
The reaction is carried out at 5 to 40 ° C., and the polyester is obtained by continuing the reaction at the same temperature. After completion of the reaction, unreacted aldehyde compounds, water, acetic acid and the like are mainly distilled off under reduced pressure.

In the above reaction, the weight of the ketene blown into the reactor can be known by measuring the amount of addition of the reactor, and the moles of water and acetic acid contained in the blown ketene can be determined. The number is determined by gas chromatography (TCD) analysis. Unreacted ketene
Decomposed by acetic acid trap.

The degree of polymerization of the polyester produced by such a method, that is, m and n in the formula (I) are 4 to 2
About 7 and preferably 10 to 16, and the viscosity at 80 ° C. of the polyester having such an average polymerization degree is as follows:
Preferably 40-4000 cp, more preferably 400
３3700 cp. Accordingly, such polyesters have good process workability such as transfer, storage, and decomposition,
When the aldehyde compound is crotonaldehyde, the production efficiency of sorbic acid using this polyester is also improved.

The polyester thus produced is used for various purposes. For example, polyester obtained from crotonaldehyde and ketene can be converted to sorbic acid by a method of thermal decomposition, a method of hydrolysis in the presence of an alkali catalyst, a method of hydrolysis with a mineral acid, and the like. Among these,
Hydrolysis with a mineral acid, particularly hydrochloric acid, is preferred from the viewpoint that the decomposition results and the quality of the obtained sorbic acid are improved. Furthermore, hydrolysis can be performed in the presence of a saturated fatty acid in that the decomposition temperature of the polyester can be lowered without increasing the concentration of mineral acid, and sorbic acid with extremely low contamination of tar-like substances can be obtained. preferable.

The mineral acids used in the hydrolysis reaction include:
Hydrochloric acid, sulfuric acid and the like. The concentration of the mineral acid (particularly hydrochloric acid) is not particularly limited, but is preferably 15 to 40% by weight,
More preferably, it is 25 to 36% by weight. The amount of hydrogen chloride is preferably 2 to 10 moles, more preferably 3 to 6 moles, in the case of hydrochloric acid, relative to 1 mole of the polyester.

Since the hydrolysis of the polyester with a mineral acid is carried out in a mineral acid which is an aqueous solution (particularly in hydrochloric acid), the saturated fatty acid is preferably a water-soluble one. Among them, carbon number 1
Five saturated fatty acids are preferred.

Specific examples of the saturated fatty acid include, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid and the like.
These may be used alone or as a mixture. Among them, acetic acid is particularly preferably used for the following reasons.

The concentration of the saturated fatty acid is not particularly limited, but is preferably 1 to 20% by weight, more preferably 3 to 15% by weight in a mineral acid, especially in hydrochloric acid.

As described above, since the terminal of the polyester is blocked with acetic acid or water, hydrolysis of the polyester produces acetic acid as a by-product. Therefore, when hydrolysis is performed, acetic acid naturally increases in the reaction solution. That is, a mineral acid containing acetic acid after hydrolysis (also called a mineral acid mother liquor)
Has a higher acetic acid content than the mineral acid mother liquor before hydrolysis. In other words, the mineral acid mother liquor is not only freshly prepared, but rather the mineral acid mother liquor after the hydrolysis of the polyester has a higher acetic acid content and can be preferably used. That is, the method of using acetic acid as a fatty acid,
Since the mineral acid mother liquor after the recovery of sorbic acid can be used repeatedly, the method is economically excellent.

The decomposition reaction is carried out at 25 to 110 ° C., preferably 40 to 85 ° C., for 15 to 240 minutes, preferably
It ends in 0 to 150 minutes.

The sorbic acid thus obtained is useful as a preservative and a fungicide, and is added to food as it is or as a salt such as a potassium salt.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. <Measurement method> 1) Average polymerization degree Calculated from the peak intensity measured by FAB-MS (manufactured by TOKIMEC). 2) Viscosity The sample was measured at 80 ° C. using an E-type viscometer (EMD type).

Example 1 150.2 of purified crotonaldehyde was placed in a reaction vessel.
g, 2.50 g of zinc isobutyrate and 0.27 g of water, and the temperature was maintained at 25 ° C. The ketene trap in the dry ice-methanol bath was pulled up, the ketene was vaporized, and 32.4 g of ketene was blown into the reaction vessel through an empty trap in a cold bath at -30 to -20 ° C (blowing time: 1 hour and 5 minutes). . The blown ketene contained a total of 42.8 mM of acetic acid and water. After blowing, 30 ~
The reaction was performed at 40 ° C. for 1 hour. After the reaction, 30-40m
The mixture was heated to 120 ° C. under a reduced pressure of mHg to distill off unreacted substances (especially crotonaldehyde) to obtain 85.8 polyester.
1 g was obtained. Table 1 shows the physical properties of the obtained polyester and the reaction rates of crotonaldehyde and ketene. Examples 2-3 and Comparative Examples 1-2

A polyester was obtained in the same manner as in Example 1 except that the amounts of ketene, crotonaldehyde, zinc isobutyrate, acetic acid and water were changed as shown in Table 1. Physical properties of the obtained polyester,
Table 1 shows the reaction rates of crotonaldehyde and ketene.
Shown in

[0033]

[Table 1]

From Table 1, in Examples 1 to 3, the sum of the number of moles of acetic acid and the number of moles of water with respect to the number of moles of ketene,
That is, by setting (A + H) / K to 0.01 to 1.0, a polyester having an average degree of polymerization and viscosity suitable for the subsequent sorbic acid production step was obtained. However, under the condition that (A + H) / K of Comparative Example 1 exceeded 1.0, polyester was not obtained because the amounts of acetic acid and water were too large. In addition, (A + H) / K of Comparative Example 2 was 0.1.
The polyester obtained under the condition of being less than 01 had an average degree of polymerization increased and the viscosity was too high.

Reference Example 100 g (0.89 mol) of the polyester obtained in Example 1 was reacted with 430 g (3.54 mol) of 30% hydrochloric acid in a mineral acid mother liquor obtained by adding acetic acid to the hydrochloric acid by 14%. The reactor was charged and reacted at an internal temperature of 49 to 51 ° C. After 120 minutes, the hydrolysis was completed (the temperature rise of the system was stopped). It was cooled from 49 ° C. to 20 ° C. over 90 minutes to obtain a reaction solution. The obtained reaction solution was separated into sorbic acid and mineral acid mother liquor by suction filtration to obtain hydrous sorbic acid, which was dried to obtain crude sorbic acid (dry cake). The production rate of sorbic acid, including isomers contained in crude sorbic acid and mineral acid mother liquor, was 91.5% based on the charged polyester.
%Met. The rate of formation of the tar-like substances contained in the crude sorbic acid and the mineral acid mother liquor was 5.1% based on the charged polyester.

[0036]

As is apparent from the above description, according to the method for producing a polyester of the present invention, the process operability such as transfer, storage and decomposition is improved, and particularly when the aldehyde compound is crotonaldehyde, It is possible to obtain a polyester having an appropriate degree of polymerization so that the production efficiency of sorbic acid becomes good.

Continuation of the front page (56) References JP-B-47-30638 (JP, B1) JP-B-45-36315 (JP, B1) JP-B-45-5789 (JP, B1) (58) Fields surveyed (Int .Cl. ⁷ , DB name) C08G 63/08

Claims (7)

(57) [Claims] 1. A method for producing a polyester by reacting an aldehyde compound and ketene, wherein the ratio of the sum of the number of moles of acetic acid and the number of moles of water to the number of moles of ketene is:
A method for producing a polyester, wherein the reaction is carried out under a condition of 0.01 to 1.0. 2. The method for producing a polyester according to claim 1, wherein the aldehyde compound is crotonaldehyde. 3. The method according to claim 1, wherein the ratio of the sum of the number of moles of acetic acid and the number of moles of water to the number of moles of ketene is 0.03 to 0.20. . 4. The method for producing a polyester according to claim 1, wherein the reaction is carried out under the condition that the ratio of the number of moles of water to the number of moles of ketene is 0.5 or less. 5. The ratio of the number of moles of acetic acid to the number of moles of ketene is 0.01 to 1.0, the ratio of the number of moles of water to the number of moles of ketene is 0.5 or less, and
The ratio of the sum of the number of moles of acetic acid and the number of moles of water is 0.01 to 1.
The method for producing a polyester according to claim 1, wherein the reaction is carried out under a condition of zero. 6. The polymerization degree of the obtained polyester is 4 to 2
The method for producing a polyester according to claim 2, wherein the polyester is 7. 7. The method according to claim 2, wherein the viscosity of the obtained polyester at 80 ° C. is 40 to 4000 cp.