JPH1095745A - Production of sorbic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain sorbic acid in a good yield, while suppressing the generation of tars, by hydrolyzing a polyester with a mineral acid in the presence of a saturated fatty acid. SOLUTION: This method for producing sorbic acid comprises hydrolyzing a polyester having repeating units of the formula with a mineral acid (e.g. hydrochloric acid) in the presence of a saturated fatty acid (e.g. acetic acid) at 25-110 deg.C for 15-240min. The polyester is obtained by polycondesing croton aldehyde with ketene under such a condition that the ratio of the sum of the mole number (A) of the acetic acid and the mole number (H) of water to the mole number (K) of the ketene [namely (A+H)/K] is 0.01-1.0. The saturated fatty acid is contained in a concentration of 1-20wt.% in the mineral acid. The method enables to lower a decomposition temperature for the polyester without enhancing the concentration of the mineral acid. The employment of acetic acid as the saturated fatty acid enables to repeatedly use the mineral acid mother solution, thereby being profitable. Sorbic acid is used as a food additive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in the production of sorbic acid by hydrolyzing polyesters, especially polyesters obtained by the reaction of crotonaldehyde with ketene, with mineral acids. More specifically, the present invention relates to a method for producing sorbic acid in which the production of tar-like substances is suppressed and the yield of a target substance is improved.

[0002]

2. Description of the Related Art As a method for producing sorbic acid by decomposing a polyester, for example, a polyester obtained from crotonaldehyde and ketene, a method of thermally decomposing a polyester, a method of hydrolyzing in the presence of an alkali catalyst, and a method of hydrolyzing with a mineral acid. There are methods for disassembly. Among these, mineral acids,
In particular, a method of hydrolyzing polyester using hydrochloric acid is a preferable method from the viewpoint of good decomposition results and good quality of sorbic acid obtained.

[0003]

However, in any of the methods, tar-like substances are by-produced during the decomposition reaction and are mixed as impurities into sorbic acid. Therefore, a special purification method for removing the impurities is required. There was a problem that a process was required. This problem also exists in hydrolysis using mineral acids. That is, in the polyester hydrolysis step, it is necessary to apply a certain amount of heat. At this time, the low-molecular-weight organic matter generated further undergoes a chemical reaction due to the heat of the reaction system and becomes a tar-like substance. It is considered that the production of this tar-like substance depends on the temperature of the reaction system, and the higher the temperature, the more the production of tar is promoted. Therefore, it is conceivable to suppress the by-product of tar-like substances by lowering the decomposition temperature of the polyester. However, in order to lower the decomposition temperature, it is necessary to increase the concentration of the mineral acid in the reaction system. If the concentration of the mineral acid is increased, the by-product of tar-like substances is promoted. Therefore, if the decomposition temperature of the polyester can be lowered without increasing the concentration of the mineral acid, sorbic acid containing very little tar-like substance can be obtained. An object of the present invention is to provide a method for producing sorbic acid by mineral acid hydrolysis of polyester, which method produces sorbic acid with very little contamination of tar-like substances.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object. As a result, when a polyester is hydrolyzed with a mineral acid, if a saturated fatty acid is present in the reaction system, tar The present inventors have found that by-products of the state substance are remarkably suppressed, and completed the present invention.

That is, the present invention provides the following (1):
The embodiments are as described in (2) to (8) below. Equation (1)

[0006]

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A method for producing sorbic acid, comprising hydrolyzing a polyester having a repeating unit represented by the formula (1) with a mineral acid in the presence of a saturated fatty acid. (2) The method for producing sorbic acid according to the above (1), wherein the mineral acid is hydrochloric acid. (3) The method for producing sorbic acid according to the above (1), wherein the polyester is a polyester obtained by reacting crotonaldehyde and ketene. (4) The polyester contains crotonaldehyde and ketene, and the ratio of the sum of the moles A of acetic acid and the moles H of water to the moles K of ketene [that is, (A + H) / K] is from 0.01 to 0.01.
The method for producing sorbic acid according to the above (3), which is a polyester obtained by reacting under conditions that give 1.0. (5) The above (1), wherein the saturated fatty acid is a water-soluble saturated fatty acid.
The method for producing sorbic acid according to any one of (1) to (4). (6) The method for producing sorbic acid according to (5), wherein the water-soluble saturated fatty acid is a saturated fatty acid having 1 to 5 carbon atoms. (7) The method for producing sorbic acid according to (6), wherein the saturated fatty acid is acetic acid. (8) The method for producing sorbic acid according to the above (1), wherein the saturated fatty acid is contained in the mineral acid in an amount of 1 to 20% by weight.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The polyester used in the present invention has the formula:

[0009]

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Any polyester having a repeating unit represented by the formula (1) can be used. Examples of such a polyester include those produced using crotonaldehyde and ketene as raw materials. Examples of the production method include a method in which purified ketene gas is blown into purified crotonaldehyde in the presence of a catalyst, and an excess of crotonaldehyde is recovered from the obtained reaction product.

Above all, when reacting crotonaldehyde with ketene, the ratio of the number of moles of acetic acid A and the number of moles of water H present in the reaction system to the number of moles of ketene K, ie, (A + H) / K Is 0.01 to 1.0, preferably 0.0
The polyester obtained by reacting under the conditions of 3 to 0.20, more preferably 0.04 to 0.14, has an optimum degree of polymerization of 4 to 27, and has good sorbic acid production efficiency. It is particularly preferable because the workability of the process such as transfer, storage and disassembly is good.

The polyester obtained has the formula:

[0013]

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[0014]

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

The mineral acids used in the hydrolysis reaction include:
Preferably, hydrochloric acid, sulfuric acid and the like are used. The concentration of hydrochloric acid is not particularly limited, but is preferably 15 to 40% by weight, and more preferably 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.

The alkyl portion of the saturated fatty acid to be coexistent may be linear or branched. Since the hydrolysis of the polyester with a mineral acid is performed in an aqueous solution of a mineral acid (particularly in hydrochloric acid), the saturated fatty acid is preferably a water-soluble one. Among them, saturated fatty acids having 1 to 5 carbon atoms are preferable. Specific examples of saturated fatty acids, for example, formic acid, acetic acid,
Examples thereof include propionic acid, butyric acid, and valeric acid, which may be used alone or as a mixture. Among them, acetic acid is particularly preferably used for the following reasons. Although the concentration of the saturated fatty acid is not particularly limited, preferably, when a mineral acid is used, it is 1 to 1 in a mineral acid, particularly, in a hydrochloric acid.
It is 20% by weight, more preferably 3 to 15% by weight.

The hydrolysis reaction is carried out at 25 to 110 ° C., preferably 40 to 85 ° C., and is completed in 15 to 240 minutes, preferably 30 to 150 minutes.

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, for example, a polyester acid is hydrolyzed in a mineral acid containing acetic acid (a mineral acid containing a saturated fatty acid is also referred to as a “mineral acid mother liquor” below), and the mineral acid mother liquor after recovering sorbic acid undergoes hydrolysis. It has a higher acetic acid content than before. In other words, the mineral acid mother liquor used in the method of the present invention is not only a newly prepared one, but rather the mineral acid mother liquor after hydrolysis of the polyester has a higher acetic acid content and can be preferably used. . That is, according to the method of the present invention, the mother liquor after recovering sorbic acid from the mineral acid mother liquor used for hydrolysis of the polyester can be used repeatedly, which is an economically superior method.

The two-stage reaction or a cooling (slow cooling) equivalent thereto is more effective. For example, after the completion of the hydrolysis reaction, that is, after the end of the exothermic reaction, the temperature at the end of the exothermic reaction is lowered by 4 ° C. and 25 ° C. or higher. 0.1-1.0
Slow cooling at a rate of ° C./min further suppresses the formation of tar-like substances.

The reaction mixture containing sorbic acid thus produced is then taken out of the system and isolated into sorbic acid by a method such as suction filtration and pressure filtration.

The obtained sorbic acid and its salts (especially potassium salts) have a preservative action and a fungicide action and are therefore useful as food additives. Sorbic acid has high solubility in solvents and fats, and as a preservative for fish meat paste, butter, cheese, etc., potassium sorbate has high water solubility, miso,
It is used as a preservative for jams and wine.

[0023]

The present invention will be described in more detail with reference to the following examples. In the following, “%” means “% by weight” unless otherwise specified.

Example 1 A reactor was charged with 150 g of purified crotonaldehyde and 0.4 g of zinc isovalerate powder, and reacted while blowing at a temperature of 30 to 40 ° C. by blowing 54 g of ketene. After completion of the reaction, the mixture was heated to 120 ° C. under a reduced pressure of 30 to 40 mmHg to distill off unreacted crotonaldehyde and by-products to obtain 136 g of polyester. Such polyester 100
g (0.89 mol) and 430 g of 30% hydrochloric acid (3.54 mol).
Mol) and a mineral acid mother liquor obtained by adding acetic acid to the hydrochloric acid by 14% was charged into the reactor, 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 a mineral acid mother liquor by suction filtration to obtain hydrous sorbic acid. The obtained sorbic acid was dried to obtain crude sorbic acid (dry cake). The production rate of sorbic acid including the isomers contained in the crude sorbic acid and the mineral acid mother liquor was 91.5% based on the charged polyester. 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.

Example 2 In Example 1, the concentration of acetic acid in the mineral acid mother liquor was changed to 8.5%, and the decomposition reaction of the polyester was carried out at 57 to 59 ° C. for 90 minutes. Over 57
A crude sorbic acid was obtained in the same manner as in the example except that the reaction solution was obtained by cooling from 20 ° C to 20 ° C. The production rate of sorbic acid including the crude sorbic acid and isomers contained in the mineral acid mother liquor was 91.91 relative to the charged polyester.
2%. The rate of formation of tar-like substances contained in the crude sorbic acid and the mineral acid mother liquor was 5.6% based on the charged polyester.

Example 3 In Example 1, the concentration of acetic acid in the mineral acid mother liquor was changed to 4%, and the decomposition reaction of the polyester was carried out at 66 to 68 ° C. for 60 minutes. 66 ° C
Sorbic acid was obtained in the same manner as in this Example except that the reaction solution was obtained by cooling the mixture to a temperature of from 20 ° C to 20 ° C. The sorbic acid production rate including the crude sorbic acid and the isomers contained in the mineral acid mother liquor was 90.7% based on the charged polyester.
%Met. The rate of formation of tar-like substances contained in the crude sorbic acid and the mineral acid mother liquor was 6.8% based on the charged polyester.

Comparative Example 1 In Example 1, the decomposition reaction of the polyester was carried out at 72 to 74 ° C. for 90 minutes without using acetic acid as the mineral acid mother liquor. 20 ° C
Crude sorbic acid was obtained in the same manner as in the example except that the reaction solution was obtained by cooling the mixture to room temperature. The yield of sorbic acid, including isomers contained in the crude sorbic acid and the mineral acid mother liquor, was 88.6% based on the charged polyester. Further, the generation rate of the tar-like substances contained in the crude sorbic acid and the mineral acid mother liquor was 7.9% based on the charged polyester.

The reaction conditions of Examples 1 to 3 and Comparative Example 1 are summarized in Table 1.

[0029]

[Table 1]

Table 2 shows the production rates of sorbic acid and tar substances in Examples 1 to 3 and Comparative Example 1.

[0031]

[Table 2]

Example 4 150.2 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 25-
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 3 shows the physical properties of the obtained polyester and the reaction rates of crotonaldehyde and ketene. The physical properties of the polyester were measured as follows. 1) Average polymerization degree: FAB-MS [TOKIMEC Corporation]
Manufactured by the Company). 2) Viscosity: The sample was measured for 80 using an E-type viscometer (EMD type).
Measured in ° C. Table 4 shows the yield of SA (sorbic acid) including isomers, the yield of tar-like substances, and the yield of tt-SA (trans-trans-sorbic acid) from the dried cake. Show.

Examples 5 to 6

A polyester was obtained in the same manner as in Example 4 except that the amounts of ketene, crotonaldehyde, zinc isobutyrate, acetic acid and water were changed as shown in Table 3. Physical properties of the obtained polyester,
Table 3 shows the reaction rates of crotonaldehyde and ketene.
Shown in Sorbic acid was produced in the same manner as in Example 1 using the obtained polyester. Table 4 shows the yield of SA including isomers, the yield of tar-like substances, and the yield of tt-SA from the dried cake for the obtained sorbic acid.

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

According to the method of the present invention, the decomposition temperature of polyester can be lowered without increasing the concentration of a mineral acid such as hydrochloric acid, and the yield of sorbic acid can be increased. In particular, when acetic acid is used as the saturated fatty acid, the mineral acid mother liquor can be used repeatedly, which is an economically advantageous method. In particular, when the polyester obtained under the condition of 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 is 0.01 to 1.0, the production efficiency of sorbic acid is particularly good. .

Claims (8)

[Claims] (1) Formula (1) A method for producing sorbic acid, comprising hydrolyzing a polyester having a repeating unit represented by the formula (1) with a mineral acid in the presence of a saturated fatty acid. 2. The method for producing sorbic acid according to claim 1, wherein the mineral acid is hydrochloric acid. 3. The method for producing sorbic acid according to claim 1, wherein the polyester is a polyester obtained by reacting crotonaldehyde with ketene. 4. The polyester comprises crotonaldehyde and ketene, and the ratio of the sum of the moles A of acetic acid and the moles H of water to the moles K of ketene (ie, (A + H) / K) is 0.0.
The method for producing sorbic acid according to claim 3, which is a polyester obtained by reacting under conditions such that the amount becomes 1 to 1.0. 5. The method for producing sorbic acid according to claim 1, wherein the saturated fatty acid is a water-soluble saturated fatty acid. 6. The method for producing sorbic acid according to claim 5, wherein the water-soluble saturated fatty acid is a saturated fatty acid having 1 to 5 carbon atoms. 7. The method for producing sorbic acid according to claim 6, wherein the saturated fatty acid is acetic acid. 8. The method for producing sorbic acid according to claim 1, wherein the saturated fatty acid is contained in the mineral acid in an amount of 1 to 20% by weight.