Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-08-07
2003-02-25
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06525218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for efficiently producing sorbic acid from a polyester, which polyester is a polymerization reaction product between crotonaldehyde and ketene. The product sorbic acid is useful, for example, as a food additive.
2. Description of the Related Art
Sorbic acid and its salts have antiseptic and antimicrobial activities and are substantially nontoxic to the human body in normal concentrations in practical use. These compounds are therefore useful as food additives. Of a variety of known processes for producing sorbic acid, a commercially important pathway is. a process of polymerizing crotonaldehyde and ketene to form an intermediate polyester, decomposing the polyester to yield a crude sorbic acid, and subjecting the crude sorbic acid to a variety of purification operations to thereby yield a purified sorbic acid. The polyester is decomposed, for example, with hydrochloric acid, with an alkali, or by heat. Sorbic acid obtained by these techniques contains a variety of colored substances, tarry substances and other impurities and is subjected to purification operations.
For example, Japanese Examined Patent Application Publication No. 44-26646 discloses a process for producing sorbic acid. In this process, a polyester obtained by a reaction between crotonaldehyde and ketene is decomposed with hydrochloric acid having a concentration of equal to or more than 35% by weight at a temperature equal to or higher than room temperature (ordinary temperature) and less than or equal to around the boiling point of the hydrochloric acid used, followed by cooling and filtrating the resulting reaction mixture to separate a crude sorbic acid, and the crude sorbic acid is rinsed with water, is then put into water and is dissolved by heating, followed by addition of activated carbon and boiling, the reaction mixture is filtrated before it gets cold, and the filtrate is gradually cooled to thereby yield a crystalline sorbic acid.
Japanese Unexamined Patent Application Publication No. 54-163516 discloses a process for producing a sorbic acid. In this process, a polyester obtained from ketene and crotonaldehyde is decomposed with hydrochloric acid in the presence of, for example, a urea compound, the resulting decomposition reaction mixture is filtrated and rinsed to yield a crude sorbic acid, followed by addition of an aqueous sodium hydroxide solution to the crude sorbic acid to thereby yield an aqueous sodium sorbate solution, the aqueous sodium sorbate solution is treated with activated carbon, is neutralized and is cooled to thereby crystallize sorbic acid.
However, these processes invite loss of sorbic acid due to the formation of tar during decomposition of the polyester or invite loss of sorbic acid due to dissolution of sorbic acid into a filtrate separated from the crystal of sorbic acid by solid-liquid separation. Additionally, in these processes, the reaction mixture must be subjected to solid-liquid separation including dissolution in a treatment solvent and recrystallization during purification operations in order to remove the tar contents and these operations invite further loss of sorbic acid to thereby markedly decrease the yield of sorbic acid. Furthermore, the resulting filtrates exhibit a very high BOD (biochemical oxygen demand) and must be treated to reduce the BOD, and such treatments require a great deal of facilities and costs.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a process for producing sorbic acid, which process can significantly reduce the amount of tar formed during decomposition of the polyester, can produce sorbic acid in a high yield, and can reduce the load on the treatment of waste filtrates formed during purification operations.
After intensive investigations to achieve the above objects focusing attention on the hydrolysis operation of the polyester with hydrochloric acid among a series of production operations for sorbic acid, the present inventors have found that the by-production of tar can be markedly inhibited by specifying ranges of the concentration of hydrochloric acid and decomposition pressure or decomposition temperature. The present invention has been accomplished based on these findings.
Specifically, the present invention provides, in an aspect, a process for producing sorbic acid. This process includes the step of hydrolyzing a polyester with aqueous hydrochloric acid solution having a concentration of less than or equal to 15% by weight under the application of pressure, which polyester is a reaction product between crotonaldehyde and ketene. In this process, the polyester may be hydrolyzed under the application of pressure (under a load) of equal to or greater than 0.05 MPa.
In another aspect, the present invention provides a process for producing sorbic acid, which process includes the step of hydrolyzing a polyester with aqueous hydrochloric acid solution having a concentration of less than or equal to 15% by weight at a temperature of equal to or higher than 100° C., which polyester is a reaction product between crotonaldehyde and ketene.
In these production processes, the polyester may be hydrolyzed with an aqueous hydrochloric acid having a concentration of from 3 to 10% by weight at a temperature of from 115° C. to 140° C. Additionally, the polyester may be hydrolyzed in such a manner that a molten sorbic acid is dispersed in a reaction mixture without layer separation. A filtrate obtained by solid-liquid separation of a reaction mixture after the hydrolysis of the polyester may be recycled and reused in the hydrolysis reaction of the polyester as part or all of the aqueous hydrochloric acid solution.
The phrase “under the application of pressure” as used herein also includes a condition in which a reaction pressure is increased by hermetically sealing a reaction system and heating the reaction system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A main feature of processes for producing sorbic acid according to the present invention is that a polyester is decomposed in a reaction system under the application of pressure (under a load) or at a temperature of equal to or higher than 100° C. with the use of aqueous hydrochloric acid solution having a relatively low concentration (i.e., a concentration of less than or equal to 15% by weight).
When a reaction is performed at a pressure of less than or equal to normal pressure (atmospheric pressure) at temperatures of lower than 100° C. and the concentration of hydrochloric acid is low, it takes long for the polyester supplied to the reaction system to completely decompose, and sorbic acid formed during the early stage of reaction is converted into tar. In contrast, when the reaction is performed under the application of pressure (under a load) or at a temperature of equal to or higher than 100° C. and the concentration of hydrochloric acid exceeds 15% by weight, the decomposition reaction itself rapidly proceeds but sorbic acid formed by decomposition is also rapidly converted into black tar.
This is probably because hydrochloric acid or free chlorine significantly affects the conversion of sorbic acid into tar and the inhibition of the conversion. Specifically, it is speculated that sorbic acid can only stably exist at predetermined temperatures within an appropriate range of hydrochloric acid concentration, and if the concentration of hydrochloric acid is less than or exceeds the appropriate range, sorbic acid is rapidly converted into tar. If the reaction is performed using water alone in the absence of hydrochloric acid, a 1,4-addition polymer (yellow tar) is formed.
In the conventional decomposition processes using hydrochloric acid, bearing operation at temperatures lower than 100° C. in mind, a concentrated hydrochloric acid is used at an early stage of reaction to thereby rapidly decompose most of the polyester, and an aging operation is then performed by lowering the temperature or decreasing the concentration of hydrochloric acid. These processe
Kamei Noboru
Kouno Mitsuhiro
Mitani Tadayuki
Birch & Stewart Kolasch & Birch, LLP
Daicel Chemical Industries Ltd.
Raymond Richard L.
Tucker Zachary C.
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