Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-05-18
2002-12-17
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06495717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing sorbic acid or its salt which is useful as, for example, a food additive. Particularly, the invention relates to a process for producing sorbic acid or its salt that has a minimized coloring and a minimized deterioration of hue over time.
2. Description of the Related Art
In various known processes for producing sorbic acid or its salt, a commercially important pathway is a process of polymerizing crotonaldehyde and ketene to form an intermediate polyester, and decomposing the polyester to yield sorbic acid. The polyester is decomposed, for example, by the aid of hydrochloric acid, an alkali or heat to yield a crude sorbic acid. The thus-prepared crude sorbic acid generally contains a variety of colored substances, tar substances, and other impurities with varying degrees of concentration, and is subjected to a purification operation.
As purification processes of sorbic acid or its salt, a treatment with activated carbon, recrystallization with water or with a mixture of water and an organic solvent, and distillation purification of a solution of sorbic acid or its salt in petroleum have been known. For example, Japanese Unexamined Patent Application Publication No. 54-163516 discloses a purification process. This process includes the steps of preparing a polyester from ketene and crotonaldehyde, decomposing the polyester with hydrochloric acid in the presence of, for example, a urea compound to yield a decomposition reaction mixture, separating the decomposition reaction mixture by filtration, and washing the residue to yield a crude sorbic acid, adding a sodium hydroxide aqueous solution to the crude sorbic acid to yield a sodium sorbate aqueous solution, treating the aqueous solution with activated carbon, neutralizing the treated solution, and cooling the neutralized solution to crystallize sorbic acid.
Japanese Examined Patent Application Publication No. 44-26646 discloses a process for producing a crystalline sorbic acid. The process includes the steps of preparing a polyester from ketene and crotonaldehyde, decomposing the polyester with hydrochloric acid having a concentration of 35% by weight or more at temperatures ranging from room temperature to around the boiling point of the hydrochloric acid used, cooling the reaction mixture, separating a crude sorbic acid by filtration, washing the crude sorbic acid with water, putting the washed crude sorbic acid into water, heating and dissolving the mixture to yield a solution, adding activated carbon to the solution, boiling the mixture, and filtering the mixture while heating, and gradually cooling the resulting filtrate to yield a crystalline sorbic acid.
Japanese Examined Patent Application Publication No. 6-27097 discloses a process for preventing the deterioration of sorbic acid. The process includes the steps of retaining a sorbic acid wet cake in an inert gas and holding the oxygen concentration in a system at 10 parts by volume or less. The sorbic acid wet cake is formed in a production process of sorbic acid and contains water and/or a solvent.
A problem of sorbic acid or an alkali sorbate purified according to the above techniques is a tendency to color after drying, which is induced by the formation of new impurities, to thereby deteriorate the commercial value of a resulting product, although no deterioration of appearance as a solid mater or an aqueous solution is observed before drying. In this connection, even if a wet cake of sorbic acid is stored in an inert gas as in the above publication, the degree of coloring of sorbic acid increases with the passage of time after drying, when a color-inducing substance is formed before the storage. Desired advantages according to this technique cannot be significantly obtained.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a process for producing sorbic acid or its salt, which can prevent the formation of a new color-inducing substance in a purification operation of sorbic acid or its salt, where the obtained sorbic acid or its salt has a minimized degree of coloring and a minimized deterioration of hue over time.
The present inventors made intensive investigations to achieve the above object, and found that when a slurry or solution of sorbic acid or its salt in production operations of sorbic acid or its salt is left standing, the hue of a sorbic acid or its salt obtained by separating the slurry or solution is deteriorated with time, and that this deterioration of hue with time can be prevented by holding the slurry or solution of sorbic acid or its salt in an atmosphere at an oxygen concentration under a specific level. The present invention has been accomplished based on these findings.
Specifically, the invention provides a process for producing sorbic acid or its salt. The process includes the step of retaining a slurry or solution containing sorbic acid or its salt while holding an oxygen concentration of a gaseous phase at 4% by volume or less, which gaseous phase is in contact with the slurry or solution containing sorbic acid or its salt.
In the above production process, the oxygen concentration of the gaseous phase may be held at 4% by volume or less while introducing an inert gas into a gaseous phase of a reservoir holding the slurry or solution containing sorbic acid or its salt, or of a conduit adjacent to the reservoir, or of both. Such inert gases include, but are not limited to, a nitrogen gas. The oxygen concentration of the gaseous phase is preferably held at 1% by volume or less.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Slurries or solutions containing sorbic acid or its salt for use in the invented process are not critical and include slurries or solutions obtained by any process. Such slurries or solutions include, but are not limited to, slurries or solutions (particularly aqueous slurries or solutions) at each step in a purification operation of sorbic acid formed by the decomposition of a polyester, which polyester is obtained from ketene and crotonaldehyde, or in a purification operation of an alkali sorbate obtained by allowing an alkali to act upon the sorbic acid.
The reaction of ketene with crotonaldehyde is generally performed in the presence of a catalyst and in the absence of or in the presence of an inert solvent. Such catalysts include, for example, simple substances or compounds of manganese, cobalt, nickel, zinc, cadmium, and other transition metals; and pyridine, picoline, and other nitrogen-containing basic compounds. Examples of the compounds of the transition metals are oxides; salts of acetic acid, salts of isobutyric acid, salts of isovaleric acid, and salts of other organic acids; salts of sulfuric acid, salts of nitric acid, and salts of other inorganic acids; chlorides and other halides; acetylacetone complex salt, and other complex salts and complexes. Each of these catalysts can be used alone or in combination. The amount of the catalyst differs according to the type of the catalyst, but is generally about 0.1 to 10% by weight relative to the weight of ketene. The reaction of ketene with crotonaldehyde is performed at a temperature of, for example, about 2° C. to 100° C.
A reaction mixture containing a polyester obtained through the reaction of ketene with crotonaldehyde is usually distilled to remove unreacted crotonaldehyde and low boiling impurities, and is then subjected to a decomposition reaction. The polyester may be decomposed by any of hydrolysis with an acid or alkali or thermal decomposition, but should be preferably decomposed by hydrolysis with a mineral acid, especially with hydrochloric acid, for a high yield. The polyester is hydrolyzed at a reaction temperature of, for example, about 10° C. to 110° C. An extremely low reaction temperature will result in a deteriorated reaction efficiency, and in contrast, an extremely high reaction temperature may increase amounts of by-produced impurities such as tar substances. When the polyester is hydrolyzed with hydrochloric acid,
Kamei Noboru
Kouno Mitsuhiro
Daicel Chemical Industries Ltd.
Killos Paul J.
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