Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-05-26
2003-07-08
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C560S182000, C560S210000, C560S211000
Reexamination Certificate
active
06590122
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing sorbic acid which is useful as food additives, and to a process for producing a polyester which is useful for the production of the sorbic acid.
BACKGROUND ART
As processes for the commercial production of sorbic acid, a process of reacting ketene with crotonaldehyde to yield a polyester and hydrolyzing the polyester in the presence of an acid or an alkali, and a process of decomposing the polyester by heat are known. For example, Japanese Examined Patent Application Publication No. 44-26646 discloses a process for producing sorbic acid. The process includes the steps of reacting ketene with crotonaldehyde in the presence of a catalyst to yield a reaction mixture, heating the reaction mixture under reduced pressure to remove unreacted crotonaldehyde and by-products of the reaction by distillation, thereby preparing a polyester containing the catalyst, decomposing the polyester with hydrochloric acid, and cooling the reaction mixture to yield sorbic acid.
A crude sorbic acid obtained by the decomposition of the polyester generally contains various colored substances and other impurities and is subjected to purification operations such as treatment with active carbon, distillation or recrystallization. The more the colored substances and other impurities are, the higher loads on the purification operation are and the more the loss of sorbic acid is.
Japanese Unexamined Patent Application Publication No. 54-163516 discloses a process of decomposing the polyester in the presence of a urea compound or the like to inhibit the formation of colored substances in the decomposition reaction of the polyester. Japanese Unexamined Patent Application Publication No. 9-227447 discloses a process of decomposing the polyester in stages and in a specific temperature range to obtain a sorbic acid which contains minimized tar content and is easily purified. However, these processes are not always commercially satisfactory, from the viewpoints of inhibitory effects of the by-production of colored substances and other impurities, the yield of sorbic acid, ease of operation, and costs.
DISCLOSURE OF INVENTION
Accordingly, an object of the invention is to provide a process for efficiently producing a sorbic acid having a satisfactory hue.
To achieve the above object, the present inventors made intensive investigations on a synthesis process of the polyester among a series of production processes of sorbic acid. As a result, they found that aldehydes and other impurities, especially high boiling impurities, contained in crotonaldehyde for use as a material of the synthesis of polyester decrease the yield of the polyester and deteriorate the hue and yield of the sorbic acid in the decomposition process of the polyester. This is probably because such impurities react with ketene. The inventors also found that the hue and yield of a crude sorbic acid obtained in the polyester decomposition process can be therefore markedly improved by setting the purity of crotonaldehyde to be supplied to a reaction system in the polyester decomposition process at a constant level or higher. The present invention has been accomplished based on these findings.
Specifically, the invention provides in an aspect a process for producing a polyester through a reaction of ketene with crotonaldehyde to yield a corresponding polyester. In the process, a crotonaldehyde with a purity of 95% by weight or more is supplied to a reaction system.
In another aspect, the invention provides a process for producing sorbic acid. This process includes the step of decomposing a polyester obtained by the aforementioned production process.
BEST MODE FOR CARRYING OUT THE INVENTION
According to the invention, ketene is reacted with crotonaldehyde to yield a polyester. The polyester is generally shown by the following formula (1):
In the above formula, R is an acetoxy group or a hydroxyl group, and n denotes an integer of 2 or more (e.g., about 3 to 40).
The invention has a main feature in that a material crotonaldehyde to be supplied to the reaction system is to have a purity of 95% by weight or more in the polyester synthesis process, by which the polyester is prepared from ketene and crotonaldehyde. When unreacted crotonaldehyde is recovered from a reaction mixture derived from ketene and crotonaldehyde and the recovered crotonaldehyde is recycled to the reaction system, the purity of the overall crotonaldehyde to be supplied including the recovered crotonaldehyde and a crotonaldehyde newly supplied to the reaction system (hereinafter referred to as “fresh crotonaldehyde”) is set at 95% by weight.
The purity of the material crotonaldehyde is preferably 97% by weight or more, more preferably 98% by weight or more, and particularly preferably 99% by weight or more.
As the fresh crotonaldehyde to be supplied to the reaction system, crotonaldehyde obtained by any production process can be used, such as crotonaldehyde obtained by the condensation of acetaldehyde, and crotonaldehyde obtained by allowing water to act on vinyl bromide in a concentrated sulfuric acid. For example, a commercially available high purity crotonaldehyde (e.g., crotonaldehyde with a purity of about 99.8% containing about 0.13% by weight of &agr;-vinylcrotonaldehyde) can be advantageously employed. An industrially obtained crotonaldehyde generally contains various impurities according to its production process. Such impurities include, for example, acetaldehyde, &agr;-vinylcrotonaldehyde, 2,4-hexadienal, and other aldehydes, 1,3-butadien-1-ol acetate, and acetone.
To improve the utilization ratio of the crotonaldehyde, crotonaldehyde should be preferably recovered from a reaction mixture derived from ketene and crotonaldehyde and be recycled to the reaction system. The recovered crotonaldehyde often contains, as impurities, paraldehyde which is by-produced in the reaction of ketene with crotonaldehyde, in addition to the &agr;-vinylcrotonaldehyde.
The present inventors made detailed investigations on the relation of impurities contained in the crotonaldehyde to be supplied to the reaction system with the yield of the produced polyester and the hue and yield of the sorbic acid obtained by the decomposition of the polyester. They found that, of these impurities, &agr;-vinylcrotonaldehyde, paraldehyde, and other aldehydes particularly decrease the yield of the polyester and deteriorate the hue and yield of the sorbic acid. The aldehydes are supposed to be converted into colored substances in the polyester synthesis process and/or polyester decomposition process.
In the polyester synthesis process, the overall crotonaldehyde to be supplied to the reaction system should have an &agr;-vinylcrotonaldehyde content of preferably less than 0.5% by weight, and more preferably less than 0.45% by weight. The overall crotonaldehyde to be supplied to the reaction system should have a paraldehyde content of preferably less than 5% by weight, more preferably less than 2% by weight, and particularly less than 0.5% by weight.
When the fresh crotonaldehyde to be supplied to the reaction system has a purity of less than 95% by weight or when the recovered crotonaldehyde is recycled to the reaction system and the overall crotonaldehyde to be supplied to the reaction system has a purity less than 95% by weight, the crotonaldehyde can be purified by, for example, distillation and other purification means to a purity of 95% by weight or more prior to supplying to the reaction system. The purification by distillation can be performed by a step for removing low boiling impurities and/or a step for removing high boiling impurities. Particularly, the combination use of a step for removing low boiling impurities and a step for removing high boiling impurities is preferred. The purity and the impurity content of the crotonaldehyde can be controlled by appropriately selecting the theoretical plate number and the reflux ratio of a distillation column.
The reaction between ketene and crotonaldehyde is generally performed in the presence
Kamei Noboru
Kouno Mitsuhiro
Yamashita Akira
Daicel Chemical Industries Ltd.
Killos Paul J.
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