Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-05-26
2002-10-08
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06462233
ABSTRACT:
1. Technical Field
The present invention relates to a process for producing sorbic acid which is useful as, for example, food additives. Specifically, the invention relates to a process which is capable of efficiently removing by-produced tar substances and other impurities to produce a highly purified sorbic acid in the production of sorbic acid through the decomposition of a polyester obtained as a polymerized product of crotonaldehyde and ketene.
2. Background Art
Sorbic acid and its salts have antiseptic and antimicrobial activities and are substantially nontoxic to the human body in normal concentrations in use. These compounds are therefore useful as food additives. In 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, and decomposing the polyester to yield sorbic acid. The polyester is decomposed, for example, by thermal decomposition or by hydrolysis in the coexistence of an alkali or acid catalyst. Of these techniques, hydrolysis with a mineral acid, particularly with hydrochloric acid is preferred, as the resulting sorbic acid has a satisfactory yield and quality.
However, according to any of these techniques, by-products are formed during a decomposition reaction and contaminate sorbic acid as impurities and cause coloring of products to thereby deteriorate the quality of products. An extra purification process is therefore required to remove the impurities. This problem also resides in hydrolysis with a mineral acid which is believed to yield relatively satisfactory decomposition results. Specifically, the problem is inevitable even if any other operation condition is added, as far as sorbic acid is prepared by the decomposition of a polyester. Demands have been therefore made to provide a purification process which is capable of efficiently removing by-produced impurities, and various attempts have been made. Generally, a combinationuse of two or more different operations can yield a more highly purified sorbic acid, but most of tar substances having a brown to dark brown color must be removed in a first stage purification operation.
A process is known which includes the steps of decomposing the polyester to yield a wet cake of crude sorbic acid, dissolving the wet cake in a hot water, removing tar portions not dissolved in the hot water by separation, and removing tar portions dissolved in the hot water by treatment with activated carbon. This process requires no special solvent and is advantageous to easily remove large amounts of tar substances. However, the solubility of sorbic acid is at most about 3% even to a hot water around 100° C., and the process requires large-sized facilities to treat large amounts of crude sorbic acid and is disadvantageous in production efficiency.
DISCLOSURE OF INVENTION
Accordingly, an object of the invention is to provide a process which is capable of easily and efficiently removing tar substances and other impurities by-produced in the decomposition of the polyester and is capable of producing a highly purified sorbic acid with a satisfactory productivity.
The present inventors made intensive investigations to achieve the above object and found that tar substances can be efficiently removed by extracting a crude sorbic acid with a hot water at a temperature exceeding 100° C. or treating the crude sorbic acid with activated carbon in a hot water at a temperature exceeding 100° C. This utilizes the fact that the solubility of sorbic acid sharply increases to a hot water having a temperature exceeding 100° C. The present invention has been accomplished based on these findings.
Specifically, the invention provides a process for producing sorbic acid. The process includes the steps of adding a crude sorbic acid to a hot water at a temperature exceeding 100° C., which crude sorbic acid is obtained by the decomposition of a polyester prepared by a reaction of ketene with crotonaldehyde, and performing at least one treatment selected from (A) a hot water extraction treatment for extracting sorbic acid with the hot water, and (B) a treatment with an activated carbon in the hot water. The temperature of the hot water may be, for example, 120° C. or lower. The amount of sorbic acid to be treated may be, for example, equal to or less than the saturated dissolution amount of sorbic acid with respect to the hot water at temperatures to treat the sorbic acid.
BEST MODE FOR CARRYING OUT THE INVENTION
The embodiments of the invention will be described in detail below. According to the invention, a polyester is decomposed to yield sorbic acid. The polyester is obtained by subjecting crotonaldehyde and ketene to a polymerization reaction. Specifically, the polyester is synthetically obtained by blowing ketene into crotonaldehyde in the presence of a catalyst such as zinc acetate, zinc isobutyrate, or &agr;-picoline at temperatures of, for example, about 20° C. to 100° C. Generally, a reaction mixture is distilled to remove excess crotonaldehyde and is then subjected to a decomposition reaction.
The polyester may be decomposed by hydrolysis with an acid or an alkali or by thermal decomposition, but is preferably decomposed by hydrolysis with a mineral acid, particularly with hydrochloric acid, for a higher yield. The polyester is hydrolyzed, for example, at temperatures ranging from about 10° C. to 110° C. When the polyester is hydrolyzed with hydrochloric acid, the concentration of hydrochloric acid is, for example, about 15 to 40% by weight, and preferably about 23 to 36% by weight.
A reaction mixture obtained through the decomposition of the polyester contains tar substances and other impurities by-produced in the reaction, in addition to the sorbic acid and the catalyst used. The production of a high quality sorbic acid therefore requires a purification process.
The invention has a main feature of including the steps of adding sorbic acid obtained through the decomposition of the polyester into a hot water at a temperature exceeding 100° C. and performing at least one treatment selected from (A) a hot water extraction treatment for extracting sorbic acid with the hot water, and (B) a treatment with an activated carbon in the hot water. As the treating temperature is higher than 100° C., these treatments are usually performed under pressure.
In the hot water extraction treatment (A) , the crude sorbic acid is sufficiently mixed with the hot water by, for example, stirring, and the resulting mixture is allowed to stand to separate the mixture to an aqueous layer containing sorbic acid and to an organic layer containing by-produced tar substances and other impurities which are not dissolved in the hot water. Thus, sorbic acid can be separated from tar substances and other impurities. In the activated carbon treatment (B), tar substances and other impurities dissolved in the hot water are adsorbed on an activated carbon, and the mixture is filtrated to remove the activated carbon to yield a highly purified sorbic acid.
These treatments (A) and (B) can be performed at any point of time during the purification process of sorbic acid subsequent to the polyester decomposition process. For example, when the polyester is hydrolyzed in the presence of an acid, the reaction mixture is generally a slurry containing sorbic acid dispersed in water, and the reaction mixture slurry is subjected to solid-liquid separation such as suction filtration or filtration under pressure. The resulting crude sorbic acid wet cake is added to a hot water and is then subjected to the above treatments. The crude sorbic acid wet cake contains tar substances and generally has a brown to dark brown color.
In the hot water extraction treatment (A) and/or the activated carbon treatment (B), if the temperature of the hot water is equal to or lower than 100° C., the solubility of sorbic acid is low and thereby the facilities must be large-sized to thereby markedly deteriorate the production efficiency of sorbic acid. If the amount of the crude sorbic acid t
Kouno Mitsuhiro
Yamashita Akira
Chaudhry Mahreen
Daicel Chemical Industries Ltd.
Killos Paul J.
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