Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-07-14
2002-10-29
Solola, T. A. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06472540
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the invention
The present invention relates to a process for producing an &egr;-caprolactone which has excellent thermal coloring resistance and polycaprolactone which has low color.
2) Prior Art
&egr;-caprolactone is produced by oxidation of cyclohexanone. An oxidation method which uses an organic peroxyacid as oxidant and a co-oxidation method in which cyclohexanone is oxidized with an aldehyde are known. Peracetic acid or perpropionic acid is used as the organic peroxyacid in the oxidation method and acetaldehyde or benzaldehyde is used as the aldehyde in the co-oxidation method.
&egr;-caprolactone is polymerized and used for foaming materials, polyesterpolyols and biodegradable plastics etc. Improvement of &egr;-caprolactone quality is desired because high quality influences rate of polymerization and color of the product. In particular, purity, acid-value, water-content and thermal coloring resistance influence the color of the polymer and rate of polymerization Japanese Laid-open patent 11-158172 (1999) describes &egr;-caprolactone with less of a low boiling point component and high purity and having lower coloring at the stage of producing or storing of monomer and producing or using of polymers.
However, &egr;-caprolactone which has excellent thermal coloring resistance and polycaprolactone which has low color were not produced using &egr;-caprolactone having fewer low boiling point components and higher purity during co-xidation of cyclohexanone and aldehyde by our study because the low boiling point components in the co-oxidation method are different from those in the oxidation using peroxyacid.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing &egr;-caprolactone which has excellent thermal coloring resistance from co-oxidation of cyclohexanone and aldehyde, and to provide polycaprolactone which has low coloring.
The present inventors assiduously conducted investigations to solve the above problems, and found that (1) a small amount of high boiling point component which influences thermal coloring resistance and is difficult to separate is produced during co-oxidation of cyclohexanone and aldehyde, (2) the high boiling point component which influences thermal coloring resistance becomes possible to separate by introducing oxygen containing gas into the &egr;-caprolactone in the presence of cobalt, (3) &egr;-caprolactone which has excellent thermal coloring resistance is produced by introducing oxygen containing gas therein and removing low boiling point carboxylic acids, to obtain &egr;-caprolactone having acid values of lower than 0.15 mgKOH/g, (4) low color polycaprolactone is produced using this &egr;-caprolactone.
Thus, the present invention provides a process for producing &egr;-caprolactone by co-oxidation of cyclohexanone and an aldehyde to form a reaction mixture containing &egr;-caprolactone, low boiling components, high boiling components and color components, wherein the reaction mixture is subjected to an oxidation treatment with an oxygen containing gas in the presence of cobalt to convert color components to high boiling components and then separating the &egr;-caprolactone from the low and high boiling components, whereby the &egr;-caprolactone recovered has an acid value of less than 0.15 mg KOH/g.
DETAILED DESCRIPTION OF THE INVENTION
The aliphatic aldehyde used in the co-oxidation method may be acetaldehyde, propionaldehyde or butyraldehyde. The aromatic aldehyde generally used in the co-oxidation method may be benzaldehyde, tolualdehyde, dimethylbenzaldehyde, trimethylbenzaldehyde, ethylbenzaldehyde, cuminaldehyde, butylbenzaldehyde, methoxybenzaldehyde, phenoxybenzaldehyde, cyclohexylbenzaldehyde and biphenylaldehyde. When these aliphatic aldehydes or aromatic aldehydes possess isomeric forms, each isomer or the mixture thereof may be used.
Purified &egr;-caprolactone is produced by removing impurities from the reaction products of co-oxidation. When acetaldehyde is used as the aliphatic aldehyde, the reaction mixture contains &egr;-caprolactone, unreacted cyclohexanone, acetic acid, acetaldehyde, adipic acid, caprolactone oligomer, caprolactone polymer and oxycaproic acid etc. When 2,4-dimethylbenzaldehyde is used as the aromatic aldehyde, the reaction mixture contains &egr;-caprolactone, unreacted cyclohexanone, 2,4-dimethylbenzoic acid, 2,4-dimethylbenzaldehyde, adipic acid, caprolactone oligomer, caprolactone polymer and oxycaproic acid etc.
When acetaldehyde is used as the aliphatic aldehyde in distillation purification of the reaction mixture, the high boiling point component of by-product such as adipic acid) caprolactone oligomer, caprolactone polymer and oxycaproic acid is removed at first, then the low boiling point component such as unreacted cyclohexanone, acetic acid and acetaldehyde is removed. When 2,4-dimethylbenzaldehyde is used as the aldehyde, unreacted cyclohexanone (boiling point 155.6° C.) is separated at first, then the high boiling point component of 2,4-dimethylbenzoic acid (boiling point 267° C.), 2,4-dimethylbenzaldehyde (boiling point 225° C.) is removed. used as the aldehyde, unreacted cyclohexanone (boiling point 155.6° C.) is separated at first, then the high boiling point component of 2,4-dimethylbenzoic acid (boiling point 267° C.), 2,4-dimethylbenzaldehyde (boiling point 225° C.) is removed.
In the present invention, the reaction mixture from the oxidation product of cyclohexanone is purified by the above method. Then, the remaining high boiling point component is removed by distillation The &egr;-caprolactone thus obtained is purified by introducing oxygen containing gas in the presence of cobalt (which is referred as “oxidation treatment”), then changing the color component to a high boiling point component and removing a small amount of low boiling point acids by distillation to obtain the &egr;-caprolactone product (boiling point 235.3° C.).
These methods of distillation purification are performed by known methods at as low a temperature and as low a pressure as possible to avoid change in quality during distillation.
In the present invention, the temperature of the oxygen containing gas introduced to the &egr;-caprolactone separated by distillation, is in the range of 80-200° C., and preferably 100-180° C. . When the temperature is too low, a long time is required to change the color component, which is difficult to separate from &egr;-caprolactone, to a high boiling point component. When the temperature is too high, &egr;-caprolactone may be polymerized and may produce low boiling point aliphtic acids and increase the acid value.
In the present invention, the color component is changed to a high boiling point component by contacting &egr;-caprolactone with oxygen containing gas in the presence of cobalt. Decomposition of &egr;-caprolactone and generation of low boiling point carboxylic acid are restrained to decrease the acid value in the presence of cobalt.
Cobalt compounds which are soluble in &egr;-caprolactone such as cobalt naphtate or cobalt octylate are used in the oxidation treatment. The amount of cobalt added to &egr;-caprolactone is 0.001-10 ppm by weight, and preferably 0.01-5 ppm by weight. When the cobalt content is too low, decomposition of &egr;-caprolactone and generation of low boiling point carboxylic acids are increased which decreases the acid value, and colored polycaprolactone is produced when &egr;-caprolactone thus oxidation treated is polymerized. When cobalt content is too high, &egr;-caprolactone is apt to polymerize spontaneously.
Generally, air is used for the oxygen containing gas and the pressure of the reaction is from one atmosphere to 10 kg/cm2. Oxygen containing gas is introduced continuously and &egr;-caprolactone accompanied by vent gas is recovered by condensation. The pressure of oxygen introduced to the &egr;-caprolactone is 0.0002-1.0 kg/cm2, and preferably 0.0005-0.1 kg/cm2. Oxygen pressure in the contacting tank is calculated from the concentration of oxygen in vent gas from
Ogawa Hiroshi
Okoshi Atsushi
Tanaka Kazuo
Mitsubishi Gas Chemical Company Inc.
Solola T. A.
Wenderoth Lind & Ponack LLP
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