Process for preparing 1,6- hexanediol and caprolactone

Details Process for preparing 1,6- hexanediol and caprolactone Process for preparing 1,6- hexanediol and caprolactone

1998-08-28

1999-11-09

Owens, Amelia

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549272, 568864, C07D31300

Patent

active

059817690

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention relates to a process for preparing 1,6-hexanediol and caprolactone, preferably in a purity of at least 99%, which are, in particular, virtually free of 1,4-cyclohexanediols, from a carboxylic acid mixture which is obtained as a by-product of the oxidation of cyclohexane to cyclohexanone/cyclohexanol using oxygen or oxygen-containing gases and by water extraction of the reaction mixture, by esterification and hydrogenation of a substream to give hexanediol and cyclization of 6-hydroxycaproic esters, with the 1,4-cyclohexanediols either being separated off in the fractionation of the esterification mixture or finally from the caprolactone. According to a modification of the process of the invention, the hydrogenation is omitted and adipic diester which can be passed on to immediate use, e.g. as lubricant, is isolated.
1,6-Hexanediol is a desired monomer building block which is used predominantly in the polyester and polyurethane sector. Caprolactone or the polycaprolactones prepared therefrom by polyaddition are used for the preparation of polyurethanes.
The aqueous solutions of carboxylic acids which are formed in the oxidation of cyclohexane to cyclohexanol and cyclohexanone (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5. Ed., 1987, Vol. A8, p. 49) as by-products, hereinafter referred to as dicarboxylic acid solution (DCS), generally comprise (calculated in % by weight on an anhydrous basis) from 10 to 40% of adipic acid, from 10 to 40% of 6-hydroxycaproic acid, from 1 to 10% of glutaric acid, from 1 to 10% of 5-hydroxyvaleric acid, from 1 to 5% of 1,2-cyclohexanediols, from 1 to 5% of 1,4-cyclohexanediols, from 2 to 10% of formic acid and also many further mono-carboxylic and dicarboxylic acids, esters, oxo- and oxa compounds whose individual contents generally do not exceed 5%. Examples which may be mentioned are acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, 4-hydroxybutyric acid and .gamma.-butyrolactone.
DE 2 321 101 and DE 1 235 879 disclose the hydrogenation of these aqueous dicarboxylic acid solutions at from 120 to 300.degree. C. and pressures of from 50 to 700 bar in the presence of catalysts comprising predominantly cobalt to give 1,6-hexanediol as main product. The hydrogenation products are preferably worked up by distillation. Even with an extremely high distillation efficiency, this work-up succeeds only incompletely, if at all, in separating the 1,4-cyclohexanediols which are unchanged in the hydrogenation from 1,6-hexanediol, so that the 1,4-cyclohexanediols which were initially present in the DCS are still present in the 1,6-hexanediol in a concentration of generally from 2 to 5%.
To counter this problem, some starting points for solutions are known:
U.S. Pat. No. 3,933,930 describes the conversion of 1,4-cyclohexanediol in aqueous solutions of adipic acid and 6-hydroxycaproic acid into cyclohexanol, cyclohexane and/or cyclohexene by catalytically prehydrogenating the mixture. This process requires the use of two different hydrogenation catalysts, one for the prehydrogenation and one for the actual carboxylic acid hydrogenation and is therefore complicated.
In DE-A 2 060 548, very pure 1,6-hexanediol is obtained by crystallization. This process too is very complicated and is also associated with considerable yield losses.
A further possible way of obtaining highly pure 1,6-hexanediol is to hydrogenate pure adipic acid or pure adipic esters in place of DCS (K. Weissermel, H. J. Arpe, Industrielle organische Chemie, VCH-Verlagsgemeinschaft Weinheim, 4th edition, page 263, 1994). However, pure adipic acid is very expensive in comparison with DCS. In addition, the carboxylic acid mixture obtained in the oxidation of cyclohexane is a waste product which should be utilized in terms of the materials present, for environmental reasons too.
Caprolactone has long been prepared industrially exclusively from cyclohexanone by the Baeyer-villiger oxidation. In this process, explosive per compoun

REFERENCES:
patent: 3933930 (1976-01-01), Dougherty et al.
patent: 5536888 (1996-07-01), Shiomi et al.
Ullmann's Encyclopedia of Industrial Chemistry, vol. A8, Coronary therapeutics to Display Technology, 48-52 1987.
Industrielle Organische Chemie, Weissermel et al., 261-265 Apr. 1994.

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