Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1998-08-28
1999-12-28
Geist, Gary
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568852, 568854, 568864, C07C 3120
Patent
active
060084189
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for preparing 1,6-hexanediol having a purity of at least 99% which is, in particular, essentially free of 1,4-cyclohexanediols, from a carboxylic acid mixture which is obtained in the oxidation of cyclohexane to cyclohexanone/cyclohexanol using oxygen or oxygen-containing gases by water extraction of the reaction mixture, by esterification of the acids, fractionation of the esterification mixture into an ester fraction free of 1,4-cyclohexanediols and a fraction comprising the 1,4-cyclohexanediols, hydrogenation of the ester fraction and purification of the 1,6-hexanediol by distillation.
1,6-Hexanediol is a sought-after monomer building block which is used predominantly in the polyester and polyurethane sector.
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, 5th Edition, 1987, Vol. A8, p. 2/9) 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 (cis and trans), from 1 to 5% of 1,4-cyclohexanediol (cis and trans), from 2 to 10% by weight of formic acid and also many further monocarboxylic and dicarboxylic acids, oxo and oxa compounds whose individual amounts 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 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% by weight.
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, 1994, page 263). 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.
It is an object of the present invention to develop a novel process in which 1,6-hexanediol can be obtained in high purity, in high yield and with justifiable outlay from DCS.
We have found that this object is achieved by a process for preparing 1,6-hexanediol from a carboxylic acid mixture comprising adipic acid, 6-hydroxycaproic acid and small amounts of 1,4-cyclohexanediols which is obtained as a by-product in the oxidation of cyclohexane to cyc
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Baur Karl Gerhard
Breitscheidel Boris
Fischer Rolf
Pinkos Rolf
Rust Harald
BASF - Aktiengesellschaft
Geist Gary
Vollano Jean F
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