Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1997-07-01
1998-06-16
Rotman, Alan L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568868, 568872, C07C 3118, C07C 2726, C07C 2974
Patent
active
057673292
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GP96/00023, filed Jan. 4, 1996.
The present invention relates to a process for the preparation of 1,6-hexanediol of high purity. The present invention relates in particular to a process which permits the separation of cyclic hexanediols, such as 1,4-dihydroxycyclohexane, and cyclic hydroxyketones, such as 4-hydroxycyclohexanone, from solutions which contain 1,6-hexanediol or 1,6-hexanediol precursors, such as adipic acid, 6-hydroxycaproic acid and/or other stripper acids (stripper acids are understood very generally as meaning mixtures of mono- and dicarboxylic acids).
It is known that 1,6-hexanediol, a diol widely used as a monomer component for polyesters, can be produced industrially by hydrogenation of adipic acid and/or 6-hydroxycaproic acid and subsequent distillation of the Chemie, 4th Edition, Vol. 7, page 228 et seq. (1974)!.
Aqueous solutions consisting of adipic acid, 6-hydroxycaproic acid and/or many other mono- and dicarboxylic acids, ie. stripper acids, are formed, for example, as a coupling product in the oxidation of cyclohexane to cyclohexanol/cyclohexanone mixtures and in the subsequent working up of the oxidation product. Such solutions contain from 10 to 50% by weight of adipic acid and 6-hydroxycaproic acid and about 0.1-3% by weight of cyclohexanediols and hydroxycyclohexanones. These cyclic diols are relatively stable to hydrogenation and therefore are substantially retained even after the hydrogenation of the abovementioned acids to 1,6-hexanediol, whereas the hydroxycyclohexanones are hydrogenated to cyclohexanediols. These cyclohexanediols are very difficult to separate from 1,6-hexanediol, even by distillation.
A possible method for removing these cyclic diols from the abovementioned solutions, for example solutions containing adipic acid, is described in U.S. Pat. No. 3,933,930. According to this, the oxidation of cyclohexane is followed by a catalytic prehydrogenation step, so that 1,4-dihydroxycyclohexane (formed in the oxidation of cyclohexane) is converted into cyclohexanol, cyclohexane and/or cyclohexene without substantial hydrogenation of, for example, adipic acid and 6-hydroxy-hexanoic acid. However, this prehydrogenation step requires the use of a hydrogenation catalyst which differs from the hydrogenation catalyst for the actual reduction, ie. for the reduction of the adipic acid and of the 6-hydroxyhexanoic acid to 1,6-hexanediol. The prehydrogenation is carried out in the presence of molecular hydrogen under high pressures (300 atm), making the total reaction even more expensive.
DE-A-20 60 548 describes a process for the purification of 1,6-hexanediol which contains small amounts of other diols by crystallization. The hexanediol purity thus achieved is stated there as 99.8%. Although this process gives very pure 1,6-hexanediol, it is disadvantageous in that it requires very high capital costs.
It is an object of the present invention to provide a process by means of which undesirable cyclic hexanediols which are difficult to separate off can be separated selectively, without expensive apparatus and relatively cheaply from solutions which either already contain 1,6-hexanediol or its precursors.
We have found that this object is achieved, according to the invention, by a simplified process as defined in claim 1. A preferred process is one in which added or heated to 300.degree. C. without the addition of a hydrogenation catalyst and without hydrogen. This makes it possible to remove the undesirable cyclic hexanediols from solutions (a) and (b) without a hydrogenation catalyst and hydrogen being required, as in U.S. Pat. No. 3,933,930. Accordingly, the cost of the apparatus required and consequently the costs for the preparation of purified 1,6-hexanediol are reduced.
Further preferred features or embodiments of the invention are evident from the following description and from the Examples.
As stated above, aqueous wash solutions--ie. stripper acids--which contain in particular adipic acid and 6-hydroxycaproic acid (altogether from abou
REFERENCES:
patent: 3524892 (1970-08-01), Horlenko
patent: 3933930 (1976-01-01), Dougherty
patent: 5659092 (1997-08-01), McNabb
WPIDS abstract of EP 790266, 1997.
WPIDS abstract of JP 09100335, 1997.
Chemical Abstract 102:132936, abstract of DE 3320260, 1984.
WPIDS abstract of DE 2060548, 1979.
Dostalek Roman
Fischer Rolf
Harder Wolfgang
Paul Axel
Pinkos Rolf
BASF - Aktiengesellschaft
M. Mach D. Margaret
Rotman Alan L.
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