Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-11-15
2001-09-11
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S852000, C568S853000, C568S854000
Reexamination Certificate
active
06288286
ABSTRACT:
DESCRIPTION
The present invention relates to a process for preparing 1,6-hexanediol from a carboxylic acid mixture obtained in the oxidation of cyclohexane to cyclohexanone/cyclohexanol with oxygen and by aqueous extraction of the reaction mixture and comprising adipic acid and 6-hydroxycaproic acid by esterification of the acids and hydrogenation, by using a carboxylic acid mixture comprising cobalt and phosphate as impurities and passing this mixture through a cation exchanger to remove these impurities and then passing the esterification mixture through an anion exchanger.
WO 97/31882 discloses a process for preparing 1,6-hexanediol from aqueous solutions of carboxylic acids obtained in the oxidation of cyclohexane to cyclohexanone/cyclohexanol with oxygen and aqueous extraction by
a) reacting the mono- and dicarboxylic acids in the aqueous dicarboxylic acid mixture with a low molecular weight alcohol to form the corresponding carboxylic esters,
b) conducting a first distillation to remove excess alcohol and low boilers from the esterification mixture obtained,
c) conducting a second distillation to separate the bottom product into an ester fraction which is essentially free from 1,4-cyclohexanediols and a fraction which includes at least the larger proportion of the 1,4-cyclohexanediols,
d) subjecting the ester fraction essentially free from 1,4-cyclohexanediols to a catalytic hydrogenation, and
e) subjecting the hydrogenation effluent to a distillation to recover 1,6-hexanediol in a conventional manner.
It has now been found that aqueous carboxylic acid mixtures comprising cobalt in the form of Co
2+
and/or Co
3+
ions in amounts of, for example, 20 to 300 ppm and phosphate in amounts of, for example, 40 to 1500 ppm as impurities from the oxidation are not directly suitable for the process of WO 97/31882.
It is an object of the present invention to provide a process for removing the aforementioned impurities from the feed solution in a simple and economical manner.
We have found that this object is achieved according to the invention by a process for preparing 1,6-hexanediol from a carboxylic acid mixture obtained as by-product in the oxidation of cyclohexane to cyclohexanone/cyclohexanol with oxygen or oxygen-comprising gases and by aqueous extraction of the reaction mixture and comprising adipic acid, 6-hydroxycaproic acid and small amounts of 1,4-cyclohexanediols by esterification of the acids and hydrogenation, by
a) reacting the mono- and dicarboxylic acids in the aqueous dicarboxylic acid mixture with a low molecular weight alcohol to form the corresponding carboxylic esters,
b) conducting a first distillation to remove excess alcohol and low boilers from the esterification mixture obtained,
c) conducting a second distillation to separate the bottom product into an ester fraction which is essentially free from 1,4-cyclohexanediols and a fraction which includes at least the larger proportion of the 1,4-cyclohexanediols,
d) subjecting the ester fraction essentially free from 1,4-cyclohexanediols to a catalytic hydrogenation, and
e) subjecting the hydrogenation effluent to a distillation to recover 1,6-hexanediol in a conventional manner, the invention comprising using an aqueous dicarboxylic acid mixture comprising more than 20 ppm of cobalt and more than 40 ppm of phosphorus in the form of phosphate and passing this aqueous dicarboxylic acid mixture through a cation exchanger and after the esterification of step (a) through an anion exchanger.
Although the use of ion exchangers to remove cations or anions is common prior art, the process of the invention is surprising because of the absence of undesirable reactions during the dewatering between the cation exchanger and the anion exchanger. The acidic cation exchanger converts phosphate into phosphoric acid, so that the distillative dewatering of the carboxylic acid solution treated with the cation exchanger was likely to give rise to acid-catalyzed reactions of 6-hydroxycaproic acid, such as elimination of the hydroxyl group or polyester formation. However, neither is the case. In fact, the phosphoric acid formed even has the advantage of acting as esterification catalyst, making it possible to reduce the amount of sulfuric acid which is added as esterification catalyst.
Aside from the treatment of the aqueous carboxylic acid mixture with the cation exchanger and the treatment of the esterification reaction mixture with the anion exchanger, the process of the invention is described in all details in WO 97/31882, incorporated herein by reference. Any statement made therein shall also apply here without any restriction whatsoever.
REFERENCES:
patent: 3551300 (1970-12-01), Longley
patent: 4482764 (1984-11-01), Herrmann
patent: 28 19 593 (1979-11-01), None
patent: 195 14930 (1996-10-01), None
patent: 97/31883 (1997-09-01), None
patent: 97/31182 (1997-09-01), None
patent: WO97/31882 (1997-09-01), None
Houben-Weyl, Methoden der Organischen Chem. vol. IV/1c 1980, pp. 16-26 and 45-67.*
Houben-Weyl, Methoden der Organischen Chem. vol. IV/1c Georg Thieme Verlag 1980, p. 45-67 & 16-26.
Gall Martin
Iffland Gabriele
Krug Thomas
Stein Frank
Barts Samuel
BASF - Aktiengesellschaft
Keil & Weinkauf
Price Elvis O.
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