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Preparation of Diols

IP.com Disclosure Number: IPCOM000235807D
Publication Date: 2014-Mar-25
Document File: 17 page(s) / 89K

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Abstract

Preparation of 1,6-hexanediol (1,6-HDO) from a carboxylic acid mixture obtained as a by-product of the catalytic or noncatalytic oxidation of cyclohexane to cyclohexanone/cyclohexanol with oxygen or oxygen-comprising gases and by water extraction of the reaction mixture or by neutralization of the by-products with bases, subsequent extraction and acidification of the salts with acids, by hydrogenating the carboxylic acids to 1,6-HDO.

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Page 01 of 17

Methods for preparation of diols

The present description relates to methods for preparation of 1,6-hexanediol (1,6-HDO) from a carboxylic acid mixture which is obtained as a by-product of the catalytic or noncatalytic oxidation of cyclohexane to cyclohexanone/cyclohexanol with oxygen or oxygen-comprising gases and by water extraction of the reaction mixture or by neutralization of the by-products with bases, subsequent extraction and acidification of the salts with acids, by hydrogenating the carboxylic acids to 1,6-HDO.

The starting material used is a dicarboxylic acid solution (DCS) formed as a by-product by the following steps:
- oxidation of cyclohexane with oxygen or oxygen-comprising gases to give mixtures of cyclohexanol, cyclohexanone and carboxylic acids having one to six carbon atoms and
- aqueous extraction of the above-described oxidation output and removal of the organic phase.

The DCS is an aqueous mixture of monocarboxylic acids comprising 1 to 7 carbon atoms, dicarboxylic acids comprising 2 to 7 carbon atoms, monoalcohols comprising 1 to 7 carbon atoms, or diols and/or esters thereof. The DCS comprises, in particular, 6-hydroxycaproic acid and adipic acid, which can lead to 1,6-hexanediol (1,6-HDO), and 5-hydroxyvaleric acid and glutaric acid, which can lead to 1,5-pentanediol (1,5-PDO). The DCS typically has the following composition, although the list does not show all the components:
water

5-95% by wt.

adipic acid

6-hydroxycaproic acid

pimelic acid

6-oxocaproic acid

5-oxocaproic acid

2-hydroxyadipic acid
3-hydroxyadipic acid
2-(5-oxotetrahydrofuran-2-yl)acetic acid 0.01 - 3% by wt. hex-2-enedioic acid
hex-3-enedioic acid
glutaric acid

5-hydroxyvaleric acid

5-oxovaleric acid

1-60% by wt.

1-60% by wt.

0-1% by wt.


0.01-5% by wt.


0.01-3% by wt.

1-6% by wt.

1-6% by wt.


Page 02 of 17

4-oxovaleric acid succinic acid

0-2% by wt.

formic acid


0.1-3% by wt.

acetic acid


0.05-0.5% by wt.

propionic acid


0.05-0.5% by wt.

butyric acid


0.05-0.6% by wt.

valeric acid


0.05-0.6% by wt.

caproic acid


0.05-0.1% by wt.

cyclohexanol


0.1-0.4% by wt.

cyclohexanone


0.05-0.2% by wt.

1,2-cyclohexanediol


0.05-5% by wt. (cis/trans mixture)

1,4-cyclohexanediol


0.05-5% by wt. (cis/trans mixture)

4-hydroxycyclohexanone


0.05-0.5% by wt.

cyclohexanedione

                              0.05-0.5% by wt. aromatics (e.g. phenol or benzene) < 0.1% by wt.

The DCS may also include peroxides (for example cyclohexane hydroperoxide) which have formed during the oxidation of cyclohexane. Peroxides are reactive and high-energy compounds which can constitute safety problems in the chemical conversion of the DCS or can favor the formation of unwanted by-products. It may therefore be advantageous to break down the peroxides before the DCS is used. Peroxides are unstable molecules which break down when heated. Therefore, the DCS can be treated thermally, preferably at temperatures of > 70°C. This can be effected in a heated stirred tank, or continuously in a heated pipeline. Since the thermal break...