Process for the distillation of alcohols

Details Process for the distillation of alcohols Process for the distillation of alcohols

1997-08-22

2000-09-12

Manoharan, Virginia

Distillation: processes, separatory

With chemical reaction

Including step of adding catalyst or reacting material

568913, 568921, B01D 334, C07C 2728

Patent

active

061172774

DESCRIPTION:

BRIEF SUMMARY
This application is the National Phase of international application PCT/EP96/00633, which has an international filing date of Feb. 14, 1996.
Aliphatic C.sub.3 -C.sub.10 -alcohols, such as n-butanol and, in particular, 2-ethylhexanol, have a high economic importance. These alcohols are preferably prepared by hydroformylation of olefins with subsequent hydrogenation of the aldehydes formed as intermediates (example: propylene.fwdarw.n/i-butyraldehyde.fwdarw.n/i-butanols) or by aldolization of straight-chain aliphatic aldehydes to give the corresponding unsaturated aldehydes and subsequent hydrogenation (example: n-butyraldehyde.fwdarw.2-ethylhexenal.fwdarw.2-ethylhexanol). Summary descriptions are found in, e.g., Ullmann's Encyclopedia of Industrial Chemistry: "Alcohols, Aliphatic" (Vol. A 1), "2-Ethylhexanol" (Vol. A 10) and "Butanols" (Vol. A 4).
Apart from as a solvent, n-butanol is principally used in the paints and coatings sector and for the preparation of carboxylic esters, in particular n-butyl acrylate and di-n-butyl phthalate (DBP).
2-Ethylhexanol is principally required as the alcohol component for the preparation of di-2-ethylhexyl phthalate (DEHP) and 2-ethylhexyl acrylate.
For these fields of application--in particular the preparation of acrylic ester--the use of high-purity alcohols is absolutely necessary. In the industrial preparation of the alcohols, the purification is exclusively performed by multistage fractional distillation. The alcohols in this case are exposed to a thermal stress over a period of several hours, bottom temperatures of 150 to 200.degree. C. being generally employed. As a consequence thereof, in the distillation of aliphatic C.sub.3 -C.sub.10 -alcohols such as butanol and 2-ethylhexanol, formation of the corresponding aldehydes occurs which can be separated off only with high expenditure under conventional conditions employed in the technique.
The object was therefore to find a simple process for the distillation of C.sub.3 -C.sub.10 -alcohols which does not have these disadvantages.
Surprisingly, it has been found that addition of small amounts of alkali metal hydroxide suppresses the formation of the corresponding aldehydes during the workup by distillation and aldehydes already present are even eliminated.
The present invention therefore relates to a process for the purification of C.sub.3 -C.sub.10 -alcohols by distillation, which comprises distilling the alcohols at 150 to 200.degree. C. in the presence of 10 to 1000 ppm of alkali metal hydroxide.
The C.sub.3 -C.sub.10 -alcohols can be straight-chain or branched. Particularly important C.sub.3 -C.sub.10 -alcohols, and more preferably C.sub.4 -C.sub.10 -alcohols to which the process of the invention can be applied are n-butanol and 2-ethylhexanol.
The alkali metal hydroxides used are preferably KOH or NaOH. The amount of alkali metal hydroxide is generally 10 to 1000 ppm, preferably 10 to 200 ppm, in each case based on the amount of the alcohol used. Preferably, the alkali metal hydroxides are added in the form of an aqueous solution.
If columns are used in the distillation, these generally have 20 to 80 trays.
As the following examples show, the addition of alkali metal hydroxide greatly decreases or even completely prevents the formation of aldehydes during the distillation of the alcohols, without other undesirable side reactions or significant reduction of the alcohol content occurring. Frequently, an aldehyde content already present in the alcohol used is even eliminated.
In the examples, the term "low-boilers" refers to components which are free of 2-ethylhexanal and boil considerably lower (at least 20 to 40.degree. C. lower) than 2-ethylhexanol and may therefore readily be separated from this by distillation. Similarly, the term "high-boilers" refers to components which are free of 2-ethylhexanal and boil considerably higher (at least 20 to 40.degree. C. higher) than 2-ethylhexanol and may therefore likewise readily be separated from this by distillation.


COMPARISON EXAMPLE 1

2-Ethylhexanol having a conte

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Chemical Engineering, vol. 2, 3rd ed. Coulson and Richardson, Backhurst and Harker 1978, p. 478.

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