Process for separating solids from aqueous 1,4-butynediol soluti

Details Process for separating solids from aqueous 1,4-butynediol soluti Process for separating solids from aqueous 1,4-butynediol soluti

1998-01-27

1999-10-26

Wilson, James O.

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568855, C07C 2726, C07C 3118

Patent

active

059732130

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for separating solids from aqueous 1,4-butynediol solutions.
1,4-Butynediol is prepared on an industrial scale from acetylene and aqueous formaldehyde solution over copper catalysts (Weissmel, Arpe, Industrielle Organische Chemie, 2nd Edition, Verlag Chemie, p. 94). Butynediol is an important intermediate from which 1,4-butanediol can be prepared by hydrogenation, this being used as an alcohol component in polyesters and being able to be converted into tetrahydrofuran by ring closure.
Butynediol is obtained industrially as an aqueous solution containing small amounts of solids. During the preparation of butynediol, secondary reactions between CO.sub.2 and formaldehyde or other intermediates in the reaction lead to the formation of red polymers which are insoluble in aqueous butynediol solution.
The polymeric solid coats all parts of the plant such as tube walls and reactor walls with a film which can be removed mechanically only with difficulty. On the other hand, if the polymeric solid remains suspended, sedimentation is uneconomical in view of the low concentration, since subsequent process steps over highly selective catalysts rule out the addition of sedimentation aids, because these have an adverse effect on the selectivity of the catalysts.
Furthermore, the butynediol solution contains solid particles which are attributable to abrasion of the catalyst. Depending on the reaction conditions in the preparation of butynediol, the proportion of abraded catalyst material is generally from 20 to 80% by weight of the solid in the aqueous solution. In general, the concentration of the solid in the aqueous butynediol solution is from about 1 to 1000 ppm. The abraded catalyst material leads to mechanical problems, particularly in pumps.
Furthermore, said solids deposit on the catalyst for the hydrogenation to butene or butanediol which generally follows the preparation of butynediol. The solid can be removed only by time-consuming and expensive stopping of plants and mechanical cleaning of affected plant parts.
It is an object of the present invention to provide a process which allows economical separation of solids from aqueous 1,4-butynediol solutions. The process should be able to be used on an industrial scale. In particular, it should be suitable for removing low concentrations of solids.
We have found that this object is achieved by a process for separating solids from aqueous 1,4-butynediol solutions, which comprises passing a solids-containing aqueous butynediol solution in the downflow mode through a column and thus bringing it into contact with a solvent which has a lower density than the solids-containing butynediol solution and forms a second phase with the latter, with the solvent rising in countercurrent to the aqueous butynediol solution, the solid accumulating at the interface between the aqueous butynediol and the solvent and the solid being removed from the column by taking off a mixture of aqueous butynediol and solvent.
The aqueous butynediol solutions to be used according to the present invention have a butynediol content which can vary within wide limits. It is generally from 25 to 75% by weight, preferably from 40 to 60% by weight and particularly preferably from 45 to 55% by weight.
The solids content of the aqueous butynediol solution used is generally from 1 to 1000 ppm, but in particular cases it can also be significantly greater, eg. up to 5% by weight. The process of the present invention is particularly advantageous for solids contents of from 2 to 500 ppm.
The removal of the solid is carried out in a column, which for the purposes of the present invention means any apparatus in which the butynediol solution can be passed from the top downward (downflow mode) in countercurrent to the solvent. On a small scale, glass columns as are used for chromatography are useful; on an industrial scale, suitable columns are, in particular, metal columns.
The butynediol solution to be purified is preferably introduced laterally into the upper part of the

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