DE1928633A1 - Process for the production of water-poor solutions of formaldehyde - Google Patents

Description

Badische Anilin- & Soda-Fabrik AG

Our reference: O.Z. 26 217 WB / Be

6700 Ludwigshafen, June 4, 1969

Process for the preparation of low-water solutions of

formaldehyde

The invention relates to a method for the production of low water or anhydrous solutions of formaldehyde by distillation of aqueous formaldehyde solutions in the presence of one with Water, alkanol or cycloalkanol forming an azeotropic mixture.

During its production, formaldehyde is generally obtained in the form of 30 to 40 percent by weight aqueous solutions. For numerous syntheses it is recommended or necessary to concentrate the solutions, e.g. for the reaction with amines N-methylol compounds. It is known to use aqueous formaldehyde solutions by various methods by distillation or by washing the vapors with water-soluble ethers or alcohols to concentrate (Ulimann's Encyclopedia of Industrial Chemistry, Volume 7, Page 667). All of these procedures result though concentrated, but more or less unstable solutions, from which polymers of formaldehyde different degrees of condensation deposit. With the water that is distilled off, significant proportions of formaldehyde are lost at the same time. In addition, solid proportions of polymerized formaldehyde are deposited at the colder parts of the apparatus, which the Reduce heat transfer to the cooling devices and lead to blockages in the pipelines.

It has now been found that anhydrous or anhydrous solutions can be used of formaldehyde in organic solvents from aqueous formaldehyde solutions is advantageous if the aqueous formaldehyde solution in the presence of an azeotropic with water Mixture forming alkanols and / or cycloalkanols distilled.

In view of the prior art, the method provides surprisingly in a simple way

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anhydrous solutions of formaldehyde in alkanols and / or cycloalkanols in better yield and without substantial formation of formaldehyde polymers. Are considered to be low-water solutions in this context, those with a proportion of 0 to 8 percent by weight of water, based on the total solution, understood. The azeotropic mixture emerging during the distillation consists essentially only of water and organic Solvent. Formaldehyde remains in the form of a more or less water-poor to anhydrous, depending on the distillation time Solution in the organic solvent of the still. The solutions made by the process are also for longer storage, e.g. up to 6 months, stable and show no significant loss of formaldehyde in subsequent reactions as a result of polymerizations.

The starting solutions are usually 20 to 80, preferably 30 to 60 percent by weight aqueous formaldehyde solutions are used. If necessary, there are also incurred during production Raw solutions that still contain impurities, e.g. methanol, can be considered. Preferred alkanols or cycloalkanols are those with 3 to 6 carbon atoms which form an azeotropic mixture with water. You can still go through under the procedural conditions inert groups and / or atoms, e.g. alkoxy groups with 1 to 3 carbon atoms, chlorine atoms, substituted be. Typically, such solvents form azeotropic mixtures with water with more than 12 weight percent water, e.g. 33 percent by weight water in the case of isobutanol, 13 percent by weight Water in the case of isopropanol, and 15 percent by weight for n-propoxyethanol, 78 percent by weight for methoxyethanol, 28 percent by weight for n-propanol, 42 percent by weight for n-butanol, 71 percent by weight for 2-ethoxyethanol, 28 percent by weight for terfc-amyl alcohol, 50 percent by weight for isoamyl alcohol,

Suitable solvents are e.g .: n-propanol, isopropanol, n-butanol, sec-butanol, amyl alcohol, ethoxyethanol, 3-methyl-2-butanol, Cyclohexanol, 2-Chlor ™ 1-propanol, 1-methoxy-2-propanol and their mixtures, preferably isobutanol or a mixture of isobutanol with n-butanol, sea-butanol, tert-butanol

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and / or isopropanol. The amount of solvent is expediently included so that after completion of the distillation a 10 to 80 percent by weight, preferably 35 to 45 percent by weight Formaldehyde solution is present in the solvent or solvent mixture used, which can easily be determined by a preliminary test is.

The distillation temperature depends in general on the solvent used or on the boiling point of the alkanol (cycloalkanol) water azeotrope, for example the boiling point of the isopropanol-water azeotrope 80 ⁰ C at 760 Torr, of the isobutanol-water azeotrope 89.8 ⁰ C, n-amyl alcohol-water azeotrope 95.8 ⁰ C. in general, the distillation at a temperature between 50 and 150 ⁰ C, preferably 75 to 100 ⁰ C, under atmospheric or superatmospheric pressure, continuously or discontinuously, carried out.

The distillation can be carried out as follows: A mixture of aqueous formaldehyde solution and organic solvent is heated to the distillation temperature at normal pressure. All apparatuses suitable for this purpose can be used as the distillation plant, for example sieve trays, Oldershaw trays, glass trays, bell trays, valve trays, packed columns, columns ^! with rotating inserts.

A (cycloalkanol) -alkanol-water azeotrope is formed, the is essentially free of formaldehyde. The distillate forms 2 liquid phases. The lower aqueous phase is discarded. the upper alcoholic layer is returned to the top of the column. The solution of remains in the still Formaldehyde in cycloalkanol or alkenol.

The solutions that can be made by the method of the invention are valuable starting materials for the methylation on nitrogen of primary and secondary amines, the production of plastics, Textile and leather auxiliaries, pesticides and adhesives. Regarding the use, refer to the named Volume by Ullmann, page 656 ff.

The parts given in the following examples are parts by weight.

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BATH

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example 1

A distillation apparatus with a tray column (selectivity 15 to 20 theoretical trays), a dephlegmator for condensing the vaporous distillate and a receiver in the form of a Florentine bottle for separating two liquid phases are used. 1000 parts of solution containing 300 parts of formaldehyde, 200 parts of water and 500 parts of isobutanol are introduced into the still. The mixture is distilled at 760 torr (distillation time 6 hours). An isobutanol-water azeotrope with approx. 33 percent by weight water at a boiling point of ₇₆₀ = 89.8 ° C. is transferred. A distillate with 2 liquid layers is obtained. The upper layer of 90 percent by weight isobutanol and 10 percent by weight water is returned to the top of the column. The lower layer (205 parts of water, 23 parts of isobutanol) is free of formaldehyde and is discarded. There remain in the bladder 755 parts of a clear, 40 weight percent formaldehyde solution in isobutanol from EP below -10 ⁰ C. The water content is 0.05 percent by weight. When stored at 20 ^° C., the solution is stable even after 6 months and shows no precipitation of formaldehyde polymers.

Example 2

The distillation is carried out as in Example 1 with n-butanol Isobutanol carried out. N-Butanol is obtained as the upper layer of the distillate, which is returned to the top of the column. The lower layer is an aqueous phase that is free from Is formaldehyde and is discarded. A clear 40 percent by weight formaldehyde solution remains as the distillation residue in n-butanol with a water content of 0.05 percent by weight. When stored, the solution is stable even after 4 weeks and shows no precipitation of polymers.

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Claims (1)

- 5 - 0 * Z. 26 217 Fatentanspruicli Process for the preparation of low-water or anhydrous solutions of formaldehyde in organic solvents from aqueous formaldehyde solutions » characterized in that the aqueous formaldehyde mixture is distilled in the presence of alkenols and / or cycloalkanols which form an azeotropic mixture with water. Badlsche AnIlIo- & Soda-Fabrik AG QO9850 / 2U4