DE1928633C3 - Process for the preparation of low-water solutions of formaldehyde - Google Patents

Description

The invention relates to a process for the preparation of low-water or anhydrous solutions of Formaldehyde by distilling aqueous formaldehyde solutions in the presence of one with water azeotropic mixture forming alkanol or cycloalkanol.

When it is produced, formaldehyde usually falls in the form of 30 to 40 percent by weight aqueous Solutions. For numerous syntheses it is recommended or necessary to concentrate the solutions, z. B. for the reaction with amines to form N-methylol compounds. It is known that aqueous formaldehyde solutions can be prepared 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 that make up polymers of formaldehyde separate different degrees of condensation. Go with the distilling water at the same time significant proportions of formaldehyde are lost. In addition, they become solid at the colder parts of the apparatus Part of the polymerized formaldehyde deposited, which the heat transfer to the cooling devices and lead to blockages in the pipelines.

US Pat. No. 2S90,994 expressly teaches (table, columns 9 to 10) that a mixture of the distillation components which contains considerable amounts of formaldehyde must be separated off. According to this teaching, mixtures with 16 to 34.6% by weight of formaldehyde must be separated off at the top and used as alcohols, ethanol, isopropanol, n-propanol and tert. Butanol can be used. On the other hand, the ratio of alcohol to water is very high and consequently the amount of water in the distillate is very low (column 9, lines 25 to 26). The distillation described is a simple concentration of an alcoholic solution and does not give any indication of possible stabilization. The table (pages 9 to 10) shows that in the alcoholic solutions at 0 ^° C. in all cases and at room temperature in all cases of formaldehyde starting solutions with more than 10% by weight of formaldehyde, polymer precipitations were observed. Only the aforementioned alkanols are used and claimed.

It has now been found that low-water or water-free, 10- bis80gewichtsprozentige solutions of formaldehyde in the organic solvents from aqueous formaldehyde solutions to give a azeotropi r ~ *

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contains medium, separates off as distillate, advantageously receives, if you have a 20 to 80 weight percent aqueous formaldehyde solution mixed with isobutanol and / or n-butanol distilled.

In view of the state of the art, the process surprisingly delivers low-water content in a surprisingly simple manner or anhydrous solutions of formaldehyde in alkanols and / or cycloalkanols in better yield and without any significant formation of formaldehyde polymers. In in this context, those with a proportion of 0 to 8% 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 one depending on the distillation time more or less water-poor to anhydrous solution in the organic solvent of the still. The solutions prepared by the process are also available for long periods of storage, e.g. B. up to 6 months, stable and show none in later implementations significant loss of formaldehyde as a result of polymerizations.

With regard to US Pat. No. 2,690,994, it was surprising that the isobutanol, n-butanol and isobutanol / n-butanol mixtures mentioned as unsuitable can be used, since the patent (column 3, lines 65 to 72) during the separation of the azeotropic mixture teaches a temperature below 8O ⁰ C, was the corresponding mixtures (boiling point of isobutanol-water azeotrope 89.8 ° C) is considered inappropriate. It was surprising that the alkanols according to the invention give highly concentrated solutions which are stable for more than 1 to 6 months at room temperature, even in 40% strength by weight formaldehyde solution. ^{If the alkanols according to the invention are stored at 0 °} C. in comparison with the alkanols given in the table of the US patent, a surprising storage stability of at least 3 months is observed for 20 to 40 percent by weight solutions according to the invention.

The starting solutions are usually 20 to 80, preferably 30 to 60 percent by weight, aqueous Formaldehyde solutions used. If necessary, raw solutions that arise during production are also used, the still impurities, z. B. methanol contain, into consideration. Preferred alkanols or Cycloalkanols are those with 3 to 6 carbon atoms that form an azeotropic mixture with water.

You can still go through under the procedural conditions inert groups and / or atoms, e.g. B. alkoxy groups with 1 to 3 carbon atoms, chlorine atoms, be substituted. As a rule, such solvents form azeotropic mixtures with water of more than 12 Wt .-% water, e.g. B. 33 wt .-% water in the case of isobutanol, 13 wt .-% water in the case of isopropanol, and 15% by weight for n-propoxyethanol, 78% by weight for methoxyethanol, 28% by weight for n-propanol, 42% by weight for n-butanol, 71% by weight for

(»Ο 2-ethoxyethanol, 28% by weight for tert-amyl alcohol, 50 % By weight for isoamyl alcohol.

Suitable solvents are 1. B .: n-propanol, isopropanol, n-butanol, sec-butanol, amyl alcohol, Äliioxyäthanol, 3-methyl-2-butanol, cyclohexanol,

<'<· 2-chloro-1-propanol, 1-methoxy-2-propanol and their Mixtures, preferably isobutanol or a mixture of isobutanol with ti-butanol, sec-butanol, tert-butanol and'or knnrnnannl. One understands the purpose

Amount of solvent so. that after completion of the distillation a 10 to 80 percent by weight, preferably 35 to 45 weight percent formaldehyde solution in the solvent or solvent mixture used is present, which can easily be determined by a preliminary test.

The distillation temperature usually depends on the solvent used! or according to the boiling point of the alkanol (cycloalkanol) -water azeotrope, e.g. B. is the boiling point of the isopropanol-water azeotrope 80 ⁰ C at 760 Torr, of the isobutanol-water azeotrope 89.8 ° C, the n-amyl alcohol-water azeotrope 95.8 ° C. In general, the distillation at a temperature between 50 and 150 ⁰ C, preferably 75 to 100 ° C, under atmospheric pressure, continuously or discontinuously.

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. As distillation systems all suitable apparatus can be used, e.g. B. Sieve bottom, Oldershaw, Glass tray, bubble cap, valve tray columns, packed columns, columns with rotating inserts.

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

The solutions which can be prepared by the process of the invention are valuable starting materials for Methylation on nitrogen of primary and secondary amines, the production of plastics, textile and leather agents, pesticides and adhesives. Regarding the use, refer to the aforementioned volume by Ullma-in, page 656 ff. referenced.

The parts indicated in the following examples mean parts by weight.

example 1

A distillation apparatus with a tray column (selectivity 15 to 20 theoretical trays) is used, Dephlegmator for condensation of the vaporous distillate and a template that is in the form of a Florentine bottle is designed to separate two liquid phases. It will be in the still 1000 parts of solution with 300 parts of formaldehyde, 200 so Parts of water and 500 parts of isobutanol were initiated.

The mixture is distilled at 760 torr (distillation time 6 hours). There is an isobutanol-water azeotrope with about 33 percent by weight of water at a boiling point of ₇ M = 89.8 ° C. 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. 755 parts of a clear, 40% by weight formaldehyde solution in isobutanol from EP below -10 ° C. remain in the bladder. 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 I with n-butanol instead of isobutanol. N-Butanol is obtained as upper Schichi des Desfillais, those in the column head is returned. An aqueous phase which is free from formaldehyde is obtained as the lower layer is discarded. A clear 40 weight percent formaldehyde solution remains as the distillation residue n-butanol with a water content of 0.05 percent by weight. In storage r ^ e solution is still after 4 Resistant for weeks and shows no precipitation of polymers.

Example 3

A distillation apparatus is used with a tray column (selectivity 15 to 20 theoretical trays), a dephlegmator for condensing the vaporous distillate and a receiver which is designed in the form of a Florentine bottle to separate two liquid phases. 1000 parts of a 50 percent by weight formaldehyde solution and 1800 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% by weight water at a _{boiling point of 7bO} = S9.8 ° C passes over. A distillate with 2 liquid layers is obtained. The upper layer of 90% by weight isobutanol and 10% by weight water is returned to the top of the column. An aqueous phase which is free from formaldehyde and which is discarded is obtained as the lower layer. A clear 45% by weight formaldehyde solution in isobutanol with a water content of 0.15% by weight remains as the distillation residue. On storage, the solution is stable even after 4 weeks and shows no precipitation of polymers.

Claims (1)

Claim: Process for the preparation of low-water or water-free, 10 to 80 percent by weight solutions of formaldehyde in organic solvents from aqueous formaldehyde solutions, whereby one an azeotropic mixture containing water and organic solvent as a distillate separates, characterized in that a 20 to 80 percent by weight, aqueous Distilled formaldehyde solution mixed with isobutanol and / or n-butanol.