SU44251A1 - The method of distillation of dilute aqueous solutions of formaldehyde - Google Patents

Description

The issue of concentration of aqueous solutions of formaldehyde is devoted to a number of patents and papers published in the periodical scientific and technical press. Most of the methods, however, have been developed in relation to the existing method for producing formaldehyde from methyl alcohol.

In connection with the development in the USSR of methods for the oxidation of hydrocarbons, as a result of which one of the main products is formaldehyde in the form of low concentration solutions, the question of processing solutions obtained as a primary product into a commercial product, formalindehyde, becomes urgent. , or on paraformaldehyde.

Fractionated distillation of dilute formaldehyde solutions gives mostly unsatisfactory results and a more reliable method is their concentration under vacuum, described in German patent no. 489644. A distillation method based on using the properties of azeotropic mixtures of water with any liquids, described in German patent No. 558470, according to the author, can hardly give satisfactory results.

The author of the present invention proposes a method for producing formal (32)

on or paraformaldehyde, based on the fact that, when adding some hydrochloric or sulfuric acid additives or their soluble salts to the initial formaldehyde solution, the vapor composition above the solution is enriched with formaldehyde, resulting in a higher formaldehyde content when distilling the formaldehyde solution with the above distillate than the original solution. With an increase in the salt concentration in the solution, the enrichment factor ages. Account, which makes it possible in some cases to immediately obtain a solution containing 36 formaldehyde, whereas with the usual fractional distillation of pure formaldehyde solutions at atmospheric pressure, the figures are more than 31-32; about formaldehyde in distillate. Another important consequence of these additives is that almost all of the formaldehyde present in the initial solution goes into the distillate during distillation and the residue from distillation contains almost no formaldehyde.

How much the formaldehyde content in the vapors increases in the case of an additive, for example, calcium chloride, compared with a solution that does not contain additives, can be seen from the following table:

Example. For distillation, 635.3 g of the initial solution containing 23.6% (149.9 g) of formaldehyde and 20.3% (129.0 g) of calcium chloride. After distillation (without a reflux condenser), the following was obtained:

distillate 394.1 g with a content of 36.7% formaldehyde (144.8 g).

In the rest:

formaldehyde 5.1 g

calcium chloride. . . 129.0 ,,

water 107.1

241.2 g

Paraformaldehyde can be obtained by distilling a formaldehyde formaldehyde solution with the addition of even larger amounts of calcium chloride. From the obtained de-Stillate, when standing, it is released

the precipitate of paraformaldehyde, in some cases, immediately after cooling, the distillate is converted into a pasty Paraformaldehyde.

Re-distillation with the addition of the above compounds can be used to concentrate highly diluted solutions.

Experience also shows the feasibility of combining vacuum distillation (at a residual pressure of not more than 30 mm Hg), followed by distillation at atmospheric pressure.

The subject matter of the invention.

Claims (2)

1. A method of distilling dilute aqueous solutions of formaldehyde, in order to obtain concentrated solutions of it and paraformaldehyde, characterized in that hydrochloric or sulfuric acids or their water-soluble salts are added to an aqueous solution of formaldehyde before distillation. 2. A method according to claim 1, wherein the distillation of the formaldehyde solution by adding the substances listed in paragraph 1 to an aqueous solution of formaldehyde is concentrated by partial distillation of the water in a vacuum.