DE1185600B - Process for the production of formic acid-free, pure, monomeric formaldehyde - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school KL: C 07 c

Number:
File number:
Registration date:
Display day:

German KL: 12 ο-7/01

1185 600
P 28504IV b / 12 ο
December 28, 1961
January 21, 1965

Lead in the manufacture of essentially pure formaldehyde from its aqueous solutions Side reactions, such as the Cannizaro reaction, lead to the formation of formic acid. The presence of Formic acid is undesirable because it catalyzes many reactions which tend to decrease the formaldehyde yield.

For example, according to German Auslegeschrift 1 057 086, pure formaldehyde is converted by reaction of an alcohol with aqueous formaldehyde to form an aqueous mixture which is the hemiformal containing the alcohol, removing water by dehydrating the mixture and recovering it of the purified formaldehyde obtained by pyrolysis containing the hemiformal of the alcohol Solution made.

It was found that the presence of formic acid in the solution of formaldehyde in Water and alcohol during the final stage of this process to catalyze a reunion of Alcohol and formaldehyde and thereby a reduction in the yield.

One might expect this problem to be solved by neutralizing the formic acid present with a strong base such as sodium hydroxide, because the reaction of such a base with Formic acid leads to the corresponding formate, the presence of which in a process in the Auslegeschrift 1 057 086 described type should not be expected to be disadvantageous. It has, however demonstrated that the presence of sodium or potassium formate in the final stage of the above Process leads to an increase in the amount of high-boiling by-products and both the yield of formaldehyde as well as the degree of alcohol production. It also forms at The presence of sodium or potassium formate on the internal surfaces of the apparatus is considerable Amount of sticky "candy-candy" material, which increases the heat exchange efficiency of the Seriously disturbs the apparatus. On the other hand, neutralization of formic acid by means of ammonium hydroxide leads to a heavy deposit of formaldehyde polymer in the entire apparatus, whereby frequent shutdown and cleaning of the device becomes necessary.

Also the removal of formic acid by means of anion exchange resins, such as those used by the British Patent 573 051 disclosed for alcohol-free aqueous formaldehyde solutions is in the present case alcohol-containing mixture cannot be carried out, since the exchange resin is dissolved by the alcohol for the production of formic acid-free, pure, monomeric formaldehyde

Applicant:

EI du Pont de Nemours and Company,
Wilmington, Del. (V. St. A.)

Representative:

Dr.-Ing. W. Abitz, patent attorney,

Munich 27, Pienzenauer Str. 28

Named as inventor:
Carl Earle Schweitzer,
Wilmington, Del. (V. St. A.)

Claimed priority:

V. St. v. America dated December 28, 1960 (78 845)

attacked and is thus reduced in its effectiveness.

Compared to the neutralization process mentioned, it has now surprisingly been found that Alkaline earth formates do not have the disadvantages described above and despite their considerable solubility in water (e.g. for calcium formate at 0 ° C 16%) in a mixture of alcohol, water, formaldehyde and hemiformal have sufficiently low solubility to be removed by filtration to be able to.

The invention therefore relates to a process for the production of formic acid-free, pure, monomeric formaldehyde from alcohol and formaldehyde solutions containing at least 5 percent by weight of water by removing the water by distillation and thermal decomposition of the formaldehyde hemiacetal containing distillation residue, which is characterized in that one of the solution an alkaline earth oxide or hydroxide is added before the distillation and the solution is used to remove insolubles Filtered material.

The formaldehyde is obtained from the neutralized solution by first distilling off the water and then applying sufficient heat to pyrolyze the hemiformal of the alcohol. the The amount of water during the neutralization is at least 5 percent by weight, preferably 5 to 15 percent by weight, especially 7%. In terms of the need for water removal, it is economical expedient, an amount of water of more

409 769/430

than 15% to avoid. Preferably the formaldehyde content is 15 to 40%, while a remainder 45 to 80% is made up of alcohol. (When determining the preferred proportions, this is Hemiformal considered on the basis of its components.)

The alkaline earth oxides or hydroxides can be added as a powder, as a suspension in a liquid or by passing the formaldehyde solution to be purified through a resting layer of the alkaline earth oxides or hydroxides. The aqueous solution containing formaldehyde and alcohol is particularly preferably prepared by the process of US Pat. No. 2,848,500; According to the preferred embodiment of the invention, the alkaline earth oxide or hydroxide is added to the starting mixture of alcohol, formaldehyde and water, which was obtained by the process according to this patent specification, the mixture is then filtered, freed from water by distillation and the dehydrated hemiform is pyrolyzed. It is expedient to work with an alcohol which boils at at least 95 ° C. at atmospheric pressure and, apart from one hydroxyl group, is free of any substituent group which is reactive with formaldehyde under the process conditions. Cyclohexanol or another primary or secondary aliphatic or cycloaliphatic alcohol which contains 5 to 10 carbon atoms in the molecule and boils at at least 120 ° C. at atmospheric pressure is particularly preferably used as the alcohol.

The following examples serve to further illustrate the invention.

example 1

To a mixture of cyclohexanol, 12.32% water and formaldehyde, which is 0.0310 percent by weight Contains formic acid, 0.02 percent by weight calcium hydroxide is added. The mixture is stirred overnight at room temperature. After filtering off insoluble substances, the mixture is obtained analytically a formic acid content of 0.0071 percent by weight. After the water has been distilled off the mixture heated to 75 ° C at 30 torr to decompose the formaldehyde hemiacetal and the pure Formaldehyde.

Example 2

To 1840 parts by weight of a mixture of formaldehyde, cyclohexanol and cyclohexylhemiformal, containing 0.2 percent by weight water and 0.0440 percent by weight formic acid 1.26 parts of calcium hydroxide were added. After stirring, the solution is filtered and on its Analyzed formic acid content, 0.0395 percent by weight being obtained (comparative experiment). The use of bromothymol blue as an indicator also shows the lack of neutralization. at Add enough water to the mixture to bring the ίο water content to around 7 percent by weight, the indicator shows an immediate neutralization. Further processing to obtain formaldehyde as in example 1.

¹ S example 3

A solution of formaldehyde in cyclohexanol, which contains 19.1 percent by weight formaldehyde, 9.5 percent by weight water and 0.0332 percent by weight formic acid, is passed through a layer of calcium oxide 1.7 cm in diameter and ^{at a rate of about 7 cm 3 of solution per minute} 19 cm in length. The material flowing off gives analytically 0.0120 percent by weight of formic acid.

The same feed solution is made with 0.43 parts by weight calcium hydroxide per 700 parts solution treated, stirred for 10 minutes and analyzed, the formic acid content of the solution being less than 0.0005 weight percent. Further processing to obtain the formaldehyde as in the example 1.

Example 4

(Comparison test)

This example, in conjunction with Table I, compares the effects of various alkaline substances in mixtures of formaldehyde and cyclohexanol for side reactions. One admits a solution of formaldehyde, cyclohexanol and about 5% water in small amounts different Compounds according to the table and the resulting solution evaporated by heating for 30 minutes 150 ° C. The vapors are then condensed and analyzed to determine the loss of formaldehyde and Determine cyclohexanol by the formation of high-boiling by-products. In a control experiment a mixture is used which is essentially free of formic acid; in the other attempts the same mixture is used with the addition according to the table.

Table I.
Losses due to the formation of high-boiling products when the mixture is heated to 150 ° C for 30 minutes

Addition based on the total weight
of the mixture

Formaldehyde loss, Cyclohexanol loss, based on formaldehyde based on cyclohexanol weight in charge weight in charge mixture mixture 0.04 0.02 1.00 0.02 *) 1.10 0.11 **) 0.30 0.04 0.35 0.03 * # *)

Control sample

0.02% sodium hydroxide
0.02% sodium formate.
0.05% calcium formate ..
0.02% calcium hydroxide
0.01% ammonia

*) In addition to the losses mentioned, 3.4 percent by weight of cyclohexanol forms a sugar-candy residue.

**) In addition to the losses mentioned, 1.5 percent by weight of cyclohexanol forms a sugar-candy residue.

***) The experiment is interrupted due to the formation of large amounts of solids in the initial stage of the heating period.

5 6

Example 5 This mixture is added according to the tables

A mixture of cyclohexyl hemiformals is added - various amounts of calcium hydroxide are added,

the composition, based on the weight of the resulting mixture was moved 2 ¹ / »hours, filtered and

Total mixture, used: analyzed. When the mixture is filtered, a

Water,% 10.6 5 about one and a half times as long as the period

Formaldehyde, 16.0% treatment of the non-calcium hydroxide

Cyclohexylformate,% · 10 ~ ⁴ 300 Cyclohexylhemiformalgemisches required, but the

Formic acid,% x 10 ~ ⁴⁶²⁴ filtration can be carried out is not difficult.

Cyclohexylhemiformal residue

Tabel!!

Ca (OH) δ excess
about the theoretically
required amount

Remaining formic acid

o / o · ΙΟ- *

Removal of residual formic acid
Cyclohexyl formate

o / o · ΙΟ- ⁴

Residual calcium, ° / o · ^10-4
calculated from the
Weight of
remaining

Solids *)

Flames-

photometric

certainly

50
100

130 48 57

79 92 91

300
300
300

72
54
43

63

54
35

*) Calculated on the assumption that the calcium remaining dissolved in the cyclohexylhemiformal mixture is calcium formate is.

Example 6

A portion of cyclohexylhemiformal is after treatment with calcium hydroxide according to Example 5 dehydrated dehydrated. The following table showing the analytical values before and after dehydration indicates the further reduction in formic acid and calcium concentrations.

35

40

Before the After Dehydra Dehydra tization tization Free water in percent by weight 10.0 5.4 Formic acid,% x 10 ~ ⁴ 128 90 Cyclohexyl formate,% 10 ~ * ... 200 150 Formaldehyde in percent by weight 16.6 16.9 Calcium,% · ΙΟ " ⁴ 71 5

The present invention proves to be an improved working step of the U.S. patent process 2,848,500 as particularly valuable. It is also used to neutralize the formic acid in Alcoholic formaldehyde solutions obtained in other ways are advantageous; you can do such Heat solutions for formaldehyde recovery without the undesired by-products described above leading to causing reactions.

Claims (4)

Patent claims: 1. Process for the production of formic acid-free, pure, monomeric! Formaldehyde" from alcohol and formaldehyde solutions containing at least 5 percent by weight of water Removal of the water by distillation and thermal decomposition of the formaldehyde hemiacetal containing distillation residue, thereby characterized in that an alkaline earth oxide or hydroxide is added to the solution before the distillation added and the solution filtered to remove insoluble material. 2. The method according to claim 1, characterized in that the reaction with a Carries out solution with a water content between 5 and 15 percent by weight. 3. The method according to claim 2, characterized in that the reaction with a Solution with a formaldehyde content of 15 to 40 percent by weight, the remainder alcohol and water, performs. 4. The method according to any one of claims 1 to 3, characterized in that the reaction with a solution carried out by reacting an alcohol with aqueous formaldehyde solution to form a mixture containing the half-formal of the alcohol has been. Considered publications:
German Auslegeschrift No. 1057 086;
British Patent No. 573 051;
Beilstein's Handbook of Organic Chemistry, 2, 1920, p. 15. 409 769/430 1.65 © Bundesdruckerei Berlin