DE1235282B - Process for stabilizing aqueous formaldehyde solutions against cloudiness and precipitation - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Inta .:

C07C 47/05?

C 07 c

German class; 12 ο -7/01

Number.
File number:
Registration date:
Display day:

1235 282
F 45831IV b / 12 ο
April 15, 1965
March 2, 1967

The invention relates to a method for stabilization aqueous formaldehyde solutions against cloudiness and precipitation.

It is known that formaldehyde in aqueous solution tends to change to a higher molecular weight water-insoluble form. This property of formaldehyde, which is documented by that the solution becomes cloudy (often with the formation of precipitates) occurs particularly at low temperatures and higher concentrations. But also other factors, e.g. B. the pH of the formaldehyde solution, affect the rate of formation of the higher molecular weight compounds.

Both in terms of transport costs and energy and reaction space savings The further processing of formaldehyde is of general interest, the formaldehyde concentration of the solutions not to drop below 40 percent by weight, but even more recently solutions with concentrations of 37 percent by weight, *> 40 percent by weight and more on the market bring.

This is possible either by using the formaldehyde solutions until further processing Keeps formaldehyde concentrations warm accordingly * 5 or that substances are added which strongly inhibit the polymerisation tendency of formyldehyde, so-called Stabilizers.

It is Z. B. known that methyl alcohol or urea and similar compounds are used as stabilizers. However, a major disadvantage of these compounds is that, depending on the temperature, they have to be added in amounts of 3 to 15 parts per 100 parts of formaldehyde solution. Some of these amounts of stabilizer are undesirable during further processing, are mostly lost and make formaldehyde more expensive. Other stabilizers are also known, such as melamine, triazine derivatives and other nitrogen-containing products such as betaines or acid amides, some of which are added to the formaldehyde solution in low concentrations well below 1%. However, such solutions contain nitrogen and in some cases show unsatisfactory stabilization, ie the solutions stabilized with the above products can only be stored at relatively high temperatures. In addition, to stabilize formaldehyde solutions, cellulose derivatives such as methyl cellulose or hydroxypropylmethyl cellulose, and also pectins, gelatin, and carragheen as well as polyvinyl alcohol and other polyhydric alcohols and ethers, acetals and esters of these polyhydric alcohols can be used. Some of the above methods for stabilizing aqueous
Formaldehyde solutions against cloudiness
and precipitations

Applicant:

Paint factories Bayer Aktiengesellschaft,
Leverkusen

Named as inventor:

Dr. Wulf von Bonin,

Dr. Raimund Wambach,

Dr. Hermann WoIz, Leverkusen

These substances are also used in combination with UV rays in the stabilization of formaldehyde solutions applied. Unfortunately, there are the most essential of the above compounds In spite of the low concentrations, this gives rise to disruptions in the further processing of the formaldehyde. In addition, the stabilizing effect is still very poor in some cases.

In contrast, the invention relates to a process for stabilizing aqueous formaldehyde solutions up to turbidity and precipitation, and characterized in that aqueous formaldehyde solutions graft polymers of esters of vinyl alcohol on Polyalkyloxyden or hydrolysis products thereof is added and the formaldehyde solutions then heated for 3 to 20 hours to temperatures above 6O ⁰ C. The solutions are preferably heated to 80 to 120 ^° C. for 10 to 16 hours. The formaldehyde solutions obtained in this way are not only distinguished by good cold stability, but can also be further processed without disrupting melamine, phenol, ketone and urea resin production. The stabilizers are also free of nitrogen. These stabilizers are used in amounts of 0.0001 to 1 percent by weight, based on the total solution, preferably 0.001 to 0.2%.

709 517!

ϊ 235

The graft polymers are prepared in a known manner by free-radical polymerization of esters of vinyl alcohols with carboxylic acids, preferably aliphatic carboxylic acids with 1 to 4 carbon atoms, in the presence of polyalkylene oxides. For this purpose, polyethylene oxides with molecular weights are best suitable for over 500.

The hydrolysis of these graft polymers can take place in the presence or absence of additional solvents in an acidic or basic medium. In an acidic medium, organic, but expediently, inorganic acids, such as phosphoric acids, sulfuric or hydrochloric acid, are used. In addition to ammonia or amine, "ABaIi" and alkaline earth metal hydroxides are preferred as bases. The resulting hydrolysis products can be used directly as stabilizers .:. :; -u / '. C'. '. "::.": ·. . ''. ''■.

The manufacture of the. Stabilizers are in the following to ensure that the invention can be reworked specified. Unless otherwise specified, the parts represent parts by weight.

The graft polymers summarized in the table below are produced by placing polyethylene oxide with an average molecular weight of 1550 _{in an N 4} ^{atmosphere, heating it to 120 4} C and then grafting in the solution of activator in vinyl acetate so slowly that there is little monomer backfiow is to be observed. After the dropwise addition, the mixture is stirred for a further 4 hours.

Polyethylene oxide 1550,

Parts

Vinyl acetate parts

AzodiisobutyronitriL. Parts

Benzoyl peroxide, parts ..,

Graft polymer No. 112 (314

500 500

.2. 3

400

600

300

700

Graft polymer Ni. T jvurde '. Under the name "Stabilizer 1" tested. "'.' ·.

The acidic saponification of the graft polymers is summarized in the table below. The reaction mixture formed during the saponification is ^{freed from excess volatile constituents by concentration at 100 °} C. and can then be used as a stabilizer.

Stabilizer no. .:; 4 ■ - · ■ '■■ 5 ' 2 3 3/1000,. '. · 4/1000 1/1000 2/1000 .500 . 550 400 .450 - 4.0 4.0 .. .. .3,5 3.5 · ■ ·, · 350 .400, 300 300 95 ·· ■ -. ; .95. 95 95 17th 17: 17th "'- 17

Graft polymer no./parts

Methanol, parts

Conc. H ₂ SO ₄ , parts

H ₂ O, parts

Temperature, ⁰ C ■; .'-,

Response time in hours.

The saponification in a basic environment is the example or days in one. Precipitation or in a flocculate of the graft polymer 1 ;;. Described: The graft formation over. "■■■ :.

^^ 'Τ-Α ΐ ^^ - ^^ - ^ ^^^ Ι ί ^''' Testtemperätur: + 3.Up + ^b 4 ^C.::. 'Displaced and information below nut various ^r ■ ■■

which amounts of NaOH -refluxed, for formaldehyde concentration: 37 percent by weight
Slightly volatile substance at 10O ⁰ C driven off. 45
The remaining mass can be used directly as a stabilizer ^: ϊ
can be used.

Graft polymer 1, parts

Methanol, parts ■ .. * ..

H ₂ O, parts

NaOH, parts ..... ...

Reaction temperature, ° C _:
Response time in hours

Stabilizer. No.

120
.175
55
2.5

about 85
8th

55

Stabilization of a 37 weight percent formaldehyde solution with polyvinyl alcohol as described in Example 1 of British Patent 968 762

1. The test was carried out in such a way that the time until the onset of the first cloudiness was determined. This cloudiness disappears after a few more hours

65

stabilizer stabilizer
concenitra
tion in.
Weight
percent stability Polyvinyl alcohol .. 1 0.01 8 hours

The superiority of the new stabilizers results from the following comparative tests:

In contrast, the stability of an aqueous formaldehyde solution is the same concentration with the same Stabilizer concentration according to Example 2 42 hours.

Compare with Table 1 of British Patent 968 762

■ 2. A 44 weight percent formaldehyde solution, free of methanol, got so much 1 weight percent mixed aqueous solution of the graft polymer of the stabilizer 2 that the stabilizer concentration was about 0.01 weight percent. After that, the formaldehyde solution was so far with water diluted so that the formaldehyde concentration was 40.2 percent by weight. The solution was now 16 hours

heated to 90 ^{0 C.} After cooling, testing was carried out using the method described above.

Test temperature: 25 to 28 ⁰ C.
Formaldehyde concentration: 40.2 percent by weight.

stabilizer

stabilizer
concentration in
Weight percent

Graft polymer

of the stabilizer 2 about 0.01 after 2 months

still clear, then stopped the attempt

According to British patent 968 762 40.8 percent by weight formaldehyde solution below 1 percent by weight Methanol.

Test temperature as specified in Table 1:25 to 40 ⁰ C.

stability

stabilizer stabilizer
concentra
tion in
Weight
percent stability Polyvinyl alcohol ... 0.01 after 54 days
slightly cloudy

Stabilizer concentration

stability

in which the solution is still completely at the test temperature remains clear.

Test temperature: +3 to +4 ⁰ C.

The following examples illustrate the invention.

example 1

A 1 percent by weight aqueous solution is prepared from stabilizer 1, of which so much is then added to about 38 percent by weight formaldehyde (free of methanol, pH about 3.3) that the concentration of the stabilizer, based on the total solution, is about 0.01 Weight percent is. The solution is adjusted to exactly 37 percent by weight and heated 8 hours to 8O ⁰ C. After cooling to the test temperature of Stabilisieruagseffekt is determined in that the time is determined, in which the solution still remains entirely clear at the test temperature of 4-3 ⁰ C to +4.

Stabilizer concentrate stability 0.01 percent by weight 42 hours

Example3

The stabilizers 3,4 and 5 are also dissolved again to l ° / _o aqueous solutions. From 37 to 38 percent by weight formaldehyde (methanol content 0.1 percent by weight, pH 3.2) and the aqueous stabilizer solutions, three samples are now prepared according to the information in Example 2, in which the concentration of formaldehyde is 37 percent by weight and that of methanol 0.1 percent by weight and the respective stabilizer is 0.01 percent by weight. Thereafter

«Ο the three samples are ^{heated to 90 °} C. for 16 hours. Then tested according to the information in Example 2.

Test temperature: +3 to +4 ⁰ C.

25th

Stabilisa
gate
No. StabÜisatoronzentrra-
tion in
Weight percent stability
the formaldehyde
solution
in hours 2
3
4th 0.01
0.01
0.01 47
63V ₂
47

Example 4

The stabilizer 6 is also dissolved in water to form a 1% solution. Of this aqueous solution (pH temperature 2O ⁰ C, free of methanol, about 3.0) is in turn to 38- to 43gewichtsprozentiger Forraaldehydlösung so much is added that the concentration of the stabilizer, based on the total aqueous solution is about 0.003 weight percent. The formaldehyde concentration is then adjusted more precisely to 37 weight percent, and the solution was heated 10 hours at 8O ⁰ C. The cold stability of the formaldehyde solution was determined in the usual way after cooling to the test temperature of +3 to +4 ^{0 C.}

24 hours about 40 minutes

55

In the total solution 0.01 percent by weight

Unstabilized 37 weight percent Formaldehyde solution

Example 2

Stabilizer 2 is dissolved in water to form a 1% solution. Of this aqueous stabilizer solution (pH free of methanol, about 3.1) is so much to the 38- to 43gewichtsprozentigen, about 50 to 9O ⁰ C hot formaldehyde solution is added that the concentration of the stabilizer, based on the total aqueous solution, about 0, 01 weight percent. Then it provides the exact formaldehyde concentration to 37 percent by weight and heating the formaldehyde solution for 14 hours 9O ⁰ C. After cooling to the test temperature, the stabilization effect is determined in that the time is determined,

Stabilizer concentration stability 0.003 weight percent 22 hours

Claims (1)

Claim: A process for stabilizing aqueous formaldehyde solutions up to turbidity and precipitation, characterized in that aqueous formaldehyde solutions graft polymers of the vinyl esters is added to PoIyalkylenoxyden alcohols or hydrolysis products thereof and the formaldehyde solutions then heated for 3 to 20 hours to temperatures above 6O ⁰ C. Considered publications:
British Patent No. 968,762;
French patent specification No. 1,336,037. 709 517/547 2.67 © Bundesdruckcrei Berlin