JPS584741A - Aqueous solution of formalin - Google Patents

Abstract

PURPOSE:To inhibit the increase in the formation of formic acid and pH change effectively, by adding a very small amount of a water-soluble salt of nitrous acid, e.g. sodium nitrite, as an formic acid inhibitor to an aqueous solution of formic acid. CONSTITUTION:Preferably 0.001-0.0005% water-soluble alkali or alkaline earth metallic salt of nitrous acid which is soluble in an aqueous solution of formic acid, e.g. sodium nitrite, potassium nitrite, calcium nitrite or barium nitrite, is added to the aqueous solution of formalin to inhibit the formation of formic acid even in the case of storage at a high temperature and give the aqueous solution having the stabilized quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aqueous formalin solution in which the production of formic acid is suppressed.

Conventionally, formalin aqueous solutions with a formaldehyde concentration of 37% (by weight, hereinafter the same) have been commercially available.

More recently, aqueous solutions with formaldehyde concentrations exceeding 37%, for example formaldehyde concentrations of about UO to 1.
0% formalin aqueous solution has come to be used for industrial purposes such as amino resins and phenolic resins.

Generally, formaldehyde [OH, O] is mixed with formaldehyde and methylene glycol (H2O (
OH)2'), lower polyoxymethylene glycol [H
O(01(,,O)nH], and also exists as an equilibrium mixture with lower polyoxymethylene glycol hemiformal (OH30(OH20)nH, where n is 3 or less) due to the methanol present in formalin. This equilibrium state changes depending on the formaldehyde concentration, methanol concentration, storage temperature, etc., but if the storage temperature is low, the equilibrium state becomes unstable and the lower polyoxymethylene glycol further polymerizes, forming formaldehyde. is generated, and this paraformaldehyde precipitates, making the formalin aqueous solution cloudy. Moreover, once the paraformaldehyde is generated, it cannot be redissolved by increasing the temperature, and its commercial value is significantly reduced.

Therefore, when transporting and storing a formalin aqueous solution, especially a formalin aqueous solution with a high degree of ##STR17##, in order to avoid precipitation of paraformaldehyde, the container must be kept warm and further heated to prevent the temperature from dropping.

However, when an aqueous formalin solution is stored at a high temperature for a long period of time, formic acid is produced by the oxidation reaction of formaldehyde and the Cannizzaro reaction, and the amount of formic acid in the aqueous formalin solution increases. It has been observed that this formic acid production increases rapidly as the storage temperature rises, and is further promoted by iron and other metal ions mixed in from formalin production equipment, storage containers, etc.

In this way, the amount of formic acid increases during storage and f? : For example, when producing synthetic resins such as amine resins and phenol resins, the reaction of millet formalin does not proceed properly, causing problems such as different physical properties of the product.

Various formic acid inhibitors have been studied to overcome this drawback. For example, methods of adding hexamethylenetetramine, sodium pyrophosphate, polyacrylate, etc. are known.

However, when using hexamethylenetetramine, it is necessary to add a large amount of 0.07% or more, and in formalin aqueous solutions with a low amount of formic acid, the addition of this However, it has the disadvantage that the pH increases.

If such formalin aqueous solution is used in its entirety, it will be difficult to properly adjust the pH of the reaction system during the production of the synthetic resin. On the other hand, in the case of a formalin aqueous solution containing a high amount of formic acid, the effect of suppressing formic acid production is reduced. Further, when sodium pyrophosphate or (1) acrylate is used as a formic acid production inhibitor, there is a drawback that it does not dissolve in formalin aqueous solution containing a low amount of formic acid and the aqueous solution becomes cloudy.

The present inventors have completed the present invention as a result of studying methods for suppressing formic acid production and stabilizing quality even when storage temperatures are unstable.

That is, the present invention is based on an aqueous formalin solution to which a water-soluble salt of nitrous acid is added.

Next, the present invention will be fully explained.

The effectiveness of the present invention, which suppresses the formation of formic acid by adding all the water-soluble salts of nitrous acid, increases as the formaldehyde concentration increases, and the formaldehyde concentration decreases to about 37%.
This is noticeable in aqueous solutions that are extremely depleted.

The amount of IMF nitrate added is 4! However, the higher the storage temperature of the formalin aqueous solution, the more remarkable the effect is, for example, the more remarkable the effect is at temperatures below 200° C.

The water-soluble salts of nitrite used in the present invention are alkali or alkaline earth metal salts of nitrite such as sodium nitrite, potassium nitrite, calcium nitrite, barium nitrite, etc., and are soluble in water or an aqueous Polmarine solution. Most preferably, sodium nitrite is suitable.

The nitrous acid water-soluble JD of the present invention exhibits a sufficient formic acid suppression effect by adding, for example, θ, oo, Ie to o, ooos to a formalin aqueous solution, but it is the additive piece 1 below J'J. Also, effects can be expected depending on the amount added. However, there is no particular upper limit to the amount of nitrite added, as long as it does not cause any problems when used as the raw material for the formalin aqueous solution of the present invention.

The inhibitory effect on formic acid production by the water-soluble salt of nitrous acid of the present invention is, for example, when stored at a storage temperature of At° C. for λ weeks,
Q, I/2 when the amount of formic acid produced is not adding the nitrite
~o, ipr%, while nitrous acid is 0.0/2 to 0.0/ when 0.001% of IJ is added.
It was reduced to about 100% compared to the case without additives.

In contrast, for example, hexamethylenetetramine 50.0
/%, in a formalin aqueous solution with a low formic acid concentration of 0.0/r, when stored under the same conditions as above, the amount of formic acid decreases and the pH increases. On the other hand, the formic acid concentration is O, O
! In high-concentration formalin, the amount of formic acid produced is 0.
．． 033%, which is greater than the amount of formic acid produced by the inhibitor of the present invention.

Thus, the formalin aqueous solution of the present invention increases the production of formic acid and P by adding a very small amount of water-soluble salts of nitrous acid.
H change and can be suppressed completely effectively.

EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples.

Example 1 Formaldehyde, TO, 9%, methanol 1. Nochi, formic acid 0.0/zaman, PH2,? (Glass electrode 1.Zt℃) Holter 1
) into the aqueous solution≠log>, and add sodium nitrite to this.
po, ooi% were added and stored in a constant temperature water bath at A7°C.

The increase in formic acid after 1 week and λ week is 0.00 respectively.
7% and 0.0/'I%, and the pH is ko, ?, respectively. and λ, were.

The same results were obtained even when the sample was stored in a container made of stainless steel ([3US, 27).

The amount of formic acid was determined according to the method for measuring free acid according to Japanese Industrial Standards, JI-KJ'za72.

Example λ~≠ All the formalin aqueous solutions were stored under the same conditions as in Example 1, except that all the formic acid inhibitors shown in Table 1 were added and the formalin aqueous solutions shown in Table 1 were used. The results are shown in Table 7.

Comparative Example/-2 As shown in Table 7, formalin aqueous solutions with different amounts of formic acid were used, and the formalin aqueous solutions were stored in the same manner as in Example 1, except that the formic acid inhibitor of the present invention was not used. The results are shown in Table 1.

Reference Examples 7-2 Formalin aqueous solutions were stored in the same manner as in Example 1, except that formalin aqueous solutions with different amounts of formic acid were used and hexamethylenetetramine was used as a formic acid inhibitor. The results are shown in Table 1.

Examples J to 3 and Comparative Example 3 Nitrous acid) Addition amount of IJium and nitrous acid) Example / except that the formalin aqueous solution before addition of 13um was changed
An aqueous formalin solution was stored under the same conditions as above, and the results shown in Table 2 were obtained.

Example 10~/7 and Comparative Example Hiro~/l Formalin aqueous solutions were stored under the same conditions as in Example 7, except that the formaldehyde concentration and storage temperature were changed [7] The results shown in Table 3 were obtained.

8- As is clear from the results shown in Tables 1 to 3, the formalin aqueous solution of the present invention, with the addition of an extremely small amount of formic acid inhibitor, can be used regardless of the high or low formic acid concentration and temperature conditions.
It was confirmed that formic acid production in formalin aqueous solution was suppressed and its quality was stabilized.

Applicant Nippon Kasei Co., Ltd. 12-

Claims (1)

[Claims] Formalin aqueous solution made by adding water-soluble salts of nitrous acid