JPS62148442A - Production of paraformaldehyde having high formaldehyde content - Google Patents

Abstract

PURPOSE:To obtain the titled compound, by making a slightly soluble basic alkaline earth metallic compound into finely divided solid or alcoholic suspension and adding the solid or the alcoholic suspension to a concentrated aqueous solution of formaldehyde or slurry just before solidification under cooling or during solidification under cooling and drying the solution or the slurry. CONSTITUTION:A concentrated aqueous solution of formaldehyde having <=75-<85wt% concentration is solidified under cooling and dried to give paraformaldehyde having high formaldehyde content. In the production, slightly soluble alkaline earth metallic compound (0.01-0.1wt% solubility in water) such as magnesium oxide, calcium oxide or calcium carbonate is processed into finely divided solid or suspension in a lower alcohol as a liquid medium and a small amount (about 20-100ppm, especially 40-60ppm based on paraformaldehyde) is added to the concentrated aqueous solution of formaldehyde or slurry just before solidification under cooling or during solidification under cooling and the solution or the slurry is dried.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved process for producing paraformaldehyde with a high formaldehyde content from a concentrated aqueous solution of formaldehyde.

(Prior art and its problems) The paraformaldehyde with a high formaldehyde content according to the present invention refers to one having a formaldehyde content of 85% by weight or more (hereinafter simply abbreviated as %).

Conventional paraformaldehyde had a formaldehyde content of around 80%, but in recent years, products with even higher formaldehyde content have been required as raw materials for phenol resins. For example, paraformaldehyde with a high formaldehyde content of around 90% has been It's starting to be manufactured.

Such paraformaldehyde with a high formaldehyde content (hereinafter abbreviated as high concentration paraformaldehyde).

) is usually manufactured by the following method. That is, a formaldehyde aqueous solution with a formaldehyde content of, for example, about 37 to 50%, so-called formalin, is concentrated by a method such as vacuum concentration to obtain a concentrated formaldehyde aqueous solution or slurry with a formaldehyde content of about 80%, and this is converted into a granulating base. By cooling and solidifying formaldehyde in granular form, it can be obtained by drying it at a temperature below its melting point.

However, since the above-mentioned ordinary paraformaldehyde has a low melting point of 50 to 60°C at the beginning of production, there is a problem in that it must be dried under vacuum.

Furthermore, since the paraformaldehyde used as a regular product at the time of manufacture has poor fluidity, there was also the problem of poor workability in the drying process, such as adhesion to the walls of the vacuum dryer.

For regular paraformaldehyde, after cooling and solidifying, 1
When left at a temperature of 0°C or lower, the melting point rises to 65°C or higher and the fluidity also improves, so by allowing the product to stand for a longer period of time, it becomes possible to dry it at normal pressure.

However, in order to raise the melting point to the point where it can be dried under normal pressure and improve the fluidity, it is necessary to leave it for more than 3 hours, so regular paraformaldehyde is stored in a hot pot after being cooled and solidified. Be left alone in a way.

However, as mentioned above, regular paraformaldehyde has poor fluidity after being cooled and solidified, and must be stored for 24 hours or more in order to improve its fluidity until it can be taken out smoothly from the hopper.

That is, in order to raise the melting point and improve the fluidity of conventional paraformaldehyde, a hopper is required and the paraformaldehyde must be stored in this hopper for a long time.

One possible method is to move the cooled and solidified paraformaldehyde on a belt and leave it there (banded), but this method does not pose the problem of storing it in a hopper, but it is In order to keep the belt in place for more than 3 hours, a huge length of belt is required, and this method is virtually impossible.

(Means for Solving the Problems) The present inventors have conducted extensive studies to solve the above problems based on the premise that ordinary paraformaldehyde is dried under normal pressure in order to obtain highly concentrated paraformaldehyde. As a result, they discovered that this can be achieved by adding a small amount of a sparingly soluble basic alkaline earth metal compound to regular paraformaldehyde during the manufacturing process of regular paraformaldehyde, leading to the completion of the present invention. be.

That is, the method for producing highly concentrated paraformaldehyde of the present invention is such that the formaldehyde content is 75% by weight or more and 85% by weight.
Immediately before or during cooling solidification in a method for producing highly concentrated paraformaldehyde with a formaldehyde content of 85% by weight or more by drying ordinary paraformaldehyde obtained by cooling and solidifying a concentrated aqueous formaldehyde solution or slurry. Ordinary paraformaldehyde obtained by adding a small amount of a sparingly soluble basic alkaline earth metal compound to a concentrated aqueous formaldehyde solution or rose IJ- as a finely powdered solid or a suspension in lower alcohol as a liquid medium. It is characterized by drying under normal pressure.

The present invention will be explained in more detail below.

The intermediate product of the present invention, ordinary paraformaldehyde to which a sparingly soluble alkaline earth metal is added, can be produced according to the method described in Japanese Patent Publication No. 51-6646 filed by the applicant last year.

In the method of the present invention, the formaldehyde content is, for example, 37
~50% formalin is reduced to 75% using methods such as vacuum concentration.
A concentrated aqueous solution or slurry formaldehyde having a concentration of less than 85% is obtained, and this ordinary paraformaldehyde is dried at normal pressure to obtain highly concentrated paraformaldehyde.

In the present invention, conventionally known dryers such as a band dryer, a multi-stage disc dryer, and a box dryer can be used to dry the regular paraformaldehyde. In addition, since a small amount of slightly soluble basic alkaline earth metal compound is added to the conventional paraformaldehyde of the present invention during the cooling and solidification process,
Due to this effect, even ordinary paraformaldehyde immediately after solidification has a melting point of 70°C or higher and has excellent fluidity.
It should be possible to dry it under normal pressure at a temperature of 5°C or higher.

The basic alkaline earth metal compounds that can be used in the present invention are sparingly soluble alkaline earth metal compounds such as magnesium oxide, magnesium hydroxide, magnesium carbonate, calcium oxide, and calcium carbonate, and are difficult to dissolve in water. It is as low as 0.001-0.1%. Even if such a poorly soluble basic alkaline earth metal compound is added to a concentrated aqueous formaldehyde solution or slurry with a formaldehyde content of 75% or more and less than 85% immediately before or during cooling and solidification, it will not become a formaldehyde aqueous solution. It is hardly dissolved in the liquid, and is only included in a solid state in the ordinary paraformaldehyde obtained by cooling and solidifying.

When a water-soluble strong basic substance such as sodium hydroxide is added to paraformaldehyde, the paraformaldehyde is solubilized and the formaldehyde component undergoes a crab-sotuaro reaction to produce formic acid as an impurity.

Furthermore, if a water-soluble strong basic substance is added to a concentrated formaldehyde aqueous solution or slurry, polymerization will rapidly proceed, making continuous operation of granulating groups difficult.

However, the amount of the sparingly soluble basic alkaline earth metal compound used in the present invention is in the range of about 20 to 1100 ppm, preferably 40 to 60 ppm, based on the weight of normal paraformaldehyde. If only a small amount of is added, the above-mentioned formation of formic acid or rapid polymerization will not substantially occur and no problem will arise.

A sparingly soluble basic alkaline earth metal compound is added to a concentrated formaldehyde aqueous solution before or during cooling and solidification, but as mentioned above, the basic substance is completely solubilized in the formaldehyde concentrated aqueous solution and remains in a strongly alkaline state. It is not good to keep it for a long time, so it is preferable to add it just before cooling and solidifying.

The sparingly soluble basic alkaline earth metal compound used in the present invention is optionally used in the form of a finely powdered solid or a suspension in a lower alcohol as a liquid medium. These basic alkaline earth metal compounds are hardly more soluble in lower alcohols such as methanol and ethanol than in water. Therefore, the use of a suspension using a lower alcohol as a liquid medium has the advantage of making it possible to more easily control the amount of the basic alkaline earth metal compound used in very small amounts.

Among the lower alcohols, methanol in particular is already contained in the raw material formalin, so the amount of methanol added together with the sparingly soluble basic alkaline earth metal compound does not pose a problem.

The amount of the slightly soluble basic alkaline earth metal compound used in the present invention varies depending on the quality of the formalin used as a raw material, especially the formic acid content, the formalin concentration method, the cooling solidification conditions, etc., but generally formaldehyde About 20 to 100 ppm based on M@ standard for concentrated aqueous solution or regular paraformaldehyde, preferably 4
It ranges from 0 to 60 ppm.

Even if this level of alkaline earth metal compound is mixed into paraformaldehyde, it will hardly be a problem in the normal use of paraformaldehyde (1°) , has a melting point of 70°C or higher and has excellent fluidity even immediately after cooling and solidification, so as mentioned above, immediately after cooling and solidification, it can be used in commonly known dryers such as band dryers, multi-stage disk dryers, box dryers, etc. It can be dried at normal pressure using

(Effects of the Invention) As described in detail above, in order to obtain high-concentration valaldehyde by drying ordinary paraformaldehyde, conventionally, it has been necessary to install vacuum equipment and dry it using an expensive vacuum dryer, or to dry it using an expensive vacuum dryer. Alternatively, a storage facility such as a hopper is provided, in which paraformaldehyde, an intermediate product, is stored for a long period of time and then dried, which is extremely expensive and complicated to operate.

In contrast, in the method of the present invention, a small amount of a sparingly soluble basic alkaline earth metal compound is added to the concentrated aqueous formaldehyde solution during the cooling and solidification process. The melting point of regular paraformaldehyde increases and the fluidity becomes good. Therefore, regular paraformaldehyde that has been cooled and solidified can be immediately dried at normal pressure without requiring vacuum equipment or storage equipment. The effect is extremely large without the need for

(Examples and Comparative Examples) The present invention will be specifically described below using Examples and Comparative Examples.

Example 1 Temperature 65°C obtained by vacuum concentrating 37% formalin,
Magnesium oxide fine powder equivalent to about 50 ppm was suspended in methanol and added as a 1.5% suspension to a formaldehyde concentrated aqueous solution with formaldehyde content of 80%, and then cooled and solidified with a granular solidifying group to produce 400 kg/'h.
A regular product of paraformaldehyde was obtained.

This ordinary paraformaldehyde was immediately supplied to a multi-stage disc type dryer to obtain high concentration formaldehyde with a formaldehyde content of 92%/h.

The obtained highly concentrated paraformaldehyde had very good fluidity.

Drying is at 65-68°C in the first stage for 30 minutes, and at 73-7°C in the second stage.
Drying was carried out in three stages: 70C for 30 minutes and the third stage at 88-93C for 30 minutes.

In addition, the ordinary paraformaldehyde immediately after cooling and solidification had a high melting point of about 71°C and good fluidity, so there was no problem in feeding it to the multi-stage disc dryer and there was almost no adhesion to the dryer. Ta.

Example 2 Instead of methanol suspension of fine magnesium oxide powder,
The formaldehyde content was 80.5% in exactly the same manner as in Example 1, except that the magnesium hydroxide fine powder was added as it was to the formaldehyde concentrated aqueous solution (however, the amount of magnesium hydroxide fine powder added was equivalent to about 60 ppm relative to formaldehyde). 40% of regular paraformaldehyde
I got 9/'h on 0.

This ordinary paraformaldehyde was immediately supplied to a band dryer having a wire mesh belt of 20 meshes, and
Formaldehyde content: 93 after drying at 90°C for 100 minutes
A high concentration of paraformaldehyde of 330% to 9/h was obtained.

The high concentration aldehyde obtained had very good fluidity as in Example 1.

In addition, the melting point of the regular paraformaldehyde immediately after cooling and solidification was 72°C and the fluidity was good, so as in Example 1, there was no problem in feeding it to the dryer and there was almost no adhesion to the dryer. .

Comparative Example 1 Regular paraformaldehyde having a formaldehyde concentration of 80% was produced in the same manner as in Example 1 by omitting the addition of the alkaline earth metal compound at 400/9/'h.

However, this ordinary paraformaldehyde has a melting point of 5.
Since the temperature was as low as 2°C and the fluidity was very poor, it was difficult to feed it to a multi-stage disc dryer.

For this purpose, this ordinary paraformaldehyde was stored in a hopper for a day and night to raise its melting point to 65°C and improve its fluidity, and then it was fed to a multi-stage disc dryer, and the same process as in Example 1 was carried out. After drying under the following conditions, high-concentration paraformaldehyde with a formaldehyde content of 92% was added to 320%/
h was able to be manufactured.

However, this highly concentrated paraformaldehyde obtained was
The particles were fused together and some small lumps were present.

Also, a considerable amount of highly concentrated paraformaldehyde was found inside the dryer.

Claims (1)

[Claims] (1) Regular product obtained by cooling and solidifying a concentrated formaldehyde aqueous solution or slurry with a formaldehyde content of 75% or more and less than 85% by weight.High formaldehyde content of 85% or more by drying paraformaldehyde. In a method for producing paraformaldehyde, a sparingly soluble basic alkaline earth metal compound is suspended in a concentrated aqueous formaldehyde solution or slurry immediately before or during cooling and solidification using a finely powdered solid or lower alcohol as a liquid medium. A method for producing paraformaldehyde with a high formaldehyde content, which comprises drying ordinary paraformaldehyde obtained by adding a small amount as a liquid at normal pressure.