JPH057380B2 - - Google Patents

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 of the present invention is a paraformaldehyde with a high formaldehyde content.
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 has come to be manufactured.

Such paraformaldehyde with a high formaldehyde content (hereinafter abbreviated as high concentration paraformaldehyde) is usually produced by the following method. That is, if the formaldehyde content is, for example, 37~
About 50% formaldehyde aqueous solution, so-called
Formalin is concentrated by a method such as vacuum concentration to form a formaldehyde concentrated aqueous solution or slurry with a formaldehyde content of around 80%, and this is cooled and solidified in a granulation tower etc., thereby forming a granular form with a formaldehyde content of around 80%. It can be obtained by making paraformaldehyde (hereinafter abbreviated as ordinary paraformaldehyde) and then drying this ordinary paraformaldehyde at a temperature below its melting point.

However, the above-mentioned regular paraformaldehyde
At the beginning of production, there was a problem that the melting point was as low as 50 to 60°C, so vacuum drying was required to dry it.

In addition, since the regular paraformaldehyde used at the time of manufacture had poor fluidity, there were problems in that it adhered to the walls of the vacuum dryer, resulting in poor workability during the drying process.

If normal paraformaldehyde is left at a temperature below 40°C after cooling and solidifying, the melting point will reach 65°C.
Since the temperature rises above .degree. C. and the fluidity also improves, drying at normal pressure becomes possible by allowing the time to stand in this manner.

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 hopper after being cooled and solidified. left alone.

However, regular paraformaldehyde has poor fluidity after being cooled and solidified, as described above, and must be stored for 24 hours or more in order to improve its fluidity to the point where 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.

Cooled and solidified regular paraformaldehyde is moved and left on a belt (banding).
Another option is to store the material in a hopper, but this method does not pose the problem of storing the material in a hopper, but in order to store the material on a belt conveyor for more than 3 hours, a huge length of belt is required. is virtually impossible.

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

That is, the method for producing highly concentrated paraformaldehyde of the present invention involves drying ordinary paraformaldehyde obtained by cooling and solidifying a concentrated formaldehyde aqueous solution or slurry having a formaldehyde content of 75% by weight or more and less than 85% by weight. In a method for producing highly concentrated paraformaldehyde of 85% by weight or more, a sparingly soluble basic alkaline earth metal compound, a finely powdered solid, or a lower alcohol is added to a concentrated aqueous formaldehyde solution or slurry immediately before or during cooling and solidification. This method is characterized in that a small amount of ordinary paraformaldehyde is added to form a suspension as a liquid medium and then dried at 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, is
It can be produced according to the method described in Japanese Patent Publication No. 51-6646 filed by the present applicant last year.

In the method of the present invention, formalin with a formaldehyde content of, for example, 37 to 50% is made into a concentrated aqueous solution or slurry with a concentration of 75% or more and less than 85% by a method such as vacuum concentration. A small amount of an alkaline earth metal compound is added and solidified to obtain ordinary paraformaldehyde, and this ordinary paraformaldehyde is dried under 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, the ordinary paraformaldehyde of the present invention includes:
A small amount of slightly soluble basic alkaline earth metal compound is added during the cooling and solidification process, so even ordinary paraformaldehyde immediately after solidification has a melting point of 70℃ or higher and excellent fluidity. Regular paraformaldehyde can be dried under normal pressure at a temperature of 65°C or higher immediately after being cooled and solidified.

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 have a solubility in water of 0.001. ~
It is as low as 0.1%. Even if such poorly soluble basic alkaline earth metal compounds are added to a formaldehyde concentrated aqueous solution or slurry with a formaldehyde content of 75% or more and less than 85% immediately before or during cooling and solidification, they will not become formaldehyde aqueous solutions. It is hardly dissolved in the liquid, and is only included in a solid state in the ordinary paraformaldehyde obtained by cooling and solidifying.

Generally, 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 Canitzaro reaction to produce formic acid as an impurity.

Furthermore, when a water-soluble strong basic substance is added to a concentrated formaldehyde aqueous solution or slurry, polymerization proceeds rapidly, making continuous operation of a granulation tower or the like difficult.

However, the sparingly soluble basic alkaline earth metal compound used in the present invention is added in an amount of about 100% by weight relative to ordinary paraformaldehyde.
Since the amount is in the range of 20 to 100 ppm, preferably 40 to 60 ppm, if this small amount is added, the above-mentioned production of formic acid or rapid polymerization will not substantially occur, causing no problem.

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 dissolved 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. Generally, the amount is in the range of about 20 to 100 ppm, preferably 40 to 60 ppm, based on the weight of a concentrated aqueous formaldehyde solution or regular paraformaldehyde. Even if this level of alkaline earth metal compound is mixed into paraformaldehyde, it hardly poses a problem in the normal use of paraformaldehyde.

The regular paraformaldehyde obtained in this way has a small amount of slightly soluble basic alkaline earth metal added, so it has a melting point of 70°C or higher even immediately after cooling and solidification, and has excellent fluidity.
As described above, immediately after cooling and solidifying, it can be dried at normal pressure using a commonly known dryer such as a band dryer, multi-stage disc dryer, box dryer, or the like.

(Effects of the Invention) As described above in detail, in order to obtain highly concentrated paraformaldehyde by drying ordinary paraformaldehyde, conventionally, it has been necessary to install vacuum equipment and dry it using an expensive vacuum dryer, or to Alternatively, a storage facility such as a hopper is provided, in which the intermediate product, ordinary paraformaldehyde, is stored for a long period of time and then dried, which is very 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 a concentrated aqueous solution of formaldehyde during the process of cooling and solidifying the concentrated aqueous solution. The melting point of regular paraformaldehyde increases and the fluidity becomes good. Therefore, regular paraformaldehyde that has been cooled and solidified can be dried immediately at normal pressure as it is, and can be stored using vacuum equipment or stored as before. No equipment is required and the effect is extremely large.

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

Example 1 Temperature 65 obtained by vacuum concentrating 37% formalin
℃, to a concentrated formaldehyde aqueous solution with a formaldehyde content of 80%, fine magnesium oxide powder equivalent to about 50 ppm was suspended in methanol and added as a 1.5% suspension, and then cooled and solidified in a granular solidification tower.
400 kg/h of regular paraformaldehyde was obtained.

This ordinary paraformaldehyde was immediately fed to a multi-stage disk type dryer to obtain 330 kg/h of highly concentrated formaldehyde with a formaldehyde content of 92%.

The obtained highly concentrated paraformaldehyde had very good fluidity.

Drying: 30 minutes at 65-68℃ in the first stage, 73-77℃ in the second stage
Drying was carried out in three stages: 30 minutes at 88 to 93° C. and 30 minutes at 88 to 93° C. in the third stage.

In addition, the ordinary paraformaldehyde immediately after being cooled and solidified had a high melting point of about 71°C and good fluidity, so it could be fed to the multi-stage disc dryer without any problems, and there was almost no adhesion to the dryer. Ta.

Example 2 Instead of a methanol suspension of magnesium oxide fine powder, fine magnesium hydroxide powder was directly added to a concentrated formaldehyde aqueous solution (however, the amount of fine magnesium hydroxide powder added was equivalent to about 60 ppm relative to formaldehyde). In exactly the same manner as in Example 1, 400 kg/h of ordinary paraformaldehyde having a formaldehyde content of 80.5% was obtained.

Immediately add 20% of this regular paraformaldehyde.
It is fed to a band dryer with mesh wire mesh belt and dried at 60 to 90℃ for 100 minutes to produce highly concentrated paraformaldehyde with a formaldehyde content of 93%.
Obtained 330Kg/h.

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

In addition, the melting point of ordinary paraformaldehyde immediately after cooling and solidification was 72°C and its 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 1 400 kg/h of regular paraformaldehyde with a formaldehyde concentration of 80% was produced in the same manner as in Example 1, omitting the addition of the alkaline earth metal compound.

However, this ordinary paraformaldehyde
Since the melting point was as low as 52°C and the fluidity was very poor, it was difficult to feed it to a multi-stage disk dryer.

For this purpose, this ordinary paraformaldehyde was stored in a hopper overnight to raise its melting point to 65°C and improve its fluidity, and then supplied to a multi-stage disc dryer under the same conditions as in Example 1. It was possible to produce 320 kg/h of highly concentrated paraformaldehyde with a formaldehyde content of 92%.

However, the obtained highly concentrated paraformaldehyde contained a mixture of particles in the form of small lumps due to some particles being fused together.

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

Claims (1)

[Claims] 1. The formaldehyde content is determined by drying regular paraformaldehyde 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.
In a method for producing paraformaldehyde with a high formaldehyde content of 85% by weight or more, a hardly soluble basic alkaline earth metal compound is added to a finely powdered solid formaldehyde concentrated aqueous solution or slurry immediately before or during cooling solidification. Alternatively, a method for producing paraformaldehyde with a high formaldehyde content, which comprises drying at normal pressure ordinary paraformaldehyde obtained by adding a small amount of paraformaldehyde as a suspension to a lower alcohol as a liquid medium.