JPH02167244A - Production of paraformaldehyde having high formaldehyde content - Google Patents

Abstract

PURPOSE:To obtain paraformaldehyde having high formaldehyde content at a high concentration with a simple method by cooling and solidifying an aqueous solution containing formaldehyde and drying the produced paraformaldehyde using a specific method. CONSTITUTION:An aqueous solution of formaldehyde having a formaldehyde content of 73-83wt.% is cooled and solidified to obtain paraformaldehyde, which is dried with a far infrared heater to form paraformaldehyde having a formaldehyde content of >=85wt.%. More preferably, paraformaldehyde produced by cooling and solidifying the above raw material is heated by applying warm or hot air of 30-60 deg.C for 30-240min, adjusted to <=35 deg.C, dried with a far infrared heater and cooled. The cooling is carried out with chilled air having a temperature lower than the temperature of the outer atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing paraformaldehyde with a high formaldehyde content.

[Conventional technology]

Traditionally commercially available paraformaldehyde had a formaldehyde content of around 80% by weight (hereinafter, weight% is simply referred to as %), but in recent years it has been used as a raw material for the production of phenolic resins, urea resins, melamine resins, polyacetals, etc. Furthermore, there is a demand for products with a high formaldehyde content, and products with a formaldehyde content of 90% or more have come to be manufactured.

Furthermore, when paraformaldehyde is used as the above-mentioned raw material, it is dissolved in hot water or hot water and used as highly concentrated formalin, so it is required to have good solubility in hot water or hot water.

Such paraformaldehyde with a high formaldehyde content (hereinafter abbreviated as "high concentration paraformaldehyde") is usually produced by a method such as coating. That is, formalin with a formaldehyde content of about 37 to 50% is made into a concentrated aqueous solution of formaldehyde with a formaldehyde content of about 80% by a method such as vacuum concentration, and this b1 thick aqueous solution is cooled using a granulating group or a cooling device. After solidifying into granular or scaly rose formaldehyde with a formaldehyde content of around 80% (hereinafter referred to as "conventional paraformaldehyde"), this conventional paraformaldehyde is dried at a temperature below its softening point. It was manufactured by

[Problem to be solved by the invention] However, since the softening point of conventional paraformaldehyde is as low as 50 to 60°C immediately after cooling and solidifying, it is necessary to leave it at a temperature of 40°C or less for 2 hours or more before drying to soften it. The problem is that after raising the temperature to 65-70°C, it must be dried.

If this conventional paraformaldehyde is stored in a hopper or the like, it is difficult to take out the conventional paraformaldehyde from the hopper after storage for about 2 hours, so it is necessary to store it for about 8 to 10 hours. There is a problem.

Therefore, it is unavoidable that the conventional paraformaldehyde that has been cooled and solidified must be allowed to remain on a belt conveyor for more than two hours before being supplied to the drying equipment, resulting in the problem of requiring an excessively large belt conveyor. be.

Furthermore, the drying equipment is typically a band dryer, a fluidized bed dryer,
A hot air circulation dryer or the like is used, but when conventional paraformaldehyde is dried using such a dryer, the following problems arise.

That is, the conventional paraformaldehyde in the form of granules or scales is gradually heated from the surface layer to the inside by conduction heat transfer and is dried. Therefore, in dried highly concentrated paraformaldehyde, the degree of polymerization at the surface layer is higher than that at the inside.
As a result, the solubility in hot water or hot water deteriorates.

In this way, when producing phenolic resins using highly concentrated paraformaldehyde, which has poor solubility in warm water or hot water, condensation with phenol etc. will have a negative effect on the reaction, resulting in poor quality of the resulting phenolic resins. There are problems such as variations.

There is a standard for determining the degree of solubility of rose formaldehyde in hot water or hot water.This hot water solubility is defined as the formaldehyde content in ion-exchanged water adjusted to a temperature of 80°C. The amount of formaldehyde is added and stirred so that the amount is 20%, and the time taken to completely dissolve the formaldehyde is shown. At this time, the standard for determining complete dissolution is the turbidity of the rose formaldehyde solution at Y1! The turbidity shall be 50 or less. Note that the solubility of paraformaldehyde in hot water gradually deteriorates if it is left to stand after production or taken orally. Moreover, the higher the concentration of formaldehyde in rose formaldehyde, the worse it becomes. Therefore, the solubility of conventional paraformaldehyde in hot water is about 1 to 2 minutes immediately after production after cooling and solidification, but it becomes about 10 to 15 minutes after 24 hours of production, and gradually increases after that. Become.

[Means for Solving the Problems] In view of the above circumstances, the present inventors have conducted intensive studies on a method for economically producing highly concentrated paraformaldehyde with good hot water solubility, and as a result, they have succeeded in achieving a far superior method for producing conventional paraformaldehyde. Dry using an infrared heating device, or after blowing warm air or hot air under specific temperature conditions, dry using a far infrared heating device under specific temperature conditions, and then use cold air after drying. The inventors have discovered that the above object can be achieved by cooling, and have completed the present invention.

That is, No.] of the present invention has a formaldehyde content of 78 to 78%.
In a method for producing paraformaldehyde having a formaldehyde content of 85% by weight or more by drying paraformaldehyde obtained by cooling and solidifying an 83% weight formaldehyde aqueous solution, the paraformaldehyde obtained by cooling and solidifying the A manufacturing method that dries formaldehyde using a far-infrared heating device. In the second step, the paraformaldehyde obtained by cooling and solidifying in the first step is aerated with warm air or hot air at 30 to 60°C for 30 to 240 minutes, and then heated to 35°C.
The following describes a manufacturing method characterized by adjusting the temperature of the paraformaldehyde, drying it with a far-infrared heating device, and then cooling it; and thirdly, a method of drying with a far-infrared heating device with hot air at 30 to 90°C. or a manufacturing method in which hot air is circulated; fourthly, paraformaldehyde with a high formaldehyde content obtained by drying with a far infrared heating device is cooled using cold air at a temperature below the outside air temperature; The present invention provides a method for producing paraformaldehyde with high

[Detailed disclosure of the invention]

The present invention will be explained in more detail.

In the present invention, first, conventional paraformaldehyde is produced,
This conventional paraformaldehyde is dried with a far-infrared heating device to produce high-concentration paraformaldehyde, and the conventional paraformaldehyde is produced by a conventionally known method as described above. Thereafter, this conventional paraformaldehyde is heated and dried using a far-infrared heating device, but the type of far-infrared heating device is not particularly limited, and any commonly known device can be used.

In other words, the far-infrared heating device uses the far-infrared rays as a heat source by passing current through a heating wire (heating element) built into the far-infrared heater, which is the heat source, to heat the heating element and generate far-infrared rays. There are heater types such as a dedicated type (ceramic tube type or metal tube type) and a lamp type (bobbin type or plate-socket type), but any type can be used.

Furthermore, gas burners,
It is also possible to generate far infrared rays using an oil burner or steam, and heat and dry using the far infrared rays as a heat source.

In the present invention, the conventional paraformaldehyde is irradiated with far infrared rays generated by the above-mentioned far infrared heater to dry it, but the conventional paraformaldehyde may be dried immediately after being cooled and solidified.

Therefore, in this case, the conventional paraformal material placed in the far infrared heating device has a softening point of 50 to
Since the temperature is as low as 60°C, it is necessary to dry at a temperature at which the temperature of conventional paraformaldehyde does not exceed this softening point at the start of drying. Then, as the drying progresses, the concentration of formaldehyde increases and the softening point of paraformaldehyde also increases, so that the product temperature can be increased for drying.

For this reason, the far-infrared heating device needs to be equipped with a thermometer for measuring the temperature of paraformaldehyde.

The temperature of paraformaldehyde in the far infrared heating device!
III! ff is the distance between the paraformaldehyde and the far-infrared heater, that is, the irradiation distance is il! Node or the voltage applied to the heating element of the far infrared heater! Flf
This can be easily done by executing iff.

The inventors of the present invention have further discovered a method that has low solubility in hot water and solubility in rubbing water.

In the present invention, first, conventional paraformaldehyde is produced,
This conventional paraformaldehyde is dried with a far-infrared heating device to produce high-concentration paraformaldehyde, and the conventional paraformaldehyde is produced by a conventionally known method as described above. After that, this conventional paraformaldehyde is placed in a device maintained at a temperature lower than the softening point of the conventional paraformaldehyde, 30 to 60°C, preferably 40 to 50°C, and the conventional paraformaldehyde in the device is vented. The softening rate of conventional paraformaldehyde can be increased by ventilating the tube at a speed of 0.1 m/s or more based on the empty tube and allowing the tube to ventilate for 30 to 240 minutes. If the temperature inside the device is less than 30°C, it will take a long time to raise the softening point, which is not economical, and if it exceeds 60°C, polymerization will proceed rapidly and the degree of polymerization will vary, which is not preferable.

Conventional rose formaldehyde at room temperature or 30-60℃
The softening point of conventional rose formaldehyde will rise if it is left without ventilation under the temperature conditions of Since the temperature distribution within the formaldehyde layer is different and the softening point varies, it cannot be said to be preferable in terms of manufacturing.

With this method, the softening point of conventional rose formaldehyde was 50-60℃ before treatment, but after treatment it was 70-8℃.
0"C. However, in the above method, 35
Conventional rose formaldehyde at temperatures above 30 to 2
When aerated for 40 minutes, the conventional rose formaldehyde becomes slightly soft, so the fluidity of the conventional rose formaldehyde can be improved by cooling it to below 35°C with cold air below the outside temperature. , is effective when drying conventional bulk formaldehyde using a far-infrared heating device. If this cooling is not carried out, the drying efficiency of the far-infrared heating device will deteriorate, and problems such as part of the conventional rose formaldehyde melting in the far-infrared heating device may occur, so it is better to carry out cooling. The preferred apparatus for carrying out these methods is not particularly limited to types 1 and 1, and any commonly known air circulation type band dryer can be used.

Thereafter, this conventional loose formaldehyde is dried using a far-infrared heating device, using air heated to 30 to 90°C so that the air flow rate to the paraformaldehyde in the drying device is 0, based on the empty tube. Drying is carried out by blowing hot air at a speed of 1 m/s or more so as not to raise the temperature of the product above the softening point of paraformaldehyde. Therefore,
The far-infrared heating device must be equipped with a thermometer to measure the temperature of paraformaldehyde during drying.

Immediately after the formaldehyde concentration of paraformaldehyde in the far-infrared heating device reaches the desired concentration of 85% or more, take out the paraformaldehyde from the far-infrared drying device, and use cold air below the outside temperature to reduce the aeration rate to the paraformaldehyde through the empty tube. It is preferable to rapidly cool the paraformaldehyde at a rate of O, 1 m/s or higher, and sufficiently cool the paraformaldehyde to preferably below 30°C.If the cooling after drying is insufficient, Paraformaldehyde, which has a high formaldehyde content, undergoes polymerization upon oral administration, and its solubility in hot water becomes considerably poor.

In addition, when drying paraformaldehyde, water in the paraformaldehyde evaporates and generates water vapor, so it is preferable to introduce a small amount of air into the far infrared heating device to replace the atmosphere. During drying, the formaldehyde in the rose formaldehyde also evaporates, so the air fed into the far-infrared heating device needs to be taken out of the system and recovered by a method such as absorbing the formaldehyde in water. .

Furthermore, the softening point of paraformaldehyde changes depending on the time it is left to stand after cooling and solidification and the concentration of formaldehyde. Therefore, if a relationship diagram between formaldehyde concentration and softening point is prepared in advance, which takes these into account, it will be convenient for the temperature of paraformaldehyde in Section 11 during the above-mentioned drying.

High-concentration paraformaldehyde needs to have good solubility in hot water, and since the solubility in hot water deteriorates over time after production, it is necessary that the solubility in hot water be small.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Formalin with a formaldehyde concentration of 37% was heated in a vacuum '/! The formaldehyde concentrated aqueous solution obtained by S-condensation at a temperature of 80°C and a formaldehyde content of 80% was cooled and solidified in a granulation tower to produce granular conventional bulk formaldehyde. 100% of this conventional rose formaldehyde
0g was immediately placed in a far-infrared drying device with an internal volume of 50P, and dried while feeding air into the far-infrared drying device at a flow rate of ION/h until the formaldehyde content was 92%.
705 g of highly concentrated rose formaldehyde was obtained.

For drying, first the temperature of the conventional rose formaldehyde was set to 50.
After drying at ~55°C for 1 hour, the product temperature was raised to 70~8°C and drying was continued for 30 minutes. Note that since the air fed into the far-infrared drying device contains formaldehyde gas, it was led out of the system and brought into contact with water to recover the formaldehyde content.

The hot water solubility of the obtained highly concentrated paraformaldehyde after 24 hours was measured and was found to be 11 minutes.

Example 2 A concentrated aqueous formaldehyde solution with a formaldehyde content of 81% obtained in the same manner as in Example 1 was deposited on the surface of a cooled rotating drum and cooled and solidified to produce a scale-like conventional paraformaldehyde product. 1000 g of this conventional paraformaldehyde was immediately put into the far infrared drying device used in Example 1 and dried under the same conditions as in Example 1 to obtain 710 g of highly concentrated paraformaldehyde with a formaldehyde content of 93%. .

The hot water solubility of the obtained highly concentrated paraformaldehyde after 24 hours was measured and was found to be 12 minutes.

Example 3 10 of the conventional paraformaldehyde used in Example 1
Contents 112: 00g, 32 mesh, wire mesh laid
Place paraformaldehyde in a box-shaped band dryer that can circulate warm air at 30 to 60°C, and dry it for 60 minutes while circulating warm air at 45°C so that the airflow rate to the paraformaldehyde is 1 mis. After maturing the formaldehyde, the hot air circulation was stopped, and then the paraformaldehyde was cooled with cold air at 25°C until the crystal temperature became 35°C or less, and after cooling was completed, the paraformaldehyde was taken out from the box-shaped band dryer. .

Next, the extracted paraformaldehyde was placed in a far-infrared drying device with an internal volume of 5 ON and lined with a 32-mesh wire mesh, and heated air at 60° C. was circulated and irradiated with a far-infrared heater of 1 kWh. At this time, the airflow rate to the paraformaldehyde was 1 ts/s, and the paraformaldehyde was irradiated with far infrared rays for 45 minutes while circulating hot air at 60"C. ~1o
The paraformaldehyde was stirred every minute and dried with a far infrared drying device until the formaldehyde content was reduced to 9.
Since 750 g of 1.5% paraformaldehyde was obtained, the paraformaldehyde was immediately cooled with cold air at 25°C for 10 minutes at an air flow rate of 5 II/s to bring the temperature of the paraformaldehyde to 29°C. Lowered.

The hot water solubility of the obtained 91.5% paraformaldehyde immediately after production was measured and was found to be 3 minutes. Furthermore,
The hot water solubility after 10 days of oral administration was 10 minutes.

Example 4 The paraformaldehyde taken out from the box-type band dryer in the same manner as in Example 3 was placed in the far-infrared dryer used in Example 3 and dried for 60 minutes at the same temperature and ventilation rate conditions as in Example 3. 740 g of paraformaldehyde having a formaldehyde content of 93.8% was obtained. Next, cooling was performed under the same cooling conditions as in Example 3.

The hot water solubility of the obtained 93.8% paraformaldehyde immediately after production was measured and was found to be 3 minutes as in Example 3. Furthermore, the solubility in warm water after 10 days of oral administration was 11 minutes.

Comparative Example 1 10 of conventional paraformaldehyde obtained in Example 1
00g was allowed to stand for 3 hours and then dried in a hot air circulation type box dryer to obtain 730g of highly concentrated paraformaldehyde with a formaldehyde content of 92%.

For drying, first dry the product at 60°C for 20 minutes, then raise the product temperature to 80"C for 20 minutes, and then dry at 85-90°C.
The temperature of the product was raised and the product was dried for 20 minutes.

The hot water solubility of the obtained highly concentrated paraformaldehyde after 24 hours was measured and was found to be 25 minutes.

Comparative Example 2 10 of conventional paraformaldehyde obtained in Example 1
After leaving 00g at room temperature for 2.5 hours, hot air circulation type 'R
The aeration rate of paraformaldehyde is 1 in the type band dryer.
Hot air under mis conditions, 65°C, 75°C 185
The paraformaldehyde was dried with hot air for 20 minutes under each temperature condition, and paraformaldehyde with a formaldehyde content of 191.8% was obtained. The rose formaldehyde was cooled until its temperature reached 28°C.

The hot water solubility of the obtained 91.8% rose formaldehyde immediately after production was measured and was found to be 12 minutes.

Furthermore, the solubility in warm water after 10 days of oral administration was 25 minutes.

[Function and effect of the invention]

As described in detail above, the method for producing highly concentrated paralmaldehyde of the present invention is a simple method in which conventional paraformaldehyde is irradiated with far infrared rays and dried.

Furthermore, the method for producing high-concentration valarmaldehyde of the present invention involves the production of conventional valarformaldehyde under specific temperature conditions.
This is a simple method in which the material is allowed to stay, cooled, irradiated with far-infrared rays under specific temperature conditions, dried, and then cooled.

Far infrared rays have a wavelength range of 5.6 to 1000 μm within infrared rays.
It is a type of magnetic wave of about 1 degree. Therefore, when far-infrared rays are irradiated to rose formaldehyde, heat is transferred by radiation.

Substances have their own vibrational and rotational frequencies due to differences in the mass and structural arrangement of the atoms that make up the substance, their arrangement, and the bonding forces within molecules. When a substance is irradiated with infrared rays and the frequency of the infrared rays matches the natural frequency of this vibration or rotation, the molecules absorb the energy of the infrared rays, causing the molecules to vibrate or rotate more intensely and generate heat. This is a phenomenon called resonance absorption phenomenon.
well known.

For this reason, the far infrared energy irradiated on rose formaldehyde is absorbed by the rose formaldehyde and generates heat, which dries the rose formaldehyde, but this heat generation occurs almost uniformly for the rose formaldehyde, so Drying of rose formaldehyde is also carried out uniformly with almost no difference between the surface layer and the inside.

Therefore, compared to high-concentration paraformaldehyde produced by conventional methods, there is less variation in the degree of polymerization, and as will be described later, the drying temperature is low, making it highly soluble in hot water and easy to take orally. This has the effect of producing highly concentrated paraformaldehyde with little change in solubility.

In addition, since the heating of rose formaldehyde is performed uniformly as described above, drying can be performed at a lower temperature than in the conventional method.

Furthermore, since the method of the present invention uses radiation heat transfer to transfer heat to the paraformaldehyde, the temperature increase in the air layer between the far-infrared heater and the paraformaldehyde is extremely small, and therefore the thermal efficiency is higher than that of conventional methods. There is also this effect.

Furthermore, the method of the present invention allows the conventional bulk formaldehyde obtained by cooling and solidification to be immediately dried. There is no need to provide one.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1) Paraformaldehyde obtained by cooling and solidifying a formaldehyde aqueous solution having a formaldehyde content of 78 to 83% by weight is dried to a formaldehyde content of 85% by weight.
A method for producing paraformaldehyde with a high formaldehyde content, the method comprising drying the paraformaldehyde obtained by cooling and solidifying with a far infrared heating device. 2) Paraformaldehyde obtained by cooling and solidifying a formaldehyde aqueous solution with a formaldehyde content of 78 to 83% by weight is dried to a formaldehyde content of 85% by weight.
In a method for producing paraformaldehyde of % by weight or more, the paraformaldehyde obtained by cooling and solidifying the paraformaldehyde is aerated with warm air or hot air at 30 to 60°C for 30 to 240 minutes, and then the temperature is lowered to 35°C or less. A method for producing paraformaldehyde with a high formaldehyde content, which comprises adjusting the temperature of the paraformaldehyde, drying it with a far-infrared heating device, and then cooling it. 3) The method according to claim 2, wherein when drying paraformaldehyde using a far-infrared heating device, hot air or hot air at 30 to 90° C. is circulated during the far-infrared heating. 4) After drying the paraformaldehyde with a far-infrared heating device, the paraformaldehyde with a high formaldehyde content obtained by the drying is cooled using cold air at a temperature below the outside air temperature. The method described in section.