JPH09241202A - Method for producing formaldehyde aqueous solution - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a method for producing an aqueous formaldehyde solution having a low content of methanol when producing an aqueous formaldehyde solution by oxidizing methanol using formaldehyde as a raw material. A raw material composition ratio, in particular, an air feed ratio to methanol is set to a specific range, and a gas inert to the reaction is mixed into the raw material at a specific ratio to react.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aqueous formaldehyde solution, and more particularly to a method for producing an aqueous formaldehyde solution containing methanol and air in addition to water and formaldehyde as raw materials in an extremely small amount of methanol. Regarding

[0002]

2. Description of the Related Art Aqueous formaldehyde solution is usually industrially composed mainly of methanol, air and water. In the methanol excess method, a mixed gas composed of these is usually contacted with a silver catalyst to react with each other to produce formaldehyde-containing solution. It is generally manufactured by absorbing gas in water.

The aqueous formaldehyde solution thus produced is used in various industrial fields. Among them, especially in the field of resin production such as polyurethane or polyacetal, or in the field of paraformaldehyde production, the amount of methanol contained is high. It is desired that the amount of methanol contained in the aqueous formaldehyde solution is 50% to 65% by weight, and the amount of methanol contained in the aqueous formaldehyde solution is less than 1% by weight. ing.

On the other hand, in a production process such as paraformaldehyde, hexamethylenetetramine, or polyacetal using an aqueous formaldehyde solution as a raw material, the concentration is usually less than 30% by weight.
There is a problem that a relatively dilute formaldehyde aqueous solution (hereinafter referred to as thin phor) is by-produced. That is, since such thin phor is generally extremely low in utility value, in treating this, an industrial formaldehyde aqueous solution manufacturing process is a facility in which the thin phor can also be used as a raw material. Is desired.

However, in the conventionally known production of an aqueous formaldehyde solution using formaldehyde as a raw material, there is a drawback that the obtained aqueous formaldehyde solution tends to have a relatively high methanol content. That is, as a method for producing an aqueous formaldehyde solution by bringing a mixed gas consisting of formaldehyde in addition to methanol, air and water into contact with a metal catalyst to cause a reaction, in a conventionally known method, for example, the amount of formaldehyde and water in the raw material is With a specific ratio (Japanese Patent Application Laid-Open No. 51-56407) or a method of reacting raw material methanol with air, formaldehyde and water within a specified range (Japanese Patent Publication No. 29204/1994)
was there.

However, all of the above-mentioned conventionally known methods are aimed at reducing the formation of formic acid or a polymer and obtaining an aqueous solution of formaldehyde having a particularly high concentration, and are obtained by these methods. The concentration of methanol in the product is relatively high, and as shown in the examples in the above publication, the value converted per formaldehyde concentration of 50 to 65% by weight is 1.5 to 4.0%.
It was in the range of wt% and was not a method capable of producing an aqueous formaldehyde solution having an extremely small amount of methanol, which was less than 1 wt% as described above.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a method capable of effectively treating thin phor and capable of producing a formaldehyde aqueous solution having a low methanol concentration as compared with the above-mentioned conventionally known methods. The purpose is to use formaldehyde as a raw material, and to obtain a product with a formaldehyde concentration of 50%.
It is an object of the present invention to provide a method capable of producing a formaldehyde aqueous solution having an extremely low methanol content with a yield of less than 1% by weight per unit weight% with a high yield.

[0008]

In order to achieve the above object, the present inventors decided to use a mixed gas consisting of methanol, air, formaldehyde, water, and an inert gas as a raw material, and to adjust their composition. The inventors have made extensive studies and studied conditions under which the reaction can be carried out by contacting a silver catalyst with various changes to produce a product formaldehyde aqueous solution with a low yield and a high yield.

As a result, the composition of air and inert gas with respect to methanol in the raw material has a significant effect on the amount of methanol contained in the resulting aqueous formaldehyde solution. It was found that an aqueous formaldehyde solution having an extremely low methanol concentration can be produced when the reaction is carried out in a narrow range. Furthermore, by setting the composition of water and formaldehyde in the raw materials in a specific range,
It has been found that the above-mentioned object can be more sufficiently achieved, and the present invention has been completed.

That is, in the present invention, when methanol, air, formaldehyde and water are used as raw materials and a mixed gas composed of these is brought into contact with a silver catalyst to produce a formaldehyde aqueous solution, the molar ratio of air to methanol is set to 1.75 to 2.05. In addition, a method for producing an aqueous formaldehyde solution is characterized in that a gas inert to the reaction is mixed in the raw material in the range of 0.4 to 2.0 mol per mol of the methanol and the mixture is reacted. The amount of water is in the range of 0.24 to 0.95 mol per mol of methanol, and the amount of formaldehyde in the raw material is 0.01 to 0.2 per mol of methanol.
The method according to the above or the method in the range of molar, the gas inert to the reaction is a waste gas discharged from the formaldehyde absorption step of the aqueous formaldehyde solution manufacturing process, or the method according to the above, and the feed rate of methanol in the raw material. However, 0.1 to 0.3 Nm ³ / per unit area of catalyst bed
Disclosed is a method for producing an aqueous formaldehyde solution according to any one of the items 1 to 3, which is m ² · sec (0 ° C., 1 atm conversion).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in addition to methanol, air, formaldehyde and water, a reaction-inert gas mixed in a raw material means an oxidation reaction of methanol such as nitrogen, argon or carbon dioxide. Is a gas that is not usually involved or waste gas discharged from the formaldehyde absorption step of the formaldehyde solution manufacturing process. Usually, the waste gas discharged from the formaldehyde absorption step of the formaldehyde solution manufacturing process is generally 15 to 23% by volume of hydrogen, 70 to 80% by volume of nitrogen, 0 to 3% by volume of carbon monoxide, 3 to 6% by volume of carbon dioxide, It is an inert gas that can be suitably used in the method for producing an aqueous formaldehyde solution of the present invention in view of economy and process stability, because it is composed of a small amount of water.

In the present invention, it is important to mix 0.4 mol or more of the above-mentioned inert gas with respect to 1 mol of the raw material methanol, and more preferably 0.4 to 2.0 mol. That is, when the composition ratio of the inert gas to the raw material methanol is less than 0.4 mol, the resulting formaldehyde aqueous solution has a high methanol concentration, and particularly when the concentration of methanol is less than 1 wt% when converted to 50 wt% of formaldehyde. This is because it becomes extremely difficult to obtain such substances, and if it is mixed in excess of 2.0 mol, the volumetric efficiency of the reactor becomes extremely poor, and the equipment for supplying the inert gas and the operating cost also increase. It is not preferable because it becomes uneconomical.

Further, in the present invention, in addition to mixing the inert gas in the above range, it is very important to supply air in the range of 1.75 to 2.05 mol to the raw material methanol in order to achieve the object of the present invention. Is important to. That is, if this is a supply amount of less than 1.75 mol, it is likely to be an aqueous formaldehyde solution containing much methanol,
This is because it is extremely difficult to obtain a methanol concentration of less than 1% by weight when converted to 50% by weight of formaldehyde, and when more than 2.05 mol is supplied,
This is because if the reaction temperature becomes too high, the generated formaldehyde is easily decomposed, the product yield is lowered, and the life of the catalyst is relatively shortened. This is because the object of the present invention cannot be achieved sufficiently.

Particularly in the method of the present invention, an aqueous formaldehyde solution having an extremely low methanol content can be obtained in good yield only when both the air and the inert gas to the raw material methanol are simultaneously filled within the range defined above. Since it is possible, the above numerical range is a very important requirement. The air used in the present invention means ordinary air containing approximately 21% by volume of oxygen. For example, when the oxygen content is less than this, a large amount of air corresponding to that is required. Of course it is said.

In the present invention, the formaldehyde used as a reaction raw material is usually a thin formol having a concentration of about 1 to 25% by weight, which may be fed into a vaporizer for gasifying the raw material methanol. Alternatively, a method of mixing with other raw material components after being gasified via a vaporizer provided separately may be used. When the amount of formaldehyde in the raw material is too large, the decomposition of formaldehyde produced by the reaction is promoted, and the product yield is likely to decrease.Therefore, the amount is 0.2 mol or less, usually 0.01 to 0.2 mol, based on the raw material methanol. It is preferable that

If the amount of water in the raw material is too small, the decomposition of formaldehyde produced by the reaction is promoted, and the product yield tends to decrease. If it is too large, a high-concentration formaldehyde aqueous solution is immediately added. Since it is difficult to obtain, 0.24 to 0.95 relative to the raw material methanol
It is preferred to be in the molar range.

Further, if the feed rate of the raw material to the reactor is too high or too low, formaldehyde containing a large amount of methanol tends to be produced, so that the feed rate of methanol in the raw material is determined by the catalyst bed unit. 0.1 to 0.3 Nm ³ / m ² · sec per area (0 ° C, 1 atm conversion)
It is preferably supplied in the range.

In the present invention, the raw materials consisting of methanol, air, formaldehyde, water and an inert gas are mixed with each other and then contacted with the silver catalyst in the reactor for the reaction. As the silver catalyst, it is preferable to use silver produced by electrolysis and formed into particles.

[0019]

EXAMPLES Hereinafter, the method for producing an aqueous formaldehyde solution according to the present invention will be described in more detail with reference to examples. In the following, the conversion rate means the amount (mol) of methanol involved in the reaction with respect to the supply amount (mol) of raw material methanol.
The yield is a numerical value in which the amount (mol) of formaldehyde produced is expressed in% with respect to the feed amount (mol) of the raw material methanol.

Loading of catalyst and its activation Inside the catalyst packing part (inner diameter 100 mm, SUS-310S stainless steel)
Of upright cylindrical shape that is provided with
Using a SUS304 reactor, the catalyst filling part is electrolyzed
The obtained silver catalyst was applied on the copper mesh in the order from the lower layer to the upper layer.
The particle size distribution of 10-20 mesh is 142.9g, 20-32
142.9g of mesh, 1 of 32-42 mesh
19.1g, 71.5g of 42-60 mesh, and 60-90mesh
47.6 g of mash so that each has a uniform thickness
I sown it. In addition, in order to measure the reaction temperature, the catalyst layer
A thermocouple was attached to the bottom. Next, above the reactor
Reheated nitrogen gas is sent at a flow rate of 150 Nl / min.
The catalyst layer was heated to 250 ° C and then methanol was supplied.
Feed rate is 0.2 Nm^Three/ m ^Two・ Make sure the air / me
Make sure that the molar ratio of tanol is 1.23,
Start to supply a mixed gas consisting of
After confirming the temperature rise, gradually increase the above mixed gas.
Then, the nitrogen gas supply was stopped. Then air / me
Reaction temperature reaches 590 ℃ while fine-tuning the ratio of tanol
Water for 3 hours, then add water / methanol
At the same time, add steam until the molar ratio becomes 0.84.
And keep the reaction temperature at 590 ℃ for 1-2 hours.
The dose was gradually increased. After stabilizing, further increase the air volume
The reaction temperature to 630 ° C for 24 hours.
I carried it. The catalyst was activated by the above operation. Note that
In the above, the reaction product gas flowing out from the lower part of the catalyst layer is
After being rapidly cooled to 160 ° C, three units were placed in series
Absorbed by water in the absorption process consisting of an absorption tower
Obtain formaldehyde aqueous solution from the bottom of the tower and
The gas that could not be absorbed was treated as waste gas from the top of the absorption tower.
I released it.

Example 1 Next, to the raw material fed into the reactor, the exhaust gas discharged from the formaldehyde absorption step was gradually added, and a thin form was added to the raw material composition (molar ratio). ) Are air / methanol = 1.80, water /
Methanol = 0.847, formaldehyde / methanol =
It was gradually changed to 0.133 and waste gas / methanol = 1.43, and the reaction was continued under the condition of a temperature of 600 ° C. The results obtained after 20 hours under these conditions show that the obtained formaldehyde aqueous solution has a concentration of 49.4% by weight, with 0.7% by weight of methanol and 32% of formic acid contained therein.
ppm. Table 1 shows the results. The volume composition ratios of hydrogen, nitrogen, carbon monoxide, and carbon dioxide in the waste gas in this case are 18.2% and 77.1%, respectively.
%, 0.0% and 4.7%.

Examples 2 to 8 The composition ratios of air, waste gas, water and formaldehyde to the raw material methanol were changed as shown in Table 1, and the reaction was continuously performed under the conditions shown in Table 1. The same operation as in Example 1 was carried out except that it was added. It was found that the aqueous formaldehyde solutions obtained under these conditions all had a methanol content of less than 1% by weight converted to a concentration of 50% by weight. The summarized results are shown in Table 1.

Comparative Examples 1 to 5 The composition ratios of air, waste gas, water, and formaldehyde to the raw material methanol were changed as shown in Table 1, and the reaction was carried out continuously under the conditions shown in Table 1. The same operation as in Example 1 was carried out except that it was added. Table 1 shows the results.

[0024]

[Table 1]

[0025]

As described in detail above, in the production of formaldehyde aqueous solution using thin phosphor as a raw material,
The composition of the present invention, in particular, by reacting both raw air with air and waste gas within the range described in the present invention, the methanol content per formaldehyde concentration of 50% by weight is less than 1% by weight. It is possible to obtain a low-formaldehyde aqueous solution with good yield.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining a method for producing an aqueous formaldehyde solution in Examples, in which a dotted line shows a gas flow and a solid line shows a liquid flow.

[Explanation of symbols]

 1 ... Air 2 ... Methanol 3 ... Thin foam 4 ... Vaporizer 5 ... Waste gas 6 ... Reactor 7 ... Copper mesh 8 ... Catalyst 9 ... Heat Exchanger 10 ... Reaction product gas 11 ... First absorption tower 12 ... Second absorption tower 13 ... Third absorption tower 14 ... Formaldehyde aqueous solution T ... Thermometer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masatoshi Nomura 1900, Togo, Mobara-shi, Chiba Mitsui Toatsu Chemical Co., Ltd.

Claims (5)

[Claims] 1. When methanol, air, formaldehyde and water are used as raw materials and a mixed gas composed of these is brought into contact with a silver catalyst to produce an aqueous formaldehyde solution, the molar ratio of air to methanol is set to 1.75 to 2.05, and the reaction is performed. Is a method for producing an aqueous formaldehyde solution, characterized in that an inert gas is mixed in the raw material in the range of 0.4 to 2.0 mol per mol of the methanol, and the mixture is reacted. 2. The method for producing an aqueous formaldehyde solution according to claim 1, wherein the amount of water in the raw material is in the range of 0.24 to 0.95 mol with respect to 1 mol of methanol. 3. The amount of formaldehyde in the raw material is in the range of 0.01 to 0.2 mol per mol of methanol.
The method for producing the aqueous formaldehyde solution according to claim 1 or 2. 4. The method for producing an aqueous formaldehyde solution according to claim 1, wherein the gas inert to the reaction is a waste gas discharged from the formaldehyde absorption step of the aqueous formaldehyde solution production process. 5. The method according to claim 1, wherein the feed rate of methanol in the raw material is 0.1 to 0.3 Nm ³ / m ² · sec (0 ° C., 1 atm conversion) per unit area of the catalyst bed. Method for producing aqueous formaldehyde solution.