JPH08268948A - Production of formalin - Google Patents

Abstract

PURPOSE: To obtain formalin in an economically advantageous way by making use of the methanol produced from methylamine production process to suppress the decomposition of the methanol into CO, CO2 and CH4 and to attain the improvement of effective component yield. CONSTITUTION: In producing the objective formalin using methanol and air as the main feedstocks, the methanol derived from methylamine production process is used as part or the whole of said methanol. For example, both ammonia and methanol as feedstocks are brought into contact with a solid acid catalyst such as silica-alumina at 300-400 deg.C to obtain reaction products comprising methylamine, an excess of ammonia, water as a byproduct, and unreacted methanol followed by separation, recovery or circulation of the reaction products, and 10-30wt.% of the finally obtained methanol is used as the aimed feedstock; and this feedstock gas is brought into contact with a silver catalyst, and the resultant formaldehyde is absorbed into water and condensed.

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 formalin (formaldehyde aqueous solution) containing methanol and air as main raw materials. More specifically, the present invention relates to a method for efficiently producing formalin by using methanol obtained from the methylamine production step as a part or all of a raw material.

[0002]

BACKGROUND OF THE INVENTION Formalin, which is generally used for industrial purposes, is mainly composed of methanol and air as raw materials, and steam, an inert gas or a raw material gas added with formaldehyde is used as a silver catalyst ( After contacting with excess methanol method or iron / molybdenum catalyst (excess air method), the reaction product gas obtained is led to multiple absorption towers in series, and is absorbed and condensed in water or formalin in the absorption tower to produce formalin. There is.

Methanol is oxidized by this reaction,
Formaldehyde is produced according to the equation (1), while on the other hand, a part of methanol is decomposed, for example, (2)-
According to the formula (4), CH ₃ OH + 1 / 2O ₂ → HCHO + H ₂ O (1) CH ₃ OH + O ₂ → CO + 2H ₂ O (2) CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O (3) CH ₃ OH → CH ₄ + 1 / 2O ₂ (4) CO, CO ₂ or CH ₄ , which causes the formaldehyde yield to decrease.

When the reaction is carried out by the methanol excess method, unreacted methanol is also present in the reaction product. The fractions of these reaction products, that is, formaldehyde, unreacted methanol, and decomposition products, differ depending on the conditions, but in the case of the methanol excess method, they are each about 84
Mol%, 8 mol%, 8 mol%, and about 90 mol%, 2 mol%, 8 mol% in the case of the excess air method. That is,
Even if unreacted methanol is also considered as a component that can be circulated and converted into formaldehyde, the yield of the active ingredient is only 92% in any of the methods, and 8% is CO that is unrelated to the target product. , CO ₂ or CH ₄ and is discharged to the outside of the system.

Therefore, it is extremely important to industrially produce formalin by suppressing the decomposition of methanol into CO, CO ₂ and CH ₄ and improving the yields of formaldehyde and unreacted methanol which are active ingredients. Has become a problem.

The present invention is a method for manufacturing formalin.
CO of Tanol, CO₂And CH _FourSuppresses decomposition into
And aim to improve the yield of formaldehyde
To do.

[0007]

Means for Solving the Problems As a result of intensive studies to solve these problems, the present inventors have found that, in the formalin production process, methanol obtained from the methylamine production process is used as a part or all of the raw material methanol. When used, they found that decomposition of methanol into CO, CO ₂ and CH ₄ was suppressed, and the yield of formaldehyde was improved, and they completed the present invention.

That is, the present invention is characterized in that, in the production of formalin (formaldehyde aqueous solution) containing methanol and air as main raw materials, methanol obtained from the methylamine production step is used as a part or all of the methanol. Is a manufacturing method.

The present invention will be described in detail. In the present invention, in the method for producing formalin, methanol obtained from the methylamine production step is used as part or all of the raw material methanol.

Methanol obtained in the methylamine production process used in the present invention means methanol recovered by distillation separation in the methylamine production process using ammonia and methanol as main raw materials. Methylamine is synthesized according to the following formulas (5) to (7) by contacting raw material ammonia and methanol with a solid acid catalyst such as silica-alumina or zeolite under conditions of 300 to 400 ° C. By substituting with a methyl group, monomethylamine (5), dimethylamine (6), trimethylamine (7) NH ₃ + CH ₃ OH → CH ₃ NH ₂ + H ₂ O (5) NH ₃ + 2CH ₃ OH → (CH ₃ ) ₂ NH + 2H ₂ O (6) 3 types of NH ₃ + 3CH ₃ OH → (CH ₃ ) ₃ N + 3H ₂ O (7) are produced.

The reaction product mainly consists of ammonia supplied in excess in addition to the above-mentioned three kinds of methylamine, water as a by-product and unreacted methanol. Of these, the active ingredients are separated by distillation in order. Then, it is recovered or circulated, and finally an aqueous methanol solution of about 10 to 30% by weight is obtained. In the present invention, the aqueous methanol solution, or the aqueous methanol solution obtained by distillation or methanol may be used.

To use the methanol obtained from the methylamine production process as a raw material for the production of formalin, for example, the above-mentioned methanol or aqueous methanol solution may be mixed with methanol originally used in the production of formalin. It may also be used as a complete alternative. The mixing range of methanol is preferably 3% by weight or more, more preferably 10% by weight or more.

However, when an aqueous methanol solution is used, the aqueous methanol solution after mixing or substitution must contain 80% by weight or more of methanol.

The method for producing formalin of the present invention uses methanol and air as the main raw materials according to the conventional general production method except that the methanol obtained from the methylamine production step is used for a part or all of the raw material methanol. Forming formaldehyde by contacting the gas with a silver catalyst at 550 to 700 ° C. (excess methanol method) or an iron / molybdenum catalyst at 250 to 400 ° C. (excess air method), and absorbing and condensing the formaldehyde into water or formalin. Get formalin.

The main components of the raw material gas supplied to the catalyst layer are methanol, air, water vapor, circulating formaldehyde and, if necessary, an inert gas, and the molar ratio of air to methanol is 1.4 to 2 by the methanol excess method. 0.0, and 16 or more by the excess air method.

The product gas obtained by the reaction is introduced into the first absorption tower of the absorption tower consisting of a plurality of series in accordance with a conventional general production method, and is absorbed and condensed by contacting with water or formalin under normal pressure. , Formalin is produced. Then, the formaldehyde that has not been absorbed can be circulated and again introduced into the catalyst layer together with the raw materials. The temperature of the first absorption tower is about 50 to 90 ° C, and is appropriately adjusted depending on the concentration of formalin to be obtained. If you want to obtain high-concentration formalin, set the temperature of the first absorption tower high. In this case, the unabsorbed content of the active ingredient in the first absorption tower increases, but by lowering the temperature below the second absorption tower, the escape of the active ingredient from the final absorption tower can be prevented.

By using the methanol obtained in the methylamine production process for the production of formalin in this manner, the decomposition of methanol into CO, CO ₂ and CH ₄ is suppressed, and the decomposition products accounted for in the reaction products. The rate is
It can be reduced from about 7 to 8 mol% in the past to about 4 to 5 mol%.

Although the reason for this is not clear, trace amounts of methylamines or reaction by-products contained in methanol obtained from the methylamine production process suppress decomposition of methanol into CO, CO ₂ and CH ₄ . It is supposed that it is because they are doing.

[0019]

【Example】

Example 1 A raw material gas consisting of 45 parts by weight of methanol obtained in the methylamine production step, 405 parts by weight of industrial methanol, 678 parts by weight of air, and 161 parts by weight of water was 1289 kg /
The reaction product gas was continuously contacted with a silver catalyst at a rate of hr at a temperature of 620 ° C., the reaction product gas thus obtained was cooled to 150 ° C., and introduced into an absorption column composed of three columns in series as shown in FIG. Unreacted methanol was absorbed and condensed. From the bottom of the first absorption tower, formalin having an average formaldehyde concentration of 43% by weight, methanol 4.4% by weight, water concentration 52.6% by weight, and formic acid concentration 0.005% by weight was 860 k from the bottom.
It could be continuously produced at a speed of g / hr for 120 days in a colorless and transparent state. Further, from the final top of the third absorption tower, the gas having the composition shown in Table 1 was 593 kg / h on average.
It was discharged out of the system at r. The formaldehyde and unreacted methanol contained in the exhaust gas from the tops of the third absorption towers are vapor pressure losses.

That is, the fractions of the reaction products formaldehyde, unreacted methanol, and decomposition products (CO, CO ₂ and CH ₄ ) are 86.5 mol% and 9.0 mol%,
It was 4.5 mol%.

Example 2 Example 1 was repeated except that 452 parts by weight of methanol obtained in the methylamine production process was used as the raw material methanol.
Formalin was produced in exactly the same manner as. Formaldehyde concentration of 43% by weight from the bottom of the first absorption tower,
862 kg / h of formalin with 4.3% by weight of methanol, 52.7% by weight of water and 0.005% by weight of formic acid.
It could be continuously produced at a rate of r for 120 days in a colorless and transparent state. In addition, from the final top of the third absorption tower, the gas having the composition shown in Table 1 was discharged to the outside of the system at an average of 593 kg / hr.

That is, the fractions of the reaction products formaldehyde, unreacted methanol and decomposition products (CO, CO ₂ and CH ₄ ) are 86.6 mol%, 9.1 mol%,
It was 4.3 mol%.

Comparative Example 1 Formalin was produced in exactly the same manner as in Example 1 except that 474 parts by weight of industrial methanol was used as the raw material methanol and the methanol obtained from the methylamine production process was not used. From the bottom of the first absorption tower, the average formaldehyde concentration was 43% by weight, methanol was 4.4% by weight,
120 formalin with a water concentration of 52.6% by weight and a formic acid concentration of 0.005% by weight at a rate of 856 kg / hr continuously.
It could be produced in a colorless and transparent state for a day. From the final top of the third absorption tower, the gas having the composition shown in Table 1 was discharged out of the system at an average rate of 608 kg / hr.

That is, formaldehyde, unreacted methanol and decomposition products (CO, CO
₂ and CH ₄₎ fraction of 83.5 mol%, 8.7 mol%, 7.8 mol%.

[0025]

[Table 1]

[0026]

INDUSTRIAL APPLICABILITY According to the present invention, in the formalin production using methanol and air as the main raw materials, by using the methanol obtained from the methylamine production step as a part or all of the raw materials, CO and CO _{2 of} methanol can be obtained. And the decomposition into CH ₄ is suppressed, and the yield of active ingredients (formaldehyde and unreacted methanol) is improved. In addition, there is no need to significantly change the existing equipment, which is economical and has a great effect.

[Brief description of drawings]

FIG. 1 An example of the absorption process flow in formalin production

[Explanation of symbols]

 1 Reaction Product Gas 2 Formalin 3 Third Absorption Tower Top Exhaust Gas A First Absorption Tower B Second Absorption Tower C Third Absorption Tower

Claims (1)

[Claims] 1. A method for producing formalin, characterized in that, in the production of formalin using methanol and air as main raw materials, methanol obtained from a methylamine production step is used as a part or all of the methanol.