JP2001198465A - Method for manufacturing catalyst for synthesizing formaldehyde synthesis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a ferrimolybdate catalyst for synthesis of formaldehyde by oxidizing methanol by an excess air method at a high conversion rate and a high selectivity and prolonging its service life. SOLUTION: An aqueous solution of iron (III) salt is added to an aqueous solution of a molybate to produce a slurry solution of a Mo/Fe molar ratio of 1.4-1.6. The slurry solution is subjected to a hydrothermal reaction at a temperature of 70 deg.C-boiling point for 2-10 h. Produced ferrimolybdate crystal is filtered, washed and dried, and it is molded, or carried on a carrier, and burned at 500-650 deg.C for 2-6 h to obtain an oxidation catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst for formaldehyde synthesis. More specifically, the present invention relates to a method for producing an oxidation catalyst in a method for synthesizing formaldehyde by oxidizing methanol by an excess air method.

[0002]

2. Description of the Related Art In a method of synthesizing formaldehyde by oxidizing methanol by an excess air method, an iron molybdic acid catalyst is generally used. For example,
As disclosed in JP-A-2-43638, it is prepared through the steps of mixing, washing, drying, pulverizing, molding, firing and the like of a dilute solution of a water-soluble iron salt and molybdenum salt.

However, these catalysts have a Mo / Fe molar ratio of 3 to 7, and always have a high proportion of molybdenum trioxide Mo.
Contains O ₃ . This is to prevent the formation of a molybdenum-deficient catalyst that significantly reduces selectivity when oxidizing methanol to formaldehyde. However, this excess molybdenum trioxide vaporizes in the reactor,
The deposition in the low temperature region of the catalyst bed shortens the catalyst life and causes a decrease in activity and selectivity.
In addition, these catalysts produce a large amount of oxidation products such as carbon monoxide, and lack high selectivity. On the other hand, Japanese Patent Publication No. 45-37307 discloses a firing temperature of 500 ° C.
As described above, it is disclosed that the formaldehyde selectivity is improved by reducing the surface area. However, this catalyst has a problem that the activity is further reduced by reducing the surface area due to the low purity of the active species contained therein.

In Japanese Patent Publication No. 53-44435,
A method for preparing a catalyst containing iron molybdic acid, which is an active species that does not contain free molybdenum trioxide, with high purity by applying hydrothermal synthesis in which an aqueous solution of iron and molybdenum is aged at 100 ° C. is disclosed. As a result, a catalyst having a long catalyst life and high activity can be produced. However, these catalysts do not undergo a calcination step, or
Since the catalyst is calcined at 0 ° C. or less and has a surface area of more than 10 m ² / g, its performance is not sufficient in terms of low selectivity due to generation of a large amount of carbon monoxide.

[0005]

In the above prior art, when molybdenum trioxide is contained in a high proportion in the catalyst composition, there is a problem that the catalyst life is short and the activity is low, and the surface area is increased in order to increase the selectivity. When the concentration is decreased, the activity decreases with the decrease in the number of reaction sites. On the other hand, when a catalyst containing an active species with high purity is prepared, there is a problem that selectivity is low. The present invention provides a method for producing formaldehyde which solves these problems.

[0006]

Means for Solving the Problems The present inventors have made intensive studies on the above problems and as a result have reached the present invention. That is, in the method for producing a catalyst for formaldehyde synthesis of the present invention, an aqueous solution of ferric salt is added to an aqueous solution of molybdate to make the Mo / Fe molar ratio 1.4 to 1.6 / 1.0, and the slurry containing the generated precipitate The solution is subjected to hydrothermal reaction at a temperature of 70 ° C. to a boiling point for 2 to 10 hours, and the obtained iron molybdate crystals are filtered, washed,
After drying, after molding or supporting on a carrier, 500 to 6
It is characterized by firing at 50 ° C. for 2 to 6 hours.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Molybdenum in the process of the present invention
Ammonium paramolybdate (NH_Four)₆
Mo₇O_{twenty four}・ 4H_TwoO, ammonium dimolybdate
(NH_Four)_TwoMo _TwoO₇・ XH_TwoThere is O, but in this
However, paramolybdate can be suitably used. Second
Ferric nitrate Fe (NO_Three)_Three・ 9H_TwoO, salt
Ferric chloride FeCl_Three・ 6H_TwoO etc. can be mentioned.
Of these, ferric nitrate is preferred. Molybdate is p
Adjust to an aqueous solution with an H value of 1.5 to 2.0, and add
Add an aqueous solution of ferric salt adjusted to 1.0-1.3 and stir
I do. Adjust the pH by adding a mineral acid such as nitric acid or hydrochloric acid.
Do. The resulting suspension is heated to 70 ° C. to the boiling point,
The mixture is stirred for 10 hours to transform into crystalline iron molybdate.
The suspension is then filtered and the precipitate is heated to 50-100 ° C.
After thoroughly washing with water to remove unreacted salts, 100
Dried at a temperature of ~ 130 ° C for 2 ~ 15 hours
To obtain crystals. This iron molybdate is used in tablets, phosphorus
It is molded in the shape of a brush or is carried on the surface of a carrier. As a carrier
Is alkaline earth metal silicate, zeolite, quartz, aluminum
, Silicon carbide or the like is used. In the present invention, this molding or
The catalyst is held in air at a temperature of 500 to 650 ° C.
BET surface area 10m by firing for ~ 6 hours^Two/ G
2-4m from above^Two/ G and used as a catalyst
Selectivity can be improved.

The catalyst for formaldehyde synthesis according to the method of the present invention is used as a fixed bed catalyst packed in a reactor.
Normal reaction conditions are as follows: a reaction raw material gas in which methanol is mixed with air at a gas volume ratio of 8 to 9% at a temperature of 270 to 31;
A formaldehyde synthesis reaction is performed by flowing the catalyst layer at 0 ° C. and a space velocity of 8000 to 12000 h ⁻¹ .

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 8.4 g of ammonium paramolybdate was dissolved in 400 g of pure water, and the pH was adjusted to 1.8 with concentrated nitric acid. Dissolve 13.3 g of ferric nitrate in 100 g of pure water,
A solution adjusted to pH 1.15 with concentrated nitric acid was added. The temperature of the mixed solution was raised to the boiling point, and the mixture was refluxed for 6 hours. The resulting suspension was filtered by suction, washed with 532 g of boiling water, and the obtained wet cake was dried at 120 ° C. for 4 hours to obtain an olive green powder. This catalyst has a crystallinity of 100
% Iron molybdic acid, almost 100%
The specific surface area was 13.0 m ² / g. When this catalyst was molded into a ring and calcined at 530 ° C. for 3 hours, it contained 100% of iron molybdic acid and had a BET specific surface area of 2.8 m ² /
A catalyst having a BET specific surface area of g was obtained.

The obtained catalyst (41 ml) was filled in a jacketed single tube having an inner diameter of 17 mm, and the reaction was carried out at a reaction temperature of 290 ° C. with a methanol concentration of 8% by volume with respect to air.
A mixed gas of methanol was passed at a space velocity of 10,000 h ^-1 to perform a catalytic oxidation reaction of methanol. The gas after the reaction was absorbed in water and analyzed by gas chromatography. The results are shown in Table 1.

Example 2 A catalyst was obtained and a reaction test was carried out in the same manner as in Example 1 except that the firing temperature after molding the catalyst was 560 ° C. for 3 hours. The catalyst contained 100% iron molybdic acid and had a BET surface area of 2.2 m ² / g. Table 1 shows the results of the reaction test.

Example 3 A catalyst was obtained and a reaction test was carried out in the same manner as in Example 1 except that the firing temperature after molding the catalyst was 500 ° C. for 3 hours. The catalyst contained 100% iron molybdic acid and had a BET surface area of 3.3 m ² / g. Table 1 shows the results of the reaction test.

Example 4 A catalyst was obtained and a reaction test was conducted in the same manner as in Example 1 except that the firing temperature after molding the catalyst was 650 ° C. for 3 hours. Catalyst: 3% molybdenum trioxide, 97% iron molybdic acid
The BET surface area was 2.0 m ² / g. Table 1 shows the results of the reaction test.

EXAMPLE 5 The reaction test of the catalyst in Example 2 was carried out continuously for three months, but no deterioration of the catalyst was observed, no deposition of molybdenum trioxide was observed, and no increase in pressure loss of the catalyst was observed. .

Comparative Example 1 The same procedure as in Example 1 was carried out except that firing was not performed after molding the catalyst. The BET surface area of the catalyst was 13 m ² / g, and the results of the reaction test are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated, except that the firing after forming the catalyst was performed at 450 ° C. for 3 hours. The catalyst is 100% iron molybdic acid
Contained, and the BET specific surface area was 5.1 m ² / g. Table 1 shows the results of the reaction test.

Comparative Example 3 20 g of ammonium paramolybdate was dissolved in 313 g of pure water. Thereto was added a solution of 10.5 g of ferric nitrate dissolved in 88 g of pure water and adjusted to pH 1.0 using concentrated nitric acid. After aging at 60 ° C. for 2 hours, the resulting precipitate is filtered, washed with water and dried at 135 ° C. for 10 hours. The obtained catalyst was pulverized, molded into a ring shape, and then calcined at 530 ° C. for 3 hours. The resulting catalyst is BET
The surface area was 3.4 m ² / g. Table 1 shows the results of the reaction test.
Shown in

[0019]

[Table 1]

[0020]

According to the method of the present invention, a catalyst for synthesizing formaldehyde having high activity, high selectivity and long life can be obtained.

Continued on the front page (72) Inventor Kazuhiro Kotani 1-6-6 Takasago, Takaishi-shi, Osaka Mitsui Chemicals, Inc. (72) Inventor Yoshihiro 1-6-6 Takasago, Takaishi-shi, Osaka Mitsui Chemicals, Inc. 4G069 AA02 AA03 AA08 BB07A BB07B BC59A BC59B BC66A BC66B CB19 DA06 EA02X EA02Y EC02Y FA01 FA02 FB10 FB30 FB66 FC06 FC07 FC08 4H006 AA02 AA05 AC12 AC44 BA14 BA19 BA30 CC18 BC18 BC18 BC18 BC18

Claims (1)

[Claims] 1. An aqueous solution of ferric salt is added to an aqueous solution of molybdate to make the Mo / Fe molar ratio 1.4 to 1.6 / 1.0.
The slurry solution containing the generated precipitate is hydrothermally reacted at a temperature of 70 ° C. to a boiling point for 2 to 10 hours, and the obtained iron molybdate crystal is filtered, washed, dried, molded or supported on a carrier, and then 500 to 650 ° C. B. For 2 to 6 hours.