JPH0763625B2 - Method for producing iron molybdate catalyst for oxidation - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an oxidation catalyst comprising iron molybdate or containing iron molybdate as an active ingredient.

[Conventional technology and its problems]

As the oxidation reaction, for example, a method of oxidizing methanol to obtain formaldehyde, a method of using a metal, particularly metal silver as a catalyst, and a method of using a metal oxide are conventionally known, and both methods are industrially performed. Has been done. The latter method using a metal oxide as a catalyst is superior to the method using metallic silver in that the yield of formaldehyde is high and the conversion of methanol is high, so that a formaldehyde aqueous solution containing virtually no methanol can be obtained. ing.

The preferred metal oxides for this purpose are iron and molybdenum oxides. Iron oxides have high activity but little selectivity, while molybdenum oxides have good selectivity but extremely low activity, so it is not preferable to use iron or molybdenum oxides alone. It is well known that the catalytic species active in the oxidation of methanol to formaldehyde is iron molybdate (Fe ₂ (MoO ₄ ) ₃ ), and thus the atomic ratio of molybdenum to iron is 1.5. However, the catalysts actually used in industry always contain a fairly high proportion of excess molybdenum trioxide. The reason for this is said to be to prevent the formation of molybdenum-deficient catalyst, which has poor selectivity when oxidizing methanol to formaldehyde. Also, the presence of molybdenum trioxide is said to be necessary in order to maintain the mechanical properties of the final catalyst.

The problem with such a catalyst containing excess molybdenum trioxide is that the molybdenum trioxide vaporizes under the reaction conditions and deposits at the bottom of the catalyst bed, which reduces the activity and selectivity of the catalyst, and Disintegration and clogging of the catalyst bed occur, making it practically difficult to continue the reaction. In addition, it is not economically preferable to include a large amount of expensive molybdenum trioxide that does not participate in the reaction.

Japanese Patent Publication No. 39-10304 discloses a catalyst additionally containing chromium. This shows that the stability of the catalyst is increased, but the basic composition of the catalyst remains unchanged, and the above problems have not been sufficiently solved. The conventional method for preparing these catalysts is a method in which a complex salt precipitate is formed from a solution containing soluble salts of iron and molybdenum, and the mixture is fired at a high temperature after molding. The precipitate formed in this case is a substantially amorphous solid, which is calcined to form a catalyst containing iron molybdate which is active in the oxidation of methanol to formaldehyde.

On the other hand, JP-A-51-35690 discloses a method of producing iron molybdate in which an atomic ratio of molybdenum to iron is 1.5 to 1.7 in an aqueous solution. According to this, the catalyst is produced by the following method: a) a ratio of a soluble molybdate solution of pH 1.5-5.5 and a soluble ferric salt solution such that the atomic ratio of molybdenum to iron is at least 1.5. An amorphous precipitate is obtained by mixing at a temperature of 20-80 ° C., b) heating the suspension at a temperature of 70 ° C. to boiling for at least 30 minutes to obtain at least 90% of the amorphous precipitate. C) the precipitate obtained is washed to obtain an atomic ratio of molybdenum to iron of solids of 1.5-1.7, and d) the washed product does not exceed 120 ° C. At least 30 at temperature
Dry for minutes.

The catalyst obtained by such a method is different from conventional catalysts in that it contains almost no free molybdenum trioxide and is substantially composed of iron molybdate.

However, as shown above, the embodiment for preparing the catalyst is not only very complicated, but the pH of the raw material soluble molybdate and ferric salt solutions,
Limited to 1.5-2.8 and 1.1-1.5 respectively.

In addition, when converting the formed amorphous precipitate to iron molybdate, in addition to pH value and temperature, the ratio of molybdenum to iron,
Since the amount of water and the reflux ratio of water may affect the desired iron molybdate in some cases, this operation has many limiting conditions, is complicated, and has poor reproducibility.

The present inventors have made various studies in view of the above problems, and as a result of hydrothermally synthesizing a molybdenum compound and an iron compound, iron molybdate can be easily and reproducibly obtained, and the iron molybdate is used for oxidation. The inventors have found that they are suitable as catalysts and have reached the present invention.

[Means for solving problems]

That is, the gist of the present invention is to provide a method for producing an iron oxide molybdate catalyst for oxidation from a molybdenum compound and an iron compound. A method for producing an iron oxide molybdate catalyst for oxidation is characterized by producing iron.

Hereinafter, the present invention will be described in detail.

As a raw material for the synthesis of iron molybdate in the present invention,
Compounds of molybdenum and iron are used. As the molybdenum compound, water-soluble molybdates such as ammonium paramolybdate and ammonium dimolybdate are preferably used, but other water-soluble or insoluble molybdenum compounds such as molybdenum trioxide are also used. Yes, this is one of the major advantages of this method.

The iron compound is not particularly limited in its kind, but is usually selected from soluble salts such as ferric nitrate and ferric chloride.

The amounts of molybdenum compound and iron compound used in the raw materials are
Usually, an atomic ratio of molybdenum to iron of between 1 and 2 is selected. Since the atomic ratio of iron molybdate is 1.5,
It is preferably 1.3 to 1.7. Even if the atomic ratio is larger than this, the hydrothermal method does not prevent the production of iron molybdate, but results in the presence of molybdenum trioxide and the like in addition to iron molybdate.

The molybdenum compound and iron compound are hydrothermally synthesized to produce iron molybdate.

The molybdenum compound and iron compound are usually supplied to the reaction as an aqueous solution, but the method for preparing this solution is not particularly limited. For example, an aqueous solution of each of a molybdenum compound and an iron compound may be prepared and mixed to obtain an insoluble precipitate, and this suspension may be used as a raw material. Alternatively, water may be added to a mixture of both compounds to give a suspension. If one compound is insoluble, it can be used as it is by adding it to an aqueous solution of the other compound. The amount of water added to these compounds is not particularly limited. In addition, an aqueous solution or suspension may be adjusted to a desired pH by adding, for example, mineral acid or the like,
This is not absolutely necessary.

The temperature of hydrothermal synthesis is higher than 100 ° C, and usually 200 ° C or lower. The reaction is carried out under pressure, although autogenous pressure, ie the vapor pressure of water, is usually sufficient. During hydrothermal synthesis, stirring is not always essential, but it is preferable in order to accelerate the production rate of iron molybdate. Also, the reaction time is
It is appropriately selected from about 30 minutes to several days.

The solid obtained from the hydrothermal synthesis contains iron molybdate as the main component, to which the water is then thoroughly washed. It is also a good idea to use acidic water or hot water if necessary. The washed solid is then dried at about 100 to 200 ° C to finally obtain a solid composed of iron molybdate crystals. This is iron molybdate (Fe ₂ (MoO ₄ ))
₃ ) is confirmed by X-ray analysis.

The iron molybdate thus synthesized can be used as it is or after being molded as a catalyst. Alternatively, it may be used after firing at a temperature of about 300 ° C to 600 ° C. Particularly preferred firing temperature is 350 ° C to 450 ° C
Is.

From the viewpoint of controlling the reaction, imparting mechanical strength to the catalyst particles, economic reasons, etc., the synthesized iron molybdate is mixed with a carrier component which is inactive to the reaction and molded into a suitable particle size for the reaction. Is preferable.

As the carrier component, alumina, silica, silica-alumina, titania, zirconia, diatomaceous earth, natural clay, synthetic clay or zeolite can be preferably used. Diatomaceous earth is a particularly preferred carrier component. The amount of the carrier component added to the whole catalyst is not particularly limited, but is selected from about 10% to 90%. When adding the carrier component to the iron molybdate, a binder and a lubricant may be additionally added. As a molding method, various known methods such as tableting and extrusion can be used.

In preparing the catalyst mixed with the carrier component, it is also possible to carry out the hydrothermal synthesis in the form in which the component to be the carrier is added in advance. Such a method is also advantageous in the sense that the catalyst manufacturing process can be shortened.

A small amount of a third component effective as a catalyst, such as a chromium compound, may be added during hydrothermal synthesis or in the subsequent process.

The catalyst of the present invention is extremely effective in the production of formaldehyde by the oxidation reaction, particularly the catalytic oxidation of methanol. In the reaction, it is preferable to first form the catalyst into particles having a desired size by the above-mentioned method. The reaction format is
Usually a fixed bed is used. Further, since the reaction is an exothermic reaction, it is preferable to use a tubular reactor in which a circulating fluid is usually disposed outside for heat removal.

During the reaction, a gaseous mixture containing methanol, oxygen and nitrogen is usually supplied to the catalyst of the present invention at a rate of about 5 to 15 N per hour per 1 ml of the catalyst. This reaction is usually carried out under oxygen excess conditions, but it is necessary to operate outside the explosion limit to avoid the danger of explosion.

The reaction temperature is 200 ° C to 450 ° C, preferably 250 ° C to 400 ° C.
It is carried out between ℃.

[Work]

The reason why the method of the present invention is effective for producing iron molybdate as an oxidation catalyst is not necessarily clear, but it is considered that hydrothermal conditions are equilibrium and advantageous for producing iron molybdate.

〔The invention's effect〕

The method for producing the catalyst in the present invention is remarkably simple as compared with the conventional techniques. In addition, the obtained catalyst has a high mechanical strength and does not contain excess molybdenum trioxide, so vaporization and deposition of molybdenum during the reaction does not occur, thus avoiding problems such as catalyst pulverization and reactor clogging. Therefore, stable operation can be continued for a long time, and an excellent catalyst can be obtained.

In particular, when it is used for the production of formaldehyde by oxidation of methanol, it is industrially excellent because the conversion rate of methanol is high and the selectivity to formaldehyde is high at the same time.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
This does not limit the scope of the invention.

Example 1 Commercially available ammonium paramolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄
4H ₂ O) 9.45 g is dissolved in 100 ml of deionized water to prepare an aqueous solution. Nitric acid is added to this aqueous solution to adjust the pH to 1.7. Another ferric nitrate _{(Fe (NO 3) 3 ·} 9H 2 O) and 15.0g deionized water
It was dissolved in 100 ml, and nitric acid was further added to adjust the pH to 1.15.

An aqueous solution of iron was slowly added to this aqueous solution of molybdenum with stirring at room temperature, and stirring was continued for another 30 minutes. This operation produced a yellow precipitate. At this time, the raw material had a Mo / Fe ratio of 1.44 and a pH of 1.55.

The suspension containing this precipitate is made of titanium 1 with a stirrer.
The mixture was placed in an autoclave, sealed, and heated in an electric furnace with stirring at 150 ° C. for 3 hours for hydrothermal synthesis.

After stopping the reaction, the temperature was returned to room temperature, the solid content was obtained by filtration, and this was washed and filtered with hot water several times.

The solid content thus obtained was dried at 100 ° C. overnight. The yield was 8.85 g.

In addition, when X-ray diffraction of this was measured, it was found to be iron molybdate (Fe ₂ (MoO ₄ ) ₃ ), which did not substantially contain molybdenum trioxide (MoO ₃ ).

Example 2 Hydrothermal synthesis and the subsequent treatment were carried out in the same manner as in Example 1 except that pH adjustment of an aqueous solution of molybdenum and iron was not performed with nitric acid. The yield was 7.53 g.

When X-ray diffraction of this product was measured, it was found to be iron molybdate and did not contain molybdenum trioxide.

Example 3 An aqueous solution of molybdenum and iron was prepared in the same manner as in Example 1 except that the pH was not adjusted with nitric acid, and this was mixed to give a suspension. Next, this was hydrothermally synthesized in the same manner as in Example 1 in an autoclave at 150 ° C. for 5 hours. However, stirring was not performed during the reaction.

The obtained fixed product was treated in the same manner as in Example 1 to obtain 9.77 g of fixed product.

This solid substance was not uniform in appearance, but X-ray diffraction also confirmed small amounts of molybdenum trioxide and the like in addition to iron molybdate.

Example 4 Hydrothermal synthesis was performed in the same manner as in Example 3 except that hydrothermal synthesis was carried out for 50 hours.

The X-ray diffraction measurement result of the obtained product (yield 8.50 g) showed that it was iron molybdate and contained substantially no molybdenum trioxide.

It can be seen that iron molybdate is easily formed if sufficient time is taken even without stirring.

Example 5 A suspension was prepared in the same manner as in Example 3. Next, add 37.3 g of commercially available diatomaceous earth to this and charge it in an autoclave.
Hydrothermal synthesis was carried out at ℃ for 15 hours.

When this was treated in the same manner as in Example 1 and subjected to X-ray diffraction, only iron molybdate was found in addition to diatomaceous earth.

Example 6 An aqueous solution was prepared by dissolving 15.0 g of ferric nitrate in 200 ml of water.
After adding 7.73 g of molybdenum trioxide (Mo / Fe = 1.44) to this, it was charged into an autoclave and hydrothermally synthesized at 150 ° C. for 24 hours with stirring. X-ray diffraction of the same product (yield 7.33 g) shown below showed that it was iron molybdate and was substantially free of molybdenum trioxide.

Example 7 10.16 g of ammonium paramolybdate was added to 100 m of deionized water.
15.00 g of ferric nitrate in an aqueous solution dissolved in 1 l of deionized water
An aqueous solution dissolved in ml was added to obtain a suspension. Mo / F at this time
The e ratio was 1.55.

Charge this suspension into a titanium autoclave of 1,
Hydrothermal synthesis was carried out at 150 ° C. for 3 hours with stirring. After stopping the reaction, the temperature was returned to room temperature, the precipitate was filtered, and this was washed and filtered several times with hot water, and then dried at 100 ° C. for 24 hours. The yield was 9.50 g.

The X-ray diffraction measurement result of this product showed that it was iron molybdate and contained substantially no molybdenum trioxide.

Example 8 A suspension was prepared in the same manner as in Example 7 except that ammonium paramolybdate was 10.50 g and ferric nitrate was 15.00 g. At this time, the Mo / Fe ratio was 1.60. This suspension was subjected to hydrothermal synthesis and subsequent treatment in the same manner as in Example 7 to obtain 10.15 g of a solid powder substance.

It was found by X-ray diffraction that this was mostly iron molybdate, but it contained a small amount of molybdenum trioxide.

Example 9 10.16 g of ammonium paramolybdate was added to 100 m of deionized water.
It was dissolved in 1 and nitric acid was further added to adjust the pH to 1.80. on the other hand,
Ferric chloride (FeCl ₃ .6H ₂ O) 10.03 g was dissolved in 100 ml of deionized water, and the pH was adjusted to 1.30 with aqueous ammonia. The two liquids were combined to form a suspension. At this time, the Mo / Fe ratio was 1.55.

Thereafter, this suspension was subjected to hydrothermal synthesis and subsequent treatment in exactly the same manner as in Example 7 to obtain 10.18 g of a solid powder substance.

The X-ray diffraction result of this product was iron molybdate, which contained substantially no molybdenum trioxide.

Reference Example 1 The catalyst made of iron molybdate obtained in Example 2 was tablet-molded and calcined at 400 ° C. for 2 hours in an air stream. This was crushed and the particle size was adjusted to about 2 mm. 5.2 ml (4.16 g) of this catalyst
Almost the same amount of glass beads (3 mm diameter) were mixed and diluted to obtain a glass reactor having an inner diameter of 22 mm. Methanol, air and nitrogen were added to the reactor at 4.3g / hr and 15.6N respectively.
It was supplied at a flow rate of / hr, 17.9 N / hr. The mole fractions of methanol and oxygen in the mixed gas are 8 and 9% respectively,
The gas hourly space velocity (GHSV) was 7,000 / hr.

The temperature was raised to a predetermined temperature in an electric furnace to start the reaction. The products were analyzed by gas chromatography.

The results at 70 hours after the start of the reaction were as follows.

(Reactor inlet temperature: 290 ℃, catalyst bed maximum temperature: 360 ℃) Methanol conversion: 89% Selectivity of converted methanol to formaldehyde: 9
4% Reference Example 2 The catalyst made of iron molybdate obtained in Example 7 was molded, fired and crushed in the same manner as in Reference Example 1, and 5.2 ml of this catalyst was diluted with an equal amount of glass beads and charged into a reactor. . Then, the reaction was carried out under the same reaction conditions as in Reference Example 1.

The results at 70 hours after the start of the reaction were as follows.

(Reactor inlet temperature: 250 ° C., catalyst bed maximum temperature: 340 ° C.) Methanol conversion: 96% Formaldehyde selectivity: 89% Reference Example 3 The catalyst made of iron molybdate obtained in Example 9 was the same as in Reference Example 1. After molding, firing and crushing, 5.2 ml of this catalyst was diluted with an equal amount of glass beads and charged into a reactor. Then, the reaction was carried out under the same reaction conditions as in Reference Example 1.

The results at 12 hours after the start of the reaction were as follows.

(Reactor inlet temperature: 260 ° C. Catalyst bed maximum temperature: 373 ° C.) Methanol conversion: 98% Formaldehyde selectivity: 93% Reference Example 4 80 parts of the catalyst composed of iron molybdate obtained in Example 9 and commercially available diatomaceous earth After mixing well with 20 parts, molding, firing and crushing were carried out in the same manner as in Reference Example 1, and 5.2 ml of this catalyst was diluted with an equal amount of glass beads and charged into a reactor. Then, the reaction was carried out under the same reaction conditions as in Reference Example 1.

The reaction results were as follows.

Reaction time 36 hours (Inlet temperature: 260 ℃ Maximum temperature: 350 ℃) Methanol conversion: 90% Formaldehyde selectivity: 89% Reaction time 65 hours (Inlet temperature: 290 ℃ Maximum temperature: 380 ℃) Methanol conversion: 99% Formaldehyde selectivity: 91% Reference Example 5 The iron molybdate obtained in Example 9 was catalyzed in the same manner as in Reference Example 3, and 1 ml of this was charged into a glass reactor having an inner diameter of 6 mm. The reaction was carried out by supplying 2% of n-butane and air thereto. The space velocity (GHSV) was 2000 / hr. The n-butane conversion at 450 ° C is 9.1%, and the n-butane conversion at 500 ° C is n.
-The butane conversion was 32.0%. The products were carbon monoxide and carbon dioxide.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C07C 45/29 9049-4H 47/052 9049-4H // C07B 61/00 300

Claims (5)

[Claims] 1. A method for producing an iron molybdate catalyst for oxidation from a molybdenum compound and an iron compound, wherein iron molybdate is produced by hydrothermally synthesizing the molybdenum compound and the iron compound at a temperature exceeding 100 ° C. and under pressure. A method for producing an iron oxide molybdate catalyst for oxidation, characterized by comprising: 2. The method according to claim 1, wherein the iron molybdate thus produced is mixed with a carrier component. 3. The method according to claim 1, wherein iron molybdate is produced in the presence of a carrier component. 4. The carrier component is alumina, silica, silica-
Alumina, titania, zirconia, diatomaceous earth, natural clay,
The method according to claim 2 or 3, wherein the method is one or more selected from the group consisting of synthetic clay and zeolite. 5. A method according to any one of claims 2 to 4, wherein the carrier component is diatomaceous earth.