JPH059145A - Production of formaldehyde - Google Patents

Abstract

PURPOSE:To stably produce formaldehyde by using a catalyst reduced in lowering of selectivity to formaldehyde when formaldehyde is produced by oxidation reaction of methylal. CONSTITUTION:Method for producing formaldehyde by oxidation of methylal by using a catalyst expressed by the general formula [(Mo(1-n)Wn)a Fe(1-n)(Al, Cr, In)bOc (wherein 0<=n<=0.5, 1.5<=a<=3, 0.5<b<0.95 and (c) is a value satisfying balance of valence].

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing formaldehyde by the oxidation reaction of methylal. More specifically, it relates to a method for producing formaldehyde by oxidizing methylal in the gas phase with a gas containing oxygen in the presence of a catalyst.

[0002]

2. Description of the Related Art As a method for producing formaldehyde which is important as an industrial raw material, a method of oxidizing methanol in the presence of a silver or iron-molybdenum catalyst is known. However, the concentration of formalin obtained by this method is at most 63 wt% even if it reacts stoichiometrically. On the other hand, a method for producing formaldehyde by the oxidation reaction of methylal is known, and this method results in 83 wt% formalin when the reaction is stoichiometric.
It has a feature that a high concentration of formalin can be obtained. As a catalyst for producing formaldehyde by oxidizing methylal, a catalyst having high selectivity by containing antimony, bismuth, alkali metal, etc. containing molybdenum and iron as main components is disclosed in Japanese Examined Patent Publication No. 62-10495. Japanese Patent Application Laid-Open No. 1-186831 discloses a catalyst in which tungsten, aluminum or the like is added in addition to molybdenum and iron in order to suppress an increase in layer differential pressure.

[0003]

When formaldehyde is produced by the oxidation reaction of methylal, the following three formulas are considered as the main reaction for obtaining formaldehyde. CH ₃ OCH ₂ OCH ₃ + O ₂ → 3CH ₂ O + H ₂ O CH ₃ OCH ₂ OCH ₃ + H ₂ O → CH ₂ O + 2CH ₃ OH CH ₃ OH + 1 / 2O ₂ → CH ₂ O + H ₂ O On the other hand, the following reaction is considered as the main reaction in which a by-product is formed in the oxidation reaction of methylal.

2CH ₃ OH → CH ₃ OCH ₃ + H ₂ O CH ₂ O + 1 / 2O ₂ → CO + H ₂ O 2CH ₃ OH + O ₂ → HCOOCH ₃ + 2H ₂ O 1 inch using a conventional catalyst When the oxidation reaction of methylal was carried out continuously while maintaining a constant conversion rate in the reaction tube of
It has been found that there is a phenomenon in which the selectivity of formaldehyde decreases due to an increase in by-products of dimethyl ether, methyl formate and carbon monoxide. When the catalyst was taken out and examined, molybdenum oxide was escaped from the surface of the catalyst pellets in the front part of the reaction tube, and a black discolored part was observed in the catalyst pellets in the central part and the rear part of the reaction tube. When the X-ray diffraction spectrum (anti-cathode: Cu-Kα) of this part was examined, a new peak appeared at the position of 2θ = 26.1 ° ± 0.2 ° compared to the X-ray diffraction spectrum of the catalyst before use. I found out that From these, it can be inferred that there is some correlation between the change in the catalyst, the decrease in formaldehyde selectivity, and the increase in by-products. It is not always clear what composition of the compound the peak at the position of 2θ = 26.1 ± 0.2 ° in X-ray diffraction is, but it is caused by the oxide represented by MoO ₂ or FeMoO _4. it is conceivable that.

The present invention provides a method for producing a formaldehyde by an oxidation reaction of methylal, which suppresses a decrease in formaldehyde selectivity.

[0006]

Means for Solving the Problems In the method for producing formaldehyde by the oxidation reaction of methylal, the present inventors have conducted various studies on a catalyst that does not reduce the selectivity of formaldehyde, and have completed the present invention. That is, the present invention has the general formula _{(Mo (1-n) W} n) a Fe (1-b) X b O c ( where, X is one or more elements selected from Al, Cr and In, 0 ≦ n ≦ 0.5, 1.5 ≦ a ≦ 3, 0.5
<B <0.95, c is a value that satisfies the valence balance. ) Is a method for producing formaldehyde by the oxidation reaction of methylal, characterized by using a catalyst represented by
Therefore, it is intended to provide a method capable of stably producing formaldehyde.

The present invention will be described in detail below. In the general formula _{(Mo (1-n) W} n) a Fe (1-b) X b O c ( where, X is composed of Al, Cr and In.), N
Is 0 or more and 0.5 or less, a is 1.5 or more and 3 or less, b is a value greater than 0.5 and less than 0.95, and c is a valence balance. It is a value to be satisfied. More preferably, n is 0 or more and 0.3 or less, a is 1.6 or more and 2.5 or less, and b is a value larger than 0.5 and smaller than 0.9. is there.

The reason why the catalyst of the present invention causes a small decrease in formaldehyde selectivity in the methylal oxidation reaction is not always clear, but the composition of the catalyst is F.
It is considered that at least one element X selected from Al, Cr and In was introduced in place of e at a high ratio of 0.5 <X / (Fe + X) <0.95. It is inferred from the X-ray diffraction spectrum (anticathode: Cu-Kα) that these catalysts form a solid solution, and this also indicates that the oxidation reaction of methylal is carried out for a long period of time.
This is probably because a new peak is hard to appear at the position of 2θ = 26.1 ° ± 0.2 °.

The X-ray diffraction spectrum of the catalyst is MoO ₃ , Fe ₂ (MoO ₄ ) ₃ , Al ₂ depending on the composition of the catalyst.
(MoO ₄ ) ₃ , Cr ₂ (MoO ₄ ) ₃ , In ₂ (Mo
Peaks due to O ₄ ) ₃ , Fe ₂ (WO ₄ ) ₃ and solid solutions of these compounds are obtained. However, the intensity of these peaks is not uniquely determined because it changes depending on the crystallinity depending on the calcination temperature of the catalyst and the adjustment of the sample at the time of measurement, but as an example, Fe calcined at 500 ° C. for 3 hours is used. The catalyst X-ray diffraction spectrum (anticathode: Cu-Kα) after using an oxide catalyst having a composition of _0.25 Cr _0.75 Mo _1.75 for the oxidation reaction of methylal is as shown in FIG.
2θ = 12.8 °, 15.3 °, 20.5 °, 21.8
Major peaks are obtained at diffraction positions of 2 °, 23.0 °, 25.8 °, 27.4 °, 30.3 ° and 34.1 ° (accuracy: ± 0.2 °).

For the value of X / (Fe + X), X /
When (Fe + X) ≦ 0.5, the formaldehyde selectivity tends to decrease, and the smaller the value of X / (Fe + X), the greater the tendency, and the more the position at 2θ = 26.1 ° ± 0.2 °. New peaks are also likely to appear. Also, 0.95 ≦
When X / (Fe + X) is used, the reaction activity of the catalyst is reduced, and the catalyst is no longer a practical catalyst.

Regarding n, the reaction activity becomes smaller as n becomes larger than 0.5. Regarding a, when a is less than 1.5, by-products such as carbon monoxide are increased to lower the formaldehyde selectivity, and when a is greater than 3, the molybdenum oxide escapes and deposits, etc. It causes an increase in the differential pressure over time. Examples of the raw material of each element that constitutes the catalyst of the present invention include metals, oxides, chlorides, nitrates, hydroxides, organic acid salts such as acetates, etc. There is no particular limitation. The catalyst can be prepared by a precipitation method, a coprecipitation method, an evaporation-drying method, a spray-drying method and the like which are commonly used in this field, but other methods may be used. However, the catalyst composition is MoO ₃ , Fe ₂ (MoO ₄ ) ₃ and Al _{2 which} are the respective constituent oxides.
It is difficult to obtain the effects of the present invention with a physical mixture of (MoO ₄ ) ₃ , Cr ₂ (MoO ₄ ) _3, etc., and it is preferable to obtain a desired catalyst composition at the catalyst preparation stage. Also,
When an organic salt such as chloride, nitrate or acetate is used as the raw material of the catalyst, 150 ° C. to decompose these compounds into oxides before tableting the prepared catalyst.
You may bake at the temperature of 500 degreeC. Further, in order to control the reaction activity of the catalyst, calcination is carried out at a temperature of 200 ° C. to 600 ° C. This operation may be carried out either before or after tableting of the catalyst, and the calcination time is 1 to 10 hours. Suitable,
There is no particular limitation. Oxide catalysts obtained by these methods are usually subjected to tableting molding for the reaction of methylal, but in order to facilitate tableting molding, graphite, stearic acid and other release agents are added. Is also good. The addition concentration of the release agent is 0.
It is from 01 to 10 wt%, preferably from 0.1 to 5 wt%.

The catalyst is usually tablet-molded in a cylindrical shape or a Raschig ring shape, but other shapes may be used. The apparent density of the tablet-molded catalyst is 1.5 to 2.8 g / cm ^3.
Is preferable, and more preferably 1.7 to 2.5 g / c.
m ³ , more preferably 2.0 to 2.3 g / cm ³ . If the apparent density is less than 1.5 g / cm ³ , the strength of the molded product is weak and handling is difficult. Also, 2.8 g / cm
^If it exceeds ³ , the reaction activity and the formaldehyde selectivity decrease.

The reaction temperature in the method of the present invention is 150 to
It is in the range of 500 ° C, preferably 200 to 400 ° C.
When the temperature is 150 ° C. or lower, the yield of formaldehyde is low, and when the temperature is 500 ° C. or higher, the amount of by-products such as carbon monoxide increases and the formaldehyde yield decreases, which is not preferable. In the method of the present invention, the composition of the reaction gas at the time of actual use is not particularly limited as long as it is outside the explosion range, and it can be carried out in any range. Further, an inert gas such as nitrogen may be allowed to coexist, and coexistence of water is not particularly limited. Further, although there is no particular problem if the reaction gas contains methanol, the molar ratio of methanol to methylal is 0.5 or less because the concentration of formalin obtained becomes low when the ratio of methanol becomes high. , Preferably 0.3 or less, more preferably 0.1 or less.

The space velocity (SV) of the feed gas is 2,000.
The range of ˜50,000 Hr ⁻¹ is preferable. Further, the reaction in the present invention may be carried out under any of normal pressure, increased pressure and reduced pressure.

[0015]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. The conversion of methylal and the selectivity of formaldehyde are defined as follows based on the analysis value (relative mole number) of the gas chromatograph. Conversion of methylal (%) = [1- (3 × d + e) /
T] × 100 Formaldehyde selectivity (%) = (f / U) × 100 Dimethyl ether selectivity (%) = (2 × g / U) × 1
00 Selectivity of methyl formate (%) = (2 × h / U) × 100 Selectivity of carbon monoxide (%) = (i × U) × 100 d = Relative mole of methylal e = Relative mole of methanol f = relative mole number of formaldehyde g = relative mole number of dimethyl ether h = relative mole number of methyl formate i = relative mole number of carbon monoxide T = 3 × d + e + f + 2 × g + 2 × h + i U = f + 2 × g + 2 × h + i

[0016]

[Reference Example] _{Fe (NO 3) 3 · 9H} 2 O 505g and _{Cr (NO 3) 3 · 9H} 2 O 1500g water 4400
was dissolved in ml, more, the liquid was added 1780g of 62 wt% nitric _{acid, (NH 4) 6 Mo 7} O 24 · 4H 2 O 1545
A solution prepared by dissolving g in 3900 ml of water was added with stirring. This liquid was spray-dried, and the obtained powder was calcined in air at 400 ° C. for 3 hours to obtain Fe _0.25 Cr _0.75
1200 g of oxide powder having a composition of Mo _1.75 was obtained. In order to use this powder for the oxidation reaction of methylal,
Diameter of 4 mm and height of 4 mm with an apparent density of 2.3 g / cm ^3.
Tablet-molded into a cylindrical shape.

[0017]

Example 1 The tablet press-molded body obtained in Reference Example
9 to 16 mesh obtained by crushing after calcination at 00 ° C. for 3 hours
4.5 g of quartz sand having the same particle size range was added to 1 g of the catalyst of No. 1 and mixed, and the mixture was packed in a glass reaction tube, and methylal: O was added.
A mixed gas of ₂ : H ₂ O: N ₂ = 1: 2: 0.5: 18 was supplied at SV = 45,000 Hr ⁻¹ and reacted at 300 ° C. At the initial stage of the reaction (10 hours), the conversion of methylal is 7
At 7%, the selectivity of formaldehyde was 95%, the selectivity of dimethyl ether and the selectivity of methyl formate were 3.5% and 1.5%, respectively. When this reaction was continued for 100 hours, the conversion of methylal was 72%, the selectivity of formaldehyde was 94%, the selectivity of dimethyl ether was 4%, and the selectivity of methyl formate was 2%.

After completion of the reaction, the catalyst was taken out and observed, but no particular change was observed. Also, X manufactured by Rigaku Denki
Also in the X-ray diffraction spectrum (anti-cathode: Cu-Kα) measured using the line diffractometer RAD-III B, as shown in FIG. 1, a new peak is found at the analysis position of 2θ = 26.1 ° ± 0.2 °. No change was observed, and no significant change was observed in the X-ray diffraction spectrum before and after the reaction.

[0019]

Comparative Example 1 Fe ₁ Mo was prepared by the same method as the reference example.
An oxide having the composition of _1.75 was prepared, and the obtained tablet-molded body was calcined in air at 450 ° C. for 3 hours to carry out a methylal reaction in the same manner as in Example 1. Initial reaction (10H
In r), the conversion of methylal is 76%, the selectivity of formaldehyde is 96%, and the selectivity of dimethyl ether is 3%.
%, The selectivity of methyl formate was 1%. This reaction 1
After continuing for 00 hours, the conversion rate of methylal is 44%
Then, the selectivity of formaldehyde was lowered to 84%, the selectivity of dimethyl ether was 12%, and the selectivity of methyl formate was 4%.

After the reaction was completed, the catalyst was taken out and observed, and it was found that the catalyst turned black. In the X-ray diffraction spectrum (anticathode: Cu-Kα), 2θ = 26.
A new peak appeared at the diffraction position of 1 ° ± 0.2 °. X-ray diffraction spectrum of this catalyst (cathode: Cu-K
α) is shown in FIG.

[0021]

Examples 2 to 7 Oxide catalysts were prepared in the same manner as in Reference Example, and methylal reaction was carried out in the same manner as in Example 1.
The results are shown in Table 1. Further, after the reaction was completed, the catalyst was taken out and the X-ray diffraction spectrum (anticathode: Cu-Kα) was measured, but no new peak appeared at the diffraction position of 2θ = 26.1 ° ± 0.2 °. It was

[0022]

[Comparative Example 2] An oxide having a composition of Cr ₁ Mo _1.75 was prepared in the same manner as in Reference Example, and a catalyst which was calcined in air at 450 ° C. for 3 hours was subjected to methylal reaction in the same manner as in Example 1. However, the conversion of methylal was 40% and the selectivity of formaldehyde was 90% at the initial stage of the reaction (10 hours). After 100 hours, the conversion of methylal was 33% and the selectivity of formaldehyde was 83%. This catalyst was taken out and the X-ray diffraction spectrum (anticathode: Cu-K
When α) was measured, a new peak appeared at the diffraction position of 2θ = 26.1 ° ± 0.2 °.

[0023]

[Comparative Example 3] The catalysts of Comparative Examples 1 and 2 were physically mixed in a ratio of 1: 3, and Fe _0.25 Cr _0.75 Mo, which is the same as that of Reference Example.
An oxide having a composition of _1.75 was prepared. 4 this catalyst in air
After baking at 50 ° C. for 3 hours, methylal reaction was carried out in the same manner as in Example 1. As a result, the conversion of methylal at the initial stage of the reaction (10 Hr) was 50% and the selectivity of formaldehyde was 91%. After 100 hours, the conversion of methylal was reduced to 38% and the selectivity of formaldehyde was reduced to 84%. When this catalyst was taken out and the X-ray diffraction spectrum (anticathode: Cu—Kα) was measured, 2θ = 26.1
A new peak was observed at the diffraction position of ± 0.2 °.

From these results, it was found that the effects of the present invention were difficult to obtain with a physical mixture of the constituent oxides.

[0025]

[Comparative Example 4] Fe _0.25 Cr by similar to Reference Example METHOD
An oxide having a composition of _0.75 Mo _0.68 W _1.02 was prepared, and the catalyst calcined in air at 450 ° C. for 3 hours was subjected to methylal reaction in the same manner as in Example 1. The conversion of methylal was 45% and the selectivity of formaldehyde was 88% at the initial stage of the reaction (10 hours). After 100 hours, the conversion of methylal was 38% and the selectivity of formaldehyde was 82%. When this catalyst was taken out and the X-ray diffraction spectrum (cathode: Cu-Kα) was measured, 2θ = 26.1
A slight new peak was observed at the diffraction position of ± 0.2 °.

[0026]

Example 8 In the same manner as in Reference Example Fe _0.4 Cr _0.6 Mo
Prepare an oxide powder with a composition of _1.9 and add 1 wt% of graphite to it.
Was added to form a Raschig ring shape having an outer diameter of 5 mm, an inner diameter of 2 mm, a height of 4 mm and an apparent density of 2.0 to 2.3 g / cm ³ . Furthermore, this molded catalyst is used in air for 500
It was calcined at ℃ for 3 hours.

This catalyst was filled in a reaction tube having an inner diameter of 1 inch, and methylal: methanol: H ₂ O: O ₂ : N ₂ =
1: 0.08: 0.44: 2: 18.7 mixed gas,
An inlet pressure of 1450 mmHg and an SV of 10000 Hr ^-1 were passed to carry out the reaction by controlling the temperature of the heating medium so that the conversion of methylal was maintained at 94%. After 100 hours from the start of the reaction, the temperature of the heat medium is 250 ° C., the selectivity of formaldehyde is 93%, the selectivity of dimethyl ether is 4%, the selectivity of methyl formate is 1%, the selectivity of carbon monoxide is It was 2%. After 1500 hours, heat medium temperature is 2
Although it reached 57 ° C, the reaction results did not change. The catalyst was taken out and observed, but no particular change was observed. In addition, an X-ray diffraction spectrum (anticathode: Cu-Kα)
No new peak was observed at the diffraction position of 2θ = 26.1 ° ± 0.2 °.

[0028]

[Comparative Example 5] Fe _0.75 Cr was _prepared by the same method as the reference example.
An oxide powder having a composition of _0.25 MO _2.5 was prepared, and a methylal reaction was carried out in the same manner as in Example 8. 100 hours after starting the reaction, the temperature of the heating medium is 252 ° C., the selectivity of formaldehyde is 93%, the selectivity of dimethyl ether is 3.5%, the selectivity of methyl formate is 2.5%, carbon monoxide. The selectivity was 1%. After 700 hours, the heating medium temperature was 255 ° C., but the formaldehyde selectivity decreased to 91%, and the dimethyl ether selectivity was 4.5.
%, The selectivity of methyl formate increased to 3%, and the selectivity of carbon monoxide increased to 1.5%.

When this catalyst was taken out and observed, a black discoloration was observed in a part of the catalyst, and in the X-ray diffraction spectrum (cathode: Cu-Kα) of this catalyst, 2θ = 26.1
A new peak appeared at the analysis position of ± 0.2 °.

[0030]

Comparative Example 6 Fe ₁ Mo was prepared by the same method as in Reference Example.
An oxide powder having a composition of _1.8 was prepared, a catalyst was molded in the same manner as in Example 8, and calcined at 450 ° C. for 3 hours. This catalyst was reacted with methylal in the same manner as in Example 8. The temperature of the heating medium 100 hours after starting the reaction is 25
At 4 ° C, formaldehyde selectivity is 93%, dimethyl ether selectivity is 5%, and methyl formate selectivity is 1.5.
%, The selectivity of carbon monoxide was 0.5%. 500H
After r, the heat medium temperature was 256 ° C, but the formaldehyde selectivity decreased to 88%, the dimethyl ether selectivity was 6.5%, the methyl formate selectivity was 2.5%, and the carbon monoxide selectivity was 2.5%. Selectivity increased to 3%.

When this catalyst was taken out and observed, a black discoloration was observed in a part of the catalyst, and in the X-ray diffraction spectrum (cathode: Cu-Kα) of this catalyst, 2θ = 26.1
A new peak appeared at the diffraction position of ± 0.2 °.

[0032]

[Table 1]

[0033]

INDUSTRIAL APPLICABILITY When formaldehyde is produced by the oxidation reaction of methylal, by using the catalyst of the composition of the present invention, the decrease in the formaldehyde selectivity is small, and therefore the formaldehyde can be produced stably.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction spectrum of one of the catalysts specified in the present invention when used in a reaction.

FIG. 2 is an X-ray diffraction spectrum of a catalyst other than those specified in the present invention when used in a reaction.

Claims (1)

Claims: 1. A general formula (Mo _(1-n) W _n ) _a Fe _(1-b)
X _b O _c (where X is one or more elements selected from Al, Cr and In, 0 ≦ n ≦ 0.5, 1.5 ≦ a ≦ 3, 0.5
<B <0.95, c is a value that satisfies the valence balance. ) A method for producing formaldehyde by the oxidation reaction of methylal, which comprises using a catalyst represented by