JPH0336818B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing methacrolein in high yield using a specific catalyst when producing methacrolein by oxidizing isobutylene or tert-butanol with molecular oxygen. Until now, many catalysts have been proposed as catalysts for gas phase catalytic oxidation of isobutylene or tert-butanol, such as Japanese Patent Publication No. 40-23485,
Japanese Patent Publication No. 7854/1984 proposes a catalyst containing molybdenum and tellurium, as well as nickel or lead. However, although these tellurium-containing catalysts showed some activity, they were not industrially satisfactory at all. The biggest cause of this is the deterioration of the activity of the catalyst over time. To explain in detail, tellurium oxide, which is the active component of the catalyst, is reduced to metallic tellurium during the reaction, which aggregates or scatters on the catalyst surface, resulting in a gradual decrease in activity [C.T. O'Hara et. al., hydrocarbon process (CTOhara et.al.,
Hydrocarbon Process, ) Nov. 87 (1972)]. Therefore, in order to improve this drawback, attempts have been made to stabilize the catalyst by adding several kinds of elements. The catalyst previously disclosed by the present inventors in JP-A-56-16436 is capable of sustaining considerably high conversion and high selectivity for an extremely long period of time. However, if the catalyst has higher selectivity and a higher degree of stability under harsh reducing conditions, more stable and advantageous operation can be achieved under a wide range of industrial reaction conditions. For example, improved reduction resistance stabilizes the catalytic performance under harsher reaction conditions, and even with the same oxygen concentration, it is possible to supply a larger amount of the reducing gas, isobutylene or tert-butanol. If the same reactor is used, the production amount can be increased. On the other hand, in order to efficiently generate methacrolein and suppress the sequential decomposition of methacrolein by oxygen, the oxygen concentration in the reaction gas should be kept to the minimum amount necessary for the reaction, and after passing through the catalyst layer, the gas It is desirable to carry out the reaction under conditions where there is almost no oxygen present. However, a catalyst with excellent reduction resistance that maintains high activity even under such strong reducing conditions has not yet been obtained. As a result of extensive research to address these problems, we have discovered a catalyst that has excellent reduction resistance, high activity, and high selectivity, leading to the present invention. That is, in the present invention, when producing methacrolein by oxidizing isobutylene or tertiary-butanol with molecular oxygen, the general composition Mo ₁₂ Te _a Fe _b Ni _c Cu _d X _e Y _f Pb _g O _h (However, a, b, c, d, e, f, g represent the number of moles relative to 12 moles of molybdenum, a = 0.1
~6, b=0.1~6, c=0.1~6, d=0.1~6,
The values range from e=0.1 to 8, f=0.1 to 3, and g=0 to 8. h is a value that satisfies the valences of other elements present. In the formula, X is Mg, Ca, Ba, Sr, Y is Tl, Rb,
Each represents at least one selected element among Cs. ) The present invention relates to a method for producing methacrolein, which is characterized by using a catalyst having the following. The present invention will be described in further detail below. The most important point of the present invention is the use of a catalyst having the general composition described above. In a catalyst having this general composition, the main component is molybdenum, and the amounts of other additive elements are defined by the number of moles added per 12 moles of molybdenum. In addition, tellurium, iron, and nickel are added as promoters, and these elements are indispensable for the catalyst to achieve basic activity and selectivity. If the amount added is small, the effect will be weak, and if it is added in too much, the activity will be high but the selectivity will be poor, and other undesirable effects will occur. In the case of tellurium, the amount added is in the range of 0.1 to 6, preferably in the range of 0.5 to 4. Iron ranges from 0.1 to 6;
Preferably in the range of 0.2 to 4. Nickel ranges from 0.1 to 6, preferably from 0.2 to 4. Improvement in reduction resistance, which is an important feature of this catalyst, is achieved by the combination of copper and the X component. Although copper alone has a considerable effect,
We have found that the combination of copper and component X significantly improves the performance against reduction. The X component is Mg, Ca, Ba, Sr, preferably Mg
It is. The amount of copper added is in the range of 0.1-6, preferably in the range of 0.5-5. The amount of addition of component X is 0.1~
8, preferably in the range of 0.5-6. The Y component is an alkali component of Tl, Cs, and Rb, preferably Tl. The addition of these elements significantly improves the selectivity for producing methacrolein from isobutylene or tert-butanol. Furthermore, we have previously found that the addition of the Y component has the effect of suppressing a decrease in the activity of the catalyst and maintaining the activity for a long time when copper, nickel, and iron are present within the above-mentioned ranges. The amount of this Y component added is 0.1 to 3
It is desirable that it be within the range of . Although lead is not an essential component, when added, the selectivity of methacrolein is significantly improved. However, if it is present in a large amount, the selectivity will decrease, so the amount added must be kept at 8 or less. Preferably, the amount is 6 or less. Furthermore, if a highly active reaction is expected at a lower temperature, a lead-free catalyst can be used. The catalyst of the present invention can be prepared by methods known in the art. As the raw material, not only oxides but also any material can be used as long as it forms the catalyst of the present invention by calcination. Examples include inorganic salts such as ammonium salts, nitrates, and carbonates of each element, and organic acid salts such as acetates. Preferably, compounds that are easily soluble in water or other solvents are used for convenient handling. Although the carrier may not be used, known carriers such as silica, silicon carbide, and alumina may be used. Preferably it is silica. As mentioned above, although the preparation method, raw materials, and carrier are not particularly specified, it can be prepared, for example, as follows. To an aqueous solution of ammonium molybdate, the aqueous solution of copper, nickel, thallium, and X component compounds are added, and then a tellurium compound is added. Then add an aqueous solution of water-soluble iron compounds,
Finally, add silica sol as a carrier and stir thoroughly. The solution is evaporated to dryness on a water bath to obtain a solid. The obtained solid is pre-calcined (200~400℃) in the presence of oxygen, followed by main firing (400~400℃).
1000℃). The catalyst used in the present invention may be in the form of powder, granules, or tablets, and can be molded into a shape suitable for the reactor. As the oxidation method for producing methacrolein by oxidizing isobutylene or tert-butanol, methods known in the art can be used. The reactor may be a fixed bed, fluidized bed or other type. In the reaction according to the present invention, the reaction rate is slow at low temperatures, and the generated methacrolein decomposes and the yield decreases at high temperatures.
It is carried out at a temperature range of ~450°C. The pressure for the reaction is preferably 0.5 to 10 atm in terms of absolute pressure, preferably normal pressure to 2 atm. Industrially, it is operated under normal pressure or slightly pressurized conditions. The flow rate of the raw material gas to the catalyst is generally 100 to 5000 h ^-1 in space velocity (SV), preferably 200 to 2000 h ^-1 . The composition of the raw material gas mixture is 0.5 to 4 oxygen per mole of isobutylene or tert-butanol.
The amount is moles, preferably 1.2 to 2.5 moles, and if necessary, it may be set according to the reaction rate and selectivity so as to suppress the oxygen concentration in the reaction gas to the necessary minimum amount at the end of the reaction. Although water vapor in the reaction gas is not essential, it is advantageous in terms of yield to add 1 to 30 moles per mole of isobutylene or tert-butanol.
The addition of other inert gases can be varied freely depending on changes in other compositions, and usually it is necessary to dilute the mixture to be within the explosive range of isobutylene and oxygen. Using the method of the present invention described in detail above,
Even in a reaction under a highly reducing atmosphere where the oxygen concentration in the gas at the reactor outlet is 0.5 mol% or less, the selectivity of methacrolein is 90-94%, and the conversion rate of isobutylene or tert-butanol is 95-95%.
A catalyst with dramatically improved reduction resistance, which maintains a high performance of 99.5% for an extremely long time, has been obtained, and is capable of producing methacrolein in high yield (see Figure 1). Examples will be shown below to further clarify the present invention. Example 1 300ml of 21.2g of ammonium paramolybdate
Dissolve in distilled water. This is called liquid A. Also, nickel nitrate 4.35g, copper nitrate 7.25g, magnesium nitrate 10.26g, telluric acid 4.55g, thallium acetate 0.80
Dissolve g in 300 ml of water in a separate container and use this as Solution B. Furthermore, dissolve 6.06 g of ferric nitrate and 6.62 g of lead nitrate in 300 ml of water. This is called liquid C. The above three solutions were mixed into silica sol (Snowtex).
N30, Nissan Chemical Industries, Ltd.) 160g, liquid A,
Add Solution B and Solution C in this order while stirring. Next, this slurry is evaporated to dryness on a hot water bath, and then calcined at 300° C. in air for 2 hours. Then,
The fired product was crushed into 10 to 28 meshes and heated at 650℃ for 4 hours.
Air firing was performed for a period of time. The composition of _the obtained catalyst was Mo _{12 Te 2} Fe _1.5 Ni _1.5 Mg ₄ Pb ₂ Tl _{0.3 Oh .} A Pyrex reaction tube having an inner diameter of 5 mm was filled with 3.5 g of this catalyst, and the reaction was carried out at a reaction temperature of 370°C.
Raw material gas composition is isobutylene/O ₂ /H ₂ O/He
The molar ratio was 5/7.5/20/67.5, and the contact time with the catalyst was 1.75 seconds. Analysis is Shimazu
Using a 6APrTF gas chromatograph (manufactured by Shimadzu),
Chromosolve 101 (manufactured by Shimadzu) was used as a column packing material. The results are shown in FIG. 1 and Table 1. Note that the outlet oxygen concentration is the oxygen concentration in the gas after the reaction is completed. Example 2 A catalyst Mo ₁₂ Te ₂ Fe _1.5 Ni _1.5 Cu ₃ Mg ₄ Tl _{0.3 O h} having the following composition was prepared in the same manner as in Example 1, and the _reaction was carried out at a reaction temperature of 350°C _. Summer.
The results are shown in Table 1. Example 3 A catalyst Mo ₁₂ Te ₂ Fe _{1.5 Ni 1.5} Cu ₃ Ca ₄ Tl _{0.3 Pb 2 O h} with the following composition was prepared under the same preparation conditions as in _Example 1, and the same as in Example 1 was prepared. Reacted under the reaction conditions. The results are shown in Table 1. Comparative Examples 1 to 3 For comparison, the first
Catalysts having the compositions shown in the table were prepared and reactions were carried out under the same reaction conditions. Note that potassium nitrate was used as the raw material for K in Comparative Example 3. Examples 4 to 18 Catalysts having the compositions shown in Table 2 were prepared by the same method as in Example 1, and reacted at a reaction temperature of 370 to 390°C. The results are shown in Table 2. Comparative Examples 4 to 9 For comparison, catalysts having the compositions shown in Table 3 were prepared according to the preparation method of Example 1, and the reaction was carried out under the same reaction conditions as in Example 1. The results are shown in Table 3. Examples 19-26 Catalysts having the compositions shown in Table 4 were prepared under the same preparation conditions as in Example 1. 3.5g of the catalyst with an inner diameter of 5
Filled into a Pyrex reaction tube with a reaction temperature of 350 mm.
Reacted at ~390°C. The raw material gas composition has a molar ratio of tertiary butanol/O ₂ /H ₂ O/He of 5/
The ratio was 7.5/30/62.5, and the contact time was 1.75 seconds. The results are shown in Table 4. Comparative Examples 10 to 12 Catalysts having the compositions shown in Table 4 were prepared by the same preparation method as in Example 1, and the reaction was carried out using the same raw material gas as in Example 19. The results are shown in Table 4.

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FIG. 1 shows curves of isobutylene conversion over time for Example 1 using the catalyst of the present invention and Comparative Example 2 using another catalyst.

Claims (1)

[Claims] 1. When producing methacrolein by oxidizing isobutylene or tert-butanol with molecular oxygen, the general composition Mo ₁₂ Te _a Fe _b Ni _c Cu _d X _e Y _f Pb _g O _h (however, a, b, c, d, e, f, g represent the number of moles relative to 12 moles of molybdenum, a = 0.1
~6, b=0.1~6, c=0.1~6, d=0.1~6,
The values range from e=0.1 to 8, f=0.1 to 3, and g=0 to 8. h is a value that satisfies the valence of the existing elements. In the formula, X is Mg, Ca, Ba, Sr, Y is Tl, Rb,
Each represents at least one selected element among Cs. ) A method for producing methacrolein, characterized by using a catalyst having the following. 2. The method for producing methacrolein according to claim 1, wherein X is Mg. 3. The method for producing methacrolein according to claim 1, wherein Y is Tl.