JPH0230741B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering the activity of a catalyst whose activity has decreased by continuing the reaction for a long period of time. In particular, the present invention relates to a method for restoring the activity of a catalyst whose activity has decreased due to use in a reaction by regenerating the catalyst without removing it from the reaction apparatus. It is known that the activity of heteropolyacid catalysts, which synthesize methacrylic acid by air oxidation of methacrolein, decreases during operation. This necessitates shutdown, extraction of the catalyst, and refilling, which increases maintenance costs and reduces plant operating efficiency. As a regeneration technology of free phosphomolybdic acid and/or phosphovanadomolybdic acid, JP-A-56
-163755 is known. According to the description in the specification, this method consists of the following five steps. That is, (1) the supported catalyst whose activity has decreased is extracted from the reaction apparatus. (2) Extract with an aqueous medium. (3) The catalyst activity is restored by heating under reflux. (4) Support on a carrier. (5) Fill the reactor. According to this technique, activity recovery is the step (3), but since the treatment is carried out in a liquid phase, four other steps are required, and this is not a good method from an industrial standpoint. As a result of extensive research, the present inventors have discovered that free phosphomolybdic acid and/or phosphovanadomolybdic acid recovers its activity in the presence of water vapor even in the gas phase, and has arrived at the present invention. That is, the gist of the present invention is to oxidize methacrolein in a gas phase by oxidizing a catalyst with reduced activity containing free molybdic acid and/or phosphovanadomolybdic acid used in the production of methacrylic acid using steam. 70~ in an air flow with a partial pressure of 10vol% or more
This is a method for regenerating a methacrylic acid synthesis catalyst, which is characterized by treatment at a temperature of 240°C. According to the method of the invention, the catalyst can be regenerated within the reactor, and a substantially long-life catalyst has been developed. Free phosphomolybdic acid and/or phosphovanadomolybdic acid in the method of the present invention is heated at 150°C.
In the X-ray diffraction spectrum after drying with
Triclinic type consisting of 3.49, 3.42, 3.21, 3.14, 2.99 and 2.81 Å and 9.93, 4.90, 4.44, 4.33, 3.92,
It is a mixture of what appears to be a tetragonal crystal structure consisting of 3.25, 3.07, and 2.07 Å, and the major spacings are 13.6, 8.18, 5.82, 5.33, 4.44 at room temperature and saturated vapor pressure.
It means a composition that has a diamond-shaped cubic crystal structure consisting of 4.11, 3.94, 3.53, 3.02, 2.90, and 2.67 Å and does not contain alkali metals, thallium, or ammonium radicals. Free phosphomolybdic acid and/or phosphovanadomolybdic acid containing copper also give the same X-ray spectra. A method for preparing free phosphomolybdic acid and/or phosphovanadomolybdic acid is generally used to prepare the catalyst of the present invention. As starting materials for catalyst preparation, molybdenum is molybdenum trioxide, molybdic acid, phosphomolybdic acid, phosphovanadomolybdic acid, and phosphorus is phosphoric acid, phosphorous acid, phosphorus trioxide, phosphorus pentoxide, phosphomolybdic acid, Phosphorvanadomolybdic acid and copper phosphate are used. Also,
Vanadium includes vanadium pentoxide, vanadium trioxide, vanadium tetroxide, vanadyl oxalate, vanadyl sulfate, vanadyl dichloride, vanadium phosphate,
Phosphorvanadomolybdic acid is generally used, and cuprous oxide, cupric oxide, and basic copper carbonate are generally used as copper raw materials. For preparation, a predetermined amount of raw salt is weighed out, water is added and dissolved under boiling reflux, and this is evaporated to dryness at a temperature of 100 to 150°C. The obtained dry product is further crushed into tablets to form a tablet catalyst, or sprinkled on a carrier to form a supported catalyst. Further, during evaporation to dryness, it can be impregnated into a porous carrier and dried to obtain an impregnated catalyst.
The carrier may be a powder or molded material such as silica alumina, alumina, silicon carbide, pumice, diatomaceous earth, titanium oxide, etc., which does not have methacrolein oxidation activity or methacrolein or methacrylic acid polymerization activity, or a colloidal substance such as silica sol. used. The regeneration treatment when carrying out the present invention is carried out at a temperature of 70 to 240°C.
The test is carried out under the following temperature conditions. At this time, the processing temperature is 70
If the temperature is below 0.degree. C., the treatment time tends to be long, and this is not necessarily an industrially preferable method. In addition, the higher the processing temperature, the smaller the regeneration effect.
If this is the case, it will be difficult to play even if it takes a long time. The reason for this is that catalysts mainly composed of free phosphomolybdic acid and/or phosphovanadomolybdic acid are
This is thought to be because complex structural changes occur depending on temperature and water content, and active species are formed through recycling of these structural changes. The water vapor partial pressure during the regeneration treatment may be 10 vol% or more, and preferably a range of 20 to 100 vol% is effective. Also, the gases that coexist with water vapor are air,
Both nitrogen and combustion exhaust gas are effective. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples. Note that the methacrolein reaction rate and methacrylic acid selectivity in the present specification are defined as follows. Methacrolein reaction rate = Number of moles of methacrolein consumed/Number of moles of methacrolein supplied x 100 (%) Methacrylic acid selectivity = Number of moles of methacrylic acid produced/Number of moles of methacrolein consumed x 100 (%) The analysis is Gas chromatography was used. Example 1 100g of molybdenum trioxide, 6.3g of vanadium pentoxide
g, cupric oxide 1.1 g, orthophosphoric acid (85% by weight) 8.0
After putting 1 g of pure water into a flask and adding 1 portion of pure water, the mixture was heated under reflux for 16 hours to obtain a deep red homogeneous solution. This homogeneous solution was evaporated to dryness and sieved into 10 to 16 meshes. The composition of the catalyst thus obtained was Mo ₁₂ P _1.1 V ₁ Cu _0.2 O _41.45 in atomic ratio. This catalyst was packed into a Pyrex reaction tube with an inner diameter of 17.5 mmφ, and 3.9 vol% of methacrolein, 7.2 vol% of oxygen,
A raw material gas consisting of 74.6 vol% nitrogen and 14.2 vol% water vapor was reacted at a space velocity of 2800 hr ^-1 and 340°C. Further, Table 1 shows the initial activity, changes over time, and results after regeneration treatment of this catalyst. The regeneration conditions were a gas composition of 75% water vapor, 25% air, and a temperature of 120%, and the treatment was carried out in an air stream for 16 hours.

[Table] Example 2-4 100.0 g of molybdenum trioxide, 6.3 g of vanadium pentoxide, 2.2 g of cupric oxide, and 8.0 g of orthophosphoric acid (85% by weight) were sequentially added to a flask as raw material salts, and then pure water was added. After adding 1000 ml, the mixture was heated under reflux for 16 hours to obtain a dark reddish-brown homogeneous solution. This homogeneous solution was evaporated to dryness under reduced pressure using a rotary evaporator, compressed into tablets, crushed into 10 to 16 meshes, and sieved.
The catalyst composition obtained in this way is MO ₁₂ P _1.2 V _1.2 Cu _0.48
O _39.48 . This catalyst was packed into a 17.5 mmφ Virex reaction tube, and a gas having the same composition as in Example 1 was introduced to cause a reaction. The reaction conditions were SV2800hr ^-1 and 340°C, and the catalyst performance was 85% for methacrolein reaction (hereinafter abbreviated as C _MA ) and 78% for methacrylic acid selectivity (hereinafter abbreviated as S _MAA ). This catalyst has a peak temperature of 460 under the same gas conditions.
℃ for 16 hours and then returned to 340℃ to test the catalyst performance, C _MA = 72% and S _MAA = 75%. Steam using this forced deterioration catalyst
Treatment temperature with air containing 50vol%: 80℃, 180℃,
Example 2 shows the results of regeneration treatment at 240°C.
It is shown in Table 2 as ~4. The lower the regeneration temperature, the better the efficiency.

[Table] Examples 5 to 7 Reagent phosphomolybdic acid P ₂ O ₅・24MoO ₃・nH ₂ O
(Analysis value n=60.0) 78.8g, vanadium pentoxide 3.16
g and 0.67 g of orthophosphoric acid (85% by weight) were placed in a flask, 500 ml of pure water was added, and the flask was heated under reflux for 18 hours, and the liquid was evaporated to dryness. The catalyst composition is Mo ₁₂ P _1.2 V _1.2 O ₄₂ in atomic ratio. This catalyst was placed in a gas having the same composition ratio as in Example 1.
The performance was evaluated at SV2800hr ^-1 and 350°C, and the catalysts subjected to forced deterioration treatment were regenerated by changing the water vapor partial pressure. The results are shown in Table 3 as Examples 5 to 7.

[Table] Examples 8 to 11 500 ml of pure water and molybdenum trioxide in a flask
50.0g, vanadium pentoxide 2.63g, cupric oxide
0.46g, orthophosphoric acid (85% by weight) 3.67g, boric acid
0.72 g was added and heated under reflux, and the resulting homogeneous solution was filtered, dried and sieved into 24 to 32 meshes. The catalyst composition was Mo ₁₂ P _1.1 V ₁ Cu _0.2 B _0.4 O _42.1 . The catalyst performance was 88% methacrolein reaction and 84% methacrylic acid selectivity under the same gas conditions as in Example 1 at 320°C. The catalyst performance after forced deterioration treatment at 440°C for 40 hours was 62% methacrolein reaction and 78% methacrylic acid selectivity at 320°C. The results of regenerating the degraded catalyst thus obtained by changing the coexisting gas are shown in Table 4 as Examples 8 to 11.

【table】

[Table] Examples 12 to 14 50.0 g of molybdenum trioxide, 0.55 ml of cupric oxide, and 4.0 g of orthophosphoric acid (85% by weight) were added to a flask and heated to reflux, and the solution was evaporated to dryness. The catalyst composition is Mo ₁₂ P _1.2 Cu _0.24 O _39.24 . The performance of this catalyst was SV980hr ^-1 at 340℃ under the same gas conditions as in the example.
The methacrolein reaction rate was 76% and the methacrylic acid selectivity was 76%. Forced aging treatment at 380℃
The treatment was carried out for 300 hours, and the regeneration treatment was carried out at 200°C. The results are shown in Table 5 as Examples 12 to 14.

【table】

Claims (1)

[Scope of Claims] 1. When producing methacrylic acid by vapor phase catalytic oxidation of methacrolein, a catalyst with reduced activity containing free phosphomolybdic acid and/or phosphovanadomolybdic acid as a main component is steam distilled. pressure
1. A method for regenerating a methacrylic acid synthesis catalyst, comprising treating it at a temperature of 70 to 240°C in an air flow of 10 vol% or more. 2. The method for regenerating a methacrylic acid synthesis catalyst according to claim 1, wherein the catalyst containing free phosphomolybdic acid and/or phosphovanadomolybdic acid as a main component for oxidizing methacrolein contains copper.