JPH0450062B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for regenerating a catalyst whose activity has deteriorated in a catalytic gas phase oxidation reaction. Specifically, the present invention relates to a heteropolyacid catalyst used in the production of methacrylic acid through catalytic gas phase oxidation of methacrolein, isobutyraldehyde, isobutyric acid, etc., which is subjected to continuous reaction, resulting in deterioration of activity. After the heteropolyacid catalyst is removed from the reaction tube, it is treated with a nitrogen-containing heterocyclic compound to prepare an activated catalyst again without isolating the compounds of each element constituting the catalyst substance. The present invention relates to a method for regenerating a heteropolyacid catalyst. A catalyst whose main component is a heteropolyacid consisting of the elements phosphorus-molybdenum or phosphorus-molybdenum-panadium, or a salt thereof, as a catalyst used in the gas phase oxidation of methacrolein, isobutyraldehyde, isobutyric acid, etc. to produce methacrylic acid. It is generally known that it exhibits excellent effects, and many reports regarding this have also been published. In general, industrial gas phase oxidation reactions are premised on being carried out continuously for a long period of time, during which time a large thermal load is placed on the catalyst, causing undesirable physical and chemical changes, which gradually slow down the reaction. It becomes difficult to continue. As a result, after a certain period of time, it is necessary to extract the catalyst from the reaction tube and fill it with a newly prepared catalyst, and the cost of the catalyst at this time becomes an economical burden. When performing continuous gas-phase oxidation in this way, methods for extending the life of the catalyst and methods for recovering and reactivating the catalyst after use are important issues from an economic perspective, and research on these issues is currently underway. has been desired. A method for recovering and regenerating a heteropolyacid catalyst whose catalytic activity has decreased due to use in a catalytic gas phase reaction has already been reported in the specifications of JP-A-56-163755 and JP-A-58-156351. However, according to the specification of JP-A-56-163755, the active component is separated from the degraded catalyst by a chemical method and reused, which is an economical method from an industrial standpoint. It can not be said. Also, JP-A-58-
Publication No. 156351 proposes a method for regenerating a catalyst by passing steam through it at a relatively low temperature for a long period of time without removing the catalyst whose activity has deteriorated from the reactor, but although the activity of the catalyst is recovered, methacrylic acid The selectivity is much lower than the initial performance and the regeneration effect is not sufficient. The present inventors recognized the fact that during the gas-phase oxidation of organic compounds mentioned above, the catalyst activity gradually decreases when a heteropolyacid catalyst is used to carry out a continuous reaction for a long period of time. Various analyzes were conducted on the catalyst, and it was found that the specific surface area of the catalyst had decreased compared to that of the catalyst before use, and that the structure of the heteropolyacid compound had partially collapsed, resulting in various changes that caused performance deterioration. It was confirmed. As a result of intensive study on an industrially advantageous and economically efficient method for recovering and reusing heteropolyacid catalysts whose activity has deteriorated, the present inventors have found that the catalyst whose activity has deteriorated has been converted into a compound of each constituent element. By simply dispersing the catalyst in water without isolating it, adding a nitrogen-containing heterocyclic compound to it, and treating it, if the catalyst is re-prepared from this treated mixture, it will be equivalent to or even better than the initial catalyst. It is possible to regenerate a catalyst that exhibits the above catalytic performance, and it is also possible to regenerate the entire amount of deteriorated catalyst into a new catalyst with a simple method and with good reproducibility.
The present invention was completed by discovering that this method is economically very advantageous. According to the method of the present invention, all deteriorated catalysts can be used as raw materials for the next catalyst preparation, and a catalyst with a specific structural composition exhibiting excellent catalytic performance can be prepared. It was found to be of great economic value and highly reliable. That is, the present invention can be specified as follows. (1) An oxidation catalyst used in oxidizing an organic compound by a catalytic gas phase reaction, the composition of which contains a heteropolyacid such as molybdophosphoric acid and/or molybdovanadophosphoric acid, or a heteropolyacid salt thereof. A method for regenerating a heteropolyacid catalyst, which comprises dispersing the catalyst whose activity has deteriorated in water and treating it with a nitrogen-containing heterocyclic compound. (2) The method according to (1) above, wherein the nitrogen-containing heterocyclic compound is at least one selected from the group consisting of pyridine, piperidine, piperazine, pyrimidine, quinoline isoquinoline, and derivatives of these compounds. The present invention will be explained in detail below. The heteropolyacid catalyst targeted by the present invention includes a heteropolyacid such as molybdophosphoric acid and/or molybdovanadophosphoric acid, or a metal salt such as an alkali metal or alkaline earth metal of each heteropolyacid. Catalysts containing these as main components can be mentioned. Further, as the nitrogen-containing heterocyclic compound used in the regeneration treatment of the present invention, compounds that form a salt with the above-mentioned heteropolyacid and can be eliminated can be mentioned, and a particularly preferable nitrogen-containing heterocyclic compound is pyridine. , piperidine, piperazine, pyrimidine, quinoline, isoquinoline, or their alkyl-substituted derivatives.Furthermore, the use of inorganic salts such as nitrates, sulfates, and hydrochlorides of these compounds can be used to prevent the generation of bad odors during catalyst regeneration and to remove these compounds. This is extremely convenient in terms of recovery and reuse. In the regeneration method of the present invention, for example, a part of molybdovanadophosphoric acid is used as a catalyst, and rubidium and/or
Or, using a heteropolyacid composition whose main component is an alkali metal salt such as cesium,
Regarding the case where, for example, pyridine is used as a nitrogen-containing heterocyclic compound, first, a heteropolyacid catalyst prepared by a known method is heated at a temperature higher than the normally applied reaction temperature, i.e.
The oxidation reaction of methacrolein was carried out continuously for 500 hours at 380°C and at an increased space velocity, thus placing a greater load on the catalyst than would normally be considered and forcibly accelerating the deterioration of the catalyst. When this degraded catalyst was reacted under normal reaction conditions, both the methacrolein conversion rate and methacrylic acid selectivity were significantly lower than the catalyst before accelerated degradation, and the X-ray diffraction measurement results showed that there were no differences with the initial catalyst. I couldn't help it,
Diffraction lines of molybdenum trioxide appeared, and it was recognized that a phenomenon of collapse of the molybdovanadophosphate structure had occurred. In addition, the BET specific surface area measurement results show that the value has decreased to about 60% of the initial catalyst, indicating that a large change has occurred both chemically and physically.
It was determined that this was the cause of deterioration in catalyst performance. This degraded catalyst is dispersed in water, a predetermined amount of pyridine is added, and after heating and stirring, nitric acid is added to adjust the acidity. The resulting slurry is evaporated to dryness, and after molding, it is heated at 100 to 300℃ to remove volatile components. Dry. Next, pyridine is completely eliminated under normal pressure or reduced pressure in an atmosphere of an inert gas such as nitrogen, helium, argon, carbon dioxide, etc. at a temperature of 200 to 600°C.
The catalyst was then activated in an air stream at a temperature of 100 to 400°C to obtain a regenerated catalyst. Furthermore, a regenerated catalyst can be obtained by simply heating the molded catalyst material from room temperature to 400°C in an air stream. When this regenerated catalyst was used to oxidize methacrolein under normal conditions, both activity and selectivity recovered to almost the same performance as the newly prepared catalyst before the accelerated degradation test. Further, as a result of X-ray diffraction measurement of this regenerated catalyst, the diffraction lines attributed to molybdenum trioxide, which were observed in the deteriorated catalyst, were not observed at all, indicating that the heteropolyacid structure was regenerated. Furthermore, the BET specific surface area measurement results showed almost the same value as the initial catalyst, which means that the degraded catalyst was regenerated to be chemically and physically equivalent to the initial catalyst by the regeneration method of the present invention. On the other hand, when pyridine was not used during the above regeneration treatment, the X-ray diffraction measurement results showed that the diffraction lines attributed to molybdenum trioxide did not disappear, and the BET specific surface area was lower than that of the deteriorated catalyst. In fact, it became smaller, resulting in a very unfavorable result. Moreover, in the oxidation of methacrolein, the performance was very poor compared to the initial catalyst, and was actually lower than the performance of the deteriorated catalyst, which shows how great the effect of the regeneration treatment by the method of the present invention is. The amount of pyridine used here varies depending on the composition of the initial catalyst, but can be used in the range of 5 to 50% by weight of the deteriorated catalyst. Furthermore, similar results to the pyridine treatment were observed for nitrogen-containing heterocyclic compounds described in the present invention other than pyridine. In other words, the regeneration method using a nitrogen-containing heterocyclic compound in the method of the present invention fundamentally improves the cause of activity deterioration and returns the deteriorated catalyst to an excellent initial state. It can be used as is for regeneration and can be said to be a very industrially advantageous method. EXAMPLES 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 conversion rate, methacrylic acid selectivity, and methacrylic acid single flow yield in Examples and Comparative Examples shall comply with the following definitions. Methacrolein conversion rate (mol%) = Number of moles of consumed methacrolein / Number of moles of supplied methacrolein × 100 Methacrylic acid selectivity (mol%) = Number of moles of methacrylic acid produced / Number of moles of methacrolein consumed × 100 Methacrylic acid Single flow yield (mol %) = number of moles of methacrylic acid produced/number of moles of methacrolein supplied x 100 Catalyst performance tests and deterioration acceleration tests were conducted according to the following methods. [Catalyst performance test] 40ml of catalyst molded into a cylinder shape of approximately 5mmφ x 5mmL
was filled into a stainless steel U-shaped tube with an inner diameter of 20 mmφ, immersed in a molten salt bath at a predetermined temperature, and the volume ratio of methacrolein: oxygen: nitrogen: water = 1:3:
36:10 raw material mixed gas at space velocity 1000hr ^-1
(NTP). [Accelerated deterioration test] Fill a stainless steel U-shaped tube with an inner diameter of 20 mmφ with 250 ml of the same catalyst used in the catalyst performance test.
Immersed in a molten salt bath at ℃, a raw material mixed gas with a volume ratio of methacrolein: oxygen: nitrogen: water = 2:6:32:10 was added to the tube at a space velocity of 2000 hr ^-1 (NTP).
The time was passed continuously. Example 1 353.2 g of ammonium paramolybdate and 19.5 g of ammonium metavanadate in 800 ml of heated water.
g was dissolved and stirred. Add 25.0 g of phosphoric acid (85% by weight) to this solution, and then add 160 g of nitric acid (specific gravity 1.38).
ml and 48.7 g of cesium nitrate and 2.83 g of silver nitrate in water.
A solution dissolved in 200 ml was added, and the mixture was heated and concentrated while stirring. The obtained viscous substance was molded into a cylindrical shape of 5 mmφ x 5 mmL, dried at 250°C, and then heated at 400°C in an air stream for 4 hours.
P in atomic ratio of metal elements excluding oxygen after time firing:
A catalyst having a composition of Mo:V:Cs:Ag==1.3:12:1:1.5:0.1 was obtained. From the results of X-ray diffraction (Antichode Cu-Kα) measurements, this catalyst was found to have a composition mainly composed of molybdovanadophosphoric acid and some metal salts thereof. Table 1 shows the performance and BET specific surface area measurement results of this catalyst. Using 250 ml of this catalyst, an accelerated deterioration test was conducted continuously for 500 hours, and the results shown in Table 1 were obtained. In addition, as a result of X-ray diffraction measurements, it was found that the catalyst after the accelerated degradation test did not show any noticeable difference in the initial catalyst.
Strong diffraction lines attributed to molybdenum trioxide appeared near 2θ = 27.3, 12.7, 23.3, and 25.6 degrees, indicating that the heteropolyacid structure had partially collapsed. Next, using this deteriorated catalyst, regeneration treatment was performed by the following method. 50 ml of the degraded catalyst was dispersed in 100 ml of water and heated to 70°C with stirring. After adding 5 ml of pyridine to the mixture and keeping it at 70°C for 15 minutes, 5 ml of nitric acid (specific gravity: 1.38) was added, and the mixture was concentrated with stirring. The resulting clay material was heated to 120℃ for 15 minutes.
After drying for an hour, it was molded into a cylindrical shape of 5 mmφ x 5 mmL. After drying this at 200°C, it was calcined at 430°C in a nitrogen stream for 3 hours and then at 400°C in an air stream for 2 hours to obtain a regenerated catalyst. Regenerated catalyst performance and
As shown in Table 1, the BET specific surface area measurement results showed almost the same value as the initial catalyst. Additionally, as a result of X-ray diffraction measurements, the diffraction lines around 2θ = 27.3, 12.7, 23.3, and 25.6 degrees due to molybdenum trioxide that were observed in the deteriorated catalyst had disappeared, indicating that the catalyst had the same composition as the initial catalyst. .

[Table] Comparative Example 1 The same regeneration treatment as in Example 1 was carried out except that 50 ml of the degraded catalyst of Example 1 was used and the amount of pyridine used was zero. According to the measurement results of X-ray diffraction,
The diffraction lines due to molybdenum trioxide around 2θ = 27.3, 12.7, 23.3 and 25.6 degrees did not disappear, and Table 1
As shown in Figure 2, the specific surface area was also very small, and no recovery in catalyst performance was observed. Examples 2 to 3 Regeneration was performed in the same manner as in Example 1, except that the pyridine used in the regeneration treatment in Example 1 was replaced with the same amount of piperidine or piperazine. The performance of the regenerated catalyst is shown in Table-2.

[Table] Example 4 353.2 g of ammonium paramolybdate and 9.75 g of ammonium metavanadate in 800 ml of heated water
g was dissolved and stirred. Add 80 g of pyridine and 21.1 g of phosphoric acid (85% by weight) to this solution, then add 160 ml of nitric acid (specific gravity 1.38) and a solution of 12.3 g of rubidium nitrate, 31.1 g of thallium nitrate and 4.03 g of copper nitrate dissolved in 200 ml of water and stir. The mixture was concentrated while heating.
The resulting clay-like material was molded into a cylindrical shape of 5 mmφ x 5 mm L, dried at 250°C, and then baked at 450°C in a nitrogen stream for 4 hours and then at 400°C in an air stream for 2 hours to remove the atoms of the metal elements. The ratio is P:Mo:V:Rb:
A catalyst with a composition of Tl:Cu=1.1:12:0.5:0.5:0.7:0.1 was obtained. From the results of X-ray diffraction measurements, the composition of this catalyst was found to be mainly composed of molybdovanadophosphoric acid and some metal salts thereof. An accelerated deterioration test was conducted using 250 ml of this catalyst. Table 3 shows the performance and BET specific surface area measurement results of the initial catalyst and the catalyst after the accelerated deterioration test. In addition, as a result of X-ray diffraction measurements, the catalyst after the accelerated deterioration test showed a diffraction line due to molybdenum trioxide, which was not observed in the initial catalyst, at 2θ = 27.3.
It was found that the heteropolyacid structure was partially decomposed, which was observed around 12.7, 23.3 and 25.6 degrees. Next, using this deteriorated catalyst, regeneration treatment was performed by the following method. 50 ml of the degraded catalyst was dispersed in 100 ml of water, and the mixture was stirred and heated to 70°C. Add to this 33ml of nitric acid aqueous solution with a concentration of 2N.
A solution in which 5 ml of quinoline was dissolved was added, the mixture was kept at 70°C for 20 minutes, and then heated and concentrated while stirring. this
After drying at 120°C for 15 hours, it was molded into a cylindrical shape of 5 mmφ x 5 mmL, dried at 200°C, and then calcined at 430°C in a nitrogen stream for 4 hours and then at 400°C in an air stream for 3 hours to obtain a regenerated catalyst. As shown in Table 3, the performance of the regenerated catalyst was almost the same as that of the initial catalyst.
The specific surface area also recovered, and the X-ray diffraction measurement results showed that the diffraction lines due to molybdenum trioxide, which were observed in the degraded catalyst, were not observed at all, indicating that the composition had recovered to the same composition as the initial catalyst. Comparative Example 2 The same regeneration treatment as in Example 4 was performed except that quinoline was not used during the regeneration treatment of the deteriorated catalyst in Example 4. According to the measurement results of X-ray diffraction, 2θ=27.3,
Diffraction lines around 12.7, 23.3, and 25.6 degrees did not disappear, indicating the presence of molybdenum trioxide. Furthermore, as shown in Table 3, no recovery in catalyst performance or specific surface area was observed.

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Claims (1)

[Scope of Claims] 1. An oxidation catalyst used in oxidizing an organic compound by a catalytic gas phase reaction, which contains a heteropolyacid such as molybdophosphoric acid and/or molybdovanadophosphoric acid or a heteropolyacid salt of each of them in its composition. 1. A method for regenerating a heteropolyacid catalyst, which comprises dispersing the catalyst whose activity has deteriorated in an aqueous medium and treating it with a nitrogen-containing heterocyclic compound. 2. The method according to claim 1, wherein the nitrogen-containing heterocyclic compound is at least one selected from the group consisting of pyridine, piperidine, piperazine, pyrimidine, quinoline, isoquinoline, and derivatives of these compounds.