JP2012196608A - Method for regenerating methacrylic acid producing catalyst and method for producing methacrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for regenerating a methacrylic acid producing catalyst which enables effective recovery of the catalytic activity and catalyst life of a used catalyst that is used in the production of methacrylic acid and a method for producing methacrylic acid at a good convert ratio and an excellent selectivity by using a regeneration catalyst obtained by the regeneration method.SOLUTION: In the method for regenerating the methacrylic acid producing catalyst comprising a heteropoly acid compound containing phosphorus and molybdenum, a catalyst precursor is obtained by drying aqueous slurry containing the used catalyst used in the production of methacrylic acid, an ammonium radical, nitric acid radical, and water, and after the catalyst precursor is first stage-baked at a temperature of 360-410°C in an oxidative gas atmosphere containing moisture in an amount of ≥0.1 vol.% and <2.0 vol.%, the catalyst precursor is second stage-baked at a temperature of 420-500°C in a non-oxidative gas atmosphere.

Description

  The present invention relates to a method for regenerating a catalyst for producing methacrylic acid, and a method for producing methacrylic acid using a catalyst regenerated by this method.

  When a catalyst for methacrylic acid production comprising a heteropolyacid compound containing phosphorus and molybdenum is used for a long time in a gas phase catalytic oxidation reaction using methacrolein or the like as a raw material, the catalytic activity decreases due to heat load, etc. It is known to deteriorate.

  As a method for regenerating such a deteriorated catalyst, for example, in Patent Document 1, a mixture containing a deteriorated catalyst, an ammonium root, a nitrate root and water is dried, and then at 390 ° C. in an air atmosphere containing 2% by volume of water. A method is described in which after the first stage baking, the second stage baking is performed at 435 ° C. in a nitrogen atmosphere.

JP 2008-93595 A

  However, the regenerated catalyst regenerated by the above regeneration method is not always satisfactory in terms of catalyst life.

  Therefore, the object of the present invention was obtained by a method for regenerating a catalyst for methacrylic acid production which can effectively recover the catalytic activity and catalyst life of the used catalyst used in the production of methacrylic acid, and the method. An object of the present invention is to provide a method for producing methacrylic acid with a good conversion and selectivity using a regenerated catalyst.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

  That is, the method for regenerating a catalyst for methacrylic acid production of the present invention is a method for regenerating a catalyst for methacrylic acid production comprising a heteropolyacid compound containing phosphorus and molybdenum, and is a spent catalyst used for the production of methacrylic acid, ammonium An aqueous slurry containing roots, nitrate radicals, and water is dried to obtain a catalyst precursor, and the catalyst precursor is placed in an oxidizing gas atmosphere containing water in an amount of 0.1% by volume or more and less than 2.0% by volume in the range of 360 to 360%. After the first stage baking at 410 ° C., the second stage baking is performed at 420 to 500 ° C. in an atmosphere of non-oxidizing gas.

  The method for producing methacrylic acid of the present invention regenerates a catalyst for producing methacrylic acid by the above regeneration method, and in the presence of the regenerated catalyst, a compound selected from methacrolein, isobutyraldehyde, isobutane and isobutyric acid. It is characterized by being subjected to a gas phase catalytic oxidation reaction.

  According to the regeneration method of the present invention, the catalyst activity and the catalyst life of the used catalyst used for the production of methacrylic acid can be effectively recovered, and good conversion can be achieved using the obtained regeneration catalyst. Methacrylic acid can be produced over a long period of time at a rate and selectivity.

<Catalyst for methacrylic acid production and used catalyst>
The catalyst for producing methacrylic acid to be regenerated by the present invention is composed of a heteropolyacid compound containing phosphorus and molybdenum, and may be composed of a free heteropolyacid or a salt of a heteropolyacid. It may be. Especially, what consists of an acidic salt (partially neutralized salt) of heteropolyacid is preferable, More preferably, it consists of an acidic salt of Keggin type heteropolyacid.
The catalyst preferably contains at least one element selected from the group consisting of potassium, rubidium, cesium and thallium (hereinafter sometimes referred to as element X) as an element other than phosphorus and molybdenum. It is preferable that at least one element selected from the group consisting of vanadium, copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium (hereinafter sometimes referred to as Y element) is included.

The composition of the heteropolyacid compound constituting the catalyst for producing methacrylic acid (target catalyst) is preferably as shown in the following formula (i) in the new catalyst before use.
PaMobVcXdYeOx (i)
(In the formula (i), P, Mo and V represent phosphorus, molybdenum and vanadium, respectively, X represents at least one element X selected from the group consisting of potassium, rubidium, cesium and thallium, Y represents copper, Represents at least one element (element Y) selected from the group consisting of arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium, O represents oxygen, and when b = 12, 0 < a ≦ 3, 0 ≦ c ≦ 3, 0 ≦ d ≦ 3, 0 ≦ e ≦ 3, and x is a value determined by the oxidation state of each element, wherein each of X and Y is two or more types In the case of an element, the total ratio of two or more elements may be 0 ≦ d ≦ 3 and 0 ≦ e ≦ 3 when b = 12.
In particular, the composition of the heteropolyacid compound constituting the new catalyst preferably has an atomic ratio of element X to molybdenum (X / Mo) of 0.5 / 12 to 2/12.

The catalyst for producing methacrylic acid as a new catalyst is, for example, a compound containing each of the above-described elements constituting a heteropolyacid compound (for example, oxo acid, oxo acid salt, oxide, nitrate, carbonate, bicarbonate of each element) , Hydroxides, halides, etc.), formed into a desired shape, and then fired.
Examples of the compound containing each element described above include phosphoric acid and phosphate as the compound containing phosphorus, and examples of the compound containing molybdenum include molybdate such as molybdic acid and ammonium molybdate, and molybdenum oxide. Molybdenum chloride and the like are used, and vanadium-containing compounds include vanadate, vanadate (metavanadate) such as ammonium vanadate (metavanadate), vanadium oxide, vanadium chloride, etc. The compounds included include oxides such as potassium oxide, rubidium oxide and cesium oxide; nitrates such as potassium nitrate, rubidium nitrate, cesium nitrate and thallium nitrate; carbonates such as potassium carbonate, rubidium carbonate and cesium carbonate; potassium hydrogen carbonate, carbonic acid Bicarbonate such as cesium hydrogen ; Potassium hydroxide, rubidium hydroxide, hydroxides such as cesium hydroxide; potassium chloride, rubidium chloride, cesium fluoride, cesium chloride, cesium bromide, halides such as cesium iodide is used. Examples of the compound containing the element Y include oxo acids, oxo acid salts, oxides, nitrates, carbonates, hydroxides, halides, and the like.

When a catalyst for producing methacrylic acid is used in the production of methacrylic acid in a new catalyst, the catalytic activity may be reduced due to heat load or the like.
In the production method of the present invention, the spent catalyst having a reduced catalytic activity used in the production of methacrylic acid is subjected to regeneration treatment. In addition, about the decomposition | disassembly of the active site | part in the catalyst for methacrylic acid production, it can confirm by performing X-ray diffraction (XRD) analysis about this catalyst, and detecting whether molybdenum trioxide which is a decomposition product is detected.

In the regeneration method of the present invention, the spent catalyst, ammonium root, nitrate root and water used in the production of methacrylic acid are mixed to obtain an aqueous slurry. Examples of the ammonium root material compound include ammonia and ammonium salts such as ammonium nitrate, ammonium carbonate, and ammonium acetate, and preferably ammonium and ammonium nitrate. Examples of the nitrate radical raw material compound include nitric acid and nitrates such as ammonium nitrate, preferably nitric acid and ammonium nitrate.
Moreover, when ammonium salt and nitrate are used for the compound added as a scattering component described below, these ammonium salts and nitrates are also ammonium and nitrate.

When the catalyst for methacrylic acid production is used for the production of methacrylic acid, some components of the catalyst such as phosphorus and molybdenum may be scattered. In such a case, the type of constituents scattered by fluorescent X-ray analysis or inductively coupled plasma (ICP) emission analysis is analyzed, the amount of scattering is calculated from the obtained results, and the above-mentioned aqueous slurry is prepared from the amount of scattering. It is preferable to add them accordingly.
Moreover, what is necessary is just to select suitably 1 type (s) or 2 or more types from the compound containing each element which can be used for manufacture of the above-mentioned new catalyst as a compound added as a scattering part.

When element X is present in the aqueous slurry, the aqueous slurry has an atomic ratio (X / Mo) of element X to molybdenum of 0.5 / 12 to 2/12, preferably 1.0 / 12 to 1. It is preferably adjusted to 8/12.
Specifically, the atomic ratio may be adjusted by adding at least one of a compound containing element X (element X-containing compound) and a molybdenum compound.

The mixing amount of the element X-containing compound and the molybdenum compound, etc. is analyzed by fluorescent X-ray analysis, ICP emission analysis, etc., with respect to the catalyst composition (type and amount of constituent components) of the used catalyst before being subjected to regeneration, Based on the catalyst composition of the spent catalyst, the atomic ratio of element X to molybdenum (X / Mo) in the composition after adding the element X-containing compound and / or the molybdenum compound may be determined to be in the above-described range. .
Normally, the element X-containing compound is added in consideration of the amount of molybdenum in the spent catalyst. However, when molybdenum is scattered and disappears due to heat load due to long-term use in the production of methacrylic acid. Depending on the amount of reduction, the composition of the used catalyst may be the X / Mo ratio in the aqueous slurry described above. In such a case, it is possible not to add both the element X-containing compound and the molybdenum compound. It can be.

  As the molybdenum compound and the element X-containing compound to be mixed in the preparation of the aqueous slurry, one or two or more kinds are appropriately selected from the molybdenum-containing compound and the element X-containing compound that can be used for the production of the new catalyst described above. do it.

  Moreover, when preparing aqueous slurry, the compound containing catalyst structural elements other than molybdenum and the element X can also be added as needed based on the catalyst composition of a used catalyst. As the compound containing a catalyst constituent element other than molybdenum and element X, one or more kinds may be appropriately selected from the compounds containing each element that can be used for the production of the new catalyst described above.

  The method for preparing the aqueous slurry is not particularly limited. For example, after suspending a used catalyst in water, an ammonium root raw material compound and a nitrate radical raw material compound may be added, or an ammonium root and a nitrate radical may be added. The spent catalyst may be suspended in an aqueous solution containing.

  The ratio of the nitrate radical to the ammonium root contained in the aqueous slurry is preferably 1.3 moles or less, more preferably 0.5 to 1.3 moles per mole of nitrate root. preferable. If the amount of ammonium radical is out of the above range, the catalytic activity may not be sufficiently recovered. In addition, when adding the compound containing an ammonium root and a nitrate root to a water-based slurry as a scattered part, these ammonium roots and a nitrate root are considered, and it is set as the said range.

  As water used in the preparation of the aqueous slurry, ion-exchanged water is usually used. The amount of water used is usually 1 to 20 parts by weight with respect to 1 part by weight of molybdenum (total of molybdenum contained in the used catalyst and molybdenum compound added) in the aqueous slurry.

  When preparing the aqueous slurry, the spent catalyst may be used for mixing as it is, or may be subjected to heat treatment as a pretreatment in advance.

  The treatment temperature of the heat treatment performed as a pretreatment of the spent catalyst is not particularly limited, but is preferably 350 to 600 ° C. The treatment time for heat treatment is not particularly limited, but is usually 0.1 to 24 hours, preferably 0.5 to 10 hours. Further, the heat treatment performed as a pretreatment of the used catalyst may be performed in an atmosphere of an oxidizing gas such as an oxygen-containing gas, or may be performed in an atmosphere of a non-oxidizing gas such as nitrogen.

Moreover, when the used catalyst used for preparation of an aqueous slurry is a molded object, you may use as it is, However, If necessary, it can also crush by a conventionally well-known method previously. However, if the molded body contains fibers or the like that develop the strength of the catalyst, there is a concern that the strength may decrease when the molded body is cut, so that the fibers or the like should not be cut when crushing. Is preferred.
When both the crushing treatment and the heat treatment performed as a pretreatment are performed on the spent catalyst used for the preparation of the aqueous slurry, the order of both treatments is not particularly limited, but usually the heat treatment is performed after the crushing treatment. The

The aqueous slurry is subjected to drying to obtain a catalyst precursor. As such a drying method, a method usually used in this field, for example, an evaporation to dryness method, a spray drying method, a drum drying method, an airflow drying method, or the like can be employed. The drying conditions may be appropriately set so that the water content in the aqueous slurry is sufficiently reduced, and is not particularly limited, but the temperature is usually less than 300 ° C.
The aqueous slurry is preferably heat-treated at 100 ° C. or more and aged before being dried in view of recovery of the catalyst activity. The heat treatment temperature is preferably 200 ° C. or lower, more preferably 150 ° C. or lower. Such heat treatment can usually be performed in a sealed container. The heat treatment time is usually 0.1 hour or longer, preferably 2 hours or longer, more preferably 2 to 10 hours. When the time is shorter than 0.1 hour, the activity recovery effect is not sufficiently obtained. On the other hand, 10 hours or shorter is preferable from the viewpoint of productivity.
The obtained dried product (catalyst precursor) may be calcined as it is, but is preferably formed into a ring shape, a pellet shape, a spherical shape, a cylindrical shape, or the like by tableting or extrusion. At this time, in order to increase the strength, a molding aid such as ammonium nitrate may be used in addition to ceramic fiber and glass fiber as necessary. In particular, ammonium nitrate has not only a function as a molding aid but also a function as a pore agent.

  In the case of molding as described above, the obtained molded body is subjected to a temperature and humidity control treatment, specifically, exposed to an atmosphere of 40 to 100 ° C. for 0.5 to 10 hours and a relative humidity of 10 to 60%, and then fired. Is preferable in order to recover the catalytic activity more satisfactorily. The treatment may be performed, for example, in a temperature-controlled and humidity-controlled tank, or by spraying a temperature-controlled and humidity-controlled gas on the molded body. In addition, as the atmospheric gas for the treatment, air is usually used, but an inert gas such as nitrogen may be used.

  The dried product (catalyst precursor) is calcined as it is or molded, and then subjected to the temperature and humidity control treatment and then calcined, whereby a regenerated catalyst can be obtained. In the firing, first-stage firing is performed at 360 to 410 ° C. in an atmosphere of an oxidizing gas containing moisture of 0.1% by volume or more and less than 2.0% by volume, and then 420 to 420− in an atmosphere of a non-oxidizing gas. Second stage baking is performed at 500 ° C. By performing such two-stage firing, the catalyst activity can be recovered more favorably.

The moisture contained in the atmosphere in the first stage firing is 0.1% by volume or more and less than 2.0% by volume, preferably 0.3 to 1.8% by volume, and 0.6 to 1.6% by volume. % Is more preferred. If the water content is less than 0.1% by volume, a part of the catalyst may be decomposed into MoO ₃ , and the activity of the regenerated catalyst may not be sufficiently recovered, and the water content is 2.0% by volume or more. The life of the regenerated catalyst may not be fully recovered.

The oxidizing gas used in the first stage baking is a gas containing an oxidizing substance, and examples thereof include an oxygen-containing gas. The oxygen concentration is usually about 1 to 30% by volume. As the oxygen source, air or pure oxygen is usually used, and diluted with an inert gas as necessary. Of these, air is preferable as the oxidizing gas.
The first stage firing is usually performed under an air flow of the oxidizing gas. The temperature of the first stage baking is 360 to 410 ° C, preferably 380 to 400 ° C.

  The non-oxidizing gas used in the second-stage firing is a gas that does not substantially contain an oxidizing substance such as oxygen, and examples thereof include inert gases such as nitrogen, carbon dioxide, helium, and argon. In addition, moisture may be present if necessary, but the concentration is usually 10% by volume or less. Of these, nitrogen is preferable as the non-oxidizing gas. Second-stage firing is usually performed under a stream of the non-oxidizing gas. The temperature of the second stage baking is 420 to 500 ° C, preferably 420 to 450 ° C.

  In addition, before the said baking, it is preferable to heat-process (pre-fire) by hold | maintaining a catalyst precursor at the temperature of about 180-300 degreeC in the atmosphere of oxidizing gas or non-oxidizing gas.

<Regenerated catalyst>
The regenerated catalyst thus obtained is made of a heteropolyacid compound and may be made of a free heteropolyacid or a salt of a heteropolyacid. Especially, what consists of an acidic salt of heteropolyacid is preferable, and what consists of acidic salt of a Keggin type heteropolyacid is more preferable. In addition, it is more preferable that a Keggin type heteropolyacid salt structure is formed during the heat treatment (pre-firing). The regenerated catalyst has the same preferred composition as the above-mentioned new catalyst (formula (i)), and when element X is contained, the atom of element X relative to molybdenum in the heteropolyacid compound constituting the regenerated catalyst The ratio (X / Mo) is preferably 0.5 / 12 to 2/12.

  The method for regenerating a catalyst for producing methacrylic acid according to the present invention is intended for regeneration of a used catalyst used in the production of methacrylic acid. The regeneration method of the present invention can also be carried out on a new catalyst that is not used in the production of methacrylic acid, such as a new catalyst that does not have the above performance, and even in such a case, the used catalyst was regenerated. As in the case, good effects can be obtained.

  Such a regenerated catalyst has a good recovery in catalytic activity. In the presence of this regenerated catalyst, a raw material compound such as methacrolein is subjected to a gas phase catalytic oxidation reaction, whereby methacrylic acid is converted at a good conversion rate and selectivity. Can be manufactured.

<Method for producing methacrylic acid>
In the production of methacrylic acid, a fixed-bed multitubular reactor is usually filled with a catalyst (including the regenerated catalyst according to the present invention), and a raw material compound selected from methacrolein, isobutyraldehyde, isobutane and isobutyric acid and oxygen However, it is also possible to adopt a reaction mode such as a fluidized bed or a moving bed. As the oxygen source, air is usually used, and the raw material gas may contain nitrogen, carbon dioxide, carbon monoxide, water vapor and the like as components other than the raw material compound and oxygen.

For example, when using methacrolein as a raw material, the methacrolein concentration in the raw material gas is usually 1 to 10% by volume, the water vapor concentration is 1 to 30% by volume, the molar ratio of oxygen to methacrolein is 1 to 5, and the space velocity is The reaction is carried out under the conditions of 500 to 5000 h ⁻¹ (standard condition standard), reaction temperature of 250 to 350 ° C., and reaction pressure of 0.1 to 0.3 MPa. The raw material methacrolein is not necessarily a highly purified product, and for example, a reaction product gas containing methacrolein obtained by a gas phase catalytic oxidation reaction of isobutylene or t-butyl alcohol can be used.

When isobutane is used as a raw material, the isobutane concentration in the raw material gas is usually 1 to 85% by volume, the water vapor concentration is 3 to 30% by volume, the molar ratio of oxygen to isobutane is 0.05 to 4, and the space velocity is 400. The reaction is carried out under conditions of ˜5000 h ⁻¹ (standard condition standard), reaction temperature of 250 to 400 ° C., and reaction pressure of 0.1 to 1 MPa. When isobutyric acid or isobutyraldehyde is used as a raw material, generally the same reaction conditions are employed as when methacrolein is used as a raw material.

Examples of the present invention will be described below, but the present invention is not limited thereto.
The nitrogen used in each example is substantially free of moisture.

The composition analysis of the catalyst in this example and the evaluation of the catalyst performance were performed as follows.
<Catalyst activity test>
9 g of catalyst was charged into a glass microreactor having an inner diameter of 16 mm, and raw material gas prepared by mixing methacrolein, air, steam and nitrogen (composition: methacrolein 4 vol%, molecular oxygen 12 vol%) Were supplied at a space velocity of 670 h ⁻¹ to raise the furnace temperature (furnace temperature for heating the microreactor) to 355 ° C. and then at that temperature for 1 hour. Held, then the furnace temperature was lowered to 280 ° C. The reaction was then continued for 1 hour at that temperature. From this reaction start (after setting the furnace temperature to 280 ° C.), the outlet gas (gas after reaction) after 1 hour was sampled, analyzed by gas chromatography, and methacrolein conversion rate (%) based on the following formula The methacrylic acid selectivity (%) and yield (%) were determined.

Conversion, selectivity and yield are defined as follows.
Conversion rate (%) = Mole number of reacted methacrolein ÷ Mole number of supplied methacrolein × 100
Selectivity (%) = number of moles of methacrylic acid produced ÷ number of moles of reacted methacrolein × 100
Yield (%) = [conversion (%) × selectivity (%)] ÷ 100

<Catalyst life test>
4.5 g of catalyst is packed in a glass microreactor having an inner diameter of 16 mm, and raw material gas prepared by mixing methacrolein, air, steam and nitrogen (composition: methacrolein 4 vol%, molecular oxygen 12). Volume%, water vapor 17 volume%, nitrogen 67 volume%) at a space velocity of 1340 h ⁻¹ , and the reaction is carried out at a furnace temperature of 320 ° C. for 50 days or more. During this period, methacrolein conversion is performed every 7 to 14 days Asked. The reaction time was plotted on the horizontal axis and the conversion rate was plotted on the vertical axis, the slope was determined by the least square method, and the rate of decrease in conversion rate (% / day) was calculated.

<Detection of molybdenum trioxide by X-ray diffraction measurement>
As an X-ray diffraction measuring apparatus, MiniFlex manufactured by Rigaku Corporation is used, X-ray diffraction measurement is performed by a powder method, and d value derived from molybdenum trioxide (MoO ₃ ) = position of 3.24 to 3.26 The presence or absence of diffraction lines in was observed.

<Reference Example 1>
(Preparation of new catalyst)
In 224 kg of ion-exchanged water heated to 40 ° C., 38.2 kg of cesium nitrate [CsNO ₃ ], 27.4 kg of 75 wt% orthophosphoric acid, and 25.2 kg of 70 wt% nitric acid were dissolved, and this was designated as solution A.
On the other hand, after dissolving 297 kg of ammonium molybdate tetrahydrate [(NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O] in 330 kg of ion-exchanged water heated to 40 ° C., ammonium metavanadate [NH ₄ VO ₃ ] 8.19 kg was suspended and this was used as B liquid.
The liquid A and the liquid B were adjusted to 40 ° C., and the liquid A was added dropwise to the liquid B with stirring. Then, the liquid was stirred at 120 ° C. for 5.8 hours, and then antimony trioxide [Sb ₂ O ₃ ] 10 .2 kg and 10.2 kg of copper nitrate trihydrate [Cu (NO ₃ ) ₂ .3H ₂ O] were suspended in 23 kg of ion-exchanged water and then stirred in a sealed container at 120 ° C. for 5 hours. .
The mixture thus obtained was spray-dried with a spray dryer, and 100 parts by weight of the dried powder was kneaded by adding 4 parts by weight of ceramic fibers, 13 parts by weight of ammonium nitrate, and 9.7 parts by weight of ion-exchanged water, It was extruded into a cylindrical shape having a diameter of 5 mm and a height of 6 mm. The molded body was dried at a temperature of 90 ° C. and a relative humidity of 30% for 3 hours, and then heat-treated (pre-fired) in the order of 22 hours at 220 ° C. in an air stream and 1 hour at 250 ° C. in an air stream. The temperature was raised to 435 ° C. in an air stream and held at the same temperature for 3 hours. Furthermore, after cooling to 300 ° C. in a nitrogen stream, the nitrogen is switched to air containing 3.5% by volume of water, the temperature is raised to 390 ° C. in the air stream, and the air temperature is maintained for 3 hours. After cooling to 70 ° C., a new catalyst was taken out.
This new catalyst is an acid of Keggin type heteropolyacid containing phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 12, 0.50, 0.5, 0.3 and 1.4, respectively. It consisted of salt. Molybdenum trioxide was not detected.
The results of the activity test and life test of this new catalyst are shown in Table 1.

<Reference Example 2>
(Preparation of spent catalyst and its activity test)
The new catalyst obtained in Reference Example 1 was subjected to a methacrolein catalytic gas phase oxidation reaction for a long time to obtain a used catalyst. The atomic ratio of the metal elements contained in this used catalyst is 1.3, 9.9, 0.49, 0.5, 0.3 and 1.4 for phosphorus, molybdenum, vanadium, antimony, copper and cesium, respectively. Met. Molybdenum trioxide was detected.
An activity test was performed on this spent catalyst. The results are shown in Table 1.

<Example 1>
(Preparation of regenerated catalyst)
4.20 kg of the used catalyst obtained in Reference Example 2 was added to 7.32 kg of ion-exchanged water and stirred. The type and amount of the deficient component (scattered component) of the spent catalyst with respect to the new catalyst obtained in Reference Example 1 was calculated by fluorescent X-ray analysis, and in order to compensate for this, molybdenum trioxide [MoO ₃ ] 0.65 kg, 0.06 kg of 75 wt% orthophosphoric acid and 0.004 kg of ammonium metavanadate [NH ₄ VO ₃ ] were added.
Next, a solution prepared by adding 1.44 kg of ammonium nitrate [NH ₄ NO ₃ ] to 1.08 kg of ion-exchanged water was added, and the temperature was raised to 70 ° C. and kept at the same temperature for 1 hour. Thereafter, 0.26 kg of 25 wt% aqueous ammonia was added and held at 70 ° C. for 1 hour, and then stirred at 120 ° C. for 5 hours in a sealed container. The amount of ammonium root relative to 1 mol of nitrate in this aqueous slurry A was 1.2 mol. The atomic ratio of the metal elements contained in the aqueous slurry A is 1.5, 12, 0.50, 0.5, 0.3, and 1.4 for phosphorus, molybdenum, vanadium, antimony, copper, and cesium, respectively. The atomic ratio of cesium to molybdenum was 1.4 / 12.
The aqueous slurry A was spray dried at 120 ° C. using a spray dryer, and 9 parts by weight of ammonium nitrate and 8 parts by weight of ion-exchanged water were added to 100 parts by weight of the dried product and kneaded. And extruded into a cylindrical shape having a diameter of 5 mm and a height of 6 mm. The molded body was dried at a temperature of 90 ° C. and a relative humidity of 30% for 3 hours, and then heat treated (pre-fired) in an air stream at 220 ° C. for 22 hours and 250 ° C. for 1 hour in order. A pre-calcined catalyst precursor consisting of the acid salt was obtained.
Next, after raising the temperature to 390 ° C. in an air stream of a mixed gas of air and steam (water content is 1.4% by volume) and holding at that temperature for 4 hours, The air was switched to nitrogen, the temperature was raised to 435 ° C. in a nitrogen stream, and maintained at the same temperature for 4 hours to perform the second stage baking. Then, after cooling to 70 degreeC in nitrogen stream, the reproduction | regeneration catalyst (1) was taken out.
This regenerated catalyst (1) is a Keggin-type heteropolyethylene containing phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 12, 0.50, 0.5, 0.3 and 1.4, respectively. It consisted of an acid acid salt. Molybdenum trioxide was not detected.
Table 1 shows the results of the activity test and life test of this regenerated catalyst (1).

<Example 2>
(Preparation of regenerated catalyst)
In the first stage firing in Example 1, instead of the air stream of the mixed gas of air and steam (the content of water is 1.4% by volume), the mixed gas of air and steam (the content of water is 0.1%). A regenerated catalyst (2) was obtained in the same manner as in Example 1 except that the temperature was raised to 390 ° C. in a 5 vol% flow). Molybdenum trioxide was not detected.
The results of the activity test and life test of this regenerated catalyst (2) are shown in Table 1.

<Comparative Example 1>
(Preparation of regenerated catalyst)
In the first stage firing in Example 1, instead of the air stream of the mixed gas of air and steam (the content of water is 1.4% by volume), the mixed gas of air and steam (the content of water is 2. A regenerated catalyst (C1) was obtained in the same manner as in Example 1, except that the temperature was raised to 390 ° C. in an air flow of 8 vol%). Molybdenum trioxide was not detected.
Table 1 shows the results of the activity test and life test of this regenerated catalyst (C1).

<Comparative example 2>
(Preparation of regenerated catalyst)
In the first stage firing in Example 1, instead of an air stream of a mixed gas of air and steam (water content is 1.4% by volume), 390 in an air stream (water content is 0% by volume) A regenerated catalyst (C2) was obtained in the same manner as in Example 1 except that the temperature was raised to ° C. Molybdenum trioxide was detected.
The results of the activity test of this regenerated catalyst (C2) are shown in Table 1.

In Table 1 below, the contents of water in the mixed gas of air and steam in the first stage firing are described in order from an example with a small content.

Claims (7)

A method for regenerating a catalyst for producing methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum,
An aqueous slurry containing the used catalyst, ammonium radical, nitrate radical and water used in the production of methacrylic acid is dried to obtain a catalyst precursor, and the catalyst precursor is 0.1 vol% or more and less than 2.0 vol% For first-stage baking at 360-410 ° C. in an atmosphere of oxidizing gas containing a large amount of water, followed by second-stage baking at 420-500 ° C. in an atmosphere of non-oxidizing gas Catalyst regeneration method.   The heteropolyacid compound further contains at least one element X selected from the group consisting of potassium, rubidium, cesium and thallium, and the atomic ratio (X / Mo) of element X to molybdenum contained in the aqueous slurry is 0.5 / The method for regenerating a catalyst for methacrylic acid production according to claim 1, which is 12 to 2/12.   The method for regenerating a catalyst for methacrylic acid production according to claim 1 or 2, wherein the content of ammonium radicals contained in the aqueous slurry is 1.3 moles or less per mole of nitrate radicals.   The method for regenerating a catalyst for methacrylic acid production according to any one of claims 1 to 3, wherein the aqueous slurry is heat-treated at 100 ° C or higher and then dried to obtain a catalyst precursor.   The methacrylic acid according to any one of claims 1 to 4, wherein the catalyst precursor is exposed to an atmosphere having a relative humidity of 10 to 60% at 40 to 100 ° C for 0.5 to 10 hours and then subjected to the first stage baking. A method for regenerating a catalyst for production.   The heteropolyacid compound further comprises vanadium and at least one element selected from the group consisting of copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum, and cerium. A method for regenerating a catalyst for producing methacrylic acid as described in 1.   A catalyst for producing methacrylic acid is regenerated by the regeneration method according to any one of claims 1 to 6, and a compound selected from methacrolein, isobutyraldehyde, isobutane and isobutyric acid is vapor-phased in the presence of the regenerated catalyst. A method for producing methacrylic acid, which is subjected to a catalytic oxidation reaction.