JP2010155197A - Method for regenerating catalyst for producing methacrylic acid and method for producing the methacrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for regenerating a catalyst for producing methacrylic acid, with which service life of the catalyst can be improved while satisfactorily recovering catalytic activity. <P>SOLUTION: The method for regenerating the catalyst for producing methacrylic acid from the spent catalyst obtained by using the new catalyst which consists of a heteropolyacid compound having the composition containing phosphorus, molybdenum and an alkali metal, when the methacrylic acid is produced, comprises the steps of: mixing a molybdenum compound and water in the spent catalyst; drying the obtained mixture; and firing the dried mixture. In the method, the amount of the molybdenum compound to be mixed in the spent catalyst is adjusted so that the atomic ratio of the molybdenum to the alkali metal in the heteropolyacid compound constituting the regenerated catalyst is made smaller than that of the molybdenum to the alkali metal in the heteropolyacid compound constituting the new catalyst. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a method for regenerating a used catalyst comprising a heteropolyacid compound having a composition containing phosphorus, molybdenum and an alkali metal element to regenerate a catalyst for producing methacrylic acid, and a regenerated catalyst obtained by this method. And a method for producing methacrylic acid.

  A catalyst for producing methacrylic acid composed of a heteropolyacid compound having a composition containing phosphorus, molybdenum, and an alkali metal element is a part of molybdenum due to heat load, etc. Is scattered from the catalyst and disappears, and it is known that the catalytic activity decreases.

  As a method for regenerating such a used catalyst, for example, a used catalyst in which molybdenum is partially scattered and disappeared is treated by mixing an amount of molybdenum compound corresponding to the amount lost with water and treating it. A method is reported in which the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound in the catalyst is the same as that of the new catalyst before use in the reaction (Patent Documents 1 and 2).

JP 2001-286762 A JP 2001-286863 A

  However, the regenerated catalyst regenerated by the conventional regeneration method exhibits good performance with respect to the initial catalyst activity, but is not always satisfactory in terms of catalyst life.

  Therefore, an object of the present invention is to provide a method for regenerating a catalyst for methacrylic acid production, which can improve the catalyst life while improving the catalyst activity. Furthermore, the objective of this invention is providing the manufacturing method of methacrylic acid which can maintain a favorable conversion and selectivity for a long time using the reproduction | regeneration catalyst obtained by this method.

  The present inventor has intensively studied to solve the above problems. As a result, when the spent catalyst is mixed with the molybdenum compound and water for treatment, the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is the heteropolyacid constituting the new catalyst before use. It has been found that the above problem can be solved by adjusting the mixing amount of the molybdenum compound to the spent catalyst so that the atomic ratio of molybdenum to the alkali metal element of the compound is smaller, and the present invention has been completed. .

That is, this invention consists of the following structures.
(1) A method for regenerating a catalyst for producing methacrylic acid from a used catalyst obtained by using a new catalyst comprising a heteropolyacid compound having a composition containing phosphorus, molybdenum and an alkali metal element for producing methacrylic acid, The molybdenum catalyst and water are mixed with the spent catalyst, then dried and calcined, and the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is the new product. A method for regenerating a catalyst for methacrylic acid production, comprising adjusting a mixing amount of the molybdenum compound with respect to the used catalyst so as to be smaller than an atomic ratio of molybdenum to an alkali metal element of the heteropolyacid compound constituting the catalyst.
(2) The new catalyst is represented by the following formula (I)
PaMobVcXdYeOx (I)
(In the formula (I), P, Mo and V represent phosphorus, molybdenum and vanadium, respectively, X represents at least one alkali metal element selected from the group consisting of potassium, rubidium and cesium, Y represents copper, arsenic Represents at least one element selected from the group consisting of antimony, boron, silver, bismuth, iron, cobalt, lanthanum, cerium and thallium, 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)
The regeneration method of the catalyst for methacrylic acid manufacture as described in said (1) which consists of heteropoly acid compound shown by these.
(3) When the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the new catalyst is α, and the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is β, The method for regenerating a catalyst for methacrylic acid production according to the above (1) or (2), wherein the value of β / α is 0.9 or more.
(4) The method for regenerating a catalyst for methacrylic acid production according to any one of (1) to (3), wherein a nitric acid radical and an ammonium radical are also mixed when mixing the molybdenum compound and water with the used catalyst.
(5) Regeneration of the catalyst for methacrylic acid production according to any one of the above (1) to (4), wherein the spent catalyst is subjected to heat treatment at 350 ° C. or higher before mixing the molybdenum compound and water with the spent catalyst. Method.
(6) A compound selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid in the presence of the catalyst for producing methacrylic acid regenerated by the method according to any one of (1) to (5). A method for producing methacrylic acid, which is subjected to a gas phase catalytic oxidation reaction.

  According to the present invention, when the catalyst for producing methacrylic acid is regenerated, the catalyst life can be improved while the catalyst activity is recovered well. Moreover, if the regenerated catalyst regenerated by this method is used, methacrylic acid can be produced while maintaining good conversion and selectivity for a long time.

Hereinafter, the present invention will be described in detail.
The method for regenerating a catalyst for producing methacrylic acid according to the present invention regenerates a used catalyst obtained by using a new catalyst for producing methacrylic acid (hereinafter sometimes referred to as “new catalyst”) for the production of methacrylic acid. In this method, a regenerated catalyst is obtained by performing treatment.
The catalyst for production of methacrylic acid (new catalyst) in the present invention is composed of a heteropolyacid compound having a composition essentially including phosphorus, molybdenum and an alkali metal element, and may be composed of a free heteropolyacid, It may consist of a salt of a heteropolyacid. 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.

  Preferred examples of the alkali metal element contained in the heteropolyacid compound as an essential constituent element include potassium, rubidium, cesium and the like. Further, the heteropolyacid compound preferably contains vanadium as an element other than phosphorus, molybdenum and alkali metal elements, and also includes copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum, cerium and It is desirable to contain at least one element selected from the group consisting of thallium (hereinafter also referred to as “Y element”).

A preferred composition of the heteropolyacid compound constituting the methacrylic acid production catalyst (new catalyst) is shown by the following formula (I).
PaMobVcXdYeOx (I)
(In the formula (I), P, Mo and V represent phosphorus, molybdenum and vanadium, respectively, X represents at least one alkali metal element selected from the group consisting of potassium, rubidium and cesium, Y represents copper, arsenic Represents at least one element selected from the group consisting of antimony, boron, silver, bismuth, iron, cobalt, lanthanum, cerium and thallium (that is, the Y element), O represents oxygen, and 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)

  The catalyst for producing methacrylic acid (new catalyst) includes, for example, a compound containing each of the above-described elements constituting a heteropolyacid compound (for example, oxoacid, oxoacid salt, oxide, nitrate, carbonate, hydroxide of each element) Products, halides, etc.), formed into a desired shape, and then fired. For example, phosphoric acid, phosphate and the like are used as the compound containing phosphorus, and molybdate such as molybdic acid and ammonium molybdate, molybdenum oxide, molybdenum chloride and the like are used as the compound containing molybdenum. As the compound containing a metal element, an oxide, nitrate, carbonate, hydroxide, halide, or the like is used. In addition, as the compound containing vanadium, vanadate, vanadate (metavanadate) such as ammonium vanadate (ammonium metavanadate), vanadium oxide, vanadium chloride, etc. are used. Oxo acids, oxo acid salts, oxides, nitrates, carbonates, hydroxides, halides and the like are used.

  When such a methacrylic acid production catalyst (new catalyst) is used for the production of methacrylic acid, a part of molybdenum may be scattered and disappear from the catalyst due to heat load or the like, and the catalytic activity may be lowered. In the regeneration method of the present invention, the spent catalyst having such a lowered catalytic activity is used as a target for regeneration treatment.

In the regeneration method of the present invention, a mixing step of mixing a molybdenum compound and water with the spent catalyst is essential, and then a regeneration catalyst is obtained through a drying step and a calcination step.
In the mixing step, it is important to adjust the mixing amount of the molybdenum compound based on the composition of the used catalyst used for regeneration and the composition of the new catalyst. That is, the mixing amount of the molybdenum compound with respect to the used catalyst is such that the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is equal to the molybdenum metal to the alkali metal element of the heteropolyacid compound constituting the new catalyst. Adjust so that it is smaller than the atomic ratio. In other words, in the present invention, the molybdenum compound is mixed with the spent catalyst to compensate for the scattered and disappeared molybdenum in the production of methacrylic acid. At this time, the same amount as the new catalyst is added by adding an amount corresponding to the lost amount. Instead of returning to the atomic ratio, the atomic ratio of molybdenum to the alkali metal element in the regenerated catalyst obtained by adding an amount of molybdenum less than the disappearance is made smaller than that of the new catalyst. As a result, the catalyst activity can be recovered and at the same time the catalyst life can be improved.
In particular, in the regeneration method of the present invention, the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the new catalyst is α, and the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst. When β is β, the value of β / α is preferably 0.9 or more from the viewpoint of the initial activity of the catalyst.

  Specifically, the mixing amount of the molybdenum compound in the mixing step is based on the new catalyst and the catalyst composition of the used catalyst before being used for regeneration (type and amount of constituent components) by fluorescent X-ray analysis, ICP emission analysis, or the like. By examining the difference in the composition of the two catalysts, the type and amount of the element disappeared in the production of methacrylic acid was determined. Based on the results, the obtained regenerated catalyst had a specific composition (the atomic ratio of molybdenum to the alkali metal element was What is necessary is just to determine so that it may have a composition which becomes the range mentioned above. The catalyst composition of the obtained regenerated catalyst can be analyzed and confirmed by fluorescent X-ray analysis, ICP emission analysis, or the like, as described above.

As the molybdenum compound to be mixed in the mixing step, one or more compounds selected from molybdenum-containing compounds that can be used for production of a new catalyst, such as molybdate, molybdenum oxide such as ammonium morbudenate, molybdenum oxide, and molybdenum chloride, or Two or more kinds may be appropriately selected.
As the water to be mixed in the mixing step, ion exchange water is usually used. The mixing amount of water is usually based on 1 part by weight of the amount of molybdenum atoms in the mixture obtained in the mixing step (total of molybdenum contained in the used catalyst and molybdenum contained in the molybdenum compound added in the mixing step). 1 to 20 parts by weight.

  In the mixing step, it is possible to mix a phosphorus compound and a compound containing other catalyst constituent elements with the above-described molybdenum compound and water in the spent catalyst. That is, when the methacrylic acid production catalyst (new catalyst) comprising the heteropoly acid compound is used for the production of methacrylic acid, not only molybdenum but also phosphorus and other catalyst constituent elements are partially scattered and lost from the catalyst. This may cause a decrease in catalyst activity. Therefore, when mixing the molybdenum compound, the catalytic activity can be effectively recovered by mixing the phosphorus compound or the like to compensate for the lost phosphorus or the like.

For example, when a phosphorus compound is mixed, the mixing amount is usually such that the atomic ratio of phosphorus to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is the alkali metal element of the heteropolyacid compound constituting the new catalyst. It is adjusted to be the same as the atomic ratio of phosphorus to (in other words, an amount corresponding to the disappearance of phosphorus is added to return to the same atomic ratio as that of the new catalyst). However, in order to improve the selectivity, the mixing amount of the phosphorus compound is such that the atomic ratio of phosphorus to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is the alkali metal of the heteropolyacid compound constituting the new catalyst. It is preferable to adjust so that it may become larger than the atomic ratio of phosphorus with respect to an element.
Specifically, the mixing amount of the phosphorus compound is determined so that the atomic ratio of phosphorus to the alkali metal element of the obtained regenerated catalyst is in a desired range based on the disappearance amount lost in the production of methacrylic acid, as in the case of the molybdenum compound do it.
As the phosphorus compound to be mixed in the mixing step, one or two or more types may be appropriately selected from compounds containing phosphorus that can be used for manufacturing a new catalyst, such as phosphoric acid and phosphate.

  In addition, when a compound containing the other catalyst constituent elements (elements other than molybdenum and phosphorus) is mixed, the amount of the mixture is within a range in which almost the same conversion rate, selectivity, and catalyst life are exhibited in the regenerated catalyst. If not, the atomic ratio of the element to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is not particularly limited, the atomic ratio of the element to the alkali metal element of the heteropolyacid compound constituting the new catalyst Or the atomic ratio of the element to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst may be adjusted to be equivalent to the alkali metal element of the heteropolyacid compound constituting the new catalyst. It is also possible to adjust so as to be larger or smaller than the atomic ratio of the element to.

It is preferable that the spent catalyst used in the mixing step is subjected to heat treatment at 350 ° C. or higher as a pretreatment in advance before mixing the molybdenum compound and water. Thereby, the conversion rate and selectivity in the regenerated catalyst obtained can be further improved.
The upper limit of the treatment temperature of the heat treatment performed as a pretreatment of the spent catalyst is not particularly limited, but is preferably 600 ° C. or less, more preferably 550 ° C. or less. The treatment time for heat treatment is not particularly limited, but is usually 0.1 to 24 hours, preferably 0.5 to 10 hours.

  The heat treatment performed as a pretreatment of the spent catalyst may be performed in an oxidizing gas atmosphere or a non-oxidizing gas atmosphere, but may be performed in an oxidizing gas atmosphere. Is preferred. The oxidizing gas here is a gas containing an oxidizing substance, and examples thereof include an oxygen-containing gas. In the case of using 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. . The oxidizing gas may contain moisture as required, but the concentration is usually 10% by volume or less. Of these, air is preferable as the oxidizing gas.

When the spent catalyst used in the mixing step is a molded body, it may be used as it is, but if necessary, it can be pulverized by a conventionally known method before mixing the molybdenum compound and water. However, if the molded body (used catalyst) contains fibers or the like that develop the strength of the catalyst, if these fibers are cut, there is a concern that the strength may be lowered, so that the fibers or the like are not cut. It is preferable to adjust the degree of grinding.
In addition, when both the pulverization treatment and the heat treatment performed as a pretreatment are performed on the spent catalyst used in the mixing step, the order of both treatments is not particularly limited, but usually the heat treatment is performed after the pulverization treatment. The

In the mixing step, in mixing the molybdenum compound and water with the spent catalyst, it is preferable to also mix a nitrate group and an ammonium group. Thereby, the conversion rate and selectivity in the regenerated catalyst obtained can be further improved.
In order to mix the nitrate root, as a nitrate root supply source, for example, nitric acid or a nitrate such as ammonium nitrate may be mixed. On the other hand, to mix the ammonium root, as an ammonium root supply source, for example, Ammonia and ammonium salts such as ammonium nitrate, ammonium carbonate, ammonium hydrogen carbonate, and ammonium acetate may be mixed. Preferably, nitric acid and ammonium nitrate are used as the nitrate radical source, and ammonia and ammonium nitrate are preferably used as the ammonium radical source. The ratio of the nitrate radical supply source and the ammonium radical supply source can be adjusted as appropriate, but it is effective to adjust the molar ratio of the ammonium radical to the nitrate radical to be 1.3 or less. In addition, when an ammonium root and a nitrate radical are contained in the molybdenum compound or the like to be mixed in the mixing step, the amount is adjusted in consideration of the amount thereof.

  In the mixing step, the order of mixing the components described above is not particularly limited, and may be set as appropriate.

  The mixture obtained in the mixing step is then subjected to a drying step, but before being subjected to the drying step, it is preferable to subject the mixture to aging by heating at 100 ° C. or higher in a closed container. . By subjecting the mixture obtained in the mixing step to such aging treatment, the catalytic activity can be effectively recovered. The upper limit of the heating temperature in the aging treatment is preferably 200 ° C. or less, and more preferably 150 ° C. or less. In order to obtain a sufficient activity recovery effect, the heating time in the aging treatment is usually 0.1 hour or longer, preferably 2 hours or longer, and 10 hours or shorter from the viewpoint of productivity.

  The drying method carried out in the drying step is not particularly limited, and for example, a method usually used in this field such as an evaporation to dryness method, a spray drying method, a drum drying method, and an airflow drying method may be adopted. it can. Further, the drying conditions may be set as appropriate so that the water content in the mixture is sufficiently reduced, and is not particularly limited.

  The dried product obtained in the drying step is then subjected to a firing step, but before being subjected to the firing step, a desired shape (ring shape, pellet shape, spherical shape, cylindrical shape, etc.) is necessary. A forming process for forming the film can be performed. The molding process may be performed by a method usually used in this field, such as tableting molding or extrusion molding. In the molding treatment, water, a molding aid, a pore agent and the like can be added to the dried product as necessary. Examples of the molding aid include ammonium nitrate as well as ceramic fiber and glass fiber. In particular, ammonium nitrate has not only a function as a molding aid but also a function as a pore agent.

  It is preferable that the molded body obtained by the molding process is subsequently subjected to a temperature and humidity control process. A more stable catalyst can be obtained by subjecting the temperature and humidity control treatment to the firing step. Specifically, the temperature control and humidity control treatment is performed by exposing the molded body for about 0.5 to 10 hours in an atmosphere of 40 to 100 ° C. and a relative humidity of 10 to 60%. 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, air is usually used as the atmospheric gas for the treatment, but an inert gas such as nitrogen may be used.

  The firing step can be performed by a method usually used in this field, and is not particularly limited. For example, it may be performed in an atmosphere of an oxidizing gas such as oxygen, or may be performed in an atmosphere of a non-oxidizing gas such as nitrogen, and the firing temperature is usually 300 ° C. or higher. Preferably, a two-stage firing method is employed in which the first-stage firing is performed in an oxidizing gas atmosphere and then the second-stage firing is performed in a non-oxidizing gas atmosphere. Thus, by carrying out calcination in two stages, the catalyst life can be recovered more favorably.

  When firing is performed in two stages, the oxidizing gas used in the first stage firing is a gas containing an oxidizing substance, and examples thereof include an oxygen-containing gas. In the case of using 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. . The oxidizing gas may contain moisture as required, but the concentration is usually 10% by volume or less. Of these, air is preferable as the oxidizing gas. The first stage firing is usually performed under such an oxidizing gas stream. Moreover, the temperature of 1st step | paragraph baking is 360-410 degreeC normally, Preferably it is 380-400 degreeC.

  When firing is performed in two stages, the non-oxidizing gas used in the second stage firing is a gas that does not substantially contain an oxidizing substance such as oxygen. For example, nitrogen, carbon dioxide, helium, argon, etc. An active gas is mentioned. The non-oxidizing gas may contain moisture as required, but the concentration is usually 10% by volume or less. Of these, nitrogen is preferable as the non-oxidizing gas. The second-stage firing is usually performed under such a non-oxidizing gas stream. Moreover, the temperature of 2nd-stage baking is 420-500 degreeC normally, Preferably it is 420-450 degreeC.

  In addition, it is preferable to perform the heat processing hold | maintained at the temperature of about 180-300 degreeC in the atmosphere of oxidizing gas or non-oxidizing gas as pre-baking prior to the said baking process.

  Thus, it is possible to obtain a regenerated catalyst whose catalytic activity is well recovered and whose catalyst life is improved. This regenerated catalyst is made of a heteropolyacid compound, like a new catalyst, 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.

  The method for producing methacrylic acid of the present invention comprises a compound selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid in the presence of the catalyst for producing methacrylic acid regenerated by the regeneration method of the present invention (hereinafter referred to as “ Is sometimes referred to as a “raw material compound”). Thus, by using the regenerated catalyst of the present invention, methacrylic acid can be produced while maintaining a good conversion and selectivity for a long time.

  The production of methacrylic acid is usually carried out by filling a fixed bed multi-tubular reactor with a catalyst and supplying a raw material gas containing the raw material compound and oxygen to the reactor, but is not limited thereto. It is also possible to adopt a reaction format such as a fluidized bed or a moving bed. Air is usually used as the oxygen source. The source gas may contain nitrogen, carbon dioxide, carbon monoxide, water vapor and the like as components other than the source compound and oxygen.

  The raw material compound contained in the raw material gas is not necessarily a high-purity purified product. For example, as methacrolein, a reaction containing methacrolein obtained by a gas phase catalytic oxidation reaction of isobutylene or t-butyl alcohol. Product gas can also be used. In addition, only 1 type may be sufficient as the raw material compound contained in the said raw material gas, and 2 or more types may be sufficient as it.

What is necessary is just to set the reaction conditions in manufacture of methacrylic acid suitably according to the kind etc. of the raw material compound contained in raw material gas. For example, when methacrolein is used as the raw material compound, the concentration of methacrolein 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, space. The reaction is carried out under conditions where the speed is 500 to 5000 h ⁻¹ (standard condition standard), the reaction temperature is 250 to 350 ° C., and the reaction pressure is 0.1 to 0.3 MPa. On the other hand, when isobutane is used as the raw material compound, 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 carried out under the conditions of 400 to 5000 h ⁻¹ (standard condition standard), reaction temperature of 250 to 400 ° C., and reaction pressure of 0.1 to 1 MPa. In addition, when isobutyraldehyde or isobutyric acid is used as the raw material compound, generally the same reaction conditions as when methacrolein is used as the raw material are employed.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not restrict | limited to these.
The air used below contains 2% by volume of moisture (corresponding to the atmosphere), and nitrogen used below contains substantially no moisture.

The analysis and evaluation of the catalyst obtained in each of the following examples were performed as follows.
<Catalyst composition (ratio of constituent elements)>
Using a fluorescent X-ray analyzer (“ZSX Primus II” manufactured by Rigaku Corporation), the catalyst was determined by fluorescent X-ray analysis.

<Catalyst activity test>
9 g of catalyst was filled in a glass microreactor having an inner diameter of 16 mm, and a raw material gas prepared by mixing methacrolein, air, steam and nitrogen (composition: methacrolein 4 vol%, molecular oxygen 12 vol%, Steam 17 vol%, Nitrogen 67 vol%) was supplied at a space velocity of 670 h ⁻¹ and reacted at a furnace temperature (furnace temperature for heating the microreactor) of 280 ° C. for 1 hour. The temperature was raised to 0 ° C. and reacted for 1 hour, and then the reaction was again carried out at a furnace temperature of 280 ° C. for 1 hour. Then, the outlet gas (the gas after the reaction) at the end of the reaction (that is, when 1 hour has passed since the furnace temperature was again set to 280 ° C.) was sampled and analyzed by gas chromatography, and the conversion rate ( %) And selectivity (%).

Conversion rate (%) = [number of moles of reacted methacrolein ÷ supplied methacrolein
Number of moles] × 100
Selectivity (%) = [number of moles of methacrylic acid produced ÷ reacted methacrolein
Number of moles] × 100

<Catalyst life test>
A raw material gas (composition: 4% by volume of methacrolein, 12% by volume of molecular oxygen) prepared by mixing 4.5 g of catalyst in a glass microreactor having an inner diameter of 16 mm and mixing methacrolein, air, steam and nitrogen therein. %, Water vapor 17% by volume, nitrogen 67% by volume) were supplied at a space velocity of 1340 h ⁻¹ , and the reaction was continuously carried out at a furnace temperature (furnace temperature for heating the microreactor) of 330 ° C. The outlet gas (gas after reaction) was sampled every 7 to 10 days from the start of the reaction, and the conversion rate was determined in the same manner as in the activity test. Then, the elapsed days until the conversion rate reaches about 70% and the final conversion rate (%) at that time are examined, and the conversion obtained during this period (from the start of the reaction until the conversion rate reaches about 70%). The rate data was plotted with the reaction time on the horizontal axis and the conversion rate on the vertical axis, and the slope calculated by the least square method was defined as the rate of conversion reduction (% / day).

(Reference Example 1-Preparation of a 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 297 kg of ammonium molybdate tetrahydrate [(NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O] was dissolved in 330 kg of ion-exchanged water heated to 40 ° C., ammonium metavanadate [NH ₄ VO ₃ ] 8.19kg was suspended and this was made into the B liquid.

While maintaining the temperature of the liquid A and the liquid B at 40 ° C., the liquid A was dropped into the liquid B with stirring, and the mixed liquid after the dropping was stirred at 120 ° C. for 5.8 hours in a sealed container. Next, 10.2 kg of antimony trioxide [Sb ₂ O ₃ ] and 10.2 kg of copper nitrate trihydrate [Cu (NO ₃ ) ₂ .3H ₂ O] are added to ion-exchanged water with respect to the obtained mixed liquid. It added in the state suspended in 23 kg, and it stirred at 120 degreeC after that for 5 hours within the airtight container. Next, the slurry-like mixture thus obtained is dried with a spray dryer, and 4 parts by weight of ceramic fibers, 13 parts by weight of ammonium nitrate, and ion-exchanged water are added to 100 parts by weight of the obtained dry powder. After adding 7 parts by weight and kneading, it was extruded into a cylindrical shape having a diameter of 5 mm and a height of 6 mm. The obtained molded body was dried at a temperature of 90 ° C. and a relative humidity of 30% for 3 hours, and then heat treated in the order of 22 hours at 220 ° C. in an air stream and 1 hour at 250 ° C. in an air stream (before Firing). Next, the temperature was raised to 435 ° C. in a nitrogen stream and held at the same temperature for 3 hours. After cooling to 300 ° C. in the nitrogen stream, the air stream was switched from nitrogen to air, and again 390 ° C. in the air stream. The mixture was heated up to 3 hours and held at the same temperature for 3 hours to fire. Then, after cooling to 70 degreeC in airflow, the molded object was taken out and this was made into the new catalyst.

  The resulting new catalyst is a Keggin type composition comprising phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 12, 0.5, 0.5, 0.3 and 1.4, respectively. It consisted of an acid salt of a heteropolyacid. The atomic ratio α of molybdenum to cesium in the new catalyst was 8.6 (≈12 / 1.4). When this new catalyst was subjected to the activity test and the life test, the conversion rate was 87%, the selectivity rate was 84%, and the conversion rate reduction rate was 0.2% / day.

(Reference Example 2-Preparation of spent catalyst)
The new catalyst obtained in Reference Example 1 was subjected to methacrolein catalytic gas phase oxidation reaction for a long time to obtain a used catalyst.

  The acid salt of the heteropolyacid constituting the obtained spent catalyst is 1.3, 9.6, 0.5, 0.5, 0.3 and 1 for phosphorus, molybdenum, vanadium, antimony, copper and cesium, respectively. The composition contained at an atomic ratio of .4. When this spent catalyst was subjected to the activity test, the conversion was 35% and the selectivity was 85%.

Example 1
200 g of the used catalyst obtained in Reference Example 2 was heat-treated at 450 ° C. for 5 hours in an air atmosphere. The obtained catalyst after heat treatment (used catalyst) was added to 400 g of ion-exchanged water and stirred, and then 27.2 g of molybdenum trioxide [MoO ₃ ] and 2.7 g of 75 wt% orthophosphoric acid were added. At this time, the addition amount of molybdenum trioxide compares the composition of the acid salt of the heteropolyacid in the new catalyst obtained in Reference Example 1 with the composition of the acid salt of the heteropolyacid in the used catalyst obtained in Reference Example 2. Thus, the reduction amount of molybdenum in the spent catalyst was grasped, and the amount of molybdenum atoms added was determined in a range where it was smaller than this reduction amount. In addition, the amount of addition of orthophosphoric acid was determined in the same manner as described above so that the amount of phosphorus decrease in the spent catalyst was grasped and the amount of phosphorus atoms added was the same as this amount of decrease.

Subsequently, after 69.2 g of ammonium nitrate [NH ₄ NO ₃ ] was added, the temperature was raised to 70 ° C. and held at the same temperature for 1 hour, and then 12.5 g of 25% by weight aqueous ammonia was added to reach 70 ° C. For 1 hour and then stirred at 120 ° C. for 5 hours in a sealed container to obtain a slurry mixture. The molar ratio of ammonium radicals to nitrate radicals in this slurry mixture was 1.2.

  Next, the obtained slurry-like mixture was dried at 120 ° C., and 5 parts by weight of ammonium nitrate and 7 parts by weight of ion-exchanged water were added to and kneaded with 100 parts by weight of the obtained dried product. Extruded into a 6 mm long cylinder. The obtained molded body was dried at a temperature of 90 ° C. and a relative humidity of 30% for 3 hours, and then heat treated in the order of 22 hours at 220 ° C. in an air stream and 1 hour at 250 ° C. in an air stream (before Firing). Next, the temperature is raised to 390 ° C. in an air stream and held at the same temperature for 3 hours, then the air stream is switched from air to nitrogen, the temperature is raised to 435 ° C. in the nitrogen stream and held at the same temperature for 4 hours. And fired. Then, after cooling to 70 degreeC in nitrogen stream, the molded object was taken out and this was made into the reproduction | regeneration catalyst (1).

  The obtained regenerated catalyst (1) contains phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 11.7, 0.5, 0.5, 0.3 and 1.4, respectively. It comprised the acid salt of the Keggin type heteropolyacid of the containing composition. In this regenerated catalyst (1), the atomic ratio β of molybdenum to cesium is 8.4 (≈11.7 / 1.4), and the value of β / α is 0.98 (≈ (11.7 / 1). 4) / (12 / 1.4)). When this regenerated catalyst (1) was subjected to the activity test and the life test, the results shown in Table 1 were obtained.

(Example 2)
A regenerated catalyst (2) was obtained in the same manner as in Example 1 except that the amount of molybdenum trioxide [MoO ₃ ] added was changed from 27.2 g to 22.8 g in Example 1.
The obtained regenerated catalyst (2) contains phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 11.4, 0.5, 0.5, 0.3 and 1.4, respectively. It comprised the acid salt of the Keggin type heteropolyacid of the containing composition. In this regenerated catalyst (2), the atomic ratio β of molybdenum to cesium is 8.1 (≈11.4 / 1.4), and the value of β / α is 0.95 (≈ (11.4 / 1). 4) / (12 / 1.4)). When this regenerated catalyst (2) was subjected to the activity test and the life test, the results shown in Table 1 were obtained.

(Comparative Example 1)
In Example 1, except that the amount of molybdenum trioxide [MoO ₃ ] added was changed from 27.2 g to 31.5 g, the same operation as in Example 1 was performed to obtain a comparative regenerated catalyst (C1). It was.
The obtained regenerated catalyst (C1) contains phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 12, 0.5, 0.5, 0.3 and 1.4, respectively. The acid salt of a Keggin type heteropolyacid. In this regenerated catalyst (C1), the atomic ratio β of molybdenum to cesium is 8.6 (≈12 / 1.4), and the value of β / α is 1.00 (= (12 / 1.4) / (12 / 1.4)). When this regenerated catalyst (C1) was subjected to the activity test and the life test, the results shown in Table 1 were obtained.

(Comparative Example 2)
In Example 1, except that the addition amount of molybdenum trioxide [MoO ₃ ] was changed from 27.2 g to 35.93 g, the same operation as in Example 1 was performed to obtain a comparative regenerated catalyst (C2). It was.
The obtained regenerated catalyst (C2) contains phosphorus, molybdenum, vanadium, antimony, copper and cesium in atomic ratios of 1.5, 12.3, 0.5, 0.5, 0.3 and 1.4, respectively. It comprised the acid salt of the Keggin type heteropolyacid of the containing composition. In this regenerated catalyst (C2), the atomic ratio β of molybdenum to cesium is 8.8 (≈12.3 / 1.4), and the value of β / α is 1.03 (≈ (12.3 / 1). 4) / (12 / 1.4)). When this regenerated catalyst (C2) was subjected to the activity test and the life test, the results shown in Table 1 were obtained.

Claims (6)

A method for regenerating a catalyst for methacrylic acid production from a used catalyst obtained by using a new catalyst comprising a heteropolyacid compound having a composition containing phosphorus, molybdenum and an alkali metal element for the production of methacrylic acid,
Each of the steps of mixing the spent catalyst with a molybdenum compound and water, then drying and calcining; and
The spent catalyst such that the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst is smaller than the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the new catalyst. A method for regenerating a catalyst for producing methacrylic acid, comprising adjusting a mixing amount of the molybdenum compound with respect to the catalyst. A new catalyst is represented by the following formula (I)
PaMobVcXdYeOx (I)
(In the formula (I), P, Mo and V represent phosphorus, molybdenum and vanadium, respectively, X represents at least one alkali metal element selected from the group consisting of potassium, rubidium and cesium, Y represents copper, arsenic Represents at least one element selected from the group consisting of antimony, boron, silver, bismuth, iron, cobalt, lanthanum, cerium and thallium, 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)
The regeneration method of the catalyst for methacrylic acid production of Claim 1 which consists of heteropoly acid compound shown by these.   Β / α where α is the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the new catalyst, and β is the atomic ratio of molybdenum to the alkali metal element of the heteropolyacid compound constituting the regenerated catalyst. The method for regenerating a catalyst for producing methacrylic acid according to claim 1 or 2, wherein the value of is not less than 0.9.   The method for regenerating a catalyst for methacrylic acid production according to any one of claims 1 to 3, wherein a nitrate group and an ammonium root are also mixed when mixing the molybdenum compound and water with the spent catalyst.   The method for regenerating a catalyst for methacrylic acid production according to any one of claims 1 to 4, wherein the spent catalyst is subjected to heat treatment at 350 ° C or higher before mixing the molybdenum compound and water with the spent catalyst.   A compound selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid is subjected to a gas phase catalytic oxidation reaction in the presence of the catalyst for producing methacrylic acid regenerated by the method according to claim 1. A process for producing methacrylic acid, characterized in that: