JP4352856B2 - A method for producing a catalyst for producing methacrylic acid, a catalyst for producing methacrylic acid obtained thereby, and a method for producing methacrylic acid. - Google Patents

Description

  The present invention relates to a method for producing a catalyst for producing methacrylic acid and a catalyst for producing methacrylic acid which is suitably produced by this method. The present invention also relates to a method for producing methacrylic acid using the catalyst thus obtained.

Conventionally, as a catalyst used when producing methacrylic acid by a gas phase catalytic oxidation reaction such as methacrolein, it is known that a catalyst comprising a heteropolyacid or a salt thereof is effective. This catalyst is usually produced by calcining a catalyst precursor obtained by drying an aqueous mixture of catalyst raw materials. Examples of the calcining conditions include an inert gas having an oxygen concentration of less than 5% by volume. A method of firing at 400 to 550 ° C. (see Patent Document 1), a method of firing at 300 to 500 ° C. under a gas flow containing 0.05 to 3% by volume of ammonia and / or water vapor (Patent Document 2) A method of firing at 150 to 400 ° C. in a non-oxidizing gas atmosphere (see Patent Document 3), a method of firing at 400 to 500 ° C. in an inert gas (see Patent Document 4), 0. A method of firing at 350 to 395 ° C. under the flow of a gas containing 1 to 10% by volume of oxygen (see Patent Document 5) has been proposed.
JP 57-165040 A JP 58-61833 A JP 59-66349 A JP-A-4-63139 JP-A-5-279291

  However, the catalyst for producing methacrylic acid obtained by these conventional methods does not always have sufficient catalyst activity, that is, catalyst life.

  Therefore, the present inventors have conducted extensive research to develop a catalyst for producing methacrylic acid having an excellent catalyst life, and as a result, the catalyst precursor is subjected to multi-stage calcination consisting of specific gas and temperature conditions. In order to complete the present invention, a desired catalyst is obtained, and methacrylic acid can be produced with good productivity over a long period of time by subjecting a raw material such as methacrolein to a gas phase catalytic oxidation reaction using such a catalyst. It came.

  That is, the present invention is a method for producing a catalyst for producing methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum, and the catalyst precursor is 300 to 400 ° C. in an oxidizing gas atmosphere containing 10% by volume or less of water. After the first stage firing, the second stage firing is performed at 400 to 500 ° C. in a non-oxidizing gas atmosphere, and then the third stage is performed at 300 to 400 ° C. in an oxidizing gas atmosphere containing water of 30% by volume or less. The present invention relates to a method for producing a catalyst for producing methacrylic acid, characterized by performing step firing.

The present invention is also a catalyst that can be suitably obtained by the above production method, comprising an acid salt of a Keggin type heteropolyacid containing phosphorus and molybdenum, and having a peak with an interplanar spacing of 3.38 to 3.41Å in X-ray diffraction. The ratio (I ₁ / I ₀ ) of the intensity (I ₁ ) of the peak with an interplanar spacing of 3.24 to 3.26 to the intensity (I ₀ ) of the methacrylic acid is 0.001 to 0.01. This relates to a catalyst for acid production.

  Furthermore, the present invention relates to a method for producing methacrylic acid by subjecting a compound selected from methacrolein, isobutyraldehyde, isobutane and isobutyric acid to a gas phase catalytic oxidation reaction in the presence of the catalyst thus obtained. Yes.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst for methacrylic acid manufacture which is excellent in the sustainability of a catalyst activity, ie, the point of catalyst lifetime, is provided, and methacrylic acid can be manufactured with high productivity over a long period of time with such a catalyst.

  Hereinafter, the present invention will be described in detail. The catalyst for methacrylic acid production to be produced by the present invention is composed of a heteropolyacid compound essentially containing phosphorus and molybdenum, and may be composed of a free heteropolyacid or from 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 vanadium as an element other than phosphorus and molybdenum, and at least one element selected from potassium, rubidium, cesium and thallium (hereinafter sometimes referred to as X element), It is desirable that at least one element selected from copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium (hereinafter sometimes referred to as Y element) is included. Usually, a catalyst containing phosphorus, vanadium, X element and Y element at a ratio of 3 atoms or less to 12 atoms of molybdenum is preferably used.

  As the raw material of the catalyst, a compound containing each element contained in the catalyst, for example, an oxo acid, oxo acid salt, oxide, nitrate, carbonate, hydroxide, halide or the like of each element is desired. It is used at a ratio that satisfies the atomic ratio of For example, phosphoric acid, phosphate, etc. are used as the compound containing phosphorus, and molybdic acid, molybdate, molybdenum oxide, molybdenum chloride, etc. are used as the compound containing molybdenum, and as the compound containing vanadium, Vanadic acid, vanadate, vanadium oxide, vanadium chloride and the like are used. In addition, oxides, nitrates, carbonates, hydroxides, halides and the like are used as the compounds containing the X element, and oxo acids, oxoacid salts, nitrates, carbonates, water, and the like as the compounds containing the Y element. Oxides, halides and the like are used.

  The method for producing a catalyst of the present invention is performed by subjecting a catalyst precursor prepared from the above catalyst raw material to multistage calcination comprising specific gas and temperature conditions. This catalyst precursor can be usually prepared by mixing catalyst raw materials in water to obtain an aqueous solution or an aqueous slurry, and then drying the aqueous mixture, for example, by molding the dried product. Alternatively, the dried product may be heat-treated (pre-fired) and then molded, or the dried product may be molded and then heat-treated. Here, drying of the aqueous mixed solution is preferably performed by spray drying using a spray dryer or the like, and molding of the dried product is performed in a cylindrical shape, a spherical shape, a ring shape, or the like using a molding aid as necessary. It is preferable to do this. The heat treatment of the dried product is desirably performed at a temperature of about 180 to 300 ° C. in an oxidizing gas or non-oxidizing gas atmosphere.

  As a catalyst precursor preparation method, an ammonium compound is used as a catalyst raw material or ammonia or an ammonium salt is added to obtain an aqueous mixed solution containing ammonium roots. It is desirable to heat-treat after molding. According to these formulations, a catalyst precursor composed of a Dawson type heteropolyacid salt can be obtained as a dried product, and then the heat treatment causes a transition reaction from the Dawson type to the Keggin type, resulting in the conversion from the Keggin type heteropolyacid salt. A catalyst precursor can be obtained. The catalyst precursor thus obtained is a particularly suitable target for the multistage calcination according to the present invention.

  The catalyst precursor obtained as described above is first-stage calcined at a predetermined temperature in an atmosphere of an oxidizing gas containing moisture, and then the second stage at a predetermined temperature in an atmosphere of a non-oxidizing gas. Baking, and then third-stage baking at a predetermined temperature in an atmosphere of an oxidizing gas containing moisture. By such multistage calcination, a catalyst for producing methacrylic acid having an excellent catalyst life can be produced.

  Examples of the oxidizing gas used in the first stage firing and the third stage firing include an oxygen-containing gas containing oxygen at a concentration of 1 to 21% by volume, and the oxygen source is usually air or pure oxygen. Is used. Examples of the non-oxidizing gas used in the second stage baking include inert gases such as nitrogen, carbon dioxide, helium, and argon.

  It is essential for the oxidizing gas in the first stage firing and the third stage firing to have moisture present in order to improve the catalyst life. However, if there is too much moisture, the reverse effect is obtained. Therefore, the moisture in the oxidizing gas in the first stage firing is 10% by volume or less, preferably 5% by volume or less, and usually 1% by volume or more. On the other hand, the water content in the oxidizing gas in the third stage firing is 30% by volume or less, preferably 20% by volume or less, and usually 1% by volume or more. The non-oxidizing gas in the second-stage firing can have any water content, but if present, it is usually up to 10% by volume.

  The firing temperature is 300 to 400 ° C., preferably 350 to 400 ° C. for the first stage firing, 400 to 500 ° C., preferably 400 to 450 ° C. for the second stage firing, and 300 for the third stage firing. It is -400 degreeC, Preferably it is 350-400 degreeC. If each of these calcination temperatures is less than a predetermined value, the activity of the resulting catalyst may not be sufficient, or the effect of improving the catalyst life may not be sufficient.・ Since it is easy to sinter, the resulting catalyst may not have sufficient activity.

  In addition, although each baking time is each adjusted suitably, it is about 1 to 20 hours normally. Moreover, it is desirable to perform each of these firings while circulating a gas used as an atmospheric gas.

As described above, the catalyst that can be preferably produced by the above method is a catalyst comprising an acid salt of a Keggin type heteropolyacid containing phosphorus and molybdenum, and further decomposes the catalyst during production, particularly during calcination. This is a catalyst having a low amount of molybdenum trioxide, in which the production of molybdenum trioxide (MoO ₃ ) due to the above is suppressed. The proportion of molybdenum trioxide present in the catalyst relative to the acid salt of the Keggin heteropolyacid is determined by X-ray diffraction (XRD) measurement, that is, the interplanar spacing of 3.38 to 3.41Å characteristic of the acid salt of the Keggin heteropolyacid. for the peak intensity (I _0), can be expressed as the ratio of the intensity of the peak of the characteristic interplanar spacing 3.24~3.26Å molybdenum trioxide _{(I 1) (I 1 /} I 0). The peak intensity ratio (I ₁ / I ₀ ) is preferably 0.01 or less, more preferably 0.005 or less, and usually 0.001 or more from the viewpoint of catalyst life.

  Thus, the catalyst for producing methacrylic acid provided by the present invention has an excellent catalyst life, and by using this catalyst, a raw material compound such as methacrolein, isobutyraldehyde, isobutane, and isobutyric acid is subjected to a gas phase catalytic oxidation reaction. Thus, methacrylic acid can be produced with good productivity over a long period of 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 a raw material compound and oxygen to this. It can also be adopted. 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 methacrolein is used as a raw material, the concentration of methacrolein in the raw material gas is usually 1 to 10% by volume, the molar ratio of oxygen to methacrolein is 1 to 5, and the space velocity 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. 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.

Examples 1 and 2 and Comparative Examples 1 and 2
(A) Preparation of catalyst precursor In 224 kg of ion-exchanged water heated to 40 ° C, 38.2 kg of cesium nitrate [CsNO ₃ ], 24.2 kg of 85 wt% orthophosphoric acid, and 25.2 kg of 70 wt% nitric acid were dissolved. This was designated as liquid 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 50 ° C., and the liquid A was added dropwise to the liquid B with stirring, followed by stirring at 120 ° C. for 8.5 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 added at 120 ° C. in a sealed container. Stir for hours. The slurry thus obtained was dried with a spray dryer to obtain a catalyst precursor powder composed of a Dawson type heteropolyacid salt. To 100 parts by weight of this powder, 4 parts by weight of ceramic fiber [manufactured by Toshiba Monoflux Co., Ltd., FIBERFRAX RFC400SL], 13 parts by weight of ammonium nitrate, and 9.7 parts by weight of ion-exchanged water were added and kneaded. It was extruded into a cylindrical shape with a height of 5 mm. This molded body was dried at a temperature of 90 ° C. and a humidity of 30% RH for 3 hours, and then heat-treated in an air stream at 220 ° C. for 22 hours and in an air stream at 250 ° C. for 1 hour in order. A catalyst precursor comprising a heteropolyacid salt was obtained.

(B) Production of catalyst The precursor was first-stage calcined at 390 ° C. for 3 hours in an air / steam mixed gas (1) having a water concentration (volume%) shown in Table 1, Second-stage firing at 435 ° C. for 3 hours in a stream of nitrogen / steam mixed gas (2) having a moisture concentration (volume%) shown in FIG. 1, and then air having a moisture concentration (volume%) shown in Table 1 / The third stage calcination was performed at 390 ° C. for 3 hours in a stream of steam mixed gas (3) to obtain a catalyst. This catalyst is an acid salt of a Keggin type heteropolyacid containing 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. In addition, XRD measurement (powder method, Cu-Kα ray) of this catalyst was performed by using MiniFlex manufactured by Rigaku Corporation, counter-cathode Cu, tube voltage 30 kV, tube current 15 mA, scan speed 2 ° / min, sampling performed in width 0.01 °, integration number 20 times the conditions, the intensity of the peak of the interplanar spacing 3.38~3.41Å (I ₀₎ the intensity of the peak of the interplanar spacing 3.24~3.26Å for (I ₁₎ The ratio (I ₁ / I ₀ ) was determined. The values are shown in Table 1.

(C) Catalyst activity test 9 g of the catalyst obtained in (b) above was charged into a glass microreactor having an inner diameter of 15 mm, and methacrolein 4 prepared by mixing methacrolein, air, steam and nitrogen. A raw material gas having a composition of volume%, molecular oxygen 12 volume%, and water vapor 17 volume% is supplied at a space velocity of 670 h ⁻¹ and reacted at a furnace temperature (furnace temperature for heating the microreactor) of 280 ° C. The methacrolein conversion rate and methacrylic acid selectivity after 1 hour from the start of the reaction were determined. Next, a raw material gas having the same composition as above is supplied at the same space velocity as described above, and reacted at a furnace temperature of 355 ° C. to forcibly deteriorate the catalyst. The reaction was carried out at the same space velocity as described above, and the reaction was carried out at a furnace temperature of 280 ° C., and the methacrolein conversion rate and methacrylic acid selectivity after 1 hour from the start of the reaction were determined. Table 1 shows methacrolein conversion and methacrylic acid selectivity before and after forced deterioration.

(D) Catalyst life test 4.5 g of the catalyst obtained in (b) above was charged into a glass microreactor having an inner diameter of 15 mm, and methacrolein, air, steam and nitrogen were mixed therein. A raw material gas having a composition of 4% by volume of rain, 12% by volume of molecular oxygen, and 17% by volume of water vapor was supplied at a space velocity of 1340h ⁻¹ and reacted at a furnace temperature of 310 ° C. for 50 days or more. The methacrolein conversion was determined every 10 days. When the reaction time was plotted on the vertical axis and the conversion rate was plotted on the horizontal axis, there was a substantially linear relationship, so the slope was determined by the least square method, and the rate of decrease in conversion rate (% / day) was calculated. The values are shown in Table 1.

Claims (2)

A method for producing a catalyst for producing methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum, wherein a nitrate or ammonium salt containing each element contained in the catalyst is used as a catalyst raw material, and these are mixed in water to form an aqueous solution or aqueous slurry Then, after drying this aqueous mixture, the catalyst precursor comprising a Keggin type heteropoly acid salt obtained by heat treatment at 180 to 300 ° C. is obtained in an oxidizing gas atmosphere containing 10% by volume or less of moisture. 3 after firing the first stage at 50 to 400 ° C., and calcined second stage at 400 to 500 ° C. under an atmosphere of non-oxidizing gas, and then under an atmosphere of an oxidizing gas containing 30% by volume water 300 A method for producing a catalyst for producing methacrylic acid, comprising performing third-stage calcination at ˜400 ° C.   A methacrylic acid production catalyst is produced by the production method according to claim 1, and a compound selected from methacrolein, isobutyraldehyde, isobutane and isobutyric acid is subjected to a gas phase catalytic oxidation reaction in the presence of the catalyst. Manufacturing method.