Catalyst for producing unsaturated carboxylic acid

Abstract

The present disclosure relates to a catalyst for producing an unsaturated carboxylic acid, the catalyst including a catalytic active component having a composition represented by formula (1), wherein the value of surface roughness S obtained through a surface roughness measurement with a non-contact type shape analysis laser microscope is 11.7-25.0 μm. (1): (Mo)12(V)a(W)b(Cu)c(Sb)d(X)e(Y)f(Z)g(O)h

Description

Technical Field

[0001] The present invention relates to a catalyst for producing an unsaturated carboxylic acid in a high yield by gas-phase catalytic oxidation of an unsaturated aldehyde in the presence of molecular oxygen or a molecular oxygen-containing gas, a method for producing the same, and a method for producing an unsaturated carboxylic acid using the catalyst.

Background Art

[0002] Acrylic acid is becoming increasingly important as a raw material for water-absorbing resins, adhesives, etc. Therefore, in recent years, there has been a demand for improving the performance of catalysts for producing acrylic acid by gas-phase catalytic oxidation using acrolein as a raw material. Thus, various companies have made various improvements regarding catalysts that can produce acrylic acid in a high yield and stably over a long period. For example, the following proposals have been made.

[0003] In Patent Documents 1 to 3, improvements in catalyst composition and the like have been proposed, focusing on the X-ray diffraction peaks of the catalyst active components. The catalysts disclosed in these documents have been proposed as catalysts that achieve high activity and high yield. Also, in Patent Documents 4 and 5, improvement guidelines for improving the mechanical strength of the catalyst are shown, and the catalyst performance is improved by preventing pulverization during filling. In Patent Document 6, by setting the standard deviation of the particle size of the catalyst within a specific range, the long-term stability of the catalytic reaction is improved. In Patent Document 7, it has been proposed to produce a catalyst having high catalytic performance and mechanical strength by controlling the relative centrifugal acceleration during molding using a rolling granulator. In Patent Document 8, a method for producing a high-yield catalyst by controlling the density of the catalyst molded body and the roughness of the catalyst surface has been proposed.

[0004] However, especially in the production of unsaturated carboxylic acids, improving the catalytic activity is an important issue. The advantages obtained by improving the catalytic activity are not limited to simply increasing the yield. For example, in a plant using a catalyst, if the reaction bath temperature at the initial stage of the reaction decreases due to an improvement in catalytic activity, not only does the energy cost for heating decrease, but also the thermal degradation of the catalyst is reduced, resulting in less performance degradation from a long-term perspective. As a result, stable operation and high yields can be achieved over the long term. For the above reasons, there is a need for highly active catalysts and methods for producing them.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of the above situation, an object of the present invention is to improve the catalytic activity of a catalyst for producing an unsaturated carboxylic acid by gas-phase catalytic oxidation of an unsaturated aldehyde as a raw material.

Means for Solving the Problems

[0007] As a result of intensive studies on the above-mentioned current situation and problems, the inventors of the present application have found that specific catalyst shape parameters contribute to the improvement of activity, and thus have made the present invention.

[0008] That is, the present invention relates to the following 1) to 7). 1) A catalyst for producing an unsaturated carboxylic acid, wherein the catalytic active component has a composition represented by the following formula (1), and the value of the surface roughness S obtained by measuring the surface roughness with a non-contact type shape measurement laser microscope is 11.7 μm or more and 25.0 μm or less. (Mo) 12 (V) a (W) b (Cu) c (Sb) d (X) e (Y) f (Z) g (O) h (1) (In formula (1), Mo, V, W, Cu, Sb, and O represent molybdenum, vanadium, tungsten, copper, antimony, and oxygen, respectively. X represents at least one element selected from the group consisting of alkali metals and thallium. Y represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc. Z represents at least one element selected from the group consisting of niobium, cerium, tin, chromium, manganese, iron, cobalt, samarium, germanium, titanium, and arsenic. Also, a, b, c, d, e, f, g, and h represent the atomic ratios of the respective elements. With respect to 12 molybdenum atoms, a satisfies 0 < a ≦ 10.0, b satisfies 0 ≦ b ≦ 10.0, c satisfies 0 < c ≦ 6.0, d satisfies 0 ≦ d ≦ 10.0, e satisfies 0 ≦ e ≦ 0.50, f satisfies 0 ≦ f ≦ 1.0, and g satisfies 0 ≦ g < 6.0. Also, h is the number of oxygen atoms necessary to satisfy the valences of the respective components.) 2) In the above formula (1), the catalyst for producing an unsaturated carboxylic acid according to the above 1), wherein 1.0 ≦ a ≦ 5.0, 0.50 ≦ b ≦ 3.0, 0.50 ≦ c ≦ 3.0, and 0 < d ≦ 2.0. 3) The catalyst for producing an unsaturated carboxylic acid according to the above 1) or 2), which is a catalyst in which a catalytically active component is supported on an inert carrier. 4) The catalyst for producing an unsaturated carboxylic acid according to the above 3), wherein the inert carrier is silica, alumina, or a combination thereof. 5) The method for producing a catalyst for producing an unsaturated carboxylic acid according to any one of the above 1) to 4), which has a step of forming by granulation and in which the absolute humidity MR in the granulator is 0.0235 kg-H2O / kg-DA or less. 6) The method for producing an unsaturated carboxylic acid using the catalyst for producing an unsaturated carboxylic acid according to any one of the above 1) to 4). 7) The method for producing an unsaturated carboxylic acid using a reaction tube filled with two or more kinds of the catalysts for producing an unsaturated carboxylic acid according to any one of the above 1) to 4) in multiple layers.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a catalyst having excellent catalytic activity for producing an unsaturated carboxylic acid by subjecting an unsaturated aldehyde to a gas-phase catalytic oxidation reaction.

Embodiments for Carrying Out the Invention

[0010] [Arithmetic mean roughness of the surface of the catalyst molded body] The catalyst of the present invention has a surface roughness S of 11.7 μm or more and 25.0 μm or less when the surface roughness is measured with a non-contact type shape measurement laser microscope. The surface roughness S of the catalyst can be measured, for example, with a shape analysis laser microscope VK-X1000 (manufactured by KEYENCE Corporation), etc. It is a value determined from the number N of measurement points when the surface height is measured while irradiating the catalyst surface with a laser and moving it horizontally, the height Zn at each measurement point, and the average value X of the heights at all measurement points, and can be calculated from the following formula (A). [Formula (A)] [Number] As the upper limit of the surface roughness S, more preferably, in order, they are 24.0 μm, 23.0 μm, 22.5 μm, 22.0 μm, 21.0 μm, 20.5 μm, 20.0 μm, 19.5 μm, 19.0 μm, 18.0 μm, 15.0 μm, and particularly preferably 13.0 μm. Also, as the lower limit, more preferably, in order, they are 11.8 μm, 12.0 μm, 12.3 μm, and particularly preferably 12.5 μm. Therefore, the range of S is preferably 11.8 μm or more and 24.0 μm or less, more preferably 11.8 μm or more and 23.0 μm or less, more preferably 11.8 μm or more and 22.5 μm or less, more preferably 11.8 μm or more and 22.0 μm or less, more preferably 11.8 μm or more and 21.5 μm or less, more preferably 11.8 μm or more and 21.0 μm or less, more preferably 11.8 μm or more and 20.5 μm or less, more preferably 11.8 μm or more and 20.0 μm or less, more preferably 11.8 μm or more and 19.5 μm or less, more preferably 11.8 μm or more and 19.0 μm or less, more preferably 12.0 μm or more and 18.0 μm or less, more preferably 12.3 μm or more and 15.0 μm or less, and most preferably 12.5 μm or more and 13.0 μm or less.

[0011] The inventors of the present invention have found that the catalyst exhibits higher activity as the surface of the catalyst becomes smoother within a certain range (as the surface roughness S becomes smaller within a certain range). This is because when gas is passed through a reaction tube filled with the catalyst to carry out a catalytic reaction, when a catalyst with fewer irregularities on the catalyst surface is used, the gas flow is not disturbed and it flows through the catalyst layer without staying, so the exchange of raw materials and products occurs smoothly in the vicinity of the catalyst, and as a result, an improvement in the raw material conversion rate is observed. Also, as another factor, when a catalyst with fewer irregularities on the catalyst surface is freely dropped from the upper part of the reaction tube and filled, it is less likely to get caught by other catalysts or the wall surface of the reaction tube during the dropping process, and since the catalyst is filled more densely, an improvement in the raw material conversion rate is also considered to be observed. Conversely, if the catalyst surface has too few irregularities, the residence of gas in the reaction tube becomes too little, the contact time with the catalyst decreases, and as a result, a decrease in the raw material conversion rate is observed.

[0012] [Catalyst composition] The catalyst of the present invention has a composition represented by the following formula (1). [Formula (1)] (Mo) 12 (V) a (W) b (Cu) c (Sb) d (X) e (Y) f (Z) g (O) h (1) (In the formula, Mo, V, W, Cu, Sb, and O represent molybdenum, vanadium, tungsten, copper, antimony, and oxygen, respectively. X represents at least one element selected from the group consisting of alkali metals and thallium. Y represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc. Z represents at least one element selected from the group consisting of bismuth, tellurium, silver, selenium, silicon, aluminum, boron, niobium, cerium, tin, chromium, manganese, iron, cobalt, nickel, samarium, germanium, zirconium, titanium, chromium, tantalum, lead, indium, sulfur, palladium, gallium, lanthanum, and arsenic. Also, a, b, c, d, e, f, g, and h represent the atomic ratios of the respective elements. With respect to 12 molybdenum atoms, a is 0 < a ≦ 10.0, b is 0 ≦ b ≦ 10.0, c is 0 < c ≦ 6.0, d is 0 ≦ d ≦ 10.0, e is 0 ≦ e ≦ 0.50, f is 0 ≦ f ≦ 1.0, g is 0 ≦ g < 6.0. Also, h is the number of oxygen atoms necessary to satisfy the valences of the respective components.)

[0013] In the above formula (1), the preferable ranges of a to g are as follows. The lower limits of a are, in order of preference, 0.20, 0.50, 0.80, 1.0, 1.5, 2.0, 2.2, 2.5, most preferably 2.8, and the upper limits of a are, in order of preference, 9.0, 8.0, 7.0, 6.0, 5.0, 4.5, 4.0, 3.5, most preferably 3.2. That is, as the range of a, 0.20 ≦ a ≦ 9.0 is preferable, 0.50 ≦ a ≦ 8.0 is more preferable, 0.80 ≦ a ≦ 7.0 is more preferable, 1.0 ≦ a ≦ 6.0 is more preferable, 1.5 ≦ a ≦ 5.0 is more preferable, 2.0 ≦ a ≦ 4.5 is more preferable, 2.2 ≦ a ≦ 4.0 is more preferable, 2.5 ≦ a ≦ 3.5 is more preferable, and most preferably, 2.8 ≦ a ≦ 3.2. The lower limits of b are, in order of preference, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, most preferably 1.0, and the upper limits of b are, in order of preference, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, most preferably 1.4. That is, as the range of b, 0.10 ≦ b ≦ 9.0 is preferable, 0.10 ≦ b ≦ 8.0 is more preferable, 0.20 ≦ b ≦ 7.0 is more preferable, 0.30 ≦ b ≦ 6.0 is more preferable, 0.40 ≦ b ≦ 5.0 is more preferable, 0.50 ≦ b ≦ 4.0 is more preferable, 0.60 ≦ b ≦ 3.0 is more preferable, 0.70 ≦ b ≦ 2.5 is more preferable, 0.80 ≦ b ≦ 2.0 is more preferable, 0.90 ≦ b ≦ 1.5 is more preferable, and most preferably, 1.0 ≦ b ≦ 1.4. The lower limits of c are, in order of preference, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, most preferably 1.0, and the upper limits of c are, in order of preference, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, most preferably 1.4. That is, as the range of c, 0.10 ≦ c ≦ 5.0 is preferable, 0.20 ≦ c ≦ 5.0 is more preferable, 0.30 ≦ c ≦ 5.0 is more preferable, 0.40 ≦ c ≦ 5.0 is more preferable, 0.50 ≦ c ≦ 4.0 is more preferable, 0.60 ≦ c ≦ 3.0 is more preferable, 0.70 ≦ c ≦ 2.5 is more preferable, 0.80 ≦ c ≦ 2.0 is more preferable, 0.90 ≦ c ≦ 1.5 is more preferable, and most preferably, 1.0 ≦ c ≦ 1.4. The lower limit of d is, in descending order of preference, 0.11, 0.15, 0.18, 0.20, 0.25, 0.30, 0.35, most preferably 0.40, and the upper limit of d is, in descending order of preference, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, 1.0, most preferably 0.70. That is, as the range of d, 0.11 ≤ d ≤ 9.0 is preferred, 0.11 ≤ d ≤ 8.0 is more preferred, 0.11 ≤ d ≤ 7.0 is more preferred, 0.11 ≤ d ≤ 6.0 is more preferred, 0.11 ≤ d ≤ 5.0 is more preferred, 0.15 ≤ d ≤ 4.0 is more preferred, 0.18 ≤ d ≤ 3.0 is more preferred, 0.20 ≤ d ≤ 2.5 is more preferred, 0.25 ≤ d ≤ 2.0 is more preferred, 0.30 ≤ d ≤ 1.5 is more preferred, 0.35 ≤ d ≤ 1.0 is more preferred, and most preferably, 0.40 ≤ d ≤ 0.70. The upper limit of e is, in descending order of preference, 0.40, 0.30, 0.20, 0.10. That is, as the range of e, 0 ≤ e ≤ 0.40, 0 ≤ e ≤ 0.30, 0 ≤ e ≤ 0.20 are preferred in descending order, and the most preferred range is 0 ≤ e ≤ 0.10. The upper limit of f is, in descending order of preference, 0.80, 0.50, 0.20, 0.15, most preferably 0.10. That is, as the range of f, 0 ≤ f ≤ 0.80, 0 ≤ f ≤ 0.50, 0 ≤ f ≤ 0.20, 0 ≤ f ≤ 0.15 are preferred in descending order, and the most preferred range is 0 ≤ g1 ≤ 0.10. The upper limit of g is, in descending order of preference, 5.0, 4.0, 3.0, 2.0, 1.0. That is, as the range of g, 0 ≤ g ≤ 5.0, 0 ≤ g ≤ 4.0, 0 ≤ g ≤ 3.0, 0 ≤ g ≤ 2.0 are preferred in descending order, and the most preferred range is 0 ≤ g ≤ 1.0. It should be noted that the cases where e, f, and g are 0 are particularly preferred embodiments.

[0014] When the catalyst of the present invention is used in a reaction for producing a corresponding unsaturated carboxylic acid from an unsaturated aldehyde such as acrolein or methacrolein as a raw material, particularly in a reaction for producing acrylic acid by gas-phase catalytic oxidation of acrolein with molecular oxygen or a molecular oxygen-containing gas, it is possible to achieve an improvement in catalyst activity and a reduction in differential pressure compared with known methods, and it is very effective. Further, in the process of a partial oxidation reaction accompanied by heat generation, an effect of improving stability such as a reduction in hot spot temperature can be expected. Furthermore, the catalyst of the present invention is also effective in reducing by-products that adversely affect the environment and the quality of the final product, such as carbon monoxide (CO), carbon dioxide (CO2), acetaldehyde, acetic acid, and formaldehyde.

[0015] [Method for producing catalyst, etc.] Examples of the specific steps for obtaining the catalyst of the present invention are shown below. Step a) Preparation Examples of raw materials for each element constituting the catalyst are as follows. When ammonium molybdate is used as the raw material for the molybdenum component, a high-performance catalyst can be obtained. As raw materials for tungsten, vanadium, antimony, copper and other elements, oxides or ammonium salts, carbonates, organic acid salts, hydroxides, etc. that can be converted into oxides by strong heating, or mixtures thereof, can usually be used. For example, a tungsten component raw material, a Z component raw material aqueous solution or slurry separately prepared under the conditions of 20 to 95 °C is mixed with a vanadium component raw material, a molybdenum component raw material and an antimony component raw material in a desired ratio, and after heating and stirring for about 1 hour under the conditions of 20 to 95 °C, an aqueous solution in which a copper component raw material is dissolved, and an X component raw material and a Y component raw material are added as necessary to obtain an aqueous solution or slurry containing a catalyst component. Thereafter, the aqueous solution or slurry thus obtained is collectively referred to as a preparation liquid (A). Here, the preparation liquid (A) does not necessarily need to contain all the catalyst constituent elements, and some of the elements or some of the amounts may be added in subsequent steps. Also, when preparing the preparation liquid (A), the amount of water for dissolving each component raw material, or when adding acids such as sulfuric acid, nitric acid, hydrochloric acid, tartaric acid, acetic acid for dissolution, if the acid concentration in the aqueous solution is not suitable within the range of, for example, 5 mass% to 99 mass%, the form of the preparation liquid (A) may become a clay-like mass, which will not be an excellent catalyst. Therefore, it is preferable that the form of the obtained preparation liquid (A) is an aqueous solution or slurry in terms of obtaining an excellent catalyst.

[0016] Step b) Drying Next, the above-obtained preparation liquid (A) is dried to obtain a dried powder. The drying method is not particularly limited as long as it can completely dry the preparation liquid (A). For example, drum drying, freeze drying, spray drying, evaporation to dryness, etc. can be mentioned. Among these, in the present invention, spray drying, which can dry the slurry into powder or granules in a short time, is particularly preferable. The drying temperature of spray drying varies depending on the concentration of the slurry, the liquid feeding rate, etc., but generally the temperature at the outlet of the dryer is 70 to 150 °C. Also, it is preferable to dry so that the average particle size of the obtained dried powder becomes 20 to 700 μm. Thus, a dried powder (B) is obtained.

[0017] Step c) Preliminary calcination The obtained dried powder (B) is calcined at 200°C to 500°C, preferably 300°C to 400°C, under an air flow, and the moldability, mechanical strength, and catalyst performance of the catalyst tend to be improved. The calcination time is preferably 1 hour to 12 hours. Thus, a pre-calcined body (C) is obtained.

[0018] Step d) Grinding The obtained pre-calcined body (C) is obtained as a solid (D) in which the dried powder (B) has aggregated due to pre-calcination. In order to obtain the pre-calcined powder (E) required in the next molding step, the solid (D) is ground. The grinding method is not particularly limited, and examples thereof include a roller mill, a jet mill, a hammer mill, a rotary mill, a vibration mill, and the like. At this time, the average particle diameter (pre-calcined median diameter) of the obtained pre-calcined powder (E) is preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less. In the present specification, the pre-calcined powder (E) after grinding is described as a catalyst precursor. However, at the stage of the pre-calcined body (C), if there is no aggregation and it can be used without going through the grinding step, the pre-calcined body (C) may be used as a catalyst precursor.

[0019] Step e) Molding The forming method is not particularly limited, but when forming into a columnar or ring shape, a method using a tableting machine, an extrusion molding machine, etc. is preferred. More preferably, in the case of forming into a spherical shape, the pre-fired powder (E) may be formed into a spherical shape by a molding machine, but a method of supporting the pre-fired powder (E) (including a molding aid and a strength improver if necessary) on a carrier such as an inert ceramic is preferred. Here, as the supporting method, a rolling granulation method, a method using a centrifugal fluidized coating device, a wash coating method, etc. are widely known, and there is no particular limitation as long as the pre-fired powder (E) can be uniformly supported on the carrier. However, considering the production efficiency of the catalyst and the performance of the prepared catalyst, more preferably, at the bottom of a fixed cylindrical container, with a device having a flat or uneven disk, by rotating the disk at high speed, the carrier charged in the container is vigorously stirred by the rotational motion and the revolution motion of the carrier itself, and the powder component is supported on the carrier by adding the pre-fired powder (E) and, if necessary, a molding aid and / or a strength improver, and a pore former. In addition, it is preferable to use a binder during the loading. Specific examples of the binder that can be used include water, ethanol, methanol, propanol, polyhydric alcohols, polyvinyl alcohol as a polymer binder, and an aqueous silica sol solution as an inorganic binder. Ethanol, methanol, propanol, and polyhydric alcohols are preferred, and diols such as ethylene glycol and triols such as glycerin are more preferred. By using an appropriate amount of an aqueous glycerin solution, the moldability becomes good, and a high-performance catalyst with high mechanical strength can be obtained. Specifically, a high-performance catalyst can be obtained particularly when an aqueous solution with a glycerin concentration of 5% by mass or more is used. The usage amount of these binders is usually 2 to 80 parts by mass with respect to 100 parts by mass of the pre-fired powder (E). An inert carrier having a size of usually about 2 to 8 mm is used, and the pre-fired powder (E) is supported thereon. The loading rate is determined in consideration of the catalyst use conditions, such as the space velocity of the reaction raw material and the reaction conditions such as the raw material concentration, and is usually 20% to 80% by mass. Here, when there are a molding aid, a strength improver, etc. used in the molding, the loading rate is expressed as in the following formula (4). Thus, the molded body (F) is obtained. In addition, although it has been found by the present inventors that it is difficult to maintain the mechanical strength of the present invention, it is preferable to add inert inorganic fibers as a strength improver during the supported molding. The amount of these fibers used is usually 1 to 30 parts by mass with respect to 100 parts by mass of the pre-fired powder (E).

[0020] [Regarding support] A catalyst obtained by supporting a pre-fired powder obtained by performing pre-firing after the preparation of the catalytically active component, or a pulverized pre-fired powder obtained by further subjecting the pre-fired powder to a pulverization step on an inert carrier, is particularly excellent in effect. As the material of the inert carrier, known materials such as alumina, silica, titania, zirconia, niobia, silica-alumina, silicon carbide, carbides, and mixtures thereof can be used. The particle size, water absorption, mechanical strength, crystallinity and mixing ratio of each crystal phase of the inert carrier are not particularly limited, and an appropriate range should be selected in consideration of the final performance of the catalyst, moldability, production efficiency, etc. The shape of the inert carrier is preferably spherical, but is not particularly limited, and pellet-shaped, ring-shaped, etc. are used. The mixing ratio of the carrier and the pre-fired powder is generally calculated as the loading rate from the following formula (4) depending on the charged mass of each raw material. In addition, when it is clear that additives such as a molding aid and a strength improver used remain in the catalyst even after the main firing, they are included in the total amount (denominator). [Formula (4)] Loading rate (mass%) = (mass of the pre-fired powder used for molding) / {(mass of the pre-fired powder used for molding)+(mass of the carrier used for molding)}×100 (4) The preferable upper limit as the above loading rate is 80% by mass, and more preferably 70, 60, 55, 50, 45, 40% by mass in order. Also, a preferable lower limit is 10% by mass, and more preferably 15%, 18%, and 20% by mass in that order. That is, the loading rate is preferably 10% by mass or more and 80% by mass or less, more preferably 10% by mass or more and 70% by mass or less, still more preferably 10% by mass or more and 60% by mass or less, still more preferably 10% by mass or more and 55% by mass or less, still more preferably 15% by mass or more and 50% by mass or less, still more preferably 18% by mass or more and 45% by mass or less, and the most preferable range is 20% by mass or more and 40% by mass or less.

[0021] [Regarding inorganic fibers] The catalyst of the present invention preferably contains inorganic fibers for the purpose of improving mechanical strength or the like. The material of the inorganic fibers is not particularly limited, and for example, glass fibers (glass fibers), ceramic fibers, metal fibers, mineral fibers, carbon fibers, various whiskers, etc. can be used. Among these, glass fibers treated with silane-based chemicals are particularly preferred. Also, the fiber length is not particularly limited as long as it does not inhibit the effects of the present invention, but the average fiber length is preferably about 1 to 1000 μm, more preferably about 10 to 500 μm. Furthermore, two or more kinds of these inorganic fibers can be used in combination, and it can be two or more kinds with different materials, or two kinds with the same material but different average fiber lengths.

[0022] Step f) Final firing The formed body (F) tends to improve catalytic activity and effective yield by firing at a temperature of 100 to 450°C for about 1 to 12 hours. The firing temperature is preferably 270°C or more and 420°C or less, more preferably 350°C or more and 400°C or less. As the gas to be passed, air is convenient and preferable, but in addition, nitrogen, carbon dioxide, argon, helium, a nitrogen oxide-containing gas for a reducing atmosphere, an ammonia-containing gas, hydrogen gas, and mixtures thereof can also be used as inert gases. Thus, the catalyst (G) is obtained.

[0023] [Method for measuring the surface roughness S of the spherical catalyst] In the measurement of the surface roughness S of the catalyst formed body, in order to measure an accurate value, it is necessary to measure a certain distance after avoiding the situation where the value of the surface roughness S measured due to the shape of the formed body becomes larger than the actual surface roughness. That is, if a formed body with a completely smooth surface is measured, it is necessary to determine the measurement position so that the surface height Rz, which is the value obtained by subtracting the height of the lowest point from the height of the highest point among all the measurement points, becomes 0. For example, when the formed body is cylindrical or tubular, the side surface of the formed body is measured along the axial direction. Also, in that case, the measurement distance L is set to, for example, 1 / 3 to 2 / 3 of the axial length of the formed body. When the shape of the formed body is spherical, it is particularly difficult to distinguish between the unevenness of the surface and the roundness as a sphere when the laser for measuring the height is moved in the horizontal direction, and arbitrariness is likely to occur even when correction is made. To avoid this, a spherical formed body is widely observed to find the highest position of the formed body, and a circle is drawn with a circumferential length of 1 / 3 to 2 / 3 of the catalyst particle diameter centered on the highest position of the formed body in plan view. The points on the surface of the formed body that overlap with the circle in plan view should ideally have the same height if the surface is a completely smooth formed body. Therefore, by measuring the height along the circumference of the circle, it is possible to avoid the influence of the roundness as a sphere on the height. When the measurement distance L is set to be equal to the circumferential length of the circle and measured along the circumference of the circle, the surface height Rz needs to be 150 μm or less, and preferably 100 μm or less. In the case of an extruded catalyst in the form of a cylinder or a tube, the side surface of the formed body may be measured along the extrusion axis direction. For example, when using a shape analysis laser microscope VK-X1000 (manufactured by KEYENCE), after determining the measurement range including the spherical formed body and focusing using an objective lens with a magnification of 5 times, the above measurement and analysis are automatically performed by the laser microscope, and the value of the surface roughness S of the formed body can be obtained. The laser used in this measurement is, for example, a red semiconductor laser with a wavelength of 661 nm and a maximum output of 1 mW.

[0024] [Method for adjusting surface roughness S] The value of the surface roughness S can be adjusted by changing a) the raw materials used in the process, b) the spray drying conditions in the process, c) the firing temperature and time in the process, d) the grinding method in the process and the median diameter of the pre-fired powder (E) after grinding, e) the relative centrifugal acceleration, the loading rate, the type of binder, the addition position of the binder, etc. in the process. However, it is difficult to significantly change by changing a single condition alone, and it can be preferably adjusted by optimizing two or more conditions. Several examples are shown below.

[0025] <c) Firing temperature and time in the process> As described above, the firing temperature is preferably 200°C to 500°C. However, when the firing temperature is increased, the surface roughness S tends to increase. Therefore, in terms of adjusting the surface roughness S, it is preferably less than 400°C. Also, since the surface roughness S may increase when the firing time is prolonged, it is preferably less than 5 hours. <d) Grinding method, median diameter, and centrifugal acceleration in the process> The surface roughness S can also be controlled by the method of step d). When using a ball mill, it is easy to adjust the surface roughness S, which is preferable. The surface roughness S can also be adjusted by adjusting the median diameter of the pre-fired powder (E). The median diameter of the pre-fired powder (E) is preferably 50 μm or less. Also, when step e) is granulation, the surface roughness S can be adjusted by changing the relative centrifugal acceleration during granulation according to the median diameter of the pre-fired powder (E). Specifically, when the median diameter of the pre-fired powder (E) is larger than 30 μm, if the relative centrifugal acceleration during granulation is set to 10G or less, the surface roughness S is likely to be within the desired range. <e) Relative centrifugal acceleration, temperature in the granulator, and absolute humidity by weight in the process> e) When the process is granulation, the value of the surface roughness S can also be adjusted by changing the relative centrifugal acceleration, the temperature inside the granulator, and the absolute humidity. The relative centrifugal acceleration may be about 2.0G or more and 30G or less. However, when the relative centrifugal acceleration is increased, the surface roughness S tends to decrease, although this also varies depending on the absolute humidity by weight inside the granulator. The temperature inside the granulator is preferably 5°C or more and 50°C or less. The absolute humidity by weight inside the granulator is preferably 0.0235 kg-H2O / kg-DA or less. The preferred upper limit of the absolute humidity by weight is 0.0230 kg-H2O / kg-DA, and more preferably, in order, 0.0220, 0.0200, 0.0190, 0.0180, 0.0175 kg-H2O / kg-DA. The preferred lower limit of the absolute humidity by weight is 0 kg-H2O / kg-DA, and more preferably, in order, 0.0010, 0.0020, 0.0030, 0.0040, 0.0050, 0.0060, 0.0070, 0.0100, 0.0125, 0.0150, 0.0160 kg-H2O / kg-DA.That is, the weight absolute humidity is preferably 0 kg-H2O / kg-DA or more and 0.0235 kg-H2O / kg-DA or less, more preferably 0.0010 kg-H2O / kg-DA or more and 0.0235 kg-H2O / kg-DA or less, still more preferably 0.0020 kg-H2O / kg-DA or more and 0.0235 kg-H2O / kg-DA or less, still more preferably 0.0030 kg-H2O / kg-DA or more and 0.0235 kg-H2O / kg-DA or less, still more preferably 0.0040 kg-H2O / kg-DA or more and 0.0235 kg-H2O / kg-DA or less, still more preferably 0.0050 kg-H2O / kg-DA or more and 0.0235 kg-H2O / kg-DA or less, still more preferably 0.0060 kg-H2O / kg-DA or more and 0.0230 kg-H2O / kg-DA or less, still more preferably 0.0070 kg-H2O / kg-DA or more and 0.0220 kg-H2O / kg-DA or less, still more preferably 0.0100 kg-H2O / kg-DA or more and 0.0200 kg-H2O / kg-DA or less, still more preferably 0.0125 kg-H2O / kg-DA or more and 0.0190 kg-H2O / kg-DA or less, still more preferably 0.0150 kg-H2O / kg-DA or more and 0.0180 kg-H2O / kg-DA or less, and particularly preferably 0.0160 kg-H2O / kg-DA or more and 0.0175 kg-H2O / kg-DA or less.

[0026] As described above, the temperature and weight absolute humidity inside the granulator are different from the temperature and humidity in the room where the granulation operation is performed, and mean the temperature and humidity near the chassis of the granulator. The weight absolute humidity may be measured at a point 10 cm above the chassis on the rotating shaft of the chassis of the granulator after waiting for the temperature and humidity to stabilize after the granulation operation starts (for example, after 15 minutes or more have elapsed). Examples of methods for controlling the temperature and absolute humidity in the granulator include controlling the evaporation amount of water derived from the binder, controlling the temperature of the granulator with a jacket, controlling the supply and exhaust air volumes, controlling the room temperature and humidity in the granulation chamber, and controlling the atmosphere by installing a lid or enclosure above the granulator, but are not limited thereto.

[0027] [Calculation method of weight absolute humidity] The absolute humidity, which is the ratio of the mass of water vapor to the mass of dry air, may be measured with a commercially available absolute hygrometer, or may be obtained by converting it to the weight absolute humidity MR (kg-H2O / kg-DA) according to the following formula (B), where the temperature measured with a relative hygrometer is T (°C) and the relative humidity is RH (%). [Formula (B)] MR = 0.622 * (6.1078 * 10 ^ (7.5 * T / (T + 237.3)) * RH / 100) / (1013.25 - (6.1078 * 10 ^ (7.5 * T / (T + 237.3)) * RH / 100)) ··· (B)

[0028] [Use of the catalyst] In the method for producing acrylic acid using the catalyst of the present invention, the flow method of the raw material gas may be a normal single-pass method or a recycle method, and it can be carried out under generally used conditions and is not particularly limited. For example, when the starting raw material substance is an ideal gas, it is 1 to 10% by volume, preferably 4 to 9% by volume, molecular oxygen is 3 to 20% by volume, preferably 4 to 18% by volume, water vapor is 0 to 60% by volume, preferably 4 to 50% by volume, and an inert gas such as carbon dioxide and nitrogen is 20 to 80% by volume, preferably 30 to 60% by volume. The mixed gas is filled into the catalyst of the present invention in a reaction tube at 200 to 450 °C under a pressure of normal pressure to 10 atmospheres, and the space velocity is 300 to 5000 h -1 and introduced to carry out the reaction. In the method for producing acrylic acid, one type of catalyst may be used alone, or depending on the conditions of use, different types of catalysts may be used for multi-layer filling. That is, a catalyst layer formed by dividing into a plurality of parts in the raw material gas flow direction of the reaction tube is provided, and a method of arranging the plurality of types of catalysts so that the activity becomes higher from the raw material inlet portion to the outlet portion in the raw material gas flow direction can be adopted. When using a reaction tube filled with two or more types of catalysts in multiple layers, at least one type may be the catalyst of the present invention, but it is preferably filled with two or more types of catalysts that satisfy the requirements of the present invention. There is no particular limitation on the number of divisions of the catalyst layer, but it is usually 2 to 5, preferably 2 to 3. The different types of catalysts described above do not mean only the case where the composition of the catalyst is different, but also include the case where the loading rate on the inert carrier is different or the dilution rate is different. Further, a method can also be adopted in which the catalyst highly activated by adjusting the surface roughness S of the present invention is arranged on the raw material gas outlet side, and a catalyst having relatively low activity is arranged on the raw material gas inlet side.

Examples

[0029] Hereinafter, the present invention will be described more specifically with reference to examples. In the examples, the raw material conversion rate and the selectivity were calculated according to the following formulas. Raw material conversion rate (%) = (number of moles of reacted acrolein) / (number of moles of supplied acrolein) × 100 Selectivity (%) = (number of moles of produced acrylic acid) / (number of moles of reacted acrolein) × 100

[0030] Hereinafter, examples were shown with specific examples, but the present invention is not limited to the examples as long as it does not depart from the gist thereof. The median diameter of the calcined powder (E) shown in this example is the median in the volume fraction measured using a particle size distribution measuring device LMS-2000e manufactured by Seishin Enterprise Co., Ltd. As the measurement conditions, the scattering range was set to 10 to 20%, the measurement time was 3 seconds, the number of snaps was 3000, the sample material was Fraunhofer, the dispersion medium was water, and the stirrer pump was set to 2500 rpm and measured without applying ultrasonic waves.

[0031] The temperature and humidity (relative humidity) inside the granulator shown in this example were measured at a point 10 cm above the chassis on the rotating shaft of the chassis of the granulator 15 minutes after the start of the granulation operation using a temperature and humidity meter PC-5120 manufactured by Sato Weighing Machine Mfg. Co., Ltd. The absolute humidity by weight was calculated using Equation (B) from the temperature and relative humidity obtained by the measurement.

[0032] The surface roughness S of the catalyst shown in this example was measured and analyzed using a shape analysis laser microscope VK-X1000 (manufactured by KEYENCE Corporation). Specifically, the catalyst to be measured was focused using an objective lens with a magnification of 5 times, and the measurement was performed using a red semiconductor laser with a wavelength of 661 nm and a maximum output of 1 mW. When setting the measurement distance L, the average value of the particle sizes of 100 catalyst particles measured with calipers was used as the catalyst particle size, and the measurement distance L was set within the range of 1 / 3 to 2 / 3 of the catalyst particle size. In the analysis, the condition of not setting a cut-off was adopted, and 10 molded bodies were measured, and the arithmetic mean thereof was defined as the surface roughness S.

[0033] [Example 1] <Production of Catalyst 1> The composition of the catalyst active component is Mo 12 V 3.0 W 1.2 Cu 1.2 Sb 0.50Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, copper sulfate, and antimony acetate were weighed and mixed in an aqueous solvent heated to 95 °C to obtain a preparation solution (A). This preparation solution (A) was dried by the spray drying method, and the obtained dried powder (B) was pre-fired under the conditions of 350 °C for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized with a vibration mill to obtain a pre-fired powder (E). The median diameter of the obtained pre-fired powder (E) was 21.6 μm. 5% by mass of crystalline cellulose and 5% by mass of Mild Fiber EFH150-31 manufactured by Central Glass Co., Ltd. were added to the pre-fired powder (E), and after sufficient mixing, a 20% by mass glycerin solution was used as a binder by the rolling granulation method, and it was spherically supported and molded onto an inert spherical carrier composed of a mixture of silica and alumina so that the loading rate was 33% by mass and the average value of the particle diameter was 5 mm. A rolling granulator was used for the molding, the centrifugal acceleration was 26.0 G, the absolute humidity by weight in the granulator was 0.0169 kg-H2O / kg-DA, and the temperature was 27.1 °C. Next, firing was performed under the conditions of 390 °C for 4 hours to obtain the spherical catalyst 1 of the present invention.

[0034] [Example 2] [Production of Catalyst 2] The composition of the catalyst active component is Mo 12 V 3.0 W 1.2 Cu 1.2 Sb 0.50Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, copper sulfate, and antimony acetate were weighed and mixed in an aqueous solvent heated to 95°C to obtain a preparation solution (A). This preparation solution (A) was dried by the spray drying method, and the obtained dried powder (B) was pre-fired under the conditions of 350°C for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized with a vibration mill to obtain a pre-fired powder (E). The median diameter of the obtained pre-fired powder (E) was 37.9 μm. 5% by mass of crystalline cellulose was added to the pre-fired powder (E) and thoroughly mixed. Then, using a 20% by mass glycerin solution as a binder by the rolling granulation method, it was spherically supported and molded onto an inert spherical carrier composed of a mixture of silica and alumina so that the loading rate was 33% by mass and the average value of the particle size was 5 mm. A rolling granulator was used for the molding, the centrifugal acceleration was 4.2 G, the absolute humidity by weight in the granulator was 0.0069 kg-H2O / kg-DA, and the temperature was 21.2°C. Next, firing was performed under the conditions of 390°C for 4 hours to obtain the spherical catalyst 2 of the present invention.

[0035] [Example 3] [Manufacture of Catalyst 3] The composition of the catalyst active component is Mo 12 V 3.0 W 1.2 Cu 1.2 Sb 0.50Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, copper sulfate, and antimony acetate were weighed and mixed in an aqueous solvent heated to 95°C to obtain a preparation solution (A). This preparation solution (A) was dried by the spray drying method, and the obtained dry powder (B) was pre-fired under the conditions of 350°C for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized with a vibration mill to obtain a pre-fired powder (E). The median diameter of the obtained pre-fired powder (E) was 36.7 μm. 5% by mass of crystalline cellulose was added to the pre-fired powder (E), and after sufficient mixing, a 20% by mass glycerin solution was used as a binder by the rolling granulation method, and it was spherically supported and molded onto an inert spherical carrier composed of a mixture of silica and alumina so that the loading rate was 33% by mass and the average value of the particle size was 5 mm. A rolling granulator was used for the molding, the centrifugal acceleration was 4.2 G, the absolute humidity by weight in the granulator was 0.0170 kg-H2O / kg-DA, and the temperature was 31.0°C. Next, the main firing was performed under the conditions of 390°C for 4 hours to obtain the spherical catalyst 3 of the present invention. [Comparative Example 1] [Production of Catalyst 4] The composition of the catalyst active component is Mo 12 V 3.0 W 1.2 Cu 1.2 Sb 0.50Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, copper sulfate, and antimony acetate were weighed and mixed in an aqueous solvent heated to 95 °C to obtain a preparation liquid (A). The preparation liquid (A) was dried by the spray drying method, and the obtained dried powder (B) was pre-fired under the conditions of 350 °C for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized with a vibration mill to obtain a pre-fired powder (E). The median diameter of the obtained pre-fired powder (E) was 21.8 μm. 5% by mass of crystalline cellulose and 5% by mass of Milld Fiber EFH150-31 manufactured by Central Glass Co., Ltd. were added to the pre-fired powder (E), and after thorough mixing, a 20% by mass glycerin solution was used as a binder by the rolling granulation method, and it was spherically supported and formed on an inert spherical carrier composed of a mixture of silica and alumina so that the loading rate was 33% by mass and the average value of the particle diameter was 5 mm. A rolling granulator was used for the molding, the centrifugal acceleration was 26.0 G, the absolute humidity by weight in the granulator was 0.0235 kg-H2O / kg-DA, and the temperature was 27.9 °C. Next, the main firing was carried out under the conditions of 390 °C for 4 hours to obtain the spherical catalyst 4 of the present invention.

[0036] Using the obtained catalysts 1 to 4, oxidation reactions were carried out respectively. 67.6 ml of the catalyst was filled in a reaction tube with an inner diameter of 28.4 mm, and a gas having the following composition in which oxygen and nitrogen were added to the gas obtained by gas-phase catalytic oxidation of propylene using a molybdenum-bismuth-based catalyst was introduced, and the reaction was carried out at an SV (space velocity; flow rate of raw material gas per unit time / apparent volume of the filled catalyst) of 1020 / hr and a reaction bath temperature of 260 °C. Acrolein 5.9 vol% Unreacted propylene + other organic compounds 1.7 vol% Oxygen 4.7 vol% Steam 17.2 vol% Nitrogen-containing inert gas 70.5 vol%

[0037] Table 1 shows the reaction results obtained by the oxidation reaction and the results obtained by measuring the surface roughness.

Table 1

[0038] From the results in Table 1, it was confirmed that the catalyst of the present invention has a high raw material conversion rate, that is, a high catalytic activity.

[0039] This application is based on Japanese Patent Application No. 2023-046098 filed on March 23, 2023, the content of which is incorporated herein by reference.

Industrial Applicability

[0040] According to the present invention, when producing an unsaturated carboxylic acid by subjecting an unsaturated aldehyde to a gas-phase catalytic oxidation reaction as a raw material, a catalyst having excellent catalytic activity can be provided. Therefore, a plant for producing acrylic acid can be stably operated for a long period of time, which is very useful.

Claims

1. A catalyst for producing an unsaturated carboxylic acid, having a composition in which the catalytically active component is represented by the following formula (1), A catalyst for producing an unsaturated carboxylic acid, wherein the value of the surface roughness S obtained by measuring the surface roughness with a non-contact type shape measuring laser microscope is 11.7 μm or more and 25.0 μm or less. (Mo) １２ (V) ａ (W) ｂ (Cu) ｃ (Sb) ｄ (X) ｅ (Y) ｆ (Z) ｇ (O) ｈ (1) (In formula (1), Mo, V, W, Cu, Sb, and O represent molybdenum, vanadium, tungsten, copper, antimony, and oxygen, respectively. X represents at least one element selected from the group consisting of an alkali metal and thallium. Y represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc. Z represents at least one element selected from the group consisting of niobium, cerium, tin, chromium, manganese, iron, cobalt, samarium, germanium, titanium, and arsenic. Also, a, b, c, d, e, f, g, and h represent the atomic ratios of the respective elements. With respect to 12 molybdenum atoms, a satisfies 1.0 ≦ a ≦ 5.0, b satisfies 0.50 ≦ b ≦ 3.0, c satisfies 0.50 ≦ c ≦ 3.0, d satisfies 0 < d ≦ 2.0, e satisfies 0 ≦ e ≦ 0.50, f satisfies 0 ≦ f ≦ 1.0, and g satisfies 0 ≦ g < 6.

0. Also, h is the number of oxygen atoms necessary to satisfy the valences of the respective components.)

2. The catalyst for producing an unsaturated carboxylic acid according to claim 1, wherein the catalytically active component is supported on an inert carrier.

3. The catalyst for producing an unsaturated carboxylic acid according to claim 2, wherein the inert carrier is silica, alumina, or a combination thereof.

4. A method for producing a catalyst for producing an unsaturated carboxylic acid according to claim 1, comprising a step of granulating with a granulator, wherein the absolute weight humidity MR in the granulator is 0.0235 kg-H2O / kg-DA or less.

5. A method for producing an unsaturated carboxylic acid, using the catalyst for producing an unsaturated carboxylic acid according to claim 1.

6. A method for producing an unsaturated carboxylic acid, using a reaction tube filled with two or more kinds of the catalysts for producing an unsaturated carboxylic acid according to claim 1 in multiple layers. ​

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