JP3866483B2 - Method for producing precipitate, method for producing catalyst - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a precipitate (hereinafter also referred to as a molybdenum-based precipitate) containing at least molybdenum and an A element (A is at least one element selected from the group consisting of phosphorus and arsenic). The present invention relates to a method for producing a molybdenum-based catalyst useful for various reactions.
[0002]
[Prior art]
Molybdenum-based precipitates include, for example, molybdenum solid catalysts such as the production of methyl tertiary butyl ether by etherification of isobutene and methanol, the production of methacrylic acid by dehydrogenation of isobutyric acid, and the production of methacrylic acid by gas-phase catalytic oxidation of methacrolein. As such, active research is being conducted for the purpose of industrialization. Regarding the composition and preparation method of these catalysts, many proposals have been made in the past, and in general, an oxoacid ion containing element A is present in an aqueous molybdate solution to make the solution acidic, It is known that molybdenum-based precipitates can be produced.
[0003]
[Problems to be solved by the invention]
However, in the conventional method for producing a molybdenum-based precipitate, the purity and average particle size of the obtained molybdenum-based precipitate may be insufficient.
[0004]
Moreover, most of the conventional methods for producing molybdenum-based precipitates are related to molybdenum-based precipitates containing one or two kinds of metal elements, and also for producing molybdenum-type precipitates containing three or more kinds of metal elements. Few methods describe methods that can be suitably used.
[0005]
Therefore, the present invention can produce a molybdenum-based precipitate having high purity and a desired average particle size easily and with good workability, and also suitable for producing a molybdenum-based precipitate containing three or more metal elements. It aims to provide a method that can be used.
[0006]
[Means for Solving the Problems]
According to the present invention for achieving the above object, there is provided a method for producing a precipitate containing at least molybdenum and an A element (A is at least one element selected from the group consisting of phosphorus and arsenic),
A first step in which a crude precipitate is produced and filtered in the presence of an alkali metal compound with a pH of the mixed solution containing the constituents of the precipitate being 6.5 or less;
A second step in which the crude precipitate is dissolved in aqueous ammonia, the pH of the resulting solution is adjusted to 6.5 or lower, and the precipitate is produced and filtered;
A method for producing a precipitate is provided.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
[0008]
The production method of the present invention includes at least first and second steps. In the first step, a molybdenum-based precipitate is dispersed in water, and an alkali metal compound is added thereto to prepare a mixed solution. Thereafter, the pH of the obtained mixed solution is adjusted to 6.5 or less to produce a crude precipitate, which is filtered off. In the second step, aqueous ammonia is added to the crude precipitate obtained in the first step and dissolved to prepare a solution. Thereafter, the pH of the obtained solution is adjusted to 6.5 or less, and a precipitate is formed and filtered.
[0009]
As a result of intensive studies on the production method of molybdenum-based precipitates, the present inventors have been able to produce molybdenum-based precipitates having high purity and a desired average particle size simply and with good workability by the above-described method. The above-described method has been found to be suitable for the production of molybdenum-based precipitates containing three or more metal elements.
[0010]
The reason for this is not clear, but by setting the pH to 6.5 or less in the presence of ammonium root, it is possible to realize favorable precipitation of the molybdenum-based compound in a state where embedding of impurities and the like is suppressed. I guess.
[0011]
The molybdenum-based precipitate in the present invention is not particularly limited as long as it is a precipitate containing at least molybdenum and an A element (A is at least one element selected from the group consisting of phosphorus and arsenic). A salt in which a heteropolyacid containing molybdenum as a coordination element and an A element as a central element and a Z element (Z is at least one element selected from the group consisting of potassium, rubidium and cesium) are bonded, and these And the like.
[0012]
As the basic structure of the heteropolyacid, there are known a Keggin structure, a Silverton structure, a 1:18 Dawson structure, a 1: 6 Anderson structure, etc., with a ratio of central element: coordinating element of 1:12. Examples of the method include a method in which an aqueous solution containing molybdate and an oxo acid ion of element A is acidified to form a precipitate. In addition, when obtaining a heteropolyacid containing a Z element, a Z salt of the heteropolyacid can be easily generated by dissolving the Z element compound in the form of precipitation and allowing it to exist in the form of Z ions. .
[0013]
Since the molybdenum-based precipitate obtained by the production method of the present invention has a desired average particle size with high purity, a metal element is further added to the molybdenum-based precipitate in the present invention, if necessary. Thus, a molybdenum-based solid catalyst (also referred to as a molybdenum-based catalyst) having good characteristics can be produced.
[0014]
That is, after preparing a molybdenum-based precipitate having a desired average particle diameter by the method including the first step and the second step, a metal element corresponding to the reaction system is added in order to improve the performance as a catalyst. A molybdenum-based catalyst can be produced by a process such as addition.
[0015]
Examples of the molybdenum-based solid catalyst include a molybdenum-based catalyst represented by the following general formula (1).
[0016]
A _a Mo _b V _c Cu _d D _e Y _f Z _g O _h (1)
Wherein A represents at least one element selected from the group consisting of phosphorus and arsenic; D is selected from the group consisting of antimony, bismuth, germanium, zirconium, tellurium, silver, selenium, silicon, tungsten and boron. Y represents at least one element; Y represents at least one element selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum; Z represents potassium and rubidium And at least one element selected from the group consisting of cesium; a is from 0.5 to 3, b is 12, c is from 0 to 3, d is from 0 to 3, e is from 0 to 3, f is 0 or more and 3 or less, and h is the atomic ratio of oxygen necessary to satisfy the valence of each element.)
Further, the average particle diameter of the molybdenum-based precipitate is preferably 1 μm or more, more preferably 3 μm or more, more preferably 100 μm or less, and even more preferably 70 μm or less, from the viewpoints of catalyst efficiency and handleability during washing.
[0017]
Specific examples of molybdenum-based catalysts include catalysts for the production of methacrylic acid by gas-phase catalytic oxidation of methacrolein, catalysts for the production of methyl tertiary butyl ether by etherification of isobutene and methanol, and methacrylic acid by dehydrogenation of isobutyric acid. Examples include a production catalyst.
[0018]
In the molybdenum-based catalyst manufacturing method described above, the molybdenum-based catalyst used in various reactions (also referred to as a post-use catalyst) can be used as a raw material for the molybdenum-based precipitate used in the first step. . In this case, after use, the molybdenum-based catalyst whose activity has declined due to long-term use is recovered, purified by the method for producing a molybdenum-based precipitate of the present invention, and then reactivated by adding a necessary metal element. It is possible to produce a molybdenum-based catalyst or a molybdenum-based catalyst having different reaction characteristics from those before recovery.
[0019]
In the first step in the present invention, usually, an alkali metal compound is added after a solid containing the constituents of the molybdenum-based precipitate is dispersed in water. The amount of water to be added is not particularly limited, but the amount of the obtained mixed liquid is an amount that can be easily handled as a slurry. The amount of the alkali metal compound added is preferably such that the pH of the mixed solution is 8 or more, and the pH of the mixed solution is more preferably 8.5 or more, and preferably 12 or less. Although the alkali metal compound used here is not specifically limited, For example, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium hydrogencarbonate etc. are mentioned, Especially sodium hydroxide is preferable. The alkali metal compound may be added to the mixed solution in a solid state, or may be added in advance as an aqueous solution.
[0020]
After adding the alkali metal compound, it is preferable to hold for a certain period of time in order to dissolve the metal element contained in the solid containing the constituents of the molybdenum-based precipitate. The holding time at this time is preferably 0.5 hours or more and 24 hours or less, and the holding temperature is preferably normal temperature or more and 90 ° C. or less. Further, it may be allowed to stand during the holding, but is preferably stirred.
[0021]
Then, when there exists an insoluble residue in a liquid mixture, it is preferable to remove this by filtration etc.
[0022]
Next, an acid is added to the mixed solution to adjust the pH to 6.5 or lower. Examples of the acid added for adjusting the pH include hydrochloric acid, nitric acid and sulfuric acid, and hydrochloric acid and nitric acid are particularly preferable.
[0023]
After pH adjustment, it is preferable to hold for a certain period of time in order to produce a crude precipitate. In this case, the holding time is preferably 0.5 hours or more and 24 hours or less, and the holding temperature is preferably normal temperature or more and 90 ° C. or less. Further, it may be allowed to stand during the holding, but is preferably stirred.
[0024]
As an example of the main component of the obtained coarse precipitate, a so-called Dawson-type heteropolyacid salt having a ratio of a central element such as phosphorus: molybdenum of 2:18 or a central element such as phosphorus is obtained from composition analysis and X-ray diffraction measurement. A mixture of so-called Keggin-type heteropolyacid salt and Dawson-type heteropolyacid with a ratio of: molybdenum of 1:12 is presumed. At this time, the lower the pH to be adjusted, the greater the proportion of the Keggin type heteropolyacid salt.
[0025]
If the amount of element Z is not sufficient to precipitate the heteropolyacid as a salt of element Z, preferably 0.5 mol or more, more preferably 3 mol per 1 mol of element A before adjusting the pH. As mentioned above, it is preferable to add an ammonium root raw material so that preferably 40 mol or less of ammonium roots exist. By the presence of ammonium root, more heteropolyacid can be precipitated as an ammonium salt, and the recovery rate of molybdenum and element A contained in the crude precipitate can be increased. The greater the amount of ammonium root, the higher the recovery rate of molybdenum and element A.
[0026]
The ammonium root raw material is not particularly limited as long as it is soluble, and examples thereof include aqueous ammonia, ammonium chloride, ammonium nitrate, and ammonium carbonate.
[0027]
In addition, the residual liquid which isolate | separated the molybdenum system precipitate produced | generated at the 2nd process contains a large amount of ammonium roots. Although this residual liquid may be discarded, it can be used as an ammonium root raw material to be added to the mixed liquid in the first step. In this case, it is not necessary to add a new ammonium root raw material, which is an economically preferable process.
[0028]
Further, depending on the use of the finally obtained molybdenum-based precipitate, it may be desirable that the Z element is little or not contained. In such a case, it is preferable to remove all or part of the Z element from the mixed solution before adjusting the pH to 6.5 or lower. For example, Z ions are adsorbed by a cation exchange resin. And the like. The time for removing the Z element is preferably before the pH is adjusted to 6.5 or lower. In this case, in order to efficiently recover molybdenum and element A, it is particularly preferable to add an ammonium root.
[0029]
The crude precipitate produced by the pH adjustment is separated from the remaining liquid by solid-liquid separation. The method of solid-liquid separation is not particularly limited, and can be performed by a general method such as filtration or centrifugation, and the apparatus is a general method such as a pressure filter, a vacuum filter, a filter press, or a centrifuge. An apparatus can be used.
[0030]
In the second step, ammonia solution is added to the crude precipitate obtained as described above to redissolve it, and then the pH of the solution is adjusted to 6.5 or lower by addition of an acid for reprecipitation. The state of rough precipitation when adding aqueous ammonia is not particularly limited, and may be either wet or dry.
[0031]
The amount of ammonia water added is not particularly limited as long as it dissolves the coarse precipitate, but is preferably such an amount that the pH becomes 8 or more. Ammonia water may be added to the rough precipitate, or ammonia water may be added after the rough precipitate is dispersed in water. The acid used for pH adjustment may be the same as or different from the acid used in the first step, and can be selected according to the use of the molybdenum-based precipitate. After pH adjustment, it is preferable to hold for 0.5 hours or more and 24 hours or less, and the holding temperature is preferably normal temperature or more and 90 ° C. or less. Moreover, it is preferable to stir during holding.
[0032]
The precipitate produced in the second step can be separated from the remaining liquid by solid-liquid separation operation as in the first step.
[0033]
Following the first step, it is preferable to wash the crude precipitate obtained in the first step using an acidic aqueous solution containing at least 0.01 mol / L or more ammonium root and having a pH of 6.5 or less. .
[0034]
In addition, following the second step, it is preferable to wash the precipitate obtained in the second step using an acidic aqueous solution containing at least 0.01 mol / L or more ammonium root and having a pH of 6.5 or lower. .
[0035]
In order to sufficiently suppress the change in the average particle diameter of the molybdenum-based precipitate during washing, the ammonium root concentration in the acidic aqueous solution is preferably 0.01 mol / L or more, more preferably 0.05 mol / L. L or more, more preferably 0.1 mol / L or more.
[0036]
Impurities contained in molybdenum-based coarse precipitates and precipitates include, for example, excess ammonium and nitrate radicals, chlorine and sulfur, added alkali metal compounds and salts generated from pH-adjusting acids, and the like. Depending on the application, the components in question vary. Therefore, it is preferable to select a cleaning solution as appropriate according to the use and solubility of the precipitate. From such a viewpoint, examples of the cleaning liquid in the present invention include at least one aqueous solution selected from the group consisting of an aqueous ammonium nitrate solution, an aqueous ammonium chloride solution, and an aqueous ammonium sulfate solution.
[0037]
The washing method is not particularly limited, and dispersion washing in which a washing liquid is added to and dispersed in a coarse precipitate or precipitate, followed by solid-liquid separation, or through-washing in which the washing liquid is passed through a cake-like coarse precipitate or precipitate is performed. Can do. The washing can be performed at a temperature of 0 ° C. or higher and 90 ° C. or lower. Moreover, the state of the rough precipitation after washing | cleaning and a precipitate is not specifically limited, Either a wet state and a dry state may be sufficient.
[0038]
By performing washing as described above, it is possible to achieve high purity without largely changing the average particle size of the coarse precipitate and the precipitate.
[0039]
That is, the average particle size change rate of the crude precipitate before and after washing can be preferably 50% or less, more preferably 40% or less, and still more preferably 30% or less.
[0040]
Moreover, the average particle diameter change rate of the precipitate before and after washing can be preferably 50% or less, more preferably 40% or less, and still more preferably 30% or less.
[0041]
The average particle size change rate is a value defined by 100 × | r−r ′ | / r where r is the average particle size before cleaning and r ′ is the average particle size after cleaning. .
[0042]
According to the present invention, the chlorine contained in the precipitate obtained by washing the precipitate obtained in the second step is preferably 0.10 times or less, more preferably less than 1 mol per mol of element A. It can be 0.05 mol or less, more preferably 0.03 mol or less.
[0043]
Further, according to the present invention, sodium contained in the precipitate obtained by washing the precipitate obtained in the second step is preferably 0.10 times mol or less, relative to 1 mol of element A. Preferably it is 0.05 times mol or less, More preferably, it can be 0.03 times mol or less.
[0044]
【Example】
The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples. As for the reagents, high-purity commercial products were used unless otherwise specified.
[0045]
(Analysis method)
Quantitative analysis of contained elements (or molecules) is performed by ICP emission analysis (CID high frequency plasma emission spectrometer, IRIS Advantage AP, manufactured by Nippon Jarrel Ash), atomic absorption analysis (SAS 7500, manufactured by Seiko Denshi Kogyo Co., Ltd.), ion chromatography. The graphic analysis method (Dionex DX-AQ2211) and the Kjeldahl method were used.
[0046]
Further, the average particle size of the precipitate was determined by measuring the particle size distribution with SK LASER MICRON SIZER PRO-7000 manufactured by Seishin Enterprise Co., Ltd., and determining the average particle size as the particle size at which the cumulative particle size distribution was 50%.
[0047]
[Example 1]
(A) Use of molybdenum-based catalyst: elements including 34.54 parts by mass of molybdenum, 0.93 parts by mass of phosphorus, 1.41 parts by mass of potassium, 0.76 parts by mass of vanadium and 0.57 parts by mass of copper, excluding oxygen Of the composition (hereinafter the same) is P ₁ Mo ₁₂ K _1.2 V _0.5 Cu _0.3 In a reaction tube, a mixed gas of 5% by volume of methacrolein, 10% by volume of oxygen, 30% by volume of water vapor, and 55% by volume of nitrogen is subjected to a reaction temperature of 270 ° C. and a contact time of 3.6 seconds. The reaction was performed for 2000 hours.
[0048]
(I) Removal of potassium: After completion of the reaction, the catalyst was extracted from the reaction tube, and 91 parts by mass of the catalyst after use was dispersed in 400 parts by mass of pure water. To this, 89.2 parts by mass of 45% aqueous sodium hydroxide solution was added, and after stirring for 2 hours, the residue was filtered off. This filtrate was passed through a strongly acidic styrene ion exchange resin Amberlite IR-120B (manufactured by Organo Corp.) made into Na type at SV = 1 to remove potassium.
[0049]
(C) First step: 29.9 parts by mass of 36% hydrochloric acid was added to this passing solution to adjust the pH of the solution to 8.9, and then 19.25 parts by mass of ammonium chloride (12.0 times the amount of phosphorus) Molar ammonium root amount) was added. Subsequently, 84.1 parts by mass of 36% hydrochloric acid was added with stirring to adjust the pH of the mixed solution to 1.0. In addition, as the pH became acidic by addition of hydrochloric acid, a coarse precipitate was formed, and when the pH of the solution reached 1.0, the solution was in a slurry state. Thereafter, the mixture was kept stirred at room temperature for 2 hours. The slurry containing the crude precipitate thus obtained was separated by a Nutsche vacuum filter to obtain a wet crude precipitate.
[0050]
(D) Washing step: Dispersed in a 2% mass of 2% aqueous ammonium nitrate solution (pH at room temperature: 5.2, ammonium root amount: 0.25 mol / L) for 5 minutes with respect to the obtained wet crude precipitate Then, the precipitate was again filtered off using a Nutsche filter to obtain 120.5 parts by mass of wet crude precipitate.
[0051]
(E) Second step: The wet crude precipitate thus obtained was put into 500 parts by mass of pure water, and 71.1 parts by mass of 25% aqueous ammonia was added thereto and stirred for 10 minutes. . The mixed liquid at this time was in a slurry state at first, but after 5 minutes, it became a complete solution, and the pH at that time was 8.6. Next, after the temperature of the solution was raised to 70 ° C., 99.8 parts by mass of 36% hydrochloric acid was added to adjust the pH of the mixed solution to 5.0, and the mixture was stirred and maintained at a temperature of 80 ° C. for 3 hours. Generated. The slurry containing the precipitate was cooled to room temperature and then filtered to obtain a wet precipitate.
[0052]
(F) Washing step: Next, the dispersion was washed twice with a 2% aqueous ammonium nitrate solution (pH of 5.2 at room temperature, ammonium root amount of 0.25 mol / L) twice as much as the wet precipitate. Thereafter, the mixture was filtered to obtain 110.5 parts by mass of a wet precipitate. The wet precipitate at this time was 30.55 parts by mass (12 atm%) of molybdenum, 0.90 parts by mass (1.1 atm%) of phosphorus, 0.61 parts by mass of vanadium (0.45 atm%), and 1 mol of phosphorus. It contained 11.51 moles of ammonium roots and contained 0.01 moles of sodium and 0.02 moles of chlorine per mole of phosphorus as impurities.
[0053]
Further, the wet precipitate was dispersed in the filtrate after separation of the wet precipitate in the second step of (e), and the average particle size was measured and found to be 11.5 μm.
[0054]
From the above results, by using the method including the first and second steps in the present invention, a molybdenum-based precipitate containing three or more metal elements and having good characteristics can be produced with good operability. understood.
[0055]
It was also found that the molybdenum-based precipitate can be produced satisfactorily even when potassium in the molybdenum-based precipitate is replaced with sodium.
[0056]
[Comparative Example 1]
In the same manner as in (a) to (e) of Example 1, 125.1 parts of wet precipitate were obtained. At this time, the wet precipitate contains 32.54 parts by mass of molybdenum, 0.91 part by mass of phosphorus, and 0.66 parts by mass of vanadium, and contains 10.71 times moles of ammonium roots per mol of phosphorus. It contained 0.21 moles of sodium and 0.15 moles of chlorine per mole.
[0057]
Subsequently, without performing the second step, dispersion washing was performed three times using a 2% aqueous ammonium nitrate solution (four times in total including the step (d)). With each washing step, the residual amount of sodium relative to 1 mol of phosphorus decreased to 0.13 mol, 0.11 mol, and 0.11 mol, but hardly decreased after the third washing. Moreover, although the residual amount of chlorine with respect to 1 mol of phosphorus also decreased to 0.12 mol, 0.09 mol, and 0.09 mol, it hardly decreased after the third washing.
[0058]
[Example 2]
(A) Use of molybdenum-based catalyst: 34.54 parts by mass of molybdenum, 0.93 parts by mass of phosphorus, 1.41 parts by mass of potassium, 0.76 parts by mass of vanadium, 0.57 parts by mass of copper and 1.12 parts by mass of arsenic And the composition is P ₁ Mo ₁₂ V _0.5 As _0.5 Cu _0.3 K _1.2 In a reaction tube, a mixed gas of 5% by volume of methacrolein, 10% by volume of oxygen, 30% by volume of water vapor, and 55% by volume of nitrogen is subjected to a reaction temperature of 270 ° C. and a contact time of 3.6 seconds. The reaction was performed for 2000 hours.
[0059]
(A) First step: After completion of the reaction, the catalyst was extracted from the reaction tube, and 94 parts by mass of the catalyst after use was dispersed in 400 parts by mass of pure water. To this was added 89.0 parts by mass of 45% aqueous sodium hydroxide solution, and the mixture was stirred for 1 hour, and the residue was filtered off. After adding 29.8 parts by mass of 36% hydrochloric acid to adjust the pH of the solution to 9.0, 28.90 parts by mass of ammonium chloride (ammonium root content of 12.0 times mol with respect to the total amount of phosphorus and arsenic) ) Was added. Subsequently, 48.0 parts by mass of 36% hydrochloric acid was added to adjust the pH of the mixed solution to 5.0, and the mixture was stirred and maintained at 60 ° C. for 3 hours. After cooling the mixture to room temperature, the crude precipitate was filtered off using a Nutsche vacuum filter to obtain a wet crude precipitate.
[0060]
(C) Washing step: Dispersed in a 2% mass aqueous 2% ammonium nitrate solution (pH at room temperature: 5.2, ammonium root amount: 0.25 mol / L) for 5 minutes with respect to the obtained wet crude precipitate, The crude precipitate was separated by filtration to obtain 90 parts by mass of wet crude precipitate.
[0061]
(D) Second step: The wet crude precipitate thus obtained was put into 500 parts by mass of pure water, and 55.5 parts by mass of 25% aqueous ammonia was added thereto and stirred for 10 minutes. The pH at this time was 8.7. Subsequently, 78.1 parts of 36% hydrochloric acid was added to adjust the pH of the mixed solution to 5.0, and the mixture was stirred and maintained at 60 ° C. for 3 hours. The mixture was cooled to room temperature and filtered to obtain a wet precipitate.
[0062]
(E) Washing step: The obtained wet precipitate was dispersed and washed twice with a 2% mass 2% aqueous ammonium nitrate solution (pH at room temperature: 5.2, ammonium root amount: 0.25 mol / L). Finally, 83 parts by weight of wet precipitate was obtained. At this time, the wet precipitate was 24.11 parts by mass of molybdenum (12 atm%), 0.56 parts by mass of phosphorus (0.86 atm%), 0.56 parts by mass of potassium (0.69 atm%), and 0.36 parts by mass of vanadium. (0.34 atm%), 1.12 parts by mass (0.71 atm%) of arsenic, 9.42 times moles of ammonium roots per mole of phosphorus, and 0.2 mol per mole of total phosphorus and arsenic as impurities. It contained 01 moles of sodium and 0.02 moles of chlorine.
[0063]
Further, the wet precipitate was dispersed in the filtrate after separation of the wet precipitate in the second step of (d), and the average particle size was measured and found to be 16.2 μm.
[0064]
From the above results, by using the method including the first and second steps in the present invention, a molybdenum-based precipitate containing three or more metal elements and having good characteristics can be produced with good operability. understood.
[0065]
[Example 3]
(A) First step: 94 parts by mass of the catalyst after use having the same composition as in Example 2 was dispersed in 400 parts by mass of pure water, and 89.0 parts by mass of 45% aqueous sodium hydroxide solution was added thereto, followed by stirring for 1 hour. The residue was filtered off. Subsequently, instead of ammonium chloride, 640 parts by mass of the filtrate after the second step of Example 2 (corresponding to 11 times mole of ammonium root with respect to the total amount of phosphorus and arsenic contained in the solution before addition) Then, 51.2 parts by mass of 36% hydrochloric acid was added to adjust the pH of the mixed solution to 5.0, and the mixture was stirred at 60 ° C. for 3 hours. The mixture was cooled to room temperature and then filtered by the same operation as in Example 2 to obtain a wet crude precipitate.
[0066]
(I) Washing step: Next, the wet coarse precipitate is dispersed and washed with 2% by mass of a 2% aqueous ammonium nitrate solution (pH at room temperature is 5.2, ammonium root amount is 0.25 mol / L). Of 95 parts by mass of crude precipitate was obtained.
[0067]
(C) Second step: The wet crude precipitate thus obtained was put into 500 parts by mass of pure water, and 57.5 parts by mass of 25% aqueous ammonia was added thereto and stirred and held for 10 minutes. Subsequently, 78.1 parts by mass of 36% hydrochloric acid was added to adjust the pH of the mixed solution to 5.0, and the mixture was stirred and maintained at 60 ° C. for 3 hours. The mixture was cooled to room temperature and filtered to obtain a wet precipitate.
[0068]
(D) Washing step: The obtained wet precipitate was dispersed and washed twice with a 2% by mass 2% aqueous ammonium nitrate solution (pH at room temperature: 5.2, ammonium root amount: 0.25 mol / L). Finally, 89.7 parts by weight of wet precipitate was obtained. The precipitate was 25.34 parts by mass (12 atm%) of molybdenum, 0.57 parts by mass (0.84 atm%) of phosphorus, 0.56 parts by mass (0.65 atm%) of potassium, and 0.38 parts by mass of vanadium (0. 34 atm%), 1.12 parts by mass of arsenic (0.68 atm%), 9.31-fold moles of ammonium root per mole of phosphorus, and 0.006 moles per mole of total phosphorus and arsenic as impurities Of sodium and 0.02 moles of chlorine.
[0069]
Further, the wet precipitate was dispersed in the filtrate after separation of the wet precipitate in the second step (c), and the average particle size was measured. As a result, it was 17.8 μm.
[0070]
From the above results, by using the method including the first and second steps in the present invention, a molybdenum-based precipitate containing three or more metal elements and having good characteristics can be produced with good operability. understood.
[0071]
It was also found that the filtrate produced in the second step can be used in the first step.
[0072]
[Comparative Example 2]
In the same manner as in (a) to (c) of Example 2, 95 parts by mass of wet precipitate was obtained. This precipitate is 26.16 parts by mass of molybdenum, 0.57 parts by mass of phosphorus, 0.58 parts by mass of potassium, 0.37 parts by mass of vanadium, 1.12 parts by mass of arsenic, and 9.51 times mol of 1 mol of phosphorus. It contained ammonium roots and 1.20 moles of sodium and 1.12 moles of chlorine per mole of phosphorus as impurities.
[0073]
Subsequently, without performing the second step, dispersion washing was performed 5 times using a 2% aqueous ammonium nitrate solution, and the finally obtained wet precipitate was analyzed. As a result, the residual amount of sodium and chlorine relative to 1 mol of phosphorus and arsenic in total was found. The amounts were 0.06 mol and 0.05 mol, respectively.
[0074]
【The invention's effect】
As is apparent from the above description, the first step of generating a crude precipitate with a pH of 6.5 or lower in the presence of an alkali metal compound, and the precipitate with a pH of 6.5 or lower by dissolving the crude precipitate in aqueous ammonia. By adopting a production method including at least a second step of producing a molybdenum-based precipitate having a desired average particle size with high purity even in the case of a molybdenum-based precipitate containing three or more metal elements Can be manufactured easily and with good workability.

Claims (9)

A method for producing a precipitate containing at least molybdenum and an A element (A is at least one element selected from the group consisting of phosphorus and arsenic),
A first step in which a crude precipitate is produced and filtered in the presence of an alkali metal compound with a pH of the mixed solution containing the constituents of the precipitate being 6.5 or less;
A second step in which the crude precipitate is dissolved in aqueous ammonia, the pH of the resulting solution is adjusted to 6.5 or lower, and the precipitate is produced and filtered;
A method for producing a precipitate, comprising: 2. The production method according to claim 1, wherein the mixed solution in the first step contains 0.5 times or more of an ammonium root with respect to 1 mol of the element A. 3. 3. The production method according to claim 2, wherein the ammonium root contained in the mixed liquid in the first step is supplied by adding the filtrate produced in the second step to the mixed liquid. Subsequent to the first step, the crude precipitate obtained in the first step is washed with an acidic aqueous solution containing at least 0.01 mol / L or more ammonium root and having a pH of 6.5 or less. The manufacturing method according to any one of claims 1 to 3. Subsequent to the second step, the precipitate obtained in the second step is washed with an acidic aqueous solution containing at least 0.01 mol / L or more ammonium root and having a pH of 6.5 or less. The manufacturing method according to any one of claims 1 to 4. The chlorine contained in the precipitate obtained by washing the precipitate obtained in the second step is 0.10 times or less by mole with respect to 1 mol of the A element. Manufacturing method. The sodium contained in the precipitate obtained by washing the precipitate obtained in the second step is 0.10 mol or less per 1 mol of the element A, or 6. The production method according to 6. Prior to the first step, when the constituent of the precipitate contains at least one element selected from the group consisting of potassium, rubidium and cesium, at least one selected from the group consisting of potassium, rubidium and cesium The manufacturing method according to claim 1, wherein the element is substantially removed. The following general formula (1)
A _a Mo _b V _c Cu _{d De} Y _f Z _g O _h (1)
Wherein A represents at least one element selected from the group consisting of phosphorus and arsenic; D is selected from the group consisting of antimony, bismuth, germanium, zirconium, tellurium, silver, selenium, silicon, tungsten and boron. Y represents at least one element; Y represents at least one element selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum; Z represents potassium and rubidium And at least one element selected from the group consisting of cesium; a is from 0.5 to 3, b is 12, c is from 0 to 3, d is from 0 to 3, e is from 0 to 3, f is 0 or more and 3 or less, and h is the atomic ratio of oxygen necessary to satisfy the valence of each element.)
A method for producing a molybdenum-based catalyst represented by
A method for producing a catalyst comprising at least a step of preparing the precipitate having an average particle size of 1 μm or more and 100 μm or less by the production method according to claim 1.