Ammonium modified diatomite as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysis, and discloses ammonium modified diatomite as well as a preparation method and application thereof, and the preparation method of the ammonium modified diatomite comprises the step of carrying out ammonium modification on diatomite by adopting ammonium salt. The content of ammonium in the ammonium modified diatomite is 1-5wt%. The ammonium modified diatomite used as the carrier has high olefin aldehyde conversion rate and olefin acid selectivity in olefin aldehyde oxidation preparation of olefin acid, and especially has high methylacrolein conversion rate and methacrylic acid selectivity in methylacrolein oxidation preparation of methacrylic acid. And the catalyst containing the ammonium modified diatomite has high stability, and can still maintain high olefine aldehyde conversion rate and olefine acid selectivity after long-time operation.

Description

Technical Field

[0001] The invention relates to the field of catalytic technology, and in particular to ammonium modified diatomaceous earth and a preparation method and application thereof. Background Art

[0002] At present, there are some public reports on supported heteropolyacid catalysts, and the carriers generally include silicon oxide, metal oxides, molecular sieves and activated carbon. Since the oxidation of methacrolein to methacrylic acid is carried out in an aerobic environment at about 300°C, it is difficult for easily oxidized carriers to exist under the reaction conditions, such as activated carbon. Silicon oxide, as a cheap inert carrier, is suitable for high-temperature oxidation reactions. CN110694687A, CN105457678A and CN107042121A report a series of supported heteropolyacid catalysts with silicon oxide as carriers for methacrolein oxidation reactions. However, due to the reaction conditions, the heteropolyacid reacts with the silicon on the surface of the carrier to generate new species, resulting in the decomposition of the Keggin structure of the heteropolyacid. Therefore, it is necessary to find a more stable carrier to improve the performance of the catalyst. The silicon oxide carrier reported in the above literature is obtained by multiple physical and chemical treatments of natural silicon-aluminum minerals. The three wastes generated in the process are serious. If natural clay is directly used as a catalyst carrier, it can not only reduce environmental pressure, but also improve economic benefits. Summary of the invention

[0003] The purpose of the present invention is to overcome the above technical problems in the prior art and to provide an ammonium-modified diatomaceous earth and a preparation method and application thereof.

[0004] In order to achieve the above object, the first aspect of the present invention provides an ammonium-modified diatomaceous earth, wherein the ammonium content of the ammonium-modified diatomaceous earth is 1-5% by weight.

[0005] The second aspect of the present invention provides a method for preparing ammonium-modified diatomite, which comprises: ammonium-modifying diatomite with ammonium salt.

[0006] The third aspect of the present invention provides ammonium-modified diatomaceous earth prepared by the method described above.

[0007] The fourth aspect of the present invention provides the use of the above-mentioned ammonium-modified diatomaceous earth and / or the ammonium-modified diatomaceous earth prepared by the above-mentioned method as a carrier in the preparation of a catalyst for oxidizing olefinic aldehyde to olefinic acid.

[0008] A fifth aspect of the present invention provides a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, the catalyst comprising ammonium-modified diatomaceous earth and a heteropolyacid supported on the ammonium-modified diatomaceous earth, wherein the ammonium-modified diatomaceous earth is the ammonium-modified diatomaceous earth described above and / or the ammonium-modified diatomaceous earth prepared by the method described above.

[0009] A sixth aspect of the present invention provides a method for preparing methacrylic acid by oxidizing methacrolein, wherein the method comprises: in the presence of the above-mentioned catalyst, allowing methacrolein to undergo an oxidation reaction with an oxidant, wherein the active component in the catalyst is a heteropolyacid.

[0010] Through the above technical solution, the present invention achieves the following beneficial effects:

[0011] (1) The catalyst prepared by using the ammonium-modified diatomaceous earth as a carrier can improve the olefin conversion rate and olefin selectivity in the preparation of olefinic acid by oxidation of olefin, especially in the preparation of methacrylic acid by oxidation of methacrolein, and has a high methacrolein conversion rate and methacrylic acid selectivity, and improves the stability of the catalyst. The catalyst can still maintain a high olefin conversion rate and olefinic acid selectivity after long-term operation.

[0012] (2) The carrier raw materials of the present invention are widely available, the carrier preparation method is simple, time-consuming, easy to operate, and conducive to industrial application, and the three wastes are less discharged during the catalyst preparation process. In the carrier preparation process of the present invention, no expensive template agent and silane coupling agent are required, and the cost of the catalyst is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the SEM image of diatomite before ammonium modification;

[0014] Figure 2 This is the SEM picture of ammonium-modified diatomaceous earth in Example 1;

[0015] Figure 3 is the thermogravimetric curve of ammonium-modified diatomaceous earth in Example 1;

[0016] Figure 4 The XRD diagram of the catalyst in Example 1 before and after the reaction of olefinic acid production by olefinic aldehyde oxidation;

[0017] Figure 5 This is the XRD diagram of the catalyst in comparative example 1 before and after the olefinic acid oxidation reaction. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0019] The first aspect of the present invention provides an ammonium-modified diatomaceous earth, wherein the content of ammonium in the ammonium-modified diatomaceous earth is 1-5% by weight.

[0020] In the present invention, the content of ammonium in the ammonium-modified diatomaceous earth can be 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, and a range consisting of any two of the above. Preferably, the content of ammonium in the ammonium-modified diatomaceous earth is 4-5 wt%.

[0021] According to the present invention, preferably, the specific surface area of ​​the ammonium-modified diatomaceous earth is 20-60 m 2 / g, more preferably 22-55m 2 / g.

[0022] The second aspect of the present invention provides a method for preparing ammonium-modified diatomite, which comprises: ammonium-modifying diatomite with ammonium salt.

[0023] According to the present invention, preferably, the ammonium salt includes at least one of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium carbonate, ammonium phosphate and ammonium acetate; more preferably, the ammonium salt includes at least one of NH4Cl, NH4NO3, (NH4)2SO4, (NH4)2CO3, NH4HCO3, (NH4)3PO4, (NH4)2HPO4 and NH4H2PO4.

[0024] According to the present invention, preferably, the content of silicon oxide in the diatomaceous earth is greater than 65% by weight, more preferably, the content of silicon oxide in the diatomaceous earth is greater than 75% by weight, and further preferably, the content of silicon oxide in the diatomaceous earth is 95-99.9% by weight.

[0025] According to the present invention, preferably, the specific surface area of ​​the diatomaceous earth is 20-60m 2 / g, more preferably 22-55m 2 / g.

[0026] According to the present invention, preferably, the conditions for the ammonium modification include: a temperature of 25-150° C. and a time of 4-96 h.

[0027] According to the present invention, preferably, the (total) amount of the ammonium salt in terms of nitrogen element is 0.1-4 mol per 100 g of diatomaceous earth, for example, 0.1 mol, 0.5 mol, 1 mol, 1.5 mol, 2 mol, 2.5 mol, 3 mol, 3.5 mol, 4 mol, and a range consisting of any two of the above.

[0028] According to the present invention, preferably, the ammonium salt is in the form of a solution and is contacted with diatomaceous earth for reaction. More preferably, the concentration of the ammonium salt in the ammonium salt solution is 0.1-2 mol / L. The solvent in the ammonium salt solution can be water or any solvent that can dissolve the ammonium salt and will not inhibit the reaction. Preferably, the solvent in the ammonium salt solution is water.

[0029] According to the present invention, usually, diatomite can be contacted with ammonium salt once, and can also be contacted with ammonium salt repeatedly, and preferably, ammonium salt is contacted with diatomite in several parts in sequence. More preferably, the mode that diatomite contacts with ammonium salt for reaction includes: ammonium salt is configured as aqueous solution, then divided into two equal parts, first diatomite is contacted with first ammonium salt aqueous solution for reaction (through suction filtration, washing, drying) to obtain a modified diatomite; and then the diatomite modified once is contacted with second ammonium salt aqueous solution for reaction (through suction filtration, washing, drying) to obtain ammonium modified diatomite. By contacting ammonium salt with diatomite for reaction in batches, the silicon in diatomite can be further avoided from reacting with heteropolyacid, and the olefinic aldehyde conversion rate and olefinic acid selectivity of catalyst, as well as the stability of catalyst, are improved.

[0030] In the present invention, the device for the ammonium modification reaction is not particularly limited, and any device that can meet the temperature required for the ammonium modification reaction can be used, for example, a reactor containing a reaction solution of diatomaceous earth and ammonium salt is placed in a water bath to carry out the ammonium modification reaction. Generally, the ammonium modification reaction is carried out under stirring, and the stirring speed can be 100-700r / min.

[0031] According to the present invention, preferably, the method further comprises solid-liquid separation of the product of the ammonium modification reaction to obtain a solid material, and then drying the solid material. Wherein, the solid-liquid separation method can be filtration, suction filtration, etc. commonly used in the art. Drying can be a drying method commonly used in the art, such as using a vacuum drying oven, a blast drying oven, a constant temperature drying oven, and a programmed temperature drying oven, etc. for drying, the drying temperature is usually 50-150°C, and the drying time is usually 12-72h.

[0032] According to the present invention, preferably, before the solid material is dried, the solid material is washed, and distilled water or deionized water can be used for washing.

[0033] The third aspect of the present invention provides ammonium-modified diatomaceous earth prepared by the method described above.

[0034] The fourth aspect of the present invention provides the use of the above-mentioned ammonium-modified diatomaceous earth and / or the ammonium-modified diatomaceous earth prepared by the above-mentioned method as a carrier in the preparation of a catalyst for oxidizing olefinic aldehyde to olefinic acid.

[0035] A fifth aspect of the present invention provides a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, the catalyst comprising ammonium-modified diatomaceous earth and a heteropolyacid supported on the ammonium-modified diatomaceous earth, wherein the ammonium-modified diatomaceous earth is the ammonium-modified diatomaceous earth described above and / or the ammonium-modified diatomaceous earth prepared by the method described above.

[0036] The inventors of the present invention speculate that this may be because the diatomaceous earth treated with ammonium salt can effectively prevent the (Keggin-type) heteropoly acid from reacting with silicon in the diatomaceous earth, thereby avoiding destruction of the structure of the (Keggin-type) heteropoly acid. As a result, the prepared catalyst has a higher catalytic performance for oxidizing olefinic aldehydes to prepare olefinic acids, and the catalyst has excellent stability.

[0037] According to the present invention, preferably, the heteropolyacid includes phosphorus, vanadium and molybdenum.

[0038] According to the present invention, preferably, the heteropoly acid is composed of A a B b C c P x V y Mo 12 O z , wherein P, V, Mo, and O represent phosphorus, vanadium, molybdenum, and oxygen, respectively; A is at least one of iron, cobalt, nickel, zinc, chromium, copper, magnesium, manganese, germanium, bismuth, zirconium, silver, barium, gallium, cerium, selenium, silicon, boron, tungsten, and lanthanide elements other than promethium; B is at least one of arsenic, tellurium, and antimony; C is an alkali metal element and / or NH4 + ; a, b, c, x, y and z are the atomic ratios of the elements, wherein a is 0-3, b is 0-3, c is 0-3, preferably 0.01-3, x is 0.5-3, y is 0.01-3, and z is the atomic ratio of oxygen element required to satisfy the valence of the above-mentioned components.

[0039] According to the present invention, preferably, the alkali metal element includes at least one of sodium, potassium, rubidium and cesium.

[0040] According to the present invention, preferably, the specific surface area of ​​the catalyst is 20-60m 2 / g.

[0041] According to the present invention, preferably, the ammonium content in the ammonium-modified diatomaceous earth is 1-5% by weight, for example, it can be 1% by weight, 1.5% by weight, 2% by weight, 2.5% by weight, 3% by weight, 3.5% by weight, 4% by weight, 4.5% by weight, 5% by weight, and a range consisting of any two of the above.

[0042] According to the present invention, the catalyst contains mesopores and micropores. Preferably, the average pore size of the mesopores in the catalyst is 3-4.6 nm, and the pore volume occupied by the mesopores accounts for 90-100% of the total pore volume. In the present invention, the average pore size of the mesopores in the catalyst can be 3 nm, 3.2 nm, 3.4 nm, 3.6 nm, 3.8 nm, 4 nm, 4.2 nm, 4.4 nm, 4.6 nm, and a range consisting of any two of the above points.

[0043] In the present invention, the percentage of the pore volume occupied by mesopores to the total pore volume can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, and the range formed by any two of the above points.

[0044] According to the present invention, preferably, the content of the carrier is 20-70% by weight based on the total weight of the catalyst. The content of each component in the catalyst of the present invention is calculated based on the feed amount.

[0045] According to the present invention, preferably, based on the total weight of the catalyst, the content of the heteropolyacid is 30-80 wt%, for example, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, and a range consisting of any two of the above.

[0046] The present invention also provides a method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, comprising: loading a heteropoly acid on ammonium-modified diatomaceous earth, preferably, the heteropoly acid contains phosphorus, vanadium and molybdenum.

[0047] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, preferably, the amount of the ammonium-modified diatomaceous earth and the heteropoly acid is such that the content of the heteropoly acid in the obtained catalyst is 30-80% by weight.

[0048] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, preferably, the ammonium-modified diatomaceous earth and the heteropoly acid are used in such an amount that the content of the ammonium-modified diatomaceous earth in the obtained catalyst is 20-70% by weight.

[0049] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, the loading method is not particularly limited and can be a conventional choice in the art, as long as the Keggin-type heteropoly acid can be loaded on the carrier, for example, an impregnation method, a kneading method, a coating method, etc. can be used. Preferably, the loading method includes: contacting ammonium-modified diatomaceous earth with a heteropolyacid solution, and then calcining the solid phase product obtained by the contact to obtain the catalyst.

[0050] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, preferably, the contact temperature is not higher than 150°C, more preferably 40-100°C, and the contact time is 4-48h, more preferably 8-24h.

[0051] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, preferably, the calcination temperature is 300-390° C. and the calcination time is 2-10 h.

[0052] According to the method for preparing a catalyst having the function of olefinic acid production by oxidizing olefinic aldehydes of the present invention, preferably, the loading method further comprises: solid-liquid separation and drying of the mixture after contact between the ammonium-modified diatomaceous earth and the heteropolyacid solution, wherein the drying method can be one of rotary evaporation drying, freeze drying, oven drying and spray drying.

[0053] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid of the present invention, preferably, the heteropolyacid solution contains a phosphorus source, a vanadium source and a molybdenum source; wherein the molar ratio of the phosphorus source, the vanadium source and the molybdenum source is 0.5-3:0.01-3:12, wherein the phosphorus source is calculated as phosphorus element, the vanadium source is calculated as vanadium element, and the molybdenum source is calculated as molybdenum element.

[0054] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid of the present invention, the phosphorus source can be any substance that can provide phosphorus element. Preferably, the phosphorus source includes at least one of phosphoric acid, monoammonium hydrogen phosphate, diammonium hydrogen phosphate and triammonium phosphate, more preferably phosphoric acid.

[0055] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, the vanadium source can be any substance capable of providing vanadium element. Preferably, the vanadium source includes vanadium pentoxide and / or ammonium metavanadate, more preferably vanadium pentoxide.

[0056] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid of the present invention, the molybdenum source can be any substance that can provide the molybdenum element. Preferably, the molybdenum source includes at least one of molybdenum oxide, ammonium molybdate and molybdic acid, and more preferably molybdenum oxide.

[0057] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, preferably, the heteropolyacid solution further contains component A, component B and component C, wherein the molar ratio of component A, component B and component C is 0-3:0-3:0.01-3 calculated on an element basis.

[0058] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid of the present invention, preferably, component A includes at least one of an iron source, a cobalt source, a nickel source, a zinc source, a chromium source, a copper source, a magnesium source, a manganese source, a germanium source, a bismuth source, a zirconium source, a silver source, a barium source, a gallium source, a cerium source, a selenium source, a silicon source, a boron source, a tungsten source and a lanthanide metal source other than promethium.

[0059] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid of the present invention, preferably, component B comprises at least one of an arsenic source, a tellurium source and an antimony source.

[0060] According to the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, component C preferably comprises an alkali metal source and / or an ammonium source. More preferably, the alkali metal source comprises at least one of a sodium source, a potassium source, a rubidium source and a cesium source.

[0061] In the method for preparing a catalyst having the function of oxidizing olefinic aldehyde to olefinic acid in the present invention, the component A, component B and component C can be independently any substance capable of providing the above-mentioned element, for example, the hydroxide, nitrate, sulfate, chloride, acetate, carbonate, oxide of the element, or an acid containing the element. The cesium source can be cesium nitrate, the copper source can be copper nitrate, the selenium source can be selenic acid, the zinc source can be zinc acetate, the antimony source can be antimony oxide, the tellurium source can be telluric acid, the germanium source can be germanium oxide, the potassium source can be potassium hydroxide, the arsenic source can be arsenic acid, and the ammonium source can be ammonium carbonate.

[0062] In the present invention, the preparation method of the heteropolyacid solution can be a conventional method in the art, for example, method 1: the method for preparing a Keggin type heteropolyacid solution comprises: heating an aqueous solution containing a phosphorus source, a vanadium source and a molybdenum source at 50-150°C (stirring in an oil bath) for 0.5-12h to obtain a Keggin type heteropolyacid solution. Method 2: the method for preparing a Keggin type heteropolyacid solution comprises: (1) heating an aqueous solution containing a phosphorus source, a vanadium source and a molybdenum source at 50-150°C (stirring in an oil bath) for 0.5-12h to obtain a solution A; (2) mixing a solution B containing component C with a solution A and heating at 50-150°C (stirring in an oil bath) for 0.5-12h to obtain a Keggin type heteropolyacid solution. Method 3: The method for preparing a Keggin-type heteropolyacid solution comprises: (1) heating an aqueous solution containing a phosphorus source, a vanadium source and a molybdenum source at 50-150°C (stirring in an oil bath) for 0.5-12 h to obtain a liquid A; (2) mixing a liquid B containing component C with a liquid A and heating them at 50-150°C (stirring in an oil bath) for 0.5-12 h to obtain a liquid C; (3) mixing a liquid D containing component A and / or component B with a liquid C and heating them at 50-150°C (stirring in an oil bath) for 0.5-12 h to obtain a Keggin-type heteropolyacid solution.

[0063] A sixth aspect of the present invention provides a method for preparing methacrylic acid by oxidizing methacrolein, wherein the method comprises: in the presence of the above-mentioned catalyst, allowing methacrolein to undergo an oxidation reaction with an oxidant, wherein the active component in the catalyst is a heteropolyacid.

[0064] According to the present invention, preferably, the alkenal is C3-C10 The aldehyde is more preferably methacrolein.

[0065] According to the present invention, preferably, the oxidation reaction conditions include: a temperature of 280-320°C, a weight space velocity of olefinic aldehyde of 600-1600h -1 .

[0066] According to the present invention, preferably, the oxidant used in the oxidation reaction is oxygen.

[0067] According to the present invention, preferably, the molar ratio of the olefinic aldehyde to oxygen is 1:0.5-5.

[0068] According to the present invention, preferably, the method further comprises causing the olefinic aldehyde to undergo an oxidation reaction to generate olefinic acid in the presence of water and / or an inert gas. The inert gas may be an inert gas (e.g., at least one of helium, neon, argon and krypton) and / or nitrogen. The molar ratio of the olefinic aldehyde to water and the inert gas is 1:1.5-10:10-40.

[0069] According to the present invention, preferably, before the oxidation reaction, the catalyst is further formed. More preferably, the forming method can be a forming method commonly used in the art, for example, stamping forming, extrusion forming, spraying forming, tablet forming, granulation forming, kneading forming, etc.

[0070] According to a particularly preferred embodiment of the present invention, the method for preparing a supported heteropolyacid catalyst comprises:

[0071] (1) Add diatomite to NH4Cl solution, stir in a water bath at 70-80°C for 4-4.5 hours, filter, wash and dry to obtain a first modified diatomite. Then add the first modified diatomite to NH4Cl solution, stir in a water bath at 70-80°C for 4-4.5 hours, filter, wash and dry to obtain ammonium modified diatomite. The concentration of NH4Cl solution is 0.8-1 mol / L; in each ammonium modification process, the amount of ammonium modification reagent (NH4Cl) in terms of nitrogen element is 0.9-1 mol per 100 g of diatomite.

[0072] (2) 20-22 g of MoO3, 1.1-1.2 g of V2O5 and 1.2-1.3 g of H3PO4 are dissolved in 150-160 ml of water, and refluxed at 100-120° C. with stirring for 4-8 hours to form liquid A; 6.8-7 g of cesium nitrate is dissolved in water to form liquid B; liquid B is added dropwise to liquid A, and refluxed at 100-120° C. with stirring for 1-2 hours to obtain liquid C; 1.4-1.5 g of copper nitrate, 2-2.1 g of selenic acid, 1.3-1.4 g of zinc acetate, 3.4-3.5 g of antimony trioxide and 2.7-2.8 g of telluric acid are dissolved in water to form liquid D, and liquid D is added dropwise to liquid C, and refluxed at 100-120° C. with stirring for 5-6 hours to obtain heteropolyacid solution E.

[0073] (3) Add 33-35 g of ammonium-modified diatomaceous earth to solution E, stir at 60-65° C. for 12-15 h, and then dry and calcine at 370-380° C. for 3-4 h.

[0074] The present invention will be described in detail below by way of examples. In the following examples,

[0075] The reaction products were detected by gas chromatography, and the conversion of methacrolein and the selectivity of methacrylic acid were calculated;

[0076] Methacrolein conversion rate (%) = the number of moles of methacrolein consumed in the reaction / the number of moles of methacrolein added to the reactor × 100%;

[0077] Selectivity of methacrylic acid (%) = the number of moles of methacrylic acid generated in the reaction / the number of moles of methacrolein consumed in the reaction × 100%;

[0078] The content of silicon oxide in the diatomite is 99.7% by weight, and the specific surface area of ​​the diatomite is 45 m 2 / g.

[0079] The specific surface areas in the following examples were obtained using nitrogen adsorption and desorption tests.

[0080] The ammonium content in the ammonium-modified diatomaceous earth is obtained by thermogravimetry. The specific test method is to weigh 15 mg of ammonium-modified diatomaceous earth, put it into a thermogravimetric instrument, and raise the temperature to 800°C at a rate of 10°C per minute. The weight loss between 300°C and 600°C is the ammonium content.

[0081] Preparation Example

[0082] This preparation example is used to illustrate the preparation method of heteropolyacid solution

[0083] 20.0gMoO3, 1.1gV2O5 and 1.3gH3PO4 were dissolved in 150ml deionized water, refluxed at 100℃ with stirring for 8h to form liquid A; 6.8g cesium nitrate was dissolved in 20ml deionized water to form liquid B; liquid B was added dropwise to liquid A, and refluxed with stirring for 1h to obtain liquid C; 1.4g copper nitrate, 2.1g selenic acid, 1.3g zinc acetate, 3.4g antimony trioxide and 2.7g telluric acid were dissolved in 40ml water to form liquid D, liquid D was added dropwise to liquid C, and refluxed with stirring for 5h to obtain heteropolyacid solution E.

[0084] Example 1

[0085] (1) The diatomite is added to a 1 mol / L NH4Cl solution for ammonium modification, stirred in a 70°C water bath for 4 hours, filtered, washed, and dried to obtain a first-modified diatomite. Then the first-modified diatomite is added to a 1 mol / L NH4Cl solution, stirred in a 70°C water bath for 4 hours, filtered, washed, and dried to obtain ammonium-modified diatomite. In each ammonium modification process, the amount of ammonium salt (NH4Cl) in terms of nitrogen element is 1 mol per 100 g of diatomite. Among them, the ammonium and silicon oxide contents in the ammonium-modified diatomite and the specific surface area of ​​the ammonium-modified diatomite are shown in Table 1.

[0086] SEM image of diatomite before ammonium modification Figure 1 As shown, the SEM image of ammonium modified diatomite is as follows Figure 2 As shown by Figure 1-2 It can be seen that the surface of diatomite becomes rougher after ammonium modification. The thermogravimetric curve of ammonium modified diatomite is shown in Figure 3 As shown by Figure 3 It can be seen that the ammonium content in the ammonium-modified diatomaceous earth is 4 wt %.

[0087] (2) 35 g of ammonium-modified diatomaceous earth was added to the solution E obtained in the preparation example, stirred at 60° C. for 12 h, then evaporated to dryness by rotary evaporation, calcined (at 380° C. for 4 h), tableted, and sieved to obtain a 20-40 mesh heteropolyacid@diatomaceous earth catalyst. The catalyst composition was Cs3Cu 0.5 Se 0.5 Zn 0.5 Sb2TePMo 12 V@diatomite. The Keggin-type heteropoly acid content in the catalyst and the specific surface area of ​​the catalyst are shown in Table 1.

[0088] (3) 3 g of the catalyst was loaded into a fixed bed reactor of a stainless steel tube with a diameter of 10 mm and a length of 800 mm, and the reaction was carried out at 310° C. and normal pressure. The molar ratio of methacrolein: oxygen: water: nitrogen was 1:2.5:4:15, and the reaction space velocity was 1100 h -1The conversion rate of methacrolein and the selectivity of methacrylic acid after 6h and 100h of reaction are shown in Table 2, respectively. The XRD patterns of the catalyst before and after 6h of reaction are shown in Table 2. Figure 4 As shown in the figure, it can be seen that the characteristic peak of the Keggin structure of the heteropolyacid does not change before and after the reaction, indicating that the Keggin structure of the heteropolyacid is not destroyed.

[0089] The average pore diameter of the mesopores in the catalyst is 3.8 nm, and the pore volume occupied by the mesopores in the catalyst accounts for 92% of the total pore volume.

[0090] Example 2

[0091] (1) The diatomite is added to a 1 mol / L NH4NO3 solution for ammonium modification, stirred in a 100°C water bath for 12 hours, filtered, washed, and dried to obtain a first-modified diatomite. The first-modified diatomite is then added to a 1 mol / L NH4NO3 solution, stirred in a 100°C water bath for 12 hours, filtered, washed, and dried to obtain ammonium-modified diatomite. In each ammonium modification process, the amount of ammonium salt (NH4NO3) used in terms of nitrogen element is 2 mol per 100 g of diatomite. The ammonium and silicon oxide contents in the ammonium-modified diatomite and the specific surface area of ​​the ammonium-modified diatomite are shown in Table 1.

[0092] (2) 10 g of ammonium-modified diatomaceous earth was added to the solution E obtained in the preparation example, stirred at 100° C. for 4 h, then evaporated to dryness by rotary evaporation, calcined (at 380° C. for 4 h), tableted, and sieved to obtain a 20-40 mesh heteropolyacid@diatomaceous earth catalyst. The catalyst composition was Cs3Cu 0.5 Se 0.5 Zn 0.5 Sb2TePMo 12 V@diatomite. The Keggin-type heteropoly acid content in the catalyst and the specific surface area of ​​the catalyst are shown in Table 1.

[0093] (3) 3 g of the catalyst was loaded into a fixed bed reactor of a stainless steel tube with a diameter of 10 mm and a length of 800 mm, and the reaction was carried out at 320° C. and normal pressure. The molar ratio of methacrolein: oxygen: water: nitrogen was 1:2:2:10, and the reaction space velocity was 600 h -1 The methacrolein conversion and methacrylic acid selectivity after the reaction was carried out for 6 h and 100 h are shown in Table 2, respectively.

[0094] Example 3

[0095] (1) The diatomite is added to a 0.1 mol / L (NH4)2SO4 solution for ammonium modification, stirred in a 25°C water bath for 48 hours, filtered, washed, and dried to obtain a first-modified diatomite. Then the first-modified diatomite is added to a 0.1 mol / L (NH4)2SO4 solution, stirred in a 25°C water bath for 48 hours, filtered, washed, and dried to obtain ammonium-modified diatomite. In each ammonium modification process, the amount of ammonium salt used in terms of nitrogen element is 0.2 mol per 100 g of diatomite. In particular, the ammonium and silicon oxide contents in the ammonium-modified diatomite and the specific surface area of ​​the ammonium-modified diatomite are shown in Table 1.

[0096] (2) 70 g of ammonium-modified diatomaceous earth was added to the solution E obtained in the preparation example, stirred at 40° C. for 48 h, then evaporated to dryness by rotary evaporation, calcined (at 380° C. for 4 h), tableted, and sieved to obtain a 20-40 mesh heteropolyacid@diatomaceous earth catalyst. The catalyst composition was Cs3Cu 0.5 Se 0.5 Zn 0.5 Sb2TePMo 12 V@diatomite. The Keggin-type heteropoly acid content in the catalyst and the specific surface area of ​​the catalyst are shown in Table 1.

[0097] (3) 3 g of the catalyst was loaded into a fixed bed reactor of a stainless steel tube with a diameter of 10 mm and a length of 800 mm, and the reaction was carried out at 308° C. and normal pressure. The molar ratio of methacrolein: oxygen: water: nitrogen was 1:4:6:30, and the reaction space velocity was 1600 h -1 The methacrolein conversion and methacrylic acid selectivity after the reaction was carried out for 6 h and 100 h are shown in Table 2, respectively.

[0098] Example 4

[0099] (1) The diatomite is added to a 1.5 mol / L NH4NO3 solution for ammonium modification, stirred in a 70°C water bath for 4 hours, filtered, washed, and dried to obtain a first-modified diatomite. Then the first-modified diatomite is added to a 1.5 mol / L NH4NO3 solution, stirred in a 70°C water bath for 4 hours, filtered, washed, and dried to obtain ammonium-modified diatomite. In each ammonium modification process, the amount of ammonium salt used in terms of nitrogen element is 1.5 mol per 100 g of diatomite. In particular, the ammonium and silicon oxide contents in the ammonium-modified diatomite and the specific surface area of ​​the ammonium-modified diatomite are shown in Table 1.

[0100] (2) 20 g of ammonium-modified diatomaceous earth was added to the solution E obtained in the preparation example, stirred at 40° C. for 48 h, then evaporated to dryness by rotary evaporation, calcined (at 380° C. for 4 h), tableted, and sieved to obtain a 20-40 mesh heteropolyacid@diatomaceous earth catalyst. The catalyst composition was Cs3Cu 0.5 Se 0.5 Zn 0.5 Sb2TePMo 12 V@diatomite. The Keggin-type heteropoly acid content in the catalyst and the specific surface area of ​​the catalyst are shown in Table 1.

[0101] (3) 3 g of the catalyst was loaded into a fixed bed reactor of a stainless steel tube with a diameter of 10 mm and a length of 800 mm, and the reaction was carried out at 305° C. and normal pressure. The molar ratio of methacrolein: oxygen: water: nitrogen was 1:2:5:16, and the reaction space velocity was 1205 h -1 The methacrolein conversion and methacrylic acid selectivity after the reaction was carried out for 6 h and 100 h are shown in Table 2, respectively.

[0102] Example 5

[0103] (1) The diatomite is added to a 1.5 mol / L NH4Cl solution for ammonium modification, stirred in a 70°C water bath for 4 hours, filtered, washed, and dried to obtain a first-modified diatomite. Then the first-modified diatomite is added to a 1.5 mol / L NH4Cl solution, stirred in a 70°C water bath for 4 hours, filtered, washed, and dried to obtain ammonium-modified diatomite. In each ammonium modification process, the amount of ammonium salt used in terms of nitrogen element is 1.5 mol per 100 g of diatomite. In particular, the ammonium and silicon oxide contents in the ammonium-modified diatomite and the specific surface area of ​​the ammonium-modified diatomite are shown in Table 1.

[0104] (2) 20 g of ammonium-modified diatomaceous earth was added to the solution E obtained in the preparation example, stirred at 40° C. for 48 h, then evaporated to dryness by rotary evaporation, calcined (at 380° C. for 4 h), tableted, and sieved to obtain a 20-40 mesh heteropolyacid@diatomaceous earth catalyst. The catalyst composition was Cs3Cu 0.5 Se 0.5 Zn 0.5 Sb2TePMo 12 V@diatomite. The Keggin-type heteropoly acid content in the catalyst and the specific surface area of ​​the catalyst are shown in Table 1.

[0105] (3) 3 g of the catalyst was loaded into a fixed bed reactor of a stainless steel tube with a diameter of 10 mm and a length of 800 mm, and the reaction was carried out at 295° C. and normal pressure. The molar ratio of methacrolein: oxygen: water: nitrogen was 1:3.5:4.5:18, and the reaction space velocity was 905 h -1The methacrolein conversion and methacrylic acid selectivity after the reaction was carried out for 6 h and 100 h are shown in Table 2, respectively.

[0106] Comparative Example 1

[0107] The method of Example 1 was followed, except that step (1) was not included, i.e., diatomaceous earth not modified with ammonium was added to solution E. The XRD patterns of the catalyst before and after the reaction for 6 h were as follows: Figure 5 As shown in the figure, it can be seen that the characteristic peak of MoO3 appears in the XRD spectrum of the catalyst after the reaction, indicating that the Keggin structure of the heteropolyacid is destroyed and a new species MoO3 is produced.

[0108] The average pore diameter of the mesopores in the catalyst is 2.8 nm, and the pore volume occupied by the mesopores in the catalyst accounts for 83% of the total pore volume.

[0109] Comparative Example 2

[0110] The method of Example 1 is followed, except that in step (1), NH4Cl is replaced by N-[3-(trimethoxysilyl)propyl]ethylenediamine, and the amount of N-[3-(trimethoxysilyl)propyl]ethylenediamine used is half the molar amount of NH4Cl.

[0111] The average pore diameter of the mesopores in the catalyst is 2.5 nm, and the pore volume occupied by the mesopores in the catalyst accounts for 80% of the total pore volume.

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116] It can be seen from the results in Table 1 that, compared with the comparative example, the catalyst of the embodiment of the present invention still has a higher methacrolein conversion rate and methacrylic acid selectivity after 100 hours of reaction; while the methacrolein conversion rate of the catalyst of comparative example 1-2 has dropped to below 41% and the methacrylic acid selectivity has dropped to below 36% after 18 hours of reaction, indicating that the catalyst of the present invention has excellent stability.

[0117] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. An ammonium-modified diatomaceous earth, characterized in that: The ammonium content of the ammonium-modified diatomaceous earth is 1-5% by weight.

2. The ammonium-modified diatomaceous earth according to claim 1, wherein The content of ammonium in the ammonium-modified diatomaceous earth is 4-5% by weight.

3. The ammonium-modified diatomaceous earth according to claim 1, wherein The specific surface area of ​​the ammonium modified diatomaceous earth is 20-60m 2 / g, preferably 22-55m 2 / g.

4. A method for preparing ammonium-modified diatomaceous earth, characterized in that: The method comprises: using ammonium salt to perform ammonium modification on diatomite.

5. The method according to claim 4, wherein: The ammonium salt includes at least one of NH4Cl, NH4NO3, (NH4)2SO4, (NH4)2CO3, NH4HCO3, (NH4)3PO4, (NH4)2HPO4 and NH4H2PO4; And / or, the specific surface area of ​​the diatomaceous earth is 20-60m 2 / g, preferably 22-55m 2 / g.

6. The method according to claim 4, wherein: The ammonium modification conditions include: temperature of 25-150°C and time of 4-96h; And / or, the amount of the ammonium salt calculated as nitrogen element is 0.1-4 mol per 100 g of diatomaceous earth.

7. Ammonium-modified diatomaceous earth prepared by the method according to any one of claims 4 to 6.

8. Use of the ammonium-modified diatomaceous earth according to any one of claims 1 to 3 and 7 and / or the ammonium-modified diatomaceous earth prepared by the method according to any one of claims 4 to 6 as a carrier in the preparation of a catalyst for the oxidation of olefinic aldehyde to olefinic acid.

9. A catalyst having the function of oxidizing olefinic aldehyde to olefinic acid, characterized in that: The catalyst comprises ammonium-modified diatomaceous earth and a heteropolyacid supported on the ammonium-modified diatomaceous earth, wherein the ammonium-modified diatomaceous earth is the ammonium-modified diatomaceous earth described in any one of claims 1-3 and 7 and / or the ammonium-modified diatomaceous earth prepared by the method described in any one of claims 4-6.

10. A method for preparing methacrylic acid by oxidizing methacrolein, wherein: The method comprises: in the presence of the catalyst described in claim 8 or 9, allowing methacrolein to undergo an oxidation reaction with an oxidant, wherein the active component in the catalyst is a heteropoly acid.

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