CN102989479A - Selective oxidation catalyst and preparation method thereof - Google Patents

Abstract

The invention relates to a selective oxidation catalyst and a preparation method thereof. The invention relates to a multi-metal oxide catalyst and a preparation method thereof, wherein the catalyst contains a plurality of metal oxides as active components, and the active components can be represented by the following general formula: mo_aV_bNi_cCu_dSi_eA_fB_gO_x(I)；Mo_aV_bNi_cCu_dO_m (II)；Mo_aV_bSi_eAl_iO_n(III); the catalyst is suitable for producing corresponding unsaturated acid by selective oxidation of acrolein or methacrolein, can effectively inhibit the formation of higher hot spots due to the initial contact of propylene and the catalyst, and improves the selectivity of the catalyst.

Description

A kind of selective oxidation catalyst and its preparation method

technical field

The invention relates to a multi-metal oxide catalyst for the selective oxidation of acrolein or methacrolein to produce the corresponding unsaturated acid and a preparation method thereof. More specifically, the present invention relates to a multi-metal oxide catalyst with different catalytic activities coated with thermal material for multiple times, which is used to catalyze the oxidation of acrolein to acrylic acid or the oxidation of methacrolein to methacrylic acid.

Background technique

The oxidation of propylene to acrylic acid is a strong exothermic reaction. The oxidation reaction of propylene with air under the action of a catalyst first produces acrolein, and then continues to oxidize acrolein to form acrylic acid. Since the reaction is a strongly exothermic reaction, different degrees of heat zones will be generated in the macroscopic particle phase of the catalyst, and the instantaneous heat generated will continue to accumulate, which will lead to the sublimation and loss of the active components of the catalyst, which will reduce the activity of the catalyst and lead to excessive The oxidation reaction aggravates the formation of by-products, and even causes a runaway reaction, which sinters the catalyst.

"Research Progress on Oxidative Synthesis of Acrylic Acid Process and Catalyst" (Petrochemical Industry, Volume 39, No. 7, 2010) reports that the emergence of hot spots will also damage the catalyst and shorten the service life of the catalyst. Taking an 80,000-ton/year acrylic acid plant as an example, the number of tubes in the reactor for propylene oxidation to acrolein and the reactor for acrolein to acrylic acid are both about 25,000, requiring about 50 tons of acrolein and acrylic acid catalysts each. Affected by the raw material market and the acrylic acid market, the cost of catalysts per ton of acrolein and acrylic acid fluctuates accordingly, and the cost of the catalyst alone requires at least tens of millions of yuan. There are tens of thousands of reaction tubes, and it is difficult to ensure that the catalyst is not filled empty. If the catalyst is sintered quickly because of too high a hot spot, and the catalyst is replaced again in a short period of time, it can be expected that the economic loss will be huge; in addition, for acrylic acid As far as production is concerned, it should be carried out under low temperature conditions as much as possible, because the reaction requires salt baths to be heated to about 250°C, and the energy consumption for maintaining production is also a huge expense; due to the generation of hot spots, the reaction tubes are required to be resistant to high temperatures, and for tens of thousands As far as the reaction tube is concerned, the cost of the tube is a very large cost. Therefore, if the occurrence of hot spots in the catalyst bed can be effectively suppressed, huge economic benefits can be brought to large-scale industrial production.

At present, as a method of suppressing the hot spots in the catalyst layer, various schemes have been proposed, such as preparing catalysts with different activities, loading catalysts with low activity in the inlet part with high raw material concentration, and filling the reactor with low raw material concentration. The outlet section is loaded with a highly active catalyst, the method is shown below. Such as: CN1210511A, prepare a variety of supported catalysts with different activity types or place them in the reaction tube after dilution in different proportions to minimize the temperature of the hot zone; CN1572772A, adopt two layers with different activities arranged in layers along the reaction direction Or the method of two or more catalyst layers, using alumina balls as the diluent material mixed into the catalyst, changing the mixing ratio of the catalyst and alumina balls to obtain catalyst layers with different activities. CN1672790A provides a kind of catalyst of gas-phase oxidation of acrolein to produce acrylic acid, said catalyst contains molybdenum and vanadium, and contains at least one volatile catalyst poisoning component, and its amount is measured as 10 to 100ppb quality by ion chromatography, and this catalyst can reduce The temperature of the overheated part and the reduction in the efficiency of the reaction that inhibits thermal degradation. Specifically, by including a specific amount of volatile toxic components in a previously highly active catalyst, the catalytic activity temporarily decreases and the temperature of the overheated portion can be lowered.

CN200410007263.1 provides a catalyst with excellent activity, selectivity, and lifetime and long-term stable performance even under the condition of forming a hot spot, and a method for preparing acrylic acid using the catalyst. The catalyst is represented by the following general formula (1) Mo _a V _b W _c Cu _d A _e B _f C _g O _x . A is at least one selected from cobalt, nickel, iron, lead, and bismuth, B is at least one selected from antimony, niobium, and tin, and C is selected from silicon, aluminum, titanium, and zirconium. At least one, a, b, c, d, e, f, g, x respectively represent the atomic ratio of Mo, V, W, Cu, A, B, C, O, when a=12, 2≤b≤15 , 0<c≤10, 0<d≤6, 0<e≤30, 0≤f≤6, 0≤g≤60, x is a value determined by the oxidation state of each element. The catalyst cannot effectively suppress the formation of hot spots in the catalyst bed. Under relatively high hot spot conditions, the reaction device is required to have super high temperature resistance, and the subsequent separation and absorption process operating costs are also very high. CN200410048021.7 discloses a composite metal oxide catalyst for the selective oxidation reaction between a gas containing unsaturated aldehyde and a gas containing molecular oxygen in the gas phase, especially a gas phase of acrolein or methacrolein Composite metal oxide catalysts for selective oxidation to produce corresponding acrylic acid or methacrylic acid. The catalyst is a composite oxide composed of (1) molybdenum, vanadium, copper main active components and (2) essential stable components consisting of at least antimony and titanium, and (3) nickel, iron, silicon, aluminum, alkali metals, and alkaline earth metals. Among them, ② and ③ are composite oxides that can be calcined in the range of 120°C to 900°C. The catalyst exhibits high activity and long-term stability with good selectivity. CN03121882.2 discloses a composite multi-metal oxide catalyst and its preparation method, which is especially suitable for the gas-phase selective oxidation of acrolein to produce acrylic acid. The catalyst composition is Mo _a V _b Cu _c Te _d X ¹ _e X ² _f X ³ _g X ⁴ _h X ⁵ _i O _x , X ¹ is at least one element selected from tungsten and niobium, X ² is at least one element selected from magnesium, calcium, strontium and barium, X ³ is at least selected from iron, cobalt and nickel ^X4 is at least one element selected from silicon, aluminum and titanium, ^X5 is at least one element selected from antimony, tin and bismuth, the catalyst contains at least molybdenum, vanadium and copper, and then add the necessary Tellurium stabilizes molybdenum oxide and copper molybdate crystals, the main active components of the catalyst, and has sustained high activity and high selectivity during catalytic reactions, delaying the deactivation of the catalyst due to the loss of molybdenum.

There is a problem in the above-mentioned methods of suppressing hot spots. The catalyst filled in the reaction tube is diluted in various forms from the inlet to the outlet. Not only is it very troublesome to load, disassemble, separate, and recover the catalyst, but it will also reduce the utilization of the catalyst. rate, especially in the industry, the activity of the long-term operation catalyst decreases faster, which affects the life of the catalyst. Furthermore, due to the high initial activity of the catalyst, the catalyst is generally diluted in different proportions and placed in the reaction tube in sections to minimize the temperature of the hot zone. The disadvantage of this dilution method is that after the catalyst is diluted, Even if the activity of the catalyst decreases after a certain period of operation, the catalyst can no longer provide higher activity, that is to say, the actual reactivity of the catalyst is permanently reduced by dilution, unless it is reactivated and refilled.

Contents of the invention

The invention provides a catalyst with high reaction activity and selectivity and long service life, which can be used to catalyze the oxidation of acrolein to produce acrylic acid. More specifically, the present invention relates to a multi-metal oxide catalyst for the selective oxidation of acrolein to produce acrylic acid and a preparation method thereof, which is characterized in that the catalyst has a three-layer structure.

A multi-metal oxide catalyst is characterized in that the catalyst has a three-layer structure, and the main components of each layer from the inside to the outside are represented by general formulas (I), (II) and (III) respectively

Mo _a V _b Ni _c Cu _d Si _e A _r B _g O _x (I)

Mo _a V _b Ni _c Cu _d O _m (II)

Mo _a V _b Si _e Al _i O _n (III)

Wherein: Mo is molybdenum, V is alum, Ni is nickel, Cu is copper, Si is silicon, Al is aluminum, A is at least one element selected from iron, cobalt, and manganese; B is selected from tungsten, niobium, At least one element in phosphorus; O is oxygen; a, b, c, d, e, f, g, i respectively represent the atomic ratio of each element, wherein a=12, b is a number of 2-10, preferably 4 -8; c is a number of 1-10, d is a number of 1-7, preferably 1.5-5; e is a number of 2-8, f is a number of 1-3, g is a number of 1-3 A number, i is a number from 1-15; x, m and n are values determined by the oxygen of each oxide.

The present invention also provides the preparation method of the described catalyst with a three-layer structure, comprising the steps of:

The first step: preparation of catalyst inner layer matrix

(1) dissolving and mixing the compounds containing Mo, V, Ni, Cu and Si uniformly to form active component slurry (a);

(2) Dissolving and mixing the various elemental component compounds involved in A _f B _g in the general formula (I) again, as auxiliary material slurry (b);

(3) Co-precipitate the active component slurry (a) and the auxiliary material slurry (b), heat and dry, granulate and shape, and roast to obtain the catalyst inner layer matrix;

The second step: prepare the active component powder in the middle layer of the catalyst

Dissolving and mixing the compounds containing Mo, V, Ni and Cu uniformly, drying, calcining and grinding after the co-precipitation reaction to make the active component powder (c) in the middle layer of the catalyst;

Step 3: Preparation of catalyst outer layer active component powder

Dissolving and mixing the compounds containing Mo, V, Si and Al uniformly, drying, calcining and grinding to make the catalyst outer layer active component powder (d);

Step 4: Preparation of Catalyst

The active component powder (c) in the middle layer of the catalyst and the active component powder (d) in the outer layer of the catalyst are coated on the matrix of the inner catalyst layer in sequence from the inside to the outside to make a catalyst product.

In order to improve the activity and stability of the catalyst, it is best to heat-treat at 350-460°C for 3-10 hours after the catalyst inner layer matrix is formed and the active component powders of the middle layer and outer layer are coated.

The coating of every layer of active component powder of the catalyst of the present invention is preferably carried out at the same temperature, that is, the middle layer active component powder (c) and the outer layer active component powder (d) are coated At this time, the catalyst inner layer matrix, middle layer active component powder (c) and outer layer active component powder (d) are preferably kept at the same temperature, and the temperature range is preferably 40-80°C. Using this method of coating with hot material can make the adhesion of each layer of the catalyst stronger, and it is not easy to crack during the subsequent drying and heat treatment process, and the coating effect is better.

When the three-layer multi-metal oxide catalyst of the present invention is coated, it is preferable to use a binder to make the catalysts of each layer bond more firmly. Spray the binder to infiltrate the surface while the catalyst in the inner layer is rolling, and then spray the prepared catalyst powder in the middle and outer layers. The binder is one selected from water, silica sol, aluminum sol, ethanol, and glycerol. one or more species.

The inner matrix of the present invention is preferably made into a spherical shape with a diameter of 3 to 4.5 mm. If the sphere is too large, it is easy to crack after firing. The thickness of the active component powder in the middle layer coated on the inner matrix is 0.5-2 mm, preferably 0.5-1.2 mm, the thickness of the active component powder in the outer layer is 0.5-2 mm, preferably 0.5-1.0 mm, and the catalyst layer It is easy to crack when it is too thick and baked. In order to avoid cracking, it is best to dry it at 90-120°C after coating.

The precursors of the catalyst active components of the present invention may be nitrates, ammonium salts, sulfates, oxides, hydroxides, chlorides, acetates and the like of various elements. Try not to use all nitrates as active components. The oxides produced during roasting pollute the atmosphere, and are not easy to shape, and the production progress is slow, but nitrates are easy to dissolve. Nitrates are best used together with other forms of compounds, which are easy to shape. Accelerate productivity.

The active powder material of the inner layer of the catalyst of the present invention is usually preferably prepared by an extrusion molding method to complete the preparation of the catalyst inner layer matrix.

The multi-metal oxide catalyst of the present invention can be used directly or diluted with an inert carrier. The inert carrier involved may be alumina powder (pseudoboehmite, corundum powder), aluminum nitrate, silicon dioxide (silica powder) and the like.

The present invention has a three-layer structure, and the inner layer can also be called the inner layer matrix.

The present invention also provides a method for the selective oxidation of acrolein to produce acrylic acid: a fixed-bed single-tube reactor is adopted; the reaction raw materials acrolein, water and air are preheated by a preheater above 150°C and enter the reactor, heated in a salt bath, and reacted The process conditions are: salt bath temperature 245-265°C, preferably 250-260°C; space velocity 1400-2200h ^-1 , preferably 1500-1800h ^-1 , feed composition: acrolein 7-14% by volume, water vapor 10-22 %, 10-18% by volume of air, and 60-73% by volume of nitrogen; the above-mentioned three-layer multi-metal oxide catalyst is installed in the reactor. The conversion rate of acrolein is between 98.2% and 99.2%, and the selectivity of acrylic acid is between 88.0% and 90.5%. The hot spot temperature is between 279 and 290.

The present invention combines the problems that arise in the practical application of the catalyst, and then through a large number of experimental studies to obtain a method for effectively suppressing the excessive generation of hot spots, that is, under the condition of maintaining high selectivity and conversion rate, by preparing a multilayer catalyst with a three-layer structure Metal oxide catalyst, which makes the catalyst particles reduce some active components layer by layer from the bulk phase to the surface phase, that is to say, the catalyst increases the active components with different functions layer by layer from the surface phase to the bulk phase, and the outer layer not only plays the main active role In addition to the molybdenum and alum components, only the activity inhibitors silicon and aluminum are added, the active components are the least, and the corresponding activity is also the lowest. The high-concentration raw material gas first contacts with the outer layer of the catalyst, and the instantaneous reaction generates a lot of heat, which is relatively high. Active inner layer catalysts are not prone to hot spots. The active components in the middle layer and the inner layer increase sequentially, and their corresponding activity is also high, which has a dilution effect on a single catalyst particle, effectively inhibiting the formation of hot spots and the heat accumulation formed by the large amount of reaction by-products. In addition, the initial activity of the molybdenum-based composite metal oxide catalyst is high, and hot spots are easily generated in the early stage of the reaction, resulting in excessive oxidation. The three-layer multi-metal oxide catalyst in the present invention has few surface active components and low activity, can effectively suppress the generation of hot spots at the initial stage of reaction, and has good selectivity. Furthermore, after a certain period of operation, even if the activity of the outer surface of the catalyst has decreased, it is not necessary to unload the catalyst. Through simple activation treatment, the active substances in the middle and inner layer of the catalyst can play a supplementary role, so that the catalyst can run stably for a long time .

Catalyst performance indicators are defined as follows:

Acrolein conversion rate (%) = [total moles of acrolein reaction / moles of acrolein in raw materials] × 100

Acrylic acid selectivity (%) = [moles of acrolein converted to acrylic acid/total moles of acrolein reaction] × 100

Detailed ways

The following specific examples are used to illustrate the multi-metal oxide catalyst with three-layer structure and its preparation method, and the catalytic performance of the catalyst for the selective oxidation of acrolein to produce acrylic acid, but the scope of the present invention is not limited to these examples. Table 1 gives the names of the raw materials used for catalyst preparation.

Table 1. Raw material names, specifications and adoption standards

serial number name Specification adopt the standard Manufacturer 1 Ammonium molybdate A.R. GB/T657-93 Hefei Kehua Fine Chemicals 2 Ammonium metavanadate A.R. HG/T3445-2003 Beijing Shuanghuan Chemical Reagent Factory 3 Nickel nitrate A.R. HG/T3448-2003 Yixing Shensheng Catalyst Co., Ltd. 4 Copper nitrate A.R. HG/T3443-2003 Yixing Xuchi Chemical Co., Ltd.

Example 1:

Preparation of Catalyst 1

The first step: preparation of catalyst inner layer matrix

(1) Preparation of active component slurry (a)

In a 1-liter beaker, add 500 milliliters of deionized water, then add 133.2 grams of ammonium metavanadate and 302 grams of ammonium molybdate in turn, heat to dissolve and mix well, and this mixed salt solution is A. In another 200 ml beaker, add 80 ml of deionized water, under vigorous stirring, add 165.6 g of nickel nitrate and 172 g of copper nitrate successively, and heat to fully dissolve to obtain solution B. When the reaction temperature of solution A is adjusted to 60° C., the two solutions are mixed to obtain active component slurry (a).

(2) Preparation of auxiliary material slurry (b)

In a 500 ml beaker, add 100 ml of deionized water, under strong stirring and continuous heating, add 57.5 g of ferric nitrate, 76.7 g of ammonium paratungstate, and 25.6 g of silicon dioxide in sequence, stir and mix well.

(3) Preparation of catalyst inner layer matrix

The active component slurry (a) and the auxiliary slurry (b) are mixed for co-precipitation reaction to form a co-precipitation slurry, which is evaporated and concentrated to a semi-paste under continuous heating and strong stirring, and then dried in an oven at 100 ° C overnight, and then The resulting material is pulverized by a pulverizer, and sieved to obtain powder C passing through a 80-mesh sieve. Move the powder C to a kneader, continuously spray the mixed solution of deionized water and 40% silica sol, knead into a mud, and shape it into catalyst particles of φ5*5mm on the extruder-pelletizer. Calcined at 380° C. for 5 hours in a muffle furnace to obtain a catalyst product. The catalyst composition is Mo ₁₂ V ₈₀ Ni ₄₀ Cu ₅₀ Si _3.0 Fe ₁₀ W ₂₀ O _x .

The second step: prepare the active component powder in the middle layer of the catalyst

Under stirring conditions, add 85 grams of ammonium metavanadate and 256.7 grams of ammonium molybdate in 500 milliliters of deionized water, heat to dissolve and mix uniformly. This mixed salt solution is A. In another 200 ml beaker, add 105.7 g of nickel nitrate and 102.4 g of copper nitrate in 80 ml of deionized water successively under vigorous stirring, and heat to fully dissolve to obtain solution B. When the reaction temperature of liquid A was adjusted to 60°C, the two solutions were mixed and vigorously stirred. After the obtained slurry was dried, it was calcined at 390°C for 7 hours, and ground to make catalyst middle layer powder. The composition of the active components of the powder in the middle layer of the catalyst is Mo ₁₂ V ₆₀ Ni ₃₀ Cu ₃₅ O _m .

Step 3: Preparation of catalyst outer layer active component powder

Under stirring conditions, add 99.9 grams of ammonium metavanadate and 226.5 grams of ammonium molybdate in 500 milliliters of deionized water, heat to dissolve and mix evenly. This mixed salt solution is A. In another 200 ml beaker, add 80 ml of deionized water, add 34.2 g of silicon dioxide and 72.6 g of corundum powder successively under vigorous stirring, and heat to fully dissolve them to obtain solution B. The two solutions A and B were mixed and stirred vigorously. After the obtained homogeneous slurry was dried, it was calcined at 400°C for 9 hours, and ground to make the catalyst outer layer powder. The composition of the active component of the catalyst outer layer powder is Mo ₁₂ V ₈₀ Si _5.3 Al ₁₃₃ O _n .

Step 4: Preparation of Catalyst 1

Place the catalyst inner layer parent body prepared in step 1 in a round-bottomed container, put the catalyst inner layer parent body into an oven and gradually heat it to about 50°C, spray 30% glycerin solution to the catalyst parent body under the condition of container rotation, and fully moisten the catalyst body. Stop rotating under the condition of the wet catalyst inner layer parent body, put it into another round-bottomed container that rotates quickly and put the catalyst middle layer active component composition (the temperature is also kept at about 50 ℃) that is gained in step 2, and carry out coating Wrap, while continuing to spray the glycerin solution to ensure that the catalyst inner layer precursor coating is uniform. The obtained catalyst is dried at 90-110° C. and then calcined at 390° C. for 5 hours to complete the coating of the middle layer of the catalyst. The outer layer catalyst was coated according to the method of coating the middle layer catalyst, and the obtained catalyst was dried at 100°C and then calcined at 390°C for 7 hours to obtain catalyst 1.

Comparative example 1:

The inner matrix of catalyst 1 was used as comparative catalyst 1, and a ball with a diameter of 4 mm was made, and the reaction conditions were the same as those of catalyst 1.

Example 2:

Preparation of Catalyst 2

The first step: preparation of catalyst inner layer matrix

(1) Preparation of active component slurry (a)

In a 1-liter beaker, add 500 milliliters of deionized water, then add 166.5 grams of ammonium metavanadate and 302 grams of ammonium molybdate in turn, heat to dissolve and mix well, and this mixed salt solution is A. In another 200 ml beaker, add 80 ml of deionized water, under vigorous stirring, add 41.4 g of nickel nitrate and 240.8 g of copper nitrate successively, and heat to fully dissolve to obtain solution B. When the reaction temperature of liquid A was adjusted to 60°C, the two solutions were mixed, put into a hydrothermal kettle with a polytetrafluoroethylene liner, and aged in an oven at 110°C for 5 hours, and cooled after taking out to obtain the active component powder ( a).

(2) Preparation of auxiliary material slurry (b)

In a 1-liter beaker, add 100 milliliters of deionized water, under vigorous stirring and continuous heating, add 107.2 grams of manganese nitrate, 18.9 grams of niobium pentoxide, and 17 grams of silicon dioxide in sequence, stir and mix well.

(3) Preparation of catalyst inner layer matrix

The active component slurry (a) and auxiliary slurry (b) are mixed for co-precipitation reaction to form a co-precipitation slurry, which is evaporated and concentrated to a semi-paste under continuous heating and strong stirring, and then dried in an oven at 120°C overnight, and then The resulting material is pulverized by a pulverizer, and sieved to obtain powder C passing through a 80-mesh sieve. Move the powder C to a kneader, continuously spray the mixed solution of deionized water and 40% silica sol, knead into a mud, and shape it into catalyst particles of φ5*5mm on the extruder-pelletizer. Calcined at 380° C. for 5 hours in a muffle furnace to obtain a catalyst product. The catalyst composition is Mo ₁₂ V ₁₀₀ Ni ₁₀ Cu ₇₀ Si ₂₀ Mn ₃₀ P ₁₀ O _x .

The second step: prepare the active component powder in the middle layer of the catalyst

Under stirring conditions, add 113.3 grams of ammonium metavanadate and 256.7 grams of ammonium molybdate in 500 milliliters of deionized water, heat to dissolve and mix evenly. This mixed salt solution is A. In another 200 ml beaker, add 70.5 g of nickel nitrate and 146.4 g of copper nitrate in 80 ml of deionized water successively under vigorous stirring, and heat to fully dissolve to obtain solution B. When the reaction temperature of liquid A was adjusted to 60°C, the two solutions were mixed and vigorously stirred. After the obtained slurry was dried, it was calcined at 390°C for 7 hours, and ground to make catalyst middle layer powder. The composition of the active components of the powder in the middle layer of the catalyst is Mo ₁₂ V ₈₀ Ni ₂₀ Cu ₅₀ O _m .

Step 3: Preparation of catalyst outer layer active component powder

Under stirring conditions, add 99.9 grams of ammonium metavanadate and 226.5 grams of ammonium molybdate in 500 milliliters of deionized water, heat to dissolve and mix evenly. This mixed salt solution is A. In another 200 ml beaker, add 80 ml of deionized water, under vigorous stirring, add 25.6 g of silicon dioxide and 58.1 g of corundum powder in turn, heat to fully dissolve to obtain solution B. The two solutions A and B were mixed and stirred vigorously. After the obtained homogeneous slurry was dried, it was calcined at 400°C for 9 hours, and ground to make the catalyst outer layer powder. The composition of the active component of the catalyst outer layer powder is Mo ₁₂ V ₁₀₀ Si _4.0 Al ₁₀₆ O _n .

Step 4: Preparation of Catalyst 2

Place the catalyst inner layer matrix prepared in step 1 in a round-bottomed container, gradually heat the catalyst inner layer matrix to about 60°C, spray 40% silica sol solution to the catalyst matrix while the container is rotating, and fully wet the catalyst inner layer Stop rotating under the conditions of the parent body, put it into another round-bottomed container that rotates quickly and put the catalyst middle layer active component composition (temperature is also maintained at about 60°C) obtained in step 2, and coat it while continuing Spray 40% silica sol solution to ensure uniform coating of catalyst inner layer matrix. The obtained catalyst was dried at 120°C and calcined at 370°C for 8 hours to complete the coating of the middle layer of the catalyst. At about 60°C, the outer layer catalyst was coated according to the method of coating the middle layer catalyst. The obtained catalyst was dried at 110°C and calcined at 410°C for 5 hours. Hours, the catalyst 2 was obtained.

Comparative example 2:

The inner matrix of catalyst 2 was used as comparative catalyst 2, and a ball with a diameter of 4 mm was made, and the reaction conditions were the same as those of catalyst 1.

Example 3:

Preparation of Catalyst 3

The first step: preparation of the catalyst inner layer matrix

(1) Preparation of active component slurry (a)

The preparation of the active component slurry (a) is the same as that of catalyst 1. Take 218 grams of ammonium molybdate, 24.1 grams of ammonium metavanadate, 269.4 grams of nickel nitrate, 49.7 grams of copper nitrate and 24.7 grams of silicon oxide powder, and other conditions remain unchanged.

(2) Preparation of auxiliary material slurry (b)

The preparation of auxiliary material slurry (b) is the same as catalyst 1, taking 83.2 grams of iron nitrate and 83.2 grams of ammonium paratungstate, and other conditions remain unchanged.

(3) Preparation of catalyst inner layer matrix

The preparation of the catalyst inner layer matrix is the same as catalyst 1, and the composition of the catalyst inner layer matrix is: Mo ₁₂ V ₂₀ Ni ₉₀ Cu ₂₀ Si _4.0 Fe ₂₀ W ₃₀ O _x .

The second step: prepare the active component powder in the middle layer of the catalyst

The preparation of the middle layer of the catalyst was the same as that of Catalyst 1, except that 185 grams of ammonium molybdate, 30.7 grams of ammonium metavanadate, 152.5 grams of nickel nitrate, and 31.7 grams of copper nitrate were used, and other conditions remained unchanged. The middle layer composition of the catalyst is Mo ₁₂ V ₃₀ Ni ₆₀ Cu _1.5 O _m .

Step 3: Preparation of catalyst outer layer active component powder

The preparation of the outer layer of the catalyst was the same as that of Catalyst 1, except that 218 grams of ammonium molybdate, 24.1 grams of ammonium metavanadate, 12.3 grams of silica powder and 38.6 grams of aluminum nitrate were used, and other conditions remained unchanged. The composition of the outer layer of the catalyst is Mo ₁₂ V ₂₀ Si ₂₀ Al ₁₀ O _n .

Step Four: Preparation of Catalyst 3

The preparation of catalyst 3 is the same as that of catalyst 1, and other conditions remain unchanged.

Comparative example 3:

The inner matrix of catalyst 3 was used as comparative catalyst 3, and a ball with a diameter of 4 mm was made, and the reaction conditions were the same as those of catalyst 1.

Example 4:

Preparation of Catalyst 4

The first step: preparation of the catalyst inner layer matrix

(1) Preparation of active component slurry (a)

The preparation of the active component slurry (a) is the same as that of catalyst 2. Take 151 grams of ammonium molybdate, 41.6 grams of ammonium metavanadate, 144.9 grams of nickel nitrate, 17.2 grams of copper nitrate and 8.5 grams of silicon oxide powder, and other conditions remain unchanged.

(2) Preparation of auxiliary material slurry (b)

The preparation of auxiliary material slurry (b) is the same as catalyst 2, 35.7 grams of manganese nitrate and 9.4 grams of niobium pentoxide are taken, and other conditions remain unchanged.

(3) Preparation of catalyst inner layer matrix

The preparation of the catalyst inner layer matrix is the same as catalyst 2, and the composition of the catalyst inner layer matrix is Mo ₁₂ V ₅₀ Ni ₇₀ Cu ₁₀ Si ₂₀ Mn ₂₀ P ₁₀ O _x .

The second step: prepare the active component powder in the middle layer of the catalyst

The preparation of the middle layer of the catalyst was the same as that of Catalyst 2, except that 128.4 grams of ammonium molybdate, 21.3 grams of ammonium metavanadate, 88.1 grams of nickel nitrate, and 22 grams of copper nitrate were used, and other conditions remained unchanged. The middle layer composition of the catalyst is Mo ₁₂ V ₃₀ Ni ₅₀ Cu ₁₅ O _m .

Step 3: Preparation of catalyst outer layer active component powder

The preparation of the outer layer of the catalyst was the same as catalyst 2, 113.2 grams of ammonium molybdate, 31.2 grams of ammonium metavanadate, 23.4 grams of silicon oxide powder and 60 grams of aluminum nitrate were taken, and other conditions remained unchanged. The composition of the outer layer of the catalyst is Mo ₁₂ V ₅₀ Si ₃₀ Al ₃₀ O _n .

Step 4: Preparation of Catalyst 4

The preparation of catalyst 4 is the same as that of catalyst 2, the binder is silica sol, the obtained catalyst is dried at 135° C. and then calcined at 440° C. for 4 hours, and other conditions remain unchanged.

Comparative example 4:

Using the middle matrix of catalyst 4 as comparative catalyst 4, a ball with a diameter of 4 mm was made, and the reaction conditions were the same as those of catalyst 1.

oxidation reaction

In a stainless steel tube reactor with an inner diameter of φ25 mm, 35 ml of catalyst is filled, and a reaction mixture gas is introduced at a standard gaseous space velocity of 1420 h ^-1 , and the composition of the mixture gas is:

The heat medium in the reactor is molten salt, and the reaction results are shown in Table 2 and Table 3.

Evaluation result after 15 hours of reaction in table 2

Evaluation result after 1500 hours of reaction in table 3

Claims (8)

1. a multi-metal-oxide catalyst is characterized in that catalyst has three-decker, and each layer chief component is respectively by general formula (I), (II) and (III) expression from inside to outside

Mo _aV _bNi _cCu _dSi _eA _fB _gO _x (I)

Mo _aV _bNi _cCu _dO _m (II)

Mo _aV _bSi _eAl _iO _n (III)

Wherein: Mo is molybdenum, and V is alum, and Ni is nickel, and Cu is copper, and Si is silicon, and Al is aluminium, and A is at least a element in chosen from Fe, cobalt, the manganese; B is at least a element that is selected from tungsten, niobium, the phosphorus; O is oxygen; A, b, c, d, e, f, g, i represent respectively each element atomic ratio, a=12 wherein, and b is the number of 2-10, c is the number of 1-10, and d is the number of 1-7, and e is the number of 2-8, f is the number of 1-3, and g is the number of 1-3, and i is the number of 1-15; X, m and n are the numerical value by the oxygen decision of each oxide.

2. a catalyst as claimed in claim 1 is characterized in that b is the number of 4-8.

3. a catalyst as claimed in claim 1 is characterized in that d is the number of 1.5-5.

4. the preparation method of catalyst as claimed in claim 1 is characterized in that comprising the steps:

The first step: Kaolinite Preparation of Catalyst internal layer parent

(1) will contain the compound dissolving of Mo, V, Ni, Cu and Si and mixing, form active component slurries (a);

(2) again with A in the general formula (I) _fB _gEach the elemental constituent compound dissolving that relates to also mixes, as auxiliary material slurries (b);

(3) active component slurries (a) and auxiliary material slurries (b) are carried out heat drying behind the coprecipitation reaction, granulating and forming, roasting gets the catalyst inner layer parent;

Second step: Kaolinite Preparation of Catalyst middle level active component powder

To contain the compound dissolving of Mo, V, Ni and Cu and mix, catalyst middle level active component powder (c) is made in drying, roasting, grinding behind the coprecipitation reaction;

The 3rd step: the outer active component powder of Kaolinite Preparation of Catalyst

To contain the compound dissolving of Mo, V, Si and Al and mix, catalyst outer layer active component powder (d) is made in drying, roasting, grinding;

The 4th step: Kaolinite Preparation of Catalyst

Catalyst middle level active component powder (c) and catalyst outer layer active component powder (d) be coated with successively according to from inside to outside order be rolled on the catalyst inner layer parent, make catalyst prod.

5. preparation method as claimed in claim 4, it is characterized in that the catalyst inner layer parent at after the moulding and middle level and outer active component powder after wrapped, respectively at 350～460 ℃ of lower heat treatment 3～10h.

6. preparation method as claimed in claim 4 is characterized in that being coated with to be rolled under the same temperature and carrying out of every layer of active component powder of described catalyst, and temperature range is 40～80 ℃.

7. preparation method as claimed in claim 4 is characterized in that every layer of active component powder of described catalyst uses binding agent when wrapped, and binding agent is selected from one or more in water, Ludox, aluminium colloidal sol, ethanol, the glycerine.

8. preparation method as claimed in claim 4, the predecessor that it is characterized in that described catalyst activity component is a kind of in nitrate, ammonium salt, sulfate, oxide, hydroxide, chloride or the acetate of each element.