CN102989480A - Composite multi-metal oxide catalyst and preparation method thereof - Google Patents

Abstract

The present invention relates to a kind of composite multimetal oxide catalyst and preparation method thereof, it is characterized in that the composition of this catalyst can be represented by following general formula (I): Mo _a V _b W _c Ni _d A _e B _{f Sig} O _x (I) Among them: Mo is molybdenum, V is vanadium, W is tungsten, Ni is nickel, Si is silicon, Si is the carrier added in the catalyst, A is at least one element selected from copper, cobalt, and manganese; B is selected from At least one element selected from zirconium, strontium, magnesium and titanium. The catalyst of the invention can effectively reduce local heat accumulation in a fixed-bed single-tube reactor, suppress the formation of hot spots, and has the characteristics of high reactivity, selectivity and long service life.

Description

Composite multi-metal oxide catalyst and preparation method thereof

technical field

The invention relates to a composite multimetal oxide catalyst and a preparation method thereof, which are used to catalyze the oxidation of acrolein to produce acrylic acid.

Background technique

At present, acrylic acid is mainly prepared by two-step oxidation of propylene in industry. First, propylene is catalyzed in the gas phase to oxidize acrolein, and then acrolein is oxidized to acrylic acid. The oxidation reaction of acrolein is a strong exothermic reaction. Hot spots will be generated in the catalyst bed, and the heat accumulated instantaneously will continue to accumulate, which will lead to the loss and shedding of the active components of the catalyst, so that the activity of the catalyst will decrease, the life will be shortened, and the overheating will be caused. 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, more than 25,000 tubes are needed in the reactor for the oxidation of propylene to acrolein, and more than 25,000 tubes are needed in the reactor for the oxidation of acrolein to acrylic acid. More than 100 tons of acrylic acid catalyst. There are more than 50,000 reaction tubes, and it is difficult to ensure that the catalyst is not filled empty. If the catalyst is sintered quickly because the hot spot is too high, and the catalyst is replaced in a short period of time, it can be expected that the economic loss will be huge; in addition, for propylene The production of aldehyde and acrylic acid should be carried out under low temperature conditions as much as possible, because the reaction needs to be heated in a salt bath, and the energy consumption for maintaining production is also a huge expense; due to the generation of hot spots, high temperature resistance is required for the reaction tube, and for tens of thousands For reaction tubes, the cost of tube materials 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, there are many ways to reduce or avoid the accumulation of hot spots and peroxidation reaction, which can be considered from the improvement of the reaction device and the improvement of the catalyst. In terms of catalysts, such as: Japanese Patent Laid-Open No. 04-217932 proposes a method to suppress the occurrence of hot spots or heat accumulation on hot spots, that is, by preparing a variety of catalysts with different occupied volumes, and from the feed gas inlet side to In the method of reducing the occupied volume of the catalyst on the outlet side, the reaction tubes are filled sequentially, but the occupied volume of the catalyst is limited by the diameter of the reaction tube, and it is also difficult to fill the reaction tube with various catalysts. Japanese Patent Publication No. 10614/1972, US200421442A mix anti-hot spot forming catalyst, that is, an inert substance in the catalyst to dilute the catalyst, and Japanese Patent Publication No. 36739/1987 makes the catalyst into a tubular method. Furthermore, the feed gas inlet is filled with a catalyst whose active component is reduced. CN200510007929.8 provides a catalyst for catalyzing the gas-phase oxidation of acrolein to produce acrylic acid. The catalyst contains molybdenum and vanadium, and also contains at least one volatile catalyst poisoning component, the amount of which is measured by ion chromatography as 10 to 100 ppb by mass. The catalyst can reduce the temperature of the superheated part, and suppress the reduction of the reaction efficiency of 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. CN97104224.1 suppresses hot spots by calcining the catalyst that has been loaded after the catalytically active components are loaded on the carrier. The average particle diameter of the catalyst is 4-16mm, the average particle diameter of the carrier is 3-12mm, and the calcination temperature It is 500-600°C. CN01111960.8 provides a catalyst containing Mo-W-Bi-Fe, the catalyst is changed from the inlet side of the feed gas to In the way of increasing on the outlet side, the reaction zone is sequentially filled with the various types of catalysts. The catalyst is divided into at least two layers in the axial direction of the reaction tube. This catalyst is a variety of catalysts with different activity levels, which can be obtained by changing the calcination temperature and/or the type and/or amount of alkali metal elements therein. The occurrence of hot spots or heat accumulation on hot spots is effectively suppressed. CN00122609.6 provides a method for producing acrolein and acrylic acid by gas-phase oxidation of propylene, using an oxide catalyst containing Mo-Bi-Fe compound, the catalyst is filled in a fixed-bed multi-tubular reactor, the method can be used for a long time Acrolein and acrylic acid were produced stably in high yields. The method is characterized in that in each tubular reactor configured with two or more reaction zones in the axial direction, each zone is filled with different catalysts, that is, the content of Bi and/or Fe in the catalyst filled from the gas inlet end to the gas outlet end is the same as that of Mo content ratio decreased. US2009415167A discloses a method for producing unsaturated aldehydes and unsaturated acids. Two or more catalyst layers are loaded into the reactor, and each catalyst layer is a catalyst formed by catalytically active components with different pore densities and or pore sizes. Packing, the specific surface area of the catalytically active component is gradually increased from the reactor inlet to the outlet to control the pore density and or pore size, thereby suppressing the reaction hot spots. 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. CN 03121882.2 discloses a composite multi-metal oxide catalyst and its preparation method, especially suitable for acrolein gas-phase selective oxidation to acrylic acid, and its 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 An element, X ⁴ is an element selected from at least silicon, aluminum and titanium, X ⁵ is an element selected from at least antimony, tin and bismuth, the catalyst contains at least molybdenum, vanadium and copper, and the necessary addition of tellurium The main active components of the catalyst are molybdenum oxide and copper molybdate crystals, which have sustained high activity and high selectivity during the catalytic reaction, and delay the deactivation of the catalyst due to the loss of molybdenum. CN03148701.7 provides a supported catalyst, the catalyst support has a multi-dimensional structure, with a self-supporting multi-dimensional support structure of preform (such as foam, monolithic structure, fabric or others) or containing Nb ₂ O ₅ , cordierite, partially stabilized A carrier of zirconia, ceramic fibers or a mixture thereof, on which a catalyst composition comprising at least one molybdenum-containing layer, at least one vanadium-containing layer, at least one tellurium-containing layer and at least one X-containing layer is deposited in succession to form The loaded carrier is roasted to obtain the loaded catalyst. For the oxidation of paraffins to unsaturated carboxylic acids and the ammoxidation of paraffins to unsaturated nitriles, providing sufficient conversion and suitable selectivity.

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. Even if the activity of the catalyst decreases after a certain cycle, there is no way to change the dilution ratio, and the catalyst will also It can no longer provide higher activity, which not only brings troubles in loading, dismantling, separating, and recovering the catalyst, but also reduces the reactivity of the catalyst, especially in industrial long-term operation. The activity of the catalyst decreases faster, which affects the life of the catalyst. Therefore, it is necessary to develop a highly active catalyst that can effectively suppress hot spots to meet the industrial needs of high space velocity and high selectivity oxidation of propylene to acrolein and acrylic acid. In addition, under high temperature conditions, part of the active component molybdenum in the catalyst is lost from the surface of the catalyst due to sublimation. The scouring of the mixed flow of acrolein, air (oxygen), nitrogen and water vapor will also cause the loss of active components in the catalyst. In order to suppress the loss of molybdenum sublimation and cause the attenuation of activity, CN1121504 can suppress the dissipation and excessive reduction of molybdenum components by doping copper components and zirconium and/or titanium and/or cerium with specific particle size and specific surface area; CN1445020 added A small amount of tellurium plays the role of stabilizing the crystal structure of free molybdenum trioxide and copper molybdate, and the sublimation loss and excessive reduction of molybdenum are suppressed; CN1583261 is mainly composed of molybdenum, vanadium, copper, tungsten and/or niobium, and other A composite oxide composed of elements or a mixture of oxides constitutes a catalyst to suppress the loss of molybdenum.

The invention provides a catalyst for the selective oxidation of acrolein to produce acrylic acid and a preparation method thereof. During the oxidation of acrolein, the reaction can be carried out under low temperature and high load conditions.

Contents of the invention

The object of the present invention is to provide a composite multi-metal oxide catalyst for the selective oxidation of acrolein or methacrolein to produce the corresponding unsaturated acid and its preparation method. Different from the above-mentioned method of reducing hot spots, the present invention makes catalyst particles have a gradient difference in the concentration of the active component composition from the inside to the outside, which can effectively reduce the local heat accumulation of the reactor and suppress the formation of hot spots. The catalyst has the characteristics of high reaction activity and selectivity, good stability and long service life.

The present invention relates to a kind of composite multimetal oxide catalyst, and the main composition of this catalyst is represented by following general formula (I)

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

Wherein: Mo is molybdenum, V is vanadium, W is tungsten, Ni is nickel, A is at least one element selected from copper, cobalt, manganese; B is at least one element selected from zirconium, strontium, lanthanum, magnesium and titanium A kind of element; Si is silicon, silicon is the carrier added, O is oxygen; a, b, c, d, e, f, g respectively represent the atomic ratio of each element, wherein when a=12 is the basis, b is 3 A number from 10 to 10, preferably 3 to 7; c is a number from 0.5 to 5, preferably 1 to 3; d is a number from 1 to 5, preferably 1.5 to 3; e is a number from 0 to 3, f is A number from 0 to 3, g is a number from 0.5 to 30, and x is a value determined by the oxygen of each oxide. The composite multi-metal oxide catalyst has a multi-layer structure, that is, an inner and outer double-layer structure, and each layer The main composition of the catalyst is the same, but the total content of one or more of silica, alumina or silicon carbide is different, and the total content of one or more of silica, alumina or silicon carbide in the outer layer is higher than that of the inner layer The height of the parent body is calculated by mole percentage, and the concentration of each element in the outer layer of the catalyst is lower than that of the parent body in the inner layer.

The catalyst described in the present invention has a multi-layer structure, and the concentration difference can be realized mainly by adding different amounts of silica, alumina, silicon carbide and other substances in the inner and outer layers, that is to say, the outer layer of silica, alumina or silicon carbide The total content of one or more of them is higher than that of the inner layer matrix. In terms of mole percentage, the content of each element in the outer layer is 0.5-30% lower than that in the inner layer, preferably 0.5-18%. The inner layer of the catalyst of the present invention may also not add silicon.

The selective oxidation of acrolein to produce acrylic acid has a reaction temperature above 270°C, and under such high-temperature reaction conditions for a long period of time, the active component molybdenum in the catalyst is easily lost due to sublimation. A in the catalyst of the present invention is preferably copper, and B is strontium and/or lanthanum, and strontium can regulate the surface acidity of the catalyst, and the main composition of the catalyst is represented by general formula (II), wherein e is a number of 0.5 to 3, and f is A number from 0.05 to 3. Lanthanum and molybdenum, nickel, copper, etc. can form a stable crystal phase structure, which is beneficial to inhibit the loss of part of the active component molybdenum from the surface of the catalyst due to sublimation. The catalyst has good stability.

Mo _a V _b W _c Ni _d Cu _e B _f Si _g O _x (II)

Active components in the catalyst of the present invention include Mo, V, W, Ni, and one or more of cobalt, manganese, zirconium, strontium, magnesium and titanium can also be added, which is beneficial to improve the active components in silicon dioxide, etc. Dispersion and adhesion on the carrier, thereby improving the selectivity of the catalyst. In the catalyst composition general formula (I), e is a number from 0.1 to 2, and f is a number from 0.05 to 2. The concentration of the active component composition of the catalyst particles with a multi-layer structure decreases sequentially from the inside to the outside, effectively reducing the local heat accumulation in the single-tube reactor, suppressing the formation of hot spots, the catalyst is not easy to sinter, the reaction activity is stable, and it can withstand long-term stability run.

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

The composite multi-metal oxide catalyst of the present invention can be prepared by the usual preparation method, for example, the following steps can be used for preparation.

First, prepare the catalyst inner layer precursor:

Dissolving and mixing the compounds containing Mo, V, W, Ni and the related element components of A _e B _f in the general formula (I), and co-precipitating to form the inner layer matrix slurry, drying, molding, Roasting to obtain the catalyst inner layer precursor;

Secondly, prepare the outer layer catalyst slurry according to the method for preparing the catalyst inner layer matrix slurry, and add one or more materials such as silicon dioxide, aluminum oxide, and silicon carbide during the preparation of the outer layer catalyst slurry, so that each catalyst slurry in the outer layer The element concentration is lower than the concentration of the element in the inner layer;

Finally, the prepared outer layer catalyst is sequentially coated on the catalyst inner layer precursor, and the finished catalyst is obtained after roasting.

The present invention can also adopt a multi-metal oxide catalyst (III), the main composition is represented by the following formula (III): Mo _a V _b Ni _c Cu _d Nb _e Sr _f M _g N _h Si _i O _x (III), Wherein: Mo is molybdenum, V is vanadium, Ni is nickel, Cu is copper, Nb is niobium, Sr is strontium, M is at least one element selected from cobalt, iron, manganese; N is selected from zinc, lanthanum, At least one element in magnesium and boron; O is oxygen; Si is silicon, silicon is the carrier added, a, b, c, d, e, f, g, h, i represent the atomic ratio of each element respectively, wherein when When a=12 is the benchmark, b is a number from 3 to 8, c is a number from 0.5 to 6, d is a number from 0.5 to 3, e is a number from 0.05 to 2, and f is a number from 0.05 to 1.5 number, g is a number from 0.05 to 2, h is a number from 0.05 to 1.5, i is a number from 0.5 to 10, and x is a value determined by the oxygen of each oxide. The composite multimetal oxide catalyst It has a multi-layer structure, that is, an inner and outer double-layer structure. The main composition of each layer of catalyst is the same, but the total content of one or more of silica, alumina or silicon carbide is different. The outer layer of silica, alumina or carbide The total content of one or more kinds of silicon is higher than that of the matrix in the inner layer, and the concentration of each element in the outer layer of the catalyst is lower than that of the matrix in the inner layer in terms of molar percentage. In terms of mole percentage, the content of each element in the outer layer is 0.5-30% lower than that in the inner layer. In the formula (III), N is preferably lanthanum, and lanthanum, nickel, copper, etc. can form a stable crystal phase structure, which is conducive to suppressing the loss of part of the active component molybdenum from the surface of the catalyst due to sublimation, and the molybdenum content of the active component before and after the catalyst reaction is basically the same. Change, slow down the rate of activity deterioration, good catalyst activity and stability.

The present invention can also adopt a multi-metal oxide catalyst (IV), the main composition is represented by the following formula (IV): Mo _a V _b W _c Ni _d Sb _e A _f B _g Si _i O _x (IV) wherein: wherein : Mo is molybdenum, V is vanadium, W is tungsten, Ni is nickel, Sb is antimony, Si is silicon, silicon is added carrier, A is at least one element selected from strontium, iron, bismuth; B is selected At least one element from zirconium, lanthanum, magnesium and phosphorus; O is oxygen; a, b, c, d, e, f, g, i represent the atomic ratios of each element respectively, wherein when a=12 is a benchmark, b is a number from 1 to 6, c is a number from 0.5 to 5, d is a number from 0.5 to 5, e is a number from 0.05 to 2, f is a number from 0.05 to 2, and g is a number from 0.05 to 2 is a number, i is a number from 0.5 to 10, and x is a value determined by the oxygen of each oxide. The composite multi-metal oxide catalyst has a multi-layer structure, that is, an inner and outer double-layer structure, and each layer of catalyst mainly consists of The same, but the total content of one or more of silica, alumina or silicon carbide is different, and the total content of one or more of silica, alumina or silicon carbide in the outer layer is higher than that of the matrix in the inner layer , in terms of mole percentage, the concentration of each element in the outer layer of the catalyst is lower than that of the matrix in the inner layer. In terms of mole percentage, the content of each element in the outer layer is 0.5-35% lower than that in the inner layer, preferably 1-25%. In (IV), B is preferably lanthanum, and lanthanum, antimony, nickel, etc. can form a stable crystal phase structure, which is conducive to suppressing the loss of part of the active component molybdenum from the surface of the catalyst due to sublimation, and the molybdenum content of the active component before and after the catalyst reaction is basically unchanged. , Delay activity deterioration rate, good catalyst activity and stability.

The present invention can also use a multi-metal oxide catalyst (V), the main composition is represented by the following formula (V): Mo _a V _b Cu _c Ce _d A _g B _h Si _i O _x (V) wherein: Mo is molybdenum , V is vanadium, Cu is copper, Ce is cerium, Si is silicon, silicon is added carrier, A is at least one element selected from strontium, antimony, tungsten, nickel; B is selected from lanthanum, magnesium and phosphorus At least one element in O is oxygen; a, b, c, d, g, h respectively represent the atomic ratio of each element, wherein when a=12 is the benchmark, b is a number from 1 to 6, and c is 0.5 A number from 0 to 4, d is a number from 0.05 to 3, g is a number from 0 to 2, h is a number from 0 to 2, i is a number from 0.5 to 10, x is the oxygen of each oxide The value determined, the composite multi-metal oxide catalyst has a multi-layer structure, that is, an inner and outer double-layer structure, and the main composition of each layer of catalyst is the same, but the total amount of one or more of silica, alumina or silicon carbide The content is different. The total content of one or more of the outer layer of silica, alumina or silicon carbide is higher than that of the inner layer matrix. In terms of mole percentage, the concentration of each element in the outer layer of the catalyst is lower than that of the inner layer matrix. In terms of mole percentage, the content of each element in the outer layer is 0.5-35% lower than that in the inner layer, preferably 1-25%. The component cerium is conducive to the high dispersion of the components molybdenum, vanadium and copper on the carrier silica, thereby improving the utilization rate of the active components, but the addition of cerium should not be too high, because it will compete with vanadium and copper for molybdenum, and the activity On the contrary, it decreases and satisfies (b+c)/d>5. In formula (V), A is preferably tungsten and/or nickel, B is preferably lanthanum, g is a number from 0.05 to 2, h is a number from 0.05 to 2, and lanthanum, nickel, copper, etc. can form a stable crystal phase structure, It is beneficial to suppress the loss of part of the active component molybdenum from the surface of the catalyst due to sublimation, the content of the active component molybdenum remains basically unchanged before and after the catalyst reaction, delays the rate of activity deterioration, and has good catalyst activity and stability.

The above-mentioned catalysts (III), (IV) and (V) can be prepared by the usual preparation methods, and can also be prepared by the above-mentioned preparation methods.

The matrix of the inner layer of the catalyst of the present invention needs to be calcined at 300-480° C. for 3-10 hours after forming and the outer layer after coating. Compared with the catalyst not calcined separately, the activity and stability of the catalyst can be improved by repeated calcining. It can be open roasting or closed roasting, and the roasting atmosphere can be helium, nitrogen, argon and other inert gases. If the catalyst layer is too thick, it is easy to crack when roasted. In order to avoid cracks, it is best to dry at 55-125°C after coating, and then roast. The outer catalyst layer coated on the inner matrix has a thickness of 0.5-2.5 mm, preferably 1.0-2 mm.

As compounds of the constituent elements of the catalyst of the present invention, nitrates, ammonium salts, sulfates, oxides, hydroxides, chlorides, acetates and the like of each element can be used.

After the catalyst inner layer matrix slurry of the present invention is dried, it is usually preferably processed into a spherical shape, a hollow spherical shape, an elliptical shape, a cylindrical shape, a hollow cylinder, etc., preferably a hollow cylinder or spherical.

When the catalyst of the present invention is coated, it is preferable to use a binder to make the inner and outer catalysts bond more firmly. Spray the binder to infiltrate the surface while the inner layer matrix is rolling, and then spray the prepared outer layer catalyst powder, or put the inner layer matrix into the prepared outer layer catalyst slurry for rolling coating. The binder is selected from one or more of water, alcohols or ethers. Alcohols such as ethanol, propanol, butanol; ethers such as diethyl ether and butyl ether.

The surface of each layer of the catalyst of the present invention is preferably uneven and rough, which is beneficial to coating and the bonding between the inner and outer layers is firmer.

In the present invention, in order to improve the strength and pulverization degree of the catalyst, one or more of glass fiber, graphite, ceramics or various whiskers can be added to the above-mentioned outer layer catalyst.

The catalyst of the present invention can be used directly or supported on an inert carrier. The inert carrier involved may be one or a mixture of alumina, silicon dioxide, silicon carbide, etc.

The present invention also provides a method for the selective oxidation of acrolein to produce acrylic acid: a fixed-bed single-tube reactor is used; the reaction raw materials, acrolein, water, and air, are preheated by a preheater above 180°C and enter the reactor, heated in a salt bath, and reacted The process conditions are: salt bath temperature 245-265°C, preferably 250-262°C; space velocity 1400-2500h ^-1 , preferably 1500-2000h ^-1 , feed composition: acrolein 7-12% by volume, water vapor 11-18 %, 10-18% by volume of air, 60-72% by volume of nitrogen; one or more of the above-mentioned catalysts (III), (IV) or (V) are housed in the reactor. The conversion rate of acrolein is between 98.2-99.5%, and the selectivity of acrylic acid is between 88.0-91.3%. The hot spot temperature is between 279 and 291.

Because the initial reaction activity of the catalyst is very high, it is easy to generate hot spots or heat accumulation on the single-tube reactor bed, and the catalyst is easy to sinter, which is a very serious loss for the industrial production of acrolein acrylic acid. When a certain amount of water vapor is introduced into the raw material, due to the large specific heat of water, a large amount of heat of reaction can be taken away, but a large amount of water vapor will often dissolve part of the active components of the catalyst and reduce the activity. In the present invention, by preparing a composite multi-metal oxide catalyst with a multi-layer structure, there is a gradient difference in the concentration of the catalyst particle from the inside to the outside of the active component composition, and the concentration of the active component in each outer layer of the catalyst is more active than its adjacent inner layer. The concentration of components is low, so that under the condition of high space velocity reaction, due to the low concentration of active components on the outer surface of the catalyst, the corresponding activity is also low, so the formation of hot spots and the accumulation of heat can be effectively suppressed, and by-products (such as carbon oxygen compound) to increase the selectivity of the target product. The catalyst with double-layer structure has good water resistance. Moreover, after the catalyst has been running for a period of time, the catalyst has a release effect. Under the washing of the mixed air flow, even if the active components on the surface of the catalyst are partially lost, due to the high concentration of the active components of the catalyst in the inner layer, it can play a supplementary role, so it can Keep catalyst activity lasting and stable.

Catalyst evaluation performance indicators are defined as follows:

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

Selectivity of acrylic acid (%) = number of moles of acrolein converted to acrylic acid/total number of moles of acrolein reaction × 100%

Detailed ways

The following specific examples are used to illustrate the composite multimetal oxide catalyst and its preparation method, and the catalytic performance of the catalyst in the selective oxidation of acrolein to prepare acrylic acid, but the scope of the present invention is not limited to these examples.

Example 1:

Preparation of Catalyst 1

Step 1: Prepare catalyst inner layer matrix

(1) Preparation of active component slurry (a)

Under stirring conditions, take 148 grams of ammonium molybdate and 24.6 grams of ammonium metavanadate and dissolve them in 500ml of pure water (water temperature above 65°C) to obtain slurry (1), then take 64 grams of ammonium paratungstate, 5.5 grams of strontium nitrate, 17.9 grams of Copper nitrate and 10.2 g of cobalt nitrate were dissolved in 500 ml of purified water (water temperature above 65° C.), fully stirred and mixed uniformly to obtain slurry (2). Then, slurry (1) is mixed with slurry (2) to obtain slurry (3) to obtain active ingredient slurry (a).

(2) Preparation of catalyst inner layer matrix

Add 4.2 grams of silicon dioxide to the active component slurry (a), stir vigorously at 80°C for 3 hours for co-precipitation reaction, heat and dry, heat-treat at 160°C for 3 hours in nitrogen, and then extrude into φ4 .5×5mm hollow columnar particles, dried at 110°C and then calcined at 450°C for 5 hours to obtain a catalyst matrix. The composition of the catalyst inner layer matrix is: Mo ₁₂ V ₃ W _3.5 Ni ₄ Cu _1.1 Co _0.5 Sr _0.3 Si ₁

Step 2: Preparation of catalyst outer layer

(1) Preparation of active component slurry (a)

The same as the preparation of the active component slurry (a) in the catalyst inner layer precursor in Example 1.

(2) Preparation of catalyst outer layer

Co-precipitate the active component slurry (a) with 45 grams of silica powder for 2.5 hours, then heat and dry it, heat-treat it at 150°C for 3 hours in nitrogen, then roast it at 500°C for 4 hours, and process it by crushing, grinding, and sieving Obtain catalyst outer layer powder.

Step 3: Preparation of Catalyst 1

Place the catalyst inner layer parent body prepared in step 1 in a round bottom container, spray the ethanol solution to the catalyst parent body under the condition of container rotation, stop the rotation under the condition of fully wetting the catalyst inner layer parent body, and quickly put it into another rotating Put the outer layer catalyst powder obtained in step 2 into the round-bottomed container for coating, the thickness of the coating is 1.0-2.0mm, and the obtained catalyst is dried at 105°C and then calcined at 450°C for 4.5 hours to obtain catalyst 1.

Comparative example 1:

The inner layer matrix of Catalyst 1 was used as Comparative Catalyst 1, extruded into hollow columnar particles with a diameter of 5×5 mm by extruder, and the reaction conditions were the same as those of Catalyst 1.

Comparative example 2:

The outer layer of Catalyst 1 was used as Comparative Catalyst 2, and extruded by an extruder to form hollow columnar particles with a diameter of φ5×5 mm, and the reaction conditions were the same as those of Catalyst 1.

Example 2:

Preparation of Catalyst 2

Step 1: Prepare catalyst inner layer matrix

(1) Preparation of active component slurry (a)

Under stirring conditions, take 148 grams of ammonium molybdate and 40.9 grams of ammonium metavanadate and dissolve them in 500ml of pure water (water temperature above 65°C) to obtain a slurry (1), then take 54.8 grams of ammonium paratungstate and 61 grams of nickel nitrate and dissolve them in 500ml Pure water (water temperature above 65°C), fully stirred and mixed evenly to obtain slurry (2). Then, slurry (1) is mixed with slurry (2) to obtain slurry (3) to obtain active ingredient slurry (a).

(2) Preparation of catalyst precursor

Add 5 grams of silicon dioxide to the slurry (a), stir vigorously at 80°C for 2 hours for co-precipitation reaction, heat and dry, heat treat at 160°C for 3 hours in nitrogen, and then extrude it into φ4.5× Hollow columnar particles of 5 mm were dried at 60°C and then calcined at 450°C for 4 hours to obtain a catalyst matrix. The composition of the catalyst matrix was: Mo ₁₂ V ₅ W ₃ Ni ₃

Step 2: Preparation of catalyst outer layer

(1) Preparation of active component slurry (a)

The same as the preparation of the active component slurry (a) in the catalyst inner layer precursor in Example 2.

(2) Preparation of catalyst outer layer

Co-precipitate the active component slurry (a) with 14 grams of silica powder and 4 grams of graphite, heat and dry after 50 minutes, heat-treat at 160°C for 3 hours in nitrogen, and then bake at 500°C for 4 hours. Grinding and sieving to obtain catalyst outer layer powder.

Step 3: Preparation of Catalyst 2

Place the catalyst inner layer parent body prepared in step 1 in a round bottom container, spray ethanol solution to the catalyst parent body under the condition of container rotation, fully wet the catalyst inner layer parent body, and quickly put it into another rotating container containing the obtained product in step 2 Coating is carried out in a round-bottomed container on the outer layer of the catalyst. When the coating thickness is 0.8-1.0mm, take out the inner matrix and put it into another round-bottomed container and rotate it for one to two minutes before spraying the ethanol solution. Continue coating in a round-bottom container with a catalyst outer layer until the coating thickness is 1.5 to 2.0 mm, stop coating, and obtain catalyst 2 after drying at 500° C. for 3 hours.

Comparative example 3:

The inner layer matrix of Catalyst 2 was used as Comparative Catalyst 3, and extruded into hollow columnar particles with a diameter of φ5×5mm by extruder, and the reaction conditions were the same as those of Catalyst 1.

Comparative example 4:

The outer layer of Catalyst 2 was used as Comparative Catalyst 4, extruded by extruder to form hollow columnar particles of φ5×5 mm, and the reaction conditions were the same as those of Catalyst 1.

Example 3:

Step 1: Prepare catalyst inner layer matrix

(1) Preparation of active component slurry (a)

Under stirring conditions, take 148 grams of ammonium molybdate and 24.6 grams of ammonium metavanadate and dissolve them in 500ml of pure water (water temperature above 65°C) to obtain a slurry (1), then take 18.3 grams of ammonium paratungstate, 21.2 grams of copper nitrate, and 40.7 grams of nitric acid Nickel is dissolved in 500ml of pure water (water temperature above 65°C), fully stirred and mixed uniformly to obtain slurry (2). Then, slurry (1) is mixed with slurry (2) to obtain slurry (3) to obtain active ingredient slurry (a).

(2) Preparation of catalyst inner layer matrix

Add 8.4 grams of silicon dioxide to the slurry (a), stir vigorously at 80°C for 3 hours to carry out co-precipitation reaction, heat and dry, heat-treat at 160°C for 3 hours in nitrogen, and then extrude it into φ4.5× 5mm hollow columnar particles, baked at 350°C for 8 hours after drying to obtain the catalyst matrix, the composition of the catalyst inner layer matrix is: Mo ₁₂ V ₃ W ₁ Ni ₂ Cu _1.3

Step 2: Preparation of catalyst outer layer

(1) Preparation of active component slurry (a)

The same as the preparation of the active component slurry (a) and the raw materials used in the catalyst inner layer precursor in Example 3 (the following examples are the same).

(2) Preparation of catalyst outer layer

Co-precipitate the active component slurry (a) with 7.8 grams of silica powder and 5.7 grams of alumina, heat and dry after 50 minutes, heat-treat at 160°C for 3 hours in nitrogen, then roast at 400°C for 5 hours, and pulverize , grinding and sieving to obtain catalyst outer layer powder.

Step 3: Preparation of Catalyst 3

Place the catalyst inner layer parent body prepared in step 1 in a round bottom container, spray ether solution to the catalyst parent body under the condition of container rotation, stop the rotation under the condition of fully wetting the catalyst inner layer parent body, and quickly put it into another rotating In the round-bottomed container with the catalyst outer layer obtained in step 2, coating is carried out, and the thickness of the coating is 1.5 to 2.0 mm. The obtained catalyst is dried at 85° C. and then calcined at 450° C. for 4 hours to obtain catalyst 3.

Comparative example 5:

The inner layer matrix of Catalyst 3 was used as Comparative Catalyst 5, which was then extruded into hollow columnar particles with a diameter of 5×5 mm through an extruder, and the reaction conditions were the same as those of Catalyst 1.

Example 4:

Step 1: Prepare catalyst inner layer matrix

(1) Preparation of active component slurry (a)

Under stirring conditions, take 148 grams of ammonium molybdate and 57.3 grams of ammonium metavanadate and dissolve them in 500ml of pure water (water temperature above 65°C) to obtain a slurry (1), then take 36.6 grams of ammonium paratungstate, 14.6 grams of strontium nitrate, and 30.5 grams of nitric acid Nickel was dissolved in 500ml of pure water (water temperature above 65°C), and then 5.6g of titanium dioxide was added, fully stirred and mixed uniformly to obtain a slurry (2). Then, slurry (1) is mixed with slurry (2) to obtain slurry (3) to obtain active ingredient slurry (a).

(2) Preparation of catalyst inner layer matrix

Add 6.5 grams of silicon dioxide to the slurry (a), stir vigorously at 80°C for 3 hours to carry out co-precipitation reaction, heat and dry, heat-treat at 160°C for 3 hours in nitrogen, and then extrude it into φ4.5× The hollow columnar particles of 5 mm were dried at 120°C and then calcined at 350°C for 8 hours to obtain the catalyst matrix. The composition of the catalyst inner layer matrix was: Mo ₁₂ V ₇ W ₂ Ni _1.5 Sr _0.8 Ti _1.0

Step 2: Preparation of catalyst outer layer

The preparation method and the raw materials used are the same as in Example 4 catalyst outer layer (the following examples are the same), except that 6.3 grams of silicon dioxide and 20 grams of silicon carbide are added.

Step 3: Preparation of Catalyst 4

Place the catalyst inner layer parent body prepared in step 1 in a round bottom container, spray the ethanol solution to the catalyst under the condition of container rotation, spray the outer layer catalyst powder obtained in step 2 under the condition of fully wetting the catalyst inner layer parent body, and carry out coating The thickness of the coating is 0.8-1.5 mm. The obtained catalyst is dried at 80° C. and then calcined at 450° C. for 5 hours to obtain catalyst 4.

Comparative example 6:

The inner layer catalyst of Catalyst 4 was used as comparative Catalyst 6, which was calcined at 300°C for 2.5 hours, extruded into hollow columnar particles of φ5×5 mm by extruder, and the reaction conditions were the same as those of Catalyst 1.

Example 5:

Step 1: Prepare catalyst inner layer matrix

(1) Preparation of active component slurry (a)

Under stirring conditions, take 148 grams of ammonium molybdate and 73.7 grams of ammonium metavanadate and dissolve them in 500ml of pure water (water temperature above 65°C) to obtain slurry (1), then take 82.3 grams of ammonium paratungstate, 14.6 grams of strontium nitrate, 29.3 grams of Copper nitrate, 3.5 grams of potassium nitrate, 16.8 grams of magnesium nitrate, and 20.4 grams of nickel nitrate were dissolved in 500 ml of pure water (water temperature above 65° C.), fully stirred and mixed uniformly to obtain slurry (2). Then, slurry (1) is mixed with slurry (2) to obtain slurry (3) to obtain active ingredient slurry (a).

(2) Preparation of catalyst inner layer matrix

Add 12.6 grams of silicon dioxide to the slurry (a), stir vigorously at 80°C for 3 hours to carry out co-precipitation reaction, heat and dry, heat treat at 160°C in nitrogen for 3 hours, and then extrude it into φ4.5× The hollow columnar particles of 5 mm were dried at 120°C and then calcined at 480°C for 4 hours to obtain the catalyst matrix. The composition of the catalyst inner layer matrix was: Mo ₁₂ V ₉ W _4.5 Ni ₁ Cu _1.8 K _0.5 Mg _1.3

Step 2: Preparation of catalyst outer layer

Same as the preparation of the catalyst outer layer in Example 5, except that 9.7 grams of silicon dioxide, 6 grams of graphite and 36 grams of alumina were added.

Step 3: Preparation of Catalyst 5

Place the catalyst inner layer parent body prepared in step 1 in a round bottom container, spray distilled water to the catalyst parent body under the condition of container rotation, and spray the outer layer catalyst powder obtained in step 2 under the condition of fully wetting the catalyst inner layer parent body to coat The thickness of the coating is 0.8-1.2 mm. The obtained catalyst is dried at 75° C. and then calcined at 450° C. for 6 hours to obtain catalyst 5.

Comparative example 7:

The inner catalyst of Catalyst 5 was used as Comparative Catalyst 7, and then it was extruded into hollow columnar particles with a diameter of φ5×5 mm by extruder, and the reaction conditions were the same as those of Catalyst 1.

Example 6

Same as the preparation steps and raw materials of catalyst 5 in Example 5, just add 13.6 grams of lanthanum nitrate and 5.5 grams of strontium nitrate, add 7.3 grams of silicon dioxide in the inner layer; add 10.4 grams of silicon dioxide in the outer layer. The matrix composition of the inner layer of catalyst 6 is: Mo ₁₂ V ₅ W _0.7 Ni _2.8 Cu _0.8 Sr _0.3 La _0.6

oxidation reaction

The inner diameter of the fixed-bed single-tube reactor is 25 mm, and a thermocouple is installed inside. The reactor is filled with 45 ml of the above-mentioned catalyst, and heated in a salt bath. A mixed gas of 9% by volume of acrolein, 12% by volume of air, 14% by volume of water vapor, and 65% by volume of nitrogen was introduced from the inlet of the reaction tube at a space velocity of 1400 h ^-1 . The performance of the catalyst is shown in Table 1 and Table 2. The catalyst effectively suppresses hot spots, and the active components such as molybdenum are not easy to lose. The content of molybdenum and the like before and after the reaction of the catalyst is basically unchanged, and the catalytic performance of the catalyst is stable. The catalysts of Comparative Examples 1 to 7 could not effectively suppress the hot spot, and the selectivity was poor. After 1000 hours of reaction, the activity of the catalyst decreased significantly under the washing of the mixed air flow such as water vapor.

Evaluation result after 20 hours of reaction in table 1

Evaluation result after 1000 hours of reaction in table 2

Claims (15)

1. A composite multi-metal oxide catalyst, characterized in that the main composition of the catalyst consists of the following The general formula (I) represents Mo _a V _b W _c Ni _d A _e B _f Si _g O _x (I) Wherein: Mo is molybdenum, V is vanadium, W is tungsten, Ni is nickel, A is at least one element selected from copper, cobalt, manganese; B is at least one element selected from zirconium, strontium, lanthanum, magnesium and titanium A kind of element; Si is silicon, silicon is the carrier added, O is oxygen; a, b, c, d, e, f, g respectively represent the atomic ratio of each element, wherein when a=12 is the basis, b is 3 A number from 0 to 10, c is a number from 0.5 to 5, d is a number from 1 to 5, e is a number from 0 to 3, f is a number from 0 to 3, g is a number from 0.5 to 30 , x is a value determined by the oxygen of each oxide, the composite multi-metal oxide catalyst has an inner and outer double-layer structure, and the total content of one or more of the outer layer of silicon dioxide, aluminum oxide or silicon carbide is higher than that of the inner layer The height of the parent body of the layer is calculated by mole percentage, and the content concentration of each element in the outer layer of the catalyst is lower than that of the parent body in the inner layer. 2. The catalyst according to claim 1, characterized in that b is a number from 3 to 7. 3. The catalyst according to claim 1, characterized in that c is a number from 1 to 3. 4. The catalyst according to claim 1, characterized in that d is a number from 1.5 to 3. 5. according to the described catalyst of claim 1, it is characterized in that A is copper, and the composition of catalyst is represented by (II) Mo _a V _b W _c Ni _d Cu _e B _f Si _g O _x (II) wherein e is 0.1～2 a number of . 6. The catalyst according to claim 5, characterized in that B is strontium and/or lanthanum, wherein f is a number from 0.05 to 2. 7. The catalyst according to claim 1, characterized in that it is a multi-layer catalyst structure, and the content of each element in the outer layer is 0.5-30% lower than that in the inner layer in terms of mole percentage. 8. The catalyst according to claim 1, characterized in that the content of each element in the outer layer of the catalyst is 0.5-10% lower than that in the adjacent inner layer. 9. The catalyst according to claim 1, characterized in that A is at least one element selected from copper, cobalt, manganese; B is at least one element selected from zirconium, strontium, magnesium and titanium; catalyst composition In the general formula (I), e is a number from 0.1 to 2, and f is a number from 0.05 to 2. 10. The preparation method of the catalyst according to any one of claims 1 to 9, characterized in that it comprises the steps of: First, prepare the catalyst inner layer precursor: Dissolving and mixing the compounds containing Mo, V, W, Ni and the related element components of A _e B _f in the general formula (I), and co-precipitating to form the inner layer matrix slurry, drying, molding, Roasting to obtain the catalyst inner layer precursor; Secondly, prepare the outer layer catalyst slurry according to the method for preparing the catalyst inner layer matrix slurry, and add one or more substances such as silicon dioxide, aluminum oxide, and silicon carbide during the preparation of the outer layer catalyst slurry; Finally, the prepared outer layer catalyst is sequentially coated on the catalyst inner layer precursor, and the finished catalyst is obtained after roasting. 11. The preparation method of the catalyst according to claim 10, characterized in that the inner matrix is calcined at 300-480° C. for 3 to 10 hours after molding and the outer layer is coated, using open or closed calcining, The firing atmosphere is helium, nitrogen or argon. 12. the preparation method of catalyzer as claimed in claim 10 is characterized in that described catalyzer uses binding agent when coating, and binding agent is selected from one or more in water, silica sol, aluminum sol . 13. The preparation method of the catalyst as claimed in claim 10, characterized in that the catalyst is coated with a binding agent selected from one or more of alcohols or ethers. 14. The catalyst according to any one of claims 1-9, characterized in that one or more of glass fibers, graphite, ceramics or whiskers are added to each catalyst layer. 15. A multi-metal oxide catalyst, characterized in that the main composition of the catalyst is represented by the following formula (III): Mo _a V _b Ni _c Cu _d Nb _e Sr _f M _g N _h Si _i O _x (III), wherein: Mo is molybdenum, V is vanadium, Ni is nickel, Cu is copper, Nb is niobium, Sr is strontium, M is at least one element selected from cobalt, iron, manganese; N is selected from zinc, lanthanum, magnesium and At least one element in boron; O is oxygen; Si is silicon, and silicon is the carrier added, a, b, c, d, e, f, g, h, i represent the atomic ratio of each element respectively, wherein when a= When 12 is the reference, b is a number from 3 to 8, c is a number from 0.5 to 6, d is a number from 0.5 to 3, e is a number from 0.05 to 2, f is a number from 0.05 to 1.5, g is a number from 0.05 to 2, h is a number from 0.05 to 1.5, i is a number from 0.5 to 10, x is a value determined by the oxygen of each oxide, and the composite multi-metal oxide catalyst has internal and external Double-layer structure, the main composition of each layer of catalyst is the same, but the total content of one or more of silica, alumina or silicon carbide is different, and one or more of the outer layer of silica, alumina or silicon carbide The total content of the species is higher than that of the inner matrix. In mole percent, the concentration of each element in the outer layer of the catalyst is lower than that in the inner matrix. In molar percent, the content of each element in the outer layer is 0.5-30 lower than that in the inner layer. %.