Catalyst for synthesis of acrylic acid and method for preparing the same

Abstract

The application discloses a catalyst for synthesizing acrylic acid and a preparation method thereof, and belongs to the technical field of catalysts. The preparation method of the catalyst for synthesizing acrylic acid comprises three steps of preparing a catalyst active component powder, impregnation loading and drying and roasting. The catalyst for synthesizing acrylic acid obtained by the method has the advantages of high conversion rate of propenal and high yield of acrylic acid, and the conversion rate of propenal is 98.1-99.7%, the yield of acrylic acid is 97.9-99.3%, and the hot spot temperature is 225-235 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to a catalyst for synthesizing acrylic acid and a preparation method thereof, and belongs to the technical field of catalysts. BACKGROUND

[0002] Acrylic acid is an important organic chemical raw material, which has excellent polymerization performance and can be polymerized after esterification with methanol, ethanol and butanol or copolymerized with other ethylene monomers. Acrylic acid and ester polymer products are widely used in high water-absorbing resin products, detergents, adhesives, building materials, fibers and plastic processing fields. Early acrylic acid production processes include chloroethanol method, Reppe method and acrylonitrile hydrolysis method, which are gradually replaced due to high pollution and poor economy. At present, the research on acrylic acid preparation process mainly focuses on propane oxidation method and propylene oxidation method, and the propylene oxidation process has high propylene conversion rate and acrylic acid yield, which is the main method for industrial acrylic acid production.

[0003] Propylene oxidation to prepare acrylic acid is divided into one-step oxidation method and two-step oxidation method. In the one-step oxidation method process, propylene is directly reacted with air to generate acrylic acid under the action of a catalyst, and the propylene one-step oxidation method for preparing acrylic acid is conducive to reducing equipment investment, but the acrylic acid yield is low. The current research can only improve the yield to a certain extent, which is not suitable for industrial application. The two-step oxidation method is to first convert propylene into propylene aldehyde, and then react with air to generate acrylic acid. At present, domestic and foreign acrylic acid production devices all adopt the two-step oxidation method of propylene. The two-step oxidation method adopts double reactor series operation, propylene is reacted with air in the first reactor at (300-350℃) to generate propylene aldehyde, and propylene aldehyde is reacted with supplemental air in the second reactor at (200-300) ℃ to generate acrylic acid. The catalysts used are propylene oxidation catalyst for preparing propylene aldehyde and propylene aldehyde oxidation catalyst for preparing acrylic acid. Due to the rapid development of the above two kinds of catalysts, the synthesis of acrylic acid by propylene aldehyde oxidation has been widely used in industry, and the propylene aldehyde oxidation catalyst for preparing acrylic acid is generally an oxide of Mo-V series. The basic elements of the catalyst are Mo, V, and other elements added to improve the performance of the catalyst, such as Nb, Sn, Cr, W, Fe, Co, Ni, Sb, etc. As the propylene aldehyde oxidation catalyst for preparing acrylic acid, the application of the oxide of Mo-V series has been widely promoted, but the Mo-V active site of this kind of catalyst is amorphous, and the amorphous structure will gradually be damaged in the high-temperature water vapor environment of propylene aldehyde oxidation to synthesize acrylic acid. This damage mainly manifests as the loss of Mo, the active component of the catalyst, and the change of the crystal state of the catalyst. The damaged catalyst is prone to accumulate heat in the catalyst bed, causing hot spots. The hot spots will cause the local temperature to be too high, thereby reducing the yield of acrylic acid and also exacerbating the damage to the catalyst, thus causing a vicious cycle, which causes the catalyst to be rapidly deactivated, and poses a great obstacle to the stable operation of production.

[0004] Recently, the person skilled in the art improves the performance of the catalyst by changing the forming method of the catalyst in order to prolong its service life. For example, at present, the cylindrical or hollow cylindrical catalyst has the advantages of high strength and abrasion of the catalyst, more active components of the catalyst, and prolonged service life. However, in the actual production of acrylic acid, hot spots frequently occur in the catalyst bed, which leads to the decrease of the activity of the catalyst, and the catalyst needs to be regenerated frequently, which reduces the production cycle of the acrylic acid device. The spherical catalyst has the advantages of high effective utilization factor of the active components of the catalyst and effective removal of reaction heat, but it is greatly affected by the forming process, and the specific surface area of the catalyst is greatly lost, which leads to the decrease of the activity and selectivity of the catalyst.

[0005] Chinese patent CN102039143A discloses a preparation method of a catalyst for preparing acrylic acid by oxidation of propylene aldehyde. The water-soluble metal salt containing Mo, V, W, Cu and Sb components is dispersed in a water / organic phase mixed system at 30-100°C; the weight ratio of the organic solvent to water is maintained at 5-50%; the reaction generates a composite oxide precursor slurry; the water is separated by distillation process at 20-120°C under the condition of continuous supplement of the organic phase, so that the water content in the distillate is not more than 10%; then, the spray drying is performed for granulation, and the catalyst active component is prepared by calcination at 200-600°C; the primary calcined powder is mixed with a forming additive and a strength improver, and a binder is used to coat the active component on the surface of the inert carrier, and the loading amount accounts for 5-70% of the total weight of the catalyst; the formed product is dried at room temperature for 5-48 hours, and then calcined at 200-600°C for 1-15 hours to obtain the spherical catalyst with the active component loaded on the inert carrier. Although the propylene aldehyde conversion rate of the catalyst obtained by the patent can reach 98.8%, the hot spot temperature is all above 270°C, which is 20°C higher than the reaction temperature, and the rapid discharge of a large amount of reaction heat is not ideal, so the catalytic activity will decrease sharply in long-term use.

[0006] Chinese patent CN102909029A discloses a method for producing a catalyst for the production of acrylic acid, wherein: a) metal salts containing Mo, V, W, Cu, Sb components are dispersed in deionized water at 30-100 DEG C with a surfactant added in advance, and kept for 1-10 hours to form a slurry; then the slurry is dried to obtain a dry material, which is molded with an amine solvent and a liquid binder after a primary calcination treatment, and then a second calcination treatment to obtain a catalyst; b) the catalyst described in a) has a crystalline structure in the Mo-V active site of the surface layer, and an amorphous structure in the bulk phase of the catalyst; c) the thickness of the Mo-V active site with a crystalline structure in the surface layer of the catalyst described in a) is between 10 μm and 3 mm; d) the metal salts in a) wherein the source of Mo is selected from ammonium molybdate, the source of V is selected from ammonium metavanadate, W is selected from ammonium metatungstate, Cu is selected from one of copper sulfate, copper acetate, copper nitrate, and Sb is selected from antimony acetate. The technical solution of the patent is mainly to solve the problem of excessive heat point temperature caused by the accumulation of reaction heat of the catalyst, but the test data disclosed in the patent shows that the heat point temperature of the examples is all above 285 DEG C, and the heat point temperature of most examples is higher than 300 DEG C, which shows that the patent has not effectively solved the problem of slow removal of reaction heat accumulation of the catalyst.

[0007] As can be seen above, the catalyst for the oxidation of propylene aldehyde to produce acrylic acid still has problems of slow removal of reaction heat, high heat point temperature, etc., therefore, it is of great significance to develop a catalyst for the oxidation of propylene aldehyde to produce acrylic acid which can quickly remove reaction heat, has good selectivity, high yield and good stability, so as to improve the quality of acrylic acid and reduce the industrial production cost. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a catalyst for the synthesis of acrylic acid and a preparation method thereof, which realizes the following purposes: a catalyst for the synthesis of acrylic acid which can quickly remove reaction heat, has low heat point temperature, good selectivity, high yield and good stability is prepared.

[0009] To realize the above-mentioned purposes, the present application adopts the following technical solutions:

[0010] A catalyst for the synthesis of acrylic acid and a preparation method thereof, the catalyst for the synthesis of acrylic acid has a propylene aldehyde conversion rate of 98.1-99.7%, an acrylic acid yield of 97.9-99.3%, and a heat point temperature of 225-235 DEG C;

[0011] The preparation method of the catalyst for the synthesis of acrylic acid comprises three steps of preparing a catalyst active component powder, impregnation loading and drying calcination;

[0012] The following is a further improvement on the above technical solution:

[0013] Step 1, preparation of catalyst active component powder

[0014] The vanadium-containing compound, the molybdenum-containing compound, and the tungsten-containing compound are added to deionized water, and after complete dissolution by heating and stirring, a mixed salt solution is obtained. Under constant temperature stirring and reflux conditions, copper nitrate aqueous solution, indium-containing compound aqueous solution, and tin acetate are added to the mixed salt solution. After the reaction is complete, the temperature is lowered to room temperature to obtain an active component slurry. Then, spray drying is performed, followed by calcination to obtain the catalyst active component powder.

[0015] The vanadium-containing compound is one or a mixture of two of ammonium metavanadate and vanadyl sulfate in any mass ratio.

[0016] The molybdenum-containing compound is one or a mixture of two of ammonium molybdate and ammonium heptamolybdate in any mass ratio.

[0017] The tungsten-containing compound is one or a mixture of two of ammonium tungstate and ammonium metatungstate in any mass ratio.

[0018] The indium-containing compound is one or a mixture of two of indium sulfate and indium nitrate in any mass ratio.

[0019] In the mixed salt solution, the mass ratio of the vanadium-containing compound, the molybdenum-containing compound, the tungsten-containing compound, and deionized water is (15-39):(25-60):(5-40):(160-380).

[0020] The mass ratio of the mixed salt solution, the copper nitrate aqueous solution, the indium-containing compound aqueous solution, and the tin acetate is (160-360):(45-100):(25-65):(6-18).

[0021] The mass fraction of copper nitrate in the copper nitrate aqueous solution is 20-35wt%.

[0022] The mass fraction of the indium-containing compound in the indium-containing compound aqueous solution is 10-25wt%.

[0023] The constant temperature stirring is at a temperature of 90-98℃ and a stirring rate of 400-900 revolutions per minute.

[0024] The reaction is complete in 3-7 hours.

[0025] The spray drying is performed at a feed rate of 30-80mL / min, a spray pressure of 0.5-0.6MPa, an inlet temperature of 145-165℃, and an outlet temperature of 80-90℃.

[0026] The calcination is performed at a heating rate of 2-3℃ / min, heating and constant temperature to 450-650℃, and constant temperature calcination for 4-7 hours.

[0027] Step 2, impregnation of the carrier

[0028] The catalyst active component powder, liquid ceramic precursor, nano silicon carbide powder, pore-forming agent, and tetrahydrofuran are placed in a double planetary mixer, and after replacing the air in the double planetary mixer with nitrogen, the materials in the double planetary mixer are uniformly dispersed and mixed at a high speed under the condition of nitrogen sealing and low temperature in the double planetary mixer, to obtain an impregnation slurry. Then, the silicon carbide foam is placed in a vacuum tank, vacuum is applied, and the impregnation slurry is drawn into the tank by vacuum negative pressure, so that the silicon carbide foam is completely immersed in the impregnation slurry. After impregnation, the negative pressure is removed, the material is filtered out, and the surface of the filtered solid is blown clean with air, followed by low-temperature drying to obtain a catalyst semi-finished product.

[0029] The liquid ceramic precursor is one of liquid polysilazane, liquid polycarbosilane, and liquid polyborosilazane.

[0030] The number average molecular weight of the liquid ceramic precursor is 600-2000 g / mol.

[0031] The particle size of the nano silicon carbide powder is 10-100 nm.

[0032] The pore-forming agent is one of trihydrazyl-sym-triazine, N,N'-diaminocarbonyl hydrazine, and oxalyl dihydrazide, or a mixture of two or more thereof in any mass ratio.

[0033] The porosity of the silicon carbide foam is 60-85%, and the pore size is 20-30 ppi.

[0034] The mass ratio of the catalyst active component powder, liquid ceramic precursor, nano silicon carbide powder, pore-forming agent, and tetrahydrofuran is (85-150):(20-50):(8-20):(5-15):(55-110).

[0035] The low-temperature state is controlled at a temperature of 25-40℃.

[0036] The high-speed dispersion and mixing are performed at a stirring rate of 100-160 rpm, a dispersion rate of 8000-12000 rpm, and a dispersion and mixing time of 10-16 hours.

[0037] The standing impregnation is performed for 24-36 hours.

[0038] The vacuum is drawn to a vacuum negative pressure of -0.095 to -0.1 MPa.

[0039] The low-temperature drying is performed at a drying temperature of 55-85℃ for 22-38 hours.

[0040] Step 3, drying and calcining

[0041] The catalyst semi-product is placed in an oven and dried at 120-180 DEG C for 3-9 hours, then the catalyst semi-product is transferred into a muffle furnace, heated and kept at 550-700 DEG C at a heating rate of 1-3 DEG C / min, and kept at the temperature for 6-11 hours, then cooled to room temperature to obtain the catalyst for propylene acid synthesis.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] 1. In the catalyst active component, indium and tin are added, which can promote the fine crystallization of the complex oxide crystal phase of vanadium, molybdenum, tungsten and copper in the oxidation sintering process, so that the active component of the complex oxide is obtained, which not only has very high catalytic activity, but also can resist the erosion of high-temperature water vapor and the thermal shock effect caused by hot spot temperature for a long time, so the addition of indium and tin can play a very key synergistic effect to maintain the long-term stability of the catalytic activity of the catalyst.

[0044] 2. The catalyst active component powder is impregnated and coated on the inner and outer surfaces of the silicon carbide foam by impregnation loading, and in order to ensure the bonding strength of the catalyst active component powder and the silicon carbide foam, a liquid ceramic precursor capable of ceramic reaction is selected as the adhesive, and the silicon carbide foam is selected as the carrier, which mainly utilizes the high thermal conductivity of silicon carbide to promote the close combination of the catalyst active component powder and the silicon carbide foam through the ceramic reaction of the liquid ceramic precursor, so that the large amount of heat generated by the catalyst active component in the catalytic reaction process can be quickly transferred to the silicon carbide foam carrier, and then the reaction heat is quickly removed relying on the network skeleton structure of the silicon carbide foam, and in order to enhance the heat conduction efficiency between the catalyst active component and the silicon carbide foam, the present application specially adds nano silicon carbide powder with high thermal conductivity in the impregnation loading process, which utilizes the high thermal conductivity and large specific surface area of the nano silicon carbide powder itself as a high-thermal-conductivity medium to promote the rapid conduction of the heat of the catalyst active component powder to the silicon carbide foam carrier.

[0045] 3. The liquid ceramic precursor added in the present application forms a certain coverage on the catalyst active component powder during the ceramic process, in order to avoid the coverage of the catalyst active component powder, the present application adds a pore-forming agent to form micropores through thermal decomposition of the pore-forming agent to offset the coverage effect of the ceramic product, so that the catalyst active component powder maintains the original high specific surface area, which can not only ensure the close and high-strength combination of the catalyst active component powder and the silicon carbide foam carrier, but also maintain the high catalytic activity of itself.

[0046] 4, the acrylic acid synthesis catalyst obtained by the method has propenal conversion rate of 98.1-99.7%, acrylic acid yield of 97.9-99.3%, and hot spot temperature of 225-235 DEG C. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 A scanning electron microscope photo of the inner surface of the acrylic acid synthesis catalyst obtained in Example 1, magnified by 1000 times;

[0048] Figure 2 A scanning electron microscope photo of the inner surface of the acrylic acid synthesis catalyst obtained in Example 1, magnified by 10000 times. DETAILED DESCRIPTION

[0049] The preferred embodiments of the present application are described below, and it should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0050] Example 1: a preparation method of an acrylic acid synthesis catalyst

[0051] Step 1, preparation of catalyst active component powder

[0052] The vanadium-containing compound, the molybdenum-containing compound, and the tungsten-containing compound are added to deionized water, and after complete dissolution by heating and stirring, a mixed salt solution is obtained; under constant temperature stirring reflux state, the mixed salt solution is added with a copper nitrate aqueous solution, an indium-containing compound aqueous solution, and tin acetate; after the reaction is completed, the temperature is lowered to room temperature to obtain an active component slurry, which is then subjected to spray drying, and then calcination to obtain catalyst active component powder;

[0053] The vanadium-containing compound is ammonium metavanadate;

[0054] The molybdenum-containing compound is ammonium molybdate;

[0055] The tungsten-containing compound is ammonium tungstate;

[0056] The indium-containing compound is indium sulfate;

[0057] In the mixed salt solution, the mass ratio of the vanadium-containing compound, the molybdenum-containing compound, the tungsten-containing compound, and the deionized water is 28:40:30:270;

[0058] The mass ratio of the mixed salt solution, the copper nitrate aqueous solution, the indium-containing compound aqueous solution, and the tin acetate is 260:80:45:11;

[0059] The mass fraction of copper nitrate in the copper nitrate aqueous solution is 30wt%;

[0060] The mass fraction of the indium-containing compound in the indium-containing compound aqueous solution is 15wt%;

[0061] The constant temperature stirring is at 96℃ and the stirring rate is 700 rpm;

[0062] The reaction is complete and the reaction time is 4 hours;

[0063] The spray drying is controlled at a feeding speed of 60 mL / min, a spray pressure of 0.56 MPa, an inlet temperature of 155℃ and an outlet temperature of 86℃;

[0064] The calcination is at a temperature rising rate of 2.6℃ / min, the temperature is raised to 550℃ and kept constant, and the constant temperature calcination is for 6 hours.

[0065] Step 2, impregnation loading

[0066] The catalyst active component powder, the liquid ceramic precursor, the nano silicon carbide powder, the pore-forming agent and the tetrahydrofuran are put into a double planetary mixer, the air in the double planetary mixer is replaced by nitrogen, the nitrogen in the double planetary mixer is maintained in a sealed and low-temperature state, the materials in the double planetary mixer are uniformly dispersed and mixed at a high speed, and then an impregnation slurry is obtained. Then, the silicon carbide foam is put into a vacuum kettle, vacuumized, and the impregnation slurry is sucked into the kettle by vacuum negative pressure, so that the silicon carbide foam is completely immersed in the impregnation slurry. After impregnation, the negative pressure is removed, the material is filtered out, the surface of the filtered solid is blown clean by air, and then low-temperature drying is performed to obtain a catalyst semi-finished product.

[0067] The liquid is a liquid polysilazane;

[0068] The number average molecular weight of the liquid ceramic precursor is 1000 g / mol;

[0069] The particle size of the nano silicon carbide powder is 40 nm;

[0070] The pore-forming agent is trihydrazyl-sym-triazine;

[0071] The porosity of the silicon carbide foam is 75% and the pore size is 28 ppi;

[0072] The mass ratio of the catalyst active component powder, the liquid ceramic precursor, the nano silicon carbide powder, the pore-forming agent and the tetrahydrofuran is 110:40:15:11:80;

[0073] The low-temperature state is controlled at a temperature of 30℃;

[0074] The high-speed dispersion mixing is controlled at a stirring rate of the double planetary mixer of 140 rpm, a dispersion rate of 10,000 rpm and a dispersion mixing time of 12 hours;

[0075] The standing impregnation is controlled at a standing impregnation time of 33 hours;

[0076] The vacuum is drawn to -0.098 MPa.

[0077] The low-temperature drying is performed at 75 DEG C for 32 hours.

[0078] Step 3, drying and calcination

[0079] The catalyst semi-product is dried in an oven at 150 DEG C for 6 hours, then transferred into a muffle furnace, heated and kept at 650 DEG C at a heating rate of 2 DEG C / min, kept at the temperature for 8 hours, then cooled to room temperature to discharge, to obtain the catalyst for acrylic acid synthesis.

[0080] Example 2: a preparation method of a catalyst for acrylic acid synthesis

[0081] Step 1, preparation of catalyst active component powder

[0082] The vanadium-containing compound, molybdenum-containing compound, tungsten-containing compound are added into deionized water, heated and stirred to completely dissolve to obtain a mixed salt solution, under constant temperature stirring reflux state, copper nitrate aqueous solution, indium-containing compound aqueous solution, tin acetate are added into the mixed salt solution, after the reaction is completed, it is cooled to room temperature to obtain an active component slurry, then spray drying is performed, and after calcination, catalyst active component powder is obtained;

[0083] The vanadium-containing compound is vanadyl sulfate;

[0084] The molybdenum-containing compound is ammonium heptamolybdate;

[0085] The tungsten-containing compound is ammonium metatungstate;

[0086] The indium-containing compound is indium nitrate;

[0087] In the mixed salt solution, the mass ratio of vanadium-containing compound, molybdenum-containing compound, tungsten-containing compound, deionized water is 15:25:5:160;

[0088] The mass ratio of the mixed salt solution, copper nitrate aqueous solution, indium-containing compound aqueous solution, tin acetate is 160:45:25:6;

[0089] The mass fraction of copper nitrate in the copper nitrate aqueous solution is 20wt%;

[0090] The mass fraction of indium-containing compound in the indium-containing compound aqueous solution is 10wt%;

[0091] The constant temperature stirring is performed at a temperature of 90 DEG C and a stirring rate of 400 rpm;

[0092] The reaction is completed in 3 hours;

[0093] The spray drying is controlled at a feeding speed of 30 mL / min, a spray pressure of 0.5 MPa, an inlet temperature of 145 DEG C, and an outlet temperature of 80 DEG C.

[0094] The calcining is performed at a temperature increasing rate of 2 DEG C / min, and the temperature is increased to 450 DEG C and kept constant for 4 hours.

[0095] Step 2, impregnation loading

[0096] The catalyst active component powder, the liquid ceramic precursor, the nano silicon carbide powder, the pore-forming agent, and the tetrahydrofuran are placed into a double planetary mixer, the air in the double planetary mixer is replaced by nitrogen, and then the double planetary mixer is maintained in a nitrogen-sealed and low-temperature state; the materials in the double planetary mixer are uniformly dispersed and mixed at a high speed to obtain an impregnation slurry; the silicon carbide foam is placed into a vacuum tank, vacuum is applied to the tank, and the impregnation slurry is drawn into the tank to immerse the silicon carbide foam in the impregnation slurry; after impregnation, the vacuum is released, the material is discharged and filtered, the surface of the filtered solid is cleaned by air blowing, and then the solid is dried at a low temperature to obtain a catalyst semi-product.

[0097] The liquid ceramic precursor is a liquid polycarbosilane.

[0098] The number average molecular weight of the liquid ceramic precursor is 600 g / mol.

[0099] The particle size of the nano silicon carbide powder is 10 nm.

[0100] The pore-forming agent is N,N'-diaminoformohydrazide.

[0101] The porosity of the silicon carbide foam is 60%, and the pore size is 20 ppi.

[0102] The mass ratio of the catalyst active component powder, the liquid ceramic precursor, the nano silicon carbide powder, the pore-forming agent, and the tetrahydrofuran is 85:20:8:5:55.

[0103] The low-temperature state is controlled at a temperature of 25 DEG C.

[0104] The high-speed dispersion and mixing are performed at a stirring rate of 100 rpm, a dispersion rate of 8000 rpm, and a dispersion and mixing time of 10 hours.

[0105] The standing impregnation is performed for 24 hours.

[0106] The vacuum is drawn to a vacuum pressure of -0.095 MPa.

[0107] The low-temperature drying is performed at a drying temperature of 55 DEG C for 22 hours.

[0108] Step 3, drying and calcination

[0109] The catalyst semi-product is placed in an oven and dried at 120℃ for 3 hours, then the catalyst semi-product is transferred into a muffle furnace, heated and kept at 550℃ at a heating rate of 1℃ / min, kept at this temperature for 6 hours, then cooled to room temperature and discharged, to obtain a catalyst for acrylic acid synthesis.

[0110] Example 3: a preparation method of a catalyst for acrylic acid synthesis

[0111] Step 1, preparation of catalyst active component powder

[0112] The vanadium-containing compound, molybdenum-containing compound, tungsten-containing compound are added to deionized water, heated and stirred to completely dissolve to obtain a mixed salt solution, under constant temperature stirring reflux state, copper nitrate aqueous solution, indium-containing compound aqueous solution, tin acetate are added to the mixed salt solution, after the reaction is completed, it is cooled to room temperature to obtain an active component slurry, then spray drying is carried out, and after calcination, the catalyst active component powder is obtained;

[0113] The vanadium-containing compound is ammonium metavanadate;

[0114] The molybdenum-containing compound is ammonium molybdate;

[0115] The tungsten-containing compound is ammonium tungstate;

[0116] The indium-containing compound is indium sulfate;

[0117] In the mixed salt solution, the mass ratio of vanadium-containing compound, molybdenum-containing compound, tungsten-containing compound and deionized water is 39:60:40:380;

[0118] The mass ratio of the mixed salt solution, copper nitrate aqueous solution, indium-containing compound aqueous solution and tin acetate is 360:100:65:18;

[0119] The mass fraction of copper nitrate in the copper nitrate aqueous solution is 35wt%;

[0120] The mass fraction of indium-containing compound in the indium-containing compound aqueous solution is 25wt%;

[0121] The constant temperature stirring is at a temperature of 98℃ and a stirring rate of 900 revolutions per minute;

[0122] The reaction is complete, and the reaction time is 7 hours;

[0123] The spray drying is controlled at a feeding speed of 80mL / min, a spray pressure of 0.6MPa, an inlet temperature of 165℃ and an outlet temperature of 90℃;

[0124] The calcination is heated at a heating rate of 3℃ / min, heated and kept at 650℃, and kept at constant temperature for 7 hours.

[0125] Step 2, impregnation loading

[0126] The catalyst active component powder, liquid ceramic precursor, nano silicon carbide powder, pore-forming agent, and tetrahydrofuran are placed in a double planetary mixer, the air in the double planetary mixer is replaced by nitrogen, and the nitrogen in the double planetary mixer is maintained in a sealed and low-temperature state. After the materials in the double planetary mixer are uniformly dispersed and mixed at high speed, an impregnation slurry is obtained. Then, the silicon carbide foam is placed in a vacuum tank, vacuum is applied, and the impregnation slurry is sucked into the tank to completely immerse the silicon carbide foam in the impregnation slurry. After impregnation, the negative pressure is removed, the material is filtered, and the filtered solid is cleaned with air to remove the surface slurry. After low-temperature drying, a catalyst semi-finished product is obtained.

[0127] The liquid ceramic precursor is a liquid polysilazane;

[0128] The number average molecular weight of the liquid ceramic precursor is 2000 g / mol;

[0129] The particle size of the nano silicon carbide powder is 100 nm;

[0130] The pore-forming agent is oxalyl dihydrazide;

[0131] The porosity of the silicon carbide foam is 85%, and the pore size is 30 ppi;

[0132] The mass ratio of the catalyst active component powder, liquid ceramic precursor, nano silicon carbide powder, pore-forming agent, and tetrahydrofuran is 150:50:20:15:110;

[0133] The low-temperature state is controlled at a temperature of 40℃;

[0134] The high-speed dispersion mixing is performed at a stirring rate of 160 rpm, a dispersion rate of 12000 rpm, and a dispersion mixing time of 16 hours;

[0135] The static impregnation is performed for 36 hours;

[0136] The vacuum is applied to a negative pressure of -0.1 MPa;

[0137] The low-temperature drying is performed at a drying temperature of 85℃ for 38 hours.

[0138] Step 3, drying and calcination

[0139] The catalyst semi-product was dried in an oven at 180°C for 9 hours, then transferred into a muffle furnace, heated and kept at 700°C at a heating rate of 3°C / min, kept at this temperature for 11 hours, then cooled to room temperature and discharged to obtain the catalyst for acrylic acid synthesis.

[0140] Comparative Example 1: Based on Example 1, in Step 1 for preparing the catalyst active component powder, 45 parts of the indium-containing compound aqueous solution was replaced with an equal amount of 45 parts of copper nitrate aqueous solution, and the specific operation was as follows:

[0141] Step 1, preparation of catalyst active component powder

[0142] 45 parts of the indium-containing compound aqueous solution was replaced with an equal amount of 45 parts of copper nitrate aqueous solution, and the other operations were the same as in Example 1.

[0143] Steps 2 and 3 were the same as in Example 1.

[0144] Comparative Example 2: Based on Example 1, in Step 1 for preparing the catalyst active component powder, 11 parts of tin acetate was replaced with an equal amount of 11 parts of copper nitrate aqueous solution, and the specific operation was as follows:

[0145] Step 1, preparation of catalyst active component powder

[0146] 11 parts of tin acetate was replaced with an equal amount of 11 parts of copper nitrate aqueous solution, and the other operations were the same as in Example 1.

[0147] Steps 2 and 3 were the same as in Example 1.

[0148] Comparative Example 3: Based on Example 1, in Step 2 for impregnation and loading, 15 parts of nano silicon carbide powder was replaced with an equal amount of 15 parts of tetrahydrofuran, and the specific operation was as follows:

[0149] Step 1 was the same as in Example 1.

[0150] Step 2, impregnation and loading

[0151] 15 parts of nano silicon carbide powder was replaced with an equal amount of 15 parts of tetrahydrofuran, and the other operations were the same as in Example 1.

[0152] Step 3 was the same as in Example 1.

[0153] Comparative Example 4: Based on Example 1, in Step 2 for impregnation and loading, 11 parts of pore-forming agent was replaced with an equal amount of 11 parts of tetrahydrofuran, and the specific operation was as follows:

[0154] Step 1 was the same as in Example 1.

[0155] Step 2, impregnation and loading

[0156] The 11 parts of pore forming agent were replaced by 11 parts of tetrahydrofuran, and other operations were the same as in Example 1.

[0157] Step 3 was operated as in Example 1.

[0158] Catalyst performance test:

[0159] The catalysts for synthesizing acrylic acid obtained in Examples 1-3 and Comparative Examples 1, 2, 3 and 4 were loaded into a reaction tube for performance test. The reaction tube was a stainless steel tube with a diameter of 30x25 mm and a length of 4000 mm, and a stainless steel temperature measuring sleeve with a diameter of 4 mm was inserted in the tube. The heat medium was molten salt. The reaction of propylene oxide to prepare acrylic acid was simulated in a single reaction tube of an industrial device. The process conditions were as follows: total space velocity 3000 h-1, raw material gas consisting of 8% by mass of propylene oxide, 10% by mass of oxygen and 35% by mass of water vapor, and the balance being nitrogen, and salt bath temperature 220°C. The conversion rate of propylene oxide and the yield of acrylic acid were analyzed and calculated by gas chromatography. The average conversion rate of propylene oxide and the average yield of acrylic acid during the running of 500 hours and 3000 hours were calculated, and the highest hot spot temperature during the running was recorded. -1

[0160] The test results are shown in Table 1.

[0161] Table 1

[0162]

[0163] ​It can be seen from the test data in Table 1 that the maximum value of the hot spot temperature of the catalysts obtained in Examples 1-3 is only 15℃ higher than the reaction temperature during the operation of 500 and 3000 hours, and the conversion rate of propylene aldehyde can be maintained above 98.1%, and the yield of acrylic acid is higher than 97.9%, which shows that the catalyst for synthesizing acrylic acid obtained in the application can quickly remove the reaction heat, and has the advantages of low hot spot temperature, good selectivity, high yield and good stability; the hot spot temperature of Comparative Example 1 and Comparative Example 2 is significantly reduced, which may be caused by the reduction of the catalytic activity of the catalyst, the reduction of the reaction rate and the reduction of the heat release, and the conversion rate of propylene aldehyde and the yield of acrylic acid of Comparative Example 1 and Comparative Example 2 are also greatly reduced, which may be caused by the synergistic effect of the two metal elements of indium and tin on improving the catalytic activity of the catalyst; the hot spot temperature of Comparative Example 3 is greatly increased, and the conversion rate of propylene aldehyde and the yield of acrylic acid of Comparative Example 3 are also greatly reduced, which shows that the addition of nano silicon carbide powder can effectively promote the rapid export of the reaction heat in the catalyst; the hot spot temperature of Comparative Example 4 is greatly reduced, and the conversion rate of propylene aldehyde and the yield of acrylic acid of Comparative Example 4 are also greatly reduced, which may be caused by the reduction of the specific surface area of the catalyst due to the non-addition of the pore-forming agent, and thus the catalytic activity is greatly reduced.

[0164] Figure 1 is a scanning electron microscope photograph of the inner surface of the catalyst for synthesizing acrylic acid obtained in Example 1, which is enlarged 1000 times; Figure 1 Figure 2 is a scanning electron microscope photograph of the inner surface of the catalyst for synthesizing acrylic acid obtained in Example 1, which is enlarged 10000 times; Figure 2 Figure 3 is a scanning electron microscope photograph of the inner surface of the catalyst for synthesizing acrylic acid obtained in Example 1, which is enlarged 10000 times; Figure 1 It can be seen from Figure 1 that the carrier of the catalyst for synthesizing acrylic acid is an open-cell foam, and the surface of the foam skeleton is very rough, which is caused by the attachment of the catalyst active component powder on the surface of the foam skeleton; Figure 1 It can be seen from Figure 2 that the attached catalyst active component powder is not very dense, and has many small micropores; Figure 2 It can be seen from Figure 3 that the microporous structure is dense, which is caused by the decomposition of the pore-forming agent, which shows that the catalyst obtained in the application has a relatively large specific surface area, which can ensure that the catalyst has a very large catalytic reaction contact site, and thus has high catalytic activity; Figure 2It can also be seen that the active component powder of the catalyst attached to the surface of the silicon carbide foam has no obvious interface or cracks with the surface of the carrier, which shows that in the drying and calcination step, the active component powder of the catalyst is under the bonding and solidification of the liquid ceramic precursor and in the process of ceramization, the active component powder of the catalyst and the surface of the silicon carbide foam form a relatively dense and firm ceramization bonding effect, so that the molybdenum vanadium tungsten copper indium tin oxide-based catalyst powder and the surface of the silicon carbide foam can be connected together in a chemical bonding manner, and then a relatively stable ceramic phase catalyst is formed, which can give the catalyst excellent heat resistance, gas flow scouring resistance and very good high thermal conductivity, and thus has long-term stability, maintains the long-term use of the catalyst, and has long-term catalytic activity and high-efficiency removal of reaction heat.

[0165] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art can make equivalent replacement, change or modification according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for preparing a catalyst for synthesizing acrylic acid, characterized in that: the method for preparing the catalyst for synthesizing acrylic acid comprises three steps of preparing a catalyst active component powder, impregnation loading, and drying and calcination; the catalyst active component powder is prepared by adding a vanadium-containing compound, a molybdenum-containing compound, and a tungsten-containing compound into deionized water, heating and stirring to completely dissolve to obtain a mixed salt solution, adding a copper nitrate aqueous solution, an indium-containing compound aqueous solution, and tin acetate into the mixed salt solution under constant temperature stirring and refluxing, cooling to room temperature after complete reaction, obtaining an active component slurry, then performing spray drying, and obtaining the catalyst active component powder after calcination; the indium-containing compound is one of indium sulfate and indium nitrate or a mixture of the two in any mass ratio; the impregnation loading is performed by placing the catalyst active component powder, a liquid ceramic precursor, nano silicon carbide powder, a pore-forming agent, and tetrahydrofuran into a double planetary mixer, replacing the air in the double planetary mixer with nitrogen, maintaining the nitrogen sealing and low temperature state in the double planetary mixer, uniformly mixing the materials in the double planetary mixer at high speed, obtaining an impregnation slurry, placing a silicon carbide foam into a vacuum tank, vacuumizing, using vacuum negative pressure to draw the impregnation slurry into the tank, completely immersing the silicon carbide foam into the impregnation slurry, standing for impregnation, removing the negative pressure after complete impregnation, discharging and filtering, blowing the surface slurry of the filtered solid with air to clean, low-temperature drying, and obtaining a catalyst semi-product; the liquid ceramic precursor is one of a liquid polysilazane, a liquid polycarbosilane, and a liquid polyborosilazane; the number average molecular weight of the liquid ceramic precursor is 600-2000 g / mol; the particle size of the nano silicon carbide powder is 10-100 nm; the pore-forming agent is one of trihydrazino-s-triazine, N,N'-diaminoformohydrazide, and oxalyl dihydrazide or a mixture of two in any mass ratio; and the porosity of the silicon carbide foam is 60-85%, and the pore size is 20-30 ppi. 2.The method for preparing the catalyst for synthesizing acrylic acid according to claim 1, characterized in that: the vanadium-containing compound is one of ammonium metavanadate and vanadyl sulfate or a mixture of the two in any mass ratio; the molybdenum-containing compound is one of ammonium molybdate and ammonium heptamolybdate or a mixture of the two in any mass ratio; and the tungsten-containing compound is one of ammonium tungstate and ammonium metatungstate or a mixture of the two in any mass ratio. 3.The method for preparing the catalyst for synthesizing acrylic acid according to claim 1, characterized in that: in the mixed salt solution, the mass ratio of the vanadium-containing compound, the molybdenum-containing compound, the tungsten-containing compound, and the deionized water is (15-39):(25-60):(5-40):(160-380); the mass ratio of the mixed salt solution, the copper nitrate aqueous solution, the indium-containing compound aqueous solution, and the tin acetate is (160-360):(45-100):(25-65):(6-18); the mass fraction of copper nitrate in the copper nitrate aqueous solution is 20-35 wt%; and the number average molecular weight of the liquid ceramic precursor is 600-2000 g / mol. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The mass fraction of the indium-containing compound in the aqueous solution of the indium-containing compound is 10-25 wt%.

4. The method for preparing a catalyst for synthesizing acrylic acid according to claim 1, characterized in that: The mass ratio of the catalyst active component powder, the liquid ceramic precursor, the nano silicon carbide powder, the pore-forming agent and the tetrahydrofuran is (85-150):(20-50):(8-20):(5-15):(55-110).

5. The method for preparing a catalyst for synthesizing acrylic acid according to claim 1, characterized in that: The dry roasting is performed by placing the catalyst semi-product into an oven, drying at 120-180 ℃ for 3-9 hours, then transferring the catalyst semi-product into a muffle furnace, heating and keeping at 550-700 ℃ at a heating rate of 1-3 ℃ / min, keeping the temperature for 6-11 hours, then reducing the temperature to room temperature to discharge the catalyst, thereby obtaining the catalyst for synthesizing acrylic acid.

6. A catalyst for synthesizing acrylic acid prepared by the method according to any one of claims 1-5.

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