Movtenbox-based metal oxide molded catalyst, and molding method therefor and use thereof

Abstract

An MoVTeNbOx-based metal oxide molded catalyst, and a molding method therefor and the use thereof. The molding method comprises the following steps: A) mixing an MoVTeNbOx-based metal oxide raw powder catalyst, an inert substance and a sesbania powder, performing kneading, and sequentially spraying an alkaline amino acid solution, an acid solution and a halogen compound solution during the kneading process to obtain a kneaded material; B) performing extrusion molding on the kneaded material, and drying same to obtain a catalyst blank; and C) roasting the catalyst blank to obtain an MoVTeNbOx-based metal oxide molded catalyst. By introducing an alkaline amino acid, the secondary pore structure of the catalyst is optimized, and the selectivity is greatly improved. In addition, a trace amount of a halogen is introduced as an inhibitor, and the addition of the alkaline amino acid and the inhibitor makes the MoVTeNbOx catalyst have an acrylic acid selectivity of 80% or more, thereby greatly reducing the generation of by-products.

Description

MoVTeNbOx series metal oxide shaped catalyst, its shaping method and application

[0001] The present application claims priority to the Chinese patent application No. 202410706672.8, filed on June 03, 2024, and entitled "MoVTeNbOx series metal oxide shaped catalyst, its shaping method and application", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application belongs to the field of catalyst shaping technology, and particularly relates to a MoVTeNbOx series metal oxide shaped catalyst, its shaping method and application. BACKGROUND

[0003] Acrylic acid is an important unsaturated organic acid. The carbon-carbon double bond and carboxyl group in its molecular structure enable it to undergo various reactions such as polymerization and esterification, and it is widely used in various fields of national economy and people's livelihood such as coatings, adhesives, textiles, printing and dyeing, and superabsorbent resin. In 2023, the national acrylic acid production capacity was about 3.5 million tons, all of which was produced by the two-step oxidation method of propylene. Propylene is first oxidized to propylene aldehyde in the first reactor, and the latter is further oxidized to acrylic acid in the second reactor. Compared with propylene, propane is cheaper and exists in large quantities in shale gas, oilfield associated gas and refinery byproduct gas. Under specific catalysts, propane can be oxidized to acrylic acid in one step. Therefore, if propane is used to replace propylene for direct oxidation to produce acrylic acid, the production cost can be greatly reduced.

[0004] Among many catalysts, MoVTeNbOx composite metal oxide is the best catalyst in terms of comprehensive performance, with good activity, selectivity and thermal stability. According to the results of patent US005380933A, the propane conversion rate is 80.1%, the acrylic acid selectivity is 60.5%, and the yield is as high as 48.5%; on this basis, many scientists have further improved the catalyst, such as patent CN1130255C discloses "a method for producing an oxide catalyst for oxidation or ammoxidation", the general formula is Mo 1.0 V a X b Nb c Z d O nX is at least one element selected from antimony and tellurium, Z is at least one element selected from tungsten, chromium, titanium, aluminum, thallium, zirconium, hafnium, manganese, rhenium, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, zinc, boron, gallium, indium, germanium, tin, phosphorus, lead, bismuth, yttrium, rare earth elements and alkaline earth elements, and the niobium compound exists in the form of a complex during the preparation of the catalyst, the complexing agent is a hydroxyl compound bonded to an oxygen atom or a carbon atom, and the catalyst can be used for propane oxidation; the patent CN100544821C discloses a "molybdenum-vanadium-tellurium-niobium catalyst for propane selective oxidation to prepare acrylic acid and a preparation method thereof", and after fresh catalyst is subjected to high-temperature activation treatment in a reaction atmosphere, the activity can be significantly improved, and a stable state can be reached in the initial stage of the reaction.

[0005] The commonality of the above-mentioned work is how to improve the performance of the original powder catalyst, and does not involve shaping. In the laboratory level propane oxidation reaction, the catalyst particles are small and the loading amount is small, the active surface is fully exposed, the reactants fully contact with the active sites, the mass transfer resistance is very small, and there is almost no concentration gradient, so the effective factor is high, and the reaction result is close to the intrinsic kinetic characteristics. However, in actual industrial application, the catalyst loaded must be the particles with certain shape, size and strength after strict shaping. Considering the bed pressure drop and strength, the particle size of the catalyst loaded in the industrial reactor is much larger than that in the laboratory, which inevitably causes the problem of internal mass transfer resistance of the catalyst particles. The existence of internal diffusion makes the concentration of the reactants gradually decrease from the surface of the catalyst to the inside, and the concentration of the products may be just the opposite. This concentration gradient not only reduces the activity, but also reduces the selectivity of the target product, resulting in the essential difference between the macro-kinetic characteristics of the shaped catalyst and the intrinsic kinetics.

[0006] Therefore, shaping is an important preparation process to ensure the performance of the catalyst. Even if the original powder catalyst has excellent performance, it cannot be used for industrial application if the shaping is not proper.

[0007] SUMMARY

[0008] The present application aims to provide a MoVTeNbOx metal oxide shaped catalyst, a shaping method and application thereof. The shaped catalyst prepared in the present application is used for the reaction of propane selective oxidation to prepare acrylic acid under industrial conditions, and has high activity and selectivity.

[0009] The present application provides a shaping method of a MoVTeNbOx metal oxide shaped catalyst, which comprises the following steps:

[0010] A) MoVTeNbOx metal oxide original powder catalyst, inert substances and sesbania grandiflora powder are mixed and kneaded, and alkaline amino acid solution, acid solution and halogen compound solution are sprayed in sequence during the kneading process to obtain a kneaded material;

[0011] The mass of the halogen compound in the halogen compound solution is 0.002-0.03wt% of the total mass of the MoVTeNbOx-based metal oxide raw powder catalyst and the inert substance;

[0012] B) extruding the kneaded material to obtain a catalyst blank after drying;

[0013] C) calcining the catalyst blank at 180-280°C for 1-2 hours, then increasing the temperature, and continuing to calcine at 350-400°C for 1-2 hours to obtain a MoVTeNbOx-based metal oxide shaped catalyst.

[0014] Preferably, the inert substance is silicon carbide and / or quartz powder;

[0015] The mass of the inert substance is 20-60wt% of the total mass of the MoVTeNbOx-based metal oxide raw powder catalyst and the inert substance.

[0016] Preferably, the mass of the sesbania powder is 2-8wt% of the total mass of the MoVTeNbOx-based metal oxide raw powder catalyst and the inert substance.

[0017] Preferably, the basic amino acid includes one or more of lysine, histidine and arginine;

[0018] The mass of the basic amino acid is 1-8wt% of the total mass of the MoVTeNbOx-based metal oxide raw powder catalyst and the inert substance.

[0019] The mass concentration of the basic amino acid solution is 10-35wt%.

[0020] Preferably, the acid in the acid solution has a dissociation constant pKa of 2.5-5;

[0021] The acid in the acid solution includes one or more of nitric acid, sulfuric acid, lactic acid, benzoic acid, phthalic acid, oxalic acid, tartaric acid, citric acid, sulfurous acid, acetic acid, formic acid and trichloroacetic acid;

[0022] The mass of the acid in the acid solution is 1-5wt% of the total mass of the MoVTeNbOx-based metal oxide raw powder catalyst and the inert substance; and the mass concentration of the acid solution is 10-40wt%.

[0023] Preferably, the halogen compound includes one or more of HCl, HF, HBr, HI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, MgCl2 and CaCl2;

[0024] The mass concentration of the halogen compound solution is 1-10wt%.

[0025] Preferably, the mass of water in the kneaded material is 20-45wt% of the total mass of the MoVTeNbOx metal oxide raw powder catalyst and the inert substance.

[0026] Preferably, the drying in step B) specifically comprises:

[0027] First, drying at 30-60℃ for 10-48 hours, then increasing the temperature to 90-120℃ and continuing to dry for 24-48 hours.

[0028] The present application provides a MoVTeNbOx metal oxide shaped catalyst obtained by the shaping method described above.

[0029] The present application provides the use of a MoVTeNbOx metal oxide shaped catalyst described above in the industrial production of propylene acid by propane oxidation.

[0030] In the industrial production of propylene acid by propane oxidation, the loading amount of the catalyst is 1-2L, the catalyst is loaded after being diluted with porcelain balls, the volume percentage of the catalyst in the total loading amount is 70-90%, the inlet pressure of the reaction gas is 50-150KPa, the reaction gas is a mixture of propane, air, nitrogen, and water vapor, the absolute volume space velocity of propane to the catalyst is 80-150h -1 , the propane inlet concentration is 6-12%, the oxygen to propane ratio is 1-2, the water to propane ratio is 0.8-3, and the reaction temperature is 320-400℃.

[0031] The reactor is divided into three reaction zones from top to bottom, namely an upper section, a middle section, and a lower section, and the proportion of the catalyst increases in turn, the upper section catalyst accounts for 30-50% of the total loading amount of the upper section, the middle section catalyst accounts for 50-75% of the total loading amount of the middle section, and the lower section catalyst accounts for 75-100% of the total loading amount of the lower section.

[0032] The application provides a forming method of MoVTeNbOx metal oxide shaped catalyst, which comprises the following steps: A) mixing MoVTeNbOx metal oxide raw powder catalyst, inert substances and Echinochloa crusgalli powder, performing kneading, and spraying alkaline amino acid solution, acid solution and halogen compound solution in sequence in the process of kneading to obtain a kneaded material; the mass of halogen in the halogen compound solution is 0.002-0.03 wt% of the total mass of the MoVTeNbOx metal oxide raw powder catalyst and the inert substances; B) extruding the kneaded material to form a catalyst blank body after drying; C) first calcining the catalyst blank body at 180-280 DEG C for 1-2 hours, then increasing the temperature, and continuing to calcine at 350-400 DEG C for 1-2 hours to obtain the MoVTeNbOx metal oxide shaped catalyst. The application introduces alkaline amino acids on the basis of conventional acidic colloidal solvents, the amino acids have two amino groups and one carboxyl group, and the amino acids are alkaline as a whole after ionization in water, the alkaline amino acids and the conventional acidic colloidal solvents are used in combination to effectively control the strength of colloidal sol, and then the secondary pore structure of the catalyst is optimized, so that the pore size distribution is concentrated from dispersion to macropore, which is beneficial to the diffusion of acrylic acid molecules, and the selectivity is greatly improved. Meanwhile, in order to inhibit excessive oxidation, a trace amount of halogen is creatively introduced as an inhibitor in the forming process, halogen is usually regarded as a toxic substance and can poison the catalyst. The addition of the alkaline amino acids and the inhibitor makes the MoVTeNbOx catalyst obtain more than 80% of the selectivity of acrylic acid, and greatly reduces the generation of by-products. DETAILED DESCRIPTION

[0033] The application provides a forming method of MoVTeNbOx metal oxide shaped catalyst, which comprises the following steps:

[0034] A) mixing MoVTeNbOx metal oxide raw powder catalyst, inert substances and Echinochloa crusgalli powder, performing kneading, and spraying alkaline amino acid solution, acid solution and halogen compound solution in sequence in the process of kneading to obtain a kneaded material;

[0035] The mass of halogen in the halogen compound solution is 0.002-0.03 wt% of the total mass of the MoVTeNbOx metal oxide raw powder catalyst and the inert substances;

[0036] B) extruding the kneaded material to form a catalyst blank body after drying;

[0037] C) first calcining the catalyst blank body at 180-280 DEG C for 1-2 hours, then increasing the temperature, and continuing to calcine at 350-400 DEG C for 1-2 hours to obtain the MoVTeNbOx metal oxide shaped catalyst.

[0038] In the present application, the specific type or composition of the MoVTeNbOx-based metal oxide original powder catalyst is not particularly limited, and in the present application, the MoVTeNbOx-based metal oxide original powder catalyst can be a conventional MoVTeNbOx-based metal oxide original powder catalyst in the art or a commercially available MoVTeNbOx-based metal oxide original powder catalyst. Specifically, the MoVTeNbOx-based metal oxide original powder catalyst used in the present application is prepared according to the following steps:

[0039] 1) Coprecipitation:

[0040] The catalyst has a general formula (Mo+W) 1.0 V a Ce b Te c Mn d Nb e X m Y n Z p O x , wherein X is at least one of Sc, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Y, Zr, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, lanthanide series, actinide series, Hf, Ta, Re, Os, Ir, Pt, Au, Hg, Ta, Pb, Bi, Po, Y is at least one of Be, Mg, Ca, Sr, Ba, and Z is at least one of Li, Na, K, Rb, Cs, wherein a, b, c, d, e, m, n, p are the molar ratios of the corresponding elements to (Mo+W), respectively, a ranges from 0.2 to 0.4, b ranges from 0.005 to 0.2, c ranges from 0.1 to 0.25, d ranges from 0.001 to 0.1, e ranges from 0.08 to 0.18, m ranges from 0.001 to 0.05, n ranges from 0.001 to 0.05, p ranges from 0.0005 to 0.02, the molar percentage of W in (Mo+W) is preferably 10-30%, more preferably 15-25%, such as 10%, 15%, 20%, 25%, 30%, preferably a range with any of the above values as the upper or lower limit, and x is determined by the content and valence state of each element.

[0041] Dissolve ammonium molybdate, ammonium tungstate, ammonium metavanadate, telluric acid, manganese nitrate, cerium nitrate, etc. to form solution A, dissolve niobium oxalate to form solution B, add solution B to solution A to form coprecipitation slurry C, dissolve any soluble salt of X, Y, Z to form solutions D, E, F, and slowly add D, E, F to slurry C to form slurry G, adjust the pH to 1.5-3.0 with nitric acid solution, and coprecipitate at room temperature.

[0042] 2) Drying:

[0043] The slurry G is dewatered by spray drying, inlet temperature 160-200 DEG C, outlet temperature 80-110 DEG C, the feeding speed is adjusted according to the outlet temperature; the dewatering is carried out by rotary evaporator, drying temperature is 50-70 DEG C, relative vacuum degree is less than -80 KPa. The dried precursor is crushed to about 50 microns, and the powder is marked as H.

[0044] 3) calcination: the powder H is firstly calcined in oxygen atmosphere, heating rate is 0.8-3 DEG C / min, calcination temperature is 280-360 DEG C, calcination time is 2-5 h, in the calcination process, the ammonium, nitrate and oxalate in the precursor are decomposed, releasing NO, NO2, CO, CO2, N2 and other gases, the metal exists in the form of oxide after calcination, XRD has no obvious crystal diffraction peak, the catalyst is in amorphous state, and the active phase with catalytic activity has not been formed; the atmosphere is switched to oxygen-free atmosphere, which can be nitrogen, argon or helium, and the temperature is continuously increased to 560-620 DEG C, and calcination is carried out for 2 h, in the calcination process, the catalyst quality remains unchanged, and no decomposition occurs, but the M1 phase and M2 phase with catalytic activity are formed, it is generally considered that the M1 phase activates propane, and the propane is oxidatively dehydrogenated to form propylene, and the propylene is selectively oxidized to propylene acid on the M2 phase; after cooling, the obtained catalyst is crushed to about 20 microns, and marked as M.

[0045] The MoVTeNbOx metal oxide original powder catalyst, inert substance and sesbania powder are uniformly mixed and placed in a kneader.

[0046] In the forming process, the high-thermal-conductivity inert substance is added to the original powder catalyst as a carrier, and the inert substance is preferably silicon carbide and / or quartz powder; the two have the common feature of high thermal conductivity. Since propane oxidation is a strong exothermic reaction, the addition of the inert substance helps to conduct the reaction heat, avoids the generation of hot spots in the catalyst, reduces the occurrence of side reactions, and also helps to reduce the cost of the catalyst; the mass of the inert substance is preferably 20-60 wt% of the total mass of the MoVTeNbOx metal oxide original powder catalyst and the inert substance (hereinafter referred to as "powder mass"), more preferably 30-50 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, preferably a range value with any of the above values as the upper limit or lower limit; the MoVTeNbOx metal oxide original powder catalyst accounts for 40-80 wt% of the powder mass, more preferably 50-70 wt%, such as 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, preferably a range value with any of the above values as the upper limit or lower limit.

[0047] In the present application, the sesbania powder as a lubricant can reduce the extrusion pressure, so that the strip-shaped catalyst is extruded smoothly; the mass of the sesbania powder is preferably 2-8wt% of the mass of the powder, more preferably 3-6wt%, such as 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, preferably a range value with any of the above values as the upper limit or lower limit.

[0048] In the present application, the kneader can be a double-shaft kneader or a wheel mill.

[0049] In the present application, the basic amino acid is dissolved in water to prepare a basic amino acid solution, and then the basic amino acid solution is uniformly sprayed on the surface of the material during the kneading process for 30-90min.

[0050] In the present application, the basic amino acid is preferably one or more of lysine, histidine and arginine, preferably lysine and arginine, and more preferably lysine; the basic amino acid in the present application has two amino groups and one carboxyl group, and the side chain contains a protonatable basic chemical group, such as guanidino, amino, imidazole, and the number of hydroxyl negative ions generated during hydrolysis is more than that of hydrogen positive ions, and the solution is alkaline. These groups ionize in water, can regulate the strength of peptizing, help to generate macroporous structure, and make the pore distribution tend to be uniform, which is beneficial to the diffusion of product molecules and greatly improves the selectivity of the catalyst.

[0051] In the present application, the mass of the basic amino acid is preferably 1-8wt% of the mass of the powder, more preferably 2-6wt%, such as 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, preferably a range value with any of the above values as the upper limit or lower limit; the mass concentration of the basic amino acid solution is preferably 10-35wt%, more preferably 15-30wt%, such as 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, preferably a range value with any of the above values as the upper limit or lower limit; after adding the basic amino acid, the kneading is preferably continued for 30-90min, and more preferably for 45-60min.

[0052] After adding the basic amino acid solution, the present application dissolves the acid in water to prepare an acid solution, and after the kneading with the basic amino acid solution is completed, the acid solution is uniformly sprayed on the surface of the material, and the kneading is continued for 30-90min.

[0053] In the present application, the acid is preferably an inorganic acid or an organic acid, including one or more of nitric acid, sulfuric acid, lactic acid, benzoic acid, phthalic acid, oxalic acid, tartaric acid, citric acid, sulfurous acid, acetic acid, formic acid and trichloroacetic acid, more preferably an acid with a dissociation constant pKa between 2.5 and 5, such as one or more of formic acid, acetic acid, lactic acid and tartaric acid, which is used in combination with a basic amino acid, and the peptizing effect is moderate, and a catalyst particle with uniform pore distribution and large pore size can be obtained; the mass of the acid is preferably 1-5 wt% of the mass of the powder, more preferably 2-4 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, preferably a range with any of the above values as the upper or lower limit.

[0054] In the present application, the mass concentration of the acid solution is preferably 10-40 wt%, more preferably 15-35 wt%, such as 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, preferably a range with any of the above values as the upper or lower limit. After adding the acid solution, the kneading is preferably continued for 30-90 min, more preferably 30-50 min.

[0055] After the kneading of the acid solution is completed, a small amount of halogen compound is dissolved in water to prepare a halogen compound solution, which is uniformly sprayed on the surface of the material, and the kneading is continued for 30-90 min. Generally, halogen as a poison can reduce activity, but through the present application, the introduction of a small amount of halogen during the forming process can effectively inhibit side reactions and improve the selectivity of acrylic acid.

[0056] In the present application, the halogen compound is preferably a salt of halogen and / or an acid of halogen, such as one or more of HCl, HF, HBr, HI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, MgCl2 and CaCl2; the mass of the halogen is preferably 0.002-0.03 wt% of the mass of the powder, more preferably 0.008-0.025 wt%, such as 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.015 wt%, 0.02 wt%, 0.025 wt%, 0.03 wt%, preferably a range with any of the above values as the upper or lower limit. The mass concentration of the halogen compound solution is preferably 1-10 wt%, more preferably 3-8 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, preferably a range with any of the above values as the upper or lower limit.

[0057] After spraying the halogen compound solution, the kneading is continued for 30-90 min, more preferably 40-60 min.

[0058] In the present application, the total amount of water in the kneaded material is 20-45wt% of the mass of the powder, preferably 25-35wt%. If the amount of water is too small, the powder is dry, the extrusion pressure is large, the elasticity is poor, the drying is easy to break, and it is not conducive to pelletizing. If the amount of water is too high, the material is sticky, the pole is serious, the extrusion speed is slow, and it is also not conducive to pelletizing.

[0059] After obtaining the kneaded material, the present application extrudes it into a catalyst blank after drying.

[0060] The present application preferably places the kneaded wet material into an extruder to form an extruded strip, either a double screw or a single screw extruder can be used, different molds are used to extrude the powder into a column, a Laxi ring, a honeycomb, a three-leaf clover, a four-leaf clover, an internal gear, an external gear, a multi-hole plum blossom, etc. The supporting pelletizing equipment is a rotating steel wire pelletizing, a blade pelletizing or a drum pelletizing, preferably a drum pelletizing

[0061] In the present application, the drying is preferably air drying or vacuum drying, preferably first drying at 30-60℃ for 10-48h to slowly evaporate the water, and then increasing the temperature to 90-120℃ to continue drying for 24-48h. More preferably, first drying at 40-50℃ for 12-24h, and then increasing the temperature to 100-110℃ to continue deep drying for 30-40h. The particles need to be slowly evaporated at low temperature first, and the initial water evaporation rate is too fast, which is easy to cause the particles to crack, and then affect the mechanical strength.

[0062] The present application places the dried catalyst blank in an oxygen atmosphere for calcination, first calcining at 180-280℃ for 1-2h at a temperature rising rate of 0.5-2℃ / min, which should not be too fast, then continuing to increase the temperature to 350-400℃ at a temperature rising rate of 1-3℃ / min, and continuing to calcine for 1-2h to obtain the final shaped catalyst.

[0063] Preferably, first calcining at 200-260℃ for 1-2h at a temperature rising rate of 1-1.5℃ / min, then continuing to increase the temperature to 360-380℃ at a temperature rising rate of 1.5-2.5℃ / min, and continuing to calcine for 1-2h.

[0064] The present application also provides a MoVTeNbOx metal oxide shaped catalyst prepared according to the above-mentioned shaping method.

[0065] The present application also provides the use of the above-mentioned MoVTeNbOx metal oxide shaped catalyst in the industrial production of propane oxidation to prepare acrylic acid.

[0066] The MoVTeNbOx series metal oxide shaped catalyst prepared by the shaping method in the application can be applied to the industrialized production of propane oxidation to prepare propylene acid, the reactor used in the reaction has an inner diameter of 24-26 mm, is heated by molten salt or heat conducting oil, the loading amount of the catalyst is 1-2 L, the catalyst is loaded after being diluted by porcelain balls, the volume percentage of the catalyst in the total loading amount is 70-90%, more preferably 75-85%, such as 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, preferably a range value with any of the above values as the upper limit or lower limit.

[0067] The reactor is divided into three reaction zones of upper section, middle section and lower section from top to bottom, and the volume ratio of the upper section material (catalyst + porcelain ball) to the total material is 5-12%, the volume ratio of the middle section material to the total material is 13-25%, and the volume ratio of the lower section material to the total material is >70%, and the proportion of the catalyst in each reaction zone increases successively from top to bottom, and the volume fraction of the catalyst in the upper section reaction zone is 30-50% of the total loading amount of the upper section, more preferably 35-45%, such as 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, preferably a range value with any of the above values as the upper limit or lower limit; the volume fraction of the catalyst in the middle section reaction zone is 50-75% of the total loading amount of the middle section, more preferably 55-65%, such as 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, preferably a range value with any of the above values as the upper limit or lower limit; the volume fraction of the catalyst in the lower section reaction zone is 75-100% of the total loading amount of the lower section, more preferably 80-95%, such as 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, preferably a range value with any of the above values as the upper limit or lower limit.

[0068] In the present application, the inlet pressure of the reaction gas is preferably 50-150 KPa, more preferably 100-120 KPa, such as 50 KPa, 60 KPa, 70 KPa, 80 KPa, 90 KPa, 100 KPa, 110 KPa, 120 KPa, 130 KPa, 140 KPa, 150 KPa, preferably a range with any of the above values as the upper or lower limit; the reaction gas is a mixed gas of propane, air, nitrogen, water vapor, and the absolute volume space velocity of propane to the catalyst is preferably 80-150 h -1 , more preferably 100-120 h -1 , such as 80 h -1 , 90 h -1 , 100 h -1 , 110 h -1 , 120 h -1 , 130 h -1 , 140 h -1 , 150 h -1 , preferably a range with any of the above values as the upper or lower limit; in the reaction gas, the inlet concentration of propane is preferably 6%-12%, more preferably 7-11%, such as 6%, 7%, 8%, 9%, 10%, 11%, 12%, preferably a range with any of the above values as the upper or lower limit; the oxygen to alkane ratio is preferably 1-2, more preferably 1.2-1.8, such as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, preferably a range with any of the above values as the upper or lower limit; the water to alkane ratio is preferably 0.8-3, more preferably 1-2.5, such as 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, preferably a range with any of the above values as the upper or lower limit; the reaction temperature is preferably 320-400°C, more preferably 350-380°C, such as 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, preferably a range with any of the above values as the upper or lower limit.

[0069] The application provides a molding method of MoVTeNbOx system metal oxide shaped catalyst, which comprises the following steps: A) mixing MoVTeNbOx system metal oxide raw powder catalyst, inert substances and Echinochloa crusgalli powder, performing kneading, and spraying alkaline amino acid solution, acid solution and halogen compound solution in sequence in the kneading process to obtain a kneaded material; the mass of halogen in the halogen compound solution is 0.002-0.03wt% of the total mass of the MoVTeNbOx system metal oxide raw powder catalyst and the inert substances; B) extruding the kneaded material to form a catalyst blank body after drying; C) calcining the catalyst blank body at 180-280℃ for 1-2 hours, then increasing the temperature, and continuing to calcine at 350-400℃ for 1-2 hours to obtain the MoVTeNbOx system metal oxide shaped catalyst. The application introduces alkaline amino acids on the basis of conventional acidic colloidal solvents, the amino acids have two amino groups and one carboxyl group, and the whole is alkaline after ionization in water, the alkaline amino acids and the conventional acidic colloidal solvents are used in combination to effectively control the strength of the peptization, and then the secondary pore structure of the catalyst is optimized, so that the pore size distribution is concentrated from dispersion to macropore, which is beneficial to the diffusion of acrylic acid molecules, and the selectivity is greatly improved. Meanwhile, in order to inhibit excessive oxidation, trace halogen is creatively introduced as an inhibitor in the molding process, halogen is usually regarded as a toxic substance and can poison the catalyst. The addition of the alkaline amino acid and the inhibitor makes the MoVTeNbOx catalyst obtain more than 80% of the selectivity of acrylic acid, and greatly reduces the generation of by-products.

[0070] In order to further illustrate the application, the application provides a MoVTeNbOx system metal oxide shaped catalyst, a molding method thereof and application thereof are described in detail in combination with examples below, but it should not be understood as limiting the protection scope of the application.

[0071] Preparation of raw powder catalyst:

[0072] 54L of deionized water is placed in a stirred kettle and heated to 70℃, and 3965g of ammonium molybdate (H 24 Mo7N6O 24 ·4H2O), 1010.8g of ammonium paratungstate (H 40 N 10 O 41 W 12• xH2O), 927.3 g ammonium metavanadate (NH4VO3), 573.6 g cerium nitrate (Ce(NO3)3-6H2O), 1274.1 g telluric acid (H6TeO6) and 189.1 g manganese nitrate (Mn(NO3)2) solution with a concentration of 50 wt%, the former substance needs to be completely dissolved before adding the next substance, after all substances are completely dissolved, continue stirring for 1 h, then reduce the solution temperature to room temperature (25 °C), the solution is labeled as A; 1705.9 g niobium oxalate (NbC2O4-2H2O) is dissolved in 16 L deionized water, the solution is labeled as B; under stirring, solution B is added dropwise to solution A at a rate of 80 mL / min, during the dropwise addition process, the solution gradually becomes turbid and a precipitate is formed, labeled as C; 76.9 g cobalt nitrate (Co(NO3)2-6H2O), 135.5 g magnesium nitrate (Mg(NO3)2-6H2O), 11.2 g sodium nitrate (NaNO3) and 6.7 g potassium nitrate (KNO3) are respectively dissolved in 500 mL deionized water, the solutions are respectively labeled as D, E and F, solutions D, E and F are sequentially added dropwise to the coprecipitation slurry C at a rate of 10 mL / min, forming slurry G, and a 20 wt% nitric acid solution is used to adjust the pH to 2. 10 H5NbO 20 ) is dissolved in 16 L deionized water, the solution is labeled as B; under stirring, solution B is added dropwise to solution A at a rate of 80 mL / min, during the dropwise addition process, the solution gradually becomes turbid and a precipitate is formed, labeled as C; 76.9 g cobalt nitrate (Co(NO3)2-6H2O), 135.5 g magnesium nitrate (Mg(NO3)2-6H2O), 11.2 g sodium nitrate (NaNO3) and 6.7 g potassium nitrate (KNO3) are respectively dissolved in 500 mL deionized water, the solutions are respectively labeled as D, E and F, solutions D, E and F are sequentially added dropwise to the coprecipitation slurry C at a rate of 10 mL / min, forming slurry G, and a 20 wt% nitric acid solution is used to adjust the pH to 2.

[0073] The slurry G is dried and dehydrated by using a rotary spray dryer, the inlet air temperature is 180 °C and the outlet temperature is 85-90 °C, the feeding speed is adjusted according to the change of the outlet air temperature, the obtained yellow precursor powder is further dried in a vacuum drying oven at 70 °C for 48 h, and the powder is crushed to about 50 μm by using a crusher.

[0074] The obtained material is placed in a rotary tube furnace, and is calcined at a rate of 2 °C / min to 330 °C under an air atmosphere of 400 mL / min for 6 h, during the temperature rising process, the ammonium, nitrate and oxalate in the material are decomposed to release NO, NO2, CO, CO2, N2 and other gases, then the reaction atmosphere is switched to N2, and the temperature is further raised to 600 °C for 1 h, after cooling, the material is taken out, and is crushed to below 20 μm by using a super micro crusher, after removing the loss, about 4 kg of the original catalyst powder is obtained, the molar composition of the elements in the catalyst is (Mo 0.85 +W 0.15 )V 0.3 Ce 0.05 Te 0.21 Mn 0.02 Nb 0.12 Co 0.01 Mg 0.02 Na 0.005 K 0.0025 O x , and is recorded as H.

[0075] Example 1

[0076] After 1000g of raw powder H, 700g of silicon carbide and 300g of quartz powder are mixed evenly, they are placed in a double shaft kneader, 80g of foxtail millet powder with a particle size of about 100 mesh is added, and the kneader is started. During the kneading process, 300mL of lysine solution with a concentration of 20wt% is uniformly sprayed on the surface of the powder. After the spraying is completed, the kneading is continued for 45min. A 30wt% nitric acid solution is prepared, 200mL of the nitric acid solution is sprayed on the surface of the powder, and kneading is continued for 30min. Then, 200mL of a 0.1wt% NaCl solution is uniformly sprayed into the powder, and the kneading is continued for 60min before being taken out. The water accounts for 35wt% of the total mass of the powder. During the kneading process, the cover of the kneader needs to be tightly covered to maintain the stability of the moisture content. The water-powder ratio has an important influence on the plasticity and mechanical strength of the wet dough.

[0077] The kneaded material is placed in a double screw extruder, a 5mmx2mm Raschig ring mold is selected, and a drum pelletizing device is used to cut the extruded strip into granules with a length of 4mm. The catalyst is placed in a vacuum oven, first dried at 50°C for 24h to slowly evaporate the water, then the temperature is increased to 110°C, and the deep drying is continued for 36h before being taken out. The completely dried catalyst is placed in a tube furnace, and the temperature is increased to 260°C at a rate of 1.5°C / min under an air atmosphere of 500mL / min, and then calcined for 2h. Then the temperature is continued to increase to 380°C and calcined for 1.5h. Finally, about 2kg of 5mmx2mmx4mm Raschig ring catalyst is obtained.

[0078] Example 2

[0079] During the kneading process, 300mL of arginine solution with a concentration of 20wt% is sprayed on the surface of the powder, and the kneading is continued for 45min. Then, 200mL of a 30wt% tartaric acid solution is uniformly sprayed, and the kneading is continued for 30min. The remaining preparation conditions are the same as in Example 1.

[0080] Example 3

[0081] During the kneading process, 300mL of glutamic acid solution with a concentration of 20wt% is first sprayed, and the kneading is continued for 45min. Then, 200mL of a 30wt% acetic acid solution is sprayed, and the kneading is continued for 30min. The remaining conditions are the same as in Example 1.

[0082] Example 4

[0083] During the kneading process, 300mL of a mixed solution of lysine and arginine is sprayed on the surface of the powder, with the content of each acid being 10wt%. The remaining conditions are the same as in Example 1.

[0084] Example 5

[0085] During kneading, 300 mL of a mixed solution of lysine, arginine and glutamic acid was sprayed on the surface of the powder, wherein the content of lysine was 10 wt%, and the content of the other two acids was 5 wt% respectively. After kneading for 45 min, 200 mL of a mixed solution of formic acid and lactic acid was sprayed, and the content of the two acids was 15 wt% respectively. The other conditions were the same as in Example 1.

[0086] Example 6

[0087] During kneading, a solution of lysine and nitric acid was first sprayed, and then 200 mL of a KF solution with a concentration of 0.1 wt% was sprayed. The other conditions were the same as in Example 1.

[0088] Example 7

[0089] During kneading, a solution of arginine and tartaric acid was first sprayed, and then 200 mL of a mixed solution of NaCl and NaBr was sprayed, and the content of the two substances in the solution was 0.04 wt% and 0.06 wt% respectively. The other conditions were the same as in Example 2.

[0090] Example 8

[0091] During kneading, a solution of glutamic acid and acetic acid was first sprayed, and then 200 mL of a solution of NaF and MgCl2 was sprayed, and the concentration of the two substances was 0.02 wt% and 0.03 wt% respectively. The other conditions were the same as in Example 3.

[0092] Example 9

[0093] The material composition, kneading and extrusion forming process were the same as in Example 1. After the granular catalyst was formed, it was dried in a vacuum oven at 60°C for 12 h, and then the temperature was increased to 110°C for further drying for 24 h, and then the catalyst was taken out for calcination. The calcination process was the same as in Example 1.

[0094] Example 10

[0095] The material composition, kneading, extrusion forming and drying process were the same as in Example 2. The dried granular catalyst was placed in a tube furnace, and was calcined at 280°C for 2 h under an air atmosphere of 400 mL / min at a rate of 2°C / min, and then the temperature was increased to 360°C for further calcination for 2 h, and then the catalyst was taken out.

[0096] Example 11

[0097] The material composition, kneading, extrusion forming and drying process were the same as in Example 2. The dried granular catalyst was placed in a tube furnace, and was calcined at 270°C for 2 h under an air atmosphere of 400 mL / min at a rate of 2°C / min, and then the temperature was increased to 380°C for further calcination for 2 h, and then the catalyst was taken out.

[0098] Example 12

[0099] The material composition, kneading, extrusion and drying processes were the same as in Example 3. The dried granular catalyst was placed in a tube furnace and calcined at 300 mL / min air atmosphere, at a rate of 1.5°C / min to 280°C for 2 h, then at a rate of 3°C / min to 400°C for 1 h and removed.

[0100] Comparative Example 1

[0101] In the kneading process, 300 mL of deionized water was used instead of 300 mL of 20 wt% lysine solution, i.e. no lysine was added, and the remaining conditions were the same as in Example 1.

[0102] Comparative Example 2

[0103] In the kneading process, 300 mL of deionized water was used instead of 300 mL of 20 wt% lysine solution, i.e. no lysine was added, and the remaining conditions were the same as in Example 1.

[0104] Comparative Example 3

[0105] In the kneading process, 300 mL of deionized water was used instead of 300 mL of 20 wt% lysine solution, i.e. no lysine was added, and the remaining conditions were the same as in Example 1.

[0106] Comparative Example 4

[0107] In the kneading process, 200 mL of 0.8 wt% KF solution was sprayed, KF accounting for about 0.08 wt% of the total powder mass, and the remaining conditions were the same as in Example 1.

[0108] Comparative Example 5

[0109] In the kneading process, 200 mL of a mixed solution of NaCl and NaBr with a concentration of 0.8 wt% was sprayed, the concentrations of the two substances being 0.4 wt% each, and the two substances accounting for 0.08 wt% of the total powder mass, and the remaining conditions were the same as in Example 2.

[0110] Comparative Example 6

[0111] The kneading, extrusion and drying processes were the same as in Example 9. After drying the cut granular catalyst in a vacuum oven at 110°C for 48 h, it was removed for calcination, and the calcination conditions were also the same as in Example 9.

[0112] Comparative Example 7

[0113] The kneading, extrusion and drying processes were the same as in Example 10. The dried catalyst was placed in a tube furnace and calcined at 400 mL / min air atmosphere, at a rate of 2°C / min directly to 360°C for 2 h and removed.

[0114] Comparative Example 8

[0115] The kneading, extruding and drying processes were the same as in Example 11. The dried catalyst was placed in a tube furnace and calcined at 400 mL / min air atmosphere at a rate of 2°C / min to 270°C for 2 h, then continued to be heated to 450°C for 2 h and removed.

[0116] Comparative Example 9

[0117] During the kneading process, 300 mL of 20 wt% ammonia solution was sprayed on the surface of the powder to replace the lysine solution, and the rest of the process was the same as in Example 1.

[0118] Comparative Example 10

[0119] During the kneading process, 300 mL of 20 wt% urea solution was sprayed on the surface of the powder to replace the arginine solution, and the rest of the process was the same as in Example 2.

[0120] Table 1 Strength data of the shaped catalysts obtained in the Examples and Comparative Examples

[0121] Table 1 gives the strength data of the shaped catalysts. As can be seen from Table 1, the mechanical strength of the catalysts is all > 60 N / cm, meeting the strength requirements for industrial applications. The mechanical strength of Examples 1, 4, 6 and 9 is significantly higher than that of the other examples, because the ionization degree of nitric acid is large, and it is completely ionized in water. As a peptizing agent, its peptizing effect is stronger than that of formic acid, acetic acid, lactic acid and tartaric acid, and the particles are more tightly bound, so the mechanical strength is high. Referring to Examples 1, 2 and 3 and Comparative Examples 1, 2 and 3, the addition of basic amino acids has no obvious effect on the mechanical strength. Referring to Examples 6 and 7 and Comparative Examples 4 and 5, halogen also has no obvious effect on the mechanical strength. Referring to Examples 1 and 2 and Comparative Examples 9 and 10, ammonia and urea have no obvious effect on the strength. In addition, referring to Comparative Example 6 and Example 9, the water evaporation rate is too fast during the drying process, which reduces the mechanical strength, and the higher the calcination temperature, the higher the mechanical strength, as in Comparative Example 8.

[0122] Application Example

[0123] The activity evaluation was carried out by using a tubular reactor with a length of 6 m and an inner diameter of 26 mm, the catalyst loading was 1800 mL, 450 mL of porcelain balls with a diameter of 3 mm were used to dilute the catalyst, the volume ratio of catalyst to porcelain ball was 80:20, and the catalyst was loaded in three sections. First, 50 mL of porcelain balls were loaded to support, then 1476 mL of catalyst mixed with 165 mL of porcelain balls was loaded into the reactor as the lower reaction zone, 240 mL of catalyst mixed with 160 mL of porcelain balls was loaded as the middle reaction zone, 84 mL of catalyst mixed with 125 mL of porcelain balls was loaded as the upper reaction zone, and finally 100 mL of porcelain balls were loaded as the preheating zone of the reaction gas. The proportion of catalyst in the three reaction zones from top to bottom was 40%, 60% and 90%, respectively. The molten salt was used for heating, the reaction temperature was 360°C, the absolute volume space velocity of propane to pure catalyst was 90 h -1 -1, the oxygen to alkane ratio was 1.8, the propane inlet volume concentration was 7%, the corresponding propane flow rate was 162 L / h, the air gas velocity was 1388 L / h, the water vapor gas velocity was 194 L / h, the nitrogen gas velocity was 570 L / h, the total gas volume space velocity to the entire material bed was 1028 h -1 -1, and the inlet gas pressure was maintained at 80 KPa by the end outlet back pressure. Table 2 shows the single tube evaluation results of the catalyst.

[0124] Table 2 Single tube evaluation results of the catalyst

[0125] Table 2 shows the single tube evaluation results, in examples 1-5, after adding an appropriate amount of alkaline amino acid during kneading, the propane conversion rate was 57%-64%, the acrylic acid selectivity was 77%-79%, showing high conversion rate and selectivity; after introducing an appropriate amount of halogen, such as examples 6-8, the activity decreased significantly to 47%-51%, but the acrylic acid selectivity reached as high as 81%, and carbon oxides were significantly inhibited; in reference examples 9-12, drying and calcination were carried out within a proper temperature range, and the overall performance of the catalyst changed little.

[0126] Comparative Examples 1-3, without adding basic amino acid in kneading, the conversion rate is 62%-66%, slightly higher than the catalyst added with basic amino acid, but the acrylic acid selectivity is only 70%-72%, far lower than the acrylic acid selectivity of 77%-79% in Examples 1-5, and the acetic acid and carbon oxide are significantly higher; in Comparative Examples 4 and 5, excessive halogen is added, which seriously poisons the catalyst, the propane conversion rate is greatly reduced to 28% and 31%, the acrylic acid selectivity is also reduced to about 70%, and the remaining product is mainly propylene, which is 16% and 20% respectively, far more than acetic acid and carbon oxide; the water evaporation in the drying process is too fast, which does not affect the activity and selectivity, but reduces the mechanical strength (Comparative Example 6); in Reference Comparative Examples 7 and 8, the air calcination temperature is too high, which will reduce the activity and selectivity of the catalyst, and even deactivate the catalyst; in Comparative Examples 9 and 10, basic ammonia and urea solution are used to replace basic amino acid, which does not help to improve the selectivity of acrylic acid, and the acrylic acid is only about 70%, and the acetic acid and carbon oxide are high.

[0127] In Example 7, the single-pass conversion rate of propane is 49%, the selectivity of acrylic acid is 81%, and the propylene is 6%, which is an intermediate product of propane oxidation to generate acrylic acid, which can be recycled with unreacted propane to re-enter the reactor for oxidation to generate acrylic acid. The essence of propane oxidation is to generate propylene after dehydrogenation, and propylene is further oxidized to generate acrylic acid. If the recovery and utilization of propane and propylene are realized, the selectivity of acrylic acid to propane can reach 85.86%, the single consumption of propane per ton of acrylic acid is reduced to 0.711 tons, the acetic acid is 5%, which can be recovered as a high-value byproduct, and the total selectivity of acrylic acid and acetic acid is >90%. Therefore, the introduction of basic amino acid and appropriate amount of halogen in the molding process greatly improves the utilization rate of propane.

[0128] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered within the scope of protection of the present application.

Claims

1. A forming method of MoVTeNbOx-based metal oxide shaped catalyst, comprising the following steps: A) mixing MoVTeNbOx-based metal oxide raw powder catalyst, inert substance and Euphorbia Pulverata powder, kneading, and spraying alkaline amino acid solution, acid solution and halogen compound solution in sequence during the kneading process to obtain the kneaded material; the mass of halogen compound in the halogen compound solution is 0.002-0.03wt% of the total mass of MoVTeNbOx-based metal oxide raw powder catalyst and inert substance; B) extruding the kneaded material to form a catalyst blank, and drying to obtain the catalyst blank; C) calcining the catalyst blank at 180-280℃ for 1-2 hours, then increasing the temperature, and continuing to calcine at 350-400℃ for 1-2 hours to obtain MoVTeNbOx-based metal oxide shaped catalyst.

2. The molding method according to claim 1, characterized by, the inert substance is silicon carbide and / or quartz powder; the mass of inert substance is 20-60wt% of the total mass of MoVTeNbOx-based metal oxide raw powder catalyst and inert substance.

3. The molding method according to claim 1, characterized by, the mass of Euphorbia Pulverata powder is 2-8wt% of the total mass of MoVTeNbOx-based metal oxide raw powder catalyst and inert substance.

4. The molding method according to claim 1, characterized by, the alkaline amino acid includes one or more of lysine, histidine and arginine; the mass of alkaline amino acid is 1-8wt% of the total mass of MoVTeNbOx-based metal oxide raw powder catalyst and inert substance; the mass concentration of alkaline amino acid solution is 10-35wt%.

5. The molding method according to claim 1, wherein the acid in the acid solution has a dissociation constant pKa of 2.5-5; the acid in the acid solution includes one or more of nitric acid, sulfuric acid, lactic acid, benzoic acid, phthalic acid, oxalic acid, tartaric acid, citric acid, sulfurous acid, acetic acid, formic acid and trichloroacetic acid; the mass of acid in the acid solution is 1-5wt% of the total mass of MoVTeNbOx-based metal oxide raw powder catalyst and inert substance; the mass concentration of the acid solution is 10-40wt%.

6. The molding method according to claim 1, characterized by, the halogen compound includes one or more of HCl, HF, HBr, HI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, MgCl2 and CaCl2; the mass concentration of halogen compound solution is 1-10wt%.

7. The molding method according to claim 1, wherein the mass of water in the kneaded material is 20-45wt% of the total mass of MoVTeNbOx-based metal oxide raw powder catalyst and inert substance.

8. The molding method according to claim 1, characterized by, the drying in step B) specifically includes: first drying at 30-60℃ for 10-48 hours, then increasing the temperature to 90-120℃, and continuing to dry for 24-48 hours.

9. MoVTeNbOx-based metal oxide shaped catalyst obtained by the forming method according to any one of claims 1-8.

10. Use of MoVTeNbOx-based metal oxide shaped catalyst according to claim 9 in the industrial production of propylene acid prepared by propane oxidation. In the industrial production of propylene acid by propane oxidation, the loading amount of catalyst is 1-2L, the catalyst is diluted by porcelain ball and then loaded, the volume percentage of catalyst in total loading amount is 70-90%, the inlet pressure of reaction gas is 50-150KPa, the reaction gas is the mixed gas of propane, air, nitrogen and water vapor, the absolute volume space velocity of propane to catalyst is 80-150h -1 , the inlet concentration of propane is 6-12%, the oxygen to propane ratio is 1-2, the water to propane ratio is 0.8-3, and the reaction temperature is 320-400℃. The reactor is divided into three reaction zones from top to bottom, i.e. upper section, middle section and lower section, and the proportion of catalysts increases in turn, wherein the upper section catalysts account for 30%-50% of the total loading of the upper section, the middle section catalysts account for 50%-75% of the total loading of the middle section, and the lower section catalysts account for 75%-100% of the total loading of the lower section.

Images