A catalyst for melamine synthesis and a method for preparing the same

Abstract

The present application relates to the technical field of melamine preparation, and discloses a preparation method of a catalyst for melamine synthesis, which comprises the following steps: 1) dissolving sodium silicate in water, adding dilute acid dropwise until the pH is 8, then adding molecular sieve raw powder, and continuously adding dilute acid until a molecular sieve-silica gel is formed; 2) dissolving fly ash in water by using calcium oxide as a primer, then adding the fly ash into the molecular sieve-silica gel, stirring, and adjusting the pH by using an alkali solution to form a molecular sieve-silicon-aluminum colloid; 3) washing the molecular sieve-silicon-aluminum colloid with a dilute acid solution first, and then washing the molecular sieve-silicon-aluminum colloid with deionized water; 4) immersing the washing product in a weak acid solution to obtain an immersed system; 5) performing suction filtration, washing and preparation on the immersed system to obtain a spray slurry, performing spray granulation and calcination on the spray slurry, removing fine particles with a particle size less than 8 microns by screening, and finally obtaining a catalyst product. The method realizes waste utilization, saves cost and saves processes. The performance of the obtained catalyst reaches the level of existing catalysts.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of melamine preparation, and particularly relates to a catalyst for melamine synthesis and a preparation method thereof. BACKGROUND

[0002] Melamine is an important nitrogen heterocyclic organic chemical intermediate product, and is mainly used for producing melamine formaldehyde resin. As a kind of thermosetting resin, melamine has the characteristics of heat resistance, aging resistance, acid and alkali resistance, flame resistance and the like. Melamine is widely used in wood processing, paint, papermaking, textile, leather, decorative board, laminated board, composite floor, flame retardant material, water reducing agent, adhesive and melamine molding powder industries. In recent years, with the deepening of the research on melamine and the continuous improvement of people's living standards, the application field and range of melamine are also continuously expanding. In the twenty-first century, due to the market demand, the annual growth rate of melamine is more than 15%.

[0003] At present, the production of melamine is mostly completed by relying on the urea method. Urea is added into a reactor, and is subjected to fluidized contact reaction with a catalyst (silica gel catalyst or alumina catalyst or silica-alumina catalyst). The reaction is an endothermic reaction, and the molten salt carrier is circulated and heated. Urea is gasified and decomposed in the reactor to generate melamine, carbon dioxide and ammonia. The normal and low pressure method for producing melamine by using urea as raw material has very strict requirements on the catalyst, and requires that the catalyst has the advantages of high strength, high activity, large load and low price. Therefore, the selection of the catalyst and the performance of the catalyst will directly affect the production capacity, output quality, raw material consumption and running cycle of the entire melamine production device. The catalyst used in the melamine technology of BASF is γ-Al2O3, and the catalyst used in most domestic melamine production devices is coarse-pore silica gel. In the mid and late 1990s, the catalysts of the silica-alumina type began to be used in some domestic melamine production devices.

[0004] In recent years, silica-alumina catalysts are mostly used in melamine production devices, and the research on the silica-alumina catalysts is also continuously deepened. CN102580711A discloses a production method of a catalyst for synthesizing melamine by using the gas phase method of urea. The catalyst is produced by using soap and aluminum sulfate as raw materials, but the method has long process flow and complex operation, and has high production cost. CN110665521A discloses a catalyst for synthesizing melamine and a preparation method thereof. The specific surface area of the silica gel carrier used in the catalyst is only 120 m 2 / g, and it can be inferred that the specific surface area of the catalyst prepared by using the silica gel carrier is small, the urea load is small, and the catalyst prepared by using the method has high aluminum content and high cost.

[0005] In recent years, the research of the company found that the doping of molecular sieve can significantly increase the number of acid centers on the surface of silica-alumina catalyst, thereby causing the catalytic activity of melamine catalyst to be significantly improved. Meanwhile, by exploring the addition amount ratio of the molecular sieve, the catalyst also has high activity at low temperature, which reduces the probability of side reactions, reduces the deposition of by-products on the surface of the catalyst, slows down the deactivation rate of the catalyst, and improves the carrying capacity and selectivity of the catalyst. On the other hand, fly ash is one of the largest solid wastes accumulated in China. The accumulation and discharge of fly ash not only occupies a large amount of land resources, but also easily causes environmental pollution. The main components of fly ash also contain silicon and aluminum, but the application of fly ash in melamine catalyst has not been reported.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The present application aims to solve one of the above problems and provide a new catalyst for the synthesis of melamine and a preparation method thereof.

[0008] The present application is achieved by the following technical solutions.

[0009] A preparation method of a catalyst for the synthesis of melamine comprises the following steps:

[0010] 1) Dissolve sodium silicate in water, add molecular sieve raw powder when the pH is 8 by dropwise adding dilute acid, and continue to add dilute acid until a molecular sieve-silica gel is formed;

[0011] 2) Dissolve fly ash in water with calcium oxide as a primer, and then add it to the molecular sieve-silica gel, while stirring, adjust the pH with an alkali solution to form a molecular sieve-silica alumina gel;

[0012] 3) Wash the molecular sieve-silica alumina gel with a dilute acid solution first, and then with deionized water;

[0013] 4) Immerse the washed product in a weak acid solution to obtain an immersed system;

[0014] 5) Extract, wash and prepare the immersed system into a spray slurry, spray granulate the spray slurry, calcine, and screen out fine particles with a particle size less than 8 μm to finally obtain a required silica-alumina gel type catalyst product.

[0015] Further, the addition amounts of sodium silicate, molecular sieve and fly ash are in a weight ratio of 1:(0.1-0.5):(2-3).

[0016] Preferably, the molecular sieve is selected from one or more of MCM-22, ZSM-48 and MCM-56; and preferably, the silica-alumina ratio of the molecular sieve is 20-150.

[0017] Further, the dilute acid in step 1) and step 3) is dilute nitric acid or dilute sulfuric acid or dilute hydrochloric acid.

[0018] Further, the adding amount of calcium oxide in step 2) is 0.5% to 3% of the weight of fly ash; the alkali solution used is sodium hydroxide solution or potassium hydroxide solution, and the alkali solution is added in a dropwise manner, and the pH is adjusted to 7 to 8 by adding the alkali solution.

[0019] Further, the weak acid solution in step 4) is a citric acid solution, and the volume ratio of the citric acid solution to the molecular sieve-silica alumina colloid is (4 to 6) to 1.

[0020] Further, in step 5), the solid content of the spray slurry is 25wt%, the spray granulator inlet and outlet temperatures of the spray granulation are 450℃ and 115℃ respectively, the feeding pressure is 1.2MPa, and the spray granulation is carried out.

[0021] Further, in step 5), the calcination is carried out in a programmed temperature raising manner, the temperature is raised to 500 to 600℃ at a temperature raising speed of 5 to 10℃ / min, and then the calcination is continued at the temperature for 2 to 20h.

[0022] A catalyst for producing melamine is prepared by the above method.

[0023] Further, the catalyst product contains 65 to 85% of SiO2, 15 to 35% of Al2O3, and 0 to 5% of P2O5.

[0024] Compared with the prior art, the present application has the following main advantages:

[0025] 1. The present application uses fly ash to replace the aluminum source of commercially available silica alumina gel to prepare a new type of silica alumina gel catalyst, realizes the reuse of solid waste, and saves costs.

[0026] 2. In the presence of calcium oxide initiator, in an alkaline system, the silicic acid anions in fly ash will form a bond reaction with hydroxyl ions in the solution, so that the volume of fly ash increases, and it also provides an opportunity for fly ash and silica gel to recombine and bond, forming a silica alumina colloid with high interatomic bonding strength, and the final catalyst wear index is smaller than the wear rate of the molecular sieve doped catalyst prepared by the previous company.

[0027] 3. The dropwise addition of the alkali solution leads to volume expansion and bond recombination, and the subsequent acid washing will make the metal elements Fe, Ga, Ti, K, Na, etc. in the fly ash basically be dissolved, so that the system is expanded, and a separate aging and expansion step is not needed, saving the preparation process of the catalyst.

[0028] 4. The doping and weak acid impregnation of the molecular sieve can significantly increase the number of acid centers on the surface of the catalyst; at the same time, under the impregnation of the weak acid, the pore volume and specific surface area of the catalyst are increased, and the catalytic activity is improved; at the same time, some fly ash contains P element in the form of P2O5, which can further improve the catalytic activity of the catalyst.

[0029] 5. The catalyst also has high activity at low temperature, which reduces the probability of side reactions, reduces the deposition of by-products on the surface of the catalyst, slows down the deactivation rate of the catalyst, improves the load capacity and selectivity of the catalyst, and ultimately improves the conversion rate of the reaction and the yield of melamine. DETAILED DESCRIPTION

[0030] A preparation method of a catalyst for melamine synthesis, comprising the following steps:

[0031] 1) Dissolve sodium silicate in water, add molecular sieve raw powder when the pH is 8 by dropwise adding dilute acid, and continue to add dilute acid until a molecular sieve-silica gel is formed;

[0032] 2) After the fly ash is dissolved in water with calcium oxide as a primer, it is added to the molecular sieve-silica gel, and the pH is adjusted with an alkali solution while stirring to form a molecular sieve-silica-alumina colloid;

[0033] 3) The molecular sieve-silica-alumina colloid is first washed with a dilute acid solution and then washed with deionized water;

[0034] 4) The washed product is immersed in a weak acid solution to obtain an immersed system;

[0035] 5) The immersed system is filtered, washed, and prepared into a spray slurry, the spray slurry is granulated by spraying, calcined, and screened to remove fine particles with a particle size less than 8 μm, and finally a required silica-alumina gel type catalyst product is obtained.

[0036] Further, the adding amount of sodium silicate, molecular sieve and fly ash is 1: (0.1-0.5): (2-3) by weight. The molecular sieve is selected from one or more of MCM-22, ZSM-48 and MCM-56; preferably, the silica-alumina ratio of the molecular sieve is 20-150.

[0037] Further, the dilute acid in step 1) and step 3) is dilute nitric acid or dilute sulfuric acid or dilute hydrochloric acid. The amount of calcium oxide added in step 2) is 0.5% to 3% by weight of the fly ash; the alkali solution used is sodium hydroxide solution or potassium hydroxide solution, which is added dropwise, and the pH is adjusted to 7 to 8 by adding the alkali solution. The weak acid solution in step 4) is a citric acid solution, and the volume ratio of the citric acid solution to the molecular sieve-silica alumina colloid is (5 to 6) to 1. The solid content of the spray slurry in step 5) is 25 wt%, and the spray granulator inlet and outlet temperatures are 450°C, the outlet temperature is 115°C, and the feeding pressure is 1.2 MPa for spray granulation. In step 5), the calcination is carried out by programmed temperature rising, and the temperature is raised to 500 to 600°C at a rate of 5 to 10°C / min, and then the calcination is continued at this temperature for 2 to 20 h.

[0038] The final catalyst product contains 65 to 85% SiO2, 15 to 35% Al2O3, and 0 to 5% P2O5, and the total mass percentage is 100%. The apparent bulk density of the catalyst is 0.58 to 0.95 g / cm 3 , the attrition index is less than 2.0%·h -1 , the BET specific surface area is greater than 200 m 2 / g, the pore size is greater than 4 nm, and the pore volume is greater than 0.3 m 3 / g. The median particle size of the catalyst product is 80 to 115 μm, not more than 3% below 40 μm, and not more than 5% above 150 μm. The obtained catalyst is used for synthesizing melamine from urea, and the synthesis reaction is carried out in a fluidized bed reactor.

[0039] The application is further described below in conjunction with specific examples, but the application is not limited thereto.

[0040] Example 1

[0041] The present embodiment provides a preparation method of a catalyst for melamine synthesis, and the specific steps are as follows:

[0042] (1) 100 g of solid sodium silicate is dissolved in 500 mL of water, stirred to form a uniform liquid, then a 15% mass fraction of dilute nitric acid solution is slowly added, the pH of the material is adjusted until 10 g of MCN-22 molecular sieve raw powder is added when the pH is 8.0, and the stirring and dropwise addition of 15% mass fraction of dilute nitric acid are continued until the pH is 8.7 to obtain a molecular sieve-silica gel;

[0043] (2) 200 g of fly ash is uniformly mixed with 1 g of calcium oxide, then dissolved in 1000 ml of water, and then immediately added to the molecular sieve-silica gel, while stirring the system, and adjusting the pH to 7.5 by dropwise adding sodium hydroxide solution while stirring to form a molecular sieve-silica alumina colloid;

[0044] (3) The molecular sieve-silica alumina colloid is stirred and washed with a 15% mass fraction dilute nitric acid solution to remove Fe 3+ , Ca 2 + , Ti 2+ , K + , Na + , etc., and then stirred and washed with deionized water until neutral;

[0045] (4) The washed product is immersed in 4 times the volume of a citric acid solution for 2 h to obtain an immersed system;

[0046] (5) The immersed system is suction filtered and washed with water to obtain a filter cake, dilute nitric acid is added after washing to prepare a spray slurry with a solid content of 25 wt%, and when spray granulation is performed, the inlet temperature of the spray dryer is 450°C, the outlet temperature is 115°C, and the feeding pressure is 1.2 MPa. The particle size of the catalyst particles obtained after spray granulation is 90-115 μm. The dried catalyst particles are calcined in a fluidized bed furnace, the calcination is performed in a programmed temperature raising manner, the temperature is raised to 600°C at a temperature raising speed of 5-10°C / min, and then the calcination is continued at this temperature for 2 h. The calcined material is naturally cooled, then screened to remove fine particles smaller than 8 μm, and finally the required catalyst product is obtained.

[0047] Example 2

[0048] The present example provides a preparation method of a catalyst for melamine synthesis, and the specific steps are as follows:

[0049] (1) 100 g of solid sodium silicate is dissolved in 500 mL of water, stirred and dissolved into a uniform liquid, then a 15% mass fraction dilute sulfuric acid solution is slowly added, the pH of the material is adjusted until 50 g of ZSM-48 molecular sieve raw powder is added when the pH is 8, and the stirring and dropwise addition of the 15% mass fraction dilute sulfuric acid solution is continued until the pH is 9.0 to obtain a molecular sieve-silica sol;

[0050] (2) 300 g of fly ash is uniformly mixed with 9 g of calcium oxide, dissolved in 1000 ml of water, then immediately added to the molecular sieve-silica sol, and the system is stirred while the pH is adjusted to 8.0 by dropwise addition of a potassium hydroxide solution to form a molecular sieve-silica alumina colloid;

[0051] (3) The molecular sieve-silica alumina colloid is stirred and washed with a 15% mass fraction dilute sulfuric acid solution to remove Fe 3+ , Ca 2 + , Ti 2+ , K + , Na + , etc., and then stirred and washed with deionized water until neutral;

[0052] (4) The washed product was immersed in 6 times its volume of citric acid solution for 2 hours to obtain the immersed system;

[0053] (5) After impregnation, the system is filtered and washed with water to obtain filter cake. Then, dilute sulfuric acid is added to prepare a spray slurry with a solid content of 25wt%. During spray granulation, the inlet temperature of the sprayer is 450℃, the outlet temperature is 115℃, and the feed pressure is 1.2MPa. The particle size of the catalyst particles obtained after spray granulation is 90~115μm. The dried catalyst particles are roasted in a fluidized bed furnace. The roasting is carried out by programmed temperature rise at a rate of 5~10℃ / min to 550℃. Then, the roasting continues at this temperature for 2h. The roasted material is naturally cooled and then screened to remove fine particles smaller than 8μm. Finally, the catalyst product that meets the requirements is obtained.

[0054] Example 3

[0055] This embodiment provides a method for preparing a catalyst for melamine synthesis, the specific steps of which are as follows:

[0056] f1) Weigh 100g of solid sodium silicate and dissolve it in 500mL of water. Stir and dissolve it into a uniform liquid. Then slowly add a 15% dilute hydrochloric acid solution to adjust the pH of the material until it reaches 8. Add 25g of MCM-56 molecular sieve powder and continue stirring and adding 15% dilute hydrochloric acid until the pH reaches 9.2 to obtain molecular sieve-silica gel.

[0057] (2) Mix 250g fly ash and 4g calcium oxide evenly, add 1000ml water to dissolve, and then immediately add it to the molecular sieve-silica gel. At the same time, stir the system and add potassium hydroxide solution dropwise to adjust the pH to 7.5 while stirring to form molecular sieve-silica alumina colloid.

[0058] (3) The molecular sieve-aluminosilicate colloid was washed with a 15% (w / w) dilute hydrochloric acid solution to remove Fe. 3+ Ca 2 + Ti 2+ K + Na + Wait, then wash with deionized water until neutral;

[0059] (4) The washed product was immersed in 5 times its volume of citric acid solution for 2 hours to obtain the immersed system;

[0060] (5) The impregnated system is subjected to suction filtration and water washing to obtain a filter cake, and then dilute hydrochloric acid is added to prepare a spray slurry with a solid content of 25 wt%, and when spray granulation is performed, the inlet temperature of the spray dryer is 450°C, the outlet temperature is 115°C, and the feeding pressure is 1.2 MPa, and the particle size of the catalyst particles obtained after spray granulation is 90-115 μm; the dried catalyst particles are calcined in a fluidized bed furnace, and the calcination is performed in a programmed temperature raising manner, the temperature is raised to 500°C at a temperature raising speed of 5-10°C / min, and then the calcination is continued at the temperature for 2 h, the calcined material is naturally cooled, then screening is performed to remove fine particles with a size less than 8 μm, and finally the required catalyst product is obtained.

[0061] Comparative Example 1

[0062] The present example provides a preparation method of a catalyst for melamine synthesis, which is different from that of Example 1 only in that no molecular sieve is added in step (1), and a silica gel is directly obtained after the pH of the material is adjusted to 8.0, and other operation steps are the same as those of Example 1.

[0063] Comparative Example 2

[0064] The present example provides a preparation method of a catalyst for melamine synthesis, which is different from that of Example 1 only in that no alkali solution is added in step (2), and the fly ash and calcium oxide are uniformly mixed and dissolved in water, and then added to the molecular sieve-silica gel, and other operation steps are the same as those of Example 1.

[0065] Comparative Example 3

[0066] The present example provides a preparation method of a catalyst for melamine synthesis, which is different from that of Example 1 only in that there is no step (4) of impregnation with a citric acid solution, and other operation steps are the same as those of Example 1.

[0067] Comparative Example 4

[0068] The present example provides a preparation method of a catalyst for melamine synthesis, which is different from that of Example 1 only in that the amount of MCN-22 molecular sieve raw powder added in step (1) is 5 g, and other operation steps are the same as those of Example 1.

[0069] Comparative Example 5

[0070] The present example provides a preparation method of a catalyst for melamine synthesis, which is different from that of Example 1 only in that the amount of MCN-22 molecular sieve raw powder added in step (1) is 55 g, and other operation steps are the same as those of Example 1.

[0071] Comparative Example 6

[0072] The embodiment provides a preparation method of a catalyst for melamine synthesis, which is different from the comparative example 1 only in that no alkali solution is added in step (2), and the fly ash is mixed with calcium oxide, uniformly dissolved in water, and then added into the silica gel, and other operation steps are the same as those of the comparative example 1.

[0073] Comparative example 7

[0074] The embodiment provides a preparation method of a catalyst for melamine synthesis, which is different from the comparative example 1 only in that no step (4) of impregnation with a citric acid solution is performed, and other operation steps are the same as those of the comparative example 1.

[0075] Comparative example 8

[0076] The embodiment provides a preparation method of a catalyst for melamine synthesis, which is different from the comparative example 1 only in that no step (3) of washing with a dilute acid solution is performed, and other operation steps are the same as those of the comparative example 1.

[0077] The melamine catalysts prepared in the examples 1-3 and the catalysts obtained from the comparative examples 1-8 are analyzed and catalytic performance is determined, wherein the prepared catalysts and the catalysts of the comparative examples are detected according to the following standards: GB / T 19587-2004, determination of specific surface area of solid substances by gas adsorption BET method, GB / T 21650.3-2011, determination of pore size distribution and porosity of solid materials by mercury intrusion method and gas adsorption method, part 3: micropore analysis by gas adsorption method, GB / T 30905-2014, determination of element content of inorganic chemical products by X-ray fluorescence spectrometry, NB / SH / T 0954-2017, determination method of apparent bulk density of catalytic cracking catalyst, HG / T 4861-2015, chapter 4, section 2: determination of attrition index of methanol to low carbon olefin catalyst industry standard, and catalytic performance data is obtained when the fluidized bed reactor for producing melamine in a gas phase is operated stably, a gas distributor is arranged above an air inlet of the fluidized bed reactor, a carrier gas is a mixed gas of ammonia and carbon dioxide with a weight ratio of 1:1, a carrier gas flow is 25-40 kg / h, a reaction temperature is 390-420 DEG C, a catalyst loading is 50-60 kg, a urea feeding amount is 6-10 kg / h, a urea conversion rate is a ratio of a urea feeding amount of a urea washing tower to a urea feeding amount of the reactor when the device is stably operated for 72 h, and a melamine yield is a ratio of a theoretical urea amount required for producing melamine to a feeding urea amount when the device is stably operated for 72 h.

[0078] Specific results are as follows:

[0079] Table 1 physical performance indexes of the prepared melamine catalysts

[0080]

[0081] The catalysts of the above examples and comparative examples were subjected to melamine production tests under the conditions of a load of 160 g of urea / kg of catalyst-h -1 and the following catalytic performance data were obtained.

[0082] Table 2 Comparison of catalytic performance data of melamine catalysts prepared in the present application and comparative catalysts

[0083] No. Urea first conversion, % Melamine yield, % Example 1 99.5 97.6 Example 2 99.5 97.6 Example 3 99.6 98.0 Comparative Example 1 94.3 93.9 Comparative Example 2 92.2 92.2 Comparative Example 3 95.5 94.4 Comparative Example 4 96.1 95.1 Comparative Example 5 96.1 95.2 Comparative Example 6 89.1 88.1 Comparative Example 7 91.8 91.1 Comparative Example 8 91.5 90.6 Commercial silica alumina gel 99.5 97.2

[0084] The above description is intended to be illustrative and not restrictive, and one of ordinary skill in the art can make changes, modifications, replacements, and variations to the above examples within the scope of the present disclosure. Moreover, the above examples (or one or more aspects thereof) can be used in combination with each other, and these examples can be combined with each other in various combinations or arrangements.

Claims

1. A process for the preparation of a catalyst for the synthesis of melamine, characterized in that, The method comprises the following steps: 1) dissolving sodium silicate in water, adding dilute acid until pH is 8, adding molecular sieve raw powder, and continuously adding dilute acid until molecular sieve-silica gel is formed; 2) dissolving fly ash in water with calcium oxide as a primer, adding the fly ash into the molecular sieve-silica gel, and adjusting pH with an alkali solution while stirring to form a molecular sieve-silica-alumina colloid; 3) washing the molecular sieve-silica-alumina colloid with dilute acid solution first and then with deionized water; 4) immersing the washed product in a weak acid solution to obtain an immersed system; 5) filtering, washing, and preparing the immersed system into a spray slurry, spray granulating the spray slurry, calcining, and screening out fine particles with a particle size less than 8 μm to obtain a final product of a silica-alumina gel type catalyst meeting the requirements; The molecular sieve is selected from one or more of MCM-22, ZSM-48, and MCM-56.

2. The method for producing a catalyst for the production of melamine according to claim 1, characterized by, The adding amounts of the sodium silicate, the molecular sieve, and the fly ash are in a weight ratio of 1: (0.1-0.5): (2-3).

3. The method for producing a catalyst for the production of melamine according to claim 2, characterized by, The silica-alumina ratio of the molecular sieve is 20-150.

4. The method for producing a catalyst for the production of melamine according to claim 1, characterized by, The dilute acid in steps 1) and 3) is dilute nitric acid or dilute hydrochloric acid.

5. The method for producing a catalyst for the production of melamine according to claim 1, characterized by, The adding amount of calcium oxide in step 2) is 0.5%-3% of the weight of the fly ash; the alkali solution used is a sodium hydroxide solution or a potassium hydroxide solution, and the pH is adjusted to 7-8 by adding the alkali solution.

6. The method for producing a catalyst for the production of melamine according to claim 1, characterized by, The weak acid solution in step 4) is a citric acid solution, and the volume ratio of the citric acid solution to the molecular sieve-silica-alumina colloid is (4-6):

1.

7. The method for producing a catalyst for the production of melamine according to claim 1, characterized by, The solid content of the spray slurry in step 5) is 25 wt%, the spray granulator inlet and outlet temperatures are 450℃ and 115℃ respectively, the feeding pressure is 1.2 MPa, and spray granulation is performed.

8. The method for producing a catalyst for the production of melamine according to claim 1, characterized by, The calcination in step 5) is performed by using a programmed temperature raising method, the temperature is raised to 500-600℃ at a raising speed of 5-10℃ / min, and then the calcination is continued at the temperature for 2-20 h.

9. A catalyst for producing melamine, characterized by, The catalyst product is prepared by the method of any one of claims 1-8.

10. The catalyst of claim 9, wherein The catalyst product contains 65-85% of SiO2, 15-35% of Al2O3, and 0-5% of P2O5.

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