CN113694912A - Catalyst for melamine production and preparation method thereof - Google Patents

Catalyst for melamine production and preparation method thereof Download PDF

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CN113694912A
CN113694912A CN202111085942.0A CN202111085942A CN113694912A CN 113694912 A CN113694912 A CN 113694912A CN 202111085942 A CN202111085942 A CN 202111085942A CN 113694912 A CN113694912 A CN 113694912A
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catalyst
melamine
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唐印
冯瑞
于向真
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Sichuan Golden Elephant Sincerity Chemical Co Ltd
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Sichuan Golden Elephant Sincerity Chemical Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/12—Silica and alumina
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/14—Phosphorus; Compounds thereof
    • B01J27/16—Phosphorus; Compounds thereof containing oxygen, i.e. acids, anhydrides and their derivates with N, S, B or halogens without carriers or on carriers based on C, Si, Al or Zr; also salts of Si, Al and Zr
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/31—Density
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/615—100-500 m2/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/63—Pore volume
    • B01J35/633—Pore volume less than 0.5 ml/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/64—Pore diameter
    • B01J35/647—2-50 nm
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D251/00—Heterocyclic compounds containing 1,3,5-triazine rings
    • C07D251/02—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
    • C07D251/12—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
    • C07D251/26—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with only hetero atoms directly attached to ring carbon atoms
    • C07D251/40—Nitrogen atoms
    • C07D251/54—Three nitrogen atoms
    • C07D251/56—Preparation of melamine
    • C07D251/60—Preparation of melamine from urea or from carbon dioxide and ammonia
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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Abstract

The invention belongs to the field of catalyst preparation, and particularly relates to a catalyst for melamine production and a preparation method thereof. The invention adopts silica gel and pseudo-boehmite with small grain diameter, large pore volume and large pore diameter as raw materials to prepare the silica-alumina gel melamine catalyst with proper silica-alumina ratio, and the prepared catalyst has the characteristics of high activity, high selectivity, high strength, high urea feeding load, less byproducts and the like, thereby effectively reducing the catalyst loss and urea consumption of a melamine device and prolonging the operation period of the device.

Description

Catalyst for melamine production and preparation method thereof
Technical Field
The invention belongs to the field of catalyst preparation, and particularly relates to a catalyst for melamine production and a preparation method thereof.
Background
Melamine is an important nitrogen heterocyclic ring organic chemical intermediate product, is mainly used for producing melamine-formaldehyde resin, and is widely used in the fields of wood processing, coating, papermaking, textile, leather processing and the like. In recent years, with the deep research of melamine and the improvement of living standard of people, the application field and the range of melamine are more and more extensive, and the consumption is also increased rapidly.
China is the biggest melamine producing country in the world, and the production is carried out by adopting a urea method, and the production processes mainly comprise an European high-pressure method, a Dutch DSM low-pressure method, a BASF normal-pressure method and a gas-phase quenching method independently developed in China. The high-pressure process does not need a catalyst, the DSM low-pressure process, the BASF normal-pressure process and the gas-phase quenching process need the catalyst, and the quality of the catalyst can directly influence the production capacity, the product quality, the consumption of raw materials and the operation period of the device. The traditional coarse-pore microspherical silica gel is mostly adopted as a catalyst in the earlier stage of the domestic melamine device, but the catalyst has poor strength and low activity, and the feeding load of urea is only 75 g/kg.h-1The catalyst is easy to be poisoned, so that the device consumption is high, the product yield is low, and the operation period is short. Compared with silica gel microspheres, the active alumina ball catalyst has high activity, small abrasion, less by-products and feeding load of 80-130 g/kg.h-1The catalyst, but the micro powder generated by the abrasion of the alumina ball catalyst is easy to adhere to a filter bag of the filter and is not easy to remove, so that the pressure difference of a production system is rapidly increased, and the operation period of the device is influenced.
In recent years, the melamine production device mostly uses the silica-alumina gel catalyst, and the research on the silica-alumina gel catalyst is also continuous. CN102580711A discloses a method for producing melamine catalyst by synthesizing urea through a gas phase method, which adopts sodium silicate and aluminum sulfate as raw materials to produce melamine catalyst, but the method has the operations of alkali boiling, hole expanding, acid soaking and the like in the production, and has the advantages of long process flow, complex operation and high production cost. CN110665521A discloses a catalyst for synthesizing melamine and a preparation method thereof, wherein the specific surface of the silica gel carrier used is only 120m2The specific surface area of the prepared catalyst is small, the urea load is small, and the aluminum content of the catalyst produced by the method is high, and the cost is high. CN101024171A discloses a catalyst for synthesizing melamine and a preparation method thereof, and the preparation process belongs to the technical field of silicon-aluminum oxide and silicon-aluminum oxideAlumina is mechanically mixed, and the two raw materials cannot be fully combined, so that the strength and the activity of the catalyst are influenced.
CN106902799A discloses a preparation method of synthetic high-alumina silica gel, which adopts large-particle-size silica gel with the particle size of 1-3 mm, and the specific surface of the prepared catalyst is as high as 300-500 m2The catalyst has many micropores and long pore channels, does not utilize the diffusion mass transfer of materials in the pore channels of the catalyst, is easy to generate byproducts, and has short service life.
Disclosure of Invention
The invention provides a high-efficiency catalyst with simple process and low cost and a preparation method thereof based on the problems of the catalyst in the process of producing melamine by a urea method.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a catalyst for melamine production and a preparation method thereof are characterized by comprising the following steps:
(1) preparing aluminum paste: uniformly mixing pseudo-boehmite and water according to the weight ratio of 1: 1-5, and then adding a phosphoric acid or/and nitric acid solution to prepare an aluminum adhesive;
(2) mixing and pulping: adding silica gel and a filler into the aluminum gel, and uniformly mixing to prepare spray slurry with the solid content of 10-30 wt%;
(3) spray granulation: controlling the temperature, the feeding flow and the pressure of an inlet and an outlet of a sprayer to obtain catalyst particles with the median particle size of 70-110 mu m;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 500-600 ℃ at a temperature raising speed of 5-10 ℃/min, and then continuously roasting for 2-20h at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain the catalyst product meeting the requirement.
As a better implementation mode in the application, the peptization index of the pseudo-boehmite in the step (1) is more than 97 percent, and the solid content is 60-70 percent; the mass ratio of the pseudo-boehmite to the water is 1: 1-5; the acid is any one or a mixture of two of phosphoric acid and nitric acid.
As a preferred embodiment of the present application, the silica gel particle size in step (2) is not more than 30 μm, and the specific surface area is more than 350m2The pore diameter is more than 10nm, and the pore volume is more than 0.8 ml/g.
As a better embodiment in the application, the filler in the step (2) is one or more of kaolin, bentonite, activated clay and diatomite, and the addition amount of the filler is 0-50% of the total weight of the dry materials.
As a preferred embodiment in the present application, when a mixture of phosphoric acid and nitric acid is used as the acid, the weight ratio of the pseudoboehmite to the phosphoric acid and nitric acid is 1: 0-0.30: 1.00 to 2.50.
As a preferred embodiment of the present application, the catalyst prepared by the above method contains 60-80% of SiO220-40% of Al2O30 to 5% of P2O5。
As a preferred embodiment of the present application, the catalyst product has an apparent bulk density of 0.58 to 0.90g/cm3The abrasion index is less than 1.5%. h-1BET specific surface area of more than 180m2G, pore diameter is more than 6nm, pore volume is more than 0.3m3/g。
As a preferred embodiment herein, the catalyst product has a median particle size of 70 to 110 μm, a particle size of not more than 3% below 40 μm and a particle size of not more than 5% above 150 μm.
As a better implementation mode in the application, the catalyst prepared by the method is used in the process for synthesizing the melamine by taking the urea as the raw material gas phase.
As a better embodiment in the application, the catalyst is used in a fluidized bed reactor, the temperature of the fluidized bed reactor is 350-480 ℃, and the reaction pressure is 0.1-0.6 MPa.
Compared with the prior art, the invention has the beneficial effects that:
first, SiO in the catalyst prepared in the invention2And Al2O3The proportion of the catalyst is moderate, the surface of the catalyst has proper acid strength and acid density, the catalyst has high activity and high selectivity for synthesizing melamine by urea gas phase, few byproducts are produced, and the urea consumption is reduced to be less than 3.0t/t melamine.
The catalyst prepared by the invention uses silica gel with large aperture and large pore volume, the alumina gel liquid can more easily enter the pore canal of the silica gel, the silicon-aluminum atoms are uniformly distributed, the inner surface and the outer surface of the silica gel particle have higher catalytic activity, and the feeding load of urea can reach 200 g/kg.h-1The catalyst is above.
And thirdly, the catalyst prepared by the method uses silica gel with small particle size and large aperture, and the filler is added to provide a large aperture, the prepared catalyst has short aperture stroke and large aperture, and is beneficial to the diffusion and mass transfer of materials in the catalyst aperture, so that reactants and products are quickly separated from the catalyst, the generation of byproducts is reduced, and the operation period of a melamine device can be prolonged to 4-6 months.
The catalyst prepared by the method has high strength, the consumption is reduced to 0.1kg/t melamine, the apparent bulk density is relatively small, the fluidization is easy, the pressure difference of a reactor is small, and the energy consumption of the device is low.
Description of the drawings:
FIG. 1 is an electron microscope picture of the catalyst for urea-to-melamine prepared in example 1 of the present invention.
Detailed Description
A process for the preparation of a catalyst for the synthesis of melamine comprising the steps of:
(1) preparing silica-alumina gel: dissolving solid sodium silicate and sodium metaaluminate in water, stirring to form a uniform solution, adding sulfuric acid to adjust the pH of the material to 7.5-10.0 to obtain silica-alumina gel slurry, and aging, filtering and washing the slurry to obtain a silica-alumina gel filter cake containing 80-90 wt% of water;
(2) mixing and pulping: adding water into the silica-alumina gel and the filler for pulping, uniformly mixing, and then adding nitric acid to prepare spray slurry with the solid content of 10-30 wt%;
(3) spray granulation: controlling the temperature, the feeding flow and the pressure of an inlet and an outlet of a sprayer to obtain catalyst particles with the median particle size of 70-110 mu m;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 500-600 ℃ at a temperature raising speed of 5-10 ℃/min, and then continuously roasting for 2-20h at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain the catalyst product meeting the requirement.
Preferably, the modulus of the sodium silicate in the step (1) is 1.0-3.5.
Preferably, the weight ratio of the sodium silicate to the sodium metaaluminate to the water in the step (1) is 1: 0.2-0.8: 10-100, the amount of the added sulfuric acid is controlled, and the pH value of the material is adjusted to 7.5-10.0.
Preferably, the amount of the nitric acid added in the step (2) is 0.3-0.7 of the weight of the sodium metaaluminate solid.
Preferably, the filler in the step (2) is one or more of kaolin, bentonite, activated clay and diatomite, and the addition amount of the filler is 0-50% of the total weight of the dry basis of the material.
Preferably, the catalyst for producing melamine prepared by the method contains 60-80% of SiO in percentage by mass220-40% of Al2O3。
Preferably, the apparent bulk density of the catalyst is 0.58 to 0.90g/cm3The abrasion index is less than 1.5%. h-1BET specific surface area of more than 180m2G, pore diameter is more than 6nm, pore volume is more than 0.3m3/g。
Preferably, the median particle size of the catalyst product is 70-110 μm, the particle size is not more than 3% below 40 μm, and the particle size is not more than 5% above 150 μm.
Preferably, the catalyst for producing melamine prepared by the method is used for synthesizing melamine by taking urea as a raw gas phase.
Preferably, the catalyst is used in a fluidized bed reactor, the temperature of the fluidized bed reactor is 350-480 ℃, and the reaction pressure is 0.1-0.6 MPa.
In order to facilitate the understanding of the present invention, the catalyst and the preparation method thereof will be further described with reference to the accompanying drawings and the detailed description. It should not be understood that the scope of the above-described subject matter of the present invention is limited to the following examples.
In the present document,% represents wt% unless otherwise specified.
Example 1:
the embodiment provides a catalyst for melamine production and a preparation method thereof, and the preparation method comprises the following specific steps:
(1) preparing aluminum paste: weighing 800kg of water in a gelling kettle, adding 375kg of pseudo-boehmite, stirring for 30min, then slowly adding 80kg of phosphoric acid with the concentration of 85%, stirring for 30min, then slowly adding 600kg of nitric acid with the concentration of 59%, and continuously stirring for 2h to prepare transparent alumina gel;
(2) mixing and pulping: 2400kg of water, 500kg of silica gel with the particle size of 30 microns and 350kg of argil are weighed and respectively added into a gelling kettle for emulsification for 2 hours to prepare spray slurry with the solid content of 18 percent;
(3) spray granulation: spray granulation is carried out by controlling the inlet and outlet temperature of the sprayer to be 380 ℃, the outlet temperature to be 120 ℃ and the feeding pressure to be 1.2 MPa;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 600 ℃ at a temperature rise speed of 5-10 ℃/min, and then continuously roasting for 2h at the temperature;
(5) cooling and screening: cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain a catalyst product meeting the requirement;
example 2:
the embodiment provides a catalyst for melamine production and a preparation method thereof, and the preparation method comprises the following specific steps:
(2) preparing aluminum paste: weighing 1200kg of water in a gelling kettle, adding 425kg of pseudo-boehmite, stirring for 30min, then slowly adding 750kg of nitric acid with the concentration of 59%, and continuously stirring for 2h to prepare transparent alumina gel;
(2) mixing and pulping: weighing 2000kg of water, 480kg of silica gel with the particle size of 20 mu m and 500kg of diatomite, respectively adding into a gelling kettle, and emulsifying for 2 hours to prepare spray slurry with the solid content of 20%;
(3) spray granulation: spray granulation is carried out by controlling the inlet and outlet temperature of the sprayer to be 400 ℃, the outlet temperature to be 120 ℃ and the feeding pressure to be 1.4 MPa;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 550 ℃ at a temperature rise speed of 5-10 ℃/min, and then continuously roasting for 5 hours at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain the catalyst product meeting the requirement.
Example 3:
the embodiment provides a catalyst for melamine production and a preparation method thereof, and the preparation method comprises the following specific steps:
(3) preparing aluminum paste: weighing 600kg of water in a gelling kettle, adding 330kg of pseudo-boehmite, stirring for 30min, slowly adding 520kg of nitric acid with the concentration of 59%, and continuously stirring for 2h to prepare transparent alumina gel;
(2) mixing and pulping: respectively adding 1800kg of water, 550kg of silica gel with the particle size of 10 mu m and 420kg of kaolin into a gelling kettle, and emulsifying for 2 hours to prepare spray slurry with the solid content of 25%;
(3) spray granulation: controlling the inlet and outlet temperature of the sprayer to be 400 ℃, the outlet temperature to be 120 ℃ and the feeding pressure to be 1.5MPa, and carrying out spray granulation on the spray slurry;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 500 ℃ at a temperature raising speed of 5-10 ℃/min, and then continuously roasting for 8 hours at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain the catalyst product meeting the requirement.
Comparative example 1:
a melamine catalyst is prepared by the following steps:
(1) mixing and pulping: weighing 2000kg of 30% silica sol and 270kg of kaolin, respectively adding into a gelling kettle, emulsifying for 2h, and preparing into uniform slurry;
(2) preparing aluminum paste: adding 300kg of pseudo-boehmite into a gelling kettle, stirring for 30min, then slowly adding 520kg of nitric acid with the concentration of 59%, and continuously stirring for 2h to prepare spray slurry;
(3) spray granulation: spray granulation is carried out by controlling the inlet and outlet temperature of the sprayer to be 400 ℃, the outlet temperature to be 120 ℃ and the feeding pressure to be 1.5 MPa;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 500 ℃ at a temperature raising speed of 5-10 ℃/min, and then continuously roasting for 2h at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain a catalyst product.
Comparative example 2:
a melamine catalyst is prepared by the following steps:
(1) preparing aluminum paste: weighing 600kg of water in a gelling kettle, adding 300kg of pseudo-boehmite, stirring for 30min, slowly adding 520kg of nitric acid with the concentration of 59%, and continuously stirring for 2h to prepare transparent alumina gel;
(2) mixing and pulping: adding 2000kg of 30% silica sol and 270kg of kaolin into a gelling kettle respectively, and emulsifying for 2h to prepare spray slurry with the solid content of 25%;
(3) spray granulation: spray granulation is carried out by controlling the inlet and outlet temperature of the sprayer to be 400 ℃, the outlet temperature to be 120 ℃ and the feeding pressure to be 1.5 MPa;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 500 ℃ at a temperature raising speed of 5-10 ℃/min, and then continuously roasting for 8 hours at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain a catalyst product.
The melamine catalysts prepared in examples 1 to 3 and the catalysts obtained in comparative example 1 and comparative example 2 were subjected to analysis and measurement of catalytic performance, wherein the prepared catalysts and the comparative catalysts were each tested according to the following criteria:
GB/T19587-2004 gas adsorption BET method for determining specific surface area of solid matter
GB/T21650.3-2011 mercury intrusion method and gas adsorption method for measuring pore size distribution and porosity of solid material part 3
Method for measuring element content of GB/T30905-2014 inorganic chemical product by X-ray fluorescence spectrometry
Apparent bulk density determination method of NB/SH/T0954-2017 catalytic cracking catalyst
Section 2 of industrial standard chapter 4 of catalyst industry for preparing low-carbon olefin from HG/T4861-2015 methanol: determination of abrasion index
The catalytic performance data is obtained by testing when a gas-phase quenching process melamine device with 2 ten thousand tons/year operates stably, the carrier gas is a mixed gas of ammonia and carbon dioxide with the weight ratio of 1:1, the carrier gas flow is 25-40 t/h, the reaction temperature is 390-420 ℃, the catalyst loading is 50-60 t, the urea feeding amount is 6-10 t/h, the primary conversion rate of urea is the ratio of the feeding amount of a urea washing tower and the feeding amount of reactor urea when the device operates stably for 72h, and the melamine yield is the ratio of the theoretical urea amount and the feeding urea amount required by melamine produced when the device operates stably for 72 h.
The specific results are as follows:
TABLE 1
Figure BDA0003265552220000101
Figure BDA0003265552220000111
TABLE 2
Figure BDA0003265552220000112
As can be seen from Table 2, when the feed loading was 120g urea/kg catalyst. multidot.h-1No matter what kind of catalyst is used, the primary conversion rate of urea and melamine yield in melamine plant can meet the production requirement, and when the feeding load is higher than 160g of urea/kg of catalyst.h-1By using the three catalysts prepared in the embodiment of the invention, the primary urea conversion rate and the melamine yield can meet the production requirements, but by using the two catalysts in the comparative example, the primary urea conversion rate and the melamine yield are both reduced. Therefore, the catalyst prepared by the method has higher catalytic activity and selectivity, can bear higher feeding load and has more excellent catalytic performance.
Although the present invention has been described in detail with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims (10)

1. A process for the preparation of a catalyst for the production of melamine, characterized in that it comprises the following steps:
(1) preparing aluminum paste: uniformly mixing pseudo-boehmite and water in proportion, and then adding an acid solution to prepare an aluminum adhesive;
(2) mixing and pulping: adding silica gel and a filler into the alumina gel, and uniformly mixing to prepare spray slurry with solid content of 10-30%;
(3) spray granulation: controlling the temperature, the feeding flow and the pressure of an inlet and an outlet of a sprayer to obtain catalyst particles with the median particle size of 70-110 mu m;
(4) roasting: roasting the spray particles by adopting a temperature programming mode, raising the temperature to 500-600 ℃ at a temperature raising speed of 5-10 ℃/min, and then continuously roasting for 2-20h at the temperature;
(5) cooling and screening: and (3) cooling the roasted material by airflow, and removing fine particles with the particle size of less than 10 mu m in the mixed material by cyclone separation to finally obtain the catalyst product meeting the requirement.
2. Process for the preparation of a catalyst for the production of melamine according to claim 1, characterized in that: in the step (1), the peptization index of the pseudo-boehmite is more than 97%, and the solid content is 60-70%; the mass ratio of the pseudo-boehmite to the water is 1: 1-5; the acid is any one or a mixture of two of phosphoric acid and nitric acid.
3. Process for the preparation of a catalyst for the production of melamine according to claim 1, characterized in that: in the step (2), the particle size of the silica gel is not more than 30 mu m, and the specific surface area is more than 350m2The pore diameter is more than 10nm, and the pore volume is more than 0.8 ml/g.
4. Process for the preparation of a catalyst for the production of melamine according to claim 1, characterized in that: in the step (2), the filler is one or more of kaolin, bentonite, activated clay and diatomite, and the addition amount of the filler is 0-50% of the total weight of the dry basis of the material.
5. Process for the preparation of a catalyst for the production of melamine according to claim 2, characterized in that: when the acid is a mixture of phosphoric acid and nitric acid, the weight ratio of the pseudo-boehmite to the phosphoric acid and nitric acid is 1: 0-0.30: 1.00 to 2.50.
6. A catalyst prepared according to the process of any one of claims 1 to 5, wherein: the catalyst product contains 60-80% of SiO220-40% of Al2O3，0～5％P of2O5。
7. A catalyst prepared according to the process of any one of claims 1 to 5, wherein: the apparent bulk density of the catalyst product is 0.58-0.90 g/cm3The abrasion index is less than 1.5%. h-1BET specific surface area of more than 180m2G, pore diameter is more than 6nm, pore volume is more than 0.3m3/g。
8. A catalyst prepared according to the process of any one of claims 1 to 5, wherein: the median particle size of the catalyst product is 70-110 mu m, the particle size is not more than 3% below 40 mu m, and the particle size is not more than 5% above 150 mu m.
9. Use of a catalyst prepared according to any one of claims 1 to 5, wherein: the catalyst is used in the process of synthesizing melamine by using urea as a raw material gas phase.
10. Use according to claim 9, characterized in that: the catalyst is used in a fluidized bed reactor, the temperature of the fluidized bed reactor is 350-480 ℃, and the reaction pressure is 0.1-0.6 MPa.
CN202111085942.0A 2021-09-16 2021-09-16 Catalyst for melamine production and preparation method thereof Pending CN113694912A (en)

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