Preparation method of cyanamide product

Abstract

The invention provides a preparation method of a cyanamide product, which comprises the following steps: S1, mixing a raw material and a preheated solid catalyst, recording the contact time of the raw material and the preheated solid catalyst as T0, recording the uniform temperature reaching time after mixing as T1, and T1-T0 < = 3s; the raw materials comprise urea or mixed gas of ammonia gas and carbon dioxide, the temperature of the urea is less than or equal to 150 DEG C, and the temperature of the mixed gas is 150-450 DEG C; s2, carrying out gas-solid separation on the obtained reaction mixture, recording the time for completing the gas-solid separation as T2, and enabling T2-T1 to be smaller than or equal to 10s; s3, cooling the obtained gas-phase product to below 110 DEG C within F seconds, wherein the temperature is Flt; the method comprises the following steps: 1, obtaining cyanamide products; by adopting the technical scheme provided by the invention, cyanamide and / or dicyandiamide can have relatively high selectivity, so that the content of cyanamide and / or dicyandiamide in the finally obtained cyanamide product is greater than 96%.

Description

Technical Field

[0001] The present invention relates to the chemical industry field, and specifically relates to a preparation method of cyanamide products. Background Art

[0002] Monocyanamide, also known as aminocyanide, amino nitrile, English name: cyanamide, urea anhydride; molecular formula NH 2 CN. The crystal of monocyanamide is not very stable and is often stored as a 30%-50% aqueous solution; under certain conditions, monocyanamide can polymerize and transform into dicyandiamide. Monocyanamide is an important chemical raw material and can be used in the synthesis of low-toxic and broad-spectrum chemical pesticide intermediates, health products, feed additives, flame retardants, etc., with very wide uses.

[0003] Dicyandiamide, also known as cyanoguanidine, dicyanodiamide, dicyandiamide, English name: Dicyandiamide, Cyanoguanidine; chemical formula is C 2 H 4 N 4 , which is the dimer of monocyanamide and also the cyano derivative of guanidine. Dicyandiamide is a white crystalline powder, soluble in water, alcohol, ethylene glycol and dimethylformamide, almost insoluble in ether and benzene, stable when dry, and can be converted into melamine at high temperatures. As a fine chemical intermediate, dicyandiamide is used in the pharmaceutical industry to produce guanidine nitrate and sulfonamide drugs, and can also be used to prepare thiourea, stabilizer for nitrocellulose, rubber vulcanization accelerator, steel surface hardener, artificial leather filler, adhesive, etc.

[0004] At present, the industrial production of monocyanamide mainly adopts the calcium cyanamide method. The specific production process is to hydrolyze calcium cyanamide to obtain a calcium cyanamide hydrogen suspension, remove the calcium hydroxide filter residue by vacuum filtration, and then introduce carbon dioxide into the filtrate to precipitate calcium in the form of calcium carbonate to obtain a monocyanamide solution. Monocyanamide polymerizes under alkaline conditions, and then through filtration, cooling crystallization, separation, and drying, dicyandiamide is obtained.

[0005] The reaction equations are as follows:

[0006] 2CaCN 2 +2H 2 O=Ca(HCN 2 ) 2 +Ca(OH) 2

[0007] Ca(HCN 2 ) 2 +CO 2 +H 2 O=2NH 2 CN+CaCO 3

[0008] 2NH 2 CN=(NH 2 CN) 2

[0009] This method has complex processes, large equipment investment, serious pollution, high energy consumption, and the product contains a relatively large amount of free calcium ions. Moreover, the production of calcium cyanamide will also generate a large amount of soot and waste heat, which not only pollutes the environment but also wastes resources. With the advancement of new industrialization and the improvement of national policies and regulations on comprehensive resource utilization and environmental protection, the extensive production of calcium carbide deep-processing products will become unsustainable.

[0010] Using a mixture of urea or ammonia and carbon dioxide to prepare cyanamide products is also a way. Under the action of a catalyst, the mixture of urea or ammonia and carbon dioxide dehydrates to form monocyanamide, and then monocyanamide polymerizes under certain conditions to transform into dicyandiamide. The reaction equations are as follows:

[0011] CO(NH 2 ) 2 =H 2 O+NH 2 CN (monocyanamide)

[0012] CO 2 +2NH 3 =2H 2 O+NH 2 CN (monocyanamide)

[0013] 2NH 2 CN (monocyanamide)=(NH 2 CN) 2 (dicyandiamide)

[0014] Chinese patent document CN105984888A discloses a method for preparing monocyanamide using urea as a raw material. This method uses HZSM-5 zeolite modified with manganese acetate as a catalyst, ammonia as a fluidizing gas, heats urea particles to 500 - 550 °C, and then mixes and reacts with the catalyst heated to 500 - 550 °C. After absorbing ammonia and carbon dioxide in the product with dilute sulfuric acid solution and sodium hydroxide solution, a cyanamide solution is obtained. The by-product yield in this process is high, and the selectivity of cyanamide is poor.

[0015] Chinese patent document CN113651725A discloses a method for preparing dicyandiamide by recycling melamine tail gas. The main components of melamine tail gas are ammonia and carbon dioxide. The product after their reaction is directly polymerized in a polymerizer, and then cooled and crystallized in a crystallizer by exchanging heat with water through heat exchange tubes. However, this technology does not describe the product composition, and it is difficult to separate dicyandiamide from melamine.

[0016] "Research on a New Process for the Preparation of Cyanamide" (Wang Qian, Master's Thesis of Tianjin University, 2006) heats the mixed gas of urea or ammonia and carbon dioxide for feeding. Using ZSM-5 molecular sieve, Beta molecular sieve, and aluminosilicate OX-50 zeolite as catalysts, the conversion rate can reach over 88.5%. However, the product is a mixture of monocyanamide, dicyandiamide, and melamine, and the melamine content is between 9.8% and 18.5%. The product is not easily separated (see Table 2-3 in Chapter 2).

[0017] In summary, in the existing technology for preparing cyanamide products using the mixed gas of urea or ammonia and carbon dioxide as raw materials, there are generally problems of many side reactions and poor product selectivity. Therefore, there is an urgent need to develop a preparation method for cyanamide products with fewer side reactions and high selectivity. Summary of the Invention

[0018] In view of this, the present invention aims to provide a preparation method for cyanamide products with fewer side reactions and high selectivity to solve the problems of many side reactions and poor product selectivity in the existing process.

[0019] According to an embodiment of the present invention, in a first aspect, a preparation method for cyanamide products is provided, including the following steps:

[0020] S1. Mix the raw materials with the preheated solid catalyst to react. The time when the raw materials start to contact the preheated solid catalyst is denoted as T 0 , and the time when the temperature becomes uniform after mixing is denoted as T 1 , T 1 -T 0 ≤3 s;

[0021] The raw materials include urea or a mixed gas of ammonia and carbon dioxide. The temperature of the urea is less than or equal to 150 °C, and the temperature of the mixed gas is 150 °C to 450 °C;

[0022] S2. Perform gas-solid separation on the reaction mixture obtained in S1, and denote the time when the gas-solid separation is completed as T 2 , T 2 -T 1 ≤10 s;

[0023] S3. Cool the gas-phase product obtained in S2 to below 110 °C within F seconds, where F < 1, to obtain cyanamide products,

[0024] The cyanamide products include monocyanamide (NH 2 CN) and / or dicyandiamide (C 2 H 4 N 4 ),

[0025] The temperature of the preheated solid catalyst is 500°C - 750°C.

[0026] It can be understood that uniform temperature means the same temperature of the raw material and the preheated solid catalyst.

[0027] In the present invention, the selectivity of monocyanamide or dicyandiamide in the preparation method of cyanamide products reaches more than 96%. In the present invention, the content of monocyanamide or dicyandiamide in the cyanamide products is more than 96%.

[0028] In some alternative embodiments, T 1 -T 0 ≤1 s.

[0029] In some alternative embodiments, T 2 -T 1 ≤6 s.

[0030] In some alternative embodiments, F ≤ 0.1.

[0031] In some alternative embodiments, 0.01 s ≤ T 1 -T 0 ≤0.5 s.

[0032] In some alternative embodiments, 0.5 s ≤ T 2 -T 1 ≤3 s.

[0033] In some alternative embodiments, 0.001 ≤ F ≤ 0.08.

[0034] In some alternative embodiments, the temperature of the mixed gas is 150°C to 350°C.

[0035] In some alternative embodiments, the temperature of the urea is less than or equal to 120°C.

[0036] In some alternative embodiments, the particle size of the solid catalyst is 30 μm - 200 μm. Using a solid catalyst with a particle size of 30 μm - 200 μm, it can circulate under the action of the carrier gas.

[0037] In some alternative embodiments, the preparation method of the solid catalyst includes mixing the active ingredient, binder and deionized water, spray-drying and forming at 250°C - 450°C, and then calcining at 400°C - 650°C for 30 min - 6 h to obtain the solid catalyst.

[0038] The mass ratio of the active component to the binder is (5 - 70):(30 - 95).

[0039] In some alternative embodiments, the active component includes at least one of activated silica-alumina powder, ZSM-5 molecular sieve, beta molecular sieve, mordenite molecular sieve, Y molecular sieve, and MCM-22 molecular sieve. With the above-mentioned active components, the conversion efficiency of the raw materials is higher, the occurrence of side reactions is reduced, which is beneficial to the formation of monocyanamide or dicyandiamide.

[0040] In some alternative embodiments, the binder includes at least one of silica sol, silica-alumina sol, phosphoaluminate sol, pseudoboehmite, and kaolin.

[0041] In some alternative embodiments, in S3, an absorbent is used to spray the gaseous product, or the gaseous product is collided with the absorbent to rapidly cool the gaseous product; the temperature of the absorbent is 45°C - 100°C, and the pH value is 2.0 - 11.5. Spraying the gaseous product with the absorbent or colliding the gaseous product with the absorbent can rapidly cool the gaseous product, reduce the formation of melamine, and thus increase the content of monocyanamide or dicyandiamide in the cyanamide products.

[0042] In some alternative embodiments, in S1, a riser process or a downer bed process is used to achieve the rapid heating and reaction of the raw materials;

[0043] Among them, in the riser process, the raw materials and the catalyst enter from the lower part of the reaction tube, and the product and the catalyst come out from the upper part of the reaction tube; in the downer bed process, the raw materials and the catalyst enter from the upper part of the reaction tube, and the product and the catalyst come out from the lower part of the reaction tube.

[0044] In some alternative embodiments, when the pH value of the absorbent is between 2.0 and 8.0, the content of monocyanamide in the resulting cyanamide product is greater than 96%.

[0045] In some alternative embodiments, when the pH value of the absorbent is greater than 8.0, the content of dicyandiamide in the resulting cyanamide product is greater than 96%.

[0046] In some alternative embodiments, the absorbent includes at least one of water, methanol, ethanol, acetone, n-butylamine, diethylamine, propylamine, aqueous phosphoric acid solution, aqueous tetraethylammonium hydroxide solution, aqueous tetrapropylammonium hydroxide solution, aqueous sodium hydroxide solution, and aqueous potassium hydroxide solution.

[0047] Specific absorbents can more quickly reduce the temperature of the gaseous product, thus avoiding the formation of melamine.

[0048] In some alternative embodiments, the mass content of monocyanamide or dicyandiamide in the cyanamide product is greater than 96%, and the mass content of melamine is less than 1%.

[0049] In some alternative embodiments, the preparation apparatus for implementing the preparation method includes a reaction tube, a catalyst storage tank, a heater, a cyclone separator, a rapid cooler, and a feeding controller. Among them, the heater is used to preheat the solid catalyst from the catalyst storage tank; the reaction tube is used to mix and react the preheated solid catalyst with the raw material from the feeding controller; the cyclone separator is used to perform gas-solid separation on the reaction mixture to obtain the reacted catalyst and the gas-phase product; the rapid cooler is used to cool down the gas-phase product.

[0050] In some alternative embodiments, the catalyst storage tank can also be used to receive the reacted catalyst.

[0051] The preparation method first uses the heater to preheat the solid catalyst in the catalyst storage tank, and then directly contacts and mixes the preheated solid catalyst with the urea raw material provided in the feeding controller in the reaction tube, so that the urea rapidly (within 3 s) rises to 400°C - 620°C, shortening the residence time of urea in the temperature range of 135°C - 350°C, reducing the decomposition-condensation of urea, and reducing the occurrence of side reactions. Subsequently, the heated urea undergoes a dehydration reaction under the action of the catalyst to generate monocyanamide. Under the action of the raw material carrier gas, the reaction mixture containing monocyanamide and the catalyst enters the cyclone separator for rapid gas-solid separation to reduce the generation of side reactions. The separated solid catalyst returns to the catalyst storage tank, and the reaction product monocyanamide enters the rapid cooler, where it directly collides with the absorbent or is rapidly cooled after being sprayed with the absorbent to prevent monocyanamide from polymerizing into melamine, thereby highly selectively producing cyanamide products.

[0052] It can be understood that when a mixture of ammonia and carbon dioxide is used instead of urea as the raw material, the mixture can be preheated by the feeding controller in advance, and then the preheated solid catalyst is contacted and mixed with the mixture provided in the feeding controller in the reaction tube to react and generate monocyanamide. The subsequent gas-solid separation and cooling processes are the same as above and will not be elaborated here.

[0053] It should also be noted that when the pH value of the absorbent is greater than 8.0, monocyanamide will dimerize into dicyandiamide, and the finally obtained product is mainly dicyandiamide. When the pH value of the absorbent is less than or equal to 8.0, monocyanamide will exist stably, and the finally obtained product is mainly monocyanamide.

[0054] The technical solution of the present invention has the following advantages:

[0055] The preparation method of cyanamide products provided by the present invention can effectively shorten the residence time of urea in the temperature range of 135°C - 350°C, reduce the decomposition-condensation of urea, and reduce the occurrence of side reactions by controlling the temperature of the raw materials and limiting the time for mixing the raw materials and the preheated solid catalyst to reach uniform temperature to be less than 3 s, that is, the time from mixing evenly to gas-solid separation is less than 10 s; and the rapid separation of the reaction product and the solid catalyst can further effectively reduce the generation of side reactions; further, by controlling the cooling rate of the reaction product within 1 s, the polymerization of monocyanamide into melamine can be inhibited, so as to prepare cyanamide products with high selectivity. In summary, the technical solution of the present invention can reduce the occurrence of side reactions, inhibit the formation of melamine, make monocyanamide and / or dicyandiamide have high selectivity, so that the content of monocyanamide and / or dicyandiamide in the finally obtained cyanamide products is greater than 96%.

[0056] Further, a solid catalyst with a particle size of 30 μm - 200 μm is used, which can circulate under the action of the carrier gas, facilitating the progress of the reaction.

[0057] Using activated silica-alumina powder, ZSM-5 molecular sieve, beta molecular sieve, mordenite molecular sieve, Y molecular sieve, MCM-22 molecular sieve as active components, the conversion efficiency of raw materials is higher, the occurrence of side reactions is reduced, and the formation of monocyanamide or dicyandiamide is facilitated.

[0058] Further, by spraying the gas-phase product or colliding the gas-phase product with the absorbent, the gas-phase product can be rapidly cooled, reducing the formation of melamine, thereby increasing the content of monocyanamide or dicyandiamide in the cyanamide products.

[0059] Further, by controlling the pH of the absorbent to be 2.0 - 8.0, the present invention can make monocyanamide have extremely high selectivity, and the content of monocyanamide in the finally obtained cyanamide products is greater than 96%.

[0060] Further, by controlling the pH of the absorbent to be greater than 8.0, the present invention can make dicyandiamide have extremely high selectivity, and the content of dicyandiamide in the finally obtained cyanamide products is greater than 96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0062] Figure 1 It is a system diagram of the preparation method of cyanamide products provided in Embodiment 1 of the present invention;

[0063] Description of the Drawings: 1 - reaction tube; 2 - catalyst storage tank; 3 - heater; 4 - cyclone separator; 5 - rapid cooler; 6 - feeding controller. Specific Embodiments

[0064] The following embodiments are provided to better understand the present invention further. It is not limited to the best mode, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0065] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0066] Example 1

[0067] The test device required for the method for preparing cyanamide products is as Figure 1 shown, including: reaction tube 1, catalyst storage tank 2, heater 3, cyclone separator 4, rapid cooler 5, feeding controller 6; wherein, the solid catalyst in the catalyst storage tank 2 is preheated using the heater 3, and then the preheated solid catalyst is mixed and reacted with the raw materials provided in the feeding controller 6 in the reaction tube 1; the reaction system after reaction is sent to the cyclone separator 4 for separating the solid catalyst and the reaction product, the separated solid catalyst is returned to the catalyst storage tank 2, and the reaction product is sent to the rapid cooler 5 for cooling, thus obtaining the cyanamide products;

[0068] In a specific embodiment, the reaction tube 1 is selected from a downflow bed reactor, wherein the raw materials enter from the upper part of the downflow bed reactor;

[0069] In a specific embodiment, the reaction tube 1 is selected from a riser tube, wherein the raw materials enter from the lower part of the riser tube;

[0070] In a specific embodiment, the catalyst after reaction is returned to the catalyst storage tank.

[0071] Example 2

[0072] This example provides a method for preparing solid catalyst A used for preparing cyanamide products, including the following steps:

[0073] Take 500 g of pseudo-boehmite, add it to 1500 g of deionized water, then add 350 g of nitric acid with a concentration of 65% and 150 g of phosphoric acid with a concentration of 75%. While stirring, heat the slurry to 80 °C and treat it for 2 h. Then add 300 g of kaolin and continue to stir and slurry for 1 h. Then add 400 g of H-type ZSM-5 molecular sieve. Spray-dry and form the prepared slurry at 350 °C with hot air, and calcine it at 500 °C for 2 h to obtain catalyst A. Use a laser particle size analyzer (Zhuhai Omicron Instruments Co., Ltd., model LS-POP-9) to analyze its particle size, which is in the range of 35 μm to 186 μm, and the average particle size (Dv50) is 83 μm.

[0074] Example 3

[0075] This example provides a preparation method of a cyanamide product. Using the device provided in Example 1, it includes the following steps:

[0076] Use N 2 After completely replacing the air in the device, add 6 Kg of catalyst A prepared according to the scheme of Example 2 to the catalyst storage tank 2. With the assistance of N 2 gas, catalyst A circulates in the heater 3, reaction tube 1 (riser tube), cyclone separator 4, and catalyst storage tank 2. The heater 3 heats up to make the temperature of catalyst A reach 550 °C, and the circulation rate of catalyst A in the reaction tube 1 is controlled to 3.5 Kg / h.

[0077] The circulating absorbent in the rapid cooler 5 is an aqueous phosphoric acid solution (that is, the pH value of deionized water is adjusted to 4.5 with phosphoric acid), the circulation flow rate is 6 L / min, and the temperature is controlled to 50 °C.

[0078] After the preparation device is stable, add room temperature (25 °C) urea through the feeding controller 6, and send it into the reaction tube 1 with room temperature ammonia. The urea flow rate is controlled to 2 g / min, and the ammonia flow rate is controlled to 50 ml / min.

[0079] After the reaction is stable, the temperature of the reaction mixture at the outlet of the reaction tube 1 is 450 °C. Immediately, the reaction mixture enters the cyclone separator 4 for gas-solid separation to obtain a gas-phase product and the reacted catalyst B. The temperature of the gas-phase product entering the rapid cooler 5 is 400 °C. In the rapid cooler 5, the gas-phase product directly collides with the absorbent liquid, thereby quickly cooling the temperature of the gas-phase product to 50 °C; the reacted catalyst B returns to the catalyst storage tank 2 for reuse.

[0080] After measurement, the time interval between T 1 and T 0 is 0.8 s; the time interval between T 2 and T 1 is 4.5 s; the cooling time F of the gas-phase product is 0.06 s.

[0081] After stable operation for 2 h, the liquid in the rapid cooler was taken for analysis, and the analysis results are shown in Table 1.

[0082] After each test, all the liquid in the rapid cooler 5 was replaced with new liquid.

[0083] Example 4

[0084] This example provides a preparation method of a cyanamide product. The steps are similar to those of Example 3, except for the following parameter changes:

[0085] The circulation rate of catalyst A in the reaction tube 1 was controlled to 3.8 Kg / h.

[0086] The temperature was normal temperature, the urea flow rate was controlled to 2.5 g / min, and the ammonia flow rate was controlled to 60 ml / min.

[0087] After the reaction was stable, the temperature of the reaction mixture at the outlet of the reaction tube 1 (riser tube) was 480 °C, and the temperature of the gas-phase product entering the rapid cooler 5 was 420 °C.

[0088] After calculation, the time interval between T 1 and T 0 was 0.5 s; the time interval between T 2 and T 1 was 3.0 s; the cooling time F of the gas-phase product was 0.06 s.

[0089] After stable operation for 2 h, the liquid in the rapid cooler was taken for analysis, and the analysis results are shown in Table 1.

[0090] Example 5

[0091] This example provides a preparation method of a cyanamide product. The steps are similar to those of Example 3, except for the following parameter changes:

[0092] The heater 3 was heated to make the temperature of catalyst A reach 600 °C, and the circulation rate of the catalyst in the reaction tube 1 was controlled to 3.8 Kg / h.

[0093] The urea flow rate was controlled to 4.0 g / min, and the ammonia flow rate was controlled to 65 ml / min.

[0094] After the reaction was stable, the temperature of the reaction mixture at the outlet of the reaction tube 1 (riser tube) was 520 °C, and the temperature of the gas-phase product entering the rapid cooler 5 was 450 °C.

[0095] After calculation, the time interval between T 1 and T 0 was 0.3 s; the time interval between T 2 and T 1 was 2.2 s; the cooling time F of the gas-phase product was 0.04 s.

[0096] After stable operation for 2 h, the liquid in the rapid cooler was taken for analysis, and the analysis results are shown in Table 1.

[0097] Example 6

[0098] This example provides a preparation method of a cyanamide product. The steps are similar to those of Example 3, except for the following parameter changes:

[0099] The heater 3 was heated to make the temperature of catalyst A reach 580 °C. The circulation amount of catalyst A in the reaction tube 1 was controlled to 3.0 Kg / h. The circulating absorbent in the rapid cooler 5 was tetraethylammonium hydroxide solution (i.e., deionized water was adjusted to pH 10.5 with tetraethylammonium hydroxide), the circulation flow rate was 8 L / min, and the temperature was controlled to 95 °C.

[0100] After the device was stable, urea was added through the feeding controller 6 and sent into the reaction tube 1 with ammonia. The temperature of urea was at room temperature, the flow rate of urea was controlled to 2.0 g / min, and the flow rate of ammonia was controlled to 80 ml / min.

[0101] After the reaction was stable, the temperature of the reaction mixture at the outlet of the reaction tube 1 (riser tube) was 480 °C, and the temperature of the gas-phase product entering the rapid cooler 5 was 410 °C.

[0102] After calculation, T 1 and T 0 The time interval is 0.3 s; T 2 and T 1 The time interval is 3.6 s; the cooling time F of the gas-phase product is 0.06 s.

[0103] After stable operation for 2 h, the circulating liquid was taken for analysis, and the analysis results are shown in Table 1.

[0104] Example 7

[0105] This example provides a preparation method of a cyanamide product. The steps are similar to those of Example 3, except for the following parameter changes:

[0106] The heater 3 was heated to make the temperature of catalyst A reach 560 °C. The circulation amount of the catalyst in the reaction tube 1 was controlled to 3.6 Kg / h. The absorbent liquid in the rapid cooler 5 was sodium hydroxide solution (i.e., deionized water was adjusted to pH 10.0 with sodium hydroxide), the circulation flow rate was 8 L / min, and the temperature was controlled to 100 °C.

[0107] After the device was stable, urea was added through the feeding controller 6 and sent into the reaction tube 1 with ammonia. The temperature was at room temperature, the flow rate of urea was controlled to 3.0 g / min, and the flow rate of ammonia was controlled to 85 ml / min.

[0108] After the reaction is stabilized, the temperature of the reaction mixture at the outlet of the reaction tube 1 (riser) is 450 °C, and the temperature of the gas-phase product entering the rapid cooler 5 is 350 °C.

[0109] After calculation, T 1 and T 0 The time interval is 0.3 s; T 2 and T 1 The time interval is 3.2 s; the cooling time F of the gas-phase product is 0.08 s.

[0110] After stable operation for 2 h, the liquid in the cooler is taken for analysis, and the analysis results are shown in Table 1.

[0111] Example 8

[0112] This example provides a preparation method of a cyanamide product. Using the device provided in Example 1, it includes the following steps:

[0113] Using N 2 After all the air in the device is replaced, 6.5 Kg of catalyst A prepared according to the scheme of Example 1 is added to the catalyst storage tank 2. With the assistance of N 2 gas, catalyst A circulates in the heater 3, reaction tube 1 (riser), cyclone separator 4, and catalyst storage tank 2, and is heated by the heater 3 to make the temperature of the catalyst reach 620 °C. The catalyst circulation rate in the reaction tube 1 is controlled to 3.0 Kg / h, and the absorption liquid in the rapid cooler 5 is an aqueous phosphoric acid solution (i.e., deionized water adjusted to pH 4.5 with phosphoric acid), with a circulation flow rate of 8 L / min and a temperature controlled to 50 °C.

[0114] After the circulation of catalyst A and the circulating absorption liquid is stable, ammonia gas and carbon dioxide gas are introduced into the reaction tube 1 through the feeding controller 6. The gases are preheated to 350 °C, the ammonia gas flow rate is controlled to 200 ml / min, and the carbon dioxide gas flow rate is controlled to 3000 ml / min.

[0115] After the reaction is stabilized, the temperature of the reaction mixture at the outlet of the reaction tube 1 is 580 °C, and the temperature of the gas-phase product entering the rapid cooler 5 is 460 °C.

[0116] After calculation, T 1 and T 0 The time interval is 0.1 s; T 2 and T 1 The time interval is 2.4 s; the cooling time F of the gas-phase product is 0.06 s.

[0117] After stable operation for 2 h, the liquid in the rapid cooler is taken for analysis, and the analysis results are shown in Table 1.

[0118] Example 9

[0119] This embodiment provides a method for preparing a cyanamide product. Using the device provided in Embodiment 1, the method includes the following steps:

[0120] Using N 2 After all the air in the device is replaced, 6.5 Kg of catalyst A prepared according to the scheme of Embodiment 1 is added to the catalyst storage tank 2. With the assistance of N 2 gas, catalyst A circulates in the heater 3, reaction tube 1 (riser tube), cyclone separator 4, and catalyst storage tank 2. It is heated by the heater 3 to make the temperature of the catalyst reach 600 °C. The circulating amount of the catalyst in the reaction tube 1 is controlled to 3.6 Kg / h. The absorption liquid in the rapid cooler 5 is sodium hydroxide solution (that is, the pH value of deionized water is adjusted to 9.5 with sodium hydroxide), the circulating flow rate is 8 L / min, and the temperature is controlled to 98 °C.

[0121] After the circulation of catalyst A and the circulating absorption liquid is stable, ammonia gas and carbon dioxide gas are introduced into the reaction tube 1 through the feeding controller 6, preheated to 350 °C, the ammonia gas flow rate is controlled at 300 ml / min, and the carbon dioxide gas flow rate is controlled at 6000 ml / min.

[0122] After the reaction is stable, the temperature of the reaction mixture at the outlet of the reaction tube 1 is 550 °C, and the temperature of the gas-phase product entering the rapid cooler 5 is 430 °C.

[0123] After measurement, the time interval between T 1 and T 0 is 0.1 s; the time interval between T 2 and T 1 is 3.0 s; the cooling time F of the gas-phase product is 0.08 s.

[0124] After stable operation for 2 h, the circulating liquid is taken for analysis, and the analysis results are shown in Table 1.

[0125] Comparative Example 1

[0126] This comparative example provides a method for preparing a cyanamide product. The steps are similar to those in Embodiment 3, except for the following parameter changes:

[0127] Urea is added through the feeding controller 6. After being preheated to 220 °C, it enters the reaction tube.

[0128] After stable operation for 2 h, the liquid in the rapid cooler is taken for analysis, and the analysis results are shown in Table 1.

[0129] Comparative Example 2

[0130] This comparative example provides a method for preparing a cyanamide product. The steps are similar to those in Embodiment 3, except for the following parameter changes:

[0131] Heat with heater 3 to raise the temperature of catalyst A to 580 °C. Control the circulation rate of catalyst A in reaction tube 1 (riser) to 3.0 Kg / h. The circulating absorbent in rapid cooler 5 is tetraethylammonium hydroxide solution (i.e., deionized water adjusted to pH 10.5 with tetraethylammonium hydroxide), with a circulation flow rate of 8 L / min and the temperature controlled to 95 °C.

[0132] Urea is fed through feed controller 6. After being preheated to 220 °C, the urea enters the reaction tube.

[0133] After stable operation for 2 h, take the liquid in the rapid cooler for analysis. The analysis results are shown in Table 1.

[0134] Use Agilent high performance liquid chromatography (1260 Infinity II) to analyze the components of the cyanamide products prepared in the examples and comparative examples of the present invention. Chromatographic conditions: ODS chromatographic column, column temperature 50 °C, mobile phase is water and 0.25% ammonia water, HClO 4 Control the pH value to 6.3 - 6.6, flow rate 1.000 mL / min; detection wavelength 205 nm; injection volume 10 μL. Calculate the selectivity of different components based on the calibrated peak area. The results are shown in Table 1.

[0135] Table 1 Product analysis data table

[0136]

[0137]

[0138] As can be seen from Table 1, in the preparation method of the present invention, the urea conversion rate is above 98.30%. When using ammonia + carbon dioxide as raw materials, the ammonia conversion rate is above 92.50%; when preparing monocyanamide, the selectivity of monocyanamide is above 96.50%; when preparing dicyandiamide, the selectivity of dicyandiamide is also above 97.62%; at the same time, the yield of melamine is well controlled (below 1.0%).

[0139] Obviously, the above examples are only for clear illustration and not limitations on the implementation modes. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all implementation modes here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing a cyanamide product, characterized in that: The steps include: S1. Mixing the raw material and the preheated solid catalyst to react, the time when the raw material and the preheated solid catalyst start to contact is recorded as T0, and the time when the raw material and the preheated solid catalyst reach a uniform temperature after mixing is recorded as T1, T1-T0≤3s; The raw material includes urea or a mixed gas of ammonia and carbon dioxide, the temperature of the urea is less than or equal to 150° C., and the temperature of the mixed gas is 150° C. to 450° C.; S2, performing gas-solid separation on the reaction mixture obtained in S1, and recording the time for completing the gas-solid separation as T2, T2-T1≤10s; S3, cooling the gas phase product obtained in S2 to below 110°C within F seconds, F<1, to obtain a cyanamide product, The cyanamide products include monocyanamide (NH2CN) and / or dicyandiamide (C2H4N4), The temperature of the preheated solid catalyst is 500°C-750°C.

2. The method for preparing cyanamide products according to claim 1, characterized in that: T1-T0≤1s; and / or, T2-T1≤6s; and / or, F≤0.

1.

3. The method for preparing cyanamide products according to claim 2, characterized in that: 0.01s≤T1-T0≤0.5s; and / or, 0.5s≤T2-T1≤3s; and / or, 0.001≤F≤0.

08.

4. The method for preparing cyanamide products according to claim 1, characterized in that: The temperature of the mixed gas is 150°C to 350°C; And / or, the temperature of the urea is less than or equal to 120°C.

5. The method for preparing cyanamide products according to claim 1, characterized in that: The particle size of the solid catalyst is 30 μm-200 μm.

6. The method for preparing cyanamide products according to claim 5, characterized in that: The preparation method of the solid catalyst comprises: mixing the active ingredient, the binder and the deionized water, spray drying and forming at 250°C to 450°C, and then calcining at 400°C to 650°C for 30 minutes to 6 hours to obtain the solid catalyst; The mass ratio of the active component to the binder is (5-70):(30-95); And / or, the active component includes at least one of active silica-alumina powder, ZSM-5 molecular sieve, beta molecular sieve, mordenite molecular sieve, Y molecular sieve, and MCM-22 molecular sieve; And / or, the binder includes at least one of silica sol, silica-alumina colloid, phosphate-alumina colloid, pseudo-boehmite, and kaolin.

7. The method for preparing a cyanamide product according to claim 1, characterized in that S3: spraying the gas phase product with an absorbent, or causing the gas phase product to collide with the absorbent, to achieve rapid cooling of the gas phase product; the temperature of the absorbent is 45° C.-100° C., and the pH value is 2.0-11.

5.

8. The method for preparing cyanamide products according to claim 1, characterized in that: S1 adopts a riser process or a downer process to achieve rapid heating and reaction of the raw materials; Among them, in the riser process, the raw materials and catalyst enter from the lower part of the reaction tube, and the product and catalyst come out from the upper part of the reaction tube; in the downer process, the raw materials and catalyst enter from the upper part of the reaction tube, and the product and catalyst come out from the lower part of the reaction tube.

9. The method for preparing a cyanamide product according to claim 7, characterized in that: When the pH value of the absorbent is greater than 8, more than 96% of the dicyandiamide product is obtained; and when the pH value of the absorbent is between 2.0 and 8.0, more than 96% of the monocyanamide product is obtained; And / or, the absorbent includes at least one of water, methanol, ethanol, acetone, n-butylamine, diethylamine, propylamine, phosphoric acid aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrapropylammonium hydroxide aqueous solution, sodium hydroxide aqueous solution, and potassium hydroxide aqueous solution.

10. The method for preparing a cyanamide product according to any one of claims 1 to 9, characterized in that: The preparation device used to implement the preparation method includes: a reaction tube, a catalyst storage tank, a heater, a cyclone separator, a rapid cooler, and a feeding controller; wherein the heater is used to preheat the solid catalyst from the catalyst storage tank; the reaction tube is used to mix and react the preheated solid catalyst with the raw material from the feeding controller; the cyclone separator is used to perform gas-solid separation on the reaction mixture to obtain the catalyst and gas phase product after the reaction; the rapid cooler is used to cool the gas phase product; And / or, the catalyst storage tank is also used to receive the catalyst after the reaction.

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