Catalyst for catalyzing urea to simultaneously prepare cyanamide and dicyandiamide and application method thereof

Abstract

The invention provides a catalyst for simultaneously preparing cyanamide and dicyandiamide by catalyzing urea and an application method of the catalyst, and an amorphous silicon-aluminum catalyst is prepared by taking one or more of sodium silicate, silica sol, water glass and TEOS as a silicon source and one or more of aluminum sulfate, aluminum nitrate and aluminum chloride as an aluminum source. A fixed bed reactor is utilized, ammonia gas serves as carrier gas, the urea conversion rate reaches 90% or above, the cyanamide selectivity reaches 48% or above, and the dicyandiamide selectivity reaches 20% or above. The catalyst for catalyzing urea to prepare cyanamide and dicyandiamide is simple in synthesis method, high in urea conversion rate, high in cyanamide selectivity, simple in process and low in cost. The method is a low-cost and effective cyanamide and dicyandiamide preparation technology, and has a wide industrial application prospect.

Description

Technical Field

[0001] The invention relates to a synthesis method and application field of an amorphous silicon-aluminum catalytic material, and is a method for catalyzing urea to simultaneously prepare cyanamide and dicyandiamide under a new catalytic system. Background Art

[0002] Cyanamide is an important chemical raw material and plays an indispensable role in chemical production. It is mainly used as an organic chemical intermediate in the production of medicines, pesticides, health products and feed additives.

[0003] In medicine, cyanamide and its mono- or di-substituted products are often used as pharmaceutical intermediates to produce new drugs for the treatment of cancer, gastric ulcers, and hypertension, such as fluorouracil, guanethidine hydrochloride (eswanline), and guanidine.

[0004] In agriculture, cyanamide is often used as a fertilizer component added to nitrogen fertilizers. In the soil, cyanamide undergoes a series of reactions to generate dicyandiamide, which can inhibit the growth of nitrifying bacteria in the soil, adjust the pH value of the soil, and inhibit nitrification. Cyanamide can also be used as a pesticide intermediate and is a raw material for preparing pesticide products such as dioctyl myristate diacetate, cypermethrin, acetamiprid, and chlorpyrifos.

[0005] In the chemical industry, cyanamide is also often used as an intermediate in the chemical industry and has an irreplaceable position. It can be used to produce a series of fine chemical products such as tetramethylguanidine, phenylguanidine carbonate, n-butyl biguanide, cyanoimido dimethyl carbonate, and guanyl thiourea.

[0006] With the development of economy, the demand for cyanamide is increasing. It is estimated that by 2030, the global cyanamide market will reach RMB 1.9 billion, with a compound annual growth rate of about 4.3%. Therefore, the cyanamide industry has a good development prospect. At present, the production method of cyanamide is the lime nitrogen method. The raw material for producing lime nitrogen is calcium carbide, which is a high-energy consumption product. From mining to production, it consumes 3,500 degrees of electricity per ton. In addition, during the industrial production of cyanamide, solid waste discharge is relatively serious, with each ton of product producing 2 to 5 tons of dry waste residue, especially the pollution problems of calcium carbide residue and cyanamide residue. Therefore, low-energy consumption, green and clean production technology is urgently needed.

[0007] The reaction equation for preparing cyanamide by the urea method is 2H2NCONH2→H2NCN+CO2+NH3, in which ammonia can be recycled and reused, and carbon dioxide is not an air pollutant. Compared with the lime nitrogen method, the urea method for preparing cyanamide has a wide source of urea and a low price. It is a green and clean technology with low energy consumption, low cost, and extremely high atomic economy, and almost no three wastes are generated. Although the urea method has many advantages, this method has high requirements for catalysts, which restricts the development of cyanamide production technology. Therefore, it is increasingly important and urgent to develop a low-cost catalytic material with high urea conversion rate and high cyanamide selectivity.

[0008] CN117599837A discloses a process for preparing cyanamide by dehydrating urea. The HZSM-5 molecular sieve is modified by ion exchange method using metal elements M (M is one or more of Be, Mg, Ca, Sr, Ba) of Group IIA in the periodic table to prepare M-HSZM-5 catalyst. The reaction temperature is 550°C, the residence time is 1.5s, and the reaction is carried out under normal pressure. The urea conversion rate is 95% and the selectivity of cyanamide is 44%. The catalyst preparation process of this patent involves complex modification steps, the cost of the catalyst is high, and the energy consumption is increased. In addition, the patent does not mention the selectivity of dicyandiamide and other by-products. Summary of the invention

[0009] In view of the above problems, the object of the present invention is to provide a catalyst for catalyzing urea to simultaneously prepare cyanamide and dicyandiamide and an application method thereof, wherein the catalyst synthesis method is simple, does not involve a modification step, consumes low energy, and has low cost. Under appropriate reaction conditions, a very high urea conversion rate can be achieved, and the selectivity of cyanamide and dicyandiamide can be significantly improved.

[0010] The present invention is achieved through the following technical solutions:

[0011] The synthesis method of the catalyst for preparing cyanamide and dicyandiamide by catalyzing urea provided by the present invention is achieved by the following steps:

[0012] 1) Dissolve a certain amount of silicon source in 60°C deionized water. After fully dissolved, slowly add acid solution to the solution. Stir vigorously during the addition to ensure uniform precipitation. Continue to add acid solution until pH = 2-3 and continue stirring for 15 minutes.

[0013] 2) dissolving a certain amount of aluminum source in 60° C. deionized water, and adding the aluminum source dropwise to the slurry of step 1) after the aluminum source is fully dissolved, and slowly adding an alkali solution after the pH value is stabilized, and adjusting the slurry to an end point pH value of 9 to 11;

[0014] 3) The slurry obtained in step 2) was subjected to dynamic aging at 60° C. for 2 hours, and then filtered and washed repeatedly until neutral to obtain a white solid precipitate;

[0015] 4) The solid precipitate of step 3) is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-alumina catalyst.

[0016] Preferably, in the above-mentioned amorphous silicon-aluminum catalytic synthesis method, the silicon source used includes but is not limited to sodium silicate, silica sol, nano-silicon dioxide and TEOS.

[0017] Preferably, in the above-mentioned amorphous silicon-alumina catalytic synthesis method, the acid solution used includes but is not limited to sulfuric acid, nitric acid, and hydrochloric acid.

[0018] Preferably, in the above-mentioned amorphous silicon-alumina catalytic synthesis method, the aluminum source used includes but is not limited to aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0019] Preferably, in the above-mentioned amorphous silicon-alumina catalytic synthesis method, the alkaline solution used includes but is not limited to sodium hydroxide, potassium hydroxide, and ammonia water.

[0020] On this basis, the present invention provides a process for simultaneously preparing cyanamide and dicyandiamide by catalyzing urea with the above catalyst, comprising the following steps:

[0021] 1) The catalyst powder is tableted and granulated into catalyst particles of 20 to 40 mesh, and loaded into a fixed bed reactor, ensuring that the catalyst is filled in the middle section of the reactor;

[0022] 2) Using ammonia as carrier gas, the reactor temperature is 500-600°C, and the reaction is continued for a period of time;

[0023] 3) The reaction products were condensed, collected, and analyzed for conversion and selectivity.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The catalyst synthesized by the present invention has a good catalytic effect. In the case of not being modified, the urea conversion rate is not less than 90%, the cyanamide selectivity is not less than 48%, and the dicyandiamide selectivity is not less than 20%.

[0026] (2) The catalyst synthesis process is simple, and the cost is much lower than that of HZSM-5 molecular sieve. The temperature is maintained at 60°C during the synthesis process, with low energy consumption and high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 2 are XRD diagrams of Examples 2, 5, 7 and 8 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0029] Examples 1 to 8 are catalyst preparation examples.

[0030] Example 1

[0031] 1) Dissolve 22.73 g of sodium silicate in 60°C deionized water. After it is fully dissolved, slowly add nitric acid to the solution. Continue to add nitric acid while stirring vigorously until the pH is 3. Continue stirring for 15 minutes.

[0032] 2) Dissolve 20 g of aluminum nitrate in 60° C. deionized water, and add it dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0033] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0034] Example 2

[0035] 1) Dissolve 28.4 g of sodium silicate in 60°C deionized water. After it is fully dissolved, slowly add nitric acid to the solution. Continue to add nitric acid while stirring vigorously until the pH is 3, and continue stirring for 15 minutes;

[0036] 2) Dissolve 15 g of aluminum nitrate in 60° C. deionized water, and add it dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0037] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0038] Example 3

[0039] 1) Dissolve 31.8 g of sodium silicate in 60°C deionized water. After it is fully dissolved, slowly add nitric acid to the solution. Continue to add nitric acid until the pH is 3 while stirring vigorously. Continue stirring for 15 minutes.

[0040] 2) Dissolve 12 g of aluminum nitrate in 60° C. deionized water, and add dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0041] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0042] Example 4

[0043] 1) Disperse 9.6 g of nano-silicon dioxide in 60° C. deionized water. After the dispersion is uniform, slowly add nitric acid to the solution. Continue to add nitric acid until the pH is 3 during vigorous stirring. Continue stirring for 15 minutes.

[0044] 2) Dissolve 10 g of aluminum nitrate in 60° C. deionized water, and add dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0045] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0046] Example 5

[0047] 1) Disperse 24 g of nano-silicon dioxide in 60° C. deionized water. After the dispersion is uniform, slowly add nitric acid to the solution. Continue to add nitric acid until the pH is 3 during vigorous stirring. Continue stirring for 15 minutes.

[0048] 2) Dissolve 15 g of aluminum nitrate in 60° C. deionized water, and add it dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0049] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0050] Example 6

[0051] 1) Disperse 15.7 g of nano-silicon dioxide in 60° C. deionized water. After the dispersion is uniform, slowly add nitric acid to the solution. Continue to add nitric acid until the pH is 3 during vigorous stirring. Continue stirring for 15 minutes.

[0052] 2) Dissolve 7 g of aluminum nitrate in 60° C. deionized water, and add dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0053] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0054] Example 7

[0055] 1) Dissolve 28 g of sodium silicate in 60°C deionized water. After it is fully dissolved, slowly add nitric acid to the solution. Continue to add nitric acid while stirring vigorously until the pH is 3, and continue stirring for 15 minutes;

[0056] 2) Dissolve 15 g of aluminum sulfate in 60° C. deionized water, and add it dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add sodium hydroxide solution dropwise to adjust the slurry to an endpoint pH of 10;

[0057] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0058] Example 8

[0059] 1) Dissolve 28.4 g of sodium silicate in 60°C deionized water. After it is fully dissolved, slowly add nitric acid to the solution. Continue to add nitric acid while stirring vigorously until the pH is 3, and continue stirring for 15 minutes;

[0060] 2) Dissolve 15 g of aluminum nitrate in 60° C. deionized water, and add dropwise to the slurry in step 1) after it is fully dissolved. After the pH is stable, slowly add ammonia water to adjust the slurry to an end point pH of 9;

[0061] 3) The slurry obtained in step 2) is dynamically aged at 60° C. for 2 hours, filtered, and repeatedly washed until neutral to obtain a white solid precipitate. The solid precipitate is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-aluminum catalyst.

[0062] The prepared catalysts were characterized and analyzed. Figure 1The XRD characterization diagram of amorphous silicon aluminum synthesized under different conditions shows that all samples have a broad hump at 20° to 30°, which is a characteristic of amorphous aluminum silicate structure, confirming their amorphous geometry. In addition, no obvious diffraction peaks of crystalline alumina or silica phases were observed for all catalysts, indicating that Al species are uniformly integrated into the amorphous silica network.

[0063] Example 9

[0064] This example illustrates the reaction performance of the amorphous silicon-aluminum catalyst material prepared by the method of the present invention in the catalytic reaction of urea to prepare cyanamide and dicyandiamide.

[0065] 1) The catalysts obtained in Examples 1 to 8 above are tableted and granulated into catalyst particles of 20 to 40 mesh, and loaded into a fixed bed reactor, ensuring that the catalyst is filled in the middle section of the reactor;

[0066] 2) Ammonia was used as the carrier gas, the reactor temperature was 550°C, the residence time was 0.5s, and the reaction lasted for 30min;

[0067] 3) The product was collected and fixed to volume in a volumetric flask for detection, wherein the cyanamide content was determined according to the detection method of HGT 5537-2019 "Industrial Cyanamide", and the remaining by-products were analyzed by high performance liquid chromatography.

[0068] The specific results are shown in Table 1.

[0069] Table 1 Urea conversion and product selectivity

[0070]

[0071]

[0072] As can be seen from the data in Table 1, the amorphous silicon-aluminum catalytic material in the embodiment shows a high conversion ability in the catalytic reaction of preparing cyanamide and dicyandiamide from urea, and the conversion rate can reach 87.52% to 93.15%, the selectivity of cyanamide is between 39.5% and 51.89%, the selectivity of dicyandiamide is between 15.02% and 24.49%, the selectivity of melamine is between 0.46% and 0.69%, and the selectivity of water and carbon dioxide is between 26.77% and 42.04%. Under suitable conditions, the catalyst of the present invention can make the sum of the selectivity of cyanamide and dicyandiamide reach 71.85%, and has a high economic value.

[0073] The above embodiments and descriptions are only for illustrating the principles and best embodiments of the present invention. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, all of which fall within the scope of the present invention to be protected.

Claims

1. A method for synthesizing a catalyst for simultaneously preparing cyanamide and dicyandiamide from urea, comprising the following steps: 1) Dissolve a certain amount of silicon source in 60°C deionized water. After fully dissolved, slowly add the acid solution to the solution. Stir vigorously during the addition to ensure uniform precipitation. Continue to add the acid solution until the pH is 2-3 and continue stirring for 15 minutes. 2) dissolving a certain amount of aluminum source in 60° C. deionized water, and adding the aluminum source dropwise to the slurry of step 1) after the aluminum source is fully dissolved, and slowly adding an alkali solution after the pH value is stabilized, and adjusting the slurry to an end point pH value of 9 to 11; 3) The slurry obtained in step 2) was subjected to dynamic aging at 60° C. for 2 hours, and then filtered and washed repeatedly until neutral to obtain a white solid precipitate; 4) The solid precipitate of step 3) is placed in an oven and dried at 100° C. for 12 hours. The dried product is calcined at 550° C. for 5 hours to obtain an amorphous silicon-alumina catalyst.

2. The method according to claim 1, wherein in step 1), the silicon source includes but is not limited to sodium silicate, silica sol, water glass and TEOS.

3. The preparation method according to claim 1, characterized in that, in step 1), the acid solution includes but is not limited to sulfuric acid, nitric acid, and hydrochloric acid.

4. The preparation method according to claim 1, characterized in that, in step 2), the aluminum source includes but is not limited to aluminum sulfate, aluminum nitrate, and aluminum chloride.

5. The method according to claim 1, wherein in step 2), the alkali solution includes but is not limited to sodium hydroxide, potassium hydroxide, and aqueous ammonia.

6. The method of preparing cyanamide and dicyandiamide by catalyzing urea with the catalyst according to claim 1 comprises the following steps: 1) The catalyst powder is tableted and granulated into catalyst particles of 20 to 40 mesh, and loaded into the reactor, ensuring that the catalyst is filled in the middle section of the reactor; 2) Using ammonia as carrier gas, the reactor temperature is 500-600°C, and the reaction is continued for a period of time; 3) Condensing the reaction products, collecting them, and analyzing the product composition.

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