Carbon-based fertilizer prepared based on subcritical hydrothermal cracking of agricultural wastes and preparation method of carbon-based fertilizer

Abstract

The invention discloses a carbon-based fertilizer prepared on the basis of subcritical hydrothermal cracking of agricultural wastes and a preparation method. The method comprises the following steps: crushing the agricultural wastes; adding the crushed agricultural wastes, vinasse, phosphoric acid, sodium formate and water into a closed reaction kettle, and reacting at 220-280 DEG C and 10-25 MPa; after the reaction is finished, carrying out vacuum filtration to obtain a solid substance; adding monopotassium phosphate and humate into the solid substance, and mixing and granulating to obtain the carbon-based fertilizer. According to the preparation method disclosed by the invention, the agricultural wastes are subjected to hydrothermal cracking reaction, carbonization and activation processes are synchronously completed, the biological carbon matrix which is rich in humic acid and is of a hollow structure is generated, and in the subcritical hydrothermal cracking process, the hydrothermal cracking can be promoted by adding phosphoric acid and sodium formate, so that the porosity of the prepared biological carbon matrix can be remarkably improved; and then the slow-release fertilizer is prepared by mixing with other fertilizers, so that resource utilization of agricultural wastes is realized.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, specifically to a carbon-based fertilizer and its preparation method prepared from subcritical hydrothermal pyrolysis agricultural waste. Background Technology

[0002] Straw is a general term for the stems and leaves (ears) of mature crops. Straw typically refers to the residue left after harvesting the grains of wheat, rice, corn, potatoes, rapeseed, cotton, sugarcane, and other crops (usually coarse grains). More than half of the products of crop photosynthesis are found in straw. Straw is rich in nitrogen, phosphorus, potassium, calcium, magnesium, and organic matter, making it a versatile and renewable biological resource. Straw is also a type of roughage, characterized by its high crude fiber content (30%-40%) and the presence of lignin, among other nutrients.

[0003] Returning straw to the field is a method of improving soil fertility and increasing yields, widely valued globally. It eliminates air pollution caused by straw burning while simultaneously increasing soil fertility and yields. Returning straw to the field increases soil organic matter, improves soil structure, loosens the soil, increases porosity, reduces bulk density, and promotes microbial activity and crop root development. The effect of returning straw to the field on increasing fertility and yield is significant, generally increasing yields by 5% to 10%. However, improper methods can also lead to increased soil pathogens, aggravated crop diseases, and seedling loss (stunted growth). Therefore, adopting reasonable straw returning methods is essential to achieve good results.

[0004] Currently, straw is generally fermented to produce fermented organic fertilizer for use in returning to the field. However, unfermented straw may carry pathogens, which can affect plants, and the fermentation process takes a long time. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon-based fertilizer and its preparation method based on subcritical hydrothermal pyrolysis of agricultural waste. The preparation method of this invention involves hydrothermal pyrolysis of agricultural waste, simultaneously completing the carbonization and activation processes to generate a biochar matrix rich in humic acid and with a hollow structure. This biochar matrix is ​​then mixed with other fertilizers to produce a slow-release fertilizer, thereby realizing the resource utilization of agricultural waste.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] The first aspect of this invention provides a method for preparing carbon-based fertilizers from agricultural waste based on subcritical hydrothermal pyrolysis, the method comprising the following steps:

[0008] (a) Crushing agricultural waste;

[0009] (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid, sodium formate and water into a closed reactor and react at 220-280°C and 10-25 MPa.

[0010] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer.

[0011] Preferably, the agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw, and sorghum straw.

[0012] Preferably, in step (a), the particles are crushed to a particle size of 1-2 cm.

[0013] Preferably, in step (b), the mass ratio of agricultural waste, distiller's grains, phosphoric acid, sodium formate and water is 4:(1-2):(0.001-0.005):(0.01-0.05):(20-60).

[0014] Preferably, in step (b), the moisture content of the lees is not higher than 20%.

[0015] Preferably, in step (b), the reaction time is 30 to 60 minutes.

[0016] Preferably, in step (c), the mass ratio of the solid, potassium dihydrogen phosphate, and humate is (8-12):(2-4):1.

[0017] A second aspect of the present invention provides a carbon-based fertilizer prepared by the above-described method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis.

[0018] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0019] The preparation method of this invention involves hydrothermal pyrolysis of agricultural waste, simultaneously completing the carbonization and activation processes to generate a biochar matrix rich in humic acid and with a hollow structure. During the subcritical hydrothermal pyrolysis process, the addition of phosphoric acid and sodium formate can promote hydrothermal pyrolysis, significantly improve the porosity of the prepared biochar matrix, and enhance its nutrient loading capacity. Then, by mixing it with other fertilizers, a slow-release fertilizer is prepared, realizing the resource utilization of agricultural waste. Detailed Implementation

[0020] The embodiments of the technical solution of the present invention will be described in detail below with reference to the examples. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore only examples, and should not be used to limit the scope of protection of the present invention.

[0021] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by those skilled in the art to which this invention pertains.

[0022] This invention provides a method for preparing carbon-based fertilizers from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0023] (a) Crushing agricultural waste;

[0024] (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid, sodium formate and water into a closed reactor and react at 220-280°C and 10-25 MPa.

[0025] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer.

[0026] The preparation method of this invention involves hydrothermal pyrolysis of agricultural waste, simultaneously completing the carbonization and activation processes to generate a biochar matrix rich in humic acid and with a hollow structure. During the subcritical hydrothermal pyrolysis process, the addition of phosphoric acid and sodium formate can promote hydrothermal pyrolysis, significantly improve the porosity of the prepared biochar matrix, and enhance its nutrient loading capacity. Then, by mixing it with other fertilizers, a slow-release fertilizer is prepared, realizing the resource utilization of agricultural waste.

[0027] In one embodiment, the agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw, and sorghum straw.

[0028] In one embodiment, in step (a), the particles are crushed to a particle size of 1 to 2 cm.

[0029] In one embodiment, in step (b), the mass ratio of agricultural waste, distiller's grains, phosphoric acid, sodium formate, and water is 4:(1-2):(0.001-0.005):(0.01-0.05):(20-60).

[0030] In one embodiment, in step (b), the moisture content of the lees is not higher than 20%.

[0031] In one embodiment, the reaction time in step (b) is 30 to 60 minutes.

[0032] In one embodiment, in step (c), the mass ratio of the solid, potassium dihydrogen phosphate, and humate is (8-12):(2-4):1.

[0033] Another embodiment of the present invention provides a carbon-based fertilizer prepared by the above-described method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis.

[0034] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0035] Distillers' grains: Corn distillers' grains, purchased from Shandong Dongchen Biotechnology Co., Ltd.

[0036] Example 1

[0037] This embodiment describes a method for preparing carbon-based fertilizer from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0038] (a) The agricultural waste is crushed to a particle size of 1-2 cm, wherein the agricultural waste is rice straw;

[0039] (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid, sodium formate and water to a closed reactor and react at 220°C and 10MPa for 60 min. The mass ratio of agricultural waste, distiller's grains, phosphoric acid, sodium formate and water is 4:1:0.005:0.01:20.

[0040] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer. The mass ratio of the solid, potassium dihydrogen phosphate and humate is 8:2:1.

[0041] Example 2

[0042] This embodiment describes a method for preparing carbon-based fertilizer from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0043] (a) The agricultural waste is crushed to a particle size of 1-2 cm, wherein the agricultural waste is rice straw;

[0044] (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid, sodium formate and water to a closed reactor and react at 280°C and 25MPa for 30 min. The mass ratio of agricultural waste, distiller's grains, phosphoric acid, sodium formate and water is 4:2:0.001:0.05:60.

[0045] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer. The mass ratio of the solid, potassium dihydrogen phosphate and humate is 12:4:1.

[0046] Example 3

[0047] This embodiment describes a method for preparing carbon-based fertilizer from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0048] (a) The agricultural waste is crushed to a particle size of 1-2 cm, wherein the agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw and sorghum straw;

[0049] (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid, sodium formate and water to a closed reactor and react at 260°C and 20MPa for 45 min. The mass ratio of agricultural waste, distiller's grains, phosphoric acid, sodium formate and water is 4:1.5:0.003:0.03:40.

[0050] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer. The mass ratio of the solid, potassium dihydrogen phosphate and humate is 10:3:1.

[0051] Comparative Example 1

[0052] This comparative example illustrates a method for preparing carbon-based fertilizer from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0053] (a) The agricultural waste is crushed to a particle size of 1-2 cm, wherein the agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw and sorghum straw;

[0054] (b) Add the crushed agricultural waste, distiller's grains, sodium formate and water to a sealed reactor and react at 260°C and 20MPa for 45 min. The mass ratio of agricultural waste, distiller's grains, sodium formate and water is 4:1.5:0.03:40.

[0055] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer. The mass ratio of the solid, potassium dihydrogen phosphate and humate is 10:3:1.

[0056] Comparative Example 2

[0057] This comparative example illustrates a method for preparing carbon-based fertilizer from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0058] (a) The agricultural waste is crushed to a particle size of 1-2 cm, wherein the agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw and sorghum straw;

[0059] (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid and water to a sealed reactor and react at 260°C and 20MPa for 45 min. The mass ratio of agricultural waste, distiller's grains, phosphoric acid and water is 4:1.5:0.003:40.

[0060] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer. The mass ratio of the solid, potassium dihydrogen phosphate and humate is 10:3:1.

[0061] Comparative Example 3

[0062] This comparative example illustrates a method for preparing carbon-based fertilizer from agricultural waste using subcritical hydrothermal pyrolysis. The method includes the following steps:

[0063] (a) The agricultural waste is crushed to a particle size of 1-2 cm, wherein the agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw and sorghum straw;

[0064] (b) Add the crushed agricultural waste, phosphoric acid, sodium formate and water to a closed reactor and react at 260°C and 20MPa for 45 min. The mass ratio of agricultural waste, phosphoric acid, sodium formate and water is 5.5:0.003:0.03:40.

[0065] (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer. The mass ratio of the solid, potassium dihydrogen phosphate and humate is 10:3:1.

[0066] Experimental example

[0067] The solids in step (c) were prepared according to the methods of Example 3 and Comparative Examples 1-3, respectively, and then dried to obtain biochar matrix.

[0068] The specific surface area and iodine adsorption rate of the above biochar matrix were measured respectively, and the results are shown in Table 1:

[0069] Table 1

[0070] Group <![CDATA[Specific surface area (m 2 / g)]]> Iodine adsorption rate (mg / g) Example 3 778 639 Comparative Example 1 536 417 Comparative Example 2 581 425 Comparative Example 3 476 368

[0071] As shown in Table 1:

[0072] Compared to the comparative example, this application, by limiting the raw materials, enables the biochar matrix prepared in the examples to have a higher specific surface area and iodine adsorption rate, which can better load fertilizer and achieve a better slow-release effect.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis, characterized in that, The method for preparing carbon-based fertilizer based on subcritical hydrothermal pyrolysis of agricultural waste includes the following steps: (a) Crushing agricultural waste; (b) Add the crushed agricultural waste, distiller's grains, phosphoric acid, sodium formate and water into a closed reactor and react at 220-280°C and 10-25 MPa. (c) After the reaction is complete, vacuum filtration is performed to obtain a solid. Potassium dihydrogen phosphate and humate are then added to the solid and mixed and granulated to obtain the carbon-based fertilizer.

2. The method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis according to claim 1, characterized in that, The agricultural waste is selected from at least one of wheat straw, rice straw, corn straw, barley straw, and sorghum straw.

3. The method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis according to claim 1, characterized in that, In step (a), the particles are crushed to a particle size of 1-2 cm.

4. The method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis according to claim 1, characterized in that, In step (b), the mass ratio of agricultural waste, distiller's grains, phosphoric acid, sodium formate, and water is 4:(1-2):(0.001-0.005):(0.01-0.05):(20-60).

5. The method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis according to claim 1, characterized in that, In step (b), the moisture content of the lees is no higher than 20%.

6. The method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis according to claim 1, characterized in that, In step (b), the reaction time is 30 to 60 minutes.

7. The method for preparing carbon-based fertilizer from agricultural waste based on subcritical hydrothermal pyrolysis according to claim 1, characterized in that, In step (c), the mass ratio of the solid, potassium dihydrogen phosphate, and humate is (8-12):(2-4):

1.

8. The carbon-based fertilizer prepared by the method for preparing carbon-based fertilizer based on subcritical hydrothermal pyrolysis of agricultural waste as described in any one of claims 1 to 7.