Reaction-extrusion preparation process and fertilization method for weathered coal humic acid / urea-formaldehyde compound

Abstract

The present invention relates to the technical field of nonmetallic compounds, and in particular to a reaction-extrusion preparation process and fertilization method for a weathered coal humic acid / urea-formaldehyde compound. In an alkaline environment, paraformaldehyde is depolymerized into formaldehyde small molecules and reacts with urea in a system to generate monomethylol urea and dimethylol urea. Then, under the strong shearing action of screws of a twin-screw reaction extruder, macromolecular weathered coal humic acid in the system is cracked into relatively small-molecular weathered coal humic acid to expose a large number of active groups of carboxyl, some of which are immediately subjected to dehydration-condensation reaction with amino on urea-formaldehyde molecules generated by polycondensation in the reaction-extrusion process in the system to generate a weathered coal humic acid / urea-formaldehyde compound, and particles of the weathered coal humic acid / urea-formaldehyde compound are obtained. The prepared compound particles have a high compressive strength, so that the breakage of fertilizer particles during storage, transportation and application can be avoided, and a fertilization and sowing integrated machine can be used to perform fertilization while sowing, thereby saving labor, time and fertilizers.

Description

Weathered coal humic acid / urea-formaldehyde compound reaction extrusion preparation process and fertilization method Technical Field

[0001] The present invention relates to the technical field of non-metallic compounds, and in particular to a reaction extrusion preparation process of a weathered coal humic acid / urea-formaldehyde compound and a fertilizing method. Background Art

[0002] Weathered coal is a type of outcrop coal, including lignite, bituminous coal, and anthracite, found on the surface or buried in shallow coal seams. Weathering significantly alters its chemical and physical properties, reducing its calorific value and thus its combustion value. However, weathering increases its oxygen content and the resulting high content of regenerated humic acid, leading to its widespread use in industry, agriculture, medicine, and environmental protection.

[0003] Humic acid fertilizers are highly favored by farmers due to their high nutrient utilization rate, significant fertilizer efficiency, soil improvement, and significantly improved agricultural product quality. However, weathered coal, which contains large amounts of humic acid, must undergo a certain activation process to convert the bound humic acid and some free humic acid, which are difficult for crops to directly absorb, into water-soluble humic acid before it can be used in agriculture. This additional activation process increases the cost and environmental risks of using weathered coal humic acid (YHA), thus limiting its widespread use.

[0004] Urea-formaldehyde (UF) fertilizer is the earliest biodegradable polymer slow-release / controlled-release fertilizer to be successfully developed and commercialized. Under the action of microorganisms, urea-formaldehyde slowly degrades and gradually releases nitrogen nutrients. Compared with traditional fertilizers, urea-formaldehyde fertilizers do not increase the overall application cost, have a high nitrogen utilization rate, and require no topdressing after a single application, thus achieving fertilizer savings and increased efficiency. Furthermore, urea-formaldehyde fertilizers promote the formation of soil aggregates, improve soil permeability, and enhance crop root penetration, making them a promising slow-release / controlled-release fertilizer. However, conventional urea-formaldehyde fertilizers currently use aqueous formaldehyde solutions as raw materials, which present challenges such as transportation difficulties, poor storage, and a strong odor. Furthermore, urea-formaldehyde synthesis is carried out in the liquid phase, which not only makes the process difficult to control, often resulting in excessively rapid polymerization rates and poor workability, but also increases the price of urea-formaldehyde fertilizers. Previous studies have used solid paraformaldehyde to react with urea to produce urea-formaldehyde. However, the short reaction time between the solid phases results in a high initial nitrogen release rate for the prepared urea-formaldehyde. Furthermore, the nitrogen release rate of the low-polymerization fraction in urea-formaldehyde fertilizers is higher than the nitrogen requirement of crops in the early stages of growth, while the nitrogen release rate of the high-polymerization fraction is slower than the nitrogen requirement in the middle and late stages of crop growth. Therefore, for practical applications, the nutrient release time of urea-formaldehyde is often too long, longer than the time required for plant growth. These factors are the main reasons why urea-formaldehyde polymers are currently unpopular as slow- and controlled-release fertilizers, despite the fact that urea-formaldehyde has a higher nitrogen content than other commercial products.

[0005] Reactive extrusion has emerged as a new polymer material molding technology in recent years. It combines the polymerization and processing processes into one, allowing chemical reactions and continuous production to occur simultaneously within the processing machinery. Reactive extrusion utilizes an extruder as the reaction vessel and a plasticizing and extrusion system consisting of a screw and barrel as the continuous reactor. Pre-reacted raw materials, such as monomers, initiators, polymers, and additives, are added to the screw in batches or in succession through the same or different feed ports. During the screw's rotation, the raw materials are mixed, conveyed, plasticized, reacted, and finally extruded from the die. This process offers promising advantages, including the ability to achieve continuous large-scale production, low investment and cost, the use of minimal or no solvents harmful to humans and the environment, a wide range of product and raw material options, simplified polymer de-volatiles, granulation, and molding processes, high reaction efficiency, and uniform product performance.

[0006] Summary of the Invention

[0007] In order to improve the nitrogen nutrient utilization efficiency of urea-formaldehyde slow-release fertilizer and reduce its production cost, the present invention provides a weathered coal humic acid / urea-formaldehyde compound reaction extrusion preparation process and fertilization method.

[0008] The present invention is achieved through the following technical solution: a process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion, comprising the following steps:

[0009] (1) adding a calculated amount of urea, paraformaldehyde, and water into a reactor, adjusting the pH of the system, and reacting at a certain temperature for a certain time to obtain a hydroxymethylurea solution;

[0010] (2) adding a calculated amount of weathered coal humic acid and an alkaline activator to the hydroxymethylurea solution obtained in step (1), reacting at a certain temperature for a certain time to obtain a mixed solution;

[0011] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0012] (4) starting the screws of the twin-screw extruder of the reaction unit of the reaction extruder, and simultaneously starting the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, and reacting for a certain time at a set temperature and a set screw speed;

[0013] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder conveys the reaction product to the twin-screw extruder, and the twin-screw extruder extrude the reaction product at a set temperature and a set speed to obtain a strip product;

[0014] (6) The strip product obtained in step (5) is dried at a set temperature and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound with good particle shape.

[0015] Those skilled in the art can also prepare weathered coal humic acid / urea-formaldehyde compounds with various nitrogen contents by controlling the addition amounts of the reaction raw materials urea, paraformaldehyde, and weathered coal humic acid according to different needs.

[0016] As a further improvement of the technical solution of the present invention, in step (1), the mass ratio of urea to paraformaldehyde is 2 to 4:1, and the amount of water added is 10 to 50% of the total mass of urea and paraformaldehyde.

[0017] As a further improvement of the technical solution of the present invention, in step (1), the pH of the system is adjusted to 8-12, and the reaction is carried out at 30-80° C. for 1-3 hours.

[0018] As a further improvement of the technical solution of the present invention, in step (2), the amount of the weathered coal humic acid added is 10-50% of the total mass of urea and paraformaldehyde; the amount of the alkaline activator added is 0-10% of the mass of the weathered coal humic acid.

[0019] As a further improvement of the technical solution of the present invention, in step (2), after adding weathered coal humic acid and alkaline activator, the reaction temperature is 30-80° C. and the reaction time is 5-30 min.

[0020] As a further improvement of the technical solution of the present invention, in step (3), the pH value of the mixed solution is adjusted to 3-5.

[0021] As a further improvement of the technical solution of the present invention, in step (4), the extrusion temperature of the twin-screw reaction extruder of the reaction unit of the reaction extruder integrated machine is 50-90°C, the screw speed is 50-150rpm, and the reaction time is 10-30min.

[0022] As a further improvement of the technical solution of the present invention, in step (5), the extrusion temperature of the twin-screw extruder of the extrusion unit of the reaction extruder is 50-90° C., and the screw speed is 50-150 rpm.

[0023] The present invention further provides a method for fertilizing weathered coal humic acid / urea-formaldehyde compounds, which uses cylindrical particles of weathered coal humic acid / urea-formaldehyde compounds prepared by the above-mentioned weathered coal humic acid / urea-formaldehyde compound reaction extrusion preparation process, and uses a seed and fertilizer sowing all-in-one machine to apply them at the same time as sowing.

[0024] As a further improvement to the technical solution of the fertilization method of the present invention, the application amount of the cylindrical particles of weathered coal humic acid / urea-formaldehyde compound is 8 to 15 kg nitrogen per mu.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The present invention utilizes humic acid from weathered coal, which has a wide distribution, large reserves, and low price, to modify urea-formaldehyde. This not only enhances the strength of urea-formaldehyde fertilizer particles and improves their slow-release properties, but also significantly reduces the preparation cost of urea-formaldehyde. Furthermore, it achieves effective utilization of waste coal-based materials, turning waste into treasure.

[0027] (2) The present invention utilizes paraformaldehyde to replace the currently widely used formaldehyde aqueous solution, thereby avoiding the problems of transportation difficulties and storage risks of the liquid raw material formaldehyde aqueous solution. It also solves the problem of high initial nitrogen release rate of urea-formaldehyde prepared by the melt polycondensation reaction of solid paraformaldehyde and urea.

[0028] (3) The process of the present invention can simultaneously carry out the activation reaction of weathered coal humic acid, the condensation reaction of hydroxymethyl urea to generate urea-formaldehyde by extrusion, and the dehydration condensation reaction between the generated activated weathered coal humic acid and the generated urea-formaldehyde in a twin-screw reaction extruder, thereby avoiding the separate activation process of weathered coal humic acid and the large amount of activation waste generated by the process, thereby saving manpower and material resources and avoiding environmental pollution. The three-in-one reaction gives the process the advantages of low cost, greenness, high efficiency and stability.

[0029] (4) At present, the granulation of urea-formaldehyde fertilizers is still generally carried out by a crude crushing granulation method, which has the disadvantages of excessive dust, environmental pollution, and irregular particle shape. The present invention adopts a reaction extrusion granulation process that has the advantages of continuous large-scale production, low investment and cost, simplified polymer removal of volatiles, high reaction efficiency, and uniform product performance. Therefore, it has the advantages of simple process, no dust pollution, continuous production, and saving manpower and material resources.

[0030] (5) Compared with traditional urea-formaldehyde fertilizers, the present invention introduces weathered coal humic acid and allows its molecules to enter the main chain of urea-formaldehyde molecules, thereby reducing the production of easily soluble low-polymerization urea-formaldehyde while destroying the regular arrangement of urea-formaldehyde macromolecular chains, reducing the initial release rate of nitrogen nutrients from urea-formaldehyde fertilizers and simultaneously increasing the release rate of nitrogen nutrients in the middle and late stages. In addition, the mechanical properties of the prepared weathered coal humic acid / urea-formaldehyde compound particles are significantly improved, and their compression strength is more than 1.67 times that of urea-formaldehyde slow-release nitrogen fertilizers prepared by the same process. On the one hand, it can avoid the breakage of fertilizer particles during storage, transportation and application. On the other hand, it can be applied simultaneously with sowing using a seeding and fertilizer sowing machine, saving labor, time, fertilizer and effort. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0033] Figure 1 is the FT-IR spectra of weathered coal humic acid (YHA), the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and the urea-formaldehyde compound (UF) prepared in Comparative Example 1.

[0034] FIG2 is an amplified FT-IR spectrum of FIG1 at 3458 cm-1 for the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2 and the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2.

[0035] FIG3 is an amplified FT-IR spectrum of FIG1 at 1626 cm-1 for the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2 and the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2.

[0036] 4 is an XRD spectrum of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the urea-formaldehyde compound (UF) prepared in Comparative Example 1, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and weathered coal humic acid (YHA).

[0037] 5 is a thermogravimetric curve of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the urea-formaldehyde compound (UF) prepared in Comparative Example 1, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and weathered coal humic acid (YHA).

[0038] 6 is a differential curve of the thermogravimetric curves of FIG5 for the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the urea-formaldehyde compound (UF) prepared in Comparative Example 1, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and the weathered coal humic acid (YHA).

[0039] FIG7 is a compression strength test curve of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2 and the urea-formaldehyde compound (UF) prepared in Comparative Example 1.

[0040] FIG8 is a static water nutrient release curve of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2 and the urea-formaldehyde compound (UF) prepared in Comparative Example 1.

[0041] FIG9 shows the reaction mechanism of the reactive extrusion preparation process of weathered coal humic acid / urea-formaldehyde compound according to the present invention. DETAILED DESCRIPTION

[0042] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0043] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0044] The present invention provides a specific embodiment of a process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion, comprising the following steps:

[0045] (1) adding a calculated amount of urea, paraformaldehyde, and water into a reactor, adjusting the pH of the system, and reacting at a certain temperature for a certain time to obtain a hydroxymethylurea solution;

[0046] (2) adding a calculated amount of weathered coal humic acid and an alkaline activator to the hydroxymethylurea solution obtained in step (1), reacting at a certain temperature for a certain time to obtain a mixed solution;

[0047] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0048] (4) starting the screws of the twin-screw extruder of the reaction unit of the reaction extruder, and simultaneously starting the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, and reacting for a certain time at a set temperature and a set screw speed;

[0049] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder conveys the reaction product to the twin-screw extruder, and the twin-screw extruder extrude the reaction product at a set temperature and a set speed to obtain a strip product;

[0050] (6) The strip product obtained in step (5) is dried at a set temperature and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound with good particle shape.

[0051] The reaction extruder of the present invention includes a reaction unit and an extrusion unit. The twin-screw reaction extruder of the reaction unit and the twin-screw extruder of the extrusion unit are both well-known devices in the art, wherein the discharge die of the twin-screw reaction extruder is connected to the feed die of the twin-screw extruder; in addition, the vacuum devolatilization device is a component on the twin-screw reaction extruder, and the connection method between it and the twin-screw reaction extruder is well known in the art. The screw diameter of the twin-screw reaction extruder of the reaction extruder used in each embodiment of the present invention is 28 mm, and the aspect ratio is 34: 1; the screw diameter of the twin-screw extruder of the extrusion unit is 21 mm, and the aspect ratio is 36: 1.

[0052] In one embodiment provided by the present invention, in step (1), the mass ratio of urea to paraformaldehyde is 2 to 4:1, and the amount of water added is 10 to 50% of the total mass of the urea and paraformaldehyde. The chemical formula of the paraformaldehyde in this embodiment is (CH2O)n, where n=8 to 12. Preferably, the mass ratio of urea to paraformaldehyde is 2.4 to 3:1, and the amount of water added is 15 to 30% of the total mass of the urea and paraformaldehyde.

[0053] In another embodiment provided by the present invention, in step (1), the pH of the system is adjusted to 8-12, and the reaction is carried out at 30-80°C for 1-3 hours. Preferably, the pH of the system is adjusted to 9-11, and the reaction is carried out at 50-70°C for 1.5-2.0 hours.

[0054] In one embodiment provided by the present invention, in step (2), the amount of the weathered coal humic acid added is 10-50% of the total mass of urea and paraformaldehyde; and the amount of the alkaline activator added is 0-10% of the mass of the weathered coal humic acid. Preferably, the amount of the weathered coal humic acid added is 25-40% of the total mass of urea and paraformaldehyde; and the amount of the alkaline activator added is 5-10% of the mass of the weathered coal humic acid.

[0055] Specifically, the alkaline activator is potassium hydroxide or sodium hydroxide. In the present invention, the alkaline activator enhances the alkalinity of the originally alkaline reaction system. This, combined with the intense shearing action of the twin-screw extruder screws, breaks down the macromolecular weathered coal humic acid in the reaction system into relatively small molecular weight weathered coal humic acid, exposing a large number of active carboxyl groups.

[0056] In another embodiment provided by the present invention, in step (2), after adding the weathered coal humic acid and the alkaline activator, the reaction temperature is 30-80°C and the reaction time is 5-30 minutes. Preferably, after adding the weathered coal humic acid and the alkaline activator, the reaction temperature is 50-70°C and the reaction time is 10-20 minutes.

[0057] In one embodiment provided by the present invention, in step (3), the pH value of the mixed solution is adjusted to 3-5.

[0058] In another embodiment provided by the present invention, in step (4), the extrusion temperature of the twin-screw reaction extruder of the reaction unit of the reaction extruder is 50-90° C., the screw speed is 50-150 rpm, and the reaction time is 10-30 min. Preferably, the extrusion temperature of the twin-screw reaction extruder of the reaction unit of the reaction extruder is 60-80° C., the screw speed is 60-100 rpm, and the reaction time is 15-25 min.

[0059] In one embodiment provided by the present invention, in step (5), the extrusion temperature of the twin-screw extruder of the extrusion unit of the reaction extruder is 50-90°C, and the screw speed is 50-150 rpm. Preferably, the extrusion temperature of the twin-screw extruder of the extrusion unit of the reaction extruder is 50-70°C, and the screw speed is 60-80 rpm.

[0060] In another embodiment provided by the present invention, in step (6), the drying temperature of the strip product is 60-80°C.

[0061] The present invention also provides a method for fertilizing weathered coal humic acid / urea-formaldehyde compounds, which uses cylindrical particles of weathered coal humic acid / urea-formaldehyde compounds prepared by the above-mentioned weathered coal humic acid / urea-formaldehyde compound reaction extrusion preparation process, and adopts a seed and fertilizer sowing all-in-one machine to apply the fertilizer at the same time as sowing.

[0062] Furthermore, the application amount of the weathered coal humic acid / urea-formaldehyde compound cylindrical particles is 8 to 15 kg nitrogen per mu.

[0063] The specific embodiments of the present invention are described in detail below.

[0064] Example 1

[0065] A process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion comprises the following steps:

[0066] (1) Adding calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) into a reactor, wherein the mass ratio of urea to paraformaldehyde is 2.6:1, and the amount of water added is 15% of the total mass of urea and paraformaldehyde, adjusting the pH of the system to 8, and reacting at 70°C for 2 hours to obtain a hydroxymethylurea (MU) solution;

[0067] (2) adding a calculated amount of weathered coal humic acid (YHA) and potassium hydroxide solid (KOH) to the hydroxymethyl urea solution obtained in step (1), wherein the amount of weathered coal humic acid added is 25% of the total mass of urea and paraformaldehyde; the amount of KOH solid added is 10% of the mass of weathered coal humic acid; and reacting at 70° C. for 10 min;

[0068] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) to 5 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0069] (4) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, set the temperature to 60 ° C, set the screw speed to 60 rpm, and react for 30 minutes;

[0070] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the twin-screw extruder at 50° C. and 50 rpm to obtain a strip product;

[0071] (6) The strip product obtained in step (5) is dried at 80° C. and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) with good particle shape.

[0072] The prepared cylindrical pellets of weathered coal humic acid / urea-formaldehyde compound (HAUF) have a compressive strength of 3.52 MPa, a nitrogen content of 29.56 wt%, and an initial nitrogen release rate of 20.13%. When planting corn, fertilizer was applied using a seed and fertilizer machine at a rate of 50.7 kg / mu.

[0073] Example 2

[0074] A process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion comprises the following steps:

[0075] (1) Adding calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) into a reactor, wherein the mass ratio of urea to paraformaldehyde is 2.6:1, and the amount of water added is 15% of the total mass of urea and paraformaldehyde, adjusting the pH of the system to 8, and reacting at 70°C for 2 hours to obtain a hydroxymethylurea (MU) solution;

[0076] (2) adding calculated amounts of weathered coal humic acid (YHA) and potassium hydroxide solid (KOH) to the hydroxymethyl urea solution obtained in step (1), wherein the amount of weathered coal humic acid added is 43% of the total mass of urea and paraformaldehyde; the amount of KOH solid added is 10% of the mass of weathered coal humic acid; and reacting at 70° C. for 10 min;

[0077] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) to 5 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0078] (4) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, set the temperature to 60 ° C, set the screw speed to 60 rpm, and react for 30 minutes;

[0079] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the twin-screw extruder at 50° C. and 50 rpm to obtain a strip product;

[0080] (6) The strip product obtained in step (5) is dried at 80° C. and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) with good particle shape.

[0081] The prepared cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) have a compressive strength of 4.14 MPa, a nitrogen content of 25.86 wt%, and an initial nitrogen release rate of 15.92%. When planting corn, fertilizer was applied using a seed and fertilizer machine at a rate of 58 kg / mu.

[0082] Example 3

[0083] A process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion comprises the following steps:

[0084] (1) Add calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) to a reactor, wherein the mass ratio of urea to paraformaldehyde is 2:1 and the amount of water added is 10% of the total mass of urea and paraformaldehyde. Adjust the pH of the system to 8 and react at 30°C for 3 hours to obtain a hydroxymethylurea (MU) solution.

[0085] (2) adding a calculated amount of weathered coal humic acid (YHA) to the hydroxymethylurea solution obtained in step (1), wherein the amount added is 10% of the total mass of urea and paraformaldehyde; reacting at 30° C. for 5 minutes;

[0086] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) to 3 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0087] (4) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, set the temperature to 50 ° C, set the screw speed to 50 rpm, and react for 10 minutes;

[0088] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the twin-screw extruder at 50° C. and 50 rpm to obtain a strip product;

[0089] (6) The strip product obtained in step (5) is dried at 60° C. and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) with good particle shape.

[0090] The prepared cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) have a compressive strength of 3.68 MPa, a nitrogen content of 29.76 wt%, and an initial nitrogen release rate of 4.52%. When planting corn, fertilizer was applied using a seed and fertilizer machine at a rate of 50.4 kg / mu.

[0091] Example 4

[0092] A process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion comprises the following steps:

[0093] (1) Add calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) to a reactor, wherein the mass ratio of urea to paraformaldehyde is 4:1 and the amount of water added is 50% of the total mass of urea and paraformaldehyde. Adjust the pH of the system to 12 and react at 80°C for 1 hour to obtain a hydroxymethylurea (MU) solution.

[0094] (2) adding a calculated amount of weathered coal humic acid (YHA) to the hydroxymethylurea solution obtained in step (1), wherein the amount added is 30% of the total mass of urea and paraformaldehyde; reacting at 80° C. for 30 minutes;

[0095] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) to 3 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0096] (4) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, set the temperature to 90 ° C, the screw speed to 150 rpm, and react for 30 minutes;

[0097] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the product through the twin-screw extruder at 90° C. and 150 rpm to obtain a strip product;

[0098] (6) The strip product obtained in step (5) is dried at 80° C. and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) with good particle shape.

[0099] The prepared cylindrical pellets of weathered coal humic acid / urea-formaldehyde compound (HAUF) have a compressive strength of 3.72 MPa, a nitrogen content of 31.45 wt%, and an initial nitrogen release rate of 20.75%. When planting corn, fertilizer was applied using a seed and fertilizer machine at a rate of 47.7 kg / mu.

[0100] Example 5

[0101] A process for preparing a weathered coal humic acid / urea-formaldehyde compound by reactive extrusion comprises the following steps:

[0102] (1) Adding calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) into a reactor, wherein the mass ratio of urea to paraformaldehyde is 2.6:1, and the amount of water added is 15% of the total mass of urea and paraformaldehyde, adjusting the pH of the system to 8, and reacting at 70°C for 2 hours to obtain a hydroxymethylurea (MU) solution;

[0103] (2) adding a calculated amount of weathered coal humic acid (YHA) to the hydroxymethylurea solution obtained in step (1), wherein the amount added is 43% of the total mass of urea and paraformaldehyde; reacting at 70° C. for 10 min;

[0104] (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (2) to 5 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0105] (4) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, set the temperature to 60 ° C, set the screw speed to 60 rpm, and react for 30 minutes;

[0106] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the twin-screw extruder at 50° C. and 50 rpm to obtain a strip product;

[0107] (6) The strip product obtained in step (5) is dried at 80° C. and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) with good particle shape.

[0108] The prepared cylindrical particles of weathered coal humic acid / urea-formaldehyde compound (HAUF) have a compressive strength of 3.62 MPa, a nitrogen content of 26.84 wt%, and an initial nitrogen release rate of 19.33%. When planting corn, fertilizer was applied using a seed and fertilizer machine at a rate of 56 kg / mu.

[0109] Comparative Example 1

[0110] A reactive extrusion preparation process for urea-formaldehyde fertilizer granules comprises the following steps:

[0111] (1) Add calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) to a reactor, wherein the mass ratio of urea to paraformaldehyde is 2.6:1 and the amount of water added is 15% of the total mass of urea and paraformaldehyde. Adjust the pH of the system to 8 and react at 70°C for 2 hours to obtain a hydroxymethylurea (MU) solution.

[0112] (2) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the MU solution obtained in step (1) to 5 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0113] (3) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system. Set the temperature to 60°C, the screw speed to 60 rpm, and react for 30 minutes;

[0114] (4) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the product through the twin-screw extruder at 50° C. and 50 rpm to obtain a strip product;

[0115] (5) The strip product obtained in step (4) is dried at 80° C. and then pelletized to obtain cylindrical urea-formaldehyde compound particles (UF) with good particle shape.

[0116] The prepared urea-formaldehyde compound cylindrical particles UF have a compressive strength of 2.48 MPa, a content of nutrient element N of 36.94 wt%, and an initial nitrogen nutrient release rate of 24.60%.

[0117] Comparative Example 2

[0118] A reactive extrusion preparation process for a mixture of weathered coal humic acid and urea-formaldehyde comprises the following steps:

[0119] (1) Calculated amounts of urea (U), paraformaldehyde (Pf), and water (H2O) were added to a reactor, wherein the mass ratio of urea to paraformaldehyde was 2.6:1, and the amount of water added was 15 wt % of the total mass of urea and paraformaldehyde. The pH of the system was adjusted to 8, and the reaction was carried out at 70°C for 2 h to obtain a hydroxymethylurea (MU) solution;

[0120] (2) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, and then adjusting the pH of the mixed solution obtained in step (1) to 5 and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion integrated machine;

[0121] (3) Start the screw of the twin-screw extruder of the reaction unit of the reaction extruder, and at the same time start the vacuum devolatilization device of the twin-screw extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, set the temperature to 60 ° C, set the screw speed to 60 rpm, and react for 30 minutes;

[0122] (4) The calculated amount of weathered coal humic acid (YHA) and potassium hydroxide solid (KOH) are introduced into the twin-screw reaction extruder of the reaction unit of the reaction extruder, and mixed with the product obtained in step (3); the amount of weathered coal humic acid added is 43wt% of the total mass of urea and paraformaldehyde; the amount of KOH solid added is 10% of the mass of weathered coal humic acid; the temperature is set to 60°C, the screw speed is 60 rpm, and the reaction is carried out for 10 min;

[0123] (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder of the reaction extrusion integrated machine transports the viscous product to the twin-screw extruder, and extrudes the twin-screw extruder at 50° C. and 50 rpm to obtain a strip product;

[0124] (6) The strip product obtained in step (5) is dried at 80° C. and then pelletized to obtain cylindrical particles of a mixture of weathered coal humic acid and urea-formaldehyde with good particle shape.

[0125] The prepared cylindrical particles of the mixture of weathered coal humic acid and urea-formaldehyde had a compression strength of 3.13 MPa, a content of nutrient element N of 25.86 wt%, and an initial nitrogen nutrient release rate of 18.26%.

[0126] The performance tests and characterizations of the present invention all adopt the following standards:

[0127] 1) Grind the cylindrical particles and pass them through a 0.25 mm sieve to obtain the test sample powder. Take a small amount of dry powder KBr and press it into a pellet. Use a Nicolet IS50 infrared spectrometer to measure the infrared spectrum at room temperature with a scanning range of 500 to 4000 cm-1. Use an X-ray diffractometer (HAOYUAN DX-2700B) to perform XRD analysis on the sample with a scanning range of 5-80°. Under a nitrogen atmosphere, use a thermogravimetric analyzer (TA Q50) to measure the thermal stability of the sample. Set the temperature range to 30-800°C, increase the temperature by 10°C / min, and use a nitrogen flow rate of 40 mL / min.

[0128] 2) Compression Strength Test: The test was conducted using an MTS CMT5105 universal testing machine. The cylindrical particles were placed on the machine and compressed in the longitudinal direction at a pressure of 20,000 kgf and a compression rate of 1 mm / min.

[0129] 3) Slow-release performance test: The slow-release performance and initial release rate of nitrogen nutrients were characterized by a static water release test. Weigh 5.00g of fertilizer granules, put them into a 100-mesh nylon mesh bag and seal it, then place it in a bottle filled with 100mL of deionized water. Incubate it in a constant temperature water bath at 25°C, and take samples at 1, 3, 5, 7, 10, 14, and 28 days. When sampling, use tweezers to place the nylon mesh bag at the bottle mouth to drain the water. After no water drips, place it in a new culture bottle filled with 100ml of deionized water and continue culturing. Turn the original culture bottle upside down to ensure that the internal solution concentration is consistent. Take 20ml of the solution, use the sulfuric acid-hydrogen peroxide digestion method and the Kjeldahl nitrogen method to determine the nitrogen content and calculate the cumulative nutrient release rate. The test result on the first day is the initial release rate.

[0130] Figure 1 shows the FT-IR spectra of weathered coal humic acid (YHA), the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and the urea-formaldehyde compound prepared in Comparative Example 1 at 4000cm-1 to 500cm-1. In the figure, 3458cm-1 is the stretching vibration peak of -OH in the weathered coal structure, and 1626cm-1 and 1603cm-1 are the stretching vibration peaks of -NH2 and -NH- in urea-formaldehyde, respectively. The weathered coal humic acid / urea-formaldehyde compound prepared in Example 2 and the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2 all have the typical characteristic peaks of YHA and the urea-formaldehyde compound prepared in Comparative Example 1, proving that Example 2 and Comparative Example 2 are both composed of weathered coal humic acid and urea-formaldehyde.

[0131] Figure 2 shows a magnified image of the normalized infrared spectra of the weathered coal humic acid / urea-formaldehyde compound HAUF prepared in Example 2 and the mixture of weathered coal humic acid and urea-formaldehyde prepared in Comparative Example 2, located at 3458 cm⁻¹. As shown in Figure 2, the absorption peak intensity of the -OH group belonging to the weathered coal humic acid YHA in the compound of Example 2 is significantly weaker than that in the mixture of Comparative Example 2. This indicates that, compared to Comparative Example 2, prepared by physically mixing weathered coal humic acid and urea-formaldehyde, the hydroxyl groups of the weathered coal humic acid in the compound of Example 2 undergo a dehydration reaction with the amide groups in the urea-formaldehyde, resulting in a weakened hydroxyl group intensity. The FT-IR spectra demonstrate that weathered coal humic acid incorporates into the urea-formaldehyde backbone through the reaction of the -COOH functional group in its macromolecular chain with the -NH2 functional group on the urea-formaldehyde molecular chain generated by reactive extrusion.

[0132] Figure 3 is an enlarged view of the infrared spectra of the compound prepared in Example 2 and the mixture prepared in Comparative Example 2, normalized at the -NH2 stretching vibration peak at 1626 cm-1. As can be seen from Figure 3, the intensity of the absorption peak of -NH- at 1603 cm-1, which belongs to urea-formaldehyde, in the compound of Example 2 is significantly enhanced compared to that in Comparative Example 2. This corresponds to the weakening of the -COOH peak shown in Figure 2, indicating that the -COOH of the weathered coal humic acid reacts with the amide group in the urea-formaldehyde through a dehydration reaction. The FT-IR spectrum shows that the weathered coal humic acid molecules have entered the main chain of the urea-formaldehyde molecule.

[0133] Figure 4 is the XRD spectra of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the urea-formaldehyde compound (UF) prepared in Comparative Example 1, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and weathered coal humic acid (YHA). In the figure, the characteristic peaks of 12.3°, 24.9°, 26.5° and 38.5° are the characteristic diffraction peaks of YHA, and 19.4°, 22.2° and 24.8° are the characteristic diffraction peaks of UF. Typical characteristic peaks of YHA and UF appear in the weathered coal humic acid / urea-formaldehyde compound. In addition, it is not difficult to find that the crystallinity of the mixture prepared in Comparative Example 2 and the compound prepared in Example 2 are lower than that of UF prepared in Comparative Example 1, indicating that the introduction of YHA can reduce the crystallinity of UF. This will be beneficial to the degradation of weathered coal humic acid / urea-formaldehyde compound by microorganisms and increase the nutrient release rate.

[0134] Figure 5 shows thermogravimetric curves of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the UF slow-release nitrogen fertilizer (UF) prepared in Comparative Example 1, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and weathered coal humic acid (YHA). As shown in Figure 5, compared with Comparative Example 2, the overall thermal stability of the compound prepared in Example 2 is reduced, and the thermal weight loss rate of the material is higher. This is because the weathered coal humic acid and urea-formaldehyde in Example 2 react, and the weathered coal humic acid molecules enter the urea-formaldehyde molecular backbone, destroying the regularity of the urea-formaldehyde molecular chain and reducing the crystallinity of urea-formaldehyde, thereby causing the thermal stability of the material to decrease. This is conducive to improving the biodegradation rate of the modified UF and shortening the slow-release cycle, thereby solving the problem of the long slow-release cycle of UF, which is beneficial to plant growth, environmentally friendly, and can also further broaden the scope of application of UF.

[0135] Figure 6 shows the thermogravimetric differential curves of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2, the urea-formaldehyde compound (UF) prepared in Comparative Example 1, the weathered coal humic acid and urea-formaldehyde mixture prepared in Comparative Example 2, and weathered coal humic acid (YHA). The pyrolysis peak of low-polymerization urea-formaldehyde is between 90°C and 236°C, while the thermal decomposition temperature range of high-polymerization urea-formaldehyde is between 236°C and 450°C. As can be seen from Figure 6, the pyrolysis peak of the compound prepared in Example 2 at 214°C is significantly lower than that of the urea-formaldehyde compound in Comparative Example 1, indicating that the compound prepared in Example 2 contains fewer low-molecular-weight urea-formaldehyde polymers. This is because the low-polymerization urea-formaldehyde undergoes a dehydration reaction with weathered coal humic acid, thereby reducing the content of soluble low-polymerization urea-formaldehyde. This reduction in low-polymerization urea-formaldehyde content reduces the initial nitrogen release rate of the weathered coal humic acid / urea-formaldehyde compound, thereby addressing the nutrient loss problem caused by UF, which releases significantly more nitrogen than the plant's needs during the initial growth phase.

[0136] Figure 7 shows the compressive strength test curves of the weathered coal humic acid / urea-formaldehyde compound prepared in Example 2 and the urea-formaldehyde compound (UF) prepared in Comparative Example 1. The compressive strength of the compound prepared in Example 2 is 4.14 MPa, significantly higher than the 2.48 MPa of the urea-formaldehyde compound. This indicates that the weathered coal humic acid participates in the extrusion polycondensation reaction of hydroxymethylurea. Furthermore, because the weathered coal humic acid molecules contain rigid groups such as benzene rings, the resulting fertilizer exhibits high compressive strength.

[0137] Fig. 8 is the still water nitrogen release curve of the urea-formaldehyde compound (UF) prepared by the weathered coal humic acid / urea-formaldehyde compound prepared by Example 2 and Comparative Example 1. As shown in the figure, the compound prepared by Example 2, the nitrogen release rate on the 1st day is significantly lower than that of Comparative Example 1, showing that after weathered coal humic acid modification, the proportion of easily degradable low-polymerization degree urea-formaldehyde is reduced, and the early stage release rate of nitrogen nutrient decreases. On the 14th-42nd day, the nitrogen amount released by the compound of Example 2 is 1.98 times the nitrogen amount released by the UF of Comparative Example 1, showing that the nitrogen release rate in the middle and late stages of weathered coal humic acid / urea-formaldehyde compound is significantly improved compared with UF. It can be seen from this that after weathered coal humic acid modification, the early stage N nutrient release rate of urea-formaldehyde fertilizer reduces, and the N nutrient release rate in the middle and late stages improves, and such nutrient release rule will improve the utilization efficiency of fertilizer, is more suitable for plant growth demand.

[0138] Figure 9 shows the reaction mechanism of the reactive extrusion process for preparing weathered coal humic acid / urea-formaldehyde compounds according to the present invention. In the figure, m = 1-10, n = 1-5, and M = 1-100. First, in an alkaline environment, paraformaldehyde depolymerizes into small formaldehyde molecules and reacts with urea in the system to produce monomethylol urea and dimethylol urea. Subsequently, with the aid of an alkaline activator subsequently added to the reaction system to further create an alkaline environment, coupled with the intense shearing action of the twin-screw reactive extruder screw, the large-molecule weathered coal humic acid in the system is broken down into relatively small-molecule weathered coal humic acid, exposing a large number of active carboxyl groups. A portion of the active -COOH functional groups immediately undergo a dehydration condensation reaction with the -NH2 on the urea-formaldehyde molecules generated in situ during the reactive extrusion process, generating weathered coal humic acid / urea-formaldehyde compounds. Therefore, this process can simultaneously carry out the activation reaction of weathered coal humic acid, the condensation reaction of hydroxymethylurea to generate urea formaldehyde, and the dehydration condensation reaction between the generated activated weathered coal humic acid and the generated urea formaldehyde in a twin-screw reaction extruder, thereby avoiding the separate weathered coal humic acid activation process and the large amount of activation waste generated by the process, thereby saving manpower and material resources and avoiding environmental pollution. The three-in-one reaction gives the process the advantages of low cost, green, high efficiency and stability.

[0139] The above description is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions have been made with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments, and they should all be included in the scope of protection of the claims.

Claims

1. A weathered coal humic acid / urea-formaldehyde compound reaction extrusion preparation process, characterized in that: The steps include: (1) adding a calculated amount of urea, paraformaldehyde and water into a reactor, adjusting the pH of the system, reacting at a certain temperature for a certain time, and obtaining a hydroxymethyl urea solution; (2) adding a calculated amount of weathered coal humic acid and an alkaline activator to the hydroxymethyl urea solution obtained in step (1), reacting at a certain temperature for a certain time to obtain a mixed solution; (3) sealing the die between the reaction unit and the extrusion unit of the reaction extrusion machine, and then adjusting the pH of the mixed solution obtained in step (2) and injecting it into the twin-screw reaction extruder of the reaction unit of the reaction extrusion machine; (4) starting the screws of the twin-screw reaction extruder of the reaction unit of the reaction extruder, and simultaneously starting the vacuum devolatilization device of the twin-screw reaction extruder of the reaction unit of the reaction extruder to remove moisture from the reaction system, and reacting for a certain time at a set temperature and a set screw speed; (5) opening the die between the reaction unit and the extrusion unit of the reaction extrusion integrated machine, starting the twin-screw extruder of the extrusion unit of the reaction extrusion integrated machine, and then the twin-screw reaction extruder conveys the reaction product to the twin-screw extruder, and the twin-screw extruder extrude the reaction product at a set temperature and a set speed to obtain a strip product; (6) The strip product obtained in step (5) is dried at a set temperature and then pelletized to obtain cylindrical particles of weathered coal humic acid / urea-formaldehyde compound with good particle shape.

2. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (1), the mass ratio of urea to paraformaldehyde is 2-4:1, and the amount of water added is 10-50% of the total mass of urea and paraformaldehyde.

3. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (1), the pH of the system is adjusted to 8-12, and the reaction is carried out at 30-80° C. for 1-3 hours.

4. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (2), the amount of the weathered coal humic acid added is 10-50% of the total mass of urea and paraformaldehyde; the amount of the alkaline activator added is 0-10% of the mass of the weathered coal humic acid.

5. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (2), after adding weathered coal humic acid and alkaline activator, the reaction temperature is 30-80° C. and the reaction time is 5-30 min.

6. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (3), the pH value of the mixed solution is adjusted to 3-5.

7. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (4), the extrusion temperature of the twin-screw reaction extruder of the reaction unit of the reaction extruder integrated machine is 50 to 90° C., the screw speed is 50 to 150 rpm, and the reaction time is 10 to 30 min.

8. The process for preparing weathered coal humic acid / urea-formaldehyde compound by reactive extrusion according to claim 1, characterized in that: In step (5), the extrusion temperature of the twin-screw extruder of the extrusion unit of the reaction extruder is 50 to 90° C., and the screw speed is 50 to 150 rpm.

9. A method for fertilizing weathered coal humic acid / urea-formaldehyde compounds, characterized in that: The method uses cylindrical particles of weathered coal humic acid / urea-formaldehyde compound prepared by a weathered coal humic acid / urea-formaldehyde compound reaction extrusion preparation process as described in any one of claims 1 to 8, and uses a seed-fertilizer-seeding machine to apply the particles at the same time as sowing.

10. A method for fertilizing weathered coal humic acid / urea-formaldehyde compounds according to claim 9, characterized in that: The application amount of the weathered coal humic acid / urea-formaldehyde compound cylindrical particles is 8-15 kg nitrogen / mu.

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