Integrated preparation process and application method for urea-formaldehyde-based multi-nutrient biodegradable polymeric slow / controlled-release liquid fertilizer and granular fertilizer

Abstract

The present invention relates to the technical field of slow / controlled-release chemical fertilizers, in particular to an integrated preparation process and application method for a urea-formaldehyde-based multi-nutrient biodegradable polymeric slow / controlled-release liquid fertilizer and granular fertilizer. The preparation method comprises the following steps: first, preparing a hydroxymethyl urea solution, then adding a portion of the obtained hydroxymethyl urea solution into a reactor for preparing a liquid fertilizer, and finally obtaining a polymer slow / controlled-release liquid fertilizer; feeding the remaining portion of the obtained hydroxymethyl urea solution into an integrated reaction-extrusion machine, generating a urea-formaldehyde polymer by means of polycondensation reactive extrusion in a double-screw reactive extruder of a reaction unit of the integrated reaction-extrusion machine, and finally obtaining a polymeric slow / controlled-release granular fertilizer. The present invention allows for the simultaneous production of a urea-formaldehyde-based multi-nutrient biodegradable polymeric slow / controlled-release liquid fertilizer in two different forms, namely, a liquid form and a solid, granular form, using a single set of equipment, and the process is simple and environmental-friendly.

Description

Integrated preparation process and application of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410483390.6, filed on April 22, 2024, entitled "Integrated Preparation Process and Application of Urea-Formaldehyde-Based Multinutrient Biodegradable Polymer Slow / Controlled Release Liquid Fertilizer and Solid Granular Fertilizer", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention belongs to the field of slow / controlled release fertilizer technology, specifically relating to an integrated preparation process and application method of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer. Background Technology

[0004] To address the low nutrient utilization rate of traditional fertilizers, slow / controlled release fertilizers have become a hot topic in fertilizer research and application. Among them, urea-formaldehyde slow-release nitrogen fertilizers were the first to be successfully developed and commercialized, and are currently the most promising slow / controlled release fertilizer varieties, which have profound significance for promoting the upgrading of the nitrogen fertilizer industry and alleviating energy and environmental pressures.

[0005] The two most common methods for preparing urea-formaldehyde fertilizer are the dilute solution method and the concentrated solution method. The dilute solution method involves reacting urea and formaldehyde in a dilute solution to produce a urea-formaldehyde suspension. After solid-liquid separation, the suspension is dried and pulverized to produce the final product, while the mother liquor is recycled. This method produces high-quality products, but the process is complex, costly, and difficult to scale up for mass production. The concentrated solution method involves reacting urea and formaldehyde in a concentrated solution. The intermediate product is not separated into solid and liquid components but is directly solidified into the final product by adding a catalyst (curing agent). This method is simple and has lower production costs, but the resulting high-viscosity urea-formaldehyde fertilizer is difficult to automatically discharge from the reaction apparatus, thus limiting production to small batches or even laboratory settings. The difficulty in automatically discharging the high-viscosity urea-formaldehyde from the reaction apparatus is one of the main reasons why the polymerization reaction cannot be scaled up industrially and continuously. Therefore, how to automatically discharge the high-viscosity urea-formaldehyde after the polymerization reaction is a key technology for the continuous production of urea-formaldehyde fertilizer.

[0006] Patents ZL 2023 1 1054388.9 and ZL 2023 1 0237417.9 have disclosed the use of reactive extrusion technology to produce urea-formaldehyde solid fertilizer granules, effectively solving the problem of continuous production of high-viscosity urea-formaldehyde. However, with the development of fertigation technology, liquid fertilizers are gaining increasingly widespread application due to their advantages such as rapid absorption, flexible formulation, environmental friendliness, convenient application, and significant effects. To adapt to this trend, some researchers have developed urea-formaldehyde liquid fertilizers. Currently, urea-formaldehyde liquid fertilizers are mainly divided into two categories: one is clear liquid urea-formaldehyde liquid fertilizer, which is clear and transparent, mainly containing soluble triazine ketone compounds, hydroxymethyl urea, and fast-acting nitrogen fertilizers. However, clear liquid urea-formaldehyde liquid fertilizer has limited nitrogen slow-release effect and poor storage stability, requires high environmental temperature, and is prone to precipitation and deterioration. The other category is suspended urea-formaldehyde liquid fertilizer, which is obtained by controlling the reaction of urea and formaldehyde to generate urea-formaldehyde polymers with relatively low molecular weight and adding a suspending agent to the system. The system is suspended and has high viscosity. However, existing suspended urea-formaldehyde liquid fertilizers are all obtained by repeatedly adjusting the pH of the urea-formaldehyde reaction system to control the degree of polymerization of urea-formaldehyde, which is a complicated preparation process and makes it difficult to control product quality.

[0007] Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention provides an integrated preparation process and application method for urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer.

[0009] This invention is achieved through the following technical solution: an integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer, comprising the following steps:

[0010] (1) Add a certain amount of urea, formaldehyde, catalyst and water to reactor A, and react at 50-90℃ for 0.5-3h to obtain hydroxymethylurea solution; the molar ratio of urea to formaldehyde is 1.2-5:1; the amount of catalyst added is 0-5% of the total mass of urea and formaldehyde and is not 0; the water content of the raw materials in reactor A is 15-35% of the total mass of urea and formaldehyde.

[0011] (2) Add any part of the hydroxymethylurea solution obtained in step (1) to reactor B containing an acidic suspension prepared by acidic substances, water and suspending agent, and react at temperature T1 for time t1 to obtain a urea-formaldehyde viscous liquid. Then add it to a mixed liquid prepared by alkaline substances, a fertilizer system containing at least one nutrient element other than nitrogen and a nutrient enhancer. After mixing evenly, obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer.

[0012] Meanwhile, the remaining portion of the hydroxymethyl urea solution obtained in step (1) is mixed with a fertilizer system containing at least one nutrient element other than nitrogen and fed into the twin-screw reactive extruder of the reactive extrusion unit. The reaction is carried out at a temperature of T2 and a screw speed of R1 for a reaction extrusion time of t2. During this process, hydroxymethyl urea generates urea-formaldehyde polymer through a condensation reaction. Then, the twin-screw reactive extruder is used to transport the reaction product to the twin-screw extruder of the reactive extrusion unit. The product is extruded at a temperature of T3 and a screw speed of R2 to obtain strips. After drying at a temperature of T4, the product is granulated to obtain urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer.

[0013] As a further improvement to the technical solution of the present invention, in step (1), the formaldehyde is at least one of formaldehyde aqueous solution, solid paraformaldehyde, and gaseous formaldehyde; the catalyst is one or a mixture of two of potassium carbonate and potassium hydroxide.

[0014] As a further improvement to the technical solution of the present invention, in step (2), any part of the hydroxymethylurea solution is added to the acidic suspension by dripping, mist spraying or pouring; the acidic substance is an inorganic acid or an organic acid, selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid and tartaric acid; the amount of the acidic substance added is 0 to 80 wt% of the amount of water added in step (2) and is not 0; the suspending agent is an inorganic suspending agent or an organic suspending agent, selected from at least one of attapulgite, bentonite, kaolin, lignin, humic acid, alginic acid, polyvinyl alcohol, colloidal protein, xanthan gum, cellulose and starch; the amount of the suspending agent added is 0 to 5 wt% of the amount of water added in step (2) and is not 0.

[0015] As a further improvement to the technical solution of the present invention, in step (2), the temperature T1 = room temperature ~ 90℃ and the reaction time t1 = 0.1 ~ 2h.

[0016] As a further improvement to the technical solution of the present invention, in step (2), the alkaline substance is an inorganic base, a strong base weak acid salt or an organic base, selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, potassium phosphate and organic amine compounds; the amount of alkaline substance added depends on the pH value required by different soils or liquid fertilizers.

[0017] As a further improvement to the technical solution of the present invention, in step (2), the temperature T2 = 50-130℃, the screw speed R1 = 5-150rpm, the reaction extrusion time t2 = 1-30min, the temperature T3 = 50-130℃, the screw speed R2 = 5-150rpm, and the temperature T4 = 60-150℃.

[0018] As a further improvement to the technical solution of the present invention, in step (2), the fertilizer system containing at least one nutrient element other than nitrogen is selected from at least one of phosphate, potassium salt, and micronutrient fertilizer; the phosphate is selected from at least one of hydroxyapatite, ammonium dihydrogen phosphate, superphosphate, and potassium dihydrogen phosphate; the potassium salt is selected from at least one of potassium sulfate, potassium chloride, potassium nitrate, and potassium carbonate; the micronutrient fertilizer is selected from at least one of calcium sulfate, magnesium sulfate, ferrous sulfate, manganese sulfate, zinc sulfate, copper sulfate, boric acid, sodium silicate, and potassium silicate; and the nutrient synergist is selected from at least one of humic acid, amino acids, seaweed extract, gibberellin, and auxin.

[0019] As a further improvement to the technical solution of the present invention, in step (2), before the hydroxymethylurea solution obtained in step (1) is fed into the twin-screw reactive extruder of the reaction unit of the reaction extruder, the die between the reaction unit and the extrusion unit of the reaction extruder is sealed; after the hydroxymethylurea solution obtained in step (1) is fed into the twin-screw reactive extruder, the screw of the twin-screw reactive extruder is turned on, and its vacuum devouring device is started at the same time to remove the water in the reaction system; the die between the reaction unit and the extrusion unit of the reaction extruder is opened, and the twin-screw extruder of the extrusion unit of the reaction extruder is started, then the twin-screw reactive extruder will transport the reaction product into the twin-screw extruder.

[0020] This invention also provides a method for applying the urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer prepared above, including foliar spraying, seed soaking, root dipping, injection, drenching, watering, sprinkler irrigation, or drip irrigation; the application rate is 8-15 kg nitrogen / acre.

[0021] The present invention further provides a method for applying the urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer prepared above, using a seed-fertilizer integrated machine, applying solid granular fertilizer at the same time as sowing or applying solid granular fertilizer and spraying liquid fertilizer at the same time as sowing; the application rate is 8-15 kg nitrogen / mu.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer produced by the process of this invention has good fluidity and does not clump when stored for a long time; it has good dispersibility and can be mixed evenly with irrigation water in any proportion; it has good stability and has a low sedimentation rate after being mixed with irrigation water for a long time, and will not clog the irrigation system during use.

[0024] (2) Currently, the granulation of urea-formaldehyde granular fertilizer is still mainly carried out by extensive crushing and granulation methods, which have drawbacks such as large amounts of dust, environmental pollution, and irregular particle shape. The urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer produced by the process of this invention has a regular particle shape, no dust pollution in the production process, can be produced continuously, and saves manpower and material resources.

[0025] (3) The urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer produced by the process of this invention can flexibly adjust the content of macro, meso and micronutrients in the fertilizer according to the growth needs of crops, so as to meet the needs of crops for macro, meso and micronutrients throughout the entire growth cycle.

[0026] (4) The present invention realizes the production of urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer in one set of equipment. The process is simple and environmentally friendly, and can easily meet the needs of different regions for different fertilizer forms. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 shows the FTIR spectra of the urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer prepared in Example 2 at 500–4000 cm⁻¹.

[0030] Figure 2 shows the XRD patterns of the urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer prepared in Example 2.

[0031] Figure 3 shows the thermogravimetric (a) and thermogravimetric differential (b) plots of the urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer prepared in Example 2.

[0032] Figure 4 shows SEM images of the urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer prepared in Example 2.

[0033] Figure 5 shows the static water release curves of the urea-formaldehyde-based multinutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer prepared in Example 2.

[0034] The performance testing and characterization of this invention are performed using the following standards:

[0035] 1) The urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release liquid fertilizer was freeze-dried, ground, and pulverized, then passed through a 0.25mm sieve to obtain the liquid fertilizer sample powder to be tested. The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release solid granular fertilizer was directly ground and pulverized, then passed through a 0.25mm sieve to obtain the solid fertilizer sample powder to be tested. After pressing a small amount of dried KBr sample powder into a pellet, the infrared spectrum was measured at room temperature using an infrared spectrometer (Nicolet IS50) with a scanning range of 500–4000 cm⁻¹. X-ray diffractometer (HAOYUAN DX-2700B) was used to analyze the powder sample using XRD with a scanning range of 5–80°. The thermal stability of the powder sample was measured using a thermogravimetric analyzer (TAQ50) under a nitrogen atmosphere, with a temperature range of 30–800 °C, a heating rate of 10 °C / min, and a nitrogen flow rate of 40 mL / min. The surface morphology of the fertilizer was observed using a scanning electron microscope (Hitachi SU8010). A liquid fertilizer suspension was diluted 100 times and dropped onto a silicon wafer for testing and observation using a scanning electron microscope. The prepared solid granular fertilizer was also directly observed using a scanning electron microscope.

[0036] 2) Slow-release performance test: The nitrogen nutrient release performance and initial release rate were characterized by a static water release test. 5 mL of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer was added directly to a bottle containing 100 mL of deionized water, inverted three times, and incubated in a 25℃ constant temperature water bath. Samples were taken at 1, 3, 5, 7, 10, 14, and 28 days. During sampling, the supernatant was aspirated with a pipette and filtered through filter paper. 20 mL of the solution was transferred and digested using the sulfuric acid-hydrogen peroxide method. The nitrogen content was determined using the Kjeldahl method, and the cumulative nutrient release rate was calculated. The result on the first day was the initial release rate. 5.00 g of the prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release solid granular fertilizer was placed in a 100-mesh nylon mesh bag, sealed, and then placed in a bottle containing 100 mL of deionized water. The bag was incubated in a 25°C constant temperature water bath, and samples were taken on days 1, 3, 5, 7, 10, 14, and 28. During sampling, the nylon mesh bag was placed at the bottle mouth with tweezers to drain excess water until no water dripped. The bag was then placed in a new culture bottle containing 100 mL of deionized water for continued incubation. The original culture bottle was inverted to ensure a consistent solution concentration. Take 20 mL of solution, digest the solution using the sulfuric acid-hydrogen peroxide method, and determine the nitrogen content using the Kjeldahl method. Calculate the cumulative nutrient release rate, and the test result on the first day is the initial release rate. Detailed Implementation

[0037] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0039] This invention provides a specific embodiment of a process for the integrated preparation of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer, including the following steps:

[0040] (1) Add a certain amount of urea, formaldehyde, catalyst and water to reactor A, and react at 50-90℃ for 0.5-3h to obtain hydroxymethylurea solution; the molar ratio of urea to formaldehyde is 1.2-5:1; the amount of catalyst added is 0-5% of the total mass of urea and formaldehyde and is not 0; the water content of the raw materials in reactor A is 15-35% of the total mass of urea and formaldehyde.

[0041] (2) Add any part of the hydroxymethylurea solution obtained in step (1) to reactor B containing an acidic suspension prepared by acidic substances, water and suspending agent, and react at temperature T1 for time t1 to obtain a urea-formaldehyde viscous liquid. Then add it to a mixed liquid prepared by alkaline substances, a fertilizer system containing at least one nutrient element other than nitrogen and a nutrient enhancer. After mixing evenly, obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer.

[0042] Meanwhile, the remaining portion of the hydroxymethyl urea solution obtained in step (1) is mixed with a fertilizer system containing at least one nutrient element other than nitrogen and fed into the twin-screw reactive extruder of the reactive extrusion unit. The reaction is carried out at a temperature of T2 and a screw speed of R1 for a reaction extrusion time of t2. During this process, hydroxymethyl urea generates urea-formaldehyde polymer through a condensation reaction. Then, the twin-screw reactive extruder is used to transport the reaction product to the twin-screw extruder of the reactive extrusion unit. The product is extruded at a temperature of T3 and a screw speed of R2 to obtain strips. After drying at a temperature of T4, the product is granulated to obtain urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer.

[0043] In one embodiment of the present invention, in step (1), the formaldehyde is at least one of formaldehyde aqueous solution, solid paraformaldehyde, and gaseous formaldehyde; the catalyst is one or a mixture of two of potassium carbonate and potassium hydroxide.

[0044] In another embodiment of the present invention, in step (2), any portion of the hydroxymethylurea solution is added to the acidic suspension by dripping, mist spraying, or pouring; the acidic substance is an inorganic acid or an organic acid; the amount of the acidic substance added is 0-80 wt% of the amount of water added in step (2) and is not 0; the suspending agent is an inorganic suspending agent or an organic suspending agent; the amount of the suspending agent added is 0-5 wt% of the amount of water added in step (2) and is not 0. The acidic substance is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, and tartaric acid. The suspending agent is selected from at least one of attapulgite, bentonite, kaolin, lignin, humic acid, alginic acid, polyvinyl alcohol, colloidal protein, xanthan gum, cellulose, and starch.

[0045] In one embodiment of the present invention, in step (2), the temperature T1 = room temperature ~ 90°C and the reaction time t1 = 0.1 ~ 2h.

[0046] In another embodiment of the present invention, in step (2), the alkaline substance is an inorganic base, a strong base-weak acid salt, or an organic base, selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, potassium phosphate, and organic amine compounds; the amount of alkaline substance added depends on the pH value required by different soils or liquid fertilizers.

[0047] In one embodiment of the present invention, in step (2), the temperature T2 = 50-130℃, the screw speed R1 = 5-150 rpm, the reaction extrusion time t2 = 1-30 min, the temperature T3 = 50-130℃, the screw speed R2 = 5-150 rpm, and the temperature T4 = 60-150℃.

[0048] In another embodiment of the present invention, in step (2), the fertilizer system containing at least one nutrient element other than nitrogen is selected from at least one of phosphate, potassium salt, and micronutrient fertilizer; the phosphate is selected from at least one of hydroxyapatite, ammonium dihydrogen phosphate, superphosphate, and potassium dihydrogen phosphate; the potassium salt is selected from at least one of potassium sulfate, potassium chloride, potassium nitrate, and potassium carbonate; the micronutrient fertilizer is selected from at least one of calcium sulfate, magnesium sulfate, ferrous sulfate, manganese sulfate, zinc sulfate, copper sulfate, boric acid, sodium silicate, and potassium silicate; and the nutrient enhancer is selected from at least one of humic acid, amino acids, seaweed extract, gibberellin, and auxin.

[0049] In one embodiment of the present invention, in step (2), before the hydroxymethylurea solution obtained in step (1) is fed into the twin-screw reactive extruder of the reaction unit of the reaction extruder, the die between the reaction unit and the extrusion unit of the reaction extruder is sealed; after the hydroxymethylurea solution obtained in step (1) is fed into the twin-screw reactive extruder, the screw of the twin-screw reactive extruder is turned on, and its vacuum devouring device is started to remove water from the reaction system; the die between the reaction unit and the extrusion unit of the reaction extruder is opened, and the twin-screw extruder of the extrusion unit of the reaction extruder is started, then the twin-screw reactive extruder will transport the reaction product into the twin-screw extruder.

[0050] The present invention further provides an application method for the urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer prepared above, including foliar spraying, seed soaking, root dipping, injection application, drenching, watering, sprinkler irrigation or drip irrigation; the application rate is 8-15 kg nitrogen / acre.

[0051] The present invention further provides a method for applying the urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer prepared above, using a seed-fertilizer integrated planting machine, applying solid granular fertilizer at the same time as sowing or applying solid granular fertilizer and spraying liquid fertilizer at the same time as sowing; the application rate is 8-15 kg nitrogen / mu.

[0052] The specific embodiments of the present invention will be described in detail below.

[0053] Example 1

[0054] A process for the integrated preparation of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer includes the following steps:

[0055] (1) A certain amount of urea, a 37wt% formaldehyde aqueous solution, potassium hydroxide catalyst, and water were added to reactor A. The molar ratio of urea to formaldehyde in the formaldehyde aqueous solution was 1.5:1. The amount of potassium hydroxide catalyst added was 0.5% of the total mass of urea and formaldehyde. The reaction was carried out at 80℃ for 2 hours to obtain a hydroxymethylurea solution. The water content of the whole system was 35% of the total mass of urea and formaldehyde.

[0056] (2) Pour half of the hydroxymethylurea solution obtained in step (1) into reactor B containing an acidic suspension prepared by sulfuric acid, water and attapulgite as a suspending agent, wherein the sulfuric acid solute accounts for 20% of the mass of water added and the amount of attapulgite added is 1% of the mass of water; the temperature T1 = room temperature and the reaction time t1 = 0.5h, and a urea-formaldehyde viscous liquid is obtained. Then, it is added to a mixed liquid prepared by sodium hydroxide, ammonium dihydrogen phosphate and nutrient enhancer humic acid, wherein the molar ratio of sodium hydroxide to sulfuric acid added in the acidic suspension is 2:1, the mass ratio of ammonium dihydrogen phosphate to urea in step (1) is 1:2, and the mass ratio of humic acid to urea in step (1) is 0.1:1. Mix thoroughly and evenly to obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer;

[0057] The remaining half of the hydroxymethylurea solution obtained in step (1) and the mixture of ammonium dihydrogen phosphate with a mass ratio of 1:2 (urea in step (1)) were fed into the twin-screw reactive extruder of the reaction unit of the integrated reactive extrusion machine, which was sealed at the die between the reaction unit and the extrusion unit. The screw of the twin-screw reactive extruder was turned on, and its vacuum devouring device was started at the same time to remove the moisture in the reaction system. The reaction extrusion time was t2 = 30 min at a temperature of T2 = 80℃ and a screw speed of R1 = 50 rpm. During this process, hydroxymethylurea generated urea-formaldehyde polymer through a condensation reaction. Then the die between the reaction unit and the extrusion unit of the integrated reactive extrusion machine was opened, and the twin-screw extruder of the extrusion unit of the integrated reactive extrusion machine was started, so that the twin-screw reactive extruder could transport the reaction product into the twin-screw extruder. The product was extruded at a temperature of T3 = 60℃ and a screw speed of R2 = 50 rpm to obtain strips. After drying at a temperature of T4 = 80℃, the product was granulated to obtain urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer.

[0058] The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release liquid fertilizer has a nitrogen content of 18.8 g / L and a P2O5 content of 11.5 g / L, with an initial nitrogen nutrient release rate of 26.3%. When planting corn, the liquid fertilizer sprayer is used to apply fertilizer at a rate of 80 L / mu.

[0059] The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer has a nitrogen content of 30.2 wt%, a P2O5 content of 18.5 wt%, and an initial nitrogen nutrient release rate of 22.8%. When planting corn, apply fertilizer at a rate of 50 kg / mu using a seed-fertilizer co-planting machine.

[0060] Example 2

[0061] A process for the integrated preparation of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer includes the following steps:

[0062] (1) A certain amount of urea, solid paraformaldehyde, potassium hydroxide catalyst and water are added to reactor A. The molar ratio of formaldehyde structural units contained in urea to paraformaldehyde is 1.5:1. The amount of potassium hydroxide catalyst added is 0.1% of the total mass of urea and paraformaldehyde. The reaction is carried out at 70°C for 2 hours to obtain hydroxymethylurea solution. The water content of the whole system is 30% of the total mass of urea and paraformaldehyde.

[0063] (2) Pour half of the hydroxymethylurea solution obtained in step (1) into reactor B containing an acidic suspension prepared by sulfuric acid, water and suspending agent xanthan gum, wherein the sulfuric acid solute accounts for 20% of the mass of water added and the amount of xanthan gum added is 0.3% of the mass of water; the reaction time is t1 = 0.3h at temperature T1 = 60℃ to obtain a urea-formaldehyde viscous liquid, and then add it to a mixed liquid prepared by potassium hydroxide, ammonium dihydrogen phosphate, potassium sulfate and nutrient synergist amino acids, wherein the molar ratio of potassium hydroxide to sulfuric acid added in the acidic suspension is 3:1, the mass ratio of ammonium dihydrogen phosphate to urea in step (1) is 1:5, the mass ratio of potassium sulfate to ammonium dihydrogen phosphate is 1:3, and the mass ratio of amino acids to urea in step (1) is 0.5:1. Mix thoroughly to obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer;

[0064] (2) The remaining half of the hydroxymethylurea solution obtained in step (1) is mixed with ammonium dihydrogen phosphate (mass ratio of urea in step (1) to 1:5) and potassium sulfate (mass ratio of ammonium dihydrogen phosphate to 1:3) and fed into the twin-screw reactive extruder of the reaction unit of the integrated reactive extrusion machine with a sealed die between the reaction unit and the extrusion unit. The screw of the twin-screw reactive extruder is turned on, and its vacuum devouring device is started at the same time to remove the water in the reaction system. During the reaction extrusion at a temperature of T2 = 100℃ and a screw speed of R1 = 60 rpm... During the 30-minute interval t2, hydroxymethyl urea undergoes a condensation reaction to generate urea-formaldehyde polymer. Then, the die between the reaction unit and the extrusion unit of the integrated reactive extrusion machine is opened, and the twin-screw extruder of the integrated reactive extrusion machine is started. The twin-screw reactive extruder transports the reaction product into the twin-screw extruder, which is then extruded at a temperature T3 = 50℃ and a screw speed R2 = 60 rpm to obtain strips. After drying at a temperature T4 = 100℃, the strips are granulated to obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer.

[0065] The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release liquid fertilizer has a nitrogen content of 18.05 g / L, a P2O5 content of 10.9 g / L, and a K2O content of 12.9 g / L; the initial nitrogen nutrient release rate is 27.05%. When planting corn, the liquid fertilizer sprayer is used to apply fertilizer at a rate of 85 L / mu.

[0066] The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer has a nitrogen content of 35.22 wt%, a P2O5 content of 12.58 wt%, and a K2O content of 8.45 g / L; the initial nitrogen nutrient release rate is 23.65%. When planting corn, apply fertilizer at a rate of 42.5 kg / mu using a seed-fertilizer integrated planter.

[0067] In Figure 1, both the liquid and solid fertilizers prepared in this embodiment exhibit a strong -NH- stretching vibration absorption peak at 3327 cm⁻¹, which belongs to the characteristic -NHCONH-CH₂- segment of urea-formaldehyde, indicating the presence of urea-formaldehyde molecular chains in both liquid and solid fertilizers. Furthermore, both liquid and solid fertilizers show characteristic absorption peaks at 1132 cm⁻¹, belonging to the asymmetric stretching vibration of the -NH-CH₂-NH-methylene bridging bond, and a -CH₂-O-CH₂-methylene ether bond stretching vibration absorption peak at 1023 cm⁻¹. Comparison reveals that the intensity ratio of the characteristic absorption peaks in the liquid fertilizer (A₁₀₂₃ / A₁₁₃₂) is significantly greater than that in the solid fertilizer, indicating that under strong acid catalysis, the hydroxymethylurea in the liquid fertilizer forms more methylene ether bonds through a condensation reaction, i.e., more cross-linked structures, while the solid fertilizer forms more linear structures. The FTIR spectra confirm that the products possess the aforementioned structures.

[0068] In Figure 2, the liquid fertilizer prepared in this embodiment showed a distinct urea characteristic diffraction peak at 22.01°, but this peak was not significant in the spectrum of the solid fertilizer, indicating that the residual amount of raw material urea in the solid fertilizer was significantly reduced. Furthermore, both the liquid and solid fertilizers showed characteristic diffraction peaks of urea-formaldehyde at 22.64° and 24.95°, and the crystallinity of the liquid fertilizer (XC = 32.45%) was lower than that of the solid fertilizer (XC = 48.37%), indicating that the increased cross-linking structure in the liquid fertilizer inhibited the regular arrangement of the urea-formaldehyde molecular chains. The XRD pattern confirms that the product possesses the aforementioned structure.

[0069] In Figure 3, the overall thermal stability of the liquid fertilizer prepared in this embodiment is lower than that of the solid fertilizer. This is because the liquid fertilizer contains more unreacted small-molecule urea or urea-formaldehyde oligomers. This is also evident from the thermogravimetric differential plot, where the thermogravimetric peak of the liquid fertilizer at 100–250°C is significantly higher than that of the solid fertilizer, indicating that the liquid fertilizer contains more urea or urea-formaldehyde oligomers. Conversely, at 250–350°C, the thermogravimetric peak of the liquid fertilizer is significantly lower than that of the solid fertilizer, indicating that the content of high-polymerization-degree urea-formaldehyde in the liquid fertilizer is lower than that in the solid fertilizer. This is because the solid fertilizer underwent a high-temperature curing process during preparation, resulting in a higher degree of polymerization of the urea-formaldehyde molecular chains. The thermogravimetric and thermogravimetric differential plots demonstrate that the product possesses the aforementioned structure.

[0070] In Figure 4, the liquid fertilizer prepared in this embodiment consists of uniform flower-shaped particles with an average particle size of 4.76 μm. The small particle size contributes to the dispersion stability of the liquid fertilizer in the suspension. The solid fertilizer is formed by extruding and stacking urea-formaldehyde particles, and its surface has a large number of microcracks and pores, which enhances its biodegradation rate. SEM images illustrate that the product has the aforementioned structure.

[0071] In Figure 5, from 0 to 7 days, the nitrogen release rate of the liquid fertilizer prepared in this embodiment was higher than that of the solid fertilizer, further indicating that the content of unreacted urea or urea-formaldehyde oligomers in the liquid fertilizer was higher than that in the solid fertilizer. After 7 days, the nitrogen release rate of the liquid fertilizer was lower than that of the solid fertilizer, further indicating that the liquid fertilizer had a higher degree of cross-linking. Within 28 days, the cumulative nitrogen release rate of both the liquid fertilizer and the solid fertilizer was less than 80%, indicating a good slow-release effect and suitability for use in cash crops or field crops.

[0072] Example 3

[0073] A process for the integrated preparation of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer includes the following steps:

[0074] (1) A certain amount of urea, solid paraformaldehyde, potassium carbonate catalyst and water are added to reactor A. The molar ratio of formaldehyde structural units contained in urea to paraformaldehyde is 2.1:1. The amount of catalyst added is 0.05% of the total mass of urea and paraformaldehyde. The reaction is carried out at 70°C for 1.5 h to obtain hydroxymethylurea solution. The water content of the whole system is 25% of the total mass of urea and paraformaldehyde.

[0075] (2) Half of the hydroxymethylurea solution obtained in step (1) is added dropwise to reactor B containing an acidic suspension prepared by phosphoric acid, water and suspending agent bentonite, wherein the phosphoric acid solute accounts for 10% of the mass of water added and the amount of bentonite added is 1% of the mass of water; the reaction time is t1 = 1h at temperature T1 = 30℃ to obtain a urea-formaldehyde viscous liquid, and then it is added to a mixed liquid prepared by potassium hydroxide, ammonium dihydrogen phosphate and nutrient enhancer gibberellin, wherein the molar ratio of potassium hydroxide to phosphoric acid added in the acidic suspension is 3:1, the mass ratio of ammonium dihydrogen phosphate to urea in step (1) is 1:4, and the mass ratio of gibberellin to urea in step (1) is 0.05:1. After thorough mixing, a urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer is obtained.

[0076] The remaining half of the hydroxymethylurea solution obtained in step (1) and the mixture of ammonium dihydrogen phosphate (with a mass ratio of 1:4 to urea in step (1)) were fed into the twin-screw reactive extruder of the reaction unit of the integrated reactive extrusion machine, which is sealed between the reaction unit and the extrusion unit. The screw of the twin-screw reactive extruder was turned on, and its vacuum devouring device was started at the same time to remove the moisture in the reaction system. The reaction extrusion time was t2 = 10 min at a temperature of T2 = 110℃ and a screw speed of R1 = 70 rpm. During this process, hydroxymethylurea generated urea-formaldehyde polymer through polycondensation reaction. Then the die between the reaction unit and the extrusion unit of the integrated reactive extrusion machine was opened, and the twin-screw extruder of the extrusion unit of the integrated reactive extrusion machine was started, so that the twin-screw reactive extruder could transport the reaction product into the twin-screw extruder. The product was extruded at a temperature of T3 = 60℃ and a screw speed of R2 = 20 rpm to obtain strips. After drying at a temperature of T4 = 120℃, the product was granulated to obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer.

[0077] The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release liquid fertilizer contained 19.3 g / L of nitrogen, 9.7 g / L of P2O5, and 7.3 g / L of K2O; the initial nitrogen release rate was 28.3%. When planting corn, the liquid fertilizer was applied using a sprayer at a rate of 78 L / mu.

[0078] The prepared urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer has a nitrogen content of 35.2 wt%, a P2O5 content of 15.2 wt%, and a K2O content of 0.85 g / L; the initial nitrogen nutrient release rate is 24.0%. When planting corn, apply fertilizer at a rate of 43 kg / mu using a seed-fertilizer integrated planter.

[0079] 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 process for the integrated preparation of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer, characterized in that, Includes the following steps: (1) Add a certain amount of urea, formaldehyde, catalyst and water to reactor A, and react at 50-90℃ for 0.5-3h to obtain hydroxymethylurea solution; the molar ratio of urea to formaldehyde is 1.2-5:1; the amount of catalyst added is 0-5% of the total mass of urea and formaldehyde and is not 0; the water content of the raw materials in reactor A is 15-35% of the total mass of urea and formaldehyde. (2) Add any part of the hydroxymethylurea solution obtained in step (1) to reactor B containing an acidic suspension prepared by acidic substances, water and suspending agent, and react at temperature T1 for time t1 to obtain a urea-formaldehyde viscous liquid. Then add it to a mixed liquid prepared by alkaline substances, a fertilizer system containing at least one nutrient element other than nitrogen and a nutrient enhancer. After mixing evenly, obtain urea-formaldehyde based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer. Meanwhile, the remaining portion of the hydroxymethyl urea solution obtained in step (1) is mixed with a fertilizer system containing at least one nutrient element other than nitrogen and fed into the twin-screw reactive extruder of the reactive extrusion unit. The reaction is carried out at a temperature of T2 and a screw speed of R1 for a reaction extrusion time of t2. During this process, hydroxymethyl urea generates urea-formaldehyde polymer through a condensation reaction. Then, the twin-screw reactive extruder is used to transport the reaction product to the twin-screw extruder of the reactive extrusion unit. The product is extruded at a temperature of T3 and a screw speed of R2 to obtain strips. After drying at a temperature of T4, the product is granulated to obtain urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release solid granular fertilizer.

2. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (1), the formaldehyde is at least one of formaldehyde aqueous solution, solid paraformaldehyde, and gaseous formaldehyde; the catalyst is one or a mixture of two of potassium carbonate and potassium hydroxide.

3. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (2), any portion of the hydroxymethylurea solution is added to the acidic suspension by dripping, misting, or pouring; the acidic substance is an inorganic or organic acid, selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, and tartaric acid; the amount of the acidic substance added is 0-80 wt% of the amount of water added in step (2) and is not 0; the suspending agent is an inorganic or organic suspending agent, selected from at least one of attapulgite, bentonite, kaolin, lignin, humic acid, alginic acid, polyvinyl alcohol, colloidal protein, xanthan gum, cellulose, and starch; the amount of the suspending agent added is 0-5 wt% of the amount of water added in step (2) and is not 0.

4. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (2), the temperature T1 = room temperature ~ 90℃, and the reaction time t1 = 0.1 ~ 2h.

5. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (2), the alkaline substance is an inorganic base, a strong base-weak acid salt, or an organic base, selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, potassium phosphate, and organic amine compounds; the amount of alkaline substance added depends on the pH value required by different soils or liquid fertilizers.

6. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (2), the temperature T2 = 50-130℃, the screw speed R1 = 5-150 rpm, the reaction extrusion time t2 = 1-30 min, the temperature T3 = 50-130℃, the screw speed R2 = 5-150 rpm, and the temperature T4 = 60-150℃.

7. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (2), the fertilizer system containing at least one nutrient element other than nitrogen is selected from at least one of phosphate, potassium salt, and micronutrient fertilizer; the phosphate is selected from at least one of hydroxyapatite, ammonium dihydrogen phosphate, superphosphate, and potassium dihydrogen phosphate; the potassium salt is selected from at least one of potassium sulfate, potassium chloride, potassium nitrate, and potassium carbonate; the micronutrient fertilizer is selected from at least one of calcium sulfate, magnesium sulfate, ferrous sulfate, manganese sulfate, zinc sulfate, copper sulfate, boric acid, sodium silicate, and potassium silicate; and the nutrient enhancer is selected from at least one of humic acid, amino acids, seaweed extract, gibberellin, and auxin.

8. The integrated preparation process of urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled release liquid fertilizer and solid granular fertilizer according to claim 1, characterized in that, In step (2), before the hydroxymethylurea solution obtained in step (1) is fed into the twin-screw reactive extruder of the reactive extrusion unit, the die between the reactive unit and the extrusion unit of the reactive extrusion unit is sealed. After the hydroxymethylurea solution obtained in step (1) is fed into the twin-screw reactive extruder, the screw of the twin-screw reactive extruder is turned on, and its vacuum devouring device is started to remove water from the reaction system. The die between the reactive unit and the extrusion unit of the reactive extrusion unit is opened, and the twin-screw extruder of the reactive extrusion unit of the reactive extrusion unit is started. Then the twin-screw reactive extruder will transport the reaction product into the twin-screw extruder.

9. The method for applying the urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release liquid fertilizer prepared as described in claim 1, characterized in that, Application methods include foliar spraying, seed soaking, root dipping, injection, drenching, watering, sprinkler irrigation, or drip irrigation; the application rate is 8–15 kg nitrogen per acre.

10. The method for applying the urea-formaldehyde-based multi-nutrient biodegradable polymer slow / controlled-release solid granular fertilizer prepared as described in claim 1, characterized in that, Use a seed-fertilizer integrated planter to apply solid granular fertilizer at the same time as sowing, or apply solid granular fertilizer and spray liquid fertilizer at the same time as sowing; the application rate is 8-15 kg nitrogen / mu.

Images