Preparation method and application of liquid slow-release nitrogen fertilizer containing humic acid type urea formaldehyde

Abstract

The invention relates to the technical field of fertilizer manufacturing, in particular to a humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer which is prepared from the following materials in parts: 30-70 parts of urea, 25-50 parts of formaldehyde, 1-15 parts of alkali compounds, 6-30 parts of ammonia and 1-10 parts of humic acid. The invention relates to a preparation method and application of a liquid slow-release nitrogen fertilizer containing humic acid type urea formaldehyde, and the preparation method comprises the following steps: excessive formaldehyde reacts with urea and ammonia water to generate monomethylol urea and dimethylol urea, and then a hydroxymethyl Uron ring is generated; formaldehyde, ammonia water and urea are continuously added for a reaction, and hydroxymethyl urea is converted into methylene diurea and dimethylene triurea; after cooling, continuously adding a small amount of ammonia water into the reaction kettle; and finally adding humic acid to obtain the liquid slow-release nitrogen fertilizer containing humic acid type urea formaldehyde. After the reaction is completed, the pH value of the solution is 8.0-11.0, and the reaction temperature is 50-95 DEG C. The liquid slow-release nitrogen fertilizer containing the humic acid type urea formaldehyde is high in stability, stable in storage component at-20 DEG C and 54 DEG C, free of gas expansion and crystallization, invariant in storage environments with cold winter and high temperature in summer, and suitable for popularization and application in different areas and different seasons; the product is high in nitrogen content, long in slow release period and high in absorption and utilization efficiency, and effectively solves the problems of high nitrogen fertilizer consumption, short lasting period and high loss rate in agricultural growth.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid fertilizer preparation, and specifically relates to a preparation method and application of a humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer. Background Art

[0002] In recent years, the large-scale application of nitrogen fertilizers has not only caused a waste of resources, but also caused increasingly serious problems of soil acidification and compaction. How to meet the demand for nitrogen fertilizers of crops and reduce the amount of nitrogen fertilizers applied has become the focus of attention in the fertilizer industry. Urea formaldehyde slow-release nitrogen fertilizer is a high-nitrogen slow-release fertilizer with slow nutrient release, long fertilizer effect period, and high nitrogen utilization rate. The fertilizer effect period can last for more than 60 days, and its release rate is consistent with the growth rate of plants. Mechanical spraying of urea formaldehyde foliar slow-release nitrogen fertilizer can greatly reduce labor intensity and improve production efficiency. Under the same conditions, it can save a lot of time and labor costs; at the same time, it can reduce the application of traditional urea and improve the utilization efficiency of nitrogen fertilizers. It not only complies with the current national policy requirements of zero growth in chemical fertilizers, but also promotes the protection and restoration of the soil ecological environment.

[0003] Urea formaldehyde fertilizer exists in two forms, one is solid and the other is liquid. Liquid urea formaldehyde fertilizer is a water-soluble fertilizer, which is conducive to crop absorption and utilization, has a high fertilizer utilization rate, and can be used in multiple scenarios such as drip irrigation, sprinkler irrigation and flushing. It is easy to use and is one of the important directions for the development of fertilizers in the future. However, existing liquid urea formaldehyde fertilizer products are mainly imported from Italy, Spain, Australia and other countries, and are packaged and sold domestically. With the popularization of drone flight control operations and water-fertilizer integration, the domestic demand for liquid urea formaldehyde fertilizer products is also increasing. The domestic market urgently needs such products to fill the gaps in the field of liquid urea formaldehyde fertilizer technology and application market.

[0004] The existing method for preparing urea-formaldehyde slow-release nitrogen fertilizer mainly involves reacting urea and formaldehyde under certain conditions to generate a stable urea-formaldehyde compound, and then using the compound as a nitrogen fertilizer. In patent US3462256, excess urea and concentrated formaldehyde are reacted in the presence of a small amount of ammonia to obtain a urea-formaldehyde liquid fertilizer that can be stored stably for a long time. Its main components are hydroxymethyl urea and unreacted urea. In order to ensure that hydroxymethyl urea no longer polymerizes, it needs to be placed under alkaline conditions. The problem with this technical solution is that the prepared transparent liquid can only be stable for 30 days at 20-25°C, and can only be kept stable for 7 days at 0°C. Moreover, the release of nitrogen is extremely slow, and crops cannot effectively use nitrogen sources. These methods usually need to be carried out under high temperature and high pressure, which not only increases the preparation cost, but also increases energy consumption. Secondly, these methods often cannot accurately control the reaction rate of urea and formaldehyde, resulting in poor product stability of the generated urea-formaldehyde compound, which is difficult to store under high temperature, normal temperature, and low temperature conditions. In addition, the urea-formaldehyde slow-release nitrogen fertilizer produced by these methods has a poor slow-release effect and low nitrogen utilization efficiency. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a preparation method and application of a humic acid-containing urea-formaldehyde liquid slow-release fertilizer. The invention adopts a multi-step method to control the reaction process and the generation of reaction products. The reaction conditions are controlled to promote the formation of a hydroxymethyl Uron ring in the second step reaction. The formation of the Uron ring inhibits the resinification reaction of urea and formaldehyde and reduces the polymerization reaction between formaldehyde molecules, so as to improve the stability of the urea-formaldehyde liquid slow-release fertilizer in cold and hot storage environments, so that the fertilizer can be stored at -20°C and 50°C without reacting easily.

[0006] The reaction principle for preparing humic acid type urea formaldehyde slow-release nitrogen fertilizer is as follows:

[0007] Step 1: Urea, formaldehyde and ammonia undergo hydroxymethylation reaction under heating conditions to generate monomethylol urea (1) and dimethylol urea (2), as shown in (a).

[0008]

[0009] Step 2: During the reaction, the hydroxymethyl group of monomethylol urea undergoes a condensation reaction within the molecule, removing one molecule of water to form a cyclic ether structure product - monomethylol Uron ring. Monomethylol Uron can also continue to react with formaldehyde to produce a dimethylol Uron ring structure. The reaction is shown in (ii).

[0010]

[0011] Step 3: Methylolation reaction occurs between monohydroxymethylurea and urea to generate N,N-methylenediurea (3), and N,N-methylenediurea reacts with monohydroxymethylurea to generate dimethylenetriurea (4). The reaction process is as shown in (III).

[0012]

[0013] According to the above reaction principle, the present invention provides the following technical solution: A low-cost urea-formaldehyde liquid slow-release fertilizer, characterized in that the fertilizer is prepared from the following parts by weight of materials: 30-70 parts of urea, 25-50 parts of formaldehyde, 1-15 parts of alkali compounds, 6-30 parts of ammonia, and 1-10 parts of humic acid.

[0014] The urea includes large granular urea, small granular urea and powdered urea, and the nitrogen content is 46%;

[0015] The formaldehyde is formaldehyde aqueous solution, paraformaldehyde or urea-formaldehyde precondensate. The concentration of the formaldehyde aqueous solution is 42%-55%. The molecular weight range of paraformaldehyde (HO-(CH2O)n-H) is 10 < n < 100, and the formaldehyde content is 92%-98%. The urea-formaldehyde precondensate is UFC-62, with a formaldehyde content of 44%, a urea content of 18%, and a pH of 7.0-8.0;

[0016] The ammonia is ammonia water or liquid ammonia, and the liquid ammonia is a product that meets the national standard of "Liquid Anhydrous Ammonia"; the ammonia content in the ammonia water ranges from 25% to 28%;

[0017] The humic acid is a mixture of one or two of mineral-source potassium humate and biogenic potassium humate.

[0018] The water-insoluble matter of the humic acid ≤ 0.5%, the humic acid content is 40-60%, the potassium oxide content is 8-12%, the particle size ≤ 5μm, and the hard water resistance ≥ 30.

[0019] The alkali compounds are one or a mixture of two or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, potassium hydroxide, potassium carbonate, and potassium bicarbonate.

[0020] A preparation method and application of a humic acid-containing urea-formaldehyde liquid slow-release fertilizer, and the preparation method includes:

[0021] S1: adding an excess of formaldehyde, an appropriate amount of urea and a small amount of ammonia to a reactor to react and generate a mixture of monomethylol urea and dimethylol urea, wherein the molar ratio of formaldehyde, urea and ammonia is 1.0:0.5-0.8:0.01-0.5, the reaction temperature is 50-80°C, the pH value of the solution is maintained at 7.0-10.5, the reaction time is 0.5-1h, urea and formaldehyde generate monomethylol urea and dimethylol urea, different molar ratios of urea and formaldehyde and reaction conditions result in different product ratios, the ratio of urea to formaldehyde can be adjusted according to different target products, preferably dimethylol urea is synthesized;

[0022] S2: Continue the reaction, adjust the temperature to 80-95°C, react for 0.5-2h, monitor the pH of the reaction solution, add an appropriate amount of alkaline compounds to adjust the solution pH to between 8.0-11, and convert part of the hydroxymethyl urea in S1 into hydroxymethyl Uron ring.

[0023] S3: Continue to add formaldehyde, urea and ammonia to the reactor to make the total molar ratio of formaldehyde, urea and ammonia added to the reactor be 0.3-0.8:0.5-1.0:0.1-0.5, and add appropriate amount of alkaline compounds to adjust the pH to between 8.0-11, the temperature is 50-80°C, and the reaction is carried out for 0.5-2h. By controlling the proportion of each component added and adjusting the reaction temperature, the monomethylol urea and dimethylol urea produced in S1 are converted into water-soluble methylene diurea and dimethylene triurea.

[0024] S4: The temperature of the reactor is cooled to 30-40°C, and a small amount of ammonia is added to the reactor;

[0025] S5: Finally, add 1-10 parts of humic acid into the reactor and stir for 40-60 minutes;

[0026] S6: Cooling to room temperature to obtain humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer.

[0027] During the reaction, the stirring rate of the reactor was controlled at 300-800 r / min.

[0028] While adding the alkaline compound to the reactor, monitor the pH of the solution and use a pH meter to accurately measure and maintain the pH of the solution;

[0029] Preferably, the step of S1 includes:

[0030] Prepare urea, formaldehyde, water and reactor;

[0031] Add water to the reactor;

[0032] Then, urea and formaldehyde are added to the reactor in a molar ratio of 0.5-0.8:1;

[0033] An aqueous mixture of urea and formaldehyde is obtained.

[0034] Ammonia is added at the same time to adjust the pH of the solution and provide the amino groups required for the reaction. The molar ratio of urea, formaldehyde and ammonia is 0.5:0.5-1:0.1-0.3.

[0035] While adding ammonia to the reactor, monitor the pH of the solution, accurately measure it using a pH meter, and add alkaline compounds in small amounts and multiple times as needed to maintain the pH of the solution in the range of 7.0-10.5;

[0036] Allow the reaction to proceed at the set temperature for 0.5-1 hour;

[0037] Preferably, the step of S2 is:

[0038] Adjust the temperature of the reactor to 80-95°C;

[0039] Monitor the pH of the solution, use a pH meter to accurately measure, and add alkaline compounds in small amounts and multiple times as needed to maintain the pH of the solution in the range of 8.0-11.0;

[0040] Allow the reaction to proceed at the set temperature for 0.5-2 hours, and in particular, start timing when the temperature of the reaction solution rises to 80-95°C;

[0041] Preferably, the step of S3 is:

[0042] Continue to add formaldehyde, urea and ammonia, so that the total molar ratio of all added formaldehyde, urea and ammonia is 0.3-1:0.5-1:0.1-0.5;

[0043] After adding the materials, lower the temperature of the reactor to 50-80°C;

[0044] Monitor the pH of the solution, use a pH meter to accurately measure, and add alkaline compounds in small amounts and multiple times as needed to maintain the pH of the solution in the range of 8.0-11.0;

[0045] Allow the reaction to proceed at the set temperature for 0.5-2 hours;

[0046] Preferably, the step of S4 is:

[0047] Lower the reactor temperature to 30-40°C;

[0048] After the temperature is lowered, a small amount of ammonia is added to the reactor to improve the stability of the product;

[0049] Preferably, the step of S5 is:

[0050] Add 1-10 parts of humic acid to the reactor and stir until all dissolved;

[0051] In particular, humic acid should be added slowly to prevent humic acid from agglomerating in the reactor.

[0052] Preferably, S6 specifically includes:

[0053] The reaction solution in the reactor was cooled to room temperature;

[0054] The final pH value of the urea formaldehyde liquid should be between 8.0 and 11.0;

[0055] Filter the solution to remove packaging waste and residue;

[0056] Putting the prepared humic acid-containing urea formaldehyde slow-release nitrogen fertilizer into a container;

[0057] Conduct product quality and stability testing.

[0058] Preferably, the product quality detection includes content determination (total nitrogen, urea nitrogen, urea formaldehyde nitrogen, total potassium, humic acid, etc.), pH, water-insoluble matter and other indicators.

[0059] Preferably, the stability test includes low temperature (-20°C), high temperature (54°C) and room temperature storage tests, observing whether the appearance has changed after 1 hour, and observing whether the appearance has changed after 14 days and 30 days of storage, and testing its indicators.

[0060] Attached product quality testing methods:

[0061] Preferably, the total nitrogen content in the product is determined according to GB / T 8572-2010 "Determination of total nitrogen content in compound fertilizers - Titration after distillation", amide nitrogen and urea-formaldehyde nitrogen are determined according to the method in GB / T 34763-2017 "Urea-formaldehyde slow-release fertilizer", total potassium content is determined according to the method in NY / T 1977-2010 "Determination of total nitrogen, phosphorus and potassium content of water-soluble fertilizers", humic acid content is determined according to the method in NY / T 1106-2010 "Water-soluble fertilizers containing humic acid", and pH and water-insoluble matter content are determined according to NY / T 1973-2021 "Determination of water-insoluble matter content and pH value of water-soluble fertilizers".

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] 1. The humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer of the present invention has a high nitrogen content of 300 g / L-400 g / L, which meets the nitrogen demand of crops and improves the use effect of the fertilizer.

[0064] 2. The present invention adopts a three-stage urea-formaldehyde condensation process to accurately control the reaction rate of urea and formaldehyde, so that the generated urea-formaldehyde compound has a better sustained release effect and a longest lasting period of up to 60 days, which greatly improves the use efficiency of fertilizers, reduces the number of times fertilizers are used, and reduces the labor intensity of farmers.

[0065] 3. Another great advantage of the three-stage production process of the present invention is that the ratio of dimethylol urea, hydroxymethyl Uron ring, methylene diurea and dimethylene triurea in the reaction product is controlled, so that the obtained urea formaldehyde liquid slow-release nitrogen fertilizer has high storage stability, remains a clear solution at low temperature (≥-20°C) and does not freeze; does not swell at high temperature (≤54°C) and has stable components; can be stored at room temperature for more than 48 months.

[0066] 4. Reduce preparation cost and energy consumption: The preparation method of the humic acid-containing urea formaldehyde slow-release nitrogen fertilizer of the present invention is carried out at a temperature of 50-95°C, without high temperature and high pressure conditions, which greatly reduces the preparation cost and energy consumption. Compared with the prior art, the method of the present invention is more energy-saving and environmentally friendly, and meets the current social demand for green chemistry.

[0067] 5. The high-concentration foliar spraying of the humic acid-type urea formaldehyde liquid slow-release nitrogen fertilizer of the present invention is highly safe. It can be sprayed at a ratio of 1:1 by drone or 1:15 by sprayer. It is safe and does not burn leaves, thus expanding the scope of fertilizer use and improving fertilizer use efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a flow chart of the preparation steps of the present invention. DETAILED DESCRIPTION

[0069] In order to better understand the present application, a more detailed description will be made of various aspects of the present application with reference to the accompanying drawings. It should be understood that these detailed descriptions are only descriptions of exemplary embodiments of the present application, and are not intended to limit the scope of the present application in any way. Throughout the specification, the same reference numerals refer to the same elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0070] In the accompanying drawings, the size, dimensions and shapes of the elements have been slightly adjusted for ease of illustration. The drawings are for illustration only and are not strictly drawn to scale. As used herein, the terms "substantially", "approximately" and similar terms are used as terms of approximation, not as terms of degree, and are intended to illustrate the inherent deviations in measurements or calculations that would be recognized by a person of ordinary skill in the art. In addition, in this application, the order in which the processing of each step is described does not necessarily represent the order in which these processes occur in actual operation, unless otherwise specified or can be derived from the context.

[0071] It should also be understood that expressions such as "include", "including", "have", "contain" and / or "comprising" are open rather than closed expressions in this specification, which indicate the presence of the stated features, elements and / or components, but do not exclude the presence of one or more other features, elements, components and / or combinations thereof. In addition, when expressions such as "at least one of..." appear after a list of listed features, they modify the entire list of features rather than just the individual elements in the list. In addition, when describing embodiments of the present application, "may" is used to mean "one or more embodiments of the present application". And, the term "exemplary" is intended to refer to an example or illustration.

[0072] Unless otherwise defined, all words (including engineering terms and scientific and technological terms) used in this article have the same meaning as commonly understood by ordinary technical citizens in the field to which this application belongs. It should also be understood that, unless explicitly stated in this application, words defined in commonly used dictionaries should be interpreted as having the same meaning as their meaning in the context of the relevant technology, and should not be interpreted in an idealized or overly formal sense.

[0073] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0074] Example 1

[0075] The humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer is composed of 40 parts of urea, 41 parts of urea formaldehyde pre-shrinkage liquid UFC-62, 2 parts of potassium hydroxide, 10 parts of 25% ammonia water, and 7 parts of biogenic potassium humate. The preparation method is as follows:

[0076] (1) 35 parts of urea-formaldehyde pre-shrinkage liquid UFC-62, 20 parts of urea and 4 parts of 25% ammonia water were mixed and stirred in a reactor at 70° C., 0.5 parts of potassium hydroxide were added to adjust the pH to 7-10.5, the stirring time was controlled to 40 minutes, and the stirring rate was controlled to 500 r / min;

[0077] (2) adjusting the temperature of the reactor to 85°C, adding 0.5 parts of potassium hydroxide to adjust the pH to 8.0-11.0, controlling the stirring time to 100 min, and the stirring rate to 500 r / min;

[0078] (3) Add 6 parts of urea-formaldehyde pre-shrinkage liquid UFC-62, 20 parts of urea and 4 parts of ammonia water with a mass concentration of 25% to the mixed solution of step (2), stir, control the temperature to about 80°C, add 1 part (the amount of potassium hydroxide added can be adjusted according to the actual situation, and water can be used to make up when the amount added is small) potassium hydroxide to adjust the pH to 8-11, control the time to 60 minutes, and control the stirring rate to 500r / min;

[0079] (4) After the reaction in step (3) is completed, the temperature is lowered to 35° C. and 2 parts of 25% ammonia water are added;

[0080] (5) adding 7 parts of biogenic potassium humate to the solution of step (4), stirring for 60 min, and controlling the stirring rate at 500 r / min;

[0081] (6) Finally, the temperature is lowered to room temperature to obtain a humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer.

[0082] The quality inspection and stability test results of the humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer are as follows:

[0083]

[0084] Example 2

[0085] The humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer is composed of 48 parts of urea, 31 parts of 55% formaldehyde aqueous solution by mass, 2 parts of potassium hydroxide, 13 parts of 25% ammonia water by mass and 6 parts of mineral source potassium humate. The preparation method is as follows:

[0086] (1) 27 parts of 55% formaldehyde aqueous solution, 20 parts of urea and 7 parts of 25% ammonia water were mixed and stirred in a reactor at 75° C., 0.5 parts of potassium hydroxide were added to adjust the pH to 7-10.5, the stirring time was controlled to 30 minutes, and the stirring rate was controlled to 500 r / min;

[0087] (2) adjusting the temperature of the reactor to 80°C, adding 0.5 parts of potassium hydroxide to adjust the pH to 8.0-11.0, controlling the stirring time to 80 min, and the stirring rate to 500 r / min;

[0088] (3) adding 4 parts of 37% formaldehyde aqueous solution, 28 parts of urea and 4 parts of 25% ammonia water to the mixed solution of step (2), stirring the mixture, controlling the temperature at about 75° C., adding 1 part of potassium hydroxide to adjust the pH to 8-11, controlling the stirring time at 80 min, and controlling the stirring rate at 500 r / min;

[0089] (4) After the reaction in step (3) is completed, the temperature is lowered to 35° C. and 2 parts of 25% ammonia water are added;

[0090] (5) adding 6 parts of mineral source potassium humate to the solution of step (4), stirring for 60 min, and controlling the stirring rate at 500 r / min;

[0091] (6) Finally, the temperature is lowered to room temperature to obtain a humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer.

[0092] The quality inspection and stability test results of the humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer are as follows:

[0093]

[0094] Example 3

[0095] The humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer is composed of 54 parts of urea, 28 parts of 55% formaldehyde aqueous solution, 2 parts of potassium hydroxide, 13 parts of 25% ammonia water and 3 parts of mineral source potassium humate. The preparation method is as follows:

[0096] (1) 26 parts of 55% formaldehyde aqueous solution, 25 parts of urea and 8 parts of 25% ammonia water were mixed and stirred in a reactor at 50° C., 0.5 parts of potassium hydroxide were added to adjust the pH to 7-10.5, the stirring time was controlled to 30 minutes, and the stirring rate was controlled to 500 r / min;

[0097] (2) adjusting the temperature of the reactor to 85°C, adding 0.5 parts of potassium hydroxide to adjust the pH to 8.0-11.0, controlling the stirring time to 80 min, and the stirring rate to 500 r / min;

[0098] (3) Add 2 parts of 55% formaldehyde aqueous solution, 29 parts of urea and 3 parts of 25% ammonia water to the mixed solution of step (2), stir, control the temperature to about 50° C., add 1 part of potassium hydroxide to adjust the pH to 8-11, control the time to 80 min, and control the stirring rate to 500 r / min;

[0099] (4) After the reaction in step (3) is completed, the temperature is lowered to 35° C. and 2 parts of 25% ammonia water are added;

[0100] (5) adding 3 parts of mineral source potassium humate to the solution of step (4), stirring for 60 min, and controlling the stirring rate at 500 r / min;

[0101] (6) Finally, the temperature is lowered to room temperature to obtain a humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer.

[0102] The quality inspection and stability test results of the humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer are as follows:

[0103]

[0104] Due to the advanced nature of the technical solution, it can be widely used in application fields such as agricultural production, horticultural planting, and greening maintenance. First, the urea formaldehyde liquid slow-release fertilizer of the present invention has a high nitrogen content and a long slow-release period, which can effectively meet the plant's demand for nutrients during growth and improve the yield and quality of crops. Secondly, the fertilizer of the present invention has high storage stability, is easy to store and transport, and can greatly reduce the cost of agricultural production. In addition, the high-concentration foliar spraying of the fertilizer of the present invention is highly safe, which is conducive to achieving precise fertilization, improving the utilization rate of fertilizers, and reducing pollution to the environment, which meets the current social demand for environmentally friendly fertilizers. Finally, the fertilizer of the present invention is suitable for drone flight control and spraying with sprayers, which is conducive to improving the efficiency of agricultural production and meeting the needs of modern agricultural production for efficient, environmentally friendly, and intelligent fertilizers.

[0105] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0106] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A humic acid-containing urea formaldehyde liquid slow-release fertilizer, characterized in that: The fertilizer is prepared from the following materials: 30-70 parts of urea, 25-50 parts of formaldehyde, 1-15 parts of alkali compounds, 6-30 parts of ammonia and 1-10 parts of humic acid.

2. The humic acid-containing urea formaldehyde liquid slow-release fertilizer according to claim 1, characterized in that: The urea includes large granular urea, small granular urea and powdered urea, and the nitrogen content is 46%; The formaldehyde is an aqueous formaldehyde solution, paraformaldehyde or urea formaldehyde precondensate. The concentration of the aqueous formaldehyde solution is 42%-55%. The molecular weight range of paraformaldehyde (HO-(CH2O) n -H) is 10 < n < 100, the formaldehyde content is 92%-98%, the urea formaldehyde precondensate is UFC-62, the formaldehyde content is 44%, the urea content is 18%, and the pH is 7.0-8.0; The ammonia is aqueous ammonia or liquid ammonia, and the liquid ammonia is a product that meets the national standard of "Liquid Anhydrous Ammonia"; the ammonia content in the aqueous ammonia ranges from 25% to 28%; The humic acid is one of mineral-derived potassium humate and biological-derived potassium humate, or a mixture of both. The water-insoluble matter of the humic acid is ≤0.5%, the humic acid content is 40-60%, the potassium oxide content is 8-12%, the particle size is ≤5 μm, and the hard water resistance is ≥30. The alkaline compound is one or a mixture of two or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, potassium hydroxide, potassium carbonate and potassium bicarbonate.

3. A preparation method and application of a humic acid-containing urea formaldehyde liquid slow-release fertilizer, characterized in that: The preparation method comprises: S1: adding an excess of formaldehyde, an appropriate amount of urea and a small amount of ammonia to a reactor to react and generate a mixture of monomethylol urea and dimethylol urea, wherein the molar ratio of formaldehyde, urea and ammonia is 1.0:0.5-0.8:0.01-0.5, the reaction temperature is 50-80°C, the pH value of the solution is maintained at 7.0-10.5, the reaction time is 0.5-1h, urea and formaldehyde generate monomethylol urea and dimethylol urea, different molar ratios of urea and formaldehyde and reaction conditions result in different product ratios, the ratio of urea to formaldehyde can be adjusted according to different target products, preferably dimethylol urea is synthesized; S2: Continue the reaction, adjust the temperature to 80-95°C, react for 0.5-2h, monitor the pH of the reaction solution, add an appropriate amount of alkaline compounds to adjust the solution pH to between 8.0-11, and convert part of the hydroxymethyl urea in S1 into hydroxymethyl Uron ring. S3: Continue to add formaldehyde, urea and ammonia to the reactor to make the total molar ratio of formaldehyde, urea and ammonia added to the reactor be 0.3-0.8:0.5-1.0:0.1-0.5, and add appropriate amount of alkaline compounds to adjust the pH to between 8.0-11, the temperature is 50-80°C, and the reaction is carried out for 0.5-2h. By controlling the proportion of each component added and adjusting the reaction temperature, the monomethylol urea and dimethylol urea produced in S1 are converted into water-soluble methylene diurea and dimethylene triurea. S4: The temperature of the reactor is cooled to 30-40°C, and a small amount of ammonia is added to the reactor; S5: Finally, add 1-10 parts of humic acid into the reactor and stir for 40-60 minutes; S6: Cooling to room temperature to obtain humic acid-containing urea formaldehyde liquid slow-release nitrogen fertilizer. During the reaction, the stirring rate of the reactor was controlled at 300-800 r / min. As described above, the present invention adopts a multi-step method to carry out the reaction, and the main purpose is to regulate the composition and content of the target product and each component in the reaction process. The key to preparing urea formaldehyde liquid slow-release nitrogen fertilizer by a multi-step method is that the proportion of dimethylol urea, hydroxymethyl Uron ring, methylene diurea, dimethylene triurea and other products in the product can be controlled by controlling the reaction conditions such as the addition amount of each reaction raw material, pH value, reaction temperature, reaction time, etc., so as to obtain a urea formaldehyde slow-release nitrogen fertilizer with a long slow-release period and stability, which can not react in the storage environment of cold winter and high temperature in summer, and is suitable for promotion and application in different regions and different seasons.

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