Preparation method of nano suspension slow-release liquid fertilizer

Abstract

The invention belongs to the field of liquid fertilizers, and particularly relates to a preparation method of a nano suspension slow-release liquid fertilizer, which comprises the following steps: adding water into ammonium polyphosphate, methylene urea nitrogen, a hyperbranched urea polymer, phosphate and monopotassium phosphate, mixing, adding maleic acid, ethylenediamine tetra (methylene phosphonic acid), humic acid and a stabilizer, and uniformly mixing to prepare a mixed fertilizer. And dispersing the mixed fertilizer and the kaolin nano-suspension to obtain the nano-suspension slow-release liquid fertilizer. The hyperbranched urea polymer is combined with a nitrogen fertilizer to form a macromolecular nitrogen chain, a nitrogen nutrient reserve library is established in a plant body, the nano suspension can wrap the mixed fertilizer, nutrients can be continuously absorbed by crops, and the hyperbranched urea polymer is combined to achieve long-acting slow release.

Description

Technical Field

[0001] The invention relates to the field of liquid fertilizers, and in particular to a method for preparing nano-suspension slow-release liquid fertilizer. Background Art

[0002] In the modern agricultural production system, fertilizers are an indispensable source of nutrients for plant growth. Their quality and effectiveness directly affect the growth and development of crops, yield potential, and final product quality. However, for a long time, traditional fertilizers have exposed a series of problems that need to be solved during use. Among them, the most notable is the phenomenon of nutrient release too quickly. This causes a large amount of nutrients to be released rapidly in a short period of time, and the plants cannot fully absorb them in time, resulting in nutrient waste, and may even cause damage to plants due to excess nutrients. In addition, traditional fertilizers are easily adsorbed and fixed by colloidal particles in the soil, or lost with rainwater runoff and infiltration, further reducing the actual utilization rate of fertilizers.

[0003] What is more complicated is that there are many kinds of ions in the soil, such as calcium, magnesium, iron, and aluminum. These ions can often react chemically with the effective ingredients in the fertilizer to form insoluble compounds, which makes the fertilizer lose its original fertilizer effect. However, ordinary liquid fertilizers are prone to nutrient and water loss due to water erosion. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art that the slow-release effect of liquid fertilizer is poor and it cannot provide nutrients to plants for a long time, and a preparation method of nano-suspended slow-release liquid fertilizer is proposed.

[0005] The invention provides a nano-suspension slow-release liquid fertilizer, the preparation method of which comprises:

[0006] S1. Add anhydrous acetic acid and acetic anhydride in a volume ratio of (1.8-2.2):1 to a reaction vessel, add benzoic acid and hexamethylenetetramine in a mass ratio of 1:(3-4), stir and heat, add paraformaldehyde, and condense and reflux under heating at 120-130° C. to obtain an intermediate;

[0007] S2, adding the intermediate, concentrated sulfuric acid and water in a volume ratio of 1:(4-5) to a reaction vessel, heating to 90° C. for reaction for 1-5 hours, cooling after the reaction, washing with ice water for 3-4 times, filtering, and drying to obtain 5-carboxyisophthalaldehyde;

[0008] S3, add urea and water to a reaction container, stir, heat to 30-40°C until urea is completely dissolved, adjust the pH to acidic, add 5-carboxyisophthalaldehyde, heat to 50-60°C, react for 5-6h, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer;

[0009] S4, adding water to ammonium polyphosphate, methylene urea nitrogen, hyperbranched urea polymer, phosphate, and potassium dihydrogen phosphate to mix, and then adding maleic acid, ethylenediaminetetramethylenephosphoric acid, humic acid, and a stabilizer to mix evenly to obtain a mixture to obtain a mixed fertilizer;

[0010] S5. Dilute the kaolin nano suspension, add the diluted kaolin nano suspension and the mixed fertilizer into a high-speed emulsifying disperser for dispersion, and let stand for 5-10 hours after dispersion to obtain a nano suspension slow-release liquid fertilizer.

[0011] Preferably, in step S3, the volume ratio of 5-carboxyisophthalaldehyde to urea is 1:(3-4).

[0012] Preferably, in step S4, the stabilizer is one or more of sorbitol and mannitol.

[0013] Preferably, in step S5, the kaolin nanosuspension is added to water, and the mass ratio of the kaolin nanosuspension to water is (0.1-0.5):100.

[0014] Preferably, the preparation process of the kaolin nano suspension is as follows: grinding the kaolin slurry, adding the ground kaolin slurry into water to prepare a suspension of kaolin and water in a mass ratio of 1:(1.5-1.7), adding an alkaline solution dropwise to the suspension until it becomes alkaline, placing the suspension in a high-speed emulsifier disperser, and 4 -5×10 4 r / min for 1-3h, let it stand for 24-36h, add dilute hydrochloric acid to adjust the suspension pH to 6.8-7.2, and then place it in a high-speed emulsifier disperser at 3×10 4 -5×10 4 r / min for 10-20 min to obtain a kaolin nanosuspension.

[0015] Preferably, an alkaline solution is added dropwise to the suspension to make it alkaline, and the alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

[0016] The invention has the following beneficial effects: the invention prepares a kaolin nano suspension by emulsifying and dispersing kaolin and water, prepares an intermediate by treating benzoic acid and hexamethylenetetramine under the action of anhydrous acetic acid, acetic anhydride and paraformaldehyde, obtains 5-carboxyisophthalaldehyde by hydrolysis of the intermediate, reacts 5-carboxyisophthalaldehyde with urea to generate a hyperbranched aldehyde-urea polymer, then adds water to ammonium polyphosphate, methylene urea nitrogen, a hyperbranched aldehyde-urea polymer, phosphate and potassium dihydrogen phosphate to mix, then adds maleic acid, ethylenediaminetetramethylenephosphoric acid, humic acid and a stabilizer to mix evenly to prepare a mixed fertilizer, and then disperses the mixed fertilizer with the kaolin nano suspension to obtain a nano suspension slow-release liquid fertilizer.

[0017] The invention comprises the following steps: preparing an intermediate by reacting benzoic acid and hexamethylenetetramine under the action of anhydrous acetic acid, acetic anhydride and paraformaldehyde, and obtaining 5-carboxyisophthalaldehyde by hydrolysis of the intermediate; the carboxyl group and aldehyde group on the 5-carboxyisophthalaldehyde react with the amino group on the urea; the hyperbranched aldehyde-urea resin has a lower curing temperature and better thermal stability, can maintain stable performance, can provide slow and stable nitrogen nutrition, and the free formaldehyde content in the hyperbranched aldehyde-urea resin is significantly reduced, so the hyperbranched aldehyde-urea resin is more environmentally friendly than the aldehyde-urea resin; and the hyperbranched aldehyde-urea polymer thereof has a lower curing temperature and better thermal stability, can maintain stable performance, can provide slow and stable nitrogen nutrition, and can significantly reduce the free formaldehyde content in the hyperbranched aldehyde-urea resin. The structure contains multiple carbamate groups, which can combine with nitrogen fertilizers to form a large molecular nitrogen chain. The carboxyl group on 5-carboxyisophthalaldehyde and the amino group on urea can undergo a dehydration condensation reaction to form a peptide bond, which can adsorb metals in the soil and improve heavy metal pollution in the soil. This polymer has a high molecular weight and a complex network structure, which can effectively control the release time of nitrogen nutrients, making the effective period of nitrogen fertilizer reach 50-60 days; kaolin nanosuspension can wrap mixed fertilizers, allowing nutrients to be continuously absorbed by crops to achieve long-term slow release. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the reaction equation for preparing the intermediate of the present invention.

[0019] Figure 2 It is the reaction equation for preparing 5-carboxyisophthalaldehyde of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further explained below in conjunction with specific embodiments.

[0021] Embodiment 1:

[0022] The kaolin slurry was ground and added to water to prepare a mixed suspension of 30 g kaolin and 45 g water. Potassium hydroxide solution was added dropwise to the suspension until it was alkaline. The suspension was placed in a high-speed emulsifier and stirred at 5 × 10 4 r / min for 3 h, let it stand for 36 h, add dilute hydrochloric acid to adjust the suspension pH to 6.8, and then place it in a high-speed emulsifier disperser at 5×10 4 r / min for 20 min to obtain a kaolin nanosuspension.

[0023] S2. Add 18 mL of anhydrous acetic acid and 10 mL of acetic anhydride in a volume ratio into a reaction container, add 8 g of benzoic acid and 32 g of hexamethylenetetramine, stir and heat, add paraformaldehyde, and condense and reflux under heating to 120° C. to obtain an intermediate.

[0024] S3. Add 3 g of the intermediate, 5 g of concentrated sulfuric acid and 20 g of water into a reaction container, heat to 90° C. and react for 5 h. After the reaction, cool, add ice water to wash 4 times, filter, and dry to obtain 5-carboxyisophthalaldehyde.

[0025] S4. Add 40 g of urea and 200 mL of water to a reaction container, stir, heat to 30°C until the urea is completely dissolved, adjust the pH to acidic, add 10 g of 5-carboxyisophthalaldehyde, heat to 60°C, react for 5 hours, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer.

[0026] S5. 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched urea polymer, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, thereby obtaining a mixed fertilizer.

[0027] S6. Dilute the kaolin nano suspension to 0.1% of the mass of kaolin, add the diluted kaolin nano suspension and mixed fertilizer into a high-speed emulsifying disperser for dispersion, and let stand for 5 hours after dispersion to obtain a nano suspension slow-release liquid fertilizer.

[0028] Embodiment 2:

[0029] The kaolin slurry was ground and added to water to prepare a mixed suspension of 30 g kaolin and 51 g water. Potassium hydroxide solution was added dropwise to the suspension until it was alkaline. The suspension was placed in a high-speed emulsifier and stirred at 3 × 10 4 r / min for 1 h, let it stand for 24 h, add dilute hydrochloric acid to adjust the suspension pH to 7.2, and then place it in a high-speed emulsifier disperser at 3×10 4 r / min for 10 min to obtain a kaolin nanosuspension.

[0030] S2. Add 22 mL of anhydrous acetic acid and 10 mL of acetic anhydride in a volume ratio into a reaction container, add 8 g of benzoic acid and 24 g of hexamethylenetetramine, stir and heat, add paraformaldehyde, and condense and reflux under heating to 130° C. to obtain an intermediate.

[0031] S3. Add 3 g of the intermediate, 5 g of concentrated sulfuric acid and 25 g of water into a reaction container, heat to 90° C. and react for 4 h. After the reaction, cool, add ice water to wash 3 times, filter, and dry to obtain 5-carboxyisophthalaldehyde.

[0032] S4. Add 30 g of urea and 200 mL of water to a reaction container, stir, heat to 40°C until the urea is completely dissolved, adjust the pH to acidic, add 10 g of 5-carboxyisophthalaldehyde, heat to 50°C, react for 6 hours, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer.

[0033] S5. 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched urea polymer, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, thereby obtaining a mixed fertilizer.

[0034] S6. Dilute the kaolin nano suspension to 0.5% of the mass of kaolin, add the diluted kaolin nano suspension and mixed fertilizer into a high-speed emulsifying disperser for dispersion, and let stand for 10 hours after dispersion to obtain a nano-suspension slow-release liquid fertilizer.

[0035] Embodiment three:

[0036] The kaolin slurry was ground and added to water to prepare a mixed suspension of 30 g kaolin and 47 g water. Potassium hydroxide solution was added dropwise to the suspension until it was alkaline. The suspension was placed in a high-speed emulsifier and stirred at 5 × 10 4 r / min for 2 h, let it stand for 36 h, add dilute hydrochloric acid to adjust the suspension to pH 7, and then place it in a high-speed emulsifier. 4 The mixture was stirred at rpm for 15 min to obtain a kaolin nanosuspension.

[0037] S2. Add 20 mL of anhydrous acetic acid and 10 mL of acetic anhydride in a volume ratio into a reaction container, add 8 g of benzoic acid and 28 g of hexamethylenetetramine, stir and heat, add paraformaldehyde, and condense and reflux under heating to 120° C. to obtain an intermediate.

[0038] S3. Add 3 g of the intermediate, 5 g of concentrated sulfuric acid and 25 g of water into a reaction container, heat to 90° C. and react for 1 h. After the reaction, cool, add ice water to wash 3 times, filter, and dry to obtain 5-carboxyisophthalaldehyde.

[0039] S4. Add 35 g of urea and 200 mL of water to a reaction container, stir, heat to 35°C until the urea is completely dissolved, adjust the pH to acidic, add 10 g of 5-carboxyisophthalaldehyde, heat to 55°C, react for 6 hours, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer.

[0040] S5. 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched urea polymer, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, thereby obtaining a mixed fertilizer.

[0041] S6. Dilute the kaolin nano suspension to 0.3% of the mass of kaolin, add the diluted kaolin nano suspension and mixed fertilizer into a high-speed emulsifying disperser for dispersion, and let stand for 8 hours after dispersion to obtain a nano suspension slow-release liquid fertilizer.

[0042] Embodiment 4:

[0043] The kaolin slurry was ground and added to water to prepare a mixed suspension of 30 g kaolin and 49 g water. Potassium hydroxide solution was added dropwise to the suspension until it was alkaline. The suspension was placed in a high-speed emulsifier and stirred at 5 × 10 4 r / min for 1 h, let it stand for 24 h, add dilute hydrochloric acid to adjust the suspension pH to 6.8, and then place it in a high-speed emulsifier disperser at 5×10 4 r / min for 10 min to obtain a kaolin nanosuspension.

[0044] S2. Add 22 mL of anhydrous acetic acid and 10 mL of acetic anhydride in a volume ratio into a reaction container, add 8 g of benzoic acid and 28 g of hexamethylenetetramine, stir and heat, add paraformaldehyde, and condense and reflux under heating to 125° C. to obtain an intermediate.

[0045] S3. Add 3 g of the intermediate, 5 g of concentrated sulfuric acid and 23 g of water into a reaction container, heat to 90° C. and react for 3 h. After the reaction, cool, add ice water to wash 4 times, filter, and dry to obtain 5-carboxyisophthalaldehyde.

[0046] S4. Add 40 g of urea and 200 mL of water to a reaction container, stir, heat to 30°C until the urea is completely dissolved, adjust the pH to acidic, add 10 g of 5-carboxyisophthalaldehyde, heat to 60°C, react for 5 hours, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer.

[0047] S5. 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched urea polymer, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, thereby obtaining a mixed fertilizer.

[0048] S6. Dilute the kaolin nano suspension to 0.4% of the mass of kaolin, add the diluted kaolin nano suspension and mixed fertilizer into a high-speed emulsifying disperser for dispersion, and let stand for 9 hours after dispersion to obtain a nano suspension slow-release liquid fertilizer.

[0049] Comparative Example 1:

[0050] S1. 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol, and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, to obtain a mixed fertilizer, and the mixed fertilizer is added into a high-speed emulsifying disperser for dispersion, and after dispersion, it is allowed to stand for 5 hours to obtain a nano-suspended slow-release liquid fertilizer.

[0051] Comparative Example 2:

[0052] S1. Add 18 mL of anhydrous acetic acid and 10 mL of acetic anhydride in a volume ratio into a reaction container, add 8 g of benzoic acid and 32 g of hexamethylenetetramine, stir and heat, add paraformaldehyde, heat to 120° C., condense and reflux to obtain an intermediate.

[0053] S2. Add 3 g of the intermediate, 5 g of concentrated sulfuric acid and 20 g of water into a reaction container, heat to 90° C. and react for 5 h. After the reaction, cool, add ice water to wash 4 times, filter, and dry to obtain 5-carboxyisophthalaldehyde.

[0054] S3. Add 40 g of urea and 200 mL of water to a reaction container, stir, heat to 30°C until the urea is completely dissolved, adjust the pH to acidic, add 10 g of 5-carboxyisophthalaldehyde, heat to 60°C, react for 5 hours, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer.

[0055] S4, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched urea-formaldehyde polymer, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, to obtain a mixed fertilizer, the mixed fertilizer is added into a high-speed emulsifying disperser for dispersion, and after dispersion, it is allowed to stand for 5 hours to obtain a nano-suspended slow-release liquid fertilizer.

[0056] Comparative Example 3:

[0057] S1. Grind the kaolin slurry, add it into water after grinding, and prepare a mixed suspension of 30g kaolin and 45g water. Add potassium hydroxide solution dropwise to the suspension until it is alkaline, place it in a high-speed emulsifier and disperse it at 5×10 4 r / min for 3 h, let it stand for 36 h, add dilute hydrochloric acid to adjust the suspension pH to 6.8, and then place it in a high-speed emulsifier disperser at 5×10 4 r / min for 20 min to obtain a kaolin nanosuspension.

[0058] S2. 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of diurea trialdehyde polymer, 10 parts by weight of phosphate, and 5 parts by weight of potassium dihydrogen phosphate are mixed with water, and then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylenephosphoric acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are added and mixed evenly to obtain a mixture, thereby obtaining a mixed fertilizer.

[0059] S3. Dilute the kaolin nano suspension to 0.1% of the mass of kaolin, add the diluted kaolin nano suspension and mixed fertilizer into a high-speed emulsifying disperser for dispersion, and let stand for 5 hours after dispersion to obtain nano suspension slow-release liquid fertilizer.

[0060] 10mL of urea weighed from the nano-suspended slow-release liquid fertilizer was placed in a wide-mouth bottle containing 100mL of distilled water, placed in a 25°C incubator, and sampled every 48h until the 20th day of nutrient release. After each sampling, all the leachate in the wide-mouth bottle was poured out, and 100mL of distilled water was added to continue culturing in a 25°C incubator. The cumulative release rate of urea was measured three times, and the average value was taken to characterize the nutrient release.

[0061] Each urea-formaldehyde liquid slow-release fertilizer sample was tested three times, and the total nitrogen content of the urea-formaldehyde liquid slow-release fertilizer was 28%. One of the synthetic raw materials for urea-formaldehyde liquid slow-release fertilizer is formaldehyde aqueous solution. Due to incomplete chemical conversion, the product will contain different concentrations of free formaldehyde. The formaldehyde tester was used to test it three times, and the automatic nitrogen analyzer method was used to determine the total nitrogen content three times. The average value was taken to obtain the test result.

[0062] Effects of nano-suspended slow-release liquid fertilizer nutrients on fruits and vegetables, cabbage area 28.5m 2 , 7.5kg chicken manure fertilizer was applied as base fertilizer in each plot of random block group, and it was spread and covered with soil before planting. The amount of liquid fertilizer applied to each group was consistent and used in 3 times: the first topdressing was 10 days after transplanting, and the amount of fertilizer was 30% of the total amount; the second topdressing was 17 days after transplanting, and the amount of fertilizer was 40% of the total amount; the third topdressing was 27 days after transplanting, and the amount of fertilizer was 30% of the total amount. The liquid fertilizer was diluted with water and then sprinkled. Each group kept the same amount of water for each fertilization. The yield of each area was counted during the harvest period of Chinese cabbage, and 6 plants were collected. The vitamin C, soluble sugar and nitrate content of agricultural products were determined according to the principles and technical methods of plant physiological and biochemical experiments.

[0063] Table 1 is the test results of nutrient slow release of nano-suspension slow-release liquid fertilizer

[0064]

[0065] Table 2 shows the vitamin C, soluble sugar and nitrate content of agricultural products to which liquid fertilizers were applied.

[0066] VC (mg / 100g) Soluble sugar (%) Nitrate (mg / kg) Example 1 25.66 1.76 2003 Example 2 25.85 1.69 1987 Example 3 24.11 1.68 1889 Example 4 24.06 1.57 1994 Comparative Example 1 21.14 1.41 1653 Comparative Example 2 22.23 1.49 1766 Comparative Example 3 22.97 1.50 1842

[0067] As shown in Tables 1-2, the nutrient cumulative release rate and free formaldehyde mass fraction in Examples 1-4 are lower than those in Comparative Examples 1-3, the total nitrogen content in Examples 1-4 is higher than that in Comparative Examples 1-3, and the vitamin C, soluble sugar and nitrate contents of the agricultural products in Examples 1-4 are higher than those in Comparative Examples 1-3; because benzoic acid and hexamethylenetetramine are used to prepare an intermediate under the action of anhydrous acetic acid, acetic anhydride and paraformaldehyde, and the intermediate is subjected to a hydrolysis reaction to obtain 5-carboxyisophthalaldehyde, and the carboxyl and aldehyde groups on 5-carboxyisophthalaldehyde react with the amino groups on urea, the hyperbranched aldehyde-urea resin has a lower curing temperature and better thermal stability, can maintain stable performance, can provide slow and stable nitrogen nutrition, and the free formaldehyde content in the hyperbranched aldehyde-urea resin is significantly reduced, which is higher than that of aldehyde-urea. The resin is more environmentally friendly; the hyperbranched aldehyde-urea polymer contains multiple carbamate groups in its structure, which can be combined with nitrogen fertilizer to form a macromolecular nitrogen chain; the carboxyl group on 5-carboxyisophthalaldehyde and the amino group on urea can undergo a dehydration condensation reaction to form a peptide bond, which can adsorb metals in the soil and improve heavy metal pollution in the soil; this polymer has a high molecular weight and a complex network structure, can effectively control the release time of nitrogen nutrients, so that the effective period of nitrogen fertilizer reaches 50-60 days; kaolin nano suspension can wrap mixed fertilizers, so that nutrients can be continuously absorbed by crops, and nutrients can be provided slowly and continuously. The total nitrogen content in Examples 1-4 is higher than that in Comparative Examples 1-3, and the vitamin C, soluble sugar and nitrate contents of the agricultural products in Examples 1-4 are higher than those in Comparative Examples 1-3.

[0068] Comparing Comparative Example 1 with Example 1, the cumulative nutrient release rate and the free formaldehyde mass fraction in Example 1 are lower than those in Comparative Example 1, the total nitrogen content in Example 1 is higher than that in Comparative Example 1, the vitamin C, soluble sugar and nitrate contents of the agricultural product in Example 1 are higher than those in Comparative Example 1, and Comparative Example 1 does not add hyperbranched urea resin and kaolin nanosuspension, and cannot provide nutrients slowly and continuously, indicating that the nutrient sustained release effect of the comparative example is not good.

[0069] Comparing Example 2 with Example 1, the cumulative nutrient release rate and the free formaldehyde mass fraction in Example 1 are lower than those in Comparative Example 2, the total nitrogen content in Example 1 is higher than that in Comparative Example 2, and the vitamin C, soluble sugar and nitrate contents of the agricultural product in Example 1 are higher than those in Comparative Example 2. Comparative Example 2 does not add kaolin nanosuspension, which can wrap urea and enable urea to slowly and continuously provide nutrients. Without adding kaolin nanosuspension, the nutrient sustained release effect is not good.

[0070] Comparative Example 3 is compared with Example 1. The nutrient cumulative release rate and free formaldehyde mass fraction in Example 1 are lower than those in Comparative Example 3. The total nitrogen content in Example 1 is higher than that in Comparative Example 3. The vitamin C, soluble sugar and nitrate content of the agricultural product in Example 1 are higher than those in Comparative Example 3. In Comparative Example 3, the hyperbranched aldehyde-urea polymer is replaced with a diurea-trialdehyde polymer, and the properties of the hyperbranched polymer are more stable, the release of formaldehyde is lower, and it is more environmentally friendly. Although the diurea-trialdehyde polymer also has a certain slow-release effect, the stability and slow-release property are not as good as the hyperbranched polymer, so the nutrient slow-release effect of Comparative Example 3 is not good.

Claims

1. A method for preparing a nano-suspension slow-release liquid fertilizer, characterized in that: The following steps are involved: S1. Add anhydrous acetic acid and acetic anhydride to a reaction vessel, add benzoic acid and hexamethylenetetramine, stir and heat, add paraformaldehyde, heat to 120-130° C., condense and reflux for 3-4 hours to obtain an intermediate; S2, adding the intermediate, concentrated sulfuric acid and water to a reaction vessel, heating to 90° C. for reaction for 1-5 hours, cooling after the reaction, washing with ice water for 3-4 times, filtering, and drying to obtain 5-carboxyisophthalaldehyde; S3, add urea and water to a reaction container, stir, heat to 30-40°C until urea is completely dissolved, adjust the pH to acidic, add 5-carboxyisophthalaldehyde, heat to 50-60°C, react for 5-6h, and after the reaction is completed, heat and concentrate, wash, and dry to obtain a hyperbranched aldehyde-urea polymer; S4, adding water to ammonium polyphosphate, methylene urea nitrogen, hyperbranched urea polymer, phosphate, and potassium dihydrogen phosphate to mix, and then adding maleic acid, ethylenediaminetetramethylenephosphoric acid, humic acid, and a stabilizer to mix evenly to obtain a mixture to obtain a mixed fertilizer; S5. Add water to the kaolin nano suspension, and then add the diluted kaolin nano suspension and mixed fertilizer into a high-speed emulsifying disperser for dispersion. After dispersion, let stand for 5-10 hours to obtain a nano-suspension slow-release liquid fertilizer.

2. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that: In step S1, the volume ratio of anhydrous acetic acid to acetic anhydride is (1.8-2.2):

1.

3. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that: In step S1, the mass ratio of benzoic acid to hexamethylenetetramine is 1:(3-4).

4. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that: In step S2, the volume ratio of concentrated sulfuric acid to water is 1:(4-5).

5. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that: In step S3, the volume ratio of 5-carboxyisophthalaldehyde to urea is 1:(3-4).

6. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that: In step S4, the stabilizer is one or more of sorbitol and mannitol.

7. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that: In step S5, the kaolin nano suspension is added to water, and the mass ratio of the kaolin nano suspension to water is (0.1-0.5):

100.

8. The nano-suspension slow-release liquid fertilizer according to claim 1, wherein the kaolin nano-suspension is prepared by grinding kaolin slurry, adding the ground kaolin slurry into water to prepare a suspension of kaolin and water, adding an alkaline solution dropwise to the suspension until the suspension becomes alkaline, placing the suspension in a high-speed emulsifying disperser, and 4 -5×10 4 r / min for 1-3h, let it stand for 24-36h, add dilute hydrochloric acid to adjust the suspension pH to 6.8-7.2, and then place it in a high-speed emulsifier disperser at 3×10 4 -5×10 4 r / min for 10-20 min to obtain a kaolin nanosuspension.

9. The nano-suspension slow-release liquid fertilizer according to claim 8, characterized in that: The mass ratio of kaolin to water in the suspension is 1:(1.5-1.7).

10. The nano-suspension slow-release liquid fertilizer according to claim 8, characterized in that: The suspension is added dropwise with an alkaline solution to make it alkaline, and the alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

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