A kind of lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer and preparation method thereof

Abstract

The invention discloses a lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer and a preparation method thereof, and belongs to the technical field of slow-release fertilizers. The preparation method comprises: adding biomass to an alkaline solution for heating treatment, adding biomass to an acidic solution for heating treatment, and collecting a reaction solution; adding urea to the reaction solution, reacting under heating conditions, obtaining an ammonium polyphosphate-lignocellulose mixture, grinding it into powder, and then adding the powder to a potassium persulfate solution to obtain a suspension; adding potassium hydroxide, acrylic acid, acrylamide, urea and MBA to water under heating and nitrogen protection to obtain a mixed solution; mixing the suspension with the mixed solution, heating and reacting under nitrogen and stirring conditions, cutting into pieces and drying to obtain the slow-release fertilizer, which has good water and fertilizer retention capacity, strong slow-release capacity, soil structure improvement capacity and heavy metal adsorption potential, and effectively solves the problems of poor water retention capacity and poor soil improvement effect in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of slow-release fertilizers, and in particular relates to a lignocellulose-modified ammonium polyphosphate hydrogel slow-release fertilizer and a preparation method thereof. Background Art

[0002] Ammonium polyphosphate (APP) is a polyphosphate containing nitrogen and phosphorus. It is a long-chain compound composed of -POP- chains. Its molecular formula is (NH4) n+2 P n O 3n+1 , when n is large enough, it can be written as (NH4PO3) n Type I or amorphous APP often has a lower degree of polymerization and exhibits good water solubility. It is often used as a high-concentration fertilizer containing nitrogen and phosphorus elements. APP products have the advantages of improving soil agglomeration and compaction, regulating soil pH, and not being easily fixed and precipitated by soil iron and calcium ions. This allows phosphorus to move longer in the soil and more easily reach the roots of crops, promoting the absorption and utilization of phosphorus and trace elements by crops, and slow release and long-term effectiveness.

[0003] In addition, there are still many problems in the current agricultural system, such as high porosity, high irrigation and low fertilizer retention. The application effect of ammonium polyphosphate in acidic soil is also not ideal. Therefore, materials with the ability to isolate soil, repair soil, absorb large amounts of water and release it in combination with fertilizer for a long time may become a solution. For this reason, slow-release fertilizer hydrogel came into being.

[0004] Slow-release fertilizer hydrogel is often used in the slow-release process of N fertilizer due to its excellent slow-release performance. Ammonium polyphosphate, as a typical nitrogen-phosphorus compound fertilizer, can also be used as a fertilizer component in slow-release fertilizer hydrogel. On the one hand, the slow-release property of ammonium polyphosphate itself makes the release of N in the hydrogel system slower, improving the utilization efficiency of N and P; on the other hand, the isolation effect of the hydrogel can reduce the impact of the soil on ammonium polyphosphate, so that it can achieve a better release effect under acidic soil conditions. In addition, the porous hydrogel structure also shows excellent performance in soil repair and adsorption of soil heavy metals. However, most of the current porous hydrogels have the problems of poor water retention capacity and poor soil improvement effect. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer and a preparation method thereof. The slow-release fertilizer has good water and fertilizer retention capacity, strong slow-release capacity, ability to improve soil structure and potential for adsorbing heavy metals, effectively solving the problems of poor water retention capacity and poor soil improvement effect in the prior art.

[0006] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0007] A method for preparing a lignocellulose-modified ammonium polyphosphate hydrogel slow-release fertilizer comprises the following steps:

[0008] (1) adding the biomass into an alkaline solution and heating it, then adding the biomass into an acidic solution and continuing the heating, and collecting the reaction solution;

[0009] (2) adding urea to the reaction solution, reacting under heating conditions, filtering to obtain an ammonium polyphosphate-lignocellulose mixture, grinding the mixture into powder, and then adding the mixture into a potassium persulfate solution and mixing to obtain a suspension;

[0010] (3) Under heating and nitrogen protection conditions, potassium hydroxide, acrylic acid, acrylamide, urea and MBA are added to water in sequence and mixed to obtain a mixed solution;

[0011] (4) The suspension in step (2) is mixed with the mixed solution in step (3), and the mixture is heated under nitrogen protection and stirring to complete the reaction, and the mixture is cut into pieces and dried to obtain the product.

[0012] Furthermore, in step (1), the alkaline solution comprises a KOH solution with a concentration of 0.5-10%, a NaOH solution with a concentration of 0.5-10%, or an ammonia solution with a concentration of 2-30%. The mass ratio of the biomass to the alkaline solution is 1:5-100. The heating treatment temperature in the alkaline solution is 40-90° C., and the treatment time is 10-480 min.

[0013] Furthermore, in step (1), the acidic solution is a phosphoric acid solution; the mass ratio of the biomass to the phosphoric acid solution is 1:5-100; the treatment temperature in the acidic solution is 60-130° C., and the treatment time is 30-480 min.

[0014] Furthermore, in step (2), the heating reaction temperature is 150-280° C., and the reaction time is 30-240 min.

[0015] Furthermore, in step (2), the N / P molar ratio of the N element in the urea to the P element in the reaction solution is 1.2-4:1.

[0016] Furthermore, in step (2), the mass ratio of the ammonium polyphosphate-lignocellulose mixture to potassium persulfate is 5-20:1, and the mass proportion of the ammonium polyphosphate-lignocellulose in the suspension is 4-6%.

[0017] Furthermore, in step (3), the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA is 30-60:100:10-100:10-50:0.5-2.5; and the mass concentration of acrylic acid in the mixed solution is 4-6%.

[0018] Furthermore, in step (4), the volume ratio of the suspension to the mixed solution is 1-2:1-2.

[0019] Furthermore, in step (4), the heating temperature is 30-90° C., the reaction time is 10-180 min, and the stirring speed is 60-300 rpm.

[0020] A lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer is prepared by the method.

[0021] The beneficial effects produced by the present invention are:

[0022] 1. In the present invention, lignocellulose-modified ammonium polyphosphate is used as the matrix of the hydrogel slow-release fertilizer, and it is introduced into the hydrogel system by in-situ polymerization, which can greatly enhance the slow-release performance. The slow-release period of nutrients such as nitrogen and phosphorus is increased from the original two months to more than one year, which greatly improves the slow-release effect of the slow-release fertilizer.

[0023] 2. The present invention innovatively introduces lignocellulose into ammonium polyphosphate. The two are linked by ester bonds and hydrogen bonds, which effectively increases the amount of ammonium polyphosphate introduced into the hydrogel system and improves the mechanical properties of the hydrogel, so that the ammonium polyphosphate-lignocellulose hydrogel can maintain a fairly good shape after absorbing water and swelling, ensuring its effectiveness in application.

[0024] 3. The present invention innovatively adopts an in-situ treatment model, processing biomass such as lignocellulose into small molecular sugars and organic matter through an alkaline hydrolysis followed by an acid hydrolysis process and organically combining them with phosphorus at the same time, so that the organic carbon content in the soil can be increased and a synergistic effect can be exerted.

[0025] 4. The ammonium polyphosphate lignocellulose hydrogel slow-release fertilizer produced in the present invention has stronger water absorption and water retention performance than ordinary hydrogel slow-release fertilizers. After being applied to the soil, its excellent porous structure can absorb heavy metals in the soil and improve the soil structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the slow-release fertilizer in the present invention;

[0027] Figure 2 The figures are the physical pictures of the hydrogels in Example 1 and Comparative Example 1 and the physical pictures before and after swelling due to water absorption;

[0028] Figure 3 This is the distribution diagram of phosphorus in the hydrogel in Example 1, where the abscissa is the residence time and the ordinate is the ion concentration. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments.

[0030] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0031] It should be noted that relational terms such as "first" and "second" are used only 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", "comprises" 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. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0032] The features and performance of the present invention are further described in detail below in conjunction with the embodiments and drawings.

[0033] Example 1

[0034] A lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer, the preparation method of which comprises the following steps:

[0035] (1) Clean wheat straw was added to a 4% KOH solution at a mass ratio of 1:20 and heated to 90°C for 60 min. Then the wheat straw was added to a 38% phosphoric acid solution and heated to 120°C for 90 min. The reaction solution was collected.

[0036] (2) adding urea to the reaction solution so that the N / P molar ratio is 1.8, then heating to 220°C for 120 min, filtering to obtain an ammonium polyphosphate-lignocellulose mixture, ball-milling the mixture into powder, and then adding the mixture into a potassium persulfate solution and mixing. The mass ratio of the ammonium polyphosphate-lignocellulose mixture to potassium persulfate is 20:1 to obtain a suspension. The mass ratio of ammonium polyphosphate-lignocellulose in the suspension is 5%.

[0037] (3) At 70°C and under nitrogen protection, potassium hydroxide, acrylic acid, acrylamide, urea and MBA were added to water in sequence, the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA was 33:100:50:33:2.5, and stirred for 15 minutes to obtain a mixed solution. The mass concentration of acrylic acid in the mixed solution was 5%;

[0038] (4) The suspension in step (2) and the mixed solution in step (3) were mixed in a volume ratio of 1:1, heated to 60° C. under nitrogen protection and stirring at 150 rpm for 60 min, cut into pieces and dried to obtain.

[0039] Example 2

[0040] A lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer, the preparation method of which comprises the following steps:

[0041] (1) Add clean corn cobs to a 10% NaOH solution at a mass ratio of 1:10 and heat to 70°C for 100 min. Then add the corn cobs to a 38% phosphoric acid solution and continue heating to 90°C for 200 min. Collect the reaction solution.

[0042] (2) adding urea to the reaction solution so that the N / P molar ratio is 3:1, then heating to 280°C for 40 min, filtering to obtain an ammonium polyphosphate-lignocellulose mixture, ball-milling the mixture into powder, and then adding the mixture into a potassium persulfate solution and mixing. The mass ratio of the ammonium polyphosphate-lignocellulose mixture to potassium persulfate is 15:1 to obtain a suspension. The mass ratio of ammonium polyphosphate-lignocellulose in the suspension is 6%.

[0043] (3) At 90°C and under nitrogen protection, potassium hydroxide, acrylic acid, acrylamide, urea and MBA were added to water in sequence, the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA was 60:100:100:50:1.5, and stirred for 15 minutes to obtain a mixed solution, the mass concentration of acrylic acid in the mixed solution was 4-6%;

[0044] (4) The suspension in step (2) and the mixed solution in step (3) were mixed in a volume ratio of 1:1, heated to 90° C. under nitrogen protection and stirring at 300 rpm for 20 min, cut into pieces and dried to obtain.

[0045] Example 3

[0046] A lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer, the preparation method of which comprises the following steps:

[0047] (1) Add cellulose to a 6% KOH solution at a mass ratio of 1:40 and heat to 40°C for 480 min. Then add cellulose to a 38% phosphoric acid solution and continue heating to 70°C for 480 min. Collect the reaction solution.

[0048] (2) adding urea to the reaction solution so that the N / P molar ratio is 4:1, then heating to 160°C for reaction for 200 min, filtering to obtain an ammonium polyphosphate-lignocellulose mixture, ball-milling the mixture into powder, and then adding the mixture into a potassium persulfate solution and mixing. The mass ratio of the ammonium polyphosphate-lignocellulose mixture to potassium persulfate is 10:1 to obtain a suspension. The mass ratio of ammonium polyphosphate-lignocellulose in the suspension is 4%.

[0049] (3) At 50°C and under nitrogen protection, potassium hydroxide, acrylic acid, acrylamide, urea and MBA were added to water in sequence, the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA was 40:100:25:15:1, and stirred for 15 minutes to obtain a mixed solution. The mass concentration of acrylic acid in the mixed solution was 4%;

[0050] (4) The suspension in step (2) and the mixed solution in step (3) were mixed in a volume ratio of 1:1, heated to 40° C. under nitrogen protection and stirred at 80 rpm for 100 min, cut into pieces and dried to obtain.

[0051] Example 4

[0052] A lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer, the preparation method of which comprises the following steps:

[0053] (1) Add bagasse to a KOH solution with a mass ratio of 1:60 and heat to 60°C for 250 min. Then add bagasse to a phosphoric acid solution with a concentration of 38% and continue to heat to 80°C for 300 min. Collect the reaction solution.

[0054] (2) adding urea to the reaction solution so that the N / P molar ratio is 2:1, then heating to 240°C for 180 min, filtering to obtain an ammonium polyphosphate-lignocellulose mixture, ball-milling the mixture into powder, and then adding the mixture into a potassium persulfate solution and mixing. The mass ratio of the ammonium polyphosphate-lignocellulose mixture to potassium persulfate is 5:1 to obtain a suspension. The mass ratio of ammonium polyphosphate-lignocellulose in the suspension is 5%;

[0055] (3) At 30°C and under nitrogen protection, potassium hydroxide, acrylic acid, acrylamide, urea and MBA were added to water in sequence, the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA was 50:100:70:45:1.5, and stirred for 15 minutes to obtain a mixed solution. The mass concentration of acrylic acid in the mixed solution was 4%;

[0056] (4) The suspension in step (2) and the mixed solution in step (3) were mixed in a volume ratio of 1:1, heated to 50° C. under nitrogen protection and stirring at 200 rpm for 180 min, cut into pieces and dried to obtain.

[0057] Comparative Example 1

[0058] An ammonium polyphosphate hydrogel, the preparation method of which comprises the following steps:

[0059] (1) At 70°C and under nitrogen protection, potassium hydroxide, acrylic acid, acrylamide, urea and MBA were added to water in sequence, the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA was 33:100:50:33:2.5, and stirred for 15 minutes to obtain a mixed solution. The mass concentration of acrylic acid in the mixed solution was 5%;

[0060] (2) ammonium polyphosphate and potassium persulfate are mixed with water to prepare a suspension, wherein the concentration of potassium persulfate is 0.5%; ammonium polyphosphate is prepared by heating monoammonium phosphate and urea to 240°C for 180 minutes at an N / P molar ratio of 2.0, wherein the mass ratio of ammonium polyphosphate to potassium persulfate is 15:1.

[0061] (3) The mixed solution of step (1) and the suspension of step (2) were mixed in a volume ratio of 1:1, heated to 60° C. under nitrogen protection and stirring at 150 rpm for 60 min, cut into pieces and dried to obtain.

[0062] Comparative Example 2

[0063] A hydrogel, the preparation method of which comprises the following steps:

[0064] (1) At 70°C and under nitrogen protection, potassium hydroxide, acrylic acid, acrylamide, urea and MBA were added to water in sequence, the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA was 33:100:50:33:2.5, and stirred for 15 minutes to obtain a mixed solution. The mass concentration of acrylic acid in the mixed solution was 5%;

[0065] (2) Potassium persulfate was mixed with water to prepare a blank suspension with a potassium persulfate concentration of 0.5%;

[0066] (3) The mixed solution of step (1) and the blank suspension of step (2) were mixed in a volume ratio of 1:1, heated to 60° C. under nitrogen protection and stirring at 150 rpm for 60 min, cut into pieces and dried to obtain.

[0067] Test example

[0068] Taking the hydrogels in Example 1, Comparative Example 1 and Comparative Example 2 as examples, the phosphorus polymerization degree, water absorption rate (g / g), water retention time, mechanical capacity and 70% nutrient release time (days) of different hydrogels were measured. The specific measurement methods and results are shown in Table 1.

[0069] The phosphorus polymerization degree is determined according to HG / T 5939-2021 standard;

[0070] Absorption rate determination: Weigh the dry hydrogel sample, soak it in water for 2 hours, take it out, wipe off the water on the surface, weigh it, and then use the formula water absorption rate = (weight after water absorption - dry mass) / dry mass * 100%;

[0071] Determination of water retention time: Weigh the dried hydrogel sample, record the initial mass, place it in a constant temperature and humidity environment, and measure its weight at regular intervals until the weight remains essentially unchanged. The time required for this process is the water retention time;

[0072] Mechanical capacity measurement: Soak the dry hydrogel in water until it is saturated with water, then apply the same amount of pressure to different hydrogels to observe the integrity of the hydrogel;

[0073] Determination of 70% nutrient release time: Place the hydrogel in water, take it out at different intervals, dry it, and determine the nutrient content therein. The time interval for 70% nutrient release is the 70% nutrient release time.

[0074] Table 1: Test results of different hydrogels

[0075]

[0076] The unit of water absorption, g / g, refers to the weight of pure water that can be absorbed by each gram of hydrogel;

[0077] It can be seen from the data in the above table that the hydrogel prepared by the method in the present application has a higher degree of phosphorus polymerization, a higher water absorption rate and a water retention time, and has excellent mechanical properties, a long nutrient release time, and good sustained release properties.

[0078] Figure 1 Schematic diagram of the structure of the slow-release fertilizer in the present invention. It can be seen that there are a large number of pore structures inside the hydrogel in the present invention;

[0079] Figure 2The figures are the physical pictures of the hydrogels in Example 1 and Comparative Example 1 and the physical pictures before and after water absorption and swelling. It can be seen that the structure of the hydrogel in the present application is relatively intact after water absorption, while the hydrogel in Example 1 directly breaks into blocks after water absorption;

[0080] Figure 3 This is a distribution diagram of phosphorus in the hydrogel in Example 1. The results show that ammonium polyphosphate is formed in the hydrogel in Example 1.

Claims

1. A method for preparing a lignocellulose-modified ammonium polyphosphate hydrogel slow-release fertilizer, characterized in that: The following steps are involved: (1) adding the biomass to an alkaline solution and heating it, then adding the biomass to an acidic solution and continuing the heating, and collecting the reaction solution; the alkaline solution includes a 0.5-10% KOH solution, a 0.5-10% NaOH solution, or a 2-30% ammonia solution; The mass ratio of biomass to alkaline solution is 1:5-100; the heating treatment temperature in the alkaline solution is 40-90°C, and the treatment time is 10-480min; the acidic solution is a phosphoric acid solution; the mass ratio of biomass to phosphoric acid solution is 1:5-100; the treatment temperature in the acidic solution is 60-130°C, and the treatment time is 30-480min; (2) adding urea to the reaction solution, and then reacting at 150-280° C. for 30-240 min, filtering to obtain an ammonium polyphosphate-lignocellulose mixture, grinding the mixture into powder, and then adding the mixture into a potassium persulfate solution to mix well to obtain a suspension; the N / P molar ratio of the N element in the urea to the P element in the reaction solution is 1.2-4:1; the mass ratio of the ammonium polyphosphate-lignocellulose mixture to the potassium persulfate is 5-20:1, and the mass proportion of the ammonium polyphosphate-lignocellulose in the suspension is 4-6%; (3) under heating and nitrogen protection conditions, potassium hydroxide, acrylic acid, acrylamide, urea and MBA are added to water in sequence and mixed to obtain a mixed solution, wherein the mass ratio of potassium hydroxide, acrylic acid, acrylamide, urea and MBA is 30-60:100:10-100:10-50:0.5-2.5; the mass concentration of acrylic acid in the mixed solution is 4-6%; (4) mixing the suspension in step (2) with the mixed solution in step (3) in a volume ratio of the suspension to the mixed solution of 1-2:1-2, heating to 30-90° C. under nitrogen protection and stirring at 60-300 rpm, reacting for 10-180 min, cutting into pieces and drying to obtain the product.

2. A lignocellulose modified ammonium polyphosphate hydrogel slow-release fertilizer, characterized in that: The method according to claim 1 is used to prepare the product.

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