Cationic acrylamide polymer and application thereof in saline-alkali soil improvement

Abstract

The invention provides a cationic acrylamide polymer and application thereof in saline-alkali soil improvement, and belongs to the technical field of soil improvement. The cationic acrylamide polymer is lignin-based cationic polyacrylamide, and is prepared by the following method: (1) preparing cationic polyacrylamide from acrylamide and cocamidopropyl PG-dimethyl ammonium chloride; and (2) reacting the cationic polyacrylamide obtained in the step (1) with lignin to obtain the lignin-based cationic polyacrylamide. The cationic polyacrylamide is prepared by taking cocamidopropyl PG-dimethyl ammonium chloride as a raw material, chlorine atoms on the cocamidopropyl PG-dimethyl ammonium chloride react with phenolic hydroxyl groups on lignin, so that more lignin can be grafted onto the polyacrylamide, and when the polymer is used for soil improvement, the soil fertility can be better improved; and the effect of improving the soil aggregate structure is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of soil improvement, and in particular relates to a cationic acrylamide polymer and application thereof in saline-alkali land improvement. Background Art

[0002] With the continuous development of society, soil resources are seriously insufficient, and due to some unreasonable utilization, such as large-scale unreasonable application of fertilizers, excessive spraying of pesticides, over-grazing, etc., the soil has been seriously degraded. The main manifestations are soil compaction and hardening, erosion, salinization, acidification, element imbalance, chemical pollution, organic matter loss and degradation of flora and fauna. The result of soil degradation is reduced soil productivity, reduced crop quality, and even enrichment of toxic elements. Therefore, how to maintain soil quality, improve acid-base soil, eliminate soil toxicity, and reduce the spread of soil-borne diseases has become the focus of people's attention.

[0003] The application of soil conditioners is one of the important measures to repair degraded soil. Soil conditioners can effectively improve the physical and chemical properties of soil and soil nutrient status, and have a positive effect on soil microorganisms, thereby improving the productivity of degraded soil. Soil properties include soil results, soil water content, soil temperature, soil enzyme activity, soil microbial population, soil aeration conditions, soil solution concentration, and soil hydrogen ion concentration. Different types of soil conditioners have different mechanisms of action on the soil, but they all effectively improve the physical structure of the soil, reduce soil bulk density, increase soil water content, change soil chemical properties, increase soil microbial activity, increase enzyme activity, increase soil trace element content, and adjust some or all of the soil water, fertilizer, air, and heat conditions to ultimately achieve the purpose of improving soil fertility.

[0004] Polyacrylamide has good water solubility and flocculation due to the large number of amide groups it contains. In addition, the highly active amide groups of polyacrylamide can be artificially controlled through chemical reactions such as hydrolysis, degradation, aminomethylation, and hydroxymethylation. After grafting or cross-linking, various modified substances obtain branched or network structures and thus obtain target performance. Therefore, polyacrylamide has been widely used as a "hundred-industry additive" in the oil extraction, water treatment, agriculture and other industries. Polyacrylamide with a high degree of polymerization and molecular weight is often used to improve soil structure. After application, as polyacrylamide is lost over time, it will gradually transform into non-toxic and harmless substances to the environment due to mechanical fracture, chemical hydrolysis, biological hydrolysis, photolysis and other processes, such as water, carbon dioxide, ammonium nitrogen, etc., and will not destroy the acid-base balance of the soil. It is an environmentally friendly soil conditioner.

[0005] For example, Chinese patent CN103351870A discloses a soil conditioner, which includes the following components in weight ratio: 10-15 of acrylamide-acrylate copolymer crosslinked product, 20-30 of acrylamide-sodium acrylic acid copolymer, and 55-60 of montmorillonite, and is formed by chelating the components. The soil conditioner is a light yellow powder particle, which is mixed with soil to form a very loose aggregate structure soil after agglomeration reaction and hydrophobic reaction. The aggregate structure soil has an excellent solid-liquid-gas three-phase structure of fertilizer retention, water retention, and air permeability, which is greatly beneficial to the growth of plant roots.

[0006] For example, Chinese patent CN107418585A discloses a saline-alkali soil conditioner, which includes the following components by mass: 30-60 parts of polymaleic acid, 10-30 parts of acrylic acid-2-acrylamide-2-methylpropanesulfonic acid multipolymer, 1-2 parts of surfactant, and water to 100 parts. The soil conditioner provided by the present invention can effectively change the salt content of saline-alkali soil, reduce the alkalinity of saline-alkali soil, improve the state of soil particles, and improve the water retention performance of soil.

[0007] However, there are few studies on cationic polyacrylamide in the prior art, and there are few studies on its use as a soil conditioner to increase soil fertility and microbial content. Therefore, it is necessary to develop a cationic acrylamide polymer that can effectively improve soil fertility and increase soil microbial content, and to study its soil improvement effect. Summary of the invention

[0008] Based on the deficiencies of the prior art, the present invention aims to provide a cationic acrylamide polymer, which is obtained by modifying acrylamide and has a high molecular weight. The cationic acrylamide polymer can effectively improve soil fertility and soil aggregate structure in saline-alkali land improvement.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] In one aspect, the present invention provides a cationic acrylamide polymer, wherein the cationic acrylamide polymer is a lignin-based cationic polyacrylamide, and is prepared by the following method:

[0011] (1) preparing cationic polyacrylamide from acrylamide and cocamidopropyl PG-dimethylammonium chloride;

[0012] (2) reacting the cationic polyacrylamide obtained in step (1) with lignin to obtain the lignin-based cationic polyacrylamide.

[0013] Preferably, the above step (1) further comprises a chain transfer agent, wherein the chain transfer agent is a mixture of 4-chloromethylstyrene and 2-mercaptoethanol, and the mass ratio of the two is 3-5:1; preferably 4:1.

[0014] Preferably, the above step (1) also includes an initiator, and the initiator is ammonium persulfate.

[0015] Preferably, the molar ratio of acrylamide to cocamidopropyl PG-dimethyl ammonium chloride is 1.5-5:1; preferably 2-4:1; more preferably 2.5-3.5:1; further preferably 3.5:1;

[0016] Preferably, the amount of the chain transfer agent added is 0.8-1.2% of the mass of acrylamide; preferably 0.9%.

[0017] Preferably, the amount of the initiator added is 3-5% of the mass of acrylamide; preferably 4.2%.

[0018] Preferably, the reaction temperature of step (1) is 55-70°C, preferably 65°C.

[0019] Preferably, the reaction time in step (1) is 8-12 hours, preferably 10 hours.

[0020] The mass ratio of cationic polyacrylamide to lignin in the above step (2) is 1-4:1; preferably 2.5-3.5:1; more preferably 2.5:1.

[0021] The reaction temperature of the above step (2) is 70-90°C, preferably 80°C.

[0022] The reaction time of the above step (2) is 3-6 hours, preferably 5 hours.

[0023] As a preferred embodiment, the lignin-based cationic polyacrylamide is prepared by the following method:

[0024] (1) acrylamide and cocamidopropyl PG-dimethylammonium chloride are added to a reactor in a molar ratio of 1.5-5:1, and then a mixture of 4-chloromethylstyrene and 2-mercaptoethanol (mass ratio of 3-5:1) with a mass ratio of 0.8-1.2% of the mass of acrylamide is added, the temperature is raised to 55-70° C. under nitrogen protection, and then ammonium persulfate with a mass ratio of 3-5% of the mass of acrylamide is added, and the reaction is continued under nitrogen protection for 8-12 hours. After the reaction is completed, alcohol precipitation is performed, and freeze-drying is performed to obtain cationic polyacrylamide;

[0025] (2) adding the cationic polyacrylamide obtained in step (1) and lignin in a mass ratio of 1-4:1 into a reactor, adding sodium hydroxide solution, heating to 70-90° C., reacting for 3-6 hours, purifying, and freeze-drying to obtain the lignin-based cationic polyacrylamide.

[0026] The actual cationic degree of the lignin-based cationic polyacrylamide prepared by the method of the present invention is 15.4-22.6%, and the lignin grafting rate is 37.3-50%.

[0027] The present invention also provides the use of the lignin-based cationic polyacrylamide in preparing a soil conditioner.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention selects suitable chain transfer agents and initiators to make the prepared lignin-based cationic polyacrylamide have a higher cationic degree, which has a better effect on soil improvement;

[0030] (2) The present invention uses cocamidopropyl PG-dimethyl ammonium chloride as a raw material to prepare cationic polyacrylamide, and then carries out a grafting reaction with lignin to obtain lignin-based cationic polyacrylamide. The chlorine atoms on the cocamidopropyl PG-dimethyl ammonium chloride react with the phenolic hydroxyl groups on the lignin to enable more lignin to be grafted onto the polyacrylamide. The polymer is used for soil improvement to have a better effect of improving soil fertility and improving soil aggregate structure. DETAILED DESCRIPTION

[0031] The above features mentioned in the present invention or the features mentioned in the embodiments can be combined in any way. All the features explained in the specification of this case can be used in combination with any method form, and each feature disclosed in the specification can be replaced by any alternative feature that can provide the same, equal or similar purpose. Therefore, unless otherwise specified, the disclosed features are only general examples of equal or similar features.

[0032] The present invention will be further described below in conjunction with specific examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In the following examples, the implementation methods for specifying specific conditions are usually based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, all percentages and fractions are by weight.

[0033] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those known to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein can be applied to the methods of the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only.

[0034] Example 1 Preparation method of lignin-based cationic polyacrylamide

[0035] Prepared by the following method:

[0036] (1) acrylamide and cocamidopropyl PG-dimethylammonium chloride are added to a reactor in a molar ratio of 1.5:1, and then a mixture of 4-chloromethylstyrene and 2-mercaptoethanol (mass ratio of 3:1) with a mass ratio of 0.8% of acrylamide is added, the temperature is raised to 55° C. under nitrogen protection, and then ammonium persulfate with a mass ratio of 3% of acrylamide is added, and the reaction is continued under nitrogen protection for 8 hours. After the reaction is completed, alcohol precipitation is performed, and freeze-drying is performed to obtain cationic polyacrylamide;

[0037] (2) adding the cationic polyacrylamide obtained in step (1) and lignin in a mass ratio of 1:1 into a reactor, adding a sodium hydroxide solution, heating to 70° C., reacting for 3 hours, purifying, and freeze-drying to obtain the lignin-based cationic polyacrylamide.

[0038] Example 2 Preparation method of lignin-based cationic polyacrylamide

[0039] Prepared by the following method:

[0040] (1) acrylamide and cocamidopropyl PG-dimethylammonium chloride are added to a reactor in a molar ratio of 5:1, and then a mixture of 4-chloromethylstyrene and 2-mercaptoethanol (mass ratio of 5:1) with a mass ratio of 1.2% of acrylamide is added, the temperature is raised to 70° C. under nitrogen protection, and then ammonium persulfate with a mass ratio of 5% of acrylamide is added, and the reaction is continued under nitrogen protection for 12 hours. After the reaction is completed, alcohol precipitation is performed, and freeze-drying is performed to obtain cationic polyacrylamide;

[0041] (2) adding the cationic polyacrylamide obtained in step (1) and lignin in a mass ratio of 4:1 into a reactor, adding sodium hydroxide solution, heating to 90° C., reacting for 6 hours, purifying, and freeze-drying to obtain the lignin-based cationic polyacrylamide.

[0042] Example 3 Preparation method of lignin-based cationic polyacrylamide

[0043] Prepared by the following method:

[0044] (1) acrylamide and cocamidopropyl PG-dimethylammonium chloride are added to a reactor in a molar ratio of 2.5:1, and then a mixture of 4-chloromethylstyrene and 2-mercaptoethanol (mass ratio of 3.5:1) with a mass ratio of 1.1% of acrylamide is added, the temperature is raised to 60° C. under nitrogen protection, and then ammonium persulfate with a mass ratio of 3.5% of acrylamide is added, and the reaction is continued under nitrogen protection for 9 hours. After the reaction is completed, alcohol precipitation is performed, and freeze-drying is performed to obtain cationic polyacrylamide;

[0045] (2) The cationic polyacrylamide obtained in step (1) and lignin are added into a reactor in a mass ratio of 2:1, a sodium hydroxide solution is added, the mixture is heated to 75° C., reacted for 4 hours, purified, and freeze-dried to obtain the lignin-based cationic polyacrylamide.

[0046] Example 4 Preparation method of lignin-based cationic polyacrylamide

[0047] Prepared by the following method:

[0048] (1) acrylamide and cocamidopropyl PG-dimethylammonium chloride are added to a reactor in a molar ratio of 3.5:1, and then a mixture of 4-chloromethylstyrene and 2-mercaptoethanol (mass ratio of 4:1) with a mass ratio of 0.9% of acrylamide is added, the temperature is raised to 65° C. under nitrogen protection, and then ammonium persulfate with a mass ratio of 4.2% of acrylamide is added, and the reaction is continued under nitrogen protection for 10 hours. After the reaction is completed, alcohol precipitation is performed, and freeze-drying is performed to obtain cationic polyacrylamide;

[0049] (2) adding the cationic polyacrylamide obtained in step (1) and lignin in a mass ratio of 2.5:1 into a reactor, adding sodium hydroxide solution, heating to 80° C., reacting for 5 hours, purifying, and freeze-drying to obtain the lignin-based cationic polyacrylamide.

[0050] Comparative Example 1

[0051] The difference from Example 4 is that cocamidopropyl PG-dimethyl ammonium chloride is replaced by dimethyl diallyl ammonium chloride, and the rest is the same as Example 4.

[0052] Comparative Example 2

[0053] The difference from Example 4 is that only 4-chloromethylstyrene is used as the chain transfer agent, and the rest is the same as Example 4.

[0054] Comparative Example 3

[0055] The difference from Example 4 is that only 2-mercaptoethanol is used as the chain transfer agent, and the rest is the same as Example 4.

[0056] Effect test

[0057] 1. Detection of cationic degree and phenolic hydroxyl content of lignin-based cationic polyacrylamide

[0058] Cationic content detection method: colloid titration method is used for detection.

[0059] Phenolic hydroxyl content detection method: detection by aqueous phase potentiometric titration;

[0060] Lignin grafting rate = [(phenolic hydroxyl content in lignin - phenolic hydroxyl content in lignin-based cationic polyacrylamide) / phenolic hydroxyl content in lignin] × 100%.

[0061] The test results are shown in Table 1 below.

[0062] Table 1

[0063] Cationicity % Phenolic hydroxyl content mmol / g Lignin grafting rate % Lignin - 1.02 - Example 1 20.4 0.62 39.2 Example 2 15.4 0.55 46.1 Example 3 21.8 0.64 37.3 Example 4 22.6 0.51 50.0 Comparative Example 1 12.2 0.75 26.5 Comparative Example 2 10.5 0.82 19.6 Comparative Example 3 9.8 0.78 23.5

[0064] According to the test results in Table 1 above, it can be seen that the lignin-based cationic polyacrylamide prepared by the present invention has a higher cationic degree and a better lignin grafting rate, and has better fertilizer and water retention and microbial proliferation promotion effects when used for soil improvement.

[0065] 2. Water retention test of lignin-based cationic polyacrylamide

[0066] Indoor simulation experiments were conducted using air-dried soil that had passed through a 2 mm sieve to test the water retention properties of the lignin-based cationic polyacrylamide samples prepared in Examples 1-4 and Comparative Examples 1-3.

[0067] Experimental groups: control group: no modifier was added; Example 1-4 group: lignin-based cationic polyacrylamide samples prepared in Examples 1-4 were added respectively, with an addition amount of 0.25 g / kg soil; Comparative Example 1-3 group: lignin-based cationic polyacrylamide samples prepared in Comparative Examples 1-3 were added respectively, with an addition amount of 0.25 g / kg soil.

[0068] Experimental method: Wrap the bottom of a 6cm diameter PVC pipe with a 200-mesh screen and press it with a perforated bottom cover, and spread a certain amount of quartz sand on the inner bottom layer to prevent soil loss along the seams and affect the experimental results. Mix 80g of air-dried soil with the lignin-based cationic polyacrylamide sample and add it to the PVC pipe, then add 80g of air-dried soil to lay the pipe, prepare a plastic water frame with a water surface not higher than the soil surface, put the PVC pipe in, absorb water for 24 hours, take it out, let it stand until no water drops, and carefully put it in a 25℃ constant temperature and humidity chamber, and measure the overall weight of the PVC pipe at 1d, 5d and 10d respectively. Repeat the measurement 3 times for each test group, take the average value, and calculate the soil moisture content.

[0069] The test results are shown in Table 2 below.

[0070] Table 2

[0071] 1d 5d 10d Control group 25.2％ 19.2％ 15.6％ Example 1 26.2％ 23.4％ 20.7％ Example 2 25.9％ 23.2％ 20.4％ Example 3 26.4％ 23.9％ 21.2％ Example 4 26.1％ 23.5％ 21.0％ Comparative Example 1 25.9％ 22.0％ 17.8％ Comparative Example 2 25.7％ 21.9％ 18.0％ Comparative Example 3 25.8％ 21.6％ 17.5％

[0072] According to the test results in Table 2 above, the lignin-based cationic polyacrylamide prepared by the present invention has a good water retention effect. The moisture content in the PVC pipe decreases relatively slowly. After 10 days, the water content in the soil is still above 20%. In the comparative example, changing the type of reactants or the type of chain transfer agent will affect the water retention effect of the lignin-based cationic polyacrylamide to a certain extent, and accelerate the water loss relative to the embodiment.

[0073] 4. Detection of the effect of lignin-based cationic polyacrylamide on soil aggregate structure

[0074] The wet sieving method was used to measure the effect of lignin-based cationic polyacrylamide on soil aggregate structure. 0.3g / kg lignin-based cationic polyacrylamide was evenly mixed with 100g of soil and placed in a disposable plastic cup. Quartz sand was evenly spread on the surface of the soil and sealed with a breathable membrane, and then placed indoors for cultivation. An equal amount of sterile water was added to the control group. During the cultivation period, the soil moisture content was maintained at 70% of the field moisture content. 50g of soil from each treatment group was sieved with a soil aggregate structure analyzer every week. The sieve group particle size was 0.25mm. The soil was destroyed by 30 times / min of up and down shaking speed and 30min of sieving. After the end, the residual aggregates on each sieve were collected, placed in a 105℃ forced air oven for drying, and weighed. The content of aggregates larger than 0.25mm in the soil was calculated. The results are shown in Table 3 below.

[0075] Table 3

[0076]

[0077]

[0078] According to the test results in Table 3 above, the lignin-based cationic polyacrylamide prepared by the present invention can significantly increase the content of aggregates larger than 0.25 mm in the soil. The content of aggregates larger than 0.25 mm in the soil prepared by Examples 1-4 increased by more than 30% after one week of application compared with the blank group; the content of aggregates larger than 0.25 mm in the soil increased by more than 50% after two weeks of application compared with the blank group; the content of aggregates larger than 0.25 mm in the soil increased by more than 55% after three weeks of application compared with the blank group. In Comparative Examples 1-3, changing the type of reactants or the type of chain transfer agent will affect the effect of lignin-based cationic polyacrylamide on improving the soil aggregate structure to a certain extent. After use, the content of aggregates larger than 0.25 mm in the soil will be significantly reduced.

[0079] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the present invention, but the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered as the protection scope of the present invention.

Claims

1. A cationic acrylamide polymer, characterized in that: The cationic acrylamide polymer is a lignin-based cationic polyacrylamide, which is prepared by the following method: (1) preparing cationic polyacrylamide from acrylamide and cocamidopropyl PG-dimethylammonium chloride; (2) reacting the cationic polyacrylamide obtained in step (1) with lignin to obtain the lignin-based cationic polyacrylamide.

2. The cationic acrylamide polymer according to claim 1, characterized in that: Step (1) further comprises a chain transfer agent, wherein the chain transfer agent is a mixture of 4-chloromethylstyrene and 2-mercaptoethanol, and the mass ratio of the two is 3-5:

1.

3. The cationic acrylamide polymer according to claim 1, characterized in that: Step (1) also includes an initiator, and the initiator is ammonium persulfate.

4. The cationic acrylamide polymer according to claim 1, characterized in that: The molar ratio of acrylamide to cocamidopropyl PG-dimethylammonium chloride is 1.5-5:

1.

5. The cationic acrylamide polymer according to claim 1, characterized in that: The added amount of the chain transfer agent is 0.8-1.2% of the mass of acrylamide.

6. The cationic acrylamide polymer according to claim 1, characterized in that: The added amount of the initiator is 3-5% of the mass of acrylamide.

7. The cationic acrylamide polymer according to claim 1, characterized in that: The reaction temperature of step (1) is 55-70°C; the reaction time is 8-12 hours.

8. The cationic acrylamide polymer according to claim 1, characterized in that: The mass ratio of cationic polyacrylamide to lignin in step (2) is 1-4:

1.

9. The cationic acrylamide polymer according to claim 1, characterized in that: The reaction temperature of step (2) is 70-90°C; the reaction time is 3-6 hours.

10. Use of the lignin-based cationic polyacrylamide according to any one of claims 1 to 9 in the preparation of a soil conditioner.

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