Preparation method of sulfonated lignin and application of sulfonated lignin in water retention and flocculation

Abstract

The invention provides a preparation method of lignin sulfonate and application of the lignin sulfonate in water retention and flocculation, and relates to the technical field of utilization of camellia oleifera shells, the lignin sulfonate prepared through the method can be used for preparing a water-retaining agent and a flocculating agent, the obtained water-retaining agent has high water absorption, the obtained flocculating agent has the ethyl violet removal capacity, and in addition, the lignin sulfonate can be used for water retention and flocculation. When the sulfonated lignin is used for preparing the water-retaining agent and the flocculating agent, the production cost of the water-retaining agent and the flocculating agent can be reduced, the environmental pollution is reduced, and efficient recovery and cyclic utilization of resources are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of utilization of oil-tea camellia shell, and particularly relates to a preparation method of sulfonated lignin and its applications in water retention and flocculation.

Background Art

[0002] Oil-tea camellia shell is a rich biomass resource, which contains a large amount of lignin, hemicellulose and cellulose. At present, the utilization of oil-tea camellia shell mainly focuses on the extraction of tea saponin, tannin and oligosaccharide, and the lignocellulose residue after extraction is often discarded without being highly valorized. As an important biomass-based polymer material, sulfonated lignin shows extensive application potential in the fields of flocculants, water retainers, etc. due to its unique sulfonic acid groups and good water solubility. Traditional sulfonated lignin mainly comes from the by-products of the paper industry, but its performance is restricted by raw materials and processes, making it difficult to meet the requirements of efficient applications. Exploring an efficient and controllable preparation method of sulfonated lignin and exploring its functionalized applications have important scientific significance and practical value.

[0003] Organic dyes are widely used in industries such as textile, leather and food processing. The organic dyes lost during the production process are difficult to degrade and are toxic to aquatic animals, plants and microorganisms. Water pollution caused by the discharge of organic dyes has become a global environmental problem. Therefore, developing efficient flocculants for the removal of organic dyes has important environmental benefits.

[0004] Water retainers are polymer materials that can absorb and retain a large amount of water and are widely used in agriculture, forestry, horticulture and other fields to improve soil water retention capacity, reduce water evaporation, improve soil structure, etc. Traditional water retainers are mainly made of chemically synthesized materials, which have problems such as high cost and environmental unfriendliness. In recent years, with the attention to environmental protection and sustainable development, the research on preparing water retainers using natural materials has gradually increased. Therefore, developing a sulfonated lignin-based water retainer is of great significance.

Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method of sulfonated lignin and its applications in water retention and flocculation. The sulfonated lignin prepared by the present invention can be applied to the preparation of water retainers and flocculants.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation method of a water retainer based on sulfonated lignin from oil-tea camellia shell, the method comprising the following steps:

[0008] (1) After extracting saponin, tannin, and oligosaccharides from the residue of camellia oleifera fruit shells, add it to a 0.1 - 0.2 mol / L NaOH solution according to a solid - liquid ratio of 1:18 - 22. Then add sodium 3 - chloro - 2 - hydroxypropanesulfonate, and the mass ratio of sodium 3 - chloro - 2 - hydroxypropanesulfonate to the residue of camellia oleifera fruit shells is 0.1 - 0.5:1;

[0009] (2) Place the reaction system in a heating magnetic stirrer for stirring reaction. The reaction temperature is 80 - 120 °C, and the reaction time is 1 - 3 h. Use a serpentine condenser for reflux reaction. After the reaction, naturally cool the system to room temperature;

[0010] (3) Vacuum filter through a 0.4 - 0.5 μm microporous membrane to separate the solid and liquid phases. After collecting the filtrate, adjust the pH to 5.5 - 6.5 with 10% HCl solution and filter again to remove precipitate impurities;

[0011] (4) Inject the obtained clear filtrate into a dialysis bag with a molecular weight cut - off of 1000 Da, place it in 4 - 6 L of deionized water for dynamic dialysis for 48 h. After dialysis, concentrate it, transfer it to a blast drying oven, and dry it at 100 - 110 °C for 20 - 25 h to finally obtain sulfonated lignin.

[0012] In the present invention, further, in step (1), the mass ratio of sodium 3 - chloro - 2 - hydroxypropanesulfonate to the residue of camellia oleifera fruit shells is 0.3:1, in step (2), the reaction temperature is 100 °C, and the reaction time is 2 h.

[0013] The present invention also proposes the application of the sulfonated lignin prepared according to the above method, and the sulfonated lignin is applied to the preparation of a water - retaining agent.

[0014] The present invention also proposes the application of the sulfonated lignin prepared according to the above method, and the sulfonated lignin is applied to the preparation of a flocculant.

[0015] The present invention also proposes a method for preparing a water - retaining agent using the sulfonated lignin described above, and the method includes the following steps:

[0016] 1) Dissolve the sulfonated lignin in deionized water to prepare a sodium lignosulfonate solution for standby;

[0017] 2) Add acrylic acid to a beaker, then adjust its neutralization degree to 60 - 70% using a sodium hydroxide solution with a mass fraction of 25 - 35%. Then add acrylamide and stir until completely dissolved to obtain a mixed solution for standby;

[0018] 3) Add sodium lignosulfonate solution, N,N'-methylenebisacrylamide, and ammonium persulfate to the mixed solution, then heat it to 60 - 70 °C and stir for 1 - 3 hours. After the reaction, wash the product with ethanol to remove unreacted monomers and impurities, and reserve the reaction product for use;

[0019] 4) Dry the obtained reaction product at 55 - 65 °C to constant weight and crush it into granular form to obtain the water-retaining agent.

[0020] In the present invention, further, the mass ratio of acrylic acid to acrylamide is 10:1.

[0021] In the present invention, further, the mass ratio of the mixed solution, sodium lignosulfonate solution, N,N'-methylenebisacrylamide, and ammonium persulfate is 1 - 2:20 - 30:1:4.

[0022] The present invention also provides a method for adsorbing organic dyes using the sulfonated lignin as a flocculant.

[0023] In summary, due to the adoption of the above technical solutions, the present invention has at least the following beneficial effects:

[0024] 1. The present invention provides a sulfonated lignin based on oil-tea fruit shell, using the residue of oil-tea fruit shell after extracting tea saponin, tannin, and oligosaccharides as raw materials, with low cost and good economy and sustainability.

[0025] 2. The present invention first prepares sulfonated lignin from the residue of oil-tea fruit shell. The sulfonic acid group content of the sulfonated lignin prepared by the method reaches 0.92 mmol / g and the molecular weight is 3.28 kDa, with good dissolution effect;

[0026] Then, further prepare a water-retaining agent and a flocculant from lignin. In the dye removal experiment, SL100 shows excellent flocculation effect, and its removal rate of crystal violet is as high as 96.66%, which is better than commercial sulfonated lignin. In addition, by further copolymerizing SL100 with monomers such as acrylic acid and acrylamide, a sulfonated lignin-based water-retaining agent is successfully prepared. The obtained water-retaining agent has excellent water retention performance. It has abundant sulfonic acid groups, can significantly improve water absorption and water retention, and can be widely applied in agriculture, forestry, horticulture and other fields to improve soil water retention capacity, reduce water evaporation, improve soil structure, etc., and has broad application prospects.

[0027] The present invention not only provides a new idea for the high-value utilization of lignin, but also lays an experimental foundation for the development of efficient and environmentally friendly functional materials, and has important theoretical and application significance.

Description of the Drawings

[0028] Figure 1The removal rates of ethyl violet and basic blue at different dosages of sulfonated lignin (denoted as SL100) and commercial flocculant (CSL).

[0029] Figure 2 The Zeta potential of solutions with different sulfonated lignin / dye mass ratios.

Specific Embodiments

[0030] The following examples can help those skilled in the art to understand the present invention more comprehensively, but cannot limit the present invention in any way.

[0031] Example 1

[0032] This example provides a sulfonated lignin, which is obtained by the following preparation method:

[0033] (1) The residue of camellia oleifera fruit shell after extracting saponin, tannin, and oligosaccharide is mixed with 0.1 mol / L NaOH solution according to a solid-liquid ratio of 1:18 (g:ml), and then 3-chloro-2-hydroxypropanesulfonate is added. The mass ratio of 3-chloro-2-hydroxypropanesulfonate to the residue of camellia oleifera fruit shell is 0.1:1;

[0034] (2) The reaction system is placed in a thermostatic magnetic stirrer for stirring reaction. The reaction temperature is 80 °C, the reaction time is 1 h, and a snake-shaped condenser is used for reflux reaction. After the reaction, the system is naturally cooled to room temperature;

[0035] (3) The solid-liquid phase is separated by vacuum filtration through a 0.4 μm microporous filter membrane. After collecting the filtrate, the pH is adjusted to 5.5 with 10% HCl solution, and then filtered again to remove precipitate impurities;

[0036] (4) The obtained clear filtrate is injected into a dialysis bag with a molecular weight cut-off of 1000 Da, placed in 4 L of deionized water for dynamic dialysis for 48 h. After dialysis, it is concentrated, transferred to a blast drying oven, and dried at 110 °C for 20 h to finally obtain sulfonated lignin.

[0037] Example 2

[0038] This example provides a sulfonated lignin, which is obtained by the following preparation method:

[0039] (1) The residue of camellia oleifera fruit shell after extracting saponin, tannin, and oligosaccharide is mixed with 0.15 mol / L NaOH solution according to a solid-liquid ratio of 1:20 (g:ml), and then 3-chloro-2-hydroxypropanesulfonate is added. The mass ratio of 3-chloro-2-hydroxypropanesulfonate to the residue of camellia oleifera fruit shell is 0.3:1;

[0040] (2) Place the reaction system in a thermostatic magnetic stirrer and stir for reaction. The reaction temperature is 100 °C, and the reaction time is 2 h. Use a serpentine condenser for reflux reaction. After the reaction is completed, let the system cool naturally to room temperature;

[0041] (3) Vacuum filter through a 0.45 μm microporous membrane to separate the solid and liquid phases. After collecting the filtrate, adjust the pH to 6.0 with 10% HCl solution, and filter again to remove the precipitate impurities;

[0042] (4) Inject the obtained clear filtrate into a dialysis bag with a molecular weight cut-off of 1000 Da, place it in 5 L of deionized water for dynamic dialysis for 48 h. After dialysis is completed, concentrate it, transfer it to a blast drying oven, and dry it at 105 °C for 24 h to finally obtain sulfonated lignin.

[0043] Example 3

[0044] This example provides a sulfonated lignin, which is obtained by the following preparation method:

[0045] (1) After extracting saponin, tannin, and oligosaccharides from the residue of Camellia oleifera fruit shell, mix it with 0.2 mol / L NaOH solution according to a solid-liquid ratio of 1:22 (g:ml), and then add 3-chloro-2-hydroxypropylsulfonate. The mass ratio of 3-chloro-2-hydroxypropylsulfonate to the residue of Camellia oleifera fruit shell is 0.5:1;

[0046] (2) Place the reaction system in a thermostatic magnetic stirrer and stir for reaction. The reaction temperature is 80 °C, and the reaction time is 3 h. Use a serpentine condenser for reflux reaction. After the reaction is completed, let the system cool naturally to room temperature;

[0047] (3) Vacuum filter through a 0.5 μm microporous membrane to separate the solid and liquid phases. After collecting the filtrate, adjust the pH to 6.5 with 10% HCl solution, and filter again to remove the precipitate impurities;

[0048] (4) Inject the obtained clear filtrate into a dialysis bag with a molecular weight cut-off of 1000 Da, place it in 6 L of deionized water for dynamic dialysis for 48 h. After dialysis is completed, concentrate it, transfer it to a blast drying oven, and dry it at 100 °C for 25 h to finally obtain sulfonated lignin.

[0049] The applicant further tested the sulfonic acid group content and molecular weight in the sulfonated lignin obtained under different mass parts and reaction conditions, as shown in Table 1:

[0050] Table 1 Sulfonic acid group content and molecular weight of sulfonated lignin under different experimental conditions

[0051]

[0052] Among them, the experimental conditions of 0.1 g / g-1 h / 100 °C correspond to: the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to the residue of oil-tea fruit shell is 0.1:1, the reaction temperature is 100 °C, and the reaction time is 1 h. The conditions of other groups are the same as above, and so on.

[0053] According to the results in Table 1, it can be seen that the sulfonated lignin prepared under the conditions of a mass ratio of 0.3:1, a reaction temperature of 100 °C, and a reaction time of 2 h has the highest sulfonic acid group content (0.92 mmol / g) and high molecular weight (3.28 kDa).

[0054] Example 4:

[0055] This example provides a method for adsorbing organic dyes, which uses the sulfonated lignin of Example 2 as a flocculant.

[0056] The adsorption experiment is as follows:

[0057] (1) Prepare simulated wastewater solutions of crystal violet (EV) and basic blue (GB4) with an initial concentration of 100 mg / L and pH 6.5 respectively. Dissolve the 2 g / L prepared flocculant solution in distilled water with pH 6.5 and stir magnetically at 300 rpm for 1 h to achieve full dissolution. Then, mix the flocculant solution with the dye solution according to the preset mass ratios (flocculant:ethyl violet = 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1; flocculant:basic blue = 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1). Place the mixture in a constant temperature oscillator at 30 ± 0.5 °C and oscillate at 150 rpm for 30 min, then centrifuge to achieve solid-liquid separation. Finally, use a fluorescence spectrophotometer to measure the absorbance of the supernatant at the characteristic wavelengths (ethyl violet: 595 nm, basic blue: 618 nm, lignin: 205 nm). The dye removal rate is calculated according to the following formula:

[0058]

[0059] In the formula, C0 and C are the concentrations of the dye in the solution before and after treatment (mg / L), respectively.

[0060] The results are as Figure 1 shown.

[0061] Among them, Figure 1(a) shows the removal rate of ethyl violet at different dosages of sulfonated lignin (denoted as SL100) and commercial flocculant. As can be seen from the figure, when the mass ratio of SL100 to ethyl violet increases from 0.5:1 to 2.5:1, the removal rate of ethyl violet shows an upward trend, and the removal rate of ethyl violet increases from 40.38% to 96.66%. When the mass ratio of SL100 to ethyl violet is further increased to 4:1, the removal rate of ethyl violet decreases to 57.11%.

[0062] Figure 1 (b) shows the removal rate of basic blue at different dosages of SL100 and commercial flocculant. When the mass ratio of SL100 to basic blue increases from 1:10 to 1:1, the removal rate of basic blue increases from 22.20% to 90.82%. When the mass ratio of SL100 to basic blue is increased to 3.5:1, the removal rate of basic blue decreases to 42.22%. This indicates that after exceeding the optimal dosage, the removal efficiency of both dyes decreases significantly.

[0063] Comparing with the commercial sulfonated lignin, SL100 is superior to the commercial sulfonated lignin in terms of dye removal performance.

[0064] The applicant further conducts Zeta potential analysis of the dye solution:

[0065] Through Zeta potential characterization, the electrostatic adsorption mechanism between the surface charge characteristics of sulfonated lignin and cationic dyes can be analyzed, the influence law of the charge change in the dye solution system on the dye removal efficiency during the flocculation process can be clarified, and the reason for the change of the dye removal rate with the dosage of sulfonated lignin can be determined.

[0066] Figure 2 It is the Zeta potential of the solution with different mass ratios of sulfonated lignin / dye.

[0067] Among them, Figure 2 (a) shows the Zeta potential of the dye solution system at different mass ratios of SL100 / ethyl violet. It can be obtained from the figure that when neither SL100 nor commercial sulfonated lignin is added to the ethyl violet dye system, the initial Zeta potential of the ethyl violet dye solution is +4.62 mV, and the colloidal particle surface carries a net positive charge. As the mass ratio of SL100 / ethyl violet increases, the Zeta potential of the dye solution system gradually decreases. When the mass ratio of SL100 / ethyl violet increases to 4:1, the electronegativity of the dye solution system is -24.95 mV, showing a change trend of first rapidly decreasing and then gradually flattening.

[0068] Figure 2(b) Zeta potential of the basic blue dye system at different mass ratios of SL100 / basic blue. It can be obtained from the figure that the Zeta potential of the basic blue dye solution in the initial state is +1.75 mV. With the addition of SL100, the Zeta potential of the basic blue dye solution gradually shifts towards electronegativity. When the mass ratio of SL100 / basic blue increases to 4:1, the Zeta potential of the basic blue dye solution is -41.36 mV.

[0069] The comparative experiment with commercial sulfonated lignin shows that although commercial sulfonated lignin exhibits a similar potential change trend to SL100, at the same mass ratio, the potential regulation effect of commercial sulfonated lignin on the two dye solutions is lower than that of SL100. This indicates that for the removal ability of ethyl violet and basic blue dyes, the flocculant prepared in this experiment is superior to commercial sulfonated lignin. Sulfonated lignin has a better charge neutralization efficiency for basic blue. This difference may stem from the fact that basic blue molecules have a higher charge density and a more open three-dimensional structure, enabling more thorough electrostatic binding with lignosulfonic acid groups and resulting in a more complete surface charge transformation.

[0070] Combined with the analysis of the simulated experiment on wastewater dye removal, when the mass ratios of SL100 / ethyl violet and SL100 / basic blue are 2.5:1 and 1:1 respectively, large-sized flocs are formed through electro-neutralization, which is beneficial for the flocculation separation of dyes. However, when the mass ratios of SL100 / ethyl violet and SL100 / basic blue exceed 2.5:1 and 1:1 respectively, the excessive negative charge on the surface of the complex triggers an electrostatic repulsion effect, leading to the depolymerization and redispersion of the flocs, thus forming a colloidal stable system. This phenomenon also exists in the commercial sulfonated lignin system, but its critical dosage is significantly shifted backward compared to the SL100 system, further confirming that the flocculation effect of SL100 is superior to that of commercial sulfonated lignin.

[0071] Example 5:

[0072] This example provides a method for preparing a water retainer using the sulfonated lignin obtained in Example 2. The method includes the following steps:

[0073] 1) Dissolve the obtained sulfonated lignin in deionized water to prepare a sodium lignosulfonate solution for standby. The mass fraction of the sulfonated lignin and deionized water in the sodium lignosulfonate solution is 2.5%;

[0074] 2) Add acrylic acid to a beaker, then adjust its neutralization degree to 65% using a 30% sodium hydroxide solution, and then add acrylamide and stir until completely dissolved to obtain a mixed solution for standby. The mass ratio of acrylic acid to acrylamide is 10:1;

[0075] 3) Add sodium lignosulfonate solution, N,N'-methylenebisacrylamide, and ammonium persulfate to the mixed solution, then heat to 65 °C and stir for 2 hours. After the reaction is completed, wash the product with ethanol to remove unreacted monomers and impurities, and reserve the reaction product for use; the mass ratio of the mixed solution, sodium lignosulfonate solution, N,N'-methylenebisacrylamide, and ammonium persulfate is 2:25:1:4;

[0076] 4) Dry the obtained reaction product at 60 °C to constant weight and crush it into granular form to obtain the water retaining agent.

[0077] To illustrate the practical value of this embodiment, the applicant tested the performance of the water retaining agents in the following groups,

[0078] The specific method is as follows:

[0079] Weigh a certain mass of the water retaining agent (W0), soak it in deionized water, take it out after a certain time (when water absorption is saturated), and weigh it (W1) after blotting the surface moisture with filter paper.

[0080] Calculate the water absorption ratio:

[0081] Water absorption ratio (g / g) = (W1 - W0) / W0.

[0082] Water retention performance test: Place the water-absorbed water retaining agent under different temperature conditions and calculate the water retention rate:

[0083] Water retention rate (%) = (Wt - W0) / (W1 - W0) × 100%, where Wt is the weight of the water retaining agent at time t.

[0084] The grouping is as follows:

[0085] The first group: the water retaining agent described in Example 2 of this application;

[0086] The second group: the mass fraction of the sulfonated lignin solution is 1%, and the rest is the same as the first group.

[0087] Compare the water absorption rates of the above water retaining agents, as shown in Table 1:

[0088] Table 1

[0089] Water absorption ratio (g / g) The first group 28.90 The second group 25.01

[0090] Compare the water retention rates of the above water retaining agents at 25 °C and 40 °C respectively, as shown in Table 2:

[0091] Table 2

[0092]

[0093]

[0094] According to the test results, the water-retaining agent prepared by the method of this embodiment has a good water retention rate, and its water absorption ratio is high, which has important practical significance and economic value.

[0095] Although the present invention has been described in detail above with general descriptions and specific embodiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A preparation method of sulfonated lignin, characterized in that, The method comprises the following steps: (1) Add the residue of oil-tea fruit shell after extracting saponin, tannin, and oligosaccharides into 0.1 - 0.2 mol / L NaOH solution according to a solid-liquid ratio of 1:18 - 22, and then add sodium 3-chloro-2-hydroxypropanesulfonate. The mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to the residue of oil-tea fruit shell is 0.1 - 0.5:1; (2) Place the reaction system in a heating magnetic stirrer for stirring reaction. The reaction temperature is 80 - 120 °C, and the reaction time is 1 - 3 h. Use a serpentine condenser for reflux reaction. After the reaction, naturally cool the system to room temperature; (3) Vacuum filter and separate the solid-liquid phase through a 0.4 - 0.5 μm microporous filter membrane. After collecting the filtrate, adjust the pH to 5.5 - 6.5 with 10% HCl solution, and filter again to remove precipitate impurities; (4) Inject the obtained clear filtrate into a dialysis bag with a molecular weight cut-off of 1000 Da, place it in 4 - 6 L of deionized water for dynamic dialysis for 48 h. After dialysis, concentrate it, transfer it to a blast drying oven, and dry it at 100 - 110 °C for 20 - 25 h to finally obtain sulfonated lignin.

2. The method according to claim 1, characterized in that, In step (1), the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to the residue of oil-tea fruit shell is 0.3:

1. In step (2), the reaction temperature is 100 °C, and the reaction time is 2 h.

3. The application of sulfonated lignin according to any one of claims 1-2, characterized in that, The sulfonated lignin is applied to prepare a water-retaining agent.

4. Use of sulfonated lignin according to any one of claims 1-2, characterized in that, The sulfonated lignin is applied to prepare a flocculant.

5. A method for preparing a water retaining agent using sulfonated lignin as described in any one of claims 1-2, characterized in that, The method comprises the following steps: 1) Dissolve the sulfonated lignin in deionized water to prepare a sodium lignosulfonate solution for standby; 2) Add acrylic acid to a beaker, then adjust its neutralization degree to 60 - 70% with a sodium hydroxide solution with a mass fraction of 25 - 35%, and then add acrylamide, stir until completely dissolved to obtain a mixed solution for standby; 3) Add the sodium lignosulfonate solution, N,N'-methylenebisacrylamide, and ammonium persulfate to the mixed solution, then heat to 60 - 70 °C, stir and react for 1 - 3 hours. After the reaction, wash the product with ethanol to remove unreacted monomers and impurities to obtain a reaction product for standby; 4) Dry the obtained reaction product at 55 - 65 °C to constant weight and crush it into granular form to obtain the water-retaining agent.

6. The method according to claim 5, characterized in that The mass ratio of acrylic acid to acrylamide is 10:

1.

7. The method according to claim 5, characterized in that, The mass ratio of the mixed solution, sodium lignosulfonate solution, N,N'-methylenebisacrylamide, and ammonium persulfate is 1 - 2:20 - 30:1:

4.

8. A method for adsorbing organic dyes using the sulfonated lignin as claimed in any one of claims 1 - 2 as a flocculant.

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