A hierarchical porous lignin microsphere, its preparation method and application

Abstract

This invention discloses a hierarchical porous lignin microsphere, its preparation method, and its applications. The invention uses an aqueous solution of lignin alkaline solution, a crosslinking agent, and a chain extender as the aqueous phase, which is then mixed with an inner oil phase containing a surfactant and emulsified to form an O / W primary emulsion. The primary emulsion is then mixed with an outer oil phase containing a surfactant and emulsified to obtain an O / W / O type composite emulsion. Finally, a crosslinking reaction is completed under ultrasound. After the reaction is complete, the oil phase is removed, and the microspheres are washed and dried to form hierarchical porous lignin microspheres. This invention exhibits good sphere formation, controllable particle size, and abundant surface and internal pores. The microspheres possess good biocompatibility and biodegradability, and demonstrate good adsorption performance for metal ions and organic pollutants. Furthermore, they are suitable for bed adsorption and have significant application potential.

Description

Technical Field

[0001] This invention belongs to the field of porous microsphere preparation technology, specifically relating to a lignin-graded porous microsphere, its preparation method, and its application. Background Technology

[0002] Lignin is the second largest biomass resource in nature and is a natural high-molecular polymer with a three-dimensional network structure. Its molecule contains abundant active groups such as hydroxyl, carboxyl, and sulfonic acid groups. These groups can bind to metal ions through electrostatic interactions, ion exchange, or complexation, and it has potential applications in wastewater treatment.

[0003] Currently, most lignin-based adsorbents are in powder or fine particle form, which suffers from problems such as inability to be quickly recycled, high resistance when applied to bed adsorption, and some even dissolving in water, causing secondary pollution. These drawbacks limit the application prospects of lignin-based adsorbents. Lignin-based spherical adsorbents, due to their superior hydraulic properties, are suitable for bed adsorption and cause virtually no secondary pollution, thus attracting attention. However, to meet the requirements for industrial storage, transportation, and long-term cyclic use, most currently prepared lignin-based spherical adsorbents have excessively high mechanical strength, resulting in dense, non-porous microspheres that hinder pollutant entry and lead to poor adsorption performance. Therefore, to address these issues, the development of lignin-based porous microspheres is urgently needed.

[0004] Methods for preparing porous lignin microspheres generally include reverse-phase suspension polymerization and emulsion polymerization. For example, Ge et al. used alkali lignin as raw material, epichlorohydrin as a crosslinking agent, and grafted polyethyleneimine to prepare lignin microspheres via reverse-phase suspension copolymerization. Studies showed that the average particle size of the microspheres was 348 μm, and the microspheres contained a large number of amine functional groups (7.5 mmol / g), which had a positive effect on Pb. 2+ The adsorption capacity was 33.9 mg / g. Our research group radiohydrophobically modified lignin and prepared porous lignin microspheres via a W / O / W double emulsion solvent evaporation method. These microspheres exhibited high adsorption capacity for Pb. 2+ The saturated adsorption capacity was 140 mg / g. Ji Chunmei et al. prepared lignin porous phenolic resin microspheres using lignin and formaldehyde as monomers and toluene as a porogen via aqueous suspension polymerization. The lignin porous microspheres obtained by the above methods either have fewer pores, uneven sphericity, and relatively small adsorption capacity; or the particle size is too small to facilitate recycling.

[0005] In summary, there is an urgent need to develop a method for preparing lignin-based porous microspheres that have abundant pores, excellent adsorption performance, and are easy to recycle. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing lignin-graded porous microspheres.

[0007] The principle of this invention for preparing hierarchical porous lignin microspheres is as follows: On the one hand, lignin and chain extenders are linked together by a cross-linking agent. The synergistic effect of the cross-linking agent facilitating the formation of a network structure in lignin molecules and the chain extender lengthening the lignin main chain results in a higher degree of cross-linking and a more uniform distribution of cross-linking points, thereby improving the flexibility of the microspheres. Simultaneously, the lignin undergoes a certain degree of polymerization and cross-linking under ultrasonic treatment, giving the microspheres both rigidity and flexibility, thus enabling pore formation during drying. On the other hand, an O / W / O type composite emulsion is used to encapsulate the aqueous lignin solution, forming droplets that allow for the formation of regular microspheres. Simultaneously, the internal oil phase acts as a pore-forming agent; after the removal of the internal oil phase (which does not participate in the cross-linking reaction), larger pores and voids form in their original positions. Therefore, during the drying process, the pores formed by the evaporation of the aqueous phase of the microsphere and the pores formed by the removal of the internal oil phase construct the hierarchical porous structure of the lignin microspheres.

[0008] Another object of the present invention is to provide lignin hierarchical porous microspheres prepared by the above preparation method.

[0009] Another object of the present invention is to provide the application of the above-mentioned lignin graded porous microspheres.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for preparing lignin hierarchical porous microspheres includes the following steps:

[0012] (1) Mix the lignin alkaline solution, crosslinking agent and chain extender evenly to obtain a lignin aqueous solution;

[0013] (2) Mix the lignin aqueous solution and the inner oil phase containing surfactant, emulsify, and obtain O / W type primary emulsion; then mix the O / W type primary emulsion and the outer oil phase containing surfactant, emulsify, and obtain O / W / O type secondary emulsion;

[0014] (3) The O / W / O type double emulsion was subjected to ultrasonic reaction. After the reaction was completed, the oil phase was removed, washed, and dried to obtain lignin graded porous microspheres.

[0015] Preferably, in the lignin alkaline solution of step (1), the lignin is at least one of alkali lignin, solvent-based lignin, enzymatically hydrolyzed lignin, sodium lignin sulfonate, and amination-modified products of these lignins; more preferably, it is at least one of sodium lignin sulfonate, amination-modified sodium lignin sulfonate, alkali lignin, and enzymatically hydrolyzed lignin.

[0016] Preferably, the lignin alkaline solution in step (1) is obtained by adding lignin to an alkaline solution, wherein the alkaline solution is at least one of sodium hydroxide solution and potassium hydroxide solution, and the concentration of the alkaline solution is 0.5 to 2.0 mol / L; the mass fraction of lignin in the lignin alkaline solution is 40 to 65%.

[0017] Preferably, the crosslinking agent in step (1) is at least one of formaldehyde, glutaraldehyde, glyoxal, epichlorohydrin, and N,N-methylenebisacrylamide; the amount of crosslinking agent used is 30-50% of the lignin content.

[0018] Preferably, the chain extender in step (1) is at least one of ethylenediamine, hexamethylenediamine, polyetheramine, polyethyleneimine, triethylenetetramine, and diethylenetriamine; the amount of the chain extender is 0.1-15% of the lignin content.

[0019] Preferably, the inner oil phase containing surfactant in step (2) consists of surfactant and oil phase, wherein the surfactant accounts for 0.1 to 2% of the total mass of the inner oil phase.

[0020] Preferably, in the inner oil phase containing surfactant in step (2), the surfactant is at least one of Tween-80, sucrose ester, polyethylene glycol, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; and the oil phase is at least one of toluene, isoamyl alcohol, n-heptane, and ethyl acetate.

[0021] Preferably, the mass ratio of the lignin aqueous solution and the internal oil phase containing the surfactant in step (2) is 3:1 to 6:1.

[0022] Preferably, the external oil phase containing surfactant in step (2) is composed of surfactant and oil phase, wherein the surfactant accounts for 2 to 6% of the total mass of the external oil phase.

[0023] Preferably, in the external oil phase containing surfactant in step (2), the surfactant is at least one of Span-60, glyceryl monostearate, calcium stearate, and dodecylphenol polyoxyethylene ether; and the oil phase is at least one of cyclohexane, xylene, n-hexane, and liquid paraffin.

[0024] Preferably, the mass ratio of the O / W type primary emulsion and the external oil phase containing the surfactant in step (2) is 1:3 to 1:5.

[0025] Preferably, the emulsification conditions for the O / W type primary emulsion in step (2) are: shearing at 3000-6000 rpm for 10-15 min; and the emulsification conditions for the O / W / O type secondary emulsion are: shearing at 200-300 rpm for 25-40 min.

[0026] Preferably, the ultrasonic power of the ultrasonic reaction in step (3) is 150-300W; the reaction time is 30-60min.

[0027] Preferably, the method for removing the oil phase in step (3) is as follows: let it stand at normal pressure for 10 to 30 minutes, and then pour out the upper oil phase.

[0028] Preferably, the washing in step (3) is as follows: first wash with petroleum ether 3 to 6 times, then transfer the microspheres to a Soxhlet extractor and extract with ethanol for 12 to 24 hours.

[0029] Preferably, the drying in step (3) is: freeze drying at -40 to -10°C for 48 to 72 hours or drying at 30 to 70°C under a vacuum of 76 to 90 Pa for 48 to 72 hours.

[0030] A lignin-graded porous microsphere was prepared by the above method.

[0031] The lignin hierarchical porous microspheres prepared by this invention have a particle size of 50–500 μm.

[0032] The above-mentioned lignin hierarchical porous microspheres are used for the adsorption of antibiotics, pesticides, organic dyes, proteins and heavy metal ions.

[0033] Preferably, the antibiotic is at least one of tetracycline and tylosin; the pesticide is at least one of formamid and diquat; the organic dye is at least one of methylene blue, triarylmethane, and cationic red GTL; and the heavy metal ion is Pb. 2+ Ag + and Cu 2+ At least one of them.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] 1. This invention uses ultrasound-assisted polymerization. Under the action of ultrasound, lignin undergoes a certain degree of polymerization, which increases the molecular weight of lignin and improves the cross-linking strength of microspheres. At the same time, the cross-linking agent connects lignin with the chain extender, giving the microspheres a certain degree of flexibility, which is beneficial for the formation of pores after drying.

[0036] 2. The microspheres prepared by this invention have a hierarchical porous structure. A stable O / W / O type emulsion is formed using composite emulsion technology. After ultrasonic polymerization and cross-linking, the inner and outer oil phases are removed. After drying, the microspheres contain both larger pores formed by the internal oil phase and mesh pores formed by the drying of water in the three-dimensional network. The combination of these two elements forms a hierarchical porous structure.

[0037] 3. The microspheres prepared by this invention have controllable particle size. By using different masses of surfactants and emulsion shear rates, the particle size of lignin-graded porous microspheres can be adjusted from 50 to 500 μm.

[0038] 4. The lignin hierarchical porous microspheres prepared by the present invention increase the number of amine groups in the microspheres by adding chain extenders, thus providing more active sites; at the same time, their porous structure can accelerate mass transfer, realize rapid and efficient adsorption of heavy metal ions and organic pollutants, and have high mechanical strength and spherical shape, making them suitable for bed adsorption.

[0039] 5. The preparation process provided by this invention is simple, and the oil phase used can be reused through oil-water separation. The raw materials are low in cost, have high utilization rate, short synthesis time, and a yield of up to 99%. The microspheres are mainly composed of lignin, which has good biocompatibility, is environmentally friendly, and causes virtually no pollution. They can be widely used in wastewater treatment, as carriers, and in medicine. Attached Figure Description

[0040] Figure 1 This is a scanning electron microscope image of the overall structure of the lignin hierarchical porous microspheres prepared in Example 1.

[0041] Figure 2 This is a scanning electron microscope image of the surface of the lignin hierarchical porous microspheres prepared in Example 1.

[0042] Figure 3 This is a scanning electron microscope image of the cross-section of the lignin hierarchical porous microspheres prepared in Example 1.

[0043] Figure 4 This is a pore size distribution diagram of the lignin hierarchical porous microspheres prepared in Example 1.

[0044] Figure 5 The image shows the bed adsorption breakthrough curve of methylene blue on the lignin hierarchical porous microspheres prepared in Example 1.

[0045] Figure 6 The lignin hierarchical porous microspheres prepared in Example 1 are effective against methylene blue, tylosin, tetracycline, and Pb. 2+ Ag + Adsorption performance.

[0046] Figure 7 This is a scanning electron microscope image of the cross-section of the lignin microspheres prepared in Comparative Example 1.

[0047] Figure 8 This is a scanning electron microscope image of the cross-section of the lignin microspheres prepared in Comparative Example 2. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0049] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0050] Example 1

[0051] (1) Preparation of lignin aqueous solution: Dissolve 18g of sodium lignin sulfonate in 1.0mol / L sodium hydroxide solution to prepare 30g of 60wt% lignin base solution; add 7.2g of epichlorohydrin and 2.7g of polyetheramine, mix well to obtain lignin aqueous solution;

[0052] (2) Preparation of O / W / O type double emulsion: 8g of lignin aqueous solution was added to ethyl acetate containing 2wt% Tween-80 and emulsified at 6000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 144g of liquid paraffin containing 6wt% Span-60 was added to O / W primary emulsion and emulsified at 300rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;

[0053] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 240W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min. The upper oil phase was poured off and washed three times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were freeze-dried at -40℃ for 48 h to finally obtain lignin graded porous microspheres.

[0054] Example 2

[0055] (1) Preparation of lignin aqueous solution: 12g of alkali lignin was dissolved in 2.0mol / L sodium hydroxide solution to prepare 30g of 40wt% lignin alkali solution; 9.73g of formaldehyde solution (mass concentration of 37%) and 1.8g of ethylenediamine were added and mixed evenly to obtain lignin aqueous solution;

[0056] (2) Preparation of O / W / O type double emulsion: 7.5g of lignin aqueous solution was added to 7.5g of n-heptane containing 0.1wt% polyethylene glycol and emulsified at 4000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 155g of n-hexane containing 4wt% calcium stearate was added to the O / W primary emulsion and emulsified at 250rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;

[0057] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 150W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min. The upper oil phase was poured off and washed 6 times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were freeze-dried at -40℃ for 48 h to finally obtain lignin graded porous microspheres.

[0058] Example 3

[0059] (1) Preparation of lignin aqueous solution: Dissolve 15g sodium lignin sulfonate in 1.5mol / L potassium hydroxide solution to prepare 30g 50wt% lignin base solution; add 18g glutaraldehyde solution (mass concentration of 25%) and 1.5g triethylenetetramine, mix well to obtain lignin aqueous solution;

[0060] (2) Preparation of O / W / O type double emulsion: 10g of lignin aqueous solution was added to toluene containing 0.5wt% sodium dodecylbenzenesulfonate and emulsified at 4000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 180g of cyclohexane containing 6wt% dodecylphenol polyoxyethylene ether was added to O / W primary emulsion and emulsified at 250rpm for 30min using mechanical stirring to obtain O / W / O type double emulsion;

[0061] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 300W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured off, and the microspheres were washed three times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 12 h. After washing with deionized water, the microspheres were freeze-dried at -40℃ for 72 h to finally obtain lignin graded porous microspheres.

[0062] Example 4

[0063] (1) Preparation of lignin aqueous solution: 19.5g sodium lignin sulfonate was dissolved in 0.5mol / L potassium hydroxide solution to prepare 30g 65wt% lignin base solution; 7.8g N,N-methylenebisacrylamide and 0.975g diethylenetriamine were added and mixed evenly to obtain lignin aqueous solution;

[0064] (2) Preparation of O / W / O type double emulsion: 8g of lignin aqueous solution was added to isoamyl alcohol containing 0.5wt% sodium dodecylbenzenesulfonate, and emulsified at 6000rpm for 10min using a homogenizer to obtain O / W type primary emulsion; then 170g of xylene containing 2wt% glyceryl monostearate was added to O / W primary emulsion, and emulsified at 250rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;

[0065] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 200W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured off, and it was washed 3 times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were dried at 70℃ under vacuum of 76 Pa for 72 h to finally obtain lignin graded porous microspheres.

[0066] Example 5

[0067] (1) Preparation of lignin aqueous solution: 12g of solvent-based lignin (extracted from ethanol) was dissolved in a 1.0mol / L mixed solution of sodium hydroxide and potassium hydroxide to prepare a 30g 40wt% lignin alkaline solution; 9g of glyoxal solution (mass concentration of 40%) and 0.3g of hexamethylenediamine were added and mixed evenly to obtain the lignin aqueous solution;

[0068] (2) Preparation of O / W / O type double emulsion: 7.86 g of lignin aqueous solution was added to toluene containing 0.3 wt% sodium dodecyl sulfate, and emulsified at 4000 rpm for 15 min using a homogenizer to obtain O / W type primary emulsion; then 188 g of n-hexane containing 6 wt% calcium stearate was added to O / W primary emulsion, and emulsified at 250 rpm for 30 min using mechanical stirring to obtain O / W / O type double emulsion;

[0069] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 150W) for 30 min. After reacting, it was allowed to stand at normal pressure for 10 min. The upper oil phase was poured off and washed three times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were freeze-dried at -10℃ for 48 h to finally obtain lignin graded porous microspheres.

[0070] Example 6

[0071] (1) Preparation of lignin aqueous solution: 12g of amination-modified sodium lignin sulfonate (specific preparation method: dissolve 30g of sodium lignin sulfonate in 180g of deionized water, add 3g of formaldehyde solution (mass concentration is 37%), 6g of hexamethylenediamine and 5g of sodium hydroxide, stir thoroughly, react at 70℃ for 4h, after the reaction is completed, add 3mol / L hydrochloric acid dropwise while stirring to allow the amination-modified sodium lignin sulfonate to fully precipitate, wash, filter and dry to obtain the product) was dissolved in 1.5mol / L sodium hydroxide solution to prepare 30g of 40wt% lignin alkali solution; add 14.4g of glutaraldehyde solution (mass concentration is 25%) and 0.75g of polyethyleneimine, mix well to obtain lignin aqueous solution;

[0072] (2) Preparation of O / W / O type double emulsion: The lignin aqueous solution was added to 10g of n-heptane containing 2wt% Tween-80 and emulsified at 3000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 180g of n-hexane containing 2wt% Span-60 was added to the O / W primary emulsion and emulsified at 200rpm for 30min using mechanical stirring to obtain O / W / O type double emulsion;

[0073] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 200W) for 50 min, and then allowed to stand at normal pressure for 10 min. The upper oil phase was poured off and washed 6 times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, the microspheres were freeze-dried at -40℃ for 48 h to finally obtain lignin graded porous microspheres.

[0074] Example 7

[0075] (1) Preparation of lignin aqueous solution: 12g of enzymatically hydrolyzed lignin was dissolved in 1.5mol / L potassium hydroxide solution to prepare 30g of 40wt% lignin alkaline solution; 6g of N,N-methylenebisacrylamide and 0.012g of diethylenetriamine were added and mixed evenly to obtain lignin aqueous solution;

[0076] (2) Preparation of O / W / O type double emulsion: The lignin aqueous solution was added to 8g of isoamyl alcohol containing 0.5wt% sucrose ester, and emulsified at 5000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 220g of cyclohexane containing 3wt% dodecylphenol polyoxyethylene ether was added to the O / W primary emulsion, and emulsified at 300rpm for 25min using mechanical stirring to obtain O / W / O type double emulsion;

[0077] (3) Preparation of lignin graded porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 300W) for 60 min, and then allowed to stand at normal pressure for 30 min. The upper oil phase was poured off and washed three times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 12 h. After washing with deionized water, they were dried at 30°C under a vacuum of 90 Pa for 48 h to finally obtain lignin graded porous microspheres.

[0078] Comparative Example 1:

[0079] (1) Preparation of lignin aqueous solution: Dissolve 18g of sodium lignin sulfonate in 1.0mol / L sodium hydroxide solution to prepare 30g of 60wt% lignin base solution; add 7.2g of epichlorohydrin and 2.7g of polyetheramine, mix well to obtain lignin aqueous solution;

[0080] (2) Add 120g of liquid paraffin containing 6wt% Span-60 to the solution in (1) and stir at 300rpm for 40min using a mechanical stirrer.

[0081] (3) Stir the mixture of (2) by ultrasonication (power of 240W) for 60 min, let it stand at normal pressure for 10 min, pour out the upper oil phase, wash it with petroleum ether 3 times; then transfer the microspheres to a Soxhlet extractor and extract with ethanol for 24 h, wash it with deionized water and freeze dry at -40℃ for 48 h.

[0082] (4) Results: Lignin-based microspheres were obtained, but the pore structure was poor (e.g., Figure 7 ).

[0083] Comparative Example 2:

[0084] (1) Preparation of lignin aqueous solution: Dissolve 18g of sodium lignin sulfonate in 1.0mol / L sodium hydroxide solution to prepare 30g of 60wt% lignin base solution; add 9g of epichlorohydrin and mix well to obtain lignin aqueous solution;

[0085] (2) Preparation of O / W / O type double emulsion: 7.82 g of lignin aqueous solution was added to ethyl acetate containing 2 wt% Tween-80 and emulsified at 6000 rpm for 15 min using a homogenizer to obtain O / W type primary emulsion; then 141 g of liquid paraffin containing 6 wt% Span-60 was added to O / W primary emulsion and emulsified at 300 rpm for 40 min using mechanical stirring to obtain O / W / O type double emulsion;

[0086] (3) The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 240W) and reacted for 60 min. After standing at normal pressure for 10 min, the upper oil phase was poured out and washed 3 times with petroleum ether. Then the microspheres were transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, the microspheres were freeze-dried at -40℃ for 48 h.

[0087] (4) Results: Lignin-based microspheres were obtained, but the sphericity and pore structure were poor (e.g., Figure 8 ).

[0088] Comparative Example 3:

[0089] (1) Preparation of lignin aqueous solution: Dissolve 18g of sodium lignin sulfonate in 1.0mol / L sodium hydroxide solution to prepare 30g of 60wt% lignin base solution; add 10g of epichlorohydrin and 8g of polyetheramine mixed solution, mix well to obtain lignin aqueous solution;

[0090] (2) Preparation of O / W / O type double emulsion: A lignin aqueous solution was added to 9.62g of ethyl acetate containing 2wt% Tween-80, and emulsified at 6000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 173g of liquid paraffin containing 6wt% Span-60 was added to O / W primary emulsion, and emulsified at 300rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;

[0091] (3) The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 240W) and reacted for 60 minutes. After standing at normal pressure for 10 minutes, the upper oil phase was poured out and washed 3 times with petroleum ether.

[0092] (4) Result: The product is in clumps and does not form balls.

[0093] Comparative Example 4:

[0094] (1) Preparation of lignin aqueous solution: Dissolve 18g of sodium lignin sulfonate in 1.0mol / L sodium hydroxide solution to prepare 30g of 60wt% lignin base solution; add 7.2g of epichlorohydrin and 2.7g of polyetheramine mixed solution, mix well to obtain lignin aqueous solution;

[0095] (2) Preparation of O / W / O type double emulsion: 8g of lignin aqueous solution was added to ethyl acetate containing 2wt% Tween-80 and emulsified at 6000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 144g of liquid paraffin containing 6wt% Span-60 was added to O / W primary emulsion and emulsified at 300rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;

[0096] (3) The O / W / O type double emulsion obtained in step (2) is ultrasonically stirred (power is 240W), reacted for 10 min, and then left to stand at normal pressure for 10 min.

[0097] (4) Results: The solution was divided into layers, and the lower aqueous phase was a viscous liquid with no spherical products.

[0098] Example effect description:

[0099] The effect is illustrated using Example 1 as an example.

[0100] Figure 1 and Figure 2 This is a SEM image of the lignin graded porous microspheres prepared in Example 1. The microspheres are regular spherical in shape and have abundant small pores on their surface. Figure 3This is a cross-sectional SEM image of the hierarchical porous lignin microspheres prepared in Example 1. The image shows that the microspheres have a hierarchical porous structure, rich in interconnected pores. Lignin is cross-linked via ultrasonic polymerization to form microspheres with a certain mechanical strength. Furthermore, the rapid sublimation of the aqueous phase within the microspheres during drying creates numerous pores inside the microspheres.

[0101] Figure 4 This is a pore size distribution diagram of the hierarchical porous lignin microspheres prepared in Example 1. As can be seen from the figure, the pore sizes of the microspheres are mainly distributed in the ranges of 1-10 nm, 900-2000 nm, and ≥10 μm, exhibiting abundant micropores and macropores. This result is consistent with the SEM test results. Furthermore, the porosity of the microspheres is 73%, and the pore volume is 2.0 mL / g, indicating that the microspheres possess a hierarchical porous structure.

[0102] Example 1 used lignin-graded porous microspheres to simulate bed adsorption treatment of industrial wastewater. Specifically, a certain amount of lignin-grade porous microspheres was weighed and poured into a circular bed with a cross-sectional area of ​​1 cm². 2 The chromatography column was filled to a depth of 3 cm. After filling the column, pure water was injected, the lower valve was closed, and the column was soaked and moistened for 15 minutes. Then, the valve was opened and the water in the adsorbent gaps was dried using a syringe rubber bulb. Simulated wastewater at a flow rate of 1 mL / min was pumped into the column using a peristaltic pump. Samples were taken and analyzed at the effluent end at regular intervals. The breakthrough curve is shown below. Figure 5 As shown, the lignin porous microspheres can continuously treat 400 mL and 500 mg / L of methylene blue wastewater with a removal rate of 99%. Under the conditions of adsorption temperature of 30℃ and pressure of 100 kPa, the breakthrough adsorption capacity of methylene blue reaches 230 mg / g, and the adsorption utilization rate reaches 93%. This indicates that the lignin hierarchical porous microspheres can efficiently treat high-concentration methylene blue wastewater.

[0103] The lignin hierarchical porous microspheres of this invention are effective against metal ions (such as Pb). 2+ Ag + Cu 2+ It exhibits good adsorption properties for antibiotics (such as tetracycline and tylosin), organic dyes (such as methylene blue, triarylmethane, and cationic red GTL), and proteins. The lignin-graded porous microspheres from Example 1 were applied to adsorb methylene blue, tylosin, tetracycline, and Pb. 2+ and Ag +Pollutants such as microspheres. The specific application procedure is as follows: Transfer 50 mL of a certain concentration of pollutant to a 100 mL Erlenmeyer flask, add 0.1 g of microsphere sample, and incubate at 30℃ and 150 rpm for 6 hours with constant temperature shaking. After adsorption, take an appropriate amount of supernatant and filter it through a 0.22 μm aqueous filter. Dilute the filtrate to a certain concentration and test it using a UV-2450 ultraviolet spectrophotometer or a Z-2300 atomic absorption spectrometer. Figure 6 As shown, the effects of lignin hierarchical porous microspheres on methylene blue, tylosin, tetracycline, and Pb were measured. 2+ Ag + The saturated adsorption capacities reached 323.77 mg / g, 381.64 mg / g, 241.23 mg / g, 166.83 mg / g, and 220.50 mg / g, respectively, showing great potential for industrial applications.

[0104] The lignin-based hierarchical porous microspheres from Examples 1, 2, 3, 4, 5, 6, and 7 were used to adsorb methylene blue solution. The specific application procedure was as follows: 50 mL of 500 mg / L methylene blue solution was transferred to a 100 mL Erlenmeyer flask, and 0.1 g of the microsphere sample was added. The mixture was incubated at 30°C and 150 rpm for 6 hours. After adsorption, a suitable amount of the supernatant was filtered through a 0.22 μm aqueous filter. The filtrate was diluted to a certain concentration and tested using a UV-2450 ultraviolet spectrophotometer. The adsorption capacities of the four types of lignin-based hierarchical porous microspheres for methylene blue were measured to be 239.40 mg / g, 215.30 mg / g, 216.88 mg / g, 207.36 mg / g, 200.95 mg / g, 210 mg / g, and 220.25 mg / g, respectively. This demonstrates that the lignin-graded porous microspheres prepared in different implementations of the present invention all possess good adsorption capacity.

[0105] Figure 7 The image shows a SEM image of the lignin-based microspheres prepared in Comparative Example 1. It can be seen that the microspheres have a poor internal pore structure, exhibiting a large pore size. Figure 8 The image shows a SEM image of the lignin-based microspheres prepared in Comparative Example 2. The microspheres exhibit poor pore structure and are easily broken. The lignin-based microspheres prepared in Comparative Examples 1 and 2 were used to adsorb methylene blue solution. The specific application procedure was as follows: 50 mL of 500 mg / L methylene blue solution was transferred to a 100 mL Erlenmeyer flask, and 0.1 g of the microsphere sample was added. The mixture was incubated at 30°C and 150 rpm for 6 hours. After adsorption, a suitable amount of the supernatant was filtered through a 0.22 μm aqueous filter. The filtrate was diluted to a certain concentration and tested using a UV-2450 ultraviolet spectrophotometer. The adsorption capacities of the lignin-based microspheres prepared in Comparative Examples 1 and 2 for methylene blue were measured to be 151.34 mg / g and 140.25 mg / g, respectively, which were lower than those in Example 1 (239.40 mg / g).

[0106] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing lignin-graded porous microspheres, characterized in that, Includes the following steps: (1) Mix the lignin alkaline solution, crosslinking agent and chain extender evenly to obtain a lignin aqueous solution; (2) Mix the lignin aqueous solution and the inner oil phase containing surfactant, emulsify, and obtain O / W type primary emulsion; then mix the O / W type primary emulsion and the outer oil phase containing surfactant, emulsify, and obtain O / W / O type secondary emulsion; (3) The O / W / O type double emulsion was subjected to ultrasonic reaction. After the reaction was completed, the oil phase was removed, washed, and dried to obtain lignin graded porous microspheres. The crosslinking agent in step (1) is at least one of formaldehyde, glutaraldehyde, glyoxal, epichlorohydrin, and N,N-methylenebisacrylamide; the amount of crosslinking agent used is 30-50% of the lignin content; The chain extender in step (1) is at least one of ethylenediamine, hexamethylenediamine, polyetheramine, polyethyleneimine, triethylenetetramine, and diethylenetriamine; the amount of the chain extender is 0.1-15% of the lignin content; In step (2), the surfactant in the inner oil phase containing the surfactant is at least one of Tween-80, sucrose ester, polyethylene glycol, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; the oil phase is at least one of toluene, isoamyl alcohol, n-heptane, and ethyl acetate. In step (2), the surfactant in the outer oil phase containing the surfactant is at least one of Span-60, glyceryl monostearate, calcium stearate, and dodecylphenol polyoxyethylene ether; the oil phase is at least one of cyclohexane, xylene, n-hexane, and liquid paraffin. The emulsification conditions for the O / W type colostrum in step (2) are: shearing at 3000-6000 rpm for 10-15 min; the emulsification conditions for the O / W / O type double emulsion are: shearing at 200-300 rpm for 25-40 min. The method for removing the oil phase in step (3) is as follows: let it stand at normal pressure for 10 to 30 minutes, and then pour out the upper oil phase; The ultrasonic power of the ultrasonic reaction in step (3) is 150-300 W; the reaction time is 30-60 min.

2. The method for preparing lignin-graded porous microspheres according to claim 1, characterized in that, The mass ratio of the lignin aqueous solution and the inner oil phase containing the surfactant in step (2) is 3:1 to 6:1; the mass ratio of the O / W type primary emulsion and the outer oil phase containing the surfactant in step (2) is 1:3 to 1:

5.

3. The method for preparing lignin-graded porous microspheres according to claim 1, characterized in that, The lignin alkaline solution in step (1) is obtained by adding lignin to an alkaline solution, wherein the concentration of the alkaline solution is 0.5–2.0 mol / L; and the mass fraction of lignin in the lignin alkaline solution is 40–65%. The internal oil phase containing surfactant described in step (2) consists of surfactant and oil phase, wherein the surfactant accounts for 0.1-2% of the total mass of the internal oil phase; The external oil phase containing surfactant in step (2) consists of surfactant and oil phase, wherein the surfactant accounts for 2 to 6% of the total mass of the external oil phase.

4. The method for preparing lignin-graded porous microspheres according to claim 1, characterized in that, In the lignin alkaline solution of step (1), the lignin is at least one of alkali lignin, solvent-based lignin, enzymatically hydrolyzed lignin, sodium lignin sulfonate, and amination-modified alkali lignin, amination-modified solvent-based lignin, amination-modified enzymatically hydrolyzed lignin, and amination-modified sodium lignin sulfonate. The lignin alkaline solution in step (1) is obtained by adding lignin to an alkaline solution, wherein the alkaline solution is at least one of sodium hydroxide solution and potassium hydroxide solution.

5. The method for preparing lignin-graded porous microspheres according to claim 1, characterized in that, The washing process in step (3) is as follows: first wash with petroleum ether 3 to 6 times, then transfer the microspheres to a Soxhlet extractor and extract with ethanol for 12 to 24 hours; The drying in step (3) is: freeze drying at -40 to -10°C for 48 to 72 h or drying at 30 to 70°C under a vacuum of 76 to 90 Pa for 48 to 72 h.

6. A lignin-graded porous microsphere is prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the lignin hierarchical porous microspheres according to claim 6 in the adsorption of antibiotics, pesticides, organic dyes, proteins and heavy metal ions.

8. The application according to claim 7, characterized in that, The antibiotic is at least one of tetracycline and tylosin; the pesticide is at least one of formamid and diquat; the organic dye is at least one of methylene blue, triarylmethane, and cationic red GTL; the heavy metal ion is Pb. 2+ Ag + and Cu 2+ At least one of them.

Images