Preparation method and application of alkali lignin-based porous carbon material

Abstract

The present invention provides a kind of alkali lignin-based porous carbon material preparation method and application, comprise the following steps:1)In a reactor, add alkali lignin solution, formaldehyde solution and mix evenly, heat and heat for the first time under stirring condition to react, add ammonia ‑ dimethylamine ‑ epichlorohydrin polymer solution, template solution after the reaction is completed, heat and heat for the second time under stirring condition to react, cool to room temperature after the reaction is completed, filter, wash, dry, obtain precursor standby;2)Precursor is heated carbonized under inert atmosphere, cooled, and obtains alkali lignin-based porous carbon material.With alkali lignin and formaldehyde as carbon source, with ammonia ‑ dimethylamine ‑ epichlorohydrin polymer as nitrogen source, carbon source and template are self-assembled by hydrogen bond, further through the crosslinking of ammonia ‑ dimethylamine ‑ epichlorohydrin polymer to form a continuous three-dimensional network precursor, finally carbonized, obtain an alkali lignin-based porous carbon material with efficient conductive network and conductive performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of alkali lignin-based carbon materials, and in particular relates to a preparation method and application of an alkali lignin-based porous carbon material. Background Art

[0002] Lead-carbon batteries are a new type of battery that combines the high power of supercapacitors with the long life of lead-acid batteries. They offer unparalleled advantages over other battery types, particularly for hybrid vehicle applications. The primary factor impacting the lifespan of hybrid vehicles is irreversible sulfation of the negative electrode. Adding carbon materials as additives to the negative electrode leverages their high conductivity and ability to disperse discharge-active materials, improving active material utilization and inhibiting the growth of lead sulfate crystals.

[0003] my country is a major agricultural country and produces a large amount of agricultural biomass waste every year, such as straw, fruit shells, leaves, etc. Using biomass as raw materials to prepare carbon material additives can achieve effective utilization of agricultural waste and reduce the manufacturing cost of carbon materials. At present, the application of carbon materials prepared from biomass in the field of electrochemical energy storage has been relatively mature, such as the biomass porous carbon material and its preparation method and its application in lead-acid batteries disclosed in patent CN115367750B, and the modified carbon material, its preparation method, negative electrode lead paste, plate and lead-carbon battery disclosed in patent CN105958076B.

[0004] Lignin is a major component of biomass materials, the second largest renewable resource in nature after cellulose, and the most abundant aromatic natural polymer. In the pulp and paper industry, alkali lignin is a major byproduct, with a global annual production of approximately 50 billion tons. Due to the lack of efficient and comprehensive utilization technologies, most alkali lignin is directly burned as industrial waste to generate electricity or heat. Alkali lignin contains up to 50-60% carbon, making it an ideal precursor for preparing carbon materials. However, alkali lignin has a low degree of cross-linking and is a discontinuous carbon material precursor. Direct carbonization results in unstable and easily collapsed pore structures and poor porosity. Using it as an additive for lead-carbon batteries, it cannot form a complete three-dimensional conductive network, resulting in poor conductivity and severe irreversible sulfation of the active substances. As a result, alkali lignin-based carbon materials are rarely used in the lead-carbon battery field.

[0005] Therefore, it is of great significance to develop a method that can comprehensively utilize alkali lignin, a renewable resource, as an additive for lead-carbon battery carbon materials with excellent conductive properties. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for preparing and applying an alkali lignin-based porous carbon material, using alkali lignin and formaldehyde as carbon sources and an ammonia-dimethylamine-epichlorohydrin polymer as a nitrogen source. The carbon source and the template are self-assembled through hydrogen bonds, and further cross-linked by the ammonia-dimethylamine-epichlorohydrin polymer to form a continuous three-dimensional network precursor. Finally, the material is carbonized under high temperature to obtain an alkali lignin-based porous carbon material with an efficient conductive network and conductive properties.

[0007] In order to achieve the above objectives, the following technical solutions are adopted:

[0008] A method for preparing an alkali lignin-based porous carbon material comprises the following steps:

[0009] 1) Adding an alkali lignin solution and a formaldehyde aqueous solution to a reactor and mixing them uniformly, heating and heating the mixture for a first time under stirring conditions to carry out a reaction, adding an ammonia-dimethylamine-epichlorohydrin polymer solution and a template solution after the reaction is completed, heating and heating the mixture for a second time under stirring conditions to carry out a reaction, and cooling the mixture to room temperature after the reaction is completed, filtering, washing, and drying the mixture to obtain a precursor for use;

[0010] 2) The precursor is heated and carbonized under an inert atmosphere and then cooled to obtain an alkali lignin-based porous carbon material.

[0011] Furthermore, in step 1), the alkali lignin solution is obtained by uniformly mixing alkali lignin with a mixed solvent, and the mixed solvent is a mixture of water and an organic solvent in a volume ratio of 1-2:1; preferably, the organic solvent is selected from one or a combination of two or more of acetone, tetrahydrofuran, and acetone dioxane; more preferably, the mass volume ratio of the alkali lignin to the mixed solvent is 1 g: 20-30 mL.

[0012] Furthermore, in step 1), the alkali lignin has a weight-average molecular weight of 1000-3000. Lignin is an aggregate with many polar groups in its structure, especially a large number of hydroxyl groups, which form strong intramolecular and intermolecular hydrogen bonds. Therefore, lignin is insoluble in water and any solvent. However, alkali lignin is degraded lignin and can be dissolved in dilute water-reducing, alkaline or neutral polar solvents.

[0013] Furthermore, in step 1), the alkali lignin is selected from at least one of wood pulp alkali lignin, bamboo pulp alkali lignin, wheat straw pulp alkali lignin, reed pulp alkali lignin, bagasse pulp alkali lignin, and asparagus pulp alkali lignin.

[0014] Furthermore, in step 1), the concentration of the formaldehyde aqueous solution is 35-40 wt%.

[0015] Furthermore, in step 1), the stirring speed is 200-300 r / min, the first heating temperature is raised to 50-60° C., and the reaction time is 1-3 h.

[0016] Furthermore, in step 1), the ammonia-dimethylamine-epichlorohydrin polymer solution has a viscosity of 3-4 Pa·s at 25° C. and a concentration of 45-50 wt %. The ammonia-dimethylamine-epichlorohydrin polymer solution can be commercially available or homemade. If homemade, the preparation method is as follows: a dimethylamine aqueous solution and ammonia water are added to a flask equipped with a thermometer, a stirrer, a reflux condenser, and an addition funnel. The temperature is controlled at 25-40° C., a portion of epichlorohydrin is added dropwise, the temperature is increased to react, and the remaining epichlorohydrin is added during the reaction. After the reaction is completed, the solution is cooled and the pH is adjusted to obtain the ammonia-dimethylamine-epichlorohydrin polymer solution.

[0017] Furthermore, the mass ratio of the dimethylamine aqueous solution, ammonia water, and epichlorohydrin is 400-450:60-65:450-480, the concentration of the dimethylamine aqueous solution is 40-45wt%, the concentration of the ammonia water is 25-30wt%, the epichlorohydrin is added in 1-2.5 hours, the temperature is raised to 80-100°C, the reaction time is 1-3 hours, the remaining epichlorohydrin is added, and the remaining epichlorohydrin accounts for 1 / 5-1 / 4 of the total amount of epichlorohydrin. The remaining epichlorohydrin is added in 1-3 times, with each addition separated by 10-30 minutes. The cooling is cooling to 60-80°C, and the pH is adjusted to 2-3 with sulfuric acid.

[0018] Furthermore, in step 1), the template is one or a combination of two of the triblock copolymers F127 and P123, the solvent of the template solution is ethanol, and the concentration of the template solution is 3-5 wt%.

[0019] Furthermore, in step 1), the mass ratio of the alkali lignin, formaldehyde solution, ammonia-dimethylamine-epichlorohydrin polymer solution, and template is 1:1.5-1.8:1.4-1.7:0.1-0.13.

[0020] Furthermore, in step 1), the stirring speed is 200-300 r / min, the second heating temperature is raised to 60-90°C, and the reaction time is 3-5 hours. The washing is performed by alternating ethanol and water for 1-3 times, and the drying is performed at 80-100°C to constant weight.

[0021] During step 1) the first heating reaction, the phenolic hydroxyl groups on the alkali lignin react with formaldehyde to form hydroxymethyl groups, i.e., resol phenolic formaldehyde. During the second heating reaction, the resol phenolic formaldehyde and the amino groups on the ammonia-dimethylamine-epichlorohydrin polymer condense and dehydrate to form a densely cross-linked precursor. The ammonia-dimethylamine-epichlorohydrin polymer acts as a cross-linking agent in the precursor preparation process. As a quaternary ammonium surfactant, it also acts as a template. However, since the ammonia-dimethylamine-epichlorohydrin polymer is largely interspersed and buried in the continuously cross-linked precursor, a small amount of template is still required to form a porous carbon structure with a good specific surface area. The ratio of ammonia-dimethylamine-epichlorohydrin polymer to template, as well as its ratio relative to the alkali lignin and formaldehyde solution, significantly influences the prepared alkali lignin-based porous carbon material. A low relative proportion of template will result in excessive cross-linking and a weak pore structure. A high relative proportion will prevent the formation of a continuous precursor matrix, resulting in an unstable and easily collapsed pore structure after carbonization. Therefore, the mass ratio of alkali lignin, formaldehyde solution, ammonia-dimethylamine-epichlorohydrin polymer solution and template agent needs to be strictly controlled.

[0022] In step 2), the heating graphitization treatment is performed by heating the temperature to 1700-1900° C. at a rate of 3-5° C. / min and maintaining the temperature for 1-3 hours.

[0023] The present invention also provides an alkali lignin-based porous carbon material prepared by the above method.

[0024] The present invention also provides a negative electrode lead paste for a lead-carbon battery, using the alkali lignin-based porous carbon material as an additive for the negative electrode lead paste.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses alkali lignin and formaldehyde as carbon sources and an ammonia-dimethylamine-epichlorohydrin polymer as a nitrogen source. The carbon source and the template are self-assembled through hydrogen bonds, and the ammonia-dimethylamine-epichlorohydrin polymer is further cross-linked to form a continuous three-dimensional network precursor. Finally, the material is carbonized under high temperature to obtain an alkali lignin-based porous carbon material with a high-efficiency conductive network and conductive properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron microscope photograph of the porous carbon material prepared in Example 1;

[0028] Figure 2 This is a pore structure distribution diagram of the porous carbon material prepared in Example 1;

[0029] Figure 3 This is the specific surface test data of the porous carbon material prepared in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0031] Alkali lignin was purchased from Xinyi Feihuang Chemical Co., Ltd. with a weight-average molecular weight of 2500.

[0032] Preparation of alkali lignin-based porous carbon materials:

[0033] Example 1

[0034] 1) In a 2000 mL flask equipped with a thermometer, stirrer, reflux condenser, and addition funnel, add 450 g of a 40 wt% aqueous dimethylamine solution and 60.8 g of a 29 wt% aqueous ammonia solution. Then, at a temperature below 40°C, add 412.9 g of epichlorohydrin dropwise over 2 hours. After heating to 90°C and reacting for 1 hour, add 45.9 g of epichlorohydrin in three portions, each addition interval being 20 minutes. Maintain the temperature at 90°C until all additions are complete. Finally, cool the reaction mixture to 80°C, and add concentrated sulfuric acid to reduce the pH to 2.5, yielding a 50 wt% ammonia-dimethylamine-epichlorohydrin polymer solution with a viscosity of 3.55 Pa·s.

[0035] 2) Add 100g of alkali lignin and 3000mL of a mixed solvent (the mixed solvent is a mixture of water and tetrahydrofuran in a volume ratio of 2:1) to the reactor, add 180g of a 37wt% formaldehyde solution and mix them evenly. Heat to 75°C for the first time under stirring at 200r / min and react for 2h. After the reaction, add 170g of ammonia-dimethylamine-epichlorohydrin polymer solution and 200g of a 5wt% template F127 (purchased from Sigma) solution. Heat to 90°C for the second time under stirring at 200r / min and react for 5h. After the reaction, cool to room temperature, filter, wash alternately with ethanol and alcohol water three times, and dry to obtain a precursor for use;

[0036] 3) In a nitrogen atmosphere, the precursor was heated to 1700°C at a rate of 3.5°C / min and kept at this temperature for 3 hours for carbonization treatment, and then cooled to room temperature to obtain an alkali lignin-based porous carbon material. Graphitization degree I D / I G It is 0.86.

[0037] Example 2

[0038] The rest is the same as Example 1, except that the amount of ammonia-dimethylamine-epichlorohydrin polymer solution used is 140 g.

[0039] Example 3

[0040] The rest is the same as Example 1, except that the amount of template F127 (purchased from Sigma) solution used is 260 g.

[0041] Example 4

[0042] The rest is the same as Example 1, except that the amount of template F127 (purchased from Sigma) solution used is 300 g.

[0043] Example 5

[0044] The rest is the same as Example 1, except that the amount of template F127 (purchased from Sigma) solution used is 180 g.

[0045] Example 6

[0046] The rest is the same as Example 1, except that, 2) an alkali lignin solution prepared by mixing 100 g of alkali lignin and 3000 mL of a mixed solvent (the mixed solvent is a mixture of water and tetrahydrofuran in a volume ratio of 2: 1) and 150 g of a 37 wt% formaldehyde solution were added to the reactor and mixed evenly. The mixture was heated to 75 ° C. for the first time under stirring conditions of 200 r / min and reacted for 2 h. After the reaction, 140 g of an ammonia-dimethylamine-epichlorohydrin polymer solution and 260 g of a 5 wt% template F127 (purchased from Sigma) solution were added. The mixture was heated to 90 ° C. for the second time under stirring conditions of 200 r / min and reacted for 5 h. After the reaction, the mixture was cooled to room temperature, filtered, washed alternately with ethanol and alcohol water three times, and dried to obtain a precursor for standby use.

[0047] Comparative Example 1

[0048] The rest is the same as Example 1, except that 340 g of a 25 wt % diethylenetriamine aqueous solution is used instead of 170 g of the ammonia-dimethylamine-epichlorohydrin polymer solution.

[0049] Comparative Example 2

[0050] The rest is the same as Example 1, except that the template F127 is not added.

[0051] Application Example 1

[0052] Assembling lead-carbon batteries:

[0053] (1) Paste: 50 g of lead powder, 10 g of lead oxide, 0.7 g of the alkali lignin-based porous carbon material prepared in Example 1, 0.8 g of barium sulfate, 0.2 g of acetylene black, 0.8 g of sodium lignosulfonate, 0.8 g of barium stearate, and 0.9 mL of water were stirred for 10 min to obtain a lead paste.

[0054] (2) Apply lead paste evenly to the positive and negative grids (the lead-calcium alloy negative grid was purchased from Baoding Meilun Nonferrous Metals Co., Ltd., and the lead dioxide positive grid was purchased from Baoji Changli Special Metals Co., Ltd. The size of the positive and negative grids was 70mm×50mm×2mm.), and dry in an oven at 65℃ for 8h, and then at 75℃ for 6h to obtain the positive and negative plates of the lead-carbon battery. Add 150mL of a 1.035g / cm 3 The positive and negative plates were inserted into the beaker on both sides of the beaker, separated by an industrial battery AGM, to simulate a lead-carbon battery. The battery was then connected to the LAND5.8 battery testing system for formation, obtaining qualified positive and negative plates. The formation conditions were as follows: first, let it rest for 2 hours, then charge at a constant current rate of 0.05C for 1 hour, then charge at a constant current rate of 0.1C for 20 hours; after standing for 2 hours, discharge at a constant current rate of 0.1C for 1 hour, then charge at a constant current rate of 0.1C for 10 hours, charge at a constant current rate of 0.2C for 12 hours, and finally charge at a constant current rate of 0.1C for 4 hours.

[0055] (3) Lead-carbon batteries are assembled in the form of 1 positive and 2 negative plates: welding of positive and negative plates, filling of batteries with acid (density of sulfuric acid is 1.27 g / cm 3 ), battery sealing, battery detection machine activation.

[0056] Application Example 2-6, Comparative Application Example 1-2

[0057] The rest is the same as Application Example 1, except that the biomass graphitized carbon material is prepared according to Examples 2-6 and Comparative Examples 1-2.

[0058] The alkali lignin-based porous carbon materials prepared in the above examples and comparative examples were tested for pore structure and specific surface area, and the lead-carbon batteries of the corresponding use cases and comparative application examples were tested for cycle performance:

[0059] 1. Pore structure and specific surface area: measured by NOVA 1000e pore structure and specific surface area tester. The sample was degassed at 350℃ for 2h and adsorbed with liquid nitrogen at 77K and relative pressure (P / P0) 10 -6 N2 adsorption was carried out in the range of -1, and the specific surface area was calculated by the BET equation.

[0060] 2. Cycling performance: In order to study the life of lead-carbon batteries under high-rate charge and discharge (HRPSoC) working conditions, a cycling test experiment was carried out. The battery tester used in the experiment was BTS-5 V / 6 A, produced by Shenzhen Xinwei Electronics Co., Ltd. The charge and discharge system used in the test is as follows: first, the battery was left for 30 minutes, discharged at a current of 2 A for 84 minutes to reach 50% of the theoretical capacity, that is, 50% SoC. After leaving it for 5 minutes, the following steps were cycled: charge at 4A for 1 minute, leave it for 1 minute, discharge at 4A for 1 minute, and leave it for 1 minute. The upper and lower limits of the charge and discharge voltages were set to 2.9 V and 1.7 V, respectively. When any of the aforementioned cut-off voltages of the battery was reached, the cycle was terminated.

[0061] Table 1

[0062] .

[0063] As shown in Table 1, the present invention successfully prepared a porous carbon material with a mesoporous structure and high electrical conductivity. Its application in lead-carbon batteries can inhibit the growth of lead sulfate crystals and extend the battery's service life. Application Example 1 and Comparative Application Examples 1-2 clearly show that the relative ratios of the ammonia-dimethylamine-epichlorohydrin polymer and the template, as well as their ratios to the alkali lignin and formaldehyde solution, significantly influence the pore structure, specific surface area, and electrical conductivity of the porous carbon material. While the inventors have not further explored this, they speculate that the mass ratios of the alkali lignin, formaldehyde solution, ammonia-dimethylamine-epichlorohydrin polymer solution, and template affect nitrogen doping and pore structure, and thus the electrical conductivity.

[0064] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing an alkali lignin-based porous carbon material, characterized in that: The steps include: 1) adding an alkali lignin solution and a formaldehyde aqueous solution to a reactor, mixing them uniformly, heating and raising the temperature for a first time under stirring, adding an ammonia-dimethylamine-epichlorohydrin polymer solution and a template solution, heating and raising the temperature for a second time under stirring, and cooling to room temperature after the reaction, filtering, washing, and drying to obtain a precursor for later use; the template is one or both of triblock copolymers F127 and P123; and the mass ratio of alkali lignin, formaldehyde aqueous solution, ammonia-dimethylamine-epichlorohydrin polymer solution, and template is 1:1.5-1.8:1.4-1.7:0.1-0.13; 2) The precursor is heated and carbonized under an inert atmosphere and then cooled to obtain an alkali lignin-based porous carbon material.

2. The method for preparing the alkali lignin-based porous carbon material according to claim 1, characterized in that: In step 1), the alkali lignin solution is obtained by uniformly mixing alkali lignin with a mixed solvent, and the mixed solvent is a mixture of water and an organic solvent in a volume ratio of 1-2:

1.

3. The method for preparing the alkali lignin-based porous carbon material according to claim 2, characterized in that: In step 1), the organic solvent is selected from one or a combination of two or more of acetone, tetrahydrofuran, and acetone dioxane.

4. The method for preparing the alkali lignin-based porous carbon material according to claim 2, characterized in that: In step 1), the mass volume ratio of the alkali lignin to the mixed solvent is 1 g: 20-30 mL.

5. The method for preparing the alkali lignin-based porous carbon material according to claim 1, characterized in that: In step 1), the weight average molecular weight of the alkali lignin is 1000-3000.

6. The method for preparing the alkali lignin-based porous carbon material according to claim 1, characterized in that: In step 1), the concentration of the formaldehyde aqueous solution is 35-40 wt%.

7. The method for preparing the alkali lignin-based porous carbon material according to claim 1, characterized in that: In step 1), the viscosity of the ammonia-dimethylamine-epichlorohydrin polymer solution at 25° C. is 3-4 Pa·s, and the concentration is 45-50 wt %.

8. The method for preparing the alkali lignin-based porous carbon material according to claim 1, characterized in that: In step 1), the solvent of the template solution is ethanol, and the concentration of the template solution is 3-5 wt%.

9. The method for preparing the alkali lignin-based porous carbon material according to claim 1, characterized in that: In step 2), the heating carbonization treatment is performed by heating the temperature to 1700-1900° C. at a speed of 3-5° C. / min and maintaining the temperature for 1-3 hours.

10. The alkali lignin-based porous carbon material prepared by the method for preparing the alkali lignin-based porous carbon material according to any one of claims 1 to 9.

11. A negative electrode lead paste for a lead-carbon battery, comprising the alkali lignin-based porous carbon material according to claim 10 as an additive to the negative electrode lead paste.

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