A method for preparing energy storage type lignin micro / nano spheres with controllable size

Abstract

The application discloses a method for preparing energy storage type lignin micro / nano spheres with controllable morphology, and mainly relates to preparation of lignin spherical micro / nano spheres in a solid acid solvent-water system. By controlling reaction conditions such as solid acid concentration, reaction temperature and reaction time, the purpose of controllable morphology and size can be achieved, and the prepared lignin micro / nano spheres have excellent electrochemical performance and good energy storage performance. The method can realize efficient separation of lignin from wood fiber raw materials at low temperature and normal pressure, and can directly prepare microspheres in the lignin recovery process. Compared with conventional methods, the preparation method is simple, the yield is high, and large-scale preparation of lignin microspheres with controllable size can be realized. The chemical modification of lignin and the use of high-toxicity chemical reagents are avoided, cost is saved, environmental pollution is reduced, and the method has good practicability.

Description

Technical Field

[0001] This invention belongs to the field of efficient separation of wood fiber raw materials and high-value utilization of lignin, specifically involving a simple, green, and controllable method for preparing lignin micro / nanospheres with morphology and particle size. Background Technology

[0002] Currently, with the development of the domestic and international economies, people's dependence on fossil fuels is increasing. However, with the dwindling availability of fossil fuels and the environmental problems caused by the poor degradability of petroleum-based materials, humanity is forced to seek clean and biodegradable new energy sources. Biomass energy is one of the most abundant renewable resources on Earth. Lignocellulose, composed of cellulose, lignin, and hemicellulose, is an important option for petroleum substitution strategies, utilizing biorefining technology to provide materials, fuels, and chemicals. Lignin is one of the main components of lignocellulose biomass and is the second most abundant natural organic macromolecular aromatic compound in the world. It has excellent biocompatibility and superior antibacterial properties. Its unique chemical structure and high reactivity enable lignin to be widely used in production and daily life. Globally, more than 70 million tons of industrial lignin waste are generated annually, the vast majority of which is incinerated. Only about 5% of lignin is effectively utilized. Therefore, seeking efficient ways to separate and utilize lignin is beneficial to improving the high-value utilization of lignocellulose biomass.

[0003] Lignin microspheres / nanospheres are polymers of lignin with promising applications in lignin-based materials, polymer additives, catalysts, and drug carriers. Currently, research on lignin microspheres is still in its early stages, mainly due to the cumbersome preparation methods, requiring large amounts of chemical reagents and resulting in low yields. The main preparation processes for lignin microspheres can be categorized into three main types: physical methods, chemical methods, and biological methods. Physical methods include high-shear homogenization, ultrasonic methods, and ultrasonic spray freezing methods; chemical methods include acid precipitation, solvent exchange, and dialysis; and biological methods primarily involve enzymatic hydrolysis. All these methods can yield stable and dispersed lignin microspheres / nanospheres. However, these methods for preparing lignin nanospheres still have inherent drawbacks. For example, in ultrasonic, dialysis, and enzymatic hydrolysis methods, lignin must first be separated, then dissolved in a suitable organic solvent, and finally separated by ultrasonication or dialysis to obtain lignin microspheres. In addition, the above methods have a low yield of lignin microspheres, which can only be carried out on a laboratory scale and are difficult to apply on a large scale.

[0004] CN113426388A discloses a method for preparing lignin microspheres with controllable size, including the steps of constructing a eutectic solvent system, treating lignocellulose raw materials with the eutectic solvent system, and separating the reaction system to obtain lignin microspheres. The method achieves controllable lignin microsphere size by adjusting the amount of water in the eutectic solvent system. This is mainly achieved by utilizing the characteristic that adding trace amounts of AlCl3 to the eutectic solvent formed by 1,4-butanediol and choline chloride can efficiently separate lignin from lignocellulose raw materials, and that the separated lignin can be prepared into microspheres.

[0005] Therefore, finding a simpler and more efficient method for preparing lignin microspheres is key to the industrialization of lignin microspheres. Summary of the Invention

[0006] Purpose of the invention: To address the problems of cumbersome preparation methods, large amounts of chemical reagents, and low yield in existing lignin microsphere preparation methods, the technical problem to be solved by the present invention is to provide a method for preparing lignin micro / nanospheres with controllable size and good electrochemical performance, which is prepared into microspheres during the lignin separation process and has controllable size.

[0007] To address the aforementioned technical problems, this invention discloses a method for preparing morphology-controllable energy storage lignin micro / nanospheres. The method is characterized by first constructing a composite acid-water solvent system, treating lignocellulose raw materials with this system, and then separating lignin from the reaction system to obtain microspheres. The composite acid-water solvent system is obtained by mixing a solid acid with a strong acid, adding water, and heating to dissolve the mixture. The morphology and size of the lignin microspheres are controllable by controlling the reaction temperature, reaction time, acid concentration, and solid-liquid ratio of the reaction system.

[0008] The solid acid is any one of salicylic acid, maleic acid, and p-toluenesulfonic acid; the strong acid is sulfuric acid or hydrochloric acid.

[0009] The composite acid-water solvent is prepared by the following method: dilute sulfuric acid and salicylic acid are mixed at a mass ratio of 1:0.1-1:1 to obtain a composite acid. The acid concentration in the composite acid-water solvent system is 10-80 wt.%, and the concentration of dilute sulfuric acid is 1-10 wt.%. Then, water is added to the composite acid, and the mixture is heated to dissolve at 40-50°C while continuously stirring until a clear and homogeneous solid acid-water solution system is formed.

[0010] The wood fiber raw material is mixed with the composite acid-water solvent system and reacted at 60-110℃ for 10-60 min.

[0011] The solid-liquid ratio of the wood fiber raw material to the composite acid-water solvent system is 1:5-1:15.

[0012] Specifically, the separation steps are as follows: the reaction mixture is vacuum filtered on filter paper to separate the reaction solution from the solids. At the same time, the solids are washed with ultrapure water until the washing solution is neutral (the washing water and the reaction solution are combined, eventually reaching 5-10 times or more of the original volume, and the concentration of the diluted reaction solution drops to below 10 wt.%), until the total acid content in the reaction solution is diluted to 5-10 wt%, causing lignin to precipitate. The reaction solution is allowed to stand for 6-8 hours, and the obtained reaction solution is centrifuged. The obtained solid lignin is washed with water and then freeze-dried to obtain lignin microspheres. The liquid obtained after centrifugation is subjected to rotary evaporation to remove the water, and the solid acid is recovered and recycled.

[0013] The lignin micro / nanospheres prepared by the above method are also within the scope of protection of this application.

[0014] Beneficial effects: Compared with existing technologies, the advantages of this invention include:

[0015] (1) The present invention uses a salicylic acid type solid acid that can be recovered by heating and evaporation. The recovered solid acid can be recycled and the water used can also be recovered and reused by rotary evaporation.

[0016] (2) By controlling the reaction intensity (reaction temperature, reaction time, acid concentration and solid-liquid ratio), lignin micro / nanospheres of different morphologies and sizes can be directly separated from wood fiber raw materials during the lignin dissolution process.

[0017] (3) Lignin micro / nanospheres have good electrochemical properties and superior energy storage properties compared to lignin such as groundwood lignin and alkali lignin;

[0018] (4) Compared with traditional methods, the preparation method is simple (only dissolution and dilution precipitation are needed to obtain lignin micro / nanospheres), has a high yield, does not use chemical reagents, reduces toxic and harmful pollution, and has good practicality and operability. Attached Figure Description

[0019] Figure 1 These are morphology images of lignin pretreated in a composite acid-water solvent system under different reaction conditions.

[0020] Figure 2 These are the size distribution diagrams and particle sizes of lignin microspheres under different reaction conditions, where a, MWL; b, lignin obtained under C40T70t30 conditions; c, lignin obtained under C50T90t30 conditions; and c, lignin obtained under C60T110t30 conditions.

[0021] Figure 3The figures represent the electrochemical performance of lignin under different reaction conditions. Here, a is the cyclic voltammetry (CV) curve of the lignin composite electrode (measured at a scan rate of 100 mV / s); b is the galvanostatic charge-discharge (GCD) curve of the lignin composite electrode (measured at a current density of 1 A / g); c is the specific capacitance of the lignin composite electrode; d is the cyclic stability of the lignin composite electrode at a current density of 1 / g; PAn represents polyaniline; PAn / MWL represents the lignin composite electrode prepared by combining polyaniline and groundwood lignin; and PAn / L-C60 represents the lignin composite electrode prepared by combining polyaniline and lignin prepared under the conditions of C60T110t30. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0023] Example 1

[0024] A method for preparing lignin microspheres with controllable size, comprising the following steps:

[0025] 1) Mix 0.1 mol / L dilute sulfuric acid and salicylic acid at a mass ratio of 1:0.5, add ultrapure water, adjust the total acid concentration to 40 wt.%, and heat at 50°C until a homogeneous and clear liquid is formed;

[0026] 2) Mix cotton stalk powder (the cotton stalk fibers are ground to 10 mesh using a disc mill) with the composite acid-water solvent system at a solid-liquid ratio of 1:5. React at 70℃ for 30 minutes. After the pretreatment is completed, separate the reaction solution and solids using a Buchner funnel. Add 10-15 times the volume of ultrapure water to wash the solids and dilute the reaction solution at the same time. Dilute the reaction solution to a total acid concentration of less than 10 wt.%. Freeze and let the reaction solution stand for 6-8 hours.

[0027] 3) Using a centrifuge, the reaction solution after standing is separated by centrifugation. The lignin is separated from the reaction solution by solid-liquid separation. The lignin micro / nanospheres are recovered. The lignin micro / nanospheres are washed with water until the washing solution is neutral. The solution is then freeze-dried to obtain purified lignin micro / nanospheres. Their main structural composition and content are analyzed, and the lignin removal rate is calculated.

[0028] 4) The diluted reaction solution is evaporated by rotary evaporation at 60°C to recover the water. After evaporation to dryness, the solid acid is recovered for recycling.

[0029] Example 2

[0030] A method for preparing lignin microspheres with controllable size, comprising the following steps:

[0031] 1) Mix 0.1 mol / L dilute sulfuric acid and salicylic acid in a mass ratio of 1:1, add ultrapure water, adjust the total acid concentration to 50 wt.%, and heat at 50°C until a homogeneous and clear liquid is formed.

[0032] 2) Mix cotton stalk powder with the composite acid-water solvent system at a solid-liquid ratio of 1:5, react at 90℃ for 30 min, and after the pretreatment is completed, use a Buchner funnel to separate the reaction solution and solids, add 10-15 times the volume of ultrapure water to wash the solids and dilute the reaction solution at the same time, dilute the reaction solution to a total acid concentration of less than 10 wt.%, and freeze the reaction solution for 6-8 h.

[0033] 3) Using a centrifuge, centrifuge the reaction solution after it has been allowed to stand, separate the lignin from the reaction solution to form a solid-liquid mixture, recover the lignin micro / nanospheres, wash the lignin micro / nanospheres with water until the washing solution is neutral, freeze dry to obtain purified lignin micro / nanospheres, analyze the content of its main components, and calculate the lignin removal rate.

[0034] 4) The diluted reaction solution is evaporated by rotary evaporation at 60°C to recover the water. After evaporation to dryness, the solid acid is recovered for recycling.

[0035] Example 3

[0036] A method for preparing lignin microspheres with controllable size, comprising the following steps:

[0037] 1) Mix 0.1 mol / L dilute sulfuric acid and salicylic acid in a mass ratio of 1:1, add ultrapure water, adjust the total acid concentration to 60 wt.%, and heat at 50°C until a homogeneous and clear liquid is formed.

[0038] 2) Mix cotton stalk powder with the composite acid-water solvent system at a solid-liquid ratio of 1:5, react at 110℃ for 30 min, and after the pretreatment is completed, use a Buchner funnel to separate the reaction solution and solids, add 10-15 times the volume of ultrapure water to wash the solids and dilute the reaction solution at the same time, dilute the reaction solution to a total acid concentration of less than 10 wt.%, and freeze the reaction solution for 6-8 h.

[0039] 3) Using a centrifuge, centrifuge the reaction solution after it has been allowed to stand, separate the lignin from the reaction solution to form a solid-liquid mixture, recover the lignin micro / nanospheres, wash the lignin micro / nanospheres with water until the washing solution is neutral, freeze dry to obtain purified lignin micro / nanospheres, analyze the content of its main components, and calculate the lignin removal rate.

[0040] 4) The diluted reaction solution is evaporated by rotary evaporation at 60°C to recover the water. After evaporation to dryness, the solid acid is recovered for recycling.

[0041] Example 4

[0042] The lignin prepared in Examples 1-3 was characterized.

[0043] As shown in Table 1, during the pretreatment process, as the reaction intensity (reaction temperature, reaction time and acid concentration) increased, the yield of lignin increased from 23% to 81%, indicating that the increase in reaction intensity is conducive to lignin fragmentation (molecular weight decreased from 7544 g / mol to 1822 g / mol), and fragmented lignin is more easily dissolved. The yield of lignin microspheres increases with the increase in reaction intensity.

[0044] Table 1. Lignin removal rate, molecular weight, aryl ether bond content of lignin microspheres, and microsphere size in the composite acid-water solvent system pretreatment.

[0045]

[0046] Where CxxTyytzz, C represents the concentration of the composite acid (wt.%, mass fraction); T represents the reaction temperature (°C); t represents...

[0047] Reaction time (min);

[0048] MWL is groundwood lignin, a lignin sample separated by the traditional Beckman method. It is generally used as the original structure of lignin in wood fiber raw materials. As a control sample, the MWL in this experiment was separated from cotton stalks.

[0049] The content of aryl ether bonds (β-O-4' bonds) in the recovered lignin was detected by nuclear magnetic resonance (NMR) (Table 1). The β-O-4' bond content in groundwood lignin (MWL) was 51%. After treatment with a composite acid-water solvent system, the β-O-4' bond content of the lignin showed little change at C40T50T30. With further increasing the reaction intensity (C50T90T30), the content gradually decreased, dropping to 42%. Even under the strongest reaction conditions, the β-O-4' bond content remained at 29%. This relatively high β-O-4' bond content, along with a relatively high phenolic hydroxyl content of 1.54 mmol / g, indicates that the lignin degraded during pretreatment still possesses a relatively intact structure and numerous functional groups, which is beneficial for further high-value applications. Figure 3 It can be seen that the lignin samples prepared by the composite acid-water solvent system have better electrochemical performance. For example, L-C60 prepared under C60T110t30 has a much higher specific capacitance than the lignin capacitor prepared by MWL.

[0050] The electrochemical performance testing method was as follows: The prepared electrode material sample was placed in a 0.1 mol / L dilute sulfuric acid solution. An electrochemical workstation was used to test the electrochemical performance of the electrode material using a three-electrode system, with lignin composite electrode material as the working electrode, carbon rod as the counter electrode, and mercuric oxide as the reference electrode. Cyclic voltammetry (CV) was performed at a scan rate of 100 mV / s within a voltage range of 0.2–0.8 V. Galvanostatic charge-discharge (GCD) was performed at a current density of 1 A / g within a voltage range of 0.2–0.8 V. The specific capacitance of the electrode material was calculated from the GCD curve using the following formula.

[0051]

[0052] In the formula, C is the specific capacitance (F / g), I is the discharge current (A), Δt is the total discharge time (s), m is the mass of the active material in the working electrode (g), and ΔV is the potential window (V). The cyclic stability of the electrode material was evaluated by performing 200 charge-discharge cycles at 1 A / g using GCD.

[0053] The morphology and size of lignin microspheres were observed using scanning electron microscopy, and the results are as follows: Figure 1 As shown. MWL is rod-shaped. After treatment with the composite solid acid-water solvent system used in this application, the recovered lignin gradually becomes spherical and its size gradually decreases (from micrometer to nanometer scale). Figure 2 and Figure 3 It can be seen that, with the change of reaction intensity, the prepared lignin microspheres gradually change from rod-shaped to uniform spherical. Specifically, at C40T90t30, the size of the lignin microspheres decreases, and the shape transitions from rod-shaped to spherical. When the strongest condition is reached (C60T110t30), the microsphere size reaches its minimum and the morphology becomes spherical.

[0054] This invention provides a method and approach for preparing lignin microspheres with controllable size. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing energy storage type lignin micro / nano-spheres with controllable morphology, characterized in that, First, a composite acid-water solvent system is constructed. This system is then used to treat lignocellulose raw materials. Lignin is then separated from the reaction system to obtain microspheres. The composite acid-water solvent system is obtained by mixing a solid acid with a strong acid, adding water, and heating to dissolve the mixture. The morphology and size of the lignin microspheres are controllable by controlling the reaction temperature, reaction time, acid concentration, and solid-liquid ratio. The composite acid-water solvent system is prepared as follows: dilute sulfuric acid and salicylic acid are mixed at a mass ratio of 1:0.1-1:1 to obtain a composite acid. The acid concentration in the composite acid-water solvent system is 10-80 wt.%, and the dilute sulfuric acid concentration is 1-10 wt.%. Water is then added to the composite acid, and the mixture is heated to dissolve at 40-50°C with continuous stirring until a clear, homogeneous solid acid-water solution is formed. The lignocellulose raw material is mixed with the composite acid-water solvent system and reacted at 60-110°C for 10-60 min. The solid-liquid ratio of the lignocellulose raw material to the composite acid-water solvent system is 1:5-1:

15.

2. The method according to claim 1, characterized in that, The separation steps are as follows: the reaction mixture is vacuum filtered on filter paper to separate the reaction solution from the solid. At the same time, the solid is washed with ultrapure water until the washing solution is neutral. The total acid content in the reaction solution is diluted to 5-10 wt% to precipitate lignin. The reaction solution is allowed to stand for 6-8 hours. The obtained reaction solution is centrifuged. The obtained solid lignin is washed with water and then freeze-dried to obtain lignin microspheres. The liquid obtained after centrifugation is subjected to rotary evaporation to remove water and the solid acid is recovered for recycling.

3. The lignin micro / nanospheres prepared by the method of claim 1 or 2.

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