Preparation method and application of biomass porous carbon material

Abstract

A method for preparing a porous biomass carbon material comprises the following steps: washing and crushing the biomass material; preparing a flux mixture solution according to the NaCl / KCl / H2O ternary phase diagram at 20°C; immersing the crushed biomass material in the flux mixture solution and isothermally evaporating the solution at room temperature until the volume of the solution is reduced to less than 90%; performing solid-liquid separation on the solid-liquid mixture after isothermal evaporation; measuring the ion content of the separated liquid phase, and adding water or sodium chloride or potassium chloride based on the measurement results to re-saturate the liquid phase to achieve recycling; drying the separated solid phase and then ball-milling it with potassium carbonate or potassium bicarbonate, transferring the ball-milled mixture to a vacuum tube furnace for calcination to obtain the porous biomass carbon material. This method can significantly reduce the amount of flux used, enabling the flux to be recycled. The resulting porous carbon material has excellent performance and can be used in the field of supercapacitors.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon material preparation, and in particular relates to a method for preparing a biomass porous carbon material. Background Art

[0002] Porous carbon materials are a very important class of carbonaceous materials with a porous structure. They not only possess the general advantages of carbon materials, but also have advantages such as high specific surface area, high porosity, and adjustable pore structure and pore size. They are widely used in water purification, gas separation (e.g., CO2 capture) and storage, and energy storage electrode materials for supercapacitors and batteries. Porous carbon materials have excellent physical and chemical properties and their preparation is based on a wide range of raw materials with low prices, thus attracting special attention from researchers. Currently, porous carbon materials can be prepared by high-temperature pyrolysis, physical or chemical activation of organic precursors (such as coal, wood, fruit shells, or polymers). Currently, there are many reports on the preparation of porous carbon materials using inexpensive biomass resources such as sucrose, glucose, cyclodextrin, cellulose, starch, or biochar. Biomass is abundant in nature, renewable, and non-toxic, making it the most ideal precursor for preparing porous carbon materials.

[0003] Currently, a common method for preparing porous biomass carbon involves adding a certain mass ratio of potassium hydroxide to the biomass material as a pore-forming agent. This potassium hydroxide reacts with the carbon during high-temperature calcination to produce water-soluble potassium carbonate. The unreacted potassium hydroxide is then washed away with a certain concentration of hydrochloric acid. However, this method has drawbacks: on the one hand, the addition of potassium hydroxide places high demands on the high-temperature reaction vessel; on the other hand, the unreacted potassium hydroxide after calcination needs to be washed away with hydrochloric acid. A solution to this problem is to use environmentally friendly pore-forming agents such as potassium carbonate and potassium bicarbonate instead of potassium hydroxide. Potassium carbonate, for example, is a mild alkaline compound with less toxicity and corrosiveness than potassium hydroxide. Potassium carbonate oxidizes carbonaceous matter to CO, creating porosity in the carbon residue. Furthermore, potassium vapor can intercalate between carbon layers, causing expansion and disruption of the carbon microstructure, thereby creating additional porosity.

[0004] In the above-mentioned chemical pore-forming methods, the problem faced is that the pore-forming effect is affected by the uniformity of mixing the pore-forming agent and the biomass carbon material. If a good pore-forming effect is to be achieved, a flux with a low melting point needs to be added. However, the amount of flux used is relatively large and it is difficult to recycle. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a biomass porous carbon material, which can greatly reduce the amount of flux used and enable the flux to be recycled; the prepared porous carbon material has excellent performance and can be applied in the field of supercapacitors.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a biomass porous carbon material, comprising the following steps:

[0007] (1) Cleaning and crushing the biomass material;

[0008] (2) A flux mixture solution was prepared according to the NaCl / KCl / H2O ternary system phase diagram at 20°C. In the flux mixture solution, sodium chloride and potassium chloride reached a saturation point at room temperature and their mass fractions in the flux mixture solution were 20.77% and 10.45%, respectively;

[0009] (3) soaking the biomass material crushed in step (1) in a flux mixed solution and isothermally evaporating the solution at room temperature until the volume of the flux mixed solution is reduced to less than 90%;

[0010] (4) performing solid-liquid separation on the solid-liquid mixture after isothermal evaporation;

[0011] The separated liquid phase is subjected to ion content determination, and water or sodium chloride or potassium chloride is added according to the determination results to make the liquid phase reach the saturation point again;

[0012] The separated solid phase is dried and then mixed with potassium carbonate or potassium bicarbonate by ball milling. The ball-milled mixture is transferred to a vacuum tube furnace for calcination. After washing and filtering, a biomass porous carbon material with uniform pores is obtained.

[0013] Preferably, in step (1), the biomass material is crushed to a size of less than 40 mesh.

[0014] Preferably, in step (1), the biomass material is one of straw, grapefruit peel, bark, lotus pod, lotus stem, and water candle.

[0015] Preferably, in step (3), the mass volume ratio between the biomass material and the flux mixed solution is (3-5) g:50 ml; isothermal evaporation is performed until the volume of the flux mixed solution is reduced to 70%-90%.

[0016] Preferably, in step (4), the mass ratio between the dried solid phase and potassium carbonate or potassium bicarbonate is 1:(1-2).

[0017] Preferably, in step (4), the temperature in the tube furnace is raised from room temperature to 700°C at a heating rate of 5-10°C / min, then raised to 850°C at a heating rate of 3-6°C / min and kept at this temperature for 2-4h, and finally cooled naturally.

[0018] Preferably, in step (4), solid-liquid separation is performed by filtration or centrifugation; and the separated solid phase is dried in a vacuum drying oven or a freeze drying oven at 60-80° C. for more than 8 h.

[0019] The present invention also provides the application of the biomass porous carbon material obtained by the above preparation method in lithium ion batteries, supercapacitors and sewage treatment.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The present invention uses potassium carbonate or potassium bicarbonate as a pore-forming agent, thereby avoiding the corrosion of calcination equipment by potassium hydroxide and also avoiding the use of hydrochloric acid for cleaning;

[0022] (2) The present invention effectively reduces the melting temperature of a single flux by using a mixed flux (NaCl / KCl), so that the flux can play a more effective role in the calcination process;

[0023] (3) The present invention utilizes the principle of the ternary phase diagram to effectively control the uniform precipitation of the mixed flux NaCl and KCl through isothermal evaporation of the saturation point of the ternary water-salt system, so that the precipitated grains are preferentially adsorbed on the surface of the carbonaceous precursor, achieving a good combination of the flux and the carbonaceous precursor, thereby greatly improving the uniformity of mixing the pore-forming agent and the biomass carbon material during the calcination process. The prepared porous carbon material has excellent performance and can be used in the field of supercapacitors;

[0024] (4) The present invention realizes the recycling of flux (sodium chloride and potassium chloride) through a low-cost and easy-to-operate method, greatly reducing the amount of flux used, and saving energy and protecting the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the method flow of the present invention;

[0026] Figure 2 SEM images of the materials prepared in Examples 1-3, (A) Example 1, (B) Example 2, (C) Example 3;

[0027] Figure 3 The NaCl / KCl / H2O ternary system phase diagram (20°C) on which the present invention is based;

[0028] Figure 4 The charge and discharge curves of the materials prepared in Examples 1-3 and applied in supercapacitors are shown in Figures 1-3, (A) Example 1, (B) Example 2, and (C) Example 3. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] like Figure 1 As shown, a method for preparing a biomass porous carbon material comprises the following steps:

[0032] (1) Wash the biomass material lotus pod and crush it to less than 40 mesh;

[0033] (2) Prepare the flux mixed solution according to Figure 3 Based on the provided NaCl / KCl / H2O ternary phase diagram (20°C), 15.1g of sodium chloride and 7.6g of potassium chloride were dissolved in 50ml of water to prepare a flux mixture solution that reached the co-saturation point at room temperature. The mass fractions of sodium chloride and potassium chloride in the mixed solution were 20.77% and 10.45% respectively.

[0034] (3) 5 g of the biomass material crushed in step (1) was immersed in 50 mL of the flux mixture solution and isothermally evaporated at room temperature until the volume of the flux mixture solution was reduced to 90%;

[0035] (4) separating the solid-liquid mixture after isothermal evaporation by filtering or centrifuging;

[0036] The separated liquid phase is subjected to ion content measurement, and water or sodium chloride or potassium chloride is added according to the measurement results to make the liquid phase reach the saturation point again, thereby realizing recycling;

[0037] The separated solid phase was dried at 60°C in a vacuum drying oven for more than 8 hours and then mixed with potassium carbonate or potassium bicarbonate by ball milling. The mass ratio between the solid phase and potassium carbonate or potassium bicarbonate was 1:1. The ball-milled mixture was transferred to a vacuum tube furnace for calcination. The temperature in the tube furnace was increased from room temperature to 700°C at a heating rate of 5-10°C / min, and then increased to 850°C at a heating rate of 3-6°C / min and kept at this temperature for 2-4 hours. Finally, the temperature was naturally lowered. After washing and filtration, a uniformly porous biomass porous carbon material with a morphology as shown in FIG. Figure 2 As shown in (A), it can be seen from the figure that the pore size distribution of the material prepared in this embodiment is uniform.

[0038] The porous carbon material prepared in this example is applied to a supercapacitor, and the charge-discharge curve at a current density of 5 A / g is as follows: Figure 4 As shown in (A), the charge-discharge capacity at a current density of 5 A / g is 275.2 F g -1 The charge and discharge curve is a typical triangle, and the capacity is moderate and stable.

[0039] Example 2

[0040] like Figure 1 As shown, a method for preparing a biomass porous carbon material comprises the following steps:

[0041] (1) After cleaning the biomass material lotus stem, crush it to less than 40 mesh;

[0042] (2) Prepare the flux mixed solution according to Figure 3 Based on the provided NaCl / KCl / H2O ternary phase diagram (20°C), 15.1g of sodium chloride and 7.6g of potassium chloride were dissolved in 50ml of water to prepare a flux mixture solution that reached the co-saturation point at room temperature. The mass fractions of sodium chloride and potassium chloride in the mixed solution were 20.77% and 10.45% respectively.

[0043] (3) immersing 3 g of the biomass material crushed in step (1) into 50 mL of a flux mixture solution and performing isothermal evaporation at room temperature until the volume of the flux mixture solution is reduced to 87%;

[0044] (4) separating the solid-liquid mixture after isothermal evaporation by filtering or centrifuging;

[0045] The separated liquid phase is subjected to ion content measurement, and water or sodium chloride or potassium chloride is added according to the measurement results to make the liquid phase reach the saturation point again, thereby realizing recycling;

[0046] The separated solid phase was dried at 70°C in a vacuum drying oven for more than 8 hours and then mixed with potassium carbonate or potassium bicarbonate by ball milling. The mass ratio between the solid phase and potassium carbonate or potassium bicarbonate was 1:1.5. The ball-milled mixture was transferred to a vacuum tube furnace for calcination. The temperature in the tube furnace was increased from room temperature to 700°C at a heating rate of 5-10°C / min, and then increased to 850°C at a heating rate of 3-6°C / min and kept at this temperature for 2-4 hours. Finally, the temperature was naturally lowered. After washing and filtration, a uniformly porous biomass porous carbon material with a morphology as shown in FIG. Figure 2 As shown in (B), it can be seen from the figure that the pore size distribution of the material prepared in this embodiment is uniform.

[0047] The porous carbon material prepared in this example is applied to a supercapacitor, and the charge-discharge curve at a current density of 5 A / g is as follows: Figure 4 As shown in (B), the charge-discharge capacity at a current density of 5 A / g is 287.8 F g -1 The charge and discharge curve is a typical triangle, and the capacity is moderate and stable.

[0048] Example 3

[0049] like Figure 1 As shown, a method for preparing a biomass porous carbon material comprises the following steps:

[0050] (1) After washing the biomass material with water candles, crush it to less than 40 mesh;

[0051] (2) Prepare the flux mixed solution according to Figure 3 According to the provided NaCl / KCl / H2O ternary system phase diagram, 15.1g of sodium chloride and 7.6g of potassium chloride were dissolved in 50ml of water to prepare a flux mixture solution that reached the cosaturation point. The mass fractions of sodium chloride and potassium chloride in the mixed solution were 20.77% and 10.45% respectively.

[0052] (3) immersing 4 g of the biomass material crushed in step (1) into 50 mL of a flux mixture solution and performing isothermal evaporation at room temperature until the volume of the flux mixture solution is reduced to 80%;

[0053] (4) separating the solid-liquid mixture after isothermal evaporation by filtering or centrifuging;

[0054] The separated liquid phase is subjected to ion content determination, and water or sodium chloride or potassium chloride is added according to the determination results to make the solution reach the saturation point again, thereby realizing recycling;

[0055] The separated solid phase was dried at 80°C in a freeze drying oven for more than 8 hours and then mixed with potassium carbonate or potassium bicarbonate by ball milling. The mass ratio between the solid phase and potassium carbonate or potassium bicarbonate was 1:2. The ball-milled mixture was transferred to a vacuum tube furnace for calcination. The temperature in the tube furnace was increased from room temperature to 700°C at a heating rate of 5-10°C / min, and then increased to 850°C at a heating rate of 3-6°C / min and kept at this temperature for 2-4 hours. Finally, the temperature was naturally lowered. After washing and filtration, a uniformly porous biomass porous carbon material with a morphology as shown in FIG. Figure 2 As shown in (C), it can be seen from the figure that the pore size distribution of the material prepared in this embodiment is uniform.

[0056] The porous carbon material prepared in this example is applied to a supercapacitor, and the charge-discharge curve at a current density of 5 A / g is as follows: Figure 4 As shown in (C), the charge-discharge capacity at a current density of 5 A / g is 283.0 F g -1 The charge and discharge curve is a typical triangle, and the capacity is moderate and stable.

Claims

1. A method for preparing a biomass porous carbon material, characterized in that: The following steps are involved: (1) Cleaning and crushing the biomass material; (2) A flux mixture solution was prepared according to the NaCl / KCl / H2O ternary system phase diagram at 20°C. In the flux mixture solution, sodium chloride and potassium chloride reached a saturation point at room temperature, and their mass fractions in the flux mixture solution were 20.77% and 10.45%, respectively. (3) soaking the biomass material crushed in step (1) in a flux mixed solution and isothermally evaporating the solution at room temperature until the volume of the flux mixed solution is reduced to less than 90%; (4) performing solid-liquid separation on the solid-liquid mixture after isothermal evaporation; The separated liquid phase is subjected to ion content determination, and water or sodium chloride or potassium chloride is added according to the determination results to make the liquid phase reach the saturation point again; The separated solid phase is dried and then mixed with potassium carbonate or potassium bicarbonate by ball milling. The ball-milled mixture is transferred to a vacuum tube furnace for calcination. After washing and filtering, a biomass porous carbon material with uniform pores is obtained.

2. The method for preparing a biomass porous carbon material according to claim 1, characterized in that: In step (1), the biomass material is crushed to a size of less than 40 mesh.

3. The method for preparing a biomass porous carbon material according to claim 1 or 2, characterized in that: In step (1), the biomass material is one of straw, grapefruit peel, bark, lotus pod, lotus stem, and water candle.

4. The method for preparing a biomass porous carbon material according to claim 1 or 2, characterized in that: In step (3), the mass volume ratio between the biomass material and the flux mixed solution is (3-5) g:50 ml; isothermal evaporation is performed until the volume of the flux mixed solution is reduced to 70%-90%.

5. The method for preparing a biomass porous carbon material according to claim 1 or 2, characterized in that: In step (4), the mass ratio between the dried solid phase and potassium carbonate or potassium bicarbonate is 1:(1-2).

6. The method for preparing a biomass porous carbon material according to claim 1 or 2, characterized in that: In step (4), the temperature in the tube furnace is raised from room temperature to 700°C at a heating rate of 5-10°C / min, then raised to 850°C at a heating rate of 3-6°C / min and kept at this temperature for 2-4h, and finally cooled naturally.

7. The method for preparing a biomass porous carbon material according to claim 1 or 2, characterized in that: In step (4), solid-liquid separation is performed by filtration or centrifugation; the separated solid phase is dried in a vacuum drying oven at 60-80° C. for more than 8 hours.

8. Use of the biomass porous carbon material obtained by the preparation method according to any one of claims 1 to 7 in a supercapacitor.

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