CN108726517A - The method for improving rice husk base capacitance carbon volumetric capacitance - Google Patents

Abstract

The invention discloses a method for increasing the volume specific capacitance of rice husk-based capacitor carbon, which belongs to the field of biomass energy chemical industry. Three methods are used to increase the tap density and volume specific capacitance; specifically, it involves: (1) impregnating treatment with a dehydration carbon-fixing catalyst , temperature-controlled pyrolysis to increase the fixed carbon content; (2) After hydrothermal desiliconization of the pyrolytic carbon, the template carbon is treated with impregnated pitch to fill the micropores caused by gasification and increase the tap density; (3) Modified with electrode pitch Modified capacitor carbon surface to improve conductivity and tap density. Compared with the prior art, the invention prepares the rice husk-based capacitor carbon through different modification methods, and improves the tap density, volume specific capacitance, cycle stability and yield of the capacitor carbon.

Description

Method for Improving Volume Specific Capacitance of Rice Husk Based Capacitor Carbon

technical field

The invention belongs to the field of biomass energy chemical industry, and discloses a method for increasing the volume specific capacitance of rice husk-based capacitor carbon, in particular to impregnating rice husk with a dehydration carbon-fixing catalyst, impregnating asphalt to treat template carbon, and modifying electrode pitch to modify capacitor carbon to improve rice Shell carbon volume specific capacitance method.

Background technique

Biomass materials have the characteristics of wide sources and environmental friendliness. In recent years, the use of biomass as raw material to prepare capacitor carbon has received extensive attention. Rice husk is a renewable biomass resource with low price and huge output. Capacitor carbon prepared from rice husk has a multi-level pore structure and a large specific surface area. However, rice husk-based capacitor carbon is used as a supercapacitor electrode material The main problem is that the fixed carbon content of rice husk is low, the volume specific capacitance as a supercapacitor is small, and a larger volume is required to store the capacitance per unit mass, making it less commercial and not conducive to practical applications.

In order to improve the volume specific capacitance of the rice husk-based capacitor carbon, the present invention uses a dehydration carbon-fixing catalyst to treat the rice husk and then pyrolyzes it, then uses impregnated pitch to modify the desiliconized pyrolytic carbon, and after activation, treats it with electrode pitch. Asphalt is a material with high fixed carbon content and good electrical conductivity. Using asphalt to modify desiliconized pyrolytic carbon and activated carbon can increase the tap density of the material, increase the volume specific capacitance, and increase the electrical conductivity of the material. In order to improve the electrochemical performance, such as the Chinese patent document with the notification number "CN107364863A", which discloses the preparation method of modified rice husk-based activated carbon, which effectively improves the volume specific capacitance and cycle stability of rice husk-based activated carbon as an electrode material. The dehydration carbon-fixing catalyst catalyzes the dehydration of rice husks during the pyrolysis process. Controlling the temperature increases the dehydration time of rice husks during the pyrolysis process, reduces the formation of gas and liquid phases, thereby increasing the content of solid phases, thereby increasing the yield of rice husk charcoal. The rate increases the volume specific capacitance of the capacitor carbon.

The current problems of rice husk-based capacitor carbon:

1. During the pyrolysis process of rice husk, a large amount of carbon is lost in gaseous and liquid states, and the content of fixed carbon is small;

2. The conductivity of rice husk capacitor carbon is poor, which makes it difficult to transport electrolyte ions;

3. The tap density is low, which affects the volume specific capacitance.

Therefore need a kind of new technical scheme to solve this problem in the prior art.

Contents of the invention

During the pyrolysis process of rice husk, volatile matter escapes, forming a large number of micropores, and the tap density of pyrolytic carbon is low. After desiliconization and activation, the tap density of capacitor carbon is lower, resulting in low volume specific capacitance. The capacitor storage capacity of volume is little, and this has restricted the application of rice husk charcoal (or biomass charcoal) in the field of energy storage batteries and supercapacitors, and the purpose of the present invention is to provide the method for improving rice husk charcoal volume specific capacitance, with rice husk charcoal As a carbon source, the modified rice husk-based capacitor carbon material was prepared through the steps of catalyst treatment, carbonization, asphalt-modified desiliconization pyrolytic carbon, and asphalt-modified capacitor carbon. The prepared material has the characteristics of a supercapacitor electrode material with good electrochemical stability and high volume specific capacitance, and has low cost, little pollution, and environmental friendliness, and can be mass-produced.

In order to achieve the above object, the present invention adopts following technical scheme: improve the method for rice husk base capacitor carbon volume specific capacitance, it is characterized in that, this method comprises the steps:

Step 1. Sieve the rice husk to remove impurities and crush it to obtain rice husk powder. Mix the rice husk powder with the catalyst solution and perform impregnation treatment. drying at 100°C to obtain pretreated rice husk;

Step 2. Put the pretreated rice husk prepared in step 1 in a tube furnace, first heat up to 200°C-300°C, pyrolyze for 0.5h, then heat up to 500°C-600°C, and pyrolyze for 1h under nitrogen protection. Be down to room temperature, obtain pyrolysis charcoal;

Step 3: Add the pyrolytic charcoal obtained in Step 2 and the NaOH solution with a concentration of 5wt% into the reaction kettle according to the ratio of solid-to-liquid ratio 1Kg: 10L, heat and reflux for 2 hours, cool down, filter and separate, and wash the filter cake until Neutral, dried to obtain desiliconized pyrolytic carbon;

Step 4. Mix the desiliconized pyrolytic carbon obtained in step 3 with the impregnated pitch evenly, place it in a reaction kettle, raise the temperature to 150°C-250°C, impregnate it for 2h-5h under the pressure of 0.1MPa-0.6MPa, and cool After that, the asphalt impregnated precursor is obtained;

Step 5. Transfer the pitch-impregnated precursor obtained in step 4 to a tube furnace, heat up to 600°C-1000°C for carbonization for 1h-2h, and prepare pitch-impregnated pyrolytic carbon;

Step 6. Treat the asphalt-impregnated pyrolytic carbon prepared in step 5 to obtain carbon powder. Mix the carbon powder and alkali evenly according to the carbon-alkali ratio of 1: (2.0-2.5), place it in a tube furnace, and first heat it at 5°C/min The heating rate is raised to 450°C, kept for 0.5h, and then continued to rise to 700°C at a heating rate of 5°C/min, kept for 1h, and taken out after cooling down to room temperature, washed with hot deionized water until neutral, and dried at 120°C , prepared catalytic rice husk/pitch-based capacitive carbon.

The method for improving the volume specific capacitance of rice husk-based capacitor carbon adopts the method described in the above steps 1 to 6, and is characterized in that it also includes:

Step 7, preparation of asphalt modified capacitor carbon:

(1) Add the catalytic rice husk/pitch-based capacitor carbon prepared in step 6 into the asphalt suspension, stir and disperse for 0.5h-2h, heat to recover the solvent, put the solid in a drying oven, and dry at 85°C for 5h-12h, Prepare pitch/capacitor carbon mixed powder;

(2) Transfer the pitch/capacitor carbon mixed powder prepared in step (1) to a tube furnace, and under the protection of nitrogen, raise the temperature to 150°C-250°C for 1h-2h constant temperature heat treatment, and then raise the temperature to 600°C-1000°C constant temperature Heat treatment for 1h-2h, cool down, break up, and prepare pitch-modified capacitor carbon.

The impregnation treatment process described in step 1 is as follows: add rice husk powder and catalyst solution to the reactor, seal it, and heat it with steam at a heating temperature of 120°C to 130°C, and pressurize and impregnate for 1 hour; or the temperature of the heating system is 30°C ~50°C, constant temperature immersion for 24h.

The catalyst in the first step is one or a mixture of NH ₄ Cl, NH ₄ OH, HCl, H ₂ SO ₄ , H ₃ PO ₄ .

The mass concentration of the catalyst solution in the step 1 is 0%-20%.

The solid-to-liquid ratio of the rice husk powder and the catalyst solution in the step 1 is 1Kg:(5-20)L.

The preparation method of the asphalt suspension in the step 7 is: adding the asphalt powder into the solvent, stirring and dispersing for 0.5-2 hours to obtain the asphalt suspension.

The ratio of pitch to catalytic rice husk/pitch-based capacitor carbon solid content in step 7 is (10-30):100.

The solvent in the step seven is one or a mixture of cyclohexanol, absolute ethanol, acetone, tetrahydrofuran, cyclohexane, and n-hexane.

The solid-to-liquid ratio of the pitch to the solvent is (5Kg-15Kg):100L.

Through the above design scheme, the present invention can bring the following beneficial effects:

1. The rice husk used is a renewable biomass resource, and the preparation process is non-polluting and low in price; the asphalt material has a wide range of sources, low cost, environmental friendliness, and can be produced on a large scale.

2. The carbon-fixing catalyst treats rice husks, promotes dehydration, reduces the loss of gas and liquid phases during the carbonization of rice husks, and increases the content of fixed carbon.

3. Asphalt can form a flow state when it reaches the softening point temperature, and the flow state of the asphalt can modify the modified pyrolytic carbon during the activation process, thereby effectively improving the electrochemical performance of the material.

4. The fixed carbon content of asphalt is high, and co-activation with rice husk pyrolytic carbon can increase the tap density of activated carbon, thereby increasing the volume specific capacitance of the material.

5. The template carbon is treated with impregnated asphalt, and the fine carbon powder is wrapped on the particle surface with a uniform particle size, and the micropores caused by gasification are filled to increase the tap density.

Description of drawings

Fig. 1 is a schematic diagram of the specific capacitance and the number of cycles of the embodiment 1 and the embodiment 2 of the present invention when the current density is 1A/g and the constant current is charged and discharged 20,000 times.

Detailed ways

In order to show the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention. In order not to obscure the essence of the present invention, well-known methods and procedures have not been described in detail.

Example 1

(1) The raw material rice husk is screened to remove impurities, and crushed to a particle size of 10 mm to 20 mm to obtain rice husk powder, which is set aside;

(2) Place the rice husk powder obtained in step (1) in a tube furnace, and under the protection of nitrogen, heat up to 200°C at a heating rate of 5°C/min, pyrolysis and dehydration for 0.5h, and then heat up to 200°C at a heating rate of 5°C/min The heating rate is increased to 500°C, pyrolyzed for 1 hour, and pyrolytic charcoal is obtained;

(3) Mix the pyrolytic carbon obtained in step (2) with the NaOH solution with a concentration of 5wt% according to the solid-to-liquid ratio of 1Kg:10L, heat and reflux for 2h, suction filter after cooling down to room temperature, wash the filter cake with water until neutral, and dry , to obtain desiliconized rice husk pyrolytic carbon;

(4) Add the desiliconized rice husk pyrolytic carbon and sodium hydroxide obtained in step (3) into the high-mixer and mix evenly according to the mass ratio of 1:2.5, then transfer to the tube furnace protected by nitrogen, and first heat the mixture at 5°C Raise the temperature to 450°C at a heating rate of 5°C/min and keep it for 0.5h, then raise the temperature to 700°C at a heating rate of 5°C/min, keep it for 1h, wash to neutral after cooling down to room temperature, and dry at 120°C to obtain rice husk base Capacitor carbon AC1.

Example 2

(1) Sieve the raw rice husk to remove impurities, crush it to a particle size of 10mm-20mm, and add NH ₄ OH solution with a concentration of 5wt% into the reaction kettle according to the solid-to-liquid ratio of 1Kg:10L, seal and heat to 120°C, Pressure impregnation for 1 hour, suction filtration after cooling down to room temperature, the filtrate is recycled after adjusting the concentration, and the filter cake is dried at 100°C to obtain catalyst-treated rice husks for later use;

(2) Place the catalyst-treated rice husk obtained in step (1) in a tube furnace, and under the protection of nitrogen, heat up to 200°C at a heating rate of 5°C/min, pyrolyze for 0.5h, and then heat up to 200°C at a heating rate of 5°C/min. The heating rate is increased to 500°C, pyrolyzed for 1 hour, and pyrolytic charcoal is obtained;

(3) The pyrolytic charcoal obtained in step (2) is mixed with a NaOH solution having a concentration of 5wt% according to a solid-to-liquid ratio of 1Kg:10L, heated to reflux for 2h, suction filtered after being down to room temperature, and the filter cake is washed to neutrality, dried dry to obtain desiliconized pyrolytic carbon;

(4) According to the carbon-alkali mass ratio of 1:2.5, add the desiliconized pyrolytic carbon and sodium hydroxide obtained in step (3) into a tube furnace protected by nitrogen, and first heat up to Keep at 450°C for 0.5h, then raise the temperature to 700°C at a rate of 5°C/min, keep for 1h, wash to neutral after cooling down to room temperature, and dry at 120°C to obtain catalytic rice husk-based capacitor carbon AC2.

Example 3

(1) Sieve the raw rice husk to remove impurities, crush it to a particle size of 10 mm to 20 mm, and add NH ₄ OH solution with a concentration of 5wt% into the reaction kettle according to the solid-to-liquid ratio of 1Kg:10L, seal and heat to 120°C, Pressure impregnation for 1 hour, suction filtration after cooling down to room temperature, the filtrate is recycled after adjusting the concentration, and the filter cake is dried at 100°C to obtain catalyst-treated rice husks for later use;

(2) Place the catalyst-treated rice husk obtained in step (1) in a tube furnace, and under the protection of nitrogen, first raise the temperature to 200°C at a heating rate of 5°C/min, pyrolyze for 0.5h, and then raise the temperature at a heating rate To 500 ° C, pyrolysis for 1 hour, to obtain catalytic pyrolysis carbon;

(3) The catalytic pyrolytic carbon obtained in step (2) is mixed with a NaOH solution having a concentration of 5wt% according to a solid-to-liquid ratio of 1Kg:10L, heated to reflux for 2h, suction filtered after being down to room temperature, and the filter cake is washed to neutrality, drying to obtain desiliconized pyrolytic carbon;

(4) According to the mass ratio of 4:1, mix the desiliconized pyrolytic carbon obtained in step (3) with the impregnated pitch evenly, place it in a reaction kettle, raise the temperature to 200°C, and impregnate it for 2 hours under the condition of a pressure of 0.5MPa, After cooling, the pitch-impregnated pyrolytic carbon is obtained;

(5) According to the carbon-alkali mass ratio of 1:2.5, add the asphalt-impregnated pyrolytic carbon and sodium hydroxide obtained in step (4) into a tube furnace protected by nitrogen, and first heat up to Keep at 450°C for 0.5h, then raise the temperature to 700°C at a rate of 5°C/min, hold for 1h, wash to neutral after cooling down to room temperature, and dry at 120°C to obtain catalytic rice husk/pitch-based capacitor carbon AC3.

Example 4

According to the mass ratio of 6:1, the desiliconized pyrolytic carbon obtained in step (3) is mixed with the impregnated pitch evenly, and placed in the reaction kettle. The other conditions are the same as in Example 3, and the catalytic rice husk/pitch-based capacitor carbon AC4 is obtained. .

Example 5

According to the mass ratio of 8:1, the desiliconized pyrolytic carbon obtained in step (3) is mixed evenly with the impregnated pitch, and placed in the reaction kettle. The other conditions are the same as in Example 3, and the catalytic rice husk/pitch-based capacitor carbon AC5 is obtained. .

Example 6

According to the mass ratio of 10:1, the desiliconized pyrolytic carbon obtained in step (3) was mixed with the impregnated pitch evenly, and placed in the reaction kettle. The other conditions were the same as in Example 3, and the catalytic rice husk/pitch-based capacitor carbon AC6 was obtained. .

Example 7

The raw rice husk is screened to remove impurities, crushed to a particle size of 10 mm to 20 mm, mixed with HCl solution having a mass concentration of 2% according to a solid-to-liquid ratio of 1Kg:10L, and other conditions are the same as in Example 3 to obtain catalytic rice husk/asphalt Base Capacitor Carbon AC7.

Example 8

(1) According to the dry mass ratio of 4:1, the catalytic rice husk/pitch-based capacitor carbon prepared in Example 3 was added to the electrode pitch ethanol suspension, stirred and dispersed for 1 hour, the solvent was recovered by heating, and the solid was placed in a drying box , dried at 85°C for 5h to 12h to prepare pitch/capacitor carbon mixed powder;

(2) Transfer the asphalt/capacitor carbon mixed powder to a tube furnace, and under the protection of nitrogen, heat up to 200°C for 1 hour, then heat up to 800°C for 1 hour, cool down, break up, and prepare a pitch-modified capacitor Charcoal AC8.

Cyclic stability and specific capacitance of table 1 embodiment sample

Note: The volume specific capacitance and cycle stability are tested in 6moL/L KOH electrolyte.

It can be seen from Table 1 that the volume specific capacitance of the catalytic rice husk/pitch-based capacitor carbon has been greatly improved compared with the rice husk-based capacitor carbon, and the electrochemical cycle stability is also better.

Obviously, the descriptions of the above embodiments are only used to help understand the method of the present invention and its core idea, but for those of ordinary skill in the art, they can Various changes, modifications and substitutions are made to these embodiments, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (10)

1. improve the method for rice husk base capacitor carbon volume specific capacitance, it is characterized in that, the method comprises the steps: Step 1. Sieve the rice husk to remove impurities and crush it to obtain rice husk powder. Mix the rice husk powder with the catalyst solution and perform impregnation treatment. drying at 100°C to obtain pretreated rice husk; Step 2. Put the pretreated rice husk prepared in step 1 in a tube furnace, first heat up to 200°C-300°C, pyrolyze for 0.5h, then heat up to 500°C-600°C, and pyrolyze for 1h under nitrogen protection. Be down to room temperature, obtain pyrolysis charcoal; Step 3: Add the pyrolytic charcoal obtained in Step 2 and the NaOH solution with a concentration of 5wt% into the reaction kettle according to the ratio of solid-to-liquid ratio 1Kg: 10L, heat and reflux for 2 hours, cool down, filter and separate, and wash the filter cake until Neutral, dried to obtain desiliconized pyrolytic carbon; Step 4. Mix the desiliconized pyrolytic carbon obtained in step 3 with the impregnated pitch evenly, place it in a reaction kettle, raise the temperature to 150°C-250°C, impregnate it for 2h-5h under the pressure of 0.1MPa-0.6MPa, and cool After that, the asphalt impregnated precursor is obtained; Step 5. Transfer the pitch-impregnated precursor obtained in step 4 to a tube furnace, heat up to 600°C-1000°C for carbonization for 1h-2h, and prepare pitch-impregnated pyrolytic carbon; Step 6. Treat the asphalt-impregnated pyrolytic carbon prepared in step 5 to obtain carbon powder. Mix the carbon powder and alkali evenly according to the carbon-alkali ratio of 1: (2.0-2.5), place it in a tube furnace, and first heat it at 5°C/min The heating rate is raised to 450°C, kept for 0.5h, and then continued to rise to 700°C at a heating rate of 5°C/min, kept for 1h, and taken out after cooling down to room temperature, washed with hot deionized water until neutral, and dried at 120°C , prepared catalytic rice husk/pitch-based capacitive carbon. 2. improve the method for rice husk base capacitor carbon volume specific capacitance, adopt the method described in step 1 to step 6 as claimed in claim 1, it is characterized in that, also comprises: Step 7, preparation of asphalt modified capacitor carbon: (1) Add the catalytic rice husk/pitch-based capacitor carbon prepared in step 6 into the asphalt suspension, stir and disperse for 0.5h-2h, heat to recover the solvent, put the solid in a drying oven, and dry at 85°C for 5h-12h, Prepare pitch/capacitor carbon mixed powder; (2) Transfer the pitch/capacitor carbon mixed powder prepared in step (1) to a tube furnace, and under the protection of nitrogen, raise the temperature to 150°C-250°C for 1h-2h constant temperature heat treatment, and then raise the temperature to 600°C-1000°C constant temperature Heat treatment for 1h-2h, cool down, break up, and prepare pitch-modified capacitor carbon. 3. The method for improving the volume specific capacitance of rice husk-based capacitor carbon according to claim 1 or 2, characterized in that: the impregnation process described in step 1 is as follows: rice husk powder and catalyst solution are added to the reactor, sealed , use steam heating, the heating temperature is 120 ℃ ~ 130 ℃, pressure impregnation 1h; or the temperature of the heating system is 30 ℃ ~ 50 ℃, constant temperature immersion 24h. 4. The method for improving the volume specific capacitance of rice husk-based capacitor carbon according to claim 1 or 2, characterized in that: the catalyst in the step 1 is NH ₄ Cl, NH ₄ OH, HCl, H ₂ SO ₄ , H ₃ PO ₄ one or a mixture of two or more. 5. The method for increasing the volume specific capacitance of rice husk-based capacitor carbon according to claim 1 or 2, characterized in that: the mass concentration of the catalyst solution in the step 1 is 0% to 20%. 6. The method for improving rice husk-based capacitor carbon volume specific capacitance according to claim 1 or 2, characterized in that: the solid-liquid ratio of the rice husk powder and catalyst solution in the step 1 is 1Kg: (5～20) L. 7. The method for improving rice husk-based capacitor carbon volume specific capacitance according to claim 2, characterized in that: the preparation method of the asphalt suspension in the step 7 is: add asphalt powder in the solvent, stir and disperse for 0.5 ~2h, the asphalt suspension was obtained. 8. The method for improving rice husk-based capacitor carbon volume specific capacitance according to claim 2, characterized in that: the ratio of pitch and catalytic rice husk/pitch-based capacitor carbon solid content in the step 7 is (10～30) : 100. 9. The method for improving rice husk-based capacitor carbon volume specific capacitance according to claim 2, characterized in that: the solvent in the step seven is cyclohexanol, dehydrated alcohol, acetone, tetrahydrofuran, cyclohexanol, One or two mixtures of hexane and n-hexane. 10. The method for increasing the volume specific capacitance of rice husk-based capacitor carbon according to claim 8 or 9, characterized in that: the solid-to-liquid ratio of the pitch to the solvent is (5Kg˜15Kg):100L.