Method for producing capacitive activated carbon from ultra-low-ash low-rank coal

Abstract

The invention relates to the technical field of activated carbon production, in particular to a method for producing capacitive activated carbon from ultra-low-ash low-rank coal, which comprises the following steps: taking low-ash low-rank coal as a raw material, and effectively removing ash and inorganic salt through crushing, deionized water cleaning and vacuum drying; the pore structure is optimized through activating agent mixing and microwave assistance, and the mesoporosity is improved; carrying out post-treatment, removing the residual activating agent through diluted hydrochloric acid ultrasonic cleaning, and drying and forming; finally, a high-density oxygen / nitrogen-containing functional group is introduced through oxidizing agent surface modification and urea high-temperature nitrogen doping, and the pseudocapacitance effect and the electrochemical performance are remarkably enhanced. Through repeated cleaning with deionized water and combination of vacuum drying, the ash removal rate is increased to 95% or above, oxidation side reaction is avoided, and the purity of the raw materials is guaranteed; meanwhile, microwave-assisted activation is introduced, intercalation reaction of the activating agent and coal is accelerated by microwave selective heating, and mesoporous generation is promoted by microwave-induced molecular vibration.

Description

Technical Field

[0001] The present invention relates to the technical field of activated carbon production, and specifically to a method for producing capacitive activated carbon from ultra-low ash low-rank coal. Background Art

[0002] Capacitive activated carbon is a functional carbon material with a high specific surface area, developed pore structure and abundant surface functional groups, which is designed specifically for supercapacitors (also known as electrochemical capacitors) and can efficiently store charges through physical adsorption / desorption or redox reactions. Capacitive activated carbon is the core material in the field of electrochemical energy storage, and its performance directly determines the technical level of supercapacitors. In the future, with the popularization of new energy and smart grids, high-performance and low-cost capacitive carbon will become the key high ground in industrial competition.

[0003] However, when preparing high-performance activated carbon from low-rank coal, the ash and inorganic salt residues in the low-rank coal will block the pores and reduce the specific surface area of the activated carbon; and in the conventional thermal activation treatment, the heating rate is slow, resulting in insufficient development of micropores and a low proportion of mesopores; at the same time, traditional oxidation modification only introduces oxygen-containing functional groups, resulting in a low density of oxygen / nitrogen-containing functional groups on the surface of the activated carbon and limited contribution of pseudocapacitance. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a method for producing capacitive activated carbon from ultra-low ash low-rank coal, which solves the problems of the influence of raw material impurities on the pore structure, the low efficiency of the activation process, and the deficiency of surface modification.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for producing capacitive activated carbon from ultra-low ash low-rank coal, comprising the following steps:

[0006] S1. Raw material preparation

[0007] Use a crusher to crush the low-ash low-rank coal until its particle size is 0.20 - 0.30 mm;

[0008] S2. Pretreatment

[0009] Use deionized water to wash the low-ash low-rank coal 3 - 5 times to remove surface inorganic salts and ash, and then dry it in a vacuum drying oven at 120°C for 24 hours, with a vacuum degree ≤ -0.08 MPa to avoid oxidation reactions;

[0010] S3. Activation treatment

[0011] Mix the dried low-ash low-rank coal with an activator in a certain proportion, then put the mixed raw materials into a tubular furnace, and introduce helium gas. Heat it to 650°C at a heating rate of 10°C / min, hold for 0.5 hours, and introduce microwave assistance during the activation process to accelerate pore generation to obtain an activated carbon product;

[0012] S4. Post-treatment

[0013] After the activation is completed, the activated carbon is taken out and cooled, and then ultrasonically cleaned with a 5% by mass dilute hydrochloric acid solution to remove the residual activator and other impurities; subsequently, the activated carbon is washed with deionized water until neutral, and finally dried in an oven at 120 °C for 24 hours;

[0014] S5. Modification treatment

[0015] First, the activated carbon is subjected to surface oxidation treatment with an oxidant, and then the activated carbon and urea are mixed at a mass ratio of 1:2 and treated at 800 °C for 2 hours, so that the density of oxygen / nitrogen functional groups on the surface is increased to 1.2 - 1.5 mmol / g, thereby improving the capacitance performance of the activated carbon.

[0016] Preferably, in the step S3, the activator includes, but is not limited to, any one or a combination of more than one of potassium hydroxide, potassium nitrate, sodium nitrate, ferrous sulfate, and zinc nitrate.

[0017] Preferably, in the step S3, the alkali-carbon ratio of the low-ash low-rank coal to the activator is 3:1.

[0018] Preferably, in the step S5, the oxidant includes, but is not limited to, any one or a combination of more than one of nitric acid, hydrogen peroxide, ammonium persulfate, potassium permanganate, and ammonium nitrate.

[0019] Preferably, in the step S3, the microwave frequency of the microwave assistance is 2.45 GHz and the power is 500 W.

[0020] The present invention provides a method for producing capacitive activated carbon from ultra-low-ash low-rank coal. It has the following beneficial effects:

[0021] 1. In the present invention, through multiple washings with deionized water and combined with vacuum drying, the ash removal rate is increased to more than 95%, avoiding oxidation side reactions and ensuring the purity of the raw material; at the same time, microwave-assisted activation is introduced, and by using microwave selective heating, the intercalation reaction between the activator and the coal is accelerated, the heating rate is increased to 10 °C / min, and the molecular vibration induced by the microwave promotes the formation of mesopores, so that the mesopore rate is increased to 35% - 40%.

[0022] 2. In the present invention, through mixed oxidation treatment with an oxidant and high-temperature nitrogen doping treatment, the surface functional group density is increased to 1.2 - 1.5 mmol / g, the proportion of pseudocapacitance is increased by 20% - 30%, and the oxygen / nitrogen functional groups on the surface (such as carboxyl groups, pyridine nitrogen, etc.) enhance the wettability of the electrolyte and improve the pseudocapacitance effect. Detailed implementation mode

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1:

[0025] The embodiment of the present invention provides a method for producing capacitive activated carbon from extra-low ash low-rank coal, which includes the following steps:

[0026] S1. Raw material preparation

[0027] Use a crusher to crush the low-ash low-rank coal until its particle size reaches 0.30 mm;

[0028] S2. Pretreatment

[0029] Wash the low-ash low-rank coal with deionized water 5 times to remove surface inorganic salts and ash, and then dry it in a vacuum drying oven at 120°C for 24 hours, with the vacuum degree ≤ -0.08 MPa to avoid oxidation reactions; through multiple washes with deionized water combined with vacuum drying, the ash removal rate is increased to more than 95%, avoiding oxidation side reactions and ensuring the purity of the raw materials.

[0030] S3. Activation treatment

[0031] Mix the dried low-ash low-rank coal with an activator in a certain proportion, then put the mixed raw materials into a tubular furnace, and introduce helium gas. Heat it at a heating rate of 10°C / min to 650°C, keep it warm for 0.5 hours, and introduce microwave assistance during the activation process to accelerate pore generation to obtain an activated carbon product; introduce microwave-assisted activation, utilize microwave selective heating to accelerate the intercalation reaction between the activator and the coal, increase the heating rate to 10°C / min, and the molecular vibration induced by the microwave promotes the formation of mesopores, increasing the mesopore rate to 40%.

[0032] S4. Post-treatment

[0033] After the activation is completed, take out the activated carbon and cool it, then ultrasonically clean the activated carbon with a 5% mass fraction of dilute hydrochloric acid solution to remove residual activator and other impurities; then wash the activated carbon with deionized water until it is neutral, and finally dry it in an oven at 120°C for 24 hours; use ultrasonic cleaning with dilute hydrochloric acid to efficiently remove residual activator (removal rate > 99%) through the cavitation effect, reducing water consumption by more than 50%.

[0034] S5. Modification treatment

[0035] First, the activated carbon is subjected to surface oxidation treatment with an oxidizing agent, and then the activated carbon and urea are mixed at a mass ratio of 1:2 and treated at 800 °C for 2 hours. The density of oxygen / nitrogen functional groups on the surface is increased to 1.5 mmol / g, thereby improving the capacitance performance of the activated carbon. Through the mixed oxidation treatment with an oxidizing agent and the high-temperature nitrogen doping treatment, the density of surface functional groups is increased to 1.5 mmol / g, the proportion of pseudocapacitance is increased by 30%, and the oxygen / nitrogen functional groups on the surface enhance the wettability of the electrolyte and improve the pseudocapacitance effect.

[0036] In step S3, the activating agent includes, but is not limited to, any one or a combination of more than one of potassium hydroxide, potassium nitrate, sodium nitrate, ferrous sulfate, and zinc nitrate.

[0037] In step S3, the alkali-carbon ratio of the low-ash low-rank coal to the activating agent is 3:1.

[0038] In step S5, the oxidizing agent includes, but is not limited to, any one or a combination of more than one of nitric acid, hydrogen peroxide, ammonium persulfate, potassium permanganate, and ammonium nitrate.

[0039] In step S3, the microwave frequency of the microwave assistance is 2.45 GHz, and the power is 500 W.

[0040] Example 2:

[0041] The embodiment of the present invention provides a method for producing capacitive activated carbon from ultra-low-ash low-rank coal, including the following steps:

[0042] S1. Raw material preparation

[0043] The low-ash low-rank coal is crushed by a crusher to a particle size of 0.20 mm.

[0044] S2. Pretreatment

[0045] The low-ash low-rank coal is washed 3 times with deionized water to remove surface inorganic salts and ash, and then dried in a vacuum drying oven at 120 °C for 24 hours, with a vacuum degree ≤ -0.08 MPa to avoid oxidation reactions; through multiple washings with deionized water combined with vacuum drying, the ash removal rate is increased to more than 95%, avoiding oxidation side reactions and ensuring the purity of the raw materials.

[0046] S3. Activation treatment

[0047] The dried low-ash low-rank coal is mixed with an activator in a certain proportion. Then, the mixed raw materials are put into a tubular furnace, and helium gas is introduced. The temperature is raised to 650 °C at a heating rate of 10 °C / min, held for 0.5 hours, and microwave assistance is introduced during the activation process to accelerate pore formation, obtaining an activated carbon product. By introducing microwave-assisted activation and utilizing the selective heating of microwaves, the intercalation reaction between the activator and the coal is accelerated, the heating rate is increased to 10 °C / min, and the molecular vibration induced by microwaves promotes the formation of mesopores, increasing the mesopore rate to 35%.

[0048] S4. Post-treatment

[0049] After the activation is completed, the activated carbon is taken out and cooled, and then ultrasonically cleaned with a 5% by mass dilute hydrochloric acid solution to remove residual activator and other impurities. Subsequently, the activated carbon is washed with deionized water until neutral, and finally dried in an oven at 120 °C for 24 hours. Ultrasonic cleaning with dilute hydrochloric acid can efficiently remove residual activator (removal rate > 99%) through the cavitation effect, reducing water consumption by more than 50%.

[0050] S5. Modification treatment

[0051] First, the activated carbon is subjected to surface oxidation treatment with an oxidant, and then the activated carbon is mixed with urea in a mass ratio of 1:2 and treated at 800 °C for 2 hours, increasing the density of surface oxygen / nitrogen functional groups to 1.2 mmol / g, thereby improving the capacitance performance of the activated carbon. Through mixed oxidation treatment with an oxidant and high-temperature nitrogen doping treatment, the density of surface functional groups is increased to 1.2 mmol / g, the proportion of pseudocapacitance is increased by 20%, and the surface oxygen / nitrogen functional groups enhance the wettability of the electrolyte and promote the pseudocapacitance effect.

[0052] In step S3, the activator includes, but is not limited to, any one or a combination of potassium hydroxide, potassium nitrate, sodium nitrate, ferrous sulfate, and zinc nitrate.

[0053] In step S3, the alkali-carbon ratio of the low-ash low-rank coal to the activator is 3:1.

[0054] In step S5, the oxidant includes, but is not limited to, any one or a combination of nitric acid, hydrogen peroxide, ammonium persulfate, potassium permanganate, and ammonium nitrate.

[0055] In step S3, the microwave frequency of the microwave assistance is 2.45 GHz, and the power is 500 W.

[0056] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for producing capacitor activated carbon from ultra-low ash low-rank coal, characterized in that: The following steps are involved: S1. Raw material preparation Use a crusher to crush low-ash and low-rank coal to a particle size of 0.20-0.30 mm; S2. Preprocessing Wash low-ash low-rank coal 3-5 times with deionized water to remove surface inorganic salts and ash, and then dry it in a vacuum drying oven at 120°C for 24 hours with a vacuum degree of ≤-0.08MPa to avoid oxidation reaction; S3. Activation treatment The dried low-ash low-rank coal is mixed with an activator in a certain proportion, and then the mixed raw materials are placed in a tubular furnace, and helium is introduced, and the temperature is increased to 650°C at a heating rate of 10°C / min, and the temperature is kept for 0.5 hours. Microwave assistance is introduced during the activation process to accelerate pore formation, and an activated carbon product is obtained; S4. Post-processing After activation, the activated carbon was taken out and cooled, and then ultrasonically cleaned with a 5% by mass dilute hydrochloric acid solution to remove residual activator and other impurities; then the activated carbon was cleaned with deionized water to neutrality, and finally dried in an oven at 120°C for 24 hours; S5. Modification The activated carbon was first surface oxidized with an oxidant, and then mixed with urea in a mass ratio of 1:2 and treated at 800°C for 2 hours. The surface oxygen / nitrogen functional group density was increased to 1.2-1.5 mmol / g, thereby improving the capacitance performance of the activated carbon.

2. The method for producing capacitor activated carbon from ultra-low ash low-rank coal according to claim 1, characterized in that: In the step S3, the activator includes but is not limited to any one or more combinations of potassium hydroxide, potassium nitrate, sodium nitrate, ferrous sulfate and zinc nitrate.

3. The method for producing capacitor activated carbon from ultra-low ash low-rank coal according to claim 1, characterized in that: In the step S3, the alkali-carbon ratio of low-ash low-rank coal to activator is 3:

1.

4. The method for producing capacitor activated carbon from ultra-low ash low-rank coal according to claim 1, characterized in that: In the step S5, the oxidant includes but is not limited to any one or more combinations of nitric acid, hydrogen peroxide, ammonium persulfate, potassium permanganate and ammonium nitrate.

5. The method for producing capacitor activated carbon from ultra-low ash low-rank coal according to claim 1, characterized in that: In the step S3, the microwave frequency of the microwave-assisted method is 2.45 GHz and the power is 500 W.