A method of adsorbing nitrogen gas

Abstract

The application discloses a method for adsorbing nitrogen, which comprises the following steps: putting pitch-based activated carbon balls as adsorbents into a reactor, and introducing nitrogen into the reactor for adsorption. The pitch-based activated carbon balls have the advantages of rich micropores, low-temperature resistance, and large mechanical strength, etc. In a low-temperature state, the pitch-based activated carbon balls can adsorb a large amount of nitrogen, so that the nitrogen can quickly undergo capillary condensation in the pore channel, a large amount of nitrogen can be adsorbed, and the vacuum state inside the reactor can be maintained.

Description

Technical Field

[0001] This application relates to a method for adsorbing nitrogen gas, which belongs to the field of activated carbon adsorption. Background Technology

[0002] Spherical activated carbon, as a novel functional material, possesses not only the adsorption properties of traditional activated carbon but also exhibits superior performance in areas such as increasing packing density and reducing bed pressure drop due to its unique geometric shape and microporous structure. It is widely used in catalyst supports and environmental protection. Based on the raw material, spherical activated carbon can be classified into coal-based, polymer resin-based, and pitch-based spherical activated carbon. Among them, pitch-based spherical activated carbon, prepared from pitch, exhibits higher adsorption performance and lower ash content. Summary of the Invention

[0003] According to one aspect of this application, nitrogen gas is adsorbed at low temperature using carbon balls. Taking advantage of the abundant micropores, low temperature resistance, and high mechanical strength of pitch-based activated carbon balls, a large amount of nitrogen gas can be adsorbed at low temperature, causing the nitrogen gas to rapidly undergo capillary condensation in the pores and maintaining a vacuum state inside the reactor.

[0004] The technical solution adopted in this application is as follows:

[0005] A method for adsorbing nitrogen gas includes the following steps:

[0006] In the reactor, pitch-based activated carbon balls are used as adsorbents, and nitrogen gas is introduced for adsorption.

[0007] Optionally, the carbon balls are 10 to 40 mesh in size.

[0008] Optionally, the carbon balls are 20 to 28 mesh in size.

[0009] Optionally, the average pore size of the carbon spheres is 0.8 to 1.6 nm.

[0010] Optionally, the specific surface area of ​​the carbon spheres is 700–1800 m². 2 / g.

[0011] Optionally, the specific surface area of ​​the carbon spheres is 700 m². 2 / g、1150m 2 / g、1300m 2 / g, 1450m 2 / g, 1600m 2 / g、1800m 2 Any value in / g, or any range of values ​​between the two.

[0012] Optionally, the ash content of the carbon spheres has a pore volume of 0.5–1.2 μm. 3 / g

[0013] Optionally, the process of introducing nitrogen gas includes evacuating the reactor to a vacuum state.

[0014] Optionally, the vacuum state is a vacuum degree of ≤-90kPa in the reactor.

[0015] Optionally, the reactor is cooled in liquid nitrogen.

[0016] Optionally, the reactor is cooled in liquid nitrogen to a temperature of -200 to -190°C.

[0017] Optionally, the cooling device is a Dewar flask containing liquid nitrogen or a liquid nitrogen circulation pump.

[0018] The adsorption of nitrogen is judged by observing the change in the vacuum degree inside the reactor. When the vacuum degree of the reactor is >-90kPa, it is considered to be adsorption saturation.

[0019] Optionally, the carbon balls are obtained by the following preparation method:

[0020] S1. Mix the raw materials containing asphalt powder and naphthalene in a weight ratio of 1:0.01 to 0.5 evenly in a reaction vessel, heat to 80 to 150°C at a heating rate of 1 to 9°C / min, hold at the temperature for 0.1 to 5 hours, cool and then pulverize to obtain 20 to 200 mesh naphthalene-containing asphalt particles.

[0021] S2. Weigh and mix the naphthalene-containing asphalt particles obtained in step S1 with crosslinking agent, initiator, surfactant, and oily solvent in a weight ratio of 1:(0.1~1):(0.01~0.5):(0.01~0.5):(0.5~500) and place them in a reaction vessel. Then, heat the mixture to 100~200℃ at a heating rate of 1~7℃ / min and hold it at that temperature for 0.5~5h. Then, clean the mixture with a cleaning agent and dry it at 60~120℃ to obtain naphthalene-containing asphalt balls.

[0022] The initiator is selected from at least one of benzoyl peroxide and tert-butyl peroxide; the crosslinking agent is selected from at least one of divinylbenzene and 1,3-butadiene; the surfactant is selected from at least one of polyvinyl alcohol and sodium octadecylbenzenesulfonate; the oily solvent is selected from at least one of methyl silicone oil, mineral oil, and vegetable oil; and the cleaning agent is selected from at least one of petroleum ether, carbon tetrachloride, benzene, and kerosene.

[0023] S3. The naphthalene-containing asphalt balls obtained in step S2 are heated to 150-350℃ at a heating rate of 0.1-5℃ / min under vacuum conditions of -100 to -50 kPa and held at that temperature for 0.5-2 hours to obtain modified asphalt balls.

[0024] S4. The modified asphalt balls obtained in step S3 are heated to 750-900℃ under a nitrogen atmosphere at a heating rate of 3-10℃ / min and held at that temperature for 0.5-2h. Then the nitrogen atmosphere is switched to a water vapor atmosphere and held at that temperature for 0.5-6h to obtain carbon ball adsorbent.

[0025] The beneficial effects that this application can produce include:

[0026] The nitrogen adsorption method provided in this application utilizes the advantages of abundant micropores, low-temperature resistance, and high mechanical strength of pitch-based activated carbon balls. Under low-temperature conditions, it can adsorb a large amount of nitrogen, causing the nitrogen to rapidly undergo capillary condensation in the pores and maintaining a vacuum state inside the reactor. Attached Figure Description

[0027] Figure 1 This is a photograph of the carbon ball adsorbent prepared in Preparation Example 1 of this application. Detailed Implementation

[0028] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0029] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0030] The total nitrogen adsorption capacity in the reactor is calculated as: saturated adsorption time * nitrogen flow rate, in mL.

[0031] The nitrogen adsorption capacity per unit volume is calculated as: total nitrogen adsorption capacity in the reactor / volume of carbon ball adsorbent, in mL / mL.

[0032] The nitrogen adsorption capacity per unit mass is calculated as: total nitrogen adsorption capacity in the reactor / (carbon ball adsorption bulk density * volume), with units of mL / g.

[0033] Preparation Example 1

[0034] 100g of asphalt powder and 20g of naphthalene (asphalt powder:naphthalene weight ratio = 1:0.2) were added to a high-pressure reactor, sealed, and stirred until homogeneous. The mixture was then heated to 120℃ and held at that temperature for 2 hours. After cooling, it was pulverized to 200 mesh to obtain naphthalene-containing asphalt particles. Then, the obtained naphthalene-containing asphalt particles, divinylbenzene (crosslinking agent), benzoyl peroxide (initiator), and polyvinyl alcohol (surfactant) were weighed and mixed in a weight ratio of 1:0.3:0.05:0.02, and added to a reactor containing methyl silicone oil (methyl silicone oil to naphthalene-containing asphalt particles weight ratio = 10:1). The reactor was sealed and stirred until homogeneous. The intermediate product was heated to 150℃ at a rate of 5℃ / min and held at that temperature for 1 hour. After cooling, the intermediate product was separated and repeatedly washed with petroleum ether to remove the attached methyl silicone oil. Finally, it was dried at 120℃ to obtain naphthalene-containing pitch balls. Then, under vacuum conditions (vacuum degree -50kPa), the temperature was increased to 200℃ at a rate of 5℃ / min and held at that temperature for 1 hour to react and obtain modified pitch balls. The modified pitch was then carbonized at 900℃ at a rate of 8℃ / min under a nitrogen atmosphere for 2 hours. After switching to steam, it was activated at a constant temperature for 4 hours. After cooling to room temperature, carbon ball adsorbent was obtained. The carbon ball particle size was 20-28 mesh and the bulk density was 0.58 g / mL.

[0035] Preparation Example 2

[0036] 100g of asphalt powder and 10g of naphthalene (asphalt powder:naphthalene weight ratio = 1:0.1) were added to a high-pressure reactor, sealed, and stirred until homogeneous. The mixture was then heated to 120℃ and held at that temperature for 2 hours. After cooling, it was pulverized to 200 mesh to obtain naphthalene-containing asphalt particles. Then, the obtained naphthalene-containing asphalt particles, divinylbenzene (crosslinking agent), benzoyl peroxide (initiator), and polyvinyl alcohol (surfactant) were weighed and mixed at a weight ratio of 1:0.3:0.05:0.02, and added to a reactor containing methyl silicone oil (methyl silicone oil to naphthalene-containing asphalt particles weight ratio = 10:1). The reactor was sealed and stirred until homogeneous. The intermediate product was heated to 150℃ at a rate of 5℃ / min and held at that temperature for 1 hour. After cooling, the intermediate product was separated and repeatedly washed with petroleum ether to remove the attached methyl silicone oil. Finally, it was dried at 120℃ to obtain naphthalene-containing pitch balls. Then, under vacuum conditions (vacuum degree -50kPa), the temperature was increased to 200℃ at a rate of 5℃ / min and held at that temperature for 1 hour to react and obtain modified pitch balls. The modified pitch was then carbonized at 900℃ at a rate of 8℃ / min under a nitrogen atmosphere for 2 hours. After switching to steam for constant temperature activation for 4 hours, the carbon ball adsorbent was obtained after cooling to room temperature. The carbon ball particle size was 20-28 mesh and the bulk density was 0.52 g / mL.

[0037] Preparation Example 3

[0038] 100g of asphalt powder and 20g of naphthalene (asphalt powder:naphthalene weight ratio = 1:0.2) were added to a high-pressure reactor, sealed, and stirred until homogeneous. The mixture was then heated to 120℃ and held at that temperature for 2 hours. After cooling, it was pulverized to 200 mesh to obtain naphthalene-containing asphalt particles. Then, the obtained naphthalene-containing asphalt particles, divinylbenzene (crosslinking agent), benzoyl peroxide (initiator), and polyvinyl alcohol (surfactant) were weighed and mixed in a weight ratio of 1:0.3:0.05:0.02, and added to a reactor containing methyl silicone oil (methyl silicone oil to naphthalene-containing asphalt particles weight ratio = 10:1). The reactor was sealed and stirred until homogeneous. The intermediate product was heated to 150℃ at a rate of 5℃ / min and held at that temperature for 1 hour. After cooling, the intermediate product was separated and repeatedly washed with petroleum ether to remove the attached methyl silicone oil. Finally, it was dried at 120℃ to obtain naphthalene-containing pitch balls. Then, under vacuum conditions (vacuum degree -80kPa), the temperature was increased to 200℃ at a rate of 5℃ / min and held at that temperature for 1 hour to react and obtain modified pitch balls. The modified pitch was then carbonized at 900℃ at a rate of 8℃ / min under a nitrogen atmosphere for 2 hours. After switching to steam, it was activated at a constant temperature for 4 hours. After cooling to room temperature, carbon ball adsorbent was obtained. The carbon ball particle size was 20-28 mesh and the bulk density was 0.55 g / mL.

[0039] Comparative Preparation Example 1

[0040] The dried coconut shells are crushed, sieved, and destoned to obtain granules with a particle size of 2-5 mm. The granules are then soaked in a 2% potassium hydroxide aqueous solution at room temperature for 2 hours. After soaking, the granules are drained and placed in a carbonization activation furnace. The carbonization activation furnace is heated to 650°C at a rate of 10°C / min and then kept at a constant temperature for 2 hours to facilitate the discharge of volatile oil fumes. Next, a composite activator made by mixing carbon dioxide and water vapor is fed into the carbonization activation furnace at a ratio of 0.1 kg composite activator / kg carbon per hour. The temperature is then raised to 750°C at a rate of 3°C / min and held constant for 1 hour to facilitate the discharge of volatile oil fumes. The temperature is then raised again to 950°C at a rate of 3°C / min and held constant for 3 hours. After carbonization activation, the furnace is cooled to 500°C by air cooling and the flow of composite activator is stopped. Nitrogen gas is then introduced to continue cooling to below 100°C before the material is discharged. After the discharged material cools to room temperature, it is washed four times with water at a mass ratio of 5:1 (water to carbon). Multiple washes further reduce the ash content in the activated carbon. After washing, the material is dried at 150°C for 5 hours and then pulverized to obtain high-strength, low-ash coconut shell activated carbon with a bulk density of 0.52 g / mL.

[0041] Comparative Preparation Example 2

[0042] A modified activated carbon adsorbent, by weight, comprises the following raw materials: 400 parts coconut shell activated carbon, 400 parts coal-based activated carbon, 400 parts wood-based activated carbon, 65 parts bentonite, 38 parts coal tar, and 5 parts methylcellulose.

[0043] Bentonite was pulverized and calcined in a calcining furnace at 600℃ for 4 hours. The calcined bentonite was then removed and mixed with coconut shell activated carbon, coal-based activated carbon, wood-based activated carbon, coal tar, and water to form a slurry. The slurry was heated to 70℃ and ground for 3 hours to obtain a 200-300 mesh slurry. After drying, the resulting particles were sprayed with an aqueous solution of methylcellulose and heated to coat the particles with a methylcellulose film. After drying, the particles were pulverized to obtain a 20-28 mesh modified activated carbon adsorbent with a bulk density of 0.53 g / mL.

[0044] Example 1

[0045] Add 10 mL of the carbon ball adsorbent prepared in Example 1 to the reactor, seal it, and use a vacuum pump to evacuate the reactor to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (10 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 210 mL / mL.

[0046] Example 2

[0047] Add 10 mL of the carbon ball adsorbent prepared in Example 1 to the reactor, seal it, and use a vacuum pump to evacuate the reactor to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (20 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 190 mL / mL.

[0048] Example 3

[0049] Add 10 mL of the carbon ball adsorbent prepared in Example 1 to the reactor, seal it, and use a vacuum pump to evacuate the reactor to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (40 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 185 mL / mL.

[0050] Example 4

[0051] Add 10 mL of the carbon ball adsorbent prepared in Example 2 to the reactor, seal it, and use a vacuum pump to evacuate the reactor to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (20 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 220 mL / mL.

[0052] Example 5

[0053] Add 10 mL of the carbon ball adsorbent prepared in Example 3 to the reactor, seal it, and use a vacuum pump to evacuate the reactor to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (20 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 210 mL / mL.

[0054] Comparative Example 1

[0055] Take 10 mL of the carbon ball adsorbent prepared in Example 1 and add it to the reactor. Seal the reactor and use a vacuum pump to evacuate it to a vacuum state at room temperature. Introduce nitrogen gas (20 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 0 mL / mL.

[0056] Comparative Example 2

[0057] Add 10 mL of coconut shell activated carbon prepared in Comparative Preparation Example 1 to the reactor, seal it, and use a vacuum pump to evacuate the reactor to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (20 mL / min), observe and record the change in the vacuum degree inside the reactor, and record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 120 mL / mL.

[0058] Comparative Example 3

[0059] Take 10 mL of the modified activated carbon adsorbent prepared in Comparative Preparation Example 2 and add it to the reactor. Seal the reactor and use a vacuum pump to evacuate it to a vacuum state at room temperature. Place the reactor in a Dewar flask containing liquid nitrogen and cool it for 10 min. Then, introduce nitrogen gas (20 mL / min) and observe and record the change in the vacuum degree inside the reactor. Record the gas introduction time when adsorption saturation is reached (vacuum degree > -90 kPa). Calculate that the nitrogen adsorption capacity per unit volume of carbon ball adsorbent is 10 mL / mL.

[0060] The adsorption data of Examples 1-5 and Comparative Examples 1-3 are shown in the table below.

[0061]

[0062]

[0063] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for adsorbing nitrogen gas, characterized in that, Includes the following steps: In the reactor, pitch-based activated carbon balls are used as adsorbents, and nitrogen gas is introduced for adsorption. Before introducing nitrogen, the reactor is evacuated to a vacuum state. The vacuum state is defined as a vacuum degree of ≤-90kPa in the reactor; The process of introducing nitrogen includes cooling the reactor in liquid nitrogen.

2. The method according to claim 1, characterized in that, The size of the asphalt-based activated carbon balls is 10-40 mesh.

3. The method according to claim 1, characterized in that, The average pore size of the asphalt-based activated carbon balls is 0.8~1.6 nm.

4. The method according to claim 1, characterized in that, The specific surface area of ​​the asphalt-based activated carbon balls is 700~1800 m². 2 / g.

5. The method according to claim 1, characterized in that, The pore volume of the asphalt-based activated carbon balls is 0.5~1.2 m. 3 / g.

6. The method according to claim 1, characterized in that, The reactor is cooled in liquid nitrogen to a temperature of -200 to -190°C.

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