Method for producing hydrogen and solid carbon by controlling carbon characteristics via bidirectional methane supply

Abstract

The present invention relates to a method for producing a large amount of hydrogen and high-quality solid carbon by controlling carbon characteristics and efficiently decomposing methane into hydrogen and solid carbon by means of plasma, by supplying methane bidirectionally, specifically in mutually opposing directions, rather than in a single direction under the same energy density. The present invention provides a method for producing hydrogen and solid carbon by means of plasma, comprising the steps of: a) supplying a plasma-forming gas to a triple torch-type plasma jet device to generate a plasma jet; b) supplying methane gas to the plasma jet and thermally decomposing the methane gas to produce hydrogen and solid carbon; and c) filtering the solid carbon.

Description

A method for producing hydrogen and solid carbon by controlling carbon properties by supplying methane in two directions

[0001] The present invention relates to a method for producing hydrogen and solid carbon, which controls the properties of carbon and produces a large amount of hydrogen by supplying methane in two directions rather than supplying methane in one direction when the energy density is the same.

[0002] Plasma pyrolysis has long been attracting attention for the production of carbon materials. Recently, it has been shown to produce not only solid carbon but also hydrogen. However, the solid carbon produced through mass hydrogen production is known to be of relatively low quality, such as carbon black. Conversely, increasing the energy density to produce high-quality solid carbon, such as graphene nanoflakes, reduces the economic feasibility of the process.

[0003] Accordingly, there is a need for technology that can simultaneously achieve high added value of solid carbon and mass production of hydrogen.

[0004] The problem to be solved by the present invention is to control the properties of carbon by supplying methane in two directions, specifically, in directions facing each other, rather than supplying methane in one direction when the energy density is the same, and to provide a method for efficiently decomposing methane into hydrogen and solid carbon using plasma, thereby producing a large amount of hydrogen and high-quality solid carbon.

[0005] One aspect of the present invention is a method for producing hydrogen and solid carbon using plasma, comprising the steps of: a) supplying a plasma forming gas to a triple torch-type plasma jet device to generate a plasma jet; b) supplying methane gas to the plasma jet and thermally decomposing it to produce hydrogen and solid carbon; and c) filtering the solid carbon.

[0006] In the present invention, in the step a), the plasma forming gas is nitrogen (N2) gas, and is supplied at a flow rate of 5 to 50 L / min per single torch, and the input power may be 10 to 70 kW.

[0007] In the present invention, in the step b), the temperature of the plasma jet may be 5,000 to 7,000 K, and the speed of the plasma jet may be 500 to 2,000 m / s.

[0008] In the present invention, in step b), the methane gas can be supplied at a flow rate of 20 to 150 L / min.

[0009] In the present invention, in step b), the methane gas may be composed of a first methane gas supplied in the direction of plasma generation and a second methane gas supplied in a direction facing the first methane gas.

[0010] In the present invention, the flow rate of the first methane gas may be 15 to 90 L / min, and the flow rate of the second methane gas may be 5 to 60 L / min.

[0011] In the present invention, the conversion rate of the supplied methane may be 80% or more, the selectivity of the generated hydrogen may be 60% or more, and the content of the generated solid carbon may be 30% by weight relative to the total weight of the decomposed methane.

[0012] In the present invention, the generated solid carbon may be graphene nanoflakes.

[0013] Another aspect of the present invention is solid carbon manufactured by the above manufacturing method.

[0014] The present invention can efficiently decompose methane into hydrogen and solid carbon by using triple thermal plasma, and can efficiently decompose methane with low power.

[0015] In addition, the present invention can produce high-quality solid carbon such as graphene nanoflakes rather than carbon black by supplying methane in directions facing each other.

[0016] Figures 1 and 2 are drawings showing a triple torch type plasma jet device according to the present invention.

[0017] Figure 3 is a diagram showing the methane gas conversion rate, hydrogen selectivity, and acetylene selectivity according to the first methane gas and second methane gas flow rates.

[0018] Figure 4 is a diagram showing the solid carbon content according to the first methane gas and second methane gas flow rates.

[0019] Figure 5 shows SEM and FE-TEM images of solid carbon produced according to the first and second methane gas flow rates.

[0020] Figure 6 is a solid carbon Raman spectrum generated according to the first methane gas and second methane gas flow rates.

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Like reference numerals designate similar parts throughout the specification.

[0022] Additionally, when the terms “about,” “approximately,” or similar expressions such as “at least” are used in connection with a numerical value in the present invention, it is intended that a theoretical, experimental, statistical, or empirical error of ±10%, ±7%, ±5%, ±3%, ±2%, or ±1% based on that numerical value is allowed.

[0023]

[0024] Fig. 1 is a drawing showing a triple torch type plasma jet device according to the present invention, and Fig. 2 is a drawing showing a reaction tube in the triple torch type plasma jet device.

[0025] Referring to FIG. 1, a triple torch type plasma jet device includes a reaction tube (100) that provides a space where a plasma jet is formed and where a raw material is thermally decomposed and cooled; a torch unit (200) provided on one side of the reaction tube (100) to supply a heat source to the supplied raw material; a gas supply unit (300) connected to the reaction tube (100) to supply plasma discharge gas and raw material gas to the reaction tube (100) through a supply line; a power supply unit (400) electrically connected to the torch unit (200) to supply power; a filter unit (500) that filters out solids from the material thermally decomposed and cooled in the reaction tube; and a discharge unit (600) that discharges gas that has passed through the filter unit; wherein the torch unit (200) is arranged such that a plurality of torches are arranged at equal intervals in a direction in which the raw material is supplied, and plasma jets generated from the plurality of torch units (200) can be merged. In addition, the torch section (200) includes a first supply section (700) to which first methane gas is supplied at the center, and a second supply section (800) to which second methane gas is supplied is formed at the bottom of the reaction tube (100).

[0026] The first methane gas and the second methane gas supplied from the first supply unit (700) and the second supply unit (800) can be supplied in directions facing each other, and by being supplied in directions facing each other as described above, the efficiency of methane thermal decomposition can be improved.

[0027] In addition, the distance between the first methane gas supply unit (700) and the second methane gas supply unit (800) may be 5 to 30 cm, and the methane thermal decomposition efficiency may be improved within the above range.

[0028] The above reaction tube (100) is a space where the raw material gas is thermally decomposed by a plasma jet and the decomposed gas is cooled.

[0029] The above torch unit (200) may be equipped with three torches, which may be arranged at equal intervals.

[0030] It is preferable that the generation of the triple torch-type plasma jet used in the present invention is non-transferred.

[0031] In the present invention, a triple torch type plasma jet device generates a direct current arc discharge between a cathode made of a tungsten rod and an anode inside a nozzle made of copper, and a plasma forming gas flows in as a swirling flow from the rear so that the plasma jet forming gas is heated by the arc, and a non-transferred plasma jet is generated in which a violent plasma jet is ejected from the anode nozzle, thereby decomposing supplied methane into hydrogen and solid carbon, and the solid carbon may be graphene nanoflakes (GNFs).

[0032] The above plasma jet is a high-speed jet with high activity and an ultra-high temperature ranging from thousands to tens of thousands of K, which is a warm gas composed of electrons, ions, atoms and molecules generated from a torch using a direct current arc or high-frequency inductively coupled discharge.

[0033] The triple plasma used in the present invention can form a wider high-temperature field than a single plasma, and thus, can improve the amount of byproducts generated per unit time.

[0034]

[0035] Hereinafter, the methane thermal decomposition method according to the present invention will be described in detail.

[0036] One aspect of the present invention is a method for producing hydrogen and solid carbon using plasma, comprising the steps of: a) supplying a plasma forming gas to a triple torch-type plasma jet device to generate a plasma jet; b) supplying methane gas to the plasma jet and thermally decomposing it to produce hydrogen and solid carbon; and c) filtering the solid carbon.

[0037] In the present invention, the triple torch type plasma jet device can use the plasma jet device described above.

[0038] Step a) is a step of generating a plasma jet by supplying plasma forming gas to a triple torch type plasma jet device.

[0039] The above step a) is a step for specifying plasma operating conditions for creating a high enthalpy plasma jet to improve methane decomposition efficiency.

[0040] In the above step a), the plasma forming gas may be nitrogen (N2) gas. The flow rate of the nitrogen gas may be 5 to 50 L / min per single torch, preferably 10 to 45 L / min per single torch, and more preferably 10 to 30 L / min. If the flow rate of the plasma forming gas is less than 5 L / min per single torch, the temperature or enthalpy of the plasma jet may increase, thereby increasing the methane decomposition efficiency relative to the energy density, but the plasma may become unstable, thereby reducing the durability of the torch. If the flow rate exceeds 50 L / min per single torch, a stable non-transferred plasma jet may be formed, but the temperature or enthalpy of the plasma jet may decrease, thereby reducing the methane decomposition efficiency relative to the energy density.

[0041] The above input power may be 10 to 70 kW, and preferably 20 to 40 kW. If the above input power is less than 10 kW, the input energy is reduced, making it difficult to form plasma, which may result in a deterioration in the quality of the carbon produced, resulting in the formation of carbon black. If the input power exceeds 70 kW, excessive plasma may be formed, which may result in an increase in temperature, thereby reducing the efficiency of hydrogen production during methane decomposition.

[0042] In the above step b), the temperature of the plasma jet formed by supplying nitrogen gas may be 5,000 to 7,000 K, and the speed of the plasma jet may be 500 to 2,000 m / s.

[0043] If the temperature of the plasma jet is less than 5,000 K, the enthalpy may decrease, which may reduce the methane decomposition efficiency. If it exceeds 7,000 K, the enthalpy may increase, which may increase the decomposition efficiency, but may reduce the durability of the plasma torch. Therefore, the above range is preferred.

[0044] In the present invention, in the step b), when the input power changes from 10 to 70 kW, the methane gas can be supplied at a flow rate of 20 to 150 L / min, and at this time, the energy density can be 36 to 90 kJ / L_CH4, and preferably, the flow rate of the methane gas can be 30 to 70 L / min.

[0045] If the flow rate of the methane gas is less than 15 L / min, the energy density may exceed 90 kJ / L_CH4, which may reduce the hydrogen production efficiency, and if the flow rate of the methane gas exceeds 150 L / min, the energy density may decrease to less than 36 kJ / L_CH4, The temperature inside the reactor may be lowered, so that carbon black is formed instead of graphene nanoflakes. The above flow rate, L / min, is standard liters per minute (slpm).

[0046] In the above step b), the methane gas may be composed of a first methane gas supplied in a direction in which plasma is generated and a second methane gas supplied in a direction facing the first methane gas, and by the methane gas being composed of the first methane gas and the second methane gas supplied in a direction facing each other, the selectivity of hydrogen can be improved and graphene nanoflakes, which are solid carbon, can be produced.

[0047] If the above methane gas is composed only of the first methane gas, the selectivity for hydrogen may decrease, so it is preferable to be composed of the first methane gas and the second methane gas.

[0048] The flow rate of the first methane gas may be 15 to 90 L / min, and the flow rate of the second methane gas may be 5 to 60 L / min, and preferably, the flow rate of the first methane gas may be 20 to 40 L / min, and the flow rate of the second methane gas may be 10 to 30 L / min. When the flow rate of the first methane gas is less than 15 L / min and the flow rate of the second methane gas is less than 5 L / min, the energy density may exceed 90 kJ / L_CH4, and thus the hydrogen production efficiency may decrease, and when the flow rate of the first methane gas exceeds 90 L / min and the flow rate of the second methane gas exceeds 60 L / min, the energy density may decrease to less than 36 kJ / L_CH4, The temperature inside the reactor may be lowered, so that carbon black is formed instead of graphene nanoflakes. The above flow rate, L / min, is standard liters per minute (slpm).

[0049] Additionally, in the present invention, it is preferable that the first methane gas is in excess of the second methane gas.

[0050] The above step c) is a step of filtering solid carbon, and specifically, a step of recovering solid carbon, undecomposed methane gas, and hydrogen. In the above step c), cooling may be performed to recover solid carbon, undecomposed methane gas, and hydrogen, and the cooling may be natural cooling.

[0051] Additionally, in addition to the solid carbon, un-decomposed methane gas and hydrogen, by-products may be additionally recovered, and the by-products may be polycyclic aromatic hydrocarbons (PAHs).

[0052]

[0053] *In addition, the solid carbon can be separated through a cyclone filter, and the separated solid carbon can be used in various fields, and the solid carbon can be graphene nano flakes.

[0054] In the present invention, the conversion rate of the supplied methane may be 80% or more, the selectivity of the generated hydrogen may be 60% or more, and the content of the generated solid carbon may be 30% by weight relative to the weight % of the supplied methane. Preferably, the conversion rate of the supplied methane may be 95% or more, the selectivity of the generated hydrogen may be 80% or more, and the content of the generated solid carbon may be 30 to 40% by weight relative to the weight % of the supplied methane.

[0055] Another aspect of the present invention is solid carbon manufactured by the above manufacturing method, wherein the solid carbon may be graphene nanoflakes.

[0056] Hereinafter, the present invention will be described in more detail through the following examples and experimental examples.

[0057]

[0058] Examples and Comparative Examples

[0059]

[0060] *Nitrogen was supplied as a plasma forming gas to the torch section of the triple torch type plasma jet device shown in FIGS. 1 and 2, and a plasma jet was generated under the operating conditions shown in Table 1 below. At this time, the temperature of the plasma jet was 5,000 to 7,000 K, and the speed of the plasma jet was 500 to 2,000 m / s.

[0061] Next, the first methane gas and the second methane gas were supplied to a triple torch-type plasma jet device as shown in Table 1 below, and thermally decomposed into hydrogen, solid carbon, and acetylene. Finally, the decomposed product and unreacted methane gas were naturally cooled, and the solid carbon was collected through a cyclone filter, and then hydrogen, acetylene, and methane were recovered.

[0062] Here, commercially available methane (99.95%, Hwaseung Gas Tech, Korea) was used, and the operation time was 20 minutes.

[0063]

[0064] Classification Comparative Example 1 Comparative Example 2 Example 1 Example 2 Plasma forming gas N2 N2 N2 N2 Forming gas flow rate single torch [L / min] [slpm] (Plasma forming gas flow rate per single torch) 15 15 15 15 Input power [kW] (Plasma input power) 30 30 30 30 Thermal efficiency of a torch (%) (Torch thermal efficiency) 70 70 70 70 1 st CH4 Flow rate [L / min][slpm](1st methane gas flow rate)502040302 nd CH4 Flow rate [L / min] [slpm](Secondary methane gas flow rate)0301020Operating Pressure [kPa](Pressure)101.325101.325101.325101.325

[0065] Experimental Example 1: Methane conversion rate, hydrogen and acetylene selectivity according to the first and second methane gas flow rates.

[0066] The methane gas conversion rate, hydrogen selectivity, and acetylene selectivity according to the above examples and comparative examples were calculated according to the following mathematical equations 1 to 3, and the results thereof are shown in Fig. 3. In Fig. 3, Comparative Example 1 was shown as 50:0, Comparative Example 2 as 20:30, Example 1 as 40:10, and Example 2 as 30:20.

[0067]

[0068] [Equation 1: Methane Conversion Rate]

[0069]

[0070] [Mathematical Formula 2: Hydrogen Selectivity]

[0071]

[0072] [Mathematical Formula 3: Acetylene Selectivity]

[0073]

[0074] Referring to Figure 3, it can be confirmed that the hydrogen selectivity is significantly higher when the second methane gas is injected than when the second methane gas is not supplied (Comparative Example 1).

[0075] It can be confirmed that the hydrogen selectivity in cases where the second methane gas is injected (Examples 1 and 2) is 80% or more.

[0076]

[0077] Experimental Example 2: Solid carbon selectivity according to the first and second methane gas flow rates.

[0078] The solid carbon selectivity (% of weight converted compared to the methane input) according to the above examples and comparative examples was calculated according to the following mathematical formula 4, and the results thereof are shown in Fig. 4. In Fig. 4, Comparative Example 1 was shown as 50:0, Comparative Example 2 as 20:30, Example 1 as 40:10, and Example 2 as 30:20.

[0079]

[0080] [Equation 4: Solid Carbon Selectivity]

[0081]

[0082] Referring to Fig. 4, it can be confirmed that the generated solid carbon is about 35% by weight or more of the weight % of the decomposed methane gas.

[0083]

[0084] Experimental Example 3: Solid carbon according to the first and second methane gas flow rates

[0085] The solid carbon according to the above examples and comparative examples was photographed using SEM and FE-TEM (Field Emission Transmission Electron Microscopy, Talos F200X G2, Thermo Fisher Scientific, USA) and shown in Fig. 5, and the Raman spectrum of the carbon was measured using a Raman spectrometer (DXR3xi Raman Imaging Microscope, Thermo Fisher Scientific, USA) with a laser frequency of 514 nm and shown in Fig. 6. In Figs. 5 and 6, Comparative Example 1 was shown as 50:0, Comparative Example 2 was shown as 20:30, Example 1 was shown as 40:10, and Example 2 was shown as 30:20.

[0086]

[0087] Referring to the above Figures 5 and 6, it can be confirmed that in the case of Examples 1 and 2, the form of the solid carbon is in the form of graphene nano flakes, while in Comparative Example 2, it is in the form of carbon black.

[0088]

[0089] [Explanation of symbols]

[0090] 100: Reaction tube 200: Torch section

[0091] 300: Gas supply unit 400: Power supply unit

[0092] 500: Cyclone filter 600: Discharge

[0093] 700: 1st supply section 800: 2nd supply section

[0094] The present invention can produce high-quality solid carbon such as graphene nanoflakes rather than carbon black by supplying methane in opposite directions.

Claims

1. a) A step of generating a plasma jet by supplying plasma forming gas to a triple torch type plasma jet device; b) a step of supplying methane gas to the plasma jet and thermally decomposing it to produce hydrogen and solid carbon; and c) a step of filtering solid carbon; comprising; Method for producing hydrogen and solid carbon using plasma.

2. In paragraph 1, A method for producing hydrogen and solid carbon using plasma, wherein in the above step a), the plasma forming gas is nitrogen (N2) gas, is supplied at a flow rate of 5 to 50 L / min per single torch, and the input power is 10 to 70 kW.

3. In paragraph 1, A method for producing hydrogen and solid carbon using plasma, wherein in the above step b), the temperature of the plasma jet is 5,000 to 7,000 K and the speed of the plasma jet is 500 to 2,000 m / s.

4. In paragraph 1, A method for producing hydrogen and solid carbon using plasma, wherein in the above step b), the methane gas is supplied at a flow rate of 20 to 150 L / min.

5. In paragraph 1, A method for producing hydrogen and solid carbon using plasma, wherein in the above step b), the methane gas is composed of a first methane gas supplied in the direction of plasma generation and a second methane gas supplied in a direction facing the first methane gas.

6. In paragraph 5, A method for producing hydrogen and solid carbon using plasma, wherein the flow rate of the first methane gas is 15 to 90 L / min and the flow rate of the second methane gas is 5 to 60 L / min.

7. In paragraph 1, The conversion rate of the supplied methane is 80% or more, The selectivity of the hydrogen generated above is 60% or more, The content of the above-mentioned generated solid carbon is 30% by weight relative to the total weight of decomposed methane. Method for producing hydrogen and solid carbon using plasma.

8. In paragraph 1, A method for producing hydrogen and solid carbon using plasma, wherein the solid carbon produced above is graphene nano flakes.

9. Solid carbon manufactured by the manufacturing method of any one of paragraphs 1 or 8.

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