CN110963481B - Method for preparing hydrogen and carbon nano tube by cracking methane in series by two catalysts - Google Patents

Method for preparing hydrogen and carbon nano tube by cracking methane in series by two catalysts Download PDF

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CN110963481B
CN110963481B CN201911390318.4A CN201911390318A CN110963481B CN 110963481 B CN110963481 B CN 110963481B CN 201911390318 A CN201911390318 A CN 201911390318A CN 110963481 B CN110963481 B CN 110963481B
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CN110963481A (en
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蒋炜
刘强
吴潘
刘长军
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Sichuan University
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    • B01J8/04—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds the fluid passing successively through two or more beds
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    • B01J8/06—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds in tube reactors; the solid particles being arranged in tubes
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    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/22—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of gaseous or liquid organic compounds
    • C01B3/24—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of gaseous or liquid organic compounds of hydrocarbons
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    • C01B2203/1041—Composition of the catalyst
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1241—Natural gas or methane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Abstract

The invention provides a method for preparing hydrogen and carbon nano tubes by cracking methane in series by two catalysts, which comprises the following process steps in sequence: (1) respectively filling an upstream catalyst for quickly producing hydrogen and a downstream catalyst for producing carbon nano tubes into an upstream reactor and a downstream reactor which are connected in series, simultaneously inputting hydrogen and nitrogen to activate the upstream catalyst and the downstream catalyst, and then purging with nitrogen; (2) methane and nitrogen are simultaneously input into an upstream reactor, methane is rapidly cracked into hydrogen and solid carbon under the catalytic action of an upstream catalyst, the formed hydrogen-rich mixed gas enters a downstream reactor, methane in the hydrogen-rich mixed gas is cracked into carbon nano tubes and hydrogen under the catalytic action of the downstream catalyst, the carbon nano tubes are deposited on the downstream catalyst and collected, and the hydrogen-rich mixed gas is discharged from the downstream reactor and collected. By using the method, the yield of the hydrogen can be improved, and the carbon nano tube with excellent quality can be obtained.

Description

Method for preparing hydrogen and carbon nano tube by cracking methane in series by two catalysts
Technical Field
The invention belongs to the field of energy and chemical engineering, and relates to a method for preparing hydrogen and carbon nanotubes by cracking methane.
Background
Hydrogen energy is a clean energy source, and the energy density is up to 142.82 kJ/kg; carbon nanotubes are widely used as a novel functional material in energy storage, sensors or electronic devices due to their special properties. Therefore, the method has important significance for converting the methane with the energy density of only 5.62kJ/kg into the hydrogen with high energy density and the carbon nano tube serving as a novel functional material.
In the prior art, Methane pyrolysis (CMD for short) is used for preparing hydrogen and a nano carbon material, and the pyrolysis reaction can be carried out at the temperature of over 1200 ℃ under the non-catalytic condition; when the catalyst exists, the required temperatures of different catalysts are different, and the common reaction temperature is 500-800 ℃. Because the use of a catalyst can lower the reaction temperature, the pyrolysis of methane is usually carried out under catalytic conditions, but only one catalyst is selected for the pyrolysis process. As can be seen from the mechanism of catalytic methane pyrolysis, the catalytic conditions required to obtain high purity hydrogen and high quality carbon nanotubes are different. For the hydrogen production process, the cracking rate needs to be as high as possible to obtain a large amount of hydrogen, for the production of high-quality carbon nanotubes, the requirements of carbon transfer and deposition rate need to be met, and the cracking rate required for the production of carbon nanotubes is much lower than that required for the production of a large amount of hydrogen. Therefore, it is impossible to pyrolyze methane with two different cracking rates using only one catalyst during the pyrolysis of methane, and it is difficult to simultaneously increase the yield of hydrogen and ensure the quality of carbon nanotubes.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for preparing hydrogen and carbon nano tubes by cracking methane in series through two catalysts so as to simultaneously improve the yield of the hydrogen and obtain the carbon nano tubes with excellent quality.
The technical scheme of the invention is as follows: based on different catalysis conditions required for obtaining high-purity hydrogen and high-quality carbon nano tubes, the CMD reaction is carried out in two stages, wherein a hydrogen production catalyst is used in the first stage to ensure the hydrogen production amount, and a carbon nano tube production catalyst is used in the second stage to carry out pyrolysis on methane in the hydrogen-rich mixed gas formed in the first stage so as to prepare the carbon nano tubes with excellent quality.
The invention discloses a method for preparing hydrogen and carbon nano tubes by cracking methane in series through two catalysts, which sequentially comprises the following process steps:
(1) respectively filling an upstream catalyst for quickly producing hydrogen and a downstream catalyst for producing carbon nano tubes into an upstream reactor and a downstream reactor which are connected in series, simultaneously inputting hydrogen and nitrogen to activate the upstream catalyst and the downstream catalyst, and then purging with nitrogen;
(2) simultaneously inputting methane and nitrogen into an upstream reactor, rapidly cracking the methane into hydrogen and solid carbon under the catalytic action of an upstream catalyst, enabling the formed hydrogen-rich mixed gas to enter the downstream reactor, cracking the methane in the hydrogen-rich mixed gas into carbon nano tubes and hydrogen under the catalytic action of the downstream catalyst, depositing the carbon nano tubes on the downstream catalyst to be collected, and discharging the hydrogen-rich mixed gas from the downstream reactor to be collected;
the temperature of the activation treatment, the purging treatment and the reaction temperature of methane cracking are determined by the type of the upstream catalyst contained in the upstream reactor and the type of the downstream catalyst contained in the downstream reactor.
And the hydrogen-rich mixed gas discharged from the downstream reactor consists of hydrogen, nitrogen and a small amount of uncracked methane, and the collected hydrogen-rich mixed gas discharged from the downstream reactor is separated to obtain the high-purity hydrogen. The method for purifying hydrogen from the hydrogen-rich mixed gas adopts the prior art, which is disclosed in the research on novel four-tower pressure swing adsorption hydrogen purification process (Lvracon, Tianjin university, 2003.), and then the method disclosed in the prior art is adopted for separating methane from nitrogen, which is disclosed in CN201711378587.X (a carbon adsorbent for separating methane and nitrogen and a preparation method thereof).
In the method, the upstream catalyst arranged in the upstream reactor is NiFeAl or NiFeCu/Al 2 O 3 Or Ni/TiO 2 The downstream catalyst arranged in the downstream reactor is FeMg or CoMo/Al 2 O 3 (ii) a When the upstream catalyst is NiFeAl or Ni/TiO 2 When the temperature of the activation treatment is 700 ℃, the reaction temperature of methane cracking is 600 ℃, and the temperature of the purging treatment is gradually reduced from 700 ℃ to 600 ℃; when the upstream catalyst is NiFeCu/Al 2 O 3 When the temperature of the activation treatment, the temperature of the purging treatment and the reaction temperature of methane cracking are all 700 ℃; the downstream catalyst FeMg or CoMo/Al 2 O 3 The activation treatment temperature, the purging treatment temperature and the methane cracking reaction temperature of (2) are all 700 ℃.
Preparation of upstream catalyst NiFeAlAs described in the detailed description section below, the upstream catalyst NiFeCu/Al 2 O 3 Reference is made to the preparation of thermal decomposition of methane to COx-free hydrogen and carbon over Ni-Fe-Cu/Al 2 O 3 catalytes (International Journal of Hydrogen Energy,2016.41(30): p.13039-13049.DOI: 10.1016/j.ijhydyne.2016.05.230), upstream catalyst Ni/TiO 2 For the preparation of (1) see, Carbon produced by the catalytic composition of methane on nickel, Carbon derivatives and Carbon structures as a function of catalytic properties (Journal of Natural Gas Science)&Engineering,2016.32: p.501-511.DOI: 10.1016/j.jngse.2016.04.027); preparation of the downstream catalyst FeMg, described in the following section of the detailed description, the downstream catalyst CoMo/Al 2 O 3 The preparation refers to the preparation of single-walled carbon nanotubes by cracking Co-Mo series catalysts with high Co content (molecular catalysis, 2003(3):161 and 167., DOI:10.3969/j. issn.1001-3555.2003.03.001).
In the method, the number and the serial connection mode of the upstream reactor and the downstream reactor have the following three modes:
1. the upstream reactor and the downstream reactor are both one, and in the whole process flow, the two reactors are always connected in series.
2. The upstream reactor is one, the downstream reactors are two, and the two reactors are respectively named as a first downstream reactor and a second downstream reactor, and in the reaction process, the first downstream reactor, the second downstream reactor and the upstream reactor are alternately connected in series.
3. The upstream reactor is one, the downstream reactors are two, and the two downstream reactors are respectively named as a first downstream reactor and a second downstream reactor, in the whole process flow, the first downstream reactor and the second downstream reactor are always connected with the upstream reactor in series, and the first downstream reactor and the second downstream reactor are connected in parallel.
In the above form 1, when the upstream catalyst contained in the upstream reactor is 100mg, the downstream catalyst contained in the downstream reactor is 100mg, the flow rate of methane is 10 to 30ml/min, and the flow rate of nitrogen is 40 to 60ml/min, the reaction time for methane cracking is at least 240 min.
In the above-mentioned type 2, when the upstream catalyst contained in the upstream reactor is 100mg, the downstream catalyst contained in the first downstream reactor is 50mg, the downstream catalyst contained in the second downstream reactor is the same as the downstream catalyst contained in the first downstream reactor in type and weight, the flow rate of methane is 10 to 30ml/min, and the flow rate of nitrogen is 40 to 60ml/min, the reaction time for cracking methane is at least 120min when the first downstream reactor and the upstream reactor are connected in series, and the reaction time for cracking methane is at least 120min when the second downstream reactor and the upstream reactor are connected in series.
In the above-mentioned 3 rd form, when the upstream catalyst contained in the upstream reactor is 100mg, the downstream catalyst contained in the first downstream reactor is 50mg, the downstream catalyst contained in the second downstream reactor is the same as the downstream catalyst contained in the first downstream reactor in terms of the kind and weight, the flow rate of methane is 10 to 30ml/min, and the flow rate of nitrogen is 40 to 60ml/min, the reaction time for methane cracking is at least 240 min.
The time of the activation treatment and the purge treatment of the upstream catalyst and the downstream catalyst is mainly related to the weight of the upstream catalyst loaded in the upstream reactor and the downstream catalyst loaded in the downstream reactor, and the flow rates of the activation gas and the purge gas.
For the above mode 1, when the upstream catalyst contained in the upstream reactor is 100mg, the downstream catalyst contained in the downstream reactor is 100mg, the flow rate of nitrogen introduced for activation treatment is 60-70 ml/min, and the flow rate of hydrogen is 20-30 ml/min, the upstream reactor and the downstream reactor are respectively heated to the activation treatment temperature at a heating rate of 8-10 ℃/min, and the on-line activation treatment is carried out for at least 2 hours; and after the activation treatment is finished, closing the hydrogen, introducing nitrogen with the flow rate of 40-50 ml/min at the purging treatment temperature, and performing purging treatment for at least 1 h.
In the case where the upstream reactor is one and the downstream reactor is divided into a first downstream reactor and a second downstream reactor, the connection mode between the first downstream reactor and the upstream reactor and the connection mode between the second downstream reactor and the upstream reactor during the activation treatment and the purge treatment adopt the above-mentioned type 3, that is, the first downstream reactor and the second downstream reactor are connected in series with the upstream reactor, and the first downstream reactor and the second downstream reactor are connected in parallel; when the upstream catalyst arranged in the upstream reactor is 100mg, the downstream catalyst arranged in the first downstream reactor is 50mg, the downstream catalyst arranged in the second downstream reactor is the same as the downstream catalyst arranged in the first downstream reactor in type and weight, the flow rate of nitrogen introduced for activation treatment is 60-70 ml/min, and the flow rate of hydrogen is 20-30 ml/min, respectively heating the upstream reactor and the first downstream reactor to the activation treatment temperature at the heating rate of 8-10 ℃/min, and carrying out online activation treatment for at least 2 h; and after the activation treatment is finished, closing the hydrogen, introducing nitrogen with the flow rate of 40-50 ml/min at the purging treatment temperature, and performing purging treatment for at least 1 h.
Compared with the prior art, the method has the following beneficial effects:
1. because the upstream catalyst for quickly producing hydrogen and the downstream catalyst for producing the carbon nano tubes are respectively filled in the upstream reactor and the downstream reactor which are connected in series, methane is quickly cracked into hydrogen and solid carbon under the catalytic action of the upstream catalyst to form hydrogen-rich mixed gas, the hydrogen production amount is effectively ensured, and methane in the hydrogen-rich mixed gas from the upstream reactor is cracked into the carbon nano tubes and the hydrogen with excellent quality under the catalytic action of the downstream catalyst, so that the yield of the hydrogen is improved, and the carbon nano tubes with excellent quality are obtained.
2. The method has simple process and convenient operation, and is beneficial to realizing industrial production.
Drawings
FIG. 1 is a schematic view of a reaction apparatus used in the method of the present invention, in which 1-1: a first gas storage tank for holding methane; 1-2: a second gas storage tank for containing hydrogen gas; 1-3: a third gas storage tank for containing nitrogen; 2-1: a first flow meter; 2-2: a second flow meter; 2-3: a third flow meter; 2-4: a fourth flow meter; 2-5: a fifth flow meter; 3: a pressure gauge; 4-1: an upstream reactor; 4-2: a first downstream reactor; 4-3: a second downstream reactor; 5-1: a first switch; 5-2: a second switch; 5-3: a third switch; 5-4: a fourth switch; 5-5: a fifth switch; 6-1: a flow meter workstation; 6-2: a gas chromatograph workstation; 7: a gas chromatograph; 8-1: a first tail gas storage tank; 8-2: and a second tail gas storage tank.
FIG. 2 is a graph showing the yield of hydrogen in example 2.
FIG. 3 is a Raman plot of carbon nanotubes from the downstream catalyst in example 2.
Figure 4 is a TGA plot of carbon nanotubes for the downstream catalyst in example 2.
FIG. 5 is a Scanning Electron Microscope (SEM) image of carbon nanotubes of the downstream catalyst of example 2.
FIG. 6 is a graph showing the yield of hydrogen in example 3.
FIG. 7 is a Raman plot of carbon nanotubes from the downstream catalyst in example 3.
FIG. 8 is a TGA plot of the downstream catalyst carbon nanotubes of example 3, wherein (A) the plot is a TGA plot of the downstream catalyst carbon nanotubes in the first downstream reactor, and (B) the plot is a TGA plot of the downstream catalyst carbon nanotubes in the second downstream reactor.
FIG. 9 is a Scanning Electron Microscope (SEM) image of carbon nanotubes of the downstream catalyst of example 3.
FIG. 10 is a graph showing the yield of hydrogen in example 4.
FIG. 11 is a Raman plot of carbon nanotubes from the downstream catalyst in example 4.
FIG. 12 is a TGA graph of downstream catalyst carbon nanotubes in example 4, wherein (A) the graph is a TGA graph of downstream catalyst carbon nanotubes in a first downstream reactor, and (B) the graph is a TGA graph of downstream catalyst carbon nanotubes in a second downstream reactor.
FIG. 13 is a Scanning Electron Microscope (SEM) image of carbon nanotubes of the downstream catalyst in example 4.
Fig. 14 is a graph showing the yield of hydrogen in comparative example 1.
FIG. 15 is a Raman plot of carbon nanotubes of the catalyst of comparative example 1.
Figure 16 is a TGA plot of carbon nanotubes for the catalyst of comparative example 1.
FIG. 17 is a Scanning Electron Microscope (SEM) image of carbon nanotubes of the catalyst in comparative example 1.
Fig. 18 is a graph showing the yield of hydrogen in comparative example 2.
Fig. 19 is a Raman plot of carbon nanotubes for the catalyst of comparative example 2.
Figure 20 is a TGA plot of carbon nanotubes for the catalyst of comparative example 2.
FIG. 21 is a Scanning Electron Microscope (SEM) image of carbon nanotubes of the catalyst in comparative example 1.
Detailed Description
The method for preparing hydrogen and carbon nanotubes by cracking methane in series by two catalysts according to the present invention is further illustrated by the following examples in combination with the accompanying drawings. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In examples 2, 3 and 4 below, the upstream catalyst used was NiFeAl and the downstream catalyst used was FeMg.
In comparative example 1 described below, the catalyst used was NiFeAl; in comparative example 2 below, the catalyst used was FeMg.
The preparation method of the catalyst NiFeAl comprises the following steps:
and preparing NiFeAl by a coprecipitation method. Nickel nitrate hexahydrate (Ni (NO) 3 ) 2 ·6H 2 O), ferric nitrate nonahydrate (Fe (NO) 3 ) 3 ·9H 2 O) and aluminum nitrate (Al (NO) 3 ) 3 ) Dissolving in deionized water to prepare mixed metal nitrate solution with total concentration of 0.6mol/L, wherein Ni in the mixed metal nitrate solution 2+ 、Fe 3+ 、Al 3+ In a molar ratio of Ni 2+ :Fe 3+ :Al 3+ 2:1: 1; mixing anhydrous sodium carbonate (Na) 2 CO 3 ) Dissolving in deionized water to prepare Na with the concentration of 1mol/L 2 CO 3 The solution acts as a precipitant. Take 100mL of Na 2 CO 3 The solution was filled into a beaker and then charged with Na 2 CO 3 Placing the beaker of the solution in a water bath kettle at 60 ℃, installing a mechanical stirrer, and allowing the solution to stand for Na 2 CO 3 After the solution temperature reaches 60 ℃ and is stableDropwise adding a mixed metal nitrate solution into the beaker under stirring, wherein the dropwise adding amount of the mixed metal nitrate solution is limited by the pH value of a liquid system in the beaker being 4; then add Na dropwise to the beaker with stirring 2 CO 3 Solution, Na 2 CO 3 The dropping amount of the solution is limited by the pH value of a liquid system in the beaker being 9; the reaction was then stirred at a constant temperature of 60 ℃ for 12 h. In the whole stirring process, the rotating speed of the stirring paddle is controlled at 300 r/min. And after the reaction is finished, taking the beaker filled with the reaction liquid out of the water bath, standing to precipitate a reaction product, removing a supernatant, washing the precipitated reaction product with deionized water for 5 times, filtering to obtain the reaction product after washing, drying the reaction product at 105 ℃ for 12 hours, grinding and screening, putting powder with the particle size of 20-40 meshes obtained by screening into a crucible, roasting the powder at 500 ℃ for 5 hours by using a muffle furnace, and cooling the powder to room temperature along with the furnace to obtain the upstream catalyst NiFeAl.
The preparation method of the catalyst FeMg comprises the following steps:
and preparing FeMg by a coprecipitation method. Mixing ferric nitrate nonahydrate (Fe (NO) 3 ) 3 ·9H 2 O) and magnesium nitrate (Mg (NO) 3 ) 2 ) Dissolving in deionized water to prepare mixed metal nitrate solution with total concentration of 0.6mol/L, wherein in the mixed metal nitrate solution, Fe 3+ With Mg 2+ 1: 10; mixing anhydrous sodium carbonate (Na) 2 CO 3 ) Dissolving in deionized water to prepare Na with the concentration of 1mol/L 2 CO 3 The solution acts as a precipitant. Take 100mL of Na 2 CO 3 The solution was filled into a beaker and then charged with Na 2 CO 3 Placing the beaker of the solution in a 60 ℃ water bath kettle, installing a mechanical stirrer, and allowing Na to stand 2 CO 3 After the solution temperature reaches 60 ℃ and is stable, dropwise adding a mixed metal nitrate solution into the beaker under stirring, wherein the dropwise adding amount of the mixed metal nitrate solution is limited by the pH value of a liquid system in the beaker being 4; then add Na dropwise to the beaker with stirring 2 CO 3 Solution, Na 2 CO 3 The dropping amount of the solution is limited by the pH value of a liquid system in the beaker being 9; the reaction was then stirred at a constant temperature of 60 ℃ for 12 h. In the whole stirring process, the rotating speed of the stirring paddle is controlled at 300 r/min. After the reaction is finishedTaking out the beaker filled with the reaction liquid from the water bath, standing to precipitate a reaction product, removing a supernatant, washing the precipitated reaction product with deionized water for 5 times, filtering to obtain the reaction product after washing, drying the reaction product at 105 ℃ for 12 hours, grinding and screening, putting powder with the particle size of 20-40 meshes obtained by screening into a crucible, roasting the powder with a muffle furnace at 500 ℃ for 5 hours, and cooling the powder with the furnace to room temperature to obtain the downstream catalyst FeMg.
In the following examples 2, 3 and 4 and comparative examples 1 and 2, the hydrogen yield was calculated as follows:
Figure BDA0002342738940000061
in the formula, Y H2 Is the hydrogen yield; v H2 For H in hydrogen-rich mixed gas 2 Flow rate, unit is ml/min; v CH4 The flow rate of methane in the feed gas is expressed in mL/min.
Example 1
This example is a reaction apparatus used in the method for preparing hydrogen and carbon nanotubes by cracking methane with two catalysts in series according to the present invention, and the structure of the reaction apparatus is shown in fig. 1, and the reaction apparatus comprises a first gas storage tank 1-1 for containing methane, a second gas storage tank 1-2 for containing hydrogen, a third gas storage tank 1-3 for containing nitrogen, a first flow meter 2-1, a second flow meter 2-2, a third flow meter 2-3, a fourth flow meter 2-4, a fifth flow meter 2-5, a pressure gauge 3, an upstream reactor 4-1, a first downstream reactor 4-2, a second downstream reactor 4-3, a flow meter workstation 6-1, a gas chromatograph workstation 6-2, a gas chromatograph 7, a first switch 5-1, a second switch 5-2, a third switch 5-3, a third switch 2, a fourth flow meter 2-3, a fourth flow meter 2-4, a fourth flow meter 2-5, a fourth flow meter 2, a fourth flow meter, a fifth flow meter, a fourth flow meter, a sixth flow meter, a, A fourth switch 5-4, a fifth switch 5-5, a first tail gas storage tank 8-1 and a second tail gas storage tank 8-2. The upstream reactor 4-1, the first downstream reactor 4-2 and the second downstream reactor 4-3 are all fixed bed reactors and mainly comprise a heating furnace and a reaction tube, wherein the reaction tube is a 316L stainless steel tube, the tube diameter is 8mm, and the tube length is 800 mm. The gas chromatograph 7 is equipped with a TCD detector and a TDX-01 detection column, and is used for detecting tail gas components and calculating the methane conversion rate and the hydrogen yield. The first switch 5-1, the second switch 5-2, the third switch 5-3, the fourth switch 5-4 and the fifth switch 5-5 are all three-way switches.
The combination mode of the components, the instruments and the meters is as follows: a first gas storage tank 1-1 for containing methane, a second gas storage tank 1-2 for containing hydrogen and a third gas storage tank 1-3 for containing nitrogen are respectively connected with a gas inlet of an upstream reactor 4-1 through pipe fittings, a first downstream reactor 4-2 and a second downstream reactor 4-3 are connected in parallel, gas inlets of the first and second downstream reactors are respectively connected with a tail gas outlet of the upstream reactor 4-1 through pipe fittings, and tail gas outlets of the first and second downstream reactors are respectively connected with a gas inlet of a gas chromatograph 7 through pipe fittings; a first flow meter 2-1, a second flow meter 2-2 and a third flow meter 2-3 are respectively arranged at gas outlets of a first gas storage tank 1-1, a second gas storage tank 1-2 and a third gas storage tank 1-3, and a fourth flow meter 2-4 and a fifth flow meter 2-5 are respectively arranged at gas inlets of a first downstream reactor 4-2 and a second downstream reactor 4-3; the pressure gauge 3 is arranged on a pipe fitting for connecting the air inlet of the upstream reactor 4-1 and the air outlets of the three air storage tanks; a first switch 5-1 and a second switch 5-2 are respectively arranged on a pipe fitting connected with an air inlet of a first downstream reactor 4-2 and an air inlet of a second downstream reactor 4-3, a third switch 5-3 and a fourth switch 5-4 are respectively arranged on a pipe fitting connected with a tail gas outlet of the first downstream reactor 4-2 and a tail gas outlet of the second downstream reactor 4-3, and a fifth switch 5-5 is arranged at an air inlet of a gas chromatograph 7 and is connected with the third switch 5-3 and the fourth switch 5-4 through pipe fittings; the flowmeter workstation 6-1 is used for controlling each flowmeter and obtaining gas flow data detected by each flowmeter, and the gas chromatograph workstation 6-2 is used for detecting tail gas components and calculating the methane conversion rate and the hydrogen yield; the first tail gas storage tank 8-1 is connected with an exhaust port of the gas chromatograph 7 through a pipe fitting, and the second tail gas storage tank 8-2 is connected with the third switch 5-3 and the fourth switch 5-4 through pipe fittings.
Example 2
In this example, the reaction apparatus described in example 1 was used, and the gas inlet path of the second downstream reactor 4-3 was blocked by adjusting the first switch 5-1, the second switch 5-2, the third switch 5-3, the fourth switch 5-4, and the fifth switch 5-5, so that both the upstream reactor and the downstream reactor were formed as one reactor, and the two reactors were always connected in series in the whole process.
In this example, the upstream reactor 4-1 contained 100mg of an upstream catalyst NiFeAl, and the downstream reactor 4-2 contained 100mg of a downstream catalyst FeMg.
The process comprises the following steps:
(1) introducing nitrogen gas into an upstream reactor 4-1 at the flow rate of 70ml/min and hydrogen gas into the upstream reactor 4-1 at the flow rate of 30ml/min, respectively heating reaction tubes in the upstream reactor 4-1 and a downstream reactor 4-2 to 700 ℃ at the heating rate of 10 ℃/min under the atmosphere, and carrying out online activation treatment on an upstream catalyst and a downstream catalyst for 2 h; then, closing hydrogen, introducing nitrogen with the flow rate of 50ml/min into the upstream reactor 4-1, keeping the temperature of the reaction tube in the downstream reactor 4-2 at 700 ℃ under the atmosphere, reducing the temperature of the reaction tube in the upstream reactor 4-1 to 600 ℃ at the speed of 2 ℃/min, and purging for 1 h;
(2) keeping the temperature of a reaction tube in an upstream reactor 4-1 at 600 ℃ and the temperature of a reaction tube in a downstream reactor 4-2 at 700 ℃, simultaneously introducing nitrogen at a flow rate of 50ml/min and methane at a flow rate of 20ml/min into the upstream reactor 4-1, rapidly cracking methane into hydrogen and solid carbon under the catalytic action of an upstream catalyst, introducing the formed hydrogen-rich mixed gas into the downstream reactor 4-2, cracking methane in the hydrogen-rich mixed gas into carbon nano tubes and hydrogen under the catalytic action of the downstream catalyst, and controlling the reaction time to be 243min (the reaction time is the time interval between the start time and the end time of introducing the nitrogen and the methane into the upstream reactor).
In the reaction process, pressure drop changes in the reaction tubes of the upstream reactor 4-1 and the downstream reactor 4-2 are monitored by a pressure gauge 3, the hydrogen-rich mixed gas discharged from the upstream reactor 4-1 and the hydrogen-rich mixed gas discharged from the downstream reactor 4-2 in different reaction time periods are respectively introduced into a gas chromatograph 7 for detection by switching a three-way switch, the hydrogen yield in different reaction times is calculated, and the detection result is shown in fig. 2. As can be seen from FIG. 2, the total hydrogen yield is highest at 43min, reaching about 57%, and then decreases with increasing reaction time, and at 243min, the total hydrogen yield decreases to about 46%, and the reactor pressure drop increases to 0.39 MPa.
After the reaction is finished, the mass and the content of the carbon nanotubes cracked from methane in the hydrogen-rich mixed gas under the catalytic action of the downstream catalyst are respectively detected by a Raman (Raman) detector and a thermogravimetric analyzer (TGA), and the detection results are shown in fig. 3 and fig. 4. The G peak on the Raman curve in FIG. 3 (Raman shift ≈ 1580cm -1 ) With peak D (Raman shift ≈ 1340 cm) -1 ) The ratio of the peak areas of (A) and (B) is called R value and is used for characterizing the graphitization degree of the carbon deposit, and according to the peak areas of G peak and D peak in figure 3, the R of the carbon deposit nanotube of the downstream catalyst in the embodiment is calculated to be 2.36 (see Tuinstra, F.and J.L.Koenig, Raman spectra of graphite. journal of Chemical Physics,1970.53(3): p.1126-1130.). In FIG. 4, the carbon deposition weight loss mainly has two positions on the TG curve, which are 350-470 ℃ and 470-720 ℃ respectively, wherein the former is the weight loss of the amorphous carbon, the latter is the weight loss of the carbon nano tube, and the carbon deposition nano tube on the downstream catalyst with unit mass is calculated to be 1.52g/g cat (analysis and calculation method see Chenping, catalytic cracking CH 4 Or the spectral characterization of the structural properties of the carbon nano tube made of CO, the proceedings of higher school chemistry 1998.19(5) p.765-769.)
The downstream catalyst and the carbon nanotubes deposited thereon were analyzed by Scanning Electron Microscopy (SEM), the SEM photograph being shown in fig. 5.
In this embodiment, the detected gas discharged from the gas chromatograph 7 enters the first tail gas storage tank 8-1 to be collected, and the hydrogen-rich mixed gas discharged from the downstream reactor 4-2 enters the second tail gas storage tank 8-2 to be collected.
Example 3
In this example, the reaction apparatus described in example 1 was used, and the first switch 5-1, the second switch 5-2, the third switch 5-3, the fourth switch 5-4, and the fifth switch 5-5 were adjusted so that the first downstream reactor 4-2 and the second downstream reactor 4-3 were connected in series with the upstream reactor 4-1, respectively, and the first downstream reactor 4-2 and the second downstream reactor 4-3 were connected in parallel during the activation treatment and the purge treatment; the first downstream reactor 4-2, the second downstream reactor 4-3 and the upstream reactor 4-1 are alternately connected in series during the reaction.
In this example, the upstream reactor 4-1 contained 100mg of the upstream catalyst NiFeAl, and the first downstream reactor 4-2 and the second downstream reactor 4-3 contained 50mg of the downstream catalyst FeMg.
The process comprises the following steps:
(1) introducing nitrogen gas into an upstream reactor 4-1 at the flow rate of 70ml/min and hydrogen gas into the upstream reactor 4-1 at the flow rate of 30ml/min, respectively heating reaction tubes in the upstream reactor 4-1, a first downstream reactor 4-2 and a second downstream reactor 4-3 to 700 ℃ at the temperature rise rate of 10 ℃/min under the atmosphere, and carrying out online activation treatment on an upstream catalyst and a downstream catalyst for 2 h; then, closing hydrogen, introducing nitrogen with the flow of 50ml/min into the upstream reactor, keeping the temperature of the reaction tubes in the first downstream reactor 4-2 and the second downstream reactor 4-3 at 700 ℃ under the atmosphere, reducing the temperature of the reaction tube in the upstream reactor 4-1 to 600 ℃ at the speed of 2 ℃/min, and carrying out purging treatment for 1 h;
(2) the temperature of the reaction tube in the upstream reactor 4-1 is maintained at 600 ℃ and the temperature of the reaction tube in the first downstream reactor 4-2 and the second reactor 4-3 is maintained at 700 ℃, the first downstream reactor 4-2 and the upstream reactor 4-1 are first connected in series by adjusting the first switch 5-1 and the second switch 5-2, the gas inlet passage of the second downstream reactor 4-3 is cut off, and when the reaction time reaches 120min, the first downstream reactor 4-2 and the second downstream reactor 4-3 are switched, that is, the first switch 5-1 and the second switch 5-2 are adjusted, the gas inlet passage of the first downstream reactor 4-2 is cut off, the second downstream reactor 4-3 and the upstream reactor 4-1 are connected in series, and the reaction time is 122 min. In the whole reaction process, nitrogen is introduced into an upstream reactor 4-1 at a flow rate of 50ml/min and methane is introduced into the upstream reactor at a flow rate of 20ml/min, the methane is rapidly cracked into hydrogen and solid carbon under the catalytic action of an upstream catalyst, the formed hydrogen-rich mixed gas enters a first downstream reactor 4-2 or a second downstream reactor 4-3, and the methane in the hydrogen-rich mixed gas is cracked into carbon nano tubes and hydrogen under the catalytic action of a downstream catalyst. The reaction time is the time interval between the start time and the end time of the introduction of nitrogen and methane into the upstream reactor.
In the reaction process, the pressure drop changes in the reaction tubes of the upstream reactor 4-1, the first downstream reactor 4-2 and the second downstream reactor 4-3 are monitored by a pressure gauge 3, the hydrogen-rich mixed gas discharged from the upstream reactor 4-1 and the hydrogen-rich mixed gas discharged from the first downstream reactor 4-2 or the second downstream reactor 4-3 in different reaction periods are respectively introduced into a gas chromatograph 7 for detection by switching a three-way switch, the hydrogen yield in different reaction periods is calculated, and the detection result is shown in fig. 6. As can be seen from fig. 6, when the first downstream reactor 4-2 and the upstream reactor 4-1 are connected in series, the total hydrogen yield reaches the highest value of about 60% after 42min of reaction, and then decreases with the increase of reaction time, the second downstream reactor 4-3 and the upstream reactor 4-1 are connected in series after switching, the total hydrogen yield sharply increases to about 67% after 122min of reaction, and then decreases with the increase of reaction time, and the total hydrogen yield decreases to about 48% after 242min of reaction. The pressure drop is not influenced by the switching of the downstream reactor and shows a continuous increasing trend, and the pressure is increased to about 0.35MPa when the reaction time is 242 min.
After the reaction, the mass and content of the carbon nanotubes cracked from methane in the hydrogen-rich mixed gas under the catalysis of the downstream catalyst were respectively detected by a Raman (Raman) detector and a thermogravimetric analyzer (TGA), and the detection results are shown in fig. 7 and 8. The ratio of the peak area of the G peak to the peak area of the D peak on the Raman curve is called R value for characterizing the graphitization degree of the carbon deposit, and according to the peak areas of the G1 peak, the D1 peak on the Raman curve of the downstream catalyst-1 in FIG. 7 and the peak areas of the G2 peak and the D2 peak on the Raman curve of the downstream catalyst-2, calculated, in this example, R of the carbon deposit nanotube of the downstream catalyst-1 in the first downstream reactor 4-2 and the downstream catalyst-2 in the second downstream reactor 4-3 is 2.60 (see Tuinstra, F.and J.L.Koenig, Raman Spectrum of graphite. journal of Chemical Physics,1970.53(3): p.1126-1130.); in fig. 8(a), the weight loss of the carbon deposit mainly has two positions on the TG curve, which are 350 to 460 ℃ and 460 to 650 ℃, respectively, and in fig. 8(B), the weight loss of the carbon deposit mainly has two positions on the TG curve, which are 350 to 460 ℃ and 460 to 650 ℃, respectively, wherein the former is the weight loss of the amorphous carbon, and the latter is the weight loss of the carbon nanotube, and the unit mass in the first downstream reactor 4-2 is calculatedThe amount of carbon nanotubes deposited on the downstream catalyst-1 was 0.78g/g cat The carbon nanotubes on the downstream catalyst-2 per unit mass in the second downstream reactor 4-3 was 0.83g/g cat (the analysis and calculation method is shown in Chen Ping-Na, the spectral characterization of the structural performance of the carbon nano tube prepared by catalytic cracking CH4 or CO, the report of higher school chemistry, 1998.19(5): p.765-769.).
The downstream catalyst and the carbon nanotubes deposited thereon were analyzed by Scanning Electron Microscopy (SEM), and the SEM photograph is shown in fig. 9.
In this embodiment, the detected gas discharged from the gas chromatograph 7 enters the first tail gas storage tank 8-1 to be collected, and the hydrogen-rich mixed gas discharged from the first downstream reactor 4-2 and the second downstream reactor 4-3 enters the second tail gas storage tank 8-2 to be collected.
Example 4
In this embodiment, the reaction apparatus described in embodiment 1 is used, and the first switch 5-1, the second switch 5-2, the third switch 5-3, the fourth switch 5-4 and the fifth switch 5-5 are adjusted, so that the first downstream reactor 4-2 and the second downstream reactor 4-3 are respectively connected in series with the upstream reactor 4-1, and the first downstream reactor 4-2 and the second downstream reactor 4-3 are connected in parallel in the whole process.
In this example, the upstream reactor 4-1 contained 100mg of the upstream catalyst NiFeAl, and the first downstream reactor 4-2 and the second downstream reactor 4-3 contained 50mg of the downstream catalyst FeMg.
The process comprises the following steps:
(1) introducing nitrogen gas into an upstream reactor 4-1 at a flow rate of 70ml/min and hydrogen gas into the upstream reactor 4-1 at a flow rate of 30ml/min, respectively heating reaction tubes in the upstream reactor 4-1, a first downstream reactor 4-2 and a second downstream reactor 4-3 to 700 ℃ at a heating rate of 10 ℃/min in the atmosphere, and carrying out online activation treatment on an upstream catalyst and a downstream catalyst for 2 h; then, closing hydrogen, introducing nitrogen with the flow rate of 50ml/min into the upstream reactor, keeping the temperature of the reaction tubes in the first downstream reactor 4-2 and the second downstream reactor 4-3 at 700 ℃ under the atmosphere, reducing the temperature of the reaction tubes in the upstream reactor 4-1 to 600 ℃ at the speed of 2 ℃/min, and purging for 1 h;
(2) keeping the temperature of a reaction tube in an upstream reactor 4-1 at 600 ℃, simultaneously introducing nitrogen and methane into the upstream reactor 4-1 at the flow rate of 50ml/min and the flow rate of 20ml/min at 700 ℃, rapidly cracking methane into hydrogen and solid carbon under the catalytic action of an upstream catalyst, uniformly dividing the formed hydrogen-rich mixed gas into two parts, respectively introducing the two parts into the first downstream reactor 4-2 and a second downstream reactor 4-3, cracking the methane in the hydrogen-rich mixed gas into carbon nanotubes and hydrogen under the catalytic action of a downstream catalyst, and controlling the reaction time to be 242min (the reaction time is the time interval between the start time and the end time of introducing the nitrogen and the methane into the upstream reactor).
In the reaction process, the pressure drop changes in the reaction tubes of the upstream reactor 4-1, the first downstream reactor 4-2 and the second downstream reactor 4-3 are monitored by a pressure gauge 3, the hydrogen-rich mixed gas discharged from the upstream reactor 4-1 and the hydrogen-rich mixed gas discharged from the first downstream reactor 4-2 and the second downstream reactor 4-3 at different reaction periods are respectively introduced into a gas chromatograph 7 for detection by switching a three-way switch, the hydrogen yield at different reaction periods is calculated, and the detection result is shown in fig. 10. As can be seen from FIG. 10, the total hydrogen yield was the highest at 22min for both the upstream catalyst and the downstream catalyst-1, which was 65%. The total hydrogen yield of the upstream catalyst and the downstream catalyst-2 was the highest at 32min, and was 74%. Then, the total hydrogen yield is in a descending trend along with the increase of the reaction time, and the total hydrogen yield is reduced to about 48 percent and about 56 percent at 242min and 232min respectively. The pressure drop is increased to about 0.19MPa when the reaction time is 242 min.
After the reaction is finished, the mass and the content of the carbon nanotubes cracked from methane in the hydrogen-rich mixed gas under the catalytic action of the downstream catalyst are respectively detected by a Raman (Raman) detector and a thermogravimetric analyzer (TGA), and the detection results are shown in fig. 11 and 12. The peak area ratio of the G peak and the D peak on the Raman curve is called R value and is used for characterizing the graphitization degree of carbon deposition, and according to the peak areas of the G1 peak and the D1 peak on the Raman curve of the downstream catalyst-1 and the peak areas of the G2 peak and the D2 peak on the Raman curve of the downstream catalyst-2 in the graph 11, the calculation result shows that the catalyst has the advantages of high mechanical strength, high mechanical strength and the likeIn the examples, R of the downstream catalyst-1 carbon nanotubes in the first downstream reactor 4-2 was 3.25, and R of the downstream catalyst-2 carbon nanotubes in the second downstream reactor 4-3 was 2.95 (see Tuinstra, F.and J.L.Koenig, Raman spectra of graphite. journal of Chemical Physics,1970.53(3): p.1126-1130.); in FIG. 12(A), the carbon weight loss is mainly at two positions on the TG curve, namely 350-460 ℃ and 460-650 ℃, respectively, in FIG. 12(B), the carbon weight loss is mainly at two positions on the TG curve, namely 350-470 ℃ and 470-650 ℃, respectively, wherein the former is the weight loss of amorphous carbon, and the latter is the weight loss of carbon nanotubes, and the calculated weight loss of the carbon nanotubes on the downstream catalyst-1 with the unit weight in the first downstream reactor 4-2 is 1.23g/g cat The carbon nanotubes on the downstream catalyst-2 per unit mass in the second downstream reactor 4-3 was 1.92g/g cat (analysis and calculation methods see Chenping. catalytic cracking CH 4 Or the spectral characterization of the structural performance of the carbon nano tube made of CO, the report of higher school chemistry 1998.19(5): p.765-769.).
The downstream catalyst and the carbon nanotubes deposited thereon were analyzed by Scanning Electron Microscopy (SEM), the SEM photograph being shown in fig. 13.
In this embodiment, the detected gas discharged from the gas chromatograph 7 enters the first tail gas storage tank 8-1 to be collected, and the hydrogen-rich mixed gas discharged from the first downstream reactor 4-2 and the second downstream reactor 4-3 enters the second tail gas storage tank 8-2 to be collected.
Comparative example 1
This comparative example used the reaction apparatus described in example 1, and formed a connection mode in which only the upstream reactor 4-1 was provided in the entire process flow by adjusting the first switch 5-1, the second switch 5-2, the third switch 5-3, the fourth switch 5-4, and the fifth switch 5-5.
In this comparative example, the upstream reactor 4-1 contained 100mg of NiFeAl as the catalyst.
The process comprises the following steps:
(1) introducing nitrogen at the flow rate of 70ml/min and hydrogen at the flow rate of 30ml/min into an upstream reactor 4-1, heating a reaction tube of the upstream reactor 4-1 to 700 ℃ at the heating rate of 10 ℃/min under the atmosphere, and carrying out online activation on a catalyst for 2 hours; then, closing hydrogen, introducing nitrogen with the flow rate of 50ml/min, and cooling the temperature of a reaction tube in the upstream reactor 4-1 to 600 ℃ at the speed of 2 ℃/min under the atmosphere, and carrying out purging treatment for 1 h;
(2) keeping the temperature of a reaction tube in the upstream reactor 4-1 at 600 ℃, introducing nitrogen at a flow rate of 50ml/min and methane at a flow rate of 20ml/min into the upstream reactor 4-1 simultaneously, and rapidly cracking the methane into hydrogen and solid carbon under the catalytic action of a catalyst, wherein the reaction time is controlled to be 270min (the reaction time is the time interval between the start time and the end time of introducing the nitrogen and the methane into the upstream reactor).
In the reaction process, the pressure drop change of the upstream reactor 4-1 is monitored by a pressure gauge 3, the tail gas of the upstream reactor 4-1 in different reaction time periods is led into a gas chromatograph 7 for detection by switching a three-way switch, the hydrogen yield in different reaction time periods is calculated, and the detection result is shown in figure 14. As can be seen from fig. 14, the catalyst gave the highest hydrogen yield of 55% at 50 min. The total hydrogen yield is in a descending trend along with the increase of the reaction time, and the total hydrogen yield is reduced to about 44 percent in 270 min. The pressure drop increased to about 0.46MPa at 270min of reaction.
After the reaction is finished, the mass and the content of the solid carbon cracked from methane under the catalytic action of the catalyst are respectively detected by a Raman (Raman) detector and a thermogravimetric analyzer (TGA), and the detection results are shown in fig. 15 and fig. 16. The ratio of the peak areas of the G peak and the D peak on the Raman curve is referred to as an R value for characterizing the degree of graphitization of the carbon deposit, and according to the peak areas of the G peak and the D peak on the Raman curve of the catalyst in FIG. 15, the R of the catalyst after reaction in this comparative example was calculated to be 1.02 (see Tuinstra, F.and J.L.Koenig, Raman spectra of graphics. journal of Chemical Physics,1970.53(3): p.1126-1130.); in fig. 15, the carbon deposition weight loss mainly has two positions on the TG curve, which are 350-500 ℃ and 500-720 ℃, respectively, where the former is the weight loss of amorphous carbon and the latter is the weight loss of carbon nanotubes, and the calculated carbon deposition nanotube on the catalyst is 5.10g/g cat (analysis and calculation methods see Chenping. catalytic cracking CH 4 Or the spectral characterization of the structural Properties of carbon nanotubes made from COThe higher school chemistry bulletin, 1998.19(5): p.765-769).
The catalyst and the solid carbon deposited thereon were analyzed by Scanning Electron Microscopy (SEM), and the SEM photograph is shown in fig. 17.
Comparative example 2
This comparative example used the reaction apparatus described in example 1, and formed a connection mode in which only the upstream reactor 4-1 was provided in the entire process flow by adjusting the first switch 5-1, the second switch 5-2, the third switch 5-3, the fourth switch 5-4, and the fifth switch 5-5.
In this comparative example, the upstream reactor 4-1 contained 100mg of FeMg as the catalyst.
The process comprises the following steps:
(1) introducing nitrogen at the flow rate of 70ml/min and hydrogen at the flow rate of 30ml/min into an upstream reactor 4-1, heating a reaction tube of the upstream reactor 4-1 to 700 ℃ at the heating rate of 10 ℃/min under the atmosphere, and carrying out online activation treatment on a downstream catalyst for 2 h; then, closing the hydrogen, introducing nitrogen with the flow rate of 50ml/min, keeping the temperature at 700 ℃, and carrying out purging treatment for 1 h;
(2) keeping the temperature of a reaction tube in the upstream reactor 4-1 at 700 ℃, simultaneously introducing nitrogen at a flow rate of 50ml/min and methane at a flow rate of 20ml/min into the upstream reactor 4-1, and cracking the methane into hydrogen and carbon nanotubes under the catalytic action of a catalyst, wherein the reaction time is controlled to be 120min (the reaction time is the time interval from the beginning time to the end time of introducing the nitrogen and the methane into the upstream reactor).
In the reaction process, the pressure drop change of the upstream reactor 4-1 is monitored by a pressure gauge 3, the tail gas of the upstream reactor 4-1 in different reaction time periods is led into a gas chromatograph 7 for detection by switching a three-way switch, the hydrogen yield in different reaction time periods is calculated, and the detection result is shown in fig. 18. As can be seen from FIG. 18, the hydrogen yield decreased from the first 41% to 3% at 120 min. The pressure drop is increased to about 0.46MPa when the reaction time is 120 min.
After the reaction is finished, the mass and the content of the carbon nanotubes cracked from methane under the catalytic action of the catalyst are respectively detected by a Raman (Raman) detector and a thermogravimetric analyzer (TGA), and the detection results are shown in fig. 19 and 20. RamaThe ratio of the peak area of the G peak to the peak area of the D peak on the n-curve is referred to as the R value for characterizing the degree of graphitization of the carbon deposit, and from the peak areas of the G peak and the D peak on the Raman curve of the catalyst in FIG. 19, it was calculated that in this comparative example, the R of the catalyst after the reaction was 6.72 (see Tuinstra, F.and J.L.Koenig, Raman spectra of graphics. journal of Chemical Physics,1970.53(3): p.1126-1130.); in fig. 20, the weight loss of the carbon deposit on the TG curve mainly has two positions, which are 350-460 ℃ and 460-650 ℃, respectively, where the former is the weight loss of the amorphous carbon and the latter is the weight loss of the carbon nanotube, and the carbon nanotube on the catalyst is calculated to be 0.75g/g cat (analysis and calculation method see Chenping, catalytic cracking CH 4 Or the spectral characterization of the structural performance of the carbon nano tube made of CO, the report of higher school chemistry 1998.19(5): p.765-769.).
The catalyst and the carbon nanotubes deposited thereon were analyzed by Scanning Electron Microscopy (SEM), and the SEM photograph is shown in fig. 21.
As can be seen from the above comparative examples, it is difficult to simultaneously increase the yield of hydrogen and obtain carbon nanotubes of excellent quality by pyrolyzing methane using one catalyst.

Claims (7)

1. The method for preparing hydrogen and carbon nano tubes by cracking methane with two catalysts in series is characterized by comprising the following process steps in sequence:
(1) respectively filling an upstream catalyst for quickly producing hydrogen and a downstream catalyst for producing carbon nano tubes into an upstream reactor and a downstream reactor which are connected in series, simultaneously inputting hydrogen and nitrogen to activate the upstream catalyst and the downstream catalyst, and then purging with nitrogen;
(2) simultaneously inputting methane and nitrogen into an upstream reactor, rapidly cracking the methane into hydrogen and solid carbon under the catalytic action of an upstream catalyst, enabling the formed hydrogen-rich mixed gas to enter a downstream reactor, cracking the methane in the hydrogen-rich mixed gas into carbon nano tubes and hydrogen under the catalytic action of the downstream catalyst, depositing the carbon nano tubes on the downstream catalyst to be collected, and discharging the hydrogen-rich mixed gas from the downstream reactor to be collected;
the upstream catalyst arranged in the upstream reactor is NiFeAl or NiFeCu/Al 2 O 3 Or Ni/TiO 2 The downstream catalyst arranged in the downstream reactor is FeMg or CoMo/Al 2 O 3 ；
When the upstream catalyst is NiFeAl or Ni/TiO 2 When the temperature of the activation treatment is 700 ℃, the reaction temperature of methane cracking is 600 ℃, and the temperature of the purging treatment is gradually reduced from 700 ℃ to 600 ℃; when the upstream catalyst is NiFeCu/Al 2 O 3 When the temperature of the activation treatment, the temperature of the purging treatment and the reaction temperature of methane cracking are all 700 ℃;
the downstream catalyst FeMg or CoMo/Al 2 O 3 The activation treatment temperature, the purging treatment temperature and the methane cracking reaction temperature are all 700 ℃.
2. The method for preparing hydrogen and carbon nano tubes by cracking methane through two catalysts in series according to claim 1, which is characterized in that an upstream reactor and a downstream reactor are both one, and the two reactors are always connected in series in the whole process flow.
3. The method for preparing hydrogen and carbon nanotubes by cracking methane with two catalysts in series according to claim 1, wherein the upstream reactor is one, the downstream reactors are two, namely a first downstream reactor and a second downstream reactor, and the first downstream reactor, the second downstream reactor and the upstream reactor are alternately connected in series during the reaction.
4. The method for preparing hydrogen and carbon nanotubes by cracking methane with two catalysts in series according to claim 1, wherein the number of the upstream reactors is one, the number of the downstream reactors is two, and the two downstream reactors are named as a first downstream reactor and a second downstream reactor, in the whole process flow, the first downstream reactor and the second downstream reactor are always connected with the upstream reactor in series respectively, and the first downstream reactor and the second downstream reactor are connected with each other in parallel.
5. The method of claim 2, wherein the reaction time for methane cracking is at least 240min when the upstream catalyst in the upstream reactor is 100mg, the downstream catalyst in the downstream reactor is 100mg, the flow rate of methane is 10-30 ml/min, and the flow rate of nitrogen is 40-60 ml/min.
6. The method of claim 3, wherein when the upstream catalyst of the upstream reactor is 100mg, the downstream catalyst of the first downstream reactor is 50mg, the downstream catalyst of the second downstream reactor is the same as the downstream catalyst of the first downstream reactor in type and weight, the flow rate of methane is 10-30 ml/min, and the flow rate of nitrogen is 40-60 ml/min, the first downstream reactor and the upstream reactor are connected in series to crack methane for at least 120min, and the second downstream reactor and the upstream reactor are connected in series to crack methane for at least 120 min.
7. The method of claim 4, wherein the reaction time for methane pyrolysis is at least 240min when the upstream catalyst in the upstream reactor is 100mg, the downstream catalyst in the first downstream reactor is 50mg, the downstream catalyst in the second downstream reactor is the same as the downstream catalyst in the first downstream reactor in type and weight, the flow rate of methane is 10-30 ml/min, and the flow rate of nitrogen is 40-60 ml/min.
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CN113929054B (en) * 2021-11-18 2022-07-08 无锡碳谷科技有限公司 Hydrogen recovery device of methane catalytic cracking instrument

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101054159A (en) * 2007-06-01 2007-10-17 西北大学 Method of preparing high-purity hydrogen gas and cooperatively growing carbon nano-tube
CN101337655A (en) * 2008-08-29 2009-01-07 清华大学 Process for preparing hydrogen gas and nanometer carbon by catalyzing and cracking methane at low temperature
CN101485989A (en) * 2009-02-24 2009-07-22 上海大学 Catalyst for cracking coke tar component in coke oven gas and preparation method thereof
CN102583242A (en) * 2012-03-09 2012-07-18 大连理工大学 Method for preparing hydrogen gas through catalytic cracking of methane
CN109928361A (en) * 2019-03-19 2019-06-25 中国矿业大学 A kind of carbon nanotube and hydrogen production system and method with self-catalysis function

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20170012745A (en) * 2015-07-23 2017-02-03 에스케이이노베이션 주식회사 Catalyst of synthesis of multi-walled carbon nanotube and method of manufacturing multi-walled carbon nanotube

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101054159A (en) * 2007-06-01 2007-10-17 西北大学 Method of preparing high-purity hydrogen gas and cooperatively growing carbon nano-tube
CN101337655A (en) * 2008-08-29 2009-01-07 清华大学 Process for preparing hydrogen gas and nanometer carbon by catalyzing and cracking methane at low temperature
CN101485989A (en) * 2009-02-24 2009-07-22 上海大学 Catalyst for cracking coke tar component in coke oven gas and preparation method thereof
CN102583242A (en) * 2012-03-09 2012-07-18 大连理工大学 Method for preparing hydrogen gas through catalytic cracking of methane
CN109928361A (en) * 2019-03-19 2019-06-25 中国矿业大学 A kind of carbon nanotube and hydrogen production system and method with self-catalysis function

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
"Methane Catalytic Cracking to Make COx Free Hydrogen and Carbons (Nanotubes, Microfibers, Microballs)";Lizhen Gao et al.;《Advanced Materials Research》;20090831;第79-82卷;第585-588页 *
"甲烷催化裂解技术研究进展";王文华等;《材料导报》;20110610;第25卷(第6期);第116-120页 *

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