CN110921653A - Method for preparing multi-walled carbon nano-tubes after deoxidizing coal bed gas - Google Patents

Method for preparing multi-walled carbon nano-tubes after deoxidizing coal bed gas Download PDF

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CN110921653A
CN110921653A CN201911238942.2A CN201911238942A CN110921653A CN 110921653 A CN110921653 A CN 110921653A CN 201911238942 A CN201911238942 A CN 201911238942A CN 110921653 A CN110921653 A CN 110921653A
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coal bed
deoxidation
gas
bed gas
reaction
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陈秉辉
唐旭光
郑进保
谢建榕
叶松寿
吴钊男
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Xiamen University
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Xiamen University
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/16—Preparation
    • C01B32/162—Preparation characterised by catalysts
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/06—Multi-walled nanotubes

Abstract

The invention discloses a method for preparing a multi-walled carbon nanotube by deoxidizing coal bed gas, which mainly comprises the following steps: firstly, introducing oxygen-containing coal bed gas into a fixed bed deoxidation reactor filled with a deoxidation catalyst, and then introducing volatile organic compounds to carry out deoxidation reaction until the oxygen content in the coal bed gas is lower than 0.5%; introducing the coal bed gas subjected to catalytic deoxidation into a fluidized bed reactor to perform a chemical catalytic growth method (CCVD) to prepare a multi-walled carbon nanotube crude product; and finally, soaking the prepared crude product in dilute nitric acid, stirring and refluxing, rinsing with water, and drying. The method provided by the invention mainly utilizes the reaction of methanol steam and oxygen in the coal bed gas to generate water and carbon dioxide under the action of the catalyst, thereby not only solving the problem of O in the coal bed gas2The potential safety hazard caused by the existence of the catalyst is overcome by low-temperature deoxidization, and the defects that the existing fixed bed coal bed methane deoxidization causes methane to crack, the methane concentration in the product gas is low and the methane loss rate is high are overcomeHigh degree of problem.

Description

Method for preparing multi-walled carbon nano-tubes after deoxidizing coal bed gas
Technical Field
The invention belongs to the technical field of coal bed gas, and particularly relates to a method for preparing a multi-walled carbon nanotube by deoxidizing the coal bed gas.
Background
Multi-walled carbon nanotubes (MWCNTs) were discovered by doctor Ijima, a japanese electron microscope expert, in 1991, and can be regarded as a nano-scale tubular material consisting of six-membered carbon rings, which is rolled in a certain manner like a graphite plane (or curved surface). The multi-walled carbon nanotube has many excellent properties, such as excellent electrical conductivity, good thermal conductivity, ultrahigh strength and tensile strength, large specific surface area, high-efficiency catalytic performance and the like, so that the multi-walled carbon nanotube has wide application prospects in the fields of energy sources, chemical and physical sensors, catalytic materials, composite materials and the like.
After 30 years of development, the carbon sources of the multi-walled carbon nanotubes are various, and saturated hydrocarbons such as acetylene, acetone, ethylene, n-pentane, propylene, methanol, toluene, methane and the like, unsaturated hydrocarbons, aromatic hydrocarbons and oxygen-containing organic matters can be used as the carbon sources. And the coal bed gas with low price can be used as the carbon source of the multi-walled carbon nano-tube after the deoxidization process.
Coal bed gas (commonly called gas) exists in coal beds in large quantities, is combustible gas adsorbed in the coal beds, and contains a large amount of hydrocarbon compounds, namely methane. In the process of mining coal mines, the existence of coal bed gas brings great potential safety hazards to the safety production of the coal mines, and due to the explosive property of the coal bed gas, coal mine underground accidents are very easily caused if the coal bed gas is carelessly processed. At present, for CH4The coal bed gas with the content of more than 60 percent is relatively mature by utilizing the technology; and CH4Coal bed gas, which is relatively low in concentration and air entrained, is generally only used on site and is mostly burned and then released to the atmosphere. According to statistics of CH discharged from coal mining industry in China every year4Up to 194 hundred million m3And great resource waste is caused. Furthermore, methane is a greenhouse gas whose greenhouse effect is CO2More than 20 times of the total amount of the coal bed gas, and the global greenhouse effect is intensified by discharging a large amount of coal bed gas into the atmosphere. Therefore, the efficient utilization of the coal bed gas is of practical significance.
In coal bed gas except CH4The remaining constituents are mostly nitrogen and oxygen, the presence of which can lead to safety problems,has become a bottleneck for restricting the utilization of the coal bed gas with medium and low methane concentration. This further increases the risk of use due to the wider explosive limits of methane and oxygen. Therefore, how to deoxidize coal bed gas is one of the key technologies for coal bed gas utilization.
The current deoxidation technology has two main types: one is physical deoxidation, which comprises low-temperature deep cooling, pressure swing adsorption, membrane separation, gas magnetic separation and the like; the other is chemical deoxidation, which comprises catalytic deoxidation and coke combustion deoxidation.
The principle of the low-temperature cryogenic technology is two-stage rectification. The patent with publication number CN101531560A discloses a method for purifying methane from oxygen-containing coal-bed gas by low-temperature liquefaction separation, which comprises the following steps: firstly, the raw gas of the oxygen-containing coal bed gas is cooled, and then the cooled oxygen-containing coal bed gas is rectified to obtain the separated and purified methane. Although the liquefaction and separation are carried out at low temperatures, the oxygen content of the waste gas is concentrated and increased as the methane concentration increases during the separation, which results in a high probability of being in the range of combustion and explosion of methane at a certain stage, and there is a great safety risk.
The pressure swing adsorption technology is based on physical absorption of gas molecules by an adsorbent, and utilizes the characteristics that the adsorbent is easy to adsorb high-boiling-point components and low-boiling-point components under the same pressure, the adsorption amount is increased under high pressure, and the adsorption amount is reduced under low pressure. The raw material gas of the oxygen-containing coal bed gas passes through the adsorbent bed layer under high pressure, high boiling point impurity components are selectively adsorbed, low boiling point components are difficult to adsorb and pass through the adsorbent bed layer to achieve separation of different components, then the adsorbed components are desorbed under reduced pressure to regenerate the adsorbent, and impurities are adsorbed and separated again. The key to this process is that the adsorbent must have a higher capacity for methane than the other components of the gas (excluding water) and also requires a greater separation coefficient for methane and nitrogen, but methane is readily desorbed from the adsorbent. The method has high requirements on the adsorbent, and the mixture of the methane and the oxygen which are easy to desorb is easy to be within the explosion limit.
Although deoxidation by a membrane separation method has the advantages of no phase change, simple equipment, small occupied area and the like, the defects are that the permeability of each component of the mixed gas to a membrane is different, the permeation quantity of the mixed gas is related to the permeability coefficient of each component, the area of the permeation membrane and the partial pressure difference of the gas components on two sides of the membrane, and the loss of product gas is caused in the separation process. In addition, the explosion limit of methane is also sharply increased with increasing pressure, which is a safety problem in the membrane separation deoxidation method.
The second type is a chemical deoxidation method, which is based on the principle that methane and oxygen in coal bed gas undergo catalytic combustion reaction under the action of a catalyst to achieve the purpose of deoxidation, and the main reaction is as follows:
CH4+2O2→CO2+2H2O
CH4→C+2H2
although the method can remove the oxygen in the coal bed gas, the consumed methane volume is about half of the oxygen in the coal bed gas. Publication No. CN101613627A discloses an oxygen-containing coal bed gas catalytic deoxidation process, which has the following principle: mixing the oxygen-containing coal bed gas and the coal bed gas product gas returned at a certain circulation ratio, and allowing the mixture to enter a fixed bed adiabatic catalytic reactor for reaction, wherein methane in the coal bed gas reacts with oxygen to generate carbon dioxide and water, so that the oxygen concentration in the coal bed gas product gas is reduced. The process can effectively remove oxygen in the oxygen-containing coal bed gas with the oxygen concentration of 1-15%, and the lower oxygen content in the obtained product gas eliminates the danger in the subsequent coal bed gas separation process. However, the light-off temperature of catalytic combustion of methane is high, and methane is consumed, while a catalyst resistant to high temperature is more required.
The principle of the coke combustion method is to remove O in the coal-bed gas by the combustion reaction of coke and oxygen in the coal-bed gas2The main reaction is as follows:
C+O2→CO2
2C+O2→2CO
CH4+2O2→CO2+2H2O
the disadvantages of this method are: the deoxidation reaction temperature is too high, and methane can generate cracking reaction. For example, in patent publication No. CN1919986, oxygen in the methane-rich gas is reacted with coke under high temperature, so that part of methane is reacted with oxygen to achieve the purpose of deoxidation. The defects are obvious, the precious coke resources are consumed, the consumption cost of the coke is about 50 percent of the whole operation cost, and methane is cracked and consumed in the deoxidation process.
In conclusion, it is necessary to develop a coalbed methane deoxidation process which does not consume methane in the deoxidation process, has good safety, good deoxidation effect and low cost, and particularly, the process which can utilize the coalbed methane subjected to deoxidation in time has a very promising application prospect.
Disclosure of Invention
The invention aims to provide a method for preparing multi-walled carbon nanotubes by using deoxidized coal bed gas and application thereof, and the solution of the invention is as follows:
a method for preparing a multi-walled carbon nanotube after deoxidizing coalbed methane comprises the following specific steps:
(1) introducing the oxygen-containing coal bed gas into a fixed bed deoxidation reactor filled with a deoxidation catalyst, and then introducing volatile organic compounds to carry out deoxidation reaction until the oxygen content in the coal bed gas is lower than 0.5%; wherein the deoxidation catalyst takes one of metals Pt, Pd or Ru as an active component and takes Al2O3Or TiO2One of the active components is a carrier, the weight percentage of the active component is 0.5 to 5 percent, and the balance is the carrier; the outlets of the multistage fixed bed deoxygenation reactors except the fixed bed deoxygenation reactor at the last stage are provided with coolers for removing water vapor;
(2) introducing the deoxidized coal bed gas carrying water vapor from the final stage fixed bed deoxidation reactor into a fluidized bed reactor for catalytic preparation of carbon nano tube reaction to obtain a multi-walled carbon nano tube crude product; the catalyst for the reaction for preparing the carbon nano tube by catalysis takes metal Ni as an active component, MgO as a carrier, the weight percentage of the metal Ni is 40-60%, and the balance is the carrier;
(3) and (3) soaking the crude multi-walled carbon nanotube product prepared in the step (2) in dilute nitric acid, stirring and refluxing, rinsing with deionized water, and drying to obtain the high-purity multi-walled carbon nanotube.
Preferably, CH of the coal bed gas in the step (1)430-60% of O2The content is 7-15%.
Preferably, the volatile organic in step (1) is methanol vapor.
Preferably, the reaction conditions of the fixed bed catalytic deoxidation in the step (1) are as follows: the reaction temperature is 50-100 ℃, the reaction pressure is 0.1-0.3 MPa, and the gas space velocity of the coal bed gas is 5000h-1～15000h-1Wherein the gas concentration of the methanol vapor is 1-6%.
Preferably, the reaction conditions for catalytically preparing the carbon nanotubes in the step (2) are as follows: the reaction temperature is 600-800 ℃, the linear speed of the deoxidized coal bed gas is 20-40 cm/s, and the reaction time is 1-3 h.
Preferably, the concentration of the dilute nitric acid in the step (3) is 2.0M, the soaking temperature is 110 ℃, and the stirring reflux time is 10-12 h.
The principle of the invention is as follows: volatile organic compound is utilized to react active metal Pt, Pd or Ru and carrier Al2O3Or TiO2The oxygen in the oxygen-containing coal bed gas and the metal catalyst are deoxidized in a one-stage or multi-stage fixed bed deoxidation reactor to produce water and carbon dioxide under the catalysis of the metal catalyst, and the specific reaction mechanism is as follows: 2CH3OH+3O2→2CO2+4H2And O, continuously consuming oxygen in the coal bed gas, introducing the deoxidized coal bed gas serving as a raw material gas into a fluidized bed for preparing the multi-walled carbon nano tube by a chemical catalytic growth method (CCVD), and ensuring that the concentration of methane and oxygen at the outlet of each section of fixed bed is below the explosion limit by adopting a multi-stage fixed bed deoxidation reaction.
Compared with the existing deoxidation method of the coal bed gas, the invention has the following advantages:
(1) the coal bed gas deoxidation method provided by the invention can remove oxygen in the coal bed gas at a lower temperature, does not consume methane in the deoxidation process, and can be used for preparing the carbon nano tubes in time along with the continuous improvement of the methane concentration, so that the energy consumption of the coal bed gas deoxidation is reduced, the utilization efficiency of the deoxidized coal bed gas is improved, and the method has the advantages of energy conservation and environmental protection.
(2) The coal bed gas deoxidation method provided by the invention adopts the multistage fixed bed deoxidation reactor according to the composition of the coal bed gas, so that the explosion limit of methane and oxygen can be effectively avoided, and the oxygen can be efficiently removed.
(3) The invention does not arrange a cooler at the outlet of the last section of the deoxidation fixed bed reactor, and utilizes a small amount of water vapor generated by the deoxidation reaction to participate in the preparation of the multi-walled carbon nano-tube, so that the multi-walled carbon nano-tube has fewer impurities and better quality.
(4) The coal bed gas deoxidation method provided by the invention not only solves the problem of O in the coal bed gas2The method also solves the problems that the existing coal bed gas deoxidation method adopts a fixed bed to deoxidize so that methane is cracked, the methane concentration in the product gas is low, the methane loss rate is high and the like.
(5) The method for deoxidizing the coal bed gas can solve the problem of utilization of the deoxidized coal bed gas, the deoxidized coal bed gas is directly used for preparing the multi-walled carbon nano tubes, the coal bed gas can be directly utilized to produce the multi-walled carbon nano tubes in a factory built in a coal mine area, and the problems of transportation cost and safety of the coal bed gas can be greatly reduced.
Detailed Description
The present invention will be described in further detail with reference to examples. It is also to be understood that the following examples are intended to illustrate the present invention and are not to be construed as limiting the scope of the invention, and that the particular materials, reaction times and temperatures, process parameters, etc. listed in the examples are exemplary only and are intended to be exemplary of suitable ranges, and that insubstantial modifications and adaptations of the invention by those skilled in the art in light of the foregoing description are intended to be within the scope of the invention. The examples, where specific techniques or conditions are not indicated, are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by manufacturers, and are all conventional products which can be purchased in the market.
Example 1:
0.5％Pt/Al2O3the preparation steps of the deoxidation catalyst are as follows: take 0.664g H2Pt Cl6·6H2O was added to 700ml of distilled water, stirred until the Pt salt was completely dissolved, and 49.75g of Al was added2O3Stirring the carrier at room temperature for 12H, filtering, sequentially washing the obtained solid with ethanol and deionized water for 3 times, each time washing with 100ml of washing solution, drying the obtained solid in an oven at 80 deg.C for 8H, and drying the dried solid in 5% H2/95％N2Roasting in mixed gas at 300 ℃ for 3h to obtain the oxygen-containing coal bed gas deoxidation catalyst, which is recorded as 0.5% Pt/Al2O3。
The preparation method of the multi-wall carbon nanotube catalyst prepared from 40% Ni/MgO comprises the following steps: 70.81gNi (NO)3)2·6H2Dissolving O in 115ml water to prepare Ni (NO)3)2·6H2Adding 35.71g of MgO into the O transparent solution, stirring the obtained mixture for 6 hours, soaking the mixture overnight, drying the obtained solid in an oven at 100 ℃ for 12 hours, and roasting the dried solid in a muffle furnace at 550 ℃ for 3 hours. The corresponding dosage of each reagent is adjusted, and the catalyst with the Ni content of 60 percent, namely 60 percent Ni/MgO, can be prepared by using the same method.
The catalytic deoxidation reaction steps are as follows:
(1) will CH4The content is 30% and O2Oxygen-containing coal bed gas with the content of 15 percent is introduced into a reactor filled with 50g of deoxidation catalyst 1 percent of Pt/Al2O3The first-stage fixed bed deoxidation reactor is filled with methanol steam for deoxidation reaction, the reaction temperature is 150 ℃, the reaction pressure is 0.3MPa, the gas space velocity of coal bed gas is 5000h < -1 >, the gas concentration of the methanol steam is controlled to be 6 percent, the deoxidation coal bed gas in the first-stage fixed bed is subjected to gas phase chromatography to remove water steam generated by the reaction, the oxygen concentration in the deoxidation coal bed gas is 6.88 percent, and then the mixed gas obtained by the reaction is continuously filled with 0.5 percent Pt/Al which is filled with 50g of deoxidation catalyst2O3In the second stage fixed bed deoxygenation reactor, the first stage fixed bed is contacted with the first stage fixed bedControlling the gas concentration of methanol steam to be 6% under the same reaction temperature, pressure and airspeed of the reactor, continuing to perform deoxidation reaction, measuring the oxygen concentration in outlet coal bed gas to be 1.38% after the deoxidation coal bed gas in the second-stage fixed bed passes through an outlet cooler to remove water vapor generated by the reaction, introducing mixed gas obtained at the outlet of the second-stage reactor into a reactor containing 50g of deoxidation catalyst 0.5% Pt/Al2O3The gas concentration of the continuously introduced methanol steam in the third-stage fixed bed deoxidation reactor is 3% at the same reaction temperature, pressure and airspeed as those of the first-stage fixed bed reactor, the deoxidation reaction is continuously carried out, and the oxygen concentration in the coal bed gas at the outlet of the third-stage fixed bed is directly measured to be 0.27% without passing through an outlet cooler. Gas composition at final outlet is CH4Concentration 30.38%, O2Concentration of 0.27%, CO2Concentration 9.94%, CH3OH concentration 2.26%, H2O concentration 1.46%, N2The concentration is 55.69%;
(2) introducing the coal bed gas which is obtained in the step (1) and carries water vapor with the concentration of 1.46% after catalytic deoxidation into a fluidized bed reactor for catalytic preparation of carbon nano tubes, wherein the catalyst for preparing the carbon nano tubes is 40% of Ni/MgO, the feeding amount is 50g, the reaction temperature is 800 ℃, the linear speed of the deoxidized coal bed gas is 40cm/s, and the reaction time is 3h, so that 76.4g of a multi-wall carbon nano tube crude product (the yield is 52.8%) is obtained;
(3) and (3) soaking the carbon nanotube crude product prepared in the step (2) in 1.5L of 2.0M dilute nitric acid at 110 ℃ for 6h, stirring and refluxing the obtained mixture for 12h, filtering, repeatedly washing the obtained solid with 1L of deionized water for three times, and drying the washed solid in a vacuum drying oven at 100 ℃ for 6h to obtain 68.75g of high-purity multi-wall carbon nanotubes (the yield is 37.5%).
Example 2:
5％Ru/Al2O3the preparation steps of the deoxidation catalyst are as follows: 5.131 gGluCl was taken3Adding into 700ml distilled water, stirring until the Ru salt is completely dissolved, adding 47.5g calcined Al2O3Stirring the carrier at room temperature for 12h, filtering, washing the obtained solid with ethanol and deionized water sequentially for 3 times each time100ml of washing solution, drying the obtained solid in an oven at 80 ℃ for 8H, and drying the dried solid in 5% H2/95％N2Roasting in mixed gas at the roasting temperature of 300 ℃ for 3h to obtain the oxygen-containing coal bed gas deoxidation catalyst, which is recorded as 5% Ru/Al2O3And (4) catalyzing deoxidation reaction.
The catalytic deoxidation reaction steps are as follows:
(1) will CH4The content is 45% and O2Oxygen-containing coal bed gas with the content of 12 percent is introduced into a reactor filled with 50g of deoxidation catalyst 5 percent Ru/TiO2Then methanol steam with the gas concentration of 6 percent is introduced into the first-stage fixed bed deoxidation reactor for deoxidation reaction, the reaction temperature is 50 ℃, the reaction pressure is 0.1MPa, the gas space velocity of the coal bed gas is 10000h < -1 >, the gas concentration of the methanol steam is controlled to be 3 percent, the deoxidation coal bed gas in the first-stage fixed bed is subjected to gas chromatography to remove water vapor generated by the reaction, the oxygen concentration in the coal bed gas is measured to be 5.41 percent, and then the mixed gas obtained by the reaction is continuously introduced into a reactor filled with 50g of deoxidation catalyst, 5 percent of Ru/TiO and the like2In the second-stage fixed bed deoxidation reactor, under the same reaction temperature, pressure and airspeed as those of the first-stage fixed bed reactor, the gas concentration of methanol steam is controlled to be 6%, the deoxidation reaction is continuously carried out, the oxygen concentration in the coal bed gas at the outlet of the second-stage fixed bed is measured to be 1.08% after the water steam generated by the reaction is removed from the deoxidation coal bed gas in the second-stage fixed bed through an outlet cooler, and the mixed gas obtained at the outlet of the second-stage reactor is introduced into a reactor filled with 50g of deoxidation catalyst 5% Ru/TiO2In the third-stage fixed bed deoxidation reactor, the gas concentration of the methanol steam is controlled to be 3% under the same reaction temperature, pressure and airspeed as those of the first-stage fixed bed reactor, the deoxidation reaction is continuously carried out, and the oxygen concentration in the coal bed gas at the outlet of the third-stage fixed bed is directly measured to be 0.22% without passing through an outlet cooler. Gas composition at final outlet is CH4Concentration 45.17%, O2Concentration of 0.22%, CO2Concentration 7.89%, CH3OH concentration 2.41%, H2O concentration 1.16%, N2The concentration is 43.16%;
(2) after carrying coal bed gas with the water vapor concentration of 1.16% after catalytic deoxidation, the coal bed gas prepared in the step (1) enters a fluidized bed reactor for catalytic preparation of carbon nano tubes, wherein the catalyst for preparing the carbon nano tubes is 60% of Ni/MgO, the feeding amount is 50g, the reaction temperature is 600 ℃, the linear speed of the deoxidized coal bed gas is 20cm/s, and the reaction time is 1h, so that a crude product of the carbon nano tubes of 99.15g g (the yield is 98.3%) is prepared;
(3) and (3) soaking the carbon nanotube crude product prepared in the step (2) in 1.5L of 2.0M dilute nitric acid at 110 ℃ for 6h, stirring and refluxing the obtained mixture for 10h, filtering, repeatedly washing the obtained solid with 1L of deionized water for three times, and drying the washed solid in a vacuum drying oven at 100 ℃ for 6h to obtain 87.25g of high-purity multi-wall carbon nanotubes (the yield is 74.5%).
Example 3:
1％Pd/TiO2the preparation steps of the deoxidation catalyst are as follows: 0.833g of PdCl is taken2Adding into 700ml distilled water, stirring until Pd salt is completely dissolved, adding 49.5g calcined Al2O3Stirring the carrier at room temperature for 12H, filtering, sequentially washing the obtained solid with ethanol and deionized water for 3 times, each time washing with 100ml of washing solution, drying the obtained solid in an oven at 80 deg.C for 8H, and drying the dried solid in 5% H2/95％N2Roasting in mixed gas at 300 ℃ for 3h to obtain the oxygen-containing coal bed gas deoxidation catalyst, which is recorded as 1% Pd/Al2O3And (4) catalyzing deoxidation reaction.
The catalytic deoxidation reaction steps are as follows:
(1) will CH4The content is 60% and O2Oxygen-containing coal bed gas with the content of 7 percent is introduced into the coal bed gas containing 50g of deoxidation catalyst and 1 percent of Pd/TiO2The first-stage fixed bed deoxidation reactor is filled with methanol steam for deoxidation reaction, the reaction temperature is 100 ℃, the reaction pressure is 0.3MPa, the gas space velocity of coal bed gas is 15000h < -1 >, the gas concentration of the methanol steam is controlled to be 3 percent, the deoxidation coal bed gas in the first-stage fixed bed is subjected to gas phase chromatography to remove water steam generated by the reaction, the oxygen concentration in the coal bed gas is 3.17 percent, and then the mixed gas obtained by the reaction is continuously filled with 1 percent Pd/TiO filled with 50g of deoxidation catalyst2The gas concentration of methanol steam is controlled to be 2% in the second-stage fixed bed deoxidation reactor under the same reaction temperature, pressure and airspeed as the first-stage fixed bed reactor, the deoxidation reaction is continued, the oxygen concentration in the coal bed gas at the outlet of the second-stage fixed bed is measured to be 0.64% after the water steam generated by the reaction is removed from the deoxidation coal bed gas in the second-stage fixed bed through an outlet cooler, and the mixed gas obtained at the outlet of the second-stage reactor is introduced into a reactor filled with 50g of deoxidation catalyst 1% Pd/TiO2In the third-stage fixed bed deoxidation reactor, the gas concentration of the methanol steam is controlled to be 1% under the same reaction temperature, pressure and airspeed as those of the first-stage fixed bed reactor, the deoxidation reaction is continuously carried out, and the oxygen concentration in the coal bed gas at the outlet of the third-stage fixed bed is directly measured to be 0.13% without passing through an outlet cooler. Gas composition at final outlet is CH4Concentration 60.59%, O2Concentration of 0.13%, CO2Concentration 4.63%, CH3OH concentration 0.66%, H2O concentration of 0.68%, N2The concentration is 33.32%;
(2) introducing the coal bed gas which is obtained in the step (1) and carries water vapor with the concentration of 0.68% after catalytic deoxidation into a fluidized bed reactor for catalytic preparation of carbon nano tubes, wherein the catalyst for preparing the carbon nano tubes is 40% of Ni/MgO, the feeding amount is 50g, the reaction temperature is 800 ℃, the linear speed of the deoxidized coal bed gas is 40cm/s, and the reaction time is 3h to obtain 140g of multi-wall carbon nano tube crude product (the yield is 180%);
(3) and (3) soaking the carbon nano tube crude product prepared in the step (2) in 1.5L of 2.0M dilute nitric acid at 110 ℃ for 6h, stirring and refluxing the obtained mixture for 12h, filtering, repeatedly washing the obtained solid with 1L of deionized water for three times, and finally drying the washed solid in a vacuum drying oven at 100 ℃ for 6h to obtain 120.4g of high-purity multi-wall carbon nano tube (the yield is 141%).
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (6)

1. A method for preparing a multi-walled carbon nanotube after deoxidizing coal bed gas is characterized by comprising the following specific steps:
(1) introducing the oxygen-containing coal bed gas into a multistage fixed bed deoxidation reactor filled with a deoxidation catalyst, and then introducing volatile organic compounds to perform deoxidation reaction until the concentration of methane and oxygen at the outlet of each section of fixed bed is below the explosion limit until the oxygen content of the coal bed gas at the outlet of the fixed bed deoxidation reactor is lower than 0.5 percent from the last; wherein the deoxidation catalyst takes one of metals Pt, Pd or Ru as an active component and takes Al2O3Or TiO2One of the active components is a carrier, the weight percentage of the active component is 0.5 to 5 percent, and the balance is the carrier; the outlets of the multistage fixed bed deoxygenation reactors except the fixed bed deoxygenation reactor at the last stage are provided with coolers for removing water vapor;
(2) introducing the deoxidized coal bed gas carrying water vapor from the final stage fixed bed deoxidation reactor into a fluidized bed reactor for catalytic preparation of carbon nano tube reaction to obtain a multi-walled carbon nano tube crude product; the catalyst for the reaction for preparing the carbon nano tube by catalysis takes metal Ni as an active component, MgO as a carrier, the weight percentage of the metal Ni is 40-60%, and the balance is the carrier;
(3) and (3) soaking the crude multi-walled carbon nanotube product prepared in the step (2) in dilute nitric acid, stirring and refluxing, rinsing with water, and drying to obtain the high-purity multi-walled carbon nanotube.
2. The method for producing multi-walled carbon nanotubes by deoxygenating coalbed methane as claimed in claim 1, wherein CH of coalbed methane in step (1)430-60% of O2The content is 7-15%, and the balance is nitrogen.
3. The method for producing multi-walled carbon nanotubes by deoxygenating coalbed methane as claimed in claim 1, wherein the volatile organic compound in step (1) is methanol vapor.
4. The method for preparing multi-walled carbon nanotubes by deoxygenation of coal bed methane as claimed in claim 1, wherein the reaction conditions of the fixed bed catalytic deoxygenation in step (1) are as follows: the reaction temperature is 50-150 ℃, the reaction pressure is 0.1-0.3 MPa, and the gas space velocity of the coal bed gas is 5000h-1～15000h-1The gas concentration of the methanol vapor is 1-6%.
5. The method for preparing multi-walled carbon nanotubes by deoxygenating coalbed methane according to claim 1, wherein the reaction conditions for catalytically preparing the carbon nanotubes in the step (2) are as follows: the reaction temperature is 600-800 ℃, the linear speed of the deoxidized coal bed gas is 20-40 cm/s, and the reaction time is 1-3 h.
6. The method for preparing the multi-walled carbon nanotubes by deoxidizing the coal bed gas as claimed in claim 1, wherein the concentration of the dilute nitric acid in the step (3) is 2.0M, the soaking temperature is 110 ℃, and the stirring reflux time is 10-12 h.
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