Coal-based carbon nanotube for deoxidizing low-concentration coal bed gas and preparation and purification methods thereof
阅读说明：本技术 一种用于低浓度煤层气脱氧的煤基碳纳米管及其制备和纯化方法 (Coal-based carbon nanotube for deoxidizing low-concentration coal bed gas and preparation and purification methods thereof ) 是由 王影 吕学枚 刘俊 张天开 李金鑫 赵钰琼 张静 李国强 罗云焕 于 2019-10-10 设计创作，主要内容包括：本发明属煤层气脱氧技术领域,提供一种用于低浓度煤层气脱氧的煤基碳纳米管及其制备和纯化方法。煤基碳纳米管为烟煤催化热解所得到的煤表面连接的碳纳米管；初始煤基碳纳米管中碳纳米管占煤质量百分比为10-20 wt%。成本较低,并且煤本身有多孔的特性,促使煤基碳纳米管成为一个具有多孔结构的活性炭纳米管。用煤基碳纳米管能处理高含氧煤层气并同时纯化煤基碳纳米管,整个过程对煤层气安全高效利用提供了一个新思路,节能减排并拓宽利用途径。微波加热可以使介电常数更高的煤基碳纳米管升温,避免了高含氧煤层气的加热过程,使得整个过程避免了爆炸的温度而更加安全。用微波加热煤料使煤料升温更容易,也保证了煤料温度不宜过高和过快。(The invention belongs to the technical field of coal bed gas deoxidation, and provides a coal-based carbon nanotube for deoxidation of low-concentration coal bed gas and a preparation and purification method thereof. The coal-based carbon nano tube is a carbon nano tube connected with the surface of coal obtained by the catalytic pyrolysis of bituminous coal; the carbon nano-tubes in the initial coal-based carbon nano-tubes account for 10-20 wt% of coal by mass. The cost is low, and the coal has the characteristic of porosity, so that the coal-based carbon nanotube is promoted to be an activated carbon nanotube with a porous structure. The coal-based carbon nano tube can be used for treating high-oxygen-content coal bed gas and purifying the coal-based carbon nano tube at the same time, and the whole process provides a new idea for safe and efficient utilization of the coal bed gas, saves energy, reduces emission and widens utilization approaches. The microwave heating can heat the coal-based carbon nano tube with higher dielectric constant, thereby avoiding the heating process of high oxygen-containing coal bed gas, and ensuring that the whole process avoids the explosion temperature and is safer. The microwave heating of the coal material makes the temperature rise of the coal material easier and also ensures that the temperature of the coal material is not too high or too fast.)
1. A coal-based carbon nanotube for deoxidizing low-concentration coal bed gas is characterized in that: the coal-based carbon nano tube is a carbon nano tube connected with the surface of coal obtained by catalytic pyrolysis of bituminous coal; wherein: the carbon nano-tubes in the initial coal-based carbon nano-tubes account for 10-20 wt% of coal by mass.
2. The method for preparing the coal-based carbon nanotubes for deoxidizing the low-concentration coal bed gas, which is described in claim 1, is characterized in that: the method comprises the following steps:
(1) weighing 100 parts of crushed coal-based carbon nanotubes, placing the crushed coal-based carbon nanotubes in oxygen-containing coal bed gas at low airspeed, and performing an oxygen adsorption process on the oxygen-containing coal bed gas by using the coal-based carbon nanotubes for 1-2 hours;
(2) after the oxygen adsorption process in the step (1) is finished, heating the coal-based carbon nano tube to 100-300 ℃ at the heating rate of 1-10 ℃/min, keeping the temperature for 10-60 min, and moving the coal-based carbon nano tube to a reactor containing a microwave heater and a stirring device;
(3) carrying out microwave heating on the coal-based carbon nanotubes in the step (2) in an intermittent manner, introducing coal bed gas at 20-150 ℃ and 5000-plus 100000 h < -1 > space velocity while heating, stirring at 1-10r/min to ensure that the coal-based carbon nanotubes are fully contacted with the coal bed gas, and keeping the duration of the whole deoxidation process for 1-24h until the oxygen concentration in the oxygen-containing coal bed gas is reduced to be below 4.5 vol%;
(4) when the oxygen content of the deoxidized coal bed gas obtained in the step (3) is higher than 4.5vol%, repeating the process of the step (3) on the oxygen-containing coal bed gas; when the duration of the deoxidation process is more than 2 hours or the temperature of the coal-based carbon nano tube is raised to 450 ℃, introducing steam with the air speed of 1000-10000h < -1 > to cool or eliminate carbon deposition inhibiting the growth of the coal-based carbon nano tube;
(5) refluxing the deoxidized coal bed gas obtained in the step (3) with 0-50 vol% of volume ratio, introducing the coal-based carbon nanotube for regeneration, and continuously taking the regenerated coal-based carbon nanotube as a deoxidizing raw material to reenter the step (1) to participate in the deoxidation of the coal bed gas;
(6) finally obtaining the coal-based carbon nano tube and the coal bed gas with the oxygen content of less than 4.5 wt% after deoxidation.
3. The method for preparing coal-based carbon nanotubes for deoxidation of low-concentration coalbed methane according to claim 2, wherein the method comprises the following steps: the granularity of the coal-based carbon nano tube crushed in the step (1) is 0.01-10 mm; the oxygen-containing coal bed gas comprises oxygen, methane and nitrogen, and the volume percentages of the oxygen-containing coal bed gas, the methane and the nitrogen are respectively as follows: 4-20 vol%, 30-80 vol%, 10-60 vol%; the space velocity of the oxygen-containing coal bed gas is 1000-10000h-1。
4. The method for preparing coal-based carbon nanotubes for deoxidation of low-concentration coalbed methane according to claim 2, wherein the method comprises the following steps: in the step (3), the microwave heating power is 1-30KW, and the use frequencies are 915 MHz and 2450 MHz; the continuous heating time of microwave single heating is less than or equal to 10 minutes, and the microwave heating process is stopped when the temperature of the coal material is more than 300 ℃.
5. The method for preparing coal-based carbon nanotubes for deoxidation of low-concentration coalbed methane according to claim 2, wherein the method comprises the following steps: the mass fraction of the carbon nano-tube in the prepared coal-based carbon nano-tube reaches 30-50%.
Technical Field
The invention belongs to the technical field of coal bed gas deoxidation, and particularly relates to a coal-based carbon nanotube for deoxidation of low-concentration coal bed gas and a preparation and purification method thereof, and particularly relates to a method for producing the coal-based carbon nanotube with higher purity while reducing oxygen content in the deoxidation process of the coal bed gas.
Background
Carbon nanotubes are widely used because their unique one-dimensional structures have excellent characteristics in mechanical, electrical, thermal and adsorption aspects, but their large-scale application market is severely limited by the price of expensive carbon nanotubes. The development of a macro technology for preparing low-cost carbon nanotubes has been one of the most challenging directions in the field of carbon nanomaterials.
Coal-based carbon nanotubes refer to carbon nanotubes which are produced by taking coal as a substrate and contain coal-based materials, ZL201810309097.2 and ZL 201810590741.8 are processes for preparing the coal-based carbon nanotubes by directly pyrolyzing the coal, and the coal is carbonized under the condition of a catalyst.
ZL 201711086932.2 utilizes pyrolysis gas of coal to prepare graphite and carbon nano-tubes, but does not carry out purification technology, and the purity of the obtained coal-based carbon nano-tubes is low.
The coal bed gas refers to hydrocarbon gas which is stored in a coal bed, takes methane as a main component, is mainly adsorbed on the surface of coal matrix particles, and is partially dissociated in coal pores or dissolved in coal bed water. The processing difficulty is increased when the coal bed gas contains oxygen, mainly because the explosion limit of the oxygen-containing gas in the methane is 5-15%, serious industrial accidents such as explosion and the like can be caused when the production enterprises process the oxygen-containing gas carelessly slightly, and therefore the content of the oxygen in the processed coal bed gas is required to be lower than the explosion limit.
The coal is a good porous adsorption material, when the carbon nano tubes are tightly combined with the coal, the adsorption performance of the coal-based carbon nano tubes is improved, the retention process of the adsorption of the coal-based carbon nano tubes is that the adsorbed oxygen forms oxygen-containing functional groups on the surface of the coal and can be used as a substrate for the growth of the carbon nano tubes, and the adsorption of the oxygen is also helpful for reducing the oxygen-containing concentration in part of coal bed gas. Under the condition of low temperature, the coal can be oxidized by oxygen in the air to form CO or CO2The carbon nanotube gain-loss electronic process is beneficial to accelerating the oxidation process, so that the oxygen content in the coal bed gas can be obviously reduced under low-temperature oxidation, the coal bed gas is purer, the possibility of subsequent explosion is reduced, and meanwhile, the coal is oxidized by the oxygen to form CO or CO2The process is also a purification process of the carbon nano tube, so that a comprehensive utilization process is technically implemented.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a coal-based carbon nanotube for deoxidizing low-concentration coal bed gas and a preparation and purification method thereof.
The invention is realized by the following technical scheme: a coal-based carbon nanotube for deoxidizing low-concentration coal bed gas is a carbon nanotube connected with the surface of coal obtained by catalytic pyrolysis of bituminous coal; wherein: the carbon nano-tubes in the initial coal-based carbon nano-tubes account for 10-20 wt% of coal by mass.
The method for preparing the coal-based carbon nanotube for deoxidizing the low-concentration coal bed gas comprises the following steps:
(1) weighing 100 parts of crushed coal-based carbon nanotubes, placing the crushed coal-based carbon nanotubes in oxygen-containing coal bed gas at low airspeed, and performing an oxygen adsorption process on the oxygen-containing coal bed gas by using the coal-based carbon nanotubes for 1-2 hours;
(2) after the oxygen adsorption process in the step (1) is finished, heating the coal-based carbon nano tube to 100-300 ℃ at the heating rate of 1-10 ℃/min, keeping the temperature for 10-60 min, and moving the coal-based carbon nano tube to a reactor containing a microwave heater and a stirring device;
(3) carrying out microwave heating on the coal-based carbon nanotubes in the step (2) in an intermittent manner, introducing coal bed gas at 20-150 ℃ and 5000-plus 100000 h < -1 > space velocity while heating, stirring at 1-10r/min to ensure that the coal-based carbon nanotubes are fully contacted with the coal bed gas, and keeping the duration of the whole deoxidation process for 1-24h until the oxygen concentration in the oxygen-containing coal bed gas is reduced to be below 4.5 vol%;
(4) when the oxygen content of the deoxidized coal bed gas obtained in the step (3) is higher than 4.5vol%, repeating the process of the step (3) on the oxygen-containing coal bed gas; when the duration of the deoxidation process is more than 2 hours or the temperature of the coal-based carbon nano tube is raised to 450 ℃, introducing steam with the air speed of 1000-10000h < -1 > to cool or eliminate carbon deposition inhibiting the growth of the coal-based carbon nano tube;
(5) refluxing the deoxidized coal bed gas obtained in the step (3) with 0-50 vol% of volume ratio, introducing the coal-based carbon nanotube for regeneration, and continuously taking the regenerated coal-based carbon nanotube as a deoxidizing raw material to reenter the step (1) to participate in the deoxidation of the coal bed gas;
(6) finally obtaining the coal-based carbon nano tube and the coal bed gas with the oxygen content of less than 4.5 wt% after deoxidation.
The granularity of the coal-based carbon nano tube crushed in the step (1) is 0.01-10 mm; the oxygen-containing coal bed gas comprises oxygen, methane and nitrogen, and the volume percentages of the oxygen-containing coal bed gas, the methane and the nitrogen are respectively as follows: 4-20 vol%, 30-80 vol%, 10-60 vol%; the space velocity of the oxygen-containing coal bed gas is 1000-10000h-1。
In the step (3), the microwave heating power is 1-30KW, and the use frequencies are 915 MHz and 2450 MHz; the continuous heating time of microwave single heating is less than or equal to 10 minutes, and the microwave heating process is stopped when the temperature of the coal material is more than 300 ℃.
The mass fraction of the carbon nano-tube in the prepared coal-based carbon nano-tube reaches 30-50%.
The coal-based carbon nanotube is prepared from bituminous coal by a catalytic pyrolysis method, and comprises coal and carbon nanotubes tightly connected with the surface of the coal, wherein the carbon nanotubes in the initial coal-based carbon nanotube account for 10-20 wt% of the coal; in the staying process after the temperature rise in the step (2), the adsorbed oxygen forms a growth substrate of the carbon nano tube mainly containing oxygen functional groups on the surface of the coal, and the oxygen content of the coal bed gas is reduced.
The coal-based carbon nanotube prepared by the method has low cost, and the coal has the characteristic of porosity, so that the coal-based carbon nanotube is promoted to be an activated carbon nanotube with a porous structure. The oxygen content of the coal bed gas is an intractable matter, and if the oxygen content of the coal bed gas is not completely treated, the possibility of explosion can be caused.
The retention process of the coal-based carbon nanotube adsorption is to enable the adsorbed oxygen to form oxygen-containing functional groups on the surface of coal, and the oxygen-containing functional groups can be used as a substrate for the growth of the carbon nanotubes, and the adsorption of the oxygen is also helpful for reducing the oxygen concentration in part of coal bed gas. Under the condition of low temperature, the coal can be oxidized by oxygen in the air to form CO or CO2The carbon nanotube gain-loss electronic process is beneficial to accelerating the oxidation process, so that the oxygen content in the coal bed gas can be obviously reduced under low-temperature oxidation, the coal bed gas is purer, the possibility of subsequent explosion is reduced, and meanwhile, the coal is oxidized by the oxygen to form CO or CO2The process is also a purification process of the carbon nano tube, so that a comprehensive utilization process is technically implemented.
The oxidation combustion temperature of the carbon nano tube is generally above 500 ℃, and the coal-based carbon nano tube with higher dielectric constant can be heated by just microwave heating when microwave heating is adopted, so that the heating process of high-oxygen-content coal bed gas is avoided, and the whole process is safer due to the fact that the explosion temperature is avoided. The microwave heating of the coal material makes the temperature rise of the coal material easier and also ensures that the temperature of the coal material is not too high or too fast.
In general, the coal-based carbon nanotubes can be used for treating high-oxygen-content coal bed gas and purifying the coal-based carbon nanotubes at the same time, a new idea is provided for safe and efficient utilization of the coal bed gas in the whole process, and the coal-based carbon nanotubes have the effects of saving energy, reducing emission and widening utilization ways.
The oxidation combustion temperature of the carbon nano tube is generally above 500 ℃, so that the heating in the whole process needs to be controlled, and the microwave heating needs to be adopted because the external heat source cannot be stopped immediately. The microwave heating can just raise the temperature of the coal-based carbon nano tube with higher dielectric constant, thereby avoiding the heating process of high oxygen-containing coal bed gas, and ensuring that the whole process is safer due to the avoidance of explosion temperature. The microwave heating of the coal material makes the temperature rise of the coal material easier and also ensures that the temperature of the coal material is not too high or too fast.
Drawings
FIG. 1 is a schematic representation of a coal-based carbon nanotube without oxidative purification; FIG. 2 is a schematic representation of carbon nanotubes deoxygenated from coalbed methane; FIG. 3 is a graph of initial oxygen-containing coal bed gas (10 vol%) as a function of adsorption time; FIG. 4 is a graph showing the change in oxygen content of an oxygen-containing coal-bed gas (10 vol%) with respect to heating temperature.
Detailed Description