CN114538415A - A method for preparing carbon nanotubes with wax as carbon source - Google Patents

Abstract

The invention relates to the technical field of carbon nanotube preparation, and specifically discloses a method for preparing carbon nanotubes by using wax as a carbon source. The described method for preparing carbon nanotubes by using wax as carbon source comprises the following steps: (1) taking raw wax, putting it into a first-level electric heating furnace, and heating it under the protection of protective gas to obtain pyrolysis gas; (2) ) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst to carry out catalytic reaction, and carbon nanotubes are obtained after the reaction is completed. The invention provides a brand-new method for preparing carbon nanotubes by using wax as a raw material; the preparation process of the method is simple, and is suitable for large-scale industrial production; in particular, the invention can use low-cost wax as a raw material to improve the value of low-cost wax , and make the carbon source easy to transport, break the original limitation, and also help to reduce the production cost of carbon nanotubes.

Description

A method for preparing carbon nanotubes with wax as carbon source

technical field

The invention relates to the technical field of carbon nanotube preparation, in particular to a method for preparing carbon nanotubes by using wax as a carbon source.

Background technique

Carbon nanotubes have been attracting attention since their appearance in the 1990s. Its structure is a coaxial circular tube with several layers to dozens of layers composed of carbon atoms arranged in a hexagonal shape. Its structure is stable and its diameter varies from 2 to 25 nm. Wait. Carbon nanotubes are light in weight and have high tensile strength and impact strength, as well as excellent electrical and thermal conductivity. With the in-depth research on them in recent years, broader application prospects have been continuously shown. Based on their excellent properties, carbon nanotubes have been used in supercapacitors, anti-corrosion materials, solar cell conductors, catalysts and their carrier materials, biosensors, electromagnetic shielding materials, composite material reinforcements, hydrogen storage materials and other fields. It is foreseeable that there will be more application scenarios for carbon nanotubes in the future.

With the development of the domestic carbon nanotube market, the synthesis of carbon nanotubes is no longer limited to the laboratory. At present, the mainstream methods for synthesizing carbon nanotubes are: solid-phase pyrolysis, glow discharge, gas combustion, laser burning Etching method, arc discharge method, chemical vapor deposition method (CVD method), spray pyrolysis method, etc. Among them, arc method, laser evaporation method and chemical vapor deposition method have been realized in industrial production, which are more in line with the needs of industrial production and use. , CVD method is more economical and easy to operate than other methods, and can be produced on a large scale. The synthesized carbon nanotubes are of good quality and high purity. The price of carbon nanotubes varies from hundreds of thousands to hundreds of thousands of RMB per ton according to different types and qualities. The current carbon source of carbon nanotubes is gaseous hydrocarbons (such as acetylene, methane, ethane, ethylene, butane, butadiene, etc.) separated from chemical raw materials. Such carbon sources are easily regulated and inconvenient to transport. Minor operational errors are prone to accidents. More types of carbon sources are also worth exploring and applying.

Usually, the waxes we come into contact with can be divided into four categories: vegetable waxes, animal waxes, mineral waxes, and synthetic waxes. Synthetic wax refers to the artificial use of chemical raw materials to synthesize wax, and the price is much cheaper than natural wax. Depending on the type of synthetic wax, the price per ton ranges from 6,000 to 15,000 yuan. Among them, the use of waste plastics to make wax is also called cracking wax, such as polyethylene cracking into polyethylene wax. The processing of cracked wax currently includes cracking kettle method and extrusion method. The former belongs to batch processing and is suitable for small batch production, while the latter belongs to continuous production and is suitable for factories with large output and high production capacity. In addition, there are lower-priced Fischer-Tropsch waxes, waxes in by-products of polymer synthesis, and recycled waste waxes. The quality of these waxes is not as good as the application effect of high-quality waxes, and the ingredients cannot be guaranteed. They can only be used for low-end purposes, such as auxiliary additives, production of color particles, etc. The economic value is low, and there is a lot of room for improvement.

Wax is a mixture of various alkanes, with short molecular chain length, molecular weight ranging from 1500 to 7000, melting point of 100 to 120 °C, and gasification at less than 400 °C. This process is also accompanied by the cleavage of carbon chains, resulting in shorter carbon chains. It is envisaged that the vaporized wax/cracking gas at this time can grow into carbon nanotubes under the action of catalysts, but there is no method for preparing carbon nanotubes from such waxes at present. Therefore, it is of great application value to explore ways to improve the utilization value of low-cost waxes and to find new carbon sources that are convenient for transportation to prepare carbon nanotubes.

SUMMARY OF THE INVENTION

In order to overcome the above deficiencies in the prior art, the present invention provides a method for preparing carbon nanotubes by using wax as a raw material.

The technical scheme of the present invention is as follows:

A method for preparing carbon nanotubes with wax as carbon source, which comprises the following steps:

(1) Get the raw wax, put it into a first-level electric heating furnace, and under the protection of protective gas, heat treatment to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst to carry out catalytic reaction, and carbon nanotubes are obtained after the reaction is completed.

The inventor has explored the above-mentioned brand-new method for preparing carbon nanotubes by using wax as a carbon source through a large number of experiments and explorations. The method has a simple preparation process and is suitable for large-scale industrial production.

Preferably, the wax described in step (1) is selected from one or more combinations of Fischer-Tropsch wax, cracked wax, petroleum wax, garbage wax, black wax, green wax and recycled wax.

The method of the invention is especially suitable for Fischer-Tropsch wax, cracked wax, petroleum wax, garbage wax, black wax, green wax and recycled wax; the raw material cost of such wax is relatively low, and the selection of such wax as raw material can effectively reduce the production cost of carbon nanotubes.

Preferably, the heat treatment in step (1) refers to treatment at 350-450° C. for 30-60 min.

Most preferably, the heat treatment in step (1) refers to treatment at 400° C. for 45 min.

Preferably, the protective gas described in step (1) is nitrogen.

Preferably, in step (1), ammonium bicarbonate is also added to the raw wax.

Although the above method of the present invention can successfully prepare carbon nanotubes, the carbon conversion rate of the prepared carbon nanotubes is not high; repeated studies have shown that no matter how to optimize the heat treatment and thermocatalytic reaction conditions and how to adjust the catalyst, None of the carbon conversions obtained could exceed 40%.

Therefore, how to further improve the carbon conversion rate of carbon nanotubes in the process of preparing carbon nanotubes from wax using the method of the present invention is a technical problem that the inventor urgently needs to solve. In order to solve this problem, the inventor surprisingly found in a large number of experiments that adding ammonium bicarbonate to the raw wax before the first-stage electric heating furnace reaction can further improve the carbon conversion rate of high carbon nanotubes.

Preferably, the weight ratio of wax to ammonium bicarbonate is 8～12:1;

Most preferably, the weight ratio of wax to ammonium bicarbonate is 10:1.

The inventor's further research shows that the degree of improvement of the carbon conversion rate of carbon nanotubes is also closely related to the amount of ammonium bicarbonate added. However, when the amount of ammonium bicarbonate added was outside the above range, the increase in carbon conversion was not particularly significant.

Preferably, the catalyst described in step (2) is selected from one or more combinations of transition metals, metal compounds or decomposable/reducible metal components.

Preferably, the transition metal is selected from one or more combinations of iron, molybdenum, nickel, vanadium, copper, manganese, cobalt, and tin.

Preferably, the catalyst described in step (2) consists of iron, nickel and aluminum oxide;

The weight ratio of iron, nickel and aluminum oxide is 1-2:1-2:3-6.

Most preferably, the weight ratio of iron, nickel and aluminium oxide is 1:1:3.

Preferably, in step (2), the weight amount of the catalyst is 3-6% of the weight of the raw wax;

Most preferably, the weight amount of the catalyst in step (2) is 5% of the weight of the raw wax.

Preferably, the conditions for the catalytic reaction in step (2) are: the catalytic reaction is carried out at 700-800° C. for 1-3 hours.

Beneficial effects: The present invention provides a brand-new method for preparing carbon nanotubes with wax as raw material; the method has a simple preparation process and is suitable for large-scale industrial production. Further, in the present invention, ammonium bicarbonate is added to the raw wax before the first-stage electric heating furnace reaction, which can further improve the carbon conversion rate of high carbon nanotubes; The value of carbon source is easy to transport, which breaks the original limitation and also helps to reduce the production cost of carbon nanotubes.

Description of drawings

1 is a scanning electron microscope image of the carbon nanotubes prepared in Example 1.

Detailed ways

The present invention is further explained below in conjunction with specific embodiments, but the embodiments do not limit the protection scope of the present invention.

Example 1 The method for preparing carbon nanotubes with wax as carbon source

(1) Take the Fischer-Tropsch wax, put it into a first-level electric heating furnace, and heat it at 400°C for 40min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 750° C. for 2 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:1:3, and the weight of the catalyst is 5% of the weight of the Fischer-Tropsch wax.

Embodiment 2 The method for preparing carbon nanotubes with wax as carbon source

(1) Take the cracked wax, put it into a first-level electric heating furnace, and heat it at 350 ° C for 60 min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and carrying out a catalytic reaction at 800° C. for 1 hour, and after the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 2:1:6, and the weight amount of the catalyst is 6% of the weight of the cracked wax.

Example 3 The method for preparing carbon nanotubes with wax as carbon source

(1) Take the recycled wax, put it into a first-level electric heating furnace, and heat it at 450°C for 30min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 700° C. for 3 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:2:3, and the weight amount of the catalyst is 3% of the weight of the recovered wax.

Example 4 The method for preparing carbon nanotubes with wax as carbon source

(1) Get Fischer-Tropsch wax and ammonium bicarbonate, put them into a first-level electric heating furnace, and heat-treat at 400 DEG C for 40min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 750° C. for 2 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

In step (1), the weight ratio of Fischer-Tropsch wax and ammonium bicarbonate is 10:1;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:1:3, and the weight of the catalyst is 5% of the weight of the Fischer-Tropsch wax.

The difference between Example 4 and Example 1 is that in Example 4, ammonium bicarbonate was added to the raw material Fischer-Tropsch wax before the first-stage electric heating furnace reaction; wherein, the weight ratio of the Fischer-Tropsch wax to ammonium bicarbonate was 10:1.

Example 5 The method for preparing carbon nanotubes with wax as carbon source

(1) Get Fischer-Tropsch wax and ammonium bicarbonate, put them into a first-level electric heating furnace, and heat-treat at 400 DEG C for 40min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 750° C. for 2 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

In step (1), the weight ratio of Fischer-Tropsch wax and ammonium bicarbonate is 8:1;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:1:3, and the weight of the catalyst is 5% of the weight of the Fischer-Tropsch wax.

The difference between Example 5 and Example 1 is that in Example 5, ammonium bicarbonate was added to the raw material Fischer-Tropsch wax before the first-stage electric furnace reaction; wherein, the weight ratio of the Fischer-Tropsch wax to ammonium bicarbonate was 8:1.

Example 6 The method for preparing carbon nanotubes with wax as carbon source

(1) Get Fischer-Tropsch wax and ammonium bicarbonate, put them into a first-level electric heating furnace, and heat-treat at 400 DEG C for 40min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 750° C. for 2 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

In step (1), the weight ratio of Fischer-Tropsch wax and ammonium bicarbonate is 12:1;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:1:3, and the weight of the catalyst is 5% of the weight of the Fischer-Tropsch wax.

The difference between Example 6 and Example 1 is that in Example 6, ammonium bicarbonate is added to the raw material Fischer-Tropsch wax before the first-stage electric heating furnace reaction; wherein, the weight ratio of the Fischer-Tropsch wax to ammonium bicarbonate is 12:1.

Example 7 The method for preparing carbon nanotubes with wax as carbon source

(1) Get Fischer-Tropsch wax and ammonium bicarbonate, put them into a first-level electric heating furnace, and heat-treat at 400 DEG C for 40min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 750° C. for 2 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

In step (1), the weight ratio of Fischer-Tropsch wax and ammonium bicarbonate is 4:1;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:1:3, and the weight of the catalyst is 5% of the weight of the Fischer-Tropsch wax.

The difference between Example 7 and Example 1 is that in Example 7, ammonium bicarbonate was added to the raw material Fischer-Tropsch wax before the first-stage electric furnace reaction; wherein, the weight ratio of the Fischer-Tropsch wax to ammonium bicarbonate was 4:1.

Example 8 The method for preparing carbon nanotubes with wax as carbon source

(1) Get Fischer-Tropsch wax and ammonium bicarbonate, put them into a first-level electric heating furnace, and heat-treat at 400 DEG C for 40min under nitrogen protection to obtain pyrolysis gas;

(2) Passing the pyrolysis gas into a secondary electric heating furnace containing a catalyst, and performing a catalytic reaction at 750° C. for 2 hours. After the reaction is completed, it is cooled to room temperature with the furnace and taken out to obtain carbon nanotubes;

In step (1), the weight ratio of Fischer-Tropsch wax and ammonium bicarbonate is 20:1;

The catalyst in step (2) is a catalyst composed of Fe, Ni and Al ₂ O ₃ in a weight ratio of 1:1:3, and the weight of the catalyst is 5% of the weight of the Fischer-Tropsch wax.

The difference between Example 8 and Example 1 is that in Example 8, ammonium bicarbonate was added to the raw material Fischer-Tropsch wax before the first-stage electric heating furnace reaction; wherein, the weight ratio of the Fischer-Tropsch wax to ammonium bicarbonate was 20:1.

Table 1. Carbon conversion rate of carbon nanotubes prepared by the method of the present invention

It can be seen from the experimental data in Table 1 that carbon nanotubes can be successfully prepared by using wax as raw material in Examples 1-3 according to the method of the present invention; but the carbon conversion rate of the obtained carbon nanotubes is not particularly high, The carbon conversion of Example 1 was at most 40%.

It can be seen from the experimental data in Table 1 that the carbon conversion rates of the carbon nanotubes prepared in Examples 4 to 6 are greatly improved compared with that in Example 1. This shows that: according to the method of the present invention, adding ammonium bicarbonate to the raw wax before the first-stage electric heating furnace reaction, and controlling the weight ratio of wax to ammonium bicarbonate to be 8-12:1, can greatly improve the carbon nanometer Tube carbon conversion.

As can be seen from the experimental data in Table 1, the carbon nanotubes prepared in Examples 7 and 8 have higher carbon conversion rates than those in Example 1, but they are not obvious, and their carbon conversion rates are far lower. In implementation 1; this shows that the degree of improvement of the carbon conversion rate of carbon nanotubes is also closely related to the amount of ammonium bicarbonate added. The carbon conversion rate of carbon nanotubes can be improved; and when the addition amount of ammonium bicarbonate is outside the above range, the carbon conversion rate cannot be greatly improved.

Claims (10)

1. A method for preparing carbon nanotubes by using wax as a carbon source is characterized by comprising the following steps:

(1) taking raw material wax, putting the raw material wax into a primary electric heating furnace, and heating under the protection of protective gas to obtain pyrolysis gas;

(2) and introducing the pyrolysis gas into a secondary electric heating furnace containing a catalyst to perform catalytic reaction, and obtaining the carbon nano tube after the reaction is finished.

2. The method for preparing carbon nanotubes by using wax as a carbon source as claimed in claim 1, wherein the wax in step (1) is selected from one or more of Fischer-Tropsch wax, cracking wax, petroleum wax, garbage wax, black wax, green wax and recycled wax.

3. The method for preparing carbon nanotubes using wax as a carbon source as claimed in claim 1, wherein the heat treatment in the step (1) is a treatment at 350 to 450 ℃ for 30 to 60 min;

most preferably, the heat treatment in step (1) means a treatment at 400 ℃ for 45 min.

4. The method for preparing carbon nanotubes using wax as a carbon source as claimed in claim 1, wherein the protective gas in step (1) is nitrogen.

5. The method for preparing carbon nanotubes using wax as a carbon source as claimed in claim 1, wherein ammonium bicarbonate is further added to the raw wax in the step (1).

6. The method for preparing carbon nanotubes by using wax as a carbon source according to claim 1, wherein the weight ratio of wax to ammonium bicarbonate is 8-12: 1;

most preferably, the weight ratio of wax to ammonium bicarbonate is 9: 1.

7. The method for preparing carbon nanotubes using wax as a carbon source as claimed in claim 1, wherein the catalyst in the step (2) is one or more selected from transition metals, metal compounds and decomposable/reducible metal components.

Preferably, the transition metal is selected from one or more of iron, molybdenum, nickel, vanadium, copper, manganese, cobalt and tin.

8. The method for preparing carbon nanotubes using wax as a carbon source as claimed in claim 1, wherein the catalyst in the step (2) is composed of iron, nickel and alumina;

wherein the weight ratio of iron to nickel to aluminum oxide is 1-2: 3-6;

most preferably, the weight ratio of iron, nickel and alumina is 1:1: 3.

9. The method for preparing carbon nanotubes by using wax as a carbon source according to claim 1, wherein the weight of the catalyst in the step (2) is 3-6% of the weight of the raw material wax;

most preferably, the catalyst is used in step (2) in an amount of 5% by weight of the feedstock wax.

10. The method for preparing carbon nanotubes by using wax as a carbon source as claimed in claim 1, wherein the conditions of the catalytic reaction in the step (2) are as follows: carrying out catalytic reaction for 1-3 h at 700-800 ℃.

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