JPH0624721A - Method for producing fullerenes - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the production efficiency of fullerenes. [Configuration] Thermal plasma 1 generated from plasma gun 7
Into 1, the carbon-containing compound raw material such as benzene and CS ₂ is continuously supplied to the nozzle 4 together with the carrier gas, and reacts in the plasma reaction section 3 to generate fullerenes, soot and the like. This product is cooled and collected in the collection container 13 or the like. The gas raw material is supplied as it is together with the carrier gas. The liquid or solid raw material is vaporized and then supplied together with a carrier gas. [Effect] The production efficiency of fullerenes is extremely high, the supply nozzles are not clogged, and fullerenes can be produced stably over a long period of time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently producing fullerenes.

[0002]

BACKGROUND OF THE INVENTION Fullerenes are closed cage-like carbon allotropes of high carbon number such as C ₆₀ and C ₇₀ . C ₆₀ is truncated 2
It has a zero-hedral soccer-ball-like molecular structure.

In the conventional method for producing fullerenes, graphite is evaporated (for example, vaporized by laser irradiation, vaporized by resistance heating with high current density, vaporized by arc discharge between graphite electrodes, etc.), and the generated carbon gas is cooled. It is known how to do it.

As another conventional method for producing fullerenes, there is a method in which a benzene / O ₂ / Ar premixed gas is burned under a low pressure and the generated gas is cooled.

[0005]

In the former method for producing fullerenes, conductive solid graphite (having a large heat of vaporization decomposition and a high vaporization temperature) must be used, and the evaporation rate is low, and further There is a problem of low energy efficiency (less than 1%). There is also a problem that it is difficult to continuously supply the raw material.

In the latter method for producing fullerenes, the control range of temperature conditions is limited to the steady combustion temperature range, and the ultimate combustion temperature is about 1800K, so complete pyrolysis of the raw material is difficult. Also, if O ₂ is supplied more than necessary,
The amount of raw materials lost by combustion increases, and the fullerenes that are generated may be oxidized and decomposed.
However, there is a problem that it is difficult to balance and optimize the amount of O ₂ required.

Therefore, these methods are unsuitable for mass production of fullerenes.

[0008]

According to the method for producing fullerenes of claim 1, a thermal plasma is generated, and a gaseous raw material of a carbon-containing compound is supplied into this together with a carrier gas to heat and decompose it. A method for producing fullerenes, in which a reaction gas is cooled to collect solids, and fullerenes are separated from the collected matter, wherein the gas raw material vaporizes a liquid or solid carbon-containing compound at room temperature. It is a thing.

In the method for producing fullerenes according to claim 2, thermal plasma is generated, and a gaseous raw material of a carbon-containing compound is supplied into this together with a carrier gas to heat and decompose it.
A method for producing fullerenes in which the reaction gas is cooled to collect solids and the fullerenes are separated from the collected matter, wherein the gas raw material is a gas at room temperature.

The present invention will be described in more detail below.

In the present invention, the method of generating thermal plasma is preferably a method of heating and ionizing a specific type of plasma gas. Specifically, DC arc discharge plasma jet type plasma gun mechanism, 100 kHz to 10 GHz
A high frequency induction thermal plasma generation mechanism is exemplified.

The DC arc discharge plasma jet generation mechanism and the high frequency induction thermal plasma generation mechanism may be used together to generate thermal plasma. In this case, stable thermal plasma can be generated over a wide volume with respect to changes in the feed rate of raw materials, and a large amount of fullerenes can be synthesized at high speed.

As the plasma gas, He, Ar,
Or He / H ₂ , Ar / H ₂ , He / O ₂ , Ar / O
₂ , He / Ar / H ₂ , He / Ar / O ₂ , He / Ar
/ H ₂ / O ₂ or He / Ar / H ₂ O is preferred.
This gas is heated and ionized by using an appropriate means to generate thermal plasma. Maximum reached temperature of thermal plasma is 2000
K or higher, preferably 3500 to 15000K.

The carbon-containing compound raw material supplied to the thermal plasma is preferably a compound containing carbon in an atomic ratio of 65% or less of the whole. These are generally
Of the carbon-containing compound raw materials, complete thermal decomposition is relatively easy and is an inexpensive raw material, so fullerenes can be synthesized at high efficiency at low cost.

Specifically, as the raw material, in the case of an organic substance, the following compounds are preferable.

Monocyclic aromatic compounds and heteroaromatic compounds such as benzene, pyridine, cyclopentadiene, pyrrole, furan and thiophene, or their methyl, hydroxy or mercapto substituents, naphthalene, quinoline, indene, indole and benzofuran. ,
Condensed polycyclic aromatic compounds such as benzothiophene, anthracene, acridine, phenanthrene, phenanthridine, fluorene, carbazole, dibenzofuran, dibenzothiophene, acenaphthylene, pyrene, fluoranthene, and condensed polycyclic heteroaromatic compounds, or their methyl, hydroxy. Or a substituted mercapto, biphenyl, 2,2 ′-(or 4,4 ′-) bipyridine, o
-(Or m- or p-) terphenyl and other polycyclic ring-assembled aromatic compounds and polycyclic ring-assembled heteroaromatic compounds, or their methyl, hydroxy, or mercapto substituents, o- (or p- ) Benzoquinone, 1,
Aromatic ketones and quinones such as 4-naphthoquinone, 9,10-anthraquinone and 9-fluorenone, or their methyl, hydroxy or mercapto substitutions,
Unsaturated aliphatic hydrocarbons such as ethylene, 1-butene, 1,3-butadiene, acetylene, 1-butyne, 1,3-butadiyne, or their methyl, hydroxy, or mercapto substituted compounds, methane, ethane, propane , N-
Saturated aliphatic hydrocarbons such as (or iso) butane, n- (or iso or neo) pentane, n-hexane, cyclohexane, n-heptane and n-octane, or their methyl, hydroxy or mercapto substitution products.

For inorganic substances, CS ₂ , CO and the like are preferable as the raw material. In particular, in the case of CS ₂ , fullerene can be synthesized by extremely easily thermally decomposing without undergoing the dehydrogenation reaction which is essential in the case of an organic substance. In the synthesis of fullerenes using a plasma gas that does not contain H _{2, in} the case of an inorganic raw material, there is no by-product of organic matter, so fullerene separation and purification from the product is easy.

The above-mentioned raw materials are generally high in cost because they are relatively easy to undergo complete thermal decomposition among carbon-containing compounds and are gas or inexpensive raw materials which can be easily vaporized and continuously supplied when the raw materials are supplied. Fullerenes can be efficiently synthesized at low cost.

The above carbonaceous compound raw materials may be used alone or in combination of two or more.

When the carbon-containing compound is a gas at room temperature, the carbon-containing compound is supplied into the thermal plasma together with the carrier gas. When the carbon-containing compound is liquid or solid at room temperature, it is vaporized and supplied together with the carrier gas into the thermal plasma. When the gaseous carbon-containing compound is supplied by this method, the nozzle clogging due to the precipitation of carbon at the tip of the carbon-containing compound raw material supply nozzle that opens near the thermal plasma is prevented. Moreover, by making it gaseous, it is easy to stably and continuously supply the raw material.

When a plurality of kinds of raw materials are mixed and used, especially when their phases (gas / liquid / solid phase) are different,
It is good to supply as follows. First, the raw materials in the gas phase are mixed in advance, and all the raw materials in the liquid and solid phases are mixed in advance to form a single solution, which is quantitatively supplied. afterwards,
The solution is heated and vaporized, and then the two are mixed to form a single gas phase, which is then accompanied by a carrier gas having an appropriate flow rate and supplied to the thermal plasma.

If unfavorable reactions such as reaction occur due to mixing of the raw materials, if the solid-phase raw materials are difficult to dissolve in the liquid phase, and if there is a large difference in vaporization temperature between the liquid and solid-phase raw materials. When there is a problem in batch supply, the problematic raw material components should be supplied in a separate system.

Further, by heat exchange with excess heat generated from the entire system such as radiant heat of thermal plasma and waste heat of water cooling,
Heating and vaporizing the liquid and / or solid phase raw materials improves the overall energy efficiency.

When the carbon-containing compound is a gas at room temperature, it can be quantitatively supplied by a regulator or a mass flow controller. When the carbon-containing compound is a liquid at room temperature, it can be supplied in a fixed amount by a constant pump or the like. When the carbon-containing compound is a solid (powder), it can be quantitatively supplied by a drop type powder feeder such as an hourglass, a rotary feeder or a screw feeder.

A carrier gas containing no carbon compound is used. As the carrier gas, any of the gases used to generate the plasma described above is preferable.

When a liquid or solid carbonaceous compound raw material is vaporized and used, a carrier gas may be mixed during the vaporization or a carrier gas may be mixed after the vaporization.

The raw material supplied into the thermal plasma is
After being heated to 000K or more, preferably 2500K or more, heat is radiated. At this time, it is made to stay in the temperature range of 1300 K or higher for 1 to 500 ms, preferably in the temperature range of 2500 to 1300 K for 10 to 100 ms.

The internal pressure of the plasma reaction part formed by this thermal plasma is preferably maintained at 10 to 300 Torr.
In this thermal plasma, carbon generated by decomposition is clustered to generate fullerenes. The product containing the fullerenes is cooled and collected as a solid content.

The method of cooling the gas containing the reaction product includes plasma gas / natural cooling of the reaction product or adiabatic expansion; an inert gas such as He, N ₂ and Ar at a low temperature or a mixed gas. By adding (including liquefied gas) to the plasma gas / reaction product; heat exchange cooling such as by contacting the plasma gas / reaction product with a water cooled wall. At this time, in order to prevent denaturation of the generated fullerenes and outflow due to non-coagulation, cooling is performed as quickly as possible to 400 ° C. or less, preferably about 100 ° C. or less in the cooling section. The amount of exhaust heat required for cooling depends on the supply rate of the plasma gas and the raw material and the amount of supply energy for plasma generation.

The product thus cooled and solidified is collected by a collecting means (for example, a collecting wall and / or a bag filter). In the case of cooling by standing cooling or heat exchange, the cooling means and the collecting means can also serve as both.

It is preferred that the product is completely collected by the collecting means. For this purpose, the shape of the collecting means is determined so that the gas flow rate in the collecting means is preferably 1 m / s or less. In the process of plasma reaction, organic substances, soot, and the like are often produced as by-products, and in this case, fullerenes and a mixture thereof are collected. The method of separating the collected product includes reverse sublimation by reheating the product and recooling the volatile gas, and extraction with a solvent in which fullerenes are soluble. These may be used in appropriate combination.

In the case of separation using a solvent which may alter the fullerenes at high temperature, such as in the case of extraction, the plasma generation system, plasma reaction section, cooling system, trapping system from the raw material supply system. It is preferable to operate by completely separating the path leading to the collecting system and this separation system. At this time, it is advisable to perform mechanical desorption in advance and transfer the desorbed product to an airtight / isolated extractor. Also in the case of reverse sublimation, it is preferable to first perform mechanical desorption and then transfer it to an airtight and isolated reverse sublimator and then carry out it.

When fullerenes are separated by reverse sublimation, the fullerene is heated to an appropriate temperature in an atmosphere of an inert gas such as He, N ₂ or Ar, or mixed, and then the volatile gas is cooled and recovered. To do. The heating temperature is preferably about 400 ° C. or higher at 10 ⁻⁶ Torr, about 500 ° C. or higher at normal pressure, and the cooling temperature is preferably 100 ° C. or lower.

In the case of separating fullerenes by extraction, a volatile solvent which dissolves the formed fullerenes well without chemically changing as a solvent, for example, liquid saturated or unsaturated hydrocarbons having 10 or less carbon atoms, benzene. , Toluene, CS ₂ , pyridine and the like are preferably used.

A batch type extractor such as a Soxhlet extractor can be used as the extractor. At this time, the extraction can be accelerated by heating, irradiation with ultrasonic waves, or the like.
In these methods, fullerenes are separated and collected from soot and the like which are by-products.

Thereafter, if necessary, fullerenes are isolated and purified by liquid chromatography, supercritical fluid chromatography or the like.

In the above synthetic method of fullerenes,
The inside of the path from the raw material supply system to the plasma generation system, the plasma reaction unit, the cooling system, and the collection system is shielded from the outside air. In order to shut off from the outside air, as shown in FIG. 1, the whole member or main part of the path may be installed in the chamber 20 exhausted by the vacuum pump 19. It should be noted that only the inside of the path may be configured as a piping system so as to be shielded from the outside air.

[0038]

According to the method for producing fullerenes of the present invention, a gas, liquid or powdery carbonaceous compound raw material can be continuously supplied. In addition, since these raw materials have a lower decomposition temperature and a higher decomposition rate than graphite, they can be sufficiently heated and decomposed within the residence time in thermal plasma, and fullerenes can be rapidly synthesized with energy efficiency. Further, unlike the method of heating and decomposing the raw material by combustion, fullerenes can be synthesized without supplying excessive O ₂ or supplying O ₂ at all.

In addition, in the present invention, since the gaseous carbon-containing compound raw material is supplied to the thermal plasma while being accompanied by the carrier gas, the raw material is carbonized and clogged at the outlet of the carbon-containing compound supply nozzle to the thermal plasma. Moreover, it is possible to prevent the raw material from staying in the supply pipe. Therefore, the raw material can be stably and continuously supplied.

From the above, it is extremely effective as a method for mass-producing fullerenes.

[0041]

【Example】

Example 1 FIG. 1 is a vertical sectional view showing a method for producing fullerenes in which thermal plasma is generated by a DC arc discharge plasma jet.

The plasma gun 7 to which the plasma gas supply pipe 6 is connected comprises a cylindrical anode (made of copper or graphite) 8 and a central cathode (made of tungsten or graphite) 9. The plasma gas described above flows from the cathode 9 toward the anode 8 and is sufficiently mixed. A direct current voltage is applied between the anode 8 and the cathode 9 to cause arc discharge, and a jet 11 of thermal plasma is provided downstream of the anode 8.
Give rise to. Both poles are water cooled to prevent wear. The carbon-containing compound raw material is continuously supplied to the downstream side from the raw material supply nozzle 4 together with the carrier gas, and the plasma reaction unit 3 is provided in the cooling and collecting container 13 on the downstream side to cause the reaction. Container 1
3 is water cooled. The plasma gun 7 and the container 13 are arranged in the chamber 20. The inside of the chamber 20 is exhausted by an exhaust pump 19.

5 cm at a position about 30 cm downstream from the anode 8.
The baffle plate 12 made of α-silicon carbide (SiC) at the corner is installed,
Apply the raw material / plasma jet to this, and baffle plate 12
The reaction was performed while measuring the temperature. When this baffle plate 12 is used, the cooling efficiency is increased.

The flow rate controller 2 passes through the raw material line 21.
The liquid raw material supplied in a fixed amount in 2 and the carrier gas supplied in a fixed amount by the flow rate controller 24 via the gas line 23 are introduced into the mixer 25. A heater-type preheater 29 is incorporated in the mixer 25, and the liquid raw material is heated and vaporized. The vaporized raw material and carrier gas are mixed in the mixer 25.
In the line heater 30 after being mixed in an appropriate amount ratio in
It is supplied from the nozzle 4 to the thermal plasma 11 through the attached mixed gas supply line 26.

In the apparatus shown in FIG. 1, liquid benzene as a raw material was supplied from the raw material supply system as He as a carrier gas (flow rate 2 liter / min) at a rate of 3 ml / min. This benzene is 8 in the heater type preheater 29.
Preheated to 0 ℃, vaporized, and then line heater 3
It is supplied to the nozzle 4 while being kept warm at 0, and is supplied into the thermal plasma 11 about 2 cm downstream of the plasma gun 7.

As the plasma gas, Ar was supplied at a rate of 20 liters / min and He was supplied at a rate of 20 liters / min (the above flow rates are all at room temperature and atmospheric pressure).

The other main conditions are as follows.

Plasma gun power 25 to 40 kW (including water cooling loss) Reaction part internal pressure 55 Torr Reaction part temperature 1200 to 1500 K Cooling and collecting container 13 Terminal outlet gas temperature 8 at initial stage
0 ° C. After that, gradually increased to 130 ° C.

As a result, the raw material residence time in the plasma jet was about 1 ms. As a result, about 30 g of soot-like substances (including C ₆₀ and C ₇₀ ) adhered and formed on the inner surface of the container 13 when the raw material was supplied for 30 minutes. When this product was scraped out and extracted with toluene,
Insoluble component of it (fullerene C ₆₀ +
C ₇₀ ) was about 0.2 g in the most frequent trial.

During this time, the pipe 26, the mixer 25, and the nozzle 4
No retention of raw materials and no adherence of carbides were observed.

FIG. 2 shows an ultraviolet-visible absorption spectrum of the insoluble component in a toluene solvent. The spectra of the insoluble component are 314 nm, 334 nm, 363 nm, 3
It has peaks or shoulders at 81 nm and 407 nm, and a gentle peak near 460 to 480 nm.
It can be seen that it is the sum of the C ₆₀ and C ₇₀ spectra of the standard sample of the reference data.

FIG. 3 shows the electron impact ionization mass spectrum of the insoluble component. 7 corresponding to the mass number / charge of the monovalent and divalent cations of C ₆₀ and C ₇₀ , respectively.
Peaks at 20, 360 (C ₆₀ ) and 840, 420 (C ₇₀ ) are seen. From these, it was confirmed that fullerenes C ₆₀ and C ₇₀ were synthesized.

The same apparatus as in Example 1 was used to add acetylene, which is a gas raw material, at a rate of 2 l / min to He.
An attempt was made to synthesize fullerenes by supplying them with a carrier gas mixed with 2 liters / min. In the electron impact ionization mass spectrum of the toluene extract of the product, monovalent and divalent cations of C ₆₀ and C ₇₀ were obtained. Corresponding peaks were observed, indicating that fullerenes can be similarly synthesized. In this case, the heater type preheater 29 and the line heater 3
0 was unnecessary.

Comparative Example 1 In Example 1, when the heater type preheater 29 and the line heater 30 were not operated, about 6 m after the start of operation.
In, the clogging occurred at the outlet of the nozzle 4 due to the adhesion of the raw material carbide, and the subsequent operation was difficult.

Further, when the carrier gas was stopped, benzene remained in the mixer 25 in a liquid state.

[0056]

As described above, according to the method for producing fullerenes of the present invention, fullerenes can be produced while continuously supplying the raw materials and without supplying excessive O ₂ or supplying O ₂ at all. Can be synthesized. Further, the raw material supply nozzle is not clogged at all. Therefore, fullerenes can be stably produced, and can be continuously produced for a long period of time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a fullerene producing apparatus used in a method according to an embodiment of the present invention.

FIG. 2 is an analysis result (ultraviolet-visible absorption spectrum of a toluene solution) of generated fullerenes in Examples of the present invention.

FIG. 3 is another analysis result (electron impact ionization mass spectrum) of the generated fullerenes in the example of the present invention.

[Explanation of symbols]

 7 Plasma Gun 8 Anode 9 Cathode 12 Baffle Plate 13 Cooling Collection Container 19 Exhaust Pump 20 Chamber 25 Mixer 29 Heater Preheater 30 Line Heater

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Hatta No. 1 Yawata Kaigan Dori, Ichihara City, Chiba Mitsui Engineering & Shipbuilding Co., Ltd. Chiba Works

Claims (2)

[Claims] 1. A thermal plasma is generated, and a gaseous raw material of a carbon-containing compound is supplied into this together with a carrier gas to heat and decompose it, and the reaction gas is cooled to collect a solid content. A method for producing fullerenes for separating fullerenes from a collection, wherein the gas raw material is a vaporized liquid or solid carbon-containing compound at room temperature. 2. A thermal plasma is generated, and a gaseous raw material of a carbon-containing compound is supplied together with a carrier gas to heat and decompose it, and the reaction gas is cooled to collect a solid content, and the solid content is collected. A method for producing fullerenes for separating fullerenes from a collection, wherein the gas raw material is a gas at room temperature.