JP2008189790A - Method for producing carbon microspheres - Google Patents

Abstract

A method for producing carbon microspheres having a relatively large particle diameter with an arithmetic average particle diameter dn of about 450 to 1000 nm is provided.
In a method for producing carbon microspheres in which hydrocarbon gas is supplied to an external heating furnace and pyrolyzed,
1. Hydrocarbon gas concentration 50-100 vol%,
2. Heating rate of external heating furnace is 100 ℃ / second or less
3. The internal temperature of the external heating furnace is 800-1100 ° C,
4. Retention time in the furnace for pyrolysis is 8.0-30 seconds,
A method for producing carbon microspheres, characterized in that the setting control is performed.
[Selection figure] None

Description

  The present invention relates to a method for producing carbon microspheres suitably used as black pigments composed of black fine particles used for electronic paper or black matrix, PTC elements, semiconductor encapsulants, or negative electrode materials for lithium secondary batteries, etc. Production of carbon microspheres having a relatively large particle diameter of about 450 to 1000 nm as measured by an electron microscope, a small particle aggregate, and a narrow particle size distribution width Regarding the method.

  Carbon black is known as a fine carbon microsphere. Carbon black is consumed in large quantities as a reinforcing material for rubber, including tires, and is widely used for other applications such as colorants, pigments, and paints.

  The types of carbon black are generally classified according to the production method, and are roughly classified into an incomplete combustion method of raw material hydrocarbons and a thermal decomposition method. Of these, the oil furnace method, one of the incomplete combustion methods, uses coal-based or petroleum-based hydrocarbon feedstock as the raw material, introduces liquid or gaseous fuel and a large amount of air into a special reactor, A hydrocarbon feedstock is continuously supplied in the form of high-temperature combustion gas formed by complete combustion in the form of a mist to burn part of the feedstock, and the remaining hydrocarbon feedstock is pyrolyzed and converted to carbon black. Is.

  The oil furnace black produced by this oil furnace method is capable of producing carbon black having a wide range of particle characteristics and is easily mass-produced.

  And, the furnace black for rubber is classified according to the particle diameter, and the particle diameter ranges widely from 11 to 19 nm of SAF grade carbon black to 61 to 100 nm of SRF grade carbon.

  Oil furnace black has a complex agglomeration structure in which fine spherical basic particles are branched in an irregular chain from the formation process, and usually several to several tens of basic particles are fusion-bonded. It consists of a three-dimensional structure. This three-dimensional structure is called a structure, and its size is evaluated by the DBP absorption amount.

  It is impossible to unravel this particle agglomeration structure and separate it into the individual basic particles that make up the structure, because the basic particles are tightly fused and bonded, using oil furnace black. It is not possible to obtain a carbon sphere with a proper particle shape.

  In addition, thermal black obtained by pyrolyzing hydrocarbon raw materials is a thermal storage chamber type cracking furnace in which refractory bricks are stacked in a checkered form, and pyrolyzes carbon and hydrogen using natural gas as raw materials. Is characterized in that carbon black having a large particle diameter can be obtained, the development of the structure is small, the DBP absorption is small, that is, the aggregate structure of the carbon black particles is small. For example, the arithmetic average primary particle diameter of FT class carbon black is 101 to 200 nm, the DBP absorption is 30 to 50 ml / 100 g, the arithmetic average primary particle diameter of MT class carbon black is 180 to 500 nm, and the DBP absorption is 30 to It is about 50 ml / 100 g. Therefore, it can be said to be a carbon sphere having a large particle diameter exceeding 100 nm and having a relatively small aggregate structure in which particles are bonded.

  Thermal black having such particle characteristics cannot be manufactured by directly applying the manufacturing technique of the oil furnace method. Therefore, the present applicant, as a manufacturing technique of carbon black having particle properties equivalent to thermal black, uses gaseous hydrocarbons that are thermally decomposed by an endothermic reaction as raw materials, and the raw material gas is supplied in a reducing atmosphere at a supply concentration of 5 to 50 vol%. A manufacturing method (Patent Document 1) was developed in which a gas stream was fed into an externally heated reactor held in a reactor and pyrolyzed at a temperature of 1400 ° C. or higher in a laminar flow with a Reynolds number of 2300 or less.

  However, the carbon black obtained by this manufacturing technique exhibits the property that the agglomerates are likely to develop although the raw material gas is thermally decomposed under the condition of a high linear flow velocity, and the produced particles collide and become a property having a low specific surface area. . In addition, the pyrolysis temperature is high, and the carbon black production yield is low at low temperatures.

  As an improvement technique, a liquid or solid hydrocarbon raw material is heated and vaporized at room temperature, and the vaporized hydrocarbon raw material gas is kept in an oxygen-free atmosphere at a gas concentration of 0.01 to 2.0 vol% together with a carrier gas. A method for producing carbon black (Patent Document 2) was proposed, which was introduced into a thermal pyrolysis furnace and thermally decomposed by heating to a temperature of 1000 to 1400 ° C. By this method, carbon black having particle properties equivalent to thermal black having an arithmetic average primary particle size of 160 to 500 nm and a DBP absorption of 40 ml / 100 g or less can be produced. However, since the gas concentration is low, the productivity is low and the particle size distribution of the particle aggregate is broadened.

Therefore, the present applicant has further researched and proposed a carbon microsphere which is designed to suppress the broadening of the particle size distribution of the particle aggregates and to develop a carbon microsphere with a narrow particle size distribution width and small variation. did. That is, in Patent Document 3, the arithmetic average particle diameter dn by an electron microscope is 20 to 150 nm, and s / dn indicating the degree of variation is 0.1 to 0.3 (where s is a standard deviation of dn). There are carbon microspheres having particle properties in which the ratio Dst / dn of the Stokes mode diameter Dst indicating the size of the particle aggregate to the arithmetic average particle diameter dn is 1.2 or less, and pyrolysis of hydrocarbon gas together with hydrogen gas After introduction into the preheating zone of the furnace and pyrolysis under the conditions of hydrocarbon gas concentration of 0.01 to 40 vol%, Reynolds number of 1 to 20, and temperature of 1100 to 1300 ° C. in the subsequent heating zone, the obtained carbon spheres are further removed. A manufacturing method in which heat treatment is performed at a temperature of 600 to 2000 ° C. in an oxygen atmosphere is disclosed.
JP 07-034001 A Japanese Patent Laid-Open No. 10-168337 JP 2004-211012 A

  Patent Document 3 discloses that a carbon microsphere having a single spherical form with a sharp particle size distribution and a small particle aggregation structure by introducing hydrocarbon gas into a pyrolysis furnace together with hydrogen gas and slowly pyrolyzing at a relatively low temperature. Is to be manufactured.

  However, since this method suppresses the thermal decomposition reaction of hydrocarbon gas by hydrogen gas, it is easy to produce undecomposed tar-like substances. In order to remove this tar-like undecomposed carbonaceous material, heat treatment is performed in an oxygen-free atmosphere. The manufacturing conditions become complicated, and the particle diameter of the carbon microspheres obtained is relatively small, such as 20 to 150 nm. Thus, there is a problem that it is difficult to manufacture the carbon microspheres having a large particle diameter required by the application.

  Therefore, the present inventors have conducted intensive research to solve these problems, increasing the hydrocarbon concentration when pyrolyzing hydrocarbons as much as possible, and temperature conditions at the time of pyrolysis, such as the heating rate, heat The effects of decomposition temperature, thermal decomposition time, etc. were examined from various perspectives.

  As a result, a method has been developed that can produce carbon microspheres having a large particle size, for example, an arithmetic average particle size dn measured by an electron microscope of about 450 to 1000 nm. That is, an object of the present invention is to provide a method capable of efficiently producing carbon microspheres having a large particle diameter by a simple method.

In order to achieve this object, a method for producing carbon microspheres according to the present invention includes a method for producing carbon microspheres in which hydrocarbon gas is supplied to an external heating furnace and thermally decomposed.
1. Hydrocarbon gas concentration 50-100 vol%,
2. Heating rate of external heating furnace is 100 ℃ / second or less
3. The internal temperature of the external heating furnace is 800-1100 ° C,
4. Retention time in the furnace for pyrolysis is 8.0-30 seconds,
It is characterized by controlling the setting.

  According to the present invention, large particles can be obtained by thermally decomposing at a relatively low temperature by supplying a high concentration of hydrocarbon gas to the external heating furnace and controlling the heating rate and residence time in the furnace for pyrolysis. It becomes possible to produce carbon microspheres having a diameter, specifically, carbon microspheres having an arithmetic average particle diameter dn measured by an electron microscope of about 450 to 1000 nm. Furthermore, according to the present invention, carbon microspheres can be produced efficiently with high yield and high productivity.

  FIG. 1 is an explanatory view illustrating the overall configuration of an apparatus applied to the carbon microsphere manufacturing method of the present invention. In FIG. 1, 11 is a gas cylinder filled with a hydrocarbon source gas (for example, propane gas), 12 is a gas cylinder filled with an inert carrier gas (for example, nitrogen gas), and 13 is a flow meter. In addition, 14 is a raw material tank in the case of using a hydrocarbon raw material which is liquid at normal temperature instead of hydrocarbon gas, 15 is a heater, and the hydrocarbon raw material which is liquid at normal temperature is vaporized by heating and supplied in a gaseous state.

  Reference numeral 17 denotes an external heating furnace that thermally decomposes hydrocarbon gas as a raw material and converts it into carbon microspheres. Reference numeral 18 denotes a heating device for heating the external heating furnace 17 to a predetermined temperature. Appropriate heating methods such as induction heating, resistance heating, or a heating tube through which combustion gas flows are applied. The furnace temperature of the external heating furnace 17 is detected by a thermocouple or a radiation thermometer, and the furnace temperature is controlled to a predetermined temperature by the temperature controller 19.

  The cracked gas containing the carbon microspheres after pyrolysis is cooled by the cooling pipe 20, and after separating and collecting the carbon microspheres in the collection chamber 23, the cracked gas is completely burned in the combustion device 25 via the water tank 24. Are discharged outside the system.

  The hydrocarbon gas used as a raw material includes aliphatic hydrocarbons such as methane, ethane, propane, butane, ethylene, propylene, and butadiene, monocyclic aromatic hydrocarbons such as benzene, toluene, and xylene, and many types such as naphthalene and anthracene. Cyclic aromatic hydrocarbons and natural gas, city gas, liquefied natural gas, liquefied petroleum gas, etc. can be used. If the raw material hydrocarbon is liquid or solid at room temperature, it is vaporized by heating and used in gaseous form To do.

  In addition, an inert gas such as nitrogen or argon, helium, neon, xenon, or krypton is used as the carrier gas when the carrier gas is used together with the hydrocarbon gas supplied to the external heating furnace.

  In the process of producing carbon microspheres, the raw material hydrocarbon gas is first pyrolyzed to produce carbon intermediate core particles, and the carbon core particles collide with each other and fuse together. Carbon particles are formed. Furthermore, in the process of the thermal decomposition reaction, it is considered that these fine carbon particles are repeatedly coalesced and deposited to grow into larger particles, and carbon fine particles are formed.

  In this process, the particle properties of the carbon microspheres are affected by the temperature gradient when the hydrocarbon gas supplied to the external heating furnace is pyrolyzed, the hydrocarbon gas concentration, etc. The collision frequency of nuclear particles increases as the furnace temperature increases and the hydrocarbon gas concentration increases. Further, it is considered that the growth of fine carbon particles into larger particles is mainly influenced by the furnace temperature, the residence time in the furnace, and the like.

  In other words, the production of carbon core particles is promoted, the collision frequency between carbon core particles is increased, and the formation of fine carbon particles and the growth of grains are important in producing carbon fine particles having a large particle diameter. It becomes an important factor.

From this point of view, the present invention sets the pyrolysis conditions for hydrocarbon gas.
1. Hydrocarbon gas concentration 50-100 vol%,
2. Heating rate of external heating furnace is 100 ℃ / second or less
3. The internal temperature of the external heating furnace is 800-1100 ° C,
4. Retention time in the furnace for pyrolysis is 8.0-30 seconds,
The setting is controlled.

  A high hydrocarbon gas concentration is advantageous because the production of carbon nuclear particles increases and the collision frequency between carbon nuclear particles also increases. However, the higher the concentration, the more rapidly these reactions proceed. Undecomposed carbonaceous material is likely to be produced, and carbonaceous material is likely to be deposited in the furnace. Therefore, the present invention makes it possible to increase the concentration of hydrocarbon gas to be supplied by appropriately setting the temperature conditions for thermal decomposition, and the hydrocarbon gas is supplied at a gas concentration of 50 to 100 vol%.

  When the hydrocarbon gas concentration is less than 50 vol%, the existence density of the generated carbon core particles becomes low, the collision frequency between the carbon core particles decreases, and further, the growth of the formed fine carbon particles sufficiently proceeds. No longer. On the other hand, the higher the hydrocarbon gas concentration, the better for increasing the size of the carbon microspheres. Ultimately, the hydrocarbon gas is supplied to the external heating furnace at a concentration of 100 vol%.

  The concentration of the hydrocarbon gas is adjusted by controlling the flow rate ratio between the hydrocarbon gas and the carrier gas.

  If the hydrocarbon gas supplied to the external heating furnace is rapidly pyrolyzed, conversion to carbon proceeds at a stretch, so that intermediate carbonaceous materials are easily generated without being sufficiently decomposed into carbon. Various carbonaceous materials from carbon microspheres to carbonaceous materials are liable to cause problems such as depositing in the furnace and blocking the inside of the furnace.

  Therefore, in the present invention, the temperature rise rate of the external heating furnace is set to 100 ° C./second or less and the furnace temperature is set to 800 to 1100 ° C. as temperature conditions for thermal decomposition.

  When the temperature rising rate exceeds 100 ° C./second, the hydrocarbon gas is rapidly pyrolyzed, so that various carbonaceous substances are generated and accumulated in the furnace. It becomes difficult to produce small carbon microspheres. Also, if the furnace temperature is below 800 ° C, the hydrocarbon gas is thermally decomposed and conversion to carbon becomes insufficient. On the other hand, if it exceeds 1100 ° C, the thermal decomposition reaction of the hydrocarbon gas proceeds rapidly and the particle size is large. It is difficult to form carbon microspheres, and the hydrocarbon gas concentration cannot be set high.

  In order to generate carbon microspheres having a large particle diameter, it is effective to retain the hydrocarbon gas for a long time in the temperature range where the hydrocarbon gas is thermally decomposed. In the present invention, the residence time in the furnace in the temperature range where the pyrolysis is performed is 8.0. It is characterized by being set and controlled in a range of ˜30 seconds. In order to lengthen the residence time in the furnace, a method of simply slowing the flow rate of hydrocarbon gas in the furnace is conceivable, but there is a problem that the production yield and productivity are lowered.

  For this reason, the present invention adjusts the substantial residence time in the furnace in a temperature range where the temperature rise rate of the external heating furnace is set low and is thermally decomposed. The residence time in the furnace can also be adjusted by changing the furnace length of the heating furnace.

  Thus, the present invention sets and controls the concentration of hydrocarbon gas supplied to the external heating furnace, the heating rate and temperature in the external heating furnace, and the residence time in the furnace, thereby controlling the carbon core particles. A relatively large particle size with an increased average particle size, for example, an arithmetic average particle size dn measured by an electron microscope of about 450 to 1000 nm, by increasing the frequency of generation and collision of the carbon core particles, and further promoting particle growth It is possible to efficiently produce carbon microspheres.

  Hereinafter, the present invention will be specifically described in comparison with comparative examples.

Examples 1-5
Methane gas and propane gas were used as the raw material hydrocarbon gas, and nitrogen gas was used as the carrier gas. An opaque quartz tube furnace having an inner diameter of 210 mm and a length of 1500 mm was used for the external heating furnace, and a cylindrical heater having an inner diameter of 155 mm and a length of 800 mm was used for the heating zone, and the heating was controlled to a predetermined temperature.

  This tubular furnace was supplied with varying the flow rate ratio of hydrocarbon gas and nitrogen gas and pyrolyzed. At this time, carbon microspheres were produced by setting and controlling the hydrocarbon gas concentration, heating rate, furnace temperature, furnace residence time, and the like under different conditions. In Examples 4 and 5, thermal decomposition was performed by supplying only hydrocarbon gas without using nitrogen gas.

Comparative Examples 1-3
Propane gas was used as the raw material hydrocarbon gas, and nitrogen gas was used as the carrier gas. An opaque quartz tubular furnace having an inner diameter of 210 mm and a length of 1500 mm was used for the external heating furnace, and a cylindrical heater having an inner diameter of 155 mm and a length of 400 mm was used for the heating zone, and the heating was controlled to a predetermined temperature.

  This tubular furnace was supplied with varying the flow rate ratio of hydrocarbon gas and nitrogen gas and pyrolyzed. At this time, carbon microspheres were produced by setting and controlling the hydrocarbon gas concentration, heating rate, furnace temperature, furnace residence time, and the like under different conditions. In Comparative Example 2, thermal decomposition was performed by supplying only hydrocarbon gas without using nitrogen gas.

  For these carbon microspheres, the arithmetic average particle diameter dn and the production yield were determined by the following method, and the obtained results are shown in Table 1 together with the production conditions.

Arithmetic average particle diameter dn;
After a sample of carbon microspheres is dispersed in chloroform for 30 seconds at a frequency of 28 kHz using an ultrasonic disperser, the dispersed sample is fixed to a carbon support film (for example, “Powder Physical Properties”, edited by Powder Engineering Institute p68 (c) “Water surface membrane method”). This was photographed directly with an electron microscope at a magnification of 10,000 times and a total magnification of 100,000 times, and the diameter of 1000 carbon microspheres was randomly measured from the obtained photograph, and the arithmetic average particle was created from a histogram created by dividing the photons every 14 nm. The diameter dn was determined.

Production yield;
It was calculated from the weight of carbon in the supplied hydrocarbon gas and the weight of the separated and collected carbon microspheres.

  In Examples 1 to 5, since the production conditions were appropriately controlled, good growth of the carbon core particles progressed, and the carbon microparticles having a relatively large particle diameter with an arithmetic average particle diameter dn measured by an electron microscope of about 450 to 1000 nm. A sphere could be manufactured. Moreover, it was able to produce efficiently without depending on the kind of hydrocarbon gas.

  On the other hand, in Comparative Example 1, since the hydrocarbon gas concentration is low, the reaction ends with the collision frequency of the carbon core particles being small and the particle growth is insufficient, and carbon microspheres having a small arithmetic average particle diameter dn are obtained. It was. In Comparative Example 2, the hydrocarbon gas at a high concentration abruptly undergoes a pyrolysis reaction, and a large amount of undecomposed carbonaceous material was generated and deposited in the furnace. In Comparative Example 3, since the furnace temperature was too low, the conversion of hydrocarbon gas to carbon was insufficient, and the formation of carbon microspheres was not observed.

It is explanatory drawing which illustrated the whole structure of the apparatus applied to the manufacturing method of the carbon microsphere of this invention.

Explanation of symbols

11 Hydrocarbon gas 12 Carrier gas 13 Flow meter 14 Liquid hydrocarbon raw material tank 15 Heater 16 Pressure gauge 17 External heating furnace 18 Heating device 19 Temperature controller 20 Cooling pipe 21 Valve 22 Vacuum pump 23 Collection chamber 24 Water tank 25 Combustion apparatus

Claims (1)

In the method for producing carbon microspheres in which hydrocarbon gas is supplied to an external heating furnace and pyrolyzed,
1. Hydrocarbon gas concentration 50-100 vol%,
2. Heating rate of external heating furnace is 100 ℃ / second or less
3. The internal temperature of the external heating furnace is 800-1100 ° C,
4. Retention time in the furnace for pyrolysis is 8.0-30 seconds,
A method for producing carbon microspheres, characterized in that the setting control is performed.

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