JP2008169084A - Method for producing carbon microsphere - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method producing a carbon microsphere having reduced flocculation, and in which the distribution width of flocculated grains is narrow and shows sharp distribution properties at a low cost. <P>SOLUTION: In the method where a hydrocarbon gas is thermally decomposed, so as to produce a carbon microsphere, a hydrocarbon gas is fed to an external heat type cracking furnace 17 where heating is controlled to two stages together with air, the concentration of the hydrocarbon gas to be fed to the prestage region in the external heat type cracking furnace is set to 10 to 50 vol%, the flow rate of the hydrocarbon gas is set to 0.02 to 4.0 m/sec, the temperature of the prestage region in the external heat type cracking furnace is controlled to ≤900°C, and the temperature of the poststage region is controlled to 1,000 to 1,400°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a black pigment composed of black fine particles used for electronic paper and black matrix, or a carbon microsphere suitably used for a PTC element, a semiconductor encapsulant, a negative electrode material for a lithium secondary battery, and more particularly a carbon microsphere. The present invention relates to a technique for producing low-cost carbon microspheres having a small aggregate size and a narrow distribution width of aggregated particles and exhibiting sharp distribution properties.

  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, The hydrocarbon feedstock is injected into the high-temperature combustion gas formed by complete combustion and continuously supplied in the form of a mist to burn a portion of the feedstock, and the remaining most of the hydrocarbon feedstock is carbon black. It is pyrolyzed to hydrogen.

  The oil furnace black produced by this oil furnace method is capable of producing a carbon black having a particle property over a wide range 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 agglomerated structure and separate it into the individual basic particles that make up the structure because the basic particles are firmly fused and bonded. A particle-shaped carbon sphere cannot be obtained.

  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 that the aggregated structure in which the particles are bonded is relatively small, and the carbon sphere has a large particle diameter exceeding 101 nm.

  On the other hand, channel blacks that are useful as pigments for inks, paints, etc. are fine particles with an arithmetic average primary particle size of about 10 to 20 nm, a high structure, and a large aggregate structure in which many carbon black fine particles are bonded. It is very different from a single particle shape.

  It is extremely difficult to produce thermal black having such particle characteristics by directly applying the oil furnace manufacturing technique. Therefore, the present applicant, as a production 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 has a property that the aggregated particles are easily developed although the produced particles collide and have a low specific surface area because the linear flow velocity is high. In addition, this production method has a high thermal decomposition temperature and a low carbon black production yield 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 measured 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 Stokes mode diameter Dst and arithmetic mean particle diameter dn indicating the size of the particle aggregate 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 for the heat treatment 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

  These methods prevent combustion of hydrocarbon gas and control the thermal decomposition reaction in an inert gas atmosphere such as argon or helium, or in a non-oxidizing atmosphere such as nitrogen or hydrogen, that is, in an oxygen-free atmosphere. A thermal decomposition reaction is performed.

  However, if this thermal decomposition reaction can be performed in an oxygen-containing atmosphere, for example, in air, it is clear that the manufacturing cost is advantageous. Thus, the inventors have studied a method for producing carbon microspheres by pyrolyzing hydrocarbon gas in an atmosphere containing oxygen. And it discovered that it was possible also in the air as an atmosphere to thermally decompose by adjusting the temperature conditions to thermally decompose and specifying the density | concentration of raw material hydrocarbon gas, and a gas flow rate.

  In other words, the present invention has been completed based on this finding, and its purpose is to have a special atmosphere for carbon microspheres that have little aggregation of carbon microspheres and have a narrow distribution width of the aggregated particles and a sharp distribution property. The object is to provide a production method that can be produced at low cost by thermally decomposing hydrocarbon gas in air.

  The method for producing carbon microspheres according to the present invention for achieving the above object is a method for producing carbon microspheres by pyrolyzing hydrocarbon gas, wherein the hydrocarbon gas is heated and controlled in two stages together with air. Supplying to the thermal cracking furnace, setting the concentration of hydrocarbon gas to be supplied to the upstream region of the external heating cracking furnace to 10 to 50 vol%, and the flow rate of hydrocarbon gas to 0.02 to 4.0 m / sec, The temperature of the front | former area | region of an external heating type cracking furnace is controlled to 900 degrees C or less, and the temperature of a back | latter stage area | region is controlled to 1000-1400 degreeC.

According to the present invention, there is little agglomeration of spherical particles, and the distribution width of the agglomerated particles is narrow and shows a sharp distribution property. Electronic paper, black matrix, PTC element, semiconductor encapsulant, or negative electrode material for lithium secondary battery It is possible to produce carbon microspheres that are preferably used for such as low cost.

  Hydrocarbon gases include aliphatic hydrocarbons such as methane, ethane, propane, butane, ethylene, propylene, and butadiene, monocyclic aromatic hydrocarbons such as benzene, toluene, and xylene, and polycyclic aromatics such as naphthalene and anthracene. A group hydrocarbon, natural gas, city gas, liquefied natural gas, liquefied petroleum gas, and the like can be used. When the raw material hydrocarbon is liquid or solid at room temperature, it is vaporized by heating and used in a gaseous state.

  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, methane gas), 12 is a blower or gas cylinder for supplying air as a carrier gas, and 13 is a flow meter. In addition, 14 is a raw material tank in the case of using a hydrocarbon raw material liquid at normal temperature instead of hydrocarbon gas, and 15 is a heating device.

  17 is an external heating type cracking furnace, and 18 is a heating device for controlling the external heating type cracking furnace 17 to a predetermined temperature. For example, an appropriate heating method such as high-frequency induction heating, resistance heating, or flowing a combustion gas. Applies.

  FIG. 2 is a schematic view illustrating 17 external heat cracking furnaces applied to the carbon microsphere manufacturing method of the present invention. The external heat cracking furnace 17 is divided into a front stage region 17-1 and a rear stage region 17-2. Has been. The front region 17-1 is controlled to a predetermined temperature by the heating device 18-1 and the controller 19-1, and the rear region 17-2 is controlled to a predetermined temperature by the heating device 18-2 and the controller 19-2. Is done.

  The hydrocarbon gas as the raw material is supplied to the front stage region 17-1 of the external heating type cracking furnace 17 using air as a carrier gas, and then thermally decomposed into carbon microspheres through the subsequent stage region 17-2. In this case, the concentration of the hydrocarbon gas in the mixed gas of hydrocarbon gas and air supplied to the upstream region 17-1 is set to 10 to 50 vol%, and the flow rate of the hydrocarbon gas is set to 0.02 to 4.0 m / Set to sec.

  The concentration of the hydrocarbon gas is set to 10 to 50 vol%. When the concentration is less than 10 vol%, the gas flow rate needs to be lowered, and the adhesion of the powder to the reaction tube wall becomes remarkable. Moreover, when it exceeds 50 vol%, it is difficult for a uniform reaction to proceed, and it is difficult to obtain a sharp particle distribution and causes a phenomenon that the reaction tube is blocked.

The hydrocarbon gas flow rate is set to 0.02 to 4.0 m / sec.
If it is less than / sec, powder adheres to the reaction tube wall and becomes prone to clogging. On the other hand, if it exceeds 4.0 m / sec, the flow of hydrocarbon gas becomes uneven and the particle size distribution becomes wide. In addition, the sufficient residence time of the hydrocarbon gas in the furnace cannot be obtained, the thermal decomposition reaction does not proceed sufficiently, and the amount of unburned fuel increases. The flow rate of the hydrocarbon gas can be set by changing the flow rate of the hydrocarbon gas to be supplied and inserting a reaction tube having a different tube diameter into the external heating cracking furnace 17.

  A part of the hydrocarbon gas supplied to the front region 17-1 of the external heat cracking furnace burns with air, so that the temperature rises rapidly. In addition, the flow rate increases rapidly and the residence time is shortened, so that the generated carbon microspheres are easily atomized. In order to eliminate this influence, the temperature of the preceding region is controlled to 900 ° C. or lower.

  Next, in the rear region 17-2 of the external heat cracking furnace, the temperature is controlled to 1000 to 1400 ° C. in order to allow sufficient residence time to grow the carbon particles and increase the size. Note that the length of the rear region is designed to an appropriate length in consideration of the residence time.

  The internal temperature of the external thermal cracking furnace is detected by a thermocouple or a radiation thermometer, and controlled to a predetermined temperature by the controller 19-1 and the controller 19-2, and the cracked gas containing carbon microspheres after pyrolysis After cooling with the cooling pipe 20, the carbon microspheres are separated and collected in the collection chamber 23, and then the combustion gas is completely burned by the combustion device 25 via the water tank 24 and discharged out of the system.

  In this way, according to the method for producing carbon microspheres of the present invention, it is possible to produce carbon microspheres that exhibit a sharp distribution property with a narrow aggregated particle distribution width and a sharp distribution property, with less aggregation of carbon microspheres. It becomes possible.

  Specifically, carbon microspheres having particle characteristics of a primary particle diameter dn of 100 to 450 nm, an aggregate Stokes mode diameter Dst of 200 to 600 nm, and a distribution width ΔDst / Dst of 0.40 to 0.85 are obtained. Since they can be produced, these carbon microspheres can be suitably used as an electronic paper, a black matrix, a PTC element, a semiconductor encapsulant, or a negative electrode material for a lithium secondary battery.

These particle characteristics are measured by the following method.
Primary particle diameter dn (nm);
After the sample is dispersed in chloroform for 30 seconds at a frequency of 28 kHz by an ultrasonic disperser, the dispersed sample is fixed to a carbon support membrane (for example, “Powder Physical Properties”, edited by the Powder Engineering Society p68 (c) “Water surface membrane method” "by). 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 particles was randomly measured from the obtained photo, and the arithmetic average primary particles were created from a histogram created by dividing each 14 nm. Find the diameter.

Stokes mode diameter Dst and half width ΔDst (nm) of the aggregate;
The dried carbon microspheres are mixed with a 20 vol% aqueous ethanol solution containing a small amount of a surfactant to prepare a dispersion having a carbon content of 0.1 kg / m ³ , and this is sufficiently dispersed with ultrasound to prepare a sample. . A disc centrifuging device (manufactured by Joyes Robert, UK) was set to a rotation speed of 100 s ⁻¹ , and 0.015 dm ^{3 of} spin solution (2 wt% glycerin aqueous solution, 25 ° C.) was added, and then a buffer solution of 0.001 dm ³ ( 20 vol% ethanol aqueous solution, 25 ° C.). Next, after adding 0.0005 dm ³ of carbon dispersion liquid at a temperature of 25 ° C. with a syringe, centrifugal sedimentation was started, and simultaneously the recorder was operated, and the distribution curve shown in FIG. 3 (horizontal axis; carbon dispersion liquid was added with a syringe). Elapsed time, vertical axis; absorbance at a specific point changed with centrifugal sedimentation of the carbon sample). Each time T is read from this distribution curve and substituted into the following equation (Equation 1) to calculate the Stokes equivalent diameter corresponding to each time.

In Equation 1, η is the viscosity of the spin liquid (0.935 × 10 ⁻³ Pa · s), N is the disk rotation speed (100 s ⁻¹ ), r ₁ is the radius of the carbon dispersion injection point (0.0456 m), r ₂ is the absorbance radius to the measurement point (0.0482m), ρ _CB is the density of carbon ^{(kg / m 3), ρ} 1 is the density of the spin fluid (1.00178kg / ^{m 3).}

  The maximum Stokes equivalent diameter in the Stokes equivalent diameter and absorbance distribution curve thus obtained (FIG. 4) is the Stokes mode diameter Dst (nm). The difference (half-value width) of the Stokes equivalent diameter is taken as ΔDst (nm).

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

Examples 1-4
Carbon microspheres were manufactured using the external heat type pyrolysis furnace 17 (an opaque quartz tube having an inner diameter of 145 mm and a length of 1500 mm) shown in FIG. Among them, the front region 17-1 of the external heating type pyrolysis furnace 17 is 850 mm long, the heating device 18-1 is 250 mm long, the rear region 17-2 is 650 mm long, and the heating device 18-2 is long. The length was set to 150 mm, and the temperature was controlled to a predetermined temperature by the controller 19-1 and the controller 19-2. The furnace temperature was detected at the central positions A and B of the heating devices 18-1 and 18-2.

  Butane or methane was used as the hydrocarbon gas, and the hydrocarbon gas concentration and the gas flow rate were changed together with the air, and the resultant was supplied to the upstream region 17-1 of the external heat pyrolysis furnace 17. At this time, carbon microspheres were manufactured by controlling the front region 17-1 and the rear region 17-2 at different temperatures.

Comparative Examples 1-4
Using the same external heating type pyrolysis furnace 17 as in the embodiment, heating is performed only by the heating device 18-2 in the rear region 17-2, that is, hydrocarbon gas is supplied and heated without temperature control in two steps. Disassembled. Butane or methane was used as the hydrocarbon gas, and it was supplied with nitrogen or air while changing the hydrocarbon gas concentration and gas flow rate, and pyrolyzed at different temperatures to produce carbon microspheres.

  The particle characteristics of these carbon microspheres were measured and are shown in Table 1 together with the production conditions.

  From Table 1, the hydrocarbon gas concentration and hydrocarbon gas flow rate to be supplied to the externally heated cracking furnace are specified, and the temperature conditions in the front and rear zones of the cracking furnace are set in two stages to perform thermal cracking in an air atmosphere. The carbon microspheres of Examples 1 to 4 produced as described above were carbon microspheres obtained by thermal decomposition without temperature control in two stages of the former region and the latter region in the nitrogen atmosphere of Comparative Examples 1 to 3. Has equivalent particle characteristics.

  That is, according to the production method of the present invention, it can be seen that carbon microspheres having particle characteristics that are the same as in a nitrogen atmosphere can be produced even in an air atmosphere. In addition, it is recognized that the comparative example 4 thermally decomposed in the air atmosphere is inferior in particle characteristics because the thermal decomposition conditions deviate from the temperature conditions specified in the present invention.

It is explanatory drawing which illustrated the whole structure of the apparatus applied to the manufacturing method of the carbon microsphere of this invention. It is the figure which showed typically the external heating type cracking furnace applied to the manufacturing method of the carbon microsphere of this invention. It is the distribution curve which showed the elapsed time after adding the dispersion liquid of the carbon microsphere at the time of Dst measurement, and the change of the light absorbency by centrifugal sedimentation of the carbon microsphere. It is a distribution curve which shows the relationship between the Stokes equivalent diameter obtained at the time of Dst measurement, and a light absorbency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Hydrocarbon gas cylinder 12 Air cylinder 13 Flowmeter 14 Liquid hydrocarbon raw material tank 15 Heating device 16 Pressure gauge 17 External heating type cracking furnace 17-1 Front stage area of external heating type cracking furnace 17-2 Rear stage area of external heating type cracking furnace 18 Heating device 18-1 Heating device 18-2 in the former stage Heating device 19-2 in the latter stage region 19-1 Controller 19-2 in the former stage heating device Controller 20 in the latter stage heating device Cooling pipe 21 Valve 22 Vacuum pump 23 Collection chamber 24 Water tank 25 Combustion equipment

Claims (1)

  In a method for producing carbon microspheres by pyrolyzing hydrocarbon gas, the hydrocarbon gas is supplied to an externally heated cracking furnace that is heated and controlled in two stages together with air, and is supplied to a preceding stage of the externally heated cracking furnace. The concentration of the hydrocarbon gas is set to 10 to 50 vol%, the flow rate of the hydrocarbon gas is set to 0.02 to 4.0 m / sec, the temperature of the front stage region of the external heating type cracking furnace is controlled to 900 ° C. or less, and the rear stage region The method of manufacturing the carbon microsphere characterized by controlling the temperature of 1000-1400 degreeC.

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