JP2005281127A - Production process for carbonized product and carbonized product obtained by the process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production process for a useful carbonized product by a simple apparatus and steps. <P>SOLUTION: The production process for the carbonized product is characterized by comprising the following steps (a) to (b): (a) a step in which a plurality of metal-made or ceramic-made granular matters are charged into a heat treating apparatus which is maintained at a temperature of ≥400 to ≤700°C and allowed to flow therein and in which a carbonized product precursor is fed into the above apparatus and subjected to heat treatment, whereby the carbonized product is adhered on the surface of the above granular matters and (b) the step in which the carbonized product adhered on the surface of the granular matters is heated at a higher temperature than the heat treating temperature in the step (a) and ≤900°C, whereby the carbonized product is separated from the granular matters. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used as a raw material for carbon materials used as power storage materials such as electric double layer capacitor electrode materials and negative electrodes for lithium secondary batteries, and as a raw material for graphite materials used in high-tech fields such as semiconductors, nuclear power, nuclear fusion, and aerospace. Applicable carbonized product production method, carbonized product obtained by the production method, activated carbon for electric double layer capacitor electrode obtained by activating the carbonized product, and lithium metal obtained by graphitizing the carbonized product The present invention relates to a carbon material for a secondary battery negative electrode.

  Conventionally, when producing a granular or powdery carbonized product from heavy oil, coal tar, or petroleum pitch, an initial heat-treated product in the form of a block or a small block has been produced, and molding and pulverization have been performed after carbonization. For example, when pitches are used as raw materials, heat treatment is generally performed using a muffle furnace or an atmospheric furnace to produce an insoluble and infusible initial heat-treated product, which is carbonized and then molded, pulverized, and classified. there were. However, in such a method, the steps are complicated and the productivity is low, and industrialization is difficult.

  In addition, the synthetic pitch obtained by polymerizing condensed polycyclic hydrocarbons such as naphthalene and methylnaphthalene in the presence of hydrogen fluoride and boron trifluoride in the super strong acid catalyst is several There was a characteristic of melting and foaming to 10 times the volume. For this reason, the method of carbonization as it is has a drawback that it is difficult to industrialize because the volumetric efficiency is extremely low.

In order to suppress melt foaming in the carbonization process, a granular or powdered carbonized product is charged in the reactor in advance, and heat treatment is performed by supplying raw material pitch and the like while stirring with a stirring blade or a twin-screw rotating machine. Is disclosed (for example, see Patent Document 1). However, in these methods, a carbonized material having a low specific gravity is used as a medium, so that lumps are easily formed, and in order to sufficiently flow the contents, a complicated stirring mechanism is required, which leads to an expensive apparatus. there were.
JP 7-286181 A

An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a cheap and useful method for producing a carbonized product with a simple apparatus and process.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have made a plurality of particles of metal or ceramics flow in the heat treatment apparatus maintained at a constant temperature. By supplying a carbonized precursor to the heat treatment apparatus, the carbonized material adheres to the surface of the granular material, and the carbonized material attached by further processing at a temperature higher than the heat treatment temperature easily peels from the granular material. Activated carbon obtained by activating the peeled carbonized material is useful as an electrode material for an electric double layer capacitor, and a carbon material obtained by heat treating the peeled carbonized material at a temperature exceeding 900 ° C. The present invention has been found to be useful as a negative electrode material for secondary batteries. That is, the present invention is as follows.
(1) A method for producing a carbonized product comprising the following steps (a) and (b).
(A) In a heat treatment apparatus maintained at a temperature of 400 ° C. or higher and 700 ° C. or lower, a plurality of particles made of metal or ceramics are charged and flown, and a carbonized precursor is supplied into the apparatus. A step of attaching a carbonized product to the surface of the granular material by heat treatment
(B) A step of separating the carbonized material from the granular material by heating the carbonized material adhering to the surface of the granular material to a temperature higher than the heat treatment temperature in the step (a) and a temperature of 900 ° C. or less.
(2) The method for producing a carbonized product according to the above (1), wherein the carbonized precursor is obtained by polymerization in the presence of hydrogen fluoride and boron trifluoride using a condensed polycyclic hydrocarbon as a raw material.
(3) The method for producing a carbonized product according to the above (1) or (2), wherein the heat treatment apparatus used in the step (a) is a rotary kiln.
(4) The method for producing a carbonized product according to the above (3), wherein the peripheral speed of the rotary kiln when heat treating the carbonized precursor is in the range of 0.1 to 10 m / min.
(5) The method for producing a carbonized product according to any one of (1) to (4), wherein the charged amount of the granular material with respect to the internal volume of the heat treatment apparatus is in the range of 1 to 50 vol%.
(6) The method for producing a carbonized product according to any one of the above (1) to (5), wherein the true specific gravity of the granular material is 2 g / cc or more.
(7) The method for producing a carbonized product according to any one of (1) to (6), wherein the granular material is stainless steel, alumina, or zirconia.
(8) A carbonized product obtained by the method according to any one of (1) to (7) above.
(9) An electric double layer capacitor obtained by adding 1 to 4 parts by weight of an alkali metal hydroxide to 1 part by weight of the carbonized product described in (8) above and subjecting it to activation treatment in a temperature range of 400 to 900 ° C. Activated carbon for electrodes.
(10) A carbon material for a negative electrode of a lithium secondary battery obtained by heat-treating the carbonized material according to (8) above at a temperature exceeding 900 ° C.

  By carrying out the present invention, an inexpensive and useful carbonized product can be produced with a simple apparatus and process, and its industrial significance is extremely great.

  The carbonized precursor (hereinafter referred to as raw material carbon) used in the present invention is not particularly limited, and for example, petroleum pitch, coal tar pitch, PVC (chlorinated polyvinyl), synthetic pitch and the like are used. Among them, condensed polycyclic hydrocarbons such as naphthalene, methylnaphthalene, anthracene, phenanthrene, acenaphthene, acenaphthylene, and pyrene are used as super strong acids as shown in Japanese Patent No. 2931593, Japanese Patent No. 2621253, or Japanese Patent No. 2526585. Unlike other pitches, synthetic pitches obtained by polymerizing in the presence of hydrogen fluoride and boron trifluoride as the catalyst are most suitable because of their high chemical purity, controllable properties, and high crystallinity. Used.

  The heat treatment apparatus used in the present invention is not particularly limited as long as it can withstand a high temperature of at least 400 ° C. and has a mechanism for flowing the granular material charged in the apparatus. Either a vertical type or a horizontal type may be used, and there is no problem even if a stirring blade, a spiral, or the like is used as a mechanism for causing the granular material to flow. The material such as the reactor and the stirring blade is not particularly limited as long as it can withstand the temperature required for heat treatment and the corrosiveness of the generated inorganic gas and raw material carbon, but typical materials include stainless steel and the like. It is done.

  The granular material used in the present invention is used as a heat medium and a moving medium, and the material is not limited, but is selected from those made of metal or ceramic from the viewpoint of quality and availability. Of these, stainless steel, alumina, zirconia, and the like that are relatively inexpensive and excellent in hardness and toughness are suitable. The true specific gravity of the granular material is preferably 2 g / cc or more. When the true specific gravity is 2 g / cc or more, it is difficult to form a lump of carbonized material, and it becomes easy to maintain fluidity.

  The shape of the granular material is not particularly limited as long as it does not have a sharp pointed portion, and may have irregularities on the surface, but a sphere or an elliptical sphere is preferably used. Most preferably, it is a spherical object usually used for industrially produced ball mills or bearings. Use of sharply shaped granular materials is not preferable because the edges and the surface of the reactor and granular materials are scratched or impurities are mixed due to the scratches.

  The size of the granular material is not particularly limited because there is an optimum size depending on the size of the apparatus, the operating conditions, the material of the granular material, etc., but in the case of a spherical shape, for example, in the range of 1 mm to 100 mm in diameter. Is used. Those having a diameter of 10 mm to 50 mm are preferably selected. Moreover, there is no restriction | limiting in the kind of granular material used at once, A single kind may be sufficient and it may use 2 or more types together at once.

  In the method of the present invention, a plurality of granular materials made of metal or ceramics are charged and flowed into a heat treatment apparatus maintained at a temperature within a certain range, and carbon is supplied by supplying raw carbon into the apparatus. A step of attaching a chemical compound to the surface of the granular material (step (a)), and heating the granular material to which the carbonized material is adhered to a temperature higher than the heat treatment temperature of step (a) and not higher than 900 ° C. The process (process (b)) which isolate | separates a carbonized material from this granular material by this is included. The step (b) may be performed following the step (a) using one heat treatment apparatus, and the contents are transferred to another heat treatment apparatus after the step (a) using a plurality of heat treatment apparatuses. After that, step (b) may be performed.

  In the step (a), the amount of the granular material charged into the heat treatment apparatus varies depending on the type of the heat treatment apparatus, the type of the granular material, etc., but is 1 to 50 vol%, preferably 3 to 30 vol with respect to the internal volume of the heat treatment apparatus. %, More preferably in the range of 5 to 15 vol%. When the amount is too large, the amount of raw material carbon is reduced, so that the production efficiency is lowered. On the other hand, when the amount is too small, the carbonized material adheres firmly to the inner wall surface (transmission surface) of the heat treatment apparatus and is not preferable because it does not peel off even if the step (b) is performed.

  In the case of performing the heat treatment in the step (a), the granular material charged in the heat treatment apparatus is caused to flow by the stirring apparatus or by rotating the apparatus main body like a rotary kiln. The stirring speed of the stirring blade and the rotation speed of the kiln are not particularly limited because they are determined according to the size of the apparatus, the properties of the raw material carbon, the type of the granular material, the supply speed of the raw material carbon, and the like. When a rotary kiln is used as the heat treatment apparatus in step (a), the peripheral speed of the kiln main body is usually in the range of 0.1 to 10 m / min, preferably 0.5 to 8 m / min, more preferably 1 to 1. The range is 5 m / min. When the peripheral speed is too fast, the carbonized material is likely to adhere to the wall surface, and when the peripheral speed is too slow, the heat transfer efficiency is lowered and the production speed is lowered.

  The heat treatment temperature in the step (a) depends on the properties and feed rate of the raw material carbon, but is usually performed in the range of 400 to 700 ° C., for example, the presence of hydrogen fluoride and boron trifluoride in the superacid catalyst for the condensed polycyclic hydrocarbon. In the synthetic pitch obtained by polymerization under the heat treatment, heat treatment is performed in the range of 500 to 600 ° C. If the heat treatment temperature is too low, a large amount of carbonized material adheres to the transmission surface of the heat treatment apparatus, which is not preferable. On the other hand, if the heat treatment temperature is too high, a heterogeneous carbonized product is not preferable. Moreover, the supply of the raw material carbon in the step (a) may be continuous or intermittent as long as the temperature in the heat treatment apparatus is constant.

  In the step (b), after the step (a) is completed, the carbonized material is peeled from the granular material by heating the granular material to which the carbonized material is attached to a temperature higher than the heat treatment temperature of the step (a). The temperature necessary for peeling off the carbonized product in this step depends on the type of raw carbon, but is usually 500 ° C. or higher and 900 ° C. or lower. The exfoliated carbonized material and the granular material are separated by using a device such as a vibration sieve device, and the granular material is recovered and reused.

  If necessary, the carbonized material separated from the granular material is converted into a desired carbon material through a firing process at a higher temperature, an activation process, a pulverization process, a classification process, or a molding. The carbon material is used as a raw material for power storage materials such as electrode materials for electric double layer capacitors and negative electrode materials for lithium secondary batteries, and high-tech fields such as semiconductors, nuclear power, nuclear fusion, and aerospace. Used.

  When the carbonized material obtained by the present invention is used as an electrode material for an electric double layer capacitor, the carbonized material obtained by separation from the granular material in the step (b) is used as a raw material after further high-temperature treatment if necessary. . First, the carbonized product is pulverized to an average particle size of about 15 μm and mixed with an activator. As the activator, zinc chloride or an alkali metal compound is used. Among the alkali metal compounds, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide are preferable, and potassium hydroxide is particularly preferable. When potassium hydroxide is used, 1 to 4 parts by weight of potassium hydroxide is uniformly mixed with 1 part by weight of the carbonized powder, and heated to 400 to 900 ° C. under an inert gas stream. Hold for 20 hours. After completion of the reaction, the mixture is allowed to cool, washed with water or alcohol, and dried to obtain activated carbon for an electric double layer capacitor electrode.

When the carbonized material obtained by the present invention is used as a carbon material for a negative electrode of a lithium secondary battery, the carbonized material obtained by separating from the granular material in the step (b) is pulverized and used at a temperature exceeding 900 ° C. Accordingly, a high purity and highly graphitizable carbon powder can be obtained by heat treatment at a predetermined temperature of 2000 ° C. or lower. Further, by performing heat treatment at a temperature of 2000 ° C. or higher, a graphite powder for a lithium secondary battery negative electrode having a high purity and a high graphitization degree is produced.
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Production example (Manufacture of raw material pitch)
A 43 L autoclave made of Hastelloy equipped with a heating device, a stirring device, an outlet, and a nitrogen introduction line was charged with 15 kg of naphthalene, 750 g of hydrogen fluoride, and 635 g of boron trifluoride. After heating up to 270 degreeC in 1 hour, it heated at the same temperature for 4 hours, stirring. Subsequently, the upper outlet was gradually opened to normal pressure, and heated nitrogen at 350 ° C. was introduced to completely remove the catalyst, thereby obtaining a raw material pitch having a softening point of 230 ° C.

Example 1
A rotary kiln with a retort internal volume of 10 L (diameter: 20 cm) equipped with a kerosene burner heating device, a raw material supply device, a nitrogen circulation device, and an exhaust gas line, a stainless steel ball with a diameter of 3/4 inch (true specific gravity: 7.9 g / cc) ) Was charged in an amount of 5 kg (6.4 vol%). An operation of continuously feeding the raw material pitch obtained in the production example at 1 kg / h while keeping the internal temperature constant at 550 ° C. while rotating the kiln at 6 rpm (circumferential speed: 3.8 m / min) under nitrogen flow. 3 hours. After cooling, the contents were taken out, and the carbonized product was uniformly attached to the balls. Further, the carbonized material adhering to the ball was heated to 700 ° C. in a tubular furnace at 5 ° C./min in a nitrogen atmosphere, and kept at this temperature for 2 hours. After standing to cool, the carbonized product separated from the balls was 2.4 kg.

  In order to evaluate as an electrode material for an electric double layer capacitor, the following treatment was performed. The carbonized product was pulverized to an average particle size of 15 μm by an impact pulverizer, 2 parts by weight of potassium hydroxide was uniformly mixed with 1 part by weight of the obtained carbon powder, and 700 ° C. at 5 ° C./min in a nitrogen atmosphere. The temperature was raised to 0 ° C., and the activation treatment was carried out at this temperature for 3 hours. After cooling to room temperature, it was poured into 2-propanol, and filtration and washing with water were repeated until the filtrate became neutral.

The obtained activated carbon was mixed at a weight ratio of 90: 5: 5 of activated carbon: conductive filler (Ketjen black): binder (Teflon (registered trademark)) to prepare an electrode. For the electrode evaluation, a glass bipolar cell was used, and a glass fiber separator was sandwiched between a pair of electrodes and accommodated in the cell. As the electrolytic solution, propylene carbonate in which 1 mol / liter of tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) was dissolved was used.

Charged to a voltage of 2.7 V at a constant current of 100 mA / g in an argon atmosphere at room temperature, and further charged at 2.7 V for 2 hours, then discharged to 0 V at a constant current of 100 mA / g and discharged. The capacitance was calculated from the amount of electricity. The capacitance was calculated according to the following formula based on the carbon weight (activated carbon) in both the positive and negative electrodes. The capacitance Cv (F / cc) per volume was calculated by multiplying the capacitance Cw (F / g) per weight by the electrode density.
Capacitance Cw (F / g) = Discharge electric quantity (AH / g) × 3600 / 2.7
As a result, the capacitance per weight was 37.0 F / g, the capacitance per volume was 34.0 F / cc, and the electrode density was 0.92 g / cc.

Example 2
The raw material pitch was carbonized under the same conditions as in Example 1 except that the rotation speed of the kiln was 2 rpm (peripheral speed: 1.3 m / min).
In order to evaluate as an electrode material for an electric double layer capacitor, a pulverization process and an activation process were performed in the same manner as in Example 1. Capacitance was measured using the obtained activated carbon. As a result, the capacitance per weight was 37.5 F / g, the capacitance per volume was 36.0 F / cc, and the electrode density was 0.95 g / cc.

Example 3
The raw material pitch was carbonized under the same conditions as in Example 1 except that the rotation speed of the kiln was 12 rpm (circumferential speed 7.5 m / min).
In order to evaluate as an electrode material for an electric double layer capacitor, a pulverization process and an activation process were performed in the same manner as in Example 1. Capacitance was measured using the obtained activated carbon. As a result, the capacitance per weight was 36.0 F / g, the capacitance per volume was 29.2 F / cc, and the electrode density was 0.81 g / cc.

Example 4
A SUS310 rotary kiln with a retort internal volume of 150 L (diameter: 60 cm) equipped with an electric heater, raw material supply device, nitrogen flow device, exhaust gas line, product discharge port, zirconia ball with a diameter of 25 mm (true specific gravity: 6.0 g / cc) ) Was charged 60 kg (6.7 vol%). An operation in which the internal temperature is kept constant at 550 ° C. and the raw material pitch obtained in the production example is continuously supplied at 20 kg / h while rotating the kiln at 2 rpm (circumferential speed 3.8 m / min) under nitrogen flow. For 5 hours. Next, the temperature was raised to 700 ° C. and kept at this temperature for 1 hour. After cooling, the contents were discharged and the carbonized product separated from the ball was 25.2 kg.
In order to evaluate as an electrode material for an electric double layer capacitor, the obtained carbide was subjected to activation treatment after pulverization in the same manner as in Example 1. Capacitance was measured using the obtained activated carbon. As a result, the capacitance per weight was 39.3 F / g, the capacitance per volume was 38.1 F / cc, and the electrode density was 0.97 g / cc.

Example 5
3 kg of alumina balls (true specific gravity: 3.9 g / cc) having a diameter of 15 mm were charged in a 5 L stainless steel reaction kettle equipped with an electric heater, stirrer, nitrogen flow device and exhaust gas line (17 vol%). ). Stirring was performed at a rotation speed of 30 rpm in a nitrogen atmosphere, and an operation of continuously supplying the raw material pitch at 120 g / hr while keeping the internal temperature constant at 550 ° C. was performed for 3 hours. When it was taken out after cooling, the carbonized product was uniformly attached to the ball. Further, the carbonized product was heated to 700 ° C. in a tubular furnace at 5 ° C./min in a nitrogen atmosphere and held at this temperature for 2 hours. After standing to cool, the carbonized product separated from the balls was 300 g.
In order to evaluate as an electrode material for an electric double layer capacitor, the carbonized material separated from the ball was treated in the same manner as in Example 1. Capacitance was measured using the obtained activated carbon. As a result, the capacitance per weight was 39.4 F / g, the capacitance per volume was 36.6 F / cc, and the electrode density was 0.93 g / cc.

Example 6
In order to evaluate as a negative electrode material for a lithium secondary battery, the carbonized powder obtained in Example 1 was graphitized in argon at 3000 ° C. for 1 hour. 10 parts by weight of polyvinylidene fluoride powder (binder) is added to 90 parts by weight of the obtained graphite powder (average particle size: 15 μm), and after blending and mixing dimethylformamide as a solvent, it is applied onto a copper foil and dried. A test piece for evaluation was cut out into 1 cm square. Next, a solution (concentration: 1.0 mol / L) in which LiPF ₆ was dissolved in two kinds of mixtures having a blending ratio of ethylene carbonate / diethyl carbonate of 1/1 was used as an electrolytic solution, and a polypropylene microporous film having a thickness of 50 μm. A half cell was prepared using as a separator. Note that lithium metal having a diameter of 16 mm and a thickness of 0.5 mm was used as a counter electrode. In addition, a small piece of lithium metal was used as a reference electrode in the same manner as the counter electrode.
Constant current charging was performed until the electrode potential of the test piece for evaluation with respect to the reference electrode reached 1 mV at a current density of 0.2 mA / cm ² . Subsequently, constant current discharge was performed until the electrode potential of the test piece for evaluation with respect to the reference electrode was 1.5 V at a current density of 0.2 mA / cm ^{2. The} charge capacity was 367 mAh / g, and the discharge capacity was 340 mAh / g. The charge / discharge efficiency was 92.0%.

Comparative Example 1
The rotary kiln used in Example 1 was charged with 1 kg of the raw material pitch obtained in the production example, heated up to 550 ° C. over 1 hour while rotating at 6 rpm (peripheral speed: 3.8 m / min), then 3 at the same temperature. Maintained for hours. When it was taken out after being allowed to cool, a part of the contents overflowed from the retort, and a uniform carbonized product was not obtained as a whole.

Comparative Example 2
The same heat treatment operation as in Example 1 was carried out except that 5 kg (true specific gravity: 1.5 g / cc) of carbonized powder after heat treatment obtained in Example 1 was charged in place of 5 kg of stainless steel balls. I did it. When it was taken out after being allowed to cool, the carbonized product adhered to the inner wall of the kiln and could not be taken out.

Claims (10)

A method for producing a carbonized product comprising the following steps (a) and (b):
(A) In a heat treatment apparatus maintained at a temperature of 400 ° C. or higher and 700 ° C. or lower, a plurality of particles made of metal or ceramics are charged and flown, and a carbonized precursor is supplied into the apparatus. A step of attaching a carbonized product to the surface of the granular material by heat treatment
(B) A step of separating the carbonized material from the granular material by heating the carbonized material adhering to the surface of the granular material to a temperature higher than the heat treatment temperature in the step (a) and a temperature of 900 ° C. or less.   2. The method for producing a carbonized product according to claim 1, wherein the carbonized precursor is obtained by polymerization in the presence of hydrogen fluoride and boron trifluoride using a condensed polycyclic hydrocarbon as a raw material.   The method for producing a carbonized product according to claim 1 or 2, wherein the heat treatment apparatus used in step (a) is a rotary kiln.   The method for producing a carbonized product according to claim 3, wherein the peripheral speed of the rotary kiln when the carbonized precursor is heat-treated is in the range of 0.1 to 10 m / min.   The method for producing a carbonized product according to any one of claims 1 to 4, wherein a charged amount of the granular material with respect to an internal volume of the heat treatment apparatus is in a range of 1 to 50 vol%.   The true specific gravity of a granular material is 2 g / cc or more, The manufacturing method of the carbonized material in any one of Claims 1-5.   The method for producing a carbonized product according to any one of claims 1 to 6, wherein the granular material is stainless steel, alumina, or zirconia.   Carbonized material obtained by the method according to any one of claims 1 to 7.   An activated carbon for an electric double layer capacitor electrode obtained by adding 1 to 4 parts by weight of an alkali metal hydroxide to 1 part by weight of the carbonized product according to claim 8 and performing an activation treatment in a temperature range of 400 to 900 ° C.   The carbon material for lithium secondary battery negative electrodes obtained by heat-processing the carbonized material of Claim 8 at the temperature over 900 degreeC.