JP6504392B2 - Method of producing carbon fine particles - Google Patents

Description

The present invention relates to how to produce the carbon particles from the black liquor and the like to be discharged in the paper mill.

  Conventionally, in a paper mill, a large amount of black liquor is discharged in a digestion process, and the black liquor contains an organic chemical such as lignin in addition to alkaline chemicals such as sodium and sulfur derived from a digestion chemical solution.

  At present, various studies are being made on the effective utilization of lignin contained in this black liquor. For example, Patent Document 1 proposes a method for producing carbon fine particles from a lignin-containing solution. According to this proposal, a lignin-containing solution is formed into fine droplets and dried to form fine particles, and the fine particles are thermally decomposed to produce carbon fine particles. The same document expects that carbon fine particles produced in this manner will be substitutes such as carbon black.

  The same document also proposes making hollow carbon fine particles to be produced, and proposes mixing an inorganic salt with a lignin-containing liquid before being formed into fine droplets. As a proposal of mixing an inorganic salt with a lignin-containing solution, in addition to Patent Document 1, there is also a proposal of mixing lithium carbonate with a lignin-containing solution (see Patent Document 2).

  The above documents also disclose various test results, and it is clarified that the carbon fine particles produced are useful. However, all of the above documents remain at the laboratory level and do not propose methods for industrialization or mass production.

  Moreover, when the present inventors conducted various tests, they found that the dispersion liquid in which the obtained carbon fine particles were dispersed was inferior in conductivity.

JP, 2009-155199, A JP, 2010-168251, A

The main object of the present invention is to provide is to provide a manufacturing how carbon fine particles having no problems with mass production possible, and electrically conductive.

The present invention for solving this problem is as follows.
[Invention of Claim 1]
A method of producing carbon fine particles from a lignin-containing solution, which comprises:
The lignin-containing solution is acidified and dehydrated to form a dehydrated cake,
The slurry of this dewatered cake is mixed with inorganic salt,
The obtained slurry containing the inorganic salt is formed into droplets with a solid content concentration of 1.0% or less , and dried to obtain inorganic salt-containing fine particles,
The inorganic salt-containing fine particles are thermally decomposed to remove the inorganic salt to obtain carbon fine particles,
A method of producing carbon fine particles characterized by

[Invention according to claim 2]
The droplet formation is performed such that the spray pressure of the slurry containing the inorganic salt is 0.5 MPa to 1.3 MPa.
The method for producing carbon fine particles according to claim 1.

[Invention of Claim 3 ]
A method of producing carbon fine particles from a lignin-containing solution, which comprises:
The lignin-containing solution is acidified and dehydrated to form a dehydrated cake,
The slurry of this dewatered cake is mixed with inorganic salt,
The mixture of the inorganic salts, have rows such that the inorganic salt is 10 to 30 times the mass of the lignin in said slurry,
The slurry containing the obtained inorganic salt is formed into droplets and dried to obtain inorganic salt-containing fine particles,
The inorganic salt-containing fine particles are thermally decomposed to remove the inorganic salt to obtain carbon fine particles,
A method of producing carbon fine particles characterized by

[Invention of Claim 4 ]
The lignin-containing solution is acidified and dehydrated to form a dehydrated cake,
The slurry of this dewatered cake is mixed with inorganic salt,
The slurry containing the obtained inorganic salt is formed into droplets and dried to obtain inorganic salt-containing fine particles,
The inorganic salt-containing particles were thermally decomposed, to obtain a carbon-containing particulates to remove inorganic salts,
The average secondary particle diameter of the fine carbon particles you less 4.0 .mu.m,
A method of producing carbon fine particles characterized by

[Invention of Claim 5 ]
The specific surface area shall be the 900m ² / g or more,
The method for producing carbon fine particles according to claim 5.

[Invention of Claim 6 ]
The oil absorption amount shall be the 600ml / 100g or more,
The method for producing carbon fine particles according to claim 5.

According to the present invention, mass production possible, and the manufacturing how carbon fine particles having no conductivity issues.

It is a manufacturing equipment flow figure of carbon particulates (a lignin extraction process etc. are shown). It is a manufacturing equipment flow figure of carbon particulates (inorganic salt mixing process, a droplet formation and drying process, a thermal decomposition process, etc. are shown). It is a manufacturing equipment flow figure of carbon particulates (a washing process, a drying process, etc. are shown). It is a detailed flow figure of a washing process. They are a sample photograph (1) of carbon particulates, and a magnified sample photograph (2) of an outer shell portion of the carbon particulates. It is a sample photograph (1) of carbon particulate concerning another example, and an expansion sample photograph (2) of an outer shell part of this carbon particulate. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in a case where dropletization is performed at a flow rate of 4.0 L / h. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in a case where dropletization is performed at a flow rate of 2.2 L / h. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in a case where dropletization is performed at a flow rate of 2.0 L / h. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in a case where dropletization is performed at a flow rate of 1.6 L / h. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in case dropletization is performed by spray pressure 0.5MPa. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in case dropletization is performed at spray pressure 1.0MPa. They are a sample photograph (1) (2) of carbon particulates in case solid content concentration of slurry which is formed into droplets is set to 6.00%, and a magnified sample photograph (3) of the carbon particulates. They are a sample photograph (1) (2) of carbon particulates in case solid content concentration of slurry which is formed into droplets is 1.00%, and a magnified sample photograph (3) of the carbon particulates. They are a sample photograph (1) (2) of carbon particulates in case solid content concentration of slurry which is formed into droplets is 0.80%, and a magnified sample photograph (3) of the carbon particulates. They are a sample photograph (1) (2) of carbon particulates in case solid content concentration of slurry which is formed into droplets is 0.50%, and a magnified sample photograph (3) of the carbon particulates. They are a sample photograph (1) (2) of carbon particulates in case solid content concentration of slurry which is formed into droplets is 0.10%, and a magnified sample photograph (3) of the carbon particulates. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in the case of making a mineral salt into droplets 3 times as many as lignin of lignin. They are a sample photograph (1) of carbon particulates in, and a magnified sample photograph (2) of the carbon particulates in the case where the inorganic salt is dropped as 10 times the mass of lignin. They are a sample photograph (1) of carbon particulates in, and an expansion sample photograph (2) of this carbon particulates in the case of making a mineral salt into droplets 30 mass times of lignin, and making it into droplets.

Next, an embodiment of the present invention will be described.
In the present invention, a solution after extraction with bioethanol can be used as a lignin-containing solution as a raw material, but in the following, an example of using black liquor discharged in a digestion process of a paper mill is exemplified. Explain to.

[Dilution of black liquor etc.]
The black liquor discharged in the digestion process of the paper mill is usually concentrated to a degree that can be self-combustible in the concentration process, and the concentrated black liquor is burned in a recovery boiler to recover heat and the like. In addition, alkaline chemicals contained in black liquor are reduced and reused as cooking chemicals.

  The concentration step of the black liquor is equipped with a concentration apparatus such as an evaporator (evaporator), and the solid content (total solid: TS) concentration of the black liquor (which was about 10% by mass to 20% by mass at the beginning) It is concentrated until it becomes about 60 mass%-80 mass% only [concentration].

  In the present embodiment, a black liquor in the middle of concentration in the concentration step, preferably a black liquor having a concentration of 20% by mass to 35% by mass, is used. However, the concentration of black liquor is usually performed in multiple stages from the viewpoint of the relationship between the amount of treatment and the capacity of equipment, scale prevention, etc. There are cases where black liquor having a concentration of 20% by mass to 35% by mass does not exist. In such a case, dilute the high concentration black liquor and use it.

  Specifically, for example, as shown in FIG. 1, low concentration (for example, concentration 10% by mass to 20% by mass) black liquor X1, medium concentration (for example, concentration 50% by mass to 60% by mass) black liquor In the case where black liquor X3 having a high concentration (for example, a concentration of 60% by mass to 80% by mass) is present, first, a part or all of the medium concentration black liquor X2 is drawn To the dilution tank 20 through the flow path R1. This delivery can also be changed to a method of delivery using a container or the like, depending on the local conditions, for example, the positional relationship between the place where the black liquor is concentrated and the place where the dilution tank 20 is provided.

  In the dilution tank 20, the black liquor is mixed with water W such as filtered fresh water so that the concentration of the black liquor becomes 20% by mass to 35% by mass, preferably 25% by mass to 30% by mass, more preferably Is diluted to 25% by mass to 28% by mass. When the concentration of black liquor is diluted to less than 20% by mass, the efficiency of lignin extraction (recovery) is deteriorated, which may make it unsuitable for industrialization or mass production. On the other hand, when the concentration of the black liquor is more than 35% by mass, the contact between the black liquor and the acidification gas G1 may be uneven in the acidification step described later. Furthermore, when the concentration of the black liquor is more than 35% by mass, the ash fraction of the first dewatered cake C1, which will be described later, may not be sufficiently reduced.

  The black liquor in the dilution tank 20 can be heated if necessary, and can be, for example, 30 ° C to 60 ° C, preferably 30 ° C to 45 ° C.

[First acidification etc.]
The black liquor diluted in the dilution tank 20 is sent to the acidification treatment tank 30 through the flow path R2, and is supplied to the acidification treatment tank 30. In the acidification treatment tank 30, the acidification gas G1 is directly blown into the tank 30 to acidify the black liquor to lower the pH of the black liquor (acidification treatment).

  As the acidifying gas G1, for example, sulfuric acid gas, organic acid gas, hydrogen chloride gas, hydrogen nitrate gas, carbon dioxide gas, chlorine dioxide gas, etc. can be used, but carbon dioxide gas or carbon dioxide gas containing gas It is preferred to use.

  When carbon dioxide gas is used as the acidifying gas G1, the carbon dioxide gas can be newly prepared, but the exhaust gas G4 from the bag filter 91 described later and the external heat jacket 100a provided for the rotary kiln 100 can be used. It is preferable to use the exhaust gas G5 as all or part of the acidifying gas G1. By using the exhaust gases G4 and G5, it is possible to reduce the emission of carbon dioxide gas in the exhaust gases G4 and G5, that is, the greenhouse gas, and it is possible to prevent global warming.

  Furthermore, in the present embodiment, in order to more reliably prevent the solid content from being precipitated in the acidification treatment tank 30, the stirring blade 31 with the motor M as a driving source is provided in the acidification treatment tank 30. The black liquor is stirred by the stirring blade 31.

  In the above-mentioned acidification step, the blowing of the acidifying gas G1 is preferably performed so that the pH of the black liquor which is initially 13 or higher is preferably 8.5 to 10, more preferably pH 9.0 to pH 9.5. I do. In the case of blowing of the acidifying gas G1 such that the pH of the black liquor exceeds 10, lignin may not be sufficiently precipitated.

  If the concentration of black liquor rises due to the transport process of black liquor, precipitation of lignin, sodium etc., water W such as filtered fresh water is appropriately supplied into the acidification treatment tank 30 to adjust the concentration of black liquor It is preferable to do.

[First dehydration etc.]
The black liquor in which lignin is deposited is fed through the flow path R3 to the filter press 40 which is a dewatering means, and pressed into the filter press 40. The black liquor pressed into the filter press 40 is further squeezed and dewatered.

  The dehydrated filtrate D1 discharged as a result of this press-in or squeezing can be disposed of as a waste solution, but it is preferable to return it to the black liquor concentration step 10 by passing it through the flow path R4. As a result of this return, ash such as sodium contained in the dehydrated filtrate D1 is also returned to the concentration step 10. Therefore, it becomes possible to reuse as a cooking chemical by reducing the ash content such as sodium. The dehydrated filtrate D1 usually contains 20 to 25% by mass of an ash content such as sodium.

  Dehydration in the filter press 40 produces a dewatered cake C1 (hereinafter, this dewatered cake C1 is also referred to as “first dewatered cake C1”). The ash fraction of the first dehydrated cake C1 is preferably 0% by mass to 20% by mass, and more preferably 0% by mass to 15% by mass. If the ash fraction of the first dewatered cake C1 exceeds 30% by mass, the ash fraction of the second dewatered cake C2, which will be described later, may not be sufficiently reduced.

  Dewatering in the filter press 40 is preferably performed so that the moisture content of the first dehydrated cake C1 is 40% by mass to 60% by mass, and more preferably 45% by mass to 55% by mass . Dehydration to a water content of less than 40% by mass has no significant effect on removing ash such as sodium from the first dewatered cake C1, which is not preferable in terms of cost-effectiveness. On the other hand, if the water content exceeds 60% by mass, there is a possibility that the ash content such as sodium can not be sufficiently removed from the first dewatered cake C1.

[Concentration control and second acidification etc.]
The first dewatered cake C1 obtained in the filter press 40 is transported to the slurrying tank 50 using a container or the like, and is supplied to the slurrying tank 50. Water S such as filtered fresh water and acid A such as sulfuric acid are supplied to the slurrying tank 50 together with the first dewatered cake C1, the first dewatered cake C1 is slurried, and acidification is promoted. The slurrying is performed so that the solid content concentration of the obtained slurry S1 is 15% by mass to 30% by mass, preferably 20% by mass to 25% by mass. Further, the acidification (supply of the acid A) is carried out so that the obtained slurry S1 has a pH of 1.0 to 4.0, preferably a pH of 1.5 to a pH 2.5.

  The supply of the acid A can be performed in the process of slurrying the first dewatered cake C1 or can be performed after completely slurrying. Moreover, as acid A, the thing of pH1.0-pH2.5 can be used, for example.

[Second dehydration etc.]
The slurry S1 obtained by adjusting the concentration and pH in the slurrying tank 50 (by advancing the acidification) is again sent to the filter press 40 through the flow path R5 and the above-described flow path R3, and is pressed into the filter press 40 Do. The pressure injection of the slurry S1 is preferably performed as quickly as possible after adjusting the pH, more preferably within 10 hours, particularly preferably within 5 hours. After adjusting the pH, if the time to press-in exceeds 24 hours, even if the ash fraction of the first dewatered cake C1 is adjusted to 20% by mass, the ash fraction of the second dewatered cake C2 is 3.0 mass There is a possibility that it can not be less than%. According to the test by the present inventors, the ash fraction of the second dewatered cake C2 was 8% by mass to 10% by mass when the time until the pressure injection was performed after adjusting the pH was 24 hours.

  The slurry S1 pressed into the filter press 40 is further squeezed and dewatered. The dewatered filtrate D2 discharged as a result of this press-in or squeezing can be disposed of as a waste liquid, but as in the case of the dewatered filtrate D1 described above, it should be returned to the black liquor concentration step 10 through the flow path R4. Can. By this return, it is possible to reuse the ash content such as sodium contained in the dehydrated filtrate D2 as a cooking chemical. However, the ash content contained in the dehydrated filtrate D2 is usually 15% by mass to 18% by mass. Therefore, waste disposal is also a useful choice.

  When the dewatering of the slurry S1 is completed, water (washing water) W such as filtered fresh water is supplied to the filter press 40 and squeezed again. The slurry S1 is washed by the supply and squeezing of the wash water W, and the ash fraction of the resulting dewatered cake C2 (hereinafter, this dewatered cake C2 is also referred to as the “second dewatered cake C2”) decreases.

  The washing of the slurry S1 can be performed only with the washing water W, but if necessary, the washing water W can be mixed with an acid A such as sulfuric acid to form a diluted acid, and this diluted acid can also be used. The diluted acid is preferably at pH 1.0 to pH 4.0, more preferably at pH 1.0 to pH 2.5.

  The ash fraction of the washing filtrate D3 discharged with the washing of the slurry S1 is usually 1% or less, and it is not efficient to return it to the concentration step 10 like the dehydration filtrates D1 and D2. Therefore, it is preferable to dispose of the waste liquid. However, when the acid A is mixed with the washing water W and washed as a diluted acid, it is preferable to flow to the slurrying tank 50 through the flow path R6 and to supply it to the slurrying tank 50. Since the acid (A) contained in the washing filtrate D3 is recycled by the supply of the washing filtrate D3, the amount of acid A to be newly added can be reduced.

  After the supply of the washing water W and the pressing again, the filter press 40 is blown with a replacement gas G2 such as nitrogen or air. By the blowing of the replacement gas G2, the water in the second dewatered cake G2 is replaced by the replacement gas G2, and the water content and the ash content decrease further.

  The moisture content of the secondary cake C2 obtained is preferably 40% by mass to 65% by mass, more preferably 45% by mass to 65% by mass, and particularly preferably 50% by mass to 65% by mass.

  The ash fraction of the second dehydrated cake C2 is preferably 0.0% by mass to 3.0% by mass, more preferably 0.0% by mass to 1.0% by mass, particularly preferably 0.0% by mass It is -0.5 mass%. In this embodiment, the first dewatered cake C1 obtained in the filter press 40 is once made into a slurry, dewatered again in the filter press 40, and the ash fraction of the second dewatered cake C2 is significantly reduced. It is intended. Therefore, the above slurrying and dehydration may not be repeated if the ash fraction can be sufficiently lowered. In addition, the effect by lowering an ash content rate is mentioned later.

  The second dehydrated cake C2 contains lignin as a main component (eg, 35% by mass to 60% by mass, preferably 45% by mass to 50% by mass), and lignin is in a state of being extracted from so-called black liquor . Therefore, mass production of black liquor, which is lignin-containing liquor, as it is, can be significantly facilitated as compared to the case where it is subjected to the process described below.

  In this embodiment, the dewatering means for obtaining the dewatered cake C1 and the dewatering means for obtaining the dewatered cake C2 are the same, and the filter press 40 is used as the dewatering means.

  From this point of view, it is preferable to make the dewatering means for obtaining the dewatered cake C1 identical to the dewatering means for obtaining the dewatered cake C2 from the viewpoint of the installation area etc. It is preferable to separate the dewatering means for obtaining the dewatered cake C1 from the dewatering means for obtaining the dewatered cake C2.

  It is also conceivable to use, for example, a belt press instead of the filter press as the dewatering means.

[Addition of inorganic salt etc.]
As shown in FIG. 2, the second dewatered cake C2 is transported to the stirring tank 70 using a container or the like, and is supplied to the stirring tank 70. In addition, water W such as inorganic salt X and filtered fresh water is supplied to the stirring tank 70. The inorganic salt X and the water W can also be supplied directly to the stirring tank 70 separately. However, in order to stabilize the process in the stirring tank 70, both X and W are once supplied to and mixed with the preparatory tank 60, and then sent to the stirring tank 70 through the flow path R7 and supplied to the stirring tank 70 It is preferable to do.

  As the inorganic salt X, sodium metasilicate is preferably used, and sodium metasilicate and sodium hydroxide are more preferably used in combination.

  The mixing mass ratio of lignin and inorganic salt X such as sodium metasilicate in the second dewatered cake C2 is 1:10 to 30 when importance is attached to the oil absorption of the finally obtained carbon fine particles. Preferably, 1:10 to 15 is more preferable.

  If the mixing mass ratio of the inorganic salt X is less than 10 times by mass, the oil absorption can not be sufficiently improved. When the content of the inorganic salt X is high, the conductivity of the finally obtained carbon fine particles is slightly reduced, but the dispersibility is improved. Therefore, the dispersion obtained by dispersing the carbon fine particles has a large conductivity. It will not be a problem.

  On the other hand, when the mixing mass ratio of the inorganic salt X exceeds 30 mass times, it becomes difficult to remove the inorganic salt X (in this embodiment, this removal is performed in the filter press 120 described later), and the inorganic salt There is a problem of reduced conductivity due to the retention of X.

  The stirring tank 70 of the present embodiment is provided with a stirring blade 71 driven by the motor M. By the stirring by the stirring blade 71, lignin and inorganic salt X in the second dehydrated cake C2 are uniformly mixed. Moreover, it is preferable to equip the stirring tank 70 or the above-mentioned preliminary | backup tank 60 with a heating apparatus, in order to enable the process in high concentration.

[Dropletization and drying etc.]
The slurry S2 containing lignin and inorganic salt X obtained in the stirring tank 70 is sent to the spray dryer 80 which is a dropletization / drying means through the flow path R8, and is dropletized and dried in the spray dryer 80. In the spray dryer 80, for example, air is blown from the air blowing means F, and the slurry S2 is sprayed from a spray nozzle (not shown). In addition, as a spray nozzle, a two fluid nozzle, a four fluid nozzle, etc. can be used, for example.

  When the slurry S2 is sent to the spray dryer 80, it is preferable to pass through a filter 75 such as a sieve. Passing the screen 75 prevents clogging of the spray nozzle by undissolved matter in the slurry S2.

  As the screen 75, for example, one of 150 to 250 mesh, preferably one of 200 mesh can be used.

  Hot air G3 is blown into the spray dryer 80 together with the slurry S2, and the slurry S2 is formed into droplets and dried to form inorganic salt-containing fine particles.

  The lignin concentration of the slurry S2 blown into the spray dryer 80 is preferably 4% by mass to 10% by mass and 6% by mass to 8% by mass on the premise that the ratio of lignin to inorganic salt X is constant. It is more preferable that there be. When the lignin concentration is less than 4% by mass, the particle size may not be maintained. On the other hand, when the lignin concentration exceeds 10% by mass, it may be difficult to remove the inorganic salt X in the filter press 120 described later.

  In the range of 4% by mass to 8% by mass of lignin concentration, the lignin concentration and the bulk specific gravity of the finally obtained carbon fine particles are linked, and when the lignin concentration is increased, the powder obtained by spray drying 80 On the other hand, when the lignin concentration is lowered, the bulk specific gravity of the powder obtained by the spray drying 80 tends to be high. Therefore, by adjusting the lignin concentration, it is possible to control the bulk specific gravity of the carbon fine particles finally obtained and the thickness of the shell.

  In the case of the above droplet formation, it is preferable to make solid content concentration of slurry S2 containing inorganic salt X into 1.0 mass% or less, and it is more preferable to make it 0.1 mass%-0.4 mass%. When the solid content concentration exceeds 1.0% by mass, the average secondary particle diameter of the finally obtained carbon fine particles may not be sufficiently reduced. On the other hand, when the solid content concentration is less than 0.1% by mass, particles may not be formed.

  In addition, the flow rate of the slurry S2 containing the inorganic salt X is not limited at the time of droplet formation, but 1.3 L / h to 1.9 L / h is preferable, and 1.3 L / h to 1. It is more preferable to set it as 5 L / h. If the flow rate is below 1.3 L / h, there may be problems with particle formation. On the other hand, when the flow rate exceeds 1.9 L / h, the average secondary particle size of the finally obtained carbon fine particles may not be sufficiently reduced.

  Furthermore, the droplet formation is preferably performed so that the spray pressure of the slurry S2 containing the inorganic salt X is 0.7 MPa to 1.3 MPa, and more preferably 0.5 MPa to 1.0 MPa. . If the spray pressure is less than 0.5 MPa, the average secondary particle size of the finally obtained carbon fine particles may not be sufficiently reduced. On the other hand, if the spray pressure exceeds 1.3 MPa, particles may not be recovered in the recovery facility.

  In addition, the temperature of the hot air G3 blown into the spray dryer 80 is preferably 280 ° C to 330 ° C, and more preferably 280 ° C to 320 ° C. It is particularly preferable that the temperature of exhaust air from the spray dryer 80 be 120 ° C. by adjusting the temperature in this manner.

  The inorganic salt-containing fine particles obtained in the spray dryer 80 are powdery, and are preferably blown by a fan to the cyclone 90 through the flow path R 9 and collected by the cyclone 90.

  In the cyclone 90, the inorganic salt-containing particles are collected and discharged from the bottom. On the other hand, the exhaust gas after the inorganic salt-containing particles are collected is blown to the bag filter 91 through the flow path R11. In the bag filter 91, fine inorganic salt-containing particles remaining in the exhaust gas are collected.

  The exhaust gas G4 after fine inorganic salt-containing particles are collected in the bag filter 91 can be exhausted to the atmosphere, but is sent to the acidification treatment tank 30 through the flow path R12 provided with the exhaust fan F2 to be acidic It is preferable to use it as the chemical gas G1. The exhaust gas G4 contains carbon dioxide gas and also has heat. Therefore, by using the exhaust gas G4 as the acidifying gas G1, the effective use and reduction of the carbon dioxide gas can be realized, and the heat of the exhaust gas G4 can be effectively used.

  Although a scrubber or the like may be used instead of the bag filter 91, the bag filter 91 may be used from the viewpoint of effective use of the heat of the exhaust gas G4 (for example, the exhaust gas G4 has a temperature of about 120 ° C.). It is preferable to use

[Pyrolysis etc.]
The inorganic salt-containing fine particles collected in the cyclone 90 and the bag filter 91 are sent through the flow path R10 to the external heat type rotary kiln 100 provided with the external heat jacket 100a which is a thermal decomposition means, supplied into the rotary kiln 100 and thermally decomposed. Do.

  The thermal decomposition is preferably performed at 600 ° C. to 1,400 ° C., more preferably at 950 ° C. to 1,400 ° C., and in the case of efficiently improving the electrical conductivity of the obtained carbon fine particles, 1,000 ° C. to 1,200 ° C. Is preferred.

  Furthermore, the thermal decomposition is preferably performed for 1 hour to 6 hours, and more preferably for 2 hours to 3 hours. Although the inorganic salt-containing fine particles of the present embodiment are hollow, if the thermal decomposition is rapidly performed, the water vapor concentration in the system increases, and the lignin component may be melted and the hollow shape can not be maintained. Moreover, in order to prevent water and crystal water contained in the inorganic salt-containing fine particles from remaining in the rotary kiln 100, it is preferable to stand at a temperature of 100 ° C. to 200 ° C. for 1 hour to 4 hours before the thermal decomposition treatment. .

  The thermal decomposition gas N1 generated at the time of thermal decomposition is used as a gas for combustion of the hot blast stove 101 which supplies hot air to the outer thermal jacket 100a. By using this thermal decomposition gas N1, it is possible to reduce the amount of use of the fuel N2 such as LPG gas to be newly supplied to the hot blast stove 101.

  The combustion gas generated by the hot blast furnace 101 is supplied into the external heat jacket 100 a and used as an external heat source of the rotary kiln 100. Further, the exhaust gas G5 discharged from the external heat jacket 100a after being used as an external heat source contains carbon dioxide gas as in the case of the exhaust gas G4, and also has heat. Therefore, it is preferable to send the exhaust gas G5 to the acidification treatment tank 30 through the flow path R13 and use it as the above-mentioned acidification gas G1. By using the exhaust gas G5 as the acidifying gas G1, it is possible to realize effective use and reduction of the emission amount of carbon dioxide gas, and the heat of the exhaust gas G5 is effectively used.

  The inorganic salt-containing fine particles C3 thermally decomposed in the rotary kiln 100 contain inorganic salts X derived from inorganic salts X mixed with the second dewatered cake C2, although the organic matter is thermally decomposed and carbonized. Therefore, next, the inorganic salt-containing fine particles C3 are washed to remove the inorganic salt from the inorganic salt-containing fine particles C3. The details will be described below.

[Slurrying etc.]
As shown in FIG. 3, the thermally decomposed inorganic salt-containing fine particles C3 are transported to the slurrying tank 110 using a conveyor or the like, and supplied to the slurrying tank 110. Water S such as filtered fresh water is supplied to the slurrying tank 110 together with the inorganic salt-containing fine particles C3, and the inorganic salt-containing fine particles C3 are slurried. The slurrying is performed so that the solid content concentration of the obtained slurry S3 is 10% by mass to 30% by mass, preferably 15% by mass to 20% by mass.

  The slurrying tank 110 is provided with a stirring blade 111 driven by a motor M. By the stirring by the stirring blade 111, the dispersion of the inorganic salt-containing fine particles C3 is rapidly performed, and the dispersion concentration is made uniform.

  The slurry S3 in the slurrying tank 110 can be heated, for example, to 60 ° C., if necessary. This heating is performed by heating the water W supplied to the slurrying tank 110, or by heating the slurrying tank 110 itself, or using the heat held by the inorganic salt-containing fine particles C3 after thermal decomposition. Can be done.

[Dehydration etc.]
The slurry S3 obtained in the slurrying tank 110 is sent to the filter press 120, which is a dewatering means, through the flow path R15, and pressed into the filter press 120. However, when the slurry S3 is to be transported, it is preferable to pass the slurry S3 through a filter screen 115 as a filter. By passing the slurry S3 through the screen 115, it is possible to uniformly remove the inorganic salt in the filter press 120, and it is possible to prevent the production of carbon fine particles in which the inorganic salt is not partially removed.

  It is also conceivable to use, for example, a belt press instead of the filter press 120 as the dewatering means. Further, as the screen 75, for example, one having 150 mesh to 250 mesh, preferably one having 200 mesh can be used. Furthermore, prior to pressing the slurry S3 into the filter press 120, the inorganic salt contained in the slurry S3 can be precipitated to remove the precipitated inorganic salt.

  The press-in filtrate D4 generated when the slurry S3 is pressed into the filter press 120 can be disposed of as a waste solution, but it is preferable to return it to the above-mentioned spare tank 60 and supply it to this spare tank 60. The filter press 120 is a means for removing the inorganic salt X, and the press-in filtrate D4 contains the inorganic salt X. Therefore, the inorganic salt X contained in the press-in filtrate D4 is recycled by returning the press-in filtrate D4 to the preliminary tank 60, and the amount of the inorganic salt X to be newly supplied to the preliminary tank 60 is reduced. be able to.

  In the present embodiment, as described above, the ash fraction of the second cake C2 is set to 3.0% or less. Therefore, the press-in filtrate D4 contains almost no ash derived from the digesting chemical, and therefore there is no risk that the ash will immediately be highly concentrated even if the press-in filtrate D4 is returned, that is, reused. Therefore, return of press fit filtrate D4 can be repeated multiple times, which is a great advantage in industrialization. The present inventors have confirmed that the press-in filtrate D4 can be used repeatedly about 30 times when the ash fraction of the second dehydrated cake C2 is 3%.

  The press-in filtrate D4 can be immediately returned to the preliminary tank 60, but as shown in FIG. 4, the pH and the electric conductivity are detected by the detection means 121, and the condition of the press-in filtrate D4 is confirmed. It is preferable to return it to the reserve tank 60. The pressure-in filtrate D4 at this time is usually pH 12 to pH 14, preferably pH 13 to pH 14. The electrical conductivity is usually 13 S / m to 20 S / m, preferably 18 S / m to 20 S / m.

  After the slurry S3 pressed into the filter press 120 is positively washed with water W such as filtered fresh water, it is primarily squeezed. The concentration of the inorganic salt X in the primary filtrate D5 discharged during the forward washing and the primary pressing is extremely reduced by the water W used for the forward washing of the inorganic salt X-containing one. Therefore, it is not efficient to return to the reserve tank 60, and preferably to the slurrying tank 110. The primary filtrate D5 discharged in this step preferably has a pH of 12 to 14, preferably 13 to 14, from the viewpoint of maintaining the pH at which the inorganic salt X is easily dissolved in the subsequent secondary washing. Is more preferable. The electrical conductivity is usually 8 S / m to 12 S / m, preferably 10 S / m to 12 S / m.

  When the primary pressing is finished, backwashing is performed using water W, and further secondary pressing is performed to obtain a dewatered cake C4. Further, when this secondary compression is completed, a replacement gas G6 such as nitrogen or air is blown into the filter press 120. By the blowing of the replacement gas G6, the moisture containing the inorganic salt X in the dehydrated cake C4 is replaced by the replacement gas G6, and the water content and the content rate of the inorganic salt X are further reduced.

  The secondary filtrate D6 discharged at the time of backwashing, secondary pressing and gas replacement can be immediately treated with waste liquid, but the pH and electric conductivity are detected by the detecting means 121, and is the inorganic salt X removed? It is preferable to check whether or not the progress of cleaning is in progress. In addition, secondary filtrate D6 discharged | emitted in this process is pH 8.0-pH 9.5 normally, Preferably it is pH 8.0-pH 9.0. The electrical conductivity is usually 100 μS / m to 1200 μS / m, preferably 100 μS / m to 500 μS / m.

  In this respect, when the removal of the inorganic salt X has not sufficiently proceeded, the treatment in the filter press 120 is further repeated, or the drying described below is performed, and then the dried product is slurried, and the filter press 120 etc. The removal of inorganic salt X can be advanced by utilizing.

[Drying etc]
The dewatered cake C4 is transported to various types of dryers such as natural convection type, constant temperature type, circulation type and the like using a container or the like, and dried by the dryer 130. However, since carbon fine particles have a very low bulk density, it is preferable to use a constant-temperature drier to dry, from the viewpoint of preventing scattering by hot air. The drying temperature is preferably 100 ° C to 130 ° C, more preferably 110 ° C to 130 ° C. This drying gives a dried product of carbon fine particles.

  The carbon fine particles obtained as described above preferably have an average secondary particle diameter of 4.0 μm or less, more preferably 1.0 μm to 2.0 μm, and particularly preferably 1.0 μm to 1.5 μm. When the average secondary particle diameter exceeds 4.0 μm, the dispersibility becomes worse, and the conductivity of the resin etc. in which the obtained carbon fine particles are dispersed becomes inferior.

  Here, the average secondary particle diameter of the carbon fine particles can be adjusted by adjusting the flow rate, the spray pressure, the solid content concentration, the blending ratio of the inorganic salt X, and the like in the droplet formation described above. Specifically, when the flow rate is reduced, the spray pressure is increased, the solid content concentration is reduced, and the blending ratio of the inorganic salt X is increased, the average secondary particle size decreases.

  The secondary particle diameter means the diameter of aggregated particles of primary particles. Incidentally, the structure means a structure in which primary particles are simply connected, and the presence means the shape of carbon fine particles before being crushed or dispersed.

Further, the resulting carbon particles has a specific surface area is preferably 900 meters ² / g or more, more preferably 900m ² / g~980m ² / g, particularly preferably 900m ² / g~960m ² / g. When the specific surface area is less than 900 m ² / g, the contact between the carbon fine particles is deteriorated, and the conductivity of the obtained dispersion of carbon fine particles is deteriorated.

  Furthermore, the carbon fine particles obtained have an oil absorption of preferably 600 ml / 100 g or more, more preferably 600 ml / 100 g to 1000 ml / 100 g, and particularly preferably 600 ml / 100 g to 800 ml / 100 g. When the oil absorption amount is less than 600 ml / 100 g, the dispersibility is deteriorated, and the conductivity of the dispersion in which the obtained carbon fine particles are dispersed is deteriorated.

  In addition, for example, in rubber applications, pigment applications, electric material applications, etc., it is required that the dispersibility of the carbon fine particles obtained is good, that the conductivity is good, etc. Therefore, the carbon fine particles have a hollow structure Solid structure is preferred.

  On the other hand, the dewatered cake C4 can be transported to the dispersion tank 141, where it can be mixed with water W such as filtered fresh water, an organic solvent or the like to form a dispersion of carbon fine particles (slurry). The dispersion liquid of carbon fine particles is sent to a wet crusher 140 such as a bead mill through a flow path R21, and the carbon fine particles are wet-crushed in the wet crusher 140. By this wet grinding, for example, carbon fine particles having a size of 1 μm to 20 μm are ground to 50 μm to 200 nm.

  The carbon fine particles after the wet pulverization can be commercialized as liquid products as they are, or can be flowed to the dryer 130 through the flow path R22 and dried in the dryer 130 to be commercialized as dried products.

Next, it will be clarified that the present invention can be mass-produced.
The tests were carried out using black liquor (pH 14, solid content concentration 50% by mass to 60% by mass) discharged in the digestion process of a paper mill. This black liquor was first diluted to two types of concentration 20 mass% and concentration 30 mass% using filtered fresh water.

  Next, carbon dioxide gas was blown into the diluted black liquor to lower the pH to 9 to 10 (first acidification). During the acidification, the temperature of the black liquor was 25 ° C. In addition, during this acidification, it was noted that the black liquor was stirred to homogenize the liquor.

The acidified black liquor was pressed into a filter press (filtration area 0.6 m ² , filter chamber volume 7.8 L, filter cloth: made of polypropylene) and pressed to obtain a first dewatered cake (primary cake). The pressing pressure was 0.5 MPa and the pressing pressure was 1.5 MPa. At this time, gas replacement with replacement gas was not performed. The primary cake had a pH of 9 to 10, a moisture content of 40% by mass, and 50% by mass.

  The primary cake was slurried with filtered fresh water so that the solid content concentration was 30% by mass. At this time, sulfuric acid having a concentration of 22% by mass was added to lower the pH of the slurry to 1.0 to 4.0 (second acidification).

  The acidified slurry was again pressed into the filter press, and further primary compression, washing and secondary compression to obtain a second dewatered cake (secondary cake). The pressing pressure was 0.5 MPa, and the primary pressing pressure and the secondary pressing pressure were 1.5 MPa. Filtered fresh water was used as washing water. The supply pressure of this filtered fresh water was 0.5 MPa. The secondary cake had a pH of 1.0 to 2.5, a moisture content of 40% by mass to 50% by mass, and an ash fraction of 0.5% by mass to 3.0% by mass. Since the ash fraction of the secondary cake was below the planned value (3.0 mass%), the process proceeded to the next step without repeating washing and the like.

  The secondary cake was slurried so that the solid content concentration was 14.3 (mass / volume)% and 28.6 (mass / volume)%. During the slurrying, sodium metasilicate and sodium hydroxide were added as inorganic salts. This addition was carried out so that 2.96 kg of sodium metasilicate and 0.18 kg of sodium hydroxide were added to 1.0 kg of lignin. In addition, according to this addition amount, when solid content concentration is 16.5 (mass / volume)%, concentration of lignin will be about 4 (mass / volume)%, and solid concentration 33.1 (mass / volume) In the case of%), the concentration of lignin is about 8 (mass / volume)%.

  The slurry after the addition of the inorganic salt was formed into droplets by an spray dryer and dried to obtain inorganic salt-containing fine particles. The temperature of the slurry supplied to the spray dryer was 40 ° C. to 80 ° C., the temperature of the hot air supplied to the spray dryer was 320 ° C., and the temperature of the gas exhausted from the spray dryer was 120 ° C. The inorganic salt-containing fine particles were collected (collected) using a cyclone. The composition of the collected inorganic salt-containing fine particles was lignin: inorganic salt: water = 2: 6.28: 0.82 on a mass basis.

  The inorganic salt-containing fine particles were subjected to pyrolysis (baking) of the organic component using an externally heated rotary kiln. The thermal decomposition temperature was 700 ° C., and the baking time was 2 hours. The inorganic salt-containing fine particles after pyrolysis were lignin: inorganic salt: water = 0.5: 4.5: 0.0 on a mass basis.

  The inorganic salt-containing fine particles after pyrolysis were slurried using warm filtered fresh water. This slurrying was performed such that the solid content concentration was 10% by mass and 20% by mass. The obtained slurries all had a temperature of 60 ° C.

The slurry of inorganic salt-containing fine particles is pressed into a filter press (filtration area: 0.6 m ² , filter chamber volume: 7.8 L, filter cloth: made of polypropylene), followed by forward washing, primary pressing, back washing, secondary pressing, gas Substitution was performed to obtain a dewatered cake. The pressing pressure was 0.2 MPa, the primary and secondary pressing pressures were 1.5 MPa, the cleaning solution supply pressure was 0.1 MPa, and the replacement gas supply pressure was 0.5 MPa. Filtered fresh water was used as the washing solution, and air was used as the replacement gas. The component composition of the dewatered cake was lignin: inorganic salt: water = 0.48: 0.01: 3.8 on a mass basis. This result shows that the inorganic salt is sufficiently removed.

  The dewatered cake after removing the inorganic salt was dried using a constant temperature drier. The drying rate was 0.12 kg / day. Moreover, the drying temperature was 120 ° C. Sample photographs of the carbon fine particles (dried product) thus obtained are shown in FIG. 5 and FIG. (1) of FIG. 5 is a sample photograph of the obtained carbon microparticles (secondary particles), and (2) is a sample photograph in which the outer shell portion of the carbon microparticles is enlarged. Moreover, FIG. 6 is another sample photograph. From these photographs, it can be seen that the obtained carbon fine particles (secondary particles) are hollow, and the outer shell is made porous by the nanoscale primary particles (see FIG. 6). Therefore, it can be used as a filler or the like for automobile tires.

Next, it will be clarified that the present invention can be mass-produced and does not have a problem regarding conductivity.
Carbon fine particles were produced under the production conditions shown in Table 1. The physical properties of the obtained carbon fine particles are shown in Table 2, and the evaluations regarding the conductivity and dispersibility are shown in Table 3. In addition, regarding the dispersibility, the cross-sectional view of the resin and the resin was observed, and the case where the particles were not aggregated was regarded as “good”, and the case where the particles were aggregated was regarded as “bad”.

  From the above results, according to the present invention, it was found that carbon fine particles can be manufactured smoothly and reliably, and mass production is possible. Further, from the comparison between Example 1 and Comparative Example 1, if the flow rate of the slurry, the spray pressure, and the solid content concentration at the time of droplet formation are adjusted, the average secondary particle diameter of the finally obtained carbon fine particles is reduced. It has been found that the conductivity of the carbon fine particle itself can be improved. It is considered that the improvement of the conductivity of the carbon microparticles themselves leads to the improvement of the conductivity of the dispersion in which the carbon microparticles are dispersed.

  On the other hand, it was found from the comparison between Example 2 and Example 1 and Comparative Example 1 that the conductivity of the carbon fine particles was not improved when the ratio of the inorganic salt was increased. However, in this embodiment, the dispersibility of the carbon fine particles is improved, which is considered to lead to the improvement of the conductivity of the dispersion. In addition, according to Example 1 (it is not preferable to increase the proportion of the inorganic salt) if only to improve the conductivity (it is preferable not to increase the proportion of the inorganic salt), the carbon fine particles of Example 2 have a significantly high oil absorption, When used in the technical field where it is also required to have a high oil absorption while having minimum conductivity, the carbon fine particles of Example 2 are considered to be preferable.

Next, it will be clarified that the production method of the present invention can control the average secondary particle diameter of carbon fine particles.
(Relationship between particle size and flow rate)
When making the slurry containing inorganic salt into droplets, the flow rate of the slurry is changed to 4.0 L / h, 2.2 L / h, 2.0 L / h, 1.6 L / h to produce carbon fine particles. did. The spray pressure at the time of droplet formation was 0.5 MPa. Further, sodium metasilicate and sodium hydroxide were used as inorganic salts, and the blending ratio (lignin: sodium metasilicate: sodium hydroxide) was 1: 3: 0.18. Furthermore, the solid content concentration of the slurry containing the inorganic salt was 6.0%.

  Sample photographs of the obtained carbon fine particles are shown in FIGS.

  As a result of this test, it was found that when the flow rate of the slurry containing the inorganic salt was reduced, the average secondary particle size of the obtained carbon fine particles became smaller.

(Relationship between particle size and spray pressure)
When the slurry containing the inorganic salt was formed into droplets, the spray pressure (spray pressure) of the slurry was changed to 0.5 MPa and 1.0 Mpa to produce carbon fine particles. The flow rate for droplet formation was 1.6 L / h. Further, sodium metasilicate and sodium hydroxide were used as inorganic salts, and the blending ratio (lignin: sodium metasilicate: sodium hydroxide) was 1: 3: 0.18. Furthermore, the solid content concentration of the slurry containing the inorganic salt was 1.0%.

  Sample photographs of the obtained carbon fine particles are shown in FIG. 11 and FIG.

  As a result of this test, it was found that when the spray pressure of the slurry containing the inorganic salt is increased, the average secondary particle size of the obtained carbon fine particles becomes smaller.

(Relation between particle size and concentration)
The solid content concentration of the slurry when the slurry containing the inorganic salt is dropped is changed to 6.00%, 1.00%, 0.80%, 0.50%, 0.10%, and carbon is changed. Microparticles were produced. The flow rate for droplet formation was 1.6 L / h. The spraying pressure was 0.5 MPa. Further, sodium metasilicate and sodium hydroxide were used as inorganic salts, and the blending ratio (lignin: sodium metasilicate: sodium hydroxide) was 1: 3: 0.18.

  The sample photograph of the obtained carbon fine particle is shown in FIGS.

  As a result of this test, it was found that when the solid content concentration of the slurry containing the inorganic salt is lowered, the average secondary particle diameter of the obtained carbon fine particles is reduced.

(Relationship between particle size and inorganic salt)
Carbon fine particles were manufactured by changing the mixing ratio of the inorganic salt to lignin to 3 times by mass, 10 times by mass, and 30 times by mass the slurry to be formed into droplets. Sodium metasilicate and sodium hydroxide were used as inorganic salts. Moreover, the conditions for droplet formation were a flow rate of 1.6 L / h and a spray pressure of 1.0 MPa.

  Sample photographs of the obtained carbon fine particles are shown in FIGS.

  As a result of this test, it was found that the average secondary particle diameter of the obtained carbon fine particles becomes smaller when the ratio of the inorganic salt is increased.

  INDUSTRIAL APPLICABILITY The present invention is applicable as a method of producing carbon fine particles from black liquor and the like discharged in a paper mill and as carbon fine particles.

  DESCRIPTION OF SYMBOLS 10 ... concentration process, 20 ... dilution tank, 30 ... acidification processing tank, 40 ... filter press, 50 ... slurrying tank, 60 ... spare tank, 70 ... stirring tank, 80 ... spray dryer, 90 ... cyclone, 91 ... bug Filter, 100: rotary kiln, 110: slurrying tank, 120: filter press, 130: dryer, 140: wet crusher, 141: dispersion tank, C1: first dewatering cake, C2: second dewatering cake, G1 ... acidified gas.

Claims (6)

A method of producing carbon fine particles from a lignin-containing solution, which comprises:
The lignin-containing solution is acidified and dehydrated to form a dehydrated cake,
The slurry of this dewatered cake is mixed with inorganic salt,
The obtained slurry containing the inorganic salt is formed into droplets with a solid content concentration of 1.0% or less , and dried to obtain inorganic salt-containing fine particles,
The inorganic salt-containing fine particles are thermally decomposed to remove the inorganic salt to obtain carbon fine particles,
A method of producing carbon fine particles characterized by The droplet formation is performed such that the spray pressure of the slurry containing the inorganic salt is 0.5 MPa to 1.3 MPa.
The method for producing carbon fine particles according to claim 1. A method of producing carbon fine particles from a lignin-containing solution, which comprises:
The lignin-containing solution is acidified and dehydrated to form a dehydrated cake,
The slurry of this dewatered cake is mixed with inorganic salt,
The mixture of the inorganic salts, have rows such that the inorganic salt is 10 to 30 times the mass of the lignin in said slurry,
The slurry containing the obtained inorganic salt is formed into droplets and dried to obtain inorganic salt-containing fine particles,
The inorganic salt-containing fine particles are thermally decomposed to remove the inorganic salt to obtain carbon fine particles,
A method of producing carbon fine particles characterized by The lignin-containing solution is acidified and dehydrated to form a dehydrated cake,
The slurry of this dewatered cake is mixed with inorganic salt,
The slurry containing the obtained inorganic salt is formed into droplets and dried to obtain inorganic salt-containing fine particles,
The inorganic salt-containing particles were thermally decomposed, to obtain a carbon-containing particulates to remove inorganic salts,
The average secondary particle diameter of the fine carbon particles you less 4.0 .mu.m,
A method of producing carbon fine particles characterized by The specific surface area shall be the 900m ² / g or more,
The method for producing carbon fine particles according to claim 5. The oil absorption amount shall be the 600ml / 100g or more,
The method for producing carbon fine particles according to claim 5.