JP2014141372A - Method and facility for producing carbon fine particulate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mass-producible method for producing carbon fine particulates.SOLUTION: In a method for producing carbon fine particulates from a lignin-containing liquid, a first dewatered cake C1 is obtained by acidifying the lignin-containing liquid and succeedingly conducting dehydration, a second dewatered cake C2 is obtained by slurrying the first dewatered cake C1, advancing acidification, and succeedingly again conducting dehydration, inorganic salt-containing fine particulates are obtained by slurrying the second dewatered cake C2, mixing the slurry with an inorganic salt X and succeedingly conducting liquid droplet formation and drying, and the carbon fine particulates are obtained by thermal decomposition of the inorganic salt-containing fine particulates and succeedingly removing the inorganic salt X therefrom.

Description

  The present invention relates to a method and equipment for producing carbon fine particles from black liquor discharged in a paper mill.

  Conventionally, in a paper mill, a large amount of black liquor is discharged in the cooking process, and this black liquor contains organic substances such as lignin in addition to alkaline chemicals such as sodium and sulfur derived from the cooking chemical. At present, various studies have been made on the effective use of lignin contained in the black liquor. For example, Patent Document 1 proposes a method for producing carbon fine particles from a lignin-containing liquid. In this proposal, the lignin-containing liquid is formed into fine droplets and dried to form fine particles, and the fine particles are thermally decomposed to produce carbon fine particles. The document expects that the carbon microparticles produced in this way will be an alternative to carbon black and the like. The same document also proposes to make the produced carbon fine particles hollow, and proposes mixing an inorganic salt with the lignin-containing liquid before forming into microdroplets. As a proposal for mixing an inorganic salt with a lignin-containing liquid, in addition to Patent Document 1, there is also a proposal for mixing lithium carbonate with a lignin-containing liquid (see Patent Document 2).

  The above literature also discloses various test results, and clarifies that the produced carbon fine particles are useful. However, all of the above documents remain at the laboratory level, and do not propose a method for industrialization or mass production. Moreover, the above literature only discloses that black liquor can be used as the lignin-containing liquid. However, using black liquor as the lignin-containing liquid and making it into fine droplets as it is is not suitable for industrialization and mass production.

JP 2009-155199 A JP 2010-168251 A

  The main problem to be solved by the present invention is to provide a production method and production equipment of carbon fine particles that can be mass-produced.

The present invention for solving this problem is as follows.
[Invention of Claim 1]
A method for producing carbon fine particles from a lignin-containing liquid,
After acidifying the lignin-containing liquid, dehydration to obtain a first dehydrated cake,
Slurry and acidify the first dehydrated cake, and then dehydrate again to obtain a second dehydrated cake.
This second dewatered cake is slurried and mixed with an inorganic salt, and then dropletized and dried to obtain inorganic salt-containing fine particles,
After pyrolyzing the inorganic salt-containing fine particles, the inorganic salt is removed to obtain carbon fine particles.
A method for producing carbon fine particles.

[Invention of Claim 2]
Acidification of the lignin-containing liquid is performed in a range where the pH remains at 8.5 or more and with stirring.
The method for producing carbon fine particles according to claim 1.

[Invention of Claim 3]
As the lignin-containing liquid, a black liquid having a pH of 13 or more is used.
The method for producing carbon fine particles according to claim 1 or 2.

[Invention of Claim 4]
As the lignin-containing liquid, a black liquor having a solid content concentration of 50 to 60% by mass diluted to a solid content concentration of 20 to 35% by mass is used.
The manufacturing method of the carbon microparticles of any one of Claims 1-3.

[Invention of Claim 5]
The dehydrated filtrate discharged when obtaining the first dehydrated cake is sent to the black liquor concentration step.
The method for producing carbon fine particles according to claim 3 or 4.

[Invention of Claim 6]
The pH is adjusted to 1.0 to 4.0 by proceeding with the acidification.
The manufacturing method of the carbon fine particle of any one of Claims 1-5.

[Invention of Claim 7]
The inorganic salt is mainly composed of sodium metasilicate and sodium hydroxide,
The manufacturing method of the carbon fine particle of any one of Claims 1-6.

[Invention of Claim 8]
The mass mixing ratio of the second dehydrated cake, the sodium metasilicate and the sodium hydroxide is 1: 2.96 to 8.88: 0.18 to 0.54.
The method for producing carbon fine particles according to claim 7.

[Invention of Claim 9]
The slurry after mixing the inorganic salt is passed through a filter, and then the droplets are formed and dried.
The method for producing carbon fine particles according to any one of claims 1 to 8.

[Invention of Claim 10]
Acidification of the lignin-containing liquid is performed by blowing acidification gas into the lignin-containing liquid.
The manufacturing method of the carbon fine particle of any one of Claims 1-9.

[Invention of Claim 11]
Collecting inorganic salt-containing fine particles obtained by droplet formation and drying, and using exhaust gas generated during the dust collection as the acidifying gas;
The method for producing carbon fine particles according to claim 10.

[Invention of Claim 12]
The inorganic salt-containing fine particles are collected using a cyclone and a bag filter in this order.
The method for producing carbon fine particles according to claim 11.

[Invention of Claim 13]
The pyrolysis is performed using a rotary kiln equipped with an external heat jacket,
The pyrolysis gas discharged from the rotary kiln is used as a combustion gas for a hot air furnace for supplying hot air to the outer heat jacket,
Using exhaust gas discharged from the external heat jacket as the acidified gas,
The method for producing carbon fine particles according to any one of claims 10 to 12.

[Invention of Claim 14]
Removal of the inorganic salt is performed by slurrying the inorganic salt-containing fine particles after pyrolysis, press-fitting into a filter press, and pressing.
The method for producing carbon fine particles according to any one of claims 1 to 13.

[Invention of Claim 15]
After slurrying the inorganic salt-containing fine particles after the thermal decomposition, and prior to press-fitting into the filter press, pass through the filter,
The manufacturing method of the carbon microparticles of any one of Claims 1-14.

[Invention of Claim 16]
The ash content of the second dehydrated cake is 3.0% or less,
And the press-fit filtrate discharged from the filter press is used when mixing and slurrying the second dehydrated cake and the inorganic salt.
The manufacturing method of the carbon fine particle of any one of Claims 1-15.

[Invention of Claim 17]
A facility for producing carbon fine particles from a lignin-containing liquid,
First acidifying means for acidifying the lignin-containing liquid;
Means for dehydrating the lignin-containing liquid acidified by the first acidification means;
Means for slurrying the dehydrated cake obtained by the dehydration;
A second acidification means for promoting acidification of the slurry during or after the slurrying;
Means for returning the acidified slurry to the dewatering means;
Means for slurrying the dehydrated cake obtained by dehydration after the return;
Means for mixing with the inorganic salt in the slurry during or after the slurrying;
Means for dropletizing and drying the slurry mixed with the inorganic salt;
Means for thermally decomposing inorganic salt-containing fine particles obtained by droplet formation and drying;
Means for removing the inorganic salt from the inorganic salt-containing fine particles obtained by the thermal decomposition to obtain carbon fine particles;
A facility for producing carbon fine particles, comprising:

  According to the present invention, a carbon fine particle production method and production equipment capable of mass production are obtained.

It is a manufacturing equipment flow chart of carbon particulates (lignin extraction process etc.). It is a manufacturing equipment flow diagram of carbon fine particles (inorganic salt mixing process, droplet formation and drying process, thermal decomposition process, etc.). It is a manufacturing equipment flow diagram of carbon particulates (cleaning process, drying process, etc.) It is a detailed flowchart of a washing | cleaning process. They are a sample photograph (1) of carbon fine particles and an enlarged sample photograph (2) of the outer shell portion of the carbon fine particles. It is a sample photograph (1) of the carbon microparticles according to another example and an enlarged sample photograph (2) of the outer shell portion of the carbon microparticles.

  Next, an embodiment of the present invention will be described. In the present invention, a bioethanol-extracted solution or the like can be used as the lignin-containing liquid as a raw material, but in the following, an example in which black liquor discharged in a paper mill cooking process or the like is used is used. Explained.

[Dilution of black liquor, etc.]
The black liquor discharged in the cooking process of the paper mill is normally concentrated to such an extent that self-combustion is possible in the concentration step, and the concentrated black liquor is burned in a recovery boiler to recover the amount of heat. The alkaline chemical contained in the black liquor is reduced and reused as cooking chemical.

  The black liquor concentration step is provided with a concentrating device such as an evaporator (evaporator), and the black liquor solid content (total solid: TS) concentration (hereinafter simply referred to as “TS”), which was about 10 to 20% by mass. It is also concentrated until it becomes about 60 to 80% by mass.

  In this embodiment, a black liquor that is in the middle of concentration in the concentration step, preferably a black liquor having a concentration of 20 to 35% by mass, is used. However, the concentration of the black liquor is usually performed in multiple stages from the viewpoint of the relationship between the processing amount and the equipment capacity, scale prevention, and the like, and there may be no black liquor having a concentration of 20 to 35% by mass. In such a case, a black liquor with a high concentration is diluted and used.

  Specifically, for example, as shown in FIG. 1, a black liquor X1 having a low concentration (for example, a concentration of 10 to 20% by mass), a black liquor X2 having a medium concentration (for example, a concentration of 50 to 60% by mass), and In the case where a high concentration (for example, a concentration of 60 to 80% by mass) of black liquor X3 is present, first, a part or all of the medium concentration of black liquor X2 is extracted and diluted through a flow path R1 including a pipe or the like. Flow to tank 20. This flow can be changed to a method of transporting 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, water W such as filtered clean water is mixed into the black liquor until the concentration of the black liquor is 20 to 35% by mass, preferably 25 to 30% by mass, more preferably 25 to 28%. Dilute to mass%. If the concentration of the black liquor is diluted to less than 20% by mass, the efficiency of lignin extraction (recovery) deteriorates, which may make it unsuitable for industrialization and mass production. On the other hand, when the concentration of the black liquor exceeds 35% by mass, the contact between the black liquor and the acidified gas G1 may be uneven in the acidification step described later. Furthermore, when the concentration of the black liquor exceeds 35% by mass, there is a possibility that the ash content of the first dehydrated cake C1 described later cannot be lowered sufficiently.

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

[First acidification, etc.]
The black liquor diluted in the dilution tank 20 is sent to the acidification tank 30 through the flow path R <b> 2 and supplied to the acidification tank 30. In the acidification tank 30, acidified gas G1 is blown directly into the tank 30 in order to acidify the black liquor to lower the pH of the black liquor (acidification treatment).

  As the acidification 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 is used. It is preferred to use.

  In addition, when carbon dioxide gas is used as the acidifying gas G1, the carbon dioxide gas can be newly prepared. However, the exhaust gas G4 from the bag filter 91 described later and the external heat jacket 100a provided in the rotary kiln 100 can be used. It is preferable to use the exhaust gas G5 as all or part of the acidified gas G1. By using the exhaust gases G4 and G5, it is possible to reduce the discharge of carbon dioxide gas in the exhaust gases G4 and G5, that is, greenhouse gases, which is a measure against global warming.

  Further, in the present embodiment, in order to more reliably prevent the solid content from precipitating in the acidification tank 30, a stirring blade 31 using the motor M as a drive source is provided in the acidification tank 30. The black liquor is stirred by the stirring blade 31.

  In the above acidification step, the acidification gas G1 is blown so that the black liquor initially having a pH of 13 or more preferably has a pH of 8.5 to 10, more preferably a pH of 9.0 to 9.5. I do. When the acidified gas G1 is blown such that the pH of the black liquor exceeds 10, lignin may not be sufficiently precipitated.

  When the concentration of black liquor increases due to the black liquor flow process, lignin, sodium precipitation, 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 this.

[First dehydration, etc.]
The black liquor on which the lignin is deposited is sent to the filter press 40 as dehydrating means through the flow path R3 and is press-fitted into the filter press 40. The black liquor press-fitted into the filter press 40 is further squeezed and dehydrated. The dehydrated filtrate D1 discharged along with the press-fitting and squeezing can be disposed of as a waste liquid, but is preferably returned to the black liquor concentration step 10 through a flow path R4. By this return, ash such as sodium contained in the dehydrated filtrate D1 is also returned to the concentration step 10. Therefore, by reducing the ash such as sodium, it can be reused as a cooking chemical. The dehydrated filtrate D1 usually contains 20 to 25% by mass of ash such as sodium.

  The dewatering cake C1 is generated by dehydration in the filter press 40 (hereinafter, this dewatering cake C1 is also referred to as “first dewatering cake C1”). The ash content of the first dehydrated cake C1 is preferably 0 to 20% by mass, more preferably 0 to 15% by mass. If the ash content of the first dehydrated cake C1 exceeds 30% by mass, the ash content of the second dehydrated cake C2 described later may not be sufficiently reduced.

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

[Concentration adjustment and second acidification]
The first dewatered cake C1 obtained in the filter press 40 is conveyed to the slurrying tank 50 using a container or the like and supplied to the slurrying tank 50. The slurry tank 50 is supplied with water W such as filtered fresh water and acid A such as sulfuric acid together with the first dewatered cake C1, and the first dewatered cake C1 is slurried and acidified. This slurrying is performed so that the solid content concentration of the obtained slurry S1 is 15 to 30% by mass, and preferably 20 to 25% by mass. Further, the acidification (supply of acid A) proceeds so that the resulting slurry S1 has a pH of 1.0 to 4.0, preferably a pH of 1.5 to 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 the slurry is completely slurried. Moreover, as acid A, the thing of pH 1.0-2.5 can be used, for example.

[Second dehydration, etc.]
The slurry S1 obtained by adjusting the concentration and pH (advancing acidification) in the slurrying tank 50 is sent again to the filter press 40 through the flow path R5 and the flow path R3, and is press-fitted into the filter press 40. To do. The press-fitting of the slurry S1 is preferably performed as quickly as possible after adjusting the pH, more preferably within 10 hours, and particularly preferably within 5 hours. When the time until press-in exceeds 24 hours after adjusting the pH, even if the ash content of the first dewatered cake C1 is adjusted to 20% by mass, the ash content of the second dehydrated cake C2 is 3.0% by mass. % Or less. According to the test by the present inventors, when the time until press-fitting after adjusting the pH was 24 hours, the ash content of the second dehydrated cake C2 was 8 to 10% by mass.

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

  When the dehydration 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 supplying and squeezing the washing water W, and the ash content of the resulting dewatered cake C2 (hereinafter, this dewatered cake C2 is also referred to as “second dehydrated cake C2”) decreases.

  The slurry S1 can be washed 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 be used. The diluted acid is preferably pH 1.0 to 4.0, more preferably pH 1.0 to 2.5.

  The washing filtrate D3 discharged along with the washing of the slurry S1 usually has an ash content of 1% or less, and it is inefficient to return it to the concentration step 10 like the dehydrated filtrates D1 and D2. Therefore, it is preferable to dispose of the waste liquid. However, when the cleaning water W is mixed with the acid A and washed as a diluted acid, it is preferably fed to the slurrying tank 50 through the flow path R6 and supplied to the slurrying tank 50. Since the acid (A) contained in the washing filtrate D3 is reused by supplying the washing filtrate D3, the amount of the acid A newly added can be reduced.

  After supplying the washing water W and re-squeezing, the filter press 40 is blown with a replacement gas G2 such as nitrogen or air. By blowing this replacement gas G2, the water in the second dehydrated cake G2 is replaced by the replacement gas G2, and the water content and the ash content are further reduced.

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

  The ash content of the second dehydrated cake C2 is preferably 0.0 to 3.0% by mass, more preferably 0.0 to 1.0% by mass, and particularly preferably 0.0 to 0.5% by mass. It is. In this embodiment, the first dehydrated cake C1 obtained in the filter press 40 is once slurried and dehydrated again in the filter press 40, thereby significantly reducing the ash content of the second dehydrated cake C2. Intended. In addition, the effect by this is mentioned later.

  The second dehydrated cake C2 contains lignin as a main component (for example, 35 to 60% by mass, preferably 45 to 50% by mass), and lignin is extracted from so-called black liquor. Therefore, compared with the case where the black liquor which is a lignin containing liquid is used as it is for the process demonstrated below, it will become remarkably easy to mass-produce.

  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 that the dewatering means for obtaining the dehydrated cake C1 and the dewatering means for obtaining the dehydrated cake C2 are the same from the viewpoint of the equipment installation area and the like. It is preferable to separate the dehydrating means for obtaining the dehydrated cake C1 and the dehydrating means for obtaining the dehydrated cake C2. As a dehydrating means, for example, a belt press or the like may be used instead of the filter press.

[Addition of inorganic salts, etc.]
As shown in FIG. 2, the second dehydrated cake C <b> 2 is conveyed to the stirring tank 70 using a container or the like and supplied to the stirring tank 70. In addition, the stirring tank 70 is supplied with water W such as inorganic salt X and filtered fresh water. The inorganic salt X and the water W can also be directly supplied to the stirring tank 70 separately. However, in order to stabilize the processing in the stirring tank 70, both X and W are once supplied to the preliminary tank 60 and mixed, 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 this.

  As the inorganic salt X, it is preferable to use sodium metasilicate, and it is more preferable to use sodium metasilicate and sodium hydroxide in combination.

  When sodium metasilicate and sodium hydroxide are used in combination, the mixing mass ratio of lignin, sodium metasilicate and sodium hydroxide in the second dehydrated cake C2 is 1: 2.96 to 8.88: 0. It is preferable to set it as 18-0.54, and it is more preferable to set it as 1: 2.96: 0.18 (2: 5.92: 0.36). If lignin: sodium metasilicate and sodium hydroxide are less than 1: 2 on a mass basis, it may be difficult to remove both (inorganic salt X) in the filter press 120 described later. Moreover, when there is little quantity of the inorganic salt X, there exists a possibility that the particle shape of the carbon fine particle obtained by the said inorganic salt X melting | dissolving during thermal decomposition may not be maintained. On the other hand, when lignin: sodium metasilicate and sodium hydroxide exceed 1:20 on a mass basis, the hollow carbon fine particles collapsed unintentionally upon processing in the filter press 120 and the dryer 130 described later, There is a risk that the hollow shape cannot be maintained.

  The stirring tank 70 of this embodiment is provided with a stirring blade 71 using the motor M as a drive source. By the stirring by the stirring blade 71, the lignin and the inorganic salt X in the second dehydrated cake C2 are evenly mixed. In addition, the stirring tank 70 or the above-described preliminary tank 60 is preferably provided with a heating device in order to enable processing at a high concentration.

[Dropping and drying, etc.]
The slurry S2 containing the lignin and the inorganic salt X obtained in the stirring tank 70 is sent to the spray dryer 80, which is droplet forming / drying means, through the flow path R8, and droplets are formed 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).

  Here, when the slurry S2 is flowed, it is preferable to pass a screen 75, which is a filter. By passing the screen 75, the spray nozzle is prevented from being clogged with undissolved substances in the slurry S2. In addition, as the screen 75, the thing of 150-250 mesh, for example, Preferably the thing 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 to 10%, more preferably 6 to 8% on the assumption that the ratio of lignin to the inorganic salt X is constant. If the lignin concentration is less than 4%, the outer shell of the inorganic salt-containing fine particles does not have a sufficient thickness, and the inorganic salt-containing particles that are hollow may collapse unintentionally and may not be able to maintain the hollow shape. is there. On the other hand, if the lignin concentration exceeds 10%, the outer shell of the inorganic salt-containing fine particles becomes too thick, and it may be difficult to remove the inorganic salt X by the filter press 120 described later.

  In the range of lignin concentration of 4 to 8%, the lignin concentration and the bulk specific gravity of the carbon fine particles finally obtained are linked, and when the lignin concentration is increased, the bulk specific gravity of the powder obtained by spray drying 80 is increased. 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 increase. Therefore, by adjusting the lignin concentration, the bulk specific gravity and the thickness of the outer shell of the finally obtained carbon fine particles can be controlled.

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

  The inorganic salt-containing fine particles obtained in the spray dryer 80 are in the form of a powder, and are preferably sent by the fan through the flow path R9 to the cyclone 90 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 sent 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 the fine inorganic salt-containing particles are collected in the bag filter 91 can be exhausted into the atmosphere, but is sent to the acidification treatment tank 30 through the flow path R12 provided with the exhaust fan F2, and is acidified. It is preferable to use it as the conversion gas G1. The exhaust gas G4 contains carbon dioxide gas and has heat. Therefore, by using the exhaust gas G4 as the acidified gas G1, the carbon dioxide gas can be effectively used and the emission amount can be reduced, and the heat of the exhaust gas G4 can be effectively used. A scrubber or the like can be used instead of the bag filter 91. However, from the viewpoint of effective use of heat of the exhaust gas G4 (the exhaust gas G4 has a temperature of about 120 ° C., for example), the bag filter 91 is used. Is preferred.

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

  This thermal decomposition is preferably performed at 600 to 1000 ° C, more preferably at 700 to 950 ° C, and in order to improve the electrical conductivity of the obtained carbon fine particles, it is preferably performed at 900 to 1000 ° C. .

  Furthermore, this thermal decomposition is preferably performed over 1 to 6 hours, and more preferably over 2 to 3 hours. Since the inorganic salt-containing fine particles of this embodiment are hollow, if this thermal decomposition is carried out rapidly, the water vapor concentration in the system increases, and the lignin component may melt and the hollow shape may not be maintained. In order to prevent moisture and crystal water contained in the inorganic salt-containing fine particles from staying in the rotary kiln 100, it is preferable to leave the temperature at 100 to 200 ° C. for 1 to 4 hours before the thermal decomposition treatment.

  The pyrolysis gas N1 generated during the pyrolysis is used as a combustion gas in the hot air furnace 101 for supplying hot air to the outer heat jacket 100a. By using this pyrolysis gas N1, the amount of fuel N2 such as LPG gas newly supplied to the hot stove 101 can be reduced.

  The combustion gas generated in the hot stove 101 is supplied into the external heat jacket 100 a and used as an external heat source for 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 and has heat, like the exhaust gas G4. Therefore, the exhaust gas G5 is also preferably sent to the acidification tank 30 through the flow path R13 and used as the acidification gas G1 described above. By using the exhaust gas G5 as the acidified gas G1, the carbon dioxide gas can be effectively used and the emission amount can be reduced, and the heat of the exhaust gas G5 can be effectively used.

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

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

  The slurrying tank 110 is provided with a stirring blade 111 using a motor M as a drive source. By the stirring by the stirring blade 111, the inorganic salt-containing fine particles C3 are rapidly dispersed, and the dispersion concentration is made uniform.

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

[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 is press-fitted into the filter press 120. However, when the slurry S3 is fed, it is preferable to pass the slurry S3 through a screen 115 as a filter in the middle. By passing the slurry S3 through the screen 115, the inorganic salt in the filter press 120 can be removed uniformly, and a situation in which carbon fine particles from which some of the inorganic salt has not been removed is produced can be prevented.

  As the dehydrating means, for example, a belt press may be used instead of the filter press 120. Moreover, as the screen 75, for example, a screen having a mesh size of 150 to 250 mesh, preferably a screen having 200 mesh can be used. Furthermore, prior to press-fitting the slurry S3 into the filter press 120, the inorganic salt contained in the slurry S3 can be precipitated and the precipitated inorganic salt can be removed.

  The press-fitted filtrate D4 generated when the slurry S3 is press-fitted into the filter press 120 can be disposed of as a waste liquid, but is preferably returned to the preliminary tank 60 and supplied to the preliminary tank 60. The filter press 120 is a means for removing the inorganic salt X, and the press-fit filtrate D4 contains the inorganic salt X. Therefore, by returning the press-fit filtrate D4 to the reserve tank 60, the inorganic salt X contained in the press-fit filtrate D4 is reused, and the amount of the inorganic salt X newly supplied to the reserve tank 60 is reduced. be able to.

  By the way, in this embodiment, as described above, the ash content of the second cake C2 is set to 3.0% or less. Therefore, the press-fitted filtrate D4 contains almost no ash derived from cooking chemicals, and therefore even if the press-fed filtrate D4 is returned, that is, reused, there is no possibility that the ash will be immediately concentrated. Therefore, the return of the press-fit filtrate D4 can be repeated a plurality of times, which is a great advantage in industrialization. In addition, the present inventors have confirmed that the press-fit filtrate D4 can be repeatedly used about 30 times when the ash content of the second dehydrated cake C2 is 3%.

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

  The slurry S3 press-fitted into the filter press 120 is subjected to primary squeezing after being positively washed with water W such as filtered fresh water. Although the primary filtrate D5 discharged during the normal washing and primary pressing contains the inorganic salt X, the concentration of the inorganic salt X is extremely thin due to the water W used for the normal washing. Therefore, returning to the preliminary tank 60 is not efficient and is preferably returned to the slurrying tank 110. In addition, it is preferable to set it as pH12-14 from the viewpoint that the primary filtrate D5 discharged | emitted in this process maintains the pH in which the inorganic salt X is easy to melt | dissolve in the subsequent secondary washing. Is more preferable. Moreover, electrical conductivity is 8-12 S / m normally, Preferably it is 10-12 S / m.

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

  The secondary filtrate D6 discharged during backwashing, secondary squeezing and gas replacement can be immediately subjected to waste liquid treatment, but the pH and electrical conductivity are detected by the detection means 121, and the inorganic salt X is removed. It is preferable to confirm whether or not, that is, the progress of cleaning. In addition, the secondary filtrate D6 discharged | emitted in this process is pH 8.0-9.5 normally, Preferably it is pH 8.0-9.0. The electrical conductivity is usually 100 to 1200 μS / m, preferably 100 to 500 μS / m.

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

The carbon fine particles obtained as described above are preferably hollow with an average particle size of 1 to 20 μm, more preferably an average particle size of 1 to 12 μm, and an outer shell thickness of 50 to 200 nm. The bulk density is 40-60 kg / m ³ . Therefore, it is very lightweight and can be used as, for example, a filler for automobile tires.

  However, depending on the application, it is not important that the carbon fine particles are hollow, and it may be required to be finer, have good dispersibility in a liquid, have good conductivity, etc. (for example, rubber applications) , Pigments, electrical materials, etc.). Therefore, in such a case, the dewatered cake C4 is transported to the dispersion tank 141, and mixed with water W such as filtered fresh water or an organic solvent in the dispersion tank 141 to form a dispersion of carbon fine particles (slurry). . The carbon fine particle dispersion is flowed to the wet pulverizer 140 such as a bead mill through the channel R21, and the carbon fine particles are wet pulverized in the wet pulverizer 140. By this wet pulverization, for example, the carbon fine particles which have been 1 to 20 μm are pulverized until the carbon fine particles become 50 to 200 nm.

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

Next, examples of the present invention will be described.
The present inventors conducted tests using black liquor (pH 14, solid content concentration 50-60 mass%) discharged in the cooking process of a paper mill. This black liquor was first diluted into two types with a concentration of 20% and a concentration of 30% 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 this acidification, the temperature of the black liquor was 25 ° C. In this acidification, attention was paid so as to homogenize the liquid by stirring the black 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 squeezed to obtain a first dehydrated cake (primary cake). The press-fitting pressure was 0.5 MPa, and the pressing pressure was 1.5 MPa. At this time, gas replacement with a replacement gas was not performed. The primary cake had a pH of 9 to 10 and a moisture content of 40% and 50%.

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

  The acidified slurry was pressed again into the filter press, and further subjected to primary pressing, washing and secondary pressing to obtain a second dehydrated cake (secondary cake). The press-fitting 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 the washing water. The supply pressure of this filtered clean water was 0.5 MPa. The secondary cake had a pH of 1.0 to 2.5, a moisture content of 40 to 50%, and an ash content of 0.5 to 3.0%. Since the ash content of the secondary cake was less than the expected value (3.0%), the process proceeded to the next step without repeating washing and the like.

  The secondary cake was slurried so that the solid concentration was 14.3 (mass / volume)% and 28.6 (mass / volume)%. In this slurry formation, sodium metasilicate and sodium hydroxide were added as inorganic salts. This addition was performed so that sodium metasilicate was 2.96 kg and sodium hydroxide was 0.18 kg with respect to 1.0 kg of lignin. According to this addition amount, when the solid concentration is 16.5 (mass / volume)%, the concentration of lignin is about 4 (mass / volume)%, and the solid content concentration is 33.1 (mass / volume). )%, The concentration of lignin is about 8 (mass / volume)%.

  The slurry after the addition of the inorganic salt was formed into droplets with a spray dryer and dried to form inorganic salt-containing fine particles. The temperature of the slurry when supplied to the spray dryer was 40 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 component constitution 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 thermally decomposed (baked) with an organic component using an externally heated rotary kiln. The thermal decomposition temperature was 700 ° C. and the firing time was 2 hours. The inorganic salt-containing fine particles after pyrolysis were lignin: inorganic salt: water = 0.5: 4.5: 0.0.

  The inorganic salt-containing fine particles after pyrolysis were slurried using warm filtered fresh water. This slurrying was performed so that there were two types of solid content concentrations of 10% and 20%. All of the obtained slurries had a temperature of 60 ° C.

The inorganic salt-containing fine particle slurry is press-fitted into a filter press (filtration area 0.6 m ² , filter chamber volume 7.8 L, filter cloth: made of polypropylene), and further forward cleaning, primary pressing, reverse cleaning, secondary pressing, gas Substitution was performed to obtain a dehydrated cake. The press-fitting pressure was 0.2 MPa, the primary pressing pressure and the secondary pressing pressure were 1.5 MPa, the cleaning liquid supply pressure was 0.1 MPa, and the replacement gas supply pressure was 0.5 MPa. Filtered fresh water was used as the cleaning liquid, and air was used as the replacement gas. The component composition of the dehydrated cake was lignin: inorganic salt: water = 0.48: 0.01: 3.8. From this result, it can be seen that the inorganic salt is sufficiently removed. In addition, according to the test by the present inventors, when the mass of the inorganic salt added to the secondary cake is 9.0 kg with respect to 1.0 kg of lignin, the inorganic salt contained in the dehydrated cake is 4 kg. The inorganic salt could not be removed when the mass of the inorganic salt added was 0.98 kg with respect to 1.0 kg of lignin. From this, it was found that the inorganic salt added to the secondary cake is preferably 280 parts by mass or more with respect to 100 parts by mass of lignin.

  The dehydrated cake after removing the inorganic salt was dried using a constant temperature dryer. The drying rate was 0.12 kg / day. The drying temperature was 120 ° C. Sample photographs of the carbon fine particles (dried product) thus obtained are shown in FIGS. 5 and 6. (1) in FIG. 5 is a sample photograph of the obtained carbon fine particles (secondary particles), and (2) is a sample photograph in which the outer shell portion of the carbon fine particles is enlarged. 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 porous with nanoscale primary particles (see FIG. 6). Therefore, it can be used as a filler for automobile tires.

  The present invention is applicable as a method and equipment for producing carbon fine particles from black liquor discharged in a paper mill.

  DESCRIPTION OF SYMBOLS 10 ... Concentration process, 20 ... Dilution tank, 30 ... Acidification tank, 40 ... Filter press, 50 ... Slurry tank, 60 ... Preliminary tank, 70 ... Agitation tank, 80 ... Spray dryer, 90 ... Cyclone, 91 ... Bug Filter, 100 ... Rotary kiln, 110 ... Slurry tank, 120 ... Filter press, 130 ... Dryer, 140 ... Wet grinder, 141 ... Dispersion tank, C1 ... First dehydrated cake, C2 ... Second dehydrated cake, G1 ... acidified gas.

Claims (17)

A method for producing carbon fine particles from a lignin-containing liquid,
After acidifying the lignin-containing liquid, dehydration to obtain a first dehydrated cake,
Slurry and acidify the first dehydrated cake, and then dehydrate again to obtain a second dehydrated cake.
This second dewatered cake is slurried and mixed with an inorganic salt, and then dropletized and dried to obtain inorganic salt-containing fine particles,
After pyrolyzing the inorganic salt-containing fine particles, the inorganic salt is removed to obtain carbon fine particles.
A method for producing carbon fine particles. Acidification of the lignin-containing liquid is performed in a range where the pH remains at 8.5 or more and with stirring.
The method for producing carbon fine particles according to claim 1. As the lignin-containing liquid, a black liquid having a pH of 13 or more is used.
The method for producing carbon fine particles according to claim 1 or 2. As the lignin-containing liquid, a black liquor having a solid content concentration of 50 to 60% by mass diluted to a solid content concentration of 20 to 35% by mass is used.
The manufacturing method of the carbon microparticles of any one of Claims 1-3. The dehydrated filtrate discharged when obtaining the first dehydrated cake is sent to the black liquor concentration step.
The method for producing carbon fine particles according to claim 3 or 4. The pH is adjusted to 1.0 to 4.0 by proceeding with the acidification.
The manufacturing method of the carbon fine particle of any one of Claims 1-5. The inorganic salt is mainly composed of sodium metasilicate and sodium hydroxide,
The manufacturing method of the carbon fine particle of any one of Claims 1-6. The mass mixing ratio of the second dehydrated cake, the sodium metasilicate and the sodium hydroxide is 1: 2.96 to 8.88: 0.18 to 0.54.
The method for producing carbon fine particles according to claim 7. The slurry after mixing the inorganic salt is passed through a filter, and then the droplets are formed and dried.
The method for producing carbon fine particles according to any one of claims 1 to 8. Acidification of the lignin-containing liquid is performed by blowing acidification gas into the lignin-containing liquid.
The manufacturing method of the carbon fine particle of any one of Claims 1-9. Collecting inorganic salt-containing fine particles obtained by droplet formation and drying, and using exhaust gas generated during the dust collection as the acidifying gas;
The method for producing carbon fine particles according to claim 10. The inorganic salt-containing fine particles are collected using a cyclone and a bag filter in this order.
The method for producing carbon fine particles according to claim 11. The pyrolysis is performed using a rotary kiln equipped with an external heat jacket,
The pyrolysis gas discharged from the rotary kiln is used as a combustion gas for a hot air furnace for supplying hot air to the outer heat jacket,
Using exhaust gas discharged from the external heat jacket as the acidified gas,
The method for producing carbon fine particles according to any one of claims 10 to 12. Removal of the inorganic salt is performed by slurrying the inorganic salt-containing fine particles after pyrolysis, press-fitting into a filter press, and pressing.
The method for producing carbon fine particles according to any one of claims 1 to 13. After slurrying the inorganic salt-containing fine particles after the thermal decomposition, and prior to press-fitting into the filter press, pass through the filter,
The manufacturing method of the carbon microparticles of any one of Claims 1-14. The ash content of the second dehydrated cake is 3.0% or less,
And the press-fit filtrate discharged from the filter press is used when mixing and slurrying the second dehydrated cake and the inorganic salt.
The manufacturing method of the carbon fine particle of any one of Claims 1-15. A facility for producing carbon fine particles from a lignin-containing liquid,
First acidifying means for acidifying the lignin-containing liquid;
Means for dehydrating the lignin-containing liquid acidified by the first acidification means;
Means for slurrying the dehydrated cake obtained by the dehydration;
A second acidification means for promoting acidification of the slurry during or after the slurrying;
Means for returning the acidified slurry to the dewatering means;
Means for slurrying the dehydrated cake obtained by dehydration after the return;
Means for mixing with the inorganic salt in the slurry during or after the slurrying;
Means for dropletizing and drying the slurry mixed with the inorganic salt;
Means for thermally decomposing inorganic salt-containing fine particles obtained by droplet formation and drying;
Means for removing the inorganic salt from the inorganic salt-containing fine particles obtained by the thermal decomposition to obtain carbon fine particles;
A facility for producing carbon fine particles, comprising: