JPH0431492A - Manufacture of superclean carbonaceous pitch - Google Patents

Abstract

PURPOSE:To obtain the title pitch which can realize improvements in the strength and elastic modulus of carbon fiber by removing most part of ash contained in the raw material to produce a carbonaceous pitch and then removing the ash remaining therein. CONSTITUTION:The raw material of carbonaceous pitch (e.g. pyrolytic tar) is heated so as to provide a viscosity of 0.05-90Pa.s and filtered through a filter made of a sintered metal having a pore diameter of 0.05-5mum and a porosity of 50% or higher in an inert atmosphere under a pressure of 1-100kgf/cm<2> for 1-3hr to remove most part of the contained ash, thus giving a material having an ash content as low as at most 100ppm. This material is subjected to thermal decomposition and polycondensation to give a carbonaceous pitch. This pitch is filtered through the aforementioned filter, which is clogged to an appropriate degree by passing the aforementioned raw material through it for 1-3hr, to remove the remaining ash, thus giving a superclean carbonaceous pitch having an Fe content of 2ppm or less, an Al content of 1ppm or less, an Si content of 3.3ppm or less, and a total content of Fe, Al, and Si of 5ppm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing ultra-clean carbonaceous pitch suitable for producing carbon materials, particularly high-performance carbon fibers.

[Conventional technology]

BACKGROUND ART Conventionally, there has been a demand for the development of high-performance materials having light weight, high strength, high elastic modulus, etc. in various industrial fields such as automobiles, aircraft, and others, and carbon molding materials, carbon fibers, etc. have been attracting attention from this viewpoint.

In particular, the method of manufacturing carbon fiber from carbonaceous pitch is considered important as a method for manufacturing inexpensive and high-performance carbon fiber, and much research has been conducted in recent years, and the performance of carbon fiber obtained from carbonaceous pitch has been has also improved.

However, since the pitch fibers obtained from carbonaceous pitch are extremely fragile, many measures have been taken to handle the yarn in subsequent processes6.Furthermore, in recent years, the amount of ash remaining in carbonaceous pitch has increased. As it has become increasingly clear that thread breakage occurs when spinning pitch fibers from carbon pitch, and that it has a significant effect on the physical properties of the final product, carbon fiber, it has become clear that clean carbon pitch with low ash content can be obtained. This has become an important issue.

As a method for removing the ash content in carbonaceous pitch, the raw material tar, which is the raw material for producing carbonaceous pitch, is centrifuged to reduce the ash content to 0.005% by weight (5% by weight).
0pp■) or less (Japanese Patent Laid-Open No. 58-8
No. 1619) and raw material tar are heated to 50 to 200°C and passed through an electrostatic precipitator to remove ash, and then subjected to pyrolysis polycondensation to reduce the ash content in the mesoface pitch product to 0.1.
Method to reduce weight to below (1,ooopp■) (Unexamined Japanese Patent Publication No. 6
3-162785)7 On the other hand, as a method for directly removing ash from carbonaceous pitch, a method of centrifuging carbonaceous pitch under high centrifugal force (Japanese Unexamined Patent Publication No. 6
0-34619) has been proposed.

[Problem to be solved by the invention]

However, in the method of removing ash from raw material tar, for example, even if the ash content is reduced to fOppm (0,001%), the ash content accumulates about 10 to about 90 times during the pitch manufacturing process, resulting in a -〇〇〇pp has the disadvantage that it rises to 100%, and there is also the problem that metal flakes off and gets mixed in due to corrosion or wear of reaction vessels, piping, etc. On the other hand, the method of directly removing ash from carbonaceous pitch has the disadvantage that since carbonaceous pitch is a highly viscous substance, it is difficult to remove fine particles and it is difficult to reduce the ash content. Therefore, the residual ash content in the pitch after the ash removal treatment was usually about 509P.

In the process of developing carbon fiber with even higher strength and higher modulus, the present inventors discovered that the ash content in the pitch was approximately 50 ppIl.
Even if it is 1, it may cause structural defects, and especially if high temperature firing is performed at 2,000℃ or higher, it may be difficult to develop strength due to the formation of pores in the fibers. I understand.

In addition, in order to develop higher strength, simply increase the ash content by 50%.
It was found that it is not sufficient to reduce the ash content to less than ppm, and that certain elements in the ash have a large effect on the development of strength.

Therefore, in order to eliminate structural defects due to ash content in carbonaceous pitch and obtain ultra-high strength carbon fiber.

The emergence of a new ultra-clean carbonaceous pitch has been desired.

In order to solve these problems, the present inventors have previously proposed a method for producing ultra-clean carbonaceous pitch in which carbonaceous pitch is filtered using a sintered metal filter (
(Japanese Patent Application No. 2-79827), it was found that this method has the drawback that the filtration rate of carbonaceous pitch is slow.

Therefore, it is an object of the present invention to overcome these problems, that is, to provide an extremely low content of specific elements in the ash.
The object of the present invention is to provide a rapid manufacturing method for ultra-clean carbonaceous pitch that allows stable and easy production of high-performance carbon fibers.

[Means to solve the problem]

The above object is achieved by the method for producing ultra-clean carbonaceous pitch according to the present invention.

That is, according to the present invention, the raw material for producing carbonaceous pitch is first subjected to a first ash removal treatment to remove most of the ash content (the ash content is 1100 pp or less).

Next, after producing carbonaceous pitch using the obtained low ash raw material, the obtained carbonaceous pitch is further subjected to a second ash removal treatment to remove residual ash in the carbonaceous pitch. Provided is a method for producing ultra-clean carbonaceous pitch for carbon materials, characterized by the following.

In the method of the present invention, the ash removal process is performed in two stages, so the ash removal rate in each step can be increased, and as a result, ultra-clean pitch can be obtained more quickly than in conventional methods. I can do it.

In the first ash removal treatment in the present invention, it is preferable that the viscosity of the carbonaceous pitch raw material ranges from 0.0 OIPa-s to 10
This is carried out by filtration using a filter in a temperature range of Pa-s. In this case, since the viscosity of the raw material is low, the ash removal process can be carried out quickly. Further, the second ash removal treatment is preferably performed by filtration using a filter in a temperature range where the viscosity of the carbonaceous pitch is from 0.05 Pa-s to 90 Pa-s.

By the above-mentioned first and second ash removal treatments of the present invention,
Fe content in carbonaceous pitch is 2 ppm or less, AQ content is IP
An ultra-clean carbonaceous pitch suitable for producing carbon materials that has a PPP and Si content of 3.3 ppm or less and a total amount of Fe, AQ, and Sj components of 5 ppm or less is easily produced. .

Note that the Fe content, Af1 content, and Si content herein are values determined by the following method. That is, the sample pitch is treated with concentrated sulfuric acid, heated and carbonized, and then incinerated at 755±25°C. After melting this ash with sodium carbonate, dissolve it in hydrochloric acid and water to obtain a sample. For this sample solution, the luminescence intensity of each element of Fe, A11l, and Si was measured using an inductively coupled plasma emission spectrometer (ICP emission spectrometer), and the concentration of each element in the sample was determined from a calibration curve prepared in advance. were determined and classified into Fe, AQ, and Si, respectively. As the ICP emission spectrometer, an "rICPS-1000" sequential type manufactured by Shimabara Seisakusho was used.

As mentioned above, the carbonaceous pitch obtained by the production method of the present invention has an Fe content of 2 ppm or less and an AQ content of 1 ppm.
It is preferable that the ash content is 3.3 ppm or less, and the total amount of Fe content, AQ content, and 84 content is 5 ppm or less.
．． It exists as particles with a size of 1 or less. Due to such a low ash content, when carbon fibers are produced from the carbonaceous pitch obtained in the present invention according to a conventional method, structural defects in the carbon fibers due to the elements in the pitch are eliminated;
Ultra-high strength carbon fibers can be obtained stably and easily. In addition to the above-mentioned Fe, AQ, and Sj contents, ash usually contains trace amounts of Ni and Cr, but as mentioned above, if the Fe content is 2 ppm or less and the AA content is is l
ppm or less and Sj content is 3°3 ppm or less, and the total amount of Fe content, AQ content, and Si content is 5 ppm or less, so that high-performance carbon materials, especially ultra-high strength,
An ultra-clean carbonaceous pitch from which high modulus carbon fibers can be produced is obtained.

Furthermore, the Fe content in the pitch is 0.8 ppm or less, the AQ content is O95 ppm or less, and the Si content is 1.4 ppm or less, and the total amount of Fe content, AQ content, and Si content is 2 ppm.
It is particularly preferable that it be less than or equal to m.

Furthermore, if carbon fibers are manufactured using carbonaceous pitch in which the total amount of Fe, AQ, and Si exceeds 5 pp■, defects will occur inside the carbon fibers, making it impossible to obtain carbon fibers with sufficient high strength. . In particular, in the case of high-temperature firing of 2,000°C or higher, the development of strength decreases. Also, although the reason is unclear, even if only the Fe content exceeds ZPP-, the strength development is not sufficient7.Similarly, only the AQ content exceeds lppm or S
Even if only the j portion exceeds 3.3 ppm+, the strength is not sufficiently developed.

In order to produce high-performance carbon materials, especially carbon fibers with ultra-high strength and high modulus, as mentioned above, the Fe content is 2 ppm or less, the AQ content is 1 ppm or less, and the Sj content is 3.3 ppm or less. Furthermore, it is necessary that the pitch be an ultra-clean carbonaceous pitch containing elements below a specific value, such as a total of Fe, AQ, and Si of 5 ppm or less.

The raw material carbonaceous pitch used in the present invention is a known starting material,
For example, mesophase pitch (optically anisotropic It may also be a membrane pitch made from aromatic hydrocarbons, a pitch containing an optically anisotropic phase and an optically isotropic phase, or an optically isotropic pitch. For example, when producing ultra-high-strength, high-performance carbon fiber from mesoface pitch obtained by pyrolysis polycondensation, the mesoface content is 70%.
~100% mesophase pitches are preferred, particularly mesophase pitches containing substantially 100% mesophases are most preferred.

When producing mesoface pitch by thermally decomposing and polycondensing the starting material tar, etc., attempting to increase the content of the optically anisotropic phase increases the softening point of the resulting mesoface pitch; The spinning temperature will inevitably be high, but
This makes spinning difficult and prone to yarn breakage.

Therefore, in the production of mesoface pitch, thermal polycondensation is stopped halfway and the polycondensate is reduced to 350 to 400%.
The optically anisotropic phase with high density (hereinafter referred to as AP phase) is deposited in the lower layer while growing and maturing, and the optically anisotropic phase with lower density in the upper layer is deposited. It is preferable to adopt a method in which the isotropic phase (hereinafter referred to as IP phase) is separated and taken out from a portion with a large amount. Details of this method are described in JP-A-57-119984.

A more preferable method for producing mesoface pitch is as described in JP-A-58-180585.
The carbonaceous pitch, which contains a suitable amount of phase and has not yet become excessively heavy, is subjected to a centrifugation operation in a molten state to quickly obtain A.
This is a method in which the P phase portion is allowed to settle.

According to this method, the AP phase accumulates in the lower layer (layer in the direction of centrifugal force) while coalescing, and the AP phase forms a continuous layer with approximately 80% or more of the AP phase, with a small amount of the IP phase in the crystalline or The pitch is dispersed in tiny spherical bodies. In this case, the boundary between both layers is clear, and only the lower layer can be separated from the L layer, making it easy to produce mesoface pitch that has a high AP phase content and a low softening point, and is therefore easy to spin. can. According to this method, the AP phase content is 95%.
As described above, mesoface pitch having a softening point of 230° C. to 320° C. can be obtained economically in a short time.

The membrane pitch obtained in this way has a low softening point despite its homogeneity and high orientation, and therefore has essentially excellent melt spinning properties. However, even when such pitch is used, yarn breakage and fluffing occur during spinning, but this is caused by wear of the catalyst and equipment already mixed in the raw material for producing pitch,
This is largely due to foreign matter that gets mixed in due to corrosion, etc.

In the present invention, it is preferable to perform filtration treatment using a filter for both the first ash removal treatment performed at the raw material stage for carbonaceous pitch production and the second ash removal treatment performed after carbonaceous pitch production. In case of filtration treatment, the pore size is 0
Using a filter with 005 to 5 voices, under an inert gas atmosphere, the filtration pressure is 1 to 100 kgf/CI! It will be implemented under 2. In this case, the filter is one that has the above-mentioned fine pore size and is heat resistant, such as a sintered metal filter, a wire mesh filter, or a metal powder-filled filter (temperature range where the pitch viscosity is 0.05 to 90 Pa-s). (as the maximum temperature may reach 300-400°C) is used.

Among the above filters, sintered metal filters are particularly preferably used. The sintered metal filter used is stainless steel (e.g. SυS 316L).
Short fibers are laminated and sintered, and the pore size is 0.05-5. ,
Especially 0.1-14, porosity 50% or more, especially 60-8
About 0% is preferable. When the pore size exceeds 5/all, the ash trapping efficiency decreases, and conversely, when the pore size is less than 0.05, it is difficult to manufacture a filter with fine holes. Further, it is preferable that the porosity be large, but if it is too large, the mechanical strength of the filter will decrease. The pore size is measured by the bubble point method, which is a known method.

In addition to disc filters, various types of filter elements can be used, including pleated cylindrical filters, flat cylindrical filters, tube filters, and leaf disc filters.

The sintered metal filter has a smaller pore diameter, is superior in stability, and has a higher ash retention ability than a wire mesh filter, a metal powder-filled filter, or the like.

In the present invention, the first ash removal treatment performed at the raw material stage for carbonaceous pitch production and the second ash removal treatment performed after the production of carbonaceous pitch are both performed in one stage of filtration treatment using the above-mentioned filter. Clean carbonaceous pitch can be obtained by performing this process, but if you want to obtain a raw material for producing even cleaner carbonaceous pitch and a cleaner pitch, two or more filtration operations are performed using a sintered metal filter with a small pore size. This is achieved by doing the following.

As the first stage filtration pressure filter, the pore size is 0705~
A 5P sintered gold filter is used. As the second stage filtration pressure filter, carbonaceous pitch manufacturing raw material or carbonaceous pitch containing ash is passed through a filter with a pore size of 0.05-5s+ for at least 1 to 3 hours or more, so that the filter eyes Those that are moderately clogged with fine ash particles are used. In addition, the second
Use one that has been used for 1 to 3 hours or more as the second stage filter.

Furthermore, when used as a third-stage filter, finer particles can be captured, and cleaner carbonaceous pitch production raw material and carbonaceous pitch can be obtained.

In this case, the first stage filtration treatment is 1 to 100 kgf/
It is carried out under an inert atmosphere under a pressure of aJ. Also,
It is preferable that the latter stage filtration treatment using the filter pre-coated with ash as described above is carried out under an inert atmosphere, following the first stage filtration treatment, at a viscosity within the same range as the first stage. In order to obtain pitch, it is preferable to perform two or more stages of filtration processing as described above for both the first and second ash removal processing, but in order to increase the filtration speed, the first stage filter is It is also possible to carry out filtration while regenerating the filter by backwashing it every time the filter becomes clogged, and to use the downstream filter as it is for a long time.

So far, we have described filtration using a filter as a method for removing ash at the raw material stage for carbonaceous pitch production, but as another method,
A method of centrifugal separation under a centrifugal force of 0OOG, a method of removing ash by passing the raw material through the electrode surface of an electrostatic precipitator, etc. can also be applied.

Further, the first ash removal treatment performed at the stage of raw material for production of carbonaceous pitch may be performed by diluting with a solvent such as benzene, toluene, xylene, etc. Note that after the first ash treatment, removing the light content in the raw material, or after removing the light content in the raw material, performing the first ash removal treatment may be adopted as necessary.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is of course not limited thereto.

Example 1 A heavy residual oil with a specific gravity Q of 992, a carbon content of 88.9% by weight, and a hydrogen content of 9.8% by weight, produced as a by-product in the catalytic cracking of vacuum gas oil, was converted to normal pressure using a vacuum distillation apparatus. The residue was distilled to 415° C. to obtain a residual tar with a yield of 73% by weight.

The resulting residual tar has a specific gravity of 1,062 and a carbon content of 8.
9.1% by weight, hydrogen content 9.7% by weight, ash 0.22
Weight % (2,200 pP), viscosity at 100° C. was 14.7 centistokes.

This residual tar was introduced into a filtration device and subjected to a first ash removal process. As a filter, a sintered metal filter made of stainless steel (SO8316L) with a pore size of 1-mm (Japanese line flIell: NP-1) was used to perform the filtration process. The diameter of the filter is 60+u+
Met.

2 kg of the above-mentioned residual tar was introduced into a filtration device equipped with the above-mentioned filter, and filtration was performed.

The atmosphere was nitrogen gas, and the atmosphere was pressurized with nitrogen gas. The pressure during filtration was 20 kgf/cd. The temperature during filtration was 100°C, and the viscosity of the cooled residue was 0.01
It was 3 Pa-s. The time required for filtration was 40 minutes. The ash content in the residual tar after the filtration treatment was 30 ppm.

Put 20kg of this tar into a reactor with an internal volume of 30Q,
3. At 415°C with sufficient stirring under normal pressure nitrogen gas flow.
Heat treated for 5 hours, softening point 240℃, quinoline solubility 13
．． 9% by weight, approximately 55% when observed with a polarizing microscope 111 [M]
A pitch containing an optically anisotropic phase of 23.0% by weight was obtained.

The temperature of this pitch is controlled at 350°C, and a predetermined flow rate of 20
The yield of pitch collected from the heavy liquid outlet was 51% by weight, which was fed at mA/min, controlled the rotor temperature at 350°C, and was continuously separated into heavy liquid and light liquid by a centrifugal force of 5.0OOG. , a softening point of 268° C., a quinoline solubility of 28.1% by weight, and an optically anisotropic phase observed with a polarizing microscope of 97%.

The obtained membrane pitch is introduced into a filtration device, and the second
The following ash removal treatment was performed. As a filter, a sintered metal filter made of stainless steel (SLIS316L) with a pore size of 0.1 mm [manufactured by Nihon Dansen Co., Ltd.: N
Filtration treatment was performed using P-2013. The diameter of the filter was 60 mm.

Into a filtration device equipped with such a filter, 250 g of the liquid crystal pitch obtained by separation with a centrifuge was introduced,
Filtration was performed. The atmosphere was a nitrogen gas atmosphere, and filtration was performed under pressure with nitrogen gas. The pressure during filtration is 40
The test was carried out at kgf/cd. The temperature during filtration was 340°C, and the viscosity of the menface pitch was 9 Pa-s.

The filtration time for 250 g of mesoface pitch was 50 minutes.

The Fs content in the ultra-clean pitch obtained in this way is 1,5
ppm, AQ content is 0.4ppm, Si content is 2.9ppm
m, and the total amount of Fe, i, and Si is 4.8p.
I finished it with a pie.

The obtained ultra-clean mesoface pitch was 0°3mm in diameter.
The mixture was filled into a spinning machine with a single-hole nozzle, melted at a temperature of 335° C., extruded under nitrogen pressure, wound onto a bobbin at the bottom of the nozzle, and spun at a take-up speed of 500 m/min. During spinning for 1 hour, the yarn did not break even once.

Next, this pitch fiber was made infusible at 230°C in an oxygen atmosphere for 1 hour, and then heated at a rate of 1.50°C at a rate of 20°C/min.
Carbonization was performed by raising the temperature to 0°C to obtain carbon fibers. The obtained carbon fibers had a fiber diameter to, an opm, and a tensile strength of 3.
The tensile modulus was 4 GPa and the tensile modulus was 260 GPa.

Furthermore, graphite fibers were obtained by firing to 2,500°C.

The obtained graphite fiber has a fiber diameter of 9.9-1 and a tensile strength of 3.6.
It had an extremely high quality of 0 Pa and tensile modulus of 740 GPa.

Example 2 The first ash removal treatment performed at the raw material stage for carbonaceous pitch production and the second ash removal treatment performed after carbonaceous pitch production were carried out using two filters. It was treated in the same manner as in Example 1.

In the first ash removal process performed at the raw material stage for the production of carbonaceous pitch, the first stage filter is made of stainless steel (SO3316L) with a diameter of 60 mm and a pore size of 1-.
) A clean new sintered metal filter [manufactured by Nippon Seiren M: NP-1] was installed, and as the second stage filter, the raw material (residual tar) had been filtered for 1 hour beforehand. The ash content in the residual tar was precoated on the same sintered metal filter as above. The filtration time for 2 kg of residual tar was 50 minutes. The ash content in the residual tar after the filtration treatment was 20 ppm. The second ash removal treatment performed after the production of carbonaceous pitch was performed using stainless steel (SO5316L) with a pore diameter of 0°IIs as the first stage filter. ) 112, and as the second stage filter, the mesoface pitch separated in advance with a centrifuge was filtered for 1 hour to remove the ash content in the mesoface pitch. A precoated filter was mounted on the same sintered metal filter as above. Menface pitch 250g
The filtration time was 60 minutes.

The Fe content in the ultra-clean pitch obtained in this way was 0.2p.
pm, AQ component is 0. lppm+, Si content is 0, 4pp
m, and the total amount of Fe, AQ, and Si is O0
It was 7 ppm. When the ash particles were observed with a scanning microscope, the majority of the particles were 0.05. It was below cs.

When the obtained ultra-clean mesoface pitch was spun in the same manner as in Example 1, there was no yarn breakage even once during spinning for 1 hour.

Carbon fibers obtained by firing to 1,500°C in the same manner as in Example 1 had a fiber diameter of 10.07a, a tensile strength of 3, and 5G.
Pa, tensile modulus of elasticity 260 GPa, 2,500°C
The graphite fibers obtained by firing up to 10% had extremely high quality, with a fiber diameter of 9.9 pm, tensile strength of 4.5 GPa, and tensile modulus of 750 GPa.

Comparative Example 1 The same process as in Example 1 was carried out, except that the centrifuged mesophase pitch (ash content: 250 ppp) containing a 99% optically anisotropic phase was spun as it was.

In this case, thread breakage during spinning occurred 12 times per hour. 1. The tensile strength of carbon fiber obtained by firing at 500°C was 2.
, 4GPa, tensile modulus is 250GPa, 2,
The tensile strength of graphite fiber obtained by firing at 500℃ is 1,
The tensile strength was significantly lower and the tensile modulus was also lower than in Example 7, which was 7 GPa and the tensile modulus was 600 GPa.

Comparative Example 2 First step at the stage of carbonaceous pitch production raw material (residual tar)
The treatment was carried out in the same manner as in Example 1, except that the following ash removal treatment was not performed. In this case, it took 4 hours to filter 250 g of menface pitch.

The Fe content in the ultra-clean pitch thus obtained was 1°Ei
ppm, AQ part is 0.4pp+s, Si part is 2.9p
pm, and the total amount of Fe, AΩ, and Si is 4
, 9 ppm.

The obtained pitch was spun in the same manner as in Example 1, and carbon fibers and graphite fibers were produced in the same manner as in Example 1.
The tensile strength and tensile modulus of the fired graphite fiber were at the same level as in Example 1.

However, in this comparative example, it is clear that it takes a long time to obtain the same level of ultra-clean pitch as in the example.

〔Effect of the invention〕

Since the method of the present invention has the above-mentioned structure, the ash content, especially the content of specific elements, is extremely low. Therefore, when carbon fiber is manufactured using the ultra-clean pitch obtained by the method of the present invention, Carbon fibers with high strength and high modulus can be produced. In particular, when fired at high temperatures, defects within the fibers that were conventionally observed do not appear, and graphite fibers with ultra-high strength and high modulus of elasticity can be produced.

Moreover, according to the method of the present invention, such ultra-clean carbonaceous pitch can be easily and quickly produced.

As described above, the carbon fibers and graphite fibers produced from the pitch obtained by the method of the present invention are free from defects and have characteristics of high strength and high elastic modulus.
As a reinforcing fiber for lightweight structural materials for space development, buildings, etc.
It can be used very effectively.

Furthermore, the ultra-clean pitch obtained by the method of the present invention is
It can also be used as an excellent matrix material for carbon/carbon composite materials because it has no defects under high temperature firing.

The above discussion has focused on mesoface pitch systems, but it also applies to optically isotropic pitch systems.

It has the advantage of being able to produce defect-free general-purpose carbon fibers or other carbon materials.

Furthermore, when the pitch obtained by the method of the present invention is used, it has the advantage that the spinnability in the carbon fiber manufacturing process can be improved more than ever before.

Claims (1)

[Claims] (1) The raw material for producing carbonaceous pitch is first subjected to a first ash removal treatment to remove most of the ash content, and then the obtained low-ash content raw material is used to produce carbonaceous pitch. ,
A method for producing ultra-clean carbonaceous pitch for carbon materials, characterized in that the obtained carbonaceous pitch is further subjected to a second ash removal treatment to remove residual ash in the carbonaceous pitch.