JP2598112B2 - Filtration method of pitch for carbon fiber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filtering coal-based or petroleum-based pitch to obtain pitch suitable for producing pitch-based carbon fiber.

2. Description of the Related Art Pitch suitable as a raw material for carbon materials, especially pitch-based carbon fibers, generally needs to be homogeneous and thermally stable. Especially in the production of pitch-based carbon fibers, yarn breakage and unevenness of fineness in the melt spinning process are a major industrial problem, and in order to spin them, a homogeneous material at the melt spinning temperature that does not contain foreign matters such as solids or gel-like substances It is necessary to supply a pitch excellent in spinnability to the spinning process.

Here, the foreign material is a solid particle such as carbon or a metal element compound originally contained in the pitch raw material, a coked carbon particle generated during the production of the pitch, a gel material which has been locally polymerized, or a pitch production device. And contaminants. Before the melt spinning, a uniform pitch is obtained through a molten pitch through a fine filtration network or a filtration device composed of a filter aid layer and a filtration network in order to remove these foreign substances. Is generally performed not only for the molten pitch but also for the molten polymer.

For example, as a method of removing foreign substances in the molten polymer, as a method using a filter of a specific size aperture,
There are JP-A-59-88924, JP-A-59-112030, JP-A-61-108716, and the like, and JP-A-52-5311 and JP-A-52-5311 using a filter aid layer. Kuniaki 51-32728
No. Gazette.

In the case of a molten pitch, it is basically possible to remove foreign substances by the same method as for a molten polymer.However, in the case of a pitch, the starting material is not uniform in the production method, and the thermal decomposition polymerization reaction is mainly used. Due to the production method, the controllability of the reaction is inferior, the amount of foreign substances is larger than that of ordinary polymers, and it is often difficult to filter. For this reason, in the case of pitch, it is difficult to completely remove foreign matter by a conventionally known filtering method using only a filter medium, and even if a filter medium capable of removing foreign matter is selected, the period during which filtration can be performed is extremely short, and the filter medium is consumed. In addition, the cost of regeneration is increased, and the cost of filtration becomes expensive.

In addition, in order to completely remove the foreign matter of the pitch by a precoat filtration method in which the filter aid layer is previously loaded on a filter net or the like, the filter aid particles used for the precoat layer are finely divided or the precoat layer is thickened. For this reason, the filtration pressure loss is large, and the precoating method is complicated. Therefore, it is difficult to increase the size and the filtration cost must be expensive. Further, it is difficult to regenerate and wash the filter medium, and there is a problem that the cost of filtration is extremely high for industrial implementation.

Problems to be Solved by the Invention The biggest problem when industrially performing the filtration of the molten pitch is that the foreign matter in the molten pitch cannot be specified, so that a filtration method suitable for the foreign substance could not be selected. On the point.

The specific difficulty of the foreign matter in the pitch is that the molten pitch is a completely opaque black body, making it impossible to observe optical foreign matter, and those containing quinoline-insoluble components such as mesophase pitch, It has not been possible to determine the amount of foreign matter based on the solvent-insoluble content or the like, and it was conventionally impossible to obtain information on the size of the foreign matter.

Thus, the present invention provides information on the amount and size of foreign matter present in a molten pitch, and provides a more economical method for filtering pitch for carbon fibers.

Means for Solving the Problems That is, the gist of the present invention is to provide a diatomaceous filter aid having an average diameter of 1 to 10 times the average diameter of the foreign matter originally contained in the pitch by 0.5 to 10 times the amount of the foreign matter. The present invention provides a method for filtering pitch for carbon fiber, wherein the pitch added at a volume ratio of not more than twice is melted and filtered at a viscosity of 1 poise to 3000 poise and a filtration pressure difference of 30 kgf / cm ² or less. It is in.

In the present invention, a diatomaceous filter aid is added to the molten pitch, and the apparent filter cake specific resistance value, the apparent filter cake porosity, and the filter aid are based on the amount of the filter aid obtained by the body feed filtration. From the relation of the amount of addition, information on the size and amount of foreign matter originally present in the molten pitch is found, and an optimum filtration method is provided based on the information.

This is based on a model for estimating the porosity of binary mixture particles (eg, Materials, Vol. 23, No. 133, p. 752 (1964)) and Kozeny-
From the relationship between the Carman equation and the specific resistance value of the filter cake (eg, filtration mechanism, published by Jinjinshokan, p. 105, 1978), the ratio of the average particle size of the added filter aid to the particle size of the foreign matter, and the presence in the pitch In this case, the volume fraction of the foreign matter is calculated by an estimation method.

First, the relationship between the amount of foreign matter in the pitch and the diameter of the aid particles and foreign matter that satisfies the relationship between the apparent filter cake porosity and the amount of the filter aid obtained by the experiment is determined using a porosity estimation model. The size and quantity of the foreign matter cannot be specified from this estimation, and a relationship between the size and quantity of the foreign matter that satisfies the measured value can be obtained.

Next, based on the relationship between the apparent filter cake specific resistance value obtained from the experiment and the amount of filter aid added, the relationship between the size and amount of the foreign matter obtained earlier was identified based on the estimation formula starting from the Kozeny-Carman equation. The size and amount of foreign matter in the pitch are determined.

When quantifying foreign matter in the pitch by this method, especially in the case of a mesophase pitch that requires a relatively long-term pyrolysis polymerization reaction under high temperature, the amount of foreign matter is relatively large, usually 100 ppm in the molten pitch From the results, it was found that about 1000 ppm of foreign matter was contained. At this time, the size of the foreign matter was several μm to several tens μm in average diameter. The foreign matter quantification method carried out by the present inventors is not limited to the foreign matter in the molten pitch is a simple solid particles, even if the foreign matter that shows a complex behavior consisting of a mixture of solids and gel-like substances, the filtration state In order to directly observe the behavior of the foreign matter in the filter, it is considered to be an index that appropriately gives the optimum filtration conditions.

The present inventors have found from the knowledge obtained by the quantification of foreign matter in the molten pitch, especially in the case of mesophase pitch for spinning, that the body using a diatomaceous filter aid is used in view of the relationship between the size and amount of foreign matter in the molten pitch. It was clarified that feed filtration was suitable, and the range in which the effect was exhibited was closely related to the amount and size of foreign matter, and the optimum conditions existed in a relatively narrow range.

That is, the size of the diatomaceous filter aid is 1 to 10 times, preferably 2 to 5 times the average diameter of the foreign matter in the molten pitch, and the amount added is the volume of the foreign matter in terms of volume. 0.5 times or more and 10 times or less, preferably 2 times to 5 times, and the filtration pressure at this time is 30 kgf / cm ² or less, preferably 20 kgf / cm ² or less, and substantially completely removes foreign matter. By the body feed filtration, the viscosity of the molten pitch is from 1 poise to 3000 poise, preferably from 10 poise to 500 poise, so that foreign substances in the pitch can be economically and industrially removed.

The foreign matter in the molten pitch changes with the melting temperature, and in order to obtain a pitch excellent in spinnability substantially free of foreign matter, the filtration temperature is preferably lower than the filtration temperature that gives the melt spinning viscosity, and the viscosity of the molten pitch is 1 poise to 3000 poise. It is necessary to perform filtration at a pressure of preferably 10 poise to 500 poise.

Further, the properties of the foreign matter contained in the molten pitch and the diatomaceous filter aid added in the present invention vary depending on the filtration pressure.
/ cm ² or less, preferably 20 kg / cm ² or less.

Further, the pitch particularly suitable for the filtration method according to the present invention,
The average diameter of foreign matter existing in the molten pitch is 1μm or more and 40μ
m, preferably 5 μm or more and 20 μm or less.

The effect is best exhibited when the amount of foreign matter is 50 ppm or more and 5000 ppm or less, preferably 100 ppm or more and 1000 ppm or less in volume fraction. This is because even with the use of the precision filter medium alone with a foreign matter amount of less than 50 ppm, the filtration practicable period is relatively long, and the filtration method that is carried out with ordinary polymers can be easily used. . Conversely, if the amount of foreign matter in the molten pitch exceeds 5000 ppm, the amount of the filter aid to be added also increases, and the cake formed by the filtration grows quickly and the period during which the filtration can be performed is significantly shortened, making it impossible to perform economical filtration. .

In the pitch specifically adjusted as a pitch for carbon fiber,
Although the present invention is almost in a range where the present invention can be applied, the effect when the present invention is applied to a mesophase pitch having an optically anisotropic region serving as a raw material for high-grade carbon fiber having 70% by volume or more is particularly significant. large. Of course, even for isotropic pitch, which is a general-purpose carbon fiber raw material, if the foreign matter in the molten pitch is within the above range, the filterability is significantly improved by performing the filtration method according to the present invention.

The filter aid to be added is irregular in shape, has a large specific surface area, has many voids in the particles, and can withstand high temperatures of 400 ° C. or more. In particular, the present invention is suitable from the viewpoint including the above.

The addition of the diatomaceous filter aid is performed by pulverizing the pitch containing foreign matter in a solid state at room temperature into powder or granules, adding a predetermined amount of the diatomaceous filter aid thereto, mixing in a solid state, and melting the mixture. And subject to filtration. Alternatively, a predetermined amount of the diatomaceous filter aid is added to the pitch in a molten state, dispersed in the molten pitch by a stirring action or the like, and subjected to filtration. Alternatively, before pitch production, after adding a diatomaceous filter aid to coal tar or petroleum heavy oil as a pitch raw material, a pitch is produced using this raw material oil, and the pitch is subjected to filtration. Is also good.

However, in any case, when dispersing the diatomaceous filter aid in the pitch, it is important that the dispersion be carried out within a stirring and mixing operation range that does not destroy the foreign matter originally present in the diatomaceous filter aid or the molten pitch.

The melt pitch to which the diatomaceous filter aid was added was passed through a known filtration device, and the viscosity of the melt pitch was 1 poise to 3000 poise, and the filtration pressure at this time was 30 kg / c.
Filter at m ² or less.

The filter medium of the filtration device used here is not particularly limited as long as it is used for filtration of a normal molten polymer or the like, but since foreign matter is trapped by the diatomaceous filtration aid, it is necessary to filter It is not necessary to use a high-precision fine filtration network or the like.

It is sufficient that the filtration network is such that the diatomaceous filter aid is trapped.However, if leakage of the diatomaceous filter aid at the very beginning of filtration cannot be ignored, ISO-4572
The particle size at the 95% collection point measured by the method described in
A filter medium having a size of 30 μm or less may be used.

According to the present invention, the foreign matter in the pitch is not captured by the filter medium, so that a plain weave, a tatami weave, a twill tatami weave, etc. of a single or multi-layered wire mesh is used to separate the cake from the filter medium and to remove the filter medium. Washing and regeneration are also easy and particularly preferable. Thus, according to the present invention, an expensive precision filter medium is not used, and foreign matter is substantially completely removed with a filter medium excellent in washing and regenerating, and the practicable period of the filtration becomes extremely long. Can be performed.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the present invention, various physical property values used to represent the characteristics of the pitch-based carbon fiber and the raw material pitch are defined as follows.

(1) Tensile strength and tensile modulus The tensile strength properties were measured according to the method shown in JIS-R-7601.

(2) Viscosity and softening point The viscosity was measured using a concentric rotating double cylinder viscometer. The softening point is the temperature at which the apparent viscosity calculated from the Hagen-Poiseuille equation using a flow tester is 20,000 poise.

(3) Content of optically anisotropic region The mesophase in the present invention is an optically anisotropic region that can be determined by embedding a cooled and solidified pitch in a resin or the like, polishing the surface, and observing with a reflection polarization microscope. Refers to a structure showing anisotropy. The optically anisotropic content refers to the area ratio of the anisotropic structure observed and observed as described above.

Example Coal tar pitch having a softening point of 80 ° C. as a raw material, and using tetrahydroquinoline as a hydrogenation solvent, 120 kgf / cm ²
After reacting at 440 ° C. for 20 minutes under reduced pressure, the solvent and low boiling fraction were removed at 270 ° C. under reduced pressure to obtain a hydrotreated pitch. After heat-treating this at 480 ° C. under normal pressure, a mesophase pitch was obtained except for a low boiling point component. This pitch has a softening point
At 304 ° C., the toluene-insoluble content was 85% by weight, the quinoline-insoluble content was 14% by weight, and the optically anisotropic content was 95% by volume.

The obtained pitch was pulverized to about 10 mesh at room temperature, diatomaceous filter aid particles having an average particle diameter of 20 μm were added and mixed well, and the filtration area was 12.6 cm ² , and the cross-sectional area of the filtration chamber was The pitch filter aid mixture was inserted into a Nutsche type filter device in which a part was rapidly reduced to 0.07 cm ² , and heated under a nitrogen gas atmosphere to melt the pitch. Thereafter, the viscosity was adjusted to 100 poise at a temperature of 340 ° C., and constant pressure filtration was performed at a pressure of 7 kgf / cm ² .

Filtration experiments were carried out with different addition amounts of the diatomaceous filter aid in five conditions, with the addition amount of the diatomaceous filter aid being from 0.1% by weight to 1.0% by weight.
The relationship between the filtration time and the filtrate volume is in accordance with the cake filtration rule, and from this, the Journal of Chemical Engineering, Vol. 14, No. 2,
According to the method described on page 1 (1988), the apparent filter cake specific resistance and the apparent cake porosity based on the amount of the filter aid added at each amount were determined.

From these results, it was estimated that the size of the foreign matter originally existing in the molten pitch was 9.0 μm, and the amount was 700 ppm by volume, and the size of the foreign matter was clarified.

Examples 1 to 5 Diatomaceous filter aids under the conditions shown in Table 1 were added to the above mesophase pitch melted at 340 ° C under a nitrogen gas atmosphere and mixed well with a stirrer. The diatomaceous filter aid mixed molten pitch, a twill weave with wire mesh of filtration area 0.2 m ^2, 2000 mesh × 200 mesh, 12 mesh × 64
A filtration device using three layers of mesh wire mesh as a filter medium, a filtration temperature of 340 ° C., a viscosity of 100 poise, and a filtration speed of 10
Constant speed filtration was performed at kg / m ² hr. Table 1 shows the results of the filtration execution time until the filtration pressure reached 10 kgf / cm ² .

Comparative Example 1 to Comparative Example 3 When filtration was performed under the same conditions as in the example without adding particles to the pitch used in the examples 1 to 5, (Comparative Example 1)
Table 1 shows the results of the filtration execution times when the particles under the conditions shown in Table 1 were added and filtration was performed under the same conditions as in the examples (Comparative Examples 2 and 3).

Example 6 Using a coal tar pitch having a softening point of 80 ° C. as a raw material and tetrahydroquinoline as a hydrogenation solvent, 120 kg / cm ²
After reacting at 440 ° C. for 10 minutes under reduced pressure, the solvent and low boiling fractions were removed at 270 ° C. under reduced pressure to obtain a hydrotreated pitch.
After heat-treating this at 450 ° C under normal pressure, the pitch excluding the low boiling point component is an optically isotropic pitch having a softening point of 245 ° C, a toluene-insoluble component of 60% by weight, and a quinoline-insoluble component of a trace amount. I got

The obtained pitch is pulverized at room temperature to about 10 mesh, diatomaceous filter aid particles having an average particle diameter of 20 μm are added and mixed well, and then the size and amount of foreign substances present in the molten pitch in the same manner. I asked. From this result, the size of the foreign matter originally present in the molten pitch was 7.0 μm, and the amount was 250 ppm by volume.

The diatomaceous filter aid under the conditions shown in Table 1 was added to the above isotropic pitch melted at 280 ° C. with a viscosity of 100 poise under a nitrogen gas atmosphere and mixed well with a stirrer. This diatomaceous filter aid mixed molten pitch is filtered with a filtration area of 0.2 m ² , 2000
A filtration device that uses three layers of a mesh mesh of 200 mesh × 200 mesh twill woven weave and a wire mesh of 12 mesh × 64 mesh, and has a filtration temperature of 280 ° C and a viscosity of 100 poise, and a filtration speed of 10 kg / m ² hr. At a constant speed. Filtration pressure is 10kgf / c
Table 1 shows the results of the time required for the filtration to reach m ² .

Comparative Example 4 Table 1 shows the results of the filtration execution time when filtration was performed under the same conditions as in Example 6 without adding particles to the pitch used in Example 6.

The pitch substantially free of foreign matter obtained in Examples 1 to 5 was melt-spun by a conventionally known method using a spinning machine having a nozzle pack having 1000 nozzle holes. In each case, the yarn was wound. At a speed of 340 m / min, it was confirmed that the pitch fiber having a yarn diameter of 12 μm was stably spun over 5 hours or more without yarn breakage or the like.

The pitch fiber obtained in this manner is immersed in air for 200 hours.
The temperature was raised at a rate of 0.5 ° C./min from the temperature of 300 ° C. to 300 ° C., and the temperature was maintained as it was for 1 hour to perform infusibility treatment. Thereafter, the temperature was raised to 2300 ° C. at a rate of 50 ° C./min in argon gas, and heat treatment was performed at that temperature for 15 minutes to obtain carbon fibers. When the tensile strength and tensile modulus of this carbon fiber were measured, the yarn diameter was 10
μm, strength 310 Kgf / mm ² , modulus of elasticity 43 tf / mm ² , and was a carbon fiber showing excellent physical properties.

On the other hand, when the pitch obtained in Comparative Example 1 was spun under the same conditions, thread breakage occurred in about 15 minutes. The physical properties of the obtained carbon fiber were a yarn diameter of 10 μm, a strength of 295 kgf / mm ² and an elastic modulus of 40 tf / mm ² , and a slight decrease in physical properties was observed.

Effect of the Invention According to the present invention, a pitch excellent in spinnability can be industrially implemented at a lower cost than a conventional method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuaki Kurosaki 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside the New Technology Research Laboratories of Nippon Steel Corporation (72) Inventor Teruo Iwashita 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Within Nippon Steel Corporation 1st Technical Research Institute (72) Inventor Norio Tomioka 1618 Ida, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Nippon Steel Corporation 1st Technical Research Institute (56) References JP, A) JP-A-2-58597 (JP, A)

Claims (2)

(57) [Claims] 1. An average diameter of a foreign substance originally contained in a pitch of 1
Diatomaceous filter aid with an average diameter of not less than 2 times and not more than 10 times,
A pitch for carbon fiber, wherein pitch added at a volume ratio of 0.5 to 10 times the amount of foreign matter is melted and filtered at a viscosity of 1 poise to 3000 poise and a filtration pressure difference of 30 kgf / cm ² or less. Filtration method. 2. The method for filtering pitch for carbon fibers according to claim 1, wherein the pitch is a mesophase pitch containing at least 70% by volume of an optically anisotropic region.