JPH0431493A - 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 centrifuging a carbonaceous pitch to remove most part of ash contained therein and then filtering it through a filter. CONSTITUTION:A carbonaceous pitch melted by heating to 280-400 deg.C so as to provide a viscosity of 0.05-90Pa.s is centrifuged on a centrifugal separator at a centrifugal force of 10,000-40,000G to remove most part of ash contained therein, giving a carbonaceous pitch having an ash content of 100ppm or less. This pitch is 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 gas atmosphere under a filtering pressure of 1-100kgf/cm<2> 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 pitch fibers obtained from carbonaceous pitch are extremely fragile, many measures have to be taken in handling the yarn in subsequent steps.

Furthermore, in recent years, it has become increasingly clear that the amount of ash remaining in carbonaceous pitch has an extremely large effect on yarn breakage when spinning pitch fibers from carbonaceous pitch and on the physical properties of the final product, carbon fiber. As the number of carbonaceous pitches increases, obtaining clean carbonaceous pitch with low ash content 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 in the tar to 0°005% by weight (5% by weight).
0 ppm) or less (Japanese Patent Application 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 the amount to less than 1,000 ppm by weight (Japanese Unexamined Patent Publication No. 6
3-162786) is disclosed.

On the other hand, a method for directly removing ash from carbonaceous pitch is to centrifuge carbonaceous pitch under high centrifugal force (
Japanese Unexamined Patent Publication No. 60-34619) has been proposed.

[Problem to be solved by the invention]

However, in the method of removing ash from raw tar, even if the ash content is reduced to 10 ppm (0,001%), the ash content accumulates about 10 to 90 times during the pitch manufacturing process, resulting in a There is a drawback that the concentration increases to ~900 ppm, and there is also a 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 ash removal treatment was usually only about 50PP1. Even if it is about 50 ppm, it can cause structural defects, especially 2,
It has been found that when high-temperature firing is performed at 000°C or higher, it is difficult to develop strength due to the formation of pores in the fibers. In addition, in order to develop higher strength, it is insufficient to simply reduce the ash content to 50pp+n or less.
It was found that certain elements in the ash significantly influenced the development of strength.

Therefore, in order to eliminate structural defects caused by the ash content in carbonaceous pitch and obtain ultra-high strength carbon fibers, a new ultra-clean R
The desired appearance of the quality pitch was achieved.

In order to solve these problems, the present inventors 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, the object of the present invention is to overcome these problems, namely to reduce the content of specific elements in the ash to an extremely low level.
It is an object of the present invention to provide a method for producing ultra-clean carbonaceous pitch by which high-performance carbon fibers can be stably obtained easily and quickly.

[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 carbonaceous pitch is first subjected to a first ash removal treatment by centrifugation to remove most of the ash content, with an ash content of 10 lppm or less, and then a filter is used. Provided is a method for producing ultra-clean carbonaceous pitch for carbon materials, characterized in that residual ash in the carbonaceous pitch is removed by subjecting it to a second ash removal process by filtration.

In the method of the present invention, the ash removal process is performed separately in the primary and secondary stages, so the ash removal rate in each step can be increased, and as a result, ultra-clean pitch can be quickly produced compared to conventional methods. can be obtained.

The first ash removal treatment in the present invention is preferably carried out when the viscosity of the carbonaceous pitch is from 0.05 Pa-s to 90 Pa.S.
In a temperature range of 10,000 to 40,0OOG
This is done by centrifugation under the centrifugal force of Further, the second ash removal treatment is preferably carried out by filtration using a filter in a temperature range where the viscosity of the carbonaceous pitch is from 0°05 Pa-8 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, An content is lp
pm or less and Si content is 3.3pprrr or less, and the total amount of Fe content, AQ content, and Si content is 5pp.
An ultra-clean carbonaceous pitch suitable for producing carbon materials having a particle diameter of less than m is easily produced.

Note that the Fe component, Ap component, and Sj component herein are values obtained 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. The ash content is melted with sodium carbonate, and then dissolved with hydrochloric acid and water to obtain a sample solution. For this sample solution, the luminescence intensity of each element of Fe, ^Q, S, and i was measured using an inductively coupled plasma emission spectrometer [(ICP emission spectrometer W), and the luminescence intensity of each element in the sample was measured using a calibration curve prepared in advance. The concentration of each element was determined, and these were defined as the Fe content, AQ content, and Si content, 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.
and Si content is 3.3 ppm or less, and F
It is preferable that the total amount of e, AQ, and Si components is 5 ppm or less, but most of these ash components have a particle size of 0.5 ppm or less.
It exists as particles smaller than one voice. Due to such a low ash content, when carbon fibers are produced from the carbonaceous pitch obtained according to the present invention according to a conventional method, structural defects in the carbon fibers due to the above elements in the pitch are eliminated, resulting in ultra-high strength. carbon fibers can be obtained stably and easily. The ash content is normal.

In addition to the above-mentioned Fe content, AQ content, and Si content, a trace amount of Ni content,
It contains Cr, etc., but as mentioned above, the Fe content is 2ppm or less, the AQ content is 1ppm or less, and Si
By setting the content to 3°3 ppm or less and the total amount of Fe content, AQ content, and Si content to 5 ppg or less, it is possible to produce high-performance carbon materials, especially carbon fibers with ultra-high strength and high modulus of elasticity. Ultra-clean carbonaceous pitch is obtained.

Furthermore, the Fe content in the pitch is 0.8 ppm or less, the AQ content is 0.5 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 to set it to m or less.

Note that if carbon fibers are manufactured using carbonaceous pitch in which the total amount of Fe, AQ, and Si exceeds 5 ppm, 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. Further, although the reason is not clear, strength development is not sufficient when only the Fe content exceeds 2 ppm. Similarly, only the AQ portion is ippm or Si
Even when the amount 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 IPPIII or less, and the Si content is 3.3 ppm.
It is necessary that the ultra-clean carbonaceous pitch contains elements below a specific value, such as a total of Fe content, AQ content, and Si content 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 mesophase 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 is preferred, especially mesophase containing substantially 100% mesophase is 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 menface pitch, thermal polycondensation is stopped halfway and the polycondensate is reduced to 350 to 400%.
The optically anisotropic phase (hereinafter referred to as AP phase) with high density is deposited while growing and maturing in the lower layer, and this is deposited in the optical anisotropic phase with lower density in the upper layer. 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 menface 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 M (layer in the direction of centrifugal force) while coalescing, and the AP phase forms a continuous layer with approximately 80% or more of it, with a small amount of IP phase in the crystalline layer. Alternatively, the pitch becomes dispersed in minute spherical bodies. In this case, the boundary between both layers is clear, the lower layer can be easily separated from the upper layer, and the AP phase content is high and the softening point is low.
Therefore, mesophase pitch that is easy to spin can be produced. According to this method, mesoface pitch having an AP phase content of 98 or more and a softening point of 230°C to 320°C can be obtained economically in a short time.

The mesoface 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 a pitch is used, yarn breakage and fluffing occur during spinning, but these problems are caused by wear of the catalyst and equipment already mixed in the raw material for producing the pitch,
This is largely due to foreign matter that gets mixed in due to corrosion, etc.

In the present invention, the carbonaceous pitch obtained by the reaction is first subjected to a first ash removal treatment by centrifugation to remove most of the ash content (the ash content is below 100 ρpmJ).

Ash removal treatment by centrifugation involves centrifuging carbonaceous bits, such as mesoface pitch, in its molten state to separate a solid slurry layer containing many ash particles with high specific gravity from mesoface pitch. It's a method. This solid slurry layer has fine ash particles attached to the cylinder of the rotating body of the centrifugal separator, and is generally in the same phase. The centrifugal separation operation is a processing operation that applies high-speed rotation to a fluid, collects a phase with a higher specific gravity in the fluid to a lower layer (in the direction of centrifugal force), and separates it. As a method, an operation using a so-called centrifugal separator, particularly a continuous type centrifugal separator that continuously discharges the heavy phase and the light phase, is advantageously used.

The centrifugation operation is performed when the viscosity of the carbonaceous pitch is 0.05 Pa・
It is preferable to carry out the reaction in a temperature range of S to 90 Pa-s. If the pitch viscosity is higher than 90 Pa-s,
Fine ash particles are included in the mesophase pitch component, and it is difficult to remove the fine ash particles even if a very large centrifugal force is applied for a long time. On the other hand, if it is less than 0.05 Pa-s, the temperature of the carbonaceous pitch will become too high, and there is a possibility that the thermal decomposition polycondensation reaction of the pitch will proceed. The temperature of the carbonaceous pitch that gives the viscosity varies depending on the properties of the pitch, but is within the range of 280 to 400°C for boat fishing.

Further, the centrifugal force acceleration of the centrifugation operation is at least 1
0,000G, in particular a range of 10,000 to 40,000G can be employed. Note that there are restrictions in terms of equipment when using 50,000 OOG or more.

In addition, the pre-adapted pitch of the carbonaceous pitch as described above,
If a method is adopted in which mesophasic pitch is subjected to a centrifugation operation in a molten state to obtain mesoface pitch with a high concentration and a low softening point, the first ash removal treatment of the present invention can be carried out at the same time in the centrifugation operation ( That is, IP,
3 layers (AP and solid slurry layers are separated at the same time), there is no need to separately perform ash removal treatment by centrifugation.

In the present invention, after the carbonaceous pitch is subjected to the first ash removal treatment, it is then subjected to a second ash removal treatment by filtration using a filter to remove residual ash in the pitch. Ru. This filtration process has a pore size of 0.05~
The filtration is carried out using a 5 pm filter under an inert gas atmosphere and at a filtration pressure of 1 to 100 kgf/cm. A material that has a fine pore size of .

Among the above filters, sintered metal filters are particularly preferably used. The sintered metal filter used is stainless steel (for example, SUS 316L).
Short fibers are laminated and sintered, and the pore size is 0.05-57m.
, especially 0.1-1prR1 porosity 50% or more''-1 especially 6
It is preferably about 0 to 80%. If the pore diameter exceeds 57 m, the ash trapping efficiency will decrease;
There is a problem in that it is difficult to fabricate filters with fine meshes below the door. 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, such as 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, clean carbonaceous pitch can be obtained by performing one stage of filtration treatment using the filter as a second ash removal treatment on carbonaceous pitch, but even cleaner pitch can be obtained. In some cases, this can be achieved by performing two or more filtration operations using a sintered metal filter with a small pore size.

For the first stage filtration layer filter, the pore size is 0.05~
A sintered metal filter of No. 5 is used. As the second stage filtration layer filter, carbonaceous pitch containing ash is passed through a filter with a pore size of 0.05 to 5 pores for at least 1 to 3 hours or more, so that fine ash particles A material that is moderately clogged is used. In addition, as the second stage filter, 1 to
If a filter that has been used for 3 hours or more is used as a third stage filter, finer particles can be captured and a cleaner 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 pressure of a#. In the case of mesoface pitch, it is preferable to carry out at a temperature of usually 300 to 400°C.

Further, it is preferable that the subsequent 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 filtration treatment.

In order to obtain ultra-clean carbonaceous pitch, it is usually preferable to perform two or more stages of filtration as described above, but in order to increase the filtration speed, the first stage filter should be backwashed every time the filter becomes clogged. It is also possible to carry out filtration while regenerating the filter, and use the downstream filter as it is for a long time.

〔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 of 0.992, 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
% by weight (2,200 ppm), the viscosity at 100° C. was 14.7 centistokes.

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
．． Pitch containing about 55 grams of optically anisotropic phase was obtained with a yield of 23.0% by weight when observed with a polarized R machine gun using a 9-weight stone.

This pitch is temperature-controlled at 350°C and a predetermined flow rate of 20-7 is transferred to a cylindrical continuous centrifuge with a rotor effective internal volume of 200-7.
While controlling the rotor temperature at 350° C., the liquid was continuously separated into a heavy liquid and a light liquid using a centrifugal force of 20.0 OOG. At this time, the first ash removal treatment was also carried out. The yield of the pitch collected from the heavy liquid outlet was 52% by weight, the softening point was 268°C, and the quinolinated content was 28.5% by weight. Ill with a polarizing microscope! The optically anisotropic phase observed was 99%. The ash content in this liquid crystal pitch was 50 ppm. The time required for the first ash removal was 18 minutes.

The obtained mesoface 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 (SUS316L) with a pore diameter of 0.1 [manufactured by Nippon Seiren Co., Ltd.: NP-2] is used.
The filtration process was performed using 013. The diameter of the filter was 60-m.

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/cJ. The temperature during filtration was 340°C, and the viscosity of mesoface pitch was 9 Pa-8.

The filtration time for 250 g of carbonaceous pitch was 65 minutes.

The Fe content in the ultra-clean pitch obtained in this way was 1.5p.
pm, AQ content is 0.4ppm, Si content is 2.8ppm
The total amount of Fe, AQ and Si is 4.7p.
It was pm.

The obtained ultra-clean mesoface pitch was 0.3 m in diameter.
Filled into a spinning machine with a single-hole nozzle of m and heated to a temperature of 335°C.
It was extruded under nitrogen pressure, wound up on a bobbin at the bottom of the nozzle, and spun at a take-off speed of 500+n/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 1.500°C at 20°C/min.
Carbonization was performed by raising the temperature to ℃ to obtain carbon fibers. The obtained carbon fiber had a fiber diameter of 10°Ops and a tensile strength of 3.4.
GPa, and the tensile modulus was 260 GPa.

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

The obtained graphite fiber had a fiber diameter of 9.974 and a tensile strength of 3.
It was extremely high quality with a tensile modulus of 6 GPa and a tensile modulus of 740 GPa.

Example 2 The same process as in Example 1 was carried out, except that the second ash removal process by filtration using a filter was performed using two stages of filters. As the first stage filter,
Stainless steel (S) with a diameter of 60nv+ and a pore size of 0.1
A clean new sintered metal filter made of O5316L (Nippon Seiren @: NP-201) was installed, and as the second stage filter, the mesoface pitch was filtered for 1 hour beforehand. The same sintered metal filter as above was pre-coated with the fine ash contained in menface pitch, and was then attached to the filter. The filtration conditions for precoating the second-stage filter were a temperature of 340°C and a pitch viscosity of 9 Pa·S. Filtration was performed by gradually increasing the pressure from near atmospheric pressure with nitrogen, and the final pressure was 40 kgf/s.
AI? It was hot.

After having such a filter configuration, 250 g of liquid crystal pitch obtained by centrifugation was introduced into a filtration device and filtered. The atmosphere was a nitrogen gas atmosphere, and filtration was performed under pressure with nitrogen gas. The temperature during filtration is 340℃,
The viscosity of the pitch was 9 Pa-s. The pressure during filtration was 40 kgf/cd. Mesoface pitch 250
The filtration time for g was 75 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 0.3pp+n
The total amount of Fe, AQ and Si is 0.6p.
It was pm.

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 fiber diameters of io, ops, and tensile strengths of 3 and 6.
GPa, tensile modulus is 260 GPa, and 2,500
The graphite fibers obtained by firing to ℃ were of extremely high quality, with a fiber diameter of 9.8 μm, a tensile strength of 4.5 GPa, and a tensile modulus of 750 GPa.

Comparative Example 1 The same process as in Example 1 was carried out, except that the mesoface pitch (ash content 250 ppm) containing a 99% optically anisotropic phase after centrifugation in Example 1 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 1.7
GPa and tensile modulus were 600 GPa. Compared to Example 1, the tensile strength was significantly lower and the tensile modulus was also lower.

Comparative Example 2 The carbonaceous pitch obtained by the reaction was treated in the same manner as in Example 1, except that the first ash removal treatment was not performed. In this case, it took 4 hours to filter 250 g of mesoface pitch (secondary ash removal treatment).

It is clear that an ultra-clean pitch can be obtained more quickly in Examples 1 and 2 than in this comparative 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.

Although the mesoface pitch system has been mainly described above, even when the pitch is optically isotropic, it has the advantage that defect-free general-purpose carbon fibers or other carbon materials can be manufactured.

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 carbonaceous pitch is first subjected to a first ash removal process by centrifugation to remove most of the ash contained in it, and then subjected to a second ash removal process by filtration using a filter. A method for producing ultra-clean carbonaceous pitch for carbon materials, characterized by removing residual ash in the carbonaceous pitch.