METHOD OF PREPARING PITCH FOR CARBON FIBER

Abstract

Disclosed herein is a method of preparing an isotropic pitch for carbon fiber having a high softening point, and more particularly, a method of preparing an isotropic pitch for carbon fiber by mixing petroleum residues with C9 fraction to form a mixture and then heating the mixture to perform heat polymerization. With the method of preparing an isotropic pitch according to the present invention, a separate catalyst is not required, and the isotropic pitch for carbon fiber having a low softening point may be prepared with a high yield even at a relatively low temperature.

Description

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method of preparing an isotropic pitch for carbon fiber having a high softening point, and more particularly, to a method of preparing an isotropic pitch for carbon fiber by mixing petroleum residues with C9 fraction to form a mixture and then heating the mixture to perform heat polymerization. With the method of preparing a pitch according to the present invention, a separate catalyst is not required, and the isotropic pitch for carbon fiber having a low softening point may be prepared with a high yield even at a relatively low temperature.

2. Description of the Related Art

A carbon material has a carbon content of about 95% or more, and carbon materials applying various properties of carbon have been developed for various uses. As a raw material of the carbon material, all of the carbon compounds may be used in principle, but an appropriate raw material may be generally selected according to the desired physical properties of a final product and manufacturing cost.

Among them, as a petroleum based target raw material, fluidized catalytic cracker (FCC), decant oil (DO), pyrolyzed fuel oil (PFO) have been spotlighted as a raw material appropriate for high value carbon materials such as high strength carbon fibers or needle coke due to their high aromaticity and low contents of sulfur and insoluble components.

According to the related art, a method of preparing an isotropic pitch from heavy oil samples such as the PFO has been mainly divided into a method of heat-treating a precursor pitch from which light oil components are removed at about 400° C. for a long time of about 14 hours or more and a method of fractioning the heavy oil samples in an appropriate range using a solvent such as benzene or toluene and then heat-treating the fractured material.

In this regard, as the carbon materials for various uses has been developed, various methods such as a method of using a catalytic carbonization reaction, a method of using a vacuum heat treatment process, and the like, have been attempted.

A carbonization process of reforming the heavy oil components such as the PFO to form a pitch means a series of processes of pyrolyzing oil components, discharging gas and light oil components to the outside of the system, and simultaneously cyclizing, aromatizing, and polycondensing molecules activated by formation of radicals.

Here, while a polycondensation reaction occurs, planar molecules of a condensed polycyclic aromatic group are laminated in parallel with each other to form a liquid crystal referred to as a mesophase and having intermediate properties between a solid and a liquid. In this case, the laminated molecules are optically divided into an isotropic pitch and an anisotropic pitch according to the degree at which the molecules are laminated or the orientation when the molecules are arranged.

Generally, a pitch based carbon fiber is mainly divided into a liquid crystal pitch based carbon fiber and an isotropic pitch based carbon fiber according to the kind of pitch, which is a precursor. The liquid crystal pitch based carbon fiber is prepared using a liquid crystal pitch as the precursor, which is optically anisotropic, and the isotropic pitch based carbon fiber is prepared using the isotropic pitch as the precursor, which is optically isotropic. Describing mechanical properties of the prepared carbon fiber, the liquid crystal pitch based carbon fiber has high strength and high elasticity, but the isotropic pitch based carbon fiber has general mechanical properties such as low strength and low elasticity.

The pitch based carbon fiber is generally prepared by melt-spinning the pitch, which is the precursor, using a spinning machine to fiberize the pitch, oxidation-stabilizing the fiberized pitch at about 150° C. to about 350° C. under oxidation atmosphere for a predetermined time, and treating the oxidation stabilized pitch at about 700° C. to about 3000° C. under inert atmosphere for a predetermined time according to the use.

It is known that at the time of preparing the carbon fiber, a preparing cost of the fiber is affected by a cost of the precursor pitch, a spinning property of the precursor pitch, a rate of the oxidation stabilization, a carbonization yield after carbonization, and the like, and in view of a time required for each of the processes, an oxidation stabilization process in which a long reaction time is essential requires the longest time. Therefore, it is important to develop a precursor pitch having excellent oxidation stabilization performance.

As described above, the pitch precursor for the pitch based carbon fiber is mainly divided into the liquid crystal pitch and the isotropic pitch. As a method of preparing an isotropic pitch used as a raw material of the isotropic pitch based carbon fiber and having a softening point of about 200° C. or more, there are a method of removing low molecular weight components from a coal tar pitch by vacuum distillation and solvent extraction, a method of condensing low molecular weight components of the raw material by simple heat condensation to convert the components into high molecular weight components, and a method of preparing the isotropic pitch using the two methods described above. However, the isotropic pitch having relatively narrow molecular weight distribution may be prepared from a raw material having wide molecular weight distribution by these methods, but there are disadvantages in view of homogeneity of the prepared pitch and the spinning property thereof. For example, the yield may be low and components that may be easily liquid-crystallized at the time of heating may remain.

A method of preparing a high softening point isotropic pitch, a precursor of isotropic carbon fiber, by removing quinoline-insolubles from a coal tar pitch, which is a raw material, hydrogenating the quinoline-insolubles removed coal tar pitch, and then separating oxidizing gas has been disclosed in Japanese Patent Laid-Open Publication No. 1994-256767.

In addition, a method of adding dinitronaphthalene, or the like, at the time of heat treatment for preparing a pitch in order to increase a softening point of an isotropic pitch precursor has been disclosed in Japanese Patent Laid-Open Publication Nos. 1993-132767 and 1993-132675.

However, as described above, hydrogenation of the pitch is performed by carrying out the reaction at a high temperature using an expensive hydrogenation catalyst and then removing the hydrogenation catalyst, which increases the preparing cost of the precursor pitch. Further, nitrogen oxides added in order to increase the softening point is expensive, and the actual reaction is not homogeneously carried out, such that a melt-spinning property of the prepared pitch precursor may be deteriorated.

In addition, a method of preparing a high softening point pitch from naphtha cracking residues using a complex of BF₃-ether as a polymerization catalyst has been disclosed. However, in this case, since BF₃-ether used as the catalyst is significantly expensive, this method may not be appropriate for a large scale preparing process.

Recently, a method of preparing an isotropic pitch using a coal tar pitch and petroleum based vacuum residues as raw materials and using halogen and a halogen compound as polymerization additives has been disclosed in Korean Patent Application Nos. 1997-0036064 and 1997-0036065.

However, there is a limitation in preparing the isotropic pitch precursor for carbon fiber having excellent melt-spinning property and oxidation stability and a high carbonization yield under relatively mild conditions with a high yield by the above-mentioned method according to the related art using the naphtha cracking residues as the raw material.

Particularly, it may be impossible to prepare the high softening point isotropic pitch precursor for isotropic carbon fiber having excellent properties as the precursor pitch with a high yield of about 35 weight % or more by using the naphtha cracking residues, particularly, the pyrolyzed fuel oil (PFO) as the raw material and adding halogen and the halogen compound thereto, followed by simple polymerization and removal of low molecular weight materials.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a method of preparing an isotropic pitch for carbon fiber having a high softening point, and more particularly, a method of preparing an isotropic pitch for carbon fiber by mixing petroleum residues with C9 fraction to form a mixture and then heating the mixture to perform heat polymerization. With the method of preparing an isotropic pitch according to the present invention, a separate catalyst is not required, and the isotropic pitch for carbon fiber having a low softening point may be prepared with a high yield even at a relatively low temperature.

According to an exemplary embodiment of the present invention, there is provided a method of preparing a pitch for carbon fiber including: a mixing step of mixing petroleum residues with C9 fraction to form a mixture; a primary heating step of primarily heating the mixture to induce a chain extension reaction; a secondary heating step of raising a temperature after the primary heating to remove low boiling point materials; and a tertiary heating step of raising a temperature after the secondary heating to induce a condensation reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are scanning electronic microscope (SEM) photographs of carbon fiber prepared using a pitch prepared according to a first exemplary embodiment of the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Details of embodiments will be described below with reference to the accompanying drawings.

Various advantages and features of the present invention and methods accomplishing thereof will become apparent from the following description of embodiments with reference to the accompanying drawings. However, the present invention is not limited to the exemplary embodiment disclosed herein but will be implemented in various forms. The exemplary embodiments make disclosure of the present invention thorough and are provided so that those skilled in the art can completely understand the scope of the present invention. Therefore, the present invention will be defined by the scope of the appended claims.

Hereinafter, a method of preparing a pitch for carbon fiber according to an exemplary embodiment of the present invention will be described in detail.

The method of preparing a pitch for carbon fiber according to the exemplary embodiment of the present invention may include: 1) a mixing step of mixing petroleum residues with C9 fraction to form a mixture; and 2) a heating step of heating the mixture. First, 1) the mixing step of mixing the petroleum residues with the C9 fraction to form the mixture will be described.

The petroleum residues and the C9 fraction are put into a reactor and mixed with each other at room temperature.

Here, the petroleum residues are a carbon source of the pitch for carbon fiber, and in the present invention, it is preferable that the petroleum residues include particularly pyrolyzed fuel oil (PFO) as naphtha cracking residues. The PFO, which is generated at a bottom of a naphtha cracking center (NCC), has high aromaticity and resin content, such that the PFO is appropriate for the method of preparing a pitch according to the present invention.

The PFO includes various aromatic hydrocarbons, and naphthalene and methylnaphthalene derivatives account for about about 25-35% thereof. Specific examples of the naphthalene and methylnaphthalene derivatives may include ethylbenzene, 1-ethenyl-3-methyl benzene, indene, 1-ethyl-3-methyl benzene, 1-methylethylbenzene, 2-ethyl-1,3-dimethyl benzene, propylbenzene, 1-methyl-4-(2-propenyl) benzene, 1,1a,6,6a-tetrahydro-cycloprop[a]indene, 2-ethyl-1H-indene, 1-methyl-1H-indene, 4,7-dimethyl-1H-indene, 1-methyl-9H-fluorene, 1,7-dimethyl naphthalene, 2-methylindene, 4,4′-dimethyl biphenyl, naphthalene, 4-methyl-1,1′-biphenyl, anthracene, 2-methylnaphthalene, 1-methylnaphthalene, and the like.

In the present invention, the petroleum residues, that is, the carbon source may be a carbon source from which low boiling point materials are removed. Since the low boiling point materials are mostly volatilized to thereby not participate in a reaction, a yield as a pitch is significantly low, and hydrocarbons in the C3 to C8 range belong thereto. In the case of using the carbon source from which the low boiling point materials are removed, the high softening point pitch may be prepared with a higher yield.

Meanwhile, the C9 fraction mixed with the petroleum residues so as to react with the petroleum residues according to the present invention has mainly 9 carbon atoms, and a specific example thereof may include styrene, vinyltoluene, indene, a-methylstyrene, or benzene/toluene/xylene (BTX).

Aromaticity fa of the C9 fraction according to the exemplary embodiment of the present invention may be preferably about 40 to 60%. In the case in which the aromaticity is less than about 40%, raw materials capable of participating in a polymerization reaction are insufficient, such that products may be paraffinized, and the yield may be low, and in the case in which the aromaticity is more than about 60%, there may be a problem such as rapid coking at the time of heat polymerization.

In the mixture of petroleum residues and the C9 fraction, C9 fraction may be mixed at a content of about 10 parts to about 50 parts by weight, based on 100 parts by weight of the petroleum residues. In the case in which the content of the C9 fraction is less than about 10 parts by weight, based on 100 parts by weight of the petroleum residue, an amount of C9 fraction participating in the reaction is small, such that it may be difficult to prepare the desired pitch, and in the case in which the content is more than about 50 parts by weight, undesired products may be produced due to a polymerization reaction of an excess C9 fraction itself.

Hereinafter, 2) the heating step of heating the mixture will be described.

The heating step may be performed by multi-step heating in two steps or more.

More specifically, the heating step may include a primary heating step of primarily heating the mixture; a secondary heating step of raising a temperature after primary heating; and a tertiary heating of raising a temperature after secondary heating.

In the primary heating step, the mixture of the petroleum residues and the C9 fraction are primarily heated to induce a chain extension reaction.

In the primary heating step, double bond chains of the C9 fraction are released to form free radicals, such that the chain extension reaction that the petroleum residues and the chain are extended occurs. Compounds having an aromatic structure form bonds via the radicals and have a form in which a plurality of aromatic structures are included in a long chain.

Here, a heating temperature may be preferably about 80° C. to about 100° C. In the case in which the heating temperature is lower than about 80° C., formation of the radical from the C9 fraction may be impossible, and in the case in which the heating temperature is higher than about 100° C., there may be a problem in termination of the chain extension reaction.

In addition, a heating time may be preferably about 1 hour to about 2 hours. In the case in which the heating time is shorter than about 1 hour, a sufficient reaction may be impossible, and in the case in which the heating time is longer than about 2 hours, the mixture may be solidified during the reaction due to cross-linking of the chain structure after the reaction is terminated.

In the secondary heating step, after the primary heating is completed, the temperature is raised to remove the low boiling point materials.

Since the coking slowly occurs at a final target temperature of the heat polymerization (about 360° C.), the coking is decreased and the low boiling point materials are removed by having an intermediate temperature section in the secondary heating step.

Here, a secondary heating temperature obtained by raising the temperature after primary heating may be preferably about 250° C. to about 300° C. In the case in which the heating temperature is lower than about 250° C., it may be difficult to remove the low boiling point material, and in the case in which the heating temperature is higher than about 300° C., a coking reaction may occur in addition to removing the low boiling point materials.

In addition, the heating time may be preferably about ½ hour to about 2 hours. In the case in which the heating time is shorter than about ½ hour, sufficient removal of the low boiling point materials may be impossible, and in the case in which the heating time is longer than about 2 hours, the coking may occur.

In the tertiary heating step, after the secondary heating is completed, the temperature is raised to induce the condensation reaction.

In the tertiary heating step, the temperature may arrive at a target temperature of the heat polymerization, and the condensation reaction of the petroleum residues and the C9 fraction may occur, such that a pitch having a high softening point of about 240° C. or more, preferably about 240° C. to about 300° C. may be finally synthesized.

Here, a tertiary heating temperature obtained by raising the temperature after secondary heating may be preferably 320 to about 360° C. In the case in which the heating temperature is lower than about 320° C., the condensation reaction and removal of the residual low boiling point material may be impossible, and in the case in which the heating temperature is higher than about 360° C., the reactant may be lost due to a cracking reaction and a rapid coking reaction, and a coking problem may be generated.

In addition, a heating time may be preferably about 3 hours to about 8 hours, but more preferably about 3 hours to about 4 hours. In the case in which the heating time is shorter than about 3 hours, the condensation reaction and removal of the residual low boiling point material may be impossible, and in the case in which the heating time is longer than about 8 hours, coking and cracking problems may be generated.

Hereinafter, preferable Examples of the present invention will be described. The following Examples are provided in order to describe the present invention in detail, and the scope of the present invention is not limited thereto.

EXAMPLE

(1) Preparation of High Softening Point Pitch

After pyrolyzed fuel oil (PFO) as a carbon source and C9 fraction were put into a reactor and mixed with each other, the mixture was subjected to primary, secondary, and tertiary heating processes, such that a heat polymerization reaction was carried out.

After the heat polymerization reaction was terminated, un-reacted or poorly reacted molecules were removed by passing nitrogen gas at a flux of 1 L/min for 2 hours, thereby obtaining the desired high softening point optically isotropic pitch.

Reaction conditions of each of the Examples were shown in the following Table 1.

	TABLE 1
	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7
Mixing ratio	1:0.25	1:0.25	1:0.25	1:0.4	1:0.25	1:0.25	1:1
(petroleum
residues:C9
fraction)
Aromaticity	52	52	44	52	52	81	52
(%) of C9
fraction
Low boiling	Removed	Not	Removed	Removed	Removed	Removed	Not
point		removed					removed
materials in
petroleum
residue
Primary	2	2	1	2	2	2	0.5
heating time
(h)
Primary	100	100	100	90	100	100	70
heating
temperature
(° C.)
Secondary	1	1	2	1	1	1	1
heating time
(h)
Secondary	260	240	260	260	260	290	260
heating
temperature
(° C.)
Tertiary	4	4	4	3	5	4	8
heating time
(h)
Tertiary	360	360	330	360	360	400	360
heating
temperature
(° C.)

2) Softening Point and Yield of the Obtained Pitch

The softening point and yield of the pitch prepared in the Examples were measured and shown in the following Table 2.

	TABLE 2
	Softening point (° C.) of
	the obtained pitch	Yield (%)
	Example 1	270	38
	Example 2	268	40
	Example 3	281	35
	Example 4	258	43
	Example 5	326	24
	Example 6	344	25
	Example 7	350 or more	27

(3) Preparation of Carbon Fiber

The carbon fiber was prepared through spinning, oxidation, and carbonization processes, which is a general method, using the pitch prepared in Example 1.

SEM photographs of the carbon fiber prepared using the pitch synthesized in the Example were shown in FIGS. 1a (front view) and 1b (cross-sectional view).

As shown in FIGS. 1a and 1b, in the case of using the pitch prepared under the optimized synthetic conditions according to the present invention, sphere-shaped insoluble components were not formed, and the finally prepared carbon fiber was isotropic.

(4) Experiments of Tensile Strength and Modulus of Elasticity of the Prepared Carbon Fiber

Tensile strength and modulus of elasticity of carbon fibers a1 to a10 using the pitch synthesized in Example 1 were shown in the following Table 3.

As shown in Table 3, in the case of using the pitch prepared under the optimized synthetic conditions as in Example 1 of the present invention, it may be confirmed that the carbon fiber having excellent physical properties (average tensile strength of 1 GPa and modulus of elasticity of 56 GPa) was prepared.

	TABLE 3
	Maximum	Tensile	Tensile	Modulus of elasticity
	load	strength	strain	(Automatic Young's)
	(N)	(GPa)	(%)	(GPa)
a1	0.2341	1.0015	2.3777	45.6034
a2	0.1456	0.6228	1.8005	37.2215
a3	0.3232	1.3830	2.4544	58.7958
a4	0.2087	0.8931	1.8943	48.2015
a5	0.2355	1.0078	1.5824	65.6378
a6	0.2800	1.1979	1.9017	63.4660
a7	0.1945	0.8321	2.7709	33.3722
a8	0.4029	1.7241	1.6097	116.6022
a9	0.2077	0.8886	1.8540	50.6760
a10	0.1586	0.6786	1.6505	42.0814
Average	0.2391	1.0229	1.9896	56.1658
Standard	0.08	0.33	0.40	23.77
deviation

With the method of preparing a pitch according to the exemplary embodiment of the present invention, since the reactivity of petroleum residues and C9 fraction is excellent, the high softening point isotropic pitch may be obtained with the high yield without using a separate catalyst.

Hereinabove, although specific embodiments of the present invention have been described, various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should be not construed as being limited to the described exemplary embodiments but be defined by the appended claims as well as equivalents thereto.

Although the present invention has been described with reference to the limited embodiments, the present invention is not limited to the above-mentioned embodiments but may be variously modified and changed from the above description by those skilled in the art to which the present invention pertains. Therefore, the scope and spirit of the present invention should be understood only by the following claims, and all of the equivalences and equivalent modifications to the claims are intended to fall within the scope and spirit of the present invention.

Claims

1. A method of preparing a pitch for carbon fiber, the method comprising:

a mixing step of mixing petroleum residues with C9 fraction to form a mixture; and

a heating step of heating the mixture.

2. The method of claim 1, wherein the heating step is performed by multi-step heating in two steps or more.

3. The method of claim 1, wherein the heating step includes:

a primary heating step of primarily heating the mixture;

a secondary heating step of raising a temperature after the primary heating; and

a tertiary heating step of raising a temperature after the secondary heating.

4. The method of claim 3, wherein a heating temperature in the primary heating step is about 80° C. to about 100° C.

5. The method of claim 3, wherein a heating time in the primary heating step is about 1 hour to about 2 hours.

6. The method of claim 3, wherein in the primary heating step, a chain extension reaction is induced.

7. The method of claim 3, wherein a heating temperature in the secondary heating step is about 250° C. to about 300° C.

8. The method of claim 3, wherein a heating time in the secondary heating step is about ½ hour to about 2 hours.

9. The method of claim 3, wherein in the secondary heating step, low boiling point materials are removed.

10. The method of claim 3, wherein a heating temperature in the tertiary heating step is about 320° C. to about 360° C.

11. The method of claim 3, wherein a heating time in the tertiary heating step is about 3 hours to about 8 hours.

12. The method of claim 3, wherein in the tertiary heating step, a condensation reaction occurs.

13. The method of claim 1, wherein the petroleum residues include naphtha cracking residues.

14. The method of claim 1, wherein the petroleum residues include pyrolyzed fuel oil (PFO).

15. The method of claim 1, wherein the petroleum residues comprise a substance from which low boiling point materials are removed.

16. The method of claim 1, wherein the C9 fraction has aromaticity of about 40% to about 60%.

17. The method of claim 1, wherein in the mixture, the C9 fraction is mixed at a content of about 10 parts to about 50 parts by weight, based on 100 parts by weight of the petroleum residues.