Process for the conversion of pitch into crystalloidal pitch

Crystalloidal pitch is obtained by subjecting solid pitch particles measuring not more than 5 mm in cross-sectional equivalent diameter to a treatment to prevent cohesion and subsequently bringing the cohesion-proof solid pitch particles into contact with a non-oxidative gas at temperatures of from 350.degree. C to 550.degree. C while maintaining a gas flow rate sufficient to provide a suspension wherein the gas constitutes at least 30% by volume. The crystalloid pitch is useful as a precursor for various carbon products.

FIELD OF THE INVENTION 
This invention relates to a process for the conversion of plain pitch into 
crystalloidal pitch, and more particularly to a process for the production 
of the so-called crystalloidal pitch which serves as the precursor for 
carbon products. 
BACKGROUND OF THE INVENTION 
Generally, ordinary pitch has an amorphous structure. When this pitch is 
heated to temperatures of about 350.degree. C. to 550.degree. C. in an 
inert gas atmosphere, the molecules of the pitch undergo a thermal 
polycondensation reaction and become oriented to give rise to a kind of 
optically isomeric liquid crystal within the pitch. This liquid crystal is 
otherwise called a mesophase. The condition in which the mesophase occurs 
and grows can be observed with the aid of a polarizing microscope. The 
mesophase consists of pitch-forming aromatic molecules which have been 
oriented and associated together through their own interaction. The 
mesophase can be observed as anisotropic spherules under a polarizing 
microscope. A pitch of the type which contains such a mesophase is 
referred to as "crystalloidal pitch." 
In recent years, it has been reported that shaped articles of carbon 
(graphite) having high density, high strength and isotropy can be produced 
by subjecting the crystalloidal pitch or mesophase, obtained by solvent 
extraction from the crystalloidal pitch in a powdered form, to compression 
molding and baking the compression molded articles. Since the 
crystalloidal pitch has heretofore been produced by heating and melting 
ordinary pitch in a container, the viscosity of the pitch is gradually 
increased during conversion with resulting nonuniformity of temperature 
distribution in the pitch. Thus the conversion of the pitch into a 
homogeneous crystalloidal pitch is difficult to attain by the prior art 
method. It is, therefore, impossible to consistently obtain a 
crystalloidal pitch with a constant mesophase content. To obtain a 
crystalloidal pitch having a high mesophase content, i.e., to obtain a 
mesophase of high purity, it has heretofore been customary to extract the 
mesophase fraction from the crystalloidal pitch containing same by use of 
a solvent such as quinoline or anthracene oil. This conventional process 
has the disadvantage that the raw pitch and the solvent must be used in 
large quantities and the solvent must be recovered after use. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a novel 
process capable of consistently producing crystalloidal pitch of a 
prescribed mesophase content. This and other objects of the present 
invention will become apparent from the following description of the 
present invention. 
The present invention is characterized by the steps of subjecting solid 
pitch particles measuring not more than 5 mm in cross-sectional equivalent 
diameter to a treatment for protecting the solid pitch particles against 
cohesion, thereafter bringing the thus treated solid pitch particles into 
contact with a non-oxidative gas at temperatures of from 350.degree. C. to 
550.degree. C. to form a suspension of pitch particles wherein the gas 
constitutes not less than 30% by volume. 
The term "cross-sectional equivalent diameter" is used in the specification 
on the assumption that the solid pitch particles occur in definite shapes 
such as spheres, cubes and rectangular parallelepipeds, and the areas and 
volumes of the particles of the assumed shapes are equivalent to those of 
the actual particles. The term is used to refer to the diameter of the 
central cross sections of the hypothetical particles.

DETAILED DESCRIPTION OF THE INVENTION 
As the raw material for the present invention, various types of pitch such 
as, for example, coal pitch, petroleum pitch and any pitches produced as 
by-products in chemical industries can be used. For ease of handling and 
for smooth operation such as the fusion-proofing treatment described below 
and heat treatment, it is desirable to use pitch having a softening point 
of not less than about 70.degree. C. By the term "softening point" used 
herein is meant the temperature at which one gram of a pitch sample placed 
in a cylinder having a cross-sectional area of 10 mm and provided at the 
lower end thereof with a nozzle 1 mm in diameter begins to flow out of the 
nozzle when a load of 10 kg/cm.sup.2 is applied to the specimen and at the 
same time the cylinder is heated externally to elevate the temperature of 
the specimen at a temperature increase rate of 5.degree. to 15.degree. 
C./min. Such an apparatus for softening point determination is the flow 
tester made by Shimadzu Seisakusho Ltd. In the present invention, a given 
pitch is converted into solid pitch particles not more than 5 mm in 
cross-sectional equivalent diameter for the purpose of producing 
crystalloidal pitch. The preparation of the solid pitch particles is 
accomplished simply by crushing or molding the pitch raw material. It is 
essential that the solid pitch particles have a cross-sectional equivalent 
diameter of not more than 5 mm, preferably not more than 3 mm. Those 
particles having a cross-sectional equivalent diameter of 5 mm or more are 
not suitable, for they tend to effervesce and undergo thermal deformation 
in the course of the heat treatment for conversion into a crystalloid. The 
shape of the solid pitch particles is not critical. They may assume shapes 
such as, for example, spheres, fibers, cylinders and even indefinite 
shapes. In the preparation of the solid pitch particles, the pitch used as 
the raw material is preferably molded in the form of spheres if its 
softening point is low, and when the pitch has a high softening point it 
may be crushed, if necessary. The pitch used as the raw material may be 
molded in the form of fibers for the purpose of producing carbon fibers. 
The present invention requires the solid pitch particles to be treated by 
one of the procedures (1), (2) or (3) described below so as to protect the 
individual pitch particles against mutual fusion or cohesion. 
1. Fusion-proofing by coating the surface of the solid pitch particles with 
a metal, metal salt, thermosetting resin, etc.: 
Where the coating is made with a metal, adoption of a conventional chemical 
plating method will suffice. By plating, the surface of the solid pitch 
particles can easily be coated with a metal such as copper, chromium, 
nickel or silver. Coating with a metal salt can be accomplished by 
immersing the solid pitch particles in an aqueous solution of the metal 
salt and then drying the impregnated pitch particles. The metal salts 
which can be used for this purpose are chlorides of such metals as nickel, 
iron and aluminum. Such a chloride functions as a catalyst in the 
polycondensation of pitch by the heat treatment described below and 
consequently serves to harden the surface of the solid pitch particles, 
making it possible to prevent the solid pitch particles from cohering. 
Coating with a thermosetting resin can be accomplished by forming a coat 
of a thermosetting resin such as phenol resin, furan resin or epoxy resin 
on the surface of the solid pitch particles and subsequently allowing the 
coat to harden. 
2. Fusion-proofing treatment effected by formation of an oxidized coat on 
the surface of the solid pitch particles: 
This treatment can be accomplished by simply allowing the solid pitch 
particles to come into contact with an oxidative gas selected from among 
oxygen, ozone, sulfur oxides, nitrogen oxides (for example, N.sub.2 
O.sub.5, N.sub.2 O.sub.3 and NO.sub.2) and halogens, or a mixed gas 
consisting of one or more oxidative gases and an inert gas selected from 
among nitrogen, argon, steam and complete combustion gases at room 
temperature or a temperature higher than room temperature but lower than 
the softening point of the solid pitch particles. Alternatively, the 
formation of an oxidized coat on the surface of the solid pitch particles 
can be produced by the so-called wet oxidation method which is effected by 
immersing the solid pitch particles in a solution of an oxidizing agent 
such as hydrogen peroxide, chlorate, hypochlorite, perchlorate, nitric 
acid, ferric chloride, perchromate, mixed acid, permanganate or 
peracetate. The procedure for formation of the oxidized coat should be 
conducted at a temperature lower than the softening point of the solid 
pitch particles, no matter which of the aforementioned procedures may be 
adopted. Since the softening point of the solid pitch particles rises in 
proportion to the extent of the oxidation, however, the temperature of the 
reaction system may be allowed to rise to the level of 350.degree. C. (the 
temperature at which the solid pitch particles begin to undergo conversion 
into a crystalloid) without the pitch particles becoming mutually fused or 
deformed. Particularly in the case of solid pitch particles having a large 
cross-sectional equivalent diameter, such elevation of temperature proves 
advantageous in the sense that the time of treatment can be curtailed. It 
is difficult to define the time required for the formation of the oxidized 
coat, because the time will vary to a great extent depending on the 
particular kind of oxidizing agent and the magnitude of the treatment 
temperature. Generally, the time required ranges from several minutes to 
several hours. 
3. Fusion-proofing treatment effected by removing low-boiling components or 
low-melting components from the solid pitch particles by extraction: 
This treatment can be effected by extraction with a solvent which is 
capable of effectively and selectively dissolving the low-boiling 
components or low-melting components of the pitch particles and which is 
substantially incapable of dissolving other pitch components. Examples of 
solvents which meet such requirements are acetone, methylethyl ketone, 
benzene, toluene, hexane, heptane, cyclohexane, methyl alcohol, chloroform 
and carbon tetrachloride which may be used singly or in the form of a 
mixture of two or more members. Proper selection of a solvent from the 
aforementioned group of solvents, will depend on the nature of the pitch. 
By extraction, there can be obtained solid pitch particles of residual 
pitch components having a softening point of from 340.degree. to 
400.degree. C. and insusceptible to mutual fusion or cohesion. When solid 
pitch particles having a softening point of not more than 340.degree. C. 
are obtained, the individual pitch particles are not protected against 
mutual fusion. It then becomes necessary to subject the solid pitch 
particles resulting from the extraction treatment, to a treatment wherein 
the solid pitch particles are allowed to stand in an atmosphere of a 
substantially non-oxidative gas at temperatures between the softening 
point and the flow point of the solid pitch particles for a period of from 
several minutes to a few score minutes (this treatment will be referred to 
hereinafter as "preliminary heat treatment"), and subsequently to subject 
the preliminarily treated particles to the procedure of (2). This 
preliminary heat treatment serves the purpose of softening and shrinking 
the surface of the solid pitch particles to a slight extent without 
causing any deformation of the pitch particles and consequently, closing 
the pores on the surface and uniformizing the surface condition. Thus, it 
enables the solid pitch particles to retain their shape in good order in 
the subsequent regular heat treatment which is described below. 
In selecting between procedures (1), (2) and (3) described above it is wise 
to take into due consideration such factors as the shape of the solid 
pitch particles, the property of pitch itself and the extent to which the 
conversion of pitch into a crystalloidal pitch as the final product is 
effected. The fusion-proofing treatment may be effected by adopting the 
procedures of (2) and (3) in combination. In the case where solid pitch 
particles happen to contain low-boiling components or low-melting 
components to some extent, the treatment of the solid pitch particles by 
the procedure of (1) or (2) alone may, at times, fail to satisfactorily 
attain the object of the fusion-proofing treatment. Besides, when solid 
pitch particles which have been treated by the procedure of (1) or (2) are 
subjected to the heat treatment to be described hereinbelow, the particles 
yield to an undesirable phenomenon of effervescence and cause a 
degradation in the quality of the crystalloidal pitch to be finally 
obtained. When the treatment by the procedure of (2), for example, is 
carried out thoroughly for the oxidation to proceed amply into the solid 
pitch particles so that the object of the fusion-proofing treatment may be 
fully attained on the solid pitch particles containing low-boiling 
components or low-melting components, these solid pitch particles are 
converted into oxidized pitch particles and consequently throw an obstacle 
in the way of the heat treatment to be given for conversion into a 
crystalloidal pitch. Where the treatment by the procedure of (2) is given 
to such solid pitch particles as contain a certain amount of low-boiling 
components or low-melting components, therefore, it is preferable to 
subject these pitch particles to the treatment of procedure (3) either 
before or after the treatment of procedure (2) so as to strip these 
components from the pitch particles by extraction. This additional 
treatment ensures success of the fusion-proofing treatment and facilitates 
the heat treatment for conversion of pitch into a crystalloidal pitch. 
Subsequently, in the present invention the solid pitch particles, 
fusion-proofed as described above, are subjected to a heat treatment in 
which the pitch particles are contacted with a non-oxidative gas at 
temperatures of from 350.degree. to 550.degree. C. while maintaining a 
"void ratio" of not less than 30% by volume. The term "void ratio" as used 
herein means the proportion occupied by the non-oxidative hot gas in a 
given volume of the dispersed system consisting of the solid pitch 
particles and the current of the hot gas. As long as the void ratio is not 
less than 30% by volume, the heat treatment can be conducted uniformly and 
smoothly in a short period of time. Examples of the non-oxidative gases 
which serve the purpose described above include nitrogen, argon, hydrogen, 
steam and complete-combustion gases. The dispersed system formed by 
keeping the solid pitch particles in contact with the non-oxidative gas 
may assume the form of a fluidized bed, a fixed bed or a perfect moving 
bed. The temperature at which the heat treatment described above is 
carried out should fall in the range of from 350.degree. to 550.degree. 
C., because the conversion of the solid pitch particles into a 
crystalloidal pitch is substantially unattainable where the temperature is 
below the lower limit of 350.degree. C. On the other hand, the solid pitch 
particles undergo carbonization so abruptly as to hinder the proper 
conversion into the crystalloidal pitch where the temperature exceeds the 
upper limit of 550.degree. C. The heat treatment time may be suitably 
selected in accordance with the temperature to be used. Generally, the 
time required is several hours at temperatures of from 380.degree. C. to 
450.degree. C. When the solid pitch particles are subjected to the heat 
treatment of the foregoing description, the mesophase forms and grows 
within the solid pitch particles, with the result that there is finally 
obtained a crystalloidal pitch. 
According to the present invention, the solid pitch particles are heat 
treated by exposure to the current of a hot gas as described above. 
Because of the particular nature of the heat treatment, the time of 
treatment and the temperature of treatment can be freely changed so 
rapidly that the degree of conversion to a crystalloidal pitch can readily 
be adjusted as desired. Further, the present invention enjoys the 
advantage that because the solid pitch particles to be treated have a 
small size, the treatment can be accomplished with great rapidity and high 
productivity. Microscopically, precursors of various types suitable for 
isotropic to heterotropic carbon products can readily be produced by the 
process of the present invention by properly varying the shape of solid 
pitch particles used as the starting material. Where the solid pitch 
particles are in the form of globules and are consequently isometric, the 
crystalloidal components (mesophase) occur and grow macroscopically in an 
isotropic arrangement. Where the solid pitch particles are in the form of 
fibers, the crystalloidal components occur mainly in the direction of the 
major axis. It is also possible to produce a carbon material of high 
density and high strength by preparing a carbon precursor capable of being 
sintered by adjusting the degree of crystalloid conversion, finely 
pulverizing the produced precursor, molding the resultant powder without 
use of a binder and baking the molded powder. 
The crystalloidal pitch thus obtained according to the present invention 
can be used for the production of carbon and graphite products of 
unusually high quality and, therefore, can be used extensively in the 
field of electrical products, in the field of mechanical products such as 
seals and bearings, in the field of atomic power and in the field of 
chemical products such as impervious and anticorrosive containers, etc. 
The present invention will be described more specifically below by 
reference to preferred embodiments of the invention. It should be noted, 
however, that the present invention is not limited in any way by these 
examples. 
EXAMPLE 1 
A petroleum pitch having a softening point of 100.degree. C. and a benzene 
insolubles content of 40% was molded into globules 0.5 mm in average 
diameter. The pitch globules thus molded were extracted with hexane at 
room temperature and further extracted with benzene at room temperature 
and thus stripped of about 25% by weight of their low-boiling components. 
After this treatment by extraction, the pitch globules showed a softening 
point of 330.degree. C. Then, the pitch globules were heated to 
350.degree. C. in a fluidized bed of a void ratio of 60% formed with a 
current of hot nitrogen gas supplied at a linear velocity of 30 cm/sec. 
When the temperature of the globules leveled off, air was introduced into 
the system to give an oxygen content of 4% in the current of hot gas so as 
to oxidize the surfaces of the pitch globules for a period of 10 minutes. 
The introduction of air was then discontinued and the system was elevated 
to 420.degree. C. at a temperature increase rate of 100.degree. C./hour. 
At a temperature of 420.degree. C., the system was allowed to stand for 
four hours, with the current of nitrogen gas continued. The crystalloidal 
pitch globules thus obtained were found to have a quinoline solubles 
content of 8% and a fixed carbon value of 93% and to possess a sintering 
property. These globules were pulverized to an average diameter of 10 .mu. 
and thereafter molded under pressure of 1 ton/cm.sup.2 and finally 
graphitized. The graphite thus produced had a bulk density of 2.05, a 
bending strength of 1100 kg/cm.sup.2 and a porosity of 5%. 
EXAMPLE 2 
A pitch having a softening point of 270.degree. C. was prepared by 
distilling off the low-boiling fraction from the tar by-produced in the 
production of acetylene and ethylene by the thermal cracking of crude oil 
at elevated temperatures. This pitch was molded by melting to form pitch 
beads measuring 1 mm in average diameter. The pitch beads were subjected 
to the fusion-proofing methods described below. Thereafter, the 
fusion-proofed pitch beads were converted into a crystalloidal pitch. 1. 
Fusion-proofing treatment by the wet oxidation method: 
A 1% sodium hypochlorite aqueous solution (available chlorine 
concentration) was adjusted to pH 5.5 by addition of acetic acid. To the 
resultant solution the pitch beads were added in the amount of 50 g per 
liter and maintained at 40.degree. C. for two hours for oxidation. Then, 
the pitch beads were washed thoroughly with water and dried in a current 
of hot air at 100.degree. C. Thereafter, the pitch beads were placed in an 
inert gas atmosphere in a rotary kiln operated at a rate of 30 rpm and 
were advanced therein through heating zones maintained at successively 
higher temperatures ranging from over 270.degree. C. to 550.degree. C. so 
as to have the temperature thereof elevated at a temperature increase rate 
of 180.degree. C./hour. At various temperatures, the beads under treatment 
were sampled and tested for presence or absence of mutual fusion between 
individual beads and for degree of conversion into crystalloidal pitch. 
The degree of conversion to crystalloidal pitch was determined by 
dissolving 1 g of a given specimen in 100 g of quinoline, agitating the 
resultant solution at 40.degree. C. for 12 hours, passing the solution 
through a glass filter No. G-3 and weighing the insoluble fraction 
separated by this filtration. In this case, however, the quinoline 
insolubles contained in the raw material prior to the start of the 
conversion into the crystalloidal pitch were not regarded as part of the 
crystalloidal pitch. The amount of quinoline insolubles produced by the 
surface oxidation was negligibly small. Table 1 shows the relation between 
the temperature and the amount of crystalloidal pitch produced. 
TABLE 1 
______________________________________ 
Temp- 
erature Fusion *Amount of 
Speci- 
at time of crystalloidal 
Shape of** 
men of sam- individual pitch produced 
crystalloidal 
No. pling beads (wt %) pitch 
______________________________________ 
1 300.degree. C. 
-- 0 -- 
2 350 -- 15 Spheres 
3 380 -- 60 Large Spheres 
4 400 -- 80 Coalescence of 
spheres 
5 450 -- 89 Flow pattern 
6 550 -- 95 Flow pattern 
______________________________________ 
*The values in this column represent the amounts of crystalloidal pitch 
formed as a quinoline insoluble fraction. 
**As viewed in cross-section through a polarizing microscope. 
As is evident from the foregoing results, the proper conversion to 
crystalloidal pitch can be accomplished by operating in the range of from 
350.degree. C. to 550.degree. C. and a product can be obtained in any 
desired shape, ranging from crystalloidal globules to a fluid structure 
having individual crystalloidal globules combined into one continuous 
mass. FIG. 1 represents a photograph taken through a polarizing microscope 
of specimen No. 1, which is seen to be free from occurrence of mesophase. 
FIG. 2 is a photograph taken of specimen No. 3, which clearly shows 
occurrence of Spheres (mesophase) and the presence of a fusion-proofing 
coat. Specimen No. 4, the photomicrograph of which is shown in FIG. 3, was 
subjected to a heat treatment in an inert gas atmosphere at 2400.degree. 
C. and then tested for graphitization. The results were as follows: 
Specific gravity (as immersed in n-butanol) 2.15, LC (002), 280 A, d.002, 
3.375 A. 
2. Fusion-proofing treatment by air oxidation: 
The same pitch beads as used in (1) above were fluidized in a current of 
hot gas (N.sub.2) supplied at a rate of 50 liters/min. (gas void ratio 
70%) and heated instantaneously to the neighborhood of the softening point 
of pitch. They were maintained at that temperature for 30 minutes. 
Thereafter, the introduction of air into the current of hot gas was 
started at a rate to give an oxygen content of 4% by volume in the current 
of hot gas so as to oxidize the surface of pitch beads for 2 hours. Then, 
the introduction of air was stopped. Again, in the current of N.sub.2 gas 
alone, the pitch beads were heated to 400.degree. C. at a temperature 
increase rate of 180.degree. C./hour. At 400.degree. C., the beads were 
allowed to stand to determine the relationship between the duration of 
heating and the degree of conversion. Throughout this period, the heating 
of the system was controlled by adjusting the temperature of the hot gas 
(N.sub.2), 
The results were as shown in Table 2. 
Table 2 
______________________________________ 
Length of standing 
Amount of crystalloid 
at 400.degree. C (hr) 
formed (%) 
______________________________________ 
0 80 
0.5 83 
1 87 
3 90 
5 93 
______________________________________ 
3. Fusion-proofing treatment by the chemical metal plating method (copper 
coat): 
A mixture obtained by adding 8.5 ml of ammonium chloride solution (13 N) to 
100 ml of a 100 g/lit. copper sulfate solution was diluted with water to 1 
liter. 50 g of pitch beads were introduced into the resultant solution and 
then 0.5 g of hydrosulfite and a small amount of Rochell salt was 
introduced to plate the beads at 26.degree. C. for 5 minutes. The plated 
beads were formed into a fixed bed having a gas void volume of 38% and 
heated at 380.degree. C. for 2 hours by a current of a complete-combustion 
gas containing no free oxygen for conversion into crystalloidal pitch. 
Consequently, there were obtained crystalloidal pitch beads showing 
substantially no sign of mutual fusion and having a crystalloidal content 
of 69%. The quinoline insolubles formed as a consequence of the plating 
treatment were not regarded as part of the crystalloidal content mentioned 
above. The plate formed on the surface had a thickness of about 1.mu. . 
When the crystalloidal pitch beads thus formed were treated in 
hydrochloric acid solution, the plate vanished completely leaving behind 
crystalloidal pitch beads of a refined quality. When 60 g of these 
crystalloidal pitch beads and 40 g of coal pitch (having a softening point 
of 70.degree. C.) were agitated together for thorough dispersion at 
300.degree. C. for 2 hours, there was produced a crystalloidal pitch which 
had a softening point of 200.degree. C. and which was extremely easy to 
melt-mold. When this pitch was extruded through a nozzle 1 mm in diameter, 
the crystalloidal component thereof was observed under a polarizing 
microscope to be oriented in the direction of the major axis. 
4. Fusion-proofing treatment by use of thermosetting resin: 
A resol type phenol resin was diluted with methanol to a 1% solution. In 
this solution, the pitch beads were immersed so as to be coated with the 
phenol resin. The coated pitch beads were subjected to a heat treatment at 
150.degree. C. for 30 minutes to thoroughly set the phenol coat. The 
coated pitch beads were then held in the form of a fluidized bed in a 
current of N.sub.2 gas supplied at a rate of 50 liters/min. so as to 
elevate their temperature to 550.degree. C. at a temperature increase rate 
of 180.degree. C./hour for the purpose of conversion. The crystalloidal 
pitch beads thus obtained were found to have undergone conversion while 
retaining their original form, though the individual beads were partly 
fused. The degree of conversion was found to be 98%. The quinoline 
insoluble fraction originating in the phenol resin was 2%. 
5. Fusion-proofing treatment by use of metal salt: 
In 1 liter of a methanol solution containing 2% nickel chloride, 50 g of 
pitch beads were placed. Then the beads were separated by filtration, 
dried in a current of hot air and thereafter heated in a fluidized bed to 
390.degree. C. at a temperature increase rate of 90.degree. C./hour. The 
beads were allowed to stand at 390.degree. C. for 5 hours. The degree of 
conversion was found to be 90%. 
EXAMPLE 3 
A pitch having a softening point of 290.degree. C. was prepared from a tar 
obtained by the thermal cracking of crude oil at elevated temperatures. 
The quinoline insoluble content of this pitch was found to be less than 
1%. Absence of mesophase from this pitch was confirmed by observation with 
a polarizing microscope. This pitch was extruded by a melt-spinning 
machine at 350.degree. C. to produce pitch fibers 100.mu. in diameter. 
The pitch fibers were packed in such a way as to leave a gas void ratio of 
80% and a current of a nitrogen-air mixture (oxygen concentration of 4%) 
at 270.degree. C. was introduced upwardly through the packed mass of pitch 
fibers so as to uniformly oxidize the surface of the fibers for 30 
minutes. The quinoline insoluble content formed as a consequence of this 
oxidation was found to be 10% by weight. The pitch fibers were then heated 
in an atmosphere of N.sub.2 to 400.degree. C. at a temperature increase 
rate of 30.degree. C./hour and allowed to stand at that temperature for 
five hours. The fibers obtained at the end of the 5-hour period had a 
crystalloidal content of 95%, with the crystals oriented in the direction 
of the fiber axis as is seen in the photograph of FIG. 4. FIG. 5 is a 
photograph showing a cross-section of such pitch fibers. This photograph 
shows that the crystals are oriented in the form of concentric columns 
relative to the axis of the fibers. The fibers were further subjected to a 
heat treatment in an argon atmosphere up to 2400.degree. C. without 
applying tension. When the resultant pitch fibers were tested by the 
ordinary method using X-rays, the degree of orientation was found to be 
85%. These facts, as to the orientation of the fibers, are such as could 
be foreseen on the basis of carbon fiber technique of the past, but have 
been brought to light for the first time by the present invention. 
EXAMPLE 4 
A pitch having a softening point of 150.degree. C. was produced from 
so-called ethylene bottom oil obtained by the thermal cracking of naphtha 
at elevated temperatures. This pitch was melted at 200.degree. C., dropped 
on a disk rotating at a high rate of speed to produce short fibers 0.5 mm 
in average diameter. Then, in a rotary kiln, the short fibers were 
instantaneously heated to 150.degree. C. with a current of steam and 
maintained at this temperature for five hours. After elimination of 
low-boiling components, introduction of air was started (to give an oxygen 
content of 8%) to oxidize the fibers for two hours. Then, the introduction 
of air was stopped. The fibers were heated in the steam up to 550.degree. 
C. at a temperature increase rate of 90.degree. C./hour for the purpose of 
conversion. The crystalloidal content was found to be 95%. When the fibers 
were heated at 2400.degree. C. to be carbonized and graphitized in the 
argon current, there were obtained short fibers having an orientation 
degree of 90% and a specific gravity of 2.45. Observation under a 
polarizing microscope revealed that the thickness of the oxidized coat 
formed on the fibers was about 20.mu. . 
EXAMPLE 5 
In a coal pitch (having a softening point of 78.degree. C.), 3% iron 
chloride was incorporated as a conversion accelerator. The resultant 
mixture was uniformly melted at 150.degree. C. and then allowed to cool. 
Thereafter, the resultant solid mixture was crushed with a hammer mill and 
then classified to produce particles having a particle size distribution 
in the range of from 5 mm to 1 mm. The particles were immersed in 6 N 
nitric acid solution and treated therein at 60.degree. C. for 1 hour. 
Thereafter, the impregnated particles were heated to 450.degree. C. in the 
form of a fluidized bed having a void volume of 50%, with an inert gas 
current at a temperature increase rate of 30.degree. C./hour for 
conversion. The degree of conversion was found to be 90%. The 
crystalloidal pitch particles thus obtained were crushed with a hammer 
mill, molded at room temperature under pressure of 600 kg/cm.sup.2 and 
then baked and graphitized by the ordinary method. The results were as 
shown in Table 3. 
Table 3 
______________________________________ 
Physical properties of graphite 
(20 mm in diameter .times. 10 mm in height) 
______________________________________ 
Bulk density 1.90 
Porosity 8.0% 
Bending strength 850 kg/cm.sup.2 
Resistance 25 .times. 10.sup.-4 .OMEGA.cm 
Shore hardness 79 
______________________________________ 
EXAMPLE 6 
A pitch having a softening point of 150.degree. C. was prepared from a tar 
by-product from the thermal cracking of crude oil at elevated 
temperatures. This pitch was extruded through nozzles 0.1 mm in diameter 
and taken up on a roll to produce filaments measuring 20 .mu. in diameter. 
The filaments were immersed in methanol at 40.degree. C. for 5 hours and 
then dried in air to have their softening point elevated to 280.degree. C. 
Subsequently, the filaments were heated instantaneously to 285.degree. C., 
in the form of a fixed bed having a void ratio of 80% by volume, with an 
inert gas current (N.sub.2 fed at the rate of 10 liters/min.) and left to 
stand at 285.degree. C. for 30 minutes. Then, introduction of air was 
started to control the total oxygen content of the mixed system at 4% by 
volume, so that the filaments were subjected to an oxidizing treatment for 
five minutes. At the end of the oxidizing treatment, the introduction of 
air was stopped and the filaments were heated up to 400.degree. C. at a 
temperature increase rate of 180.degree. C./hour with the N.sub.2 current 
and allowed to stand at that temperature for two hours, with the result 
that the crystalloidal content attained full growth. The filaments were 
bound together, oriented and again heated to 1000.degree. C. at a 
temperature increase rate of 180.degree. C./hour. X-ray analysis revealed 
that the filaments thus obtained showed an orientation degree of 80%. By 
an additional heat treatment (carried out at 2400.degree. C.), the 
filaments were improved in orientation degree to 90%. At this point, the 
filaments were found to have a specific gravity of 2.15. 
EXAMPLE 7 
A pitch having a softening point of 170.degree. C. was prepared from a tar 
by-product from the thermal cracking of crude oil at elevated 
temperatures. From this pitch, pitch fibers measuring 10.mu. in average 
diameter were obtained by the melting method. The pitch fibers were 
subjected to an extraction treatment with acetone at 40.degree. C. for 5 
hours to be stripped of low-melting components. Consequently, there were 
obtained pitch fibers having a softening point of 370.degree. C. In a 
column-type heater, the fibers were heated to 100.degree. C., in the form 
of a fixed bed having a void ratio of 80% by volume, by nitrogen gas at a 
temperature increase rate of 100.degree. C./hour. The fibers were free 
from mutual fusion and measured 7.mu. in average diameter. Observation of 
the fibers under a polarizing microscope revealed that the crystals were 
arranged in the direction of the major axis relative to the direction of 
length and in the form of concentric circles relative to the cross section 
taken in the diametric direction.