CA1051806A - Process for the conversion of pitch into crystalloidal pitch - Google Patents

Abstract

PROCESS FOR THE CONVERSION OF PITCH
INTO CRYSTALLOIDAL PITCH

ABSTRACT OF THE DISCLOSURE:
Crystalloidal pitch is obtained by subjecting solid pitch particles measuring not more than 5 mm in cross-sectional equivalent diameter to a treatment for proofing the individual particles against mutual fusion and subsequently bringing the fusion-proofed solid pitch particles into contact with a non-oxidative gas at temperatures of from 350°C to 550°C and, during the contact, allowing the solid pitch particles to retain a void ratio of not less than 30% by volume. The crystalloid pitch is useful as a precursor for various carbon products.

Description

1o5~806 F LD 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 is an amorphous substance in itself. When this pitch is heated to temperatures of about 350C to 550~C in an inert gas atmosphere, the molecules of the pitch are mutually poly-condensed because of a thermal poly-condensation reaction and are 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 molecules of an aromatic property which have been oriented and associated together through their own inter-action. 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." The production of such crystalloidal pitch is referred to by the same token as "conversion of pitch into crystalloidal pitch."

In recent years, it has been reported that shaped articles of carbon (graphite) enjoying large 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 compres-sion molding and baking the compression molded articles. This technique has been attracting keen attention as a new process - 1 - .~

1051~306 available for the production of carbon products. Since the crystalloidal pitch has heretofore been produced by heating and melting the ordinary pitch in some container, viscosity of the pitch is gradually increased during production of the crystalloidal pitch with the result of nonuniformity of tem-perature distribution in the pitch and the conversion of the pitch into a homogeneous crystalloidal pitch is still difficult to attain. It is, therefore, impossible to obtain the cry-stalloidal pitch with a constant mesophase content at all times. To obtain a crystalloidal pitch having a high mesophase content, namely to obtain a mesophase of high purity, it has heretofore been customary to extract the mesophase fraction from the crystalloidal pitch composed of mesophase in conjunc-tion with a non-mesophase by use of a solvent such as quino-line or anthracene oil. This conventional process has a dis-advantage that the operation becomes complicated because the raw pitch and the solven~ must be used i~ large quantities and the solvent must be recovered after use.
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.
According to the present invention, crystalloidal pitch is produced by providing a bed of solid amorphous pitch parti-cles, said particles being not more than 5 mm in cross-sectional equivalent diameter, said bed having a gas void space of not less than 30% by volume; treating the surfaces of said pitch particles in said bed by coating, oxidation or solvent ex-traction to reduce susceptibility to cohesion; and contacting said particles in said bed with a hot non-oxidative gas to heat said particles to a temperature within the range of from 350-550C. and convert the pitch to the crystalloidal state.
~ - 2 -105~806 The term "cross-sectional equivalent diameter" is used in the specification hereof on the assumption that the solid pitch particles occur in definite shapes such as spheres, cubes and rectangular parallelepipeds, and the areas and - 2a -3, 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 assumed particle shapes.

BRIEF DESCRIPTION OF THE DRAWING:
In the attached drawings:
Fiq. 1 is a photograph taken through a polarizing microscope of the cross section of pitch beads which measured 1 mm in average diameter and which had undergone a heat treatment at 300C;
Fig. 2 is a photograph taken through a polarizing microscope of the cross section of pitch beads which measured 1 mm in average diameter and which had undergone a heat treatment at 380C;
Fig. 3 is a photograph taken through a polarizing microscope of the cross section of pitch beads which measured 1 mm in average diameter and which had undergone a heat treatment at 400C;
Fig. 4 is a photograph taken through a polarizing microscope of the longitudinal cross section of pitch fibers which measured 100 ~ in diameter and which had been treated in accordance with the present invention and;
Fig. 5 is a photograph taken through a polarizing microscope of the cross section of pitch fibers of Fig. 4 which had been treated in accordance with the present invention.
As the raw materiai for the purpose of the present invention, there can be used a variety of different pitches such as, for example, coal pitch, petroleum pitch and any of the ptiches by-produced in chemical industries. For ease of handling during processing, it is desirable to -1051~306 use pitch of the kind having a softening point of not less than about 70C. By the term "softening point" used herein is meant the temperature at which one gram of a specimen pitch 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/cm2 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 to 15C/min. This softening point is generally measured by use of a flow tester made by Shimadzu Seisakusho Ltd. In the case of 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 used as the raw material. It is essential that the solid pitch particles be possessed of a cross-sectional equivalent diameter of not more than 5 mm, preferably not more than 3 mm. Those having a cross-sectional equivalent diameter of 5 mm or more are not suitable, for they tend to effervescs and undergo thermal deformation in the course of the heat treatment which is to be given, as will be described afterward, for conversion into a crystalloid. The shape of the solid pitch particles is not limited specifically. They may assume any preferable 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 when the softening point thereof is low, and the pitch having a high softening ~os~806 point may be crushed, if necessary. The pitch used as the raw material is molded in the form of fibers for the purpose of finally producing carbon fibers.
Then, the present invention requires the solid pitch particles to be treated by one of the procedures (1), (2) an~
(3) described below so as to render the individual pitch particles proof against mutual fusion.
(1) Fusion-proofing treatment effected by coating the surface of the solid pitch particles with metal, metal salt, thermosetting resin, etc.:
Where the coating is made with a metal, adoption of the ordinary chemical plating method will suffice. By this method, the surface of the solid pitch pàrticles can easily be coated with a metal such as copper, chromium, nickel or silver.
In the case of the coating made with a metal salt, it can be accomplished by immersing the solid pitch particles in an aqueous solution of the metal salt and then drying the impregnat-ed 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 poly-condensation of pitch by the heat treatment to be described hereinbelow and consequently serves to harden the surface of the solid pitch particles, making it possible to prevent the solid pitch particles from mutual fusion. The 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:

In this case, the treatment can be accomplished by simply allowing the solid pitch particles to come into cont~ct with an oxidative gas selected from among oxygen, ozone, sulfur oxides, nitrogen oxides (for example, N2O5, N2O3 and NO2) and halogens, or a mixed gas consisting of one or more oxidative gases and an inert gas selected from among nitrogen, argon, steam and perfect-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 thé solid pitch particles can be attained by the so-called wet oxidation method which is effected by immersing the solid pitch particles in the solution of an oxidizing agent such as hydrogen peroxide, chlorate, hypochlorite, perchlorate, nitric acid, ferric chloride, perchromate, mixed acid, permanganate or peracetate.
Such formation of the oxidized coat is required to be carried out 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 progress of the oxidation, however, the temperature of the xeaction system may be allowed to rise to the level of 350C (the temperature at which the solid pitch particles begin to undergo conversion into a crystalloid) without the pitch particles being fused mutually or deformed. Particularly in the case of solid piteh 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, for the time is variable to a great extent depending on the particular kind of oxidizing agent and the magnitude of the temperature for the treatment. 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:
In this case, the treatment can be effected by extracting the solid pitch particles at room temperature by using a solvent which is capable of effectively 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 the solvent which meets such requirements include 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.
In the selection of a proper solvent from the aforementioned group of solvents, a wise rule is to pick a particular solvent that suits the property of pitch itself making up the solid pitch particles more than any other members of the group.
By this treatment of extraction, there can be obtained solid pitch particles made of residual pitch components possessed of a softening point of from 340 to 400C and insusceptible to mutual fusion. When solid pitch particles having a softening point of not more than 340C are obtained, the individual pitch particles are not rendered proof against mutual fusion.
In this case, it is necessary that the solid pitch particles resulting from the extraction treatment be subjected to a treatment which is effected by allowing the solid pitch particles 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 scores of minutes (which treatment will be referred to hereinafter as "preliminary heat treatment"), and subsequently be subjected to the treatment by 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 entailing 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 will be described hereinbelow.

In the selection of a proper procedure for the fus~on-proofing treatment from among the procedures of (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 ~uality 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 convertedinto 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 proc~dure 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 the solid pitch particles to the treatment by the procedure of (3~
either before or after the treatment by the procedure of (2) so as to strip the components from the pitch particles by extraction.
This additional treatment ensures accomplishment of the object of the fusion-proofing treatment and permits effective performance of the heat treatment for conversion of pitch into a crystalloidal pitch.
Subsequently, the solid pitch particles, fusion-proofed as described above, are subjected to a heat treatment which is effected by keeping the pitch particles in contact with a non-oxidative gas at temperatures of from 350 to 550C while allowing the particles to retain a void ratio of not less than 30% by volume. The term "void ratio" as used herein means the proportion occupied by a hot gas (non-oxidative 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 given uniformly and smoothly to the solid pitch particles in a short period of time. Examples of the non-oxidative gas which serves the purpose described above include nitrogen, argon,hydrogen, steam and complete-combustion gases. ~he dispersed system formed by keeping the solid pitch particles in g contact with the non-oxidative gas assumes 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 is required to fall in the range of from 350 to 550C
because the conversion of the solid pitch particles into a crystalloidal pitch is substantially unattainable where the temperature is below the lower limit of 350C of the range and 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 550C of the range. The heat treatment time may be suitably selected in due consideration of its relation with the temperature to be used.
For example, at high temperatures, the time may be short.
Generally, the time required is several hours at temperatures of from 380C to 450C. When the solid pitch particles are subjected to the heat treatment of the foregoing description, the mesophase occurs and attains growth within the solid pitch particles, with the result that there is finally obtained a crystalloidal pitch.
As described above, the solid pitch particles are given a heat treatment preferably by exposure to the current of a hot gas. 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 deg ee of conversion to a crystalloidal pitch can readily be adjusted as desired. Further, the present invention enjoys an advantage that because the solid pitch particles to be treated have a small size, the treatment can be accomplished with a speed sufficient to greatly improve product-ivity. Microscopically, precursors of various types suitable for isotropic to heterotropic carbon products can readily be produced by the process of the present invention by 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 pre-paring a carbon precursor possessed of a sintering property by adjusting the degree of crystalloid conversion, finely pulver-izing the produced precursor, molding the resultant powderwithout 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 containers and anticorrosive containers, etc.
The present invention will be described more specifi-cally hereinbelow with 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 100C
and a benzene insolubles content of ~0% 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 to be strlpped of about 25% by weight of low-boiling components. After this treatment by extraction, the pitch globules showed a softening point of 330C. Then, the pitch globules were heated to 350C
by being held in the form of a fluidized bed of a void ratio of 60% in a current of hot nitrogen gas supplied at a linear velocity of 30 cm/sec. At the time when the temperature of the globules reached the level, blowing of air into the system was started to give an oxygen content of 4% to the current of hot gas so as to have the surface of pitch globules oxidized for a period of 10 minutes. Then, the introduction of air was dis-continued and the system was elevated to 420C at a temperature increase rate of 100C/hour. At a temperature of 420C, 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 ~axbon yalue of 93% and to possess a sintering property. These globules were pulverized to an average diameter of 10 ~ and thereafter molded under pressure of 1 ton/cm2 and finally graphitized. The graphite thus produced had a bulk density of 2.05, a bending strength of 1100 kg/cm2 and a porosity of 5%.

EXAMPLE 2:
A pitch having a softening point of 270C was prepared by distilling out a low-boiling fraction from the tar by-produced in the production of acetylene and ethylene by the thermal cracXing of crude oil at elevated temperatures. This pitch was molded by the melting process to afford pitch beads measuring 1 mm in average dia~Rter. The pitch beads were subjected to the fusion-proofing treatment by the methods described hereinbelow, to have the beads' surface proofed against fusion. Thereafter, the fusion-proofed pitch beads were converted into a crystalloidal pitch.

-(1) Fusion-proofing treatment by wet oxidation method:
A 1% sodium hypochlorite aqueous solution (available chlorine concentration) was adjusted to pH 5.5 by addition of acetic acid thereto. To the resultant solution the pitch beads were added at a ratio of 50 g per liter and maintained at 40C
for two hours to undergo oxidation. Then, the pitch beads were washed thoroughly with water and dried in a current of hot air at 100C. Thereafter, the pitch beads were placed under 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 270C to 550C so as to have the temperature thereof elevated at a temperature increase rate of 180C/hour. At stated 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 amount of conversion to the crystalloidal pitch was obtained by dissolving 1 g of a given specimen in 100 g of quinoline, agitating the resultant solution at 40C 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 auinoline insolubles produced in consequence of the surface oxidation was negligibly small. Table 1 shows the relation between the temperature and the amount of crystalloidal pitch produced.

te,l U~ O
. ~
~ h O h h rl O O O Q~ ~1 O ~ J td t~' ~: PJ
O ~ C) U~ ~Q 0 0 ~ ~ ~
~11 ~ I o ~ O N
a) ~ ~1 h ID ~ h ~J -~1 0 P~ O t~) ~1 a) 3 3 Id ~ .C h (~ O O
.~: h P~ ~ O ~ ~1 ~ ~) ~1 U~ O u~ ~:1 C.) 0 ~4 h 0 0 P~
. C.) ~IS
41 .t O
~1 ~
rd ~ u~ . O
. ~0-0 ~ ~ ~ ~
P O O
. ~ ~I I~J O Lt~ O O c~ U) O
~ ~u .
~1 . ~ ~o a~

~ . ~ tQ
E~ 0-~ ~ ~ ~ '~ O
rl Q) ~q ~ ~ ,_1 ~1 0 ~ ~ O O ~l i4,1 u s~
~0 ~
~0 ~q :S O C~ . ~ h 0 a) ~: O O h . ~ 1 o o o o o o ~ OO O
a) ,l ~1 O u~~ ~ o u~ In ~1 ~1 U
E3 ~ ~ ~ r~ ~ ~3 o ~ ~ ~a ~ u ~ ~ ' ~ ~C
.~ .
u o ~ ~ ~ ~
~Z
~n .

As is evident from the foregoing results, the proper conversion to crystalloidal pitch can be accomplished by selecting the temperature freely in the range of from 350C to 550C and the product can ~e 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 likewise 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 2400C and then tested for graphitizing property.
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 *reatment by air oxidation method:
~ he same pitch beads as used in (lj above were fluidized in the current of hot gas (N2) 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 blowing of air into the current of hot gas was started at a rate to give an oxygen content of 4% by volume to the curr~nt of hot gas so as to have the surface of pitch beads oxidized fo~r two hours. Then, the introduction of air was stopped.
Again, in the current of N2 gas alone, the pitch beads were heated to 400C at a temperature increase rate of 180C/hour.
At the temperature of 4dooc, the beads were allowed to stand ~051806 for the purpose of finding the relation between the length of standing and the degree of conversion. Throughout this standing, the heating of the system was effected by adjusting the temperature of the hot gas (N2).
The results were as shown in Table 2.

Table 2 Length of standing Amount of crystalloid at 400C (hr.) formed (%) O.S 83 .

(3) Fusion-proofing treatment by chemical metal plating method (copper coat):
A mixture having 8.5 ml of ammonium chloride solution (13~1) added to lO0 ml of a lO0 g/lit.copper sulfate solution was diluted with water to l liter. In the resultant solution, 50 g of pitch beads were placed and then 0.5 g of hydrosulfite and a small amount of Rochell salt were introduced to plate the beads at 26C. for five minutes. The plated beads were caused to form a fixed bed involving a gas void ratio of 38% and heated at 380C. for two hours with the current of a complete-combustion gas containing no free oxygen so as to be converted 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 form.ed in consequence of the plating were not regarded as part of the crystalloidal content mentioned above. The plate formed on the surface had a thickness of about ll,. 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 piont of 70C.) were added to each other and were agitated for thorough dispersion at 300C. for two hours, there was pro-duced a crystalloidal pitch which had a softening point of 200C. and which was extremely easy to melt-mold. Wnen this pitch was extruded through a nozzle l 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 l~o solution. In this solution, the pitch beads were immersed so as to be coated with the pnenol resin. The coated pitch beads were subjected to a heat treatment at 150C. for 30 minutes to thoroughly set the phenol coat. The coated pitch beads were then held in the form of a fluidized bed in the current of N2 gas supplied at a rate of 50 liters/min.
so as to elevate the temperature thereof to 550C. at a temp-erature increase rate of 180C/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-o. The quinoline insoluble fraction originating in the phenol resin was 2%.

(5) ~usion-proofing treatment by use of metal salt:
In l liter of a methanol containing 2% nickel chloride solution, 50 g of pitch beads were placed. Then the beads were separated by filtration, dried in the current of hot air and thereafter heated in the form of a fluidized bed to 390C at a temperature increase rate of 90C/hour. The beads were allowed to stand at the temperature of 390C for five hours.
The degree of conversion was found to be 90%.

EXAMPLE 3:

A pitch having a softening point of 290C was prepared from a tar obtained in 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 meso-phase from this pitch was confirmed by observation with a polarizing microscope. This pitch was extruded by a melt-spinning machine at 350C to produce pitch fibers 100 ~ in diameter. The pitch fibers were packed so as to involve a gas void ratio of 80~ and the current of a nitrogen-air mixed gas (oxygen concentration of 4~) at 270C 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 in consequence of this oxidation was found to be 10% by weight. Then, in the atmosphere of N2 the pitch fibers were heated to 400C at a temperature increase rate of 30C/hour and allowed to stand at that temperature for five hours. The fibers obtained at the end of the five-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 ~rystals are oriented in the form of concentric columns relative to the axis of fibers. The fibers were further subjected to a heat treatment in an argon atmosphere up to 2400C without being specifically exposed to tension. When the resultant pitch fibers were tested by the ordinarv method using X rays, the degree of orientation was found to be 85%. These facts, as to the orientation property of the fibers, are such as could be foreseen on the basis of carbon fiber technique of the past.
They have been brought to light for the first time by the present invention.

EXAMPLE 4:

.
A pitch having a softening point of 150C was produced from so called ethylene bottom oil obtained by the thermal cracking of naphtha at elevated temperatures. This pitch was melted at 200C, dropped on a disk rotating at a high rate of speed to produce short fibers 0.5 mm in average diamèter. Then, in a rotary kiln, the short fibers were instantaneously heated to 150C 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 550C at a temperature increase rate of 90C/hour for the purpose of conversion. The crystalloidal content was found to be 95%. When the fibers were heated at 2400C 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 ~.

10518~6 EXAMPLE 5:
In a coal pitch (having a softening point of 78C), iron chloride was incorporated as the conversion accelerator at a ratio of 3%. The resultant mixture was uniformly melted at 150C and then allowed to cool off. 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 6N nitric acid solution and treated therein at 60C for one hour. Thereafter, the impregnated particles were heated, in the form of a fluidized bed involving a void ratio of 50%, to 450C with an inert gas current at a temperature increase rate of 30C/hour for the purpose of 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/cm2 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 x 10 mm in height) _ Bulk density l.gO
A Porosity _~4~ ~0 70 Bending strength 850 kg/cm2 Resistance 25 x 10 4 Qcm Shore hardness 79 105~806 EXAMPLE 6: -A pitch having a softening point of 150C was preparedfrom a tar by-produced in 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 ~ in diameter. The filaments were immersed in methanol at 40C for five hours and then dried in the air to have the softening point thereof elevated to 280C.
Subsequently, the filaments were heated, in the form of a fixed bed involving a void ratio of 80% by volume, instantaneous-ly to 285C with an inert gas current (N2 fed at the rate of10 liters/min.) and left to stand at the temperature of 285~

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 ~00C at a temperature increase rate of 180C/hour with the N2 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 1000C at a temperature increase rate o 180C/hour. X-ray analysis revealed that the filaments thus obtained showed an orientation degree of 80%. By an additional heat treatment (carried out at 2400C), 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 170C was prepared from a tar by-produced in the thermal cracking of crude oil at elevated temperatures. From this pitch, pitch fibers measuring 10 ~ in average diameter were obtained by the melting method The pitch fibers were subjected to an extraction treatment with acetone at 40C for five hours to be stripped of low-melting components. Consequently, there were obtained pitch fibers having a softening point of 370C. In a column-type heater, the fibers were heated, in the form of a fixed bed involving a void ratio of 80% by volume, to 100C by nitrogen gas at a temperature increase rate of 100C/hour. The fibers were free from mutual fusion and measured 7 ~ 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.

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for converting pitch to a crystalloid, which process comprises:
a. providing a bed of solid amorphous pitch particles, said particles being not more than 5 mm in cross-sectional equivalent diameter, said bed having a gas void space of not less than 30% by volume;
b. treating the surfaces of said pitch particles in said bed by coating, oxidation or solvent extraction to reduce susceptibility to cohesion; and c. contacting said particles in said bed with a hot non-oxidative gas to heat said particles to a temperature within the range of from 350°-550°C. and convert the pitch to the crystalloidal state.

2. The process of claim 1 wherein said treatment for reducing susceptibility to cohesion is by coating the surface of the pitch particles with a metal, metal salt, or thermosetting resin prior to contact with said non-oxidative gas.

3. The process of claim 1 wherein said treatment for reducing susceptibility to cohesion is by oxidizing the sur-faces of said particles.

4. The process of claim 1 wherein said treatment for reducing susceptibility to cohesion is by extracting low-boiling components or low-melting components from said pitch particles.

5. The process of claim 3 additionally comprising extract-ing low-boiling components or low-melting components from said solid pitch particles by contacting said particles with a solvent.

6. The process of claim 2 wherein said metal is copper, chromium, nickel, or silver.

7. The process of claim 2 wherein said metal salt is a chloride of nickel, iron or aluminum.

8. The process of claim 2 wherein said thermosetting resin is a phenolic resin, a furan resin, or an epoxy resin.

9. The process of claim 3 wherein said oxidizing is accomplished by contacting said pitch particles with at least one oxidative gas.

10. The process of claim 5 wherein said oxidizing is accomplished by contacting said pitch particles with at least one oxidative gas.

11. The process of claim 9 or 10 wherein said oxidative gas is oxygen, ozone, an oxide of sulfur, an oxide of nitrogen, or a halogen.

12. The process of claim 9 wherein said oxidative gas is diluted with an inert-gas selected from the group consisting of nitrogen, argon, steam, and complete-combustion gas.

13. The process of claim 12 wherein said inert gas is selected from the group consisting of nitrogen, argon, steam and complete-combustion gas.

14. The process of claim 3 or 5 wherein said oxidizing is by contacting said pitch particles with an oxidizing agent selected from the group consisting of hydrogen peroxide, chlorides, hypochlorites, perchlorates, nitric acid, ferric chloride, dichromates, acids, permanganates, and peracetates.

15. The process of claim 4 or 5, wherein said solvent is selected from the group consisting of acetone, methylethyl ketone, benzene, toluene, hexane, heptane, cyclohexane, methyl alcohol, chloroform, carbon tetrachloride and mixtures thereof.

16. The process of claim 1 wherein said non-oxidative gas is nitrogen, argon, hydrogen, steam or a complete-combustion gas.

17. The process of claim 1 wherein the particles are fluidized by the hot non-oxidative gas.

18. The process of claim 1 wherein said amorphous pitch has a softening point of not less-than about 70°C.