Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3~ 7
,
GRAPHITE STRUCTURES AN~ METHOD FOR PROD~CTION THER~OF
~ACKGROUND OF THE INVENTION
The present invention relates to graphite materials
and, more specifically, to graphite structures o light
weight and excellent elasticity and to a method for the
production of such structures.
Generally available carbon materials, whether
carbonaceous or graphitic, are characterized in that they
are rigid structures and possess high Young's modulus.
Light-weight carbon materials, on the other hand, include
carbon foams, hollow carbon spheres and expandable
graphite.
Carbon foams have been prepared either by foaming,
- 15 curing and calcining polyurethane or phenol resins or by
forming and calcining hollow carbon spheres with the aid
oE a binder (see USPs 3121050, 3342555 and 3302999, and
Inada, et al., "Carboni', No. 69, page 36, 1972). Such
foams are found to have a bulk density of the order of
about 0.5 g/cm3, but their graphitized structures have
poor flexibility and are thus rigid.
Hollow carbon spheres have been produced by the
melting and atomi~ing of Eoam-containing pitches into
spherical form, followed by calcination (see
Amagi, "Materials", Vol. 16, page 31S, 1971~. Such
spheres are relatively light-weight materials, as
expressed in terms of bulk density of 0.1 to 0.3 g/cm3,
but are rigid for lack of flexibility.
i' Expandable graphite has generally been made by the
oxidation and heat-treatment oE naturally occurring scaly
graphite. This graphite is light in weight as expressed
in terms of its coefficient of expansion which may reach
a factor of several hundreds, but may be subjected to
compression molding, as will be appreciated from the fact
that it is usable as the starting material for graphite
sheets. Graphite sheets obtainable from such an
expandable graphite are flexible and possess elasticity
.. ~
2 ~3~)6~7
to such an extent that they are restorable to their
original form after a compression load has been applied
thereto and removed therefrom.- For that reason, they are
said to excel in air-tightness when used as packing
material. However, such sheets are oF a densified
structure, and typically show a compressibility of as
small as about 40~ and a recovery of as small as about
- 20~, when they are subjected to a compression load of 350
kg/cm2 ~Saito, "Kogyo Zairyo" ("Industrial Materials"),
Vol. 20, page 34, 1985].
On the other hand, mesocarbon microbeads obtained by
the separation of minute mesophase-spheres Eormed at the
- incipient stage of carbonization of pitchesiare one form
of carbonaceous mesophases. In one method proposed in
- 15 Japanese Patent Laid-Open Publication No. 60(1985~-
1508319, a microporous carbonaceous material is obtained
by nitrating and heat-treatiny such microbeads. However,
this method produces only microporous structures by that
heat treatment ~ithout giving rise to any substantial
increase in volume, and is not directed to reductions in
weight.
SUMMARY OF T~E INVENTION
The present invention has been accomplished in view
of the foregoing and has its object to provide graphite
structures which are light in weight but have excellent
elasticity and a method for production of such a
structure.
The present graphite structures of light weight and
excellent elasticity are characterized by a packing
density of 0.5 g/cm3 or lower and a recovery of 50~ or
higher at a compressibility of 10 to 90~.
The method for the preparation of graphite
structures according to this invention is characterized
by the steps of treating a carbonaceous material with
nitric acid or a mixture of nitric and sulfuric acids and
graphitizing the same at a temperature of 2,400C or
higher.
~L3~6~g7
DETAILED DESCRIPTION OF THE INVENTION
Carbonaceous Material
The carbonaceous materials used as the starting
materials for the graphite structures of this invention
are preferably carbonaceous mesophases prepared by heat
- treatment of pitches that are heavy bituminous materials
and/or green coke.
As the starting carbonaceous materials, use may be
made oE any kind of pitches which produce the
graphitizable carbon. Examples are coal tar pitch, coal
base pitch such as liqueEied coal pitch, naphtha tar
pitch produced as a by-product during the thermal
- cracking of distillate residues of petroleum and naphtha,
petrolic pitch such as, or instance, FCC decanted oil
produced as a by-product in the fluid catalytic cracking
(FCC) process of naphtha, etc. and pitch obtained from
the thermal cracking of synthetic high molecules, e.g.,
PVC, and the like. These pitches are heat-treated at
about 350 to 500C, thereby forming carbonaceous
mesophases (including green coke). The formation of
carbonaceous mesophases is easily ascertainable by the
observation of the heat-treated products under a
polarized-light microscope. In other words, the
carbonaceous mesophase is identified as optically
anisotropic texture in the pitch that is optically
isotropic one. In view of the morphology of carbonaceous
mesophase, it is required at this time that the heat
treatment proceed through its gentle stage, i.e., the
; early stage of the process of carbonization where single
mesophase-spheres are formed to so-called bulk mesophase
where such spheres grow and coalesce with each other.
The reason is that any substantial increase in volume is
not achieved by treating mesocarbon microbeads separated
at the stage of single spheres~ with a mixed sulfuric-
nitric acid and then heat-treating them, although they
are a sort of carbonaceous mesophase.
4 ~.3~6~3197
The heat-treatment conditions For the formation o~
carbonaceous mesophase are determined depending upon the
- elemental analysis of carbonaceous mesophase separated
from heat-treated pitches. The conditions should
preferably be such that, among the elements, hydrogen in
particular is present in an amount of 2~ by weight or
more. The reason is that this takes part in the next
treatment with a mixed sulfuric-nitric acid, i.e., the
amount of the nitro group introduced in the aromatic
nucleus substitution reaction.
- - It is, therefore, necessary to avoid excessive heat
treatment, since semicoke obtained by solidifying the
- total amount of pitches under severe heat-treatment
conditions has a hydrogen content of at most 2%, so that
- 15 its volume does not substantially increase even upon
- being treated with a mixed acid and then heat-treated.
It is understood that the mesocarbon microbeads have a
hydrogen content of as much as about 4% but are unlikely
to increase in volume, as already mentioned.
2~ The separation of carbonaceous mesophase from the
heat-treated pitches is carried out by precipitation
or~and) solvent fractionation. More specifically, upon
being allowed to stand in a molten state, the heat-
treated pitches settle down and can be recovered.
When the heat-treated pitches are dissolved and
dispersed in a solvent such as an organic solvent, e.g.,
quinoline or pyridine, or an aromatic oil containing much
aromatic compounds, e.g., anthracene or creosote oil,
they can be recovered as components insoluble matter in
such solvents.
Acid Treatment
The carbonaceous materials are treated with nitric
acid or a mixture of sulfuric and nitric acids.
Both sulfuric and nitric acids are preferably used
in high concentrations; at least 95% for sulfuric acid
and at least 60~ Eor nitric acid. ~owever, neither need
be fuming sulfuric acid nor fuming nitric acid. More
5 ~ '6q:~7
preferable results are obtained with the use of a mixture
of nitric and sulfuric acids rather than nitric acid
alone. When used, the mixed acids are preferably such
that sulfuric and nitric acids are in a volume ratio
ranging from 30:70 to 0:100. It is to be noted, however,
that the optimum volume ratio ranges from 30:70 to 70:30.
Hereinafter, the mixture of sulfuric and nitric acids
will simply be referred to as the mixed acids or acid
mixture.
10The carbonaceous materials are added into nitric
acid or the mixed acids, and are agitated, or allowed to
stand, at a temperature ranging from 0 to 150C for 5
minutes to 5 hours. The reaction temperature and time
are determined by the degree of increase in the volume of
the carbonaceous materials achieved in the next heat-
treatment step. In general, the lower the temperature,
the longer the time will bel while the higher the
temperature, the shorter the time will be. Aftér the
treatment, the product is thoroughly washed with water
and dried. It is to be noted, however, that the
neutralization of the product with an alkaline metal salt
Eor the removal of the acid is preferably avoided, since
the alkali metal is then likely to remain.
Heat Treatment
25The carbonaceous materials treated with the acid as
described above are heat-treated at a temperature of 250
to 300C.
This treatment causes the volume of the carbonaceous
materials to increase several times to several tens of
times. The rate of volume increase at this time is
considered to be a factor in the acid treatment
conditions. Of the heating conditions in said
temperature range, the heating rate, whether high or low,
has little or no influence upon the rate of volume
increase This is because the decomposition of
carbonaceous materials occurs in a narrow temperature
range in the vicinity of approximately 250C. ~ence,
6 ~ 3Ir~6 0 ~
this treatment is not necessarily carried out in the Eorm
oE a separate step. This means thatj unless any handling
problem arises due to the increase in volume, the heat
treatment may be followed immediately by graphitization.
Graphitization
The carbonaceous materials heat-treated or àcid-
treated as described above are heat-treated to a
temperature of 2,~00C or higher for graphitization. If
the graphitization temperature is lower than ~,400C, a
graphite structure having the desired properties cannot
be obtained, since both its compressibility and recovery
decrease, although its weight is light. The higher the
- temperature, the more the flexibility will be; however, a
graphitization temperature of 3~000C or lower is
preferable in view of economical considerations.
This treatment makes it possible to produce graphite
structures which are of light weight and excellent
elasticity.
The thus produced graphite structure is of light
weight, as expressed in terms of its packing density oE
at most 0.5 g/cm3. When put in a cylindrical vessel and
receiving a load from above, this graphite structure is
compressed. At this time, the compressibility is
proportional to the load applied. Even when a very high
compressibility of as high as 9o% is applied, a recovery
of 50% or higher is obtained after the removal of the
load. A load corresponding to a compressibility of 90%
or higher is 500 kg/cm2 or higher. Even when a load oE
9,000 kg/cm2 is applied, a recovery of 50% or higher is
obtained. Thus, the graphite structures according to the
present invention possess unique and excellent properties
that the conventional carbonaceous materials do not.
Reference will now be made to the examples of the
present invention. However, it is to be understood that
the present invention is by no means limited to the
description of such examples.
Example 1
7 ~L3~6~
Two ( 2 ) kg of a FCC decanted oil, from which low-
boiling components having a boiling point of not higher
than about 500C had previously been removed by
distillation under reducded pressure, was heat-treate~
under agitation to 500C in a nitrogen gas stream in a
- vessel of 5 liters, and were held at that temperature for
2 hours. Afterwards, the heating and stirring were
stopped to cool off the vessel. When the internal
temperature of the vessel reached 400C, that temperature
was maintained by heating. After the elapse of 3 hours
Erom the beginning o cooling-off, about 1.6 kg of a
pitch-like product was removed from the vessel through a
hole set in the lower portion thereof. An about 2-fold
amount of quinoline was added to this pitch-like product,
and the mixture was heated at 90C for dissolution and
dispersion. Then, the insoltlble component was
centrifuged and supplied with fresh quinoline and then
heated and centrifuged. After this operation had been
repeated five timesi the insoluble coponent was amply
~ashed with benzene and acetone and dried. The insoluble
component thus obtained in an amount of 1.2 kg was found
to show an anisotropic flow texture by the observation of
its structure under a polarization microscope. Then,
this insoluble component was llsed as the carbonaceous
mesophase.
The elemental composition of the carbonaceous
mesophase prepared in this manner was~
carbon 93.2~,
Hydrogen 3.8%, and
Nitrogen 0.7%.
Five (5) g of the mesophase having a particle size of
1.17 to 0.70 mm was added in small portions to 100 ml of
a mixed acid consisting of 97% concentrated sulfuric acid
and 67~ concentrated nitric acid in a volumetric ratio of
50:50 in a Erlenmeyer flask of 300 ml in vo]ume. After
8 ~"3~;i6~7
the total amount of the mesophase had been added, the
flask was heated for Go minutes in an oil bath previously
heated to 100C. Then, the product was filtered out
through a glass filter (No. 4), sufficiently washed with
water, and was dried. The yield was 129.6% by weiyht.
The product was placed in a cylindrical glass vessel of
500 ml, and then it was in turn held for 30 minutes in a
salt bath previously heated to 300C. The yield was
81.7% by weight with respect to the starting carbonaceous
mesophase.
The packing density of this product was measured in
the following manner. Ten ~10) to fifteen (15) cc of a
sample, as precisely weighed and calculated as volume,
was placed in a graduated measuring cylinder of 20 ml,
and its volume was measured aEter it had been confirmed
that no volume change occurred upon being tapped well.
The packing density was calculated from the volume and
weight and was found to be 0.03 g/cm3, a figure
indicating that the volume increase was 28 fold, since
the packing densi~y of the carbonaceous mesophase as
starting material was 0.83 g/cm3.
Next, the product was heat-treated to 2,800C at a
heating rate of 400C/hr. in an argon gas stream and then
held at that temperature for 30 minutes for
graphitization The yield was- 38.2~i by weight with
respect to the carbonaceous mesophase, and the packing
density 0.10 g/cm3. The elastic recovery was determined
in the following manner. In a cylindrical vessel of 10
mm inner diameter was put 0.5 g of the graphitized sample
on which a load of 100 g/cm2 was applied from above. The
sample's volume at this time was used as the reference
volume (ho)~ A load of 500 g/cm2 was then impressed on
the sample to determine its volume (hl). The load was
subsequently removed from the sample to determine its
volume (h2). The compressibility and recovery were
calculated by the following equations:
. 9 1 3Ir36 ~ 3'~
Compressibility (%) = {(ho-hl)/ho} x 100
Recovery (%) - {(h2-hl)/(ho-hl)} x 100
The compressibility calculated in this manner was
9.5%, and the recovery 100%. The compressibility and
recovery of this sample dete.rmined under varied loads are
shown in Table 2. The compressibility, which increases
with increase in load, reaches 90% or higher at 500
kg/cm2 or larger, with the .recovery reaching as high as
75%, and is as high as 96% even at 9r300 kg/cm2, with the
recovery reaching as high as 58~.
Table 1 also shows the results obtained with the
same starting carbonaceous mesophase which was treated
with the mixed acids consisting of sulEuric and nitric
acids in varied volume ratios and under varied mixed
acid-treatment and graphitization conditions.
o ~.3~ '7
. . _
O 00 ~ O
U~ t) ~ ~ ~ C`l O O O O ~ 1
pt a ~ o o o ci o o o ;o o o o o
- ~- ----~ p~
~J dP ~ ~ a~ ~ ~ ~ ~ a~ ~ ~ ~ oo a~
c: ~ 3 co~
V a ~ o
~ o ~ -~ o o o o o c~ o o o o o o ~
) ~ c~ ~o o o o o o
C~ P. --C`i C`~ C~ C~ C`~ ' C`l C`l C;l- C~ ~^ N ^ C~)
_ V
d~ ~ ~ O eo U:~ ~ CD CO CD ~ O U~
Q~ ~ ~ ~
~, 3 ~ O
~:1 O E _
~ ~ ~ ~ ~ 9
o ~ ~ '3
~ C~ o 10 U~ 10 o o o o o o
~, ~ . ~:~
.~ U
~ 1 Z c o o o o o o o o o o o ~a
U ' U~ U:~ lC~ o .~
P~ .
,~ 7~
fi l ~ ~ Z
11 ~3~ ;C~7
The compressibility and recovery of these
graphitized products were measured. The results are set
froth in Table 2.
Table 2
Exp. Load Compres- Recovery
Nos. (kg/cm2) sibility ~%) (~)
. .... _ .... ..
0.5 9.5 100
1~0 10.3 100
Z.o 12 83
: 4.0 18 75
I 5.0 22 75
38 75
500 8~ 75
1,500 91 75
5,500 96 67
.. __ 9,300 96_ _ 58
1.0 2.8 100
2.0 8.3 100 :
4.0 11 85
. 5.0 23 ~ 83
2 . 10 32 83
500 85 82
1,500 92 73
5,500 92 77
9,300 93 77
_ . _ _
. 1.0 4.8 100
2.0 9.5 100
4.0 . 17 85
i' 3 l5o~o 41 8835
500 87 77
. 1,500 84 77
. 5,500 92 72
. _ ~,300 96 ..
12 ~ 3~
. Table 2 (bis)
. ....... ____ :
Exp . Load Compres- Recovery
Nos, ~kg/cm2) sibility ~%) (%)
1.0 3.0 100
2.0 9.1 lO0
d"O 12 8~
5.0 22 88
A~ 10 33 85
500 85 80
1,500 91 78
5,500 91 75 .
9,300 92 71
..
500 86 32
1,500 86 32
__9,300 93 33
19 60
7 10 38 52
9,300 _ 96 50
21 33
8 10 34 25
9,300 93 23
. ... _._
9 9,300 70_ lds
. .5 32 66
Z5 10 10 58 63
9,300 95 55
,
. 5 15 80
12 10 36 80
;, 9,300 83 70
Example 2
The elemental analysis of a carbonaceous mesophase
obtained in a similar manner as in Example 1 was:
Carbon 92.9 %
Hydrogen 4.1 %, and
Nitrogen 0.5 %.
3 ~.3~6~'7
Five (5) 9 of the mesophase product, which had been
classified to a particle size of 0.70 to 0.3S mm, were
treated in the mxied acid in a similar manner as
described in Example 1 and were then heat-treated at
300C for 3 minutes. The product was further heat-
treated to 2,800C in a Tamman-furnace, wherein it was
held for 30 minutes for graphitization. The
compressibility and recovery of the obtained graphite
structure were measured. The packing densities of
graphitized structures obtained with the mixed acid in
varied volume ratios under varied treatment conditions
are shown in Table 3, and the compressibility and
recovery thereof in Table 4.
14. ~
_
C ~ r~
Y U~ U ~ ~ ~ ~ ,~, o ~
~J C ~ o o o o o o o
~ a~-- Q)
. .. -- ~_ . . ~
~a~ c~O~ 0~. C`J O U~ ~ ~ ~ O
c ':-~ 3 t~ CDoo ~3
V C . . _ O
.,~ ~
'~ ~ ~ o o o o o o o
U ~ a~ o~
Q~ -C`J^ C`~ C`;
. E~ .~ .
. _ ~ ~
_
C~ o U)
.
a~ ,,,, 0!7 U~ CO O t-- N ~1 .
~ 3 ~ JJ
E~ O ~ ^ ~ O ~, ~
O _ ,
V
~ ~ `'3
,~ ~ ~ U ~ _, ~ ~ o~ 'O
E~ ~ ~ : .
E~ U
~S U: .. _.. _
i., X O- ooooooo
~ '~t-~o .a
:>~, .C
o ..
~ c~ a)
1~ ~ ~ Z
L~ -
15 ~3(; ~7
Table 4
. ~ _. .___ .. __
Exp. Load Compres- Recovery
Nos.tkg/cm2)sibility (~) (~)
_
13 10 48 40
9,30~ 95 33
_ .. .. ... _
14 9,300 9~ Gl
_ _ 27 85
lo 47 76
9,300 93 57
. _ . . _ .
IG 9,300 92 61
. _
17 9,300 94 56
18 9,300 95 4~1
_
19 9,300 92 ~4
.. _ . __
Example 3
Green coke obtained by the delayed coking process
was pulverized to a particle size oE 0.35 to 0.15 mm with
the elemental analysis being carbon: 91.8%, hydrogen~
3.6%, and nitrogen: 1.4~. Five (5) g of the pulverized
product was treated at 150C for 5 hours in the mixed~
acid consisting of 97~ sulfuric acid and 67~ nitric acid~
in a volume ratio of 50:50. After Eiltration, the~
;~ product was amply washed with water and dried. The yie~ld~
was 120.8%. The product was then heat-treated for 30'
minutes in a furnace previously heated to 300C. The
thus heat-treated product was graphitized at 2,800C for
,~ 30 minutes by a Tamman-furnace. The yield was 69.4%~and
the packing density 0.48 g/cm3. The compressibility and
recovery of the thus graphitized structure were
determined as in Example 1 and found to be respectively~
16 ~3~6[)~
21~ and 67~ under a load of 3 kg/cm2 and respectively 43
and 57~ under a load of 10 kg/cm2.
; Comparative Example
The carbonaceous mesophase used in Example 1 was
heat-treated at 800C for 30 minutes in a nitrogen gas
stream. The elemental analysis of the obtained product
was 94 1~ of carbon, 1.8% of hydrogen, and 1.3~ of
nitrogen. This product was treated at 150C for 5 hours
with mixed acids consisting of 97~ sulfuric acid and 67
nitric acid in a volume ratio of 50:50. After
filtration, ample water-washing was applied. The yield
was 107.6~. The thus treated product was heat-treated
for 30 minutes in a furnace previously heated to 300C,
and was then graphitized at 2,800C for 30 minutes by a
Tamman-furnace. A graphitized structure was obtained in
a 89.6~ yield with a packing density of 0.78 g/cm3. The
compressibility and recovery of that structure were
determined as in Example 1 and were found to be
respectively 5.2% and 33% under a load of 2 kg/cm2 and
respectively 70~ and 29% under a load of 9,300 kg/cm2.
- 30
