Technology for manufacture of pure fullerenes C60, C 70 and a concentrate of higher fullerenes

Article abstract of DOI:10.1134/S1070427207030196

An integrated technology for manufacture of fullerenes was developed. It includes the following stages: synthesis of a fullerene black, extraction of a mixture of fullerenes from the black, preliminary separation of the mixture into concentrates enriched in C₆₀ and C₇₀ fullerenes, and production of C₆₀ and C₇₀ fullerenes of purity exceeding 99.5 and 98.0 wt %, respectively, from the concentrates.

Full text of DOI:10.1134/S1070427207030196

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 3, pp. 448 455. Pleiades Publishing, Ltd., 2007.
Original Russian Text Yu.S. Grushko, V.P. Sedov, V.A. Shilin, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 3, pp. 450 457.
NANOTECHNOLOGIES
AND NANOMATERIALS
Technology for Manufacture of Pure Fullerenes C60, C70
and a Concentrate of Higher Fullerenes
Yu. S. Grushko, V. P. Sedov, and V. A. Shilin
Konstantinov Institute of Nuclear Physics, Russian Academy of Sciences, Gatchina, Leningrad oblast, Russia
Received September 28, 2006; in final form, December 2006
Abstract An integrated technology for manufacture of fullerenes was developed. It includes the following
stages: synthesis of a fullerene black, extraction of a mixture of fullerenes from the black, preliminary separa-
tion of the mixture into concentrates enriched in C60 and C70 fullerenes, and production of C60 and C70
fullerenes of purity exceeding 99.5 and 98.0 wt %, respectively, from the concentrates.
DOI: 10.1134/S1070427207030196
The development of nanotechnologies is a priority
of the XXI century and, beginning in 2000, has been
attracting considerable investment in all the developed
countries of the world. In 2007, the Federal Target
Program Development of the Infrastructure of Nano-
technologies in the Russian Federation in 2007 2010
is brought in force in Russia. According to estimates,
no less than 25% of current nanotechnological designs
are, and will be, associated with use of fullerenes.
However, despite the considerable progress in studies
of fullerenes and development of technologies for
their production, a number of problems have not been
resolved, which hinders wide application of fullerene
nanostructures. The major problem is high cost of
production, separation, and purification of fullerenes.
The integrated technology for manufacture of ful-
lerenes, suggested in this paper, includes stages of FB
synthesis, extraction of a mixture of fullerenes from
the black, and subsequent separation and purification
of the fullerenes (see scheme). This technology has
been used for more than 10 years at the St. Petersburg
Institute of Nuclear Physics for production of kilo-
gram amounts of C of 99.5% purity (here and here-
60
inafter, the composition of fullerenes is given in
weight percents).
Manufacture of FB by electric-arc evaporation
of graphite. The fullerene-containing carbon black
produced by the electric-arc method, as a rule, con-
tains a mixture of fullerenes with the following con-
tent of the main components (wt %): C 65 88, C
60
70
12 30, and C
1 5. A specific feature of the
n>70
Several methods for synthesis of fullerenes are
presently known [1 10]. The most preferable of these
are the electric-arc technique [9] and method of in-
complete combustion of hydrocarbons (benzene,
toluene, etc.) [6]. Other methods have been poorly
studied and can be only used on a limited scale.
electric-arc method is that it produces, together with a
carbon black containing up to 20 wt % fullerenes, also
so-called cathode deposits containing up to 40 wt %
multilayer carbon nanotubes, which a valuable materi-
al for nanotechnologies.
The designs of electric-arc carbon-black generators
(EACBGs), developed by now, provide, under certain
conditions, a fullerene yield of up to 43 wt % [5].
However, the increase in the fullerene yield entails a
decrease in the evaporation rate of graphite [15]. It has
been noted [2] that, as the diameter of the electrodes
being evaporated increases, the yield of fullerenes
should necessarily decrease. This circumstance serves
as a certain limitation in developments of a high-
capacity EACBG design [5, 16 19].
In both methods, the main synthesis product is
the so-called fullerene-containing carbon black (FB).
In addition to fullerenes, the black contains amorph-
ous carbon and, in the case of incomplete combustion
of hydrocarbons, also impurities of polycondensed
aromatic hydrocarbons.
A characteristic distinction of fullerenes from other
structures composed of pure carbon is their ability to
dissolve in organic solvents. This enables recovery of
fullerenes from FB by extraction with organic solvents
[11 14].
Processing of FB with low content of fullerenes is
unprofitable because of the increasing expenditure of
448

TECHNOLOGY FOR MANUFACTURE OF PURE FULLERENES C60, C70
Integrated flowsheet for manufacture of fullerenes
449
Production
of fullerene-containing
carbon black
Nanostructured
carbon
Extraction of fullerenes from FB.
Multiple washing of the black
with a solvent and filtration.
Collection and evaporation
of filtrates. Preliminary enrichment
of the extract in C60 fullerene
Carbon black
Solution
of C70 concentrate
(65 5%)
Fractional enrichment
(preconcentration) of the extract
in C60 fullerene
Preparation of solution
of C60 concentrate
Chromatographic purification
of solution of C60 concentrate.
Preparation of C60 fullerene
Process
for production
of pure
C70 fullerene
of commercial purity (99.5%)
Commercial C60 product
(99.5% purity)
Commercial C70 product
(98% purity)
electric power, solvents, and labor per gram of the
final product. The experience of EACBG exploitation
made it possible to find a balance between the content
of fullerenes in a black and the output capacity that
would be optimal from the profitability standpoint.
The optimal output characteristics are provided both
by limiting the diameter of a graphite rod being
evaporated (as a rule, to 6 15 mm) and by choosing
the rate of its evaporation. The generator designs used
show the best performance with rods (electrodes) 6
8 mm in diameter. In prolonged operation modes, the
average yield of fullerenes varies within 6 10% of
the mass of the fullerene-containing carbon black,
which, in turn, constitutes 35 50% of the mass of the
evaporated graphite (the rest is the cathode deposit).
The yield of the carbon black can be raised by revers-
ing the polarity of the electrodes for back evapora-
tion of the cathode deposit. However, the evaporation
of the cathode deposit is slow because of its high
electrical resistivity, which makes the gain in the
output capacity insignificant.
The fullerene yield is markedly raised if water-
cooled screens, coils, and other devices that shield
fullerenes from the detrimental action of hard UV
radiation of the arc are present in the evaporation
chamber [5, 18]. The yield of fullerenes also depends
on the purity of the graphite material. The best results
were obtained with domestic raw materials on MPG-6
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450
GRUSHKO et al.
Table 1. Parameters of an extraction installation for
extraction of fullerenes from electric-arc FB
resolved by incorporating the electric-arc unit into a
computer-controlled multiunit system [10]. This will
markedly diminish loss of time for unit recharging.
Parameter
Value
3
Extraction of fullerenes from FB. Several meth-
ods are known for recovery of fullerenes from FB [11,
12, 14]. Their principal disadvantage consists in long
duration of extraction and filtration and low degree of
fullerene recovery ( 70 wt %). The solvents used
in the process of fullerene recovery from carbon black
should satisfy the following requirements: high solu-
bility of fullerenes, as low boiling point as possible,
low fire and explosion hazard, low toxicity, and low
cost. Published data (e.g., [20, 21]) on the solubility
of fullerenes in various solvents can be used to com-
pose a list of solvents best suitable for large-scale ex-
traction: toluene, o-xylene, o-dichlorobenzene, 1,2,4-
trichlorobenzene, and 1,2,4-trimethylbenzene. Of
these, o-xylene was chosen as satisfying the above
requirements to the fullest extent. C and C fuller-
Maximum weight of FB charged into extractor,
kg
Preferable mass of FB charge, kg
1.5 2.0
Extractant/FB ratio, liters of solution/kg of FB 10 12
Number of extraction cycles
Duration of agitation (extraction), h:
first cycle
3
1
second cycle
third cycle
3
6
Efficiency of extraction process (3 cycles), %
92 95
Residual content of fullerenes in carbon black 0.2 0.3
(3 cycles), %
Irrecoverable loss of solvent, %
9.0
Duration of extraction process (3 cycles), h
15 17
60
70
enes have a comparatively high solubility in o-xylene
spectroscopic graphite rods of ultrapure 7-2 and
7-3 grades [TU (Technical Specifications) 48-4802-
14 88].
1
at 25 C: 8 10 and 15 g l , respectively. Use of
o-xylene instead of toluene, which frequently serves
as an agent for extraction of fullerenes from carbon
black, makes it possible to considerably reduce the
volumes of the solutions being processed and thereby
to minimize the dimensions of the basic process ap-
paratus. The extraction installation developed in this
study includes a mechanical stirrer with a filter, col-
lectors for solutions and solvent, and a vacuum evap-
orator. The following parameters were found when
using this installation: optimal mass of carbon black
charged into the extractor, solvent/carbon black ratio,
duration and number of repetitions of the extraction
procedure, loss of the solvent via its capture by the
carbon black, extraction efficiency, and residual con-
tent of fullerenes in the carbon black. The values of
these parameters are listed in Table 1.
An EACBG of basic design was used to process
225 kg of graphite rods (6 mm in diameter, 200 mm
long). The capacity of the generator in terms of
evaporation of graphite rods was, on the average,
100 g per hour. The mean fullerene content of FB was
6 8 wt %.
It was found in a prolonged exploitation of a work-
ing prototype of an electric-arc generator that main-
taining the fullerene yield at a level not lower than
6 wt % in continuous operation requires that the heli-
um atmosphere in the evaporation chamber should be
renewed at regular intervals of time. This is necessary
because impurities released from the graphite being
evaporated (trace amounts of sorbed moisture, at-
mospheric oxygen, etc.) accumulate and suppress
generation of fullerenes. A promising technical solu-
tion concerning the removal of FB from the electric-
arc zone with a directed flow of inert gas (helium) and
its collection in special containers proved to be poorly
efficient for the given case because the system for
helium recycling is bulky and complicated in use.
A more practically feasible procedure is that with
periodic renewal of the helium atmosphere in the
evaporation chamber, correlated with maintenance
stops.
To accelerate the extraction process, the filtration
was carried out under a nitrogen pressure of up to
2
5 kg cm . A suspension of carbon black in the solv-
ent was mechanically agitated at 2 3 revolutions per
second. The material remaining on the filter is com-
posed of a solid phase (carbon black, 40 wt %) and
a captured solvent (60 wt %), and, therefore, solvent
regeneration requires that an additional operation,
vacuum evaporation of the solvent from carbon black,
should be performed.
As can be seen from Table 1, the extraction process
is long and labor-consuming and involves a consider-
able irrecoverable loss of the solvent. The previously
developed sublimation technique [22, 23] is devoid of
the above-mentioned disadvantages. This method con-
Thus, the presently used electric-arc FB generators
have limited output capacity, mainly determined by
the evaporation parameters of the graphite material.
The problem of raising the FB yield can be partly
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 3 2007

TECHNOLOGY FOR MANUFACTURE OF PURE FULLERENES C60, C70
451
sists in the following: A bulk finely dispersed carbon
black is mixed in a certain proportion with a nonin-
flammable mixture of solvents and agitated until free-
flowing and no-dust-forming grains are formed (com-
paction). Then the resulting product is charged into a
sublimation apparatus and fullerenes are sublimed at
a temperature of 500 800 C and residual pressure of
0.1 1.0 Pa and condensed on a water-cooled remov-
able collector. The conditions under which the sub-
limation occurs with an 88 90 wt % yield in 1 1.5 h
were experimentally found. Experiments performed on
larger FB samples demonstrated that a large-scale sub-
limation installation can be, in principle, developed.
of C and C are well-resolved (the distance bet-
60
70
ween the peaks is 11 times the width of the C line at
60
half-maximum) and the relative content of impurities
can be easily determined.
Enrichment of the extract by fractional concen-
tration. At present, numerous technical solutions that
enable production of pure fullerenes C , C and
60
70
C
are known [24 26, 28 34]. These solutions are
n>70
mostly based on the chromatographic method, which
produces, in some cases, very pure solutions of C
60
and C fullerenes of purity exceeding 99.5 and 98%,
70
respectively. A disadvantage of the chromatographic
method is its low output capacity in terms of the
target component.
A prompt analysis was made using spectrophotom-
etry or microcolumn high-performance liquid chro-
The previously revealed property of the anomalous
matography (HPLC) on the C phase with a 60 : 40
temperature dependence of the solubility of C ful-
18
60
acetonitrile toluene mixture as eluent. Chromatogra-
lerene [20, 21, 24 28] served as a basis for a method
of fullerene purification by fractional concentration
[28]. The method of fractional crystallization [26, 27]
phy on this phase enables reliable observation of C ,
60
C , and their oxides, but, in this case, the peaks of
70
can produce C fullerene of 99.5% purity; however,
the higher fullerenes are strongly broadened and their
analysis is difficult. For analysis of high-purity fuller-
enes and higher fullerenes, we used chromatographic
columns specially developed by Nacalai Tesque Inc.
(Japan) for analysis and separation of fullerenes and
metallofullerenes: analytical/semipreparative Cosmosil
BuckyPrep 4.6 250 column and preparative Cos-
mosil BuckyPrep 10 250 column. The stationary
phase of both of these columns is pyrenylpropyl silica
gel. Standard analyses and separations use as the
mobile phase (eluent) pure toluene. The sample
volume and the eluent flow rate were 20 l and
60
the process involves numerous stages and the yield of
the target product is very low, only several percents
[27]. In [26], a mixed solvent composed of toluene
and 1,3-diphenylacetone was used. Three stages of
crystallization yielded C of 99.5% purity, according
60
to HPLC analysis. With this method, the total yield of
pure C fullerene was 69% relative to the mass of the
60
starting extract (at initial C content of the extract
60
equal to 84%). The main disadvantages of this tech-
nique are as follows: large solvent volumes are used
because of the low solubility of fullerenes in this
solvent, toluene should be completely removed from
the solvent after performing the procedure, high tem-
perature (110 C) is necessary, duration of each stage
is long, a difficultly available solvent component is
used (1,3-diphenylacetone), and the mixed solvent is
to be regenerated. Therefore, this technique should
also be considered labor-consuming and poorly effi-
1
1 ml min for the analytical column, and 4 ml and
1
4.7 ml min in preparative separations. The peaks
were recorded by absorption at a wavelength of
330 nm. The ratio of the molar extinctions of C and
70
C
at this wavelength is 0.76.
60
A single-stage analysis on the analytical column is
sufficient for analysis of C with a 99.5%+ purity. In
60
cient despite the high yield of pure C .
60
analysis of ultrapure (99.9%+) C , a weighed portion
60
The technique we suggest here employs, to obtain
of the substance to be analyzed is preliminarily en-
riched with impurities on the preparative column.
pure C , a kind of liquid chromatography, flash
60
chromatography or flash filtration. This separation
method can be used in those cases when the retention
time of the components being separated differs by
a factor of more than several tens. This method is
devoid of the principal disadvantage of the classical
chromatography, low output capacity, because it does
not require a fixed one-time charging of a limited
amount of the starting material. However, the service
life of the sorbent in this technique is limited by its
capacity for impurities being sorbed. Therefore, in
order to make longer the working time of a column
In this case, a fraction that follows C is taken. This
60
fraction is concentrated to a certain volume and its
aliquot is taken for analysis on the analytical column.
The main impurities in pure C are monoxide C O
60
60
and C . On these columns, the retention time of ful-
70
lerene oxides exceeds that for the corresponding un-
oxidized fullerenes, in contrast to the case of the C
18
phase (octadecyl silica gel), on which the oxides are
eluted earlier than the corresponding fullerenes with
a 60 : 40 acetonitrile toluene mixture as eluent. Under
the above-mentioned analytical conditions, the peaks
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 3 2007

452
GRUSHKO et al.
Table 2. Main parameters of the FC process
Fraction composition, wt %
Mass of deposit, wt % rela-
tive to starting extract,
for each stage
Solvent : crystals,
FC stage Time, h
deposit
filtrate
1
ml g
C60
C70
C60
C70
First
Second
Third
1.5
2.0
3.0
10
19
15
87.0
92.0
96.7
13.0
8.0
3.3
31.4
75.4
84.6
68.6
24.6
15.4
79.5
66.3
60.8
without replacement of the sorbent, the content of
the component being purified in the raw material
should be as high as possible.
following composition (wt %): C O 2.2, C 94.9,
60 60
C
2.9. This concentrate is a good half-product for
70
production of pure C by flash-chromatographic puri-
60
fication.
To obtain a concentrate of this kind, with a C
60
The fractional enrichment procedure enables the
content of up to 96%, a procedure for enrichment of
the starting raw material for flash chromatography,
fractional concentration (FC), was developed. The FC
process is for the most part performed in three stages,
the yield of the enriched product remains high, and
following: (1) production of a concentrate with a C
content sufficiently high for practical use in further
flash-chromatographic purification; (2) removal of
60
C
from the starting extract in a smaller number of
70
stages; (3) choice of the FC mode in which a first-
the content of C fullerene in the concentrate is as
60
stage solution with high C content, suitable for
high as 96 2%. The procedure consists in the follow-
60
subsequent preparation of this fullerene, is formed;
(4) determination of the conditions in which filtrate
solutions of second and third stages have a composi-
tion close to that of the starting extract and the extract
formed in the first stage of FC, respectively, which
enables their use in the subsequent cycles of enrich-
ment; (5) reduction of the volume of fractions with
ing. A fullerene extract with a C content of 72 85%
60
is dissolved in a certain amount of o-xylene heated to
80 85 C until a saturated solution is formed, this
solution is filtered on a vacuum filter heated to the
same temperature, and the separated crystals are dried
under reduced pressure to constant mass. As a result,
the crystals are enriched with C fullerene, and the
60
a low content of expensive C .
filtrate, with C fullerene. The composition and yield
70
70
of the enriched concentrate of C depends on the
60
In continuous processing of fullerene extracts, the
composition of the starting extract of fullerenes and
solvent/crystals ratio. A decrease in the enrichment
was observed on making longer the time for which the
saturated fullerene solution is heated. In the multistage
enrichment scheme, the decrease in enrichment be-
comes noticeable already in the third stage, with no
enrichment occurring at a larger number of stages.
Presumably, this is due to cross oligomerization of
yield of the C concentrate is optimized and the loss
60
of C is reduced to a minimum.
70
Production of pure C fullerene. Several meth-
60
ods for preparation of a pure C fullerene are known:
60
chromatographic [29 36], fractional crystallization
[26, 27], selective extraction [37, 38], and chemical
techniques that use complexing agents, such as, e.g.,
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) [39] or
calixarenes [40], or those based on functionalization
of the fullerene molecule (bromination [41] etc.). As
already noted, the most efficient method for produc-
C
and C under the action of temperature. It was
60
70
found that the total time of all thermal treatments,
including the duration of agitation and hot filtration,
should not exceed 7 h. With account of this limitation,
a process scheme of FC was developed. This scheme
enables effective enrichment of extracts of virtually
tion of pure C is flash chromatography. The best, as
60
regards the output capacity, stationary phase in puri-
fication of C fullerene by this method are activated
60
any composition in C fullerene, with a considerable
60
carbons with a large specific surface area, e.g., of
Darco (Fluka) or DCL GDC (Waterlink Sutcliffe Car-
bons) brands [42] or sorbents based on these carbons.
Solvents of aliphatic or aromatic nature or mixtures of
these, o-xylene in the given case, are commonly used
as the mobile phase.
yield of the final product. Table 2 lists the results of
FC of C fullerene at the initial C /C ratio of
60
60 70
75/25.
It follows from the results presented that three
stages of FC give in a 60% yield a concentrate of the
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TECHNOLOGY FOR MANUFACTURE OF PURE FULLERENES C60, C70
453
The use of a granulated activated carbon as a sorb-
ent enabled application of a simple version of gravita-
tional liquid chromatography. The choice of o-xylene
for preparing the starting solution is due to the fact
that o-xylene has been used previously for extraction
and fractional concentration. An additional advantage
of o-xylene over toluene frequently used for this pur-
pose [37] is that, in this case, solutions with high con-
centration of fullerenes can be prepared; as a result,
solutions with considerably smaller working volumes
can be used and the duration of the chromatographic
process can be made markedly shorter.
0.1%. An advantage of the technology developed con-
sists in that first portions of the eluate contain high-
purity C fullerene (better than 99.9%). At a flow
60
1
2
rate of the liquid phase exceeding 0.2 ml min cm ,
the fraction of such a product in the total output can
be markedly raised, which improves the profitability
of the production process.
With this technology used on a working equipment
at St. Petersburg Institute of Nuclear Physics, Russian
Academy of Sciences, the average rate of 99.5% C
manufacture with double-shift work was 1 2 g h (or
60
1
500 600 g per month). The developed flowsheet can
be used without any significant change for manufac-
A saturated solution of a mixture of fullerenes in
o-xylene, with a C
content of about 96%, is
60
ture of C fullerene in an amount exceeding 10 kg
60
continuously fed into the column, and the eluate con-
tains C , in which no C or higher fullerenes are
per month.
60
70
Manufacture of pure C fullerene. Flash chro-
70
detected. The process of chromatographic purification
matography on activated carbon cannot be used to
separate C from C because C is sorbed on the
is monitored by the concentration of C fullerene in
70
the eluate. To obtain, e.g., C of 99.5% purity, the
70
60
70
60
carbon considerably more firmly than C . Therefore,
process is terminated when C appears at the outlet
60
70
it is advisable to use a combination of several meth-
in a concentration exceeding 0.1 %. After C appears
70
ods for large-scale manufacture of pure C fullerene
at the outlet, the supply of the feeding solution is ter-
minated and pure solvent is fed into the column. The
70
[43]. The technology we suggest includes the follow-
ing sequence of procedures: enrichment of a mixture
of C /C fullerenes with C fullerene by fractional
washing is performed to a C concentration in the
60
1
eluate equal to 0.1 0.2 g l . Further washing is in-
60 70
70
concentration to a level of 85 92%; flash chromato-
graphic purification of the concentrate obtained to re-
move the admixture of higher fullerenes on activated
advisable for practical reasons.
The mobile phase is supplied at a velocity of 0.2
1
2
1
2
0.8 ml min cm (preferably 0.4 0.5 ml min cm ).
If the process is carried out at a lower rate, the purity
of the product obtained is improved, but the output
capacity of the process decreases. An increased flow
rate of the mobile phase not only impairs the quality
carbon; separation of trace amounts of C by frac-
60
tional purification to obtain pure (98%) C fullerene.
70
The fractional concentration from o-xylene, which
is an efficient and high-output-capacity technique for
enrichment of C , has also been successfully used for
of C obtained, but also leads to a decrease in the
60
60
enrichment of C fullerene [44].
amount of the pure product obtained in a single cycle
of use of the sorbent.
70
The stage of fractional concentration in C fuller-
70
ene is continuation of the first stage of fractional en-
The yield of pure C is 72 78% relative to the
60
richment with C fullerene. The concentrate obtained
amount of the concentrate charged, with 15 18%
being the loss for irreversible sorption and up to 10%
70
in this stage (20 22% relative to the weight of the
starting mixture of fullerenes) is a supersaturated solu-
representing a material in which the content of C
70
1
tion (up to 26 g l ), from which crystals containing
fullerene exceeds 0.5% (raw material for further re-
cycling). The solvent is removed from the solution
85 92% C precipitate upon cooling. The yield of
70
the crystals depends on temperature and duration of
crystallization, and can be as high as 80% relative to
the material contained in the filtrate at 24 C. The
collected at the column outlet and crystals of pure C
60
fullerene. Analysis shows that crystals of C fuller-
60
ene, as a rule, contain, in addition to an insignificant
impurity of C fullerene, that of the oxide C O in
1
mother liquor contains 2 3 g l of fullerenes and is
70
60
enriched in C fullerene, compared with crystals.
60
an amount of up to 1.5 2.0% in some cases. Activated
carbon has low selectivity with respect to this im-
purity, whose fraction increases in the course of
chromatographic purification. This impurity can be
removed in several ways. The most efficient way is
vacuum treatment of the crystals obtained. This meth-
Depending on the composition of the starting ex-
tract, the crystals obtained may contain admixtures of
higher fullerenes in an amount of up to 4 5%. Such
a high content of higher fullerenes makes their re-
covery feasible. This procedure can be effectively per-
formed with 1,2,4-trichlorobenzene by multistage frac-
od can reduce the content of the oxide C O to 0.05
60
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 3 2007

454
GRUSHKO et al.
tional concentration. It was found experimentally that
these fullerenes will long exceed that of fullerenes
produced by the electric-arc technique.
the content of higher fullerenes in C crystals can be
70
reduced from 4 5 to 0.7 0.8% at room temperature
in three to four stages. In this case, concentrates are
obtained in all stages, which contain up to 10% higher
CONCLUSIONS
fullerenes. The crystalline concentrate of C fullerene
70
(1) A semicommercial technology for manufacture
of pure C and C fullerenes was developed.
is further dissolved in o-xylene and subjected to
chromatographic purification on activated carbon. The
impurity of higher fullerenes is completely removed
in this stage.
60
70
(2) An apparatus for production of up to 1 kg of
a fullerene-containing carbon black in 24 h was
designed and fabricated.
The process we suggest allows production of pure
(3) An apparatus for recovery of a mixture of ful-
lerenes from a fullerene-containing carbon black, with
a monthly processing capacity of up to 40 kg of car-
bon black, was designed and fabricated.
C
fullerene in considerable amounts. For example,
70
the concentrate of C fullerene, obtained in the first
70
stage of fractional concentration from the starting
mixture of fullerenes, contains less than 2% higher
fullerenes, whereas a single cycle of two-stage crystal-
(4) An installation for chromatographic purifica-
lization can give C fullerene with the purity better
tion of C (to 99.5 or 99.9%), with a monthly output
70
60
than 98%. The total yield of pure C exceeds 100 g
capacity of up to 500 g of 99.5% C , was designed
70
60
in a cycle (48 h) per 1000 g of the starting mixture of
and fabricated.
fullerenes [composition (%): C /C 75/25]. Presence
60 70
(5) The flowsheet developed can be used to pro-
of higher fullerenes in the starting extract in an
amount exceeding 2% diminishes nearly twofold the
yield of pure fullerene and makes nearly twice longer
duce up to 100 g of C (98%) in a month on the
70
already existing equipment, provided that the content
of higher fullerenes in the starting C concentrate is
70
the purification of the C concentrate to remove
70
less than 2%. An additional special procedure for re-
moval of higher fullerenes was developed for obtain-
impurities. Therefore, additional one or two stages of
crystallization are necessary for obtaining C fuller-
70
ing C fullerene of 98% purity from a concentrate
70
ene of 98% purity if more than 2% higher fullerenes is
with increased content of higher fullerenes.
contained in the starting C concentrate.
70
The scheme suggested can be used to obtain, with-
out any significant modification of the available in-
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70
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