ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 6, pp. 941! 944. + Pleiades Publishing, Inc., 2006.
Original Russian Text + G.G. Shelopin, D.S. Pashkevich, D.A. Mukhortov, V.B. Petrov, Yu.I. Alekseev, 2006, published in Zhurnal Prikladnoi
Khimii, 2006, Vol. 79, No. 6, pp. 951!954.
PROCESSES AND EQUIPMENT
OF CHEMICAL INDUSTRY
Synthesis of Perfluoroalkanes by Fluorination
of Graphite with Elementary Fluorine
in a Vertical Ascending Gas-Dust Flow
G. G. Shelopin, D. S. Pashkevich, D. A. Mukhortov, V. B. Petrov, and Yu. I. Alekseev
Prikladnaya Khimiya Russian Scientific Center, Federal State Unitary Enterprise, St. Petersburg, Russia
Received September 12, 2005; in final form, February 2006
Abstract-Synthesis of lower pefluoroalkanes, tetrafluoromethane, hexafluoroethane, octafluoropropane,
and decafluorobutane, in a high-temperature reaction of graphite with fluorine in a reactor with a vertical
ascending gas-dust flow was studied.
Tetrafluoromethane (TFM), hexafluoroethane (HFE),
octafluoropropane (OFP), and decafluorobutane (DFB)
are large-tonnage products used in processing (etching)
of silicon in the semiconductor industry .
Tetrafluoromethane is produced in a high-temper-
ature reaction of an immobile (fixed) bed of graphite
with fluorine . The rest of the above-listed per-
fluorocarbons are industrially manufactured by vari-
ous methods, mainly with the use of ozone-hazardous
chlorine-containing raw materials . At the same
time, TFM, HFE, OFP, and DFB can be synthesized
from graphite and fluorine .
The primary goal of this study, which continues
earlier investigations , is to search for conditions of
carbon fluorination in which a mixture of perfluoro-
alkanes, containing HFE, OFP, and DFB in commer-
cial amounts, is formed.
A study of the process of fluorination of graphite
with a mixture of fluorine and nitrogen (or argon) in
a fluidized bed  at various concentrations of fluo-
rine in the gas phase enabled a conclusion that syn-
thesis of CF
, and C
at a temperature
of about 600oC occurs in accordance with the two-
stage scheme in which synthesis of a solid carbon
is followed by its thermal decom-
position. The composition of the products formed in
thermal decomposition of carbon polyfluoride de-
pends on presence of gaseous fluorine in the decom-
position zone. An increase in its amount makes smaller
the fraction of fluorocarbons with a longer carbon
chain. Therefore, spatial separation of the synthesis
zone from the zone of thermal decomposition of car-
bon fluoride can lead to an increase in the fraction of
hydrocarbons with the number of carbon atoms ex-
ceeding unity in the gaseous reaction products.
It was impossible to achieve a stable separation of
the zone of (CF
synthesis and decomposition in
a reactor with a fluidized bed. Therefore, it was sug-
gested to study synthesis of perfluoroalkanes from
graphite and fluorine in a reactor in which (CF
synthesized in a vertical ascending gas-dust flow and
decomposed in a fixed bed of a powder at a higher
To study the fluorination of graphite in a gas-dust
flow, a laboratory installation schematically shown in
Fig. 1 was created. The installation comprises an ejec-
tor 1, uptake pipe 2 (inner diameter 9 mm, length
1.2 m), separator 3, and down pipe 4 of diameter
20 mm. Filter 5 and solid-phase-expenditure meter
6 are installed in the separator of the reactor. Pipes 2
and 4 are equipped with electric heaters and with
immersion-type and wall thermocouples.
The basic part of the installation is ejector unit 1,
which forms a gas-dust flow of a prescribed composi-
tion from nitrogen and graphite. The working prin-
ciple of this unit is based on mixing of, and energy
exchange between, two flows with different pressures
to give a mixed flow with an intermediate pressure.