Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 1, pp. 31−35.
Pleiades Publishing, Ltd., 2010.
Original Russian Text
D.A. Mukhortov, I.A. Blinov, E.S. Kurapova, P.S. Kambur, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 1,
OF SYSTEMS AND PROCESSES
Solubility of Nitrogen Triﬂ uoride and Tetraﬂ uoromethane
in Perﬂ uorinated and Highly Halogenated Fluids
D. A. Mukhortov, I. A. Blinov, E. S. Kurapova, and P. S. Kambur
Prikladnaya Khimiya Russian Scientiﬁ c Center, Federal State Unitary Enterprise, St. Petersburg, Russia
Received October 29, 2009
Abstract—Volume solubility of nitrogen trifluoride and tetrafluoromethane in water and perfluorinated and
highly halogenated fluids was determined. An absorption method for deep purification on nitrogen trifluoride to
remove tetrafluoromethane in order to obtain a high-purity electronic gas was suggested.
Nitrogen triﬂ uoride NF
(NTF) is one of the most
promising gaseous carriers of ﬂ uorine for silicon etching
in the semiconductor industry. Of particular importance
for application of NTF in this ﬁ eld is its purity. On the
market, mostly NTF grades with the content of the main
substance of no less than 99.9% are represented. Most
of impurities (O
, HF, CO, CO
are separated from NTF by methods commonly used in
chemical engineering: alkaline puriﬁ cation, gas treatment
on zeolites, cryogenic rectiﬁ cation).
Of particular importance is the content of
tetraﬂ uoromethane CF
(TFM) in NTF, because presence
of this substance adversely affects the performance of
NTF. Commonly, the content of TFM is not higher than
700 ppm, whereas for the high-purity gas, its concentration
should not exceed 25 ppm. Separation of TFM from NTF
presents a severe difﬁ culty because these substances
have almost the same boiling points and similar chemical
activities at temperatures lower than 300–400°C.
Tetraﬂ uoromethane is contained in commercial NTF
because of the presence of carbon in technological raw
materials or expendable materials. The concentration
of TFM in the NTF gas synthesized by ﬂ uorination of
nitrogen-containing compounds with ﬂ uorine may be
as high as several thousand parts per million. The main
sources of TFM are the following: carbon-containing
compounds as a raw-material carrier of nitrogen; ﬂ uorine
always containing TFM because of the ﬂ uorination of the
carbon anode used in the electrolyzer for manufacture of
ﬂ uorine; ﬂ uorinated carbon-containing construction and
expendable materials used in technological apparatus;
ﬂ uorinated carbon or nickel (industrial nickel contains
carbon) anode in electrolytic synthesis of NTF.
Thus, development of industrial methods for
minimizing the concentration of TFM in NTF is a rather
topical task. Various techniques for NTF puriﬁ cation to
remove TFM are known: adsorption on solid adsorbents,
rectification with a capturing agent, and cryogenic
extractive rectiﬁ cation.
To absorption techniques using solid adsorbents
belongs, for example, the method  in which adsorption
occurs on synthetic zeolites of 5A type with general
O, which are rather
selective toward NTF under certain conditions.
In another technique , the selective adsorption of
NTF is performed with dehydrated erionite at temperatures
of –30 to 30°C, with TFM displaced by an inert gas.
Adsorption methods have a number of disadvantages:
amount of waste NTF enriched in TFM and
necessity for regular replacement of the zeolite because
of its deactivation by NTF.
A rectiﬁ cation technique is known in which capturing
agents (e.g., HCl) are used to separate NTF and TFM
. For this method, an installation was developed, in
one of whose options an effective of a capturing agent is
introduced into the distillation column at a point lying at
the level at which the mixture of CF