Gas-phase reaction of CCl2F2 (CFC-12) with methane.

Article abstract of DOI:10.1016/S0045-6535(03)00658-1

Gas-phase reaction of CFC-12 (CCl2F2) with methane was carried out in a plug flow reactor over the temperature range of 873-1123 K. The major organic halocarbons formed during the reaction were C2F4, C2H2F2, CHClF2, CH3Cl, C3H2F6 and CCl3F. The formation of all products except C2H2F2 decreased with temperature, while the selectivity to C2H2F2 (difluoroethylene) increased with temperature and reached approximately 80% at 1123 K. Under these reaction conditions, methane acts as hydrogen and carbon source, resulting in the formation of an unsaturated C2 hydrofluorocarbon from two C1 precursors.

Full text of DOI:10.1016/S0045-6535(03)00658-1

Chemosphere 53 (2003) 1189–1191
www.elsevier.com/locate/chemosphere
Short Communication
Gas-phase reaction of CCl2F2 (CFC-12) with methane
*
Md. Azhar Uddin, Eric M. Kennedy , Bogdan Z. Dlugogorski
Process Safety and Environment Protection Group, School of Engineering, The University of Newcastle,
Callaghan, NSW 2308, Australia
Received 27 February 2003; received in revised form 28 May 2003; accepted 11 June 2003
Abstract
Gas-phase reaction of CFC-12 (CCl2F2) with methane was carried out in a plug flow reactor over the temperature
range of 873–1123 K. The major organic halocarbons formed during the reaction were C2F4, C2H2F2, CHClF2, CH3Cl,
C3H2F6 and CCl3F. The formation of all products except C2H2F2 decreased with temperature, while the selectivity to
C2H2F2 (difluoroethylene) increased with temperature and reached ꢀ80% at 1123 K. Under these reaction conditions,
methane acts as hydrogen and carbon source, resulting in the formation of an unsaturated C2 hydrofluorocarbon from
two C1 precursors.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: CFC-12; Methane; Dehydrohalogenation; Difluoroethylene
1. Introduction
ported the gas-phase hydrodehalogenation of halon
1301 (CF3Br) and halon 1211 (CBrClF2) with methane,
where methane was used as a hydrogen donor and/or
methylating agent (Li et al., 1999; Li et al., 2000; Howe
et al., 2002). The products of the reaction between CBrF3
and methane were CHF3 and CH3Br, while the reaction
between CBrClF2 and methane produced mainly CHClF2
and CH3Br at lower temperatures with C2H2F2 forming
with high selectivity at more elevated temperatures.
In this study, we report for the first time the gas-
phase reaction of CCl2F2 with methane. This novel gas-
phase reaction presents a potentially new pathway for
the conversion of CFCs to hydrofluorocarbons using
methane as a hydrogen donor and/or methylating agent.
The major reaction product, C2H2F2, is a highly valued
precursor for the production of Viton, a temperature
and corrosion resistant fluoropolymer.
Restrictions on the use of ozone depleting chemicals
such as chlorofluorocarbons (CFCs) and brominated
chlorofluorocarbons or brominated fluorocarbons (ha-
lons) have initiated intensive research into methods for
disposal of stockpiled CFCs and halons. The hydrode-
halogenation reactions of these chemicals constitute
the core of processes for their conversion to hydrofluo-
rocarbon replacements. For example, the catalytic
hydrodechlorination of CFCs with hydrogen over sup-
ported palladium catalysts has been studied widely for
the production of hydrofluorocarbons (Takita et al.,
1990; Coq et al., 1993; Karpinski et al., 1996; Mali-
nowski et al., 1998; Early et al., 1999; Ahn et al., 2000;
Moulijn et al., 2000). However, the major drawback of
catalytic hydrodechlorination is the lack of stability of
catalysts under the severe (acidic) reaction conditions
(Moon et al., 1998; Wiersma et al., 1998). We have re-
2. Experimental
* Corresponding author. Tel.: +61-2-4921-6177; fax: +61-2-
4921-6920.
2.1. Materials
CFC-12 (CCl2F2) was obtained from ACTROL
(Australia) having a purity of >99%. CH4 (99.5%) and
E-mail addresses: eric.kennedy@newcastle.edu.au, cgek@
alinga.newcastle.edu.au (E.M. Kennedy).
0045-6535/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0045-6535(03)00658-1

1190
Md.A. Uddin et al. / Chemosphere 53 (2003) 1189–1191
N2 (99.99%) were purchased from BOC GASES. All
gases were used in the reaction without further purifi-
cation.
C H F
CH Cl
CHClF
CCl F
C F
14
12
10
8
80
60
40
20
0
C H F
2.2. Gas-phase reaction of CCl2F2 with methane
HF
HCl
6
The gas-phase reaction of CCl2F2 with methane was
carried out in an alumina plug flow reactor over the
temperature range of 873–1123 K at atmospheric pres-
sure. A reactant gas stream (CH4:CCl2F2:N2 ¼ 1:1:10)
passed through the reactor at a total flow rate of ap-
proximately 65 cm3/min (STP). The volume of the re-
action zone was maintained at 1 cm3 such that the
residence time varied from 0.29 to 0.22 s for 873 to 1123
K. Gaseous halocarbon products were analysed with an
on-line micro GC and an off-line GC/MS after passing
through a NaOH scrubber. The amount of mineral acids
(HF and HCl) liberated during the reaction was quan-
tified periodically with an off-line ion chromatograph.
4
2
0
1150
950
1000
1050
Temperature, K
1100
Fig. 2. Product selectivity for the gas-phase reaction of CCl2F2
with CH4. CCl2F2:CH4:N2 ¼ 1:1:10, total flow rate ¼ 65 cm3/
min (molar feed rate of CCl2F2 ¼ 14.50 mmol/h).
The halocarbon products formed during the pyrolysis of
CCl2F2 (not shown in Fig. 2) were CClF3, CCl3F and
C2Cl2F2 at 923 K and selectivity of both CClF3 and
C2Cl2F2 increased and that of CCl3F decreased with
temperature. In the presence of methane, the major
products formed include C2F4, CCl3F, C2H2F2, CHClF2,
CH3Cl, and C3H2F6. In addition to organic halocar-
bons, mineral acids (HF and HCl) are also formed
during the reaction. With the increase of reaction tem-
perature, production of all other halocarbon species
except C2H2F2 declined, while the selectivity to C2H2F2
increased and reached ꢀ80% at 1123 K. Although not
quantified, trace amount of hydrocarbons such as C2H4
and C2H6 were detected in the product and at higher
temperature carbon deposition inside the reactor was
also observed. The ion chromatographic results reveal
that in excess of 90% of the fluorine is retained in
the hydroflurorcarbon products whereas ꢀ80% of the
chlorine in feed CCl2F2 is released as HCl. Although the
actual reactions involved in this gas-phase process are
not clear at this stage, we suggest the following path-
ways for the formation of the major compounds (in
bold):
3. Results and discussion
Fig. 1 shows the conversion of CCl2F2 and CH4
against the reaction temperature. The conversion of
CCl2F2 commenced at around 923 K and increased with
temperature. In the absence of CH4, the conversion of
CCl2F2 was approximately 25% at 1123 K, while CCl2F2
conversion increased to 43% in the presence of CH4 at
the same temperature. The conversion of CH4 was ap-
proximately at the same level as that of CCl2F2. It is
worth mentioning that in the absence of CCl2F2, methane
remained inactive over the entire range of temperature
studied (873–1123 K). Similar results were observed in
the gas-phase reaction of methane with halon 1211
(CBrClF2) (Tran et al., 2001).
Fig. 2 shows the selectivity of reaction products and
the rate of formation of mineral acids (HF and HCl).
50
CFC conversion: CFC/CH = 1/0 (Pyrolysis)
4
CCl2F2 ! CClFÅ þ ClÅ ðinitiation stepÞ
CFC conversion: CFC/CH = 1/1
4
2
40
30
20
10
0
CH conversion: CFC/CH = 1/1
4
4
ClÅ þ CH4 ! CHÅ þ HCl ðmethane activation stepÞ
3
CClFÅ þ CHÅ ! ½CClF2CH3ꢁ ! C2H2F2 þ HCl
2
3
ðmajor pathway at elevated temperaturesÞ
Other reactions which also occur include:
CClFÅ þ CH4 ! CHClF2 þ CHÅ
2
3
CHÅ þ ClÅ ! CH3Cl
3
850
900
950
1000
1050
1100
1150
CClFÅ þ CHÅ ! ½CClF2CH3ꢁ ! CF2: þCH3Cl
Temperature, K
2
3
Fig. 1. Gas-phase reaction of CCl2F2 with CH4.
2CF2:! C2F4

Md.A. Uddin et al. / Chemosphere 53 (2003) 1189–1191
1191
Karpinski, Z., Early, K., dÕItri, J.L., 1996. Catalytic hydrode-
chlorination of 1,1-dichlorotetrafluorethane by Pd/Al2O3.
Hydrodechlorination of CH2Cl2 over Pd/c-Al2O3. Correla-
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J. Catal. 164, 378–386.
In other related studies of the gas-phase reaction of
halons (1211 and 1301) with methane, we found that
halons are more readily hydrodehalogenated than
CFCs, most probably due to the facile cleavage of C–Br
bonds leading to the formation of active species which
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Li, K., Kennedy, E.M., Dlugogorski, B.Z., 1999. Gas-phase
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B: Env. 19 (2), L79–L86.
4. Conclusions
Gas-phase reaction of CFC-12 (CCl2F2) with meth-
ane was carried out in a plug flow reactor over the
temperature range of 873–1123 K. The major organic
halocarbons formed during the reaction were C2F4,
C2H2F2, CHClF2, CH3Cl, C3H2F6 and CCl3F. The
formation of all products except C2H2F2 decreased with
temperature, while the selectivity to C2H2F2 increased
with temperature and reached ꢀ80% at 1123 K. Under
these reaction conditions, methane acts as hydrogen and
carbon source, resulting in the formation of an unsatu-
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Moon, D.J., Chung, M.J., Park, K.Y., Hong, S.I., 1998.
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