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R. Hu et al. / Journal of Fluorine Chemistry 185 (2016) 91–95
Table 6
GC and GC–MS operation conditions.
Parameters
GC
GC–MS
Instrument
Column
Carrier gas flow rate [mL
Column temperature [ꢀC]
Shanghai Huaai GC-9560
Shimadzu GC–MS-QP2010 ultra
DB-VRX (60.0 m ꢄ 0.32 mm ꢄ 1.8
mm)
Rxi-5Sil MS (30.0 m ꢄ 0.25 mm ꢄ 0.25
mm)
ꢅ
minꢁ1
]
6,N2
200
1
2,He
180
1
Injection volume [
mL]
Split ratio
1:50
250
220
1:50
250
Injection temperature [ꢀC]
Detector (FID) temperature [ꢀC]
Ion source temperature [ꢀC]
Scan range
200
m/z 35.00–500.00
HFC-134a (190.79 kJ molꢁ1); however, experimentally only a small
amounts of side-products including CF2 = CHF were formed. The
formation of CF2 = CHF required that the reaction be carried out at
high temperatures in the presence of catalyst [30–32]. Theoretical
calculations of transition state energies (Table 5) showed that
formation of possible by-products such as CF2CHF (295.36 kJ
molꢁ1), CF2BrCHFBr (209.44 kJ molꢁ1) and CF2BrCH2F (166.51 kJ
molꢁ1) required higher energies compared to the main products
such as CF3CHFBr (52.73 kJ molꢁ1) and CF3CFBr2 (41.08 kJ molꢁ1).
Therefore, it was easy to avoid by-products at the relatively low
reaction temperature in the gas-phase bromination of HFC-134a. In
this paper, higher than 60% selectivity of CF3CFBr2 was achieved at
temperatures lower than 600 ꢀC.
K-type sheathed thermocouples evenly distributed throughout the
surface of the reactor, showing that the temperature deviation was
controlled within ꢃ5 ꢀC), an exhaust gas treatment system and a
test analysis system. A thermocouple placed in the center of the
sorbent bed was used to measure the reaction temperature.
Experiments were carried out in the system described above. A
mixture of HFC-134a and Br2 in a certain molar ratio was added to
the reaction tube at a preset temperature. The out gases passed
through water and a KOH solution to neutralize the formed HBr.
The exiting gas was then analyzed by gas chromatography-mass
spectrometry (GC–MS). The operating conditions of the GC and
GC–MS are shown in Table 6.
The MS data were as follows:
+
3. Conclusions
1. CF3CH2F, m/z: 83, CF3CH2+; 69, CF3+; 63, CF2C+; 51, CHF2
.
2. CF3CFBr2, m/z: 260, +CF3CFBr2; 191, +CFBr2; 180, CF3C+FBr; 161,
The gas-phase bromination of HFC-134a was investigated
experimentally and theoretically in this study. In this reaction,
HFC-134a started to react with Brꢂ at approximately 400 ꢀC, and the
optimal reaction temperature for the CF3CFBr2 production was
approximately 550 ꢀC. The conversion yield of HFC-134a was
greater than 98%, and the selectivity of CF3CFBr2 was greater than
60% under the following optimal reaction conditions: pressure of
0.1 MPa, T = 550 ꢀC, Br2/HFC-134a = 2:1, contact time = 15 s.
CF3CFBr2 and CF3CHFBr were the main bromination products. A
small amount of three by-products including CF2 = CHF,
CF2BrCHFBr and CF2BrCH2F was detected. The reaction intermedi-
ates, reaction path and products were theoretically analyzed using
the Gaussian software package. The results of theoretical
calculations were consistent with the experimental results, and
experimental and theoretical analysis results were also in good
agreement. In a sense, the gas-phase bromination of HFC-134a
provided a potential method for continuous industrial production
of CF3CFBr2.
CF3C+Br; 111, +CFBr; 100, CF3C+F; 91, +CBr; 81, CF3C+; 69, +CF3; 50,
+
CF2
.
3. CF3CHFBr, m/z: 181, CF3C+HFBr; 161, CF3CBr; 111, +CFBr; 100,
CF3C+F; 91, +CBr; 81, CF3C+; 69, +CF3; 51, CHF2
.
+
4. CF2 = CFH, m/z: 82, CF2 = CF+; 63, CF2 = C+; 51, +CHF2.
5. CF2BrCHFBr, m/z: 241, CF2BrC+HFBr; 221, CF2BrC+Br; 161,
CF2BrC+HF; 140, CF2BrC+; 130, +CF2Br; 110, +CFBr; 31, +CF.
+
6. CF2BrCH2F, m/z: 161, CF2BrC+HF; 140, CF2BrC+; 130, CF2Br; 50,
+CF2; 31, +CF.
4.2. Computational methods
To elucidate the gas-phase bromination of HFC-134a, in this
work, theoretical analysis was performed using the Gaussian
03 software packages. All possible reaction pathways for the
reaction system were examined using density functional theory
calculations, which provided a method for good understanding of
the origin of the reaction products identified in experiments. The
geometries of the major reactants, products, possible intermedi-
ates and transition structures were fully optimized using the B3LYP
functional with the 6–311 + +G (d, p) basis set [33–35]. The
vibrational frequencies of the reactants, products and the
intermediates were all real, whereas the transition state structures
exhibited only one imaginary frequency. The intrinsic reaction
coordinate (IRC) calculations at the B3LYP/6–311 + +G (d, p) level
confirmed the connections between reactants, intermediates,
transition structures and products [34–37].
4. Experimental and computational methods
4.1. Experimental
HFC-134a (purity > 99.9%) was purchased from Sinochem
Lantian Co., Ltd. (Zhejiang, China), elemental bromine (99.85%
pure) was purchased from China National Pharmaceutical Group
Corporation (Beijing, China). The HFC-134a flow rate was
controlled by a mass flowmeter (D07-7B/ZM, Beijing Seven-star
Electronics Co., Ltd., China) and the flow rate of elemental bromine
was controlled by a high pressure liquid metering pump (Leadfluid,
TYD01) capable of feeding between 0.05 and 20.0 mL minꢁ1. The
reaction system consists of an alumina ceramic tube (40.0 cm in
length, 1.0 cm inner diameter), a programmable temperature
control device (the temperature of the reactor was measured
and controlled by the temperature control device with three
References
[1] M. Gelmont, M. Yuzefovitch, D. Yoffe, R. Frim, Preparation of bromine-
containing aromatic compounds and their application as flame retardants, US
Patent 2015329447 (2015).
[2] M. Zhang, A. Buekens, X. Li, J. Hazard. Mater. 304 (2016) 26–39.