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I.W. Sutherland et al. / Applied Catalysis A: General 471 (2014) 149–156
in the feed was insufficient for chlorination to be complete (a
chlorocarbon: Cl2 ratio of 3:1 was used). The present work, Part
2, builds on the previous study and examines (i) the effects of oper-
ation under chlorine-rich conditions (a chlorocarbon: Cl2 ratio of
1:3 is used) and (ii) the effect of alteration of the chlorine supply
when operating under oxychlorination conditions.
Details of the flow apparatus, on-line analyses and the proto-
cols used for flow experiments have been described previously
[31]. Feedstocks were those used for experiments carried out
under chlorine-lean conditions [31] with the addition of anhy-
drous hydrogen chloride (Linde, 99.5%), and dioxygen (BOC, 5%
O2/N2). Pressure was limited via a pair of mercury-filled lutes to
ensure that the reactor pressure did not exceed 0.5 bar g. Reaction
data are reported as feed conversions, product yields and selec-
tivities, defined according to standard practice [34]. Carbon mass
balances were determined in all chlorination/dehydrochlorination
reactions; they are reported explicitly when they contain features
of note The analytical procedure described previously [31] to obtain
chlorine mass balances (relative error 10%) was used to measure
yields of Cl2 from the catalytic oxidation of HCl to Cl2.
The catalyst under consideration here is the same commercial
grade oxychlorination catalyst [35] as examined in Part 1 [31].
to use, it was calcined at 673 K in flowing N2 for 4 h and is charac-
terized by a BET surface area of 71.6 m2 g−1 and a pore volume of
0.25 cm3 g−1 [31].
Fig. 1. The dehydrochlorination ((1) and (4)) and chlorination ((2) and (3)) pro-
cesses that connect CHCl2CHCl2 with CHCl=CCl2 and CCl2=CCl2. Possible oligomer
formation ((5) and (6)). A pathway for reaction (5) is identified in Section 3.1.1. A
pathway for reaction (6) is inferred in Section 3.1.2.
The experiments reported in Part
1 [31] established the
importance of certain reaction pathways accessible at elevated
temperatures even in the absence of a catalyst. A mixing vessel,
packed with quartz beads (diameter 2 mm), was fitted within the
furnace immediately before the reactor. This arrangement ensured
complete mixing and thermalization of the reactant gases. Simi-
lar measurements are undertaken here and, as before, the catalyst
was replaced with ground quartz. These experiments, which ensure
comparable contact times, are useful in defining non-catalytic
pathways. Previously we have referred to non-catalyst assisted
processes as being ‘homogeneous’ [31], however we acknowl-
edge that the quartz does provide some form of ‘hold-up’ in
the hot zone, which could possibly influence reaction probabili-
ties. Thus, these type of reactions could more correctly be called
‘quasi-homogeneous’, however, for completeness and additionally
recognising the caveat described above, we will continue to use the
term ‘homogeneous’ in this context.
Nitrogen was used as a carrier gas for the chlorocarbon and a
diluent for the feedstream to give a total volumetric flow rate of
per(II)/KCl/attapulgite catalyst were then examined over a range of
conditions that have direct connectivity with an industrial process,
scheme that was reported earlier [31], notably an increased role for
the chlorination route occurring via CHCl=CCl2 (reactions (1) then
(2) in Fig. 1) compared with the direct chlorination of CHCl2CHCl2
(reaction (3) in Fig. 1). They have also allowed clarification of
conditions under which oligomerization, with its undesirable envi-
ronmental and economic effects (reactions (5) and (6)), may occur.
3.1. Reactions under chlorine-rich conditions
3. Results and discussion
under homogeneous conditions, i.e. in the absence of CuII catalyst
The temperature relationships for mean conversions of
CHCl2CHCl2 and mean carbon mass balances for 1,1,2,2-
The reaction profile is similar to that observed under chlorine
lean conditions in that CHCl=CCl2 is the only product observed,
however, mean conversions of CHCl2CHCl2 at a given tempera-
ture, Fig. 2(a) are higher than those observed under a chlorine-lean
regime [31]. The most significant difference is that the carbon
mass balance shows a significant deficit (ca. 20%) at 623 K and
above, Fig. 2(b). It is suggested that, when conversion of CHCl2CHCl2
becomes significant, the high concentration of carbon-centred radi-
cals present, leads to the chlorine atom initiated formation of
dimeric and oligomeric species, which being relatively involatile,
results in the carbon mass imbalance observed. These results
The results from the previous study [31] establish the reac-
tion pathways connecting 1,1,2,2-tetrachloroethane with tri- and
tetrachloroethene under chlorine-lean conditions (3:1 chlorocar-
bon: Cl2 mol ratio). One of the reaction parameters that potentially
might control the selectivity of the system is the chlorine sup-
ply. Although radical chlorinations, for example chlorination of
1,1,2,2-tetrachloroethane to give pentachloroethane, appear to be
disfavoured kinetically compared with dehydrochlorinations, for
example 1,1,2,2-tetrachloroethane to trichloroethene, increasing
of the supply of chlorine on reaction selectivity and outcomes, the
effect of increasing the relative chlorine concentration was exam-
ined. Specifically, the chlorocarbon feed (CHCl2CHCl2 or CHCl=CCl2)
to dichlorine mol ratio was changed from 3:1 (i.e. chlorine-lean), as
used in our previous study [31], to 1:3, i.e. a chlorine-rich regime.