posted on 2021-01-15, 23:13authored byGuozhan Jiang, D. A. Sanchez Monsalve, Peter Clough, Ying Jiang, Gary A. Leeke
The
dechlorination of chlorine containing hydrocarbons in pyrolysis
vapor is poorly understood. In order to shed new light on the dechlorination
mechanism, a model mixture composed of iso-octane doped with 2-chlorobutane,
2-chloroethylbenzene, and chlorobenzene was used to study the dechlorination
of chlorinated hydrocarbons by alkali adsorption. These three chlorinated
hydrocarbons were selected as they can be typically produced from
the pyrolysis of mixed plastic waste containing polyvinyl chloride
(PVC). The mixture is pumped continuously through a Na2CO3 or CaCO3/alumina bed, and GC-MS is used
to identify the dechlorination products and to follow the dechlorination
reactions. When chlorine is bonded to an aliphatic carbon with an
adjacent aliphatic hydrogen, the chlorinated compound first undergoes
a dehydrochlorination reaction to form HCl and olefins, and subsequently
the HCl is reacted with the alkali in the absorbents. In our experiments,
2-chlorobutane is converted to 2-butene, and 2-chloroethylbenzene
is converted to styrene. The formation of HCl and subsequent reaction
with alkali components in the absorbent is verified by IR spectroscopy
and XRD. In the presence of an alkali, the aliphatic chlorinated hydrocarbons
underwent dechlorination at a temperature of 180 °C. The removal
of chlorine from aromatic chlorinated compounds operates in a different
mechanism, in which the C–Cl bond scission is promoted significantly
by the presence of an alumina and hydrocarbon medium. It was found
that chlorobenzene undergoes dechlorination forming phenol and benzene.