Pyrolysis Reactions of (2-Chloroethyl)benzene

Abstract

Pyrolysis of polyvinyl chloride (PVC) is considered an alternative to traditional, mechanical methods of recycling. However, there is insufficient research conducted on the thermal decomposition pathways of PVC, particularly the fate of chlorinated hydrocarbons generated during the chemical recycling process. One significant product from the pyrolysis of PVC is (2-chloroethyl)benzene. Using a hyperthermal tubular reactor and matrix-isolation FTIR techniques, the pyrolysis products of gas-phase (2-chloroethyl)benzene were identified. Following pyrolysis at 1400 K, the FTIR spectra indicated the formation of HCl, styrene, phenylacetylene, benzene, vinylacetylene, acetylene, propyne, ethylene, and propargyl radical.

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(2-Chloroethyl)­benzene.

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A temperature study of (2-chloroethyl)­benzene, comparing the argon-matrix FTIR spectrum of an unheated sample to those collected following pyrolysis at temperatures ranging from 900 to 1400 K. All samples were 0.07% mixtures in argon.

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Argon-matrix FTIR spectrum of 0.07% (2-chloroethyl)­benzene (bottom trace) and a spectrum collected following pyrolysis of the sample at 1400 K.

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Argon-matrix FTIR spectrum of pyrolyzed 0.07% (2-chloroethyl)­benzene and a benchmark spectrum of 0.1% styrene in argon.

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Argon-matrix FTIR spectrum of pyrolyzed 0.07% (2-chloroethyl)­benzene and a benchmark spectrum of 0.1% phenylacetylene in argon.

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Argon-matrix FTIR spectrum of 0.07% (2-chloroethyl)­benzene (bottom trace) and a spectrum collected following pyrolysis of the sample at 1400 K. The band marked with an asterisk could belong to either vinylacetylene or styrene. Small oscillations in the baseline are due to an etalon effect of a relatively thin argon matrix.

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Argon-matrix FTIR spectrum of 0.07% (2-chloroethyl)­benzene (bottom trace) and a spectrum collected following pyrolysis of the sample at 1400 K.

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Argon-matrix FTIR spectrum of 0.07% (2-chloroethyl)­benzene (bottom trace) and a spectrum collected following pyrolysis of the sample at 1400 K. The bands marked with an asterisk are CO or CO-cluster contaminants derived from reactions of the hot SiC tube with trace amounts of oxygen. These were also observed in control experiments with heated argon.

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Argon-matrix FTIR spectrum of 0.07% (2-chloroethyl)­benzene (bottom trace) and a spectrum collected following pyrolysis of the sample at 1400 K. The band labeled with an asterisk could belong to both styrene and phenylacetylene.

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Structures of species, referenced in Figures and , involved in the reactions of (2-chloroethyl)­benzene forming styrene and phenylacetylene, optimized at the B3LYP/6-311++G­(d,p) level of theory.

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Pathway of (2-chloroethyl)­benzene (2CEB) forming phenylacetylene via molecular elimination mechanisms with zero-point corrected energies in kJ/mol, relative to the energy of anti-(2-chloroethyl)­benzene. The anti- to gauche-isomerization is shown as well.

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Pathway of (2-chloroethyl)­benzene (2CEB) forming phenylacetylene via single-bond scission mechanisms with zero-point corrected energies in kJ/mol, relative to the energy of anti-(2-chloroethyl)­benzene.