# Breaking Down Polychlorinated Biphenyls and Aryl Chlorides: A Computational Study of Thermal-, Pressure-, and Shear-Induced Decomposition

## TL;DR

This study uses simulations to understand how PCBs and similar chemicals break down under different conditions, aiming to improve safe disposal methods.

## Contribution

The study introduces new insights into PCB decomposition mechanisms using reactive MD simulations and DFT validation.

## Key findings

- PCB 77 decomposition is sensitive to temperature and chlorine positions, leading to varied products.
- DCT shows promising decomposition pathways and is suggested for further experimental study.
- Pyrolysis-based methods risk producing hazardous byproducts like dioxins if not properly managed.

## Abstract

Reactive molecular dynamics (MD) simulations were used
to study
the decomposition of aryl chlorides, including polychlorinated biphenyls
(PCBs), under varying conditions. Using the ReaxFF force field, which
models bond breaking and formation, the study focused on PCB 77 (3,3′,4,4′-tetrachlorobiphenyl)
and compared it to safer alternatives: 1,2-dichlorobenzene (DCB) and
3,4-dichlorotoluene (DCT). Density functional theory (DFT) calculations
validated decomposition pathways and enthalpies of C–Cl bond
homolytic cleavage, revealing a multistep radical mechanism. Analysis
showed that the decomposition rate and product distribution were sensitive
to temperature and Cl-binding positions, emphasizing the complexity
of PCB breakdown. Decomposition products were analyzed to understand
the efficiency and safety of current remediation processes, such as
incineration, which can produce hazardous byproducts like dioxins
if poorly managed. The results suggested DCT as a promising candidate
for further investigation in laboratory experiments due to its decomposition
pathways and relevance to PCB analogues. This study advances knowledge
of PCB degradation mechanisms, informing safer, sustainable remediation
strategies, and highlighting the risks of pyrolysis-based approaches.