A ReaxFF-based molecular dynamics study of the pyrolysis mechanism of hexamethyldisiloxane

Hexamethyldisiloxane (MM) is one of the commonly used working fluids of organic Rankine cycle at medium and high temperatures, but there is a risk of decomposition of organic working fluids in high temperature environment. In this study, the pyrolysis mechanism of MM is analyzed by using ReaxFF force field and density functional theory (DFT). During the simulation process, three initial reaction routes were observed. By calculating the reaction energy barriers, it is found that the fracture of C-Si bond is the main initial reaction of pyrolysis. In the MM pyrolysis process, small molecule gases such as CH4, C2H6 and H-2, linear siloxane represented by C8H24O2Si3(MDM)are the main thermal decomposition products. Free radical attacking reaction and free radical binding reaction are the main formation mech-anism of methane. The intermediate condensation reaction is the formation mechanism of MDM. Most of the chain reactions are exothermic reactions, which can provide the energy for the system and further promote the decomposition of MM.(c) 2022 Elsevier B.V. All rights reserved.