Microscopic Mechanism of Cellulose Bond Breaking and Bonding Based on Molecular Dynamics Simulation

Qing Zhou,Yiyi Zhang,Mengzhao Zhu,Hanbo Zheng,Bilian Liao,Chaohai Zhang,Jiefeng Liu

doi:10.1109/access.2019.2958411

Qing Zhou, Yiyi Zhang + Show 5 more

Open Access

https://doi.org/10.1109/access.2019.2958411

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Abstract

The ReaxFF molecular dynamics simulation and Monte Carlo method were adopted to analyze the pyrolysis process of cellulose in insulating papers from the perspective of microscopic atom. Molecular dynamics failed to continuously describe the motion behavior of an atom. According to this principle, the system can only calculate the atomic state on the node and then move the atom by a time step to continue calculating the atom. This paper would put forward the optimal step setting method of cellulose thermal decomposition in insulating paper: setting one step every other 0.1 fs. Specifically, for small molecules with a simple structure, such as H2O, the step size was set to 0.4 fs or less, while the step size of macromolecules with complex structures (CH2O2) should be set to 0.2 fs or less. In addition, the relationship between the step size and the temperature to which the system was heated was given as well in this paper. In previous literatures, empirical values were used to set the step size. This study would not only provide a theoretical basis for the study on the bond formation and fracture process of cellulose pyrolysis products, but also offer the data and guidance for related fields in the future, thus rendering an efficient simulation process.

Highlights

Oil-immersed power transformer is the core equipment of power transmission and transformation system, whose safe and effective operation depends on multiple factors, such as service life, safety and aging [1]–[4]
INFLUENCE OF STEP SIZE ON HEATING As can be seen from Figure 3, as the step size of point A was 0.1 fs, the system reached a set temperature of 1900 degrees when it ran to about 200 fs
The formation and breaking of chemical bonds are analyzed by setting different step sizes at intervals of 0.1 fs, and the relationship between the step size and the heating rate is obtained

Summary

Introduction

Oil-immersed power transformer is the core equipment of power transmission and transformation system, whose safe and effective operation depends on multiple factors, such as service life, safety and aging [1]–[4]. The cellulosic insulating paper is a type of solid insulation material, which is widely used in electrical equipment such as wires and cables, transformers and capacitors [7], [8]. In the process of operation, the transformer insulation paper would have pyrolysis reaction under the joint action of multiple. The final products of cellulose pyrolysis at high temperatures are H2O, CH2O2, CO, CO2, methanol, ethanol, free radicals and small molecular acids [13]–[16]. It was found that the transformer oil contained methyl, ethyl, methoxy and hydroxyl according to the gas chromatography-mass spectrometry analysis of the liquid products of rapid pyrolysis of cellulose by Liao Yanfen and other scholars from Zhejiang University [17], [18].

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