Pyrolysis Mechanism of Wheat Straw Based on ReaxFF Molecular Dynamics Simulations

Abstract

Biomass has played an increasingly important role in the consumption of energy worldwide because of its renewability and carbon-neutral property. In this work, the pyrolysis mechanism of wheat straw is explored using reactive force field molecular dynamics simulations. A large-scale wheat straw model composed of cellulose, hemicellulose, and lignin is built. After model validation, the temporal evolutions of the main pyrolysis products under different temperatures are analyzed. As the temperature rises, the gas production increases and the tar yield can decrease after peaking. Relatively high temperatures accelerate the generation rates of the main gas and tar species. CO and CO 2 molecules mainly come from the cleavage of CHO 2 radicals, and numerous H 2 O molecules are generated on account of dehydration. Moreover, the evolution of six functional groups and pyran and phenyl rings as well as three types of bonds is also presented. It is observed that the phenyl rings reflect improved thermostability. Finally, the pyrolytic kinetics analysis is conducted, and the estimated activation energy of wheat straw pyrolysis is found to be 56.19 kJ/mol. All these observations can help deeply understand the pyrolytic mechanism of wheat straw biomass.

The Catalytic Effect of Pt on Lignin Pyrolysis: A Reactive Molecular Dynamics Study

“…The Kinetics Committee of the International Union of Thermal Analysis and Calorimetry (ICTAC) recommends the use of multiple heating rates to calculate the activation energy, avoiding a single heating rate [44]. The activation energy calculation of biomass pyrolysis at 2000 K was also studied by Liu et al [45]. Therefore, this study selected three groups of heating rates of 2 K/ps, 4 K/ps, and 6 K/ps for calculation.…”

Atomistic Modeling of Lignocellulosic and Carbonaceous Fuels and Their Pyrolysis Reactions: A Review

“…Liu et al 90 constructed a wheat straw model using cellulose as six linear chains with 100 1,4 β-D-glucopyranose monomers, hemicellulose modeled as a combination of two types of arabinoxylans, and lignin as 11 lignin molecules; each molecule has 25 C 9 units linked together. The three lignocellulosic models were within a cubic box with periodic boundary conditions employing the amorphous cell module of Materials Studio (Figure 4d).…”

“…Reproduced with permission from Zhou et al89 Copyright 2020, Wiley-VCH GmbH. (d) Amorphous and disorganized model of biomass 90.…”

Review on Characterization of Biochar Derived from Biomass Pyrolysis via Reactive Molecular Dynamics Simulations

“…On the other hand, classical approximations of quantum systems, while computationally (relatively) easy to implement, produce simpler models that lack fundamental chemical properties such as reactivity and charge transfer. The recent work by van Duin et al [51][52][53][54][55][56][57][58][59][60][61][62][63][64] carefully incorporated limited non-locality (to simulate quantum behavior) via empirical bond order potentials, overcoming the limitations of non-reactive classical MD approximations while largely preserving the computational simplicity of classical MD. The reactive system force field, ReaxFF, was developed.…”

“…These developments have far-reaching implications and are discussed in recent papers focusing on MD of combustion and energy systems, gas/liquid/solid fuel oxidation, pyrolysis, catalytic combustion, electrochemistry, nanoparticle synthesis, heat transfer, phase change, and fluid mechanics. Due to the practical availability of MD simulations of large-scale reactive chemical systems, the reactive force field (ReaxFF) system was developed and successfully applied to biomass systems [29,30,[50][51][52][53][54][55][56][57][58][59]. ReaxFF uses a general relationship between chemical bond distance and bond order to separate atoms.…”