Effect of H₂O on the Transformation of Sulfur during Demineralized Coal Pyrolysis: Molecular Dynamics Simulation Using ReaxFF

Abstract

Reactive force field molecular dynamics (ReaxFF-MD) (reactive force field molecular dynamics) is a promising method for exploring complex chemical reactions, allowing a better understanding of sulfur transformation during coal pyrolysis. In this work, we built three pyrolysis systems with different H2O contents to explore the effect of H2O on the transformation of sulfur during demineralized pyrolysis by ReaxFF-MD. Product distributions, sulfur-containing bonds, and the path of organic sulfur in different systems were analyzed. We found that H2O could accelerate the pyrolysis process, reduce the semicoke yield, and increase the production of gas components significantly, including H2S gas. By adding H2O during pyrolysis, more sulfur in semicoke and heavy tar converted to gas and light tar, respectively. H2O not only promoted the cleavage of C–S bonds but also generated more H free radicals to form SH free radicals, thereby promoting the removal of organic sulfur.

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

“…By adopting the bond-order formalism in a classical approach, ReaxFF implicitly describes the chemical bonds without costly QM calculations, giving insight into the biomass pyrolysis process and its carbonization. It can describe the bond breaking and formation during the chemical reactions, thereby exploring the complex carbonization reaction mechanisms at a nano/microscale, including different pyrolysis processes of various feedstocks as well as other chemical process mechanisms for producing biochar or other carbonaceous materials [29,30,52,55,59,64,[76][77][78][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100], such as thermochemical reactions in combustion and energy systems [50,53,57,101], energetic and dissociative water properties under various conditions [56], properties of carbon nano-rings, carbon nanotube bundles, and crosslinked epoxy resins [66,67,102], inclusion of geometry-dependent charge calculations [75], to name a few. Biomass can produce biochar through thermochemical processes such as pyrolysis, gasification, and combustion [77].…”

“…More importantly, the balance considerations of biochar designs, such as the balance between effectiveness and stability, function and risk, effectiveness and cost, etc., were systematically analyzed and discussed [26,27]. To determine the synergistic effects of biomass feedstock species, reactor types, operating conditions, and post-treatments on biochar activation and functionalization, the surface chemistry, physiochemistry, structural, and molecular characterization of the produced biochar, as well as the relationships between process parameters and biochar surface morphology and internal microstructure, have been intensively studied since the last few decades [28][29][30]. The surface chemistry, structural, and molecular characterization of the produced biochar have been investigated using various advanced characterization techniques.…”

“…Raman spectroscopy (Raman), scanning electron microscopy (SEM), specific surface area and pore size analyzer, high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), XPS, etc., provide simple and non-destructive means to achieve this goal, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) can be used semi-quantitatively [32,33]. To characterize the structure of biochar at the molecular level, HR-TEM, Raman, XPS, etc., can be used [30,34]. The 3D morphology and distribution of biochar pores can be studied by using a density analyzer, X-ray computed tomography (XCT), and SEM [35][36][37].…”

“…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.…”

Computational Study on the Microscopic Adsorption Characteristics of Linear Alkylbenzene Sulfonates with Different Chain Lengths on Anthracite Surface

“…With the development of science and technology, it is becoming a reality to use computer simulations to explain the macroscopic properties from a microscopic point of view [51][52][53][54][55][56][57][58][59]. In particular, MD simulation has proven to be a useful tool for analyzing coal interface properties at the molecular level [60][61][62][63][64][65][66]. Traditional experiments screen flotation agents and dust suppression agents by trial-and-error method.…”