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Hexamethyldisiloxane (HMDSO) is one of the main impurities in the syngas produced from sewage and landfill plants. In order to utilize this syngas or control the characteristics of the generated silica particles, it is crucial to understand the chemical kinetics of HMDSO combustion. This study investigated the process of HMDSO combustion using synchrotron radiation mass spectrometry (SRMS), gas chromatography (GC), and ReaxFF molecular dynamics simulations. First, the force field used for ReaxFF simulation was validated by comparing the energies of different bond lengths, bond angles, and dihedral angles with the ones from DFT calculations. Good agreements were found. Then, ReaxFF simulations of HMDSO combustion with this force field were conducted under various conditions, which include different equivalence ratios (0.67, 1.0, and 1.5) and temperatures ranging from 2000 to 3500 K. The oxidation characteristics of HMDSO were analyzed, including the evolution of gas products and particle formation. Finally, based on the results from experiments and ReaxFF simulations, the reaction pathways, reaction lists, and reaction kinetics data during HMDSO combustion were obtained. A detailed reaction mechanism was proposed and validated by applying it in modeling the H2/HMDSO/O2 combustion systems. The temperature and part of the gas products such as CO and CO2 as well as SiO could be well predicted. [ABSTRACT FROM AUTHOR]

The pyrolysis kinetics of hexamethyldisiloxane (HMDSO) at various temperatures was studied using the reactive force field (ReaxFF) molecular dynamics simulations. Reaction rate constants and the main pyrolysis pathways were explored at the initial decomposition stage of HMDSO and intermediates decomposition stage. The activation energy and pre‐exponential factor describing the reaction rate constants were obtained and further validated by experimental data and DFT theoretical calculations. The formation of C5H15OSi2 fragment by Si–C bond dissociation was dominant at the initial decomposition stage of HMDSO at the simulation temperatures of 2500–4000 K. The subsequent reaction pathways involved the formation of C5H14OSi2 and C4H11OSi2. After that, the pathways were different for 2500 and 3000 K. At 4000 K, small silicon‐containing fragments were formed, including CH3Si, CH4Si, and C3H9Si, etc. The simulations also revealed that the major hydrocarbons generated during HMDSO pyrolysis were CH3 and CH4. Also, CH4 formation was more important in the end of HMDSO pyrolysis when simulation temperature was over 3500 K. [ABSTRACT FROM AUTHOR]

Silica nanoparticles have been widely applied in many fields due to their excellent properties. SiO2 generation is crucial for silica particle formation, but in a swirling reactor the SiO2 generation is still unclear. In this study, numerical simulations are performed to investigate the SiO2 generation and distributions of temperature and velocity during silica particle synthesis using a swirling reactor. A computational model is first developed to describe the heat and mass transport in the swirling turbulent flame. Simulation models are validated with experimental data in the case without SiO2 chemistry. Then, effects of the fuel velocity and swirl number on SiO2 generation are investigated. Results show that most of the SiO2 molecules are generated in the region far away from reactor inlets and a relatively high SiO2 generation efficiency is obtained for a fuel velocity of 32.7 m/second. Distributions of the flame temperature, velocity and SiO2 concentration are found to vary with the swirl number and high chemical reaction rates for SiO2 generation are obtained when a swirl number of 0.5 is employed. Uncertainty analysis shows that the average relative errors of the results from different models are within 18%. [ABSTRACT FROM AUTHOR]

A comprehensive computational model is first presented, which is capable of describing multispecies turbulent reacting flow and particle formation and deposition. Then a detailed mechanism for SiCl4/H2/O2 reaction system is proposed and applied to the prediction of a counterflow laminar diffusion flame. Good agreement in flame temperature is obtained between numerical results and experimental data, and the augmented 30-reaction SiCl4 submechanism in the detailed mechanism has a significant impact on the SiO2 formation rate. To employ the detailed mechanism in three-dimensional simulations, the reduction of reaction mechanism is performed to eliminate inconsequential species and reactions. The physiochemical process in a silica glass furnace is first simulated with the detailed mechanism to obtain realistic sample compositions. Then, the directed relation graph (DRG) method is employed to construct three comprehensive skeletal mechanisms by considering all accessed compositions in the fused silica glass synthesis, and further analyzethe governing chemical kinetics. The predicted total SiO2 deposition on glass ingot is found to depend on mechanism reduction, and the species SiCl and HOCl are important for the formation of SiO2 and OH. While only two species and seven reactions are removed from the detailed mechanism even though the reduction threshold error of 0.15 has been employed. It is also found that the number of important chemical species and reactions is significant only in a narrow region, which indicates a great potential in local adaptive mechanism reduction. Therefore, the dynamic adaptive chemistry (DAC) is used to generate a small locally valid skeletal mechanism. For the same accuracy in temperature and SiO2 mass fraction, DAC method obtains higher speedup factor than that of DRG method. [ABSTRACT FROM AUTHOR]