Evolution mechanism of cellulose during hydrothermal process based on ReaxFF force field
The cellulose-water model system was established and optimized by using Materials Studio software,and the molecular dynamic simulation of the cellulose hydrothermal reaction process was conducted by using LAMMPS software.The evolution law of the hydrothermal products and the hydrothermal reaction mechanism of the cellulose were simulated and studied.The results show that temperature is an important factor affecting the distribution of hydrothermal products of cellulose.With the increase of the hydrothermal temperature,cellulose decomposition intensifies,the relative content of hydrothermal solid products in the system decreases sharply,the aromaticity and calorific value of the solid products increase,and the hydrophilicity decreases.The relative contents of heavy tar and light tar increased first and then decreased,and the reaction of secondary cracking of tar into small molecules intensified.With the increase of hydrothermal temperature,the production of CO2 and H2in the system continued to increase,the production of formic acid showed a trend of increasing first and then decreasing,and the difference of formaldehyde was small.The simulation results also show that H2O molecules participated in the hydrothermal reaction of cellulose mainly in the form of hydrated hydrogen ions(H3O+).With the increase of the hydrothermal temperature,the ionization reaction of water molecules and the dehydration reaction of cellulose were enhanced.The analysis of hydrothermal mechanism of cellulose showed that the cellulose depolymerization paths included the decomposition into glucose and the dehydration into L-glucan.During the rearrangement isomerization process of the glucose monomer,the main intermediates such as furans and aldehydes were formed by dehydration and retrograde aldol condensation reactions from the three transition state structures of enediol.The research on the cellulose hydrothermal reaction mechanism can provide a theoretical basis for the biomass hydrothermal conversion.
biomasshydrothermal treatmentcelluloseReaxFF reactive force fieldreaction path
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