Investigation of the hydrothermal carbonization process of furan compounds derived from cellulose using molecular dynamics

Abstract

The conversion of biomass, such as cellulose, into carbonaceous materials by hydrothermal carbonization (HTC) has great potential as an energy source. This study was conducted to investigate the effects of temperature, water, and reactants on product distribution during the HTC process. The carbonization reaction mechanism was determined using the ReaxFF method, and the results showed that high temperature accelerated the HTC charring process. Although the rate of reactant polymerization increased at high temperatures, this also led to an increase in the decomposition of gaseous products. Simulation results showed that water played a dual role as both a solvent and reactant in HTC; this role hindered the formation of certain carbon-containing gases, which in turn facilitated the HTC process. It was also observed that 5-hydroxymethylfurfural (HMF) and furfural did not interact, but furfural was converted at a faster rate. At 2200 K, HMF polymerized within 3000 ps to form an insoluble polymer with considerable molecular weight. Based on the formation of the polymer, it was evident that reactive small molecule compounds continued to participate in polymerization. An aromatization reaction occurs during polymerization, leading to the formation of stable fragments with high aromaticity; therefore, polymerization and aromatization reactions are the two fundamental processes driving carbonation reactions. These processes give rise to the production of insoluble polymers characterized by an amorphous network structure and high aromaticity, and polymers with atomic weights exceeding 1000 can be formed under suitable conditions. The results indicate that it is relatively simple to study the HTC mechanism using molecular dynamics methods.