Understanding hydropyrolysis mechanism of β-O-4 type lignin dimer

Hydropyrolysis has been demonstrated as a highly effective method in the production of fuels and high-value chemicals. However, limited research has been conducted on the reaction mechanism under hydrogen conditions, which necessitates further investigation. In order to examine the impact of hydrogen, experiments were conducted on a high-pressure pyrolyzer using 1-methoxy-2-phenethoxybenzenene with β-O-4 linkage. The results indicated that hydrogen promoted the depolymerization and reduced the formation of heavier compounds, leading to an increase in the production of the monomer phenols and aromatic compounds. Experiments were further conducted at different pressures. The results obtained from reactive molecular dynamics simulations exhibited the pyrolysis mechanisms. The cleavage of Cβ-O, Cph-O, and Cα-Cβ bonds, as well as demethylation and demethoxylation processes during hydropyrolysis were observed. The initial reaction commenced with Cβ-O bond cleavage, which was enhanced by the presence of hydrogen. Subsequent reactions were categorized into three types: decomposition or isomerization reaction, coupling with radical groups containing carbon, and combination with hydrogen molecules or hydrogen radicals. The direct reactions between the model compound molecules and hydrogen molecules or hydrogen radicals, as well as primary hydrogen abstraction reactions and hydrogen elimination reactions were explored. These simulations offer valuable insights into understanding the influence of hydrogen at the molecular level.