Highly efficient production of monocyclic aromatics from catalytic co-pyrolysis of biomass and plastic with nitrogen-doped activated carbon catalyst

Nitrogen-doped activated carbon catalysts (NAC) were prepared via a two-step process involving the co-carbonization of coconut shell and urea, followed by activation with KOH. These NAC were then employed in the catalytic co-pyrolysis of corn stover (CS) and high-density polyethylene (HDPE) using a fixed bed reactor. The characterization results demonstrated that nitrogen doping led to a larger specific surface area, an enhanced microporous structure, and abundant nitrogen-containing functional groups, which facilitated the production of liquid and promoting the selectivity of monocyclic aromatics (MAHs). The introduced pyridinic-N and pyrrolitic-N provided sufficient active sites for deoxygenation, cracking, aromatization, and Diels-Alder reactions of co-pyrolysis vapors that augmented the formation of MAHs, as well as high calorific value syngas including H2, CH4, and C2+ hydrocarbons. The highest MAHs yield of 62.41% was achieved at a urea to coconut shell ratio of 0.8, whereas an excessive amount of urea resulted in cyclization and polymerization reactions of MAHs to form polycyclic aromatics (PAHs). Accordingly, controlling temperature and catalyst to raw material ratios enabled further regulation of the production and selectivity of MAHs. NAC with a better pore structure and more active sites exhibited excellent catalytic activity for value-added MAHs production in the co-pyrolysis of CS and HDPE, benefiting the resource utilization of organic solid waste with carbon-based catalysts.