Maximizing aromatic hydrocarbon production through catalytic pyrolysis of lignocellulosic residues over ZSM-5 zeolite...

This study investigates the influence of lignocellulosic biomass properties on aromatic hydrocarbon (AR) production by catalytic pyrolysis using a ZSM-5 zeolite as catalyst in a fixed-bed reactor. First, using a batch reaction system, vine and olive pruning, oak, and wheat straw were tested as feedstocks. A high lignin content in the biomass increased both char yield and bio-oil oxygen content, although not affecting AR production. In contrast, a high alkali and alkaline metal content reduced the AR yield. Oak was selected for the catalyst-bed temperature optimisation in a continuous reactor, as this biomass led to a low char yield and a bio-oil with a reduced oxygen content and a significant AR share. The highest AR carbon yield (15.1 wt% during the first hour of reaction) was achieved at 450 °C. Higher temperatures (500 °C) promoted severe cracking reactions leading to gases, while lower temperatures (400 °C) provoked a faster catalyst deactivation due to enhanced deposition of carbonaceous matter with a higher concentration of oxygenated oligomeric/heavy species. AR formation from light oxygenates, followed by the oligomerization/cyclization/aromatization pathway, is affected earlier along the time on stream than through Diels-Alder condensation reactions.