Catalytic pyrolysis of pine needles: Role of zeolite structure and SiO2/Al2O3 ratio on bio-oil yield and product distribution

Renewable and sustainable energy production has gained significant attention to meet sustainable development goals (SDGs). Pine needles, an abundant typical forestry residue, can be used as a renewable biomass source for sustainable energy production. Pyrolysis is a well-established and commercialized technique for the thermochemical valorization of lignocellulosic biomass. The present work focuses on improving the bio-oil yield by introducing SiO₂-Al₂O₃-based catalysts, including different zeolites and SiO₂-Al₂O₃ materials with varying SiO₂-Al₂O₃ ratios, during the pyrolysis. Bio-oil yield increased from 45.2 wt.% to 47.2 wt.% with the introduction of SiO₂-Al₂O₃ catalysts and increased to 51.2 wt.% and 50.6 wt.% with HZSM-5 and Y-zeolite, respectively, and decreased to 40.0 wt.% with β-zeolite catalyst. The pyrolysis experiments of physically mixed biomass and catalyst were carried out in a fixed-bed down-flow reactor. Various process parameters such as temperature, retention time, and catalyst-to-biomass ratio were examined to evaluate their effect on product yield. The catalyst's introduction slightly decreased phenolic compound content, enhancing carbonyl and hydrocarbon production. Maximum improvement in bio-oil yield by 6 wt.% was achieved using an H-ZSM-5 catalyst at 450°C temperature and 30 min residence time with a catalyst-to-biomass ratio of 1:4.