Optimizing pine needle pyrolysis: the role of pre-treatment in boosting bio-oil quality for sustainable energy production

This study investigates the transformative potential of pre-treatment methods on the pyrolysis of pine needles, a plentiful forestry residue in Uttarakhand, India. The work focuses on how various pre-treatment strategies-chemical treatments using dilute acid (5 wt.%) and alkali (5 wt.%) solutions, as well as thermal torrefaction-affect biomass properties, the pyrolysis process, and the quality of the resulting bio-oil. Characterization of pre-treated samples revealed substantial changes compared to untreated pine needles. Proximate analysis indicated significant reductions in ash content, with the most considerable decrease observed in acid-treated samples. Additionally, there were notable reductions in volatile matter and moisture content, while fixed carbon content increased across all treatments, particularly in torrefied samples. Ultimate analysis demonstrated an increase in carbon content and a reduction in oxygen content for acid-treated and torrefied samples, whereas alkali treatment exhibited the opposite trend. Alkali treatment led to the highest mass loss (50%) due to extensive lignin and hemicellulose removal while torrefaction led to the lowest mass loss (20%). When evaluating the pyrolysis of pre-treated samples under these optimized conditions, significant changes in product distribution were observed. Acid treatment enhanced bio-oil yield to 46.5%, whereas alkali and torrefaction reduced yields to 30% and 35.5%, respectively. Notably, torrefaction yielded the highest quality bio-oil with the highest phenolics content, an HHV value of 25 MJ/kg and the lowest water content (21.5%), highlighting its efficacy as a pre-treatment method for improving energy production from biomass. By understanding how different pre-treatment strategies affect biomass properties and pyrolysis processes, this work paves the way for more efficient, cost-effective biomass valorization, promoting the use of pine needles as a viable, renewable feedstock for biofuel production.