Valorisation of residual biomass by pyrolysis: influence of process conditions on products

Abstract

In the context of sustainable residual biomass management, this work explores the pyrolysis process of residual biomass using a bench-scale fixed bed reactor. The main focus is to comprehensively analyze the effects of diverse forest and agroforestry biomass, pyrolysis temperature (350, 450 and 550 °C) and heating rate (2, 10 and 30 °C min⁻¹) on the yield of the products biochar, bio-oil and permanent gas, and on the composition of biochar and permanent gas. This analysis provides a valuable collection of insights to support the advancement of pyrolysis projects and their expansion into industrial production, facilitating the creation of versatile products. The study showed that the biochar, bio-oil and permanent gas yields were between 0.22 and 0.47, 0.26 and 0.59 and 0.17 and 0.41 kg kg⁻¹ dry biomass, respectively. The pyrolysis of olive pomace has the maximum biochar yield, that of eucalyptus sawdust has the maximum bio-oil yield, and that of giant reed has the maximum permanent gas yield. The increased temperature led to a decreased biochar yield and an increased bio-oil yield. The increased heating rate led to a decreased biochar yield and an increased bio-oil yield. Biochar has a carbon content above 0.7 kg kg⁻¹ dry ash free, with an LHV between 24.2 and 30.5 MJ kg⁻¹ dry biochar, suggesting potential for soil enrichment and the energy vector. Permanent gas has an LHV between 5.4 and 9.7 MJ Nm⁻³, and seems useful as a thermal energy source to support the pyrolysis process.