Pyrolysis processes for bio-oil production: analysis of the hazards of the reaction products

The need of producing energy from renewable resources has brought in the course of time to the development of several “clean” technologies. Pyrolysis-based energy densification processes of biomass residues are more and more becoming an interesting route for bio-oil production. Pyrolysis is the chemical decomposition of organic materials, i.e. biomass, by application of heat in the absence of oxygen. During pyrolysis processes, biomass is converted into a solid fraction (char), a liquid phase (tar) and incondensable gases (e.g. hydrogen, methane, carbon monoxide and carbon dioxide). The high heating values of these fractions are usually exploited to produce energy. The chemical characterization of the pyrolysis products, and in particular of tar components, is usually a list of very different substances, that usually are more harmful than the biomass feed. Thus, the safety of pyrolysis prcesses may be affected by the possible harm of the products formed. As a matter of facts, accidental conditions occurring in a pyrolysis process may lead to the undesired dispersion of these products, whose effects on humans and environment have to be quantified. Moreover, the actual understanding of the inherent hazards of bio-fuels with respect to conventional fuels should be a core issue for the sustainability assessment of bio-energy processes. The aim of the present study is the development of a specific approach to characterize the hazard of the products formed during pyrolysis processes. Conventional experimental protocols were applied to screen the possible pyrolysis products. A specific methodology based on toxicological, physical and chemical parameters was then applied for the assessment of the hazard due to these products. The methodology was applied to understand the potential harm of bio-oil formed in the pyrolysis of some biomass samples.