Energetic and exergetic study of the pyrolysis of lignocellulosic biomasses, cellulose, hemicellulose and lignin

Energy and exergy analyses were performed to evaluate the pyrolysis of the lignocellulosic biomasses, beech wood and flax shives, and the pyrolysis of biomass principal compounds (cellulose, hemicelluloses and lignin) as well. The reaction took place in a semi-continuous reactor at 500 °C within an intermediary pyrolysis regime. Lignin showed the lowest heat for pyrolysis, with 0.86 MJ/kgRaw material, followed by cellulose (1.21 MJ/kgRaw material) and hemicellulose (1.43 MJ/kgRaw material). The heat for pyrolysis for the pseudo-components was inferior to those obtained for the biomasses. Beech wood heat for pyrolysis was 1.97 MJ/kgBiomass and that for flax shives was 2.2 MJ/kgBiomass. The thermal behavior of the biomasses was similar to that of hemicellulose and cellulose, as the bio-oils seemed to have closest energetic and exergetic distribution of chemical families as compared to the lignin bio-oil. For all pyrolysis tests, bio-oil represented the stream with lowest anergy. As values were between 0.08 and 0.57 MJ/kgBio-oil. Pyrolysis of the pseudo-components showed lower exergy destruction rate than pyrolysis of the biomasses; this can be a result of the competition of thermal reactions between cellulose, hemicellulose and lignin within the biomass during pyrolysis. Meanwhile, less exergy was destroyed in flax shives pyrolysis (2.00 MJ/kgBiomass) than beech wood pyrolysis (2.1 MJ/kgBiomass).