Transformations of biomass internal oxygen at varied pyrolysis conditions

Pine bark, characterized by high oxygen content (41 wt.%) typical of biomass, was submitted to pyrolysis at varied conditions in order to follow the regularities of oxygen transformation. The effect of water, a catalyst and molecular hydrogen on the yield and composition of pyrolysis products, and their oxygen content were studied. The volatiles, liquid fractions soluble in selected solvents, and solid products of pyrolysis were characterized by ultimate analysis, FTIR-spectroscopic and chromatographic methods. It was demonstrated that, depending on pyrolysis conditions, 46–79 wt.% of oxygen of the original biomass can be transformed into water and 17–43 wt.% into CO2. The maximum amount of water is produced at catalytic hydropyrolysis, and the maximum amount of CO2 at pyrolysis with supercritical water. The yields of total bio-oil and charcoal with considerably reduced oxygen content were 11–19 and 30–41 wt.%, respectively. Though a significant portion of oxygen compounds was separated by extraction with polar solvents like water and acetone, the benzene-soluble oil fraction was characterized by a wide spectrum of oxygenates as well. As for the biomass, the role of oxygen in both quantitative and qualitative pyrolytical transformations is dominant being strongly influenced by pyrolysis conditions.