Investigation of the Chemical Properties of Biochar and Bio-oil from Woody Biomass

Biomass pyrolysis stands as a promising technology in the transition to a more sustainable energy system. The energy sector is one of the main contributors of greenhouse gas emissions, thus increasing the share of renewable energy sources is fundamental to decrease reliance on fossil fuels. Pyrolysis is the thermochemical valorization of biomass, converting it into valuable products such as biochar, bio-oil and gases. In this way, biomass can be transformed in a range of products including fuels, chemicals, fertilizers, adsorption materials and catalysts. This work is founded on the experiments carried out in a laboratory scale pyrolysis plant, at BEST Bioenergy and Sustainable Technologies GmbH in Wieselburg, Austria. Lignocellulosic biomass, particularly poplar wood pellets, has been used as feedstock. The influence of operational parameters, in particular temperature, has been investigated through characterization of the two main products, biochar and bio-oil. The results highlight the critical role of process temperature on product yields and properties. Increasing temperatures, in the range 300°C-500°C, favored higher gas yields, with a gradual decrease of biochar content. Biochar obtained at higher temperatures showed low moisture and volatile content, alongside with a rising carbon content. This confirmed the high stability of biochar and the flexibility of the process to obtain biochar with specific properties, by controlling temperature. The condensable portion of gases has been collected through a fractional condensation unit, to effectively separate compounds based on their volatility. The resulting three collected liquid fractions confirmed the efficiency of this downstream approach. Among these fractions, the one obtained at 80°C had a complex chemical composition, as demonstrated by FT-IR spectra, in line with that of typical bio-oils. Moreover, storage conditions investigations showed that the best way to avoid aging effect on liquid fractions, is to store them at cooler temperatures, such as at -10°C.