High-quality bio-oil production via fluidized bed fast pyrolysis of biomass

The use of biomass-derived fuels aimed at integrating and/or replacing conventional fossil fuels, has attracted increasing interest in the last decade following the pattern of the sustainable transport development in the context of the 'Initiative for Global Leadership in Bioenergy'. Among the multiplicity of processes adopted for biomass conversion, fast pyrolysis looks very promising, resulting in a liquid product (i.e., bio-oil) that represents a green alternative to crude oil for the production of liquid fuels, chemicals and intermediate materials within the bio-refinery context. Moreover, the conversion of biomass into bio-oil, fits well with the concept of the progressive transition from traditional 'short chain' biomass conversion methods, typically characterized by lower energy conversion yields, towards "long chain" transformation processes, based on intermediate bioenergy vectors, as reported in the IRENA (2016) and IEA (2016) bulletins on the implementation of advanced liquid biofuels. Pyrolysis oil is, in fact, an energy-dense intermediate that can be economically transported, thus offering an opportunity for connecting decentralized conversion processes with centralised upgrading treatments. In principle, the process is suitable for a broad range of feedstocks and may tolerate variations in feedstock composition, potentially taking advantage of lower-cost feedstocks. The heart of fast pyrolysis processes is the pyrolyzer; among the several technologies currently available, fluidized bed reactors stand out since they are able to ensure superior thermal and fluid dynamic performance. Strategies commonly adopted for optimizing the pyrolysis process include the use of catalysts and co-pyrolysis, which can be either catalytic or non-catalytic. The use of catalysts (mainly acidic zeolites and metal oxides), in particular, pushes the selectivity to specific products, ensures lower energy consumption and shorter reaction times, in addition to deoxygenation and reforming of the pyrolysis vapours coming from the parent feedstock. However, the downside of this approach is the reduction in the bio-oil yield caused by additional contribution of catalytic cracking. In this context, the present work reports on the preliminary results obtained, within the BIOFEEDSTOCK project, with the aim of comparing the performances, in terms of yield and quality of bio-oils, of the catalytic and the non-catalytic fast pyrolysis treatment of different biomass feedstocks in a fluidized bed reactor. In more details, the performed experimental campaign includes four main macro-activities, namely: i) characterization of the selected biomass feedstock by commonly used analysis techniques (i.e., proximate and ultimate; calorific value, ICP-MS analysis, etc.); ii) non-catalytic pyrolysis tests at 500 °C on the investigated feedstocks including high quality spruce wood (SW), wheat straw (WS) and olive stone (OS), which are characterized by different chemical-physical properties (water content, quantity of ash, etc.); iii) in situ catalytic pyrolysis tests on two of the investigated biomass feedstock; iv) preliminary study of the impact of the temperature on the performance of non-catalytic fast pyrolysis.