The study of pyrolysis is gaining increasing importance, as it is not only an independent process but is also a first step in the gasification or combustion process. Pyrolysis refers to the thermal decomposition of biomass and organic compounds in the absence of oxygen to produce biochar, oil and/or gas, depending on the temperature and reaction time. In slow pyrolysis charcoal or biochar is produced (temperature ~300°C, reaction time of hours). In fast pyrolysis (t° 400-500°C, reaction time of minutes or seconds) and flash pyrolysis (t° >700°C, reaction time of fractions of a second) mainly a liquid bio-oil is formed [49]. All pyrolysis products (char, oil, gas) can be used for the generation of heat and power. The dark-brown mobile liquid produced by fast pyrolysis can serve as an intermediate for a wide variety of applications. Clean-up, conditioning, and stabilization of the bio-oil are necessary to convert it into a product suitable for delivery to a petroleum refinery or future biorefinery, where it can be further upgraded to renewable biofuels (diesel, ethanol, bio

jet fuel) and chemicals [49, 50]. Pyrolysis offers the possibility of decoupling liquid fuel production from energy production by converting the biomass into a liquid with increased energy content that can be easily stored and transported and that has a more consistent (and specified) quality compared to the solid biomass.

Despite rapid development over the last few decades, bio-oil production through pyrolysis is still an immature technology and is not commercially feasible yet. Pyrolysis bio-oil needs to overcome many technical, economic and social barriers to compete with traditional fossil fuels [51]. In particular, the complexity of the bio-oil constitutes a big challenge.