LAUSR

Advanced Biofuels steadily developed during recent year, with several highly innovative processes and technologies explored at various scales: among these, lignocellulosic ethanol and CTO (Crude Tall Oil)-biofuel technologies already achieved early-commercial status, while hydrotreating of vegetable oils is today fully commercial, with almost 3.5Mt/y installed capacity worldwide. In this context, microalgae grown in salt-water and arid areas represent a promising sustainable chain for advanced biofuel production but, at the same time, they also represent a considerable challenge. Processing microalgae in an economic way into a viable and sustainable liquid biofuel (a low-cost mass-product) is not trivial. So far, the most studied microalgae-based biofuel chain is composed by microorganism cultivation, lipid accumulation, oil extraction, co-product valorization, and algae oil conversion through conventional esterification into Fatty Acids Methyl Esters (FAME), i.e. Biodiesel, or Hydrotreated Esters and Fatty Acids (HEFA), the latter representing a very high quality drop-in biofuel (suitable either for road transport or for aviation). However, extracting the algae oil at low cost and industrial scale is not yet a mature process, and there is not yet industrial production of algae-biofuel from these two lipid-based chains. Another option can however be considered: processing the algae through dedicated thermochemical reactors into advanced biofuels, thus approaching the downstream processing of algae in a completely different way than separation. The present work examines the possible routes for thermochemical conversion of microalgae into liquid biofuels, distinguishing between dry-processes (namely Pyrolysis, PO) and wet-processes (near critical-water HydroThermal Liquefaction, HTL). A literature review on algae-HTL was carried out, distinguishing between batch and continuous experiments, and compared to original results from algae pyrolysis. In particular, pyrolysis was carried out on both starved (lipid-accumulated) and non-starved microalgae. Typical composition of major products is given for both PO and HTL, comparing the main characteristic of the products.