Catalytic upgrading bio-oils obtained from hydrothermal liquefaction of µ-algae . – RAFBIOALG

Thanks to their fast growth and their high lipids content, micro-algae are considered as potentially-excellent candidates to provide third generation biofuels in the future. Nevertheless, some knowledge gaps still need to be tackled. In the downstream of the value chain, the challenge is to reach technically- and regulatory-compliant biofuels which can be fulfilled using chemical upgrading. The objective of the project RAFBIOALG is to explore a thermocatalytic route for the valorization of micro-algae into biofuels, including a two-step process with first a hydrothermal liquefaction to get a bio-oil and then a catalytic upgrading to reach transportation fuels specifications. The ambitious objective here is also to experiment a fully-integrated process starting from the micro-algae cultivation and encompassing all subsequent steps. To reach this target, we will start with the cultivation of four different types of micro-algae which are selected according to their biomass and lipid productivity and their ability to thrive on water recycled from harvesting, hydrothermal liquefaction and upgrading steps, in a closed virtuous loop. The production of the selected micro-algae will be optimized in order to reach the required feedstocks for downstream operations. Among the various valorization processes which can be applied to micro-algal biomass, we will use continuous hydrothermal liquefaction (HTL) which is regarded as one of the most promising technology to produce algal fuels, since it avoids the energetic burden associated to deep drying of the biomass. HTL is able to treat a wide range of different biomasses to produce a biocrude, a kind of green petroleum with a relatively high heating value (HHV=30-36 MJ/Kg) and with a residual oxygen content in the range of 10 to 15%w and nitrogen content in the order of 3 to 5%. The parameters of the continuous HTL will be optimized to the selected micro-algae. After separation of the bio-crude from water and in order to improve the quality of the HTL bio-oil towards fuels or chemicals, further catalytic steps will be assessed to remove the residual O and N compounds. For this purpose, we will address the development of O-, N-resistant catalysts which are highly needed to reach appropriate fuel properties. Hence, specific hydrotreating catalysts will be designed and tested. Then, the burning properties of the bio-oils and refined biofuels produced along these different steps will be characterized and compared to those of primary reference fuels (iso-octane and n-heptane). Since we are aiming at evaluating the technical and environmental performance of the proposed algae-to-fuel chain, techno-economic analysis (TCA) and life cycle analysis (LCA) will be carried out and used for designing and assessing the integrated process.