Kinetics of biobased bitumen synthesis from microalgae biomass by hydrothermal liquefaction
Résumé
Worldwide, about 100 million tons of bitumen are used per year. Mainly from petroleum refining, although bitumen can exist in natural form, this material is used because of its unique combination of properties: adhesion, impermeability to water and specific thermo rheological behaviour. Due to petroleum dependency, the future of petroleum-based bitumen is uncertain, especially in road construction field [1], [2]. In this context, alternative bitumen binders from renewable resources are most likely to be an issue [3]. The Algoroute project funded by the French National Agency for Research (ANR) tries to mimic the geological process of petroleum formation in a faster way. This process started with the sedimentation of microalgae biomass in oceans' depths which then turned progressively into petroleum by the increased of both temperature and pressure. Algoroute partners have shown microalgae biomass can be converted via hydrothermal liquefaction into an hydrophobic product having similar rheological properties with petroleum bitumen [3], [4]. However the similitude between the geological formation and hydrothermal liquefaction also suffers from some distinctions. If reaction temperature and time seem to be important factors, some other less explored factors, such as heating/cooling rate, algae/water ratio or loading level of reactor might have a significant impact on quality and yield of the hydrophobic phase. One of the aims of this project is to fully understand the physical and chemical phenomena taking place during hydrothermal liquefaction. To do so, hydrothermal liquefaction is studied with three different reactor scales: i) High pressure DSC crucibles (30 µL.) are used to perform thermal analysis during hydrothermal liquefaction in a Differential Scanning Calorimeter. ii) A commercial stirred pressure reactor (300 mL) was instrumented with 9 thermocouples in different locations inside the reaction media, allowing to monitor the temperature fields together with global pressure, and stirrer's rotation torque. Fast heating and quenching of the reaction media are obtained with an induction coil and a mixed air/water spray cooler (figure A). iii) The same system is used with intermediate scale Swagelok non-instrumented reactors (30 mL.) allowing the screening of reaction temperatures and residence time on typically 3g of biomass batches.
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