Hydrothermal liquefaction and upgrading of micro-algae (biodiesel)

Micro-algae can be grown in open ponds, closed photobioreactors, or in heterotrophic bioreactors (no light required). Once grown, the whole algae cell is hydrothermally liquefied (HTL) via the same process used for terrestrial biomass. The algal bio-oil is separated from the remaining products and can be sent to hydrotreatment (common in petroleum refineries) to be upgraded to a drop-in biodiesel (renewable diesel). The remaining solids, water and carbon dioxide are treated and recycled to the cultivation step, while remaining off-gases provide heat, electricity or hydrogen. As with all algal biofuel systems, the main challenge arises from the high cost of harvesting and cultivation, as well as reducing the energy/water/nutrient/land footprint of the system. However, algae can be grown on non-arable land, avoiding competition with food. Benefits of using the HTL route with micro-algae include HTL's ability to handle wet feedstocks, and its use of all algae components (lipids, carbohydrates, proteins), removing the need to cultivate high lipid content and extraction.