(449d) Evaluating and Improving a Kinetic Model for the Hydrothermal Liquefaction of Microalgae

Hydrothermal liquefaction in hot compressed water converts wet algal biomass into an energy-dense biocrude. Hydrothermal treatment of biomass to produce biofuels circumvents energy and resource intensive steps of drying and solvent extraction. We have developed a reaction network and kinetic model to describe the hydrothermal liquefaction of microalgae slurries [1]. Assuming lumped product fractions and pseudo first-order kinetics, we simplified the modeling of hydrothermal liquefaction while maintaining accuracy to describe a complex system of reactions. We will report the estimated Arrhenius parameters, rates, and sensitivity of each reaction pathway in the reaction network. We calculated activation energies of the gas formation pathways during liquefaction to be 66 and 80 kJ/mol, which are within range to a previously reported value of 71 kJ/mol [2]. We verified the validity of the reaction network and kinetic model with additional liquefaction experiments and data from other researchers using the same microalga. By incorporating the biochemical content of the algae into the model we are able to unify results between microalgae with varying composition of lipids, proteins, and carbohydrates. We determined that the optimized conditions for maximizing biocrude yield are at >300 °C and <20 min.

[1] PJ Valdez, PE Savage, Reaction Network for the Hydrothermal Liquefaction of Nannochloropsis sp., Manuscript Submitted, Algal Res., March 2013.

[2] Q Guan, PE Savage, C Wei, Gasification of alga Nannochloropsis sp. in supercritical water, J. Supercrit. Fluids 61 (2012) 139-145.