UC San Diego

Continually rising energy needs in conjunction with negative externalities of fossil fuel use demand the diversification of energy resources. However, fossil hydrocarbons are also used as raw materials for a vast web of manufacturing of industrial and consumer goods. The use of plant based raw materials as substitutes for fossil materials in fuels and manufacturing has been demonstrated successfully, and microalgae are an extremely diverse and promising resource in this category. One of the chief challenges in the implementation of a bio-economy is efficient processing and conversion of biomass to platform chemicals. In order to maximize extraction efficiency, pretreatment is employed to effect cell rupture. Many pretreatment processes have been implemented using empirical operating curves, but the fundamental energy requirements of the cell disruption process have not been thoroughly explored. To fill this void, a constitutive model of cell rupture energy is derived here and implemented for low frequency power ultrasound processing of Chlorella vulgaris. A sensitivity analysis of the constitutive model is performed, identifying cell diameter as a high sensitivity input. Measured distribution of microalgae cell diameters is then used as a fixed input to Monte Carlo simulations of cell rupture energy from the constitutive model. The influence of growth media on microalgal growth rate is then investigated, and the resultant biomass subjected to power ultrasound processing to determine the effect of media choice on processing efficiency. The theoretical kinetics of cell rupture via power ultrasound induced cavitation is developed next. A reactor model is introduced to convert reactor kinetics to reaction zone kinetics. An elementary reaction model is then developed in the context of the constitutive model, leading to the introduction of an alternative reaction mechanism employing a critical distance parameter to capture the relative energies and proximity of cells and cavitation bubbles. This reaction mechanism is extended to generate an explicit expression for the cell disruption first order rate constant in terms of cell properties and power ultrasound operating parameters. This rate constant is mapped over the parameter space, then used to back-calculate cavitation rate, and finally extended to incorporate PDF parameter inputs.