Biodiesel production from microalgae: a techno-economic analysis from biomass harvesting to biodiesel refining

A key aspects of the industrialization of microalgae-to-biofuel processes is the characterization/improvement of unit operations involved in the downstream process. Typically, the process includes: biomass harvesting and concentration, oil extraction, transesterification, and methyl-esters purification. Industrial scale biodiesel processes are strongly affected by the transesterification strategy. Biodiesel from virgin vegetable oil or waste cooking oil can be produced through acid-, alkaline-, heterogenous-catalysed or supercritical processes depending by the level of free fatty acid. The selection between batch and continuous processes depends on transesterification kinetics. To the Author knowledge, very few attempts are reported regarding the assessment of biodiesel integral processes from microalgae. The present work reports on the assessment of a cost-effective flow-sheet for the production of biodiesel from microalgae intensive cultivation. The study was based on approximated costestimation methods integrated with the simulation software Aspen Plus®. Several scenarios were investigated regarding the lipid extraction, transesterification and solvents recovery steps. The design variables were selected so as to correspond to the main degrees of freedom of the process as number of equilibrium stages, solvent recycle flow rate, transesterification time, methanol to triacylglycerols ratio, plate number and reflux ratio of the distillation unit for methanol recovery. A preliminary determination of plausible values of the venture profit of the process was attempted as a function of operating conditions. It should be pointed out that the analysis was based on a very limited data base of photobioreactor pilot plants (open literature). Additional data would be required to increase the reliability of the process assessment